Isolation of Metals

• Process of obtaining pure metals from their ores
• Various methods used for isolation
• Today we will focus on the isolation of aluminium from alumina

Alumina (Aluminum Oxide)

• Main ore for the extraction of aluminium
• Formula: Al₂O₃

Bayer Process

• Most widely used method for isolation of aluminium from alumina
• Developed by Karl Josef Bayer in 1888
• Steps involved:
  1. Digestion
  2. Clarification
  3. Precipitation
  4. Filtration
  5. Calcination
  6. Electrolysis

Digestion

• Crushed alumina is mixed with hot concentrated caustic soda (NaOH) solution
• Purpose: Dissolving alumina to form sodium aluminate (NaAlO₂)
• Equation: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

Clarification

• Sodium aluminate solution is cooled and treated with some aluminum hydroxide (Al(OH)₃)
• Purpose: Clarifying the solution by removing impurities
• Equation: NaAlO₂ + Al(OH)₃ + H₂O → NaAl(OH)₄

Precipitation

• Co2 is bubbled through the clarified solution
• Purpose: Precipitation of pure aluminum hydroxide (Al(OH)₃)
• Equation: NaAl(OH)₄ + CO₂ + 2H₂O → Al(OH)₃ + NaHCO₃

Filtration

• The precipitate of aluminum hydroxide is filtered
• Purpose: Separation of the precipitate from the solution
• The remaining sodium bicarbonate solution is recycled for the next precipitation process

Calcination

• The aluminum hydroxide precipitate is heated strongly
• Purpose: Conversion of aluminum hydroxide to alumina
• Equation: 2Al(OH)₃ → Al₂O₃ + 3H₂O

Electrolysis

• Alumina (Al₂O₃) is dissolved in molten cryolite (Na₃AlF₆)
• Cryolite lowers the melting point of alumina
• Purpose: Extraction of aluminum metal through electrolysis
• Equation: Al₂O₃ → 2Al³⁺ + 6e^-

Electrolysis (Continued)

• Aluminum ions migrate towards the cathode and get reduced
• At the cathode, aluminum ions gain electrons and convert into molten aluminum metal
• Equation: 2Al³⁺ + 6e^- → 2Al

Physical Properties of Aluminium

• Atomic number: 13
• Atomic mass: 26.98 g/mol
• Melting point: 660.32°C
• Boiling point: 2519°C
• Density: 2.70 g/cm³

Chemical Properties of Aluminium

• Reacts with oxygen to form a protective layer of aluminum oxide (Al₂O₃)
• Reacts with halogens to form aluminum halides (AlCl₃, AlBr₃, AlI₃)
• Reacts with acids to liberate hydrogen gas (H₂)
• Reacts with bases to form aluminates (Al(OH)₄^-)

Uses of Aluminium

• Construction industry (doors, windows, frames)
• Transportation industry (aircraft, automobiles)
• Packaging industry (cans, foils)
• Electrical industry (wires, cables)
• Household utensils (pots, pans)

Aluminium Alloys

• Alloy: A mixture of a metal with one or more other elements
• Aluminium alloys are widely used due to their superior properties
• Examples:
  • Duralumin (with copper, manganese, and magnesium)
  • Alnico (with aluminum, nickel, and cobalt)
  • Aluminium-silicon alloys (with silicon for increased strength)

Environmental Impact of Aluminium Extraction

• Energy Intensive: Extraction of aluminium requires a significant amount of energy, contributing to carbon emissions
• Deforestation: The mining of bauxite, the main source of alumina, often leads to deforestation
• Air and Water Pollution: Refining processes lead to the release of toxic chemicals and pollutants
• Land Degradation: Mining activities can cause irreversible damage to landscapes

Recycling Aluminium

• Aluminium can be recycled multiple times without losing its properties
• Recycling saves energy and reduces greenhouse gas emissions
• Recycling can be done through melting and re-molding or by using molten salt electrolysis
• Recycling aluminum requires only 5% of the energy needed to produce new aluminum

Aluminium Hydride (AlH₃)

• Aluminium hydride is an important compound
• It is a white solid that releases hydrogen gas when reacted with water
• Used as a source of hydrogen in fuel cells and in the production of certain chemicals

Aluminium Oxide (Al₂O₃)

• Aluminum oxide has various applications due to its properties
• Used as an abrasive in sandpapers and grinding wheels
• Used as a catalyst in some chemical reactions
• Forms gemstones like ruby and sapphire when impurities are present

Aluminium Chloride (AlCl₃)

• Aluminium chloride is a white solid that absorbs moisture from the air
• Used as a catalyst in many organic reactions, such as the Friedel-Crafts reaction
• Often prepared by the reaction of aluminum with chlorine gas

Summary

• Aluminium is obtained from alumina through the Bayer process
• Alumina is dissolved in molten cryolite and electrolyzed to obtain pure aluminium
• Aluminium has various physical and chemical properties
• It finds applications in industries such as construction, transportation, and packaging
• Recycling aluminium is an energy-efficient and environmentally friendly option

Alloys of Aluminium

• Aluminium can be alloyed with other metals to enhance its properties
• Examples of aluminium alloys:
  • Aluminum-copper alloys (duralumin)
  • Aluminum-silicon alloys
  • Aluminum-magnesium alloys
  • Aluminum-zinc alloys

Duralumin

• Duralumin is an aluminum-copper alloy
• It contains about 4% copper, 1% magnesium, and traces of manganese
• Properties:
  • High strength
  • Corrosion-resistant
  • Lightweight
• Applications:
  • Aircraft construction
  • Structural components in buildings
  • Automotive industry

Aluminum-Silicon Alloys

• Adding silicon to aluminum increases its strength and fluidity
• Used in the manufacturing of engine parts and cylinder heads
• Exhibits good thermal conductivity and wear resistance

Aluminum-Magnesium Alloys

• Aluminum-magnesium alloys have high strength-to-weight ratios
• Commonly used in aerospace applications
• Benefits:
  • Lightweight
  • High corrosion resistance
  • Excellent weldability

Aluminum-Zinc Alloys

• Aluminum-zinc alloys exhibit excellent mechanical properties
• Known as zinc-aluminum or aluminum-zinc-magnesium alloys (ZAM)
• Applications:
  • Roofing material (galvalume)
  • Automotive body panels
  • Electrical appliances

Reactions of Aluminium

• Aluminium reacts with various substances due to its reactivity
• Reactions:
  • Reaction with oxygen
  • Reaction with acids
  • Reaction with bases

Reaction with Oxygen

• Formation of a protective layer of aluminum oxide (Al2O3)
• Equation: 4Al + 3O2 → 2Al2O3

Reaction with Acids

• Aluminum reacts with acids to liberate hydrogen gas (H2)
• Examples:
  • Aluminum + hydrochloric acid → aluminum chloride + hydrogen gas
  • 2Al + 6HCl → 2AlCl3 + 3H2

Reaction with Bases

• Aluminum reacts with bases to form aluminates (Al(OH)4-)
• Equation: 2Al + 2OH- + 6H2O → 2Al(OH)4-

Summary

• Aluminium can be alloyed with other metals to enhance its properties
• Examples include duralumin, aluminum-silicon alloys, aluminum-magnesium alloys, and aluminum-zinc alloys
• Reactions of aluminum include reactions with oxygen, acids, and bases
• These reactions result in the formation of aluminum oxide, liberation of hydrogen gas, and formation of aluminates