Question

Why are metal sulphides and carbonate converted into metal oxides prior to reduction during extraction of metals?

Answer 1

Conversion of concentrated ore into metal oxide
It is easier to obtain metals from their oxides rather than from carbonates or sulphides. So the ore is first converted into an oxide. A carbonate ore is first converted into oxide ore by calcination. A sulphide ore is converted into oxide ore by roasting.

1. Calcination process
It is the process of heating the concentrated ore at a temperature not sufficient to melt the ore. The water content and the volatile impurities also get expelled. Zinc carbonate in its ore calamine (ZnCO3) is calcinated to obtain zinc oxide (ZnO).



ZnCO3 -------------> ZnO + CO2
calcination
2. Roasting process
It is the process of heating the concentrated ore in the presence of excess air. Volatile impurities also get expelled.
Zinc sulphide in its ore zinc blende ( ZnS) is roasted to obtain zinc oxide (ZnO).

Answer 2

This is done because oxides are easier to reduce into pure metals. For eg
ZnO + C -----> Zn + CO