Abstract
Cysteine-functionalized chitosan magnetic nano-based particles were synthesized for the sorption of light and heavy rare earth (RE) metal ions (La(III), Nd(III) and Yb(III)). The structural, surface, and magnetic properties of nano-sized sorbent were investigated by elemental analysis, FTIR, XRD, TEM and VSM (vibrating sample magnetometry). Experimental data show that the pseudo second-order rate equation fits the kinetic profiles well, while sorption isotherms are described by the Langmuir model. Thermodynamic constants (ΔG°, ΔH°) demonstrate the spontaneous and endothermic nature of sorption. Yb(III) (heavy RE) was selectively sorbed while light RE metal ions La(III) and Nd(III) were concentrated/enriched in the solution. Cationic species RE(III) in aqueous solution can be adsorbed by the combination of chelating and anion-exchange mechanisms. The sorbent can be efficiently regenerated using acidified thiourea.
Highlights
The recovery of heavy metals from dilute aqueous systems requires the development of new technologies for their concentration and separation [1]
Chitosan-magnetite particles are chemically modified to prevent their dissolution in acidic media; aldehyde crosslinking may result in the loss of sorption capacity, because some amine groups are involved in the crosslinking reaction [8,31], so epichlorohydrin had been used as the crosslinking agent
The crosslinking mono-functional agent is used to form covalent bonds with the carbon atoms linked to the hydroxyl groups of chitosan [32]
Summary
The recovery of heavy metals from dilute aqueous systems requires the development of new technologies for their concentration and separation [1]. Flocculation, coagulation, adsorption, ion exchange, membrane filtration, electrodeposition and chemical precipitation are the most conventional processes for the treatment of metal-bearing effluents. Most of its advantages are related to the wide availability of this renewable resource and its easy derivatization: it is readily chemically modified and can be physically conditioned under different forms [5] This material is generally more hydrophilic than synthetic materials, such as polystyrene-divinylbenzene, polyethylene and polyurethane, which are commonly used as support for chelating and ion-exchange resins. The solubility of chitosan in acid media is a critical issue to be addressed for stable application; it is generally necessary to cross-link the biopolymer (by chemical modification) for extending the use of the biopolymer for a broader range of use (especially in terms of pH characteristics). The grafting of new functional groups on the backbone of chitosan increases the density of the sorption site and may change the sorption sites and the sorption mechanism, resulting in an increase of sorption capacity and a better selectivity for targeted metals [11]
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