電絮凝外文翻譯--鋁電極電絮凝脫色活性染料（英文）

1、Decolorization of Reactive Dye Solutions by Electrocoagulation Using Aluminum ElectrodesO. T. Can, M. Bayramoglu, and M. Kobya*Engineering Faculty, Department of Environmental Engineering, Gebze Institute of Technology,

2、41400 Gebze, TurkeyThe removal of pollutants from effluents by electrocoagulation has become an attractive method in recent years. This paper deals with the batch removal of the reactive textile dye Remazol Red RB 133 fr

3、om an aqueous medium by the electrocoagulation method using aluminum electrodes. The effects of wastewater conductivity, initial pH, current density, stirring rate, dye concentration, and treatment time on the decoloriza

4、tion efficiency and energy consumption have been investigated. Aluminum hydroxypolymeric species formed during an earlier stage of the operation efficiently remove dye molecules by precipitation, and in a subsequent stag

5、e, Al(OH)3 flocs trap colloidal precipitates and make solid-liquid separation easier during the flotation stage. These stages of electrocoagulation must be optimized to design an economically feasible electrocoagulation

6、process.1. IntroductionThe pollution induced by dyestuff losses and discharge during dying and finishing processes in the textile industry has been a serious environmental problem for years; dyes in the wastewater underg

7、o chemical as well as biological changes, consume dissolved oxygen from the stream, and destroy aquatic life because of their toxicity.1 It is therefore necessary to treat textile ef- fluents prior to their discharge int

8、o the receiving water. Traditional methods for dealing with textile waste- water consist of various combinations of biological, physical, and chemical methods.2 Common biological treatment processes are often ineffective

9、 in removing dyes which are highly structured polymers with low biodegradability.3 Various physical-chemical tech- niques are also available for the treatment of aqueous streams to eliminate dyes; chemical coagulation fo

10、llowed by sedimentation4 and adsorption are the widely used ones,5 but other advanced techniques are often applied, e.g., UV,6,7 ozonation,8 ultrasonic decomposition, or combined oxidation processes.9-11 Meanwhile, high

11、treatment costs of these methods have stimulated, in recent years, the search for more cost-effective treat- ment methods. Electrocoagulation is a process consisting of creating metallic hydroxide flocs within the wastew

12、ater by electrodissolution of soluble anodes, usually made of iron or aluminum. This method has been practiced for most of the 20th century with limited success. Recently, however, there has been renewed interest in the

13、use of electrocoagulation owing to the increase in environmen- tal restrictions on effluent wastewater. In the past decade, this technology has been increasingly used in developed countries for the treatment of industria

14、l wastewaters.12-14 Electrocoagulation has been proposed for the treatment of various effluents such as waste- water containing food and protein wastes,15 textile wastewater,16 aqueous suspensions containing kaolinite,be

15、ntonite, and ultrafine particles,17,18 fluoride-contain- ing water,19 restaurant wastewater,20,21 textile dye solutions,22,23 and smelter wastewater containing harm- ful arsenic.24The purpose of this study is to conduct

16、an experimen- tal investigation on the removal of a reactive textile dye (Remazol Red RB 133) from the wastewater using the electrocoagulation method. Several fundamental aspects regarding the effects of wastewater condu

17、ctivity, initial pH, current density, stirring rate, dye concentration, and time on the dye removal efficiency are explored.2. ElectrocoagulationGenerally, three main processes occur during elec- trocoagulation: (a) elec

18、trolytic reactions at electrode surfaces; (b) formation of coagulants in the aqueous phase; (c) adsorption of soluble or colloidal pollutants on coagulants and removal by sedimentation or flota- tion. The main reactions

19、at the electrodes areIf the anode potential is sufficiently high, secondary reactions may occur also, such as direct oxidation of organic compounds and of Cl- ions present in waste- water:20The chlorine produced is a str

20、ong oxidant that can oxidize some organic compounds. On the other hand, the cathode may be chemically attacked by OH- ions generated during H2 evolution at high pH values:25Al(aq)3+ and OH- ions generated by electrode re

