Aluminium sulfate, alternatively spelt either aluminum or 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 referred to as a type of alum. Alums are a class of related compounds typified by AB(SO4)2.12H2O. 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•16H2O and octadecahydrate Al2(SO4)3•18H2O are the most common. The heptadecahydrate, whose formula can be written as 2(SO4)3•5H2O, occurs naturally as the mineral alunogen.
Read more about Aluminium Sulfate: Preparation, Uses, Chemical Reactions