In the quest for sustainable and abundant energy resources, the extraction of uranium from seawater has emerged as a promising avenue. Uranium, a key component in nuclear fuel, is traditionally obtained from terrestrial ores. However, as demand for nuclear energy rises and concerns about the environmental impact of conventional mining grow, researchers are exploring innovative methods to harness the vast uranium reservoirs present in seawater.
Seawater is an immense reservoir of uranium, with estimates suggesting that it contains approximately 4.5 billion metric tons of this valuable resource. While the concentration of uranium in seawater is low— about 3 parts per billion—it represents a virtually limitless supply compared to the finite terrestrial uranium deposits. Several techniques have been explored to extract uranium from seawater, each with its advantages and challenges. The most common modes include absorption onto materials like amidoxime-based polymers, ion exchange resins and advanced materials like metal-organic frameworks (MOFs).
A recent breakthrough published in ACS Central Science introduces a novel material designed to significantly enhance the electrochemical extraction of hard-to-get uranium ions from seawater. To create their electrode, Rui Zhao, Guangshan Zhu and team began with flexible cloth woven from carbon fibre. This cloth then underwent a coating process involving two specialised monomers, subsequently polymerised for stability. Following this, hydroxylamine hydrochloride treatment was applied to introduce amidoxime groups to the polymer cloth. The inherent porous nature of the cloth facilitated the creation of numerous miniscule pockets, providing an ideal environment for amidoxime to easily entrap uranyl ions.
In the experimental setting, the researchers utilised the coated cloth as a cathode in seawater obtained either naturally or spiked with uranium. A graphite anode was introduced, and a cyclic current was established between the electrodes. Over time, bright yellow, uranium-based precipitates accumulated on the cathode cloth. Upon reaching its saturation, the cloth undergoes a chemical treatment process to release the uranyl. Subsequently, the liberated uranyl must further undergo refining procedures akin to those employed for ore extracted from a conventional mine, before it can be utilised in reactors.
In the tests using seawater sourced from the Bohai Sea, near Northern China, the electrodes extracted 12.6 milligrams of uranium per gram of the coated active material within a 24-day period. The capacity of the coated material surpassed that of the majority of the other materials tested for uranium extraction by the team. Additionally, the application of electrochemistry for ion entrapment proved to be approximately three times faster than the natural accumulation process on the cloth.
Pros and cons
The advantages of this material lie in its simplicity, affordability, reusability and eco-friendly nature. It does not require any chemical additives or catalysts and does not generate any harmful by-products or waste. Moreover, it also has a high selectivity for uranium over other metals and ions in seawater.
Nevertheless, it harbours certain drawbacks that impede its practical utilisation and scalability. Since there is a low uranium concentration in seawater, the material needs to be deployed in large volumes of water to achieve significant uranium extraction, hindering its efficiency. The material’s sensitivity to the pH and salinity conditions of seawater also impacts its stability and performance. This requires careful control and adjustment of operating parameters to ensure optimal functionality. Additionally, there exists a possibility that the material may not capture all uranium ions in seawater, particularly those bound to other elements or molecules, leading to incomplete or inefficient uranium extraction.
Unique Uranium
Uranium (symbol U and atomic numbver 92) is a silvery-grey metallic element in the actinide series of the Periodic Table
A new possibility
The researchers assert that their work presents a highly effective technique for capturing uranium from seawater, potentially unlocking the oceans as novel reservoirs of nuclear fuel. The heightened efficiency and capacity of the developed electrodes position them as promising candidates for widespread implementation, contributing to the sustainable and economically feasible extraction of uranium from seawater. The findings hold significant implications for the future of nuclear energy, offering a cleaner and more accessible source of fuel.