Elsevier

Chemical Engineering Journal

Volume 167, Issue 1, 15 February 2011, Pages 112-121
Chemical Engineering Journal

Adsorptive removal of Cr(III) and Fe(III) from aqueous solution by chitosan/attapulgite composites: Equilibrium, thermodynamics and kinetics

https://doi.org/10.1016/j.cej.2010.12.009Get rights and content

Abstract

Adsorption of Cr(III) and Fe(III) onto chitosan/attapulgite composites (CTS/ATP) was investigated with respect to pH, temperature, initial concentration and binary solution. Equilibrium data, at various temperatures, were described by the Langmuir, Freundlich isotherm models. The Freundlich isotherm model was fitted to the experimental data significantly better than the Langmuir isotherm. In a binary solution, the combined effect of adsorbing one metal ion in the presence of the other metal ion reduced the adsorption capacity of either metal ion. The kinetic data was well fitted to the intraparticle diffusion equation, which indicated that the three adsorption steps belonged to the pseudo-second-order adsorption process. Intraparticle diffusion increased with the increase in adsorbate concentration while film and pore diffusion decreased. The thermodynamics parameters (positive values of ΔH°, ΔS° and negative values of ΔG°) indicated the binding systems between CTS/ATP and adsorbate were endothermic, entropy gained and spontaneous in nature.

Introduction

Human activities such as electro-plating, smelting contaminated the wastewaters with heavy metal ions, which would be harm to the environment [1]. The concentrations of traces of heavy metal ions in matrices as environmental samples are below the detection limit, a preconcentration–separation procedure is needed to improve the detection limits. The widely used preconcentration–separation methods for heavy metal ions include solvent extraction [2], co-precipitation [3], cloud point extraction [4], [5], ion exchange [6], membrane filtration [7] and solid-phase extraction (SPE) [8], [9]. Among the preconcentration–separation techniques mentioned above, SPE is one of the efficient techniques for the trace or ultratrace amount of heavy metal ions duo to its simplicity and economy [10].

Chitosan (CTS) has many reactive amino groups and hydroxyl groups, which is beneficial for the adsorption of metals from solution [11], [12], [13]. However, CTS is only soluble in few dilute acid solutions due to its crystalline nature, and it has drawbacks of swelling and unsatisfying mechanical property, which limits its applications. To improve the properties of CTS, abundant studies have been devoted to the modification of the CTS surface by cross-linking with functional agents, such as glutaraldehyde, ethyleneglycol diglycidyl ether and epichlorhydrin [14], [15]. Recent researches proved CTS-based inorganic composites could be applied to adsorptive remove of heavy metal ions. Various inorganic materials such as silica gel [16], clay minerals [17], zeolite [18], metallic oxide [19] and carbon nanotubes [20] have been used up to now.

Attapulgite (ATP) is a hydrated octahedral layered magnesium aluminum silicate mineral with large surface area, excellent chemical stability and strong adsorption [21], [22]. Although ATP possesses high adsorption capabilities, the modification of its structure can successfully improve its capabilities. In this work, CTS/ATP composites are applied as an adsorbent for the removal of chromium and iron ions from aqueous solution of both single and binary systems. The adsorption properties such as equilibrium, kinetics and thermodynamics were demonstrated by batch mode adsorption experiments.

Section snippets

Instruments and apparatus

Scanning electron microscopy (SEM) images were obtained at 15.0 kV on the field emission scanning electron microscope (USA) after gold plating. X-ray diffraction (XRD) was performed on Siemens D5005 powder X-ray diffractometer. Infrared spectra (4000–400 cm−1) was recorded on a Nicolet NEXUS 470 FT-IR apparatus (U.S.A.). The specific surface area, pore volume of the adsorbents were measured according to the Brunauer–Emmett–Teller (BET) model using single point analysis and a Flowsorb II 2300 from

Characteristic of CTS/ATP composites

The elemental analysis shows that the lignin had the following percentage composition (%): C, 2.625; H, 1.117; N, 9.651. The average pore diameter was 1.527 Å and the specific surface area of the CTS/APT composites was 64.68 m2 g−1 measured by the N2-BET method.

To characterize the size and shape of the CTS/APT composites, SEM was conducted. Fig. 1 presents the typical SEM images of ATP and the CTS/APT composites, indicating that the products are well-dispersed with CTS. It is seen from the

Conclusions

The combination of CTS and ATP was performed. The adsorptions of metal ions by CTS/ATP were significantly higher than those of ATP and CTS. Equilibrium data were well described by Freundlich isotherm models, indicating multilayer adsorption for Cr(III) and Fe(III) onto CTS/ATP composites. Kinetics experiments showed that CTS/ATP composites offered fast kinetics for adsorption of Cr(III) and Fe(III), and the diffusion-controlled process as the essential adsorption rate-controlling step was also

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (nos. 21077046and 30970309) and Ph.D. Programs Foundation of Ministry of Education of China (no. 20093227110015).

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