Adsorptive Recovery of Rare Earth Elements: Current Progress, Challenges and Emerging Perspectives

In the modern era of increased usage of high-technology and regular goods, the 14 rare earth elements (REEs) are regarded as one of the essential elemental resources. The natural ore resources and recovery from spent materials are subsequently burdened by the expanding worldwide demand for REEs, which is increasing at 3.7 to 8.6% rate. Wasted REEs are considered emergent micro-pollutants worldwide in terrestrial and marine ecosystems. As a result, the extraction and recovery of REEs from waste streams, particularly wastewater, has grown in importance and desirability. The present review explores the various adsorptive recovery techniques, including conventional activated carbon, zeolites, and membranes, to advanced techniques like nanomaterials, nanotubes, and novel synthesized materials to extract REEs from wastewater. The factors that govern effective adsorption include the surface area of the adsorbent, pore size, pH of the solution, and contact time of adsorbate with adsorbent. Several characterization techniques to elucidate adsorption mechanisms were discussed. Several mechanisms underlie the REE adsorption, which may entail several simultaneous processes based on the particular adsorbent and the adsorption environment. The importance of desorption techniques and the sustainable recovery of REEs from wastewater is presented to reduce risks to the environment and human health.