Citation
Evaluation of Sorbent Technology to Prevent Heavy Metal Emission and Leaching from Combustion of Chromated Copper Arsenate (CCA) Treated Wood

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Title:
Evaluation of Sorbent Technology to Prevent Heavy Metal Emission and Leaching from Combustion of Chromated Copper Arsenate (CCA) Treated Wood
Creator:
MISRA, ANADI
Copyright Date:
2008

Subjects

Subjects / Keywords:
Arsenic ( jstor )
Ashes ( jstor )
Calcium ( jstor )
Cements ( jstor )
Chromium ( jstor )
Combustion ( jstor )
Hydroxides ( jstor )
Leaching ( jstor )
Oxides ( jstor )
Sorbents ( jstor )
City of Gainesville ( local )

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Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright Anadi Misra. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Embargo Date:
8/31/2007
Resource Identifier:
649814539 ( OCLC )

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EVALUATION OF SORBENT TECHNOL OGY TO PREVENT HEAVY METAL EMISSION AND LEACHING FROM COMB USTION OF CHROMATED COPPER ARSENATE (CCA) TREATED WOOD By ANADI MISRA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2006

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Copyright 2006 by Anadi Misra

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iii ACKNOWLEDGMENTS First and foremost, I would like to thank my advisor, Dr. Chang-Yu Wu, for being a great mentor, guide and friend and making my graduate education a great learning experience. Then I would lik e to thank my committee members, Dr. Timothy Townsend and Dr. Helena Solo-Gabriele, for their c onstant guidance and in sightful suggestions. I would also like to convey my heartfelt thanks to all my lab mates and friends at the University of Florida for making my colle ge experience enjoyable and memorable. Finally, I would like to expre ss my sincere gratitude towards my family and friends in India, whose constant love and support have contributed in my success all through my life.

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iv TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES............................................................................................................vii LIST OF FIGURES...........................................................................................................ix ABSTRACT......................................................................................................................x ii CHAPTER 1 BACKGROUND..........................................................................................................1 1.1 Wood Treatment: Processes And Chemicals.........................................................1 1.2 Consumption Of Treated Wood In Industry..........................................................4 1.3 Past Studies On Characteristi cs Of Treated Wood And Wood Ash......................6 1.4 Issues With Incinera tion Of CCA-Treated Wood...............................................10 1.5 Sorbent Technology.............................................................................................12 1.5.1 Techniques used for Introducing Mi neral Sorbents in Combustion Environments...................................................................................................14 1.5.1.1 Fixed bed reactor...........................................................................14 1.5.1.2 Moving bed reactor.......................................................................15 1.5.1.3 Fluidized bed reactor.....................................................................15 1.5.1.4 Sorbent injection...........................................................................16 1.5.2 Application of Sorbents for Meta l Capture at High Temperature.........18 1.6 Mechanism...........................................................................................................21 1.6.1 Aerosol Size Fractionation Method (ASFM).........................................22 1.6.2 Impact of Competition...............................................................................23 1.6.3 Calcination and Sintering.......................................................................24 1.6.4 Speciation of Adsorbate and Adsorbent................................................26 1.6.5 Summary................................................................................................27 2 OBJECTIVES.............................................................................................................28 2.1 Survey of Available Pollution Control Technologies..........................................28 2.2 Screening of Potential Materials for Preventing Leaching of CCA Metals from Incineration Product.......................................................................................28

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v 3 ARSENIC POLLUTION C ONTROL TECHNOLOGIES........................................29 3.1 Introduction..........................................................................................................29 3.2 Consumption of Arsenic in US............................................................................30 3.3 Health Hazards Associated with Arsenic............................................................32 3.3.1 Acute (Short-Term) Health Effects........................................................32 3.3.2 Chronic (Long-Term) Health Effects.....................................................32 3.4 Available Technologies for Control of Arsenic Pollution...................................33 3.5 Available Thermal Processes for CCA Treated Wood: Emission control..........35 3.5.1 Incineration............................................................................................35 3.5.1 Co-incineration......................................................................................37 3.5.2 Pyrolysis.................................................................................................38 3.5.3 Gasification............................................................................................39 3.6 Available Technologies for Capture of Arsenic in Air........................................40 3.6.1 Technologies used for Capturing Arsenic Emissions from Combustion of CCA-Treated Wood................................................................41 3.6.2 Overview of Arsenic Capt ure in Other Processes..................................42 3.7 Sampling of Trace Arseni c Concentration in Air................................................45 3.8 Conclusions..........................................................................................................49 4 SCREENING OF POTENTIAL MA TERIALS FOR PREVENTING METAL LEACHING FROM INCINERATION PR ODUCT OF CCA-TREATED WOOD..52 4.1 Materials..............................................................................................................52 4.1.1 Sorbent Materials...................................................................................52 4.1.2 CCA Chemicals.....................................................................................56 4.2 Methods...............................................................................................................60 4.2.1 Toxicity Characteristic Leachi ng Procedure (EPA SW 846 Method 1311)........................................................................................................Â…Â…60 4.2.2 Liquid Digestion (EPA SW 846 Method 3010 A).................................64 4.2.3 Solid Digestion (EPA SW 846 Method 3050 B)...................................66 4.2.4 ICP-AES Analysis (EPA SW 846 Method 6010B)...............................67 4.2.5 X-Ray Diffraction Analysis...................................................................70 4.3 Methodology........................................................................................................71 4.4 Results..................................................................................................................7 3 4.4.1 Leaching.................................................................................................73 4.4.1.1 Arsenic..........................................................................................73 4.4.1.2 Chromium......................................................................................75 4.4.1.3 Copper...........................................................................................77 4.4.2 Volatilization Retention.........................................................................79 4.4.2.1 Arsenic..........................................................................................80 4.4.2.2 Chromium......................................................................................81 4.4.2.3 Copper...........................................................................................83 4.4.3 Leaching Retention................................................................................84 4.4.3.1 Arsenic..........................................................................................85 4.4.3.2 Chromium......................................................................................85 4.4.3.3 Copper...........................................................................................86

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vi 4.4.4 Speciation...............................................................................................92 4.4.5 pH Effects..............................................................................................97 4.4.6 Correlation between Leaching of CCA Metals......................................99 4.4.7 Correlation between Volatilizati on Retention of CCA Metals............102 4.5 Conclusions........................................................................................................107 5 SUMMARY AND RECOMMENDATIONS..........................................................110 APPENDIX A DETAILED LEACHING RESULTS.......................................................................115 B DETAILED VOLATILIZATION RETENTION RESULTS..................................124 C DETAILED SPECIATION CHARACTERIZATION RESULTS AND X-RAY DIFFRACTION PATTERN GRAP HS FOR THE SAMPLES................................131 D DETAILED LEACHATE pH RESULTS................................................................161 LIST OF REFERENCES.................................................................................................163 BIOGRAPHICAL SKETCH...........................................................................................176

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vii LIST OF TABLES Table page 1-1: Composition of CCA-Type A, B, and C......................................................................3 1-2: Retention Requirement s for CCA-Treated Wood........................................................3 1-3: Average Metal Concen tration (mg/kg) in CCA-Tr eated Wood and Other Wood Types.......................................................................................................................... 7 1-4: Regulatory Limits for CCA Metals..............................................................................7 1-5: Average TCLP Values for CCA-Treated Wood and Other Wood Types....................8 1-6: Sorbents used for Capturi ng Metals at High Temperature.........................................20 3-1: Arsenic Fact Sheet......................................................................................................31 3-2: Standards and Regulati ons for Inorganic Arsenic......................................................34 3-3: Summary of Air Pollution Control Devices in Combustion Facilities in Florida......35 3-4: Arsenic Capture Efficien cy of Lab-Scale Flue Gas Cleaning Equipments used in Some Studies............................................................................................................42 3-5: Properties of Different Filt er Media for Arsenic Sampling........................................47 3-6: NIOSH Methods for Arsenic Sampling.....................................................................49 4-1: Performance of Mineral Sorbents Against CCA Metals Reported in the Literature..55 4-2: List of Sorbents Used fo r Metal Capture in Experiments..........................................56 4-3: Properties of Metal Com pounds Used in Metal Spike...............................................57 4-4: Molar Ratio of CCA Me tals in Type C Chemical......................................................57 4-5: Mass Ratio of Compounds in Spike...........................................................................57 4-6: List of Materials Us ed in the Experiments.................................................................60

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viii 4-7: Recommended Wavelength and Estimated Instrument Detection Limit for CCA Metals.......................................................................................................................68 4-8: Potential Interferences in Analyte Con centration (in mg/l) when Interferants were Introduced at 100 mg/l Level...................................................................................69 4-9: Summary of Speciation Characterization Results......................................................95

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ix LIST OF FIGURES Figure page 3-1 Relative Oxygen Requirements fo r Various Thermal Processes.............................37 4-1 Flowchart of Experimental Procedure......................................................................62 4-2 Arsenic Leaching from Sorbents..............................................................................75 4-3 Chromium Leach ing from Sorbents.........................................................................77 4-4 Copper Leaching from Sorbents..............................................................................79 4-5 Percentage Arsenic Volatiliz ation Retention in Sorbents........................................81 4-6 Percentage Chromium Volati lization Retention in Sorbents...................................83 4-7 Percentage Copper Volatilization Retention in Sorbents.........................................84 4-8 Leaching Retention for Arsenic...............................................................................86 4-9 Leaching Retention for Chromium..........................................................................87 4-10 Leaching Retention for Copper................................................................................88 4-11 Percentage Arsenic Leached, Re tained in Ash and Volatilized...............................89 4-12 Percentage Chromium Leached, Retained in Ash and Volatilized..........................90 4-13 Percentage Copper Leached, Re tained in Ash and Volatilized................................91 4-14 Leachate pH for Sorbent-Spike Samples at Different Temperatures.......................97 4-15 Variation in Concentration of CCA Metals with Final pH of Leachate...................99 4-16 Leaching Correlation Graph between Arsenic and Chromium..............................100 4-17 Leaching Correlation Graph between Arsenic and Copper...................................101 4-18 Leaching Correlation Graph between Chromium and Copper...............................102 4-19 Volatilization Retention Correla tion between Arsenic and Chromium.................104

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x 4-20 Volatilization Retention Correla tion between Arsenic and Copper.......................105 4-21 Volatilization Retention Correla tion between Chromium and Copper..................106 5-1 Conceptual Diagram of Proposed Thermal System...............................................114 C-1 XRD Pattern for Spike Sample at 700 oC..............................................................136 C-2 XRD Pattern for Alumina – Spike Sample at 700 oC............................................136 C-3 XRD Pattern for Attapulgite Clay – Spike Sample at 700 oC................................137 C-4 XRD Pattern for Calcium Hydroxide – Spike Sample at 700oC............................137 C-5 XRD Pattern for Cement – Spike Sample at 700 oC..............................................138 C-6 XRD Pattern for Diatomaceous Earth – Spike Sample at 700 oC..........................138 C-7 XRD Pattern for Ferric Oxide – Spike Sample at 700 oC......................................139 C-8 XRD Pattern for Kaolin – Spike Sample at 700 oC................................................139 C-9 XRD Pattern for Magnesium Hydroxide – Spike Sample at 700 oC.....................140 C-10 XRD Pattern for Silica – Spike Sample at 700 oC.................................................140 C-11 XRD Pattern for Spike Sample at 900 oC..............................................................146 C-12 XRD Pattern for Alumina – Spike Sample at 900 oC............................................146 C-13 XRD Pattern for Attapulgite Clay – Spike Sample at 900 oC................................147 C-14 XRD Pattern for Calcium Hydroxide – Spike Sample at 900 oC...........................147 C-15 XRD Pattern for Cement – Spike Sample at 900 oC..............................................148 C-16 XRD Pattern for Diatomaceous Earth – Spike Sample at 900 oC..........................148 C-17 XRD Pattern for Ferric Oxide – Spike Sample at 900 oC......................................149 C-18 XRD Pattern for Kaolin – Spike Sample at 900 oC................................................149 C-19 XRD Pattern for Magnesium Hydroxide – Spike Sample at 900 oC.....................150 C-20 XRD Pattern for Silica – Spike Sample at 900 oC.................................................150 C-21 XRD Pattern for Spike Sample at 1100 oC............................................................156 C-22 XRD Pattern for Alumina – Spike Sample at 1100 oC..........................................156

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xi C-23 XRD Pattern for Attapulgite Clay – Spike Sample at 1100 oC..............................157 C-24 XRD Pattern for Calcium Hydroxide – Spike Sample at 1100 oC.........................157 C-25 XRD Pattern for Cement – Spike Sample at 1100 oC............................................158 C-26 XRD Pattern for Diatomaceous Earth – Spike Sample at 1100 oC........................158 C-27 XRD Pattern for Ferric Oxide – Spike Sample at 1100 oC....................................159 C-28 XRD Pattern for Kaolin – Spike Sample at 1100 oC..............................................159 C-29 XRD Pattern for Magnesium Hydroxide – Spike Sample at 1100 oC...................160 C-30 XRD Pattern for Silica – Spike Sample at 1100 oC...............................................160

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xii Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EVALUATION OF SORBENT TECHNOL OGY TO PREVENT HEAVY METAL EMISSION AND LEACHING FROM COMB USTION OF CHROMATED COPPER ARSENATE (CCA) TREATED WOOD By Anadi Misra August 2006 Chair: Chang Yu Wu Major Department: Environmental Engineering Sciences Chromated copper arsenate (CCA) is a popular wood preservative applied to wood products to prevent environmental decay during outdoor use and is often burned inadvertently to produce energy. Incineration re sults in volatilization of metals during combustion and an accumulation and subsequent leaching of metals in ash. This poses health and environmental concerns. Past stud ies have shown that many mineral sorbents are effective in controlling heavy metal vola tilization in the air phase during combustion. Therefore the objective of this study was to identify mineral sorbents that can minimize leaching of heavy metals from the incinerato r ash and evaluate the viability of thermal processes in existing facilities as an opti on for the management of CCA wood waste in the state of Florida. Since arsenic is the me tal of greatest concern in the combustion of CCA-treated wood, a literature survey wa s conducted on available arsenic pollution control technologies and equipment. From th e survey results, co-incineration, coupled

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xiii with the use of sorbent te chnology, appears to be the most promising amongst the existing techniques in the short term. Use of a combination of air pollution control devices, e.g., a wet scrubber combined with an electrostatic precipita tor, is suggested for emission control and impregna ted filters are recommended fo r sampling of arsenic in ambient air. Experiments were carried out usi ng metal spikes with an equivalent mass of metal corresponding to 3.68 pounds per cubic f eet (pcf) of CCA-treated wood (treated with CCA type C chemical). The spike-sorbent samples were heated at 700 oC, 900 oC and 1100 oC for 30 minutes. A portion of the resi dual was leached using the toxicity characteristic leaching procedure. The leach ate and ash were digested and analyzed by inductively coupled plasma spectroscopy to determine the meta l content. X-ray diffraction analysis of the residue was conduc ted to determine the crystalline speciation of the products. The results showed that alkaline earth sorbents (cement, calcium hydroxide and magnesium hydroxide ) and ferric oxide (at 1100 oC) showed great promise in reducing the leaching of arsenic and c opper from the incinerator ash. Regarding chromium, low leaching was observed for the alumino-silicate group (alumina and silica at all temperatures, and kaolin at higher temperatures), ferric oxide and magnesium hydroxide (at 1100 oC). Volatilization of metals was also reduced due to the metalsorbent binding, up to 60% in some cases, depe nding on the type of sorbent used and the system temperature. Speciation characterizati on results reveal the formation of several metal-metal and metal-mineral compounds (e.g., insoluble Ca3(AsO4)2 and highly soluble CaCrO4) which may have resulted in different leaching behavior of each metal-sorbent pair under different combustion conditions.

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1 CHAPTER 1 BACKGROUND 1.1 Wood Treatment: Processes And Chemicals Wood exposed to the outdoor atmosphere a nd in direct contact with soil and water is more prone to decay. For protecting th e wood from biological deterioration during outdoor use and to delay its combustion due to fire, a wood preservation process is carried out which involves impregnating the w ood with chemicals to make it resistant to decay and insects. Pressure treatment of wood is a popular option which involves transferring chemicals into th e wood by carrier fluids (wat er, oil) under pressurized conditions. Pressure treatment forces a chemi cal preservative deep into the wood. This technique is much more effective than simply soaking the wood in the chemical [1].The wood is first placed into a large cylindrical holding tank, and the tank is depressurized to remove all air. The tank is then filled with the preservative under high pressure, forcing it deeply into the wood fibers. The tank is then drained and the remain ing preservative is reused [2]. The wood is removed from the ta nk and is then used for decks, mailbox and light posts, swing sets, playscapes, picnic tables, landscape ties, underwater dock pilings, ocean-side boardwalks, telephone utility pole s and also residential building foundations in some parts of the country. Treatment ch emicals utilized duri ng the wood preserving process are separated into four major categor ies which include waterborne preservatives, oil-borne preservatives, creosote, and fire-ret ardants [3]. The first three categories of chemicals help prolong the useful life of w ood products by protecting them against insect and fungal attack.

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2 The first chemical in these categories, creosote, is a complex mixture of chemicals distilled from coal tar and is produced by condensing vapors from heated carbon-rich sources, such as coal or wood. Most comm on uses for creosote treated wood include railroad and bridge ties. The second categ ory of wood preservatives is oil-borne preservatives, which utilize oil to carry th e treatment chemical into wood. Oil-borne preservatives include copper naphthenate, zi nc naphthenate and pentachlorophenol. The most common of these is pentachlorophenol wh ich is used to trea t utility poles and crossarms [4]. Neither pentachlorophenolnor creosote-treated wood are used in residential applications. Wate rborne preservatives belong to the third category of wood preservative chemicals and are the focus of disc ussion in this report. They utilize water as the carrier fluid during the treating process. Af ter treatment, the water evaporates leaving behind the treatment chemicals. The most common waterborne chemicals are chromated copper arsenate (CCA), acid copper chro mate (ACC), ammoniacal copper arsenate (ACA), chromated zinc chloride (CZC), a nd ammoniacal copper zinc arsenate (ACZA). CCA chemical, which was the focus of this research, is the most common amongst these waterborne preservatives and represented over 90% of the U.S. waterborne preservative market till 2004 [5]. CCA is composed of the oxides of chromi um, copper, and arsenic. Copper serves as a fungicide while arsenic protects the wood against insects. Chromium fixes the copper and arsenic to the wood. CCA can be separated into Type A, B, or C depending upon the relative proportions of metals in each (Table 1-1). The most common formulation for CCA is Type C [6]

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3 Table 1-1: Composition of CCA-Type A, B, and C CCA-Type A CCA-Type B CCA-Type C Chromium as CrO3 65.5% 35.3% 47.5% Copper as CuO 18.1% 19.6% 18.5% Arsenic as As2O5 16.4% 45.1% 34.0% Source: [5] The amount of CCA utilized to treat the wood or retention level depends upon the particular application for the wood product (T able 1-2). Low retention values (0.25 and 0.40 lb/ft3) are used for plywood, lumber, and timbers if the wood is used for above ground and freshwater contact applications [3]. Higher retention values (0.60 lb/ft3) are required for load bearing wood components like pilings, structural poles, and columns in wood foundations. The highest rete ntion levels (0.8 and 2.5 lb/ft3) are required for wood components which are used for foundati ons involving saltwater contact [3]. Table 1-2: Retention Requirements for CCA-Treated Wood Source: [5] CCA-treated wood has been a popular choice as it produces no odor and its surface can be easily painted. The general appearan ce of the wood doesnÂ’t change at low retention values, thus the aesth etic quality is not compromise d. It was considered suitable for indoor use, as opposed to creosote-treat ed or pentachlorophenol treated wood and was generally used for interior parts of a wood structure in contact with the floor [3]. Drawbacks of the wood include a strong green color at high retention values. Due to the presence of hazardous metals in it, it canÂ’t be used in applications which come in contact Application Retention Value (lb/ft3) Above Ground: lumber, timbers and plywood 0.25 Ground/Freshwater contact: lumber, timbers and plywood 0.40 Salt water splash, wood foundations : lumber, timbers, plywood and structural poles 0.60 Foundation/Freshwater: Pilings and Columns 0.80 Salt water immersions: Pilings and Columns 2.50

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4 with food or drinking water. Recently, concerns over the possible release of arsenic upon direct contact with the wood have led the i ndustry to issue a vol untary phase out from most residential uses beginning from 2004 [7]. 1.2 Consumption Of Treated Wood In Industry Creosote is the oldest of the preservativ es and has been in use for over a century now. CCA is relatively new. Its commercial use began in the 1970s. Due to its various advantages and superiority over other wood pres ervatives, it was used in over 70% of the total treated wood product sold before it was pha sed out from residential applications [3]. In 1970, the total volume of treated wood produc ts was 248 million cubic feet (mcf) and CCA-treated wood account for 16% of it. By 1996, the total volume of treated wood had increased to 591 mcf with CCA-treated products accounting for 79% of it [3]. Before being phased out of most residen tial and some commercial applications beginning from 2004, CCA represented roughly 75% of the treated wood market by wood product volume. Among waterborne preser vatives, CCA represented over 97% of the market. In 1997, 40% of all treated poles and pilings and over 90% of treated lumber, timbers, posts, and plywood were treated with CCA. Approximately 144 million pounds of the chemical were utilized in the U.S. in 1997 to produce 450 million cubic feet of treated wood product [8]. The climate of Florida is very conducive to the growth of insects and fungi hence creating a need for treated wood products. As a result, Florida ha s a significant wood treatment industry within and n ear its borders. Florida along w ith its neighboring states of Georgia, Alabama and Mississippi accounts for 25% of the treatment plants across the nation. Therefore disposal of tr eated wood products is of great importance in these states. The State of Florida used to produce between 6 and 15% of the U.S. production of CCA-

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5 treated wood products in any gi ven year [3]. Assuming an average service life of 25 years for treated wood, it is anticipa ted that the total quantity of treated wood disposed will increase in the near future and that the characteristics of the waste stream will also change. It is predicted that the increased use of CC A-treated wood and the new phase out on the use of CCA wood products for most re sidential uses (effec tive 2004) will lead to greater presence of CCA wood waste in disposal sector. Hence, it is predicted that the disposal sector will observe a shift from disposal of larger quantities of creosoteand pentachlorophenoltreated wood waste to the disposal of wood treated by CCA in the near future [3]. The phase out of CCA – treat ed wood products from most residential uses resulted in a drastic decrease in consump tion of arsenic in wood preservatives from 19200 metric tons (mt) in 2003 to 4450 mt in 2004 [9, 10]. Although the total consumption of arsenic went down to 6800 mt in 2004, wood preservatives still accounted for about 65% of it [9, 10]. Due to the phase-out, large amounts of arsenic treated wood waste are expected in the disposal sector in the near fu ture. It is estimated that the annual disposal qua ntity of arsenic from wood preservatives, which was around 600 mt in 2004 is expected to peak in 2008 by reaching a figure of 730 mt of arsenic disposed per year. Arsenic disposal quantities are expected to decrease to a steady value of 320 mt per year after the year 2040 [11] . The prolonged leaching characteristic of disposed CCA-treated wood is expected to impact the environment over the next few decades. The cumulative mass of arsenic from treated wood products disposed of in Florida landfills was estimated at 5200 mt in the year 2000. By 2040, this amount is

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6 expected to increase to 26000 mt [11, 12]. Hence large quantities of arsenic from the wood wastes are expected in the dis posal sector in the near future. 1.3 Past Studies On Characteristics Of Treated Wood And Wood Ash Table 1-3 shows the background metal concen trations obtained from past literature to compare and contrast CCA-treated wood fr om other wood types. Table 1-3 shows the elemental analysis of different types of w ood, categorized as burned and unburned. Data from Table 1-3 indicates that untreated wood has significantly lower concentrations of arsenic, chromium, and copper than CCA-t reated wood for both unburned and burned wood samples. Table 1-4 shows the federal a nd Florida state regulat ory limits for each metal in different cases. Regulatory limits fo r the land application of sewage sludge have been utilized in some cases to regulate the land application of other wastes. At federal level, two sets of limits are established for elemental metal concentrations. “Ceiling concentration” represents maximum values for land applicati on whereas “pollution concentration” limits are stricter and are subj ect to less regulatory ove rsight. It should be noted here that chromium is not regulated for land application of biosolids from which the federal limits have been derived. Florida ma intains a stricter set of soil clean-up goals and they have been considered as guidelines for regulating land application of wastes in the state. Florida guidelines provide elem ental concentrations for residential and industrial land uses. By comparing table 1-3 an d table 1-4, it can be observed that arsenic and chromium concentrations from both CCA wood and CCA wood ash are well above these limits. Copper concentration also exceed s these limits in most of the cases. Table 1-5 depicts the toxici ty characteristic leaching pr ocedure (TCLP) values for each case. If a waste fails the TCLP test it is considered hazardous unless it has been

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7 provided a regulatory exempti on. Details about the TCLP pr otocol are covered in the procedures section. Table 1-3: Average Metal Concentration (mg/kg) in CCA-Treated Wood and Other Wood Types Unburned Ash Metal Untreated Wood (mg/kg) CCA Treated (mg/kg) Untreated Wood (mg/kg) CCA Treated (mg/kg) Arsenic 2.0 1200 67 33,000 Chromium 7.0 2100 51 16,000 Copper 3.7 1100 120 22,000 Source: [3, 13-15] A comparison with the regulatory limits in table 1-4 shows that CCA-treated wood and ash exceeds the limits for both federal and state regulations; hence they canÂ’t be land applied. Table 1-4: Regulatory Limits for CCA Metals Regulatory Limits Federal (Land Application) Flor ida (Soil Cleanup Target Level) Direct Exposure Metal Ceiling (mg/kg) Pollution (mg/kg) Industrial (mg/kg) Residential (mg/kg) Arsenic 75 41 3.7 0.8 Chromium Not Regulated Not Regulated 430 290 Copper 4300 1500 140,000 105 Source: [4, 16] TCLP analysis (Table 1-5) indicates th at arsenic concentration in unburned and burned samples of CCA-treated wood are in ex cess of the toxicity characteristic (TC) limit for arsenic. Other wood types, both unbur ned and ash, meet the regulatory limits. Chromium leaching is below its TC limit, even in the case of CCA treated wood. Although copper is not considered a hazardous me tal for its toxicity characteristic, its leaching is very low, both for CCA treated and other wood ash. Leaching of CCA-treated wood ash has been investigated by various researchers and excessive leaching of arsenic, copper and in some cases, chromium has been reported

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8 [17-21]. Past studies have shown that even sm all fractions of CCA wood, as low as 5% of total by mass in waste stream, can result in the exceedance of TCLP limits [18, 19]. Townsend et al. [22] conducted TCLP expe riments on wood sawdust gathered from various sources. In general, copper show ed maximum leaching followed by arsenic. Chromium displayed the least leaching of all the three metals. The mean copper concentration was 9.9 mg/L ( 4.0–16.6 mg/L). The mean concentrations of arsenic and chromium were 7.0 mg/L (3.7–12.5 mg/L) a nd 2.6 mg/L (1.1–4.1 mg/L), respectively [22]. According to the authors, in the case of TCLP, c opper leaches more than arsenic and chromium because it has greater affin ity for complexation with acetate. However, both arsenic and chromium have TC concentrat ion limits of 5 mg/L, while copper is not a TC metal (i.e., a waste can not be a TC hazar dous waste because of copper). Out of the 13 different samples investigated in this study, 11 exceeded the TC limit for arsenic. None of the samples exceeded th e TC limit for chromium [22]. Table 1-5: Average TCLP Values for CCA-Treated Wood and Other Wood Types Unburned Ash Metal Toxicity Characteristic Regulatory Limit (mg/L) Other Wood (mg/L) CCA Treated (mg/L) Other Wood (mg/L) CCA Treated (mg/L) Arsenic 5 0.11 8 0.20 180 Chromium 5 0.01 2.3 1.8 0.2 Copper Not Applicable ----0.29 0.06 Source: [3, 13-15] Solo-Gabriele et al. [23] studied the ch aracteristics of CCAtreated wood ash. It was found that CCA wood ash failed TC limit for arsenic in all cases and chromium in some cases. Results show that the TCLP leachate concentrations for arsenic and copper generally increased for samples characterized by higher retention levels. On the contrary, chromium showed the greatest leachable concentrations for samples having lower

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9 percentage of CCA chemical. Further investigat ion [24] revealed th at chromium in the ash produced from samples containing lower CCA retention levels was converted from trivalent chromium [Cr(III)] to hexavalent chromium [Cr(VI)], potentially due to differences in pH and variations in oper ating conditions. Cr(VI) is more mobile under acidic conditions, hence increased the leachable fraction of total chromium. It was also observed that the majority of the mass was a ssociated with the fine ash, and for arsenic and chromium, more metal leached out from fine r ash relative to large ash particles. The opposite relationship was observed for a fe w of the copper data points [23]. Under U.S. federal regulations, a waste can be classified as hazardous if it is a listed waste or if it exhibits any of the four characteristic s of ignitability, corrosivity, reactivity, and toxicity (40 CFR 261). A lthough the excess leaching of arsenic from CCA-treated wood samples has been widely reported, the regu lations (40 CFR 261.4 b (9)) exclude unburned CCA-treated wood disposed of by the end-user, from a hazardous designation regardless of its ch aracteristics. Therefore CCA-treated wood is managed in the same manner as domestic waste. However, ash from the combustion of CCA-treated wood is not provided an exemption. Of the four characteristics, toxic ity is the one that would likely be a potential issu e with wood ash [25]. If a solid waste is determined to be hazardous, it must be managed according to a strict series of c ontrols that include requirements for record keeping, storage, transportation, treatment and disposal. The management of a hazardous waste is typica lly at a much greater cost to the waste generator relative to a non-h azardous solid waste [25]. Hence ash treatment is necessary to ensure cost-effective disposal

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10 1.4 Issues With Incineration Of CCA-Treated Wood In 1996, 13 million cubic meters of CCA-treated wood were produced accounting for about 79% of all the treated wood in th e United States. Disposal forecasts indicate that approximately 31.0 mcf of CCA chemical was disposed of in USA during 1996. By 2005, this figure was projected to reach 141.5 mc f for USA. It is estimated that by 2015, it will reach 386.4 mcf for USA [3 ]. In the state of Florid a, CCA-treated wood production increased substantially during the 1980s a nd 1990s with an annual production averaging 7.2 mcf. Peak annual production occurred in 1994 with an annual production of 42.4 mcf of CCA-treated wood. Production dropped from 31.8 mcf in 2003 to 10.6 mcf in 2004 after the industry-sponsored phase out of CCA wood products. Disposal forecasts indicate that the peak annua l disposal is expected to occur during 2008 with a maximum of 24.7 mcf disposed in that ye ar. Disposal quantities are ex pected to decline to a steady state of 10.6 mcf afte r the year 2040 [11]. Due to the concerns over the health risks a ssociated with arseni c, the industry and the US Environmental Protection Agency (E PA) agreed to phase-out CCA treated wood from most residential uses, e ffective on January 01, 2004 [26]. As a consequence, it is expected that a high volume of CCA-treate d wood coming out of service will enter the waste stream that needs to be disposed of properly. Most of the CCA wood is disposed of in construction and demolition (C & D) debr is landfills along with other wood wastes [27]. Recycling of wood from C & D debris is common. Energy recovery was found to be the primary disposal pathway for the r ecycled wood waste [2]. There are several advantages associated with thermal process for disposal of waste. Firstly, the ash volume is significantly less than the wood waste, hence prolongi ng the lifetime of a landfill.

