The relative importance of three different Al species (Al-a, Al-b and Al-c) in polyaluminum silicate chloride (PASiC) was investigated in terms of coagulation removal efficiency and floc characteristic during the coagulation of humic acid-kaolin clay (HA-Kaolin) synthetic solution. Coagulation performance of PASiC (Al/Si molar ratio of 10:1) was also compared with that of polyaluminum chloride (PAC). Three PASiC coagulants with Al-a, Al-b and Al-c dominant in one of them were denoted as PASiC(a), PASiC(b) and PASiC(c), respectively. The results showed that PASiC(b) performed the best turbidity and DOC removal, followed by PASi(c) and PASiC(a), while PASiC(b) and PASiC(c) removed UV254 more efficiently than PASiC(a). At low dosages (1-4 mg/L), flocs formed by PASiC(b) and PASiC(c) coagulation had higher zeta potential than those by PASiC(a) coagulation. However, order of zeta potential was PASiC(a) > PASiC(c) > PASiC(b) at high dosage of 18 mg/L. Both coagulation efficiency and zeta potential were observed to be maximal at pH of 6. Zeta potential of formed flocs formed by PASiC(c) coagulation was the highest followed by PASiC(b) and PASiC(a) (in decreasing order) in pH range of 4-8, while PASiC(a) coagulation showed highest zeta potential followed by PASiC(b) and PASiC(c) at pH 9. The average size of flocs formed by three PASiC coagulants varied according to the following order: PASiC(a) > PASiC(b) > PASiC(c). The floc equivalent diameters obtained by PASiC(b) coagulation were invariable with pH variation. Strength factors and recovery factors of flocs formed by PASi(c) coagulation were larger than those by PASiC(a) and PASiC(b) coagulation within all investigated pHs. (c) 2013 Elsevier B.V. All rights reserved.