ABSTRACT
An alum shale soil, developed on sulfide-bearing rocks, was treated with organic matter at the rate of 0 and 4% and was placed in temperature-controlled climate chambers at 9 and 21°C to study the partitioning and reaction kinetics of 109Cd and 65Zn. Soil subsamples, collected at time intervals ranging from 0.5 to 8760 h (1 yr) after spiking the soil with 109Cd and 65Zn, were subjected to a seven-step sequential extraction procedure. Soil adsorption of 109Cd and 65Zn was rapid, but the subsequent transfer of the metals toward irreversibly sorbed fractions was a much slower process. The 109Cd and 65Zn concentrations decreased in fractions F1 to F3 and increased in fractions F5 and F6 with time. The concentrations of 109Cd and 65Zn determined in the seven extracts were used in a three-component soil-water kinetic model to calculate the kinetics of 109Cd and 65Zn partitioning between the water-soluble, reversibly sorbed, and irreversibly sorbed fractions. The addition of organic matter reduced the rate of 109Cd and 65Zn transfer into the irreversibly sorbed fraction, and the potential mobility of 109Cd and 65Zn were thus increased by the addition of organic matter. Increased temperature, on the other hand, enhanced the rate of transfer and the potential mobility was reduced. The interaction between organic matter and temperature affected both the rates of transfer and the pseudo equilibrium constants.