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11 Secondly, incineration of C&D debris wood containing CCA-treated wood may provide a valuable energy source. Historical estimates indicate that over half of the CCA-treated wood waste in Florida is burned to produce en ergy [3]. Disposal of CCA-treated wood via incineration may be problematic due to th e possible volatilization of metals at high temperature and accumulation and subsequent le aching of metals in the ash. This could pose serious health and environmental probl ems. CCA wood ash has been reported to leach arsenic and in some cases chromium , beyond TCLP limits [21, 22] and therefore can not be disposed of as regular waste. R ecent studies have suggested an increase in leaching of Cr from CCA-treated wood drawn from alkaline environments such as C & D debris landfill. It is suspected that the c onversion of Cr(III) to Cr(V I) may be responsible for this [24]. Among the metals contained within CCA, arse nic is the most toxic to humans and studies have shown that long-term exposures to CCA wood may resu lt in an increased cancer risk [1]. Arsenic is considered a se mi-volatile metal. During high-temperature combustion of fuel containing arsenic, ma ny arsenic compounds vaporize and generally recondense on very fine particulate matter when the combustion air cools down. While particulate control devices such as baghouses or electrostatic precip itators (ESPs) can be good options for controlling particulate emissi on (depending on the characteristics of the arsenic compounds formed), they are not good at controlling arsenic particulates present in submicron range and in the vapor phase. Also, the leaching from arsenic containing ash can pose a problem for ash disposal. During wood preservation, the Cr(VI) presen t in CCA solution is converted to Cr(III) in the wood matrix [ 21]. However, in some cases, combustion of CCA wood

PAGE 25

12 results in oxidation of Cr(III) to Cr(VI) [24]. Cr(VI) is much more toxic to humans than Cr(III) [28]; hence it should also be account ed for. Copper too, is toxic to aquatic organisms [29] and care should be taken while disposing copper containing wastes in sensitive aquatic ecosystems. Besides concerns over the potential toxicity of these wastes, another concern regarding burning them is th e potentially lower h eating value of CCA wood compared to regular wood, which may se t a combustion facilityÂ’s capacity limit. These issues addressed above evidence the need to control emi ssion of CCA metals during the combustion process and to minimi ze their leaching from the resultant ash. Recent research studies have shown the poten tial of injecting mineral sorbents into combustion system for controlling arsenic and other metals [2, 30]. Section 1.5 gives an overview of sorbent technology and its application in capturing heavy metals like arsenic, chromium and copper. 1.5 Sorbent Technology Various processing and manufacturing i ndustries face environmental problems related to emission of particulate matter in the exhaust gases. The release of toxic substances into the air in the form of partic ulates is a matter of great concern, as it can lead to severe health and environmental impact s. The emission of toxic heavy metals is of special concern in various indus trial boilers which use coal or other biological fuels and in hazardous & municipal wast e incinerators. Trace metals in flue gas streams are generally classified into three groups based on their vo latility and partitio ning in flue gas. Broadly, metals like beryllium (Be), chromium (Cr), manganese (Mn) and nickel (Ni) are considered least volatile; arse nic (As), cadmium (Cd) and lead (Pb) are considered semivolatile; and mercury (Hg) and selenium (Se) are considered the most volatile. The least

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13 volatile metals are found both in bottom ash & fl y ash; semi volatile metals are enriched in fly ash; and highly volatile metals are predominantly in va por phase in flue gases [31]. When semi volatile metals such as arseni c, lead & cadmium enter the incinerator, they vaporize if their vapor pressure is suffi cient to allow vaporization in the temperature range encountered. Later, as the temperature of the gas stream decreases, these metal vapors nucleate and condense to form particul ates. These semi-volatile metals are usually enriched in the submicron size range [32]. A ll standard air pollution control devices have the lowest collection efficiency in the submicron range. Hence these particles are collected and removed less effectively. Due to their small size, these particles have low settling velocities so they travel to the fa rthest regions from th eir origin. When human beings are exposed to these submicron particle s, they penetrate deep into lungs and get deposited there causing severe h ealth problems [33]. When inci nerator ash is disposed of in landfills, the heavy metals contained in the ash may leach out and contaminate the soil and groundwater [23]. Recent research studies have shown the poten tial of injecting mineral sorbents in combustion systems for controlling arsenic and other heavy metals [2, 30]. The metals interact with sorbents in ai r stream, condense on them and undergo chemisorption at high temperatures. The metal–sorbent compounds t hus formed have a particle size in the supermicron range so they are very effici ently captured by electr ostatic precipitators (ESP) and baghouses. Another major advantage is that these toxic metals are transformed into stable, non-toxic and non leachable com pounds [2, 34, 35] that become suitable for landfill disposal.

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14 Some of the sorbent materials identified in those studies like li me have been used in flue gas treatment for removing SO2 [36] and in other industri es such as power plants and waste incinerators. Another typical example of use of sorbents is activated carbon for mercury removal in combustion systems [37] . Coal is a major fuel consumed for generating electricity; he nce, cleaning up coal combustion exhaust is a big challenge in all industrial boilers. Bakker et al., 2003 [38] have s hown the effectiveness of a manganese-based sorbent for high temperatur e desulphurization a nd coal gas cleaning. Emission of lead and cadmium during incine ration of different kinds of solid and hazardous waste is another major issue. Alumina and silica based sorbents were found to be effective in capturing Pb & Cd under incineration conditions [39, 40]. 1.5.1 Techniques used for Introducing Mineral Sorbents in Combustion Environments Various methods like fixed bed reac tor (FBR), moving bed reactor (MBR), fluidized bed reactor (FLBR) and sorbent inject ion (SI) have been repo rted in literature for introducing mineral sorbents in air phase at high temperatures. Amongst all methods, FLBRs are the most popular [41-45] and are wi dely used in the chemical industry. They are essential to the production of key co mmodity and specialty chemicals such as petroleum, polymers, and pigments. Recently, di rect injection of sorbents in gas phase has gained acceptance [2, 31]. A brief descript ion of each of these methods is provided next with a special focus on FLBR and SI techniques which are popular for removing pollutants in gas phase. 1.5.1.1 Fixed bed reactor It is a common catalytic reactor that consis ts of tubes and parallel arrays of tubes filled with solid catalyst part icles. A FBR is a form of continuous flow reactor where the

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15 sorbent is packed in a column or as a flat bed and the substrate and product streams are pumped in and out of the reactor at the same rate. The FBRs are used for a variety of oxidation reactions and synthesis of new co mpounds. The main advantages of FBR are their easy application to la rge scale production, high efficiency, low cost and ease of operation [46]. One of the drawbacks associated with FBR is that the fixed solid phase in the reactor exhibits variable temperatures at different locations because of limited mixing of reactants resulting in lo wer yield reactions [47]. They also exhibit considerable pressure loss in air phase systems and hence are seldom used [48]. 1.5.1.2 Moving bed reactor The MBR is specifically designed fo r sorbent reactions accompanied by deactivation of sorbent since fresh sorbent is continuously added to replace the spent species. Sorbent regeneration via gas-solid re action can also be undertaken in a moving bed unit. While the process goes on, fresh sorben t is introduced slowly at the top of the bed, and spent sorbent is removed at the bot tom with the same rate [49]. Hence, the sorbent activity decreases in the downward direction. Also, care has to be taken to remove only the solid particles and not allow any gas to escape. The MBR is similar to the FBR in terms of processing of gas stream. Such reactors are consequently steady-state units and hence, analysis is somewhat simpler than for the FBRs [50]. 1.5.1.3 Fluidized bed reactor The FLBR consists of sorbents suspende d in a highly agitated condition by fluid flow through the reactor, resembling a boi ling liquid. Two phases are apparent, a relatively sorbents-fr ee bubble (gas) phase and a sorben ts-rich emulsion phase [49]. The fluidized powder can be handled as a liquid and can be mixe d easily. It can be fed into the reactor, and withdrawn from it, in conti nuous flows. Heat can be supplied or removed

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16 easily via the walls of the vessel or submerge d tubes. Therefore, fluidized bed reactors are often considered practica lly isothermal. Heat is unifo rmly distributed throughout the reactor due to continuous mixing. Hence, th e temperature difference between solids and gas is much smaller than in FBRs due to c onsiderable mass transfer resistance between the gas and the emulsion phase. Therefore, z ones of variable temperature donÂ’t occur in FLBRs [50]. FLBRs are used for a variety of organic and inorganic reactions. If the mobile phase in the reactor is replaced by gas, it can be used as a dryer in addition to a reactor. In the two modes, whether the mobile phase is liq uid or gas, the reactions occur between the solid and liquid or solid and gas phases. Th is technique has been used for converting metals into metal oxides, sulfides, and nitrid es by heating fine metal particles at high temperatures under the appropria te gaseous environment [47]. 1.5.1.4 Sorbent injection SI technique is commonly used for cleaning up acidic gases in flue gas. The sorbent is injected into the flue gas duct. The injecti on creates turbulence that results in mixing of the sorbent with the flue gas. Adsorption of acid gases by the sorbent begins in the flue gas ductwork. An expansion/reaction chamber is often included to increase the residence time of the gases in the system, allowing more time for the reaction to occur. The sorbent and reaction products are carried by flue gas to the particulate cont rol device, where the solids are collected. If a fabric filter is used as the particulate control device, acid gas removal may be further enhanced by reaction with the sorbent collected in filter cake. The sorbent injection rate depends on the ac id gas content of the flue gas and should provide adequate sorbent for ne utralization of the acid gases. As particle size decreases,

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17 the surface area to volume ratio increases, which improves the efficiency of acid gas collection [51]. A common application of sorbent technology is in flue gas desulfurization (FGD) where a sorbent, usually Ca(OH)2, is injected into the flue gas in the upper reaches of the boiler. Upon injection, Ca(OH)2 immediately dehydrates to form a high surface area calcium oxide (CaO) whic h reacts readily with SO2 and O2 and SO3 to form gypsum or calcium sulphate (CaSO4), a dry powder which remains suspended in flue gas. The resulting particles, c onsisting of fly ash, hydrated calcium sulfite & sulfate and unreacted sorbent, are transported out of the boiler to be captured in an ESP or baghouse [52]. The capture efficiency is dependent on many fact ors: the temperature, oxygen and moisture content of the flue gas, cont act time between sorbent & meta l and the characteristics of the sorbent (e.g., sintered sorb ent, porosity, admixture of other sorbing agents). SI has the potential to significantly increase the dust loading and alter the characteristics of the particulate matter enteri ng the dust collector. With fabric filters, this generally poses no problems. However, due to the increased dust loading, the ESPs may need more enhancements to maintain particulate emissions and opacity within compliance limits. SO3 injection and humidification ar e two approaches to enhancing ESP performance, which are compatible with SI. The biggest advantage of SI is that it can easily be retrofitted to existing combus tion facilities although the particle removal system may have to be upgraded to collect the relatively larger load of particles [53]. Disadvantages of SI include the fact that relatively large amo unt of sorbents are required due to the relatively lower efficiency of meta l capture by dry particle s. Also, the rate of sorbent injection must be high enough to ach ieve satisfactory capture efficiency [51].

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18 1.5.2 Application of Sorbents for Me tal Capture at High Temperature Metallic air toxics in flue gases are found in various elemental or oxidized forms and in solid or vapor states. These metal lic compounds originate from fuel combustion (coal and other fossil fuels) and incineration of solid and hazardous wastes. Efforts are being made to capture these metals in the ai r phase and inhibit thei r volatilization in the feed by using mineral sorbents which chemical ly bind to these toxi cs, thus neutralizing them, increasing their thermal stability (hen ce increasing their retention in feed) and increasing their particle size (thus enabling their capture by particulate control devices). Table 1-6 lists some of the studies conducted by researchers to test the applicability of various sorbents under different operating condi tions to capture a vari ety of heavy metals under incineration conditions. However, if th e production process in these industries (such as cement production) is used for cont rolling of metal emissions, there may be public concerns regarding product contamina tion. On the other ha nd, the contamination may not be high because the concentration of metals will be very low if CCA wood is only a small fraction of the total wood be ing burned. Also, the product would contain stabilized metal-mineral compounds; so the leach ing levels may be low. Nevertheless, all these issues need to be addressed. Many studies in the past have focused on the control of metal emissions using sorbents in coal combustion processes, wh ile not much work has been done on CCA wood combustion using sorben t technology. Coal combustion studies canÂ’t be applied directly to CCA wood combustion as the fuels are different, both in terms of temperatures encountered during combustion and the con centration of metals in them. Limited leachability data is available on sorbent-me tal interactions in CCA metals. Also, not much is known about the characteristics of CCA wood and sorbent mixture ash in

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19 combustion systems and the reason for the vari ation in leaching beha vior with different sorbents.

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20 Table 1-6: Sorbents used for Capt uring Metals at High Temperature Sorbent Test Conditions Metals Reference Ca based, Mg based, Na based In feed, 600-900 oC As, Cu, Cr [2] Kaolinite, Attapulgite Clay, Bauxite, Silica, Alumina, Diatomaceous earth In feed, 500900 oC As, Cr,Cd, Pb, Ni [35] Kaolinite, Hydrated lime, limestone, bauxite In gas stream, 1000-1300 oC As, Hg, Se, Sb [31] Kaolinite, Limestone, Alumina, Water In gas & feed, 700-900 oC Cr, Cu, Pb, Cd [54] Sand, Alumina In feed 700-900 oC Pb [41] Kaolinite In gas, 550 oC Fe, Ni, V, Zn [55] Kaolinite In gas, 1000-1300 oC Pb, Cd, Na [56] Silica In gas, 600-800 oC Pb [57] Limestone, Sand, Alumina In feed, 500-1000 oC Pb, Cd [45] Hydrated Lime, Kaolinite, Alumina, Silica In feed, 400-1000 oC As [58] Limestone, Bentonite, Alumina, Calcinated Limestone In feed, 750-900 oC Pb [42] Bauxite, Kaolinite, Emathlite, Limestone In feed, 500-800 oC Pb, Cd [40] Sand, Limestone, Alumina In feed, 400-1000 oC Pb [43] Aluminosilicate compounds impregnated with lime + traces of other metal oxides In gas, 800-1000 oC Na, K, Pb [59] Kaolinite In gas, 300-2300 oC Ba [60] Diatomaceous Earth, Alundum, Silica Gel, Attapulgite Clay, Activated Bauxite In gas, 800-950 oC Gaseous NaCl, KCl [61] Hydrated Lime In gas, 400-600 oC Se [62] Limestone, Bauxite, Zeolite In feed, 600-900 oC Cr, Pb, Cd [44] TiO2 In gas, 700-900 oC Coal combustion particles [63] Bauxite In gas, 800-900 oC NaCl, KCl vapors [64] Hence this study focused on identifying mineral sorbents that can minimize emission and leaching of heavy metals fr om CCA wood under combustion conditions. Characterization studies were car ried out to determine the speci ation of the products in an

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21 attempt to explain the varia tion in leaching behavior of CCA wood ash with different sorbents. 1.6 Mechanism This section gives an overview of the va rious mechanisms and models for metal capture and transformation using sorbents in air phase as reported in the literature. Problems and challenges encountered in using so rbents at high temperature environments are also discussed. Generally speaking, chemisorption is the dominant mechanism for metal adsorption by sorbents at high temperature. Experime ntal studies [65] broadly classify the mechanism based on volatility of metals. For less volatile metals, chemisorption is the dominant mechanism with physical processe s of particle growth like condensation, coagulation and sedimentation gaining some importance when reaction time is increased. For semi-volatile metals, both physical and ch emical adsorption is important, depending on the reaction environment. For highly vol atile metals, physical molecular adsorption and particle growth processes appe ar to be the major mechanisms. Kaolinite is a popular sorbent studied by va rious researchers [31, 66] for capturing heavy metals in combustion environments and is also being used in this study. In general, reactions of semi-volatile metals (Pb, Na, C d, etc.) with dispersed kaolinite aerosols are very similar. Understanding th e reaction of kaolinite with se mi-volatile metals may give insights into its reactivity with arsenic, which is also a semi-volatile metal. Gale et al. [67] investigated mechanisms of interacti on between a dispersed kaolinite aerosol and vaporized Na & Pb. When kaolinite is inject ed into the furnace, dehydroxylation causes the kaolinite alumina layer to convert from octahedral co-ordination to tetrahedral coordination, forming meta-kaolinite. Then the metal vapors diffuse through mesopores into

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22 the interstitial sites on the al umina layer surface of the kao lin particle platelets [67]. When Na initially reacts with meta-kaolin ite, Na-alumino-silicates are formed causing meta-kaolinite to revert from the reactive te trahedral co-ordination to a more stable octahedral coordination. This transformation cau ses some free silica to be released from the sorbent matrix, hence forming some Na-s ilicates too. As the r eaction proceeds, the meta-kaolin crystal structure breaks down into silicates and aluminates, which are soluble in water. Eutectic melting plays a key role in the r eactivity of kaolinite aerosol. A eutectic point is defined as the lowest temperatur e at which a combination of two or more substances will melt [68].The metal-sorbent reaction rate and sorbent utilization is enhanced by eutectic melting in three ways. First, the melting of the sorbent breaks apart and opens up the tightly packed crystal, allowing space to accom modate more metal atoms, and even metal-sorbent compounds. The breakdown of alumino-silicates to aluminates & silicates provides additional freedom to combine with more metals (freer valences/active sites), increasing the sorbent ut ilization rate to up to twice of what is calculated based on stoichiometry. Finally, a surface renewal melt may also permit access to unutilized sorbent material [67]. This surface renewal mechanism is based on the assumption that a partial particle collapse may impede access to some reactive material. However, melting also closes mesopores, hence deactivating them. This rate of deactivation increases with temperature [67]. 1.6.1 Aerosol Size Fractionation Method (ASFM) To develop a practical scale technology, the rate of metal sorption by sorbents at high temperature must be quantified. For th is purpose, an aerosol size fractionation approach has been proposed by Davis et al. [ 32] to determine the extent of metal vapor–

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23 sorbent interaction above the metal dew point. The ASFM is based on the principle that any metal vapor that has not reacted with the sorbent stays in vapor phase. This assumption is valid when air samples are with drawn above the dew point of the metal in question. An ASF system was designed by Davis et al. [32] to have a rapid quench probe to withdraw the metal vapors and a low pressu re impactor to collect the metal–sorbent particles. A simple 1st order kinetic model was then pr oposed to calculate the reaction rate and the extent of reaction of the meta l-sorbent system. Reaction rate was calculated using that model and found to be as 8*10-10 cm3 gas/mol sorbents [32]. 1.6.2 Impact of Competition CCA wood combustion in a practical sc ale technology will involve a lot of elements. Besides the CCA metals, sulfur, ch lorine and other elements may be present and may compete for the available sorbent and CCA metals. Therefore, it is necessary to understand the impact of competition on so rbent efficiency. Davis et al. [32] determined that the reaction rate for the capture of cadmium by kaolinite was almost 4 times smaller than the capture of sodium. Given the esti mate of the rate of cadmium capture by kaolinite, a kinetic model describing simple competition for reactive sites does not appear to account for the experimental observations in multi-metal systems involving sodium, cadmium and kaolinite. Hence it is possible that sodium also inhibits cadmium capture by kaolinite besides competing for reactive sites [ 32]. Within a full-scale incinerator or coalfired boiler, acid gases and other metals may have a significant impact on the speciation of individual metals. Chlorine, for example, has a complicated speciation path [69], which in turn has a significant impact on mercury speciation [70, 71]. However, the major impact of SO2 and chlorine observed on capture of semi-volatile metals (like Na and Pb) by kaolinite has been to change the dew point of the reactive metal species, and

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24 thus change the time available for reaction [ 72, 73]. The impact of multiple metals in a single flue gas has also been investigated. The presence of several semi-volatile metals has been shown to significantly alter the reac tion rate of these metals with kaolinite through enhancing and inhi biting interactions. 1.6.3 Calcination and Sintering Calcium hydroxide is an important part of the experimental matrix in the experimental system used in this project. Theref ore, it is important to have an idea of the involved mechanism while using Ca(OH)2 as a sorbent and also some of the typical problems like sintering which are enc ountered in using it. When Ca(OH)2 is injected into the furnace, it decomposes or calcines to high-surface-area, highporosity CaO following this equation: O H CaO OH CaHeat 2 2) ( The highly reactive CaO then reacts with SO2 in the presence of O2 to form solid CaSO4 as: 4 2 22 1 CaSO O SO CaO Contrary to calcination, which acts as an activation step, the sulfation reaction is a deactivation phenomenon which resu lts in the build-up of the CaSO4 product layer and, hence, a loss in available surface area. A nother mechanism by which active surface area is lost is thermal sintering. In sintering, the grains coalesce to form larger grains, reducing the surface area and porosity of reactive CaO [74]. Both calcination and sintering phenomena are extremely important in determ ining the effectiveness of sorbent in removing SO2 from combustion gases, and occu r very rapidly under upper-furnace temperatures of 850-1200 oC. Bortz et al. [75] reporte d 70% calcination of Ca(OH)2

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25 particles within the first 25 ms of the reaction at 700 oC. Similar observations have been made regarding calcination by other studies, t oo [76]. Inadequate sorbent/gas mixing and slow particle heat-up could be the possible r easons for the low calcination rate reported in some studies [77]. Available reports regarding sintering suggest a very fast sintering rate leading to rapid reduction in surface area within 100-200 ms [78] of the reaction. For small sizes (< 10 microns) of sorbent particles, intra-par ticle heat and mass transfer do not offer any significant resistan ce to calcination [79]. Calcination rate was found to be proportional to the available surf ace area of the unreac ted particle [76, 79]. However, the available surface area changes w ith temperature. At high temperatures (> 700 oC), CaO surface area is readily lost due to sintering. Studies with pre-calcines suggest that the rate of surface area reduc tion is proportional to the square of the instantaneous surface area [80]. Besides te mperature, a substan tial enhancement of sintering was observed in the presence of H2O and CO2 in the combustion gas. Simultaneous modeling of calci nation and sintering of CaCO3 sorbent [81] suggested that sintering of the product CaO surrounding th e un-decomposed sorbent core causes diffusional resistance to the outgoing CO2 gas which may limit the calcination rate at a later stage. It was suggested that a similar resistance to H2O diffusion may be rate limiting for Ca(OH)2 decomposition. Ghosh-Dastidar et al . [82], studied the kinetics of calcinat ion and sintering of Ca(OH)2 powder between 900-1050°C temperature range. A mathematical model was developed based on first-order decomposition kinetics and a second-or der sintering rate equation, which satisfactorily describes the tim e-resolved experimental data. At 1050°C, a high extent of calcination of about 90% was observed, whereas for the lower

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26 temperatures of 900°C and 950°C, about 50% and 70% calcination was observed, respectively. Considerable si ntering occurred at high temperatures, which drastically reduced the CaO surface area [ 82]. The mathematical model also matched the surface area evolution data for the temperature range, accurately representing the experimental observation that the highest peak surface area is achieved at the intermediate temperature of 950°C. The model predicted an initial increase a nd then a drop in the surface area to an asymptotic value for all three temperatures. The authors concluded that opting for a lower temperature will help in producing a higher surface area and preserving it for a longer time, however it will fail to achieve subs tantial decomposition of the hydroxide, hence leading to a lower sorbent utilization. Als o, a decrease in the r eaction temperature will reduce reactivity of sorbent with flue gases/metals. Hence an optimum condition for sorbent injection has to be determined, to ach ieve superior sorbent utilization and high metal/pollutant capture [82]. 1.6.4 Speciation of Adsorbate and Adsorbent The speciation of adsorbate and adsorben t is also known to affect the sorption behavior of metals with sorbents and other properties like leacha bility of ash [83]. Earlier, while discussing cal cination, the importance of sp eciation of adsorbents was outlined by showing the different sorp tion behavior betw een CaO and Ca(OH)2 . Here, the specific case of mercur y speciation (adsorbate) is discussed briefly. Mercury emissions from coal-fired power plants are highly dependent upon mercury speciation. Elemental mercury (Hg0), which constitutes the majority of the mercury leaving the furnace, is insoluble and therefore able to pass through a scrubber into the smokestack [70]. However, in the presence of chlorine, Hg0 is first oxidized via Cl into HgCl which,

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27 in turn, is subsequently oxidized by Cl2 into HgCl2 with an associated regeneration of Clatoms [70, 84]. HgCl2 is water-soluble. Therefore, it ca n be easily dissolved in scrubbing solutions used for SO2 removal and be efficiently removed. Speciation of reaction products has been discussed in detail in the results section in this study. 1.6.5 Summary Various sorbents have been tested to captu re trace metals by different researchers. Alumino-silicate compounds and alkali earth elemen ts form a large part of these sorbents. Given the variety of sorbents, metals and ope rating conditions, it is difficult to predict the exact nature of their inter action. However, some specific cases involving commonly used sorbent-metal pairs were discussed. The mechan ism of kaolinÂ’s interaction with sodium was discussed in detail. ASFM was found to be a good technique to determine the sorption rate of metals by sorbents. It was al so observed that multi-metal systems inhibit sorption not only by competition for reactive sites but also by adversely affecting the interaction of other metals with sorbents. Si ntering of sorbents at high temperature leads to considerable loss of surface area hence affecting sorbent capacity. So, for Ca-based sorbents, an optimum temperature range should be worked out to effectively utilize the sorbent. Speciation of both the adsorbent and adsorbate affects their chemical and physical properties and hence their capture. Mo re rigorous studies are needed to increase our understanding of meta l-sorbent interaction at high temperatures.

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28 CHAPTER 2 OBJECTIVES The overall goal of this study was to evalua te the utility of so rbent technology for CCA wood disposal in combus tion environments. Specifically, two major tasks were carried out in this project to address the questi ons laid out above. Details of each task are discussed in the following subsections. 2.1 Survey of Available Pollution Control Technologies Information regarding available pollution control technologies and equipment for controlling arsenic emission a nd leaching from combustion f acilities was collected from the literature. 2.2 Screening of Potential Materials for Pr eventing Leaching of CCA Metals from Incineration Product The specific objective of this task was to evaluate metal-sorbent interaction in combustion environment for various mineral so rbents. The following steps were carried out a. Tested a series of sorbents with CCA metals to determine the leaching characteristics of the products b. Performed characterization studies on CCA metal-sorbent residues to understand their leaching behavior c. Determined the most suitable mineral sorbent(s) and optimal operating condition(s) for controlling heavy metal leaching in combustion systems during incineration of CCA wood

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29 CHAPTER 3 ARSENIC POLLUTION CONTROL TECHNOLOGIES 3.1 Introduction Arsenic is a naturally occurring element wide ly distributed in the earth's crust. In the environment, arsenic is found in combin ation with oxygen, chlorine, and sulfur to form inorganic arsenic compounds . Arsenic in animals and plants combines with carbon and hydrogen to form organic arsenic compound s. Arsenic occurs na turally in soil and minerals and therefore can enter the air, water, and land from wind-blown dust and may get into water from runoff and leaching. Arseni c cannot be destroyed in the environment. It can only change its form. Precipitation can remove arsenic dust par ticles from the air. Many common arsenic compounds can dissolve in water and most of them end up in soil or sediment. Fish and shellfish can accumula te an organic form of arsenic called arsenobetaine, which is relatively less harmful [85]. Inorganic forms of arsenic, such as that found in CCA-treated wood, tend to be more toxic. For human health, even ingesting small amounts of inorganic arsenic present in food and water or breathing air containing ar senic can be harmful. Exposure can occur through breathing CCA wood sawdust or sm oke from its combustion. Geographical locations having unusually high na tural levels of arsenic in rock are also sources of exposure. Work involving arsenic production or use, such as copper or lead smelting, wood treating, or pesticide application can also cause exposure to humans [85]. Inorganic arsenic compounds are mainly us ed to preserve wood. CCA is a major arsenic based treatment chemical used to preserve wood. Although it is no longer used in

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30 the U.S. for residential uses; it is still used in industrial applications. Organic arsenic compounds are used as pesticides, primarily on cotton plants. Inor ganic arsenic is a known human carcinogen [86]. It is used in the industry primarily in the form of arsenic trioxide. It is also used as a pure metal and in the form of arsine gas. The most common end-use for arsenic in the U.S. is as a wood preservative. So me firms also use arsenic as an intermediary in the manufacture of el ectronic products. Table 3-1 provides some details about the commonly occurring forms of arsenic. Arsenic is listed as a human health hazard in several lists. Besides being listed as a carcinogen, it has been listed as cardiovascul ar or blood toxicant [87], developmental toxicant [87], gastrointestinal or liver toxicant [88, 89] a nd neuro-toxicant [87]. It has also been ranked as one of the most hazardous compounds (worst 10%) based on its impact on the ecosystem and human health [90]. The total environmental releases ( The sum of chemicals released to the environmen t: air, surface water, underground injection and land, including only chemic als and companies covered by national emissions reporting systems .) of arsenic, both organic and i norganic, are estimated at 401 million pounds after hydrochloric acid and zinc compoun ds thus making it a pollutant of serious concern [91]. 3.2 Consumption of Arsenic in US The production of arsenic within the U.S. historically occurred as a smelting byproduct of copper, lead, gold, and silver. Th e U.S. arsenic production peaked in 1944 with 24,800 metric tons and U.S. represented the major global supplie r of arsenic [92]. Since then, the U.S. output of arsenic has gradually declined a nd it stopped producing arsenic after 1985 [93].

