SOLVENT EXTRACTION OF URANIUM( VI) AND THORIUM( IV) FROM NITRATE MEDIA BY CARBOXYLIC ACID AMIDES

ABSTRACT

A series of nineteen N-alkyl carboxylic acid amides (R.CO.NHR') has been prepared, in which the alkyl groups R and R' have been varied in order to introduce different degrees of steric complexity into the compounds. A smaller number of N,N-dialkyl amides (R.CO.NR₂) and non-substituted amides (R.CO.NH₂) has also been prepared for comparison purposes. These amides were characterized by measurement of their boiling points, melting points, refractive indices and densities.|The solvent extraction of uranium(VI) and thorium(IV) from sodium nitrate media by solutions of the amides in toluene was studied. Increasing steric bulk of the alkyl groups R and R' was found to cause a marked decrease in the extraction of thorium, with a much smaller effect on the extraction of uranium, thus considerably enhancing the separation between these metals. Vapour pressure osmometry studies indicate that the N,N-alkyl amides are self-associated in toluene solution, with aggregation numbers up to about 2.5 for 0.6 M solutions at 35°C. In contrast, the N,N-dialkylamides behave as monomers under these conditions. The distribution ratios for the extraction of uranium and thorium show second- and third-order dependences, respectively, on the extractant concentration for both the N-alkyl and N,N-dialkyl amides.     

THE EFFECT OF TEMPERATURE ON THE EXTRACTION OF NITRIC ACID AND PLUTONIUM(IV) NITRATE WITH 30 VOL.% TRIBUTYL PHOSPHATE (TBP)

Abstract

Own and published data were evaluated for characterizing the effect of temperature on the distribution of nitric acid and plutonium(IV). The solutes were distributed between 30 vol.% TBP in an aliphatic diluent and aqueous solutions containing nitric acid and zero to macro amounts of plutonium(IV) and uranyl nitrates. The temperature dependence of the distribution ratios is described with empirical model equations and examples of the dependence in the absence and presence of uranium(VI) are given. Taking infinite dilution of all solutes of the system as a standard state, the enthalpy change of the extraction reaction could be estimated as ?17 kJ/mol for nitric acid but no numerical estimate was possible for plutonium(IV).     

DILUENT EFFECT ON THE EXTRACTION OF URANIUM(VI) FROM HYDROCHLORIC ACID SOLUTIONS BY TRIOCTYLMETHYLAMMONIUM CHLORIDE

ABSTRACT

The extraction of uranium(VI) from hydrochloric acid solutions by trioctylmethylammonium chloride (TOMAC) has been examined using various diluents such as benzene, chlorobenzene, o-dichlorobenzene, toluene, m-xylene, nitrobenzene, carbon tetrachloride, chloroform and 1,2-dichloroethane. It was found that by assuming a regular solution, the distribution coefficient and the enthalpy change associated with the metal extraction can be expressed in terms of the solubility parameter of TOMAC, diluent and the complex formed in the organic phase and their molar volumes. Additionally an empirical relation holds between distribution coefficient and the viscosity of diluent. Further results for the extraction of divalent manganese, cobalt, copper, zinc and cadmium from hydrochloric acid solutions by TOMAC are investigated in comparison with those of uranium(VI).     

POLYNITROGEN REAGENTS,IN METAL SEPARATION. PART 5 THE EXTRACTION OF URANIUM(VI) FROM SULPHURIC,NITRIC AND HYDROCHLORIC ACID MEDIA WITH ALKYLDIAMHONIUM EXTRACTANTS.

