Effect of surface equilibria on the electrokinetic behaviour of Pb and Cd ions in kaolinite

Abstract

AbstractBACKGROUNDElectrokinetic remediation of fine‐grained soils polluted by heavy metals is affected by the equilibria between dissolved and sorbed ions; pH can also influence the surface equilibria. Geochemical models which describe the behaviour of different surface sites and their interactions with heavy metal ions have to be considered for a good mathematical representation of an electrokinetic process.RESULTSCd2+ and Pb2+ sorption isotherms were performed at different pH values using kaolinite as sorbent. Electrokinetic tests were performed with samples of kaolinite spiked with Cd2+ and Pb2+ at 0.7 and 2 V cm−1: the concentration profiles were obtained experimentally at different treatment times. The pH in the compartments was conditioned by acetate buffer. On the basis of the experimental results, a numerical model was formulated to simulate ion transport under an electric field combining the diffusion–advection equations with a two‐sites geochemical model taking into account ion exchange and surface complexation of the metal ions, as well as the protonation–deprotonation reactions of the surface sites.CONCLUSIONSThe process was effective for cadmium removal, while a strong dependence on pH was observed for lead removal. The model allowed prediction of time/space profiles in solid and liquid phase: a good agreement with the experimental data was obtained under all the conditions adopted. © 2014 Society of Chemical Industry