Removal of azo and anthraquinone dyes from aqueous solutions by Eichhornia Crassipes

Removal of azo and anthraquinone dyes from aqueous solutions by Eichhornia Crassipes

ARTICLE IN PRESS Water Research 38 (2004) 2967–2972 Removal of azo and anthraquinone dyes from aqueous solutions by Eichhornia Crassipes M.M. El Zaw...

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ARTICLE IN PRESS

Water Research 38 (2004) 2967–2972

Removal of azo and anthraquinone dyes from aqueous solutions by Eichhornia Crassipes M.M. El Zawahry*, M.M. Kamel Dyeing, Printing & Auxiliary Department, National Research Centre, Cairo, Egypt Received 1 August 2000; received in revised form 1 September 2001; accepted 29 November 2001

Abstract The rate of adsorption of two azo and four anthraquinone anionic dyes on Eichhornia Crassipes (E.C.) has been studied. Raw E.C. and three aminated derivatives of E.C. with different nitrogen percent were used as dye adsorbents. The parameters studied include the amount of substrate, shaking time, chemical structure, concentration of dyestuff and pH of dyeing bath. Simple kinetic adsorption models of dynamics and adsorption parameters for the Langmuir and Freundlich isotherms were determined. A higher nitrogen percent of aminated E.C. showed a higher adsorption capacity than other derivatives. The kinetic adsorption models indicate that the decolourization was complete in a relatively short time (10 min) and the reaction taking place is of the first order. The equilibrium data fit well with the Freundlich model of adsorption for the six dyes. Only dye IV (C.I.A Acid Blue 25) conform both Freundlich and Langmuir adsorption isotherms. r 2004 Published by Elsevier Ltd. Keywords: Azo dyes; Anthraquinone dyes; Eichhornia Crassipes and its aminated derivatives; Dye adsorbents; Decolourization Freundlich and Langmuir’s model

1. Introduction Textile industries use large amounts of salts, ionic dyes, inorganic catalysts, detergents, finishing and bleaching agents that add to the dissolved solids concentration of the wastewater which discharge huge volumes of aqueous effluents to rivers and lakes. This consequently adversely affects the health of living beings, fertility of the soil and therefore is a source of many of man’s illnesses. Methods for colour removal are more systematically classified as follows: activated sludge systems, membrane filtration, coagulation and flocculation and water treatment plant design reliability [1]. Adsorption is a physicochemical process, which offers great potential as a means of producing quality effluent [2]. Various adsorbent wastes are used in colour removal processes *Corresponding author. Fax: +20-2-335-7807. E-mail address: [email protected] (M.M. El Zawahry). 0043-1354/$ - see front matter r 2004 Published by Elsevier Ltd. doi:10.1016/S0043-1354(01)00526-7

such as activated carbon, chitosan and natural wastes (e.g. cellulose derivatives, wood pulp, peat, feathers, hair, sawdust) and clay adsorption is one of the techniques which is comparatively more useful for the removal of dye from wastewater [3]. While each of these various decolourization methods is effective to some extent, none of these is effective for all dye classes. All these treatment techniques on colour removal should not eliminate, the possibility of colour reduction at the source and some of these methods are relatively expensive, leaving the final environmental problem unsolved. The need to explore possibilities of utilizing unconventional materials as sources of wastewater treatment is extremely valuable. Water hyacinths [Eichhornia Crassipes (E.C.)] [4] an aquatic plant, has spread from the American tropics and assumed a largely pan-tropical distributions and show many extreme risks. It was recorded in Egypt in the last decade of the 19th century, but it did reach the plague proportions exhibited nowadays in the Nile Delta. E.C. is the most troublesome and abundant of weeds in the

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River Nile and its canals. The dry matter in the standing crop weigh 50 tons/feddan. It could be one of the promising aquatic plants which may be used as a green forage during summer period and feed stuff for domestic animal. Eichhornia crassipes removed nutrients and heavy metals which was a toxic element from sewage and sludge ponds which indicate that E.C. could play a role against environmental pollution [5]. Recently, utilization of E.C. in the removal of colour from wastewater of textile dyeing processes was studied [6–12]. The aim of this work is to assess the ability of E.C. and its aminated derivative to adsorb six dyes that included reactive and acid azo and anthraquinone dyes from their solutions due to their ionic charge. The rate of dye adsorption process was studied including the influence of the type and amount of E.C., pH of the dye bath, shaking time and dye concentration. Simple kinetics models and equilibrium data for both Freundlich and Langmuir isotherm were determined.