21、actions (1) and (2) react to form various monomeric species such* To whom correspondence should be addressed. Tel.: +90- 262-6538457. Fax: +90-262-6538490. E-mail: kobya@ gyte.edu.tr.Anode: Al f Al(aq)3+ + 3e (1)Cathode:

22、 3H2O + 3e f 3/2H2 + 3OH- (2)2Cl- f Cl2 + 2e (3)2Al + 6H2O + 2OH- f 2Al(OH)4 - + 3H2 (4)3391 Ind. Eng. Chem. Res. 2003, 42, 3391-339610.1021/ie020951g CCC: $25.00 © 2003 American Chemical Society Published on Web 06

23、/11/2003tration are investigated on three process responses: decolorization efficiency, decolorization capacity (kilo- grams of dye removed per kilograms of total dissolved Al), and electrical energy consumption (kilowat

24、t hour per kilogram of dye removed). 4.1. Effect of the Initial pH. The effect of pH is investigated between 3 and 11. According to the elec- trode reactions (1) and (2), Al3+ and OH- ions are generated in the molar rati

25、o 1:3; meanwhile, for the polymeric species precipitating at pH 5-6, this ratio is less than 3, between 2 and 2.5. This means that the OH-ion accumulates in the aqueous phase during the process, and its concentration is

26、dictated not only by the initial pH but also by the reaction kinetics and equilibria occurring in this complicated aqueous system. As seen in Figure 3a, by increasing the initial pH from 3 to 9, the final pH increases ap

27、proximately from 8 to nearly 9, where it remains almost constant because of the buffering capacity of the system Al(OH)3/Al(OH)4-, which decreases the final pH from high values down to 9.4 by consuming OH- according to r

28、eaction (11).A low initial pH retards the formation of Al(OH)3 flocs and stimulates the formation of hydroxypolymeric spe- cies; as seen in Figure 3a, high efficiencies obtained with low initial pH values, e.g., 3, resul

29、t from an efficient precipitation of dye molecules, according to the mech- anism outlined by eqs 5 and 6. The decolorization efficiency shows a constant plateau for the initial pHbetween 5 and 9 and then falls again for

30、higher pH values. The decolorization capacity, as seen in Figure 3b, exhibits the same trends. As found by electrode weight measurements, the initial pH has a negligible effect on the total masses of dissolved electrodes

31、. This suggests that the dye precipitation process is primarily responsible of the high decolorization efficiency, and adsorption of the dye polymeric species colloidal pre- cipitates by Al(OH)3 flocs has a more secondar

32、y effect. Moreover, it is clear that, especially at high pH values above 9, the quantity of flocs diminishes according to eq 11; thus, the decolorization efficiency and capacity fall.Finally, the electrical energy consum

33、ed per kilogram of dye removed, as seen in Figure 3b, is also dependent on the initial pH; an acidic or neutral initial medium is beneficial for low electrical energy consumption. The sudden increase of energy consumptio

34、n above pH 9 is due to the same causes diminishing decolorization performances.4.2. Effect of Conductivity. The effect of conductiv- ity is investigated between 250 and 4000 µS/cm by using NaCl as the supporting ele

35、ctrolyte. As seen in Figure 4a, the decolorization efficiency decreases steadily as the conductivity increases. The final pH of the medium and the mass of dissolved anodes are almost indepen- dent of the varying conducti

36、vity. Thus, the decrease in the decolorization efficiency with increasing conductivity may not be attributed to these factors, but it may be attributed to a change in the ionic strength due to changing conductivity of th

37、e aqueous medium. Ionic strength affects clearly the kinetics and equilibria of reactions between charged species occurring during electrocoagulation.Figure 3. Effect of the initial pH (a) on the decolorization efficienc

38、y and (b) on the energy consumption and decolorization capacity (conductivity, 2000 µS/cm; current density, 10 mA/cm2; dye concentration, 250 mg/L; stirring rate, 200 rpm; treatment time, 10 min).Al(OH)3 + OH- S Al(

39、OH)4 - (11)Figure 4. Effect of conductivity (a) on the decolorization efficiency and (b) on the energy consumption and decolorization capacity (current density, 10 mA/cm2; dye concentration, 250 mg/L; stirring rate, 200