Aluminium sulfate, alternatively
spelt aluminum sulfate, aluminium sulphate, or aluminum sulphate;
is a chemical compound with the formula Al2(SO4)3. Aluminium
sulfate is mainly used as a flocculating agent in the
purification of drinking water and waste water treatment plants,
and also in paper manufacturing.
Aluminium sulfate is sometimes
incorrectly referred to as alum but alums are closely related
compounds typified by KAl(SO4)2.*2H2O. The anhydrous form occurs
naturally as a rare mineral millosevichite, found e.g. in
volcanic environments and on burning coal-mining waste dumps.
Aluminium sulfate is rarely, if ever, encountered as the
anhydrous salt. It forms a number of different hydrates, of which
the hexadecahydrate Al2(SO4)3•*6H2O and octadecahydrate
Al2(SO4)3•*8H2O are the most common. The heptadecahydrate, whose
formula can be written as [Al(H2O)6]2(SO4)3•5H2O, occurs
naturally as the mineral alunogen.
