Highly Efficient Separation of Trivalent Minor Actinides by a Layered Metal Sulfide (KInSn₂S₆) from Acidic Radioactive Waste

The elimination of trivalent minor actinides (Am³⁺, Cm³⁺) is of great concern for the safe management and operation of nuclear waste geological repository and environmental remediation. However, because of the effects of protonation, most of the present sorbents exhibit inferior removal properties toward minor actinides at low pH values. Finding stable ion-exchangers with high sorption capacities, fast kinetics, and good removal toward minor actinides from highly acidic solution remains a great challenge. This work reports a new family member of KMS materials with a robust acid-stable layered metal sulfide structure (KInSn₂S₆, KMS-5) bearing strong affinity toward trivalent minor actinides. KMS-5 can simultaneously separate trivalent ²⁴¹Am and ¹⁵²Eu from acidic solutions below pH 2 with high efficiency (>98%). The ion-exchange kinetics is extremely fast (<10 min) and the largest distribution coefficient is as high as 5.91 × 10⁴ mL/g. KMS-5 is also capable of efficiently removing ²⁴¹Am from acidic solution containing various competitive cations in large excess. In addition, the ion exchange process of ²⁴¹Am by KMS-5 is reversible and the loaded material can be easily eluted by high concentration of potassium chloride. This work represents the first case for efficient minor actinides removal from highly acidic solution using layered metal sulfide materials.