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Questions and Answers
What is the purpose of the coke powder layer in the electrorefining of aluminum?
What is the purpose of the coke powder layer in the electrorefining of aluminum?
- To enhance the conductivity of the electrolyte
- To act as a catalyst for the reaction
- To increase the density of the molten aluminum
- To prevent corrosion at the liquid-solid-air interface (correct)
Which component of the electrolyte mixture is essential for adjusting density in the electrorefining process?
Which component of the electrolyte mixture is essential for adjusting density in the electrorefining process?
- CaF2
- Cryolite
- BaF2 (correct)
- Al2O3
Why is copper deliberately added to impure aluminum during the electrorefining process?
Why is copper deliberately added to impure aluminum during the electrorefining process?
- To improve the flow of electricity
- To increase the density for layer separation (correct)
- To promote the oxidation reaction
- To enhance thermal conductivity
What occurs at the cathode during the electrorefining process of aluminum?
What occurs at the cathode during the electrorefining process of aluminum?
What is the primary purpose of adding cryolite in the electrolytic reduction of Al2O3?
What is the primary purpose of adding cryolite in the electrolytic reduction of Al2O3?
Which chemical species is formed in the Bayer process when aluminum hydroxide reacts with sodium hydroxide?
Which chemical species is formed in the Bayer process when aluminum hydroxide reacts with sodium hydroxide?
In the electrolytic reduction process, what role does the carbon lining of the iron tank serve?
In the electrolytic reduction process, what role does the carbon lining of the iron tank serve?
What is the result of the reaction between CO2 and hydroxide ions in the context of aluminum processing?
What is the result of the reaction between CO2 and hydroxide ions in the context of aluminum processing?
What is an adverse effect of impurities in bauxite during the extraction of alumina?
What is an adverse effect of impurities in bauxite during the extraction of alumina?
Which component is NOT part of the molten mixture used in the Hall process?
Which component is NOT part of the molten mixture used in the Hall process?
During the electrolytic reduction of alumina, what is produced at the anode?
During the electrolytic reduction of alumina, what is produced at the anode?
In the Bayer process, which compound is primarily removed from bauxite to purify alumina?
In the Bayer process, which compound is primarily removed from bauxite to purify alumina?
What occurs at the anode during the Hall Process?
What occurs at the anode during the Hall Process?
Why is pure Al2O3 not used as the electrolyte in the Hall Process?
Why is pure Al2O3 not used as the electrolyte in the Hall Process?
Which of the following statements accurately describes the behavior of impurities in the Hall Process?
Which of the following statements accurately describes the behavior of impurities in the Hall Process?
What is the primary reason that aqueous solutions of Al salts cannot be used as electrolytes?
What is the primary reason that aqueous solutions of Al salts cannot be used as electrolytes?
What reaction occurs at the cathode during aluminum extraction from Al(NO3)3?
What reaction occurs at the cathode during aluminum extraction from Al(NO3)3?
Why is molten AlCl3 unsuitable as an electrolyte?
Why is molten AlCl3 unsuitable as an electrolyte?
In the Hall Process, what does the bottom layer typically represent?
In the Hall Process, what does the bottom layer typically represent?
What is the role of the hydroxide ions at the anode during the electrolysis with aqueous aluminum nitrate?
What is the role of the hydroxide ions at the anode during the electrolysis with aqueous aluminum nitrate?
Flashcards
Electrorefining of Aluminium
Electrorefining of Aluminium
A process to purify aluminium by using electrolysis. Impure aluminium is taken as anode, and the graphite rod is cathode.
Electrolyte in Aluminium Electrorefining
Electrolyte in Aluminium Electrorefining
Molten mixture of cryolite and BaF2, saturated with Al2O3. BaF2 is used instead of CaF2 to adjust density
Graphite rods in Electrorefining
Graphite rods in Electrorefining
Graphite rods act as electrodes in the electrolytic cell, connecting the electrical circuit
Impure Aluminium
Impure Aluminium
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Copper melt purpose
Copper melt purpose
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Electrolytic reduction of Al2O3
Electrolytic reduction of Al2O3
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Molten alumina composition
Molten alumina composition
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Electrolytic reduction container
Electrolytic reduction container
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Anode material
Anode material
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Cathode material
Cathode material
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Cryolite
Cryolite
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Fluorspar
Fluorspar
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Powdered coke layer
Powdered coke layer
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Electrolysis of Aluminum
Electrolysis of Aluminum
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Aluminum Anode
Aluminum Anode
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Aluminum Cathode
Aluminum Cathode
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Molten Cryolite Electrolyte
Molten Cryolite Electrolyte
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Impurities in Aluminum
Impurities in Aluminum
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Why not use pure Al2O3?
