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Difficulty: HardGeneral Principles of Metallurgy and Metal Extraction

During the industrial extraction of zinc from its principal ore, zinc blende (ZnSZnS), the concentrated sulfide ore undergoes thermal conversion in excess air before metal recovery. Which set of balanced chemical equations correctly represents the roasting step and the subsequent reduction step using carbon (coke)?

  1. Roasting: 2ZnS(s)+3O2(g)→2ZnO(s)+2SO2(g)2ZnS(s) + 3O_2(g) \rightarrow 2ZnO(s) + 2SO_2(g); Reduction: ZnO(s)+C(s)→Zn(g)+CO(g)ZnO(s) + C(s) \rightarrow Zn(g) + CO(g)Answer
  2. B
    Roasting: ZnS(s)+2O2(g)→ZnSO4(s)ZnS(s) + 2O_2(g) \rightarrow ZnSO_4(s); Reduction: ZnSO4(s)+C(s)→Zn(s)+SO2(g)+CO(g)ZnSO_4(s) + C(s) \rightarrow Zn(s) + SO_2(g) + CO(g)
  3. C
    Roasting: 2ZnS(s)+O2(g)→2Zn(s)+2SO2(g)2ZnS(s) + O_2(g) \rightarrow 2Zn(s) + 2SO_2(g); Reduction: Zn(s)+C(s)→ZnC(s)Zn(s) + C(s) \rightarrow ZnC(s)
  4. D
    Roasting: ZnS(s)+H2O(g)→ZnO(s)+H2S(g)ZnS(s) + H_2O(g) \rightarrow ZnO(s) + H_2S(g); Reduction: ZnO(s)+CO2(g)→Zn(s)+CO(g)+O2(g)ZnO(s) + CO_2(g) \rightarrow Zn(s) + CO(g) + O_2(g)

Answer

The correct sequence of reactions involves roasting zinc blende in excess oxygen to produce zinc oxide and sulfur(IV) oxide (2ZnS+3O2→2ZnO+2SO22ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2), followed by reduction of zinc oxide with coke at high temperature to produce zinc gas and carbon(II) oxide (ZnO+C→Zn+COZnO + C \rightarrow Zn + CO).
Roasting zinc blende (ZnSZnS) in excess oxygen gas converts the sulfide ore into zinc oxide (ZnOZnO) while liberating sulfur(IV) oxide (SO2SO_2). In the reduction furnace, carbon (coke) reduces zinc oxide to zinc metal vapor (ZnZn) and carbon(II) oxide gas (COCO) because the reaction takes place above the boiling point of zinc.

Step-by-Step Solution

1
Identify the chemical nature of the roasting process in metallurgy.
Roasting involves heating concentrated sulfide ores (ZnSZnS) in an abundant supply of atmospheric oxygen (O2O_2).
Sulfide ores are difficult to reduce directly to metals; converting them to oxides makes subsequent reduction thermodynamically feasible.
2
Write and balance the roasting reaction equation.
2ZnS(s)+3O2(g)→2ZnO(s)+2SO2(g)2ZnS(s) + 3O_2(g) \rightarrow 2ZnO(s) + 2SO_2(g)
Zinc sulfide reacts with oxygen gas to yield solid zinc oxide and sulfur(IV) oxide gas byproduct.
3
Identify the reduction process of zinc oxide using coke.
ZnO(s)+C(s)→Zn(g)+CO(g)ZnO(s) + C(s) \rightarrow Zn(g) + CO(g)
Carbon (coke) acts as a reducing agent at elevated temperatures (~1400 °C), stripping oxygen from zinc oxide. Because the temperature exceeds zinc's boiling point (907 °C), zinc is collected as a gas (vapor) and condensed.

Key Concept

Metallurgical stages of sulfide ore extraction: Roasting (conversion to oxide) followed by pyrometallurgical carbon reduction.
Estimated Time:2m 0s
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Topics

General Principles of Metallurgy and Metal Extraction

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