Innovative synthesis of polytitanium chloride by electrodialysis: Identification of Ti-based hydroxyl polymers and coagulation performance

Biocompatibility of titanium (Ti) and recycling of the coagulated sludge to produce functional nanoparticles make the popularization of Ti-based coagulants highly attractive. Slow alkaline titration (SAT) method was commonly used to synthesize polytitanium coagulants, but cannot control the formation of dominant flocculation species due to the fast hydrolysis. We propose the innovative preparation of Ti-based coagulants by electrodialysis (ED) to control the directional transfer of electrons and regulate the rate of the micro-interface reaction. An efficient polytitanium chloride (PTC) was successfully prepared by ED method with TiCl4 as precursor, denoted as E-PTC. Results from electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) proved the generation of the Ti-based hydroxyl polymers with various degrees of polymerization benefiting from the controllable migration of ions during ED process. The predominant Ti-based species changed from the small/median polymers to the large ones with increasing ED period. This was evidenced by Ti-Ferron assay that high Tib (34.35%) and Ti-c (47.05%) fractions were obtained in E-PTC after 8 h of ED period. The resulting E-PTC had stronger coagulation capability for both surface water and municipal wastewater treatment than the conventional ones. Compared with the conventional Al-based and Fe-based coagulants, E-PTC achieved 15% to 30% higher removal of organic matter, and produced the flocs with larger size, faster growth rate, better dewaterability, stronger strength and recoverability. This study provided the efficient ED method for the preparation of Ti-based coagulants with superior flocculation performance.

Automated summary

The innovative preparation of titanium-based coagulants by electrodialysis (ED) method has been shown to improve the coagulation capability, leading to higher removal of organic matter and the production of larger and stronger flocs.