Characterization and application of poly-ferric-titanium-silicate-sulfate in disperse and reactive dye wastewaters treatment.

A novel coagulant poly-ferric-titanium-silicate-sulfate (PFTS) was synthesized and employed to treat two typical kinds of dye wastewaters-disperse blue and reactive yellow. The results indicated that PFTS with a Si/Fe molar ratio of 0.02 exhibited superior coagulation performance, especially under alkaline condition. The residual turbidity after coagulation by PFTS was only half of that after coagulation by poly-ferric-titanium sulfate (T-PSF). The sludge volume index was also reduced by PFTS compared to T-PSF in reactive dye treatment. Through the structure and morphology investigation of PFTS, it was found that new bonds of Si-O-Fe, Si-O-Ti and Fe-OH (Si-OH) were formed, and multi-branched structures and expanded surface area were generated. Additionally, compared with T-PSF, the floc strength and the floc size were also enhanced by PFTS, which was attributed to the polymerization between polysilicic acid and Fe/Ti which formed multi-branched structures, and finally adsorption and bridging ability of the coagulant was improved. Furthermore, the floc formed in reactive yellow wastewater treatment was larger and looser than that formed in disperse blue wastewater, with poorer strength and recovery ability, which can also interpret the better coagulation efficiency in disperse dye water treatment. From the results of coagulant characterization, zeta potential and flocs properties, it can be inferred that charge neutralization by the positive charged hydrolysate of coagulant was identified as the critical effect in disperse dyes removal, while the sweep and adsorption of metal hydroxyl compound formed during the hydrolysis of coagulants were considered to play a key role in reactive dye removal.