Extraction of Critical Elements–Gallium, Germanium, and Indium–Using Ionic Liquids: A Review

Gallium (Ga), germanium (Ge), and indium (In) are essential elements that are extensively used in high-technology products in many fields. These metals are listed as critical elements by many governments and private players because they face potential supply risks due to geopolitics and stockpiling. Gallium, germanium, and indium do not form primary minerals that can be economically exploited on their own. Instead, they are obtained as by-products during the primary extraction of other minerals, as well as from the processing of metallurgical and electronic waste. This review focuses on the extraction of these technologically critical elements from leach solutions of multiple sources using ionic liquids (ILs) with special emphasis on the extraction mechanism and selectivity criteria. Generally, many ILs reviewed have low selectivity toward Ga, Ge, and In compared to Fe(III), Al(III), and Zn(II), which are typically present in high concentrations. Rational design of task-specific ILs, ILs recycling, process scaling-up, and detailed economic viability studies need to be adequately investigated to accelerate the potential commercialization of ILs in the extraction of these critical materials.