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The Roasting Process

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Title: The Roasting Process


1
The Roasting Process
2
Although the zinc makes up 60 of the concentrate
it is largely in sulphide form.
3
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.
4
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5
As a result of the roasting process.
6
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.
7
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!
8
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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10
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.
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