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.