Impregnation synthesis of a novel macroporous silica-based TODGA polymeric composite and its application in the adsorption of rare earths in nitric acid solution containing diethylenetriaminepentaacetic acid

A macroporous silica-based N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) polymeric composite (TODGA/SiO2-P) was synthesized. It was done through impregnation and immobilization of TODGA molecule into the pores of the SiO2-P particles utilizing a vacuum sucking technique. The macroporous SiO2-P particles were the silica-based organic/inorganic composite synthesized by immobilizing styrene–divinylbenzene copolymer inside SiO2 through the complicated polymerization reaction. The adsorption of rare earth (RE(III)) elements onto TODGA/SiO2-P was investigated in HNO3 solution containing diethylenetriaminepentaacetic acid (DTPA), an acidic multi-dentate chelating agent. It was found that in the presence of 0.05 M DTPA, NO3- and H+ had significant effect on the TODGA/SiO2-P adsorption due to the competition reactions of RE(III) with different species, H4DTPA− and H2DTPA3−. With an increase in the concentration of NO3- from 0.115 M to 3.015 M, the adsorption of RE(III) onto TODGA/SiO2-P increased noticeably. On the other hand, RE(III) showed strong adsorption at 0.1 M H+, weak adsorption at around pH 2, and no adsorption in excess of pH 2.3. In a 0.1 M H+–0.115 M NO3-–0.05 M DTPA solution, a change of the distribution coefficient of RE(III) onto TODGA/SiO2-P with an increase in atomic number of RE(III) from La(III) to Lu(III) was investigated. The silica-based TODGA/SiO2-P polymeric composite showed strong adsorption for heavy RE(III) over the light one. In a 0.01 M H+–1.0 M NO3-–0.05 M DTPA solution, the effect of the ratio of solid phase to liquid one on the relationship of the distribution coefficient of RE(III) with the change in atomic number of RE(III) was also studied. Based on the complicated disassociation equilibrium of DTPA, the influence of the concentrations of NO3- and H+ on the adsorption of TODGA/SiO2-P for RE(III) was demonstrated. This makes the partitioning of RE(III) and MA(III) together from high level liquid waste (HLLW) by the polymeric composite TODGA/SiO2-P promising.