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31 Table 3-1: Arsenic Fact Sheet Arsenic Arsenic Trioxide Arsenic Pentoxide Arsine Gas Chemical formula As As2O3 As2O5 AsH3 Common Name – White Arsenic Arsenic Anhydride – CAS Number 7440-38-2 1327-53-3 1303-28-2 7784-42-1 Water Solubility None Slightly SolubleSoluble – U.S. now imports all of its arsenic de mands [94]. In 2001, 25000 metric tons of arsenic was imported, out of which 88% was used for wood preserva tives. Electronics and nonferrous alloys accounted for 4% of U.S. arsenic consumption in that year. Arsenic is used as a dopant in silicon wafers and in the processing of gallium arsenic crystal. It is also used in the manufacture arsine gas, wh ich is used to make super-lattice materials, light wave devices, and high performance integr ated circuits. Arsenic is used in copper alloys to increase their corrosion resistance and te nsile strength. It is used as an additive (0.01% to 0.5%) to increase the strength of pos ts and grids in lead acid batteries [94, 95]. Ceramics and glass products accounted for 3% of the total consumption in 2001. Arsenic compounds serve as fining agents to di sperse air bubbles and color in glass manufacturing and control the rate of crysta l growth in the glass ceramics industry [9496]. About 4% arsenic was consumed by agricu ltural chemicals like pesticides, weed killers and insecticides. With the discovery of the hazards of arsenic and the development of organic-based herbicides and pesticides, arsenic use in agri culture has declined steadily since the 1930s and 1940s, when an estimated 45,000 metric tons of arsenic-based insecticides were used annually [95]. As late as 1975, agricultural ch emicals accounted for over 80% of the total arsenic consumption in the U.S. In the 1990s, agricultural use of arsenic was limited to

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32 the herbicides di-sod ium methane arsenate and monosodi um methane arsenate, for weed control in cotton fields and accounted for 4-6% arsenic consumption over the past couple of decades [10, 94-96]. Due to the phase out of CCA-treated wood products from residential uses, the consumption of arsenic has gone down to 8000 metric tons in 2005 [9, 10]. In spite of that, wood preservatives accounted for about 65% of the arsenic consumed in 2004 [9]. Thus wood preservatives represent a large port ion of arsenic consumption in US. It was estimated that in 2001, world-wide wood pres ervation industry trea ted approx. 30 million cubic meters of wood each year and approximately 2/3rd of this volume was treated with CCA [97]. Hence large amounts of arsenic treated wood wa ste are expected in the disposal sector in the years to come. 3.3 Health Hazards Associated with Arsenic 3.3.1 Acute (Short-Term) Health Effects Acute inhalation of arsenic can cause nausea, vomiting, diarrhea, and abdominal pain and/or irritation of the nose and throat [95] Skin and eye contact can cause irritation and burning [95] Arsine gas is lethal to humans even at low doses between 25 and 50 ppm [95] 3.3.2 Chronic (Long-Ter m) Health Effects Inorganic arsenic is a know n carcinogen [86]. The U.S. EPA classifies inorganic arsenic as a Group A carcinogen, a human carcinogen of high carcinogenic hazard. The inhalation of inorganic arsenic is str ongly associated with lung cancer and its ingestion has been linked to skin, bl adder, liver, and lung cancers [95] Inorganic arsenic is also suspected to be a reproductive hazard for humans and animals [87] Chronic human inhalation of inorganic arseni c is associated with irritation of the skin and mucous membranes (dermatitis, conjunctivitis, pharyngitis, and rhinitis)

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33 Chronic oral exposure can result in kidne y, liver, or stomach damage, as well as anemia, skin lesions, and holes or ulcers in the bone dividing the inner nose [88, 89] The EPA regulates arsenic under the authority of six environmental statutes Clean Air Act (CAA), Clean Water Act (CWA), Co mprehensive Environmental Responsibility, Compensation and Liability Act (CERCLA, popularly known as “Superfund”), Resource Conservation and Recovery Act (RCRA), Emergency Planning and Community Right-toKnow Act, and Safe Drinking Water Act [95] . Hence arsenic is th e element of greatest concern amongst all CCA metals. Table 32 summarizes the various standards and regulations for inorganic arsenic. 3.4 Available Technologies for Control of Arsenic Pollution Since treated wood forms most of the sour ces of arsenic pollution, future waste minimization focuses on the use of alterna tive wood treatment preservatives devoid of arsenic. Efforts are being made to substitute CCA treated wood by other materials (untreated cedar, teak, etc) and to use w ood modification treatments to increase its longevity. Emphasis is being laid on prev enting overuse of preserved wood and minimization of wood waste during construction [98]. In spite of these waste minimization e fforts, disposal of CCA treated wood continues to be important in the next few decades due to the la rge quantities of CCAtreated wood which is still in use and is present in the disposal sector. The efforts to deal with the problems associated with CCAtreated wood are at tw o levels (i) Source Reduction (ii) Efficient management of CC A-wood waste. The management options can broadly be classified as – Reuse – as garden borders, posts, fence components, mulch, etc.

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34 Recycling – Wood based composites [101], extraction of CCA metals by chemical, biological and electrodialyt ic methods [90, 91, 102, 103] Treatment and Destruction [2, 104-108] – Wood liquefaction, thermal destruction by combustion, pyrolysis and gasification Landfill Disposal Table 3-2: Standards and Regula tions for Inorganic Arsenic Agency Focus Level Comments American Conference of Governmental Industrial Hygienists Air: workplace 10 µg/m3* Advisory; TLV/TWA+ National Institute for Occupational Safety and Health Air: workplace 2 µg/m3 Advisory; 15minute ceiling limit Occupational Safety and Health Administration Air: workplace 10 µg/m3 Regulation; PEL++ over 8-hour day U.S. Environmental Protection Agency Water 10 ppb Regulation; maximum contaminant level in drinking water Food and Drug Administration Food 0.5-2 ppm Regulation; applies to animals treated with veterinary drugs *µg/m3: micrograms per cubic meter; ppb: parts per billion; ppm: parts per million +TLV/TWA (threshold limit value/time-wei ghted average): time-weighted average concentration for a normal 8-hour workday or 40-hour workweek to which nearly all workers may be repeatedly exposed ++PEL (permissible exposure limit): highest le vel averaged, over an 8-hour workday, to which a worker may be exposed. Source: [99, 100] This project focuses on option 3, the th ermal destruction of CCA-treated wood waste by combustion. There are two steps involv ed in the safe disposal of CCA-treated wood waste by thermal processes – Reduce emission from sources by adopting optimal thermal technology – Amongst the various thermal processes available, to determine the optimal set of operating conditions (temperature, treatment time, fu el/air ratio etc.) to minimize emissions of hazardous substances. Efficiently capture all the arsenic emitted – It is practically impossible to have no hazardous emissions from the thermal tr eatment of CCA-treated wood waste;

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35 hence, efforts are made to capture all of the arsenic generated. Various air pollution control devices are used by industries to control ai r emissions. Table 3-3 summarizes the types of ai r pollution control devices available in combustion facilities in Florida. The data for the list was last accessed in Oct, 2004 from the online permit list available at the Florida Department of Environmental Protection website. It is important to keep in mind the available pollution control devices in the industry to propose a technology which can be effectively utilized by the industry Table 3-3: Summary of Air Pollu tion Control Devices in Com bustion Facilities in Florida Type of Boiler Type of Air Pollution Control Devices Cement Kilns ESP, Baghouse Coal fired plants ESP to control particulate matter (PM), Wet limestone FGD unit to control sulfur dioxide (SO2), Wet caustic scrubber to control PM and SO2, SNCR to control NOX, Limestone scrubber, Low-NOX burners, Fabric filter baghouse for PM, Hot side and cold side ESP for PM, Spray dryer absorber Wood Waste Boilers Fly ash arrestor, we t scrubber, Multicyc lone, wet caustic scrubber to control PM and SO2, SNCR to control NOx, hot side and cold side ESP for PM, venturi scrubber, multiple tube dry collectors, multi-vane cyclone, continuous opacity monitoring (COM), wet vent uri scrubber, Joy type Impingement Scrubber (equivalent to spray dryer absorber for SO2), fabric filter for PM, Wet ESP Waste To Energy (WTE) Plants Baghouses, spray dry absorbers, activated carbon injection system, SNCR, auxiliary gas burners, dry scrubber, mercury abatement systems, ESP, activated carbon injection systems (ACI) for control of Hg a nd certain organic emissions 3.5 Available Thermal Processes fo r CCA Treated Wood: Emission control In this subsection, the thermal processe s commonly used for CCA-treated wood and the pros and cons of each are reviewed. There are three main types of thermal processes available – Incinera tion, Pyrolysis (slow, flash) and Gasification. Figure 3-1 summarizes the relative oxygen requirements for each. 3.5.1 Incineration Combustion of CCA-treated wood waste is the simplest of all techniques.

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36 Advantages – Easy to replicate and hence can be used at industrial level with minor retrofitting of boilers and air pollu tion control devices Can be coupled with other industrial proce sses (such as production of cement, coal or steel ) without the need for separate combustion boilers Can be coupled to a recycling process by using extensive gas cleaning system to control air emissions. For instance, the ar senic collected by wet scrubbers can be recycled to the CCA solution production uni t and the ash containing arsenic, copper and chromium can be processed in a c opper smelter [95, 109] or recycled through chemical or electroche mical processes [110]. Disadvantages – Extensive gas cleaning equipment required The arsenic trioxide dust collected in filters poses problems for workers, hence from that point of view, wet methods are preferred Wood burning is often accompanied by form ation of polychlorinated dibenzo-pdioxins (PCDD) and polychlorinated di benzofurans (PCDF). The amount depends on the type of wood burned and the combus tion parameters. PCDD/ F formation is of special concern for com bustion of CCA-treated wood as it is rich in copper which acts as a catalyst fo r its formation [111-114] Unlike gasification and pyrolysis, no sec ondary fuels are produced and the energy generated has to be us ed instantaneously Hence, incineration can be an option for th e disposal of CCA treated wood waste or mixed wood waste. Various studies [31, 115117] have utilized mineral sorbents to effectively reduce arsenic emissions during co al combustion. The ash formed is non-toxic and non-leachable [2]. Such techniques show considerable promise for disposal of CCAtreated wood via incineration.

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37 gasification by pyrolysis pyrolysis for liquids pyrolysis for charcoal gasification by partial oxidation close coupled combustion close coupled gasification starved air incineration combustion oxygen (% stoechiometric) 125 0 25 50 75 100 Figure 3-1: Relative Oxygen Requirements for Various Thermal Processes (Source: [118]) 3.5.1 Co-incineration Co-incineration involves simultaneous or sequential combustion of two or more fuels. This technique is very popular in some industries, especially in cement kilns, where waste tires are burnt along with coal. Advantages – It is more economical as co-incinerati on can also be carried out in huge power plants and not just in incinerators It also combines the benefits of regular incineration process. For example, coincineration in a waste incinerator wo uld require minor re trofits only [119] Since CCA wood will be a secondary fuel, its constant supply is not an issue as in the case of incineration of CCA wood alone Mixing of fuels can compensate for the low heating value of CCA wood waste. Also, the components of the other fuel (m unicipal waste, coal, etc.) may scavenge the CCA metals It is easier to comply with emission legisl ation due to the dilution in concentration of the CCA metals in the emitted air and in the ash

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38 Disadvantages – The total emission may still be high, even though the concentration of CCA metals may be lower Regulations may prohibit mixing of wastes The lower concentration of arsenic in flue gas may make its removal more challenging According to Helsen et al., in spite of th ese drawbacks, co-incineration seems to be the best available short term solution fo r thermal treatment of wood waste [118]. 3.5.2 Pyrolysis The chemical decomposition of organic ma terials by heating in the absence of oxygen and any other reagents is called pyr olysis. Pyrolysis done in the absence of moisture at very low residence times (< 2 se c) and high heating rate s is called flash/fast pyrolysis. Flash pyrolysis can be used for pr oduction of pyrolysis oil, which can be used as a secondary fuel. Advantages – Arsenic volatilization is lower than in in cineration and gasification due to lower temperatures PCDD/F formation is minimized due to absence of oxygen Metal compounds form agglomerates and can be recovered easily from the residue [120-122] Disadvantages – Arsenic volatilization is s till non-zero as arsenic is highly volatile even at temperatures below 300 oC [123] Lower temperatures (typical pyrolysis temperatures are < 500 oC) result in slow wood decomposition rates and very long reaction times Leaching or CCA metals possible from the residue if it is disposed

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39 Arsenic content in pyrolysis oil is between 5 – 18% hence it can’t be used as a fuel [120] 3.5.3 Gasification Gasification is a process that converts carbonaceous materials, such as coal, petroleum, petroleum coke or biomass, into carbon monoxide and hydrogen. It is a three step process involving pyrolysi s / de-volatilization of carbonaceous fuels followed by the combustion of char to form carbon dioxide and carbon monoxide, which provides heat for the subsequent gasification reactions. The first two steps occur very rapidly. In the third step, gasification occurs as the char reacts with carbon dioxide and steam to produce the syn gas (H2 + CO, diluted with CO2 + H2O + N2) which can be converted more efficiently to energy than wood. However, it is yet to be prov en in practical systems or pilot-scale studies [118]. Advantages – Syn gas can be used as a fuel and has a much high energy efficiency as compared to wood Since the process uses limited amount of oxygen, a lower amount of gas cleanup is required as compared to incineration High gasification temp eratures (~1100-1500 oC) eliminate the possibility of formations of PCDD/Fs High temperatures may result in the formation of metallic arsenic (potential reduction by CO), which is much easier to capture than arsenic trioxide as it has a higher sublimation temperature and doesn’t go through a liquid phase upon cooling [118] Disadvantages – Very efficient air pollution control devices are required to captur e all of the arsenic released during gasification In order to capture arsenic tr ioxide at such high temperatur es, it is required to have all the arsenic released in metallic form, which is mostly not possible

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40 The high temperature and fine particle size requirement make it an expensive technique An extensive review of available thermoch emical conversion processes for disposal of CCA-treated wood waste by Helsen et al. [118] suggests that co-incineration may be the best short-term solution for disposal. Th e authors emphasize the need for a long term sustainable solution for dispos al involving maximum possible recycling. They identified low temperature (380°C) pyrolysis in a m oving bed and high temperature gasification (1100-1500°C) in a metallurgical furnace as the potential candidates for the future. Both technologies aim at recovering the metals and energy (as sec ondary fuels) contained in the CCA treated wood waste. However, their f easibility on a practical scale remains to be seen and there are concerns over the potential leaching of CCA metals on disposal of the residue. The experimental results to be disc ussed in subsequent chapters show that incineration of CCA-treated wood waste usi ng sorbent technology to capture the metal emissions also provides a viable option. 3.6 Available Technologies fo r Capture of Arsenic in Air All of the thermal processes for CCA-treat ed wood waste discussed above will lead to volatilization of arsenic; hence appropriate arsenic cap turing devices are required. Arsenic capture is challenging as it is highl y volatile and exists bot h in particulate and vapor form in combustion flue gas. The cu rrent air pollution control technologies in combustion systems like ESPs, baghouses, scrubbers and cyclones can only collect particulate matter efficiently. Th eir efficiency is the lowest in the submicron range which is of concern as many volatile metals are en riched in that size range. Very few successful tests have been carried out on a industrial scale for the specific case of thermal conversion of CCA-treated wood [124].

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41 The use of standard emission sampling methods can’t give a reliable estimate of the submicron particles and fumes formed duri ng combustion/pyrolysis of CCA treated wood [125]. Rapid cooling, to c ondense the fumes, can clog the system very quickly. Moreover, the lab-scale studies on CCA w ood combustion report arsenic mass balances far below 100% [105, 126] possibly due to inco mplete sampling of the arsenic released. Since very little information is availabl e regarding arsenic sampling and capture on industrial scale for CCA treate d wood, a discussion of arse nic control technologies in other processes like coal combustion, waste in cineration and metallurg ical operations is provided. The experience with other industrial processes can be helpful in the design of appropriate arsenic sampling and capture methods. 3.6.1 Technologies used for Capturing Ar senic Emissions from Combustion of CCA-Treated Wood Various combustion studies conducted on CCA-treated wood waste report a variable percentage of vola tilization of arsenic, from 8 – 95%. The amount of arsenic volatilized depends on various operational parameters and conditions like reactor temperature, residence time, air flow rate, oxyg en partial pressure, th e chlorine and sulfur content and the impregnation process us ed for wood [105, 120, 127, 128]. Combustion trials conducted in an ex isting incinerator showed hi gher arsenic emissions than European target values [95, 126]. The air pollu tion control devices c onsisted of a ventury scrubber and ESP. Since arsenic is enriched in fine particle s, scrubbing of gases has been recommended [129]; however, ventury scrubbe rs aren’t very efficient in capturing submicron particles. Table 3-4 summarizes some of the flue gas cleaning equipment used on lab scale and their efficiency in collec ting arsenic. One major drawback of these

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42 technologies is that they can only treat a small volume of air at a time and hence can’t be directly used in i ndustrial processes. As discussed previously, th e introduction of mineral so rbents in the combustion system has been proposed as a solution for both the problem of metal emission and the problem of metal leaching from the combus tion ash [2, 117, 130]. Sorbents chemically adsorb arsenic to form non-toxic and non l eachable compounds and also increase their particle size facilitating their capture by particulate control de vices. Alkaline earth metals and alkali metals have been identified as potential candidates for capturing arsenic. However, the presence of sulfur and chlorine in the combustion system may affect the performance of sorbents by competing with ar senic and depleting the available sorbent. Table 3-4: Arsenic Capture E fficiency of Lab-Scale Flue Gas Cleaning Equipments used in Some Studies Flue gas cleaning equipment As mass balance Reference 2 bubblers: empty+2%NaOH or glass beads + 2% mono-ethanolamine 20-90% [131] Three spiral traps, chilled with ice water(0 oC), dry ice-methanol (-60 oC) and liquid N2(-190 oC) 50-80% [105] Glass transfer tube + glass fiber filter + TBAH (Tetra Butyl Ammonium Hydroxide) impregnated cellulose filter 61-104% [127] Quartz cooling tube + cellulose ester membrane filter impregnated with Na2CO3 sol. Additional impinger as backup (50 ml of 1 M HNO3) 80 – 100% [132] Source: [124] 3.6.2 Overview of Arsenic Capture in Other Processes This section discusses some of the t echniques adopted for arsenic sampling and arsenic control on lab-scale as we ll as in pilot scale studies to give an idea of the rationale behind arsenic capture. To convert them into field-scale technologies for CCA-treated wood incineration, some modifications will be required. A lab scale study [133] was conducted by passing the gas stream through a bed of different adsorbent particles for

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43 removal of arsenious oxide (As4O6). The temperature of flue gas was simulated to 200 oC. It was found that surface-active agents such as activated carbon, silica gel, and molecular sieve 13X adsorbed As4O6 vapor strongly [133]. However, some of these sorbents may not work at high temperatures . Another study utilized filters impregnated with aqueous glycerol and polyethylenimine polymer solution to capture the particulate and volatile arsenic compounds simultaneously [134]. Results showed that the average arsenic trioxide collection efficiency for a se ries of three filters was 96% for flowrates between 15-23 l/min. The authors [134] also suggested that tetra butyl ammonium hydroxide (TBAH) may be a very ef ficient collection substrate for As2O3 vapors. Demange et al. developed a sampling train c onsisting of a pre-filter (quartz fiber filter impregnated with Na2CO3) to retain particulates and As2O3 vapor, followed by two quartz fiber filters (impregnated with AgNO3) to trap arsine gas (AsH3) [135]. Arsine is a colorless, non-irritating, toxic gas with a m ild garlic odor and is formed when arsenic comes in contact with an acid. It is most commonly used in the semiconductor and metals refining industries. Exposure to arsine can cau se serious health effects; hence its emission also needs to be controlled. As discusse d earlier, it is hard to implement these technologies on a large scale. On an industrial scale, arsenic containing wa stes are usually burned in a rotary kiln incinerator. An U.S. EPA study conducted in a rotary kiln incinera tor showed that the total mass balance of arsenic ranged from 38 %-73% of the input arsenic [136]. Facilities using an ESP and a wet scrubber (using lime and NaOH) reported that the arsenic which escapes the ESP is capture d by a wet scrubber [137].

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44 Coal combustion is another important source of arsenic emissions. Estimates indicate that it acc ounts for 2-5% of the total arse nic emissions from anthropogenic sources globally [116]. Arsenic exists both in vapor phase and as fine particles in flue gas. Besides being a hazardous air pollutant it self, it also poisons th e selective catalytic reduction (SCR) catalyst (by occupying the active sites) which controls NOx. Hence it is important to control arsenic em issions in coal combustion. In jecting mineral sorbents in flue gas has proven to be an effective tec hnique for reducing arseni c emission from coal combustion. The sorbents adsorb the arseni c vapors/fine particle s at high combustion temperatures forming large sized particles which can be easily captured by ESPs. Lime based sorbents have been found to be very effective in capturi ng arsenic. Depending on the operating conditions and the type of sorb ent used, the fly ash is sometimes non-toxic and non-leachable and hence can be disposed of easily [31, 115-117]. Some researchers have suggested co-incinerating coal with municipal solid waste (MSW) so that the calcium present in MSW can scavenge arsenic [138]. Arsenic occurs naturally in copper or es, e.g., in the mineral tennantite (Cu12As4S13). In the metallurgic industry, the purification of copper ores also results in the volatilization of arsenic. Arsenic gets converted to gaseous state and leaves the smelter as flue gas. A typical gas cleaning system used for copper smelting consists of lime injection, followed by activated carbon injection and dilution with air to cool it down before it enters the baghouse. Although the concentration of arse nic emitted may be lowered by using this method, the absolute amount is still a matter of concern. In metallurgical processes, arsenic removal by using lime is giving way to iron based sorbents. Lime precipitation, which was widely used in the past, is be ing abandoned as a result of strong evidence

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45 showing that calcium arsenate compounds deco mpose slowly in contact with atmospheric CO2 to form calcium carbonate and soluble ar senic acid. Hence formation of insoluble ferric arsenate compounds is preferred [139]. 3.7 Sampling of Trace Arsenic Concentration in Air In order to develop an efficient practical scale technology, it is important to have an accurate estimate of the actual concentration of arsenic in flue gas, hence it is critical to understand and evaluate the various sampli ng techniques. A variety of sampling and analytical techniques have been used to meas ure trace metal concentrations in ambient air including impingers, ESPs and filters. For a series of impingers, it is essential that the amount caught by the last impinger should be close to zero to have a high overall efficiency [140]. Sample presence in the la st impinger indicates the possibility of an unknown amount of sample which may have pa ssed through all the impingers without getting collected. Hence it is important to assess the sampling conditions well before determining the sampling train length. One ma jor disadvantage of impingers is that the collected samples may get absorbed by impinger walls. To collect the absorbed samples, thorough washing with NaOH is required [141]. Filters are being favored these days over other collection media due to their high collection efficiency for all pa rticulate matter. They also ha ve relatively high efficiency in collecting micron and submicron particle s [142]. Table 3-5 be low list the commonly used filters and their major properties. Different filter media have been considered for the determination of trace metals in air, such as glass fiber, quartz fiber, membrane filters and Teflon filters. An important consideration in selecting the most appropriate filter medium for collection of trace elements in pa rticulate matter is the background metal

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46 concentration of the filter material (blank va lue). Filters are typically characterized by high collection efficiency and low hygroscopi city (doesnÂ’t absorb water readily). Impregnated filters are gaining popularity th ese days due to their ability to capture both particulate arsenic and arsenic oxide va por simultaneously. The vapors are contained by reacting with the impregnating media, e .g., for a filter impregnated with sodium carbonate (Na2CO3), the following reaction occurs: 2 2 3 2 3 2CO 2NaAsO CO Na O As There are various national standard me thods for arsenic sampling. Table 3-6 summarizes NIOSH Method 7901 (f or arsenic trioxide samp ling) and Method 6100 (for arsine sampling). The working ra nge for Method 7901 is 0.001 to 0.06 mg/m3 for a 200 liter air sample. This method collects partic ulate arsenic compounds as well as arsenic trioxide vapor. If only the tota l particulate arsenic is of in terest, the use of the treated filter and analysis of the backup pad is not required. Other particulate arsenic compounds can interfere with the sampling of arsenic trioxide [143]. The working range for Method 6001 is 0.0003 to 0.06 ppm (0.001 to 0.2 mg/m3) for a 10 liter air sample. This is an elemental analysis and is not compound-sp ecific. Other arsenic compounds (gases or aerosols) may be collected on the sampler and can be erroneously repo rted as arsine. The aerosols can be removed from sampling by placing a cellulose ester filter in front of the charcoal tube. Relative humidity can also aff ect the capacity of charco al to absorb arsine [144]. Besides the NIOSH standards, the U.S. EPA Reference Methods have been set up to provide industry with a r easonable and reliable means of demonstrating compliance with applicable regulations. EPA Method 108 [145] is used for the determination of particulate and gaseous arsenic emissions. Pa rticulate and gaseous arsenic emissions are

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47 withdrawn isokinetically from the source and are collected on a glass-mat filter and in water. The collected arsenic is then anal yzed by AAS. EPA Method 108A [146] is used for the determination of arsenic in ore sample s. Arsenic bound in ore samples is liberated by acid digestion and analyzed by flame AAS. Table 3-5: Properties of Different Filt er Media for Arsenic Sampling Filter Type Glass Fiber Quartz Fiber Membrane Teflon Blank Value of As (ng/cm2) 40 – 60 0.5 – 5 0.1 – 4 0.3 Typical Filter Size 20.3 X 25.4 cm 20.3 X 25.4 cm Circular – 25 mm, 37 mm, 47 mm Circular – 37 mm, 47 mm Circular – 25 mm, 37 mm, 47 mm Physical Properties Borosilicate glass fiber White opaque surface, diffuses transmitted light Melts at ~500 oC Low flow resistance Quartz fibers White opaque surface, diffuses transmitted light Melts at > 900 oC Moderate flow resistance Cellulose nitrate mixed esters and cellulose acetate White opaque surface, diffuses transmitted light pore sizes from 0.025-8 µm Melts at ~70 oC High Flow resistance -Prone to electrostatic charge Thin membrane between Polymethylpentane ring -White surface, nearly transparent, minimal diffusion of transmitted light Melts at ~60 oC High flow resistance Pore sizes from 1.2-10 µm Chemical Properties High blank levels Adsorbs HNO3, NO2, SO2 and organic vapors High blank weight Low blank levels for ions Passively adsorbs organic vapors and little HNO3, NO2, SO2 Resistant to chemical attack by all fluids Passively adsorbs organic vapors High blank weight Usually low blank levels. Made of carbon-based material so inappropriate for carbon analysis Inert to adsorption of gases Low blank weight Compatible Analysis Methods Gravimetry, OA, XRF, PIXE, INAA, AAS, ICP/AES, IC, AC ICP/AES, ICP/MS, IC, A, T, TOR, TMO, TOT, OA Gravimetry, OM, TEM, SEM, XRD, biomedical applications Gravimetry, OA, XRF, PIXE, INAA, AAS, ICP/AES, ICP/MS, IC, AC Source: [142, 147]

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48 AAS = Atomic Absorption Spectroscopy AC = Automated Colorimetry IC = Ion Chromatography ICP/AES = Inductively-Coupled Plasma w ith Atomic Emission Spectrophotometry ICP/MS = Inductively-Coupled Plas ma with Mass Spectrophotometry INAA = Instrumental Neut ron Activation Analysis OA = Optical Absorption or Light Transmission OM = Optical Microscopy PIXE = Proton-Induced X-Ray Emissions SEM = Scanning Electron Microscopy T = Thermal Carbon Analysis TEM = Transmission Electron Microscopy TMO = Thermal Manganese Oxidation Carbon Analysis TOR = Thermal/Optical Re flectance Carbon Analysis TOT = Thermal/Optical Transmission Carbon Analysis XRD = X-Ray Diffraction XRF = X-Ray Fluorescence

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49 Table 3-6: NIOSH Methods for Arsenic Sampling NIOSH Method 7901 (As2O3) NIOSH Method 6001 (AsH3) Filter/Sampler Na2CO3impregnated,0.8µ m cellulose-ester membrane + backup pad Solid Sorbent Tube (coconut shell charcoal, 100 mg/50 mg) Flow Rate 1 to 3 L/min 0.01 to 0.2 L/min Min 30 L @ 0.01 mg/m3 0.1 L @ 0.05 ppm Volume Max 1000 L 10 L Measurement Technique Atomic Absorption, Graphite Furnace Atomic Absorption, Graphite Furnace Regulatory Limits OSHA : 0.01 mg/m3 (As) NIOSH: C 0.002 mg/m3 (As)/15 min; carcinogen ACGIH: 0.01 mg/m3; carcinogen OSHA : 0.05 ppm NIOSH: C 0.002 mg/m3/15 min; carcinogen ACGIH: 0.05 ppm; carcinogen (1 ppm = 3.19 mg/m 3 @ NTP) OSHA – Occupational Safety and Health Administration NIOSH – National Institute for O ccupational Safety and Health ACGIH – American Conference of G overnmental Industrial Hygienists Source: [143, 144] 3.8 Conclusions Arsenic is a naturally occurring element wi dely distributed in the earth’s crust. Both inorganic and organic arsenic compounds are used in miscellaneous anthropogenic activities. The total environm ental releases of arsenic are the third highest amongst all chemicals in US. Arsenic is rated as one of the most hazardous compounds to the ecosystem and human health and hence must be regulated carefully. Wood preservatives, especially CCA, accounted for most of the arsenic consumption in US till 2004. Hence a large quantity of arsenic-treated wood is in use and is present in significant amounts in the disposal sector as well. Its presence in th e disposal sector is predicted to increase heavily in the near future.

