Trace element characterization of coal wastes. Fifth annual progress report, October 1, 1979-September 30, 1980

During the past year we continued our research on environmental control technologies as they relate to coal preparation wastes and extended our assessments to include studies of high-sulfur Appalachian coal cleaning wastes. The most promising control technology for dealing with high-sulfur coal wastes consists of sequential slurry coating of the waste with lime and limestone. Codisposal of coal wastes and alkaline soils or mine overburdens is partly effective in controlling the leachate quality under steady-state conditions. Comparisons between trace element concentrations predicted by chemical equilibrium models and those obtained in experiments with coal waste leachates yielded good agreements for the major cations (Al, Ca, Fe) but, except for fluoride, the major anions were not well accounted for. The observed trace element concentrations were all significantly lower than predicted. Calcination experiments have shown that high-sulfur coal waste from Appalachia (Plant K) behaves differently than other wastes we have studied. The high cost of this technology ($1.39 to $9.84/ton product) places it outside the realm of economic feasibility at this time. We have also completed an assessment of the Plant K coal wastes. These materials are similar to those from the Illinois Basin and their leachates are often very acidic, with pHmore » values sometimes less than 2. Several trace elements have shown discharge severities greater than unity (Fe, As, Ni, Mn, Al), but iron is by far the worst offender, with values sometimes greater than 100. Results of the EPA Extraction Procedure, used to classify solid wastes under the Resource Conservation and Recovery Act, compare favorably with those of our own leaching experiments for those elements analyzed (Ag, As, Ba, Cd, Cr, Hg, Pb, Se). However, coal wastes release substantial quantities of other trace elements not included in the protocols at present (Fe, Al, Ni, Mn, Zn, Cu).« less