| Nuclear energy is expected to become the best choice to replace fossil fuels due to its advantages of clean environmental protection,low cost and high energy density.The most critical element in nuclear energy is uranium,so how to recover and enrich uranium from nature is the biggest problem.Due to the limited uranium reserves in terrestrial minerals,researchers gradually turned their attention from land to sea.It is well known that the traditional physical adsorption method has the limitation of poor selectivity and low efficiency.On the country,the electrochemical extraction method with large adsorption capacity,fast adsorption speed and other advantages gradually attracted the attention of researchers.In this work,a series of iron or copper metal-based nanomaterials and their derivatives were prepared for the purpose of designing efficient electrochemical uranium extraction materials and clarifying the mechanism of electrochemical uranium extraction.The performance and mechanism of electrochemical uranium extraction from seawater were systematically investigated.（1）Nano reduced iron powder（NRI）was prepared by reducing iron trichloride with sodium borohydride.The whole process of uranium extraction was tracked by in situ physical characterization,and the application of electrochemical iron cycle（EIC）mechanism in seawater uranium extraction was also investigated.On the one hand,the evolution of species and valence states on the electrode surface during the electrochemical uranium extraction process was revealed by means of quasi-in-situ XRD,quasi-in-situ XPS and in-situ Raman.On the other hand,the rationality of electrochemical iron cycle mechanism was proved by XPS experiment.The extraction capacity and removal efficiency of NRI under EIC mechanism were nearly 5 times higher than those of traditional physical adsorption.In the seawater containing20 and 50 ppm uranyl ions with agitation under the voltage of-0.1 V,the extraction capacities were 456.37 and 528.54 mg·g-1,respectively,and the removal rates were close to 100 and52.22%,respectively.This work deepened the understanding of electrochemical seawater uranium extraction from transition metal-based nanomaterials.（2）Based on the understanding of EIC mechanism,sulfur doping modification was carried out on the basis of reduced iron powder,and Fe S@Fe nanomaterial with excellent performance was obtained.On the one hand,the addition of sulfur improved the surface roughness of nano-reduced iron powder,which was beneficial to capture uranyl ions in solution.On the other hand,the Fe S nanosheets could increase the contact area between the nanoreduced iron powder and the solution,which was conducive to the reduction of uranyl ions.The evolution of species and valence states on electrode surface during electrochemical recovery was revealed by in-situ Raman,quasi-in-situ XPS and XRD.In addition,the electrochemical uranium extraction performance of Fe S@Fe was better than that of nano iron powder.In the seawater containing20 and 50 ppm uranyl ions with agitation under the voltage of-0.1 V,the extraction capacity were 456.37 mg·g-1 and 755.03 mg·g-1,and the removal rate were close to 100 and 74.60%,respectively.The results show that Fe S@Fe has excellent performance of uranium extraction and certain advantage.（3）Nano reduced copper powder（NRC）was prepared by sodium borohydride reduction method.Through basic clear physical characterization such as XRD,quasi in-situ XPS and Raman,the uranium extraction mechanism of NRC was explored.In other words,the nano copper powder reduced the uranyl ions in the solution to uranium oxide and deposits on the electrode surface,and the nano copper powder itself was oxidized to copper ore or copper oxide.Based on its strong reducing ability,NRC electrode also showed good recovery performance in seawater by applying a reasonable potential.In the seawater containing 50 ppm uranyl ions with agitation under the voltage of-0.9 V,the extraction capacity was 651.93 mg·g-1,and the removal rate was close to 57.66%. |
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