Question

Which of the following metal(s) is(are) extracted from its(their) sulfide ore(s) by self-reduction/air reduction method?

• A. Cu
• B. Al
• C. Au
• D. Pb

Hint:

Self-reduction is used for extracting metals like copper from their sulfide ores, where the ore is heated in the presence of air to oxidize the sulfur and reduce the metal.

Answer 1

The Correct Option is A, D

Self-reduction/air reduction method:

This method is used for extracting metals from their sulfide ores where:

• The sulfide ore is partially roasted in limited air to form the metal oxide
• The remaining sulfide ore then reacts with the oxide to produce the metal
• No external reducing agent is needed

General reaction: $$2MS + 3O_2 \rightarrow 2MO + 2SO_2$$ (partial roasting) $$2MO + MS \rightarrow 3M + SO_2$$ (self-reduction)

Requirements:

• Metal should be relatively less reactive
• Metal oxide should be easily reduced by the sulfide
• Metal should be below hydrogen in the reactivity series

Analyzing each metal:

(A) Cu (Copper):

• Extracted from Cu₂S (copper sulfide)
• Process: Partial roasting converts some Cu₂S to Cu₂O
• Self-reduction: Cu₂S + 2Cu₂O → 6Cu + SO₂
• Uses self-reduction 

(B) Al (Aluminum):

• Extracted from Al₂O₃ (bauxite)
• Very reactive metal
• Requires electrolytic reduction (Hall-Héroult process)
• Does NOT use self-reduction 

(C) Au (Gold):

• Found in native state or extracted by cyanide process
• Too noble to exist commonly as sulfide ore
• Does NOT use self-reduction

(D) Pb (Lead):

• Extracted from PbS (galena)
• Process: Partial roasting converts some PbS to PbO
• Self-reduction: PbS + 2PbO → 3Pb + SO₂
• Uses self-reduction 

Answer: (A) Cu and (D) Pb