THIRD PHASE FORMATION IN EXTRACTION OF THORIUM NITRATE BY MIXTURES OF TRIALKYL PHOSPHATES

ABSTRACT

This paper reports the results of the studies on third phase formation during the extraction of thorium nitrate from zero free acidity solutions by mixtures of trialkyl phosphates. The phosphates used are tri n-butyl phosphate(TBP), triiso butyl phosphate(TiBP), tri sec butyl phosphate (TsBP) and tri n-amyl phosphate(TAP). The results indicate that small additions of a homologous phosphate can alter the Limiting Organic Concentration (LOC) above which the third phase formation takes place and thus can be advantageously utilised. Use of mixtures of the trialkyl phosphates as extractant can thus obviate the need for adding modifiers such as alcohols to the organic phase for avoiding third phase formation.     

THIRD PHASE FORMATION IN NITRIC ACID EXTRACTION BYn-OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYL-METHYLPHOSPHINE OXIDE

ABSTRACT

The third phase formation was studied as a function of n-octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and tri-M-butyl phosphate (TBP) concentrations and temperature in the extraction of nitric acid. The concentration fractions of CMPO and TBP in the second and the third phases were determined by gas chromatography. Both CMPO and TBP were found to be enriched in the third phase. The concentrations of nitric acid in the second and the third phases relatively agreed with the calculated concentrations based on the extraction equilibrium constants of nitric acid by CMPO and TBP. The extraction of Np with the third phase formation was also discussed.     

THREE LIQUID PHASES IN THE EXTRACTION OF HIDRO-CHLORIC ACID WITH MIXTURE OF DIISOPROPYL ETHER AND n-PENTYL ALCOHOLM1

ABSTRACT

Extraction systems containing diisopropyl ether (IPE) are interesting due to some of their characteristics such as the formation of a third liquid phase (heavy organic phase) or extraction enhancement under given conditions

The influence of temperature (15–40°C), initial acid concentration (5·6–8·1 mol/L) and initial composition of mixed solvent (5–30° vol. of alcohol) on phase volumes and acid distribution in the system HCl - H₂O - IPE - n-pentyl alcohol was examined. The appearance of the third phase is highly dependent on all the parameters mentioned above. The temperature of 15°C, considered as the most interesting, was chosen for more detailed experiments. The dependence of acid extraction on solvent composition was also observed, and it is connected with the change of the number of coexisting phases. Contrary to very low partial distribution ratios between the heavy organic phase and the aqueous phase (below 1) the partial distribution ratios between the heavy organic phase and the aqueous phase are relatively high (between 7 and 54)     

Actinide Third Phase Formation in 1.1 M TBP/Nitric Acid/Alkane Diluent Systems

Abstract

Additional information on the organic phase speciation of Np and Pu was obtained in order to further understand the impact on third phase formation. In the Np(VI) extraction system, indications of the presence of a species associated with the absorbance at 1210 nm appears to be consistent with an increased tendency for third phase formation. Attempts to couple this absorption peak to a higher order nitrate species were inconclusive, and further study is required. For Pu(VI), continued evidence has emerged suggesting a role of higher order nitrate species in third phase formation.     

EFFECT OF NITRIC ACID EXTRACTION ON PHASE BEHAVIOR,MICROSTRUCTURE AND INTERACTIONS BETWEEN PRIMARY AGGREGATES IN THE SYSTEM DIMETHYLDIBUTYLTETRADECYLMALONAMIDE (DMDBTDMA) / n-DODECANE / WATER: A PHASE ANALYSIS AND SMALL ANGLE X-RAY SCATTERING (SAXS) CHARACTERISATION STUDY

ABSTRACT

Among the different problems to be solved when designing a liquid-liquid solvent extraction process, third phase formation. i.e. the splitting of the organic phase into two layers when extracting high concentration of solutes, like nitric acid or metallic nitrates (here trivalent f ions), is one of the most important to address. In some conditions the formation of a “third phase” is observed with dimethyldibutyltetradecylmalonamide (DMDBTDMA), a potential extractant used in the DIAMEX process

We have investigated the phase behavior of the system DMDBTDMA / n-dodecane / water / HNO₃, in the acceptable concentration limits for the DIAMEX process.     

