Cadmium complexation by solid waste leachates

Abstract

A previously reported method for determination of Cd species in solid waste leachates has been applied to ten leachate samples representing five different types of solid waste: refuse compost, flyash from coal combustion, sewage sludge, refuse incineration residues and landfilled municipal waste. The leachates were spiked with Cd (< 100 μg Cd 1 −1) to obtain comparable concentrations in the investigated samples. For each sample, at two different Cd concentrations, free divalent Cd and complexed Cd were determined. Furthermore, the complexed fraction was operationally separated into labile complexes, slowly labile complexes and stable complexes. Leachates originating from the same type of solid waste showed different fractions of Cd, in particular with respect to free divalent Cd and stable Cd complexes. Only coal flyash showed almost identical fractions of Cd in the two leachates. The latter is due to the predominant hydroxy complex formation. In all leachates, the labile and slowly labile Cd complexes were predominant, accounting for a total of 69–100% of the leachate Cd concentrations. The fractions of free divalent Cd and stable Cd complexes varied highly, <0.1–33% and <0.2–25%, respectively. However, in most cases both categories did not exceed 10%. The obtained results stress the importance of considering Cd species and not only total Cd concentrations, when evaluating the fate of Cd in the environment.