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50 Thermal treatment of wood waste is comm on. However, it is not a problem-free option as it leads to emissions of arsenic and also the enrich ment of CCA metals in ash. The conventional particulate control devices can’t eff ectively control submicron emissions of arsenic. Hence the thermal pro cesses for arsenic need to be evaluated to determine the best available thermal technology. The popular thermal treatment technologies are – incinera tion/co-incineration, gasifi cation and pyrolysis. Coincineration appears to be the most promising technology amongst the existing techniques in the short term. Coupling co-incin eration with sorbent injection in feed and gas stream can result in the dual benefit of control submicron particulate emissions by forming thermally stable, submicron size part iculates as well as forming non-toxic, non leachable ash which can be disposed of eas ily. Some lab scale studies have shown the efficiency of lime-based and alumino-silicate sorbents for controlling metal emissions and leaching from CCA wood. Pilo t-scale studies need to be carried out to determine its applicability in industrial processes. Capture of arsenic emissions during thermal treatment of CCA wood is a challenging task as it exists in both particulate form as well as vapor state. An evaluation of the existing options suggest s that the use of a combina tion of air pollution control devices. For instance, using a wet scrubber combined with an ESP or a baghouse seems to be the best available technique to comb at arsenic emissions. However, a substantial amount of arsenic still escapes the devices. Injection of mineral sorbents in the flue gas increases the size of the particulates hence they can be efficiently captured by using a baghouse or an ESP. This technique has been successful in controlling arsenic emissions in coal combustion and can be applied to wood waste too.

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51 Various techniques are available for samp ling of arsenic in ambient air. Many studies have used a series of impingers to simultaneously capture particulate and vapor emissions. However, their efficiency is not ve ry high and there is a problem of absorption of samples by the impinger walls. Filters ha ve become increasingly popular for arsenic sampling due to their high particulate capture efficiency. Impregnate d filters can capture arsenic vapors as well. The sampling sta ndards for arsenic and arsenic compounds and arsine gas are regulated by NIOSH and EPA.

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52 CHAPTER 4 SCREENING OF POTENTIAL MATER IALS FOR PREVENTING METAL LEACHING FROM INCINERATION PRODUCT OF CCA-TREATED WOOD As discussed in Chapter 1, an extended li terature review reve als that many mineral sorbents can successfully scavenge metal vapor s. However, in most of the ‘heavy metal – sorbent’ interactions, leaching of heavy me tals from the product may be an issue of concern, and only limited leachability data is available. Consequently, in this study, experiments were carried out to obtain insights into the metal – sorbent interaction and to assess how the interactions govern the leachi ng behavior of the ash. As there are many varieties of sorbent materials, the objective of this study wa s to screen candidates based on their leachability characteristics and select the suitable ones for more comprehensive testing in future studies. The ultimate goal was to determine the optimal material and operating conditions that would allow combus tion of CCA treated wood as a disposal option for the wood waste. 4.1 Materials 4.1.1 Sorbent Materials Fifteen potential sorbents which were used in past studies were shortlisted, which included alumina, alundum, attapulgite cl ay, bauxite, bentonite, calcium hydroxide, cement, diatomaceous earth, emathlite, ferric oxide, kaolin, magnesium hydroxide, silica, titanium dioxide and zeolite. The sorbent materi als chosen belong to two categories: pure chemicals (alumina, calcium hydroxide, ferri c oxide, magnesium hydroxide, silica and titanium dioxide) and minerals (alundum, a ttapulgite clay, bauxite, bentonite, cement,

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53 diatomaceous earth, emathlite, kaolin and zeo lite). A mineral cont ains a variety of elements. By comparing the leaching behavi or of a metal in a mineral and in a pure compound, it is possible to identify the reac tive element (with re spect to leaching) governing its leaching behavior. For example, the comparison of leaching behavior of silica and magnesium hydroxide can give us insights into the reactive element in attapulgite clay, a compound made of magnesium and silicon. The criteria for choosing these sorben ts were that they should have good performance (with respect to leaching and ga s phase capture) against heavy metals (or CCA metals if possible). Additi onally, they should be cheap a nd readily available so that they can be used on an industrial scale. Ou t of the fifteen sorbents chosen initially, alundum, bentonite, emathlite and titanium di oxide were eliminated by comparison of their performance relative to other sorbents in the list. Two more materials were removed from the list with reasons discussed below: Zeolite is part of the alumino-silicate group and is expected to behave similarly to other alumino-silicates chosen. Bauxite was initially listed because it is a commonly occurring mineral and displayed good vaporization and leaching retention [31, 35] ag ainst CCA metals. Unfortunately, there was no cheap source ava ilable for bauxite and therefore it was removed from the list. Since bauxite is also a mineral in the alumino-silicate spectrum, its performance is expected to be similar to other alumino-silicates chosen. The reason thus warrants its elimination from the matrix. Table 4-1 shows the performa nce of Ca-based sorbents, alumina, silica, kaolin, attapulgite clay, diatomaceous earth, bauxite and an alumino-silicate based zeolite with respect to leaching and vaporiza tion retention of CCA metals as given in past studies. Based on this, six sorbents – calcium hydroxide, kaolin, alumina, silica, diatomaceous earth and attapulgite clay were chosen for th e final experimental matrix. In addition, three more candidate materials were added to the list for the following reasons:

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54 Magnesium hydroxide was added to the group as a representative of alkali earth metals and to test if the conclusions drawn from the performance of Ca-based sorbents could be extended to other alkali earth metals. Ca-based sorbents have been effective in controlling arseni c leaching from CCAtreated wood based on past studies [2]. Calcium is a major constituent of cement hence the leaching and volatilization rete ntion properties exhibited by cement are expected to be similar to th at of Ca-based sorbents. On e of the goals of this study was to propose a technology which can be implemented in the industry. Cement kilns, which burn waste derived fuels such as scrap tires, could be a potential option for burning CCA wood if cement coul d successfully reduce the leachability and volatilization of CCA me tals. Therefore, it was necessary to investigate the effectiveness of cement as a sorbent material. Cement -CCA wood composites have been used in some studies [101, 148] as a recycling alternat ive for CCA wood and have shown increased compressive stre ngth due to the presence of chromium. Cement-CCA wood composites leach very little arsenic and copper. However, increased formation and leaching of Cr(VI) has been reported [149]. The effect of aluminum and silicon, the other major constituents of cement, on its leaching and vaporization behavior also needs investigation. Ferric oxide was added to the experimental matrix based on its use in metallurgical processes, where formation of insoluble ferric arsenate compounds like scorodite (FeAsO4.2H2O) is a popular method for disposal of arsenic [139]. Iron is also known to form ferrous chromite (FeCr2O4), a commonly occurring mineral which is insoluble in water and s lightly soluble in acids. He nce iron based sorbents may have a good potential for capturing both ar senic and chromium. A steel mill can be used to implement the technique. Amongs t Fe-based minerals, ferric oxide was chosen as it is cheap and readily availabl e. Furthermore, it’s a major constituent of steel & coal fly ash. Table 4-2 shows the final experimental ma trix with the nine chosen sorbents. Particle size was not considered as a criter ion for comparing the leaching behavior of these sorbents. Although part icle size is known to be an important parameter in chemically adsorbing metal vapors, it is econom ically viable to use the sorbent material as received, without controlling its particle size. Hence, the sorbent materials were used in whatever the standard particle size was av ailable in the market. In these experiments, pure chemicals (containing CCA metals) were used to obtain data regarding leachability and speciation of CCA metals on applicati on of sorbents. While the wood composition may affect the ‘sorbent–metal’ interaction, the use of pure metal compounds will provide

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55 fundamental baseline to understanding the na ture of interaction between sorbents and heavy metals. Table 4-1: Performance of Mineral Sorbents Against CCA Metals Reported in the Literature Performance Sorbent % Vaporization retention % Leaching retention Test Conditions Reference As-80-85% As-100% Cr-75-85% Cr-0%or less Ca based Cu-75-85% Cu-95% Sorbent addition in feed, 600-900 oC, CCA wood fuel [2] As-90-100% As-90-95% Kaolinite Cr90-95% Cr0-30% As-90-100% As-90-95% Attapulgite Clay Cr90% Cr0% As-90-95% As-70-95% Bauxite Cr85% Cr75-100% As-90-100% As-45-65% Silica Cr85% Cr50-95% As-90-100% As-90-95% Alumina Cr100% Cr70-80% As-90-100% As-55% Diatomaceous earth Cr90% Cr70-100% Sorbent addition in feed, 500900 oC, Simulated waste stream [35] As-160-210% Hydrated Lime Cr-40-60% As-165% Limestone Cr-30-40% As-75-135% Kaolinite Cr-40-60% As90-110% Bauxite Cr25-50% Sorbent injection in gas phase, 10001300 oC , pilot scale coal combustion [31] Cr 27%, 80-86% Kaolinite Cu 22%, 64-110% Cr 25%, 74-101% Aluminum Oxide Cu 22%, 65-84% Cr 29%, 76-78% Limestone Cu 20%, 73-104% Cr 33%, 91% Water Cu 24%, 70-82% 700-800 oC, simulated waste, sorbent injection in feed(without and with Cl or S additive) [54] Zeolite Cr 50-80% Calcined limestone Cr 30 60% sorbent injection in feed, 600-900 oC, simulated waste [44]

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56 Table 4-2: List of Sorbents Used for Metal Capture in Experiments Name of Sorbent Chemical formula Molecular Weight (g) CAS # Alumina Al2O3 102.0 1344-28-1 Attapulgite Clay* Si16Mg H3.6O 5.9 167.7 _ Calcium Hydroxide Ca(OH)2 74.1 1305-62-0 Cement* Si9Al3Ca 29.3 S0.8 H3Fe1O57 2508.6 _ Diatomaceous Earth* Si106Al4.6Ca 0.3 Mg0.5Fe2O229.5 7119.7 61790-53-2 Ferric Oxide Fe2O3 159.7 1309-37-1 Kaolin H2Al2Si2O8-H2O 258.2 1332-58-7 Magnesium Hydroxide Mg(OH)2 58.3 1309-42-8 Silica SiO2 60.1 7631-86-9 * The formula and molecular weight are approximates based on % composition. Varies according to mineral composition In these experiments, pure chemicals (cont aining CCA metals) we re used to obtain data regarding leachability and speciation of CCA metals on applic ation of sorbents. While the wood composition may affect the ‘s orbent–metal’ interaction, the use of pure metal compounds will provide fundamental ba seline to understanding the nature of interaction between sorben ts and heavy metals. 4.1.2 CCA Chemicals Since it was difficult to obtain the actu al CCA chemical owing to its ban from residential uses, a metal spike was prepared containing all the three CCA metals in the same mass ratio as the CCA Type C chemical . Arsenic (V) oxide, chromium (III) nitrate nonahydrate and copper (II) nitrate 2.5 hydrate we re used to prepare the metal spike as they are readily soluble in water. Table 4-3 lists the details about the compounds used for the formation of metal spike. Table 4-4 shows the molar ratio of CCA metals in CCA

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57 type C chemical. A metal spike was prep ared containing the metal compounds in the mass ratio as shown in Table 4-5. Table 4-3: Properties of Metal Compounds Used in Metal Spike Metal Compound CAS # Chemical formula Molecular Weight (g) Solubility in water Chromium(III)nitrate nonahydrate 7789-02-8 Cr(NO3)3.9H2O 400.13 Soluble Copper(II)nitrate,2.5hydrate 19004-19-4 Cu(NO3)2.2.5H2O224.6 Soluble Arsenic (V) Oxide 1327-53-3 As2O5 197.84 Soluble Table 4-4: Molar Ratio of CCA Metals in Type C Chemical CCA compound % composition of CCA Type C (by weight) Molecular Mass of CCA compound (g) Mole of each compound/ 100 g CCA Normalized Molar ratio of compound Normalized Molar ratio of CCA metals CuO 18.5 79.6 0.232 1.57 1 CrO3 47.5 100 0.475 3.21 1.61 As2O5 34 230 0.148 1.00 1.00 Table 4-5: Mass Ratio of Compounds in Spike Metal Compounds Molecular Weight (g) Mass required based on CCA metal molar ratio (g) Normalized Mass ratio (g) Cu(NO3)2.2.5H2O 224.6 224.6 1.54 Cr(NO3)3.9H2O 400.13 820.26 5.62 As2O5 230 146.05 1 Metal concentration in the spike samp le was; As – 13000 mg/l, Cr – 14600 mg/l and Cu – 8800 mg/l. The spike sample had a re tention level equal to 3.68 pcf of treated wood. The conversion of ml of CCA spike to pounds per cubic feet (pcf) of treated wood is based on the assumption that if an e quivalent amount of wood is used in the experiments, it has to be treated to a retenti on level of 3.68 pcf in order to have the same mass of CCA metals in each sample as in the metal spike. Calculations showing the conversion are given below.

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58 1 g As2O5, 1.54 grams Cu(NO3)2.2.5H2O, 5.62 grams Cr(NO3)3.9H2O in 50ml water Mass of As in 50 ml water = (150/230) * 1 = 0.652 g Mass of Cu in 50 ml water = (63.6/224.6)*1.54 = 0.436 g Mass of Cr in 50 ml water = (52/400.13)*5.62 = 0.7304 g Since density of water is 1 g/cc, so 50 ml water = 50 g water (1 cc = 1 ml) Typical density of wood = 33 pcf = 0.529 g/cc ( 1 ft = 30.48 cm, 1 lb = 454 g) 50 g water = 26.45 g wood The calculations below assume the same volume of wood used as the amount of water used for preparing the spike solution. Then the treatment le vel of the wood is determined by calculations so that it contai ns the same mass of CCA chemicals as the spike solution used in this study. As (mg/kg) = (652 mg of As) / (0.02645 kg of wood) = 24650.3 mg/kg Cr (mg/kg) = (730.4 mg of Cr) / (0.02645 kg of wood) = 27614.4 mg/kg Cu (mg/kg) = (436 mg of Cu) / (0.02645 kg of wood) = 16483.9 mg/kg Fraction of As in CCA Type C = (0.34) * (150/230) = 0.222 Fraction of Cr in CCA Type C = (0.475) * (52/100) = 0.247 Fraction of Cu in CCA Type C = (0.185) * (63.5/79.5) = 0.148 Fraction of O in CCA Type C = 1 – (0.222 + 0.247 + 0. 148) = 0.383 For X pcf of treated wood As (mg/kg) = wood kg As mg wood lb wood kg wood ft wood lb CCA mg As mg CCA lb CCA mg wood ft CCA lb X 3 . 24650 2 . 2 1 33 1 222 . 0 2 . 2 103 6 3 X = 3.66 pcf For verification, similar calculati ons were performed on Cr & Cu

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59 Cr (mg/kg) = wood kg Cr mg wood lb wood kg wood ft wood lb CCA mg Cr mg CCA lb CCA mg wood ft CCA lb X 4 . 27614 2 . 2 1 33 1 247 . 0 2 . 2 103 6 3 X = 3.69 pcf Cu (mg/kg) = wood kg Cu mg wood lb wood kg wood ft wood lb CCA mg Cu mg CCA lb CCA mg wood ft CCA lb X 9 . 16483 2 . 2 1 33 1 148 . 0 2 . 2 103 6 3 X = 3.675 pcf Hence, average X = 3.675 pcf = 3.68 pcf Thus the spike sample used in the expe riments had a retention level equal to 3.68 pcf of treated wood. 50 ml of the spike was mixed with 20 g of sorbent in 75 ml porcelain crucibles. This quantity of sorbent was chosen as a minimum of 15 g of residue is required to complete the various analysis steps such as leaching and digestion te sts. Furthermore, it was essential to provide sufficient sorbent fo r reacting with metals based on excess of stoichiometric ratio for the formation of commonly occurring compounds of the metals with key elements in sorbents. Typically the common metal-mineral compounds formed are: CaCrO4, AlAsO4, Ca3(AsO4)2, CaCr2O4, Ca2As2O7, CrFeAs2, Cr2SiO4, CuFe2O4, FeCr2O4, CuFe2O4, MgHAsO4, Fe2(AsO3)4, MgCrO4, MgCr2O4, Cu2MgO3 etc. The molar ratio of CCA metal to mineral never exceeded 1:3 in these compounds. The molar ratio of the CCA metals to sorbent used in experiment s was much in excess to this ratio. Hence it can be safely assumed that the sorbent was pr esent in excess amount to react with all the available CCA metals. Table 4-6 shows the deta ils of materials used in the experimental process.

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60 Table 4-6: List of Material s Used in the Experiments Chemical Catalogue # (Fisher Scientific., unles s specified) Alumina 8660-0791N Arsenic (V) Oxide AA14668-22 Attapulgite Clay E ngelhard.com DC150 Calcium Hydroxide AC219180010 Cement Florida Rock Industries–Newberry Cement Plant Chromium (III) nitrate nonahydrate AC21920-5000 Copper(II) nitrate, 2.5-hydrate AC40585-5000 Diatomaceous Earth S75114 Ferric Oxide S93241 Kaolin AC21174-0010 Magnesium Hydroxide M342-500 Porcelain Crucibles 08-215-2 Silica S150-3 4.2 Methods Figure 4-1 depicts the flowchart of the expe rimental steps used in this study. The processes used in these steps are described below. 4.2.1 Toxicity Characteristic Leaching Procedure (EPA SW 846 Method 1311) TCLP is a laboratory test designed to si mulate anaerobic leaching conditions in a municipal landfill. It is used to determine the mobility of both organic and inorganic analytes present in liquid, solid, and multipha se wastes and employs an acetate buffer leaching fluid to simulate the effect of decomposing municipal waste [150]. Wastes containing less than 0.5% dry solid material are called liquid wastes and they can be directly filtered using a 0.6 to 0.8 µ m glass fiber filter to remove any particle impurities. The filtrate is defined as the TCLP extract and can then be analyzed as TCLP leachate. Wastes containing greater than or equal to 0.5% solids, are term ed as solid wastes. For these wastes, the liquid, if any, is separated from the solid phase and stored for later analysis. The particle size of the solid phase is evaluated to see if size reduction is

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61 necessary. The particle size of solids should be smaller than 1 cm in its narrowest dimension so that it is capable of passi ng through a 9.5 mm (0.375 inch) standard sieve. Filamentous waste materials (e.g., paper, clot h etc.) are required to have a specific surface area greater than or equal to 3.1 cm2/g. If the surface area is smaller or the particle size larger than thos e described above, the solid samp le has to be prepared for extraction by crushing, cutting, or gri nding to the required limits [150].

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62 Figure 4-1: Flowchart of Experimental Procedure The fluid employed for extraction is a func tion of the alkalinity of the solid phase of the waste. Hence sample pH is an impor tant criterion in choosi ng an extraction fluid for TCLP. To measure pH, 96.5 ml of reagent water is added to 5 g of the sample. The solution is then covered with watch-glass a nd is stirred vigorously for 5 minutes using a

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63 magnetic stirrer. The pH is then measured and recorded. If the pH is <5.0, extraction fluid #1 is used. Extraction fluid # 1 consis ts of 5.7 ml glacial acetic acid (CH3CH2OOH, trace metal grade, 99.5%) and 64.3 ml of 1N NaOH, and is diluted by water to a volume of 1 liter so that the pH of this fluid is 4.93 0.05. If the pH is >5.0, then 3.5 ml 1N HCl is added, the solution is stirred briefly and then is covered with a watc h-glass and heated at 50 oC for 10 minutes. After that, the solution is allowed to cool to room temperature and the pH is recorded. If the pH is now < 5.0, extr action fluid #1 is used. If the pH is still >5.0, extraction fluid #2 is used. Extraction flui d # 2 consists of 5.7 ml glacial acetic acid diluted to 1 liter with reagent water so that the pH of this fluid is 2.88 + 0.05 [150]. The rationale behind using different extraction fluids for these pH ranges is that usually alkaline samples require a str onger acidic extraction fluid to give comparable results. The solid sample and the extraction fluid ar e mixed together with liquid/solid ratio of 20:1 and placed in an extraction vessel. The vessel is then rotated for 18 + 2 hours at 30 + 2 rpm to extract the solid phase. After ex traction, the liquid extr act is separated from the solid phase by filtration in a special h azardous waste filteri ng device. For these experiments, borosilicate glass fiber filters with 0.7 µ m pore size, 142 mm diameter (fisher scientific catalogue# 09-753-25J) meeting USEPA requirements for TCLP are used. Filters are acid-washed before bei ng used as per the regulations. Following collection of the TCLP extract, the pH of the extract is recorded. The liquid extract/ TCLP extract is then acidified with concentr ated nitric acid (unless precipitation occurs) to a pH < 2 to preserve the sample and prev ent further extraction. Later, the TCLP extract is digested using liquid digestion so that it can be analyzed using inductively coupled plasma atomic emission sp ectroscopy (ICP-AES) [150].

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64 The toxicity characteristic of a solid waste is determined following the TCLP protocol. Limits are set on the maximum allo wable concentration of contaminants based on various environmental and health effects fo r different cases. If the concentration of any of these contaminants (metals or organi c compounds) in the leachate is at or above these limits, then the waste is hazardous by th e toxicity characteristic. In the case of CCA-containing wood ash, only arsenic, chro mium and copper should be a matter of concern. It should be noted th at copper analysis is not required when performing the TCLP test since copper is not considered a TC hazardous metal. The TC limits for both arsenic and chromium are 5 mg/l [150]. 4.2.2 Liquid Digestion (EPA SW 846 Method 3010 A) This digestion procedure is adopted for TCLP extracts to enable analysis ICP-AES. The liquid digestion step helps in determina tion of the amount of metals present in the leachate by extracting all the metals present in it using strong acids, which break metal compounds into their ionic constituents and th erefore they can be detected by the ICPAES [150]. In this process, a small amount (usually 3 ml) of pure concentrat ed nitric acid (trace metal grade, 67-70% acid) is added to a know n amount of leachate (usually 50-100 ml) in a Griffin beaker. The beaker is covered with watch glass and the mixture is then refluxed in a hot plate or equivalent heating source at temperatures slightly below boiling point of water (90-95 oC). The refluxing is continued till the mixture evaporates to a low final volume (~5ml). During the process, efforts ar e taken to ensure that the sample does not boil and that no portion of the bo ttom of the beaker is dry. If the sample goes dry, it must be discarded and the samples must be re-prepa red; otherwise, low recoveries will result. The refluxing step is repeated with additional po rtions of nitric acid until the digestate is

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65 light in color or until its colo r has stabilized. After the digest ate has been brought to a low volume again, it is refluxed with 1:1 hydrochl oric acid (trace metal grade, 34-37%) for an additional 15 minutes to disso lve any precipita te or residue resulting from evaporation. The sample is then filtered using Whatman as hless filter papers (41 grade, 110 mm dia, particle retention > 20-25 µm) to remove silic ates and other insoluble material that could clog the nebulizer of the ICP-AES. After filt ration, the final sample volume is brought up to the original leachate volume digested (50100 ml usually). The sample is then analyzed by ICP-AES [150]. Spiked samples are employed to dete rmine accuracy of the method. A known amount of arsenic, chromium and copper is added to a few samples and they are processed along with other samples. After the ICP analysis, matrix spike recoveries are calculated by the following formula: sample in the spike the of e known valu K sample spiked non for the value measured X sample spiked for the value measured X : where ) X (X 100 Recovery %u s u s K Spiked samples are included with each ba tch of samples processed. The purpose of the matrix spike is to monito r the performance of the anal ytical methods used, and to determine whether matrix interferences exist. Use of other internal calibration methods, modification of the analytical methods, or us e of alternate analytical methods may be needed to accurately measure the analyte c oncentration in the TCLP extract when the recovery of the matrix spike is below the e xpected performance of the analytical method [150].

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66 4.2.3 Solid Digestion (EPA SW 846 Method 3050 B) This method provides digestion procedure fo r the preparation of sediments, sludges and soil samples for analysis by ICP-AES. This method is not a total digestion technique for most samples. It is a very strong acid di gestion that will dissolv e almost all elements that could become ‘environmentally availabl e’. By design, elements bound in silicate structures are not normally dissolved by this pr ocedure as they are not usually mobile in the environment [150]. For the digestion of samples, a representativ e 1-2 gram (wet weight) or 1 gram (dry weight) sample is mixed with 10 ml of 1:1 HNO3 and refluxed at 90-95 oC for 10-15 minutes. If brown fumes are generated, indicating oxidation of the sample by HNO3, additional portions of HNO3 (5 ml of pure HNO3) are added until no brown fumes are given off, indicating completion of reaction with HNO3. Refluxing with HNO3 is carried out for a maximum of two hours. The flask is covered with a ribbed watch glass to allow the solution to evaporate to approximately 5 ml without boiling. The next step is oxidation using hydr ogen peroxide (H2O2) to facilitate dissolution of elements not dissolved by nitric acid. In this step, 3 ml of 30% H2O2 solution is added to the samples digested using nitric acid and refluxed at 90-95 oC. The flask is covered with watch glass to avoid losses due to exce ssively vigorous effervescence [150]. More hydrogen peroxide solution is added with warming, 1 ml at a tim e, until the effervescence is minimal or until the general sample appearance is unc hanged. A maximum of 10 ml of 30% H2O2 is added to the digestate. The samples are covered w ith watch glass and heat ed till the volume has been reduced to approximately 5 ml. For ICP-AES analyses, an additional step using hydrochloric aci d is involved to dissolve any residues or precipita tes formed during refluxing of digestate. In this step, 10

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67 ml of concentrated HCl is added to the digest ate, then it is covere d with watch glass and is refluxed at 90-95 oC for 15 minutes. After cooling, the pa rticulates in th e digestate are removed by filtration using Whatman No. 41 filter paper (or equivalent) and the filtrate is diluted to 100 ml with reagent water. Th e sample can then be analyzed by ICP-AES [150]. Spiked duplicate samples, as descri bed in the liquid digestion process are processed with each set of analysis. The a pproximate linear upper ranges for detection by ICP-AES for a 2 gram digested sample fo r arsenic, chromium and copper is 1,000,000 mg/kg. These ranges may vary with sample matrix, molecular form, and size. 4.2.4 ICP-AES Analysis (EPA SW 846 Method 6010B) ICP-AES quantitatively determines trace el ements, including metals, in solution. It operates on the principle of atomic emission by atoms ionized in the argon plasma. Light of specific wavelengths is emitted as electrons return to the ground state of the ionized elements, quantitatively identifying the species present. This method is applicable to the three CCA metals of concern in this pr oject. ICP-AES requires digestion (or an equivalent processing) of samples (as describe d above) prior to analysis. Detection limits, sensitivity, and the optimum and linear concen tration ranges of the elements can vary with the wavelength, spectrometer, matr ix and operating conditions [150]. Table 4-7 lists the recommended analytical wavelengths and estimated instrumental detection limits for CCA metals in clean aque ous matrices. The instrument detection limit data may be used to estimate instrument and method performance for other sample matrices. The wavelengths listed are recomm ended because of their sensitivity and overall acceptance. Other wavelengths may be substituted (e.g. in the case of an interference) if they can provi de the needed sensitivity a nd are treated with the same corrective techniques for spect ral interference. The estimated instrumental detection

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68 limits shown are provided as a guide for an instrumental limit. The actual method detection limits are sample dependent and may vary as the sample matrix varies [150]. Table 4-7: Recommended Wavelength and Es timated Instrument Detection Limit for CCA Metals Element Recommended Wavelength (nm) Estimated Instrument Detection Limit (µg/l) Arsenic 193.696 35 Chromium 267.716 4.7 Copper 324.754 3.6 Source: [150] In ICP-AES, samples are nebulized to gene rate aerosols and the resulting aerosols are transported to the core of an inductively coupled plasma torch which is at a very high temperature (~8000 oC). At such high temperatures, the elements present in the aerosols get thermally excited and the electrons pres ent in the elements absorb the energy and reach an excited state. When they return to the ground state, they release the energy absorbed in the form of elec tromagnetic radiations of a specific wavelength. The energy transfer for electrons when they fall back to the ground state is unique to each element as it depends upon the electronic conf iguration of the orbitals of the specific element. This light is collected by the spect rometer and passes through a diffr action grating that serves to resolve the light into a spectrum of its constituent wavelengths. Within the spectrometer, this diffracted light is then collected by wavelength and amplified to yield an intensity measurement that can be c onverted to an elemental concentration by comparison with calibration standards [150]. Various types of interferences may be encountered in this technique. Spectral interferences are caused by background emission fr om continuous or recombination phenomena, stray light from the line emission of high concentration elements, overlap of a spectral line from another element, or unr esolved overlap of molecular band spectra.

