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개요
Aluminum is produced by electrolysis of alumina (Al₂O₃) dissolved in molten cryolite (Na₃AlF₆) at 960 degrees C — the Hall-Heroult process independently invented by Charles Martin Hall and Paul Heroult in 1886. This is the most electricity-intensive metal production process, consuming approximately 13-16 kWh per kg of aluminum. Global production exceeds 70 million tons annually, with China producing over 55%. The alumina feedstock is produced from bauxite ore by the Bayer process. Aluminum's high strength-to-weight ratio makes it essential for transportation, construction, and packaging.
화학 공정
Alumina is dissolved in a bath of molten cryolite (Na₃AlF₆) with AlF₃ additions at 960-970 degrees C in a steel pot lined with carbon cathode. Carbon anodes are consumed as they react with the oxygen from alumina, producing CO₂. Molten aluminum (99.7-99.9% pure) sinks to the bottom of the cell and is periodically siphoned out. A single potline contains 300-600 cells in series at 4-5 V each, carrying 300,000-500,000+ amperes.
Cathode: Al³⁺ + 3e⁻ → Al(liquid)
Anode: C + 2O²⁻ → CO₂ + 4e⁻ (carbon anode consumed at ~0.4 kg C/kg Al)
원자재
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Alumina (Al₂O₃) — Bayer process from bauxite ore (Aluminum source)
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Cryolite (Na₃AlF₆) — Synthetic (from NaOH + HF + Al(OH)₃) (Electrolyte solvent (lowers Al₂O₃ melting point from 2,072 to 960 degrees C))
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Carbon anodes (pre-baked or Soderberg) — Petroleum coke + coal tar pitch (Consumable electrode)
최종 제품
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Primary aluminum (Al) — Transportation, construction, packaging, electronics (99.7-99.9% purity, alloyed for specific applications)
Environmental Impact
Aluminum smelting consumes approximately 3% of global electricity. CO₂ emissions come from anode consumption (~1.5 t CO₂/t Al) and electricity generation. PFC greenhouse gases (CF₄, C₂F₆) are emitted during anode effects — 10,000-25,000x more potent than CO₂. The Bayer process generates red mud (iron oxide waste) — approximately 150 million tons annually.
안전 고려사항
- ⚠ Molten aluminum at 960 degrees C — catastrophic if it contacts water (steam explosion)
- ⚠ Extremely high DC currents (300,000-500,000+ amps) — electrocution and arc flash hazard
- ⚠ Hydrogen fluoride (HF) emissions from electrolyte — toxic and corrosive
- ⚠ Carbon anode handling involves carcinogenic coal tar pitch volatiles
최근 혁신
Inert (non-consumable) anodes producing oxygen instead of CO₂ are in pilot stage (Elysis JV by Rio Tinto/Alcoa).
Mechanical vapor recompression in Bayer process reduces energy by 30%.
Secondary aluminum recycling requires only 5% of the energy of primary production.
Direct lithium extraction from Bayer process liquor is being explored.
생산 규모
70000000
톤/년
$170 billion
시장 가치