Advances in Photocatalysis and Electrocatalysis of Uranium Extraction in Complex Environments

Abstract

Uranium, as the most important fuel for nuclear power operation, is crucial to ensure the sustainable development of nuclear power. However, the supply-demand contradiction of uranium resources in China has become increasingly prominent, and the gap needs to be filled by overseas development and international market procurement. The photoreduction and electroreduction of uranium under complex conditions are mainly targeted at uranium containing radioactive wastewater, real seawater, and other systems. Uranium containing radioactive wastewater comes from the processes of uranium mining, uranium enrichment, uranium conversion, and manufacture of nuclear fuel elements, with the characteristics of complex interfering ions. Although the total amount of uranium in seawater is very large, the concentration of uranium in seawater is low, making the extraction of uranium from seawater extremely challenging. On the one hand, the reserves of uranium in seawater are nearly a thousand times higher than those on land; on the other hand, the entire application process of the nuclear industry produces a large amount of uranium containing radioactive wastewater. If efficient separation of uranium from seawater and uranium containing radioactive wastewater can be achieved, it can promote the secondary supply of uranium resources and alleviate the supply-demand contradiction of uranium resources in China. Therefore, the development of uranium recovery and extraction technology from seawater and uranium containing radioactive wastewater is important for the sustainable development of the nuclear industry. This paper reviews the recent research progress in separating uranium in complex environments such as seawater and uranium containing radioactive wastewater. In terms of uranium speciation analysis, it describes the coordination environment of complex environmental uranyl and summarizes the advantages of photocatalysis and electrocatalysis in the fields of uranium extraction from uranium containing radioactive wastewater and seawater. In terms of designing photocatalysts, strategies such as element doping, metal loading, defect engineering, and introducing heterojunctions have been summarized for the preparation of photocatalytic semiconductor materials. The modification of functional groups on heterojunctions to regulate their energy band structure had introduced, which improved the overall performance of the material. The integration of selective adsorption and catalytic reduction, electrochemical methods can reduce soluble uranyl ions to neutral and insoluble products for separation, with advantages such as fast kinetics, wide extraction concentration range, and large separation capacity. However, there are also many key technical challenges in the practical application process, such as the competition between multiple cations and uranyl ions in complex systems, and the problem of excessive energy consumption caused by the competing reaction of water splitting during the cathodic uranium extraction process. In terms of electrocatalysis, various aspects such as electrode carrier selection, electrochemical device design, defect engineering, surface engineering, interface engineering, and microbial electrochemistry have been summarized to design electrocatalytic materials. In terms of key technical bottlenecks, combining photocatalysis and electrocatalysis technology with challenges in complex scenarios such as uranium speciation analysis, material functionalization design, intermediate reaction species analysis, uranium extraction mechanism analysis, cost control, and real-world application outcomes, relevant research have focused on challenges such as efficient photocatalytic reduction of uranium under natural light, identification of intermediate uranium species, uranium extraction from uranium containing radioactive wastewater, and seawater extraction from real ocean environments.

Keywords

• uranium resources
• seawater uranium extraction
• uranium containing radioactive wastewater extraction
• photocatalysis
• electrocatalysis