Recent Advances in the Application of Greener Solvents for Extraction, Recovery and Dissolution of Precious Metals and Rare Earth Elements from Different Matrices

The demand for precious and rare earth elements is gradually increasing mainly due to the advancement in their various industrial applications. However, the mining industry is facing challenges of natural resource depletion and it is predicted that in the near future there will be no natural sources of these metals. Therefore, several studies have been conducted to recover precious and rare earth elements from secondary resources such as spent industrial catalysts, jewellery, magnets, automobile parts, and electronic and industrial effluents. For this reason, solvent extraction using ionic liquids has attracted a lot of attention. This is because ionic liquids have improved properties such as non-volatility, non-flammability and low toxicity (when compared with tradition organic solvents used in the recovery of precious metals and rare earth elements). In addition, ionic liquids can be used to separate, extract and recover ionic species without the aid of a ligand, thus rendering them as the best ion-exchange extractants. In this chapter, the application of ionic liquids for the extraction, dissolution and recovery of precious metals and rare earth elements from waste (secondary resources) is reviewed. Special attention is given to solvent extraction which has proven to be one of the most widely used methodologies for metal recovery. This is due to the attractive features such as simplicity, flexibility and rapidity. Application of deep eutectic solvents (known to be greener than traditional ionic liquids) has been discussed to tackle existing challenges of ionic liquids.