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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 oxide is an amphoteric substance, meaning it can react with both acids and bases, such as hydrofluoric acid and sodium hydroxide, acting as an acid with a base and a base with an acid, neutralising the other and producing a salt. Al 2 O 3 + 6 HF → 2 AlF 3 + 3 H 2 O Al 2 O 3 + 2 NaOH + 3 H 2 O → 2 NaAl(OH) 4 (sodium aluminate)
Sodium aluminate is also formed by the action of sodium hydroxide on elemental aluminium which is an amphoteric metal. The reaction is highly exothermic once established and is accompanied by the rapid evolution of hydrogen gas. The reaction is sometimes written as: 2Al + 2NaOH + 2H 2 O → 2NaAlO 2 + 3H 2
Similarly to the nucleophilic carbon center in the carbene, the lone pair on the aluminium center binds to the first azide equivalent. Nitrogen gas is liberated. With the second equivalent of azide, a five-member ring is formed. Aluminium (I) systems undergo reactions with azides in the same fashion as carbenes. [10]
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 ...
The aluminium takes an oxygen atom from sodium hydroxide, which in turn takes an oxygen atom from water, and releases two hydrogen atoms. The reaction thus produces hydrogen gas and sodium aluminate. In this reaction, sodium hydroxide acts as an agent to make the solution alkaline, which aluminium can dissolve in. 2 Al + 2 NaOH + 2 H 2 O → 2 ...
Nitrosyl chloride is produced as a by-product; it bubbles out of the solution as a gas. More conveniently, the salt can be made by reacting nitric acid with aluminium hydroxide . Aluminium nitrate may also be prepared a metathesis reaction between aluminium sulfate and a nitrate salt with a suitable cation such as barium, strontium, calcium ...
The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide) and was developed by Carl Josef Bayer.Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (Al 2 O 3), the rest being a mixture of silica, various iron oxides, and titanium dioxide. [1]