Design of new adsorbents using elemental sulfur and NaX Zeolite for selective removal of radioactive cesium

Abstract

To eliminate the radioactive cesium, $^{137}Cs^+$, various inorganic adsorbents have been investigated extensively. However, most of highly selective adsorbents are either too expensive or difficult to scale up because they are only focused on the additional interaction between $^{137}Cs^+$ and adsorbents. Although the conventional zeolites are economic and commercially available, they have critical drawback which is low selectivity under competitive conditions ($Na^+, K^+, Mg^{2+}, and Ca^{2+}$). Therefore, in this work, to develop low cost and highly selective adsorbent, we used a commercial NaX zeolite and elemental sulfur. We sublimated the elemental sulfur into the NaX zeolite and it increases the adsorption selectivity to $Cs^+$. Cs XPS analysis shows that the sulfur donates its lone pair of electrons to ion-exchanged $Cs^+$. The enhanced $Cs^+$ selectivity can be explained by HSAB (Hard Soft Acid Base) theory so that sulfur, one of the soft base, interacts more actively with $Cs^+$, relatively soft acid, than other alkali and alkaline earth metals ($Na^+, K^+, Mg^{2+}, and Ca^{2+}$).