Aluminum Extraction
提炼铝 tí liàn lǚ
Aluminum 铝 lǚ is normally extracted from its the ore (mineral) bauxite 铝矾土 lǚ fán tǔ that contains aluminium oxide 氧化铝 yǎng huà lǚ, Al2O3, . Bauxite 铝矾土 lǚ fán tǔ is not soluble in water and must be melted to release its ions. Cryolite (sodium hexafluoroaluminate Na3AlF6) 冰晶石 bīng jīng shí is added to lower the melting point 熔点 róng diǎn of aluminium oxide 氧化铝 yǎng huà lǚ to 9000C from 20450C.
Using carbon 碳 tàn electrodes, the molten aluminium oxide 氧化铝 yǎng huà lǚ is electrolysed (subjected to electrolysis 电解 diàn jiě). The ions available in the electrolyte 电解质 diàn jiě zhì are aluminium Al3+ ions and oxide O2- ions.
The aluminium cations Al3+ migrate to the cathode (carbon 碳 tàn lining) and are discharged.
Al3+(l) + 3e- → Al(s) .
Gain of Electrons ⇨ Reduction (GER)
Reduction happens at the cathode.
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The oxide anions O2- migrate to the anode (carbon 碳 tàn electrodes) and are discharged.
2O2-(l) → O2(g) + 4e-
Loss of Electrons ⇨ Oxidation (LEO)
Oxidation happens at the anode.
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The overall equation for the above is
2Al2O3 → 4Al(l) + 3O2(g)
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The carbon 碳 tàn anode has to be replaced from time to time as it is corroded in the electrolysis 电解 diàn jiě process.
C(s) + O2(g) → CO2(g)
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