G.W. Mason

Fractional extraction of the lanthanides as their di-alkyl orthophosphates

Abstract The extraction of lanthanides(III) and yttrium(III) into a solution of di(2-ethyl hexyl) orthophosphoric acid (symbolized as HDEHP) in a carrier solvent from aqueous mineral acid phases has been investigated as a function of HDEHP concentration in the organic phase, mineral acid concentration in the aqueous phase, and Z, using the radioactive-tracer technique and employing americium as a normalizing element. The distribution ratio, K, defined for a given radioactive nuclide as its concentration in the organic phase divided by its concentration in the aqueous phase, has been found to have a direct third-power dependency upon the HDEHP concentration in the organic phase and an inverse third-power dependency upon the mineral acid concentration in the aqueous phase. In experiments involving gross concentrations of extracting cation, it has been shown that none of the anion associated with this cation in the initial aqueous phase reports in the equilibrated organic phase. On the basis of these data, the extracting species has been formulated as M(DEHP)3, possibly with solvate water. Operationally, HDEHP may be considered as the high-acid analogue of thenoyl trifluoroacetone (symbolized as HTTA); and analogously the M(DEHP)3 is tentatively considered to be a chelate complex. A plot of log K vs. Z is well represented by a straight line of positive slope corresponding to an average value of r, defined as the ratio of KZ + 1 to KZ, of 2·5. This average r of 2·5, to be compared with the value of 1·63 as the ratio of molar aqueous solubilities of the dimethyl phosphates of adjacent lanthanides as reported by Marsh , is sufficiently large to make fractionation of lanthanides by liquid-liquid partition an attractive possibility. Successful application of such a technique to a gross sample has been demonstrated. In the plot of log K vs. Z, Y falls on the straight line if given an artificial Z approximately 67·6, as it does in Marshs plot of log molar solubility vs. Z for the lanthanide dimethyl phosphates.

ACIDIC ESTERS OF ORTHOPHOSPHORIC ACID AS SELECTIVE EXTRACTANTS FOR METALLIC CATIONS, TRACER STUDIES

Abstract The extraction of Sc(III), Y(III), La(III), Pm(III), Tm(III), and Am(III) into solutions of (GO)PO(OH) 2 and (GO) 2 PO(OH) in toluene as carrier solvent from aqueous mineral acid phases has been investigated as a function of solvent concentration in the organic phase, hydrogen ion concentration in the aqueous phase, the nature of G, and the position of M(III) in the periodic table, using the radioactive-tracer technique. The distribution ratio, K , defined for a given radioactive nuclide as its concentration in the organic phase divided by its concentration in the aqueous phase, has been found, for all of the M(III) examples studied, to have an inverse third-power dependency upon the hydrogen ion concentration in the aqueous phase in both the (GO)PO(OH) 2 and (GO) 2 PO(OH) systems. The solvent dependencies have been found to be direct first-power in the (GO)PO(OH) 2 systems and direct third-power in (GO) 2 PO(OH) systems. Since the (GO) 2 PO(OH) solvents have been shown to be dimeric, the extracted species is postulated as M III {H[(GO) 2 PO 2 ] 2 } 3 . The (GO)PO(OH) 2 solvents have been shown to be polymeric. A postulated “dimer” mechanism of extraction suggests that the extracted species is M III {H[(GO)PO 3 H] 2 } 3 . However, an alternative suggested “infinite polymer” mechanism of extraction seems equally likely. Specifically, solvents in which G is 2-ethyl hexyl, symbolized as EH, and para (1,1,3,3-tetramethyl butyl)phenyl, symbolized as Oo, have been investigated. In both the (GO)PO(OH) 2 and (GO) 2 PO(OH) systems the Oo solvent shows a higher K than the EH solvent. In the Oo systems, the K S (an empirical stability constant) for the di-ester is higher than that for the mono-ester for each of the members of the vertical group Sc, Y, La, Ac. In the EH systems, the K S for the di-ester is the larger for Sc by a factor of approximately 30 and the smaller for Ac by a factor of approximately 10 −5 . In all of the systems that K (and K S ) values are compressed toward the bottom of the group in the vertical group, Sc, Y, La, Ac, i.e. the ratio of the K (or K S ) of oneelement to that of the element immediately below it decreases downward.

Hydrogen bonding in organophosphoric acids

Association in organophosphoric acids due to hydrogen bonding appears to be stronger than that in monocar☐ylic acids. Molecular weights obtained by freezing-point studies show that the following monobasic phosphoric acids are dimeric in benzene and naphthalene: bis-(2-ethylhexyl), bis-(phenyl), bis-(2,6-dimethylheptyl-4), bis-[p-(1,1,3,3-tetramethylbutyl). The dibasic phosphoric acids, mono-(2-ethylhexyl) and mono-[p-(1,1,3,3-tetramethylbutyl) phenyl] were found to be polymeric in these solvents. Distribution studies of these acids between immiscible organic phases gave additional information as to their states of aggregation, and in addition indicated the strong interaction between these acids and a hydrogen bonding solvent, such as ethylene glycol. Infra-red studies of these acids in carbon tetrachloride show that no non-associated OH spectra appear in the fundamental and overtone regions.

