In reaction :

\(FeO + SiO_2 \longrightarrow FeSiO_3\)

What is slag among three compounds involved in metallurgy of copper?

\(FeSiO_3\)

The correct answer is option 3. \(FeSiO_3\).

In metallurgy, particularly in the extraction and purification of metals such as copper, a key step involves the removal of impurities. The reaction you provided:

\(FeO + SiO_2 \longrightarrow FeSiO_3\)

is a slag-forming reaction, essential in the purification process. Let us break down the details:

Understanding the Reaction Components

\(FeO\) (Iron(II) oxide)

\(FeO\) is a basic oxide that forms as an impurity during the smelting of copper ores, particularly in sulfide ores like chalcopyrite (CuFeS₂). When copper sulfide is roasted in the presence of oxygen, \(FeO\) forms from the oxidation of iron in the ore. In metallurgical processes, basic oxides like \(FeO\) need to be removed because they can affect the purity of the metal.

(SiO_2\) (Silicon dioxide)

\(SiO_2\), or silica, acts as an acidic flux. A flux is a substance that is added to the furnace during smelting to combine with impurities (like \(FeO\)) and form a compound that can be separated from the molten metal. \(SiO_2\) helps convert the basic \(FeO\) impurity into a more manageable form by reacting with it to form slag

\(FeSiO_3\) (Iron silicate)

\(FeSiO_3\) is iron silicate, a slag formed in the reaction between \(FeO\) and \(SiO_2\). Slag is a molten by-product that floats on the surface of the molten metal. Being less dense than the metal, it can be easily skimmed off, removing impurities like iron oxides

Purpose of Slag Formatio

In the metallurgy of copper, the primary goal is to separate the metal from its impurities. The slag-forming reaction plays a critical role in this:

During smelting, \(FeO\) (a basic oxide impurity) is undesirable because it can interfere with the purity of the molten copper.

To remove this impurity, \(SiO_2\) (acidic flux) is added to the furnace. The \(SiO_2\) reacts with \(FeO\) to form \(FeSiO_3\) (iron silicate slag). \(FeSiO_3\), being a silicate, is a non-metallic by-product. It has a lower density than the molten copper and floats on the surface, allowing for easy removal.

Significance of the Reaction in Copper Metallurgy

In the smelting of copper ores, one of the major impurities is iron. To purify the copper, iron must be removed. The process typically involves roasting the copper ore in a furnace, leading to the formation of \(FeO\) as an impurity. By adding \(SiO_2\) (silica), the iron impurity is removed as iron silicate slag:

\(FeO + SiO_2 \longrightarrow FeSiO_3\)

This reaction ensures that iron impurities are removed from the molten copper in the form of \(FeSiO_3\) slag.

Detailed Role of Slag in the Copper Smelting Process

In the blast furnace or reverberatory furnace used for copper smelting, the temperature is kept high enough to keep both the metal and the slag in a molten state. As slag (FeSiO₃) forms, it floats on top of the molten copper because it has a lower density. The slag is then skimmed off the top and discarded, or in some cases, used for other industrial purposes like construction materials.

Why \(FeSiO_3\) is the Slag

The term slag refers to the waste product formed during the metallurgical process. In this case, the reaction of iron(II) oxide (FeO) with silica (SiO₂) forms iron silicate (FeSiO₃), which is non-metallic and considered waste. Slag is essential because it helps trap impurities and facilitates the purification of metals like copper.

Thus, \(FeSiO_3\) is the correct answer as it is the slag formed during the reaction in the metallurgy of copper.