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霍尔-埃鲁法

1886-04-23

Charles Martin Hall
Paul Héroult

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The Hall-Héroult process is the major industrial 方法 for smelting aluminum. It involves dissolving alumina (aluminum oxide, Al₂O₃) in molten cryolite (Na₃AlF₆) and electrolyzing the molten salt bath. Aluminum metal is deposited at the cathode, while oxygen from the alumina reacts with the carbon anode, producing carbon dioxide. This process made aluminum widely available and affordable.

在霍尔-埃鲁法出现之前，铝被认为是一种贵金属，比黄金更珍贵，因为从铝矿石中提取铝极其困难。该工艺在高温下进行，温度约为940-980°C，在大型电解槽（称为电解池）内进行。氧化铝的熔点非常高（超过2000°C），直接电解不切实际。霍尔-埃鲁法的关键创新在于使用熔融的冰晶石作为溶剂，它可以溶解氧化铝，而且熔点更低，从而显著降低所需的能量。

The cell consists of a steel shell lined with carbon, which serves as the cathode. Carbon blocks suspended in the electrolyte bath act as the anode. During electrolysis, aluminum ions from the dissolved alumina are reduced at the cathode, forming molten aluminum which sinks to the bottom of the pot and is periodically tapped off: [latex]Al^{3+} + 3e^- \rightarrow Al(l)[/latex]. At the anode, oxide ions are oxidized to form oxygen gas. This oxygen immediately reacts with the hot carbon anode, forming carbon dioxide: [latex]2O^{2-} + C(s) \rightarrow CO_2(g) + 4e^-[/latex]. Because the carbon anodes are consumed in the process, they must be replaced regularly. The overall reaction is [latex]2Al_2O_3 + 3C \rightarrow 4Al + 3CO_2[/latex].

The process is extremely energy-intensive, consuming a significant portion of the world’s electricity. This is why aluminum smelters are often located near sources of inexpensive hydroelectric power. The high energy consumption also makes recycling aluminum highly advantageous, as it requires only about 5% of the energy needed to produce primary aluminum from ore.