Countercurrent Actinide Lanthanide Separation Process (ALSEP) Demonstration Test with a Simulated PUREX Raffinate in Centrifugal Contactors on the Laboratory Scale

An Actinide Lanthanide Separation Process (ALSEP) for the separation of trivalent actinides (An(III)) from simulated raffinate solution was successfully demonstrated using a 32-stage 1 cm annular centrifugal contactor setup. The ALSEP solvent was composed of a mixture of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and N,N,N′,N′-tetra-(2-ethylhexyl)-diglycolamide (T2EHDGA) in n-dodecane. Flowsheet calculations and evaluation of the results were done using the Argonne’s Model for Universal Solvent Extraction (AMUSE) code using single-stage distribution data. The co-extraction of Zr(IV) and Pd(II) was prevented using CDTA (trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid) as a masking agent in the feed. For the scrubbing of co-extracted Mo; citrate-buffered acetohydroxamic acid was used. The separation of An(III) from the trivalent lanthanides (Ln(III)) was achieved using citrate-buffered diethylene-triamine-N,N,N′,N″,N″-pentaacetic acid (DTPA), and Ln(III) were efficiently back extracted using N,N,N′,N′-tetraethyl-diglycolamide (TEDGA). A clean An(III) product was obtained with a recovery of 95% americium and curium. The Ln(III) were efficiently stripped; but the Ln(III) product contained 5% of the co-stripped An(III). The carryover of Am and Cm into the Ln(III) product is attributed to too few actinide stripping stages, which was constrained by the number of centrifugal contactors available. Improved separation would be achieved by increasing the number of An strip stages. The heavier lanthanides (Pr, Nd, Sm, Eu, and Gd) and yttrium were mainly routed to the Ln product, whereas the lighter lanthanides (La and Ce) were mostly routed to the raffinate.

Structural Systematics of Lanthanide(III) Picrate Solvates: Hexamethylphosphoramide and Octamethylpyrophosphoramide Adducts

Crystalline products of the reactions of lanthanide picrates, Ln(pic)3 (pic=2,4,6-trinitrophenoxide), with hexamethylphosphoramide (hmpa) and octamethylpyrophosphoramide (ompa) have been characterised by single-crystal X-ray diffraction studies. With hmpa and lighter lanthanides (La, Sm, Eu), isomorphous species (monoclinic, P21/c, Z 4) of stoichiometry [Ln(pic)3(hmpa)3]·0.5H2O, have been defined where the molecular units in the lattice contain 9-coordinate Ln with tricapped trigonal-prismatic coordination geometry. The picrate ligands are bidentate through phenoxide-O and 2-nitro-O, with the latter occupying the capping positions, while the hmpa ligands are singly O-bound to one trigonal face. Heavier lanthanides (Gd, Lu) and Y have been found to give isomorphous (monoclinic, P21/n, Z 4) species of stoichiometry [Ln(pic)3(hmpa)2], with 8-coordinate Ln of an irregular geometry best considered as close to that of a bicapped trigonal-prism. The picrate ligands chelate in the same manner as in the lighter Ln complexes but with one spanning a trigonal edge, and the hmpa-O donors occuping two apices of the other trigonal face. The ligand ompa has been found to act as a bidentate chelate in all isolated species, displacing one picrate from the metal ion coordination sphere to give ionic complexes. For La, Nd, and Gd, isomorphous (monoclinic, P21/n, Z 4) complexes of stoichiometry [Ln(pic)2(ompa)2(OH2)](pic)·0.5H2O containing 9-coordinate, tricapped trigonal-prismatic Ln with a single aqua ligand have been defined, while for Er, Yb, Lu, and Y, both the coordinated and lattice water molecules are lost in isomorphous (monoclininc, P21/c, Z 8) 8-coordinate, square-antiprismatic species of stoichiometry [Ln(pic)2(ompa)2](pic). For Er, further polymorphs, one monoclinic, P21/c, and the other triclinic, , have also been characterised.

Minerals-concentrators of rare-earth elements in basites-ultrabasites intrusives of Norilsk district

The conditions of being, the history of formation and transformation of minerals-concentrators of rare-earth elements (REE) - apatite minerals group and epidote minerals group, have been studied and described. Allanite has been determined to be mostly developed in the halos of the fluid action a solid contact of sulfide ores containing rich pneu matolytic mineralization of the platinum-group elements (PGM) and gold. Apatite and allanite are found among sulfides and in rims of the fluid action over the drops of sulphides in the horizon of the disseminated ores. The composition of Apatite-I has evolved from a OH-containing chlorapatite to chlorapatite containing up to 2,3 wt. % of lanthanides; Apatite-II - from OH-Cl-bearing fluorapatite to fluorapatite. The lanthanides reieased during replacement of chlorapatite-I by fluorapatite-II, probably entering the composition of the produced pneumatoiytic alianite-(Ce). In the areas of mineral ores with imposed metamorphism, the pneumatoiytic apatite partially or totally is substituted by hydroxyapatite-III, allanite - by water-containing allanite with the content of the epidote and clinozoisite minals - 30-35 mol. %. The spectra of REE distribution in apatite have been determined to reflect more accurately their ratios in rocks, the spectra of REE distribution for allanite are characterized by a steeper slope from lighter to heavier lanthanides. The ratio of La, Ce and Nd in chlorapatite corresponds to the distribution of these elements as in the host picrite horizon, as well in the rocks of the intrusives as a whole. Allanite, in return, is more enriched in cerium and lanthanum and depleted in neodymium.

Adducts of aqua complexes of Ln3+ with a di-hydroxylated symmetrical octamethyl-substituted cucurbituril: potential applications for isolation of heavier lanthanides

In the present work, we have demonstrated that t(OH)2OMeQ[6] could be used for isolating heavy lanthanides from their lighter counterparts.

Coordination of Ln3+ in ortho-tetramethyl-substituted cucurbituril supramolecular assemblies formed in the presence of cadmium nitrate: potential applications for isolation of heavier lanthanides

Coordination in supramolecular assemblies was investigated by reacting a series of lanthanide cations (Ln3+) and a new alkyl-substituted cucurbituril, (o-TMeQ[6]).