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69 Physical interferences are caused by effects associated with the sample nebulization and transport processes. Changes in viscosity and surface tension can cause significant inaccuracies, especially in samples cont aining high dissolved solids or high acid concentrations. Another problem that can occur with high dissolved solids is salt buildup at the tip of the nebulizer, affecting aerosol fl ow rate and causing instrumental drift [150]. Chemical interferences include molecular compound form ation, ionization effects, and solute vaporization effects. Chemical interfer ences are highly dependent on matrix type and the specific analyte element. Memory interferences result when analytes in a previous sample contribute to the signals m easured in a new sample. Memory effects can result from sample deposition on the uptake tu bing to the nebulizer and from the build up of sample material in the plasma torch and spray chamber. The site where these effects occur is dependent on the element and can be minimized by flushing the system with a rinse blank between samples. High salt c oncentrations can cause analyte signal suppressions and confuse interference tests. Normally, these effects are not significant with the ICP technique, but if observed, can be minimized by careful selection of operating conditions (incident power, observa tion position, etc.), by buffering of the sample, by matrix matching, and by standard addition procedures. Inter-element interferences are also possible if the wavelength of the element of interest is very close to that of another element. Table 4-8 summarizes the effect of interference of some of the commonly occurring elements on CCA metals [150]. Table 4-8: Potential Interferen ces in Analyte Concentration (in mg/l) when Interferants were Introduced at 100 mg/l Level Interferant Analyte Al Ca Cr Cu Fe Mg Mn Ni Ti V Arsenic 1.3 0.441.1 Chromium 0.0030.04 0.04

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70 Copper 0.0030.05 0.02 Interference values are in mg/l Source: [150] Dashes indicate that no interference was observed even when interferants were introduced at the following levels: Al 1000 mg/l, Mg 1000 mg/l, Ca 1000 mg/l, Mn 200 mg/l, Cr 200 mg/l, Ti 200 mg/l, Cu 200 mg/l, V 200 mg/l and Fe 1000 mg/l. For this thesis, the Perkin-Elmer Plasma 3200 Inductively Coupled Plasma Spectroscopy (ICP) system was used. It is equipped with two m onochromators covering the spectral range of 165-785 nm with a grat ed ruling of 3600 lines/m m. The system is capable of analyzing materials in both orga nic and aqueous matri ces with a detection limit range of less than 1 part per million (ppm). 4.2.5 X-Ray Diffraction Analysis X-Ray Diffraction (XRD) is a crystallogr aphic technique in which the pattern produced by the diffraction of X-rays through the closely spaced la ttice of atoms in a crystal is recorded and then analyzed to reve al the nature of that lattice. X-Rays are transverse electromagnetic radiations, simila r to visible light, but much shorter in wavelength [151]. For X-Ray crystallogra phy, the commonly used wavelengths vary from 0.5-2.5 angstroms, the same as typical inte r-atomic distances in crystalline solids. Thus they can be diffracted from crystallin e minerals which possess regularly repeating atomic structures. For diffraction, typically the K lines are used. The K line which is always present with K, at a slightly shorter wavelength, is filtered out using an absorbing film. Diffraction occurs as wave s interact with a regular stru cture whose repeat distance is about the same as the wavelength. The X-ra ys scattered from cr ystalline solids undergo constructive interference when BraggÂ’s equa tion is followed [151]. The equation is given by,

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71 2dsin N 2 measures eter diffractom the reasons, practical for n, diffractio of angle planes atomic o between tw spacing or spacing atomic inter d angstroms in ngth ray wavele X 3 2, 1, integer positive any N where The XRD Philips APD 3720 instrument was us ed for characterizing the samples in the experiments. In XRD technique, a beam of X-rays is focused on a powdered sample where crystals have varied and random orie ntation. The sample is subjected to the characteristic X-rays ( K line) at angles varying from 0-120 degrees. The intensity and 2 of the diffracted x-ray beam are measure d. A diffraction pattern records the X-ray intensity as a function of 2 [151]. The peaks of intensity observed based on the diffraction pattern are matched with a sta ndard database to determine the compound being formed. This technique also leads to an understanding of the material and molecular structure of the sample. 4.3 Methodology Figure 4-1 depicts a flowchart summarizing th e experimental steps. First, a metal spike was prepared (described above) contai ning all the three CCA metals in the same mass ratio as CCA Type C chemical. The spike was mixed with various sorbents in 75 ml porcelain crucibles. Twenty grams of sorbent wa s added to 50 ml of spike. Each sorbentspike sample was prepared in triplicate to minimize experimental errors and get an estimate of the average properties of the residue. The samples were first heated in a muffle furnace (Fisher Isotemp Programmable Forced Draft Furnace, 650 and 750 series, M odels #58 and #126) at temperatures below the boiling point (~90 oC) for 14 hours to evaporate the wa ter in the solution so as to

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72 minimize losses due to boiling. The furnace was then raised to a temperature of 700 oC, 900 oC and 1100 oC and kept at that temperature for 30 minutes. The time taken by the furnace to reach these temperatures ranged fr om 1 to 3 hours. These temperatures were chosen as they are commonly encountered at combustion facilities in industrial boilers. Here, the capacity of the furnace (maximum possible temperature of 1125 oC) being used for the experiments set up the upper limit for temperatures tested. The residue was extracted from crucibles and grinded to pow dered form using a coffee grinder (Kitchen Aid BCG100OB Onyx Black Coffe e Grinder). A portion of the residual was leached following the TCLP procedure described in section 5.2.1. Each sorbent-spike sample was thoroughly mixed and then a 10 g portion of the sample was transferred to a 250 ml polyethylene container using an acid-rinsed spoon. Then 200 ml of the appropriate extraction fluid were added to the container resulting in the 20:1 liquid/solid ratio that the method required. The container was then placed on a rotary extracto r (Analytical Testing Corporation) for 18+ 2 hours. After rotation, the sample wa s pressure filtered in special hazardous waste filters. This leaching test wa s used to determine whether a solid waste is a hazardous waste or not for its toxicity char acteristic. Two different types of extraction fluids were used in the TC LP procedure following the crite ria described in section 5.2.1. For alumina, attapulgite clay, diatomaceous earth, ferric oxide, kaolin and silica, extraction fluid 1 was used (pH= 4.93 + 0.05). For cement, calcium hydroxide and magnesium hydroxide, extraction fluid 2 was used (pH= 2.88 + 0.05). The % spike recovery from digested samples was betw een 80-120% of the original samples. The TCLP leachate was digested using 50 ml of leachate for each sample as per the liquid digestion method described in section 5.2.2. A por tion of the residue was digested for the

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73 total metal content analysis using solid di gestion method discussed in section 5.2.3. All digested samples were analyzed using ICPAES (section 5.2.4) to determine the metal content in the two digestates. XRD analys is (section 5.2.5) of th e residue was conducted to determine the crystalline sp eciation of the products. The 2 value for the analysis varied from 10-70 degrees. Continuous s canning was done using a step size of 0.02 . Time per step was chosen as either 0.5 s or 1 s depending on the characteristics of the sample and the ratio of intensities to noise. PC Identify software was used determine the compounds corresponding to the peak s observed in the XRD pattern. 4.4 Results This section summarizes the leachi ng (4.4.1), leaching retention (4.4.2), volatilization retention (4.4.3) , speciation characterizati on (in 4.4.4) and leachate pH (4.4.5) results from heating the metal-sorbent samples at 700 oC, 900 oC & 1100 oC. Correlation graphs are presented between As-Cr, As-Cu and Cr-Cu for leaching and volatilization (4.4.6 and 4.4.7). 4.4.1 Leaching Figures 4-2, 4-3 & 4-4 report metal leach ing from incineration ash in mg/l. Leaching results are the most important part of this study as the experimental system was primarily designed to examine the sorbent mate rialsÂ’ capability in reducing the leaching. Leaching is defined as the amount of metal leaching (in mg/l) from the ash after the TCLP test. 4.4.1.1 Arsenic Fig 4-2 reports leaching results for arsenic. The baseline leaching was very high, at around 745 mg/l at 700 oC, ~639 mg/l at 900 oC and ~601 mg/l at 1100 oC. All the sorbents showed some reduction in leaching le vel for arsenic. It can be observed that

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74 cement, calcium hydroxide and magnesium hydr oxide leach less than the TC limit of 5 mg/l of arsenic at all three temperatures. No specific temperature dependence was observed for cement and calcium hydroxide . However, for magnesium hydroxide, leaching decreased with increase in temperat ure. Alumina, silica, diatomaceous earth, attapulgite clay and kaolin leach more than the TC limit of arsenic at all three temperatures. For 700 oC and 900 oC batches, arsenic leaching broadly followed the following trend: alumina, silica < diatomace ous earth < kaolin < attapulgite clay. However, alumina, attapulgite clay, kaolin and silica exhibited lowe r arsenic leaching at 1100 oC. A possible reason for low leachability of arsenic with these sorbents at 1100 oC could be the relatively lower availability of arsenic for leaching due to its high volatilization at higher temperat ures. Another possible reason could be the formation of acid-insoluble arsenic compounds at that temper ature. Ferric oxide leached more than the TC limit of arsenic at 700 oC and 900 oC. However, it leached < 5 mg/l of arsenic at 1100 oC. In a CCA-wood ash leaching study co nducted by Solo-Gabriele et al.[23], arsenic leaching varied from 0.1-1000 mg/l with the highest leaching observed for samples characterized by high retention levels . Iida et al. [2] reported arsenic leaching ranging from 0.1-200 mg/l with the lower leaching values observed with Ca(OH)2 sorbent and the higher ones for pure CCA ash. The detailed results with each sorbent are given in appendix A. The different leaching behavior observed with different sorbents could be due to the difference in speciation of products. For instance, the formation of acid-insoluble arsenic compounds with some so rbents could have resulted in their low solubility in TCLP solution (w hich is acidic in nature) a nd hence resulted in their low leachability. Leaching trends were also im pacted by pH with lower arsenic leaching

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75 observed at high leachate pH. Detailed discussions regardin g impact of volatilization, speciation and pH on leaching will be disc ussed in subsequent sub-sections. SORBENTS B A SE LI NE A LUM I N A A TT AP ULG I T E CLAY C ALC I UM HY D RO XIDE CEMENT D I A TO M A CE O US E A RTH FERRIC OXIDE KAOLIN M A GN E SIUM H Y DROXIDE S I LICA As LEACHED (mg/l) 0.01 0.1 1 10 100 1000 10000 TC Limit(5 mg/l) 700oC 900oC 1100oC TC Limit Figure 4-2: Arsenic Le aching from Sorbents 4.4.1.2 Chromium Fig 4-3 reports leaching results for ch romium. The baseline leaching was around 733 mg/l at 700 oC and 900 oC and ~58 mg/l at 1100 oC. All the sorbents showed some reduction in leaching level for chromium. It can be observed that alumina, silica & ferric oxide leached less than the TC limit of 5 mg/l of chromium at all three temperatures. Kaolin leaches less than TC limit for chromium at 900 oC & 1100 oC. Diatomaceous Earth leached less than 15 mg/l at all thr ee temperatures. Cement and calcium hydroxide leached chromium excessively (~100 mg/l) at all three temperatures. Magnesium hydroxide followed this trend for 700 oC and 900 oC batches. However, it leached close to the TC limit of chromium at 1100 oC. All sorbents except alumina exhibited an inverse

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76 temperature relationship with respect to leac hing, i.e., leaching decrea sed with increase in reaction temperature. Variati on in speciation of products wi th increase in temperature may be responsible for this trend. One of th e reasons for very low leaching of chromium from alumina, attapulgite clay, diatomaceous earth, silica, kaolin a nd ferric oxide at 1100 oC may have been the excessive volatilization of chromium at that temperature leaving very little chromium available for leaching. Solo-Gabriele et al. [23] reported chromium leaching from various wood ash samples be tween 0.2-25 mg/l with the highest leaching observed for samples characterized by low re tention levels. Iida et al. [2] reported chromium leaching ranging from 17~1100 mg/l with the lower leaching values observed for pure CCA ash and higher ones observed for Ca(OH)2 and Na2CO3 sorbents. Leaching trends were also impacted by pH with high chromium leaching observed at high leachate pH. Detailed discussions regard ing impact of volatili zation, speciation and pH on leaching will be discussed in subseque nt sub-sections. Generally speaking, the alumino-silicate sorbents showed good chromi um retention with alumina, ferric oxide and silica exhibiting very low chromium leaching below TC limit. Kaolin and diatomaceous earth too exhibited low chromium retention, close to the TC limit in the entire temperature range and hence can also be used in practical facilities where chromium concentrations arenÂ’t that high. Magnesium hydroxide leached chromium close to its TC limit at 1100 oC. Considering its good performa nce against arsenic, it may be an ideal sorbent for high temperature combustion of CCA-treated wood. The detailed leaching results for each sorbent with resp ect to chromium are given in appendix A.

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77 SORBENTS BASELINE ALU MI NA ATTAPULGITE CLAY CALCIUM HYDR O XI D E CEMEN T DIATOMACEOUS EARTH FER RIC OXID E KAOLIN MAGN ESI U M HY D ROXIDE S ILIC A Cr LEACHED(mg/l) 0.01 0.1 1 10 100 1000 10000 TC Limit (5 mg/l) 700oC 900oC 1100oC TC Limit Figure 4-3: Chromium Leaching from Sorbents 4.4.1.3 Copper Fig 4-4 reports leaching results for Coppe r. The baseline leaching was around 566 mg/l at 700 oC, 490 mg/l at 900 oC and ~469 mg/l at 1100 oC. Since copper is not considered hazardous for its toxicity characteri stic, there is no TC limit for it. However, its excessive leaching can harm aquatic ec osystems and therefore warrants monitoring. All the sorbents showed good leaching rete ntion (< ~50 mg/l) for copper. Cement, calcium hydroxide and magnesi um hydroxide leached less than 10 mg/l of copper at all three temperatures. All other sorbents also exhibited good leaching retention for copper. Alumina and ferric oxide exhibited a decrease in leaching with increase in temperature. No specific temperature dependence trend was exhibited by other sorbents. Leaching trends didnÂ’t appear to be heavily imp acted by pH although relatively lower copper leaching was observed at high pH. Speciation resu lts indicate the high affinity of copper

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78 to form compounds with the elements present in the sorbents as well as the other two CCA metals. This characteristic may have led to lesser leaching of copper from the sorbent-spike samples. Solo-Gabriele et al. [23] reported copper leaching from various wood ash samples between 0.07-15 mg/l with th e highest leaching observed for samples characterized by high retenti on levels. Iida et al. [2] reported copper leaching ranging from 1~900 mg/l with the lower leaching values observed for Ca(OH)2 sorbent and higher ones observed for Na2CO3 sorbent. Copper leaching from pure CCA wood ash in this study was ~100 mg/l. Since copper is not a TC hazardous metal, its leaching level may not be considered limiting as opposed to arsenic and chromium. Based on these results, it can be concluded that any sorben t exhibiting low leaching level for arsenic and chromium will work well for copper too. The issue of copper leaching is important as arsenic based preservatives ar e increasingly being replaced by copper based preservatives and there is growing concer n over leaching of copper from wood treated with those preservatives. The detailed results fo r each sorbent are given in appendix A.

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79 SORBENTS B ASE LIN E ALUM I N A ATT A PU L GI T E CLAY C A LCIU M H Y DROXIDE CEMEN T DI A TO M A C EO U S EA R TH F ERR I C OXIDE KA OL I N MAGNESIUM HYD R OX I DE SILICA Cu LEACHED(mg/l) 0.01 0.1 1 10 100 1000 10000 700oC 900oC 1100oC Figure 4-4: Copper Leaching from Sorbents 4.4.2 Volatilization Retention Figures 4-5, 4-6 & 4-7 report the percentage volatilizat ion retention of metals during heating of sorbent-spike samples. Volatil ization retention (VR) is calculated as the fraction of metal that remains in sorbent-me tal ash over the metal content in the spike. Detailed VR results are provided in appendix B. Since the system was not specifically designed to control VR, relativ ely lower VR was observed for this study as compared to others [2]. 100 ' ' spike in metal CCA of mass ash spike sorbent in metal CCA of mass VR

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80 4.4.2.1 Arsenic Fig 4-5 reports VR results for arsenic. The baseline VR was very low, at around 6.3% at 700 oC, ~4.8% at 900 oC and ~4.7% at 1100 oC. The retention amongst sorbents ranged from 20 – 40%. No specific temperat ure dependence trends were observed. A higher retention level for arsenic with Ca-based sorbents is reported in literature for CCA wood at lower concentrations. However, in the experimental system used, the temperature increase from ambient to desi gnated temperature was gradual, due to the long heating times (1-3 hours) encountered in the muffle furnace. At lower temperatures, arsenic and arsenic compounds are physica lly adsorbed onto sorbents. Chemical transformation proceeds at hi gher temperatures. Therefor e volatilization may have occurred during heating, before reaching th e high temperature required for chemical adsorption. Hence, relatively low VR is obser ved as compared to other studies where the time taken to reach the designated temperatur e wasn’t too large. Another possible reason for no specific VR trend could be its depende nce on the physical properties besides the chemical properties. Physical properties like pa rticle size of sorbent, particle size of the metal, interstitial spaces etc. which were not considered for these experiments could have affected retention. Iida et al. [2] reported arsenic VR in pure CCA ash as ranging from 67-54% when temperature was increased from 600 oC to 900 oC. VR increased to above 80% with the addition of Ca(OH)2 and Na2CO3 sorbents. The retention in CCANa2CO3 system decreased to 54% at 900 oC.

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81 SORBENTS B A SE L INE ALUMINA ATTA P ULGI T E CLAY CALCI U M HYDR O XIDE CEMEN T D IA TO MAC EOU S E AR TH F E RR I C O XIDE KAOLI N M AGN E SI U M H YDR O X I DE SILI C A % VR for As 0 20 40 60 80 100 700oC 900oC 1100oC Figure 4-5: Percentage Arsenic Volatilization Retention in Sorbents 4.4.2.2 Chromium Figure 4-6 reports VR results for chromium . The baseline VR was very low, at around 6.3% at 700 oC, ~4.8% at 900 oC and ~4.7% at 1100 oC. With sorbents, VR ranged from 0 – 60%. Cement, calcium hydr oxide and magnesium hydroxide showed better retention than other sorbents, especially at 1100 oC. All sorbents except these three had a very low VR at 1100 oC. All alumino-silicate sorbents exhibited inverse temperature dependence, i.e., VR decreased wi th increase in temperature. All sorbents except ferric oxide showed a drastic change in VR from 900 to 1100 oC. For alkali earth sorbents, an increase in VR is observed for 1100 oC. For alumino-silicates, a drastic decrease in VR is exhibited at 1100 oC. These results may have occurred due to changes

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82 in speciation between 900 – 1100 oC. In the case of alkali earth sorbents, the volatile compounds may have transformed into non-vol atile ones at higher temperature whereas aluminosilicates may have formed more vol atile compounds in this temperature range. Another possible reason for lo w chromium VR from alumino-silicates could be the formation of Cr(NO3)3.9H2O which has a boiling/decomposition temperature of ~100 oC. Prior to heating the sorbent-spike samples, they were kept at 90-95 oC for 14 hours to minimize losses due to boiling which is very close to the boiling point of Cr(NO3)3.9H2O. Since alumino-silicates have relatively lower affinity for nitrate, nitrate present in the spike may have combined with chromium to form the above menti oned chromium nitrate in the presence of alumino-silicates. In the case of alkali-earth so rbents, alkali-earth nitrates may have been formed preferen tially over chromium nitrate. Hence high chromium VR was observed for these sorbents . The low VR by alumino-silicates resulted in the low availability of chromium for leaching, hence could be a possible reason for excessively low chromium leaching at 1100 oC for some alumino-silica tes. Iida et al. [2] reported chromium VR in pure CCA ash as ranging from 64-43% when temperature was increased from 600 oC to 900 oC. VR increased from 77% to 87% with the addition of Ca(OH)2 sorbent when temperature was increased from 600 oC to 900 oC. Na2CO3 sorbent showed high VR, over 80% which reduced to ~60% at 900 oC.

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83 SORBENTS BASE LI N E ALUMINA ATTAPU L G I TE C LA Y CA LC IUM HYDROXIDE CEME N T DIA T OMA CE OU S E A R T H FER R IC OXID E KAOLIN M A GN E SIU M H YDR OX I D E SILICA % VR for Cr 0 20 40 60 80 100 700oC 900oC 1100oC Figure 4-6: Percentage Chromium Volatilization Retention in Sorbents 4.4.2.3 Copper Figure 4-7 reports VR results for copper. The baseline VR was low, but higher than arsenic and chromium. For 700 oC, VR was at 16.8% , it was ~13% at 900 oC and ~12% at 1100 oC. For copper, retention was relatively higher at 2060%. Ferric oxide showed the highest retention, above 40% , at all three temperatures. All sorbents tested showed moderate to good VR for copper across all temperatures. No specific temperature dependence trend was observed for any sorben t or group of sorbents. Like arsenic, a possible reason for no specific VR trend could be its dependence on the physical properties besides the chemical properties. P hysical properties like particle size of sorbent, particle size of the metal, interstiti al spaces etc. which were not considered for

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84 these experiments could have affected rete ntion. Variation in sp eciation of products across temperatures for different sorbents may have been another reason for such variability in VR for copper. SORBENTS BASE LI N E ALUMINA ATTAPU L G I TE C LA Y CA LC IUM HYDROXIDE CEME N T DIA T OMA CE OU S E A R T H FER R IC OXID E KAOLIN M A GN E SIU M H YDR OX I D E SILICA % VR for Cu 0 20 40 60 80 100 700oC 900oC 1100oC Figure 4-7: Percentage Copper Vola tilization Retention in Sorbents Copper VR for pure CCA wood ash, as reporte d by Iida et al. [2] varied from 8770% when temperature was increased from 600 oC to 900 oC. No significant impact on VR was observed on the addition of Ca(OH)2 and Na2CO3 sorbents. 4.4.3 Leaching Retention Leaching Retention (LR) is defined as the fraction of metal present in the ash that didnÂ’t leach out. LR is expresse d as a percentage. All sorben ts show a high LR, greater than 80%, for all the three temperatures whic h shows that in all the leaching scenarios

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85 encountered, a significant portion of the CCA me tals still remained in the ash. However, it should be noted that in real life scenario s involving prolonged leaching, lower LR may be possible. 100 ash in metal of mass leachate in metal of mass ash in metal of mass LR 4.4.3.1 Arsenic Figure 4-8 reports LR results for arseni c. The baseline LR is around 80% at all three temperatures. All sorbents exhibit good LR for arsenic at all temperatures, between 80-100%. No specific temperature depende nce was observed. Alkali earth metals displayed very high LR, close to 100%. Here, it should be kept in mind that very high LR, over ~98%, is required to leach arsenic be low TC limit. Only alkali earth sorbents fulfill that criterion. 4.4.3.2 Chromium Figure 4-9 reports LR results for chromium . The baseline LR is around 80% at all three temperatures. All sorbents exhibit good LR for chromium at all temperatures, between 80-100%. Alumina, ferric oxide, kaolin and silica showed excellent LR, close to 100% in some cases. However, no specific temperature dependence was observed for alumino-silicates and ferric oxid e. For alkali earth sorbents, LR increased with increase in temperature. Here, it should be kept in mind that very high LR, over ~98%, is required to leach chromium below TC limit. Only some al umino-silicates and fe rric oxide fulfill that criterion.

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86 SORBENTS BASELINE AL UMIN A AT TAP U LGI TE CLAY C AL C I U M H YD R O XI D E C EMEN T D I ATOMACEOUS EAR TH FER R IC OXID E KAOL I N MAGNESIU M H YD R OXID E SILIC A % LR for As 0 20 40 60 80 100 700oC 900oC 1100oC Figure 4-8: Leaching Retention for Arsenic 4.4.3.3 Copper Figure 4-10 reports LR results for copper. The baseline LR is around 90% at all three temperatures. All sorbents exhibit exce llent LR for copper at all temperatures, between 90-100%. However, no specific temp erature dependence was observed for any sorbent. CopperÂ’s strong affinity for fo rmation of bi-metalli c and metal-sorbent compounds which could be a possi ble reason for such a high LR. A very high LR, over ~98%, is required to leach copper around 10 mg/l or below. Only alkali earth sorbents fulfill that criterion.

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87 SORBENTS B A SE LI N E A LUMI N A AT T A P ULGIT E C LAY CA L CI U M HY D ROX I DE CE M E N T DIA T OMACEOUS E A RTH F E RR I C OXID E KAOLIN M A GN ES I U M H Y DROXID E SILICA % LR for Cr 0 20 40 60 80 100 700oC 900oC 1100oC Figure 4-9: Leaching Retention for Chromium Figures 4-11, 4-12 and 4-13 show the mass balance between the leaching, volatilization and retention fractions for each metal-sorbent sample at different temperatures. These graphs give an estimate of the relative distribution of each metal in the leachate, ash and volatiles. The various pe rcentages here are calculated with respect to the original mass of each metal in 50 ml of spike, i.e., 652 mg of As, 730 mg of Cr and 436 mg of Cu. The fraction of me tal retained in ash depicted here should not be confused with the LR results which are calculated using the metal cont ained in the ash and not the metal input.

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88 SORBENTS BA SEL I N E ALUMINA AT TAPUL G ITE CL AY CAL C IUM HYD R OXIDE CEMENT DIATOMA C E O US EAR T H FERRIC O XI D E KAOLIN MAGNESIUM HYDROXIDE S IL I CA % LR for Cu 0 20 40 60 80 100 700OC 900oC 1100oC Figure 4-10: Leaching Retention for Copper As evident from these results, leaching frac tion forms a very small part of the total metal distribution, typically less than 1% for mo st of the cases. The bulk of the metal is in the form of volatiles which is expected as the system wasnÂ’t designed specifically for VR. The remaining metal is found in the ash. No significant trends were observed. However, it can be seen from the chromium mass balance graphs for 1100 oC batch for alumina and silica that almost all of chromi um was part of the volatile fraction which may have led to the low availability of Cr for leaching at that temperature.

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89 700 o C Arsenic Mass Balance 0 20 40 60 80 100 900 o C Arsenic Mass Balance 0 20 40 60 80 100 1100 o CSORBENTS SPIKE A LU MINA A TT A PU LGI TE C LAY C ALCIUM H Y D R OXIDE CEMENT DIAT O M AC EO US E ARTH FER R I C O XI D E KAOLIN MAGNESIUM HYDROXI D E SI LICA Arsenic Mass Balance 0 20 40 60 80 100 % Leached % in Ash % Volatilized Figure 4-11: Percentage Ar senic Leached, Retained in Ash and Volatilized

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90 700 o C Chromium Mass Balance 0 20 40 60 80 100 900 o C Chromium Mass Balance 0 20 40 60 80 100 1100 o CSORBENTS SPIKE A L UMINA ATT A P UL GITE CL A Y CAL CI UM HY DRO XIDE CEMENT DIA TO MA CE O US E A RTH FERRIC OXIDE K A O LIN MA G NE S IU M HY DROX I DE S I L ICA 0 20 40 60 80 100 Chromium Mass Balance % Leached % in Ash % Volatilized Figure 4-12: Percentage Chromium Leach ed, Retained in Ash and Volatilized

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91 700 oC Copper Mass Balance 0 20 40 60 80 100 900 oC Copper Mass Balance 0 20 40 60 80 100 1100 oCSORBENTS SPIKE ALUMINA A T TA P U LG IT E C LA Y C A L C I UM HYDRO X IDE C E MENT DIATOMACEO U S E A R T H FERRIC O X ID E K A OLIN MAG N E S I U M HY D ROXIDE SILI CA Copper Mass Balance 0 20 40 60 80 100 % Leached % in Ash % Volatilized Figure 4-13: Percentage Copper Leached, Retained in Ash and Volatilized

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92 4.4.4 Speciation Figures C-1 to C-30 show XRD results for all sorbent-spike residue at all three temperatures. If the compounds formed are crystalline in nature, their presence is indicated by the XRD technique. Table 4-9 summarizes the major metal-mineral compounds whose presence has been indicated by XRD. As shown in the table, a large variety of metal-mineral compounds are forme d. It is also observe d that copper has high affinity for forming compounds with arsenic and chromium besides the mineral sorbents. XRD analysis is not quantitativ e hence XRD results can not be used to pinpoint the major compounds contributing to the leaching behavior. However, it still provides useful qualitative information regarding possible pr oduct speciation in the residue. Such information is critical in providing ex planation for the leaching behavior. The sensitivity or the limit of detection of the XRD technique is material and matrix dependent. In a specific matrix, it prim arily depends on the crystal structure and electron density of the material being investig ated. For instance, in the XRD analysis of asbestos, the limit of detection for asbestos in talc or calcite is 0.2% and it is 0.4% in heavy X-Ray absorbers like Fe2O3 [152]. Another study found the detection limit of quartz to be 10 µg and for cristobalite as 50 µg [153]. Therefore any specific detection limit for the materials used in this study can’t be determ ined. Amongst the large variety of compounds identified, information regarding the acid solubility is available for a few. The acid solubility is an impor tant property as the leaching so lution is acidic in nature. Hence, compounds soluble in acidic conditions ar e likely to leach out during TCLP tests. In case of chromium, compounds like CuCr2O4, Cr2O3, Cr(OH)3, CaCr2O4, CrO(OH), FeCr2O4, MgCr2O4, etc. were formed, which ar e insoluble in acids (chromium is present as Cr(III)). Hence they may not le ach out of the TCLP solution contributing to

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93 the low leachability of chro mium from alumino-silicates, ferric oxide and magnesium hydroxide (for 1100 oC batch). Although acid-insoluble compounds like CaCr2O4 were also formed with calcium hydroxide, they may have been minor products considering high chromium leaching from calcium hydroxi de. On the other hand, in compounds like MgCrO4, Cu3CrO6, CuCr2O7.2H2O, CaCrO4, CrO3 and CuCrO4, chromium is present as Cr(VI) which is highly mobile and may have contributed to high chromium leaching in alkali earth sorbents (except magnesium hydroxide for 1100 oC batch) and attapulgite clay (for 700 oC and 900 oC batches). For arsenic, compounds like Cu3(AsO4)2, As2O5, Cu2As2O7, etc. were formed, which are soluble in acids, hence may have contributed to the high leaching of arsenic and copper from alumino-silicates and ferric oxide (except for 1100 oC batch). On the other hand, acid-insoluble compounds like AlAsO4, Ca2As2O7, Ca3(AsO4)2, MgHAsO4, etc. were also formed, which may have contributed to the low leaching of arsenic from alkali earth sorbents. In spite of the formation of acid-insoluble compounds like AlAsO4, all aluminum based sorbents exhibit high arsenic leaching hence it is likely that these compounds must have been minor reaction products. For copper, a large variety of metal-metal and metal-mineral compounds were formed. Acidsolubility information is available rega rding only a few. Some of them like Cu3(AsO4)2, Cu2As2O7, Cu3CrO6, CuCr2O7.2H2O, and CuCrO4 may be acid-soluble while others like CuCr2O4 may be acid-insoluble. It is possible that acid-in soluble copper compounds may have dominated the products w ith alkali-earth sorbents resulting in extremely low copper leaching from those sorbents. On the othe r hand, formation of a mixture of both acidsoluble (e.g. Cu3(AsO4)2) and acid-insoluble compounds (e.g. CuCr2O4) may have contributed to the moderate leaching of coppe r from alumino-silicates and ferric oxide.

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94 The metal spike exhibited excessive leaching for all three CCA metals. This may have resulted from the dominance of acid sol uble compounds in the product (e.g. CuCrO4, Cu3(AsO4)2). Detailed speciation results are provided in Appendix C. Speciation results in the CCA-Sorbent study conducted by Iida et al. [2] show the formation of compounds like Cr2O3, As2O3, CuCr2O4, Cu3AsO4(OH)3, Ca5(CrO4)3OH, Na2CrO2, Na3AsO4, NaAsO2, Na3AsO4.12H2O, etc. which possibly affected the leaching and VR characteristics in that study.

