Effect of multiple factors on the adsorption of Cd in an alluvial soil from Xiba, China.

The effects of organic matter, free Fe oxides and Mn oxides in an alluvial soil on adsorption of Cd were studied through selective chemical extraction and adsorption experiments. Compared to untreated soil, after H2O2 treatment for removal of organic matter and NH2OH·HCl treatment for removal Mn oxides, the distribution coefficient (Kd) decreased by a maximum of 25.2% and 64.1%, respectively. After dithionite-citrate-bicarbonate treatment for removal of free Fe oxides, Kd increased by 1670.2%. After increasing the solution pH from 2 to 3, Kd increased by 2842.1%, whereas after increasing the solution pH from 3 to 7, the adsorption tended stabilize. As the ionic strength increased from 0.001 M to 0.1 M NaNO3, Kd gradually decreased, whereas at the same ionic strength, Kd decreased as the initial concentration of Cd increased. The effects of different background electrolytes on Cd adsorption was as follows: Ca2+ > Mg2+ > K+ > Na+ for cations and Cl- ≈ SO42- > NO3- for anions. The adsorption capacity of Cd increased as the increased of temperature, and it's a spontaneous endothermic process. The pseudo second-order rate model described the process of Cd adsorption well.