(550h) Adsorption of Rare Earth Elements in Phosphorous Functionalized Nanoporous Carbon

Due to a worldwide shortage of supply of rare earth elements and their critical applications in energy and defense sectors, researchers are currently looking for a sustained supply of those elements. Neodymium (Nd) and Dysprosium (Dy) are two of those highly valued rare earth elements and one of the possible ways to maintain a constant supply is to recover them from waste permanent magnets. Selective adsorption in a suitable nanoporous material is considered to be a benign and inexpensive way to recover those precious elements. In this research, phosphorus functionalized nanoporous carbon was synthesized from biomass with the BET surface area of 837 m²/g and 0.9 atom% phosphorus. The adsorption of neodymium and dysprosium were in the range of 335–344 mg/g upto their initial concentration of 500 ppm in water and such adsorption amount is higher than that of majority of the adsorbents reported in literature. The adsorption capacity of iron (Fe(III)) under the similar conditions was one order of magnitude lower and it suggests a possible separation of these rare earth elements from iron present in the waste magnets. X-ray photoelectron spectroscopy (XPS) studies on both Nd and Dy-adsorbed carbons revealed a small shift in the P-2p_3/2 energy level of phosphorus towards a higher energy level hereby suggesting a possible formation of metallic phosphates. Additionally, XPS also indicated a small amount of carbonates and oxides of rare earth elements that might have been formed on the surface of adsorbents. The overall results suggest that this carbon can be used as a potential sorbent for enrichment and separation of Nd and Dy.