Recovery of germanium and indium from leaching solution of germanium dross using solvent extraction with TOA, TBP and D2EHPA

Germanium and indium are considered by many economies as critical raw materials. Therefore, investigation on possible methods of selective extraction of these elements from natural sources is getting increasing attention. The paper presents the results of solvent extraction tests of real sulphate solution obtained by leaching of dross and containing 5.15 g/dm(3) Ge, 1.52 g/dm(3) In and 5.81 g/dm(3) Zn. In the first stage initial solution was doped with tartaric acid (citric and ascorbic acid were also tested) and germanium was extracted with trioctylamine (TOA)-tributyl phosphate (TBP) system. It was found that addition of complexing agent was necessary to achieve germanium extraction with TOA. Then, germanium was stripped with sodium hydroxide solution. Germanium extraction yield was >99%, while its stripping yield was 66-69%. Moreover, indium and zinc extraction yields were < 1%, therefore the operation was very selective. Additionally, it was found that stripping may be performed only if NaOH concentration was in the range between 10 and 20%. The reason was precipitation of germanium from aqueous phase at low NaOH (<10%) concentrations and formation of third phase and emulsion at higher NaOH levels (>20%). In the second stage, indium was recovered from the raffinate obtained after germanium extraction. Di-(2-ethylhexyl) phosphoric acid (DEHPA/D2EHPA) was used as an extractant and hydrochloric acid as a strippant. Indium extraction and stripping yields were > 98%, while zinc extraction yield was <1% allowing selective separation of In form Zn. It was found that solvent extraction using investigated system (3-stage germanium extraction, 3-stage germanium stripping, 2-stage indium extraction and 2-stage indium stripping) may be applied for selective recovery of germanium and indium.