Selective Capture Mechanism of Radioactive Thorium from Highly Acidic Solution by a Layered Metal Sulfide.

Thorium as a potential nuclear fuel for the next-generation thorium-based molten salt reactors holds significant environmental and economic promise over the current uranium-based nuclear reactors. However, because thorium (Th) usually coexists with other rare earth elements, alkali or alkaline earth metals in minerals, or highly acidic radioactive waste, seeking acid-resistant sorbents with excellent selectivity, high capacity, and fast removal rate for Th is still a challenging task. In this work, we investigated a robust layered metal sulfide (KInSnS, KMS-5) for Th removal from strong acidic solutions. We report that KMS-5 could capture Th from a 0.1 M HNO solution with extremely high efficiency (∼99.9%), fast sorption kinetics (equilibrium time < 10 min), and large distribution coefficient (up to 1.5 × 10 mL/g). Furthermore, KMS-5 exhibited excellent sorption selectivity towards Th in the presence of large amounts of competitive metal ions like Eu, Na, and Ca. This extraordinary capture property for Th is attributed to the facile ion exchange of Th with K in the interlayers and subsequent formation of a stable coordination complex via Th-S bonds. These results indicate that KMS-5 is a promising functional sorbent for the effective capture of Th from highly acidic solutions.