Interaction of stevensite with Cd2+ and Pb2+ in aqueous dispersions

The experimental process of adsorption of Pb(II) and Cd(II) onto clay mineral is studied here in order to evaluate the capacity for removal for these two heavy metal ions. This study is performed under various conditions such as initial solution pH, chemical clay modification conditions, initial metal ion concentration and contact time. The experimental isotherm data are analysed using Temkin, Langmuir and Freundlich equations and it is shown that models produce comparable equilibrium correlation results. The isotherm curves show very clearly the selectivity of the clay for the lead ions but also significant amounts of cadmium are removed as well. Adsorption kinetics data were tested using pseudo-first-order and Intraparticle diffusion models. Adsorption mechanism studies revealed that the process was complex and followed both surface adsorption and particle diffusion. The rate-controlling parameters and diffusion coefficients were determined using the Crank and McKay diffusion models. It was found that the adsorption occurs through film diffusion and the particle diffusion becomes the rate-determining step for each metal ion.