Chemical controls on the fate of mercury and lead codisposed with municipal solid waste

Mercury and lead were among several toxic metals codisposed in test lysimeters with municipal solid waste. Results of analysis of leachates from these landfills during the acid phase of landfill operation have indicated that control of mercury in these systems is a consequence of reduction of divalent mercury to neutral mercury metal. This process was found to occur whether sulfide was present or not. Dissolved mercury in these leachates will exist virtually entirely as chloride complexes. Control of lead solubility was dependent on the presence or absence of sulfide. In the presence of sulfide lead would precipitate as the sulfide while in its absence, the controlling solid was the sulfate. Soluble lead speciation involved significant fractions of both chloride and sulfate complexes. While sulfide has not been detected directly in these systems, levels necessary to control lead solubility were so low as to be indetectable by available methodology and thus its involvement cannot be precluded. Since some circumstantial evidence supportive of sulfate control has been obtained, the complete elucidation of chemical control mechanisms in these systems is not possible.