What are the main steps in producing zinc by electrolysis?

The production of zinc by electrolysis is a critical hydrometallurgical process used to achieve high-purity metal (99.99 percent or more). The main steps are as follows:

• Preparation of Zinc Sulfate Solution: Zinc sulfide concentrates are first roasted in fluidized-bed roasters to remove sulfur and produce zinc oxide calcines. These calcines are then leached in dilute sulfuric acid to create a zinc sulfate solution.12
• Purification: This is a critical necessity because the presence of impurities can lower the hydrogen overvoltage and interfere with zinc deposition. Purification occurs in two stages:
  1. Removal of Iron: Iron is removed as a solid residue, typically as jarosite, goethite, or hematite.1
  2. Cementation: Other metallic impurities, such as copper, nickel, cadmium, cobalt, and germanium, are removed from the solution using zinc dust.1
• Electrolysis: The purified solution is processed in lead-lined concrete cells. The cells use anodes made of lead (containing 0.5–1.0 percent silver) and cathodes made of aluminum sheet. Zinc is deposited onto the cathodes, which are stripped every 24 to 48 hours. The collected zinc is then remelted in an induction furnace and cast into ingots or pigs.1