The separationSeparation of rare earth elements (REEsrare earth elements (REEs)) through traditional means remains one of the primary barriers to meeting current market demands for REEsRare earth elements (REEs) in critical sectors such as electric vehicles and defense technologies. We propose a new method of REERare earth elements (REEs) separationSeparation and purification which utilizes functionalized low-cost materials such as cellulose and other common substrates to adsorb dilute REEsRare earth elements (REEs) in an aqueous solutionSolution. The substrate can be functionalized with molecules that exhibit ionic radii dependent adsorptionAdsorption behavior. We demonstrate that with carefully tuned chemistry, high purity lanthanidesLanthanides can be generated in only a few adsorptionAdsorption-desorption cycles from an initially diluted and mixed feed source. We aim to explore the mechanism underlying the selectivity of this material as well as ways that this can be further tuned to optimize metalMetal purity from the process.