Copper-cobalt cake as a potential source of germanium

Abstract

Germanium is an important element used in crucial industry sectors like optical fibers for telecommunication or IR optics for night vision systems. However, its global output is limited. It is estimated that its annual global production is ca. 140 tons. Therefore, many world economies, including USA and EU, consider it as a critical raw material. One of the potential sources of germanium is zinc metallurgy. It is assumed that only 3% of germanium present in processed zinc ores is recovered. It was found that during the technological processes of Polish zinc smelters some by-products containing elevated germanium concentrations are produced. In the paper, potential germanium sources, including copper-cobalt cake obtained during the purification of zinc electrolyte and dross from the feeding furnace, are presented. The main components of the cake are cadmium, zinc, copper, nickel, cobalt, and lead, while the dross contains mainly zinc (>65%). Results of leaching tests for both materials using aqueous sulfuric acid solutions are shown. In the case of the cake, wet and dried material was investigated. It was found that the germanium leaching yield for the dried material reached 99%, while for the wet one was 46-86%, depending on leaching conditions (without or with oxidant). On the other hand, the germanium leaching yield for the dross reached 55%. Further processing of the solutions obtained after germanium leaching from the copper-cobalt cake was also analyzed. Two ways were proposed, including precipitation with tannic acid and solvent extraction with addition of complexing agents using a trioctylamine extractant.