For the extraction of metals like Zinc and Iron (middle of reactivity series) from their sulfide ores, which p

Question

For the extraction of metals like Zinc and Iron (middle of reactivity series) from their sulfide ores, which process is primarily used?

Examoogle · Accepted Answer

The correct answer is Option B: Roasting followed by reduction with carbon. Metals in the middle of the reactivity series, such as Zinc ($Zn$) and Iron ($Fe$), are typically found as sulfide or carbonate ores. These ores are first converted into metal oxides through roasting or calcination, followed by reduction using a suitable agent like carbon (coke).

Step-by-Step Solution & Concepts:
Metals in the middle of the reactivity series, such as Zinc ($Zn$) and Iron ($Fe$), are typically found as sulfide or carbonate ores. These ores are first converted into metal oxides through roasting or calcination, followed by reduction using a suitable agent like carbon (coke).

Working Principle: Roasting involves heating the sulfide ore in the presence of excess air to convert the sulfide into an oxide: $2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2$. Once the metal oxide ($ZnO$) is obtained, it is reduced to metal using carbon as a reducing agent: $ZnO + C \rightarrow Zn + CO$. Carbon acts as an effective reducing agent for metals with moderate reactivity because it has a higher affinity for oxygen at elevated temperatures.

Key Formulas: $2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2$ — Roasting reaction for Zinc sulfide; $ZnO + C \rightarrow Zn + CO$ — Carbon reduction of Zinc oxide

Key Points: Roasting is exclusively for sulfide ores.; Calcination is used for carbonate ores.; Carbon is not suitable for highly reactive metals (like $Na, K, Ca$) as they have higher affinity for oxygen than carbon does.; Sulfur dioxide gas produced during roasting is often a byproduct collected to produce sulfuric acid.

Advantages: Economically viable due to the low cost of carbon/coke.; High efficiency for medium reactivity metals.

Disadvantages: Produces sulfur dioxide gas which is a major atmospheric pollutant and source of acid rain.; Requires high temperatures which consume significant energy.

Applications: Extraction of Zinc from Zinc blende ($ZnS$).; Extraction of Iron from Siderite ($FeCO_3$) (though blast furnace often uses coke directly).

Additional Info: Electrolysis is reserved for highly reactive metals ($K, Na, Ca, Mg, Al$) because carbon cannot reduce these oxides.. Roasting occurs in the presence of air, whereas calcination occurs in the absence or limited supply of air.

Answer: B is correct — Metals in the middle of the reactivity series are first roasted to produce oxides and subsequently reduced using carbon as a reducing agent.

Exam Tip: Always check the ore type: if the ore name ends in 'ide' (like Sulfide), choose Roasting. If it ends in 'ate' (like Carbonate), choose Calcination.

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Option A: Electrolysis

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Option C: Calcination followed by electrolysis

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Option D: Direct displacement by oxygen

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