Chemical Engineering and Processing 44 (2005) 1013–1017

Catalytic oxidation of the dye wastewater with hydrogen peroxide

Zumin Qiua,b,∗, Yunbing Hea, Xiaocheng Liua, Shuxian Yua

a School of Environmental and Chemical Engineering, Nanchang University, Nanchang Jiangxi 330029, Chinab Key Laboratory of Poyang Lake Ecology and Bio-resource Utilization, Nanchang University, Ministry of Education, Nanchang 330029, China

Received 1 March 2004; received in revised form 28 January 2005; accepted 28 January 2005Available online 16 March 2005

Abstract

This article presented an approach for the treatment of dye wastewater using H2O2 and heterogeneous catalysts. In order to screen outan effective catalyst, a series of catalysts containing transition metals were prepared by impregnation and precipitation methods. The resultsindicate that Cu is a promising catalyst as it eliminated almost totally the chroma of the acid scarlet aqueous solution accompanied with agood chemical oxygen demand (COD) removal rate. The results also show that the catalysts prepared by precipitation were more effectivethan those prepared by impregnation. Moreover, the activity decrease of the catalyst was not changed between batches, and the catalysts couldb©

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eywords:Dye wastewater; Hydrogen peroxide; Heterogeneous; Copper; Impregnation; Precipitation

. Introduction

It has been estimated that about 15% of the dyes producedn the world are released into environment during theirynthesis and processing[1], causing serious environmentalontamination. Thus, it is important to make some treatmentefore release. Various methods have been applied for

heir treatment, including coagulation[2,3], denitrification4], biodegradation[5], absorption [6,7], and oxidationrocesses[1,8–12]. The oxidation technologies, in whichontaminants are converted into carbon dioxide and water,ave been successfully used for the treatment of the wastew-ter containing organic pollutants. Hydrogen peroxide haseen found useful in the treatment of wastewater and isften referred as a friendly oxidant because the oxidationyproducts are water and oxygen.

The technology using hydrogen peroxide to treat dyeastewater has two different methods, homogeneous andeterogeneous reaction. In the homogeneous reaction, metal

ons such as Fe2+and Cu2+ are used as the catalysts. Inenton reaction (a homogeneous reaction), the key step is

the formation of hydroxyl radicals from hydrogen peride [11,13–16]. The organic compounds RH existed inwastewater can be oxidized by hydroxyl radicals into•,which can be further, oxidized into carbon dioxide andter. However, metallic salts catalyst may cause seconpollution.

The other one is heterogeneous catalytic reaction. Mresearchers have studied the treatment of dye wastewameans of wet oxidation via heterogeneous catalysts[17–21].And this method, using heterogeneous catalysts and hgen peroxide, has been found a good one for the treatmwastewater.

The aim of this study was to find a good heterogeneoualyst to treat dye wastewater effectively. The catalyst whelp to promote the decomposition of hydrogen peroxidform hydroxyl radicals.

2. Materials and methods

2.1. Materials

∗ Corresponding author. Tel.: +86 791 830 5149; fax: +86 791 830 5124.E-mail address:qiuzm@ncu.edu.cn (Z. Qiu).

All chemicals used in the experiment were analyticallypure reagents.

d.

255-2701/$ – see front matter © 2005 Elsevier B.V. All rights reserveoi:10.1016/j.cep.2005.01.004

1014 Z. Qiu et al. / Chemical Engineering and Processing 44 (2005) 1013–1017

2.2. Preparation of catalyst

�-Al2O3 (gamma-alumina) was washed repeatedly withdistilled H2O at first, dried and then activated at 300◦C[22]. The catalyst was prepared by two different methods,namely, the conventional impregnation method [denoted asM–Al2O3(I), M is Cu, Zn, Ni or Mn], and precipitationmethod [denoted as M–Al2O3(P), M is Cu, Zn, Ni or Mn].Details of the preparation of the catalyst were described asfollows: the M–Al2O3(I) catalysts were prepared by impreg-nating 10 g�-Al2O3 powder into 40 mL nitrate of metal (Cu,Ni or Mn) or zinc acetate aqueous solution of 5 (wt.% ofmetal). Then the solution was stirred for 4 h at room temper-ature. After filtration, the deposit was dried for 4 h at 100◦C,and then calcined in air at 450◦C for 4 h.

