Recovery of rare earths from industrial waste residues: a concise review

Between 2000 and 2012, China has been producing more than 95% of the annual world supply of the rare-earth elements (REEs). Due to large and increasing domestic demands, China has introduced tight export quota for rare earths. These quota cause rare-earth supply risks outside China, but they also stimulate other countries to look for other rare-earth resources and to develop their own rare-earth industry. The shortage of rare earths stimulates the prospection for new rare-earth deposits, the development of new mines and the re-opening of older mines that had been closed in the past because of economic reasons. The supply risk of rare earths also provides a boost to the research on the recycling of rare earths from End-of-Life consumer goods. Up to now, rare-earth recycling (research) has focused on relatively small volumes of End-of-Life waste with a high REE content. However, rare-earths are also present in lower concentrations in a multitude of industrial residues. This review, therefore, discusses the possibilities to recover rare earths from residues such as pyrometallurgical slags, bauxite residue (red mud), phosphogypsum, mine tailings and waste water. All these waste streams have in common that they only have low REE concentrations, but are available in very large volumes. This implies that these industrial waste streams could provide significant amounts of rare earths, provided efficient recycling flow sheets can be developed.