Although flocculants such as aluminum and iron salts have a good decolorization effect for disperse dyes, sulfur dyes, and vat dyes, for water-soluble dyes, the decolorization effect is not ideal. As a new type of cationic polymeric flocculant, PolyDADMAC has a 100% cationic degree and special chemical structure, which makes it in good flocculation and decolorization effect. Therefore, PolyDADMAC has become a popular flocculating and decolorizing product for dye wastewater, but its decolorization effect is also affected by the following factors.
1. The effect of molecular weight on the decolorization of PolyDADMAC dye wastewater
When the dosage of PolyDADMAC is insufficient, it can not completely neutralize the negative charges of dye molecules, which will lead to the failure of some dye molecules to form neutral molecules and precipitate from the solution; when the dosage of PolyDADMAC is too large, the neutral dye molecules which have been precipitated may be positively charged due to the excessive positive charges, which will lead to the mutual repulsion of dye molecules and the formation of stable colloidal solution. Therefore, only when the dosage of PolyDADMAC is appropriate, can all dye molecules form neutral molecules, precipitate from the solution, and be removed by flocculation. In addition, the higher the intrinsic viscosity of PolyDADMAC is, the less the optimal dosage is, and the better the decolorization effect is.
2. The effect of pH value on decolorization of dye wastewater
Different pH values of the solution have different effects on the structure of flocculants and the molecular structure of dyes. Therefore, the ability of flocculants to combine dyes and the aggregation performance and size of precipitates generated by the reaction are different, which leads to different sedimentation removal capacity. So there is an optimal pH range for general flocculants, while PolyDADMAC has a wide range of pH values for the treatment of reactive dyes and disperse dyes.