Development of Fe3S4/Fe7S8 magnetic nanosheets and their selective and efficient extraction of uranium(VI) in seawater

It is of great strategic value for the recovery of uranium resources in seawater. In this work, Fe 3 S 4 /Fe 7 S 8 was synthesized by hydrothermal method to extract the radioactive nuclides of U(Ⅵ). Results of batch experiment discovered that Fe 3 S 4 /Fe 7 S 8 exhibited good U(Ⅵ) removal performance in a wide pH response range, and also had satisfactory selectivity towards uranyl ions even in the presence of co-existing ions (such as K + , Na + , Mg 2+ , Ca 2+ , Cl - , SO 4 2- ). At the temperature of 25°C and pH of 9, the adsorption achieved equilibrium after 120 min with the maximum adsorption capacity of 257.07 mg/g. In addition, the 5 successive adsorption-regeneration experiment and the real seawater experiment of trace U(Ⅵ) adsorption implied that Fe 3 S 4 /Fe 7 S 8 had outstanding reusability and practical application potential in U(Ⅵ) extraction. XRD results showed that the magnetic adsorbent was composed of Fe 3 S 4 and Fe 7 S 8 , with a high crystallinity and stable structure. The ratio of iron to sulfur was close to 7:8 according to semi-quantitative results of SEM-EDS . Further characterization analysis of FTIR and XPS revealed that the removal mechanism of Fe 3 S 4 /Fe 7 S 8 towards U(Ⅵ) mainly included the complexation of S(-Ⅱ), and the reduction of S 2− , S 2 2- and Fe(Ⅱ).