Abstract
The precipitation and complexation scheme of cadmium in sanitary landfilllayer is studied by investigating the reaction equilibrium among Cd2+, OH-, Cl- and CO32-. First, the scheme and equilibrium constants of the reactions among those species in pure water was determined. From these experiments, it is found that not only the precipitaion reactions but also the complexation reactions should be taken into accounton estimating the total concentration of dissolved cadmium, [Cdt] and so a set ofequations are obtained for calculating [Cdt]. The equilibrium constants in this work agree well with published. Secondly, the same reactions were observed in leachate, which had been sampled form three sanitary landfill sites. The observed [Cdt] with various concentrations of OH-, Cl- and CO32- are estimated compatively well by using the set of equations above mentioned. Finally, based on these results, the variation of [Cdt] and other dissolved species in various conditions of pH, Cl- and CO32- are considered and so it is found that the minimum [Cdt] in the range of pH 7 to 11 isabout 0.2 mg/l.
