Question

Explain why sulphide ores are subjected to roasting while carbonate ores are subjected to calcination before reduction explain the two processes .

Answer 1

Dear User,
Carbonate ores are subjected to calcination while sulphide ores are subjected to roasting. Calcination is the heating of ore in the absence or presence of minimum amount of air whereas, roasting is the heating of ore in excessive air at a temperature below the melting point of the metal.These processes are done to convert the ores into oxide form.
Cabonate ores can yield oxides merely by heating. They decompose to give oxides.Air is not required for their conversion to oxides. For eg. ZnCO₃.
${\mathrm{ZnCO}}_3\left(\mathrm{s}\right)\stackrel{\mathrm{Calcination}}{\to }\mathrm{ZnO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$
Whereas, sulphide ores need oxygen for their conversion to oxides. Eg. ZnS
$2\mathrm{ZnS}+3{\mathrm{O}}_2\to 2\mathrm{ZnO}\left(\mathrm{s}\right)+2{\mathrm{SO}}_2$
Roasting is employed only in case of sulphides because it is an expensive method as compared to calcination.