Towards zero-waste valorisation of rare-earth-containing industrial process residues: a critical review

The supply risk for some critical rare-earth elements (REEs), which are instrumental in many cleantech applications, has sparked the development of innovative recycling schemes for End-of-Life fluorescent lamps, permanent magnets and nickel metal hydride batteries. These waste fractions represent relatively small volumes, albeit with relatively high rare-earth contents. Rare earths are also present in lower concentrations in a multitude of industrial process residues, such as phosphogypsum, bauxite residue (red mud), mine tailings, metallurgical slags, coal ash, incinerator ash and waste water streams. This review discusses the possibilities to recover rare earths from these “secondary resources”, which have in common that they contain only low concentrations of rare-earth elements, but are available in very large volumes and could provide significant amounts of rare earths. The success rate is set to increase if the rare-earth recovery from these industrial waste streams is part of a comprehensive, zero-waste, “product-centric” valorisation scheme, in which applications are found for the residual fractions that are obtained after removal of not only the rare earths but also other valuable (base) metals.