Synergistic effects of poly-silicon aluminum sulfate and auxiliary agents in dye wastewater decolorization

Herein, the color-removal effectiveness of nine different structured dyes was compared using self-synthesized poly-silicon aluminum sulfate (PSAS) and six commercial coagulants, namely aluminum sulfate (Alum), polymerized ferric sulfate (PFS), magnesium sulfate (MgSO₄), polymerized aluminum chloride (PAC), poly-dimethyl-diallyl-ammonium chloride (PAMDAAC) and anionic-polyacrylamide (APAM). The inorganic polymer coagulants (PAC and PSAS) showed different advantages in the coagulation process. In particular, the latter was adaptable to a wide pH range and exhibited high decolorization ability for most dyes. The color-removal rate of five dyes (two direct dyes, one disperse dye and two acid blue dyes) reached over 90% at a pH of 11. The decolorization efficiencies of reactive black 5 and reactive blue 21 dyes were relatively poor at 40.87% and 75%, respectively. However, none of the seven coagulants could achieve a satisfactory effect on the cationic dyes with stable structures. Most non-cationic dyes have the R-SO₃ ^- group, which could combine with the Al polymer or Al³⁺ in the coagulant to achieve varying degrees of dye removal. These findings were further supported by FTIR analysis. Zeta-potential analysis indicated that the decolorization of dye wastewater using PSAS was based on a charge neutralization process. Further, four kinds of auxiliaries were used to remove basic dyes. Among them, phosphomolybdic acid (PMoA) showed good performance. With a dosage of 100 mg L^-1 PMoA and 50 mg L^-1 PSAS, the decolorization rate of rhodamine B (https://www.chembk.com/en/chem/Rhodamine B) reached 94.2%. Finally, the nine pure dyes were mixed in a 1 : 1 ratio to prepare mixed-dye wastewater with a total concentration of 100 mg L^-1. The removal rate was 25.3% using PSAS. However, in the presence of PMoA, the removal rate reached 92.5%. Therefore, the combined PMoA and PSAS technology can also achieve desirable results for treating such wastewater.