3.2.3. Isoelectric point
Zeta potential values of Ti-flocs were measured and plotted against pH, as shown in Fig. 6. The IEP of Ti-flocs was found to be near pH 5, lower than the IEP values of Al(OH)3 flocs reported as pH 7–9 (Kanna et al., 2005). The measured IEP of Ti-flocs was generally in agreement with the titanium flocculation region depicted in Fig. 1, where good flocculation happened when floc zeta potential approached zero. The IEP value was also partly confirmed by the reservoir water experiment of Zhao (2011a). Their data revealed that when TiCl4 coagulant was near ‘optimal’, floc zeta potential would approach zero, corresponding to a pH value lower than 5.51. As zeta potential was a function of many variables such as water composition and coagulant dose, further research was recommended on defining the IEP range of Ti-flocs.