The M–Al2O3(P) catalyst was prepared by impregnating10 g�-Al2O3 powder into 40 mL metal nitrate or zinc acetateaqueous solution of 5 (wt.% of metal). Then 10 g precipitator(CO(NH2)2) was added to the solution, depositing in a con-stant temperature water bath at 55◦C for 4 h. After ageing,precipitating, washing and filtering, the deposit was dried at100◦C for 4 h, and then calcined in air at 450◦C for 4 h.

After the preparation, the loadings of these metalsdeposited on�-Al2O3 were found to be (5.0± 0.2 mgmetals)/(�-Al2O3 (g)) in both methods.

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Table 1Catalytic oxidation of acid scarlet solution by various heterogeneouscatalysts

Catalyst COD removal rate (%) Chroma removalrate (%)

�-Al2O3 5.7 9.8Cu–Al2O3(I) 62.1 83.1Ni–Al2O3(I) 9.1 11.7Mn–Al2O3(I) 13.2 21.4Zn–Al2O3(I) 27.8 40.2Cu–Al2O3(P)a 72.3 98.1Zn–Al2O3(P)a 33.8 53.6Mn–Al2O3(P)a 18.9 32.8

COD0 = 632.5 mg/L, 1.5 g catalyst, 2.5 mL H2O2, initial pH≈ 4.0, reactiontime: 120 min, temperature: 70◦C.

a The precipitator is CO(NH2)2 and the pH is variable in the process.

preparation method also influenced the activity of catalyst.The catalysts prepared by precipitation were more effectivethan those prepared by impregnation. The results indicatethat the catalyst containing Cu prepared by precipitationwas suitable for the removal of both COD and chroma fromwastewater.

3.2. Effect of different precipitators

Table 2 showed the effects of three kinds of catalystsprepared with different precipitators. The catalysts preparedwith precipitator NH4HCO3 and CO(NH2)2 were better interms of the COD and chroma removal rates. The catalystprepared with precipitator NH3·H2O promoted the decom-position of H2O2, but the COD and chroma removal rates didnot decrease significantly. While the catalysts prepared withNa2CO3 or NaHCO3 had weaker activity in the removal ofCOD and chroma.

3.3. Effect of the amount of CO(NH2)2

Fig. 1showed the effect of CO(NH2)2 concentration on thecatalytic activity. COD and chroma removal rates increasedwith the increase in the ratio of CO(NH2)2/�-Al2O3 (g) whenthe ratio was below 0.5. A relatively higher value was ob-tained when the ratio was between 0.5 and 1, but decreasedw undtN ot hichw

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.3. Catalytic reaction

Experiments were carried out in a glass reactor (1000nder agitation. After adding Acid Scarlet GR and the c

yst, the glass reactor was placed in a water thermostatemperature in the thermostat was kept at 70◦C. The reactiotarted with the addition of H2O2.

.4. Analysis

COD was measured by dichromate method[23]. Thehroma was determined by the absorbance of the sot 510 nm[1].

. Results and discussion

.1. Screening tests

Table 1presented the results of the degradation of thecarlet aqueous solution (1000 mg/L) at 70◦C. FromTable 1,t can be found that the catalyst without transition mhowed weak catalytic activity in hydrogen peroxideomposition. Although H2O2 is a strong oxidant, it failed txidize the dye hue. So some metals were loaded on thier of �-Al2O3. As shown inTable 1, the COD and chromemoval rates increased when catalysts contained tranetals. And the type of transition metals had a great influn the removal rate of COD and chroma. The activity oas in the sequence of Cu > Zn > Mn > Ni >�-Al2O3. The

hen the ratio was over 1. The optimum ratio was foo be 1. The hydrolysis products of CO(NH2)2 are OH− andH4

+. Different CO(NH2)2/�-Al2O3 (g) ratios would lead the formation of different compounds on the catalyst, would affect catalytic activity[24].

able 2ffect of the precipitator on the catalytic activity

recipitator COD removal rate (%) Chroma remorate (%)

a2CO3 26.7 42.8aHCO3 33.6 51.2H3·H2O 53.2 79.0H4HCO3 72.5 98.4O(NH2)2 72.3 98.1

Z. Qiu et al. / Chemical Engineering and Processing 44 (2005) 1013–1017 1015

Fig. 1. Effect of the amount of CO(NH2)2 on catalytic activity, (�) CODand (�) colority.

