Coagulation performance and flocs properties of a new composite coagulant: Polytitanium–silicate–sulfate

• A new composite coagulant–polytitanium–silicate–sulfate was synthesized and used in synthetic fulvic acid water treatment.
• NOM removal was improved by polytitanium–silicate–sulfate in this study, especially polytitanium–silicate–sulfate0.07.
• Floc size was enlarged by polytitanium–silicate–sulfate when compared to polytitanium sulfate.
• Floc strength factor and recovery factor were enhanced by polytitanium–silicate–sulfate when compared by PTS.
• Floc formed by polytitanium–silicate–sulfate has a relatively looser structure with a lower Df value.

A new composite coagulant, polytitanium–silicate–sulfate (PTSS) was synthesized by polytitanium sulfate and polysilicic acid with different Si/Ti molar ratios (PTSS with different Si/Ti molar ratio of 0.1, 0.07, 0.05, and 0.02 was denoted as PTSS0.1, PTSS0.07, PTSS0.05 and PTSS0.02, respectively). Coagulation performance and flocs properties of PTSSs in fulvic acid–kaolin synthetic water treatment were studied by a series of jar tests. Results showed PTSS0.07 achieved better coagulation performance in residual turbidity and NOM removal than other PTSS. Zeta potential of these coagulants decreased as Si/Ti molar ratio increased. It showed that the higher the Si/Ti molar ratio led to larger the flocs size. In addition, strength factor and recovery factor of flocs were enhanced by adding polysilicic acid. Moreover fractal dimension decreased and flocs showed loose structure by adding negatively charged polysilicic acid.