Novel N-Substituted 2,2′-Oxydiacetic Acid Diamide-Functionalized Silica Resins: an Efficient Sorbent for Removal of U(VI) and Th(IV) Present in Nitric Acid-Rich Effluents

In view of the limited availability of acid-stable solid-phaseextractants for removal of U(VI) and Th(IV) present in nitric acid-richeffluents, two novel N-substituted 2,2 & PRIME;-oxydiacetic acid diamide-functionalizedsilica resins (denoted as R1 and R2) are synthesized by the successiveprocesses of condensation of 3-aminopropyl triethoxysilane (APTES)on silica gel followed by chemical modification of the -NH2- group using 2-((N,N-dialkylcarbamoyl)methoxy)acetic acid. Synthesized resins were characterizedby ATR-FTIR, solid-state C-13/Si-29 (CP/MAS) NMR,TGA, and SEM-EDS techniques. Notably, high sorption efficiencies ofU(VI) and Th(IV) were obtained at 4.0 M HNO3 feed acidity,highlighted by their high K (d) (mL g(-1)) values, R1: U(VI): 5.5 x 10(3), Th(IV):1.2 x 10(4); R2: U(VI): 4.2 x 10(3), andTh(IV): 1.01 x 10(4), respectively. 0.01 M HNO3, Na2CO3, and oxalic acid can act as suitabledesorbing agents for both resins R1 and R2 loaded with U(VI) and Th(IV).Maximum desorption of U(VI) and Th(IV) can be achieved using 10(-3) M of Na2CO3 and oxalic acid,respectively. In contrast to the other solid-phase extractants, theN-substituted 2,2 & PRIME;-oxydiacetic acid diamide-functionalizedextractants have exceptionally high acid stability. UV-VISspectroscopic study of the feed and raffinate solutions used in thecolumn study confirms effective removal of U(VI) and Th(IV).