ABSTRACT

A variety of a1kyldiammonium extractants (tertiary and quaternary) were used to extract uranium(VI) from sulphuric, nitric and hydrochloric acid media. The performance of these extractants was compared with that of Aliquat-336 and Alamine-336. Extractions from dilute uranium(VI) solutions were carried out in order to simulate conditions employed in the local mining industry     

DILUENT AND EXTRACTANT EFFECTS ON THE ENTHALPY OF EXTRACTION OF URANIUM(VI) AND AMERICIUM(III) NITRATES BY TRIALKYL PHOSPHATES

ABSTRACT

The effect of various diluents such as n-hexane, n-heptane n-octane, isooctane, n-decane, n-undecane, n-dodecane, n-tetradecane, n-hexadecane, cyclohexane, benzene, toluene, p-xylene, mesitylene and o-dichlorobenzene on the enthalpy of extraction of uranyl nitrate by tri-n-amyl phosphate (TAP) over the temperature range 283 K - 333 K has been studied. The results indicate that the enthalpy of extraction does not vary significantly with the diluents studied. Also enthalpies of extraction of uranyl nitrate and americium(III) nitrate by neutral organo phosphorous extractants such as tri-n-butyl phosphate (TBP), tri-n-amyl phosphate (TAP), tri-sec-butyl phosphate (TsBP), tri-isoamyl phosphate )TiAP) and tri-n-hexyl phosphate (THP) have been studied. An attempt has been made to explain the trends, on the basis of the nature of the solvate formed and the different terms which contribute to the overall enthalpy change.     

IDENTIFICATION OF THE RATE LIMITING STEP LOCUS IN THE EXTRACTION OF Ni(II) By DINONyLNAPHTHALENESULPHONIC ACID

Experimental results are presented and discussed that demonstrate the interfacial character of the rate-limiting step (RLS) in the liquid-liquid extraction of Ni(II) by n-hexane solutions of dinonylnaphthalenesulphonic acid (HDNNS) in a non-dispersing stirred reactor. The possibility of a RLS in the bulk aqueous phase was excluded based on the classical criterion of volume-independent transfer rates per unit volume, and a criterion involving dissolution fluxes of the extractant into the aqueous phase. The aqueous diffusion film was excluded as the site to the RLS on the basis of HDNNS partition results. The combination of extractant distribution and dynamic transfer results is shown able to unequivocally identify the site of the RLS for this reactive system.     

EXTRACTION BEHAVIOUR OF TECHNETIUM AND ACTINIDES IN THE ALIQUAT-336/NITRIC ACID SYSTEM

ABSTRACT

The extraction behaviour of technetium, thorium, uranium, neptunium, plutonium, americium and curium in the Aliquat-336 (diluted with 1,3-diisopropyl benzene) - nitric acid system have been studied. Aliquat-336 (tricapryl-methyl ammonium nitrate) is a quaternary ammonium salt extracting different species with an anion exchange mechanism. Distribution data obtained are modeled by anion exchange (technetium) and ion-pair formation mechanisms (actinides) with the extraction of nitric acid included to account for the lowering of the free extractant concentration. Reasonably high distribution ratios were obtained for technetium and the tetravalent elements (Th, Np and Pu) and Aliquat-336 can therefore be useful for partitioning of these elements.     

CALORIMETRIC STUDIES OF THE SYNERGISTIC EFFECT: THE REACTION OF UO2, Ln(PMBP)3 AND Th(PMBP)4 WITH TOPO IN NITROBENZENE

Titration calorimetry has been used to measure the thermodynamics of reaction in nitrobenzene solution of PMBP complexes of lanthanides, uranyl and thorium with TOPO. The extraction from aqueous solution into chloroform solutions of PMBP and TOPO was also studied. The role of hydration effects in the extraction and synergistic reactions is discussed based on the enthalpy and entropy values of the processes. Synergism is found to result primarily from the large, positive entropies caused by the dehydration resulting from adduct addition to the PMBP complexes.     

Extraction of uranium (VI) and thorium from hydrochloric acid solutions by tri-n-butyl phosphate

The partitions of uranium (vi) and thorium between hydrochloric acid solutions and solutions of tri-n-butyl phosphate (TBP) in benzene or kerosene have been investigated at different concentrations of hydrochloric acid and solvent, and at different temperatures. An infra-red spectral study has also been made of the organic solutions obtained in the extraction of uranium. The effect of organic solvent on the extractions has also been examined.     

