Separation of rare-earth and transplutonium elements by displacement chromatography on S-957 phosphonic ion exchanger

Abstract

Sorption of transplutonium (TPE) and rare-earth (REE) elements on Purolite®S-957 ion exchanger containing phosphonic acid and sulfo groups was studied. Rare-earth elements are efficiently sorbed from weakly acidic solutions (≤0.1 M HNO 3 ). An increase in the solution acidity and introduction of sodium ions into the sorption medium lead to a decrease in the sorption. With S-957 resin, REE and TPE were separated for the first time on a phosphorus-containing sorbent by displacement chromatography in the presence of DTPA (diethylenetriaminepentaacetic acid).Phosphorus-containing ion exchangers are capable of recovering uranium and thorium from acid solutions [1,2]. Purolite®S-957 ion exchanger (hereinafter, simply S-957) containing phosphonic acid and sulfo groups exhibits the highest ability to sorb actinide ions. High affinity of phosphonic acid groups for UO 2 2+ , Th 4+ , and Pu 4+ ions allows efficient sorption of these ions from 3.0-5.0 M HNO 3 solutions.The goal of this study was to evaluate the ability of S-957 resin to sorb rare-earth (REE) and transplutonium (TPE) elements (with Eu and Am as examples) and to examine the possibility of separating REE and TPE on S-957 ion exchanger by displacement chromatography in the presence of a complexing agent, DTPA (diethylenetriaminepentaacetic acid).(24 h). Then the sorbent was filtered off with a paper filter, and the equilibrium concentration of the target component in the filtrate was determined. From the analysis results, we calculated the gravimetric distribution coefficient of the element (K d , cm 3 g -1 ), static exchange capacity (Е, mg cm -3 resin), and Eu/Am separation factor (α Eu/Am ): EXPERIMENTALThe ability of S-957 resin to sorb Eu 3+ and Am 3+ ions was studied in the batch and dynamic modes. Prior to experiments, the resin was treated in succession with 5% Na 2 CO 3 and 3 M HNO 3 solutions. After the treatment, the sorbent was thoroughly washed with distilled water and dried in air to constant weight.Batch experiments were performed by contact of a weighed portion of the air-dry sorbent with a solution aliquot for a time sufficient to attain the equilibrium(2) Е = (C 0 -C e )VK sw /m,where С 0 and С e are the sorbate ion concentrations in the initial and equilibrium solutions, respectively, g dm -3 ; V, solution volume, cm 3 ; m, ion exchanger volume, g; K sw , sorbent swelling coefficient equal to the ratio of the ion exchange volume in the wet state to its weight in the air-dry state, cm 3 g -1 , equal to 4.0 for S-957; K d Eu and K d Am , distribution coefficients of Eu and Am.The sorption isotherms were taken by contacting various weighed portions of the resin with a constant aliquot of the solution. From the data obtained, the total exchange capacity and the exchange constant were determined.Dynamic experiments were performed in the col-

Adsorption-based Separation and Recovery of Rare Earth Elements

“…Adsorbents containing di-and polyfunctional groups in addition to P-based groups have been studied for REE separation (Alexandratos & Natesan, 1999;Alexandratos & Hussain, 1995;Alexandratos & Smith, 2004b;Shumilova et al, 2012;Trochimczuk, 2000). The addition of a second functional group can enhance the behavior of the adsorbent, as in phosphorylated adsorbents, where the introduction of highly hydrophilic sulfonic acid eliminated intra-ligand hydrogen bonding, which reduced intra-ligand cooperation, and increased the accessibility of P-containing groups (Alexandratos & Smith, 2004b).…”