Ferric Sulphate:
It can be used instead of ferric chloride, but is expensive. It should be used in special cases where decolourisation and clarification of water of low temporary but high permanent hardness is desired.
FeSO4.7H2O + Ca(OH3)2 → Fe(OH)2 + CaSO4 (ppt). + 2CO2 + 7H2O
Ferrous Sulphate:
2Fe (OH)2 + O + H2O → 2Fe (OH)3 (ppt).
It should be used with sufficient lime or caustic soda to raise the pH to 8.5-10, more commonly used in industrial softening plants and industrial waste water treatment.