Recovery of indium and germanium from In-Ge residue leaching solution using solvent extraction and tannin precipitation

Selective extraction of indium and germanium from natural resources due to their important role in high-tech fields is attracting more and more attention. In this paper, indium and germanium were recovered from In-Ge residue leaching solution by the selective solvent extraction of indium with D2EHPA and the precipitation of germanium using tannin. This process included two main stages: indium-selective solvent extraction and germanium-selective precipitation. In the first stage, indium was extracted by using an organic phase containing 15% D2EHPA and 85% kerosene. The indium-loaded organic phase was washed with 0.5 M H2SO4 and then stripped by 4 M HCl solution to obtain an indium extraction ratio of 99% and a stripping ratio of 98.3%. In the second stage, the pH of the raffinate was adjusted to 3.5–4.0 with ZnO dust and then mixed with tannin. Germanium (99%) was selectively precipitated as a tannin-germanium complex. The washed tannin-germanium complex was baked at 500 °C for 3 h to produce a germanium concentrate. By studying the separation coefficients of indium, germanium, and zinc (1994 and 1093, respectively), and controlling the reaction conditions, the maximum separation of indium, germanium, and zinc was obtained. The extraction mechanism of indium from sulfuric acid solution by D2EHPA and element migration during the precipitation of germanium using tannin were also studied. This proposed process flow can be used to selectively recover germanium and indium from In-Ge residue leaching solutions.