Adsorptive Removal of Nickel from Different Soil Orders as a Function of Physicochemical Properties

Abstract

Sorption isotherm can explain the ability of soils to retention of heavy metals on solid phases, because of reducing contamination. Nickel adsorption was measured by adding 30 mL of nickel sulfate containing concentration of 20 to 1280 mg L–1 in the same concentration to 1.5 g soil samples and 0.01 M CaCl2 as background electrolyte. Six isotherms models were fitted to adsorption data and the best-fitted model match to the experimental data was determined. The amount of nickel adsorption increased with equilibrium concentrations. After that, the increasing rate decreased. The Freundlich and Temkin equations gave the best fit. At lower initial concentrations, the maximum removal percentage (97.2%) was observed in Mollisols (soil number 9) which decrease to less than 35%. The minimum removal (89.36%) was obtained in Entisols (soil number 4) which declines to 15.15%. The higher value of 1/n, Kf, b and bE in soil number 9, resulting the higher binding affinity and adsorption intensity for nickel. The distribution coefficient values were obtained from 0.028 to 0.325 mg g–1, which was the highest for soil number 9. The high clay content, organic matter percentage, and cation exchange capacity in the aforementioned soil reflect the highest tendency to retain nickel on solid phases. The apparent energy values indicated that nickel adsorption might be defined as physical adsorption. There were positive correlations between some of the adsorption coefficients and organic matter content in the studied soils. Amount of organic matter was related to the capacity of the soils to retain metals such as nickel.