Oxidising roast

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Sulfide ores are sometimes roasted in air (heated in the presence of oxygen) to convert the ore to oxide prior to leaching. During this treatment sulfur in the concentrate is oxidised to sulfur dioxide gas which is liberated during the roasting process. In this way sulfur can be removed from the ore. The sulfur dioxide gas is collected and used for sulfuric acid production.

In some cases sulfur is only partly removed which is common in the production of copper and nickel.

In other cases the sulfur is completely removed and a metal oxide is obtained, for example in the production of zinc. A complete roasting of sulfides to oxides also called dead roasting.

Examples:

  • Roasting of sphalerite to zincite:
ZnS + 3/2O2 → ZnO + SO2
  • Roasting of chalcopyrite to cuprite:
6CuFeS2 + 18O2 → 3Cu2O + 3Fe2O3 + 12SO2
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