Adsorption of strontium on different sodium enriched bentonites

Bentonites from three different deposits (Wyoming, Texas and Bogovina), with similar cation exchange capacities were sodium enriched and tested as adsorbents for Sr 2+ ions in aqueous solutions. X-ray diffraction analysis confirmed successful Na-exchange. Textural properties of the bentonite samples were determined using low-temperature nitrogen physisorption method. Significant difference in textural properties between different sodium enriched bentonites was found. Adsorption was investigated with respect to adsorbent dosage, pH, contact time and initial Sr 2+ ions’ concentration. The adsorption capacity increased with pH. In the pH range from 4-8.5 the amount of adsorbed Sr 2+ was almost constant but 2-3 times smaller than at pH »11. Further experiments were carried out on unadjusted pH since the extreme alkaline conditions are environmentally hostile and inapplicable in real systems. The adsorption capacity of all investigated adsorbents toward Sr 2+ ions was similar under investigated conditions, regardless of significant differences in specific surface area. It was shown and confirmed by Dubinin-Rasdushkevich model that cation exchange mechanism is the dominant mechanism of Sr 2+ ions’ adsorption. Developed microporous structure contributed to the Sr 2+ adsorption process. Adsorption kinetics obeyed the pseudo-second-order model. The isotherm data were best fitted with Langmuir isotherm model.