Effect of Redox Potential on Cd Solubility and Chemical Forms of Contaminated Soil

抄録

The effect of redox potential on Cd solubility and chemical forms in contaminated soil was investigated by incubation. As the incubation time elapsed, the Cd content in the submerged water decreased in accordance with lowering of soil Eh. This is considered to be attributable to the formation of cadmium sulfide. The decrease of the Cd content in submerged water was delayed for a few days from the decrease of Eh. This is because the formation of cadmium sulfide cannot occur until sulfate is reduced to sulfide by sulfatereducing bacteria. These results suggested that Cd changed into insoluble form in the order of mobility in soil. The exchangeable and inorganically-bound Cd shifted to the submerged water because the chemical equlibrium was broken by the precipitation of cadmium sulfide. The conclusion is that the insolubilizing of Cd in soil under incubation is a relatively slow process, but once the Cd dissolved into the solution, the formation of cadmium sulfide is extremely rapid.