Aluminium: anodization extraction

Hall-Heroult cell The electrolysis cell in which aluminium is extracted from purified bauxite dissolved in molten cryolite at 900°C. This cell has both a graphite anode and a graphite cathode. 

Enclosed processes are to be preferred because collection and absorption of arty emitted gases and vapoms is more easily achieved. However, open or semi-open tanks are used for some processes such as metal plating or aluminium anodizing. Effective control of emissions can be achieved with ventilation, such as push-pull over the smface of the liquid or slot extraction roimd the lip of the tank. 

Many metals are extracted from their compounds, as found in ores, by electrolytic processes. By far the most important is the Hall-Heroult process, invented in 1886, for producing aluminium from alumina, itself refined from bauxite ore. Alumina is dissolved in molten cryolite, Na3Alp6, and electrolysed, using carbon anodes and the aluminium itself as cathode. While various details are being steadily improved, the basic process is still the same today. 

Aluminium is one of the most abundant elements in the earth s crust, but, under feasible industrial conditions, can only be extracted by electrolysis. The process used is the electrolysis of aluminium hydroxide in molten cryolite (Na3AlF6) at 1030°C, pure aluminium hydroxide having been prepared from the mineral bauxite (hydrated aluminium oxide containing silica and some metal oxides such as iron) by the Bayer process. The cathode is carbon covered by molten aluminium metal and the anode is carbon, the total reaction being... 

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