METAL EXTRACTION BY ALKYL SUBSTITUTED DIPHOSPHONIC ACIDS. PART 4 P,P′-DI(2-ETHYLHEXYL) BUTANEDIPHOSPHONIC ACID

ABSTRACT

As part of an ongoing investigation of the properties of dialkyl substituted diphosphonic acids as solvent extraction reagents for metal cations, we have studied the extraction of alkaline earth cations, Fe(III) and representative actinides (Am(III), U(VI) and Th(IV)) at tracer-level concentration by o-xylene solutions of P,P′-di(2-ethylhexyl) butanediphosphonic acid, H₂DEH[BuDP]. The extractant and acid dependencies of these metal ions exhibited significant differences from those of the previously investigated analogous extractants in which the two phosphonate groups are separated by a methylene or an ethylene bridge. The aggregation of H₂DEH[BuDP] was investigated in toluene at 25° C by vapor pressure osmometry. H₂DEH[BuDP] was found to exist predominantly as a trimeric species in the 0.1-0.005 molal concentration range. Osmometric measurements and infrared spectra indicate that Ca(II) is extracted into H₂DEH[BuDP] solutions with little disruption of the structure of the extractant. Iron(III) causes significant deprotonation of the ligand and dramatically changes the apparent aggregation number. A comparison of the extraction of Ca(II), Am(III) and Fe(III) by H₂DEH[BuDP] with data obtained using bis(2-ethylhexyl) phosphoric acid (HDEHP) or 2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP]) as the extractant indicates that H₂DEH[BuDP] has characteristics similar to these monofunctional analogs. Infrared spectra of the Ca(II) and Fe(III) salts of H₂DEH[BuDP] show a shift of both v_asym (POO?) and v_sym (POO?) to lower frequencies relative to their values in the sodium salt. This indicates a symmetrical interaction between the metal ion and the phosphonate groups through chelate and/or bridging interactions.     

THE THERMODYNAMICS OF EXTRACTION OF SOME LANTHANIDE AND OTHER IONS BY DINONYLNAPHTHALENESULPHONIC ACID

The thermodynamics of extraction of some lanthanide ions and bismuth, aluminium, calcium and zinc ions from perchloric acid into solutions of dinonylnaphthalenesulphonic acid have been studied. Extraction of the trivalent ions is dominated by the entropy of complexing. Electrostriction of large complex micelles by the complexed ion is postulated in order to account for the entropy effect. In the case of divalent ions, the enthalpy of dehydration of the ion is more important. A strategy for improving the separation factors is proposed.     

SOLVENT EXTRACTION OF ZINC(II) BY ORGANOPHOSPHORUS ACIDS COMPOUNDS FROM PERCHLORATE SOLUTIONS.

ABSTRACT

The extraction of zinc from perchlorate solutions at 0.1 mol.dm^?3 of ionic strength by di(2-ethylhexyl)phosphoric acid (HDEHP), 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and di(n-octyl)phosphinic acid (H[DOP]) dissolved in toluene has been studied at 25 ° C.

The distribution coefficient was determined as a function of pH and HA concentrations and the data were analyzed both graphically and numerically using the computer program LETAGROP-DISTR.

The results showed that the data can be explained assuming the formation of ZnA₂(HA)₂ and ZnA₂HA in organic phase for all the extractants used. A correlation between extracted species and concentration of the various extractants has been found.

The predominance of the different species into the organic phase has been correlated with the difference between their extraction constants.

The anion of the ionic medium is not extracted into the organic phase.     

