Problem 79 - A Complete Resource Book in Chemistry for JEE Main

Question

During the extraction of zinc, \(\mathrm{ZnO}\) is obtained from zinc blende by (a) poling (b) roasting (c) cupellation (d) electrolytic reduction

Step-by-Step Solution

Answer

(b) roasting

Step 1: Understanding the Question

The exercise requires identifying the method by which zinc oxide \( (\mathrm{ZnO}) \) is obtained from zinc blende \( (\text{ZnS}) \) during zinc extraction. The options are poling, roasting, cupellation, and electrolytic reduction.

Step 2: Analyzing the Process of Roasting

Roasting involves heating a sulfide ore in the presence of oxygen. Zinc blende \((\mathrm{ZnS})\), a sulfide ore, reacts with oxygen during roasting to form zinc oxide \((\mathrm{ZnO})\) and sulfur dioxide \((\mathrm{SO}_2)\). The chemical reaction is: \[ \mathrm{2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2} \]

Step 3: Eliminating Other Options

- Poling: A refining process often used after extraction, not suited for converting sulfide ores to oxides. - Cupellation: A process to purify metals, typically used for silver containing impurities, not applicable to forming oxides from sulfides. - Electrolytic reduction: Used for the reduction of ions or oxides to metals in electrolytic cells, not for forming oxides from sulfides.

Step 4: Confirming the Correct Process

Roasting is the standard metallurgical process to convert zinc blende (a sulfide ore) into zinc oxide by heating it strongly in the presence of oxygen. This aligns the chemical reaction and goal with options given in the exercise.

Key Concepts

Roasting in Metallurgy

Roasting is a metallurgical process that involves heating an ore in the presence of oxygen. This process is essential for sulfide ores like zinc blende (ZnS), which need to be converted into oxides before further processing.
The role of roasting is primarily to ensure the ore undergoes chemical changes that prepare it for subsequent reduction.
In the presence of oxygen, roasting zinc blende results in the formation of zinc oxide (ZnO) and sulfur dioxide (SO₂). Roasting transforms metal sulfides into oxides, which makes the extraction of the metal more manageable.

• It increases the ore's stability by removing volatile impurities.
• It modifies the structure, making the ore porous and reactive for further extraction steps.

The major advantage of roasting lies in its ability to prepare ores for easy reduction, which is vital for metals like zinc. Overall, understanding the roasting process provides a solid foundation for comprehending many metallurgical extractions.

Zinc Blende to Zinc Oxide

The transformation of zinc blende ( ZnS) into zinc oxide ( ZnO) is a crucial step in zinc extraction. This change mainly occurs through roasting, a process where the ore is heated with abundant air.
The chemical reaction is simple yet effective: 2ZnS + 3O₂ → 2ZnO + 2SO₂.
This reaction illustrates the effective conversion of sulfide ions into oxide ions, which are then ready for reduction.
Zinc oxide is advantageous because it is more straightforward to reduce in subsequent extraction processes compared to its sulfide counterpart.

• Converts the ore into a form that can be reduced to metallic zinc.
• Prepares the metal for further refining and purification steps.

Getting from zinc blende to zinc oxide is foundational in the overall extraction process, easing the path towards obtaining pure zinc metal.

Sulfide Ore Processing

Processing sulfide ores is central to metal extraction, notably for metals like zinc from its ore zinc blende.
This process begins with the fundamental step of roasting, which transforms metal sulfides into oxides, preparing them for reduction.
Roasting for zinc extraction uses:

• Heat to alter the chemical structure of sulfide ores.
• Oxygen to facilitate oxidation into zinc oxide and sulfur dioxide.

Small details in this process ensure effective conversion and yield.
Beyond zinc, the principles of processing sulfide ores apply broadly across metallurgy for extracting various metals. The skill in this lies in choosing the right conditions and techniques to achieve optimal results, highlighting the universality and elegance of sulfide ore processing.