Extraction mechanism of germanium in sulfate solutions using a tertiary amine (N235)-based solvent extraction system

With the increasing demand for germanium in high-technology fields, the recovery of germanium has gained a great deal of attention. In this study, classical methods (including stoichiometry and saturation methods) were combined with spectroscopic methods (FT-IR, NMR, and ESI-MS) to investigate the mechanism of Ge(IV) extraction from a sulfuric acid solution using the tertiary amines (N235) and trioctyl phosphate (TOP) system. The results indicate that Ge(IV) was extracted as a Ge(OH)(HL)3 anion complex, and tartaric acid is coordinated to Ge(IV) via a CO bond from the carboxylate group. The extraction process followed an anion exchange mechanism. TOP participated in the formation of extraction complexes through hydrogen bonds in the form of GeOH⋯OP but did not co-extract germanium with N235. The extracted complex species were Ge(OH)(HL)2L·HN(R1)3 and Ge(OH)(HL)L2·[HN(R1)3]2 (R=C8H17). The apparent equilibrium constants of the extraction reactions Kex were 100.36 and 100.43 at tartaric acid/Ge(IV) ratios of 5 and 3, respectively. The thermodynamic constants for the extraction process were ΔH=−0.457 kJ·mol−1, ΔS=1.176 kJ·mol−1·K−1, and ΔG=−351.081 kJ·mol−1.