Ferrous sulfate is often used as a water purifier. In water treatment, ferrous sulfate often encounters the phenomenon that the wastewater will turn red or reverse color after adding ferrous sulfate. What causes this?

For example, when ferrous sulfate is used to treat printing and dyeing wastewater, there will be red dyeing groups in the wastewater. When the reagent added does not contain red substances, after ferrous sulfate treatment, small red precipitates will be produced, causing the water body to turn red. At this time, the red will fade after static treatment.

When the dosage of ferrous sulfate is too large, the ferrous ion produced by excessive ferrous sulfate hydrolysis is extremely easy to be oxidized into iron ion, and a large number of ferric ion will produce precipitation, which makes the water red. Or in the use of ferrous sulfate, due to improper use, poor coagulation conditions, resulting in a large number of ferrous ions precipitation, and then oxidized into ferric ions, making the water red.

When ferrous sulfate is used to remove phosphorus salt and COD in wastewater, ferrous sulfate will increase the concentration of solid suspended solids in wastewater, and the wastewater will turn red again after a few days, mainly because of phosphorus. Adding quicklime can effectively remove phosphorus and solve the problem of water quality turning red, but it is necessary to adjust the pH value of wastewater in the later stage.

Ferrous sulfate is commonly used as medicament. It is necessary to ensure the effect of ferrous sulfate according to the correct method.