Aluminium

Actually, I made this post because I was eager to write something, but I didn't have any clue to what I should write about. Because where I come from there are lots of bauxite mines and a huge mining company, I thought: why don't I write about aluminium instead? so, here I go.

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances.

Aluminium is remarkable for the metal's low density and for its ability to resist corrosion due to the phenomenon of passivization. Structural components made from aluminium and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.

Despite its prevalence in the environment, aluminium salts are not known to be used by any form of life. In keeping with its pervasiveness, it is well tolerated by plants and animals. Because of its prevalence, potential biological roles, beneficial and otherwise, for aluminium compounds are of continuing interest. ^[wikipedia]

Hystory

The name aluminium was supposedly derived from the word alum that refer to the salt alumen with the formula KAl(SO4)₂.H₂O. Alumen means bitter salt. By Humphry Davy, the metal from this salt then named alumium and then changed to aluminum. But the name then modified to be aluminium which soon be popular throughout the world, except the USA when the American Chemical Society decided that they will continue to use the term aluminum for the metal in their publications in 1925. ^{[Sugiarto, Kristian H; Suyanti, Retno D]}

Alums are useful for a range of industrial processes. They are soluble in water; have an astringent, acid, and sweetish taste; react acid to litmus; and crystallize in regular octahedra. When heated they liquefy; and if the heating is continued, the water of crystallization is driven off, the salt froths and swells, and at last an amorphous powder remains.^[wikipedia]

Bauxite

Aluminium is a lot, it is the most abundant metallic element in the Earth's crust (~8,3 % of the Earth's crust weight) and the 3^rd most abundant element next to Oxygen (O; ~45,5%) and Silicon (Si;~25,7%). Because Aluminium is very reactive, especially to Oxygen, it is never found in free, metallic form.

Bauxite is an aluminium ore that was found by P. Berthier on 1821 in Les Baux, Provence. In areas with mediteranian climates (like Europe), bauxite is found as aluminium oxide monohydrate, AlO(OH) or AL₂O₃.H₂O, while in tropical areas it is commonly found as aluminium oxide trihidrate, Al(OH)₃ or Al₂O₃.3H₂O. Bauxite's common formula is AlO_x(OH)_3-2x.

Besides bauxite, aluminium occurs in nature as other minerals, such as:

kaolin - Al₂(OH)₄.Si₂O₅ or Al₂(OH)₃.2H₂O.2SiO₂

spinel - MgAl₂O₄.Si₂O₅ or MgO.Al₂O₃

garnet - Ca₃Al₂(SiO₄)₃ or 3CaO.3SiO₃.Al₂O₃

beryl - Be₃Al₂Si₆O₁₈ or 3BeO.6SiO₃Al₂O₃

corundum - (α)-Al₂O₃

cryolite - Na₃AlF₆ ^{[Sugiarto, Kristian H; Suyanti, Retno D]}

Bauxite Refinement

Nowadays, bauxite are processed through Bayer process. First, the pure ore and impurities which mostly contains iron and silicon oxides are made into powder, this process is called grinding, then a thick solution of sodium hydroxide (NaOH) is added, because of the amfoteric property of aluminium the mix will form an aluminate solution and the silicon oxide will eventually form a silicate solution.^{[Sugiarto, Kristian H; Suyanti, Retno D]}

AL₂O₃ (s) + OH^- (aq) + 3H₂O --> 2 [Al(OH)₄]^- (aq)

SiO₂ (s) + 2 OH^- (aq) --> SiO₃^2- (aq)+ 2 H₂O

continues....