Efficient separation of hard actinides from rare earths using the functionalised silica gels

Abstract

Separation of hard actinides from rare earth metal ions is one of the challenging task as both these types of ions are hard ions. Therefore, from the view point of Hard-Soft Acid-Base principle, selecting suitable ligands is beyond the conventional procedure for their successful separation. Herein, we have proposed two oxygen donating ligands namely 1,8-dihydroxyanthraquinone functionalised silica gel (DHAFSG) and pyridine-N-oxide functionalised silica gel (PNOFSG). They have been synthesized, characterised and tested for the separation of hard actinides e.g. UO22+, Th4+ from rare earths. Interestingly, it has been found that the anions present in the aqueous medium controls the complexation and binding of the metal ions with the adsorbents. Rare earths are more selectively extracted from nitrate-carbonate medium giving the separation factors of 9 and 12 from actinides using DHAFSG and PNOFSG adsorbents respectively. Whereas, from pure nitrate medium, the hard actinides are selectively extracted and the separation factors for Th4+ from rare earths are 1000 and 4000 using PNOFSG and DHAFSG adsorbents respectively in pure nitric acid medium at pH 1. Kinetics of adsorption is fast in all the cases using DHAFSG and PNOFSG adsorbents. The performances of DHAFSG and PNOFSG have been tested for the separation of actinides from rare earths in Simulated Monazite ore Solution (SMS) in nitric acid medium. Selective separation of actinides from the rare earth elements from SMS has been obtained.