Chlorinated Coperas as coagulant

Chlorinated Copperas as coagulant

• Ferrous sulphate is known as Copperas. When chlorine is added to a solution of copperas, the two react chemically forming ferric sulphate and ferric chloride. The resulting combination is known as chlorinated Copperas. It is a valuable coagulant for removing odours especially in low pH value.
• Its chemical formula is FeSO4.7H2O.
• Copperas is added to raw water in conjunction with lime the following reaction takes place:
• FeSO4.7H2O + Ca(OH)2 -------->  CaSO4 + Fe(OH)2  +  7H2O and if copperas is added earlier to lime, the reaction that takes place is
• FeSO4.7H2O +  Ca(HCO3)2 ------------>  Fe(HCO3)2  + CaSO4  +  7H2O  and   Fe(HCO3)2  +  2Ca(OH)2 ---------->  Fe(OH)2  +  2CaCO3  +  2H2O
• The ferrous hydroxide formed in either case, gets further oxidised to ferric hydroxide  Fe(OH)2  +  O2  +2H2O  ----------------->  4Fe(OH)3
• The ferrous oxide formed in both cases is further oxidised forming ferric hydroxide by the following reaction:
• 4Fe(OH)2  O2  +  2H2O  ---------------------->  4Fe(OH)3 (Ferric hydroxide prepcipitate)
• Ferric oxide forms floc thereby helping in sedimentation.
• Copperas is widely used as a coagulant for raw waters that are NOT coloured
• It is cheaper than alum
• It functions effectively in the pH range greater than 8.5
• The quantity of copperas required is nearly the same as that of alum
• A combination of chlorine and copperas is very effective coagulant for treating waters with low pH.