INFLUENCE OF HYDROLYSIS ON THE SORPTION OF METAL-CATIONS BY SMECTITES - IMPORTANCE OF EDGE COORDINATION REACTIONS

A comparison was made between the adsorptive behaviors of Cd2+ and UO22+ relative to two smectites that differed in their ratio of edge sites to fixed-charge sites. Adsorption varied with both pH and ionic strength, consistent with sorptive contributions of ion exchange and coordination reactions to edge hydroxyls. Both clay minerals exhibited a greater affinity for UO22+ than for Cd2+, and the clay with a higher proportion of edge sites retained both ions more strongly. A computational model including fixed-charge sites and edge hydroxyls resulted in a good prediction of overall UO22+ and Cd2+ uptake to both smectites.