Fundamental mechanisms of phosphate stabilization of divalent metals in MSW combustion scrubber residues
- Univ. of New Hampshire, Durham, NH (United States)
Chemical stabilization of waste materials offers the potential to reduce the leachability of heavy metals in the waste. The principal objective during stabilization is to form new mineral phases with reduced solubilities and increased geochemical stability in a leaching environment. One stabilization agent of recent interest, particularly for Pb{sup 2+}, is PO{sub 4}{sup 3{minus}}. A patented soluble phosphate treatment process, marketed by Wheelabrator Environmental Systems as the WES-PHix process, is used in 23 MSW combustion or ash processing facilities in the United States. It is also used at 7 wire recycling facilities. The process is licensed to Kurita Water Industries Ltd. of Japan where it is marketed as the ASHNITE process. It is used in over 80 MSW combustion or ash processing facilities in Japan. Phosphate combines with over 30 elements to form about 300 naturally-occurring minerals. Metal phosphates are ubiquitous secondary minerals in the oxidized zones of lead ore deposits and as assemblages around ore bodies. They also occur in soils, sediments, and phosphatic beds. As such, they are stable with respect to pH, Eh, and mineral diagenesis. Isomorphic substitutions are very common for both divalent cations (e.g. Pb{sup 2+}, for Ca{sup 2+}) and oxyanions (e.g. AsO{sub 4}{sup 3{minus}} for PO{sub 4}{sup 3{minus}}) in these minerals. This study was designed to determine the mechanisms and reaction products of chemical stabilization of dry scrubber residues treated with soluble orthophosphate. The data gleaned from various spectroscopic analyses, leaching procedures, and geochemical modeling show that precipitation/solid solution formation rather than sorption is the immobilization mechanism and that apatite minerals and solid solutions are the principal solubility-controlling reaction products. As in nature, these minerals are geochemically stable and very insoluble.
- Research Organization:
- Solid Waste Association of North America, Silver Spring, MD (United States); Air and Waste Management Association, Pittsburgh, PA (United States); Integrated Waste Services Association, Washington, DC (United States); National Renewable Energy Lab., Golden, CO (United States); American Society of Mechanical Engineers, Yonkers, NY (United States). Solid Waste Processing Div.; Environmental Protection Agency, Research Triangle Park, NC (United States). Air Pollution Technology Branch
- OSTI ID:
- 548942
- Report Number(s):
- CONF-970440--; ON: DE97007054
- Country of Publication:
- United States
- Language:
- English
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