Effect of Uranium on Third Phase Formation in the Pu(IV)-HNO3-TBP-Dodecane System

Abstract

Third phase formation is an important phenomenon which must be taken into account while designing flowsheets for fast reactor fuel reprocessing, since this phenomenon limits the plutonium loadings in the Tri-n-Butyl Phosphate (TBP) phase. In an earlier paper, the limiting organic concentration (LOC) of Pu(IV) above which third phase formation occurs was reported for the Pu(IV)-HNO³-TBP system. In the present work, the effect of uranium on third phase formation in the Pu(IV)-HNO³-30 % TBP-n-dodecane system was studied in detail at different acidities at 303 K. The LOC decreased with organic loading of uranium at all acidities studied.     

EXTRACTION OF U(VI), Pu(IV) AND Th(IV) BY SOME TRIALKYL PHOSPHATES

ABSTRACT

This paper reports the data on the extraction of U(VI), Pu(IV) and Th(IV) from nitric acid by tri-isobutyl phosphate, tri-n-amyl phosphate, tri-isoamyl phosphate and tri-n-hexyl phosphate and provides a comparison of their extract ion behaviour with that of tri-n-butyl phosphate. Data on the third phase formation in the system Th(NO₃) ₄ ^?HNO₃ ^?1.1 M trialkyl phosphate/n-dodecane are also presented.     

Plutonium Third Phase Formation in the 30% TBP/Nitric Acid/Hydrogenated Polypropylene Tetramer System

Abstract

A study on plutonium third phase formation in 30% TBP/nitric acid/hydrogenated polypropylene tetramer (HPT) was performed. Characterization studies of HPT indicate its composition to be a mixture of many highly branched alkanes with a volatility close to n‐undecane. This composition results in about a factor of two better resistance to Pu(IV) third phase formation than dodecane. At 7 M nitric acid in the aqueous phase, the presence of Pu(VI) was observed to substantially reduce the organic phase metal concentration necessary to induce phase splitting in both diluents. Spectroscopic investigation of mixed valence systems also suggest a prominent role for Pu(VI) in the formation of the dense organic phase. Accumulation of Pu(VI) in the heavy phase, as well as certain spectral features, suggest that Pu(VI) is forming a different species, possibly a plutonyl trinitrato, with a strong tendency to form third phase.     

A SETCHENOW TYPE MODEL FOR Pu(lV) THIRD PHASE FORMATION IN NITRIC ACID - BIS(2-ETHYLHEXYL) SULPHOXIDE/DODECANE BIPHASIC SYSTEM AT 298.15 K

ABSTRACT

Formation of third phase (second organic phase) due to limiting solubility of tetravalent actinide solvates in organic solvent has been studied in a qualitative manner by several researchers. Quantitative relations for interactions among various solutes for second organic phase formation were not reported in open literature. In this contribution, an empirical model for Pu(IV) third phase formation in biphasic Pu(NO₃)₄-H₂O-HNO₃-0.4 M BESO/dodecane system at 298.15 K is reported. This model is similar to Setchenow model for salting in/out. The reported model could accommodate effect of inextractable nitrates and diluent modifiers on the limiting organic concentration of Pu(IV).     

Comprehensive Studies on Third Phase Formation: Application to U(VI)/Th(IV) Mixtures Extracted by TBP in N-dodecane

ABSTRACT

Phase splitting of tributylphosphate (TBP)/n-dodecane organic phases resulting from the extraction of UO₂(NO₃)₂, Th(NO₃)₄ and mixtures of both actinides from aqueous nitrate solutions has been investigated. Limiting organic concentrations (LOC) and metals distribution beyond third phase formation have been determined, with comparison between the cases of single metal-systems and metals mixtures. Simultaneous quantification of TBP and both metals was achieved through X-ray fluorescence (XRF) analyses. LOC studies reveal that thorium (IV) drives the third phase formation as it is the most destabilizing element in the solvent. After organic phase splitting, studies of the distributions of metals between the heavy organic phase (HOP) and the diluted organic phase (DOP) in the case of U^(VI)/Th^(IV) mixtures revealed that they are similar to those observed when both metals are alone in the solvent: Thorium (IV) has a strong affinity for the HOP, whereas uranium (VI) distributes both in HOP and in DOP. A supersaturation coefficient (N_LOC) is proposed as a new tool to account for the data obtained in the present study. Furthermore, the approach was successfully applied to analyse available data in the literature regarding thorium (IV) distribution studies after phase splitting in various TBP-alkane solvents. Such a study beyond third phase formation paves the way for studying the mechanism involved in third phase formation, as the metal is clearly identified as the key parameter.     

