Page 75 - Pharmaceutical Analytical Chemistry III

CHEMICAL TREATMENT FOR WATER PURIFICATION :

1) Coagulation and Flocculation :

- Many impurities in water are present as colloidal solids
which will not settle during sedimentation process. Their
removal is achieved by the addition of harmless chemicals
(coagulants).

- The coagulant is a metal salt which reacts with alkalinity in
water to produce gelatinous (metal hydroxide) precipitate
which incorporates the colloidal impurities. This fine
precipitate is then flocculated, by means of gentle motion,
to produce settlable solids. Examples of coagulants are Al3+
and Fe3+ salts.

 Al2 (SO4)3. 18H2O known as alum is the most commonly
used coagulant.