Applied Clay Science 46 (2009) 422–424
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Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c l a y
Adsorption of methylene blue from aqueous solution on pyrophyllite Jiawei Sheng ⁎, Younan Xie, Yan Zhou College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou, Zhejiang 310032, China
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Article history: Received 1 May 2009 Received in revised form 9 October 2009 Accepted 14 October 2009 Available online 24 October 2009 Keywords: Pyrophyllite Methylene blue Adsorption Acid activation
a b s t r a c t The ability of raw and modiﬁed (milled, acid activated) pyrophyllite to adsorb methylene blue has been investigated. The absorption ability of raw and modiﬁed pyrophyllite increased with pH. The adsorption capacity of the raw powders was 3.7 mg/g, and increased to 3.8 mg/g, 3.9 mg/g and 4.2 mg/g, after acid activation, milling, and acid activation followed by milling. A good agreement between the pseudo-second-order model and the experimental dada was reached. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Methylene blue (MB) has a wide variety of applications, ranging from coloring paper, acting as a temporary hair colorant, and dyeing various textile fabrics. Although not strongly hazardous, it can cause some harmful effects in humans. The runoff from the manufacturing and textile industries are discarded into rivers and lakes, altering the biological stability of surrounding ecosystems. MB is resistant to breakdown by chemical, physical and biological treatments. Color impedes light penetration, retards photosynthetic activity, inhibits the growth of biota and also has a tendency to chelate metal ions which produce microtoxicity to ﬁsh and other organisms (Babel and Kurniawan, 2003; Garg et al., 2004). The use of clean, cost-efﬁcient, and biodegradable adsorbents could be a good tool to minimize the environmental impact caused by manufacturing and textile byproducts (Stydini et al., 2004; Yi and Zhang, 2008). Adsorption is known to be a promising technique, which has great importance due to the ease of operation and comparable low cost of application in the decoloration process. Commercially activated carbon is a remarkably highly adsorbent material with a large number of applications in the remediation of contaminated groundwater and industrial wastes such as colored efﬂuents. However, activated carbon is an expensive adsorbent due to its high costs of manufacturing and regeneration. For the purpose of removing unwanted hazardous compounds from contaminated water at a low cost, much attention has been focused on various naturally occurring adsorbents such as chitosan, zeolites, ﬂy ash, coal, papermill sludge, and various clay minerals (Gücek et al., 2005). Among these adsorbents, clay minerals have been shown to
⁎ Corresponding author. College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Zhaohui No.6, Hangzhou, Zhejiang 310032, China. Tel.: +86 571 88320851. E-mail address: [email protected]
(J. Sheng). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.10.006
be the most promising alternatives due to their local availability, technical feasibility, easy engineering applications, highly speciﬁc surface area, and cost effectiveness (Stydini et al., 2004; Doğan et al., 2007; Bestani et al., 2008). Recently, the application of pyrophyllite on waste water treatment has become of great interest in China because of its abundance in local reserves as well as its inexpensiveness. A considerable amount of work has also been reported regarding the potential use of pyrophyllite in the removal of heavy metal ions and dyes (Scheidegger and Sparks, 1996; Saxena et al., 2001; Sayılkan et al., 2004; Bergaya et al., 2006). However, the adsorption properties of pyrophyllite towards MB are scarcely known. In this study, we report on the adsorption of MB on pyrophyllite from aqueous solutions. 2. Materials and methods Pyrophyllite used in this study originated from the Zhejiang province, located in the south-eastern region of China. The pyrophyllite was composed of (mass %): 66.08 SiO2, 19.92 Al2O3, 0.70 Fe2O3, 0.64 K2O, 0.21 Na2O, 0.12 CaO, and 0.27 Ti2O; mass loss 12.33. Particle sizes were analyzed by the LS-POP laser particle size analyzer. Particles were modiﬁed by activation in 0.55 mol/L HCl solution at 80 °C for 6 h. The remaining HCl was removed by washing until the pH of the dispersion was close to 7. This material was then milled in water in a Planet Style Ball Mill for 3 h. After ﬁltration, the samples were dried at 110 °C for 2 h. Methylene blue with a labeled purity of >98% was used without further puriﬁcation. The concentration changes due to MB adsorption were measured in a spectrophotometer (Shimadzu UV-2550) at 665 nm at ambient room temperature, using a 1 cm quartz cell. Adsorption of MB was studied using the batch technique by mixing 0.1–1.0 g of the adsorbent with 100 mL of MB solutions of concentrations ranging from 10 to 60 mg/L. The dispersions were shaken for a given time. A constant
J. Sheng et al. / Applied Clay Science 46 (2009) 422–424
Pyrophyllite with ideal structural formula of Al2 [Si4O10](OH)2 shows only limited substitution of Al3+ for Si4+ and minor amounts of Fe2+, Fe3+, Mg2+, and Ti4+ (Bergaya et al., 2006). Chemical analysis of acid-activated particles showed a decrease of Al3+, Fe2+ and Ti4+ ions, forming –OH groups at the vacant sites. D50 of the raw particles was 21.4 μm, while D50 of activated particles was 7.2 μm and after milling of activated particles 5.6 μm. Acid activation not only caused the surface erosion, but also some splitting of particles (Erdemoğlu and Sarıkaya, 2002). Modiﬁcation of pyrophyllite increased MB adsorption (Fig. 1). Amounts of 70.1%, 71.2%, 75.5% and 79.7% of MB (20 mg/L) were adsorbed by raw, acid-activated, milled, and milled powders after acid activation. The difference observed here may arise from different morphologies and sizes of the particles and the total speciﬁc surface area of the materials used (Eren and Afsin, 2008).
