Sorption of lead ions from aqueous solution using tree fern as a sorbent

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Abstract

This study is on sorption of lead ions on an agricultural by-product, tree fern. Equilibrium isotherms have been measured and modeled. The equilibrium sorption capacity of lead(II) was determined from the Langmuir isotherm and found to be 40.0 mg/g. Based on the assumption of the pseudo-second order mechanism, a batch sorption model was developed to predict the rate constant of sorption, the equilibrium sorption capacity and the initial sorption rate with the effect of initial lead(II) concentration and temperature. The sorption rate was found to increase with temperature, and an activation energy of approximately 87 kJ/mol was determined from the pseudo-second order rate constants. The findings of this investigation suggest that chemical sorption plays a role in controlling the sorption rate.

Introduction

Understanding the sorption of metal ions from aqueous solution is important in water pollution control. In recent years, there has been considerable interest in the use of agricultural by-products as sorbents. Table 1 is a list of the agricultural by-products available for removing lead ion from wastewaters. Investigations have been carried out to identify suitable agricultural sorbents to remove significant quantities of lead ions.

The tree fern, which is commercially available in Taiwan, is used as a sorbent for lead ions. It sorbs water easily and is marketed for horticultural uses as soil for plants. Being dark brown in colour, the tree fern constitutes mainly of lignin and cellulose (Newman, 1997). All chemical sorbents have polar functional groups (alcohols, aldehydes, ketones, acids, phenolic hydroxides and ethers) for chemical bindings (Adler and Lundquist, 1963). The tree fern, which is highly polar, is used as a specific sorbent to remove dissolved solids (transition metals and polar organic molecules).

This study investigates whether the tree fern can be used as a sorbent to remove lead ions from aqueous solutions and whether the corresponding equilibrium isotherm can be determined kinetically.

Section snippets

Materials

The raw tree fern was dried in an oven at 100 °C for a period of 24 h, and then ground and screened through a set of sieves to get particles of geometrical size 53–61 μm. The materials were stored in an air-tight plastic container before all investigations. The stock solutions of lead(II) (2000 mg/L) were prepared in distilled water using lead nitrate. All working solutions were prepared by diluting the stock solution with distilled water.

Equilibrium studies

A lead(II) solution (50 mL) with a concentration of

Equilibrium studies

Analysing the results of the isotherm data is important to develop an equation, which can be used for design purposes. To investigate the sorption isotherm, three equilibrium models, the Langmuir, the Freundlich and the Redlich-Peterson isotherm equations, were analysed. The theoretical Langmuir sorption isotherm (Langmuir, 1916), which is the best known of all isotherms describing sorption, is often used to describe sorption of a solute from a liquid solution as:qe=qmKaCe1+KaCewhere qe is the

Equilibrium studies

The equilibrium distribution of lead between the sorbent and the solution is important in determining the maximum sorption capacity of the tree fern for lead(II). To assess the different isotherms and their ability to correlate experimental results, the theoretical plots from each isotherm have been presented with the experimental data for sorption of lead(II) on tree fern at 20 °C (Fig. 1). The graph is plotted in the form of lead(II) sorbed per unit mass of tree fern qe, against the

Conclusion

The biosorption of lead ions on tree fern was investigated. Tree fern is a suitable sorbent for the removal of lead(II) from aqueous solution. The lead(II) removal was a function of initial lead ion concentration and temperature. The Redlich-Peterson and the Langmuir isotherms have higher correlation coefficients than those of Freundlich isotherm for the sorption of lead(II) onto tree fern. The pseudo-second order kinetic model was successfully applied to the experimental data, confirming that

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