SPECIFIC AND NONSPECIFIC SORPTION OF CADMIUM BY SOIL CLAYS AS INFLUENCED BY ZINC AND CALCIUM

The sorption of low concentrations of cadmium by the calcium-saturated < 2 μm fraction of four soils was studied in the presence of variable concentrations of calcium and zinc, as a model of reactions in contaminated soils. The sorbed cadmium and zinc was determined by radioisotopic procedures and partitioned experimentally into specifically and non-specifically sorbed forms. With cadmium the non-specifically sorbed form usually exceeded specifically sorbed. Specific sorption of cadmium was depressed by competition with zinc but not the reverse. The non-specifically sorbed component of sorbed cadmium, as defined by rapid exchange with calcium nitrate solution, was preferred over calcium by the clay exchanger, with separation factors of 4-10 for cadmium saturations of <1% cec. Some implications for the management of soil as a sink for heavy metal pollutants are discussed. © 1979, CSIRO. All rights reserved.