Investigation of Cadmium Desorption from Different-Sized Sediments

Using the adsorptive reaction kinetics equation and the mass conservation equation, formulas for calculating the particulate heavy metal concentration (or the residual adsorption content of unit weight of sediment) and the dissolved heavy metal concentration were deduced. Furthermore, equations for calculating the equilibrium particulate heavy metal concentration (or the equilibrium residual adsorption content of unit weight of sediment) and the equilibrium dissolved heavy metal concentration were formulated. On the basis of these theoretically deduced formulas and through laboratory reactor modeling of artificially contaminated sediments with cadmium in suspension, heavy metal desorption rates from nonuniform sediment particles were studied. Both theoretical analysis and experimental results indicate that adsorption and desorption of heavy metal pollutants to and from sediment particles are partly reversible. It is also noticed from the experiments that the adsorption and desorption rates of heavy metals to and from sediments are dependent on the content of active adsorption components in the sediments. The greater the content of active adsorption components, the higher the adsorption rate of the sediments and the lower the desorption rate. The total amount of heavy metal desorbed from sediments is directly proportional to the concentration of suspended sediment particles.