Alanine and serine functionalized magnetic nano-based particles for sorption of Nd(III) and Yb(III)

Abstract

2016) Abstract. Magnetic nano-based sorbents have been synthesized for the recovery of two rare earth elements (REE: Nd(III) and Yb(III)). The magnetic nano-based particles are synthesized by a one-pot hydrothermal procedure involving co-precipitation under thermal conditions of Fe(III) and Fe(II) salts in the presence of chitosan. The composite magnetic/chitosan material is crosslinked with epichlorohydrin and modified by grafting alanine and serine amine-acids. These materials are tested for the binding of Nd(III) (light REE) and Yb(III) (heavy REE) through the study of pH effect, sorption isotherms, uptake kinetics, metal desorption and sorbent recycling. Sorption isotherms are well fitted by the Langmuir equation: the maximum sorption capacities range between 9 and 18 mg REE g -1 (at pH 5). The sorption mechanism is endothermic (positive value of ∆ H °) and contributes to increase the randomness of the system (positive value of ∆ S °). The fast uptake kinetics can be described by the pseudo-second order rate equation: the equilibrium is reached within 4 hours of contact. The sub-micron size of sorbent particles strongly reduces the contribution of resistance to intraparticle diffusion in the control of uptake kinetics. Metal desorption using acidified thiourea solutions allows maintaining sorption efficiency for at least four successive cycles with limited loss in sorption mL of REE(III) solution at different initial concentrations (i.e., 25, 50, 75, 100, 150, 200 and 300 mg L − 1 , at pH 5) and shaking for 4 h at 300 rpm. The experiments were performed in a thermostatic chamber, at different temperatures (300±1 K, 310±1 K and 320±1 K, respectively). Uptake kinetics was performed using a sorbent dosage of 2.5 g L -1 and a concentration of 100 mg REE L -1 at 300±1 K: samples were collected under agitation at standard times and metal concentration was determined, after magnetic separation, by ICP-AES. Main experimental conditions have been summarized in