Question

Why is sulphide ore roasted before reduction

Answer 1

Answer on Question #53762 – Chemistry – Inorganic Chemistry

Question:

Why is sulphide ore roasted before reduction?

Answer:

Roasting is a method of additional purification of metal components which is used in production of metals from sulfide ores.

$$\mathrm{Cu_2S} + 2\mathrm{O_2} \rightarrow 2\mathrm{CuO} + \mathrm{SO_2}$$ $$4\mathrm{FeS_2} + 11\mathrm{O_2} \rightarrow 2\mathrm{Fe_2O_3} + 8\mathrm{SO_2}$$

Before this step, sulfide ore is already purified with froth floatation, however, it still contains light impurities including $\mathrm{As_2S_3}$, $\mathrm{Sb_2S_3}$, selenides, tellurides and $\mathrm{ZnS}$ (if it should be separated). All of them are removed as volatile materials ($\mathrm{ZnO}$, $\mathrm{As_2O_3}$, $\mathrm{Sb_2O_3}$, $\mathrm{SO_2}$) upon roasting of the ore. Contrary to sulfide reduction, an extraction of metals by reduction of oxides is the most efficient and requires minimal energy and material costs. Moreover, during roasting $\mathrm{SO_2}$ is formed in large amount, therefore, it is collected and used for production of sulfuric acid.

$$\mathrm{SO_2} + \mathrm{O_2} \rightarrow \mathrm{SO_3}$$ $$\mathrm{SO_3} + \mathrm{H_2O} \rightarrow \mathrm{H_2SO_4}$$

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