铝的电解Hall–Héroult process

Al₂O₃ 熔点高达 2072 °C，直接电解耗能太大；冰晶石能溶解 2–6% 的氧化铝，使电解温度降到 1000 °C 以下。阴极（槽底碳块上的铝液）上 Al³⁺ 被还原为铝；阳极上氧离子与碳反应生成 CO₂，碳阳极不断被消耗，需要定期更换。每吨铝约耗电 13–15 MWh，消耗约 0.4 吨碳阳极。

Alumina melts at 2072 °C, too high for direct electrolysis; cryolite dissolves 2–6% alumina and lowers the operating temperature below 1000 °C. At the cathode, the pool of molten aluminium on the carbon cell bottom, Al³⁺ is reduced to the metal; at the anode oxide ions react with carbon to give CO₂, so the anodes are consumed and replaced regularly. Each tonne of aluminium uses about 13–15 MWh of electricity and about 0.4 tonnes of anode carbon.

1825 年奥斯特、1827 年维勒用钾还原 AlCl₃ 制得少量铝，19 世纪中叶铝比黄金还贵。1886 年美国的查尔斯·马丁·霍尔和法国的保罗·埃鲁几乎同时独立发明了冰晶石-氧化铝熔盐电解法，两人都出生于 1863 年、逝世于 1914 年。1888 年拜耳发明从铝土矿制纯氧化铝的拜耳法，两者结合使铝价暴跌，铝成为大宗金属。

Ørsted in 1825 and Wöhler in 1827 made small amounts of aluminium by reducing AlCl₃ with potassium, and in the mid-nineteenth century aluminium cost more than gold. In 1886 Charles Martin Hall in the United States and Paul Héroult in France independently invented cryolite–alumina electrolysis; both were born in 1863 and died in 1914. Bayer's 1888 process for making pure alumina from bauxite completed the route, the price of aluminium collapsed, and it became a bulk metal.

电解铝是高耗电行业，碳阳极反应和全氟化碳（CF₄、C₂F₆，阳极效应时产生）排放温室气体。改进方向包括惰性阳极（放出 O₂ 而不是 CO₂）、使用水电等清洁电力和提高再生铝比例——回收铝只需原铝约 5% 的能耗。

Aluminium smelting is very power-intensive, and the carbon anode reaction and perfluorocarbons (CF₄ and C₂F₆, formed during anode effects) emit greenhouse gases. Improvements include inert anodes that release O₂ instead of CO₂, clean hydro power and more recycling: secondary aluminium needs only about 5% of the energy of primary metal.