Adsorption increased with pH (Fig. 2). All samples showed similar adsorption at pH >11. The increase may be related to the formation of negative surface charges at higher pH. Since the zero point of charge of pyrophyllite was at pH = 2.3 (Alkan et al., 2005), the pyrophyllite surface in water had a negative surface charge. The surface charge became more negative as the pH increased favoring the adsorption of MB cations. The adsorption of MB was studied by changing the content of adsorbent (0.1–1.0 g/100 mL) in the test solution while keeping the initial dye concentration (10 mg/L), temperature (20 °C) and pH (7) constant at different contact times. Removal of MB increased with increasing adsorbent mass only for contents between 0.1 g/100 mL and 0.3 g/ 100 mL, while almost no changes were observed from 0.3 g/100 mL to 1.0 g/100 mL (Fig. 3). Maximum dye removal was achieved within 5– 40 min. The kinetics of MB adsorption on raw and modiﬁed pyrophyllite samples was measured while keeping constant the initial dye concentration (10 mg/L), temperature (20 °C), adsorbent content (0.2 g/100 mL), and pH (7) (Fig. 4). The kinetic data were analyzed by t the pseudo-second-order model (Gücek et al., 2005): dq = ks ðqe −qt Þ2 , dt where ks is the rate constant and qe and qt are the amount of the MB adsorbed at equilibrium and at time t, respectively. Integration for
Fig. 1. Effect of activation of pyrophyllite on MB adsorption (adsorbent content: 0.2 g/ 100 mL; pH: 7; equilibrium time: 24 h).
Fig. 3. Effect of adsorbent content on MB absorption.
Fig. 2. Effect of pH on MB adsorption (initial MB concentration: 10 mg/L adsorbent content: 0.2 g/100 mL; equilibrium time: 24 h).
Fig. 4. Adsorption isotherms for MB onto raw and modiﬁed pyrophyllite.
temperature bath was used to keep the temperature constant at 20± 1 °C. The effect of pH was studied over a pH range of 7–11. The pH value was adjusted by the addition of 0.1 M aqueous solutions of NaOH. The reported data were averages of three independent measurements. 3. Results and discussion
J. Sheng et al. / Applied Clay Science 46 (2009) 422–424
lites are cheap and easily available in the countryside of China. The data may be useful for designing cheap treatment process using pyrophyllite for the removal of MB from dilute industrial efﬂuents. Acknowledgement The authors gratefully acknowledge the ﬁnancial support for this work from the Zhejiang Provincial Natural Science Foundation of China (2007C11104-2). References
Fig. 5. Plot of
t against time for MB onto raw and modiﬁed pyrophyllite. qt
boundary conditions t = 0 to t =t and qt = 0 to qt =qt, leads to 1 ks q2e
t qe .
Fig. 5 shows the plots of qtt against time for MB onto raw and
modiﬁed pyrophyllite. A good agreement between the pseudo-secondorder function and the experimental dada was achieved (R2 > 0.9995). The calculated rate constants (ks) of raw, acid-activated, milled and milled samples after acid activation were 1.17, 1.01, 0.74, and 0.79, respectively. 4. Conclusions The ability of pyrophyllite to adsorb methylene blue increased by acid activation and milling. Acid activation caused leaching out of Al3+, Fe2+, and Ti4+ ions. Adsorption increased with pH between pH= 7 and pH= 11. A good agreement between the pseudo-second-order model and the experimental dada was reached. Raw and modiﬁed pyrophyl-
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