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

Abstract

Radiocobalt (e.g., ⁵⁸Co and ⁶⁰Co), a critical neutron-activated corrosion product in the nuclear industry, poses great challenges due to high toxicity. Effective removal of radioactive Co²⁺ from complex environments is significantly urgent. Metal sulfide ion exchangers (MSIEs) are promising adsorbents; however, limited research has focused on Co²⁺ removal, especially from seawater and real-world radioactive waste. Herein, a layered K₂Cu₂Sn₂S₆ (CTS-1) was reported for the efficient capture of Co²⁺. The charge-balancing K⁺ ions are exchangeable, endowing CTS-1 with Co²⁺ capture ability via an ion exchange mechanism. This mechanism leads to the releasing K⁺ into solution and concurrently immobilizing Co²⁺, 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 Co²⁺ at pH 4–8 and high selectivity for Co²⁺ in various natural matrices. Impressively, in seawater (C₀^Co = 5 mg/L), CTS-1 achieved 97.38 % of Co²⁺ removal with a distribution coefficient (K_d) up to 3.817 × 10⁴ 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 ⁵¹Cr and ⁵⁸Mn. 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.