A polyaluminum chloride (PAC) coagulant was prepared from AlCl3•6H2O and Na2CO3. The Al13 species in PAC was separated and purified by the SO4 2-/Ba2+ deposition-replacement method, and characterized by 27Al-NMR and XRD. From 27Al-NMR spectroscopy, it was found that PAC obtained after separation and purification contained more Al13 (PAC-Al13, for short) than original PAC before separation and purification. In XRD spectra, a strong Al13 signal appeared in the range of 2θfrom 5°to 25°. Jar tests were performed to test the coagulation efficiency of AlCl3, PAC and PAC-Al13 in treating synthetic or actual water samples. Compared with PAC and AlCl3, PAC-Al13 gives the best results for turbidity, humic acid and color removal, and achieves the highest charge-neutralizing ability. Under the study conditions, PAC-Al13 gave about 90% humic acid removal and almost 100% dye reactive blue removal when its dosages were 4.0mg/L and 15mg/L as Al, respectively. Al13 species is a higher positive-charged and most effective polymeric Al species in water and wastewater treatment.

Poly (diallyldimethyl ammoniumchloride-vinyl trimethoxysilane) [P(DADMAC-VTMS)] and poly (diallyldimethyl ammonium chloride-acrylamide-vinyl trimethoxysilane) [P(DADMAC-AM-VTMS)], the latter a new cationically charged and hydrophobically modified flocculant, were obtained by radical polymerization initiated by potassiumpersulfate. The effects of the vinyl trimethoxysilane (VTMS) feed ratio on the intrinsic viscosity and solubility of the polymers were examined. The effects of the flocculants on turbidity removal, decolorization, and oil removal in water treatment were also studied. The introduction of VTMS increased the intrinsic viscosities of P(DADMAC-VTMS) and P(DADMAC-AM-VTMS) in comparison with the viscosities of poly (diallyldimethyl ammoniumchloride) and poly(diallyldimethyl ammoniumchloride-acrylamide) respectively, but reduced their solubilities. The introduction of VTMS also enhanced the flocculation properties of P(DADMAC-VTMS) and P(DADMAC-AM-VTMS), including turbidity removal, decolorization, and oil removal.

Poly-aluminum-chloride-sulfate (PACS) with different SO4 2-/Al3+ mole ratios and bacicity (γ) of 2.0 was synthesized using AlCl3•6H2O, Al (SO4) 3•18H2O and Na2CO3 as raw materials. The effect of SO4 2-/Al3+ ratio on the performance of PACS for removal of natural organic matter (NOM) with humic-rich actual water was examined. It was found that PACS with SO4 2-/Al3+ mole ratio of 0.0664 achieved the best NOM removal results and was selected to investigate its performance in comparison with PAC, FeCl3 and alum (Al2 (SO4) 3•18H2O). The experimental results showed that the optimum NOM removals were achieved at pH 5.0-8.2 and the dose of about 5.0mg/L as Al both for the selected PACS and PAC, at pH 5.0-6.0 and the dose of about 7.0mg/L as Fe for FeCl3, and at pH 5.0-7.0 and the dose of about 7.0mg/L as Al for alum, respectively. At the optimum conditions, the selected PACS achieved the best NOM removal result, followed by PAC, FeCl3, and then Alum. The concentration of residual aluminum in treated water by the selected PACS and PAC under the optimum coagulant conditions was approximately 115 μg/L, which can completely comply with the regulated limits.

The electrokinetic characteristics and coagulation behaviors of polyaluminum silicate chloride (PASiC) and polyaluminum chloride (PAC) were studied and compared by streaming current (SC) measurement and jar test method. The experimental results showed that the interaction between polysilicic acid characterized negative charge and hydrolyzed aluminum species result in a decrease of the charge-neutralizing ability of PAiSC, compared to PAC. The decrease has a close relationship with the basicity (B) and Al/Si molar ratio in PASiC. The less the B value and the Al/Si molar ratio, the lower the charge-neutralizing ability of PASiC is. In contrast, the preparation technique for PASiC affects the charge-neutralization of PASiC to a smaller extent. In addition, compared with PAC, PASiC may enhance aggregating efficiency and give better coagulating effects.

Aluminum-silicate polymer composite (PASiC), a new kind of inorganic coagulant, was produced by two approaches: (1) hydroxylation of the mixture of AlCl3 and fresh polysilicate (PASiCc); (2) hydroxylated polyaluminumchloride (PAC) combined with fresh polysilicate (PASiCm). The PASiC products had the following properties: Al2O3 content=6.40-7.30%, SiO2 content=0.40-0.82%, Al/Si ratios=10-20, basicity (OH/Al molar ratio, denoted B)=1.2-2.0. The coagulation behaviour of PASiC and PAC under conditions typical for coagulation and flocculation in water treatment were investigated by studying the rate of floc size development, the variety of streaming current value, the efficiency of turbidity removal and the effect of pH on the turbidity removal efficiency, and the stability of PASiC. The results detailed in this study suggest that, compared with PAC, PASiC may enhance aggregating efficiency and give better coagulating effects, but weaken charge effectiveness in coagulation process or become unstable when stored for longer time, especially at higher B value and lower Al/Si ratio. The coagulating effect of PASiC is closely linked to the preparation procedure. With the increase of B value and the decrease of Al/Si ratio, the coagulation efficiency of PASiC increases, and at the same B value and Al/Si ratio, PASiCc seems to give a little better coagulation effect than PASiCm but less stability. The Al/Si ratio should not be too low or the B value should not be too high, otherwise, the PASiC products tend to become cloudy or partly gelatinous, which will make them loss some coagulation efficiency. r 2002 Elsevier Science Ltd. All rights reserved.