Abstract
Rare earth elements (REEs) are becoming more and more significant as they play crucial roles in many advanced technologies. Therefore, the development of optimized processes for their recovery, whether from primary resources or from secondary sources, has become necessary, including recovery from mine tailings, recycling of end-of-life products and urban and industrial waste. Ionic solvents, including ionic liquids (ILs) and deep-eutectic solvents (DESs), have attracted much attention since they represent an alternative to conventional processes for metal recovery. These systems are used as reactive agents in leaching and extraction processes. The most significant studies reported in the last decade regarding the recovery of REEs are presented in this review.
Highlights
These systems are used as reactive agents in leaching and extraction processes
The elements from samarium to terbium are considered as the “middle rare earth elements” (MREEs) [2]
In conventional approaches applied for metal extraction, ionic liquids (ILs) are usually hydrophobic interact through hydrogen bonding, which leads to charge delocalization resulting in a to avoid their miscibility in the aqueous phases
Summary
Rare earth elements (REEs) as defined by the International Union of Pure and Applied. Phosphogypsum, which is a waste generated by the fertilizer these elements from coal and coal combustion by-products (coal fly ash) and the feasibility industry, has been identified as a significant source of REEs due to presence of these eleand implementation of industrial processes are under study [29,30]. The so-called “pregnant leach solutions” are subjected to an extraction/separation step using solvent extraction, ion exchange and/or precipitation [37] Among such separation techniques, solvent extraction or liquid–liquid extraction is the most commonly used process for the recovery of REEs from the different sources (primary and secondary mining, waste streams, end-of-life materials and so on). Elimination or replacement of hazardous solvents in terms of toxicity and flammability, which has a clear impact on worker safety and environmental issues, is one of the main challenges for metallurgical processes
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