Indium and Gallium Extraction using Ionic liquids: Experimental and Theoretical Study

Due to their remarkable properties, indium (In) and gallium (Ga) have been used extensively over the last two decades in the production of new electronic devices and semiconductors. Yet natural resources of these critical metals are scarce, and even more so due to the ever increasing need driven by the requirement for green technologies. It is therefore essential to recover elements like In and Ga from waste materials to meet the growth in demand. Consequently, this research studies the extraction of In and Ga using an ionic liquid solution as solvent. The investigation utilized both experimental and theoretical approaches, with In and Ga spiked EAF dust used to simulate a realistic waste matrix. Ionic liquids are emerging solvents, and EAF dust is an industrial waste containing several metals such as zinc (Zn) and iron (Fe). For the experimental part, two ionic liquids namely 1-butyl-3-methylimidazolium hydrogen sulfate [Bmim⁺HSO₄^-] and 1-butyl-3-methylimidazolium chloride [Bmim⁺Cl^-] were mixed with three oxidants iron(III) sulfate (Fe₂(SO₄)₃), potassium permanganate (KMnO₄), and hydrogen peroxide (H₂O₂) to determine the best ionic liquid and oxidant combination. For the theoretical study, density functional theory (DFT) was applied to calculate the Gibbs free energy (ΔG) and the stability of each possible complex that can form with each of the studied ionic liquid media. To this end, three imidazolium-based ionic liquids ([Bmim⁺HSO₄^-], [Bmim⁺Cl^-], [Bmim⁺HSO₃^-]) which have similar anionic parts as sulfate [SO₄^2-], chloride [Cl^-], and nitrate [NO₃^-]with the most commonly used acids as sulfuric acid (H₂SO₄), hydrochloric acid (HCl), and nitric acid (HNO₃) were selected for DFT calculations.