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95Table 4-9: Summary of Speciat ion Characterization Results Sorbent 700 oC 900 oC 1100 oC Alumina CuAlO2, Cu3(AsO4)2, CuCr2O4, Cr2(AsO3)4, Cr5O12, Cr2O3 Cu4(As2O7)O2, CuAlO2, Cu3(AsO4)2, CuCr2O4, CuCrO4, Cr2(AsO3)4, CuAs2O4, AlAsO4, Cr2O3, Cu3As CuAlO2, Cu3(AsO4)2, CuCr2O4, Cr2O3, Cr4As3, As2O5, AlAsO4, CuAs2O4, Cu3As Attapulgite Clay Cu3(AsO4)2.(OH)3, Cu3(AsO4)2.(OH), MgCrO4, Mg(H2AsO4)2.H2O, CrO(OH), Mg3Cr2(SiO4)3 Cu3(AsO4)2, Cr2(AsO3)4, CrO(OH), Cu5(AsO4)2.(OH)4, Cr2O3, Cu5As2, Cu2(AsO4)OH, Mg3(AsO4)2 Cu5(AsO4)2.(OH)4, Cu3(AsO4)2, Cu2MgO3, As2O5, CuMgSi2O6, Cu2(AsO4)OH, MgCrO4, Cr2O3 Calcium Hydroxide CuHAsO4, CaCrO4.2H2O, Ca5(AsO4)3.OH, CuCrO4, CaHAsO4.2H2O, CaCu, CrAsO4.xH2O,Ca3(AsO4)2 Ca5(AsO4)3.OH, CaCu, Ca2CuO3, Cr2O5, Ca3(AsO4)2, Ca5(CrO4)3, CaCrO4 CuHAsO4, CaCrO4.2H2O, Ca5(CrO4)3.OH, CaHAsO4.2H2O, CrAsO4.xH2O Cement Cu3As, Cu4(As2O7 )O2, Ca2As2O7, CaCrO4, CaCr2O4, Cu3(AsO4)2 Ca2As2O7, Ca5(CrO4)3, CuCrO4, CuAl2O4, CaCu2O3, Ca5Cr2SiO12, Ca2As3, CaCuO2 Cu3(AsO4)2, Ca2As2O7, Ca5(CrO4)3, CuCrO4, As2O4, Ca5(CrO4)3, CaCu2O3, Ca5CrSiO12, Cu3As, Ca2As3, CrO, Cu9.5As4, As2O4, As2O3, Al13Cr2, CaCrSi4O10 Diatomaceous Earth Cr2O3, CuCrO2, Cu3(AsO4)2, CrFeAs2, Cr2SiO4, Cu3As, CuFe2O4, AsCu9 Fe3AsO7, CuCr2O4, Cu2As3 Fe3AsO7, Cr2O3, As2O5, CuCrO2, Cu2As3, Cu3(AsO4)2, CrFeAs2, AsCu Ferric Oxide FeCr2O4, Cr2FeO2, CuFe2O4, Cu3(AsO4)2 FeCr2O4, Cr2FeO2, CuFe2O4, Cu3(AsO4)2 Fe2(AsO3)4, FeCr2O4, Cr2FeO2, Fe4As2O11, CuFe2O4, Cu3(AsO4)2, CuCrO4

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96Table 4-9: Continued. Sorbent 700 oC 900 oC 1100 oC Kaolin Cr2O3, CrO(OH), Cu5(AsO4)2.(OH)4, Cu2(AsO4)OH, Cu2(OH)2(CrO4) As2O4, AlAs, CuCr2O4, Cu4(As2O7)O2, Al(H2AsO4).H2O, Cu5(AsO4)2.(OH)4, Cr(OH)3 Cu5(AsO4)2.(OH)4, Cr2O3, CrO(OH), CrO3, Cr5O12, Cu2(AsO4)OH Magnesium Hydroxide Cu2MgO3, CuHAsO4, MgHAsO4, CuCr2O7.2H2O Cu2MgO3, Cu2O, MgHAsO4, Cu3CrO6 MgCrO4, MgCr2O4, Cu2MgO3, MgHAsO4.4H2O, Cu2(AsO4)OH.3H2O Silica As2O5, Cu5As2, Cu9.5As4, Cu3(AsO4)2, Cr2O3, Cr2(AsO3)4, CuAs2O4 SiAs2, Cu2As2O7, CuCr2O4, Cr2O3, Cr2(AsO3)4, CuAs2O4 Cu5As2, Cr2O3, CrO3, Cr2(AsO3)4, CuAs2O4 Spike Cr2O3, CrO3, CuAs2O4, Cu3(AsO4)2, Cr4As3, As2O5, Cu2As3, CrAs2, Cu2As2O7 Cu2As2O7, Cu3(AsO4)2, Cr2O5, CrO3, Cu2As3, Cr2(AsO3)4, CuAs2O4, CuCrO2, CuCrO4, CuCr2O4, Cu9As4, Cu5As2, Cu3As, Cr5As3, Cr2(AsO4)3 CrO3, Cr2(AsO4)3, Cr2(AsO3)4, CuAs2O4, Cu3(AsO4)2, CrAs2, As2O5, Cu5As2, CuO, CuCrO4, Cu3As Acid-Solubility data is available for compounds marked in bold. All acid-solubility data has been taken from The Handbook of Chemistry and Physics , 64th Edition, 1983-1984, CRC Press

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97 4.4.5 pH Effects Leachate pH can be used as an indicato r to assess the potentia l leachability of a sample. In these experiments, leachate pH was measured for all samples to assess the impact of pH on metal leaching. Figure 4-11 shows the leachate pH for various sorbentspike samples. In general, a high leachate pH (>9) was exhibited by alkali earth based sorbents. Alumino-silicate sorbents and fe rric oxide leachate pH was typically in the range of 4-6. Kaolin exhibited an unusually high pH at 900 oC and the reason for it couldnÂ’t be ascertained. Detail ed leachate pH measurements are provided in appendix D. SORBENTS BASELINE A L UM I NA ATTA P ULG I TE CL A Y CAL CI U M HYDROX IDE CEMENT DIA TO M ACE OUS E ARTH F ERR I C OXI DE KA O L IN MAGNESIUM HYDROXIDE S IL ICA pH 0 2 4 6 8 10 12 14 pH=7 700oC 900oC 1100oC pH =7 Figure 4-14: Leachate pH for Sorbent-Spik e Samples at Different Temperatures Figure 4-12 plots the concentr ations of arsenic, copper and chromium as a function of leachate pH. It can be observed that for arsenic, the leaching was higher at lower pH values (pH = 4-6) and very low leac hing at high pH (9-12). In contrast , very high

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98 chromium leaching was encountered in the high pH range (pH = 10-12) and much lower leaching was observed at low pH (4-6). High chromium leaching at high pH could be due to the formation of hexavalent chromium in alkaline conditions as reported in previous studies [24]. CopperÂ’s pH-leaching trend was so mewhat similar to arsenic: the leaching was higher at lower pH values (pH = 4-6) a nd lower at high pH (9-12). A possible reason for similarity in As-Cu leaching trend at lower pH could be the formation of leachable bimetallic As-Cu species in the products. At higher pH, non leachable alkali earth-arsenic compounds may have been formed. Details of correlation between As-Cu leaching are discussed in the subsequent sub-sections. To wnsend et al. [22] studied the impact of leachate pH on metal leaching in various CCA sawdust samples and concluded that it was a contributing factor to metal leachability. In their study, all three CCA metals showed similar leaching patterns; with high leaching observed at low (< 4) and high (> 11) pH values. Leaching was the least at ne utral/near neutral pH values. The relationship between pH and leachate co ncentrations helps explain some of the previous observations and can serve as an indicator for the leaching behavior. For example, in alkaline environments (high pH e nvironment), there is a greater possibility of leaching of chromium due to the suspected conv ersion of Cr(III) to Cr(VI). As previously discussed, other factors like speciation and complexation affect leaching besides pH. Thus while a pH relationship such as that s hown in fig. 4-12 can be helpful for assessing potential leachability; other factors impac ting leachability should not be neglected.

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99 Metal Leaching vs. pHpH 2468101214 Metal Leaching (mg/l) 0.01 0.1 1 10 100 1000 Arsenic Chromium Copper Figure 4-15: Variation in Concentration of CCA Metals with Final pH of Leachate 4.4.6 Correlation between Leaching of CCA Metals Correlation plots were drawn for molar l eaching of As-Cr, As-Cu and Cr-Cu pairs to gain insights of possible relation between speciation and leaching. It is possible that a particular metal-metal compound may be acid-soluble or acid insoluble resulting in high or low leaching respectively of that meta l pair. Temperature dependence was also observed for some sorbents indicating variati on in speciation, hence variation in leaching behavior at different temp eratures. Figure 4-13 shows th e molar leaching correlation between arsenic and chromium.

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100 Arsenic Leached (mmol/l) 0.00010.0010.010.1110 Chromium Leached (mmol/l) 0.0001 0.001 0.01 0.1 1 10 Alumina Attapulgite Clay Calcium Hydroxide Cement Diatomaceous Earth Ferric Oxide Kaolin Magnesium Hydroxide Silica 1:1 Figure 4-16: Leaching Correlation Gra ph between Arsenic and Chromium As evident from the figure, very little leaching correlation was observed for As-Cr pair. Only diatomaceous earth showed some correlation, possibly due to the formation of Cr2(AsO4)3 as a major product, which may have re sulted in the leaching of As and Cr from the residue. For other sorbents whic h show formation of compounds like CrAsO4 in XRD pattern but show no observable correla tion, may be possible that these compounds must have been minor products. Figure 4-14 shows the molar leaching corre lation between arsenic and copper. From the figure, it can be observed that a strong correlation exists between the arsenic

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101 and copper leaching from alumina, diatomace ous earth, ferric oxide, silica and kaolin (except for 900 oC samples). A possible reason for this strong correlation could be the formation of Cu3(AsO4)2, CuxAsy type of compounds (which are acid-soluble) as major products. Arsenic Leached (mmol/l) 0.00010.0010.010.1110 Copper Leached (mmol/l) 0.0001 0.001 0.01 0.1 1 10 Alumina Attapulgite Clay Calcium Hydroxide Cement Diatomaceous Earth Ferric Oxide Kaolin Magnesium Hydroxide Silica 1:1 Figure 4-17: Leaching Correlation Graph between Arsenic and Copper Alkali earth sorbents donÂ’t exhibit an y observable correlation so it can be concluded that Cu-As compounds detected in XRD analysis of their residue must have been minor products compared to th e other metal-mineral compounds like Ca3(AsO4)2, Ca2As2O7, etc. It should be noted that data points at very low concentration, which belong to alkali-earth sorbents, may not be reliable for correlation analysis. Figure 4-15 shows the molar leaching correla tion between chromium and copper.

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102 Chromium Leaching (mg/l) 0.00010.0010.010.1110 Copper Leaching (mg/l) 0.0001 0.001 0.01 0.1 1 10 Alumina Attapulgite Clay Calcium Hydroxide Cement Diatomaceous Earth Ferric Oxide Kaolin Magnesium Hydroxide Silica 1:1 Figure 4-18: Leaching Correlation Gra ph between Chromium and Copper From the figure, it can be observed th at some correlation exists between the chromium and copper leaching from diatomaceous earth possibly due to the formation of CuCrO4, CuCr2O4, etc. as one of the major products. The temperature dependence on leaching for most of the sorbents can be obs erved as many data points are clustered in groups of three with each group belongi ng to a particular temperature. 4.4.7 Correlation between Volatilization Retention of CCA Metals Correlation plots were drawn for molar VR of As-Cr, As-Cu and Cr-Cu pairs to gain insights of possible relation between sp eciation and VR. It ma y be possible that a

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103 particular metal-metal compound may be volatile or non-volatil e resulting in low or high VR respectively of that metal pair. Figure 4-16 shows the molar VR correlation between arsenic and chromium. No significant correl ation was observed for this metal pair. Figure 4-17 shows the molar VR correlat ion between arsenic and copper. Except for attapulgite clay, all other sorbents exhi bited a VR correlation trend, though in varying degrees. Some correlation was observed for di atomaceous earth, kaolin and silica. Ferric oxide showed a slightly bette r correlation than these thr ee sorbents. All alkali-earth sorbents and alumina exhibited a good correla tion between VR for arsenic and copper. The reason for this correlation could be the formation of various As-Cu-sorbent compounds as discussed in the XRD specia tion subsection. These compounds formed may be thermally stable t hus reducing volatilization.

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104 mmol of As Retained 1 10 mmol of Cr Retained 1 10 Alumina Attapulgite Clay Calcium Hydroxide Cement Diatomaceous Earth Ferric Oxide Kaolin Magnesium Hydroxide Silica 1:1 Figure 4-19: Volatilization Retention Co rrelation between Arsenic and Chromium

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105 mmol of As Retained 1 10 mmol of Cu Retained 1 10 Alumina Attapulgite Clay Calcium Hydroxide Cement Diatomaceous Earth Ferric Oxide Kaolin Magnesium Hydroxide Silica 1:1 Figure 4-20: Volatilization Retention Correlation between Arsenic and Copper Figure 4-18 shows the molar VR correlat ion between chromium and copper. As with the case of As-Cr pair, Cr-Cu pair s hows no significant corre lation in VR thereby suggesting that the formation of Cr-Cu com pounds didnÂ’t play a dominant role in their VR properties.

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106 mmol of Cr Retained 1 10 mmol of Cu Retained 1 10 Alumina Attapulgite Clay Calcium Hydroxide Cement Diatomaceous Earth Ferric Oxide Kaolin Magnesium Hydroxide Silica 1:1 Figure 4-21: Volatilization Retention Co rrelation between Chromium and Copper

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107 4.5 Conclusions In this chapter, the experimental results from heating sorbent – spike samples at 700 oC, 900 oC and 1100 oC were discussed. The objective was to evaluate various sorbent materials for their capability in reduc ing ash leachability as well as to minimize metal volatilization by conducting leaching a nd speciation charac terization studies. Various leaching, volatilization retention, leaching retenti on, speciation characterization results and pH-leaching trends were discussed. Correlation trends between the three metal pairs with respect to leaching and volatilizati on were also discussed and depicted. Results indicate that alkaline earth sorbents are ex cellent in controlling arsenic leaching in the temperature range encountered. On the other hand, alumino-silicate sorbents and ferric oxide were excellent in minimizing chro mium leaching. Low leaching for copper was shown by all sorbents. At 1100 oC, ferric oxide and magne sium hydroxide showed excellent capabilities in lowering leaching fo r all three CCA metals. No specific VR trends were observed. All sorbents displayed low to moderate VR. For some sorbents, at a specific temperature, e.g. alumino-silicates at 1100 oC, low VR led to low availability of chromium in the ash which may have re sulted in low chromium leaching. Relatively higher VR was observed in other studies fo cusing on minimization of volatilization as well. A good LR (>80%) was observed for all three metals by all sorbents. However, it should be noted that a LR around 98% or greater is required to leach As and Cr below TC limits. The XRD analysis reveal s that the speciati on of the products may have been an important factor governing the leaching beha vior. It was found that reactions which produced acid soluble compounds led to high le aching of the concerned metal. Effect of pH on leaching was also studied. Higher arse nic and copper leaching was observed at low pH (4-6) and high chromium leaching was observed at high pH (10-12). Correlation

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108 graphs were drawn for each metal pair for leaching and VR. A good correlation was observed for the As-Cu pair, both in terms of leaching and VR suggesting the possible formation of As-Cu compounds. The acid-solub ility and thermal stab ility properties of these compounds governed their leaching and VR behavior with respect to different sorbents. Based on these results, it can be conclude d that sorbents are capable of reducing metal leachability and volatilization by chemi cally combining with CCA metals to form thermally stable and acid-insoluble compounds . While speciation plays a major role in metal leaching, the effects of leachate pH shoul d also be taken into account. From the results discussed above, it can be concluded th at the leaching behavior of all three CCA metals in alkali-earth sorbents is determin ed by the metal-mineral compounds formed. On the other hand, for aluminosilicate sorbents, the form ation of bimetallic As-Cu compounds governs their leaching behavior whereas chromium leaching is determined by the formation of various chromium oxides and Cr-Cu compounds. For ferric oxide, the formation of As-C u compounds governs their leaching for 700 oC and 900 oC batches, whereas the formati on of Fe-As and Fe-Cu compounds determines their leaching behavior for 1100 oC. Chromium leaching by ferric oxide is governed by the formation of Fe-Cr co mpounds. For volatiliza tion, variation in speciation, physical properties of sorb ent particles and operational parameters (temperature etc.) could account for the variab ility in retention capab ilities of different sorbents. Pilot-scale studies can be conduc ted to optimize the operating conditions and parameters for efficiently reducing metal leaching and volatilization during combustion

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109 of CCA-treated wood. More ri gorous studies are needed to further understand metalsorbent interactions at high temperatures.

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110 CHAPTER 5 SUMMARY AND RECOMMENDATIONS Chromated Copper Arsenate (CCA) is a popular wood preservative applied to wood products to prevent environmental decay during outdoor use and hence has been predominant in the disposal sector in recent y ears. Estimates suggest that a large quantity of CCA-treated wood waste in Florida is bur ned to produce energy. Incineration results in volatilization of metals during combustion and accumulation of metals in ash which poses health and environmental concerns. Pa st studies have shown that many mineral sorbents are effective in controlling heavy me tal volatilization during incineration. In this study, the viability of thermal processes in existing facilities as an option for the management of CCA wood waste in the state of Florida wa s evaluated. Two main tasks were identified for the purpose of this study. The first task focused on the review of available arsenic pollution control technologies. Arsenic is the most hazardous of the three CCA metals and is semi-volatile; so it is released into the air during combusti on of arsenic containing fuels. Therefore, it was essential to assess the available arsenic pollution c ontrol technologies. Amongst the various available thermal techno logies, co-incineration appear s to be the most promising technology amongst the existing techniques. Co-i ncineration serves the dual purpose of dilution of arsenic concentration as well as scavenging of arsenic by materials like lime which may be present in the other fuel components. Coupling co-incineration with sorbent injection in feed a nd gas stream can result in th e dual benefit of controlling submicron particulate emissions as well as forming non-toxic, non leachable ash which

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111 can be disposed of easily. An evaluation of th e existing options suggest s that the use of a combination of air pollution control devices, e.g., using a wet scrubbe r combined with an ESP or a baghouse may offer a viable solution to combating arsenic emissions. Injection of mineral sorbents in the flue gas followe d by capture of partic ulates using a baghouse or an ESP has been successful in controlli ng arsenic emissions in coal combustion and can be applied to wood waste too. Amongst th e various techniques av ailable for sampling of arsenic in ambient air, impregnated filters appear to have the highest particulate and vapor capture efficiency. The second task was to find potential mi neral materials that can prevent metal leaching from incineration products. Laborat ory scale experiments were conducted to evaluate various sorbent materials for their cap ability in reducing ash leachability as well as to characterize the crystalline speciati on of the reaction products. Broadly speaking, the leaching behavior of all three CCA metals in alkali-earth sorbents is determined by the metal-mineral compounds formed. On th e other hand, for alumino-silicate sorbents, the formation of bimetallic As-Cu compounds governs their leaching behavior whereas chromium leaching is determined by the form ation of various chromium oxides and CrCu compounds. For ferric oxide, the fo rmation of As-Cu compounds governs their leaching for 700 oC and 900 oC batches, whereas the formation of Fe-As and Fe-Cu compounds determines their leaching behavior for 1100 oC. Chromium leaching is governed by the formation of Fe-Cr compounds fo r this sorbent. Based on these results, it can be concluded that sorbents are cap able of reducing metal leachability and volatilization by chemically combining with CCA metals to form th ermally stable and acid-insoluble compounds. While speciation pl ays a major role in metal leaching, the

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112 effects of leachate pH should also be take n into account. Similarl y for volatilization, speciation along with physical properties and operational parameters (like temperature) could account for the variability in retent ion capabilities of different sorbents. At high temperatures (>1000 oC), most of the arsenic is found in the gas phase while chromium and copper remain in the f eed. Hence, a strategy to control the leaching of metals can possibly be developed base d on these studies. A single sorbent or a combination of sorbents can be used to e ffectively control the leaching of CCA metals, e.g., using cement in the flue gas to capture arsenic and any alumino-silicate sorbent or ferric oxide in the feed to capture chromium and copper. Another possible alternative could be using ferric oxide or magnesi um hydroxide at high temperatures (~1100 oC) to capture all three CCA metal simultaneousl y, both in feed and gas phase. Figure 5-1 shows a schematic discussing these possibilities. However, effects of prolonged leaching and weathering of CCA wood samples and CCA-sorbent ash need to be determined. St udies have shown an increase in arsenic leaching from weathered wood samples due to natural chemical and biological transformations of CCA metals [154]. Such long term effects may change the chemistry of the environmental system in which the ash is disposed and may make it leachable. Therefore long term effects on disposal of CCA metal-sorbent ash need to be investigated. Since co-incineration seems to be the best available thermal process in short term for the treatment of CCA-treated wood, c hoosing a suitable co -fuel based on the knowledge of metal-sorbent intera ctions can result in effective control of the leaching and volatilization of CCA metals. For instance, co al is rich in alumino-silicate compounds,

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113 therefore burning CCA treated wood along with coal can help control chromium leaching in feed. Most coal combustion units are equi pped with lime scrubbers (for sulfur dioxide capture) which can effectively scavenge arse nic in the air phase. Similarly cement kilns also use coal as fuel which can provide al umino-silicate sorbents in the feed. In the cement making process, cement dust is presen t in the system that can scavenge the arsenic in the gas phase. Steel mills, which us e iron ores, coke (a byproduct of coal), and lime in their manufacturing process could be another possible option for burning CCA treated wood with a few modifications. MSW, which contains a large variety of elements and compounds, may be a suitable co-fuel fo r CCA-treated wood. All these facilities are usually equipped with particulate control de vices like ESPs and ba ghouses; therefore, no additional devices are required. With the growing awareness regarding th e hazardous effects of arsenic treated wood, there has been a gradual shift to coppe r based preservatives like ACQ (Alkaline Copper Quaternary) and CBA (Copper Boron Az ole) for wood treatment. Recently, there has been some concern regarding the high le aching of copper (much higher than in CCA treated wood). Since most of the sorbents used in this study (esp. al kali-earth) exhibit low leaching for copper, the results of this study can be applied to other treated wood wastes as well for their safe disposal. Future work for implementation of th is technology on full-scale may involve investigation of the impact of competition of metals, sorbents and other elements (such as sulfur and chlorine) that may be present in the system. An optimal metal/sorbent ratio for efficient control of CCA metals for a given set of operating conditions also needs to be determined. Pilot-scale studies need to be c onducted to examine these possibilities and to

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114 optimize the operating conditions and paramete rs for efficiently reducing metal leaching and volatilization during the com bustion of CCA-treated wood. Figure 5-1: Conceptual Diagra m of Proposed Thermal System

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115 APPENDIX A DETAILED LEACHING RESULTS Leaching Arsenic – The baseline leaching was ve ry high, at around 745 mg/l at 700 oC, ~639 mg/l at 900 oC and ~601 mg/l at 1100 oC. All the sorbents showed some reduction in leaching. It can be observed that cement, calcium hydroxide and magnesium hydroxide leach less than the Toxicity Ch aracteristic (TC) limit of 5 mg/l of arsenic at all three temperatures. Alumina, silica, diatomaceous ear th, attapulgite clay and kaolin leach more than the TC limit of arsenic at all three te mperatures. Ferric oxide leached < 5 mg/l of arsenic at 1100 oC. The detailed results for each sorbent are given below. In the detailed results provided below, if the leaching level is < 10 mg/l, leaching is classified as low, if between 10-50 mg/l then moderate, if greater than 50 mg/l then high. Alumina – For 700 oC batch, the average arsenic leaching was ~60 mg/l with a standard deviation ( ) of ~2.4 mg/l. The leaching was less than half for 900 oC batch, about 27 mg/l with = 2.6 mg/l. Arsenic leaching was the least for 1100 oC batch of samples, around 19 mg/l with = 2.0 mg/l. Attapulgite Clay – Excessive arsenic leach ing was observed for this sorbent. For 700 oC batch, the average arseni c leaching was ~245 mg/l with = 9 mg/l. The trend was similar for 900 oC batch with arsenic leaching at 226 mg/l and a higher standard deviation, = 18.5 mg/l. Arsenic leaching was relatively low for 1100 oC batch of samples, about 30 mg/l with = 1.8 mg/l.

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116 Calcium Hydroxide – Very low arsenic leaching was observed for calcium hydroxide. For 700 oC batch, the average arsenic leaching was very low, around 0.04 mg/l with = 0.03 mg/l. The trend continued for 900 oC batch with arsenic leaching at 0.01 mg/l and a negligible st andard deviation. For 1100 oC batch, the leaching was relatively higher, around 2.3 mg/l with = 0.2 mg/l. However, this value was still lower than the TC limit for arsenic. Hence calcium hydroxide displayed extremely low leaching level at all three temperatures. Cement – Arsenic leaching trends for cement were similar to calcium hydroxide, possibly due to the presence of calcium as a major constituent. For 700 oC batch, the average arsenic leaching had a low value of 0.7 mg/l with = 0.3 mg/l. A slightly higher leaching value of 1.8 mg/l was observed for 900 oC batch with a high of 2.2 mg/l. Lowest leaching was observed for 1100 oC batch, about 0.1 mg/l with = 0.09 mg/l. These values were still lower than the TC limit for arsenic. Hence cement too displayed excellent leaching retention at all three temperatures. Diatomaceous Earth – A variable arsenic leaching trend was observed for diatomaceous earth across the temperat ure range, with the minima at 900 oC. For 700 oC batch, the average arsenic leaching was ~55 mg/l with = 5.3 mg/l. Lower leaching was observed for 900 oC batch, about 30 mg/l with = 7.6 mg/l. Arsenic leaching was higher for 1100 oC batch of samples, around 85 mg/l with = 3.8 mg/l. Thus arsenic leaching for this sorbent, relative to the others tested in these experiments, can be categorized as moderate to high. Ferric Oxide – Arsenic leaching from ferric oxide can be described as moderate to low with increasing temperature. For 700 oC batch, moderate leaching levels of ~42 mg/l

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117 with = 4.2 mg/l were observed. Lower leaching was observed for 900 oC batch, about 15 mg/l with = 2.6 mg/l. Very low Arsenic leaching occurred at 1100 oC, about 2.4 mg/l with = 0.38 mg/l. Hence ferric oxide can be a promising sorbent for controlling arsenic leaching at higher temperatures. Kaolin – A high variability was observed in th e leaching of arsenic from Kaolin. It varied from low to excessively high at di fferent temperatures with maxima at 900 oC. For 700 oC batch, the average arsenic leaching was ~86 mg/l with = 3.8 mg/l. Very high leaching was observed for 900 oC batch, about 181 mg/l with = 15.4 mg/l. Arsenic leaching was quite low at 1100 oC, around 8 mg/l with = 0.98 mg/l. Magnesium Hydroxide – Very low arsenic leaching was observed for magnesium hydroxide similar to Ca-based sorbents. For 700 oC batch, the average arsenic leaching was around 4.2 mg/l with = 2.7 mg/l with one sample exceeding the TC limit of arsenic. For 900 oC batch, a much lower leaching value of 0.37 mg/l was observed with = 0.37 mg/l. Similar leaching results occurred for 1100 oC, with arsenic leaching of about 0.25 mg/l with = 0.15 mg/l. Hence average arsenic l eaching was below TC limits at all the three temperatures. Based on these results and results from arse nic leaching in Cabased sorbents, it can be observed that alkali earth metals show strong leaching retention for arsenic. Silica – Silica exhibited modera te arsenic leaching. For 700 oC batch, the average arsenic leaching was ~48 mg/l with = 2.9 mg/l. The trend was similar for 900 oC batch with arsenic leaching at 47 mg/l and = 1.1 mg/l. Arsenic leaching was relatively low for 1100 oC batch of samples, about 15.4 mg/l with = 0.5 mg/l.

