Aluminium Sulphate is an inorganic salt with the chemical formula Al2 (SO4)3. It is also called as alum. It occurs in nature in the anhydrous form as a rare mineral, found in volcanic environments and in burning the dumps of coal mining. Aluminium Sulphate is hygroscopic in nature.

General Properties of Aluminium Sulphate:

It is soluble in water.
It is white in colour.
It is crystalline in form.
It is non- combustible.
It can either be of ferric grade or non-ferric grade.

Production of Aluminium Sulphate:

Aluminium sulphate is commercially prepared by two ways:

By adding aluminium hydroxide to sulphuric acid
By heating aluminium metal in a sulphuric acid solution
Whichever method is used, it is carried out batch wise in a reactor and the reaction is exothermic.

Aluminium sulphate is commercially produced from aluminium hydroxide in the industry, according to the following chemical reaction:
2 Al (OH)3 + 3 H2SO4 + 8 H2O → Al2(SO4) 3.14H2O

The reaction is carried out batch wise in a stirred tank reactor, which is made of materials resistant to the acidity and heat of the reaction. Aluminium sulphate can also be manufactured by heating aluminium in a sulphuric acid, this is highly exothermic. This reaction can be represented as:

2 Al(s) + 3 H2SO4 → Al2(SO4)3 + 3 H2 (g)

Aluminium sulphate has different uses and industrial applications which are listed below:

Water Treatment
Aluminium sulphate is also utilized for the treatment of potable water as well as process water, sewage, and other industrial effluents. It promotes efficient sludge digestion and dewatering. This is due to its flocculation property, it coagulates all impurities into large particles, and lets them settle at the bottom, and hence the impurities can be filtered out of the water.It is also used to maintain the stability of the lake or reservoir. Excess Phosphorus in the lake water induces ‘booming algae’, Alum can reduce the phosphorus concentrations and maintain the phosphorus normal concentration.

Gardening
Aluminium sulphate is used in horticulture, where it is added to the soil to reduce its pH, as it hydrolyses to form aluminium hydroxide and a dilute sulphuric acid solution. This often causes the flowers to change to bright colours.

Other Application
Aluminium sulphate is used in the paper making industry as a paper sizing agent.In textile industry as as a mordant in dyeing and printing.It is also used as a waterproofing agent and accelerator in concrete.In the construction industry, it is used as a foaming agent in fire extinguishers.