Mechanistic insights into the selective recovery of rare earth elements from mine wastewater using green-synthesized silver nanoparticles

The rising demand for rare earth elements (REEs) and escalating environmental concerns have rendered the recovery of REEs a key problem. This study demonstrates the effectiveness of silver nanoparticles produced via green tea extract (GT-Ag NPs) in the selective recovery of REEs from mine wastewater, achieving separation coefficients ( K d ) ranging from 1.34 × 10 3 to 2.08 × 10 3  mL/g and recovery efficiencies of 40 %–50 %. To elucidate the mechanisms of REEs recovery by GT-Ag NPs, we performed kinetic studies and utilized several characterization techniques, such as SEM-EDS-Mapping, XRD, zeta potential measurements, FTIR, and XPS. These findings revealed that electrostatic attraction and complexation may play a crucial role in adsorbing REEs onto GT-Ag NPs. Following, for desorption process, the GT-Ag NPs were immersed in a 0.01 M sodium citrate solution, achieving over 90 % efficiency, where the desorption process primarily involved ion exchange between REEs and sodium ions, along with complexation between sodium citrate and the REEs. Notably, after four adsorption-desorption cycles, GT-Ag NPs retained 40 % of their adsorption efficiency and over 90 % desorption efficiency while maintaining more than 50 % adsorption efficiency after four column experiment cycles, further confirming the excellent reusability of GT-Ag NPs. Overall, the findings from this study offer significant understanding of REEs recovery from mine wastewater using GT-Ag NPs.