Actinide elution

Epov et al. used TEVA-Resin in the isolation of Pu for the analysis of Pu in the presence of much higher U concentrations, using the FIAS-400 fluidic system.50 These authors also selected ascorbic acid to adjust the valence state of Pu to Pu(IV). Samples were loaded and washed in 4 M HN03, removing the trivalent actinides. Elution with 1 M HN03 removed most U and some Th. Finally, 0.02 M HC1 was... 

ACTINIDE ELUTION FROM CATION EXCHANGE RESIN - DOWNFLOW MODE... 

The points for the Pu species have been connected to make a crude elution positon vs HCl concentration plot. The extreme decrease of the PuQV) elution position in going from 3.2 to 9.3 M HCl is undoubtedly due to the formation of an anionic chloride complex. The tetravalent actinides elute in this sequence Pu, Np, U, Th i. e., Th has the highest distribution coefficient at any HCl concentration. This order of elution is in accord with the decreasing hydrated radii in going from Pu to Th. Th(IV) was not... 

Ion exchange (qv see also Chromatography) is an important procedure for the separation and chemical identification of curium and higher elements. This technique is selective and rapid and has been the key to the discovery of the transcurium elements, in that the elution order and approximate peak position for the undiscovered elements were predicted with considerable confidence (9). Thus the first experimental observation of the chemical behavior of a new actinide element has often been its ion-exchange behavior—an observation coincident with its identification. Further exploration of the chemistry of the element often depended on the production of larger amounts by this method. Solvent extraction is another useful method for separating and purifying actinide elements. 

Fig. 3. The elution of tnpositive actinide and lanthanide ions. Dowex-50 ion-exchange resin was used with ammonium a-hydroxyisobutyrate as the eluant.

Actinide ions of the 111, IV, and VI oxidation states can be adsorbed by cation-exchange resins and, in general, can be desorbed by elution with chloride, nitrate, citrate, lactate, a-hydroxyisobutyrate, ethylenediaminetetraacetate, and other anions (11,12). 

Ion-exchange separations can also be made by the use of a polymer with exchangeable anions in this case, the lanthanide or actinide elements must be initially present as complex ions (11,12). The anion-exchange resins Dowex-1 (a copolymer of styrene and divinylben2ene with quaternary ammonium groups) and Amherlite IRA-400 (a quaternary ammonium polystyrene) have been used successfully. The order of elution is often the reverse of that from cationic-exchange resins. 

The applications of ion-exchange chromatography are exemplified by the selection shown in Table 4.18. Among the most notable are the separation of lanthanides and actinides using a citrate, lactate or EDTA eluting agent ... 

The transuranium elements are also separated from each other by these means (115), (122), (136) and their order of elution from the columns, which, like the rare-earths, is a function of their atomic number, has been used as important evidence of the identity of the new elements (123). Separation from the rare-earths is not possible, however, as their elution peaks coincide with those of the actinides. This separation can be made, however, using hydrochloric acid as the elutriant. The actinides form anionic chloride complexes more readily than the rare-earths and are consequently more readily removed from the cationic resin (114). 

Wish, L., E. C. Freiling and R. Bunney Ion-Exchange as a Separation Method. VIII. Relative Elution Position of Lanthanide and Actinide Elements with Lactic Acid Eluant at 87° C. J. Amer. chem. Soc. 76, 3444 (1954). 

Under given conditions, colloids do not have an impact on the migration of Sr(II), U(VI) and Np(V), which display only weak or no interaction with the colloids. While Sr(II) migrates as a weak sorbing tracer, the oxidized actinides U(VI) and Np(V) are partly eluted together with the conservative tracer, that is, without retardation. A second part of U(VI) and Np(V) appears slightly retarded probably due to the weak reversible interaction with surfaces of the fracture infill. 

Rg-14.11 Elution of IrivaJcm lanthanide and jctirade ions on a Dowex 50 canon-exchange resin with an ammonium o-hydroxyi obuiyrate eluant. The band for Lr3 is predicted. (From Katz. J. J. Morss, L. R.. Seaborg. G. T. In The Chemistry of the Actinide Elements Katz. J. J. Morss. L. R. Seaborg)... 

This paper describes a new reaction which may yield useful amounts of the product isotope following neutron capture by lanthanide or actinide elements. The trivalent target ion is exchanged into Linde X or Y zeolite, fixed in the structure by appropriate heat treatment, and irradiated in a nuclear realtor. The (n, y) product isotope, one mass unit heavier than the target, is ejected from its exchange site location by y recoil. It may then be selectively eluted from the zeolite. The reaction has been demonstrated with several rare earths, and with americium and curium. Products typically contain about 50% of the neutron capture isotope, accompanied by about 1% of the target isotope. The effect of experimental variables on enrichment is discussed. 

