Question

What changes do take place when a concentrated ore is subjected to roasting?

Answer 1

When a concentrated ore is subjected to roasting:

1. The ore is heated strongly in the presence of excess air.
2. Moisture and volatile impurities are removed.
3. Sulphide ores are converted into oxides.
4. \[\ce{2ZnS + 3O2 -> 2ZnO + 2SO2 \uparrow}\]
5. Impurities of sulphur, arsenic and phosphorus are oxidised to volatile oxides and escape.

Thus, roasting makes the ore suitable for reduction.