A review on the recovery and separation of rare earths and transition metals from secondary resources

The continuous miniaturization of modern green and advanced technologies is increasing the demand of rare earth elements (REEs). Consequently, REEs are listed as the critical metals concerning their crucial role for a clean environment. However, their resources are limited which in turn disrupt their supply chain. To tackle the supply issue and to meet future demand, there is need to exploit recycling schemes for the recovery REEs from secondary resources. This review describes comprehensively various processes developed for the separation of REEs and transition metals from secondary resources. It focuses on the hydrometallurgical route, especially solvent extraction employed to separate REEs and transition metals from potential wastes originated from different industries. The use of different commercial extractants for the recycling purposes and mechanisms involved in the extraction has been discussed in detail. (C) 2019 Elsevier Ltd. All rights reserved.