Sorption of strontium on bentonite

Sorption of Sr on bentonite was studied using the batch technique. Distribution coefficients (K-d) were determined as a function of contact time, pH, sorbent and sorbate concentration and temperature. The data were interpreted in terms of Freundlich, Langmuir and Dubinin-Radushkevich isotherms. Thermodynamic parameters for the sorption system were determined at three different temperatures. The positive value of the heat of sorption, Delta H degrees = 30.62 kJ/mol at 298 K, shows that the sorption of strontium on bentonite is endothermic. The negative value of the free energy of sorption, Delta G degrees = -10.69 kJ/mol at 298 K, shows the spontaneity of the reaction. Delta G degrees becomes more negative with increasing temperature, which shows that the sorption process is more favorable at higher temperatures. The mean free energy for sorption, E similar to 9 kJ/mol, suggests that ion exchange is the predominant mode of sorption in the Sr concentration range studied, i.e. 0.01-0.3 mol/dm(3). The presence of complementary cations depresses the sorption of strontium on bentonite in the order Ca2+>Mg2+>K+>Na+. Some organic complexing agents and natural ligands also affect the sorption of strontium. The desorption studies with ground water at low strontium loadings on bentonite show that about 90% of Sr is irreversibly sorbed on the bentonite. Copyright (C) 1996 Elsevier Science Ltd