97 research outputs found
SANS study of dialkylsubstituted diphosphonic acids and their complexes with Ca, Fe, La, Th and U in toluene
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An application of supported liquid membranes for removal of inorganic contaminants from groundwater
This review paper summarizes the results of an investigation on teh use of supported liquid membranes for the removal of uranium (VI) and some anionic contaminants (technetium(VII), chromium(VI) and nitrates) from the Hanford site groundwater. As a membrane carrier for U(VI), bis(2,4,4-trimethylpentyl)phosphinic acid was selected because of its high selectivity over calcium and magnesium. The water soluble complexing agent 1-hydroxyethane-1,1-diphosphonic acid was used as stripping agent. For the anionic contaminants the long-chain aliphatic amines Primene JM-T (primary)., Amberlite LA-1 (secondary) and trilaurylamine (tertiary) were investigated as membrane carriers. Among these amines, Amberlite LA-2 proved to be the most effective carrier for the simultaneous removal of the investigated anion contaminants. A good long-term stability (at least one month) of the liquid membranes was obtained, especially in the uranium(VI) removal. 8 refs., 4 figs., 4 tabs
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Uptake of actinides and other ions by Diphosil, a new silica-based chelating ion exchange resin
After adsorption of actinides on a phosphonic acid resin, it may be desirable to leave the actinides on the resin. It may be preferable that the polymeric resin matrix be replaced by an inorganic material, in order to prevent formation of radiolytic gases from the organic polymer. A new version of the Diphonix resin has been prepared, where the chelating diphosphonic acid groups are grafted to a silica support. This material is called Diphosil, for Diphonix on silica. This paper reports some results on equilibrium and kinetics of uptake of a number of actinide species and other metal ions of nuclear, environmental, or hydrometallurgical interest by Diphosil
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Aggregation of dialkyl-substituted diphosphonic acids and its effect on metal ion extraction.
Solvent extraction reagents containing the diphosphonic acid group exhibit an extraordinary affinity for tri-, tetra- and hexavalent actinides. Their use has been considered for actinide separation and pre-concentration procedures. Solvent extraction data obtained with P,P{prime}-di(2-ethylhexyl) methane-, ethane- and butanediphosphonic acids exhibit features that are difficult to explain without Knowledge of the aggregation state of the extractants. Information about the aggregation of the dialkyl-substituted diphosphonic acids in aromatic diluents has been obtained using the complementary techniques of vapor pressure osmometry (VPO), small angle neutron scattering (SANS), infrared spectroscopy and molecular mechanics. The results from these techniques provide an understanding of the aggregation behavior of these extractants that is fully compatible with the solvent extraction data. The most important results and their relevance to solvent extraction are reviewed in this paper
Organic and Third Phase in HNO3/TBP/n-Dodecane System: No Reverse Micelles
The composition and speciation of the organic and third phases in the system HNO3/TBP (tri-n-butyl phosphate)/n-dodecane have been examined by a combination of gravimetric, Karl Fischer analysis, chemical analysis, FTIR, and 31P NMR spectroscopy, with particular emphasis on the transition from the two-phase to the three-phase region. Phase densities indicate that third-phase formation takes place for initial aqueous HNO3 concentrations above 15 M, while the results from the stoichiometric analysis imply that the organic and third phases are characterized by two distinct species, namely the mono-solvate TBP⋅HNO3 and the hemi-solvate TBP⋅2HNO3, respectively. Furthermore, the 31P NMR spectra of organic and third phase show no significant chemical differences at the phosphorus centers, suggesting that the second HNO3 molecule in the third phase is bound to HNO3 rather than TBP. The third-phase FTIR spectra reveal stronger vibrational absorption bands at 1028, 1310, 1653, and 3200–3500 cm−1, reflecting higher concentrations of H2O, HNO3, and TBP. The molecular dynamics simulation data predict structures in accord with the spectroscopically identified speciation, indicating inequivalent HNO3 molecules in the third phase. The predicted structures of the organic and third phases are more akin to microemulsion networks rather than the distinct, reverse micelles assumed in previous studies. H2O appears to be present as a disordered hydrogen-bonded solvate stabilizing the polar TBP/HNO3 aggregates in the organic matrix, and not as a strongly bound hydrate species in aggregates with defined stoichiometry
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Synergistic effects in the extraction of metal ions by mixtures of dialkylphosphoric acids and substituted crown ethers.
The extraction of alkaline earth cations from weakly acidic solutions by three dialkylphosphoric acids and various isomers of dicyclohexano-18-crown-6, both alone and in combination in toluene solutions, has been examined to determine the effect of both the crown ether stereochemistry and the structure of the organophilic anion on the magnitude of the synergistic effects. The synergistic effects have been found to differ considerably among the crown ether isomers and to vary with the extent of alkyl chain branching in the dialkylphosphoric acid. Attempts to correlate the synergistic effects with ligand strain energies from molecular mechanics calculations are described
Transfer rate of some tervalent cations in the biphasic system HClO4, water-dinonylnaphthalenesulfonic acid, toluene—II
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Thermodynamics of the extraction of selected metal ions by Di(2-ethylhexyl) alkylenediphosphonic acids.
The thermodynamics of extraction of Am(III), Sr(II) and U(VI) from aqueous HNO{sub 3} solutions by o-xylene solutions of p,p'-de(2-ethylhexyl) methylene- (H{sub 2}DEH[MDP]), ethylene-(H{sub 2}DEH[EDP]), and butylene- (H{sub 2}DEH[BuDP]) disphosphonic acids has been studied by the temperature coefficient method in the 25.0 to 60.0 C range. Both extractive aggregation and extraction stoichiometries did not change with temperature. The extraction of Am(III) by H{sub 2}DEH[MDP], and that of U(VI) by all three extractants are strongly driven by both enthalpy and entropy variations. The extraction of Sr(II) by H{sub 2}DEH[MDP] is enthalpy driven. The extraction of Am(III) by H{sub 2}DEH[EDP] and H{sub 2}DEH[BuDP] is mainly driven by entropy changes. The extraction of Sr(II) by H{sub 2}DEH[EDP] and H{sub 2}DEH[BuDP] is characterized by an unfavorable entropy change and is not indicative of a micellar-type extraction mechanism
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Double liquid membrane system for the removal of actinides and lanthanides from acidic nuclear wastes
Supported liquid membranes (SLM), consisting of an organic solution of n-octyl-(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and tributyl-phosphate (TBP) in decalin are able to perform selective separation and concentration of actinide and lanthanide ions from aqueous nitrate feed solutions and synthetic nuclear wastes. In the membrane process a possible strip solution is a mixture of formic acid and hydroxylammonium formate (HAF). The effectiveness of this strip solution is reduced and eventually nullified by the simultaneous transfer through the SLM of nitric acid which accumulates in the strip solution. A possible way to overcome this drawback is to make use of a second SLM consisting of a primary amine which is able to extract only HNO/sub 3/ from the strip solution. In this work the results obtained by experimentally studying the membrane system: synthetic nuclear waste/CMPO-TBP membrane/HCOOH-HAF strip solution/primary amine membrane/NaOH solution, are reported. They show that the use of a second liquid membrane is effective in controlling the HNO/sub 3/ concentration in the strip solution, thus allowing the actinide and lanthanide ions removal from the feed solution to proceed to completion. 15 refs., 10 figs., 1 tab
Extraction Kinetics of Iron(III) from Aqueous Nitrate Solutions to Toluene Solutions of Tri-n-butylacetohydroxamic Acid
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