Scholarly article on topic 'Fenton Reagent Oxidation and Decolorizing Reaction Kinetics of Reactive Red SBE'

Fenton Reagent Oxidation and Decolorizing Reaction Kinetics of Reactive Red SBE Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — Hang Xu, Mei Li, Hui Wang, Juan Miao, Lei Zou

Abstract Fenton reagent was employed to treat and decolorize the wastewater of Reactive Red SBE by on-line spectrophotometry. The effects of initial FeSO4 concentration, initial H2O2 concentration, pH, reactive red SBE and temperature on the decoloration of reactive red SBE were investigated. The results show that Fenton oxidize process follows pseudo first order kinetics in the first stage and reaction activation energy is 2.608 kJ/mol. The decolorizing reaction rate constants (k) increase with the rise of FeSO4 concentration, H2O2 concentration, temperature, but decrease with the rise of reactive red SBE, and the optimum pH is 3. Initial FeSO4 concentration and initial H2O2 concentration against k are linear correlation.

Academic research paper on topic "Fenton Reagent Oxidation and Decolorizing Reaction Kinetics of Reactive Red SBE"

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Energy

ELSEVIER

Procedía

Energy Procedía 16 (2012) 58 - 64

International Conference on Future Energy, Environment, and Materials

Fenton Reagent Oxidation and Decolorizing Reaction Kinetics of Reactive Red SBE

Hang Xua*, Mei Lia, Hui Wanga, Juan Miaoa,Lei Zou

aChemical Engineering and Pharmaceutics School, Henan University of Science and Technology, Luoyang 471003, P.R. of China

Fenton reagent was employed to treat and decolorize the wastewater of Reactive Red SBE by on-line spectrophotometry. The effects of initial FeSO4 concentration, initial H2O2 concentration, pH, reactive red SBE and temperature on the decoloration of reactive red SBE were investigated. The results show that Fenton oxidize process follows pseudo first order kinetics in the first stage and reaction activation energy is 2.608kJ/mol. The decolorizing reaction rate constants (k) increase with the rise of FeSO4 concentration, H2O2 concentration, temperature, but decrease with the rise of reactive red SBE, and the optimum pH is 3. Initial FeSO4 concentration and initial H2O2 concentration against k are linear correlation.

© 2011 Published by Elsevier B. V. Selection andAn peer-review under responsibility of International Materials Science Society.

Keywords: Fenton reagent; Reactive Red SBE; kinetics; decolorizing reaction rate constant

1. Introduction

Nowadays, many reactive dyestuffs are designed by scientists to express a good characteristic about high resistance to fading caused by chemical, biological and light-induced oxidation [1] because of their resistant to oxidation and biodegradation, so the synthetic reactive dyestuffs are widespread applied in several industries including textile, paper, printing, cosmetics and pharmaceuticals [2]. But the dyeing process consumes excessive water and one of the largest groups of dye mills discharges abundant wastewater with residual dyes. Dyestuff wastewater does not been decolorized when treated aerobically by municipal sewage systems [3] due to their complex structure and synthetic origin. Obviously, one of

»Corresponding author. Tel.:+86-379-6318C101 E-mail address: xhinbj@106.com and xuhangC9@tsinghua.org.cn(H.Xu)

Fengtai Center for Disease Control and Prevention, Beijing 100071, P.R. of China

Abstract

1876-6102 © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of International Materials Science Society . doi:10.1016/j.egypro.2012.01.011

the vital problems regarding dye industries is the colored effluent which contains visible pollutants [4] and less than 1ppm of dyestuffs can cause notable water coloration [5]. Dyestuffs wastewater can be removed by chemical and physical methods including adsorption, photocatalytic oxidation [6], coagulation-flocculation and electrochemical methods, and so on. Fenton's reagent is homogenous catalytic oxidation process using a mixture of hydrogen peroxide and ferrous ions in an acidic environment [7] and Eqs. (1)—(10) are the main inorganic reactions in the solution [8]. In this paper, Fenton reagent was employed to treat and decolorize the wastewater of Reactive Red SBE (RR SBE) by on-line pectrophotometry. The effects of FeSO4 concentration, H2O2 concentration, pH, reactive red SBE and temperature on the discoloration of reactive red SBE were investigated.

Fe2+ + H 2O2 —> Fe 3+ + ^OH + OH - (1)

Fei+ + H 2O2 Fe 2+ + H + + ^OOH (2)

Fe3+ + •OOH -> Fe2+ +^OO" + H+ (3)

Fe3+ +«OO - Fe 2+ + O2 (4)

• OH + H 2O2 —>^OOH + H 2O (5)

• OH + RH — R •+ H 2O (6)

2 • OH-> H 2O2 (7)

H 2O2 + ^OH —> H 2O + •OOH (8)

• OOH + ^OH- -> H 2O + O2 (9)

• OO~ + •OOH -> OOH -+ O2 (10)

2. Experimental

2.1. Apparatus and chemical reagent

Materials: RR SBE (Reactive Red SBE, Fig. 1) was obtained from Jiangsu Shenxin dyestuffs Co. Ltd. (China) and used without further purification. H2O2 (30%), FeSO4 and H2SO4 at least analytical grade were purchased from Beijing Chemical Reagents Co. Ltd. Apparatus: UV-2102PC UV-Vis spectrophotometer (Shanghai, China), peristaltic pump, current colorimetric container and computer compose online monitoring system. Magnetic stirrer (Rongsheng Apparatus Co. Ltd.) can advantage to mix reactive materials.

