Extraction Behavior and Purification of Germanium Using an Undiluted Quaternary Ammonium Ionic Liquid in Combination with a Complexing Agent

The recovery of germanium from low-grade ores and secondary resources requires the development of new separation and purification techniques. In this work, the solvent extraction (SX) behavior of Ge­(IV) and common contaminants, that is, Zn­(II), Fe­(III), Cu­(II), and As­(III), was studied using the undiluted ionic liquid (IL) Aliquat 336 ([A336]­[Cl]). A comparison was made between HCl and H₂SO₄ extraction media. It was found that upon extraction from H₂SO₄ media, organic chloride ions were exchanged for aqueous hydrogensulfate ions. This transfer of chlorides to the aqueous phase facilitated metal extraction and resulted in a similar extraction performance for the HCl and H₂SO₄ systems. Elimination of chlorides from the system by conversion of the IL into [A336]­[HSO₄] prior to the SX allowed nearly full suppression of the extraction of Zn­(II), Fe­(III), and Cu­(II). To form an extractable anionic Ge­(IV) complex, the addition of tartaric acid, citric acid, and catechol to the aqueous phase was studied. Tartaric acid proved superior as only five equivalents were required for the quantitative extraction of Ge­(IV). A separation process for the recovery of Ge­(IV) from a synthetic zinc refinery residue leachate was developed, comprising the exclusion of chloride ions through the use of [A336]­[HSO₄] and the addition of tartaric acid to the aqueous phase. The optimized process involves the addition of five equivalents of tartaric acid and extraction with [A336]­[HSO₄] at an organic-over-aqueous volumetric phase ratio (O/A) of 1/2, resulting in the highly selective extraction of Ge­(IV). The limited amount of As­(III) that is coextracted can be scrubbed with water at O/A = 1/3. Ge­(IV) is stripped with 2.0 mol L^–1 NaOH at O/A = 1/1. [A336]­[HSO₄] can thereafter be regenerated with H₂SO₄ and reused in the next extraction cycle.