Question

Which of the following are correctly matched? (a) Zone refining - Ultra pure Ge (b) Leaching - Extraction of \(\mathrm{Au}, \mathrm{Ag}\) (c) Cyanide process - Extraction of Au (d) Electrolyte reduction - Extraction of Al

Short answer

Option (a), (b), (c), and (d) are all correctly matched.

Step-by-step solution

Understanding the Options

Review the matching options provided in the exercise: (a) Zone refining - Ultra pure Ge(b) Leaching - Extraction of \(\mathrm{Au}, \mathrm{Ag}\)(c) Cyanide process - Extraction of Au(d) Electrolyte reduction - Extraction of Al. Consider each technique or process and the related element they are associated with.

Analyzing Option (a)

Zone refining is a technique used to purify metals by eliminating impurities. It is commonly used for obtaining highly pure Germanium (Ge) and Silicon (Si). Hence, option (a) is correctly matched.

Analyzing Option (b)

Leaching is a process where certain components are dissolved and extracted from ores. It is often used for extracting \(\mathrm{Au}\) (Gold) and \(\mathrm{Ag}\) (Silver) using cyanide solutions, hence option (b) is correctly matched.

Analyzing Option (c)

The Cyanide process, also known as cyanidation, is a method used to extract gold (Au) from its ores using an aqueous cyanide solution. Thus, option (c) is correctly matched.

Analyzing Option (d)

Electrolytic reduction, also known as electrolysis, is not typically used for aluminum extraction. Aluminum is usually extracted using the Hall-Héroult process, which involves electrolysis, so while electrolytic processes are involved, the specific term might not correctly reflect the extraction in the context given. Nonetheless, it's generally understood as correct for Al.

Key concepts

Zone Refining

Zone refining is a technique employed to achieve ultra-purification of metals. This method is crucial when metals like Germanium (Ge) and Silicon (Si) are required at high purity levels for semiconductor applications. The process involves creating a molten zone that is passed along a rod of the impure metal. As this zone moves, impurities are dissolved in the melting zone and driven to one end of the rod, leaving behind a purer solid metal.

Zone refining exploits the principle that impurities tend to concentrate in the liquid phase rather than in the solid phase as a crystallizing solid forms.

• The rod is slowly heated from one end to create a narrow molten zone.
• The impurities in the molten region migrate with the molten zone towards the cooler end of the rod.
• Once the zone reaches the opposite end, it cools and solidifies, leaving behind a solid metal with reduced impurity content.

Zone refining can achieve very high purity levels, essential for the electronics industry.

Cyanide Process

The cyanide process, also known as cyanidation, is a metallurgical technique used to extract gold (Au) from its ores. This method capitalizes on the ability of cyanide ions to form a complex with gold, effectively dissolving it from the ore.

Here's a brief overview of the cyanide process:

• Crushed ore is first treated with a diluted cyanide solution.
• Gold, being soluble in cyanide solutions, forms a soluble gold-cyanide complex.
• The gold-bearing liquid is then separated from the non-valuable solid material.
• The dissolved gold is recovered from the solution through absorption onto activated carbon or by precipitation through adding zinc.

This method is highly effective for low-grade ores and allows for the economic extraction of gold, which was previously considered uneconomical.

Leaching

Leaching is a process widely used for the extraction of metals like gold (Au) and silver (Ag) from their ores. It involves dissolving the desired metal from the solid ore into a solvent. This process is particularly advantageous when dealing with ores of low concentration.

In leaching:

• A solvent, often a diluted solution of sodium or potassium cyanide, is used.
• This solvent percolates through the finely ground ore, dissolving the metal.
• The resulting metal-cyanide complex is collected in a solution.
• The valuable metal is then separated and recovered from this solution, typically by adsorption or precipitation techniques.

Leaching is favored for its efficiency in metal recovery, especially for large-scale production in mining operations.

Electrolytic Reduction

Electrolytic reduction is a method used to extract metals from their compounds by passing an electric current through the compound, causing it to decompose into its elemental form. While this method may not be directly involved in the primary extraction process of aluminum from its ore, it plays a crucial role in several metal extractions.

For metals like aluminum, the Hall-Héroult process is utilized. This process involves:

• Dissolving aluminum oxide in molten cryolite to lower its melting point.
• An electric current is passed through the solution, causing the aluminum ions to gain electrons (reduced) and form pure aluminum at the cathode.
• This aluminum is then collected and solidified.

This method is energy-intensive but essential for extracting aluminum due to its stability in compounds, emphasizing the importance of electrolysis in industrial metal production.