The use of dioctyl phosphoric acid extraction in the isolation of carrier-free 90Y, 140La, 144Ce, 143Pr, and 144Pr☆

Abstract Tracer-level cerium has been oxidized to the tetravalent state and shown to be preferentially extracted from a 10 M HNO3 aqueous phase into a 0·75 M, or 0·30 M, solution of di(2-ethyl hexyl) orthophosphoric acid in n-heptane. In this system the ratio of the K for Ce(IV) to that for Ce(III) is greater than 106, and the K for Ce(IV) is much greater than that for any trivalent lanthanide. This system has been utilized to purify 144Ce with respect to lanthanide contaminants, including its 144Pr daughter, and to prepare a highly-purified gross sample of natural cerium for neutron bombardment in the preparation of 143Pr. It has been used also in the isolation of 143Pr and 144Pr products for tracer studies and for half-life determinations. A decontamination factor, with respect to the parent 144Ce, greater than 107 was obtained for a 144Pr sample isolated and prepared for counting in a period of less than 10 min. Other di(2-ethyl hexyl) orthophosphoric acid systems employing dilute HCl or HNO3 as the opposing phase have been used for separating 90Y from its 90Sr parent and for separating 140La from its 140Ba parent and from contaminant 90Sr90Y. Decontamination factors greater than 107 have been obtained in both separations, the total processing times being less than 15 min. The following new half-life values have been obtained: 90Y, 63·97 ± 0·1 hr; 140La, 40·27 ± 0·05 hr; 143Pr, 13·59 ± 0·04 day; and 144Pr, 17·27 ± 0·04 min.

Selected Alkyl(phenyl)-N,N-dialkylcarbamoylmethylphosphine Oxides as Extractants for Am(III) from Nitric Acid Media

Abstract A new series of neutral bifunctional extractants, alkyl(phenyl)-N,N-dialkylcarbamoylmethylphosphine oxides, has been prepared and studied as extractants for Am(III) from nitric acid media. Two types of alkyl(phenyl)-N,N-dialkyl CMPO compounds were prepared, one containing N,N-diethyl groups and the other containing N,N-diisobutyl groups. The N,N-diethyl series contained hexyl(phenyl) and 6-methylheptyl(phenyl) derivatives, abbreviated HφDECMPO, and 6-MHφDECMPO, respectively. The N,N-diisobutyl series contained the n-octyl(phenyl), 6-methylheptyl(phenyl), and the 2-ethylhexyl(phenyl) derivatives, abbreviated OφD[IB]CMPO, 6-MHφD[IB]CMPO, and 2-EHφD[IB]CMPO, respectively. Third power extractant dependencies for the extraction of Am(III) from 0.5 and 3 M HNO3 were obtained at low (<0.25 M) concentrations of extractant, but higher power dependencies were obtained above 0.25 M extractant from 3 M HNO3. The HφDECMPO, 6-MHφDECMPO, 6-MHφD[IB]CMPO, and OφD[IB]CMPO [all 0.5 M in diethylbenzene (DEB)] are si...

Interrelationships in the solvent extraction behaviour of scandium, thorium, and zirconium in certain tributyl phosphate-mineral acid systems☆

Abstract The extraction behaviour of Sc and that of Th in the aqueous HCl-TBP (tributyl phosphate) system differ sufficiently that these elements are readily separable. Although the respective extraction curves tend to converge as the HCl concentration is lowered, they do not intersect. In contrast, the Sc and Th extraction curves in the HNO3-TBP systems mutually cross. The complete Zr extraction curves have not been determined, but the Zr extraction curve in the HNO3-TBP system is shown to cross both the Sc and Th curves. Consequently, in this system, any one of the three elements may be separated as product from the other two as contaminants. In the HCl-TBP system, the TBP dependency of the extraction coefficients for Sc and Th are not readily interpretable. In the HNO3-TBP system the TBP dependencies are operationally fourth-power at high HNO3 concentrations and considerably less than fourth-power at intermediate and low HNO3 concentrations. The mutual separation of a ThSc mixture and of a ThZr mixture in the HCl-TBP system and the isolation of each of the three elements as product from a ScThZr mixture in the HNO3-TBP system are demonstrated.

