Highly recyclable EDTA-crosslinked chitosan-gelatin biopolymer adsorbent for separation and recovery of rare earth elements from aqueous solution

A biopolymer adsorbent was prepared by crosslinking chitosan (CS) and gelatin (GL) with ethylenediaminetetraacetic acid (EDTA) for the separation and recovery of three famous rare earth elements (REEs), i.e., lanthanum (La(III)), cerium (Ce(III)), and europium (Eu(III)), from water. In this adsorbent, the EDTA moiety acts as a crosslinking agent, in addition to aiding in REE adsorption via coordination sites. Various parameters, including contact time, pH, initial REE concentration, reusability, and selectivity, were investigated during the REE recovery from water. The kinetic results fit better with the pseudo-second-order (PSO) kinetics model, confirming the involvement of chemisorption and external film diffusion in the rate-determining step. The isotherm data fit the Langmuir model, indicating a homogeneous surface for REE adsorption. The rate constant (k₂) values for PSO kinetics were (9.60 ± 0.05) × 10⁻⁴, (8.67 ± 0.04) × 10⁻⁴, and (10.30 ± 0.04) × 10⁻⁴ g/(mg·min), while the maximum adsorption capacities were 76.70 ± 5.70, 79.10 ± 6.80, and 86.20 ± 5.10 mg/g for La(III), Ce(III), and Eu(III), respectively. The CS-EDTA-GL adsorbent provided a good separation factor (β) in 16 REE mixtures; among them, an optimal β was observed for Eu(III) with values of 1.3838, 1.322, 1.284, 1.351, 1.4896, and 1.2792 for Eu/Sc, Eu/Yb, Eu/Tm, Eu/Y, Eu/La, and Eu/Er, respectively. Adsorption mechanism confirms the electrostatic interactions and coordination complexation role in the REE adsorption. Finally, the adsorbent was used in pure water, tap water, and two industrial wastewater samples collected at real environmental concentrations to determine its suitability for practical applications.