Problem 19 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Extraction of copper by smelting uses silica as an additive to remove : [Main Online April 10, 2016] (a) \(\mathrm{Cu}_{2} \mathrm{O}\) (b) \(\mathrm{FeS}\) (c) \(\mathrm{FeO}\) (d) \(\mathrm{Cu}_{2} \mathrm{~S}\)

Step-by-Step Solution

Answer

(c) \(\mathrm{FeO}\) is removed by silica during copper smelting.

Step 1: Understanding the Question

The problem asks which compound is removed by adding silica during the smelting process of copper. Silica acts as a flux to react with impurities.

Step 2: Identifying Possible Answers

The options are: (a) \(\mathrm{Cu}_{2} \mathrm{O}\), (b) \(\mathrm{FeS}\), (c) \(\mathrm{FeO}\), and (d) \(\mathrm{Cu}_{2} \mathrm{~S}\). We need to identify which of these reacts with silica.

Step 3: Recognizing the Role of Silica in Smelting

Silica (\(\mathrm{SiO}_{2}\)) is commonly used to remove iron oxides, such as \(\mathrm{FeO}\), during the smelting process. It forms an iron silicate slag (\(\mathrm{FeSiO}_{3}\)) that separates from the molten copper.

Step 4: Selecting the Correct Option

Since silica is used to remove \(\mathrm{FeO}\) by forming iron silicate, the answer is (c) \(\mathrm{FeO}\).

Key Concepts

Silica Flux

In the process of copper smelting, silica plays an essential role as a flux. But what exactly is a flux? It is a substance that helps remove impurities by reacting with them, forming a separable layer. Silica (\(\mathrm{SiO}_{2}\)) is particularly useful because it reacts with iron oxides present in the ore. This interaction is crucial for cleaning molten metal of useless impurities.
The primary idea is to purify the copper by separating out iron oxides through chemical reactions. Silica facilitates the removal of impurities by dissolving them into a fluid-like state called slag. This process supports the formation of a more refined copper by helping to rid the ore of unwanted materials. Consequently, silica is integral to a successful smelting process, making it a go-to flux in metal extraction.

Iron Silicate Slag

During the smelting of copper ores, the formation of iron silicate slag is an important part of impurity removal. When silica is added to the smelting furnace, it creates a reaction with iron oxide (\(\mathrm{FeO}\)). The end result of this reaction is the formation of \(\mathrm{FeSiO}_{3}\), known as iron silicate slag.
This slag has a lower density than the molten copper, allowing it to float on top and be removed easily.
Here are some key points about iron silicate slag:

• The slag separates easily, ensuring that only copper is left behind.
• It serves as a protective layer, preventing the re-oxidation of copper.
• The entire process enhances the quality of the final copper product.

By producing an iron silicate slag, the smelting process becomes efficient, enhancing the purity and quality of the copper extracted.

Metal Extraction Processes

Smelting is one of the key methods used in metal extraction processes. The goal is to extract metal in its pure form from an ore, leaving behind impurities. Silica flux and the creation of iron silicate slag are fundamental to this process. By removing unwanted elements through melting and chemical reactions, smelting helps in obtaining high-quality metal.
Key characteristics of metal extraction via smelting include:

• Use of high temperatures to melt ore and separate impurities.
• Reactions facilitated by flux to convert impurities into slag.
• Physical separation of metal and slag due to differences in density.

This method relies on flux like silica to handle the chemical side, forming slag that sinks or floats away from the base metal. Smelting, along with roasting and calcining, is part of a larger group of pyrometallurgical processes, each playing a significant role in obtaining and refining metals from their ores.