Efficient radiocobalt removal from seawater and radioactive liquid waste using a radiation-stable layered metal sulfide ion exchanger

Radiocobalt (e.g., 58 Co and 60 Co), a critical neutron-activated corrosion product in the nuclear industry, poses great challenges due to high toxicity. Effective removal of radioactive Co 2+ from complex environments is significantly urgent. Metal sulfide ion exchangers (MSIEs) are promising adsorbents; however, limited research has focused on Co 2+ removal, especially from seawater and real-world radioactive waste. Herein, a layered K 2 Cu 2 Sn 2 S 6 (CTS-1) was reported for the efficient capture of Co 2+ . The charge-balancing K + ions are exchangeable, endowing CTS-1 with Co 2+ capture ability via an ion exchange mechanism. This mechanism leads to the releasing K + into solution and concurrently immobilizing Co 2+ , which was confirmed macroscopically and microscopically. CTS-1 exhibited Langmuir maximum adsorption capacities of 33.96 and 20.72 mg/g in deionized water and seawater at 25 °C, respectively; the overall adsorption kinetics were similar in both matrices. CTS-1 displayed excellent pH durability with >99 % removal of Co 2+ at pH 4–8 and high selectivity for Co 2+ in various natural matrices. Impressively, in seawater ( C 0 Co  = 5 mg/L), CTS-1 achieved 97.38 % of Co 2+ removal with a distribution coefficient ( K d ) up to 3.817 × 10 4  mL/g, surpassing many existing adsorbents. Furthermore, CTS-1 exhibited radiation resistance; its structure and adsorption performance remained largely unchanged after a gamma radiation dose of 200 kGy. CTS-1 demonstrated the ability to remove nearly 99 % of radiocobalt from real-world radioactive wastewater, while also showing removal efficiency for other radionuclides like 51 Cr and 58 Mn. Overall, this work provides a highly promising material to tackle radiocobalt contamination in radioactive waste, greatly promoting environmental protection and safety for the radioactive industry.