The sorption of lead and cadmium species by clay minerals

Abstract

The effect of pH changes and the presence of ligands on the uptake of lead and cadmium ions by three types of clay mineral (kaolinite, illite and montmorillonite) has been investigated. ��� In the absence of ligands, metal ion adsorption increases gradually with increasing pH until a threshold pH value is exceeded, whereupon total precipitation/sorption (attributed to formation of hydroxy species) occurs. With ligands present, the threshold point tends to shift to higher pH values, the magnitude of the effect depending on the stability of the metal complex formed. Adsorption of cationic metal complexes is subject to competition from charged protonated ligand species; anionic complexes are not sorbed.