Effective and Rapid Adsorption of Sr2+ Ions by a Hydrated Pentasodium Cluster Templated Zinc Thiostannate

Separation of 90 Sr from radioactive wastewater not only is essential for human public health and environmental remediation but also bears importance for alternate medical and industrial applications. Here, we report the facile synthesis of an open framework zinc thiostannate, Na 5 Zn 3.5 Sn 3.5 S 13 ·6H 2 O ( ZnSnS-1 ), templated by hydrated pentasodium clusters. This compound exhibits an effective and rapid ion exchange property for Sr 2+ ions. The exchange kinetics conforms to a pseudo-second-order model, implying that the chemical adsorption of Sr 2+ may be the rate-determining step. According to the Langmuir–Freundlich isotherm, the maximum exchange capacity of ZnSnS-1 for Sr 2+ is 124.2 mg/g and ranks ahead of those of all the reported metal sulfide Sr 2+ adsorbents. High exchange performance is observed over the broad pH range 2.5–13, although it could be inhibited to some extent by coexisting ions, especially Na + and Ca 2+ . ZnSnS-1 shows a higher affinity for Sr 2+ compared to Cs +, and the performance is almost unaffected by the presence of coexisting Cs + even in excess amounts. Importantly, the Sr 2+ in the exchanged product can be conveniently eluted by a concentrated KCl solution, and the recycled exchanger can be further used for Sr 2+ exchange. These advantages combined with the robust framework for recycling concerns make ZnSnS-1 a highly promising exchanger for removal of radioactive Sr from the liquid nuclear waste.