SORPTION BEHAVIOUR OF URANIUM AND THORIUM ON CRYPTOMELANE-TYPE HYDROUS MANGANESE DIOXIDE FROM AQUEOUS SOLUTION

Abstract

The kinetics of sorption of uranium and thorium from aqueous nitrate solutions on cryptomelane-type hydrous manganese dioxide (CRYMO) was studied. The exchange of uranium is particle diffusion controlled while that of thorium is chemical reaction at the exchange sites. Sorption of uranium and thorium by CRYMO has been also studied as a function of metal concentrations and temperature. The sorption of both cations is found to be an endothermic process and increases markedly with temperature between 30 and 60°C. The sorption results have been analysed by the langmuir adsorption isotherm over the entire range of uranium and thorium concentrations investigated.     

TEMPERATURE EFFECTS IN THE EXTRACTION OF METAL IONS BY DIALKYL-SUBSTITUTED DIPHOSPHONIC ACIDS. I. THE Am(III) CASE

The extraction of Am(III) from HNO₃ by o-xylene solutions of P,P′-di(2-ethylhexyl) methylene- (H₂DEH[MDP]), ethylene- (H₂DEH[EDP]), and butylene- (H₂DEH[BuDP]) diphosphonic acids has been investigated. Thermodynamic parameters of the extraction process were determined by the temperature coefficient of the metal distribution ratio in the 25.0 to 60.0°C temperature range. The extractant aggregation and the extraction stoichiometries with the different diphosphonic acids did not exhibit any significant temperature dependence. Extraction of Am(III) by H₂DEH[MDP] is favored by both enthalpy and entropy variations. When Am(III) is extracted by either H₂DEH[EDP] or H₂DEH[BuDP] the process is entropy controlled. The enthalpy variation for Am(III) extraction exhibited a trend along the series H₂DEH[MDP], H₂DEH[EDP], H₂DEH [BuDP], with the reaction being exothermic for the first, thermoneutral for the second, and endothermic for the third extractant, respectively. This trend was explained as arising from the formation of progressively less stable chelate rings along the diphosphonic acids series. The zero or positive enthalpy variation with a concomitant favorable entropy variation confirm for H₂DEH[EDP] and possibly for H₂DEH[BuDP] a micellar-like type of extraction process.

     

THERMODYNAMIC STUDIES ON THE EXTRACTION OF ZINC(II)FROM HYDROCHLORIC ACID SOLUTIONS BY TRIOCTYLMETHYLAMMONIUM CHLORIDE IN VARIOUS DILUENTS

ABSTRACT

In the extraction of zinc(II) from hydrochloric acid solutions by trioctylmethylammonium chloride in various organic diluents such as benzene, chlorobenzene, o-dichlorobenzene, toluene, m -xylene, nitrobenzene, carbon tetrachloride and 2,2-dichloroethane, the heat change associated with zinc(II) extraction has been examined by calorimetry. In the case of benzene used as diluent, it is confirmed that the heat change detected can be interpretated as the summation over the change in enthalpies for the relevant steps to the extraction of zi(II), taking the change in enthalpy obtained from the temperature-dependence of the distribution coefficient into account. Applying this approach of zinc(II) extraction for other diluents, it is found that the distribution of zinc (II) between aqueous and organic phases can be explained very well by assuming a regular solution.     

RADIUM SEPARATION THROUGH COMPLEXATION BY AQUEOUS CROWN ETHERS AND ION EXCHANGE OR SOLVENT EXTRACTION

ABSTRACT

The effect of three water-soluble, unsubstituted crown ethers (15-crown-5 (15C5), 18-crown-6 (18C6) and 21-erown-7 (21C7) on the uptake of Ca, Sr, Ba and Ra cations by a sulfonic acid cation exchange resin, and on the extraction of the same cations by xylene solutions of dinonylnaphthalenesulfonic acid (HDNNS) from aqueous hydrochloric acid solutions has been investigated. The crown ethers enhance the sorption of the larger cations by the ion exchange resin, thereby improving the resin selectivity over calcium, a result of a synergistic interaction between the crown ether and the ionic functional groups of the resin. Similarly, the extraction of the larger alkaline earth cations into. xylene by HDNNS is strongly synergized by the presence of the crown ethers in the aqueous phase. Promising results for intra-Group IIa cation separations have been obtained using each of the three crown ethers as the aqueous ligands and the sulfonic acid cation exchange resin. Even greater separation factors for the radium - calcium couple have been measured with the crown-ethers and HDNNS solutions in the solvent extraction mode. The application of the uptake and extraction results to the development of radium separation schemes it discussed and a possible flowchart for the determination of ²²⁶Ra/²²⁸Ra in natural waters is presented.

