Modification of the structure of natural bentonite and study on the sorption of Cs+

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 (K_d). 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.

Sorption of 226Ra from waste effluents using Syrian bentonite

In view of environmental concern, sorption of radium on natural bentonite mineral (Aleppo, Syria) was investigated using a batch-type method. Data were expressed in terms of distribution coefficients. An attempt to increase the selectivity of bentonite for radium was made by preparing M-derivatives. Loss of mineral crystallinity in acidic media and the formation of a new phase, such as BaCO3, in Ba-derivative were evidenced by XRD characterizations. Of the cationic forms, Na-bentonite showed the highest affinity. Mechanisms of radium uptake were studied using M-derivatives and simulated radium solutions. The obtained results indicated that surface sorption/surface ion exchange were the predominant processes. The distinct sorption behaviour observed with the Ba-form was, possibly, a reflection of radium coprecipitation with barium carbonate. The competing order of macro components, likely present in waste streams, was investigated by studying different concentrations of the corresponding salt media. Sodium was found to be the weakest inhibitor. The performance of natural bentonite and the most selective forms, i.e. Ba- and Na-derivatives, to sorb radium from actual oil co-produced waters, collected form Der Ezzor Petroleum Company (DEZPC), was studied. This showed the influential effect ofpH compared with other parameters.