Investigation of hydrolysis and coagulation mechanism of poly-iron coagulant

Chemical coagulation is very important in water treatment, in which coagulant is an essential part. Pre-polymerized Al^3＋ and Fe^3＋ products have been used in practice, continuously spread for many years. However, iron-based coagulant has become the focus of studies due to cumulative biologic toxicity of residual Al in treated water. Polyferric sulfate （PFS） and poly-silicic-ferric sulfate （PSF） are all pre-polymerized polymers of Fe^3＋ salts. The hydrolysis process and species distribution of Fe^3＋ ions have been investigated extensively by many chemists and water-treatment specialists. Generally, the coagulation mechanism of conventional or pre-polymerized coagulants was often studied through jar-test, absorption experiment, microstructure observation or hydrolysis species indirectly. However, few researches have been done on the hydrolysis process of PSF in detail and on the study of the coagulation mechanism using its hydrolysis species distribution until now. In this work, PSF was prepared using water glass, ferrous sulfate and sodium chlorate by a copolymerization method. The hydrolysis species distribution was theoretically derived from pH variation during hydrolysis process of PSF compared to that of polyferric sulfate （PFS）, and then characteristics morphology, species size, Zeta potential, spectra of X-ray diffraction and infrared spectra （IR）] and coagulation performances were explored between them. Coagulation mechanism was analyzed according to hydrolysis species distribution, characteristics and coagulation performances. The results showed that PSF gives different species distribution at different pH values and characteristics from those of PFS, leading to different coagulation mechanisms between the two coagulants.

Investigation of hydrolysis and coagulation mechanism of poly-iron coagulant