Aluminium selenate, Al₂(SeO₄)₃

Aluminium selenate, Al₂(SeO₄)₃, is formed by dissolving aluminium hydroxide in selenic acid and heating to expel the excess of acid. It is soluble in water, but no hydrates have been described.

Aluminium selenate forms double selenates with the selenates of sodium, potassium, rubidium, csesium, ammonium, and thallium the formulae of which are of the type R₂^ISeO₄.Al₂(SeO₄)₃.24H₂O, i.e. they are selenium alums. They have been examined by various chemists. The densities of the selenium alums are as follows (Pettersson): -

Alum	Na	K	Rb	Cs	NH4	Tl
Density	2.067	2.204	2.134	2.224	1.890	2.503