Modeling of cadmium and nickel release from different soils

Cadmium and Ni chemical reactivities in soils are highly dependent on various soil properties. In this study, batch sorption-desorption experiments were carried out to quantify the potential of different soils to retain and release of Cd and Ni. Results revealed that several soil characteristics control Cd and Ni sorption-desorption where, the mutual effects of pH, CEC, soil carbon, clay, silt, and CaCO3 contents govern their behavior in soils. Sorption of Cd and Ni was found to be concentration dependent. The studied soils exhibited higher Ni sorption capacities than Cd (Ni-S-max > Cd-S-max). Statistical relationships between soil properties and Langmuir parameters were achieved by stepwise regression analysis. Simulations of Cd and Ni kinetic reactions were performed using a multireaction model (MRM). Cadmium and Ni exhibited sorption-desorption kinetics and hysteresis in the soils and were well simulated by MRM. The highest reversible reaction rate and low hysteresis for Cd and Ni were associated with the low soil sorption capacities. Whereas, a strong nonsingularity of sorption-desorption isotherms was observed for soils with high CaCO3 contents.