Electrokinetic rare earth mining technique gets upscaled to industrial levels

A team of metallurgists and geochemists at Guangzhou Institute of Geochemistry, working with a mechanical engineer from the Chinese Academy of Sciences, has improved their previous electrokinetic mining technique by scaling it up to industrial levels. In their paper published in Nature Sustainability, the group describes the changes they made to their system, and the results of testing they conducted at a mine.

Modern technology is reliant on multiple rare earth elements—they are used in EVs, smartphones and computers, for example. Unfortunately, mining such elements is extremely environmentally unfriendly. Huge machines are used to dig dirt and rock from large mines, where it is mixed with water and a host of toxic chemicals in order to extract the desired elements.

The process produces thousands of metric tons of toxic waste. The team in China has been working for several years to develop a cleaner way to extract the elements. It involves generating an electric field underground that coaxes the desired elements closer together and concentrates them, making for a much easier and cleaner separation process.

The new technique works courtesy of conductive plastic electrodes (CPEs) the team developed. Each is made from a blend of plastic and conductive material and can be cut to a desired length. Once ready for use, multiple holes are drilled and individual CPEs are dropped into each one. Next, ammonium sulfate is injected into the ore deposit at the site where all the CPEs have been placed.

The electrodes are activated via an external electricity source—doing so generates an electric field in the deposit between positive and negatively charged electrodes. The electrically charged field serves to move the rare elements toward the negative cathode, causing them to be concentrated, which allows for removing just that part of the ore deposit holding the concentrated elements.

Testing at a site with 176 CPEs showed the process reduced ammonia emissions by 95%. The researchers also found the technique to be 95% efficient in extracting the rare earth elements from a given mining site, a major improvement over conventional techniques that tend to achieve 40 to 60% efficiency. The researchers note that for the process to be cleaner, a renewable electric source must be used, because it uses a lot more electricity than conventional techniques.

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