3.4. Effect of the calcination temperature

The effect of the calcination temperature on the catalyticactivity was showed inFig. 2. COD and chroma removalrates increased with the increase in the calcination tempera-ture when the temperature was lower than 475◦C, the reasonfor which might be the formation of active CuO. However,when the temperature was higher than 475◦C, the CODand chroma removal rates decreased with the increase intemperature because some particles may be sintered. Hence,the optimum calcination temperature to prepare the catalystwas 475◦C. Generally, Cu/�-Al2O3 catalysts calcined below700◦C possessed highly dispersed CuO, while when thecalcination temperature was higher than 700◦C, not onlythe sintering of particles but also the formation of CuAl2O4with spinel-type structure[25] might appear, resulting in therapid decrease of the catalytic activity. In order to elucidateit, the X-ray diffraction properties of the Cu catalyst wereinvestigated. According toFig. 3, small peaks were at 2θof 33.6 and 38.7 (curve (b)), which were corresponding tothat of CuO[26]. While the peaks at 2θ of 33.6 and 38.7

F(

Fig. 3. XRD figure of CuO/Al2O3, (a) 750◦C and (b) 450◦C; (1)�-Al2O3,(2) CuO and (3) CuAl2O4.

(curve (a)) disappeared with the increase in the calcinationtemperature and some peaks were observed at 2θ of 31.4 and37 which were corresponding to that of CuAl2O4 [26]. Thisindicated that some catalysts were changed into CuAl2O4with the increase in the calcination temperature. As shownin Fig. 2 andFig. 3, the highly dispersed CuO has a higheractivity than CuAl2O4. Furthermore, the BET surface areaof the catalysts at 475, 700 and 800◦C were 112, 99 and72 m2/g, showing the sintering of the catalysts at highertemperature.

3.5. The validation of the heterogeneous reaction

During the experiment, some copper ions can be found inthe solution after the treatment, but no metal was found in thedyestuffs. This may be caused by the leaching out of somecopper ions from the catalyst. The concentration of the cop-per ions was 9.87 ppm and the COD removal rate was 76.7%(condition: COD0 = 632.5 mg/L, 1.5 g catalyst, 2.5 mL H2O2,initial pH ≈ 4.0, reaction time: 120 min, temperature: 70◦C).In order to make sure whether the catalytic reaction was ho-mogeneous or heterogeneous, experiments were carried outby adding no catalyst but 10 ppm Cu(NO3)2 solution (otherconditions were the same as above). And the COD removalrate was found to be 4.7%, which confirmed that the catalyticr

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ig. 2. Effect of the calcined temperature on catalytic activity, (�) COD and�) colority.

eaction was heterogeneous.

.6. Tests of the stability of Cu catalyst and treatment other dye aqueous solution

The stability of the Cu catalyst was shown inTable 3. Fiveuns were operated with the same catalyst at 70◦C and pHas controlled at 4.0. When the catalyst was reused dir

ts catalytic activity decreased slowly. This might be cauy the coking of the catalyst surface and the inhibitionye or organic compounds formed on some active site

he catalyst. Nevertheless, the decrease was not greahe activity of the catalyst can be recovered by recalcin the air at 450◦C for 3 h. FromTable 3, the COD and

1016 Z. Qiu et al. / Chemical Engineering and Processing 44 (2005) 1013–1017

Table 3Catalyst stability

Catalyst COD removal rate (%) Chroma removalrate (%)

Fresh 77.5 99.1Reused once 73.9 98.9Reused twice 69.0 92.4Reused third 65.6 87.2Reused fourth 62.5 85.1Reused fifth 61.1 83.6Reused sixtha 73.6 98.1

COD0 = 632.5 mg/L, reaction time: 120 min, temperature: 70◦C, pH = 4.0,3.0 mL H2O2.

a The catalyst was calcined before reuse.

chroma removal rates of the recalcined catalyst were 73.6and 98.1, which was a little lower than that of the fresh one.The difference might be caused by the poison of some activesites, which could not be recovered.

