ZINC ADSORPTION IN SOME SOILS AS AFFECTED BY EXCHANGEABLE CATIONS

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Abstract
The effect of exchangeable cations on Zn adsorption in soils was studied to understand better their contribution in the availability of applied Zn. Zn adsorption in different cation-saturated soils was in the order: H < Ca .ltoreq. Mg < K < Na. The pH of both the cation-saturated soils and the cations in question influenced Zn adsorption. The selectivity coefficient varied with the initial Zn concentration and the cations in question. The calculated values of standard free energy of adsorption for the Ca-Zn, Mg-Zn, K-Zn and Na-Zn exchange reactions were 41.3, 41.5, 31.1, and 23.6 calories/mol, respectively. The positive values indicated the nonspontaneous nature of exchange reactions and less preference of Zn on the exchange complex at low equilibrium Zn concentrations.