Extraction of Aluminium: Bayers Process
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Questions and Answers

What is the ore used in the extraction of aluminum and what is its chemical formula?

The ore used is bauxite, with the chemical formula Al2O3.2H2O.

Describe the method used for dressing of the ore in the extraction of aluminum.

The method used for dressing the ore is a chemical method involving concentrated sodium hydroxide (NaOH).

What is the main purpose of the Hall-Héroult process in aluminum extraction?

The Hall-Héroult process is used for the electrolytic reduction of pure alumina (Al2O3) to produce pure aluminum (Al).

What are the components of the electrolyte used in the electrolysis of alumina?

<p>The electrolyte consists of a mixture of fused alumina (Al2O3), cryolite (Na3AlF6), and fluorspar (CaF2).</p> Signup and view all the answers

What are the products formed at the electrodes during the electrolysis of alumina?

<p>At the cathode, pure aluminum (Al) is produced, while oxygen gas is evolved at the anode.</p> Signup and view all the answers

Why is the conversion of concentrated ore to its oxide not necessary in aluminum metallurgy?

<p>The conversion is not necessary because the ore is already in the oxide form, specifically as alumina (Al2O3).</p> Signup and view all the answers

What is the purity of aluminum typically obtained from the Hall-Héroult process?

<p>The aluminum obtained typically has a purity of about 99.5%.</p> Signup and view all the answers

Explain the significance of Bayer's process in the extraction of aluminum.

<p>Bayer's process is significant as it purifies bauxite into pure alumina (Al2O3), which is essential for aluminum production.</p> Signup and view all the answers

What role does sodium hydroxide play in the Bayer process for extracting aluminum from bauxite?

<p>Sodium hydroxide reacts with bauxite to form sodium aluminate and separates impurities by remaining unaffected due to their non-amphoteric nature.</p> Signup and view all the answers

Describe the process used to convert sodium aluminate to aluminum hydroxide.

<p>Sodium aluminate is diluted with water and reacted with additional water to precipitate aluminum hydroxide through a process called seeding.</p> Signup and view all the answers

What happens to aluminum hydroxide when heated at 1100°C?

<p>When aluminum hydroxide is heated at 1100°C, it decomposes to form pure alumina (Al2O3) and releases water vapor.</p> Signup and view all the answers

How does Hall's process differ from Bayer's process in the treatment of bauxite?

<p>Hall's process involves converting impure bauxite into sodium aluminate using sodium carbonate, while Bayer's process uses sodium hydroxide.</p> Signup and view all the answers

What is the importance of seeding in the conversion of sodium aluminate to aluminum hydroxide?

<p>Seeding provides crystals of Al(OH)3 that promote the precipitation of aluminum hydroxide from the solution.</p> Signup and view all the answers

Identify the main impurities in bauxite that are not removed during the Bayer process.

<p>The main impurities are iron(III) oxide (Fe2O3) and silicon dioxide (SiO2), which remain unaffected by sodium hydroxide.</p> Signup and view all the answers

What is the chemical reaction that occurs when aluminum hydroxide is ignited?

<p>The reaction is 2Al(OH)3 at 1100°C → Al2O3 + 3H2O (vapors).</p> Signup and view all the answers

What are the products of the first step in Hall's process for dressing ore?

<p>The products are sodium aluminate, water, and carbon dioxide gas after heating impure bauxite with sodium carbonate.</p> Signup and view all the answers

Study Notes

Extraction of Aluminium

STEP 1: Dressing of the Ore

  • Bauxite is the ore used, composed of hydrated aluminium oxide (Al2O3.2H2O).
  • The Bayer's Process is employed, which is a chemical method involving concentrated sodium hydroxide (NaOH).
  • The process converts impure bauxite into pure alumina (Al2O3).
  • Main reaction:
    • Amphoteric oxide reacts with a base at 150°C to produce salt and water.
    • Hydrolysis of the resulting salt at 50°C yields soluble and insoluble hydroxides.
    • The insoluble hydroxide, upon ignition, forms pure alumina and water.

