CATION ADSORPTION ON OXIDES AND CLAYS - THE ALUMINUM CASE

The sorption mechanisms for trace metal ions on montmorillonite have b een investigated. Complexation with surface hydroxyl groups located on the brocken edges of platelet particles is found to occur over a pH r ange similar to that observed on silica and other oxides, at comparabl e metal/site ratios. A second mechanism involving cation exchange on t he negatively charge basal plane, which does not involve proton exchan ge in our experimental conditions, has been invoked to explain the low pH behavior. Consistent with this cation exchange mechanism, adsorpti on at low pH is strongly ionic strength dependant. A quantitative mode l which involves both mechanisms is presented and tested against both cation and proton adsorption data.