Biosorption of lanthanum and cerium from aqueous solutions by Platanus orientalis leaf powder
Introduction
In recent years, lanthanoids have been in great demand for various functional materials (Kondo and Kamio, 2002). From the rare earth elements (REEs), lanthanum has special attention due to its technological importance because of increasing demands for advanced new materials. Current applications of lanthanum as a pure element or in association with other compounds are in super alloys, catalysts, special ceramics and in organic synthesis (Palmieri et al., 2002). Cerium is one of the cheapest and most abundant rare earths. However, high purity is usually required for its utilization in industry where it is used, for example, for sulfur control in steels, pyrophoric alloys, ceramic, catalyst support, and polishing powders, etc. Cerium is accompanied by other REEs in its minerals, as well as in the spent nuclear fuel (Jelinek et al., 2006).
Turkey has the second largest reserves of rare earth elements in the world. One of the most important thorium deposits with rare earths elements is situated in the Eskişehir–Beylikahir region of Turkey. The REEs content of this deposit is 4.5 × 106 ton with an average percentage of 2.78 (Altaş et al., 1999).
Many conventional methods for removing heavy metals, radionuclides and lanthanides from aqueous solution exist (Bhattacharyya and Sharma, 2004). These include adsorption, ion exchange, coagulation, floatation, hyper-filtration, chemical precipitation, and reverse osmosis. All these conventional methods have some advantages as well as disadvantages, such as disposal of chemicals, resins and adsorbents to the nature may themselves be harmful. Biosorption can be a candidate for recovery of metals from dilute industrial aqueous solutions, the extraction of radionuclides and lanthanides from mine leachates, and metal recovery or water pollution control applications (Wase, 1997). Biosorption can be defined as the removal of metal or metalloid species, compounds and particulates from solution by non-living biological material (Davis et al., 2003). The process is a rapid, reversible, economical and ecofriendly technology in comparison with conventional chemical methods (Ahuja et al., 1999). Moreover, biosorbent materials often execute high metal-loading capacity and in some cases are highly specific for certain elements of particular interest (Kazy et al., 2006). Various kinds of materials such as tree leaves, microorganisms, sawdust, bark, cone biomass are used for biosorption processes (Aoyama, 2003).
Despite their strategic and economic importance, REEs have not been evaluated much regarding their potential to be concentrated and eventually separated by the biosorption process (Palmieri et al., 2002). Recently, researchers have been focused on microorganism-based biosorbents for the adsorption of rare earth elements; Kazy et al. (2006) characterized lanthanum biosorption by a Pseudomonas sp. in terms of equilibrium metal loading, model fitting, kinetics, effect of solution pH, lanthanum-bacteria interaction mechanism and recovery of sorbed metal. The effect of different anions for the La3+ biosorption on the Sargassum polycystum Ca-loaded biomass was studied by Diniz and Volesky, (2005). Palmieri et al. (2002) investigated some basic aspects of lanthanum-Sargassum biomass interactions in batch equilibrium contact. In another study, Palmieri et al. (2000) developed a study on neodymium biosorption from acidic solution utilizing different types of biomass.
On a positive aspect, tree leaves are inexpensive and available in a great quantity. They contain various components such as polyphenolics, plant pigments and protein which can provide active sites for heavy metal binding (Aoyama et al., 2000). In previous studies, various kinds of tree leaves were used for biosorption of heavy metals such as chromium (Aoyama et al., 1999, Aoyama et al., 2000, Aoyama, 2003), nickel (Liang et al., 2002), copper (King et al., 2006, Kumar et al., 2006), cadmium (Sharma and Bhattacharyya, 2005) and lead (Al-Subu, 2002, Bhattacharyya and Sharma, 2004).
P. orientalis is a very large, wide spreading and long-lived deciduous tree in the Platanaceae family. Its native range spreads from Southeast Europe to India including Turkey and Iran.
In this study, the use of powdered leaf of P. orientalis as a biosorbent was tested for recovering lanthanum and cerium(III) ions from aqueous solution. The effects of pH, contact time, concentration and temperature on the sorption were discussed. Thermodynamic parameters and isotherm studies related with the process were performed.
Section snippets
Materials and methods
Leaves of P. orientalis used in this investigation were collected from a number of trees at Ege University Campus, Bornova, Izmir, Turkey. They were washed repeatedly with water to remove dust and soluble impurities, dried at 80°C for 24h, ground in a mortar to a very fine powder and sieved through a 125μm copper sieve and stored in a desiccator before use. The dried leaves were used as biosorbent without any chemical treatment to avoid extra expenditure.
Lanthanum and cerium stock solutions (1g
The effect of initial pH and contact time
pH is an important factor controlling the process of biosorption. The pH affects not only the surface charge of the biosorbent, but also the degree of ionization and speciation of the heavy metal in solution (Aksu and İşoğlu, 2005). 25 mL of 100 mg L− 1 lanthanum and cerium(III) were treated separately with 0.1g of powdered leaf of P. orientalis at different pHs, in a thermostatically controlled shaker at 30°C for 2h. Lanthanum biosorption at pH higher than 6.0 was not considered because
Conclusion
In present study the biosorption properties of P. orientalis powdered leaf were studied for La and Ce(III) recovery. The results obtained show that pH and initial La and Ce(III) concentrations, highly affect the uptake of the biosorbent. The Langmuir adsorption model and Freundlich equation were used for mathematical descriptions of the biosorption of La and Ce(III) ions onto P. orientalis powdered leaf. It was found that the adsorption equilibrium data fitted well to the Langmuir model.
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