Ferrous sulphate, also known as copperas, crystal of light blue or green. It can be used as flocculating agent, reducing agent, and precipitation agent for various kinds water treatment, not only obvious effect, but also cheaper.
The purpose of Ferrous Sulphate:

  1. As reducing agent:
    Chemica Formula:

Ferrous sulphate is a strong reducing agent, it can transfer hexavalent chromium to trivalent chromic ion by reduction reaction. Then adjust PH value by alkalize, transform trivalent chromic to sediment of chromium hydroxide. There is no toxic gas be generated in the whole process.
Ferrous sulphate also can adjust the pH of water.

2. As flocculating agent:
Chemical Formula:

Resultant Fe(OH)3 can adsorb impurities to purify the water.
Ferrous sulphate has strong decolorization ability. It can discolor the textile waste such as textile printing, water scrubbing, etc.
Ferrous sulphate can dislodge heavy metal ion, and sterilization, etc.
Advantage: sedimentation speed, better flocculating effects, and non-toxic.

3. As precipitation agent
Chemical Formula:
FeSO4 + H2S = FeS↓ + H2SO4

Generate precipitate with sulfide, phosphate, etc. and thus dislodge ion of sulfide, phosphate, etc.