Separation
of 90Sr 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,
Na5Zn3.5Sn3.5S13·6H2O (ZnSnS-1), templated by hydrated pentasodium
clusters. This compound exhibits an effective and rapid ion exchange
property for Sr2+ ions. The exchange kinetics conforms
to a pseudo-second-order model, implying that the chemical adsorption
of Sr2+ may be the rate-determining step. According to
the Langmuir–Freundlich isotherm, the maximum exchange capacity
of ZnSnS-1 for Sr2+ is 124.2 mg/g and ranks
ahead of those of all the reported metal sulfide Sr2+ 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 Ca2+. ZnSnS-1 shows a higher affinity for Sr2+ compared to Cs+, and the performance is almost unaffected by the presence of coexisting
Cs+ even in excess amounts. Importantly, the Sr2+ in the exchanged product can be conveniently eluted by a concentrated
KCl solution, and the recycled exchanger can be further used for Sr2+ 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.