Heavy metal speciation in landfill leachates by exchange on Chelex 100 resin

A simple operative procedure is described for the speciation of heavy metals (Pb, Cu, Ni and Cd) in landfill leachates. The procedure is based on the kinetics of metal removal from the liquid phase by a cation-chelating resin (Chelex-100) in batch tests. The metals were divided in three different classes of behaviour (free-labile fraction, slowly exchangeable fraction and stable-inert fraction). The leachate was spiked with the metals at mg L(-1) level and a strong effect of the aging time (the time elapsed between metal spike of the leachate and kinetic tests) was observed. This is to be ascribed to a slow complex formation in the spiked leachate. As a comparison, the procedure was also applied on synthetic solutions containing several simple ligands (chloride, acetate, glycinate and salycilate), proposed in the literature to model the complexing power of landfill leachates. The metals in the leachate behaved in a different way than in the synthetic solutions. The metal removal rate was in general slower than observed in the synthetic solutions and a not negligible stable/inert fraction was always present for each of the metals. The results suggest that the complexing properties of the leachate are mainly related to substances not representable by the simple ligands proposed in the literature to model these matrixes.