Critical metal recovery potential of Appalachian acid mine drainage treatment solids

Rare earth elements (REE) are critically important in clean energy technologies, but their mining and refining is energy intensive and generates significant quantities of environmentally harmful waste. The treatment of acid mine drainage (AMD), which is both a global environmental problem and a potential source of these elements, preconcentrates REE and critical metals such as manganese and cobalt into oxide/hydroxide waste products from which they can potentially be recovered. Analysis of 281 treatment solids from coal AMD remediation systems across the northern Appalachian Basin, eastern USA, indicate that the most promising solids (REE value $400 USD/metric ton) are produced in systems that use limestone or sodium hydroxide to treat low pH (< 5) AMD with elevated dissolved aluminum and manganese content. In particular, recovering REE from passive treatment systems could both subsidize treatment of AMD while reducing the environmental footprint of REE extraction.