Extraction of Rare Earth Elements from Coal Waste

Coal mining can pollute nearby waterways, producing acidic water that is rich in heavy metals. Researchers are seeking to use this coal waste to obtain rare earth elements.

In Appalachia's coal country, researchers envision turning toxic waste into wealth. The pollution left behind by abandoned mines is an untapped source of rare earth elements. Rare earths are a valuable set of 17 elements needed in everything from smartphones and electric cars to fluorescent lamps and lasers. As global demand surges and China has a near monopoly on rare earth production - with only one active mine in the U.S. - there is a strong interest in finding alternative sources, such as enhanced recycling.

Long after a coal mine closes, it can leave a dirty legacy. When some of the rocks left behind by mining are exposed to air and water, sulfuric acid is formed and heavy metals are extracted from the rocks. This acid soup can pollute waterways and harm wildlife. Paul Ziemkiewicz, director of the West Virginia Water Institute in Morgantown, acknowledges that recovering rare earths from so-called acid mine drainage doesn't fully meet the growing demand for the metals. But he points to several benefits.

Unlike ore dredged from a typical rare earth mine, coal waste is rich in the most desired rare earth elements. In addition, extraction from acid mine drainage does not produce the radioactive waste that is typically a byproduct of rare earth mines, which typically contain uranium and thorium. And from a practical standpoint, existing facilities for processing acid mine drainage could be used to collect rare earth for processing.

Ziemkiewicz and colleagues estimate that nearly 600 metric tons of rare earth elements and cobalt - another in-demand metal - could be produced annually from the several hundred sites that already treat acid mine drainage. A pilot project in West Virginia is currently using material recovered from an acid mine drainage treatment site to extract and concentrate rare earths.

Reference: https://www.sciencenews.org/article/coal-waste-rare-earth-elements-recycling

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