Geochemistry of a reclaimed coal slurry impoundment. Final technical report, September 1, 1993--November 30, 1994

The highly alkaline residue from the fluidized-bed combustion (FBC) of coal may be an environmentally acceptable material for use in neutralizing acid produced by the oxidation of pyrite in coal. slurry solids (CSS). Previous research indicated that FBC residues in mixtures with pyrite-rich CSS neutralized the acid produced by or attenuated the oxidation of pyrite in CSS. In the present research project we retrieved five drill cores from a reclaimed coal slurry impoundment, and installed three samplers in one of the core holes. The solids were chemically and mineralogically analyzed. Display of the mineralogical data on a cross section showed that pyrite was randomly distributed through much of the length of the coal slurry impoundment. Trace concentrations of heavy metals were correlated with pyrite in the core solids. Water samples were collected and analyzed. The water analyses showed that nutrients are insufficient to support plant growth without supplemental fertilization. The analytical data will provide background information necessary for the development of a predictive computer model of the kinetics of pyrite oxidation at near-neutral pH conditions. Programming of a computerized model to simulate pyrite oxidation under near-neutral pH conditions was begun. The program includes ideas from Morel and Hering (1993) and species are calculated in terms of 7 components of known concentrations. The ionic strength of the solution, the species activity coefficients, and the activities are calculated iteratively