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.