Effect of Al species in polyaluminum silicate chloride (PASiC) on its coagulation performance in humic acid–kaolin synthetic water

Abstract

The relative importance of three different Al species (Ala, Alb and Alc) 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 Ala, Alb and Alc dominant in one of them were denoted as PASiCa, PASiCb and PASiCc, respectively. The results showed that PASiCb performed the best turbidity and DOC removal, followed by PASiCc and PASiCa, while PASiCb and PASiCc removed UV254 more efficiently than PASiCa. At low dosages (1–4mg/L), flocs formed by PASiCb and PASiCc coagulation had higher zeta potential than those by PASiCa coagulation. However, order of zeta potential was PASiCa>PASiCc>PASiCb at high dosage of 18mg/L. Both coagulation efficiency and zeta potential were observed to be maximal at pH of 6. Zeta potential of formed flocs formed by PASiCc coagulation was the highest followed by PASiCb and PASiCa (in decreasing order) in pH range of 4–8, while PASiCa coagulation showed highest zeta potential followed by PASiCb and PASiCc at pH 9. The average size of flocs formed by three PASiC coagulants varied according to the following order: PASiCa>PASiCb>PASiCc. The floc equivalent diameters obtained by PASiCb coagulation were invariable with pH variation. Strength factors and recovery factors of flocs formed by PASiCc coagulation were larger than those by PASiCa and PASiCb coagulation within all investigated pHs.