Uptake of 137Cs and 85Sr onto thermally treated forms of bentonite.

This study focuses on the structural changes of bentonite upon thermal treatment at various temperatures, i.e. 150, 300 and 600, and their effect on the sorption behaviour for 137Cs and 85Sr. Thermal treatment caused gradual disappearance of the major peak of montmorillonite (at 15.15 Å) and minimization of calcite as observed by powder x-ray diffraction, in addition thermal gravimetric analysis indicated the occurrence of dehydration and dehydroxylation of the materials upon heating. Sorption experiments were carried out by batch-method and data were expressed in terms of distribution coefficients (Kd). Contact time, solution-solid ratio and radionuclide activity concentration were investigated in order to determine the optimal conditions and speculate the mechanism of the uptake. Sorption data revealed that the heated forms had lower selectivity for 137Cs than the original bentonite, while B-150 and B-300 were the best sorbents when 137Cs presents in salt media. In either case, ion exchange process of 137Cs with the crystal lattice cations (i.e. Ca2+ and Mg2+) was the governing mechanism. Contrarily, bentonite heated forms are recommended sorbents for 85Sr, especially B-600. The outperformance of thermally treated bentonites reflected chemical bonding reaction with the surface OH groups as well as precipitation of Sr(OH)2.