Preparation of a novel macroporous silica-based diglycolamide derivative-impregnated polymeric composite and its adsorption mechanism for rare earth metal ions

Abstract

Diethylenetriaminepentaacetic acid (DTPA), a multi-dentate acidic chelating agent containing five carboxyl and three amine groups all capable of protonation, is a pentabasic acid. To separate minor actinide [MA(III)] and rare earth [RE(III)] elements effectively from a HNO3 solution containing DTPA generated in the MAREC process, a functional polymeric composite impregnated with a novel macroporous silica-based diglycolamide compound, N,N,N',N'-tetraoctyl-3-oxapentane-1,5-diamide (TODGA), was prepared. Thus, the impregnated functional polymeric composite (TODGA/SiO2-P) was obtained by impregnating and immobilizing TODGA molecules in the pores of the SiO2-polymer (SiO2-P) particles (ca. 50 μm diameter) via a vacuum sucking technique. The effects of H+ ions within the concentration range 0.01-3.0 M and of NO3- ions within the range 0.1-3.115 M on the adsorption of RE(III) ions onto TODGA/SiO2-P were investigated at 298 K. It was found that in the presence of 0.05 M DTPA, the DTPA species strongly affected the adsorption of RE(III) ions. The adsorption capability of TODGA/SiO2-P depended on the competitive reactions of RE(III) ions with two species, viz. H4DTPA- and H2DTPA3-. The distribution coefficient (Kd) for RE(III) ions increased with increasing NO3- concentration, with one RE(III) ion reacting with two NO3- ions. The adsorption mechanism of RE(III) ions towards the TODGA/SiO2-P polymeric composite in HNO3 solution containing 0.05 M DTPA was suggested as: RE3+ + H4DTPA- + 2NO3- + 3TODGA/SiO2-P RE(H4DTPA) (NO3)2·3TODGA/SiO2-P The formation of H4DTPA- and RE(H4DTPA) (NO3)2 which are both capable of adsorbing with TODGA/SiO2-P was the main reason why RE(III) ions exhibited such significant adsorption in the presence of 0.05 M DTPA.