Hydrological and geochemical factors controlling the leaching of cemented MSWI air pollution control residues: A lysimeter field study

A pilot landfill (area, 16 m(2); depth 1.5 m) containing cement-stabilized air pollution control (APC) residues from municipal solid waste incinerator s (MSWI) was investigated in order to determine the hydrological and geoche mical factors that control the leaching process. Between May and August 199 6, 3 rain events were investigated. Rainfall and discharge were monitored a nd leachate samples taken for the analysis of major components. It was foun d that water from the rain events took 2-3 days to pass through the lysimet er. Leachate dilution at the beginning of rain events indicated that rainwa ter passed through the lysimeter as preferential flow. The change in the co ncentration of leachate components with time was found to be almost identic al for most components. Conductivity, dominated by Na (+) and OH (-), also positively correlated with the concentrations of Al, Cs, K, Si, sulfate, ch loride, carbonate and organic substances in the drainage discharge. The Ca concentrations were not influenced by the rain events, indicating that this component was leached by rainwater from the lysimeter cover layer. This wa s also found to apply to observed changes in Sr concentrations. Both conduc tivity and Sr were used as tracers for rainwater in the leachate and result s agreed well. The solubility of the main constituents, Ca, Si, and Al coul d be explained by thermodynamic equilibrium with the solids calcium silicat e hydrate, ettringite and possibly K-feldspar. The results indicate that th e leaching process (within the first 5 years) is dominated by pare waters b etween the cement blocks that me in equilibrium with the cement-stabilized APC residues (thus explaining the constant composition of the leachate) and is flushed out by rain events. (C) 2000 Elsevier Science B.V. All rights r eserved.