Lanthanides elution

Elution of the heavy lanthanide ferns from cation exchange corumn using ammonium 3-hydroxyisobutyratc as the eluent Note that the higher atomic number lanthanides elute first because they have smaller radii and are more strongly complied by the ammonium 2-hydroxyiso butyrate. 

Averaged values for the separation factors for adjacent pairs of lanthanides eluted with EDTA and its homologues are given in Table 1.21. The separation factors are in the range of 1.5 to 3.5 showing considerable improvement in separation factors. In the majority of cases, the separation factors with EDTA as an eluant are greater than the values obtained in methanol-nitric acid medium, which is expected based on the stability constant data for rare earth EDTA complexes. 

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

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 most important minerals of the lanthanide elements are monazite (phosphates of La, Ce, Pr, Nd and Sm, as well as thorium oxide) plus cerite and gadolinite (silicates of these elements). Separation is difficult because of the chemical similarity of the lanthanides. Fractional crystallization, complex formation, and selective adsorption and elution using an ion exchange resin (chromatography) are the most successful methods. 

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 ... 

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). 

The mixed lanthanide (III) ions (Ln3+) can be absorbed from solution at the top of a column of a cation-exchange resin RSOsNa (Section 14.4) and then selectively eluted from it, that is, swept down the column in bands by a stream of a solution of a substance that competes with the Ln3+ for sites in the resin. An acidic tribasic chelating agent H3X (usually citric acid/sodium citrate buffer) is used so that, as in reaction 17.16, the tendency for a specific Ln3+ to form neutral LnX and so escape the electrostatic... 

Lu3+ > Yb3+ >. .. > Ce3+ > La3+. More strongly bound cations require a higher concentration of H+ to be eluted. The order of selectivity coefficients for lanthanides on this column is the reverse of the order listed on page 592. 

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. 

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

The other metal ions that exhibited an appreciable reaction with Arsenazo(III) at 650nm under the separation and detection conditions used, were iron(III), zirconium(IV), thorium(IV) and the lanthanides. The lanthanides, iron(III) and zirconium(IV) were eluted at or near the solvent front before uranium(VI) and thorium(IV) was eluted after uranium(VI). 

The LiCl AIX process is based on (i) the formation of anionic chloride complexes of the tripositive actinide and lanthanide metals in concentrated LiCl solutions, (ii) the sorption of these complexes onto a strong base anion exchange resin contained in a column, and (iii) the preferential chromatographic elution of the lanthanides as a group prior to elution of the actinides. The generalized formation of the trivalent metal anionic chloride complexes is illustrated in equation (1) ... 

Elution. In general, the lanthanides are eluted first, using four column volumes of 10 M LiCl then, 90-95% of the americium and curium is eluted, using three column volumes of 9 M LiCl. The remainder of the americium and curium is eluted along with all of the heavier actinides, using two column volumes of 8 M HCl. 

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