Europium isotope separation in the HCl/HDEHP extraction system

The^153/151Eu isotope separation factor (q) for the Eu(II)/Eu(III) chemical exchange in the liquid-liquid extraction system, containing Eu (III) in di (2-ethylhexyl) phosphoric acid (HDEHP) and Eu(II) in water acidified with hydrochloric acid, was found to be 0.9993±0.0002 (2) for the single stage. Some theoretical aspects of separation of the Eu isotopes are discussed. The decisive role of the electron exchange reaction and complexation by the counter-ion in the aqueous phase is emphasized.     

Identification of Saturating Solid Phases in the System Ce2(SO4)3-H2O from the Solubility Data

Saturating solid phases, Ce₂(SO₄)₃·hH₂O, with hydrate numbers h equal to 12, 9, 8, 5, 4 and 2, have been identified by critical evaluation of the solubility data in the system Ce₂(SO₄)₃—H₂O over the temperature range 273–373 K. The results are compared with the respective TG—DTA—DSC and X-ray data. The solubility smoothing equations, transition points and solution enthalpy estimators of the identified hydrates are given. The stable equilibrium solid phases are concluded to be only Ce₂(SO₄)₃·9H₂O at 273–310 K, Ce₂(SO₄)₃·4H₂O at 310–367 K and Ce₂(SO₄)₃·2H₂O at 367–373 K. Divergencies of up to 185% in the reported solubility data are mainly due to a variety of metastable equilibria involved in the close crystallization fields, and incorrect assignments of the saturating solid phases. Since a similar variety of the hydrate numbers exists for the analogous La(III) system, it most probably also occurs for the corresponding Pu(III), Np(III) and U(III) systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relationship between the solubilities and separation factors for the co-crystallization of lanthanide ethylsulphates

Co-crystallization coefficients of lanthanide ethylsulphates [Ln(H₂O)₉] (C₂H₅SO₄)₃ were determined and compared with the solubility of these salts. In contrast to the common opinion denying any simple correlation between co-crystallization coefficients and solubilities it was established that a simple relationship does exist for ethylsulphates of light lanthanides. It was concluded that in the case of light lanthanides an almost complete compesation of activity coefficients in the RATNER equation is due to the similar structure of the hydrated cations [Ln(H₂O)₉]³⁺ in both the solid and the aqueous phase. For ethylsulphates of heavy lanthanides such a compensation was not observed, since in this case the cations in the aqueous phase are probably hydrated by 8 water molecules, while in the solid phase the coordination number is still 9. The solubility of Pm, Pu, Am and Cm ethylsulphates was determined by the method “from matrix”. Presented in part at the Italian-Polish Meeting on the Properties and the Development of Methods for Separating Lanthanide Fission Products and Transuranian Elements in Post-Irradiation Analysis of Nuclear Fuels, held in Rome, 19–26 November 1974.     

Solubility equations for the ethylsulphates of trivalent Y,Pm, Pu,Am and Cm as determined by co-crystallization

Assuming that the correlation between the cocrystallization coefficients and solubilities of the co-crystallizing ethylsulphates in the [(Ln,M) (H₂O)₉] (C₂H₅SO₄)₃–H₂O system is valid when M is changed from lanthanides into the title elements, the solubilities of the ethylsulphates of trivalent Y, Pm, Pu, Am and Cm in water at 288–318 K have been determined from the matrix. The solubilities of Y, Pm, Pu, Am and Cm ethylsulphates and of all the lanthanide ethylsulphates are given in the form of smoothing equations of the lg molality=A+B/T type. From the B parameters of the solubility equations the enthalpies of solution have been estimated. The crystallization behaviour of yttrium in the ethylsulphate system is between that of holmium and that of erbium.     

Separation of cerium from other lanthanides by leaching with nitric acid rare earth(III) hydroxide-cerium(IV) oxide mixtures

A simple operational method for separating cerium from other lanthanides in natural mixtures of cerium dioxide with lanthanide(III) hydroxides, obtained from Vietnamese parisite and Mongolian bastnasite, has been developed. The method is based on drying crude Ln(OH)₃×H₂O material in air at about 200°C within 6h, followed by leaching Ln(III) with concentrated nitric acid added carefully with stirring to the dried material/water 11.5 slurry. Under optimum conditions cerium (and Th, if present) virtually does not pass into solution while the yield of leaching and the sum of REE oxides (REO) concentration in the after-leach solution reach the maximum values of 97% (mass) and 0.18 kg·dm^–3, respectively. Besides an expected decrease of the leaching yield, roasting the starting material at 600°C results in over 7% Ce content in the Ln leached.     

Hydrate numbers of scandium sulfate as deduced from solubility data

A simple method for determination of the hydrate numbers of saturating multi-hydrate salts in developed. The method demonstrated for scandium sulfate is based upon estimation of the enthalpy of solution of the hydrates from the solubility smoothing equations. It is shown that in the Sc₂(SO₄)₃–H₂O system, contrary to common opinion, the equilibrium solid phases are: Sc₂(SO₄)₃.6H₂O at 273–295 K, Sc₂(SO₄)₃.5H₂O at 295–333 K and Sc₂(SO₄)₃.4H₂O at 333–373 K. The solubility smoothing equations for the hexa-, penta- and tetrahydrate of scandium sulfate are given.     

Covalency of Sc(III), Y(III), Ln(III) and An(III) as manifested in the enthalpies of solution of anhydrous rare earth halides

The position of scandium and yttrium within lanthanides in respect to the enthalpies of solution of anhydrous rare earth halides has been discussed. It has been indicated that although the respective shift of Sc(III) as a quasi-heavy lanthanide is less pronounced than for Y(III), the overall covalency within the trivalent ions of the scandium group, Ln(III) and An(III) included, is the most pronounced for Sc(III) due to participation of the empty orbitals in bonding: Sc(III)>An(III)>Ln(III)> Y(III). The irregularity of this trend is produced by the superimposed participation of the 5f (An(III)) and, to a lesser extent, of the 4f (Ln(III)) orbitals in bonding. The crucial factor of a maximum difference between the product and substrate coordination number (CN) of the central ion for covalency, separation factor and isotope effect in chemical exchange is emphasized.     

Protonation constants of 1-hydroxyethylidene-1,1-diphosphonic acid, diethylenetriamino-N,N,N',N',N'-penta-acetic trans-1,2-diaminocyclohexane-N,N,N',N'-tetra-acetic acid

The stepwise stability constants for the protonation of hydroxyethylidenediphosphonic acid (HEDP), diethylenetriaminopenta-acetic acid (DTPA) and diaminocyclohexanetetra-acetic acid (DCTA) have been determined potentiometrically with a hydrogen electrode at an ionic strength of 1 (KCl) and at 10-35 degrees . The data were treated by a least-squares method for estimation of DeltaH and DeltaS values.