Magnesium Silicate Polymer as a Coagulant for Reactive Dye Removal from Wastewater: Considering the Intrinsic pH in Magnesium Silicate Polymer and Coagulation Behavior

A magnesium silicate polymeric coagulant (MgSiPC), which is an inorganic polymer for dye removal from wastewater, was prepared with different pH by copolymerization. The acidity was a key factor in the preparation of the MgSiPC. In the present research, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to analyze the characterization of optimum coagulants. Additionally, the response surface method (RSM) was applied to optimize the process of coagulation-flocculation. The results of FT-IR and XRD implied that the main components of the MgSiPC with pH 1.50-2.50 were almost the same. SEM images showed that MgSiPCs with pH 1.50-2.50 exhibited different structures including cluster and lamellar shape structure, compact rod-like and network structure, and a kind of irregular geometry shape structure. In the process of coagulation-flocculation, MgSiPCs with pH 1.50-2.50 showed highly efficient coagulation performance. The removal rate of reactive yellow 2(RY2) could reach above 90% at a dosage of 50-70 mg/L and initial pH 12.00, while the removal rate of reactive blue 2 (RB2) could attain above 93% at a dosage of 50-80 mg/L and initial pH 12.00. Moreover, MgSiPCs with pH 2.00 had the highest efficiency. The results of RSM showed that the optimum combination of the MgSiPC's dosage and initial pH was 62 mg/L and 12.08 for RY2 and 78 mg/L and 12.00 for RB2, respectively. Under optimum experimental conditions, the predicted data from this model were 96% for RY2 and 100% for RB2, which was consistent with the actual experimental data. Therefore, a pH of 2.00 is considered to be the optimal acidity for preparing MgSiPCs.