Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell

doi:10.1016/j.jct.2007.10.005

The Journal of Chemical Thermodynamics

Volume 40, Issue 4, April 2008, Pages 702-709

https://doi.org/10.1016/j.jct.2007.10.005 Get rights and content

Abstract

A novel cation exchanger (TFS-CE) having carboxylate functionality was prepared through graft copolymerization of hydroxyethylmethacrylate onto tamarind fruit shell (TFS) in the presence of N,N′-methylenebisacrylamide as a cross-linking agent using K₂S₂O₈/Na₂S₂O₃ initiator system, followed by functionalisation. The TFS-CE was used for the removal of Cu(II) from aqueous solutions. At fixed solid/solution ratio the various factors affecting adsorption such as pH, initial concentration, contact time, and temperature were investigated. Kinetic experiments showed that the amount of Cu(II) adsorbed increased with increase in Cu(II) concentration and equilibrium was attained at 1 h. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The Arrhenius and Eyring equations were used to obtain the kinetic parameters such as activation energy (E_a) and enthalpy (ΔH^#), entropy (ΔS^#) and free energy (ΔG^#) of activation for the adsorption process. The value of E_a for adsorption was found to be 10.84 kJ · mol⁻¹ and the adsorption involves diffusion controlled process. The equilibrium data were well fitted to the Langmuir isotherm. The maximum adsorption capacity for Cu(II) was 64 · 10 mg · g⁻¹ at T = 303 K. The thermodynamic parameters such as changes in free energy (ΔG^∘), enthalpy (ΔH^∘), and entropy (ΔS^∘) were derived to predict the nature of adsorption process. The isosteric heat of adsorption increases with increase in surface loading indicating some lateral interactions between the adsorbed metal ions.

Introduction

Removal of toxic pollutants from water and wastewater is becoming an important process with the increase of industrial activities. Various heavy metal ions are discharged into water streams from large industrial sectors. Pb, Hg, Cr, Cd, Cu, Zn, and Ni are the most frequently found heavy metals in industrial wastewaters. Copper and its compounds are widely used in many industries and there are many potential sources of copper pollution. Copper contamination in water streams occurs mainly from metal cleaning and plating bath, fertilizer, refineries, paper and pulp, and wood preservatives [1]. The continued intake of copper by human beings leads to necrotic changes in the liver and kidney, mucosal irritation, wide spread capillary damage, depression, gastrointestinal irritation, and lung cancer [2]. According to Safe Drinking Water Act the permissible limit of copper in drinking water is 1.3 mg · dm⁻³ [3].

Adsorption is a promising technique for the removal of heavy metals from aqueous environments especially when adsorbents are derived from lignocellulosic materials [4]. Most of the lignocellulosic agricultural waste biosorbents used in sorption process are having low cost, non-hazardous, inexhaustible, highly selective for metal ions and organics and can be easily disposed by incineration. Agricultural waste products as a whole exceed 3.2 · 10⁸ tonnes/year. A number of biomaterials including saw dust [5], olive stone waste [6], grape stalk waste [7] and tea industry waste [8] are being used as sorbents for the removal of metal ions from aqueous solutions.

Since the adsorption process is influenced by the diffusion of metal ions and the surface interaction mechanism, the presence of surface functional groups on the adsorbent plays a major role in adsorption process [9]. The adsorption capacity of these biosorbents can be enhanced by graft polymerization followed by functionalisation. Through various chemical reactions surface functional groups effective for the adsorption process can be grafted onto the biomass [10].Tamarind fruit shell or hull (TFS) is an easily available agricultural waste material. In the present work, a new cation-exchanger (TFS-CE) having carboxylate functional group at the chain end is prepared by graft copolymerization of hydroxyethylmethacrylate (HEMA) onto TFS in the presence of N,N′-methylenebisacrylamide (MBA) and it is utilized for the removal of Cu(II) ions from aqueous solutions.

Section snippets

Preparation of TFS-CE

Scheme 1 represents the general procedure adopted for the preparation of TFS-CE. Fifty grams of TFS powder was suspended in 75 cm³ distilled water containing 0.346 M MBA, 0.134 M potassium persulfate (K₂S₂O₈) and 0.05 M sodium thiosulphate (Na₂S₂O₃) in a glass reactor. In order to remove the dissolved oxygen, nitrogen was purged for 10 min. HEMA (3.21 M) was added into the reaction mixture and stirred vigorously at T = 343 K for 2 h. The product probably containing cross-linked homopolymer (PHEMA)

Effect of pH on Cu(II) adsorption

The pH influences the metal chemistry in solution or the protonation or deprotonation of the adsorbent. The pH dependence of equilibrium adsorption data of Cu(II) ions in solution is shown in figure 1. From the figure it may be observed that amount of Cu(II) adsorbed increases with increase in pH and reaches maximum 4.96 mg · g⁻¹ (99.2%) and 12.24 mg · g⁻¹(97.9%) for an initial concentration of 10 mg · dm⁻³ and 25 mg · dm⁻³, respectively, at pH 6.0. The removal of Cu(II) can be written as follows: $2 TFS-COOH +$

Summary

This preliminary study concerning the adsorption capacity of TFS-CE indicated great potential for the removal of Cu(II) from aqueous solutions. The optimum pH for maximum adsorption of Cu(II) was found to be at pH 6.0. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The values of E_a, ΔH^#, ΔS^#, and ΔG^# were calculated using the Arrhenius and Eyring equations to predict the

Acknowledgements

The authors are grateful to the Professor and Head, Department of Chemistry, University of Kerala, Trivandrum for providing laboratory facilities for this work.

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Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell

Abstract

Introduction

Section snippets

Preparation of TFS-CE

Effect of pH on Cu(II) adsorption

Summary

Acknowledgements

J. Hazard. Mater.

Waste Manage.

React. Funct.Polym.

Separ. Purif. Technol.

Separ. Purif. Technol.

Carbon

Water Res.

Colloids Surf A: Physicochem. Eng. Asp.

Water Res.

Process Biochem.

Process Biochem.

Chemosphere

Water Res.