Third Phase Formation in the Solvent Extraction System Ir(IV)—Cyanex 923

Abstract

The splitting of a system from biphasic to triphasic was studied in the liquid‐liquid extraction of Ir(IV) and HCl using Cyanex 923 (C923). The limiting organic concentrations (LOC) of Ir(IV), which are the maximum possible concentrations of Ir(IV) in the organic phase without the formation of a third phase, were determined under different experimental conditions. The experimental conditions investigated were: concentrations of HCl and NaCl in the aqueous phase, concentrations of C923 and a modifier (tributyl phosphate (TBP) or decanol) in the organic phase, and an organic phase made with different diluents such as n‐octane, n‐nonane, n‐dodecane, kerosene, cyclohexane, toluene, and xylene. The formation of a third phase depends on the concentration of Ir(IV) and HCl in the aqueous phase, as well as on the other experimental conditions. The third phase appeared without Ir(IV) when the concentration of HCl in the equilibrated aqueous phase was 3.5 M and the organic phase contained 10% (v/v) C923/kerosene. The maximum LOC of Ir(IV) was obtained when the initial concentration of HCl in the aqueous phase was 2 M. The LOC of Ir(IV) can be increased though the addition of typical solvent modifiers (such as TBP or decanol) in the organic phase. The LOC of Ir(IV) varied significantly when it was extracted from an aqueous solution containing different concentrations of NaCl. The values obtained for the LOC using different diluents were in the following decreasing order: toluene ≈ xylene>cyclohexane>n‐octane>n‐nonane>kerosene>n‐dodecane. No third phase was detected when toluene and xylene were used as diluents. In the case of cyclohexane, no third phase was observed when the aqueous phase contained 4 M HCl. Spectral studies were performed to investigate the chemical composition of the third phase obtained with Ir(IV)‐HCl‐C923.     

EXTRACTION OF TRIVALENT LANTHANIDES AND ACTINIDES BY A SYNERGISTIC MIXTURE OF THENOYLTRIFLUOROACETONE AND A LINEAR POLYETHER

Abstract

Mixtures of a linear polyether, l,13-bis[8-quinolyl]-l,4,7,10,13-pentaoxatridecane, K-5, and thenoyltrifluoroacetone, HTTA, have been shown to exhibit synergistic character in the extraction of trivalent lanthanides and actinides. The effect of the addition of K-5 to the organic phase on the extractions of Ce(III), Eu(III), Tm(III), Am(III), Cm(III), Bk(III), and Cf(III) by HTTA in chloroform from 0.5M NaNO₃ at 25°C has been measured. These results indicate the extraction is enhanced by the formation of M(TTA)₃K-5 adduct in the organic phase. The organic phase stability constants for the formation of these synergistic species have been calculated for all the metals studied. The magnitude of these organic phase stability constants for K-5 are similar to other common neutral donors. The order of stability does not follow the normal trend based on charge-to-radius ratio, but follows a pattern based on size, with Am(III) being the most stable.     

THERMOMECHANICS OF THE DRYING PROCESS OF FLUID-SATURATED POROUS MEDIA

ABSTRACT

Aspects of the thermomechanics of fluid-saturated porous solids relating to the drying process of materials are discussed in the paper. From the balance equations and the principles of thermodynamics of irreversible processes, the differential equations describing the drying body deformations and induced stresses, the temperature, and the moisture content distributions are developed. The porous body is assumed to be elastically deformed and the pore space is filled with an immiscible liquid-gas mixture-the moisture. The phase transitions of liquid into gas are taken into account     

Mutual Influence of Iron(III) and Gold(III) as Macroconstituents in the Extraction Systems Forming Three Liquid Phases

Abstract

The extraction of a mixture of iron(III) and goId(III) by either pure or diluted (benzene as diluent) diisopropyl ether (IPE) from aqueous solutions of hydrochloric acid at 20°C was investigated. The dependence of metal extraction on the initial concentration of hydrochloric acid, iron(III), and IPE was studied under conditions of third phase formation. It was found that under certain conditions, gold(III) coextracted with iron(IH).     

