Effect of cations in the background electrolyte on the adsorption kinetics of copper and cadmium and the isoelectric point of imogolite

Modification of surface charge and changes in the isoelectric point (IEP) of synthetic imogolite were studied for various cations in the background electrolyte (K+, NH4+, Mg2+, and Ca2+). From the electrophoretic mobility data, it was established that the K+ (KCl) concentration does not affect the IEP of imogolite; therefore, KCl is a suitable background electrolyte. In terms of the magnitude of changes in the IEP and surface charge, the cations may be ranked in the following order: Mg2+ approximate to Ca2+ >> NH4+ >> K+. Four different kinetic models were used to evaluate the influence of Mg2+, Ca2+, NH4+, and K+ on the adsorption of Cd and Cu on synthetic imogolite. When adsorption occurs in the presence of cations with the exception of K+, the kinetics of the process is well described by the pseudo-first order model. On the other hand, when adsorption is conducted in the presence of K+, the adsorption kinetics is well described by the pseudo-second order, Elovich, and Weber-Morris models. From the surface charge measurements, the affinity between imogolite and the cations and their effect on the adsorption of trace elements, namely Cu and Cd, were established. (C) 2015 Elsevier B.V. All rights reserved.