2. Experimental 2.1. Materials 2.1.1. Eichhornia Crassipes (E.C.) Samples of E.C. were collected from freshwater canals at El-Marg region, during the summer season in 1999. The samples were thoroughly washed with tap water, the stems were cut out from the plant, air dried and then fine ground. The particles size of E.C. were determined using laser particles sizer analyzer (particle size range 0.147–1.5 mm).

Fig. 1. Structure of azo and anthraquinone dyes.

12%] according to a method described in (Sandoz Pamphlet) the literature.

2.1.2. Reagents Sandene 8425 (commercial product based on aliphatic polyamine, supplied by Sandoz) was used [13].

2.2.3. Procedure of dye adsorption Powdered aminated raw or scoured E.C. (2.5–15 g/l) was added to the aqueous solution of azo and anthraquinone dyes at a known concentration. The suspension was shaken for different intervals of time ranging from 2.5 to 120 min at room temperature. At the end of the run, an aliquot was centrifuged at 4000 rpm for 30 min. The dye concentration in the clear solution in mg/l was determined colourimetrically using Shimadzu Spectrophotometer at the maximum wavelength of the dye.

2.1.3. Dyestuffs The dyes chosen for this study are shown in Fig. 1; all the dyes were of a commercial grade.

2.2.4. Nitrogen content The percentage nitrogen content was determined by Cole and Parks modification of the semi-micro Kjeldahl method [14].

2.2. Methods 2.2.1. Scouring of E.C. The E.C. were subjected to alkali boiling using sodium hydroxide 20 g/l for 2 h in a stationary autoclave under pressure (2 kPa/cm2) at 120–130 C using L.R. 20:1. The materials were then filtered and washed thoroughly with tap water till free from alkali and finally air dried.

2.2.5. Amino content The capacity (amino content) in meq./100 g was evaluated according to the method cited in the literature [15].

3. Results and discussion 3.1. Effect of amination on dye adsorption rate

2.2.2. Preparation of chemically modified E.C. Modified E.C., raw and scoured were prepared using different concentrations of Sandene 8425 [4%, 8% and

The results obtained in Table 1 indicate that increasing the concentration of sandene is accompanied with

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higher nitrogen percent as well as amino content. Among aminated raw E.C. with 4% sandene (B), 8% sandene (C) and 12% sandene (D), 8% showed better results than aminated scoured E.C. with 4% sandene (F), the raw material (A) contains much higher amount of nitrogen and carboxyl contents than the scoured E.C. (E), this is due to the presence of amino acids. Previous investigation of E.C. is in confirmation with the obtained data and the scoured E.C. was nearly free of nitrogen (0.25%). Concerning the data of percent dye adsorption for all dyes (I–VI) it can be observed from Table 2 that percent dye adsorption follow the order D>C>B>F>A>E for all substrates. This is rather expected since the increase in cationic groups (amino content, N%) of substrates leads to more attraction of the anionic groups of the dye with higher percent dye adsorption. On the other hand, the structure of the dye plays a great role in percent dye adsorption. It depends on the presence and position of cationic nucleophilic groups as well as anionic sulphonic acid groups present in the dyestuff.

Table 1 Percentage nitrogen content and amino content of different E.C. substrates Type of E.C.

