Geochemical Factors Controlling the Mobilization of Inorganic Constituents from Fossil Fuel Combustion Residues: II. Review of the Minor Elements 论文

摘要

Abstract Past studies of the environmental aspects of fossil fuel waste disposal have focused on determining elemental concentrations, elemental distributions, and empirical rates of elemental extraction. The concentration data for the minor elements (i.e., As, B, Ba, Cd, Cr, Cu, Pb, Mn, Hg, Mo, Ni, Se, Sr, V, and Zn) are extremely variable and are dependent on fuel composition and combustion processes. Studies of elemental extraction rates have provided empirical information on short‐term leaching behavior that is relevant only to a specific waste sample. Extraction studies serve to characterize the initial states of wastes prior to disposal but generally have not provided information on the dominant weathering reactions that will control the long‐term concentrations of minor elements in the disposal environment. We propose that a more useful approach for understanding leachate chemistry involves the consideration of the thermodynamics of specific dissolution/precipitation, adsorption/desorption, and redox speciation reactions that occur during weathering in addition to empirical data. Because fossil fuel wastes are composed of high‐temperature solids that formed under conditions of combustion, this approach can be used to describe the reaction paths governing the alteration of the high‐temperature solids to assemblages of secondary solids and aqueous species that are stable in weathering environments. The depiction of leaching behavior through solubility and speciation relationships rather than through empirical interpretations of extraction rates allows one to establish bounds for the aqueous concentrations of various elements, given information on the chemistry of waste solids and on physical and chemical conditions. The determination of thermodynamic data and application of those data to understanding the leachate chemistry of the minor elements in the disposal environment remains an area where much research is needed.