Advances in Adsorption Materials and Coordination Mechanism of Functional Groups for Uranium Extraction from Seawater

Uranium is one of the most important elements in the development of nuclear industry. However, terrestrial uranium resources are limited and difficult to meet the development needs. Since seawater is rich in uranium resources (about 4.5x10(9) t), which is more than one thousand times of the known terrestrial uranium resources, how to extract uranium resources from seawater has attracted much attention. However, uranium exists in seawater in the stable carbonate of [UO2(CO3)(3)](4-), which has a very low concentration of 3.3 mu g/L, and the competitive ions especially for vanadium ions and biological contamination are serious obstacles to the extraction of uranium. Because of these complicated conditions of seawater and the extremely low concentration of uranium, uranium extraction from seawater faces many challenges. Many researchers have carried out a lot of studies, and various methods have been developed for the extraction of uranium from seawater. Among them, the adsorption method has been widely used in the extraction of uranium from seawater. This review focuses on the adsorption materials developed in recent years for uranium extraction from seawater, including inorganic materials, organic materials, inorganic-organic hybrid materials, and analyzes their advantages and disadvantages of the materials in terms of their adsorption capacity, selectivity, antimicrobial properties, stability, and recyclability. At the same time, the coordination mechanism of the typical functional groups such as amidoxime and carboxyl groups as well as other representative functional groups reported in recent years toward uranyl cations have been summarized, and the results show that in addition to amidoxime, other functional groups such as pentadentate chelating ligands also have good affinities for uranyl cations. Besides, the future development of uranium extraction materials from seawater is also prospected. This review is expected to improve our current understanding of the interaction mechanism of functional groups toward uranyl cations, and provide references for the development of efficient materials for uranium extraction from seawater.