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Evaluation of Thermal Processes for CCA Wood Disposal in Existing Facilities

This study evaluates the thermal processes for disposal of chromated copper arsenate (CCA) treated wood in existing facilities. It includes an inventory of combustion facilities, a survey of arsenic air pollution control technologies, and screening of potential materials for minimizing leaching. The results show that certain mineral sorbents successfully retain heavy metals such as arsenic, chromium, and copper, effectively preventing their emission and leaching.

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Evaluation of Thermal Processes for CCA Wood Disposal in Existing Facilities

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  1. 2005 TAG Meeting Evaluation of Thermal Processes for CCA Wood Disposal in Existing Facilities Anadi Misra1, Brajesh Dubey1, Chang-Yu Wu1, Timothy Townsend1, Helena Solo-Gabriele2 1University of Florida 2University of Miami Aerosol and Particulate Research Laboratory

  2. Overview • Background • Methodology • Task 1: Inventory of Combustion Facilities • Task 2: Survey of Arsenic air pollution control technologies • Task 3: Screening of potential materials for minimizing leaching • Results and Discussions • Summary and Future Work Aerosol and Particulate Research Laboratory

  3. Background: CCA Wood • Currently not considered hazardous under Resource Conservation & Recovery Act (RCRA) which monitors hazardous waste • Disposed alongside other wood waste in Construction & Demolition (C & D) debris landfill ~ 60% is burned to produce energy Aerosol and Particulate Research Laboratory

  4. Heavy Metal Emissions from combustion Leaching of Heavy Metals from Ash into Groundwater Background: Problems with incineration of CCA Wood Rain Contaminated Soil Ground Water National Physical Lab: www.npl.co.uk Aerosol and Particulate Research Laboratory

  5. Proposed Solution • Use mineral sorbents (e.g. lime) for • Preventing emission of metals • Preventing leaching of metals from incinerator ash • Many sorbents have good capture efficiency with respect to metal emissions ( Venkatesh et al, 1996, Kenjiro et al, 2004)  so we have focused on the leaching behavior of CCA metals on interaction with sorbents Activated Carbon Injection :www.epa.gov Aerosol and Particulate Research Laboratory

  6. Methodology • Task 1: Inventory of Existing Major Wood-Fired Capable Facilities • Task 2: Survey of Available Arsenic Air Pollution Control Technologies • Task 3: Screening of Potential Materials for Preventing Heavy Metal Leaching from Incineration Product Aerosol and Particulate Research Laboratory

  7. Task 1: Inventory of Combustion Facilities in Florida Aerosol and Particulate Research Laboratory

  8. Task 1: Inventory of Combustion Facilities in Florida (cont.) Aerosol and Particulate Research Laboratory Back

  9. Task 2: Arsenic Pollution Control Technologies Capture of emissions • Combination of filters and scrubbers • Sorbent injection combined with filtration Reduction in emissions • Co-incineration along with dilution • Low temperature pyrolysis Pyrolysis Furnace Econ Systems: www.econ.co.at Baghouse www.midstatecontracting.com Aerosol and Particulate Research Laboratory Back

  10. Task 3: Screening of Potential Materials for Preventing Heavy Metal Leaching from Incineration Product • Evaluate Potential mineral sorbents in combustion environments • Analysis of Ash by • Toxicity Characteristic Leaching Procedure (TCLP) for leaching properties • X-Ray Diffraction (XRD) to identify the crystalline composition Aerosol and Particulate Research Laboratory

  11. List of Sorbents Used in Experiments *Approximate molecular formula based on % composition. Varies according to mineral composition Aerosol and Particulate Research Laboratory

  12. Experimental Procedure • Prepared a spike sample of CCA metals having same concentration as that of CCA Type C chemical (47.5% CrO3, 18.5% CuO & 34% As2O5) • Heated sorbent and spike sample at 700oC, 900oC & 1100oC for 30 minutes • Analysis of the residue • TCLP Leaching tests • Speciation characterization by XRD Aerosol and Particulate Research Laboratory

  13. Results: Arsenic Retention in Residue • Ca(OH)2 , Cement and Mg(OH)2show over 98% retention for As at both temperatures • Alumina & Diatomaceous Earth show over 80% retention at 900oC Aerosol and Particulate Research Laboratory

  14. Results: Arsenic Leaching from Residue • Cement, Ca(OH)2 and Mg(OH)2 leach less than 5 mg/l of arsenic in both cases • All other sorbents exceed the TC limit for leaching Aerosol and Particulate Research Laboratory

  15. Results: Chromium Retention in Residue • Alumina, Silica, Kaolin & Diatomaceous Earth show over 90% retention for Cr at both temperatures • Attapulgite Clay shows higher Cr retention at 900oC • Ca(OH)2 and Cement show negligible retention Aerosol and Particulate Research Laboratory

  16. Results: Chromium Leaching from Residue • Alumina and Silica leach less than 5 mg/l of Cr at both temperatures • Kaolin leaches less than 5 mg/l of Cr at 900oC • All other sorbents exceed the TC limit at both temperatures Aerosol and Particulate Research Laboratory

  17. Results: Copper Retention in Residue • All sorbents except silica and attapulgite clay show ~80% or greater retention at both temperatures • Cement, Ca(OH)2 , Mg(OH)2 show over 98% retention at both temperatures and Kaolin at 900oC Aerosol and Particulate Research Laboratory

  18. Major XRD Results • The major metal-mineral compounds formed in spike samples are • Cu3(AsO4)2 , Ca3(AsO4)2 CuHAsO4, CaCrO4 etc., when Cement and Ca(OH)2 are used • CuCr2O4, ,when Alumina and Silica are used • Cu has high affinity for forming compounds Aerosol and Particulate Research Laboratory

  19. Summary Cement, Ca(OH)2 & Mg(OH)2 are good at retaining and preventing leaching of As & Cu Alumina & Silica are good at retaining and preventing leaching of Cr • The variation in metal-metal and metal-mineral compounds being formed could be the major reason for different retention capabilities. • Understanding their interaction will provide solution to the challenging issue of CCA wood disposal. Aerosol and Particulate Research Laboratory

  20. How can we utilize this study for effective control of heavy metals during combustion of CCA wood? Provide Ca-based sorbent A possible strategy involving • Cement, Ca-based sorbents to chemically adsorb arsenic in air stream • Alumina, Silica to retain chromium in feed As in gas phase Cr in feed Provide alumina/silica • Potentially viable option for disposal: • Cement kiln • Coal-fired power plants equipped with SO2 scrubbers • Steel mills Aerosol and Particulate Research Laboratory

  21. Acknowledgements • Financial Support by Florida Center for Solid and Hazardous Waste Management Grant# 00050891 • Major Analytical Instrumentation Center, Department of Material Science and Engineering, UF • Particle Engineering Research Center, UF • Officials at Florida Department of Environmental Protection (FDEP) • Mr. Henry Gotsch, Florida Rock Industries Inc. • Sang-Rin Lee, Clarkson University Aerosol and Particulate Research Laboratory

  22. Thank You Aerosol and Particulate Research Laboratory

  23. http://combustcca.ees.ufl.edu Aerosol and Particulate Research Laboratory

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