Magnetic flocculation of anion dyes by a novel composite coagulant

A novel nano-magnetic particles-polyferric sulfate composite coagulant (Fe3O4-PFS) was firstly produced. In this study, the pre-polymerized ion-based PFS and Fe3O4 were combined (Fe3O4-PFS) to remove a typical anion dye, Congo Red. Fe3O4-PFS with different molar ratio of PFS (30-100 mg/L) to Fe3O4 (0-600 mg/L) showed good performance at the studied pH range, especially at pH 7. The removal value increased from 29.5% to 64.8% when 500 mg/L of Fe3O4 was added into 30 mg/L of PFS. The structure and morphology property of the aggregated flocs induced by the composite coagulant were analyzed through instrumental analyses such as Fourier-transform infrared spectroscopy, X-ray diffractometer, scanning electron microscope, a physical property measurement system equipped with vibrating-sample magnetometer, and optical microscope. To study the influence of Fe3O4, fractal dimension (D-f) of flocs was investigated by employing image analysis. Finally, the effects and interactions of various factors on the treatment efficiency were studied by response surface methodology coupled with Box-Behnken design. The results showed that the Fe3O4-PFS-CR flocs induced by some local charge interactions and cheating were successfully formed. The flocs of Fe3O4-PFS-CR were lager, compacter, and denser. The surface of it exhibits rougher and more porous. This coagulant significantly decreased the dosage of inorganic coagulant, the flocculation time, and exhibited slighter pH dependence compared with PFS. The respective tests confirmed that the predominant coagulation mechanism of Fe3O4-PFS is the adsorbing-bridging. The method can greatly improve the color removal value. The novel method was highly efficient and environmentally feasible, which it seemed to hold considerable potential in the purification processes of real wastewater.