Preparation of an inorganic coagulant-polysilicate–magnesium for dyeing wastewater treatment: Effect of acid medium on the characterization and coagulation performance

Abstract

Polysilicate–magnesium (PSM) was prepared with Mg/Si molar ratios of 1.5 by co-polymerization. It is an inorganic polymer coagulant for dyeing wastewater treatment. Acid medium played an important role in the preparation of PSM. In this study, PSMs were prepared using different acids (H2SO4, HCl, HNO3 and H3PO4) as medium, which were denoted as PSM(S), PSM(Cl), PSM(N) and PSM(P) respectively. FTIR, XRD and SEM were used to analyze the structure and morphology of four types of PSM coagulants. The results show that PSM(S) and PSM(N) both have the compact gel network structure, while PSM(Cl) and PSM(P) present layer shape structure and scattered small blocky structure respectively. In the coagulation–flocculation process of dyeing wastewater treatment, PSM(S), PSM(Cl) and PSM(N) exhibit better coagulation performance compared with PSM(P). With an optimal pH of 12 and a settling time of 20 min, the color removal efficiency of the coagulant of PSM(S) can reach above 94% at a relatively lower coagulant dosage of 4 mg/L, whereas PSM(Cl) and PSM(N) brings to about 94% at a higher coagulant dosage of 8 mg/L. However, PSM(P) shows that the highest color removal efficiency reaches only about 63% at a coagulant dosage of 8 mg/L. Therefore, PSM(S) is considered as the best acid modified PSM.