Adsorption of nickel by Indian soils

Adsorption of metals from liquid into solid phase is one of the most important chemical processes which affect the behaviour and bioavailability of metals in soils, thereby exerts a major influence on their uptake by plant roots. Indian soils, representing the various soil types of tropics, were subjected to Ni treatment of different concentrations and equilibrated at room temperature. The Ni adsorbed by each soil was calculated as the difference between the amount of Ni present in the solution initially and that remaining after equilibration. Results indicated that all the soils under study follow Freundlich and linear adsorption isotherms with highly significant positive correlation. In general, adsorption capacity of the soils for Ni increased with an increase in pH of the soil, whereas, the reverse was found to be true for the rate of adsorption. Significant positive correlations (p = 0.1 - 0.001) were obtained between Freundlich's K (adsorption capacity) and pH, CEC and CaCO3 content of the soils. Also, eight soils of Maharashtra, India, were found to fit in all the three adsorption isotherms, namely, Freundlich, Langmuir and linear. The distribution coefficient (Kd) values of these soils, in general, increased with an increase in pH and CEC of the soils. Adsorption of Ni in soils followed the order: vertisol > entisol > alfisol/ultisol.