Abstract: In order to find out the effect of ferrosilicon mole ratios on the coagulation effect of ferrosilicate,six kinds of ferrosilicate were prepared with Na2SiO3· 5H2O and Fe2(SO4)3· 7H2O as raw materials,and the phase and microscopic morphology of ferrosilicate were characterized by XRD,SEM and FTIR. The effects of ferric polysilicate dosage,pH value,stirring time and other process parameters on COD removal rate were systematically studied. The results showed that:① Ferric polysilicate has a polycrystalline phase structure. With the increase of the material ratio of ferric silicate,the surface morphology changes from hollow tubular to sheet. ② With the increase of ferrosilicon mole ratios,the content of Fe(Ⅲ ) free ion and mononuclear hydroxyl complex in ferrosilicate decreased,and the electric neutralization ability of ferrosilicate decreased;The adsorption and bridging capacity of ferric polysilicate was improved with the increase of silicate polymer content. ③ For the water samples prepared by sodium butyl xanthate and No. 2 oil,the removal rate of COD could reach 48% when the dosage of ferric silicate is 4 mmol / L,the pH value is 5. 0 and the stirring time is 20 min. Compared with Fe2(SO4)3· 7H2O and polysilicic acid,the coagulability of polysilicic iron is obviously improved,and the electric neutralization and adsorption bridge work together during the coagulation process.

Key words: compound coagulant,Fe morphology distribution,Si morphology distribution,electric neutralization,adsorption bridging