Table 4showed the treatments of other dye wastewaterusing Cu catalyst and H2O2. The catalyst was also effectivewhen used to treat other dye aqueous solutions. The chromaof the dye aqueous solution degraded easier than the COD.During the experiment, the color of the dye solution was ob-served to change from red to dark-red with the addition ofH2O2, and then gradually changed to colorless. This may becaused by the formation of OH radicals which would attackthe chromophoric group (e.g. azo-group, nitro-group) first,and then attacked the intermediates (e.g. phenyl ring, naph-thalene ring and so on). In this system, the oxidation of dyemay occur in two steps[27]: at first, the intermediates wereprincipally formed and then some of the intermediates werefurther oxidized to CO2 and H2O.

3.7. The post-treatment of the wastewater

As the optimum pH should be controlled at 4.0, after treat-ment the acid solution could not be directly released into theenvironment. Furthermore, some copper ions also leachedout from the catalyst (the Cu2+ concentration was 5–10 ppm)a stan-d ted to7 en-t

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4. Conclusions

This study investigated the oxidation of dye using the het-erogeneous catalyst and H2O2 under mild conditions. Thecatalyst prepared by precipitation allowed a total eliminationof chroma and had a significant COD removal rate. The cat-alyst could be recovered between batches by recalcining inthe air at 450◦C for 3 h though there was a little decrease ofthe activity in the COD and chroma removal rates.

Acknowledgments

The authors are grateful to Prof. Jiayang Chen and Doc.Zhu Jianhang for their helpful discussions and corrections.The research work is funded by the Education Ministry ofChina and Natural Science Foundation of Jiangxi Province.

References

[1] I.A. Salem, Kinetics and mechanism of the color removal from congored with hydrogen peroxide catalyzed by supported zirconium oxide,Trans. Met. Chem. 25 (2000) 599–604.

[2] T. Hasegawa, K. Hashimoto, T. Onitsuks, et al., Characteristicsof metal-polysilicate coagulants, Water Sci. Technol. 23 (1991)1713–1722.

[3] Q. Xu, X.R. Qian, X.Y. Han, Selections of process conditions inolle.

tion

het-. Mi-

roms, En-

tep-. 21

rbichemi-ation002)

dyeem.

[ o-ps in

[ stew-

[ -ater

[ entater,

[ tionistry

nd existed in solution. In order to reach the releasingards, pH value of the treated wastewater must be adjus.0–7.5 by adding alkali. Under this condition, the conc

ration of Cu2+ would be less than 2 ppm.

able 4he treatment of other dye aqueous solutions

ategory COD0 (mg/L) COD removalrate (%)

Chroma removarate (%)

cid scarlet GR 632.5 74.2 98.5oluble blue 966.2 78.1 99.3cid black 10B 624.3 72.7 98.4irect red F 1687.1 83.2 85.7irect scarlet 4B 1330.3 82.4 84.6asic flavine O 899.3 77.7 87.3asic pink 810.1 76.9 86.5

eaction time: 120min, temperature: 70◦C, pH = 4.0, 2.5 mL H2O2, 1.5 gatalyst.

PSAFC disposal of dyeing wastewater, J. Lianyungang Tech. C15 (2001) 9–11.

[4] L.A. Robertson, E.W.J. Van Niel, et al., Simultaneous nitrificaand denitrification in aerobic chemos-tat cultures ofThiosphaeraantotropha, Appl. Environ. Microbiol. 54 (1988) 2812–2818.

[5] C. Cripps, J.A. Bumpus, S.D. Aust, Biodegradation of azo anderocyclic dyes by phanerochaete chrysosporium, Appl. Environcrobiol. 56 (1990) 1114–1118.

[6] Y.H. Jang, D.H. Shang, Removal of organic dye (Direct Blue) fsynthetic wastewater by absorptive bubble separation techniqueviron. Sci. Technol. 27 (1993) 67–72.

[7] Z.M. Shen, W.H. Wang, J.P. Jia, D.H. Wang, Study on a two scontrol composite dynamic absorption model, Acta Sci. Circum(2001) 85–87.

[8] E.G. Girenko, S.A. Borisenkova, O.L. Kaliya, Oxidation of ascoacid in the presence of phthalocyanine metal complexes. Ccal aspects of catalytic anticancer therapy. 1. Catalysis of oxidby cobalt octacarboxyphthalocyanine, Russ, Chem. Bull. 51 (21231–1236.

