Metallic zinc is primarily produced using hydrometallurgical routes, with Roast-Leach-Electrowinning (RLE) being the most widely implemented process. Maintaining high electrolyte purity prior to electrowinning is essential to prevent current efficiency losses and contamination of the final product. Electrolyte purification involves iron co-precipitation during neutral leaching, followed by zinc dust cementation targeting different impurities. When iron levels are insufficient, impurities may bypass the neutral leach stage and enter the cementation circuit. One such impurity is germanium, which has been associated with inadequate purification by interfering with cementation and promoting impurity redissolution. This study examined the behavior of germanium and its influence on impurity cementation during cold purification with zinc dust. Batch experiments were conducted using synthetic electrolytes simulating industrial compositions to evaluate the evolution of impurity concentrations and redox potential at controlled germanium levels. The effects of electrolyte composition, lead content in zinc dust and solution, pH, temperature, and the presence of oxygen were examined. Potential mitigation strategies were also assessed, including staged zinc dust addition and antimony addition to stabilize cementation reactions and reduce impurity redissolution. The results demonstrate that germanium significantly alters impurity behavior during cementation, particularly by promoting cadmium redissolution in proportion to germanium concentration. Although cadmium was initially removed rapidly, the residual concentration increased from near-complete removal in the absence of germanium to approximately one-third of its initial concentration at elevated germanium levels. Although germanium itself was cemented from solution, cadmium redissolution persisted after germanium removal, suggesting that cemented germanium species or associated electrochemical effects continue to influence the system behavior. Dissolved oxygen and elevated temperature increased impurity redissolution, whereas lower temperatures were beneficial. Lead(II) addition reduced cadmium redissolution but negatively impacted germanium and nickel removal. Staged zinc dust addition improved cadmium stability only after substantial germanium removal. Among all variables investigated, antimony addition was the most effective mitigation strategy, reducing final cadmium concentrations to below 1% of the initial value at an antimony concentration of 3.0 ppm and significantly improving cobalt removal without adversely affecting other impurities. These findings provide practical guidance for stabilizing purification in operations experiencing germanium breakthrough.
Guilherme Apostolico Bortolini (Thu,) studied this question.