Equilibria and Kinetic Studies on the Adsorption of Cadmium onto Cameroonian Wetland Clays

The possible use of clay (AL2Si3O5(OH)4, locally mined (Make pe, Cameroon), as an adsorbent, for the removal of cadmium from wastewater was investigated. Spectroscopic studies including FTIR, elemental analysis (EA), XRPD, and SEM were used for its characterization. The effect of different variables, namely: concentration of metal ions, pH and time of interaction were studied. The adsorptive property of clay was tested using Cd(II) as the model adsorbate. Equilibrium data was examined using a comparison of linear isotherm models. The adsorption behavior was well described by the linear Langmuir isotherm model, showing a monolayer adsorption capacity for Cd(II). The kinetic rates were modeled by using the Lagergren-first-order, pseudo-second-order and intra particle model. The pseudo-second-order model was found to explain the adsorption kinetics most effectively. It was also found that the pore diffusion played an important role in the adsorption and intraparticle diffusion was the rate-limiting step during the first 30 min. of interaction.