Question

Roasting of copper pyrites is done (a) To oxidize free sulphur (b) Ro remove moisture (c) To remove volatile organic impurities (d) To decompose sulphides into oxides.

Short answer

(d) To decompose sulphides into oxides.

Step-by-step solution

Understand Roasting

Roasting is a metallurgical process used to convert sulfide ores into oxides. This is done by heating the ore in the presence of oxygen. This step is crucial because many sulfide ores are not directly reducible or usable in their sulfide form.

Identify Copper Pyrites Composition

Copper pyrites, also known as chalcopyrite, is mainly composed of copper iron sulfide (CuFeS₂). The target in processing is the conversion of this sulfide into oxide forms.

Determine the Effect of Roasting on Copper Pyrites

When copper pyrites is roasted, its sulfide compounds decompose in the presence of oxygen, resulting in the formation of oxides. The general reaction involves turning sulfide ions (S²⁻) into oxide ions (O²⁻) by replacing sulfur with oxygen.

Analyze Given Options

- Option (a) 'To oxidize free sulphur' is not entirely correct as it doesn't specifically require 'free' sulfur to be targeted. - Option (b) 'To remove moisture' is irrelevant because roasting focuses on chemical conversions rather than physical drying. - Option (c) 'To remove volatile organic impurities' is not applicable as it targets sulfur compounds for oxidation. - Option (d) 'To decompose sulphides into oxides' correctly describes roasting, where sulfides are decomposed into their corresponding oxides.

Select the Correct Answer

Based on the analysis, the correct option is (d) 'To decompose sulphides into oxides' as it matches the actual purpose and process of roasting in metallurgy.

Key concepts

Metallurgical processes

Metallurgical processes are vital techniques employed in the extraction and refinement of metals from their ores. These processes are essential for obtaining pure metal from raw materials. They often involve a combination of mechanical and chemical methods.
One key metallurgical process is roasting, where sulfide ores are converted to oxides by heating them in oxygen. This process is crucial when working with ores that cannot be directly reduced from their sulfide form, like the copper pyrites.

Copper pyrites

Copper pyrites, widely known as chalcopyrite, is a significant source of copper. It is composed primarily of copper iron sulfide or CuFeS₂. This mineral is a yellowish, metallic-looking ore common in various parts of the world.
Processing copper pyrites is crucial since direct extraction of copper metal from it isn't viable. Instead, the ore needs to undergo metallurgical processes such as roasting to transform it into a form from which copper can be more effectively extracted.

Sulfide to oxide conversion

The conversion of sulfide ores into oxides is a fundamental part of the metallurgical process known as roasting. This transformation is critical because many sulfide ores cannot be directly processed for metal extraction without this step.
During roasting, the sulfide compound is exposed to oxygen, facilitating a chemical reaction where the sulfur in the sulfide is replaced by oxygen, forming an oxide. This chemical change is crucial for further processing and extraction of the desired metal.

Chalcopyrite

Chalcopyrite is one of the most important minerals for copper extraction. It exhibits a brass-yellow metallic luster and is often found with minerals such as pyrite and quartz. Due to its significant copper content, chalcopyrite is extensively mined and processed in the metallurgical industry.
The challenge with chalcopyrite lies in its composition as a sulfide, which requires roasting to convert it into oxides. This process transforms chalcopyrite into a state suitable for extracting pure copper.

Chemical reactions in roasting

Chemical reactions during roasting are centered on the transformation of sulfide ores into oxides. This is achieved by heating these ores in the presence of excess oxygen.
For copper pyrites like chalcopyrite (CuFeS₂), the primary reaction involves the breaking of sulfur bonds and their replacement with oxygen. The general equation of this transformation can be represented as: \[ 2CuFeS_2 + 5O_2 \rightarrow 2CuO + 2FeO + 4SO_2 \] This reaction highlights the conversion from sulfide to oxide, while releasing sulfur dioxide as a byproduct. Understanding this reaction is crucial for processing ores efficiently.