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.

Coal gangue is a kind of waste from coal mine processing. Polyaluminium ferric chloride (PAFC), a new type of inorganic composite coagulant, was prepared by using the waste from the Mineral Bureau of Yanzhou, China, hydrochloric acid and calcium carbonate as raw materials. The relationship between the stability of ferric ion and the ionic strength of solution was investigated. The zeta potential of PAFC hydrolysis products of PAFC and the coagulation performances under different pH value were discussed. The turbidity removal properties of PAFC, polyaluminium (PAC) and polyferric sulfate (PFS) were compared, and the color removal effect of PAFC for the wastewater containing suspended dyes was also tested. In addition, the coagulation performance of PAFC for actual wastewaters from petrochemical plant, iron and steel plant, and coal mining processing was evaluated. The experimental results suggest that PAFC took a maximum value of zeta potential at about pH 5.8 on the positive side. Compared with PAC, PAFC gives better turbidity removal performance in the range of pH from 7.0 to 8.4. PAFC gives good color removal performance on suspension dyes. PAFC also gives good wastewater purifying results for the actual wastewater. Therefore, PAFC is a high-effect and stable water treatment agent.

The chemical species distributions of polyaluminum silicate chloride (PASC) and polyaluminum chloride (PACl) determined by Al-Ferron complexation timed spectrophotometric and 27Al-NMR methods, respectively, have been compared and analyzed. The experimental results show that the species distribution and transformation of PASC are diferent from those of PACl, due to the interaction of polysilicic acid and hydrolyzed aluminum species. At the same basicity (B), the contents of, Alb, A l13 and the monomer species Almono (also determined by 27Al-NMR) in PASC are lower than those in PACl, while the contents of Alc and the Alother determined by 27Al-NMR in PASC are higher than those in PACl. The di.erences between PASC and PACl with respect to these species enlarge as the molar ratio of Al/Si in PASC decreases. Further, in PACl the ratio of Al13 to Alb closes to 1.0, indicating that the amount of the two fractions are similar. In PASC, however, such an agreement does not exist at the lower B values and Al/Si molar ratios. When the B value and Al/Si molar ratios increase, however, the amount of Al13 and Alb species tends to close. The study findings indicate that polysilicic acid can react with hydrolyzed aluminum species to form an aluminum silicate polymer composite and result in the change in species distribution of PASC.

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) ydroxylated 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.

A series of poly-aluminum-chloride-sulfates (PACS), which have different OH/Al (┌) and Al3+/SO42- mole ratios, has been prepared using AlCl3-6H2O, Al(SO4)3-18H2O and Na2CO3 as raw materials. The electrophoretic nature of PACS was investigated by electrophoresis. Laboratory experiments were undertaken to evaluate the PACS in comparison with polyaluminum chloride (PAC) for the coagulation of simulating water and actual wastewaters. The experimental results show that the ┌ value and the Al3+/SO42- mole ratio affect the electrophoretic nature of PACS. PACS has a maximum zeta potential at about a ┌ value of 1.5 and Al3+/SO42- mole ratio of 12- 16. The zeta potential of PACS varies with pH. The performance of PACS as coagulant is affected by ┌ value and Al3+/SO42- mole ratio. PACS of ┌＝2.1 and Al3+/SO42-＝15 gives best turbidity removal effectiveness. In comparison with PAC of ┌＝2.0, PACS of ┌＝2.0 and Al3+/SO42-＝16 gives higher removal efficiency for turbidity and COD, and shows the following advantages in the clarification of waters andwastewaters: rapid aggregation velocity, larger and heavier flocs, and lower required dosage.

A series of polyaluminum silicate chlorides (PASC), which have different OH_/Al and Al/Si molar ratios, has been repared by a copolymerization technique and a compositetechnique, after which the coagulation efficiency and the residual aluminum content of PASC for water treatment were compared with polyaluminum chloride (PAC) by jar test. The experimental results show that PASC has better coagulation efficiency and lower residual aluminum content than PAC, and the PASC prepared by the copolymerization technique gives a better coagulating effect than that prepared by the composite technique. In addition, the OH_/Al and Al/Si molar ratios have some effect on the coagulation effect and residual aluminum content of PASC in treated water. With increasing OH_/Al molar ratio and decreasing Al/Si molar ratio, the residual turbidity and residual aluminum content in treated water diminishes. The pH of the water sample also affects the residual aluminum content of the water and there is a lower residua aluminum content in the neutral pH range.