pH, ionic strength, and ion competition effect on Cu(II) and Ni(II) sorption by a Na-bentonite used as liner material

Abstract

The potential of a Na-bentonite to be used as liner material for the adsorption of Cu(II) and Ni(II) ions from mono, bi, and polycationic solutions was investigated by batch mode. pH and ionic strength effect on Cu(II) and Ni(II) sorption were evaluated. For isotherm sorption studies, metal solutions parameters (pH and ionic strength) were selected simulating common landfill leachate conditions in the acidogenic stage. The removal of these ions by the Na-bentonite is dominantly controlled by sorption (specifically, cation exchange) under acidic conditions, but it can be strongly enhanced by metal oxide/hydroxide precipitation under alkaline conditions. Adsorption equilibrium models for the single, binary, and multicomponent systems indicate that the Langmuir-type model can fit the experimental data very well for all of them. The co-presence of metals led to a decrease in the sorption of both metals due to competition for adsorption sites. Optimum conditions are obtained when the ionic strength of solution is low (<0.05 M), pH is higher than 6, and the metal concentration is lower than 20 mg/L. Adsorption rates indicate that in addition to its quality as a physical barrier this bentonite can also act as a chemical barrier, limiting the migration of heavy metals from security landfills.