Application of phosphonium ionic liquids to separate Ga, Ge and In utilizing solvent extraction: A review

Due to the sudden rise in demand, a shortfall in the supply of critical metals or high technology metals, especially gallium (Ga), germanium (Ge) and indium (In) is experienced throughout the globe. The different primary and secondary resources are being utilized to recover and recycle these metals through the widely accepted technique, solvent extraction (SX). The extraction of metals may be potentially achieved by compounds of negligible volatility, phosphonium ionic liquids (Phos ILs). Ionic liquids (ILs) are potential and useful compounds to separate and recover Ga, Ge and In from synthetic solutions and waste materials due to their tunable nature to achieve higher selectivity, superior physicochemical properties and diverse structural properties. Ion exchange mechanism was mainly found applicable for the extractive separation of such metals through Phos ILs. Based on the efficiency, extraction mechanism and diverse operating conditions of Phos ILs, the present review provides a comprehensive description of separation as well as recovery of Ga, Ge and In from the synthetic solutions as well as waste materials.