Question

Extraction of metal from the ore cassiterite involves (A) carbon reduction of an oxide ore (B) self-reduction of a sulphide ore (C) removal of copper impurity (D) removal of iron impurity

Short answer

The extraction of metal from the ore cassiterite involves carbon reduction of an oxide ore, which is option (A).

Step-by-step solution

Identify the Composition of Cassiterite

The first step is to recognize that cassiterite is an ore containing tin oxide, SnO2. Cassiterite is primarily composed of this tin oxide.

Understand the Metallurgy Process for Tin

The second step is to understand that the extraction of tin from cassiterite involves heating the ore with carbon to reduce the tin oxide to tin metal. This process is known as carbon reduction.

Analyze the Options

Analyze each option given in the question to determine which one correctly describes the process of extracting tin from cassiterite. Since cassiterite is an oxide ore and is reduced using carbon to extract the metal, option (A) is the correct answer.

Cross-check with Other Options

To ensure the chosen option is correct, briefly examine options (B), (C), and (D). None of these options accurately describe the process of extracting tin from cassiterite. Self-reduction applies to sulphide ores, not oxides, and removal of copper or iron impurities is not the primary process involved in the extraction of tin from cassiterite.

Key concepts

Cassiterite Extraction

The journey of tin production begins with the mineral cassiterite, which is the main source of tin in metallurgy. Cassiterite is usually found in placer deposits, where it accumulates after being weathered from the parent rock, or in primary deposits where it is located in the original hard rock formation.

To extract cassiterite, mining operations dig open pits or mine in underground tunnels. Because cassiterite has a high specific gravity, gravity-based separation techniques are commonly used to concentrate the ore before further processing. This physical pre-concentration increases the tin content while reducing the bulk of the material that needs to undergo the more costly and energy-intensive chemical extraction processes.

Carbon Reduction Process

After obtaining a more concentrated form of cassiterite, the next pivotal stage is the carbon reduction process. In this step, the tin oxide within the cassiterite is chemically transformed to produce pure tin metal. This is done by heating the tin oxide with carbon, such as coke, at high temperatures in a furnace.

The carbon acts as a reducing agent, meaning it donates electrons to the tin oxide. This electron transfer changes the oxidation state of the tin, resulting in the formation of elemental tin and carbon dioxide gas. The chemical equation for this reaction is \[ \text{SnO}_2 + 2C \rightarrow Sn + 2CO_2. \]

The carbon reduction is a robust and widely used method in metallurgy due to its efficiency in extracting metals from their oxides.

Tin Oxide Reduction

Tin oxide reduction is the heart of the tin extraction process from cassiterite. After pre-concentration, the cassiterite is subjected to high temperatures in the presence of a reducing agent—the carbon. The secret behind the success of this reduction lies in the fact that at high temperatures, carbon is more reactive with oxygen than tin is, which allows it to strip away the oxygen atoms from the tin oxide.

This process results in liquid tin, which can be poured off and cooled into solid form. Impurities that are less dense than tin float on top of the molten metal and can be removed during or after the reduction process. It is crucial to control the temperature and composition of the reaction to prevent the formation of unwanted byproducts.

Ore Purification

Once the raw tin has been produced, it often contains impurities that need to be removed to obtain the desired level of purity. One method used to refine tin is called electrorefining. This involves placing impure tin at the anode in an electrolytic cell and pure tin at the cathode. An acid or salt solution is used as the electrolyte.

When electricity is passed through the cell, tin dissolves from the anode and deposits onto the cathode, leaving impurities behind or causing them to settle out of the electrolyte. Other methods, such as liquation or vacuum distillation, may also be employed depending on the nature of the impurities. The end goal of ore purification is to produce tin that is suitable for industrial use, from solder and plating to the production of specialty alloys.