Removal of basic dyes from aqueous solutions using natural clay

Removal of basic dyes from aqueous solutions using natural clay

Desalination 249 (2009) 1377–1379 Contents lists available at ScienceDirect Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o ...

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Desalination 249 (2009) 1377–1379

Contents lists available at ScienceDirect

Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l

Removal of basic dyes from aqueous solutions using natural clay Tülin Banu İyim, Gamze Güçlü ⁎ Department of Chemical Engineering, Faculty of Engineering, Istanbul University, 34320 Avcılar, Istanbul, Turkey

a r t i c l e

i n f o

Article history: Accepted 22 June 2009 Available online 8 October 2009 Keywords: Clay Basic dye Nile Blue Brilliant Cresyl Blue Freundlich isotherm

a b s t r a c t Adsorption properties of natural clay (from Eskişehir of Turkey) were investigated by depending on different adsorption conditions such as different initial dye concentrations and contact times. The chemical composition of the natural clay was analyzed by X-ray fluorescence spectrometry (XRF). The removal of basic dyes such as Nile Blue (NB) and Brilliant Cresyl Blue (BCB) from aqueous solutions using natural clay in this study was described. After the equilibrium adsorption time of 8 h, the adsorption capacities for NB and BCB reach about 25 mg/g and 42 mg/g, respectively. Lagergren kinetic equation was used to test the experimental data to examine the controlling mechanism of adsorption processes. Adsorption data of the BCB and NB onto natural clay were fitted well by the pseudo-first-order model. The adsorption isotherms data were correlated with the Freundlich equation and the Freundlich constants Kf (mg/g) and n (intensity of adsorption) were calculated. The r2 (regression coefficients) values were 0.9835 and 0.9849 for NB and BCB, respectively. The adsorption capacities of natural clay for NB and BCB have the following order: BCB N NB. © 2009 Elsevier B.V. All rights reserved.

1. Introduction Colored organic effluent is produced in the textile, paper, plastic, leather, food and mineral processing industries [1]. The main pollution source of textile effluent emerges from the dyeing process. Dyeing and finishing wastes in the textile industry have high color and organic content. Synthetic organic dyes present certain hazards and environmental problems. Effluents discharged from dyeing industries are highly colored with low biochemical oxygen demand (BOD) and high chemical oxygen demand (COD) [2]. Disposal of these effluents into water can be toxic to aquatic life [3,4]. The dyes upset the biological activities in water bodies. They cause a health problem because they may be mutagenic and carcinogenic [5,6] and can cause severe damage to human beings such as in the liver and the central nervous system [2,7]. Methods and effluent treatment for dyes may be divided into three main categories namely physical, chemical and biological. Among them adsorption technology is generally considered to be an effective method for quickly lowering the concentration of dissolved dyes in an effluent [8]. Dyes can be effectively removed by adsorption process. Activated carbon [9,10], natural clays [11], modified clays [12,13], some industrial wastes and by-products [10] have been used as adsorbents for removal of organic compounds from waste waters. Naturally occurring clays have shown good results as an adsorbent for the removal of various metals [14,15], organic compounds [16] and various basic dyes [11]. In this work, we describe the removal of basic dyes such as Nile Blue and Brilliant Cresyl Blue from aqueous solutions using natural clay. Natural clay used as an adsorbent was obtained from Eskişehir of

⁎ Corresponding author. Tel.: +90 212 473 70 70x17757; fax: +90 212 473 71 80. E-mail address: [email protected] (G. Güçlü). 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.06.020

Turkey. It contains various amounts of dioctahedral smectites (Camontmorillonite), natural zeolites (analcime), and loughlinite, which is a kind of sepiolite [17]. Effects of various parameters such as treatment time and initial dye concentration were investigated. The Freundlich equations were used to fit the equilibrium isotherms. 2. Experimental 2.1. Materials Basic dyes [Nile Blue (NB) and Brilliant Cresyl Blue (BCB)] were obtained from Merck. The chemical structures of the dyes are shown in Fig. 1a and b. Natural clay (surface area of 80–90 m2/g) used as an adsorbent was obtained from Eskişehir of Turkey. The chemical composition of natural clay is given in Table 1. Deionized water was used in the experiments. 2.2. Instruments The chemical composition of the natural clay was analyzed by X-ray fluorescence spectrometry (XRF). Spectrophotometric measurements were carried out using Jenway 6105 UV/Vis Spectrophotometer. 2.3. Adsorption studies Natural clay, grey in color was used as an adsorbent. Firstly it was dried at 110 °C in an oven before use in the adsorption studies. Major elements of clay were determined by X-ray fluorescence spectrometry (XRF). Adsorption properties of natural clay were evaluated by depending on different adsorption conditions such as different initial

T.B. İyim, G. Güçlü / Desalination 249 (2009) 1377–1379

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Fig. 1. Chemical structure of NB and BCB. (a) NB and (b) BCB.

dye concentrations and contact times. The concentrations of the dyes were determined using UV/Vis Spectrophotometer. NB and BCB solutions were prepared by dissolving dye in deionized water to the required concentrations. The natural clay (0.2 g) was added into NB and BCB solutions (50 mL) (initial concentrations of dye solutions were 500 mg/L). The amount of residual dye in aqueous solution was followed by UV/Vis Spectrophotometer up to 24 h at pH 5. In experiments of equilibrium adsorption isotherm, a fixed amount of 0.2 g adsorbents was contacted with 50 mL of aqueous solutions NB and BCB with different concentrations (50–500 mg/L). The amount of residual dye in aqueous solution was determined by UV/Vis Spectrophotometer after 24 h. The absorbance at a specific wavelength was measured for each species: NB (638 nm) and BCB (622 nm).

