GLDA and ion exchangers: Unlocking sustainable solutions for recovery of rare earth elements

Abstract

GLDA (tetrasodium salt of N,N-bis(carboxymethyl)-L-glutamic acid) was proposed as a complexing agent for rare earth elements. The formed complexes Ln(III)-GLDA were subjected to adsorption using twelve commercial ion exchangers of different types. Ion exchangers were characterized by describing their physicochemical properties using sieve analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The stability constants of the Ln(III)-GLDA complexes in the binary systems at different Ln(III):GLDA molar ratios were determined by the potentiometric method. The effects of different process parameters (Ln(III):GLDA molar ratio, initial solution pH, phase contact time, initial solution concentrations, and temperature) on the adsorption of La(III), Nd(III), and Ho(III) ions in the presence of GLDA were investigated by the static method in the single-component systems.Kinetic, equilibrium, and thermodynamic parameters were calculated. The highest adsorption capacities were obtained for the Purolite S957 ion exchanger (139.57 mg/g for the La(III)-GLDA complexes, 152.72 mg/g for the Nd(III)-GLDA complexes, and 151.29 mg/g for the Ho(III)-GLDA complexes), Lewatit Monoplus SP112 ion exchanger (155.49 mg/g for the La(III)-GLDA complexes, 150.23 mg/g for the Nd(III)-GLDA complexes, and 132.77 mg/g for the Ho(III)-GLDA complexes). The desorption process was performed to regenerate the ion exchangers by applying hydrochloric and nitric(V) acids at concentrations of 0.5, 1, and 2 M. In addition, for La(III)-GLDA complexes, experiments were performed in the column systems.