Intraparticle diffusion processes during acid dye adsorption onto chitosan

doi:10.1016/j.biortech.2006.09.045

Bioresource Technology

Volume 98, Issue 15, November 2007, Pages 2897-2904

https://doi.org/10.1016/j.biortech.2006.09.045 Get rights and content

Abstract

The adsorption of five acid dyes onto chitosan was studied. The equilibrium capacities based on the Langmuir analysis were 1.54, 2.66, 1.11, 1.25 and 1.03 mmol/g chitosan for Orange 10 (AO10), Acid Orange 12 (AO12), Acid Red 18 (AR18), Acid Red 73 (AR73) and Acid Green 25 (AG25) respectively. The batch adsorption rate for the five systems based on an intraparticle diffusion rate parameter derived from the plots of dye adsorbed versus the square root of time indicated that the adsorption mechanism was predominantly intraparticle diffusion but there was also a dependence on pore size as the dye diffuses through macropore, mesopore and micropore respectively.

Introduction

The waste water from industry has always been a potential threat to the environment. Over 4.4 × 10⁶ m³ of aqueous waste and dye effluent were discharged per day in China (Marc, 1996) and this effluent has high BOD loading and long lasting colour that is aesthetically and environmentally unacceptable (Annadurai and Krishnan, 1997). These dyes may even be toxic and even carcinogenic (Vandevivere et al., 1998). The printing and textile industry mainly contribute to the discharge of dye effluent and the governments of different countries have enacted strict rules controlling the discharge of waste. In order to minimize the pollution, manufacturers and government officials are seeking for solutions to tackle the problem in an efficient way.

Existing effluent treatment processes can only remove half of the dyestuff lost in the residual liquors. People are looking for a system which can remove most of the colour and generate reusable water from the effluent. A range of adsorption systems for dye removal have been investigated extensively, such as trickling filter (Lin and Lin, 1993), activated sludge (Ganesh et al., 1994), chemical coagulation (Vandevivere et al., 1998), carbon adsorption (Walker and Weatherley, 2000) and photodegradation processes (Chu and Ma, 2000, Chu and Tsui, 1999).

Activated carbon is a highly effective adsorbent for water treatment, but it is an expensive adsorbent (Pollard et al., 1992). Cheaper precursors for activated carbon have been developed and tested with varying degrees of success; these include corn cob (Tsai et al., 1998), bagasse (Valix et al., 2004), pecan shells (Ahmedna et al., 2000), waste tire (Mui et al., 2004) among many others. In addition to activated carbons, several other available cheap resources have been studied, including peat (Brown et al., 2001), pith (Ho and McKay, 1999, Namasivayam et al., 2001) and other agricultural by-products (Marshall and Johns, 1996).

A limited number of dye adsorption studies have been carried out on chitin and chitosan (Knorr, 1983). Several of these references related to adsorption to treat textile effluents. There is a lack of detailed critical analysis for the adsorption of dyes onto chitosan even though high sorption capacities have been obtained in several cases.

In this work, the adsorption of five Acid Dyes, namely, Acid Orange 10 (A010), Acid Orange 12 (A012), Acid Red 18 (AR18), Acid Red 73 (AR73) and Acid Green 25 (AG25) onto chitosan in an agitated batch adsorber was studied and the concentration versus time decay curves were measured. The experimental data were measured and analysed using an intraparticle diffusion adsorption model.

Section snippets

Adsorbent

The adsorbent used was a powdered form of chitin purchased from Sigma Chemical Company (practical grade, extracted from crab shells). All raw chitin was dried at 75 °C in an oven for 6 h and then was sieved into discrete particle size range from 355–500 μm.

Absorbates

Five different commercial available textile dyestuffs were used including four azo dyes (AO10, AO12, AR18 and AR73) and one anthraquinone dye (AG25). All dyestuffs were obtained from Aldrich Chemical Co. and used without any further purification

Equilibrium isotherms

The sorption data of the five dyes on chitosan at 25 °C were analyzed by Wong et al. (2004) according to the linear form of the Langmuir isotherm (Eq. (2)) $q_{t} = \frac{K_{L} C_{e}}{1 + a_{L} C_{e}}$ The plots of specific sorption C_e/q_e against the equilibrium concentration, C_e for the five dyes are shown in Fig. 2. The isotherms of the five dyes were linear over the whole concentration range of studies and the correlation coefficient were extremely high as shown in Table 2. These results revealed the sorption data closely fit

Conclusion

The adsorption of five acid dyes AO10, AO12, AR18, AR73 and AG25 onto chitosan was studied. It was concluded that the adsorption mechanism was predominantly intraparticle diffusion but there was also a dependence on pore size as the dye diffuses through macropore, mesopore and micropore respectively.

Acknowledgement

The authors gratefully acknowledge the support of the Research Grant Council of Hong Kong SAR.

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Intraparticle diffusion processes during acid dye adsorption onto chitosan

Abstract

Introduction

Section snippets

Adsorbent

Absorbates

Equilibrium isotherms

Conclusion

Acknowledgement

Bioresour. Technol.

Bioresour. Technol.

Water Res.

Water Res.

Chemosphere

Water Res.

Resour. Conserv. Recycl.

Water Res.

Carbon

Waste Manage.

Sci. Total Environ.

Bioresour. Technol.

Chemosphere

Process Saf. Environ. Protect.