What Is The Decolourization Principle Of Ferrous Sulfate?

The decolorization principle of ferrous sulfate is mainly based on its reducibility, coagulation and synergistic effect, as follows:
1. Reduction reaction
Principle: Ferrous sulfate (FeSO₄) dissolves in water to release ferrous ions (Fe²⁺), which are reducible and can chemically react with some chromogenic organic substances in wastewater.
Function: Ferrous ions reduce the chromophore to colourless or light-coloured substances, thereby directly reducing the chromaticity of the water body.

2. Coagulation
Principle: Ferrous ions can also be used as coagulants to combine with pollutants such as dye molecules and suspended solids in wastewater through charge neutralisation, adsorption bridging and net capture.
Function: Formation of larger flocs (or alum flowers), in this process, the dye molecules are encapsulated inside the floc, and as the flocs grow and settle, they are separated from the wastewater and decolorized.

3. Synergy
Principle: In practical applications, ferrous sulfate is often used together with lime (Ca(OH)₂) to enhance the decolorization effect. On the one hand, the addition of lime regulates the pH of the wastewater to an alkaline environment (the optimal decolorization pH is usually between 9.5 and 11.5), and on the other hand, lime reacts with ferrous sulfate to form ferrous hydroxide (Fe(OH)₂) and iron hydroxide (Fe(OH)₃).
Function: These precipitates have a large specific surface area and have a stronger adsorption capacity for dye molecules, further improving the decolorization efficiency.

4. Complexation-adsorption bridging mechanism
Principle: When ferrous sulfate is decolorized, the coloured particles constantly collide with each other and condense into larger flocs under the interference of ferrous ions. This process is actually decolorized by forming a multinuclear complex with the dye molecule centred on ferrous ions, which is then removed by adsorption.
Purpose: This complexing-adsorption bridging mechanism enables ferrous sulfate to remove dye molecules from wastewater more effectively during the decolorization process.