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Why are zinc sulfide ores roasted before zinc is extracted?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
A labeled diagram of the periodic table entry for zinc, showing its atomic number 30, symbol Zn, atomic weight 65.38, electron configuration, name, hexagonal crystal structure, solid state at room temperature, and classification as a transition metal.
zinc

Zinc sulfide ores must be roasted before extraction because both primary production methods—electrolysis and smelting—require the removal of sulfur to convert the ore into a usable oxide form.1

This process is a highly exothermic oxidation reaction that serves two main purposes:

  • Preparation for Leaching: In electrolytic production, roasting transforms the concentrate into a calcine (zinc oxide). This material consists of small particles that can be efficiently leached into a sulfuric acid solution to create the zinc sulfate electrolyte necessary for the final extraction stage.12
  • Feed Optimization: For smelting in a blast furnace, a sintering process is used to create a strong, lumpy, oxidized feed that is physically suitable for the furnace environment.1

Additionally, the roasting process is environmentally and economically significant, as it allows for the recovery of sulfur dioxide gas, which is subsequently captured and processed into sulfuric acid.1