Poly-aluminum-silicate-chloride (PASiC)—a new type of composite inorganic polymer coagulant

A new inorganic polymer coagulant, poly-aluminum-silicate-chloride (PASiC), was prepared by two approaches: (1) hydroxylation of the mixture of AlCl3 and fresh polysilicic acid in Al/Si ratios ≥5, (PASiCc); (2) hydroxylated poly-aluminum-chloride (PAC) combined with polysilicic acid aged 2 h in Al/Si ratios ≥5, (PASiCm). The hydrolysis-polymerization process of Al(III) in PASiC solution was examined with pH titration method. The performances of PASiC in comparison with PAC were characterized by various experimental methods. The results have shown that there exist some interactions between aluminum species and polysilicic acid, especially at low basicity (B) value, which can play a part in the chemical structure, the molecular weight distribution, the electrokinetic characteristics and the coagulating properties of PASiC. The complexes formed when different charged aluminum species and polysilicic acid are combined have a less positive charge but a larger molecular weight than the corresponding aluminum hydrolysis products at the same pH value. Therefore, it is necessary to consider the aggregating efficiency and charge effectiveness when developing PASiC coagulant. In general, PASiC has shown a high coagulation effect, superior to that of PAC for both turbidity and color removal.