Adsorption of REEs from aqueous solutions using modified polystyrene- di (2-ethylhexyl) phosphoric acid electrospun nanofibers

Abstract

The recovery and separation of rare earth elements (REEs) is an emerging area of the current research due to their applications in modern technology and because both accessible and cost-effective approaches are required. In this study, polystyrene (PS) grafted with di(2-ethylhexyl) phosphoric acid ( D2EHPA) ligand was fabricated via the electrospinning technique. The electrospun PS/DEHPA nanofiber mats were characterised using various techniques such as HR-SEM, TGA, FTIR, XRD, BET and ICP-OES. The fabricated electrospun nanofiber materials were then used for the recovery of Nd and Sm metal ions from the aqueous solutions. The supreme sorption uptake of Nd 3+ and Sm 3+ was ˃ 100 mg/g at pH 4.0, reached at an equilibrium time of 70 min with the modified PS/DEHPA nanofiber mats. The recovery of Nd 3+ and Sm 3+ was best described by the Langmuir isotherm and followed a pseudo second-order kinetic model. Thermodynamic data, ΔG°, Δ H° and ΔS° suggest that Nd 3+ sorption onto PS/DEHPA was spontaneous and endothermic. The coordination of PS with the D2EHPA ligand occurred via hydrogen bonding while the binding of PS/DEHPA to the metal ion was likely bonded by ionic, covalent or electrostatic interactions. The reusability investigation indicates that the synthesized PS/DEHPA nanofiber mats can withstand up to four successive cycles, and the adsorption and desorption performances were over 60 %. Nd 3+ sorption in the presence of interfering Ni 2+ and Co 2+ metals was 96.82 mg g -1 (0.671 mmol g -1 ), closer to 101.46 mg g -1 (0.703 mmolg -1 ) obtained in a single metal ion solution suggesting a good selectivity of PS/DEHPA fibres towards REEs (Nd 3+ ).