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118 Chromium – The baseline leachi ng was around 733 mg/l at 700 oC and 900 oC and ~654 mg/l at 1100 oC. All the sorbents showed some leaching retention. It can be observed that alumina, silica & ferric oxide leached less than the TC limit of 5 mg/l of chromium at all three temperatures. Kaolin leaches less than TC limit for chromium at 900 oC & 1100 oC. Diatomaceous Earth leached less than 15 mg/l at all three temperatures. Cement, calcium hydroxide and magnesium hydroxide leach chromium excessively (~100 mg/l). In the detailed results provided below, if the leaching level is < 10 mg/l, leaching is classified as low, if between 10-50 mg /l then moderate, if greater than 50 mg/l then high. Alumina – Alumina showed excellent chromium retention. For 700 oC batch, the average chromium leaching was 1.9 mg/l with = 0.25 mg/l. Similar trend was observed for 900 oC batch, where leaching was about 2.3 mg/l with = 0.35 mg/l. Chromium leaching was the least for 1100 oC batch of samples, around 0.2 mg/l with = 0.23 mg/l. Thus alumina leached below the TC limit fo r chromium at all the three temperatures. Attapulgite Clay – A variable chromium leaching trend was observed for this sorbent. For 700 oC batch, the average chromium leaching was ~186 mg/l with = 12 mg/l. The trend was quite the opposite for 900 oC batch with chromium leaching at 9.9 mg/l and = 5 mg/l. Attapulgite clay leached le ss than the TC limit of chromium for 1100 oC batch of samples, about 0.16 mg/l with = 0.10 mg/l. Calcium Hydroxide – Excessive chromium leaching was observed for calcium hydroxide. For 700 oC batch, the average chromium leaching was around 346 mg/l with = 35 mg/l. The trend continued for 900 oC batch with chromium leaching at 219 mg/l and = 14 mg/l. For 1100 oC batch, the leaching was relati vely lower, around 132 mg/l with

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119 = 26 mg/l. Hence, calcium hydroxide leach ed chromium excessively at all three temperatures. The formation of Cr(VI), which is more mobile in these environments is suspected to be the reason for excessive leaching. Cement – Chromium leaching trends for cemen t were similar to calcium hydroxide. For 700 oC batch, the average chromium leaching was around 217 mg/l with = 34 mg/l. Leaching for 900 oC batch was a little lower at ~140 mg/l and = 8.3. For 1100 oC batch, the leaching was relatively lower, ~42 mg/l w ith a high standard deviation of 32 mg/l. The high standard deviation indicates the possi bility of experimental error in processing of one of the samples. Hence, cement too leached chromium excessively at all three temperatures. The formation of Cr(VI), which is more mobile in these environments is suspected to be the reason for excessive leaching. Diatomaceous Earth – Diatomaceous Earth showed low chromium leaching at all three temperatures. For 700 oC batch, the average chromium leaching was ~12 mg/l with = 0.8 mg/l. Slightly lower leaching was observed for 900 oC batch, about 10 mg/l with = 1.6 mg/l. Chromium leaching at 1100 oC was around 4.4 mg/l with = 0.35 mg/l. Thus it leached less than 15 mg /l of chromium at all thr ee temperatures. Hence in a practical scenario, where the metal concentratio ns are expected to be much lesser than the spiked samples used for this experiment, di atomaceous earth may leach chromium below its TC limit. Ferric Oxide – It showed very low chromium l eaching at all the three temperatures. For 700 oC batch, the average chromium leaching was ~4 mg/l with = 0.4 mg/l. Lower leaching was observed for 900 oC batch, where leaching was about 0.17 mg/l with = 0.08 mg/l. Chromium leaching was the least for 1100 oC batch of samples, around 0.04

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120 mg/l with = 0.01 mg/l. Thus ferric oxide leached below the TC limit for chromium at all the three temperatures. Kaolin – Kaolin also showed low leaching for chromium. For 700 oC batch, the average chromium leaching was ~7.2 mg/l with = 4.1 mg/l. For 900 oC batch, it was about 1.4 mg/l with = 0.08 mg/l. At 1100 oC, around 0.2 mg/l of chromium leached with = 0.08 mg/l. Hence kaolin leached less than TC limit for 900 oC and 1100 oC batches and close to the TC limit for the 700 oC batch. So, using Kaolin may be a viable option in field scale technologies havi ng lower chromium concentrations. Magnesium Hydroxide – Chromium leaching trends for magnesium hydroxide were similar to Ca-based sorbents. For 700 oC batch, the average chromium leaching was around 142 mg/l with = 8.8 mg/l. Leaching for 900 oC batch was lesser, around ~69 mg/l and = 2.4 mg/l. For 1100 oC batch, the leaching was ev en lower, ~5.9 mg/l with = 0.8 mg/l. Hence, magnesium hydroxide too leached chromium ex cessively at 700 oC and 900 oC possibly due to the formation of Cr(V I), which is often formed in alkaline environments. However, the leaching result for 1100 oC is close to the TC limit for chromium. Hence it may be a viable option fo r controlling chromium leaching at high temperatures. Silica – Silica exhibited very low leaching for chromium. For 700 oC batch, the average chromium leaching was ~3 mg/l with = 0.2 mg/l. The trend was continued for 900 oC batch with chromium leaching at 2.6 mg/l and = 0.21 mg/l. Chromium leaching was even lower for 1100 oC batch of samples, about 0.3 mg/l with = 0.01 mg/l. Copper – The baseline leaching was around 566 mg/l at 700 oC, 490 mg/l 900 oC and ~469 mg/l at 1100 oC. Since copper is not considered hazardous for its toxicity

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121 characteristic, there is no TC limit for it. However, its excessive leaching can harm aquatic ecosystems and therefore warrants monitoring. All the sorbents showed good leaching retention (< ~50 mg/l) for copper. Cement, calcium hydroxide and magnesium hydroxide leached less than 10 mg /l of copper at all three te mperatures. In the detailed results provided below, if the leaching level is < 10 mg/l, leaching is classified as low, if between 10-50 mg/l then moderate, if greater than 50 mg/l then high. Alumina – Alumina showed low copper leaching. For 700 oC batch, the average copper leaching was ~28 mg/l with = 4.1 mg/l. Lower leaching was observed for 900 oC batch, where leaching was about 15 mg/l with = 4.8 mg/l. Leaching was slightly lower for 1100 oC batch of samples, around 12 mg/l with = 1.3 mg/l. Thus alumina leached low-moderate levels of c opper at all the three temperatures. Attapulgite Clay – A variable copper leaching trend was observed for this sorbent with maxima at 900 oC. For 700 oC batch, the average copper leaching was ~1.4 mg/l with = 0.4 mg/l. The trend wa s quite the opposite for 900 oC batch with copper leaching at ~46 mg/l and =6.4 mg/l. Attapulgite clay leached little copper at 1100 oC, about 3.5 mg/l with = 0.10 mg/l. Calcium Hydroxide – Excellent copper retention was observed for calcium hydroxide. Negligible copper leaching occurred for 700 oC batch. Copper leached at a slightly higher value of 0.2 mg/l ( = 0.1 mg/l) for 900 oC batch. For 1100 oC batch, the leaching value was a little higher at around 6 mg/l with = 0.7 mg/l. Based on the results above, it can be concluded that calcium hydroxide shows excel lent retention for arsenic and copper.

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122 Cement – Copper leaching trends for cement were similar to calcium hydroxide. For 700 oC batch, the average copper leaching was very low, about 0.07 mg/l with = 0.11 mg/l. Leaching for the 900 oC batch was negligible. For 1100 oC batch too, the leaching level was low, ~ 0.5 mg/l with = 0.2 mg/l. Like calcium hydroxide, cement too shows excellent retention for arsenic and copper. Diatomaceous Earth – Diatomaceous Earth too show ed good copper retention at all three temperatures. For 700 oC batch, the average copper leaching was ~19 mg/l with = 1.7 mg/l. A lower leaching was observed for 900 oC batch, about 10 mg/l with = 1.9 mg/l. Copper leaching from diatomace ous earth was the maximum at 1100 oC, around 29 mg/l with = 0.4 mg/l. Ferric Oxide – It showed moderate to low copper leaching in the temperature range encountered. For 700 oC batch, the average copper le aching was ~37 mg/l with a high standard deviation ( = 23 mg/l). A little lower leaching was observed for 900 oC batch, where leaching was about 16 mg/l with = 5.6 mg/l. Copper leaching was the lowest for 1100 oC batch of samples, around 2.9 mg/l with = 0.4 mg/l. Kaolin – Kaolin also showed moderate to low leaching for copper. For 700 oC batch, the average copper leaching was 22 mg/l with = 4.4. For 900 oC batch, it was about 2.4 mg/l with = 1.3 mg/l. At 1100 oC, around 9 mg/l of copper leached with = 1.1 mg/l. Magnesium Hydroxide – Magnesium Hydroxide also showed excellent copper retention at all three temperatures. For 700 oC batch, ~0.9 mg/l copper leached with = 0.6 mg/l. Copper leaching was negligible for 900 oC batch. For 1100 oC batch too, the leaching value was quite low at 0.03 mg/l with = 0.02 mg/l. Hence magnesium

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123 hydroxide too shows excellent retention fo r arsenic and copper like its alkali earth counterparts. Silica – Silica exhibited moderate le aching retention for copper. For 700 oC batch, the average copper leaching was ~50 mg/l with = 3.1 mg/l. The trend was continued for 900 oC batch with copper leaching at ~51 mg/l and = 2.4 mg/l. Copper leaching was lower for 1100 oC batch of samples, about 20 mg/l with = 0.64 mg/l.

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124 APPENDIX B DETAILED VOLATILIZATION RETENTION RESULTS Volatilization Retention Volatilization retention (VR) is calculated as the fraction of metal that remains in sorbent-metal ash over the metal content in spike. Arsenic – The baseline VR was very low, at around 6.3% at 700 oC, ~4.8% at 900 oC and ~4.7% at 1100 oC. The retention amongst sorbents ranges from 20 – 40%. No specific trends were observed. A higher retention level for arsenic with Ca-based sorbents is reported in literature for CCA wood at lo wer concentrations. The detailed results for each sorbent are given below. Alumina – For 700 oC batch, the average arsenic VR was ~38% = 5.2. VR was lower for 900oC batch, about 26% with = 3. VR increased to 36% ( = 5.4) for 1100 oC batch of samples. A maximum variation of 12% was observed across the temperatures. Attapulgite Clay – Like alumina, no specific VR trends were observed for attapulgite clay. For 700 oC batch, the average arsenic retention was ~34% with = 4.4%. Retention for 900 oC batch was slightly higher at 37% with = 2.5%. Slightly higher retention was observed for 1100 oC batch, about 39% with = 1.6%. A maximum variation of 5% was observed ac ross the temperatures. Thus it may be concluded that VR for attapulgite clay isn’t much affect ed in the given temperature range. Calcium Hydroxide – For 700 oC batch, the average arsenic VR by calcium hydroxide was ~28% with = 9.2. VR was lower for 900 oC batch, about 18% with =

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125 0.6%. VR increased to ~40% with = 0.7% for 1100 oC batch of samples. A maximum variation of 22% was observed across the temperatures. Cement – VR trends for cement showed lesser retention at higher temperatures. For 700 oC batch, the average arsenic retention was 35% with = 5.8%. A lower VR of ~22% was observed for 900 oC batch with a high of 8.5%. VR for 1100 oC batch was slightly higher at 23% with a lower = 2.6%. A maximum variatio n of 13% was observed across the temperatures. Diatomaceous Earth – A higher VR was observed for arsenic at higher temperatures with diatomaceous earth. For 700 oC batch, the average arsenic retention was ~24% with = 4.3%. Similar retention was observed for 900 oC batch, about 23% with = 1.0%. VR was the highest for 1100 oC batch of samples, around 30% with = 6% A maximum variation of 7% was observed across the temperatures. Ferric Oxide – Not much variation was observed in arsenic VR by ferric oxide. For 700 oC batch, VR was 36% with = 8.8%. Lower retention was observed for 900 oC batch, about 30% with = 2.3%. Slightly higher arsenic VR of 32% ( = 2.4%) occurred at 1100 oC. A maximum variation of 6% was obser ved across the temperatures which can be categorized as low temperature dependence. Kaolin – No specific trend was observed for Kaolin as well. For 700 oC batch, the average arsenic retent ion was ~26% with = 1.4%. A lower retention was observed for 900 oC batch, about 20% with = 1.6%. VR increased at 1100 oC to 30% with = 2.5%. A maximum variation of 10% was observed across the temperatures. Magnesium Hydroxide – A high VR was observe d for magnesium hydroxide except for 900 oC batch. For 700 oC batch, the average arseni c retention was around 37%

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126 with = 2.9%. For 900 oC batch, a much lower retention value of 18% was observed with = 0.8%. Higher VR occurred for 1100 oC, with arsenic retention of about 41% with = 1.34%. A maximum variat ion of 23% was observed across the temperatures. Silica – Silica exhibited lower VR at higher temperatures. For 700 oC batch, the average arsenic rete ntion was 33% with = 3.1%. This value dropped to 15% for 900 oC batch with = 6%. Arsenic retention was for 1100 oC batch was about 16% with = 2.3%. A maximum variation of 18% wa s observed across the temperatures. A possible reason for no specific VR trend could be its dependence on the physical properties besides the chemical properties. Physical properties like particle size of sorbent, particle size of the metal, interstiti al spaces etc. which were not considered for these experiments could have affected retention. Chromium – The baseline VR was very low, at around 6.3% at 700 oC, ~4.8% at 900 oC and ~4.7% at 1100 oC. No specific trends were observed. For chromium, VR ranged from 0 – 60%. Cement, calcium hydr oxide and magnesium hydroxide showed better retention than other sorb ents. All sorbents except thes e three had very low VR at 1100 oC. Alumina – For 700 oC batch, the average chromium VR was ~32% = 11%. VR was lower for 900 oC batch, about 17% with = 5.3%. VR decreased considerably to 0.26% ( = 0.04%) for 1100 oC batch of samples. Thus retention by alumina shows a strong inverse co-relation with temperature showing an unexpectedly low value at 1100 oC. Attapulgite Clay – Like alumina, a strong invers e co-relation with temperature was observed for attapulgite clay. For 700 oC batch, the average chromium retention was

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127 ~24% with = 2.9%. Retention for 900 oC batch was much lower at ~13% with = 2.1%. Even lower retention was observed for 1100 oC batch, about 3.8% with = 0.33%. Calcium Hydroxide – For 700 oC batch, the average chromium VR by calcium hydroxide was ~38% with = 6.8. VR was lower for 900 oC batch, about 25% with = 0.5. VR increased to ~59% with negl igible standard deviation for 1100 oC batch of samples. A maximum variation of 34% was observed across the temperatures. Cement – VR trends for chromium by cemen t showed lesser retention at higher temperatures. For 700 oC batch, the average arseni c retention was 46% with = 9.3%. A lower VR of ~25% was observed for 900 oC batch with of 1.4%. VR for 1100 oC batch was higher at 41% with = 1.9%. A maximum variation of 21% was observed across the temperatures. Diatomaceous Earth – Higher volatilization was observed for chromium at higher temperatures with diatomaceous earth. For 700 oC batch, the average chromium retention was ~23% with = 7.9%. Lower retention was observed for 900oC batch, about 17% with = 7.9%. VR was the lowest for 1100oC batch of samples, around 1.8% with = 0.8%. Ferric Oxide – Ferric Oxide showed very low VR for chromium at higher temperatures. For 700 oC batch, VR was 47% with = 13.7. Considerably lower retention was observed for 900 oC batch, about 5% with = 0.4. Similar arsenic VR of 5.7% ( = 2.4%) occurred at 1100 oC. Hence VR for chromium by fe rric oxide decreased at high temperatures. Kaolin – Kaolin also showed very low VR for chromium at higher temperatures. For 700 oC batch, the average chromium retention was ~24% with = 2.6%. A much

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128 lower retention was observed for 900 oC batch, about 8% with = 1.2%. VR decreased at 1100 oC to 2.9% with = 1.1%. Hence VR for chromium by Kaolin decreased with increase in temperature. Magnesium Hydroxide – A high VR was observed for chromium by magnesium hydroxide except for 900 oC batch. For 700 oC batch, the average chromium retention was around 50% with = 4.4%. For 900 oC batch, a much lower retention value of 25% was observed with = 0.8%. Higher VR occurred for 1100 oC, with chromium retention of about 52% with a high standard deviation ( = 16%). A maximum variation of 28% was observed across the temperatures. Silica – Silica exhibited lower VR at higher temperatures. For 700 oC batch, the average chromium retention was 29% with = 6.3%. This value dropped to ~14% for 900 oC batch with = 2.8%. Chromium retention for 1100 oC batch was very low, about 0.4% with = 0.2%. Copper – The baseline VR was low, but hi gher than arsenic and chromium. For 700 oC, VR was at 16.8% with = 0.5%, ~13% at 900 oC with = 1.3% and ~12% with = 0.5% at 1100 oC. For copper, the retention under the presence of sorbents was relatively higher at 20-60%. Fe rric oxide showed the highest retention, above 40%, at all three temperatures. Alumina – For 700 oC batch, the average copper VR was ~43% and = 8%. VR was slightly lower for 900 oC batch, about 40% with = 0.5%. VR increased to 57% ( = 8%) for 1100 oC batch of samples. A maximum varia tion of 16% was observed across the temperatures.

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129 Attapulgite Clay – Attapulgite Clay showed lower retention at higher temperatures. For 700 oC batch, the average copper retention was ~32% with = 5%. Retention for 900 oC batch was slightly higher a 33% with = 2.5%. A lower retention was observed for 1100 batch, about 19% with = 0.8%. A maximum variat ion of 14% was observed across the temperatures. Calcium Hydroxide – For 700 oC batch, the average copper VR by calcium hydroxide was ~35% with = 6.2%. VR was similar for 900 oC batch, about 35% with = 0.8%. VR increased to ~58% with = 1.7% for 1100 oC batch of samples. A maximum variation of 23% was observed across the temperatures. Cement – VR trends for cement showed lesser retention at higher temperatures. For 700 oC batch, the average copper retention was 43% with = 7.7%. A lower VR of ~34% was observed for 900 oC batch with of 2.2%. Same VR trend was followed for 1100 oC batch, of about 34% with = 2.2%. A maximum variation of 9% was observed across the temperatures. Diatomaceous Earth – No specific VR was observed for copper with diatomaceous earth. For 700 oC batch, the average copper retention was 26% with = 6.3%. Slightly lower retention was observed for 900 oC batch, about 23% with a high standard deviation ( = 10.0%). VR was the highest for 1100 oC batch of samples, around 28% with a high standard deviation ( = 11.0%). A maximum variation of 5% was observed across the temperatures which can be categorized as low temperature dependence. Ferric Oxide – Ferric Oxide showed lower VR for copper at higher temperatures. For 700 oC batch, VR was 60% with = 3.6%. Slightly higher retention was observed for 900 oC batch, about 62% with = 0.6%. A lower copper VR of ~42% ( = 3.3%)

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130 occurred at 1100 oC. A maximum variation of 20% was observed across the temperatures. Kaolin – Kaolin showed s steady decrease in VR with increase in temperature. For 700 oC batch, the average copper retention was ~33% with = 4.0%. A slightly lower retention was observed for 900 oC batch, about 30% with = 3.2%. VR decreased further at 1100 oC to 26% with = 2.6%. A maximum variation of 7% was observed across the temperatures showing a low temperatur e dependence on rete ntion properties. Magnesium Hydroxide – Generally a high VR was observed for magnesium hydroxide with a low value 900 oC batch. For 700 oC batch, the average copper retention was around 43% with = 3.7. For 900 oC batch, a lower reten tion value of 33% was observed with = 0.4. Higher VR occurred for 1100 oC, with copper retention of about 63% with = 2.2. A maximum variati on of 30% was observed acr oss the temperatures. Silica – No specific VR trends were observed for silica For 700 oC batch, the average copper retention was ~38% with = 5.1. This value dropped to ~30% for 900 oC batch with = 11%. Copper retention for 1100 oC batch was about 32% with = 4.6%. A maximum variation of 8% was observed across the temperatures showing a low temperature dependence on retention properties.

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131 APPENDIX C DETAILED SPECIATION CHARACTERIZATION RESULTS AND X-RAY DIFFRACTION PATTERN GRAPHS FOR THE SAMPLES XRD results for 700 oC Figures C-1 to C-10 report speciation ch aracterization results for sorbent-spike residues of this batch. The major metal-mine ral compounds formed are depicted in these figures. Spike – Figure C-1 depicts XRD patte rn for pure spike residue at 700 oC. Some of the major metal compounds identified were: Cr2O3, CrO3, CuAs2O4, Cu3(AsO4)2, Cr4As3, As2O5, Cu2As3, CrAs2, Cu2As2O7, etc. A large variety of multi-metal compounds were formed. Information regarding solubility of few of these compounds is available. The metal spike exhibited excessive leaching fo r all three CCA metals. This may have resulted from the presence of acid soluble compounds like CrO3, Cu3(AsO4)2, Cr4As3, As2O5, Cu2As3, CrAs2 etc. Acid insoluble compounds like Cr2O3 were also formed. However, considering the high leaching of ch romium from metal spike it can be assumed that these acid insoluble compounds must have been formed in very small quantities. Alumina – Figure C-2 depicts XRD pattern for spike-alumina residue at 700 oC. Some of the major metal-minera l compounds identified were: CuAlO2, Cu3(AsO4)2, CuCr2O4, Cr2(AsO3)4, Cr5O12, Cr2O3, etc. Information regarding solubility of few of these compounds is available. Compounds like CuCr2O4 and Cr2O3 are insoluble in acids (chromium is present as Cr(III)); hence they may not leach out of the TCLP solution contributing to the low leachability of chro mium from alumina. On the other hand,

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132 Cu3(AsO4)2 is soluble in acids, he nce may have contributed to the high leaching of arsenic and copper from alumina. Attapulgite Clay – Figure C-3 depicts XRD pattern for spike-attapulgite clay residue at 700 oC. Some of the major metal-mi neral compounds identified were: Cu3(AsO4)2.(OH)3, Cu3(AsO4)2.(OH), MgCrO4, Mg(H2AsO4)2.H2O, CrO(OH), Mg3Cr2(SiO4)3, etc. Information regarding solubili ty of few of these compounds is available. Attapulgite shows excessive l eaching for arsenic and chromium at this temperature. It is known that compounds like Cu3(AsO4)2 are soluble in acids, hence may have contributed to the high leaching of arsenic and copper. Ot her copper and arsenic compounds like Cu3(AsO4)2.(OH)3, Cu3(AsO4)2.(OH), Mg(H2AsO4)2.H2O are similar in electronic structure and may exhibit si milar behavior. In compounds like MgCrO4, chromium is present as Cr(VI) which is highly mobile in acid ic conditions and may have contributed to chromium leaching. Calcium Hydroxide – Figure C-4 depicts XRD pattern for spike-calcium hydroxide residue at 700 oC. Some of the major metal-mi neral compounds identified were: CuHAsO4, CaCrO4.2H2O, Ca5(AsO4)3.OH, CuCrO4, CaHAsO4.2H2O, CaCu, CrAsO4.xH2O,Ca3(AsO4)2, etc. Information regarding solubility of few of these compounds is available. Compounds like CaCrO4.2H2O and CuCrO4 (chromium as Cr(VI)) are soluble in acids; hence may leach out of the TCLP solution contributing to the high chromium leachability from calcium hydroxide. Since copper leaching is quite low, it is possible that very little CuCrO4 is formed. On the other hand, Ca3(AsO4)2 is insoluble in acids, hence may have contri buted to the low leaching of arsenic. Ca5(AsO4)3.OH is another form of calcium arsena te so may be insoluble in acids too.

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133 Cement –Figure C-5 depicts XRD pattern for spike-cement residue at 700 oC. Some of the major metal-mineral compounds identified were: Cu3As, Cu4(As2O7 )O2, Ca2As2O7, CaCrO4, CaCr2O4, Cu3(AsO4)2, etc. Information regardi ng solubility of few of these compounds is available. Compounds like CaCrO4 (chromium as Cr(VI)) are soluble in acids; hence may leach out of the TCLP solution. However, CaCr2O4 (chromium as Cr(III)) is insoluble in acids. Since high chro mium leaching is observed from this sample, hence it’s possible that very little CaCr2O4 is formed. On the other hand, Ca2As2O7 is insoluble in acids, hence may have contribu ted to the low leaching of arsenic. XRD pattern also shows the form ation of highly soluble Cu3(AsO4)2, however, considering the low leachability of arsenic and copper, it is probable that it was formed in very small quantities. Diatomaceous Earth – Figure C-6 depicts XRD pattern for spike-diatomaceous earth residue at 700 oC. Some of the major metal-mi neral compounds identified were: Cr2O3, CuCrO2, Cu3(AsO4)2, CrFeAs2, Cr2SiO4, Cu3As, CuFe2O4, AsCu9 etc. Information regarding solubility of few of these compounds is available. Diatomaceous Earth shows high leaching for arsenic at this temperature. Formation of Cu3(AsO4)2, which is soluble in acids, may have contributed to the high le aching of arsenic as well as copper. Other copper and arsenic compounds like Cu3As and AsCu9 are known to decompose in acids. Copper also forms a variety of other com pounds which may be insoluble in acids and hence resulted it its lo wer leaching relative to arsenic. On the other hand, the formation of acid insoluble compounds like Cr2O3 may have resulted in low chromium leaching from diatomaceous earth.

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134 Ferric Oxide – Figure C-7 depicts XRD pattern fo r spike-ferric oxide residue at 700 oC. Some of the major metal-mine ral compounds identified were: FeCr2O4, Cr2FeO2, CuFe2O4, Cu3(AsO4)2 etc. Information regarding solubility of few of these compounds is available. Ferric oxide shows high leaching for arsenic and copper at this temperature. Formation of Cu3(AsO4)2, which is soluble in acids, may have contributed to the high leaching of arsenic as well as copper. On the other hand, the formation of FeCr2O4 (chromium exists as Cr(III)), which is only slightly soluble in acids, may have resulted in low chromium leaching from it. Kaolin – Figure C-8 depicts XRD pattern fo r spike-ferric oxide residue at 700 oC. Some of the major metal-mine ral compounds identified were: Cr2O3, CrO(OH), Cu5(AsO4)2.(OH)4, Cu2(AsO4)OH, Cu2(OH)2(CrO4), etc. Information regarding solubility of few of these compounds is available. Kaolin shows high arse nic leaching at this temperature. Formation of vari ous forms of copper arsenate, Cu5(AsO4)2.(OH)4, Cu2(AsO4)OH, etc. which may be soluble in ac ids are suspected to cause high arsenic leaching. On the other hand, the formation of acid insoluble Cr2O3 (chromium exists as Cr(III)) may have resulted in low chromium leaching from it. Magnesium Hydroxide – Figure C-9 depicts XRD pattern for spike-magnesium hydroxide residue at 700 oC. Some of the major metal-mineral compounds identified were: Cu2MgO3, CuHAsO4, MgHAsO4, CuCr2O7.2H2O, etc. Information regarding solubility of few of these compounds is available. Compounds like CuCr2O7.2H2O (chromium as Cr(VI)) are soluble in acids; hence may leach out of the TCLP solution. This might have resulted in high chromium leaching from magnesium hydroxide at this temperature. On the othe r hand, formation of MgHAsO4, which is insoluble in acids, may

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135 have contributed to the low leaching of arsenic. A variety of copper compounds like Cu2MgO3, CuHAsO4, etc. were formed. Some of them may have been insoluble in acids thus resulting in low copper leaching. Silica – Figure C-10 depicts XRD pattern fo r spike-ferric oxide residue at 700 oC. Some of the major metal-mine ral compounds identified were: As2O5, Cu5As2, Cu9.5As4, Cu3(AsO4)2, Cr2O3, Cr2(AsO3)4, CuAs2O4 etc. Information regarding solubility of few of these compounds is available. Silica shows hi gh arsenic leaching at this temperature. Formation of acid soluble compounds like As2O5, Cu5As2, Cu9.5As4, Cu3(AsO4)2 may have caused high arsenic and copper leaching. On the other hand, the formation of acid insoluble Cr2O3 (chromium exists as Cr(III)) may have resulted in low chromium leaching from it.

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136 10203040506070 0 200 400 600 800 1000 CuAs2O4CuAs2O4Cu2As2O7C u2A s3As2O5As2O5C r A s2C r A s2As2O5C u3( A s O4)2C r O3C r2O3C r O3C r2O3C r O3Intensity (arbitrary Units)2 Spike@700oCC r2O3C u A s2O4C u3( A s O4)2C r4A s3As2O5C u2A s3Cu3(AsO4)2 Figure C-1: XRD Pattern for Spike Sample at 700 oC 10203040506070 0 500 1000 1500 2000 CuAs2O4Cr2(AsO3)4C u C r2O4Cu3(AsO4)2CuAlO2Cu Cr2O4Cu3(AsO4)2Inensity (Arbitrary Units)2 Spike+Alumina@700oCC r5O1 2Cu3(AsO4)2C u C r2O4CuAlO2C r2O3Al2O3 Figure C-2: XRD Pattern for Alumina – Spike Sample at 700 oC

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137 10203040506070 0 100 200 300 400 500 600 Mg ( H2A s O4)2. H2OCrO(OH) Cu3(AsO4)(OH)3M g C r O4M g C r O4Intensity (Arbitrary Units)2 Spike+ Attapulgite Clay @700oCM g C r O4Cu2(AsO4)OHM g ( H2A s O4)2. H2OCrO(OH) Mg3Cr2(SiO4)3 Figure C-3: XRD Pattern for Attapul gite Clay – Spike Sample at 700 oC 10203040506070 0 100 200 300 400 500 Ca(OH)2C a C r O4. 2 H2O C a C r O4. 2 H2OC a H A s O4. 2 H2OC r ( A s O4) . x H2OC u C r O4C a5( C r O4)3O H C aC r O4. 2 H2OC aH A s O4C a3( A s O4)2C uH A s O4C u H A s O4C a H A s O4. 2 H2OIntensity (Arbitrary Units)2 Spike+Ca(OH)2@700oCC uH A s O4Ca(OH)2 Figure C-4: XRD Pattern for Calciu m Hydroxide – Spike Sample at 700oC

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138 10203040506070 0 100 200 300 400 500 Cu3(AsO4)2C a C r2O4C a C r O4Ca2As2O7Intensity (Arbitrary Units)2 Spike+ Cement @ 700oCCu3As Cu4(As2O7)O2Ca2As2O7C a C r O4 Figure C-5: XRD Pattern for Cement – Spike Sample at 700 oC 10203040506070 0 200 400 600 800 1000 1200 1400 Intensity (Arbitrary Units)2 Spike+Diatomaceous Earth@700oCC r2O3S i O2CuCrO2A l2S i O5C r F e A s2C r2S i O4C u3( A s O4)2C u3A s C u F e2O4A s C u9 Figure C-6: XRD Pattern for Diatomace ous Earth – Spike Sample at 700 oC

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139 10203040506070 0 100 200 300 400 500 600 C u3( A s O4)2F e2O3F e2O3F e C r2O4Intensity (Arbitrary Units)2 Spike+Fe2O3@700oCF e2O3F e C r2O4Cr2FeO2CuFe2O4C u3( A s O4)2 Figure C-7: XRD Pattern for Ferri c Oxide – Spike Sample at 700 oC 10203040506070 0 100 200 300 400 500 600 700 800 Cu2(AsO4)OH Cu5(AsO4)2(OH)4C r2O3Kaolin KaolinInensity (arbitrary Units)2 Spike+Kaolin@700oCCu2(OH)2CrO4A l2S i2O5( O H )4 ( K a o l i n )Kaolin Cu5(AsO4)2(OH)4CrO(OH)C r2O3Al2Si4O10 Figure C-8: XRD Pattern for Kaolin – Spike Sample at 700 oC

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140 10203040506070 0 500 1000 1500 2000 2500 Intensity (Arbitrary Units)2 Spike+Mg(OH)2@700OCCuHAsO4Cu2MgO3Mg H A s O4C u C r2O7. 2 H2O Figure C-9: XRD Pattern for Magnesium Hydroxide – Spike Sample at 700 oC 10203040506070 0 500 1000 1500 2000 2500 CuAs2O4Cr2O3Cr2O3C u9 . 5A s4C u5A s2C u5A s2S i O2A s2O5Intensity (Arbitrary Units)2 Spike+Silica@700oCA s2O5S i O2C u5A s2Cu3(AsO4)2Cr2O3C r2( A s O3)4 Figure C-10: XRD Pattern for Silica – Spike Sample at 700 oC

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141 XRD results for 900 oC Figures C-11 to C-20 report speciation ch aracterization results for sorbent-spike residues of this batch. The major metal-mine ral compounds formed are depicted in these figures. Spike – Figure C-11 depicts XRD patte rn for pure spike residue at 900 oC. Some of the major metal compounds identified were: Cu2As2O7, Cu3(AsO4)2, Cr2O5, CrO3, Cu2As3, Cr2(AsO3)4, CuAs2O4, CuCrO2, CuCrO4, CuCr2O4, Cu9As4, Cu5As2, Cu3As, Cr5As3, Cr2(AsO4)3, etc. A large variety of mu lti-metal compounds were formed. Information regarding solubility of few of these compounds is available. The metal spike exhibited excessive leaching fo r all three CCA metals. This may have resulted from the presence of acid soluble compounds like CrO3, CuCrO4, Cu3(AsO4)2, Cu2As3, Cu9As4, Cu5As2, Cu3As, Cr5As3, etc. Acid insoluble compounds like CuCr2O4 were also formed. However, considering the high leaching of ch romium from metal spike it can be assumed that these acid insoluble compounds must have been formed in very small quantities. Alumina – Figure C-12 depicts XRD pattern for spike-alumina residue at 900 oC. Some of the major metal-mine ral compounds identified were: Cu4(As2O7)O2, CuAlO2, Cu3(AsO4)2, CuCr2O4, CuCrO4, Cr2(AsO3)4, CuAs2O4, AlAsO4, Cr2O3, Cu3As, etc. Information regarding solubility of few of these compounds is available. Compounds like CuCr2O4 and Cr2O3 are insoluble in acids (chromium is present as Cr(III)); whereas CuCrO4, Cr2(AsO3)4 may be acid soluble due to the exis tence of chromium in hexavalent form. However, since alumina exhibits low chromium leaching, the acid soluble compounds form a small portion of all chromium compounds. Amongst arsenic and copper compounds, AlAsO4 is slightly soluble in acids, whereas Cu3(AsO4)2 and Cu3As

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142 are acid soluble. Sin ce alumina exhibits hi gh arsenic and copper leaching, hence it is probable that these acid soluble com pounds dominate in the product formation. Attapulgite Clay – Figure C-13 depicts XRD pattern for spike-attapulgite clay residue at 900 oC. Some of the major metal-mi neral compounds identified were: Cu3(AsO4)2, Cr2(AsO3)4, CrO(OH), Cu5(AsO4)2.(OH)4, Cr2O3, Cu5As2, Cu2(AsO4)OH, Mg3(AsO4)2, etc. Information regarding solubil ity of few of these compounds is available. Attapulgite shows excessive leaching for arsenic and copper at this temperature. It is known that compounds like Cu3(AsO4)2 and Cu5As2 are soluble in acids. Also, Cu5(AsO4)2.(OH)4 and Cu2(AsO4)OH are different forms of copper arsenate and maybe soluble in acids. It is suspect ed that the formation of these compounds contributes to the high leachi ng of arsenic and copper. Form ation of trivalent chromium compounds like CrO(OH), and Cr2O3 may have contributed to low chromium leaching at this temperature. Calcium Hydroxide – Figure C-14 depicts XRD pattern for spike-calcium hydroxide residue at 900 oC. Some of the major metal-mineral compounds identified were: Ca5(AsO4)3.OH, CaCu, Ca2CuO3, Cr2O5, Ca3(AsO4)2, Ca5(CrO4)3, CaCrO4, etc. Information regarding solubility of few of these compounds is available. Compounds like CaCrO4 are soluble in acids; hence may leach out of the TCLP solution contributing to the high chromium leachability from calcium hydroxide. On the other hand, Ca3(AsO4)2 is insoluble in acids, hence may have contribut ed to the low leaching of arsenic. Copper forms a variety of metal mineral compounds, some of them like Ca2CuO3cmay be acid insoluble, resulting in low coppe r leaching from this sorbent.

