How does sulfuric acid leach zinc from roasted zinc concentrate?

In the context of zinc processing, the leaching process is a fundamental step in preparing a zinc sulfate solution for electrolysis.1

The process functions as follows:

• Preparation: Zinc sulfide concentrates are first subjected to roasting, typically in fluidized-bed roasters, to remove sulfur and produce zinc oxide calcines.12
• Leaching: These calcines, which consist of small, easily treatable particles, are leached using dilute sulfuric acid.12
• Dissolution: The acid dissolves the zinc content from the calcines, creating a zinc sulfate solution.13
• Residue: This process leaves behind a solid residue that may contain other valuable metals such as lead, silver, and gold, along with a small percentage of undissolved zinc, which can be further processed through methods like slag fuming.3

Following leaching, the resulting zinc sulfate solution must undergo rigorous purification to remove impurities before it can be used in the electrolytic cell.1