Chemistry - Metallurgy Question with Solution | TestHub

The extraction of Pb from high-grade PbS (galena) primarily involves roasting and self-reduction.

A. Roasting:

$$\mathrm{PbS}+\frac{3}{2}{\mathrm{O}}_2\to \mathrm{PbO}+{\mathrm{SO}}_2\uparrow$$

This reaction converts lead sulfide to lead oxide.

B. Self-reduction:

$$2\mathrm{PbO}+\mathrm{PbS}\to 3\mathrm{Pb}+{\mathrm{SO}}_2\uparrow$$

This is the main reaction for lead extraction, where PbO reacts with unroasted PbS to form lead metal.

C. Slag formation:

$$\mathrm{CaO}+{\mathrm{SiO}}_2\to {\mathrm{CaSiO}}_3$$

This reaction forms calcium silicate slag, which helps remove impurities, especially when the ore contains silica.

D. Lead silicate formation:

$$\mathrm{PbO}+{\mathrm{SiO}}_2\to {\mathrm{PbSiO}}_3$$

This reaction forms lead silicate, which is a loss of lead as slag. While it can occur, it is generally undesirable and not a chief reaction for efficient lead extraction. It represents a loss of the desired product.

Therefore, the reaction $\mathrm{PbO}+{\mathrm{SiO}}_2\to {\mathrm{PbSiO}}_3$ is not a chief reaction for the extraction of Pb; rather, it represents a loss of lead.

The final answer is D.