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 UO2(2+) ion-exchange. The UO2(2+)-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 UO2(2+) ions in the presence of high concentrations of Na(+), Ca(2+), or HCO3(-) (the highest distribution coefficient Kd value reached 4.28 × 10(4) 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 UO2(2+)···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 UO2(2+)-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.

Unconventional ion exchangers can achieve efficient removal of [UO], Cs, and Sr ions from complex aqueous solutions and are of great interest for environmental remediation. We report two new gallium thioantimonates, [MeNH][GaSbS]·HO (FJSM-GAS-1) and [EtNH][GaSbS]·HO (FJSM-GAS-2), which present excellent ion exchange properties for [UO], Cs, and Sr ions. They exhibit high ion exchange capacities for [UO], Cs, and Sr ions ( q = 196 mg/g, q = 164 mg/g, and q = 80 mg/g for FJSM-GAS-1, q = 144 mg/g for FJSM-GAS-2) and short equilibrium times for [UO] ion exchange (5 min for FJSM-GAS-1 and 15 min for FJSM-GAS-2, respectively). Both compounds display active ion exchange with [UO] in the pH range of 2.9-10.5. Moreover, the sulfide compounds could maintain high distribution coefficients K even in the presence of excess Na, Ca, and HCO. The distribution coefficient K of 6.06 × 10 mL/g exhibited by FJSM-GAS-1 is the highest among the reported U adsorbents. The [UO]-laden products can be recycled by conveniently eluting the uranium with a low-cost method. These advantages combined with facile synthesis, as well as β and γ radiation resistance, make FJSM-GAS-1 and FJSM-GAS-2 promising for selective separations in nuclear waste remediation.

Exploring new ion-exchangers for the recovery of rare earth elements (REEs) and recycling is worthwhile for the high-tech industry and an eco-friendly sustainable economy. The efficient enrichment of low concentration REE from complex aqueous solutions containing large excess of competitive ions is challenging. Here we present a chalcogenide example as a superior REE ion-exchanger efficiently removing them from very complex aqueous solutions, (MeNH)(MeNH) SnS·1.25HO (FJSM-SnS). The material exhibits fast and efficient ion exchange behavior with short equilibrium time (<5 min), high adsorption capacity (139 mg/g for Eu, 147 mg/g for Tb, 126 mg/g for Nd), wide pH resistance (1.9-8.5), the largest distribution coefficient (K) value of 6.5 × 10 mL/g, good selectivity against Al, Fe, and Na ions, and high recovery rate (>99%) at low concentrations. Moreover, after ion-exchange, the REE in corresponding exchanged products could be easily recovered by elution. FJSM-SnS has superior capacity and faster absorption kinetics than other states of the artificial REE sorbents such as AlO/EG, clay minerals, zeolite, and activated carbon.