Why not use pure Al2O3?
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Aqueous Al Salt Electrolyte
Aqueous Al Salt Electrolyte
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Molten AlCl3 Electrolyte
Molten AlCl3 Electrolyte
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Study Notes
Bauxite Extraction
- Bauxite is the most common ore used for aluminum extraction.
- Two types of bauxite: red (impurities Fe₂O₃, SiO₂, TiO₂) and white (impurities SiO₂, Fe₂O₃, TiO₂).
- Main steps of aluminum extraction from bauxite:
- Beneficiation of bauxite to produce pure alumina
- Electrolytic reduction of pure alumina
- Electrorefining of aluminum
Bayer's Process
- Beneficiation process for red bauxite.
- Process stages shown in Figure 6.24.
- Finely powdered bauxite is digested with 45% NaOH at 150°C and 80 lb pressure for 8 hours.
- Reaction in step one: Al₂O₃ + 2OH⁻ + 3H₂O → 2[Al(OH)₄]⁻
- Reaction in step two: SiO₂ + 2NaOH → Na₂SiO₃ + H₂O
- Residue is Fe₂O₃, TiO₂ + other insoluble impurities
- Filtrate is NaAlO₂ + Na₂SiO₃
- Al(OH)₃ is precipitated (step 2) using water and a seeding agent, or CO₂.
- Pure Al₂O₃ is obtained after ignition at approximately 1100°C.
Hall's Process
- Beneficiation process for low-grade red bauxite.
- Various stages in Figure 6.25.
- Finely divided bauxite ore mixed with Na₂CO₃ and CaCO₃, fused at 1100°C.
- CO₂ is passed, and filtered to obtain Al₂O₃.
- Key reactions:
- Step 1: Al₂O₃ + Na₂CO₃ → 2NaAlO₂ + CO₂↑
- Step 2: SiO₂ + Na₂CO₃ → Na₂SiO₃ + CO₂↑
- Step 3: Fe₂O₃ + Na₂CO₃ → 2NaFeO₂ + CO₂↑
- Step 3: CaO + SiO₂ → CaSiO₃
- Step 3: 2NaAlO₂ + CO₂ + 3H₂O → 2Al(OH)₃↓ +Na₂CO₃
- Step 3: 2Al(OH)₃ → Al₂O₃ + 3H₂O
Serpeck's Process
- Beneficiation process for white bauxite in Figure 6.26
- Finely powdered bauxite + coke powder heated to 1800°C in N₂ gas.
- Reactions:
- Step 1: Al₂O₃ + 3C + N₂ → 2AIN(s) + 3CO↑
- Step 2: SiO₂ + 2C → Si↑ + 2CO ↑
- Step 3: AIN + NaOH + 3H₂O → Na[Al(OH)₄] + NH₃ + H₂O
- Step 3: Na[Al(OH)₄] → Al(OH)₃ ↓ + NaOH
Electrolytic Reduction of Al₂O₃
- Molten alumina (20%), cryolite (60%), and fluorspar (20%) are used in an iron tank.
- Carbon lining acts as the cathode.
- Graphite rod acts as the anode.
- Reactions: Al₂O₃ → 2Al³⁺ + 3O²⁻
- At cathode: Al³⁺ + 3e⁻ → Al
- At anode: 2O²⁻ → O₂ + 4e⁻
- Cryolite helps reduce melting temperature to 900°C and improve conductivity.
Electrorefining of Aluminium
- Impure aluminium mixed with copper melt is used, with a graphite lining.
- Pure Al layer acts as the cathode.
- The electrolyte is a molten mixture of cryolite, and BaF₂ or CaF₂.
- Impurities like Cu are removed by this process.
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