Stability constants of certain lanthanide(III) and actinide(III) chloride and nitrate complexes

Abstract By means of acid-dependency studies, the extractant di[para(1,1,3,3-tetramethylbutyl)phenyl] phosphoric acid, HDOΦP, in toluene as a carrier diluent has been shown to extract M(III) lanthanides and actinides from aqueous perchlorate, chloride and nitrate media as species containing none of the anions present in the aqueous phase. Consequently, extraction of M(III) lanthanides and actinides from mixed perchlorate-chloride and from mixed perchlorate-nitrate aqueous phases may be used to determine the stability constant, k c , for MCl 2+ and M(NO 3 ) 2+ . The k c values, at 22±1° C, μ = 1·0, so determined are: MCl 2+ , La(0·9 ± 0·3), Ce(0·9 ± 0·3), Pr(0·9 ± 0·3), Eu(0·9 ± 0·3), Tm(0·8 ± 0·3), Yb(0·6 ± 0·2), Lu(0·4 ± 0·2), Am(0·9 ± 0·2); M(NO 3 ) 2+ , La(1·3 ± 0·3), Ce(1·3 ± 0·3), Pr(1·7 ± 0·3),Eu(2·0 ± 0·3), Tm(0·7 ± 0·2), Yb(0·6 ± 0·2), Lu(0·6 ± 0·2), Am(1·8 ± 0·3).

Isolation of berkelium by solvent extraction of the tetravalent species

Abstract Data for the extraction of Cm(III), Bk(III), and Bk(IV) into a n -heptane solution of di(2-ethyl hexyl) orthophosphoric acid from various aqueous nitric acid phases are presented. The K value for Bk(IV) is greater than that for Bk(III) or Cm(III) by a factor approaching 10 6 . Under the oxidizing conditions used, Am remains in the trivalent state. A flow sheet utilizing this solvent extraction system and involving both the trivalent and tetravalent states of Bk has been devised. Using a raw berkelium fraction, isolated in the preliminary processing of an exhaustively neutron-irradiated plutonium sample, as feed, a Bk 249 product was isolated in approximately 97% yield with established alpha decontamination factor and beta decontamination factor of approximately 6 × 10 3 and 9 × 10 5 respectively. The total processing time, exclusive of evaporation, was less than 30 min. In an experiment involving the same flow sheet and a synthetic feed, it was demonstrated that Bk may be separated rapidly and satisfactorily from all of the following: La, Pm, Eu, Y, U, Np, Pu, Am, and Cm. Elements of Z greater than 97 were not available for testing, but it appears certain that Bk would be satisfactorily separated from any of these present in the trivalent state. It is suggested that this solvent-extraction procedure should be useful not only for the isolation of Bk from source materials, but also in milking experiments in which a Bk isotope is either the mother or daughter, especially in studies in which one or more of the nuclides involved is short-lived.

Extraction of thorium(IV) by di esters of orthophosphoric acid, (GO)2PO(OH)☆

The extraction of tracer-level Th(IV) into solutions of (GO)2PO(OH), symbolized as HDGP, in toluene as carrier solvent, where G is 2-ethylhexyl, (EH), and para(1,1,3,3-tetramethyl butyl)phenyl, (OΦ), from aqueous perchlorate, chloride and nitrate solutions has been investigated. The distribution ratio, K, has been shown to vary directly with the third power of the stoicheiometric concentration of extractant in the solvent phase (third-power solvent dependency) and inversely with the fourth power of the stoicheiometric hydrogen ion concentration in the aqueous phase (inverse fourth-power acid dependency) for the di[para(1,1,3,3-tetramethyl butyl)phenyl] phosphoric acid systems. The di(2-ethylhexyl) phosphoric acid systems display a more complicated behaviour, the K being third-power solvent dependent in each of the aqueous systems, but inverse third-power acid dependent in the nitrate systems and inverse fourth-power acid dependent in the perchlorate and chloride systems at low acidities ranging to nearly inverse third-power acid dependent at high acidities. The extracted entities are formulated as Th(DOΦP)2[H(DOΦP)2]2, Th(DEHP)2[H(DEHP)2]2 and Th(DEHP)[H(DEHP)2]2X, where X is nitrate, chloride and probably perchlorate, and tentatively postulated as co-ordination complexes of co-ordination number six. The effect of the corresponding mono esters as contaminates is discussed.

Molecular weight studies of several organophosphorus acids

Abstract Molecular weight studies of several organophosphorus acids of the types (GO)2PO(OH), (GO)G′PO(OH) and (GO)PO(OH)2 have been made in several solvents, using an isothermal distillation method. In general, the monobasic acids are dimers in solvents such as n-hexane, cyclohexane, benzene and carbon tetrachloride; monomers in methyl alcohol; and intermediate in chloroform and acetone. Mono-(2-ethylhexyl)phosphoric acid is highly polymeric in n-hexane and cyclohexane, the molecular weight being 8–14·5 times the formula weight; hexameric in benzene and carbon tetrachloride; dimeric in acetone; and monomeric in methyl alcohol. The change in state of aggregation, for both the mono and dibasic acids, as the diluent is varied, parallels the predicted variation in solute-solvent interaction.