Fig. 1 Chemical structure of Reactive red SBE 2.2. Procedures

Fenton process was performed in a beaker containing 200 ml solution, in which the specified concentration of selected dyestuff was remained. At the same time, stir, lamp and pump were applied.

The wastewater was pressed into the current colorimetric container in UV-Vis spectrophotometer by peristaltic pump. Absorbance was determined at maximal absorption peak of dye by UV-Vis spectrophotometer. When H2O2 at the calculated concentrations was added into the wastewater, the computer which was linked with spectrophotometer began to record experimental absorbance results.

3. Results and discussion

3.1. Determination of experimental wavelength

Fig. 2 shows the UV-Vis spectrums of all reactive materials from 190—700nm. The spectrums of H2SO4, Fe2+, Fe3+, H2O2 in 500—600 nm have not absorption but Reactive Red SBE in this area has a strong absorption, and maximum adsorption peak is 543 nm. So 543 nm in the visible region is determinated the experimental wavelength. The criterion equation of absorbance against Reactive SBE concentration in the 543 nm at neutral pH is A=0.02251C-0.00178, R2=0.9999 and we found UV- Vis spectrum of Reactive Red SBE has not been influenced by different acid ambient in the experiment. So the criterion equation can be used in acid and neutral circumstance.

300 400 500 Wavelength (nm)

-V H2O2:1.765mmol/L pH:3 SBE:17mg/L Temperature:15oC 0mmol/L

0.01619mmol/L

0.04856mmol/L

0.1133mmol/L

100 150 200 Time (s)

Fig.2 UV-Vis spectrum of reactants

Fig.3 Effect of initial Fe concentration

3.2. Influence rf initial Fe concentration

Tab. 1 Effect of initial Fe2+ concentration to k and tj/2 of SBE decolorization by Fenton's reagent

[Fe2+]o /mmol/L k /s-1 ti/2 /s R2 Removal (%) in 300 s

0.01619 0.01632 42.47 0.9916 37.07

0.04856 0.03655 19.00 0.9916 64.53

0.08094 0.05920 11.71 0.9893 82.20

0.1133 0.07592 9.130 0.9898 89.56

The curve of decolorization of Reactive Red SBE against time at different initial concentrations of Fe which are used concentrations of 0, 0.01616, 0.04856, 0.08094 and 0.1133 mmol/L is showed in Fig. 3. From the Fig. 3, we can be seen clearly degradation speed rate and removal effiency have a great increase with the rise of Fe2+ concentrations. The results denote that its probably can be divided two regions for

the Fenton oxidation process to degradate dye. At he beginning of the reaction, coloration of Reactive Red SBE decrease rapidly. However in the second region (>30 s), decoloration process is very slow. These experimental phenomena can be explained in two aspects. The reduce of Fe2+ and H2O2 concentration can decrease the reaction rate and intermediate products during the Fenton oxidation process engage in the reaction. From many reports, Fenton oxidation process follows pseudo first order kinetics [8, 9]. From the integral curves decolorization of Reactive Red SBE in Fig.3 degradation process do not submit first order rate law, but in the first region (<30 s) the experimental results follow first order rate law, ln(Co/C)=kt, and calculated results are showed in Tab. 1. From Tab.1 , the decolorizing reaction rate constants (k) and removal efficiency in 300 s have a great increase with the rise of initial Fe2+ concentration. Initial Fe2+ concentrations against k is linear correlation, k=0.6627[Fe2+]o+0.0033 , R2=0.9963.

3.3. Influence of initial H2O2 concentration

O 40 -

FeSO4:0.08094mmol/L pH:3

SEB:17mg/L Temperature:15oC

150 Time (s)

FeSO4:0.08094mmol/L

H2O2:1.765mmol/L

Temperature:15oC

"1V 34mg/L

25.5mg/L ~

17mg/L

8.5mg/L

50 100 150 200 250 300 Time (s)

Fig 4 Effect of initial H2O2 concentration Fig.5 Effect of initial reactive red-SBE

concentration

The curve of decolorization of Reactive Red SBE against time at different initial concentrations of H2O2 which are used concentrations from 0.3530 to 2.471 mmol/L is showed in Fig. 4 while keeping the FeSO4 dose, pH, Reactive Red SBE dose and Temperature constant at 0.08094 mmol/L, 3, 17 mg/L and 15 oC. The first order kinetics constants were simulated in Tab. 2, which carried through during the early stage. As can be seen from th Fig. 4 and Tab. 2, the addition of H2O2 from 0.3530 to 1.059 mmol/L increases the decolourization from 75.93% to 83.17% at 300 s and further increase from 1.059 to 2.471 mmol/L causes small significant change in decolourization. At the high dosage of H2O2 the decrease in decolourization is due to the hydroxyl radical scavenging effect of H2O2 (Eq. 10) and recombination of hydroxyl radicals (Eq. 7) [10]. From Tab. 2, the decolorizing reaction rate constants (k) increase with the rise of initial H2O2 concentrations. k against initial H2O2 concentration is linear correlation, k=0.02508[H2O2]o+0.01753, R2=0.9959.

