Adsorptive recovery of neodymium and dysprosium in phosphorous functionalized nanoporous carbon

Abstract

Phosphorus functionalized nanoporous carbon was synthesized from lignin by periodical reactions with potassium hydroxide and triphenylphosphine. It has the BET surface area of 837m2/g and total pore volume 0.41cm3/g along with 0.9 atom% phosphorus. The adsorption of neodymium (Nd (III)) and dysprosium (Dy(III)) were in the range of 335–344mg/g upto their initial concentration of 500ppm in water and such adsorption amount is higher than that of majority of the adsorbents reported in literature. The adsorption capacity showed negligible dependency on the solution pH. The distribution coefficients for Nd(III) and Dy(III) were within 1000 to 10,000mL/g. 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. The maximum selectivity of separation of Nd(III) and Dy(III) from iron was ca. 32 to 61. Kinetic study revealed that the adsorption of Dy was faster than that of Nd(III). The results of kinetic study were better fit with pseudosecond order kinetics. XPS studies on both Nd(III) and Dy(III)-adsorbed carbons revealed a small shift in the P 2p3/2 energy level of phosphorus towards higher energy level hereby suggesting a possible formation of metallic phosphates. Additionally, Similar studies on Nd(III) and Dy(III)-adsorbed carbon indicated small amounts carbonates and oxides of rare earth elements that might have also been formed. The overall results suggest that this carbon can be used as a potential sorbent for enrichment and separation of Nd(III) and Dy(III).