Two-stage leaching of germanium from copper cake under subsequent non-oxidizing and oxidizing conditions

Many world economies, such as the EU and the USA, consider germanium to be a critical raw material. Therefore, the development of its recovery from new sources is becoming increasingly important. The leaching of copper cake, produced during the purification of zinc electrolytes, in sulfuric acid solution is presented in the paper. The cake contained 24.7% Cu, 21.2% Cd, 16.3% Zn, 4.50% Pb, 3.96% Ni, 3.22% Co and 231 ppm Ge. The leaching of wet and dried material was examined. It was found that the highest germanium recovery was obtained in a two-stage process consisting of leaching under non-oxidizing conditions followed by pH adjustment with sodium carbonate and by oxidizing leaching of the residue from the first stage. In the first stage of leaching in 12.5% sulfuric acid and subsequent pH adjustment to >2.0 reduced germanium leaching yield to <10%. During oxidizing leaching of remaining residue in 15% sulfuric acid >99% of germanium was leached. The final solution contained 30 mg/dm3 Ge and 72.4 g/dm3 Cu. Germanium can later be recovered from the solution by precipitation with tannic acid or solvent extraction.