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Difficulty: MediumGeneral Principles of Metallurgy and Metal Extraction

During the industrial smelting stage of copper extraction from chalcopyrite (CuFeS2\text{CuFeS}_2), silicon(IV) oxide (SiO2\text{SiO}_2) is added to the furnace charge. What is the primary chemical role of silicon(IV) oxide in this process?

  1. To act as an acidic flux that combines with iron(II) oxide impurity to form a fusible slag of iron(II) trioxosilicate(IV)Answer
  2. B
    To serve as the primary reducing agent that converts copper(I) sulfide directly to metallic copper
  3. C
    To lower the melting point of the copper electrolyte during subsequent electro-refining
  4. D
    To react with acidic sulfur impurities and neutralize them into non-volatile salts

Answer

Silicon(IV) oxide acts as an acidic flux that reacts with basic iron(II) oxide to form molten iron(II) trioxosilicate(IV) slag (FeSiO3\text{FeSiO}_3).
In the extraction of copper from sulfide ores, the ore contains significant iron impurities. Smelting oxidized iron into basic iron(II) oxide (FeO\text{FeO}). Adding sand or silicon(IV) oxide (SiO2\text{SiO}_2), which acts as an acidic flux, causes a chemical reaction forming molten iron(II) trioxosilicate(IV) (FeSiO3\text{FeSiO}_3). This slag is less dense than the copper matte, allowing easy separation by skimming or tapping off.

Step-by-Step Solution

1
Identify the nature of impurities in copper ore roasting/smelting
Partial roasting of copper pyrites (CuFeS2\text{CuFeS}_2) produces iron(II) oxide (FeO\text{FeO}), which is a basic oxide impurity.
Iron impurities must be separated from copper matte (Cu2S⋅FeS\text{Cu}_2\text{S} \cdot \text{FeS}) prior to copper reduction.
2
Determine the role of the added flux
An acidic flux, silicon(IV) oxide (SiO2\text{SiO}_2), reacts with basic FeO\text{FeO} according to the equation: FeO(s)+SiO2(s)→FeSiO3(l)\text{FeO}(s) + \text{SiO}_2(s) \rightarrow \text{FeSiO}_3(l).
An acid-base reaction between flux and gangue forms a light, molten silicate layer known as slag.
3
Conclude the function of slag in pyrometallurgy
The molten slag (FeSiO3\text{FeSiO}_3) floats on top of the heavier copper matte layer and is tapped off.
Slag formation allows continuous mechanical removal of iron impurities.

Key Concept

Role of fluxes and slag formation in metallurgy
Estimated Time:1m 0s
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Topics

General Principles of Metallurgy and Metal Extraction

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