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Question
State the role of silica in the metallurgy of copper.
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Solution 1
In the metallurgy of copper, silica (SiO2) acts as an acidic flux during smelting and Bessemerisation.
During smelting, the roasted ore contains ferrous oxide (FeO) as an impurity. Silica combines with FeO to form ferrous silicate (FeSiO3), which is a fusible slag.
\[\ce{FeO + SiO2 -> FeSiO3}\]
The slag (FeSiO3) being lighter, floats on the surface of the molten matte and is removed easily.
Similarly, during Bessemerisation, FeO formed again reacts with SiO2 to form FeSiO3 slag, purifying the molten copper.
Hence, the role of silica is to remove iron impurities by forming a fusible slag of FeSiO3.
Solution 2
During roasting, copper pyrites are converted into a mixture of FeO and Cu2O. Thus, acidic flux silica is added during smelting to remove FeO (basic). FeO combines with SiO2 to form famous silicate (FeSiO3) slag, which floats over molten matte.
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