STEP 2: Conversion of Concentrated Ore

  • Direct conversion to oxide is not necessary since the ore is already in oxide form.

STEP 3: Reduction of Metallic Oxide to Metal

  • Hall-Héroult's Process is utilized for electrolytic reduction.
  • The conversion involves transforming pure alumina (Al2O3) into pure aluminium (Al).
  • The electrolyte comprises a mixture of fused alumina, cryolite (Na3AlF6), and fluorspar (CaF2); these solvents reduce the melting point and enhance conductivity.
  • Inert graphite electrodes are used.
  • The electrolysis reaction produces:
    • Pure aluminium at the cathode.
    • Oxygen gas at the anode, with potential carbon dioxide and carbon monoxide emissions due to anode oxidation.

STEP 4: Electrorefining of Impure Metal

  • This step is generally unnecessary as the electrolysis yields aluminium of about 99.5% purity.
  • If further refining is required, Hooper's Process can achieve approximately 99.9% pure aluminium.

ORES OF ALUMINIUM

  • Bauxite is the primary ore for aluminium extraction.
  • Other ores include Cryolite and Corundum.

STEP 1: DRESSING OF THE ORE - BAYER'S PROCESS

  • Concentration of bauxite ore involves purification through chemical reaction.

CONVERSION OF IMPURE BAUXITE TO SODIUM ALUMINATE

  • Reaction formula: Al2O3.2H2O + 2NaOH (150-200°C) → 2NaAlO2 + 3H2O.
  • Bauxite (impure) is treated with concentrated sodium hydroxide (NaOH) under pressure.
  • The process leverages the amphoteric nature of bauxite to react with the base, forming sodium aluminate and water.
  • Impurities like Fe2O3 and SiO2 remain unaffected due to their non-amphoteric properties.

FUNCTION OF SODIUM HYDROXIDE

  • Sodium hydroxide facilitates the separation of impurities during purification.
  • The concentrated solution reacts selectively with bauxite, leaving behind iron and silicon oxides while producing sodium aluminate.

CONVERSION OF SODIUM ALUMINATE TO ALUMINIUM HYDROXIDE

  • Reaction formula: NaAlO2 + 2H2O (50-60°C) → NaOH + Al(OH)3↓.
  • Sodium aluminate is diluted with water and seeds of Al(OH)3 are added to precipitate more aluminium hydroxide through a process called "seeding."
  • The precipitated aluminium hydroxide is filtered and dried.

CONVERSION OF Al(OH)3 TO PURE ALUMINA

  • Reaction formula: 2Al(OH)3 (1100°C) → Al2O3 + 3H2O (vap).
  • The dried Al(OH)3 is ignited to produce pure alumina, Al2O3.

ALTERNATIVE METHOD: HALL'S PROCESS

DRESSING OF ORE VIA HALL'S PROCESS

  • Impure bauxite is converted to sodium aluminate by heating with sodium carbonate.
  • Reaction formula: Al2O3.2H2O + Na2CO3 (heat) → 2NaAlO2 + 2H2O + CO2[g].
  • Carbon dioxide is bubbled into the sodium aluminate solution to precipitate aluminium hydroxide.
  • Reaction formula: 2NaAlO2 + 3H2O + CO2 → Na2CO3 + 2Al(OH)3↓.
  • The dry aluminium hydroxide is then ignited at 1100°C, resulting in pure alumina.
  • Final reaction: 2Al(OH)3 (1100°C) → Al2O3 + 3H2O (vap).

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Description

This quiz covers the stages involved in the extraction of aluminium, focusing on the dressing of bauxite ore and the chemical methods used. Understand the Bayer process and the conversion from impure bauxite to pure alumina. Test your knowledge on the chemical reactions involved in this industrial process.

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