A study of the factors controlling the adsorption of Cr(III) on modified montmorillonites

We have examined the way that the metallic ion Cr(III) is held by Na-montmorillonite and alumina pillared clay. We used several physico-chemical methods of analysis (X-ray powder diffraction, infrared absorption spectrometry, thermal analysis and chemical composition) to determine the structural formula of the Na-montmorillonite, and to clarify the effect of the introduction of the Al-13 polycations between the clay layers on its physico-chemical and structural properties. Our results show that the strength of chromium retention increases with pH. This effect is more marked in pillared than in unpillared clays. It seems that the mechanism of fixing of the metallic cations on pillared clays is more complex than a simple cationic exchange and involves the surface groups of the pillars. In other words, chromium adsorption on pillared montmorillonite is more like adsorption on an amphoteric oxide surface (such as Al2O3) than on a non-pillared clay.