N (%)

Amino content (meq./100 g)

A—Raw E.C. B—Aminated raw E.C. with 4% sandene C—Aminated raw E.C. with 8% sandene D—Aminated raw E.C. with 12% sandene E—Scoured E.C. F—Aminated scoured E.C. with 4% sandene

1.73 1.88

26.5 54.2

2.33

82.6

2.75

96.5

0.25 0.77

13.8 34.3

I II III IV V VI a

Also, structural configuration, steric hinderance, size and surface area of the dye play a great role in percent dye adsorption. 3.2. Determination of apparent dissociation constant of the substrate Fig. 2 shows the potentiometric titrations of raw E.C. and its aminated derivatives which is carried out according to [16]. The obtained data in Fig. 2 indicate that all substrates (A–D) are weak base anion exchangers. Its strength, pKb, can be evaluated from the following correlation [17]. pKb ¼ 14  pH1=2 ; where pH1/2 is the pH at half capacity. Hence, the pKb values were found to be 10.3, 10.1, 9.4 and 9.2 for substrates A, B, C and D, respectively, that revealed that the pKb value of amino anion exchanger increases on increasing its capacity. Aminated raw E.C. (12%) was chosen for the following study since better results were obtained for percent dye adsorption for both azo and anthraquinone dyes. 3.3. Effect of amount of substrate Fig. 3 shows that the percent dye adsorption increases by increasing the amount of substrate, in the range examined, slows down and then levels off after approximately 10 g substrate/l. Levelling off can be explained in terms of depletion of dye in solution and/or accumulation of dye molecules on the surface of substrate giving rise to hindering the rest of dye to diffuse inside the substrate matrix. 3.4. Effect of pH of dyeing bath

Table 2 Effect of different substrates of E.C. on the rate of dye adsorptiona Dye no.

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Dye adsorption rate (%) A

B

C

D

E

F

6.6 15.9 16.7 58.7 55.4 36.8

13.3 45.5 53.1 90.6 86.0 63.2

25.8 63.6 78.5 92.5 87.9 73.0

45.5 84.6 90.7 95.8 91.6 84.5

4.2 5.1 6.0 17.3 21.0 10.5

9.4 33.2 34.1 62.3 50.4 36.5

Concentration of dye=100 mg/l, amount of substrate 2.5 g/ l, pH=4, at room temperature, shaking time=60 min.

Fig. 4 shows that the pH of the medium plays a dominant role in the rate of dye adsorption. Both reactive and acid azo and anthraquinone dyes show better results at pH 3. It seems that the rate of dissociation of the dyes as well as the ionization of the cationic substrate dominate in the acidic medium. Dyes I and II show a sorption drop off at high pH in Fig. 4 because both dyes contain an easily ionizable phenolic – OH group in the molecule. The presence of ionizable anionic groups like –OH or –COOH in dye molecules might render decolourization less effective in alkaline textile wastewaters. 3.5. The kinetics of adsorption 3.5.1. Adsorption dynamics The rate constant for adsorption of azo and anthraquinone dyes by 12% aminated raw E.C. was

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Fig. 2. Potentiometric titration of raw and aminated raw E.C. to determine the apparent dissociation constant.

Fig. 4. Effect of pH on the adsorption of azo and anthraquinone dyes on 12% aminated raw E.C. Conditions: concentration of dye=100 mg/l, amount of substrate=10 g/l, shaking time=60 min, at room temperature.

Fig. 3. Effect of amount of 12% aminated raw E.C. on percent dye adsorption of azo and anthraquinone dyes. Conditions: concentration of dye=100 mg/l, pH=4, shaking time=60 min, at room temperature.

determined using Lagergren’s equation [18]. logðqe  qÞ ¼ log qe 

kad t; 2:303

where qe and q (both in mg/l) are the amounts of dye adsorbed at equilibrium and at time t (min), respectively, and kad (min1) is the rate constant for adsorption of dye. The values of kad using different azo and anthraquinone dyes were calculated from the slopes of the respective linear plots of logðqe  qÞ vs. t (Fig. 5) and noted in Table 3. It may be concluded from the linearity

Fig. 5. Lagergren plot for the removal of azo and anthraquinone dyes by 12% aminated raw E.C. Conditions: 100 mg/l concentration of dye, pH=3, concentration of substrate 10 g/l and at room temperature.

of Lagergren plot that the reaction taking place is of the first order. The possibility that the transport of dyestuff ions from its solution into the pores of 12% aminated E.C. is the rate controlling step, was tested by plotting a relation between the amount of dye adsorbed and the square root of time (Fig. 6). The double nature of these plots may be explained as: the initial curved portions are

