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The Hall–Héroult process is the major industrial process for smelting aluminium.It involves dissolving aluminium oxide (alumina) (obtained most often from bauxite, aluminium's chief ore, through the Bayer process) in molten cryolite and electrolyzing the molten salt bath, typically in a purpose-built cell.
Aluminium fluoride is an important additive for the production of aluminium by electrolysis. [4] Together with cryolite, it lowers the melting point to below 1000 °C and increases the conductivity of the solution. It is into this molten salt that aluminium oxide is dissolved and then electrolyzed to give bulk Al metal. [12]
Reactions of elemental fluorine with metals require varying conditions. Alkali metals cause explosions and alkaline earth metals display vigorous activity in bulk; to prevent passivation from the formation of metal fluoride layers, most other metals such as aluminium and iron must be powdered, [21] and noble metals require pure fluorine gas at ...
The direct reaction of hydrocarbons with fluorine gas can be dangerously reactive, so the temperature may need to be lowered even to −150 °C (−240 °F). [115] " Solid fluorine carriers", compounds that can release fluorine upon heating, notably cobalt trifluoride , [ 116 ] may be used instead, or hydrogen fluoride.
Aluminium smelting process: cryolite (a fluoride) is required to dissolve aluminum oxide. One third of HF (one sixth of mined fluorine) is used to make synthetic cryolite (sodium hexafluoroaluminate) and aluminium trifluoride. These compounds are used in the electrolysis of aluminium by the Hall–Héroult process. About 23 kg (51 lb) are ...
The difficulty of separating aluminium from oxygen in the oxide ores was overcome by the use of cryolite as a flux to dissolve the oxide mineral(s). Pure cryolite itself melts at 1012 °C (1285 K), and it can dissolve the aluminium oxides sufficiently well to allow easy extraction of the aluminium by electrolysis. Substantial energy is still ...
For example, metallic aluminium can reduce iron oxide to metallic iron, the aluminium itself being oxidized to aluminium oxide. (This reaction is employed in thermite .) The greater the gap between any two lines, the greater the effectiveness of the reducing agent corresponding to the lower line.
Aluminium has a high chemical affinity to oxygen, which renders it suitable for use as a reducing agent in the thermite reaction. A fine powder of aluminium reacts explosively on contact with liquid oxygen; under normal conditions, however, aluminium forms a thin oxide layer that protects the metal from further corrosion by oxygen, water, or ...