Elsevier

Bioresource Technology

Volume 96, Issue 4, March 2005, Pages 443-450
Bioresource Technology

Adsorption behaviour of Fe(II) and Fe(III) ions in aqueous solution on chitosan and cross-linked chitosan beads

https://doi.org/10.1016/j.biortech.2004.05.022Get rights and content

Abstract

A batch adsorption system was applied to study the adsorption of Fe(II) and Fe(III) ions from aqueous solution by chitosan and cross-linked chitosan beads. The adsorption capacities and rates of Fe(II) and Fe(III) ions onto chitosan and cross-linked chitosan beads were evaluated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to enhance the chemical resistance and mechanical strength of chitosan beads. Experiments were carried out as function of pH, agitation period, agitation rate and concentration of Fe(II) and Fe(III) ions. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. The kinetic experimental data correlated well with the second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. Results also showed that chitosan and cross-linked chitosan beads were favourable adsorbers.

Introduction

Water pollution by toxic metals remains a serious environmental problem and can be detrimental to living systems. Metals can be toxic pollutants that are non-biodegradable, undergo transformations, and have great environmental, public health, and economic impacts (Gupta and Sharma, 2002). In the environment, one element can be present in different chemical forms, which differ in their chemical behaviour, bioavailability and toxicity. Some elements such as iron (Mulaudzi et al., 2002), arsenic (Balaji and Matsunaga, 2002), manganese (Xue et al., 2001) and chromium (Xue et al., 2000) are mainly present in natural water as two oxidation states. For instance Cr(VI), As(III) and As(V) are known carcinogens, while Fe(II), Fe(III), Mn(II), Mn(VII) and Cr(III) are essential micronutrients for organisms and plants. However, they become toxic at higher levels.

Iron is the fourth most abundant element in the earth's crust, it is present in a variety of rock and soil minerals both as Fe(II) and Fe(III). Fe(II) is required for proper transport and storage of oxygen by means of hemoglobin and myoglobin while its oxidized forms, methemoglobin and metmyoglobin, which contain Fe(III), will not bind oxygen (Safavi and Abdollahi, 1999). Iron plays an essential role in photosynthesis and is the limiting growth nutrient for phytoplanktons in some parts of the ocean (Kieber et al., 2001). Both Fe(II) and Fe(III) are important in the biosphere, serving as an active centre of a wide range of proteins such as oxidases, reductases and dehydrases. Waste effluents from steel tempering, coal coking and mining industries, for example, contain significant quantities of iron, nickel, copper and zinc (Aksu et al., 1999).

Among the many methods available for the removal of trace metals from water namely: chemical precipitation, ion exchange, coagulation, solvent extraction and membrane processes, adsorption has been shown to be an economically feasible alternative. Activated carbon has undoubtedly been one of the most popular adsorbents for the removal of metal ions from aqueous solution and is widely used in wastewater treatment applications throughout the world (El-Shafey et al., 2002). In spite of its profilic use, activated carbon remains an expensive material since the higher the quality of the activated carbon, the greater its cost. Research interest into the production of alternative adsorbents to replace the costly activated carbon has intensified in recent years. Attention has been focused on various adsorbents which have metal-binding capacities and are able to remove unwanted heavy metals from contaminated water at low cost. Because of their low cost and local availability, natural materials such as chitosan, zeolites, clay or certain waste products from industrial operations such as fly ash, coal and oxides are classified as low-cost adsorbents (Babel and Kurniawan, 2003). Low et al. (2000) defined a low-cost sorbent as one which is abundant in nature, or as a by-product or waste material from another industry.

Chitin, poly(1  4)-2-acetamido-2-deoxy-β-D-glucan is a naturally occurring polymer extracted from crustacean shells, such as prawns, crabs, krill, insects and shrimps, and the second most abundant biopolymer next to cellulose. Chitosan is prepared from chitin by partially deacetylating its acetamido groups with a strong alkaline solution. Chitosan has been reported to have high potential for adsorption of metal ions (Guibal et al., 1998, Ngah et al., 2002a), dyes (Chiou and Li, 2002) and proteins (Zeng and Ruckenstein, 1998). Chitosan is non-toxic, hydrophilic, biocompatible, biodegradable and anti-bacterial, which has led to a very diverse range of applications in the biomedical field and in cosmetic, food and textile industries. The presence of a large number of amine groups on the chitosan chain increases the adsorption capacity of chitosan compared to that of chitin, which only has a small percentage of amino groups (Evans et al., 2002; Wu et al., 2000; Lu et al., 2001). Chitosan has both hydroxyl and amine groups that can be chemically modified. Several methods have been used to modify raw chitosan flake either physical or chemical modifications (Guibal et al., 1999; Ngah and Liang, 1999; Yang et al., 2002). Physical modifications (Onsoyen and Skaugrud, 1990) may increase the sorption properties: gel formation decreases the crystallinity of the sorbent and involves an expansion of the porous network. Chemical modifications also offer a wide spectrum of tools to enhance the sorption properties of chitosan for metals. They may increase the chemical stability of the sorbent in acid media and, especially, decrease the solubility in most mineral and organic acids. They also increase its resistance to biochemical and microbiological degradation (Guibal et al., 2000; Yang and Yuan, 2001). A cross-linking step is required to reinforce the chemical stability of the biosorbents in such acidic solutions. Although cross-linking reduces the adsorption capacity, it enhances the resistance of chitosan against acid, alkali and chemicals.

This work concentrates on the study of ferrous and ferric ions sorption onto chitosan and cross-linked chitosan beads. The influence of experimental conditions such as pH, agitation period, agitation rate and concentration of Fe(II) and Fe(III) ions was studied. The Langmuir and Freundlich equations were used to fit the equilibrium isotherm. The adsorption rates were determined quantitatively and compared by the first-order, second-order and the intraparticle diffusion model. This information will be useful for further applications of system design in the treatment of practical waste effluents.

Section snippets

Material

Samples of chitosan flakes with average molecular weights 105–106 and with a deacetylation percentage of approximately 55.94% (defined by an IR method), prepared from shells of prawns, were kindly donated by the Chitin-Chitosan Research Centre, Universiti Kebangsaan Malaysia, Bangi. Glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) purchased from Fluka were analytical-reagent grade. Doubly distilled water was used to prepare all the solutions.

Preparation of chitosan beads

Chitosan

Characterization of chitosan and cross-linked chitosan beads

Table 1 lists the characteristics of chitosan and cross-linked chitosan beads. According to the International Union of Pure and Applied Chemistry (IUPAC) classifications, the pores can be divided in broad terms according to diameter (d) into macropores (d>50 nm), mesopores (2<d<50 nm) and micropores (d<2 nm). As shown in Table 1, chitosan and cross-linked chitosan beads correspond to micropores.

The CHN composition of chitosan and cross-linked chitosan beads as determined by CHN analyzer is

Conclusion

In this study, the capacity of chitosan and cross-linked chitosan beads with glutaraldehyde, epichlorohydrin and ethylene glycol diglycidyl ether as cross-linkers to adsorb Fe(II) and Fe(III) ions from aqueous solutions was examined, including equilibrium and kinetic studies. The adsorption isotherms could be well fitted by the Langmuir equation. The adsorption capacity of chitosan beads is higher than that of cross-linked chitosan beads, but cross-linked chitosan beads are insoluble in both

Acknowledgements

The authors thank Chitin-Chitosan Research Centre, Universiti Kebangsaan Malaysia, Bangi, Malaysia, for supplying samples of chitosan. The authors also thank Universiti Sains Malaysia for the financial support under IRPA Short Term Research Grant (grant no. 305/PKIMIA/622183).

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