Competitive Sorption of Nickel and Cadmium in Soils.

Competing ions strongly affect heavy metal retention in the soil system. This study evaluated the sorption of Ni and Cd in a binary metal-Ca and ternary Ni-Cd-Ca systems in two soils; Windsor sand and Oliver loam. Competitive sorption isotherms were obtained after 24 hours reaction and exhibited L-type patterns. A Freundlich equation was applied to predict these adsorption isotherms. Freundlich distribution coefficients were higher in Ni-Ca and Cd-Ca than in Ni-Cd-Ca systems. Metal sorption was also descried using Shenindrof-Rebhun-Sheituch (SRS) equation, which represents a multi-component Freundlich-type isotherm model. The associated competitive coefficients α_ij can be viewed as a way to quantify competitive interaction. The competition coefficients indicated that the sorption of Ni by the soils was significantly inhibited by the presence of Cd. Similarly, the sorption of Cd was also suppressed by the presence of Ni ions. It was also found that when the added metal concentration increased in ternary Ni-Cd-Ca systems, the suppressed effect of the metal ion competition increased.