The amount of unreacted target element that eluted was determined by measuring its radioactivity directly in the case of actinides, and by activation analysis in the case of lanthanides. The distribution of the radioactive neutron capture product was determined by counting both the eluate and the eluted zeolite. All irradiations were done in the Oak Ridge Research reactor in a pneumatic tube facility with a thermal neutron flux of about 4 X 1013 neutrons cm-2 sec-1 or, for a few long irradiations, in a tube adjacent to the reactor core at the fluxes stated in Table VI. 

Actinides, unlike lanthanides, are a emitters. Tests made with 243Am, 241Am, and 244Cm, which have a radiation intensities (or a decay constants) in the ratio 1 17 435, gave very similar results in regard to both target elution and product yield. Therefore, if a radiation is responsible for the difference, the effect is independent of a intensity. 

Thiocyanate. — On the basis of /-orbital hybridization Diamond [351] predicted the formation of stronger actinide complexes with thiocyanate ion than for the rare earths. Subls and Chopfin [352] have studied the ion exchange behaviour of many actinide and rare earth thiocyanate complexes and have shown that europium is eluted much sooner than americium from Dowex-1 with ammonium thiocyanate. The stability constants for the formation of MSCN2+ and M(SCN)2 complexes for Nd3+, Eus+, Pu3+, Am3+, Cm3+, and Cf34 have been measured [353] and are tabulated in Table 25. It is apparent from the table that the formation... 

The first aqueous chemistry of mtherfordium showed that it eluted from liquid chromatography columns as a 4 + ion, consistent with its position in the periodic table as a d-block element rather than a trivalent actinide. Gas chromatography of the mtherfordium halides has shown the volatility sequence ZrCl4 > RfCLt > HfCl4 with a similar sequence for the tetrabromides (Fig. 15.16). Thus, mtherfordium does not follow the expected periodic table trend nor is its behavior in accord with relativistic calculations. 

Figure 19.6 Elution of tripositive lanthanide and actinide ions on Dowex-50.

Actinides can be separated from matrix elements, other radionuclides, and each other using extraction-chromatographic materials such as TEVA-Resin, TRU-Resin, and UTEVA-Resin. The capacity factors for various actinides on these resins, as a function of nitric or hydrochloric acid concentrations are shown in Figures 9.11 and 9.12.30 31127 Elution peaks or collected fractions from column separations can be... 

Using the renewable separation-column approach, TRU-Resin can be used to conduct Am-Pu separations without the need to elute the remaining actinides off the resin.83 Instead, the resin could simply be replaced prior to the next sample. In addition, it was shown that TRU-Resin could be automatically loaded into a separation column as part of an open-architecture radiochemical separation workstation, where the instrument would load the desired separation material, and then select reagents appropriate to the separation desired, all under computer control according to the operator s needs for the sample at hand.83... 

Hang et al. used a HPIC instrument to create a FI separation system that was coupled to ICP-MS, as shown in Figure 9.16.60 They packed a 30-cm column with TRU-Resin, which is a much longer TRU-Resin column than would normally be used for actinide separations. Water and diluted urine samples were loaded and washed in 3 M HN03. Gradient elution from 1.0 M HC1-0.032 M oxalic acid to 0.01 M HC1-0.032 M oxalic acid released Np, Am, and Pu. Subsequent elution with additional 0.01 M HC1-0.032 M oxalic acid released Th and U. This procedure separated actinides according to valence states, with the retention order V < III < IV < VI, and hence with release in the order Np(V), Am(III), Pu(IV), Th(IV), and... 

U(VI). The long separation column—preconditioned, loaded, and washed with 3 M HN03—was credited with the apparent retention of Np(V) and Am(III) under this elution program. These authors also examined UTEVA-Resin for this actinide analysis application but concluded that TRU-Resin was to be preferred for retention of actinides from urine. 

The TRU-Resin column served to preconcentrate the actinide of interest from urine or digested urine samples. Methods were developed for the analysis of Pu in urine, Am in urine, as well as U and Th in urine. After column washing, the actinides were eluted in a single step, using ethylenediaminetetraacetic acid for Am or Pu, and ammonium bioxalate for the U/Th determinations. Column reusability was quite limited if urine samples were not digested first. 

The Dipex extractant shown in Scheme 9.1, as actinide-Resin, has not been used in an automated separation scheme. With two phosphoryl groups, this extractant is very effective at retaining actinides, but it is difficult to recover them by elution. For laboratory analysis, schemes have been developed to strip the extractant from the resin after capturing the actinides.151... 

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