Electrokinetic mining reduces environmentally harmful mining of rare earths

A scientific team of metallurgists and geochemists from the Guangzhou Institute of Geochemistry has improved an older concept developed by a mechanical engineer from the Chinese Academy of Sciences to make the mining of rare earths more environmentally friendly. In collaboration with the engineer, the scientists have adapted his electrokinetic mining technology so that it can be used on an industrial scale. Initial tests in a mine have confirmed the ecological effectiveness of the process.

Rare earths are needed in many technical devices such as computers, smartphones and electric cars. However, the mining of this raw material is highly damaging to the environment. In order to extract the rare material, huge quantities of rock have to be moved and mixed with extreme amounts of water and various toxic chemicals to bring them to the surface. This leads to severe environmental pollution in the relevant mining areas and results in the ecological destruction of entire regions. In addition, thousands of tons of toxic waste are difficult to dispose of.

The Chinese scientific team has now refined the electrokinetic mining technique and scaled it up to an industrially usable process, as they describe in the study "Industrial-scale sustainable rare earth mining enabled by electrokinetics", which has been published in Nature Sustainability.

The mining method uses an underground electric field that is generated underground using conductive plastic electrodes (Conductive Plastic Electrodes – CPE). The electrodes consist of a mix of plastic and conductive material. They can be easily cut to the required lengths and are inserted individually into several boreholes. Ammonium sulphate is also injected into the mine around the boreholes.

A large amount of electricity is required to activate the electrodes and build up an electric field between the positively and negatively charged electrodes. Once it has been built up, the electric field moves the rare elements towards the negative cathode. This concentrates them more in one place and only a small proportion of the deposits need to be mined at any one time.

High efficiency

The scientists have already tested the process in practice. They placed a total of 176 CPEs in a mining area. Conventional methods achieve an efficiency of between 40 and 60 percent. With the electrokinetic technique, the efficiency could be increased to 95 percent. In addition, conventional processes also produce ammonia emissions. These could be reduced by 95 percent with the new process.

However, the researchers concede that the high energy consumption required to generate the underground electric field can negate the ecological balance if the energy is obtained from fossil fuels. The scientists therefore recommend obtaining the necessary electricity from renewable energy sources.

(olb)