Coal Conversion Solid Waste Disposal

The major solid waste produced at coal conversion facilities will be gasification slag or ash. To evaluate the impact of this waste on the environment, the Oak Ridge National Laboratory conducted extensive characterization and leaching studies on ash/slags that had been generated in bench-scale operations, pilot plants, and/or process development units for eight different gasification processes. These studies, designed to assess the consequences of disposal in landfills, showed that none of the leachates from these eight wastes exceeded the U.S. Environmental Protection Agency's toxicity limits. Thus, these ash/slags would be classified as nonhazardous wastes. Quantities of polynuclear aromatic hydrocarbons (PAH) that were observed in the aqueous leachates of selected ash/slags were less than 1 μg/g and appear to be of no significant environmental concern. Column elution studies revealed effluents with pH values less than three and sulfate concentrations greater than 10,000 mg/L for wastes containing sulfur concentrations from 0.3-4%. As a result, the major environmental impact associated with disposal of these solid wastes appears to be the dissolution of sulfate and the potential acidification of ground water.