Aluminate

Aluminates are salts of aluminum acid halo2 · H2O, the ( Which is amphoteric) with aluminum hydroxide is the same, in which aluminum, a complex ion [ Al (OH ) 4] - forms with hydroxide ions as ligands, as well as salts in which the anion of the condensate aluminate ion is present.

The general composition of such compounds is MI [ Al (OH ) 4], where M is a monovalent cation. Have fully condensed (anhydrous ) compounds have the general composition MIAlO2 with AlO 2 - as anion.

With divalent cations, there are numerous naturally occurring mineral compounds such as magnesium aluminate ( MgAl2O4, see spinel), zinc aluminate ( ZnAl2O4, see gahnite ) Eisenaluminat ( FeAl2O4, see Hercynite ) and manganese aluminate ( MnAl2O4 see galaxite ). Aluminium is present in all of these compounds in the oxidation state (III).

Examples

A well-known aluminate is sodium aluminate which, for example by dissolving aluminum hydroxide in sodium hydroxide solution the Bayer process for the production of aluminum from bauxite arises:

In the ion notation:

Tetrahydroxoaluminat the ion (for example: sodium tetrahydroxoaluminat ) tends to condense, forming dialuminate ions [ (HO) 3Al -O-Al (OH) 3 ] 2 -, and higher polymers. The polymerization is carried out similarly to the ortho silicic acid. The end products of such a condensation are obtained by fusion of alumina and metal oxides.

More aluminates are calcium aluminates, which are formed either by melting of aluminum oxides with lime or milk of lime by the reaction of sodium aluminate with:

Calcium aluminates can form salts with anion, for example calcium aluminate sulphates different, depending on the reaction conditions of calcium aluminate or calcium aluminate monosulphate trisulfate, which is also known as the mineral ettringite. All calcium aluminates play an important role in the cement chemistry.

Chromaluminat is obtained by heating a mixture of clay, calcium fluoride, and ammonium dichromate, and used as a ceramic paint.

Barium is produced from bauxite, barite and coal and is used for cleaning of industrial wastewater and as scale solvent.

Lead aluminate is formed by heating a mixture of lead oxide and alumina, was used as a white pigment and fixed to the manufacturing of bricks and refractory linings.