The industrial roasting of sulphides

The objective in the roasting of sulphides, such as copper sulphides and zinc sulphides, is to convert these into their corresponding oxides by reaction with 

The first successful study which clarified the mechanism of roasting, was a study of the oxidation of pyrite, FeS2, which is not a typical industrial process because of the availability of oxide iron ores. The experiment does, however, show the main features of roasting reactions in a simplified way which is well supported by the necessary thermodynamic data. The Gibbs energy data for the two sulphides of iron are, 

It can be readily calculated that pyrite will exert a sulphur dissociation pressure of 1 atmos only at 1512 K. However, when the sulphide reacts with air the main gaseous product is S02, and the reaction is then 

In all of these systems, the rate of generation at the gas-solid interface is so rapid that only a small fraction is carried away from the particle surface by convective heat transfer. The major source of heat loss from the particles is radiation loss to the surrounding atmosphere, and the loss per particle may be estimated using unity for both the view factor and the emissivity as an upper limit from this source. The practical observation is that the solids in all of these methods of roasting reach temperatures of about 1200-1800 K. 

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