Distribution coefficients for nickel and zinc in soils

Distribution coefficients (K_d) indicate the capability of a soil to retain a solute and also the extent of its movement in a solution phase. The purpose of the study was to determine K_d values for the heavy metals Ni and Zn in soils, in order to evaluate the ability of different soils to retain the metals. Batch equilibrium experiments on Ni and Zn were conducted to obtain adsorption isotherms, K_d values and distribution curves for Ni and Zn, with six concentrations of test solutions and three soils. Ni and Zn adsorption increased significantly as the concentration of the cation increased in the test solution. The range of K_d values for Zn and Ni was 140–684 and 152–388 ml g⁻¹, respectively, for the soils investigated. The Mecklenburg clay, with high cation-exchange capacity (CEC), gave high K_d values for both Ni and Zn. There was no consistent relationship between the K_d values and soil pH and organic matter. The distribution curves for Ni and Zn showed negative correlation between solution concentration of Ni and Zn and K_d values. The results of this study indicate better retardation of Zn as compared to Ni by the soils.