     

KINETICS OF URANIUM EXTRACTION BY MACROPOROUS BIFUNCTIONAL PHOSPHINIC ACID RESIN

ABSTRACT

The rate of extraction of uranium by macroporous bifunctional phosphinic acid (MPBPA) resin from nitric acid medium has been studied under particle diffusion controlled conditions. The internal diffusion coefficient was found to increase with increase in temperature and decrease with increase in particle size. The activation energies and entropies suggest that the extraction of uranium essentially follows ion exchange mechanism at low concentration of nitric acid while it is through linkage of >P=0 group of the resin at high concentrations.     

4-ACYLBIS(1-PHENYL-3-METHYL-5-PYRAZOLONES) AS EXTRACTANTS FOR f-ELEMENTS

ABSTRACT

The liquid-liquid extraction of early actinides such as thorium(IV) and uranium(VI) and trivalent lanthanoids such as neodymium(lll), europium(lll) and lutetium(lll) from nitrate solutions was studied using 4-sebacoylbis(1-phenyl-3-methyl-5-pyrazolone) (H₂SP) and 4-dodecandioyl-bis(1-phenyl-3-methyl-5-pyrazolone) (H₂DdP) in chloroform as extractants. The results demonstrate that these metal ions are extracted into chloroform as Th(SP)₂, Th(DdP)₂, UO₂(HSP)₂, UO₂(HDdP)₂, Ln(SP)(HSP) and Ln(DdP)(HDdP) with H₂SP or H₂DdP. The equilibrium constants of the above species were deduced by non-linear regression analysis. The results clearly highlight that thorium(IV) can be selectively separated from uranium(Vl) and trivalent lanthanoids when extracted from 0.2 mol/dm³ nitric acid solutions using 4-acylbis(1-phenyl-3-methyl- 5-pyrazolones). Thorium(IV), uranium(VI) and lutetium(lll) complexes of H₂SP were synthesised and characterised by IR and ¹H NMR spectral data to further clarify the nature of the complexes.     

RECOVERY OF URANIUM FROM ACID MEDIA BY MACROPOROUS BIFUNCTIONAL PHOSPHINIC ACID RESIN

ABSTRACT

The extraction of uranium from various acid media such as nitric acid, sulphuric acid, hydrochloric acid, phosphoric acid and perchloric acid by a macroporous bifunctional phosphinic acid resin (MPBPA) has been studied. The distribution coefficients for the extraction of uranium by the MPBPA resin are compared with the corresponding values reported in literature for the conventional sulphonic acid resin. The results clearly indicate the suitability of the MPBPA resin to recover uranium from different types of acid solutions of widely ranging acidities.     

RADIOLYSIS OF DIISODECYL PHOSPHORIC ACID AND ITS EFFECT ON THE EXTRACTION OF NEPTUNIUM

Radiolysis of diisodecyl phosphoric acid (DIDPA) in n-dodecane containing tributyl phosphate (TBP) was examined by analyzing concentrations of acidic extractants and H₃PO₄, and its effect on the extraction of neptuniua was studied froi the aspect of the extraction rate. For the solvent containing 0.5 fi DIDPA and 0.1 1 TBP Irradiated in the absence of HNO₃, G-values for degradation of DIDPA and for production of dibutyl phosphoric acid (DBP)were found to be 0.47 and 0.14, respectively. For the solvent irradiated in stationary contact with 0.5 M HNO3, G-value for DIDPA degradation was found to be 0.78, which ras 1.7 tines larger than the value for the solvent irradiated in the absence of HNO₃.