Heavy Metal Adsorption in Soil: Comparison of Bisolute Adsorption Models and Laboratory Experiments

Abstract

The effect of Zn and NH4 on the adsorption of Cd has been studied at a pH of 6 for two soils. The experiments were carried out for concentrations of Zn and NH4 in the ranges present in most industrial wastewaters. The competitive experiments were conducted also with wastewater from a zinc refinery. It was found that both Zn and NH4 suppressed the ability of Cd to adsorb onto soil. The adsorption of Cd and Zn was determined to be less in the refinery wastewater than that in the single solute batch experiments. Different theories have been proposed to predict the equilibrium concentrations of solutes in the bisolute system using single solute isotherm constants. Four simple mathematical models to predict equilibrium concentrations in the bisolute system have been tested for their applicability, viz., Competitive Freundlich Adsorption Model (CFAM), Modified Competitive Freundlich Adsorption Isotherm Model (MCFAM), Ideal Adsorbed Solution Theory (IAST), and the one given by Sheindorf et al. (1981), (SM). The MCFAM and the SM were found to be satisfactory in predicting the concentrations in the bisolute system and at the same time more easily incorporated into bisolute transport models.