Efficient Removal and Recovery of Uranium by a Layered Organic–Inorganic Hybrid Thiostannate

Abstract

Uranium is important in the nuclear fuel cycle both as an energy source and as radioactive waste. It is of vital importance to recover uranium from nuclear waste solutions for further treatment and disposal. Herein we present the first chalcogenide example, (Me₂NH₂)_1.33(Me₃NH)_0.67Sn₃S₇·1.25H₂O (FJSM-SnS), in which organic amine cations can be used for selective UO₂²⁺ ion-exchange. The UO₂²⁺-exchange kinetics perfectly conforms to pseudo-second-order reaction, which is observed for the first time in a chalcogenide ion-exchanger. This reveals the chemical adsorption process and its ion-exchange mechanism. FJSM-SnS has excellent pH stability in both strongly acidic and basic environments (pH = 2.1–11), with a maximum uranium-exchange capacity of 338.43 mg/g. It can efficiently capture UO₂²⁺ ions in the presence of high concentrations of Na⁺, Ca²⁺, or HCO₃^– (the highest distribution coefficient K_d value reached 4.28 × 10⁴ mL/g). The material is also very effective in removing of trace levels of U in the presence of excess Na⁺ (the relative amounts of U removed are close to 100%). The UO₂²⁺···S^2– interactions are the basis for the high selectivity. Importantly, the uranyl ion in the exchanged products could be easily eluted with an environmentally friendly method, by treating the UO₂²⁺-laden materials with a concentrated KCl solution. These advantages coupled with the very high loading capacity, low cost, environmentally friendly nature, and facile synthesis make FJSM-SnS a new promising remediation material for removal of radioactive U from nuclear waste solutions.