Cadmium desorption from the river bed sediments has been experimentally investigated. Artificially contaminated sediments with cadmium (Cd) were prepared for performing batch desorption experiments. The experiments were conducted by adding 1 g of contaminated sediment (D50 = 0.53 mm), containing different amounts of adsorbed Cd, to 50 mL of distilled water at different times (0, 5, 15, 30, 60, 120, 300, and 720 min) and shaking to reach an equilibrium desorption rate. In addition, the experiments were conducted for two agitation rates of 100 and 200 rpm. It was concluded that the cadmium ions were strongly bond to the river bed sediment; meanwhile, at the equilibrium time, up to about 7 to 29% of cadmium ions were released from the artificially contaminated sediments. It was also revealed that by increasing the flow turbulence, the amount of desorbed cadmium is slightly increased. Besides, the desorption kinetics was evaluated using eight models of zero-, first-, second-, third-order, parabolic diffusion, double parabolic diffusion, two-constant rate, and simple Elovich. The results of the evaluation showed that simple Elovich (with R2 = 0.991), double parabolic diffusion (with R2 = 0.9882), two constant rate (with R2 = 0.983), and parabolic diffusion models (with R2 = 0.846) have the best performance in calculation of Cd desorption rate from the sediments. The results of this study on kinetics of Cd adsorption and desorption onto/from the natural sediments may be useful for predicting efficiency of heavy metal decontamination in rivers.
