India, Jan. 23 -- Across Appalachia, rust-colored water seeps from abandoned coal mines, staining rocks orange and coating stream beds with metals. These acidic discharges, known as acid mine drainage, are among the region's most persistent environmental problems. They disrupt aquatic life, corrode pipes and can contaminate drinking water for decades.

However, hidden in that orange drainage are valuable metals known as rare earth elements that are vital for many technologies the US relies on, including smartphones, wind turbines and military jets. In fact, studies have found that the concentrations of rare earths in acid mine waste can be comparable to the amount in ores mined to extract rare earths.

Scientists estimate that more than 1...