Adsorption of Ce(III) and Nd(III) ions onto monosodium glutamate functionalized chitosan, xanthated chitosan and xanthogenated chitosan beads / Noorul Farhana Md Ariff

In this study, chitosan beads were modified with monosodium glutamate as well as sulphur and magnesium for the removal of precious rare earth metals ions, cerium(III), Ce(III) and neodymium(III), Nd(III) from an aqueous solution via batch sorption experiments. Three variants of modified chitosan beads were prepared which were monosodium glutamate functionalized chitosan (MSGC), xanthated chitosan (XC) and xanthogenated chitosan (XNC) beads. These adsorbents underwent several characterizations such as swelling and solubility test, determination of pH of aqueous slurry (pHslurry) and pH of zero point charge (pHzpc), fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy coupled electron dispersive spectroscopy (FESEM-EDS), pore size and surface area analysis and ultimate analysis in order to study the efficiency in removing Ce(III) and Nd(III) ions from aqueous solutions. MSGC, XC and XNC beads showed significant swelling percentage yet insoluble in acidic, basic and neutral media. Meanwhile, the values of pHslurry and pHzpc were relatively close for all types of adsorbents. FTIR showed that sulphur was successfully added into XC and XNC beads. The uneven and non-porous chitosan beads were found to be rougher and more irregular as they were modified while EDS had strengthen the fact that sodium, sulphur and magnesium were added onto MSGC, XC and XNC beads. As the pore diameter of these beads lies between 11.70 and 39.58 nm, MSGC, XC and XNC beads can be classified as mesoporous. The ultimate analysis had again proved that sulphur had been induced into XC and XNC beads.For batch sorption study, the physicochemical parameters such as the pH, stirring speed, adsorbent dosage, and stirring time were determined as to ensure the adsorption occur at optimum conditions. The optimum pH for adsorption of Ce(III) and Nd(III) ions were 4 and the optimum stirring ranged from 300 to 600 rpm. Adsorption of Ce(III) ions required 0.015 to 0.025 g of MSGC, XC and XNC beads; while Nd(III) ions required 0.01 to 0.04 g of the same adsorbents. A rapid adsorption process was observed for both Ce(III) and Nd(III) ions where it reached the equilibrium state in 30 min of stirring time. Chemisorption was suggested as the rate limiting step as the experimental data for all adsorption system followed pseudo-second-order kinetics model. Based on the adsorption isotherm results, Langmuir model fitted well the experimental data with the maximum adsorption capacities (Qmax) recorded for adsorption of Ce(III) ions onto MSGC, XC and XNC beads at 300 K were 167.5, 559.9 and 463.8 mg g-1, respectively. Meanwhile, the Qmax values recorded for adsorption of Nd(III) ions onto MSGC, XC and XNC beads were 68.3, 338.2 and 253.9 mg g-1, respectively. Based on thermodynamic study, adsorption of Ce(III) ions onto XC beads and adsorption of Nd(III) ions onto MSGC and XNC beads were endothermic nature of adsorption. Adsorption of Ce(III) and Nd(III) ions (excluding adsorption of Ce(III) ions onto XNC beads) recorded positive ΔSº which attributed to an increase of adsorbent-adsorbate interface. MSGC, XC and XNC beads were more selective to adsorb Nd(III) ions than Ce(III) ions in the binary study. The presence of Na+, K+ and Cl- slightly reduced the adsorption of Ce(III) ions onto MSGC beads, meanwhile the presence of Ca2+ and SO42- showed significant effect on adsorption of Ce(III) and Nd(III) ions onto MSGC, XC and XNC beads. The application of EDTA, HCl, HNO3, and NaOH are unable to desorbed Ce(III) and Nd(III) ions from the adsorbents.