The Roasting Process

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The Roasting Process
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Although the zinc makes up 60 of the concentrate
it is largely in sulphide form.
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The zinc must be converted to oxide form so that
it can be treated in the next stage of the
process - Leaching. In the Leaching Plant the
zinc is dissolved in sulphuric acid. If the zinc
is in sulphide form it cannot be dissolved in
sulphuric acid.
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As a result of the roasting process.
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Heat Energy (950oC)
The Roasting Plant produces two products. One is
an impure form of zinc oxide that is called
calcine. The other product is sulphur dioxide
gas.
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Calcine is the end product of roasting. Even
though it looks similar to concentrate it does
not contain sulphur.

• In addition to the zinc it still contains
• iron
• silica
• calcium
• copper
• cobalt and
• cadmium.

How can we remove these elements? More Roasting?
No, this wont work!
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The zinc in the calcine is present in four forms.

6 Zinc Sulphate
13 Zinc Ferrite
Zinc Oxide 80
A certain amount of the zinc is combined with
iron, called zinc ferrite. A small amount of
zinc sulphide is also present as a result of
incomplete roasting.
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Summary

• In the Roasting Process most of the zinc
  sulphide
• is converted into zinc oxide.
• The sulphur is removed from the zinc sulphide
  and
• is liberated as sulphur dioxide gas.
• The end product of Roasting is called calcine.
  This
• contains zinc oxide and zinc sulphate which
  are
• recoverable in the Leaching Plant.
• The zinc ferrite and zinc sulphide cannot be
• dissolved.