J.E. Powell

Cation-exchange elution sequences—I Divalent and rare-earth cations with EDTA, hedta and citrate☆

Abstract Ion-exchange elution sequences were established for some divalent and trivalent ions in elutions with those eluants commonly used for the separation of macroquantities of the rare-earth elements-ethylenediaminetetraacetic acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA) and citric acid. The order of elution of the sequence of trivalent metal ions was found to shift with respect to the sequence of divalent metal ions when the of the EDTA eluant was changed and as the composition of the separating mixture changed. A theory is presented which is of qualitative value as an aid in the description of the elution of polyvalent cation mixtures with chelating eluants.

Stability trends of 1:1 and 2:1 dialkylmalonato rare-earth chelates

Abstract The step-formation constants of the 1 : 1 and 2 : 1 malonato, diethylmalonato, di- n -propylmalonato and di- n -butylmalonato rare-earth and yttrium chelates were determined at ionic strength 0·100 (KNO 3 ) at 25·0°C by a potentiometric method. The first and second ionization constants of the ligand acids were also measured. The trend of the first formation constants with cationic radius, observed with the lanthanide malonates, is followed in the case of the dialkylsubstituted rare-earth malonates. Stability increases with complexity of the substituents, although the dimethylmalonate ligand exhibits less affinity for rare-earth cations than malonate itself. The trends manifested by the second constants are less regular. A curious odd-even stability differential is apparent in these systems with the heavier rare earths (TbLu). The differential is apparent in both b 1 , and b 1 and the cumulative effect in β 2 values is sufficient to cause reversal of the usual ion-exchange elution order in the case of the YbLu and the DyHo pairs when ammonium malonate buffer is the eluant on Dowex 50-X8.

The solubilities of lanthanum chloride 7-hydrate and lanthanum chloride 6-hydrate in water, and a study of the thermal decomposition of hydrated lanthanum chloride☆

Abstract Thermal decomposition of LaCl 3 7H 2 O results in the stepwise formation of LaCl 3 3H 2 O, LaCl 3 ·H 2 O, LaCl 3 and LaOCl. Under proper conditions either LaCl 3 6H 2 O or LaCl 3 7H 2 O may separate from aqueous solutions of lanthanum chloride. The solubilities of the 6- and 7-hydrates at various temperatures are given.

SUCCESSIVE DETERMINATION OF THORIUM AND RARE EARTHS BY COMPLEXOMETRIC TITRATIONS

Abstract Thorium can be determined quantitatively by EDTA in the presence of the light rare earths but not in the presence of the heavy rare earths. The successive determination of thorium and heavy rare earths with diethylenetriaminepenta-acetic acid (DTPA) has been found to be feasible and is described. The direct successive determination of thorium and rare earths by combined titration with DTPA and N -yethylethylenediaminetriacetic acid (HEDTA) is also discussed.

AUGMENTING THE SEPARATION OF ADJACENT PAIRS OF RARE EARTHS IN ELUTIONS WITH HYDROXYETHYLETHYLENEDIAMINETRIACETATE (HEDTA).

Abstract Rare-earth mixtures have been eluted with ammonium HEDTA at 92° with substantial gains in the separation of ErHo, HoDy, DyTb and TbGd pairs. Individual stability constants at 92° have been derived from the observed separation factors, and a simple mechanism has been proposed to account for a drastic drop in chelate stability which occurs when only the lighter rare-earth chelate species are heated from 15° to 92°. A scheme for economical recovery of pure yttrium from yttrium-lanthanide mixtures is discussed.

Displacement ion-exchange separation of ternary rare earth mixtures with chelating eluants

Abstract The separation of a ternary fixture of rare earths by displacement cation-exchange chromatography with chelating eluants can be described by constructing a distance-time diagram. The original composition of the mixture and the separation factors are the only inputs to the calculation. The points of complete separation each of the three components or the point of any partial separation can be determined. Two methods of operation are considered, viz. loading of the uncheated mixture prior to elution, and chelation of the mixture prior to its introduction to the resin.

Elution requirements for the resolution of ternary rare-earth mixtures

Abstract The treatment employed by Powell and Spedding to establish the minimum number of displacements by displacement chromatography needed to resolve the components of binary rare-earth mixtures has been extended rigolously to the case of ternary mixtures.

Structural influences on the lanthanide-actinide selectivity of some aminocarboxylates

Abstract Data for the resolution of americium from europium and terbium using 2,2′-diaminodiethylether-N,N,N′,N′-tetraacetate and 1,5-diaminopentane-N,N,N′,N′-tetraacetate are reported along with values of the formation constants of the La-Lu and Y chelates of the latter. It is shown that the minimum single-stage separation factor for Am 3+ from Ln 3+ cations, using 2,2′-diaminodiethylether-N,N,N′,-N′-tetraacetate with Dowex 50 resin, exceeds 1.7 for all Am-Ln pairs, and runs as high as 350 in the case of Am 3+ , La 3+ . The minimum of 1.7 occurs at Eu 3+ in the lanthanon sequence. A novel separation of Am 3+ , Cm 3+ and heavier actinons from each other and from all the lanthanons and yttrium appears to be feasible.

Formation constants of protonated and lanthanon N′-methylethylenediamine-N,N,N′-triacetate species

Abstract Formation constants of protonated and chelate species formed between hydrogen ion and rare-earth cations and the anion of the recently synthesized N′-methylethylenediamine-N,N,N′-triacetic acid were determined at an ionic strength of 0.100 M (KNO3) and 25° by a potentiometric method.

Application of ion-exclusion and ion-exchange techniques in preparing 2,3-dihydroxy-2-methylbutanamide and 2,3-dihydroxy-2-methylbutanoic acid from acetoin via the cyanohydrin synthesis

Abstract The techniques of ion exclusion and ion exchange have been exploited to obtain substantial yields of 2,3-dihydroxy-2-methylbutanamide and 2,3-dihydroxy-2-methylbutanoic acid, respectively, following acid hydrolysis of acetoin cyanohydrin. The reaction of acetoin with anhydrous HCN appears to be stereospecific, since the overall process yields an unexpectedly high percentage of only one of two possible diastereomeric dl -acid mixtures, namely, the racemate comprised of (2S,3R)-2,3-dihydroxy-2-methylbutanoic and (2R,3S)-2,3-dihydroxy-2-methylbutanoic acids.