Sulfur-modified chabazite as a low-cost ion exchanger for the highly selective and simultaneous removal of cesium and strontium

Low-cost inorganic ion-exchange materials with improved Cs+ and Sr2+ selectivities are of great interest for the treatment of various radioactive liquid wastes. Here the sulfur-modified chabazite (CHA) was formed by the simple encapsulation of elemental sulfur in the micropores of CHA for the cost-effective simultaneous removal of Cs+ and Sr2+. Our results showed that the Cs+ selectivity increased as the sulfur loading increased because of the enhanced Lewis acid - base interaction between sulfur and Cs+. On the other hand Sr2+ selectivity slightly increased with sulfur loading up to 5 wt% and decreased thereafter. Consequently distribution coefficients (K-d) of CHA containing 5 wt% sulfur (5S-CHA) are 3 x 10(6) mL/g for Cs+ and 2 x 105 mL/g for Sr2+ which are higher than those of previously reported Cs+ and Sr2+ ion-exchange materials. Moreover the 5S-CHA exhibited excellent simultaneous removal performances for Cs-137 and Sr-90 in simulated groundwater with Kd values of 9.1 x 10(4) mL/g for Cs-137 and 7.8 x 10(4) mL/g for Sr-90 which are much higher than or similar to those of commercial CHA and crystalline silicotitanate. Due to the easily scalable procedure using commercially available zeolites and very cheap elemental sulfur 5S-CHA has excellent potential for the treatment of a large volume of Cs-137- and Sr-90-contaminated water.