Organic modifier of poly-silicic-ferric coagulant: Characterization, treatment of dyeing wastewater and floc change during coagulation

Abstract

Organic modifier (PSFD) of poly-silicic-ferric (PSF) coagulant was prepared by adding dimethyldiallylammonium chloride (DMDAAC) as additives in PSF, and was characterized by Scanning Electron Microscopy (SEM), Photon Correlation Spectroscopy (PCS) and Fourier Transform Infrared Spectroscopy (FT-IR). Color removal and floc change during coagulation process in treating a simulated dyeing wastewater by PSFD were investigated compared to those of PSF. The results show that a similar silicate of cross-linking matter was generated in PSFD, and PSFD has greater adsorbtion capacity than PSF. The size of PSFD hydrolysis products was larger than that of PSF over a given concentration range. The size of PSFD hydrolysis products tended to change continuously and the small size of products disappeared after its hydrolysis. PSFD has better color removal at given dosage range than PSF, with the largest difference of 30%. The floc growth and settling velocity of PSFD were larger than those of PSF. Larger flocs of PSFD were formed from its small initial flocs over a very short period of time. The floc density of PSFD was greater than that of PSF, leading to a much less amount of PSFD flocs in the finished water than that of PSF.