Construction Of Iron Oxide For Electrochemical Extraction Uranium From Seawater

As a fuel for nuclear power operation,uranium is the key to ensuring the sustainable development of nuclear power.The demand for uranium resources in China is expected to reach 1.0-2.0 million tons per year by 2030.There are 4.5 billion tons of uranium resources in the ocean,which is 1000 times that of land uranium mines.Therefore,the strategy of extracting uranium from seawater is an important guarantee for the sustainable development of nuclear energy resources and nuclear power industry in our country.The traditional extraction of uranium from seawater mainly adopts selective adsorption method,but the adsorption method has slow kinetics and low efficiency due to environmental factors such as many interfering ions in seawater and extremely low uranium concentration（3.3 ppb）.As a new method for extracting uranium from seawater,electrochemistry can significantly improve the adsorption capacity and extraction efficiency of materials by directional migration of ions through applied electric field.In the electrochemical extraction of uranium,the development of electrochemical catalysts with high active sites and high coordination activity for uranyl is the key to realize the electrochemical extraction of uranium from seawater.In this paper,iron-based oxide electrocatalysts are taken as the research object.By regulating the crystal plane and interface of iron-based oxides,the interaction between O^2-site and UO₂²⁺coordination bond is studied,and the structure-activity relationship between surface interface regulation and electrochemical seawater extraction efficiency of uranium is revealed.The main achievements of this paper are as follows:（1）Fe₃O₄ nanooctahedra catalyst with exposed{222}facets were prepared by hydrothermal method.The experimental results show that the extraction efficiency and extraction capacity of Fe₃O₄ nanooctahedra with exposed{222}facets are higher in 8 mg/L uranium solution.After 8 hours of electrochemical extraction in 8.0 mg/L uranium-spiked seawater,the extraction efficiency of Fe₃O₄ nanooctahedra can reach 91.0%,which is 1.5times that of Fe₃O₄ nanocubes.In 10.0 L natural seawater,the extraction amount of uranium by Fe₃O₄ nanooctahedra was 17.5μg in 8 hours,and the extraction amount was 3.5 mg/g.The theoretical model shows that the{222}facet of Fe₃O₄ has a suitable atomic spacing,forming a pocket composed of four O atoms and two Fe atoms.Such a pocket allows UO₂²⁺to bind to four O atoms,while the low-valent Fe atoms bind to the original two O atoms of UO₂²⁺.This binding model explains the more negative adsorption energy of UO₂²⁺on{222}facets than on{200}facets and the enhanced uranium extraction by Fe₃O₄ nanooctahedra.（2）By modifying the Fe₃O₄ nanooctahedra,an interface-bonded Fe₃O₄/MoS₂ catalyst was constructed,which was more excellent than the electrochemical uranium extraction performance of Fe₃O₄.In the electrochemical extraction of uranium,the electrochemical extraction efficiency of 7 hours can reach 96.0%.In 8.0 mg/L uranium-spiked seawater,the electrochemical extraction rate can reach 87.6%in 6 hours,and the efficiency in the early stage of the electrochemical extraction process can be improved,reaching 77.3%in the first hour.In the electrochemical test of 10.0 L natural seawater,the extraction rate reached more than 80.0%,and the extraction amount of uranium reached 27.2μg.Compared with Fe₃O₄nanooctahedra,the efficiency was significantly improved.Through the interface bonding of Fe₃O₄ and MoS₂,O^2-and S^2-are coordinated with UO₂²⁺,so that Fe₃O₄ and MoS₂ have a synergistic effect.And through the interface bonding to accelerate the electron transfer rate and the amount of electron transfer,greatly improve the extraction efficiency of uranium.In summary,through the regulation of Fe₃O₄ facets and interface,the performance of uranyl coordination reduction and electrochemical seawater extraction of uranium was improved.The influence mechanism of surface and interface atomic structure and electronic structure on uranyl coordination reduction was revealed,which provided theoretical guidance and technical support for the construction of efficient electrochemical seawater extraction of uranium electrode materials.