Researchers are trying to figure out how to extract rare earths from coal ash, which could yield 11 million tons of rare earths for the U.S.Coal ash is a toxic byproduct of coal-fired power plants. Contrary to their name, rare earth metals aren’t actually rare. This means coal ash contains four to 10 times the amount of rare earths than coal mined straight from the ground. Processing coal ash for rare earths could be part of a remediation process to prevent coal ash contamination of water supplies, Bagdonas adds. If successful, Scanlon says, mining rare earths from coal ash would be the ultimate “trash to treasure.”