Though controversial in some cases, nuclear energy plays a big role in powering homes and grids across the United States. Reactors are up and running in 30 US states, and nuclear energy accounted for 19.5 percent of all electricity generated in the United States in 2015.
One of the necessary components used to generate nuclear energy is uranium, whose abundance is far greater than originally perceived. There are 7.6 million tons of uranium land deposits around the world, but a bigger untapped resource is the amount of uranium in our oceans. Between weathering and underwater deposits, there’s an estimated 4.5 billion tons of dissolved metal particles in seawater, which contains enough uranium for nuclear power plants to run on for centuries (not to mention the positive effect this would have on the environment).
While those numbers seem staggering, the individualized concentration of uranium particles in seawater is only 3 μg/l, which makes finding applicable extraction methods a daunting challenge for researchers. One of the popularly used methods of harvesting uranium from seawater is through electrochemical methods, which researchers at Stanford University in California have been studying.
The Stanford team successfully obtained uranium from seawater through a technique where a polymer-carbon electrode is used, and a pulsed electric field is applied. Since uranium usually exists in seawater as a positively charged uranium oxide compound (uranyl), most extraction methods will use adsorbent material like amidoxime polymers, where uranyl attaches (but not chemically react) to the surface.
Due to the limited number of absorption sites, the performance of this process is usually limited, especially considering how uranium concentrations are so low when compared to positively charged ions like calcium and sodium. Because of how slow interactions involving uranium absorption are, most sites are quickly occupied by these positively charged ions. The absorbed ions still carry a positive charge, and will repel uranyl ions from the material.
The electrochemical cell contains an electrolyte solution, along with two submerged electrodes that are connected to a power source. Driven through liquid by giving electrodes opposite charges, the electrical current forces positive ions to the negative electrode, while electrons and negative ions are drawn to the positive electrode. Upon attaching to the anode, the positive ions are reduced and gain electrons. The solid metal precipitates and deposits on the surface of the electrodes.
The team then used the carbon-coated anodes with amidoxime polymer and inert polymer electrode inside the electrochemical cell. The electrolyte involved was seawater, which (in some tests) contained traces of uranium. Positive uranyl, along with calcium and sodium ions were drawn to the carbon-polymer electrode through applying a short current pulse.
Amidoxime film prompted uranyl to be absorbed over other ions, which were reduced to charge-neutral uranium oxide in a solid state. Once the current was switched off, these excess ions returned to the bulk of other electrodes. The electrochemical cell outperformed the traditional material in tests. The carbon-polymer electrode extracted nine times as much uranium during the time it took the amidoxime surface to saturate.
The research team was encouraged when 96.6 percent of metal could be recovered from the surface through the application of a reverse current and acidic electrolyte, while only 76 percent could be recovered with an adsorption metal. While the results are encouraging, the research team at Stanford University knows they still have a very long way to go if they want to maximize the efficiency of their methods at extracting uranium from seawater using these methods in greater amounts.
Filed Under: M2M (machine to machine)