IDENTIFICATION OF SOLUBILITY-CONTROLLING SOLID-PHASES IN A LARGE FLY-ASH FIELD LYSIMETER

Samples of pore fluids and leachates were obtained from a large fly ash field lysimeter in central Pennsylvania. The fly ash in the lysimeter was usually only partially saturated, and only 0.3 pore volumes of water leached through the lysimeter during the 3-year study period. The samples were analyzed for major and trace inorganic anions and cations. The resulting analyses were modeled by using an equilibrium speciation/solubility code to test the hypothesis that the solubilities of at least some species in the fly ash leachate were controlled by solid phases. Potential solubility-controlling solids were identified for Al, Ba, Ca, Cr, Cu, Fe, S, Si, and Sr in the pore waters and leachates. Solid solutions appear to play an important role in controlling the concentrations of Ba, Sr, and Cr. The activity relationships were independent of location within the lysimeter and time of sampling. A laboratory experiment showed that equilibration times between these nine elements and their solubility-controlling solids were on the order of days or less. Geochemical reactions controlling the concentrations of As, B, Cd, Mo, and Se were not identified. © 1990, American Chemical Society. All rights reserved.