The production of aluminum ingots primarily consists of two stages: alumina production (Bayer process) and aluminum electrolysis (Hall-Héroult process), followed by casting to form ingots. Below is a detailed breakdown:

I. Alumina Production (Bayer Process)

1. Raw Material Preparation

• Bauxite ore (containing Al₂O₃) is crushed and ground into fine powder, then mixed with sodium hydroxide (NaOH) solution.

2. High-Pressure Digestion

• The slurry is heated in autoclaves (140–250°C), where alumina reacts with NaOH to form sodium aluminate solution:Al2O3+2NaOH→2NaAlO2+H2O

3. Settling & Separation

• The digested slurry undergoes sedimentation to remove insoluble impurities (e.g., iron, silica, forming "red mud").

4. Precipitation & Crystallization

• The sodium aluminate solution is cooled, and aluminum hydroxide seed crystals are added to precipitate Al(OH)₃:NaAlO2+2H2O→Al(OH)3↓+NaOH

5. Calcination

• Aluminum hydroxide is roasted at 1000–1200°C to produce alumina (Al₂O₃):2Al(OH)3High Temp.Al2O3+3H2O

II. Aluminum Electrolysis (Hall-Héroult Process)

1. Electrolytic Cell Setup

• Alumina is dissolved in molten cryolite (Na₃AlF₆) to form an electrolyte (~950°C), lowering the melting point.

2. Electrolysis

• Direct current is applied, triggering the reaction between alumina and carbon anodes:2Al2O3+3C→4Al+3CO2↑

• Molten aluminum collects at the cathode, while CO₂ gas is released at the anode.

3. Tapping

• Liquid aluminum is periodically siphoned from the cell using vacuum ladles and transferred to holding furnaces.

III. Ingot Casting

1. Refining

• The molten aluminum undergoes degassing (e.g., argon purging) and filtration to remove impurities. Alloying elements may be added.

2. Casting

• The refined aluminum is poured into molds (e.g., rectangular ingot molds) and cooled to solidify.

3. Post-Processing

• Ingots are marked (with batch numbers, composition), stacked, and stored or shipped for further processing.

Key Notes

• Energy Consumption: Electrolysis is highly energy-intensive (~13,500 kWh/ton of Al), accounting for >40% of production costs.

• Environmental Impact: The process emits CO₂ and perfluorocarbons (PFCs). Modern technologies (e.g., inert anodes) aim to reduce emissions.

• Recycling: Smelting scrap aluminum consumes only ~5% of the energy required for primary production, making it a sustainable alternative.