Fig. 2. The effect of the adsorption time on the adsorption of basic dyes onto natural clay.

3. Results and discussion 3.1. Kinetic studies Fig. 2 illustrates the effect of adsorption time on the adsorption efficiency. The adsorption capacities for NB and BCB increase with the increase of the adsorption time. After the equilibrium adsorption time of 8 h, the adsorption capacities for NB and BCB reach about 25 mg/g and 45 mg/g, respectively. Pseudo-first-order kinetic equation was used to test the experimental data to examine the controlling mechanism of adsorption processes. The pseudo-first-order kinetic model was suggested by Lagergren for the adsorption of solid/liquid systems and its linear form can be formulated as [18]:

Fig. 3. Pseudo-first-order kinetic plot for the adsorption of NB and BCB onto natural clay.

where qt is the adsorption capacity at time t (mg/g) and k1 (min− 1) is the rate constant of the pseudo-first adsorption applied to the present study of NB and BCB adsorptions. The k1 and regression coefficient were calculated from the linear plot of log(qe − qt) versus t (Fig. 3) and listed in Table 2. It was found that the regression coefficient for the pseudo-first-order kinetic model is high (r2 N 0.92). Adsorption data of the NB and BCB onto natural clay were fitted well by the pseudo-first-order model.

where C0 is the initial concentration (mg/L), Ce is the residual concentration at equilibrium (mg/L), V is the volume of solution (L), W is the weight of dry natural clay (g). The Freundlich equations were used to fit the equilibrium isotherms. The Freundlich equation [19] is the earliest known relationship describing the adsorption equation. Freundlich isotherms were obtained by different initial dye concentrations (50–500 mg/L) and 0.2 g dry clay dose for a constant time of 24 h. The adsorption isotherms data were correlated with the Freundlich equation and the Freundlich constants Kf (mg/g) and n (intensity of adsorption) were calculated from the following equations:

3.2. Adsorption isotherms

qe = Kf xCe

ð3Þ

The equilibrium adsorption capacity, qe (mg/g), was calculated with Eq. (2).

log qe = log Kf + 1 = n log Ce

ð4Þ

logðqe  qt Þ = log qc  ðk1 t = 2:303Þ

ð1Þ

1=n

ðC −Ce ÞxV qe = 0 W

ð2Þ

where qe is the amount of dye adsorbed (mg/g) onto natural clay. The parameters of Freundlich isotherm, Kf and n as well as the correlation Table 2 Kinetic parameters for the adsorption of NB and BCB onto natural clay.

Table 1 The chemical composition of natural clay. SiO2 (%)

Al2O3 (%)

Fe2O3 (%)

TiO2 (%)

CaO (%)

MgO (%)

Na2O (%)

K2O (%)

51.36

8.41

3.38

0.33

3.05

9.70

5.54

1.79

Basic dyes NB BCB

Kinetic parameters qe (mg/g) (exp.) 25 42

k1 (min− 1) −3

5 × 10 2.5 × 10− 1

r2 0.9385 0.9220

T.B. İyim, G. Güçlü / Desalination 249 (2009) 1377–1379 Table 3 Freundlich constants of adsorption isotherms for NB and BCB onto natural clay. Basic dyes

Freundlich constants Kf

n

r2

NB BCB

0.868 3.162

1.735 2.192

0.9835 0.9849

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and BCB onto natural clay, the n value was above the beneficial adsorption (n N 1). • Adsorption data of the NB and BCB onto natural clay were fitted well by the pseudo-first-order model. It was found that the regression coefficient for the pseudo-first-order kinetic model is high (r2 N 0.92). • The adsorption capacities of natural clay for NB and BCB have the following order: BCB N NB. Acknowledgements Natural clay sample was kindly provided by Professor G. Atun from the Chemistry Department of Istanbul University. We would like to thank Professor S. Pişkin and A. Kantürk from Yıldız Technical University for help in XRF. References

Fig. 4. Freundlich isotherm for the adsorption of basic dyes onto natural clay.

coefficients r2 are given in Table 3. Linear plots of log qe versus log Ce for the different initial dye concentrations illustrated that the adsorption follows the Freundlich isotherm (Fig. 4). Such conclusion can be drawn from data r2 that the Freundlich adsorption law is applicable to NB and BCB adsorptions onto natural clay. The r2 values were 0.9835 and 0.9849 for NB and BCB, respectively. The n values between 1 and 10 indicate beneficial adsorption [20]. For the adsorption of NB and BCB onto natural clay, the n values were above the beneficial adsorption (n N 1). The adsorption capacities of natural clay for NB and BCB have the following order: BCB N NB. 4. Conclusion Adsorption properties of basic dyes NB and BCB on the natural clay (from Eskişehir of Turkey) were investigated. Adsorption properties of the adsorbent were evaluated by depending on different adsorption conditions such as different initial dye concentrations and contact times. The isotherm data were fitted with Freundlich isotherm. The following conclusions can be drawn: • The adsorption capacities for NB and BCB increase with the increase of the adsorption time. • After the equilibrium adsorption time of 8 h, the adsorption capacities for NB and BCB reach about 25 mg/g and 42 mg/g, respectively. • Linear plots of log qe versus log Ce for the different initial dye concentrations illustrated that the adsorption follows the Freundlich isotherm. The r2 values of Freundlich equations were 0.9835 and 0.9849 for NB and BCB, respectively. For the adsorption of NB

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