Biosorption of lanthanum and cerium from aqueous solutions by Platanus orientalis leaf powder

Abstract

The biosorption of lanthanum and cerium by leaves powder of Platanus orientalis was separately determined at varying experimental conditions using a batch technique. The effects of initial pH, contact time, initial metal ion concentration and temperature were investigated. The Langmuir and Freundlich isotherms were applied to represent the adsorption process. Langmuir isotherm fits the experimental data quite well. The Langmuir monolayer capacity of the sorbent is 28.65mg g^− 1 and 32.05mg g^− 1 for La and Ce(III), respectively. Thermodynamic parameters such as standard enthalpy (ΔH°), entropy (ΔS°) and free energy (ΔG°) were calculated from the slope and intercept of the plots of lnK_d versus 1/T. The results indicated that sorption was endothermic and spontaneous in nature. The work reveals that powdered leaf of Platanus orientalis is a good choice as a biosorbent for the recovery of lanthanum and cerium from aqueous solution.

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.