Chemical Speciation in Fly Ash Leachate: Importance and Determination with Special Reference to Arsenic

摘要

The chemical form of trace elements in ash leachate is largely unknown and can only be inferred from thermodynamic considerations presuming chemical equilibrium. Unfortunately most aqueous systems in the environment are probably not at chemical equilibrium, thus speciation can only be determined with certainty by empirical methods. Exploratory studies are being performed to determine the behavior and chemical form of arsenic in natural leachate from several coal ashes. These studies have illustrated the utility of the empirical approach to leachate behavior and speciation in deciding when and where in an ash disposal system arsenic, or some other toxin, may constitute an environmental problem. Preliminary findings are suggestive of a generic problem and constitute the basis for our contention that additional research is necessary to identify the factors, such as coal type, combustion conditions, and disposal methodology, which determine the leachability and chemical form of arsenic in ash disposal systems. Additional research should examine both temporal and spatial variations in arsenic speciation (and other toxic elements which would be expected to exhibit similar behavior in the environment) in selected typical ash disposal systems. Particular emphasis should be placed on identifying the physical/chemical factors which regulate mobilization of arsenic from coal ash and speciation of arsenic (and other toxic elements) in ash leachate. (ERA citation 04:005090)