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Table 3 Adsorption kinetic parameters of different dyesa Dye no.

kad (  102 min1)

kp (  102 min1/2)

D0 (  106 cm2/s)

I II III IV V VI

2.3 3.4 3.5 4.0 3.6 3.1

3.2 4.0 4.5 5.0 4.7 3.8

2.66 3.42 3.92 5.34 4.55 3.00

a

Condition: initial dye concentration=100 mg/l, pH=3, amount of substrate 10 g/l, at room temperature (20 C).

Fig. 7. Freundlich plot for the adsorption of azo and anthraquinone dye on 12% aminated raw E.C. Conditions: 100 mg/l concentration of dyes, pH=3, amount of substrate=10 g/l, at room temperature. Fig. 6. Weber and Morris plot for the rate constants of pore diffusion of azo and anthraquinone dyes during its adsorption by 12% aminated raw E.C. Conditions: concentration of dye=100 mg/l, pH=3, amount of substrate=10 g/l and at room temperature (20 C).

attributed to boundary layer diffusion effects while the final linear portions are due to intraparticle diffusion effects. The rate constant for intraparticle diffusion kp ; using reactive and acid azo and anthraquinone dyes was determined from the slopes of the linear portions of the respective plots and are given in Table 3. The pore diffusion coefficient, D using different dyes was determined by using the following equation [19]: t1=2 ¼

0:03r20 ; D0

where t1=2 (min) is the time for the adsorption of half amount of dye, and r0 (cm) is the radius of the adsorbent. The values of D0 in Table 3 were found in the order of 106 cm2/s indicating that the adsorption process is governed by diffusion, but pore diffusion is not the only rate limiting step.

3.5.2. Adsorption isotherm The analysis of equilibrium data for the adsorption of azo and anthraquinone dyes on 12% aminated E.C. has been done in the light of both isotherm models of Freundlich and Langmuir [20,21]. The Freundlich isotherm equilibrium results are shown in Fig. 7, in which the linear plot indicates that the results conform to the Freundlich type of isotherm. The Freundlich isotherm is represented by the following equation: q ¼ KF Ce1=n ; where q (mg/g) is the equilibrium concentration of dye on the adsorbent which corresponds to the equilibrium concentration of dye in solution Ce (mg/l), whereas K [mg/g  (mg/l)]n and n (a constant with no dimension) are the Freundlich constants. The values of n and K for each dye were calculated from the slope and the intercept of the corresponding linear plot of log q against log Ce and it is generally stated that values of n in the range 2–10 mg/l represent good adsorption. The Freundlich constants were determined and are given in Table 4. Only dye IV (C.I. Acid Blue 25) conforms to both Freundlich and Langmuir isotherm modles, due to

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Table 4 Analysis of Freundlich isotherms using different dyesa Dye No.

KF [mg/g  (mg/l)]n

n

I II III IV V VI

4.9 8.7 10.0 12.0 11.2 5.8

2.00 2.22 2.27 2.90 2.86 2.10

a Condition: initial dye concentration=100 mg/l, pH=3, amount of substrate=10 g/l, at room temperature (20 C).

the linearity of both the plots. However, at low concentrations, the Langmuir equation may be applied successfully for the other five reactive and acid azo and anthraquinone dyes.

4. Conclusion The removal and/or minimization of reactive and acid azo and anthraquinone dyes from their solutions by 12% aminated raw E.C. with sandene shows a good adsorption capacity. Its strength values pKb increases with the increasing of the efficiency and capacity of the anion exchanger. The kinetics of the system have been studied, the rate constant for adsorption of azo and anthraquinone dyes values kad indicate that the reaction taking place is of the first order. The mechanism involves an initial rapid rate for the dye removal due to surface adsorption followed by pore diffusion which may be the rate governing step and/or a diffusion controlled process. Adsorption parameters for Freundlich and Langmuir isotherms were determined and the equilibrium data fit well with the Freundlich model of adsorption for six reactive and acid azo and anthraquinone.

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