Ferrous sulfate has a good effect of phosphorus removal and decolorization in water treatment. Generally, ferrous sulfate is used for coagulation decolorization of wastewater. In the decolorization process of ferrous sulfate, ferrous ion forms multi complex with pigment in wastewater, and the decolorization effect is achieved through adsorption flocculation and precipitation.

Ferrous sulfate is usually used in combination with quicklime in decolorization treatment. Ferrous hydroxide and ferric hydroxide are formed by ferrous sulfate and quicklime. The suspended particles of active pigment molecules in wastewater are flocculated to form large particles of flocs and alum, which are separated from wastewater to form decolorization effect. Moreover, quicklime can adjust the pH value of wastewater, and ferrous sulfate has the best decolorization effect in wastewater with pH value above 11. So ferrous sulfate in wastewater decolorization combined with the use of quicklime has a very important influence, when quicklime will adjust the pH value of wastewater to about 11, the decolorization effect of ferrous sulfate can be as high as 90%.

The combination of ferrous sulfate and hydrogen peroxide can destroy the color of water and achieve the effect of decolorization. However, the use of hydrogen peroxide will increase the cost, which is more expensive than quicklime. Therefore, the decolorization method of ferrous sulfate combined with quicklime not only has good effect, but also has low cost, which is the most commonly used decolorization method at present.