Tab. 2 Effect of initial H2O2 concentration to k and t1/2 of SBE decolorization by Fenton's reagent

[H2O2]o /mmol/L k /s-1 t1/2 /s R2 Removal (%) in 300 s

0.3530 0.02577 26.90 0.9937 75.93

1.059 0.04630 19.00 0.9894 83.17

1.765 0.05920 11.71 0.9893 82.20

2.471 0.08049 8.612 0.9978 85.51

3.4. Influence of initial Reactive Red SBE concentration

Tab. 3 Effect of reactive red-SBE concentration to k and t1/2 of SBE decolorization by Fenton's reagent

Reactive Red SBE /mg • L-1 k /s-1 t1/2 /s R2 Removal (%) in 300 s

8.5 0.08547 8.10 0.9927 93.30

17 0.05920 11.71 0.9893 82.20

25.5 0.04780 14.50 0.9892 77.21

34 0.03635 19.07 0.9886 69.61

Fig. 5 shows the curves of decolorization of Reactive Red SBE against time at different initial concentrations of Reactive Red SBE which are used concentrations of 8.5, 17, 25.5, 34 mg/L. Tab.3 shows the decolorizing reaction rate constant (k) and the half-value period (t1/2) according to the experimental data in the first region at different initial concentrations of Reactive Red SBE. The figure and table clearly reveal that the increase in dye concentration decreases the removal efficiency and the decolorizing reaction rate constant. Increase of dye concentration from 8.5 to 34 decrease k from 0.08547 to 0.03635 s-1 and the decolorization from 93.30% to 69.61% in 300s. The increase in dye concentration increases the number of dye molecules in the water and not the hydroxyl radical, so the removal rate decreases.

3.5. Influence of pH

The pH of the solution is an important parameter for Fenton process [11]. Fig. 6 shows the curves of decolorization of Reactive Red SBE against time at different pH (2, 3, 7). Tab. 4 shows the decolorizing reaction rate constant (k) and the half-value period (t1/2) according to the experimental data in the first region at different pH. As can be seen from the Fig. 6 and Tab. 4, pH 3 is found to be the optimum pH for both processes. However, pH 2 and pH 7 also have a good decolorizing removal. The decolorizing reaction rate constants are similar in these three reaction conditions. In many early reports, dye can not be degradated using Fenton regeant at neutral medium [11, 12]. Our results are different from early reports.

Hang; Xu et al. /Energy Procedia 16 (2012) 58 — 64 Tab. 4 Effect of pH to k and t1/2 of SBE decolorization by Fenton's reagent

pH k /s-1 ti/2 /s R2 Removal (%) in 300 s

2 0.05897 11.75 0.9898 78.11

3 0.05920 11.71 0.9893 82.20 7 0.05708 12.14 0.9903 73.51

3.6. Influence of temperature

Fig.6 Effect of pH Fig.7 Effect of temperature

For the change of temperature condition from 15 to 50 oC, the curves of SBE decreased with time from 0 to300 s show in Fig 7, while initial concentration of Fe2\ H2O2, Reactive Red SEB and pH value remained constant. The first order kinetics constants were simulated in Tab.5, which carried through during the early stage. It is shown that decolorization rate and removal efficiency could be increased with

Ea , . ln k =--+ ln A

the raise of reaction temperature. According to the expression , reaction activation

energy (Ea) could be calculated of 2.608 kJ/mol. As for the relationship between temperature and Ea, reaction occurred instantly during room temperature when value of Ea less than 63kJ/mol. Therefore, pollution water of Reactive Red SEB could be degraded when using Fenton technique in room temperature. Moreover, this method conforms to condition in reality.

Tab. 5 Effect of temperature to k and t1/2 of SBE decolorization by Fenton's reagent

9/°C k /s-1 t1/2 /s R2 Removal (%) in 300 s

15 0.05920 11.71 0.9893 82.20

28 0.06331 10.95 0.9930 82.22

50 0.06678 10.38 0.9877 89.27

4. Conclusion

Fenton reagent can rapidly damage chemical structure of Reactive Red SBE and decolorization of dye wastewater is effectively achieved. However there are some intermediates and by products existed in the Fenton process. So mineralization process is not completely. Fenton oxidization process follows pseudo first order kinetics in the first stage. Reaction activation energy (Ea) is 2.608 kJ/mol. The decolorizing reaction rate constants (k) increase with the rise of FeSO4 concentrationH2O2 concentration temperature, but decrease with the rise of reactive red SBE, and the optimum pH is 3. Initial FeSO4 concentration and initial H2O2 concentration against k are linear correlation.

Acknowledgements

This work is supported by the National Nature Science Foundation of China (No: 21006057) and China Postdoctoral Science Foundation (No: 20100470351)

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