Acid mine drainage may become a source for rare earth elements.
Article written by Debra McCown Thomas for Mining People Magazine.
The term “Rare Earth Elements” is somewhat of a misnomer. These elements – a group of 17 metals that are commonly used in producing electronics – aren’t actually all that rare.
“They’re in your backyard. If you dig it up and analyze your soil, you have rare earths there,” says Rick Honaker, professor in the University of Kentucky’s mining engineering department and principal investigator there for research on recovering REEs from coal refuse. “When you play in the sand in Florida, you are playing with rare earths because there are rare earths in that sand.”
The reason they’re called rare earths, Honaker says, is that it’s rare to find deposits that are economic to mine and process into usable form. As a result, the rising demand for these materials – which are critical for making things like electric cars, wind turbines, consumer electronics, and weapons systems – means people are looking for new sources of rare earth elements that can be processed economically in the US, a major piece of that effort is looking at potential REE sources associated with coal: coal refuse, coal ash, and acid mine drainage.
That’s because these sources have a relatively high concentration of REEs that are critically important, low in supply, and increasing in demand. Based on an assessment conducted by the U.S. Department of Energy and the National Energy Technology Laboratory, the amount of REEs that could be recovered from coal-based sources is substantial. The practical meaning of that, of course, depends on what it takes to recover them and the cost to do so relative to the price of the recovered material – but the research is very encouraging.
Since the effort began in earnest in 2014, important milestones have been reached at the University of Kentucky, West Virginia University, and others in developing and proving ways to process coal-based materials for REEs.
All three areas being looked at – acid mine drainage, coal refuse, and coal ash – could be promising domestic sources of rare earth elements, says Paul Ziemkiewicz, director of West Virginia University’s Water Research Institute, which has already built a successful pilot plant and has got the process well on its way to commercialization. “I want to see every one of these routes be successful in order to create a domestic supply chain,” Ziemkiewicz says. “Our next project – the one that we’re just starting now with DOE [the U.S. Department of Energy], we will build a roughly half-ton-a-year processing facility, and that will take acid mine drainage and create a pre-concentrate that we will then turn into a high-grade mixed rare earth oxide on site.
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