Desorption of Cadmium(II) from Artificially Contaminated Sediments

The desorption kinetics of cadmium from natural sediments was investigated. Three sediment samples from Maryland water bodies were artificially contaminated with Cd(II) and subsequently exposed to a wide range of chemical conditions in batch reactors. Dissolved Cd(II) was monitored. The highest desorption rates and extents were observed at low pH and high concentrations of CaCl₂ and EDTA (a strong Cd chelator), with reduced rates at higher pH. Nearly all of the desorption occurred within the first 30 minutes of exposure. Adsorption of Cd(II) was greatest, and desorption slowest on the sediments with the lowest sand content. A simple desorption model was developed assuming proton competition with cadmium. This model was fit to experimental data at different pH using a non-linear, least-squares analysis to obtain rate constants.