[9] I.M. Kobasa, G.P. Tarasenko, Photocatalysis of reduction of themethylene blue by Bi2S3/CdS nanocomposites, Theor. Exp. Ch38 (2002) 255–258.

10] N.B. Kolova, L.P. Kovzhina, N.M. Dmitrieva, N.V. Blinova, Phtodegradation of azo dyes with heterocyclic and benzene groupolymeric matrix, Russ. J. Appl. Chem. 75 (2001) 254–256.

11] H.L. Sheng, et al., Fenton process for treatment of disizing waater, Water Res. 8 (1997) 2050–2056.

12] S. Munevver, W.A. David, F. Akkas¸, K. Nuket, A. Filiz, Photodegradation of some dyes using Ag-loaded titanium dioxide, WAir Soil Pollut. 11 (2001) 153–163.

13] F.J. Beltran, M. Gonzalez, F.J. Ribas, P. Alvarez, Fenton reagadvanced oxidation of polynuclear aromatic hydrocarbons in wWater Air Soil Pollut. 195 (1998) 685–700.

14] C. Kang, A. Sobkowiak, D.T. Sawyer, Iron(II)-induced generaof hydrogen peroxide from dioxygen: induction of fenton chemand ketonizations, Inorg. Chem. 33 (1994) 79–82.

Z. Qiu et al. / Chemical Engineering and Processing 44 (2005) 1013–1017 1017

[15] J.T. Spadaro, L. Isabelle, V. Renganathan, Hydroxyl radical mediateddegradation of azo dyes: evidence for benzene generation, Environ.Sci. Technol. 28 (1994) 1389–1393.

[16] R.G. Zepp, Hydroxyl radical formation in aqueous reactions (pH3–8) of Iron(II) with hydrogen peroxide: the photo-fentons reaction,Environ. Sci. Technol. 26 (1992) 313–319.

[17] Y.J. Bin, W.P. Zhu, Z.P. Jiang, T. Yin, Reation kinetic of the cat-alytic wet air oxidation treatment of H-acid solution, Environ. Sci.21 (1999) 76–80.

[18] D. Jelka, L. Janez, Comparison of catalyzed and noncatalyzed oxida-tion of azo dye and effect on biodegradability, Environ. Sci. Technol.32 (1998) 1294–1302.

[19] J. Qin, et al., Catalytic wet oxidation over alumina support metals,Appl. Catal. B: Environ. 16 (1998) 261–268.

[20] Le Lecheng, et al., Improve wet oxidation for the treatment of dyeingwastewater concentrate from membrane separation process, WaterRes. 9 (1998) 2753–2759.

[21] C.H. Yang, C.C. Lee, T.C. Wen, Hypochlorite generation on Ru–Ptbinary oxide for treatment of dye wastewater, J. Appl. Electrochem.9 (2000) 1043–1051.

[22] Z.M. Qiu, X.C. Liu, Study on the multi-phase catalytic oxida-tion of dye wastewater treatment, J. Nanchang Uni. 25 (2003) 16–22.

[23] D.Q. Xu, X.H. Yuan, Z.Y. Lou, Activated carbon-H2O2 catalytic ox-idation process forp-aminophenol(PAP) degradation of water treat-ment, China Environ. Sci. 20 (2000) 111–113.

[24] X.B. Ma, Z.H. Li, B.W. Wang, G.H. Xu, Effect of Cu cata-lyst preparation on the oxidative carbonylation of methanol todimethyl carbonate, React. Kinet. Catal. Lett. 76 (2002) 179–187.

[25] T.W. Kim, M.W. Song, H.L. Koh, K.L. Kim, Surface properity andreactivity of Cu–Al2O3 catalysts for NO reduction by C3H6 influ-ences of calcinations temperatures and additives, Appl. Catal. A:Gen. 210 (2001) 35–44.

[26] X.Y. Jiang, R.X. Zhou, J.X. Mao, X.M. Zheng, Effect of additionof Sm2O3 on property of CuO–�-Al2O3 catalyst, J. Rare Earths 15(1997) 179–185.

[27] K. Fajerwerg, H. Debellefontaine, Wet oxidation of phenol by hydro-gen peroxide using heterogeneous catalysis Fe-ZSM-5: a promisingcatalyst, Appl. Catal. B: Environ. 10 (1996) 229–235.