Cadmium Adsorption on a Mixed Mineral Assemblage of Kaolinite and Hydrous Ferric Oxide

Abstract

The adsorption of Cd11 on kaolinite was investigated in batch experiments of varying metal concentrations, background electrolyte concentrations, and pH. A typical adsorption edge of Cd11 on hydrous ferricoxide (HFO) was also produced. Additionally, the adsorption of Cd11 onto multiple binary mixture ratios of kaolinite and HFO was investigated. These experimental adsorption data were interpreted in terms of surface complexation using the double diffuse layer model (DDLM). Equilibrium thermodynamic absorption parameters were established and optimized using the surface complexation modeling program JCHESS. The thermodynamic parameters established for kaolinite were determined to be very effective at predicting systems of varying ionic strength but were slightly less effective at predicting systems of varying Cd11 concentration. The thermodynamic parameters determined for kaolinite, and those optimized for HFO, |/ere applied to binary mixtures with varying ratios of kaolinite to HFO. It was determined that the established modeling parameters were very effective at predicting the adsorption of Cd11 on binary systems which contained a high ratio of kaolinite to HFO (100:1 and 1000:1) but were less effective at predicting adsorption on binary systems with a greater quantity of HFO (1:1 and 10:1). It was concluded that the model for HFO might need to be further refined, whereas the equilibrium parameters established for kaolinite were very effective at predicting the experimentally observed adsorption of Cd11 on this colloid.