SEDL / STP / STP1075-EB / STP25484S

Geochemical Basis for Predicting Leaching of Inorganic Constituents from Coal-Combustion Residues

Murarka, IP
Program Manager, Electric Power Research Institute, Palo Alto, California

Rai, D
Staff scientist and research scientist, Battelle, Pacific Northwest Laboratories, Richland, Washington

Ainsworth, CC
Staff scientist and research scientist, Battelle, Pacific Northwest Laboratories, Richland, Washington

Pages: 10    Published: Jan 1991

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Abstract

Pore waters, leachates, and waste-water extracts associated with electric utilities' wastes and waste disposal ponds exhibit extremely variable aqueous elemental concentrations. When ionic strength and aqueous complexation are accounted for, however, the activities of free species exhibit behavior with pH similar to those in equilibrium with known solid phases. By comparing observed ion activity products (IAPs) with calculated IAPs from thermodynamic data for selected solid phases, solubility-controlling solids may be indirectly identified or suggested for various elements. To date, AlOHSO⁴, Al(OH)³, BaSO⁴, CaSO⁴, Cr(OH)³/(Cr,Fe)(OH)³, CuO, SiO², SrSO⁴, ZnO, and several solid solution/coprecipitates have been suggested to be the solubility-controlling solid phases for different elements over a wide range of waste compositions, waste types, and disposal conditions. These results indicate that the composition of leachates from coal-combustion wastes, with respect to several elements, can be estimated from fundamental reactions involving solubility-controlling solids of these elements. The results obtained thus far using this approach are summarized in this paper.