Leaching of Germanium from Zinc Residue in H2SO4/SO2 Solutions

Zinc residue with high germanium, a waste solid product of hydrometallurgical zinc process is dumped continuously, causing the loss of germanium. Zinc residue was characterized by chemical analysis, X-ray diffraction, and inductively coupled plasma mass spectrometry methods. The results showed that, the mineralogical compositions of the zinc residue used in this research were zinc ferrite, gypsum, hemihydrate gypsum, anglesite, sphalerite and quartz. Approximately 58% and 20% germanium occurred in the ferrite and silicate phases, respectively. Leaching of zinc residue with high germanium was investigated as a process to recover germanium. It was found to be much more effective using sulfur dioxide as a reductant. Batch leaching tests were carried out on zinc residue with high germanium at set pressure in stirred acid solution. The effects of SO2, time, sulfuric acid concentration, temperature, liquid-to-solid ratio, and sulphur dioxide partial pressure on the germanium dissolution were studied to optimize the leaching parameters. In the presence of SO2, the results showed that the extraction of germanium was maximum of 70% while the extraction of zinc and iron were 90% and 96% under the optimal condition which was determined for 80 g of zinc residue using 56 g/L sulfuric acid, liquid-to-solid ratio of 7 mL/g and sulphur dioxide partial pressure of 200 kPa at 100°C after 120 min. Under optimal conditions, the main minerals of the reduction leaching residue were sodium iron sulfate tetrahydrate, gypsum, hemihydrate gypsum, anglesite, sphalerite and quartz. Zinc ferrite was almost entirely leached