Problem 108 - A Complete Resource Book in Chemistry for JEE Main

Question

The chemical composition of 'slag' formed during the smelting process in the extraction of copper is (a) \(\mathrm{Cu}_{2} \mathrm{O}+\mathrm{FeS}\) (b) \(\mathrm{FeSiO}_{3}\) (c) \(\mathrm{CuFeS}_{2}^{2}\) (d) \(\mathrm{Cu}_{2} \mathrm{~S}+\mathrm{FeO}\)

Step-by-Step Solution

Answer

The slag formed is \( \text{FeSiO}_3 \), option (b).

Step 1: Understand the Smelting Process

In the extraction of copper, smelting plays a key role. The purpose of smelting is to separate the metal from other elements in the ore, using heat and a reducing agent.

Step 2: Identify By-products of Smelting

During the smelting of copper, a 'slag' is formed as a by-product. This slag is primarily composed of compounds that result from the impurities or unwanted elements in the ore reacting with flux.

Step 3: Determine the Composition of Slag

In the context of copper extraction, iron is often removed as iron silicate, popularly known as 'slag'. This compound formed is typically iron silicate, which is recorded as \( \text{FeSiO}_3 \).

Step 4: Verify with Options

Compare the determined composition of slag with the given options. The options are: (a) \( \text{Cu}_2 \text{O} + \text{FeS}\), (b) \( \text{FeSiO}_3 \), (c) \( \text{CuFeS}_2 \), and (d) \( \text{Cu}_2 \text{~S} + \text{FeO}\). Option (b), which is \( \text{FeSiO}_3 \), matches the identified composition of slag.

Key Concepts

Smelting Process

One of the central processes in the extraction of copper is smelting, which involves heating the ore to separate the valuable metal from other impurities. During this process, the ore is melted at high temperatures, allowing the copper to be separated from its ore form. Here's how it works:

• The ore is mixed with a suitable fuel and a flux, which helps to remove impurities.
• A reducing agent is used to strip away the oxygen from the copper ore, often leaving behind pure copper.
• The heat generated causes a molten mixture, from which copper can be further extracted.

After heating, the molten product has separate layers of metal and waste material known as slag. Understanding this process is crucial as it indicates how copper is efficiently separated from less valuable materials.

Slag Composition

During the smelting process, as the pure metal settles down, there remains a layer of material referred to as "slag." This by-product is the residual waste that floats on top of the heavier pure metal layer. Slag comprises mainly the impurities and substances that react with the added flux. It typically includes:

• Oxides of the metals present in the ore other than copper.
• Reactions between the flux and impurities create new compounds.
• In the context of copper extraction, iron oxides react with silica (SiO extsubscript{2}) in the flux to form iron silicate (FeSiO extsubscript{3}).

Therefore, slag assists in cleaning out the impurities, making it an essential part of high-quality metal extraction.

Iron Silicate

Iron silicate, often found in the slag formed during the smelting of copper, is a result of chemical reactions between iron oxides from the ore and silica from the flux. Iron silicate has the chemical formula \( \text{FeSiO}_3 \), and is commonly referred to as fayalite. Here's why it forms and its role:

• When iron oxides in the ore combine with the flux (Silica), they form iron silicate.
• This compound is part of the melt that separates based on density during the cooling of molten materials in smelting.
• Iron silicate's formation is essential in the extraction, as it helps remove iron impurities from the final copper product.

In summary, iron silicate is pivotal in the metallurgical process for purifying the metal, ensuring that the resulting copper is high in quality and free from unnecessary elements.