Sorption of heavy metals by Lithuanian glauconite

Adsorption equilibria are evaluated for Cd(II), Pb(II) and Zn(II) on a sample of pass 200 mesh Lithuanian glauconite using two different experimental/analytical approaches. First, the impacts of total metal concentration, ionic strength and pH on adsorption capacity are quantified in terms of the Freundlich isotherm equation for isotherms conducted at a single initial pH value. Relative adsorption capacity for the metals was in the order Pb > Cd > Zn. Secondly, pH effects and sorption mechanisms were examined more closely using the triple layer-surface complexation model to describe pH-adsorption edges. Although glauconite is a complex clay mineral, a single site approach provided a satisfactory description for many of the cases studied. Discrepancies between model simulations and experimental data were observed for some instances involving large changes in ionic strength or sorbate-to-sorbent ratio when using adsorption reactions and equilibrium constants evaluated for a baseline case. Analysis of the possible contributions of multi-site adsorption, cationic exchange, mineral dissolution and desorption phenomena are required to more accurately characterize metal uptake by glauconite.