Fundamental Approach for Predicting Pore-Water Composition in Fossil Fuel Combustion Wastes

Abstract

An application of a fundamental thermochemical approach that relates the aqueous concentrations of elements to specific chemical reactions in waste/water systems is described. The approach involves the concept of waste as consisting of mixtures of discrete solids (pure solid phases and solid solution phases) that control aqueous concentrations of individual solutes through their solubilization or adsorption/desorption characteristics. Thermochemical data can then be used in conjunction with knowledge of the specific solid phases present in the wastes to calculate the aqueous concentrations of elements. This approach does not explicitly consider specific rates of kinetically controlled reactions but does incorporate empirical knowledge of the relative rates of several reaction types. Overall, the thermochemical approach is applicable to all waste types and environments, and is appropriate because (1) most waste solids that either are present or are expected to form during weathering have relatively rapid precipitation/dissolution kinetics, and (2) experimental results, enrichment of many constituents on particle surfaces, and the large specific surface areas of wastes suggest that many of the constituents present in the wastes are accessible to solution attack and are mobilized fairly rapidly. Supporting evidence for the successful application of this approach to predicting pore-water concentrations of several major and trace elements in utility wastes is discussed.