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143 Cement –Figure C-15 depicts XRD pattern for spike-cement residue at 900 oC. Some of the major metal-mine ral compounds identified were: Ca2As2O7, Ca5(CrO4)3, CuCrO4, CuAl2O4, CaCu2O3, Ca5Cr2SiO12, Ca2As3, CaCuO2 etc. Information regarding solubility of few of these compounds is available. Compounds like CuCrO4 (chromium as Cr(VI)) are soluble in acids; hence may leach out of the TCLP solution. On the other hand, Ca2As2O7 is insoluble in acids, hence may have contributed to the low leaching of arsenic. A lot of different copper compounds we re formed; some of them may have been acid insoluble resulting in low copper leaching. Diatomaceous Earth – Figure C-16 depicts XRD pa ttern for spike-diatomaceous earth residue at 900 oC. Some of the major metal-mi neral compounds identified were: Fe3AsO7, CuCr2O4, Cu2As3 etc. Information regarding solubility of few of these compounds is available. Diatomaceous earth shows high leaching for arsenic at this temperature. Formation of Cu2As3, which decomposes in acids, may have contributed to the high leaching of arsenic. On the ot her hand, the formation of acid insoluble compounds like CuCr2O4 may have resulted in low chromium leaching from diatomaceous earth. Ferric Oxide – Figure C-17 depicts XRD pattern fo r spike-ferric oxide residue at 900 oC. Some of the major metal-minera l compounds identified were: FeCr2O4, Cr2FeO2, CuFe2O4, Cu3(AsO4)2 etc. Information regarding solubility of few of these compounds is available. Ferric oxide shows high leaching for arsenic and copper at this temperature. Formation of Cu3(AsO4)2, which is soluble in acids, may have contributed to the high leaching of arsenic as well as copper. One the other hand, the formation of FeCr2O4,

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144 which is only slightly soluble in acids, may ha ve resulted in low chromium leaching from ferric oxide. Kaolin – Figure C-18 depicts XRD pattern fo r spike-ferric oxide residue at 900 oC. Some of the major metal-mine ral compounds identified were: As2O4, AlAs, CuCr2O4, Cu4(As2O7)O2, Al(H2AsO4).H2O, Cu5(AsO4)2.(OH)4, Cr(OH)3 etc. Information regarding solubility of few of these compounds is ava ilable. Kaolin shows high arsenic leaching at this temperature. Formation of variou s forms of copper arsenate compounds like Cu5(AsO4)2.(OH)4, Cu4(As2O7)O2, etc. and other compounds like AlAs, which may be soluble in acids are suspected to cause high arsenic leaching. On the other hand, the formation of acid insoluble CuCr2O4, Cr(OH)3 etc. (chromium exists as Cr(III)) may have resulted in low chromium leaching from kaolin. Magnesium Hydroxide – Figure C-19 depicts XRD pattern for spike-magnesium hydroxide residue at 900 oC. Some of the major metal-mineral compounds identified were: Cu2MgO3, Cu2O, MgHAsO4, Cu3CrO6 etc. Information regarding solubility of few of these compounds is available. Compounds like Cu3CrO6 (chromium as Cr(VI)) may be soluble in acids; hence may leach out of the TCLP solution. This might have resulted in high chromium leaching from magnesium hydrox ide at this temperature. On the other hand, formation of MgHAsO4, which is insoluble in acids, may have contributed to the low leaching of arsenic. A variety of copper compounds like Cu2MgO3, Cu2O (which is insoluble in dilute acids), etc. were forme d. Some of them may have been insoluble in acids thus resulting in low copper leaching.

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145 Silica – Figure C-20 depicts XRD pattern fo r spike-ferric oxide residue at 900 oC. Some of the major metal-minera l compounds identified were: SiAs2, Cu2As2O7, CuCr2O4, Cr2O3, Cr2(AsO3)4, CuAs2O4 etc. Information regarding solubility of few of these compounds is available. Silica shows high arsenic and coppe r leaching at this temperature. Formation of copper arsenates and SiAs2, which may have been acid soluble, could have caused high arsenic and copper leaching. On the other hand, the formation of acid insoluble CuCr2O4 and Cr2O3 (chromium exists as Cr(III)) may have resulted in low chromium leaching from silica.

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146 10203040506070 0 200 400 600 800 1000 1200 1400 1600 Cu3AsCu5As2C r2( A s O3)4C u C r O4C u C r O4Cu2As3Cr2(AsO3)4C u A s2O4C r2( A s O3)4C u3( A s O4)2C r2O5C r O3C r O3C r O3C r O3C u2A s2O7C u2A s2O7Intensity (Arbitrary Units) Spike @ 900oC 2C u2A s2O7C u3( A s O4)2C r2O5C u2A s3C u C r O2 Figure C-11: XRD Pattern for Spike Sample at 900 oC 10203040506070 0 200 400 600 800 1000 1200 1400 1600 C u A s2O4C u A s2O4C u C r2O4C u A l O2Cu3(AsO4)2C u C r2O4C u C r2O4C u A l O2C u C r O4Cu3(AsO4)2Intensity (Arbitrary Units)2 Alumina + Spike @ 900oCCu4(As2O7)O2A l2O3C u A l O2C u C r2O4C r2O3Cr2(AsO3)4Cu3AsA l A sO4 Figure C-12: XRD Pattern for Alumina – Spike Sample at 900 oC

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147 10203040506070 0 100 200 300 400 500 600 700 800 M g3( A s O4)2C u2( A s O4) O HCr2(AsO3)4C r2O3C r2O3 Attapulgite Clay + Spike @ 900oC 2Intensity (Arbitrary Units)Cu3(AsO4)2S i O2Cr2(AsO3)4CrO(OH)M g A s4C u5( A s O4)2. ( O H )4C r2O3C u5A s2Mg2SiO4M g3( A s O4)2 Figure C-13: XRD Pattern for Attapulgite Clay – Spike Sample at 900 oC 10203040506070 0 100 200 300 400 500 CaCrO4CaCrO4Ca3(AsO4)2Ca3(AsO4)2Ca5(AsO4)3.OHIntensity (Arbitrary Units)2 Ca(OH)2+ Spike @ 900oCCa(OH)2C a5( A s O4)3. O HC a C uCa2CuO3C r2O5Ca5(CrO4)3 Figure C-14: XRD Pattern for Calcium Hydroxide – Spike Sample at 900 oC

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148 10203040506070 0 100 200 300 400 500 C a C u O2C u A l2O4C a5( C r O4)3C a C u2O3C a2A s2O7CuCrO4C a2A s2O7Intensity (Arbitrary Units) Cement + Spike @ 900oC 2C a2A s2O7C a5( C r O4)3CuCrO4C u A l2O4C a5C r2S i O1 2C a C u2O3C a2A s3 Figure C-15: XRD Pattern for Cement – Spike Sample at 900 oC 10203040506070 0 200 400 600 800 1000 1200 1400 S i O2Fe3AsO7Intensity (Arbitrary Units)2 Diatomaceous Earth + Spike @ 900oCFe3AsO7S i O2CuCr2O4Cu2As3 Figure C-16: XRD Pattern for Diatomace ous Earth – Spike Sample at 900 oC

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149 10203040506070 0 100 200 300 400 500 600 700 800 Cu3(AsO4)2F e C r2O4F e2O3F e2O32 Fe2O3 + Spike @ 900oCIntensity (Arbitrary Units)F e2O3F e C r2O4Cu3(AsO4)2CuFe2O4C r2F e O2 Figure C-17: XRD Pattern for Ferric Oxide – Spike Sample at 900 oC 10203040506070 0 500 1000 1500 2000 2500 SiO2A l A sC u C r2O4Intensity (Arbitrary Units)2 Kaolin + Spike @ 900oCA s2O4A l A sCuCr2O4Cu4(As2O7)O2Al(H2AsO4)3.H2OC u5( A s O4)2( O H )4Cr(OH)3SiO2 Figure C-18: XRD Pattern for Kaolin – Spike Sample at 900 oC

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150 10203040506070 0 500 1000 1500 2000 Intensity (Arbitrary Units)2 Mg(OH)2+ Spike @ 900oCC u2M g O3Cu2OCu3CrO6MgHAsO4 Figure C-19: XRD Pattern for Magnesiu m Hydroxide – Spike Sample at 900 oC 10203040506070 0 200 400 600 800 1000 1200 1400 S i O2S i O2C u A s2O4C u A s2O4Cr2O3C u2A s2O7C u2A s2O7C u C r2O4S i A s22 Silica + Spike @ 900oCIntensity (Arbitrary Units)S i A s2C u2A s2O7C r2O3C u C r2O4C r2( A s O3)4S i O2 Figure C-20: XRD Pattern for Silica – Spike Sample at 900 oC

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151 XRD results for 1100 oC Figures C-21 to C-30 report speciation ch aracterization results for sorbent-spike residues of this batch. The major metal-mine ral compounds formed are depicted in these figures. Spike – Figure C-21 depicts XRD patte rn for pure spike residue at 1100 oC. Some of the major metal compounds identified were: CrO3, Cr2(AsO4)3, Cr2(AsO3)4, CuAs2O4, Cu3(AsO4)2, CrAs2, As2O5, Cu5As2, CuO, CuCrO4, Cu3As, etc. A large variety of multimetal compounds were formed. Information regarding solubility of few of these compounds is available. The metal spike exhi bited excessive leaching for all three CCA metals. This may have resulted from the presence of acid soluble compounds like CrO3, Cu3(AsO4)2, CrAs2, As2O5, Cu5As2, CuCrO4, Cu3As, etc. Alumina – Figure C-22 depicts XRD pattern for spike-alumina residue at 1100 oC. Some of the major metal-minera l compounds identified were: CuAlO2, Cu3(AsO4)2, CuCr2O4, Cr2O3, Cr4As3, As2O5, AlAsO4, CuAs2O4, Cu3As,etc. Information regarding solubility of few of these compounds is available. Compounds like CuCr2O4 and Cr2O3 are insoluble in acids (chromiu m is present as Cr(III)); henc e they may not leach out of the TCLP solution contributing to the low leach ability of chromium fr om alumina. On the other hand, Cu3(AsO4)2, Cr4As3, As2O5, Cu3As, etc. are soluble in acids, hence may have contributed to the leaching of arse nic and copper from alumina. AlAsO4 is only slightly soluble in acids hence may have contributed to the relatively low le aching of arsenic by alumina at this temperature as compared to the lower temperatures. Attapulgite Clay – Figure C-23 depicts XRD pattern for spike-attapulgite clay residue at 1100 oC. Some of the major metal-mineral compounds identified were:

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152 Cu5(AsO4)2.(OH)4, Cu3(AsO4)2, Cu2MgO3, As2O5, CuMgSi2O6, Cu2(AsO4)OH, MgCrO4, Cr2O3, etc. Information regarding solubility of few of these compounds is available. Attapulgite shows low leaching for chromium and copper and relatively lower leaching for arsenic as well. Very few chromium compounds were identified in the product confirming the volatilization losses at this te mperature. It is know n that compounds like Cu3(AsO4)2 (and other copper arsenates) are soluble in acids, he nce may have contributed to the leaching of arsenic and copper. Compounds like Cr2O3 are insoluble in acids (chromium is present as Cr(III)); hence they may not leach out of the TCLP solution contributing to the low leachability of chromium from attapulgite clay. MgCrO4, where chromium is present as Cr(VI) may be highl y mobile in acidic conditions. However, low chromium leaching by the sample suggests that a relatively small amount of chromium exists in that form at this temperature. Calcium Hydroxide – Figure C-24 depicts XRD pattern for spike-calcium hydroxide residue at 1100 oC. Some of the major metalmineral compounds identified were: CuHAsO4, CaCrO4.2H2O, Ca5(CrO4)3.OH, CaHAsO4.2H2O, CrAsO4.xH2O, etc. Information regarding solubility of few of these compounds is available. Compounds like CaCrO4.2H2O (chromium as Cr(VI)) are soluble in acids; hence may leach out of the TCLP solution contributing to the high chro mium leachability from calcium hydroxide. On the other hand, compounds like CaHAsO4.2H2O may be insoluble in acids, hence may have contributed to th e low leaching of arsenic. Cement –Figure C-25 depicts XRD pattern for spike-cement residue at 1100 oC. Some of the major metal-mine ral compounds identified were: Cu3(AsO4)2, Ca2As2O7, Ca5(CrO4)3, CuCrO4, As2O4, Ca5(CrO4)3, CaCu2O3, Ca5CrSiO12, Cu3As, Ca2As3, CrO,

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153 Cu9.5As4, As2O4, As2O3, Al13Cr2, CaCrSi4O10, etc. Information regarding solubility of few of these compounds is available. Compounds like CuCrO4 (chromium as Cr(VI)) are soluble in acids; hence may leach out of the TCLP solution. On the other hand, Ca2As2O7 is insoluble in acids, hence may have contri buted to the low leaching of arsenic. XRD pattern also shows the form ation of highly soluble Cu3(AsO4)2, Cu3As, Ca2As3, CrO, Cu9.5As4 etc. However, considering the low leachability of arsenic and copper, it is probable that these compounds are formed in very small quantities. Diatomaceous Earth – Figure C-26 depicts XRD patte rn for spike-diatomaceous earth residue at 1100 oC. Some of the major metal-mineral compounds identified were: Fe3AsO7, Cr2O3, As2O5, CuCrO2, Cu2As3, Cu3(AsO4)2, CrFeAs2, AsCu, etc. Information regarding solubility of few of these compounds is available. Diatomaceous Earth shows high leaching for arsenic at this temperature. Formation of Cu3(AsO4)2 and As2O5 which are soluble in acids, may have contributed to the high leaching of arsenic as well as copper. Other copper and arsenic compounds like Cu2As3 and AsCu are known to decompose in acids. Copper also forms a variety of other compounds which may be insoluble in acids and hence resulted it its lowe r leaching relative to ar senic. On the other hand, the formation of acid insoluble compounds like Cr2O3 may have resulted in low chromium leaching from diatomaceous earth. Ferric Oxide – Figure C-27 depicts XRD pattern fo r spike-ferric oxide residue at 1100 oC. Some of the major metal-mi neral compounds id entified were: Fe2(AsO3)4, FeCr2O4, Cr2FeO2, Fe4As2O11, CuFe2O4, Cu3(AsO4)2, CuCrO4 etc. Information regarding solubility of few of these compounds is available. Ferric oxide shows good leaching retention for all three CCA metals at this temperature. The low arsenic leaching may be

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154 due to the formation of Fe2(AsO3)4 and Fe4As2O11, which were not formed at the other two temperatures, and may have been soluble in acids. Also, the fo rmation of compounds like FeCr2O4 (chromium exists as Cr(III)), which is only slightly soluble in acids, may have resulted in low chromium leaching from it. Copper also forms a variety of other compounds which may be insoluble in acids and hence resulted in its lower leaching. Since metal leaching is low, it is highly probable that acid soluble compounds like Cu3(AsO4)2 and CuCrO4 were formed in very small quantities. Kaolin – Figure C-28 depicts XRD pattern fo r spike-ferric oxide residue at 1100 oC. Some of the major metal-mine ral compounds identified were: Cu5(AsO4)2.(OH)4, Cr2O3, CrO(OH), CrO3, Cr5O12, Cu2(AsO4)OH, etc. Information regarding solubility of few of these compounds is available. Kao lin shows high arsenic leaching at this temperature. Formation of vari ous forms of copper arsenate, Cu5(AsO4)2.(OH)4, Cu2(AsO4)OH, etc. which may be soluble in ac ids are suspected to cause high arsenic leaching. On the other hand, the formation of acid insoluble Cr2O3 and possibly CrO(OH) (chromium exists as Cr(III)) may have result ed in low chromium leaching from it. Since chromium leaching is low, it is probable that highly acid soluble CrO3 was formed in very low amount. Magnesium Hydroxide – Figure C-29 depicts XRD pattern for spike-magnesium hydroxide residue at 1100 oC. Some of the major metalmineral compounds identified were: MgCrO4, MgCr2O4, Cu2MgO3, MgHAsO4.4H2O, Cu2(AsO4)OH.3H2O, etc. Information regarding solubility of few of these compounds is available. Magnesium hydroxide shows good leaching retention for all three CCA metals at this temperature. Compounds like MgCr2O4, (chromium as Cr(III)) may be insoluble in acids; hence they

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155 may not leach out of the TCLP solution. This might have resulted in low chromium leaching from magnesium hydroxide at this temperature. MgCrO4 (chromium as Cr(VI)) was also formed, but considering the low leach ing of chromium, it may have been formed in small quantities only. On the other hand, formation of MgHAsO4.4H2O, which is insoluble in acids, may have contributed to the low leaching of arsenic. A variety of copper compounds like Cu2MgO3, Cu2(AsO4)OH.3H2O, etc were formed. Some of them may have been insoluble in acids t hus resulting in low copper leaching. Silica – Figure C-30 depicts XRD pattern fo r spike-ferric oxide residue at 1100 oC. Some of the major metal-mine ral compounds identified were: Cu5As2, Cr2O3, CrO3, Cr2(AsO3)4, CuAs2O4 etc. Information regarding solubil ity of few of these compounds is available. Silica shows high arsenic leaching at this temperature. Formation of acid soluble compounds like Cu5As2 may have caused high arsenic leaching. On the other hand, the formation of acid insoluble Cr2O3 (chromium exists as Cr(III)) may have resulted in low chromium leaching from it. XRD patterns indicate the formation of potentially mobile CrO3 and Cr2(AsO3)4, but the low chromium leaching suggests that these compounds were minor products.

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156 10203040506070 0 200 400 600 800 1000 A s2O5CrAs2CuAs2O4CrAs2Cr2(AsO4)3Cr2(AsO4)3Intensity (arbitrary units)2 Spike@1100OCCr2(AsO4)3CuAs2O4CrAs2CuOCu5As2CuCrO4CrO3A s2O5C r O3C u3A s Figure C-21: XRD Pattern for Spike Sample at 1100 oC 10203040506070 -200 0 200 400 600 800 1000 1200 1400 1600 1800 CuAlO2Intensity (arbitrary units)2 Spike + Alumina@ 1100oCA s2O5Cr4As3C r2O3CuCr2O4CuAlO2C u3( A s O4)2A l2O3Cr4As3A l A s O4C u3A sCuAs2O4 Figure C-22: XRD Pattern for Alumina – Spike Sample at 1100 oC

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157 10203040506070 0 200 400 600 800 1000 1200 1400 Cu2(AsO4)OHCu2MgO3As2O5As2O5Cu3(AsO4)3Cu2MgO3Cu5(AsO4)2(OH)4Intensity (arbitrary units)2 Spike+Attapulgite Clay@1100oCCu5(AsO4)2(OH)4Cu2MgO3As2O5S i O2C u M g S i2O6M g C r O4Cr2O3 Figure C-23: XRD Pattern for Attapulgite Clay – Spike Sample at 1100 oC 10203040506070 0 100 200 300 400 500 600 C u H A s O4CaHAsO4.2H2OC a ( O H )2C u H A s O4C a C r O4. 2 H2O C a C r O4. 2 H2OC a C r O4. 2 H2OIntensity (arbitrary units)2 Spike+Ca(OH)2@1100oCC u H A s O4C a C r O4. 2 H2OC a5( C r O4)3O HC a H A s O4. 2 H2OCrAsO4.xH2OC a O C a ( O H )2CaCu Figure C-24: XRD Pattern for Calcium Hydroxide – Spike Sample at 1100 oC

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158 10203040506070 0 100 200 300 400 500 600 C u9 . 5A s4A s2O3C u C r O4C u C r O4C a5C r2S i O1 2A l1 3C r2C a5( C r O4)3Ca2As2O7C a C r S i4O1 0C a5( C r O4)3Intensity (arbitrary units)2 Spike+Cement@1100oCC u3( A s O4)2Ca2As2O7C a5( C r O4)3C u C r O4A s2O4C a5C r2S i O1 2C a C u2O3A l1 3C r2C r OC u3A s Figure C-25: XRD Pattern for Cement – Spike Sample at 1100 oC 10203040506070 0 500 1000 1500 2000 2500 Intensity (arbitrary units)2 Spike+Diatomaceous Earth@1100oCF e A s O4A s2O5Cr2O3S i O2CrFeAs2Cu3(AsO4)2Cu2As3A s C uA l3F e3S i7S i O2A l2S i O5 Figure C-26: XRD Pattern for Diatomace ous Earth – Spike Sample at 1100 oC

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159 10203040506070 0 50 100 150 200 250 300 350 F e2O3FeCr2O4F e2( A s O3)4F e2( A s O3)4Intensity (arbitrary units)2 Spike+Fe2O3@1100OCF e2( A s O3)4FeCr2O4C r2F e O2F e2O3Fe4As2O11CuFe2O4Cu3(AsO4)2CuCrO4 Figure C-27: XRD Pattern for Ferric Oxide – Spike Sample at 1100 oC 10203040506070 0 100 200 300 400 500 600 700 C u2( A s O4) O HSiO2C u5( A s O4)2( O H )4Al2SiO5C r2O3C r2O3Al2SiO5C u5( A s O4)2( O H )4C u5( A s O4)2( O H )4Intensity (arbitrary units)2 Spike+Kaolin@1100oCC u5( A s O4)2( O H )4SiO2C r O3Al2SiO5Cr5O123Al2O3.2SiO2 Figure C-28: XRD Pattern for Kaolin – Spike Sample at 1100 oC

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160 10203040506070 0 1000 2000 3000 4000 5000 MgCr2O4MgCr2O4Intensity (arbitrary units)2 Spike+Mg(OH)2@1100OCMgCrO4C u2M g O3Cu2(AsO4)OH.2H2OM g H A s O4. 2 H2O Figure C-29: XRD Pattern for Magnesiu m Hydroxide – Spike Sample at 1100 oC 10203040506070 0 2000 4000 6000 8000 10000 12000 14000 SiO2C u5A s2Cr2O3Intensity (arbitrary units)2 Spike+Silica@1100OCC u5A s2Cr2O3SiO2Cr2(AsO3)4C u A s2O4 Figure C-30: XRD Pattern for Silica – Spike Sample at 1100 oC

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161 APPENDIX D DETAILED LEACHATE PH RESULTS pH Effects Leachate pH was measured for all samples to assess the impact of pH on metal leaching. A summary of the pH measurements is given below. Baseline – For 700 oC batch, the average leachate pH was 4.85 with = 0.02. pH was higher for 900 oC batch, about 5.43 with = 0.6. pH decreased to 4.97 ( = 0.03) for 1100 oC batch of samples. Alumina – For 700 oC batch, the average leachate pH was 4.85 with = 0.02. pH was higher for 900 oC batch, about 5.43 with = 0.6. pH decreased to 4.97 ( = 0.03) for 1100 oC batch of samples. Attapulgite Clay – For 700 oC batch, the average leachate pH was 6.15 with = 0.08. pH was lower for 900 oC batch, about 4.36 with = 0.02. pH increased to 5.00 ( = 0.15) for 1100 oC batch of samples. Calcium Hydroxide – For 700 oC batch, the average leachate pH was 12.47 with = 0.05. pH was lower for 900 oC batch, about 11.95 with = 0.03. pH slightly decreased to 11.91 ( = 0.02) for 1100 oC batch of samples. Cement – For 700 oC batch, the average leachate pH was 11.40 with = 0.18. pH was slightly lower for 900 oC batch, about 11.30 with = 0.20. pH marginally increased to 11.31 ( = 0.07) for 1100 oC batch of samples.

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162 Diatomaceous Earth – For 700 oC batch, the average leachate pH was 4.90 with = 0.06. pH was slightly higher for 900 oC batch, about 4.93 with negligible . pH slightly increased to 5.07 ( = 0.01) for 1100 oC batch of samples. Ferric Oxide – For 700 oC batch, the average leachate pH was 5.02 with = 0.05. pH was slightly lower for 900 oC batch, about 4.93 with = 0.04. pH slightly increased to 5.11 ( = 0.01) for 1100 oC batch of samples. Kaolin – For 700 oC batch, the average leachate pH was 4.83 with = 0.02. pH for 900 oC batch drastically increased to 12.18 with = 0.10. pH dropped to 4.99 ( = 0.02) for 1100 oC batch of samples. Magnesium Hydroxide – For 700 oC batch, the average leachate pH was 10.05 with = 0.04. pH was a little lower for 900 oC batch, about 9.73 with = 0.02. pH decreased to 9.45 ( = 0.03) for 1100 oC batch of samples. Silica – For 700 oC batch, the average leachate pH was 4.95 with = 0.01. pH was marginally lower for 900 oC batch, about 4.92 with = 0.01. pH decreased to 4.85 ( = 0.07) for 1100 oC batch of samples.

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176 BIOGRAPHICAL SKETCH Anadi Misra was born in the industrial city of Kanpur, India. He studied in Sir Padampat Singhania Education Center, Kanpur, until his senior year in high school. A meritorious student since hi s childhood, he excelled at ea ch grade level (secured 1st rank) till his senior year in high school. Right from the outset, he was involved in various extracurricular activities ranging from quiz competitio ns, debates, elocutions, literary events, soccer, and cricket and exhibited a high level of achievement in each of them. He was also entrusted with various offices of res ponsibility from an earl y age on and exhibited great leadership and managerial skills while accomplishing the different organizational tasks assigned to him. After high school, he secured an admission in to the prestigious Indian Institute of Technology (IIT) Delhi by clearing the Join t Entrance Examination (JEE), IndiaÂ’s toughest examination at the high school leve l having a success ratio of ~ 1:100. In IIT, he majored in civil engineering with focus on environmental engineering research and coursework towards the latter half of the cu rriculum. He was involve d in various research projects as an undergrad and was the recipient of the pres tigious Summer Undergraduate Research Award (SURA) for his work on a Geographical Information System (GIS) based infrastructure model of IIT Delhi. He worked on an air dispersion modeling project as a part of his bachelorÂ’s thesis. At IIT, he was a member of the Board for Recreational and Cultural Activities and organized and part icipated in various inter hostel and inter college competitions. He also held various pos itions of responsibility at the hostel level.

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177 After completing his undergraduate studies at IIT, he was accepted into the Department of Environmental Engineering Scienc es at the University of Florida (UF) as a masters student in environmental engineering. Here he worked on two main projects, the first one focused on the evaluation of therma l processes for disposal of CCA-treated wood in the state of Florida which also formed the part of his masterÂ’s thesis. He was also responsible for the development of an interactive web-based aerosol module for facilitating the learning of aerosol fundament als and applications at undergraduate and graduate level. The web module can be accessed at http://aerosol.ees.ufl.edu . At UF, he successfully maintained a GPA of 4.0 across all semesters and struck a fine balance between coursework, research and co-curricular activities. He was actively involved with various organiza tions such as Tau Beta Pi and Benton Engineering Council and mentoring activities with the Particle Engineering Research Center (PERC) UG scholarship program. He also served as the Vi ce President of the UF Chapter of Air and Waste Management Association (A&WMA) a nd was instrumental in restarting the chapter at the university. He was recognized by the Intern ational Center at UF for Outstanding Academic Accomplishment c ontinuously for the year 2005 and 2006. He was also the recipient of the Florida A& WMA scholarship for the year 2005. After graduation, he plans to work in the field of water supply and treatment in Tampa, Florida, with Black and Veatch.