Inorganic Ions’ Effect on the Coagulation of Contaminated Drinking Water Simulated with Kaolin-HA by Al13 Species in PAC1.doc
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1、精品论文大集合Inorganic Ions Effect on the Coagulation of Contaminated Drinking Water Simulated with Kaolin-HA by Al13 Species in PAC1Xu Xiuming1, Wang Yan12, Gao Baoyu 1, Xu Weiying 11 School of Environmental Science and Engineering Shandong University, Jinan, P.R.China(250100)2 Key Laboratory of Colloid
2、and Interface Chemistry Minstry of Education Jinan, China(250100)AbstractTo research the effect of coagulation conditions, especially water quality on coagulation efficiency, thecoagulation of synthetic raw water containing humic acid (HA) and kaolin by different aluminum coagulants - conventional A
3、l salts (AlCl3, Al2(SO4)3), poly-aluminum chloride (PAC) and the purified poly-aluminum chloride (Al13) - has been investigated for a wide range of conditions, including aluminum dosages in the range of 0.5 to 16 mg/L as Al2O3, pH values in the range of 3 to 10, and the possible effects of cations a
4、nd anions on coagulation efficiency. Results indicate that AlCl3, Al2 (SO4)3, PAC and the Al13 species are proved to be efficient in treating the synthetic raw water, and the coagulation efficiency may be associated with the polymerization degree of aluminum species. Water quality has varieties degr
5、ees of impact on coagulation efficiency; in particular the existence of SiO32-, HPO42-, H2PO4-, and NH4+, effluent quality has declined markedly. Moreover, Al13 species, which is thought to be the most efficient species in PAC, do not exhibit peculiar advantage in coagulation performance, contrarily
6、 it is worse than the other three coagulants especially when water contains HPO42-, and H2PO4-, and NH4+. Experiment results also showed that cations mainly affect the coagulation efficiency through influencing the molecular structure of humic acid, while anions mainly impact the system pH, and thus
7、 affect the aluminum coagulants hydrolysis- polymerization process, and ultimately change the coagulation efficiency.Key Words: poly-aluminum chloride; Al13 species; humic acid; cation; anion.1. Introduction As one of the most important natural drinking water source - surface water contains large am
8、ounts of natural organic matter,such as humic acid (HA). Besides giving the waters a yellowish color 1, taste and odor, and effecting the transfer of heavy metals in water, HA can also form disinfectionby-products 2-5 in pre-chlorination process and cause fouling problems in filtration of surface wa
9、ters. Consequently how to remove natural organic matter and turbidity in water effectively is taken into account 6-13. Enhanced coagulation is recognized as the best way 14, 15. poly-aluminum chloride (PAC), the widely used inorganic polymer coagulants in water industry, is the hydroxyl polynuclear
10、complex formed through hydrolysis-polymerization reaction in aqueous aluminum solution, and one of its more commonly accepted hydrolysates is the tridecamer (Al13O4(OH)247+, ab. Al13) 16-18. Al13 andits aggregation have great difference with other species of aluminum hydroxyl complexes in behavior,e
11、ffect and mechanism during water purification process 19-20. In the past work, a large number of subjects are stressed on the formation and conversion mechanism of Al13 species21, 22, the preparation methods of PAC containing high content of Al13 species 23, 24, and the separation, purification andi
12、dentification methods of Al13 species 25-30. And some studies are based largely on the Al () solutionof part hydrolysis 31-33, in which the structure and physical/chemical properties of Al13 species will inevitably be interfered by other coexistence forms. In consequence the ultimate coagulation eff
13、ect is the composite functions of multiple Al species; however Al13 species is only one of the important components 34-36.1 Support by the China postdoctoral Science Foundation (20080431197)- 17 -While research such as the influence of water quality during coagulation process for Al13 species is rep
14、orted rarely. In fact, the water quality (such as the coexistence of colloidal substances, ionic strength, and various cations and anions, etc.) in coagulation system is complicated and diverse. Accordingly many parameters may be effected, such as the HA molecular structure, pH values of solution an
15、d the hydrolysis-polymerization process of coagulants, finally the coagulation performance and efficiencyare inevitably influenced. This may be the reason why coagulation performance changed greatly in different water quality system for Al species.This paper describes an investigation of the coagula
16、tion behavior of Al13 species compared with other aluminum salts in different water qualities and how do these water qualities function with many controlling parameters. Through laboratory experiments with simulated contaminated drinking water, the influence of coagulants dosage, solution pH, surfac
17、e charge and ion effects have been examined. By reference to the experimental results, the suitable coagulation conditions and water quality for Al13 species to achieve its best performance and whether Al13 species are the best coagulation-flocculation species during coagulation process are identifi
18、ed.2. Materials and methods2.1 Materials and reagentsDe-ionized water was produced from a laboratory de-ionization unit and tap water was obtained from the laboratory supply. All reagents used were analytically pure grade. The four coagulants used in this study were all produced in our laboratory to
19、 provide a precise control on the coagulation reactions. PAC (OH/Al molar ratio of 2.0) was synthesized by adding pre-determinedamount of NaCO3 into AlCl3 solution under intense agitation. The temperature was kept at 70 0Cby using recycling water bath 37. Al13 species were separated and purified fro
20、m the PAC, which contains high concentration of Al13 species, using ethanol- acetone mixed precipitation method38. The detailed procedures can be found in (Gao et al., 2005; Zhao et al., 2002).Meanwhile, AlCl3 and Al2 (SO4)3 solutions were applied in this study as a special PAC with a Bvalue of 0 in
21、 this study. The four coagulants were characterized in Table 1.Table 1. Characteristics of different coagulantsCoagulantAla/ %Alb/ %Alc/ % AlCl398.5 1.50.0Al2 (SO4)398.31.70.0PAC32.531.835.7Al130.398.11.6From Table 1, it can seen that AlCl3 and Al2 (SO4)3 can be thought as monomer, PAC the mixer of
22、various Al species, and Al13 species the high-purified Al13 species.2.2 Preparation of stock solutionsThe commercialized HA (Shanghai, China) with 94.3% of the molecular weights ranging from30,000-50,000 Da was extracted from brown coal using NaOH solution. A stock solution was preparedby adding 1.0
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