THE DEPENDENCE OF THE SELECTIVITY OF THE EXTRACTION OF SOME BATHOFERROINE ION PAIRS ON THE STRUCTURE OF WATER IN THE AQUEOUS PHASE

Abstract

The paper deals with the mechanism of increasing the selectivity of some bathoferroine (tris/bathophe-nanthroline /iron/II/cation) ion pairs by adding selected nonelectrolytes to the water phase. The dependence of the bathoferroine cation hydration number and extraction selectivity on the concentration of the nonelectrolyte and temperature has been found. The dependence of the extraction selectivity on ethanol concentration in the water phase with various solvents as the organic phase has been investigated, too. Moreover, the solvation number (ethanoi) of ion association compounds tested in conditions of the best extraction selectivity has been determined

Details concerning the behaviour of the extraction system have been discussed based on the theory of the structure of liquid water.     

Solvent Penetration and Sterical Stabilization of Reverse Aggregates based on the DIAMEX Process Extracting Molecules: Consequences for the Third Phase Formation

Abstract

Studies on third phase formation during the extraction of nitric acid by malonamide extractants in various diluents are investigated. This “third phase transition” is studied from a fundamental point of view, combining vapor pressure osmometry, phase diagram, and scattering studies. The organization of the organic phases of the “malonamides/alkane/water/nitric acid” systems was studied at three “scales”: 1/at a molecular scale by determining the compositions of the extracted complexes; 2/at a macroscopic scale by determining the phase transition boundaries quantified by the limiting organic concentration (LOC) of solutes; and 3/at a supramolecular scale by analyzing the organization of the species in the organic phases (i.e. measuring the critical micellization concentration, the aggregation number, and the interactions between the aggregates). The instability (third phase apparition) has a supramolecular origin: it is a “long range” attraction between polar cores of the reverse micelles formed by the extracting agent. Water and nitric acid extraction are decoupled from these interactions. The alkyl chains of the extractant and the diluent play a symmetrical role in the physical stability of the organic phase: decreasing the diluent chain length or increasing the chain length of the complexing agent both promotes phase stability, i.e. they increase the LOC. We demonstrate here that this effect is the same as the effect observed and known for all other w/o “reverse” micelles: chains protruding from any aggregate stabilize polar solute in oil and shorts oil penetrate and swells the reverse micelles apolar layer.     

SORPTION OF PLATINUM GROUP METALS AND GOLD CHLOROCOMPLEXES BY AMINE POLYMERIC SORBENTS

ABSTRACT

The results of an investigation on the sorption of platinum group metals and gold chlorocomplexes by anion-exchangers and complexing sorbents containing amine groups from HC1 solutions are reported. The sorption mechanism is discussed on the base of the obtained extraction data. The complexformation of ruthenium(III) with the amine groups in the sorbent phase was studied by EPR method.     

Alkane-lnsoluble Trialkylammonium Double Salts Involving the Dodecamolybdophosphate Anion. II. Effect of Amine Structure on Third-Phase Formation

Abstract

In this paper, a rational basis is presented for the control of molybdenum “third phase” formation in tertiary amine extraction through appropriate selection of amine structure. The studies have been founded on the observation that third-phase formation in the amine-extraction of molybdenum is mainly caused by the formation of heteropolymolybdates, especially the dodecamolybdophosphate anion PMo₁₂O₄₀ ^3? (DMP). Eight trialkylamine structures with straight and methyl -branched, 8-to 13-carbon chains have been examined with regard to the type of third phase formed and the maximum molarity of the dissolved salt (R₃NH)₃[DMP± that can be tolerated in the solvent before precipitation occurs (i.e., the DMP “tolerance”, a type of solubility measurement). In the experiments, a standard solvent consisting of 0.05 M tertiary amine (primarily as the trialkylammonium sulfate salt) and 0.15 M n-dodecanol in n-nonane was used. For all of the amines tested, third-phase formation first involved co-extraction of Mo(VI) and phosphate from 0.1 M H₂S0₄ giving the dissolved salt (R₃NH)₃[DMP± over extended equilibration times (days to weeks). With no NaCl added to the aqueous phase, liquid third phases were obtained except in the case of triisooc-tylamine (TIOA), which gave solid (TIOAH)₃[DMP±. In the systems containing added chloride, third-phase formation involved combination of (R₃NH)₃[DMP± with     

INFLUENCE OF THE AMINE NATURE ON THE COMPOSITION OF PALLADIUM COMPLEXES IN SOLVENT EXTRACTION SYSTEMS

ABSTRACT

The extraction of palladium chloro complexes by di-n-octylamine and diamines of various structure as function of the composition of the aqueous and organic phases has been studied. The compositions of the extracted species are indicated and the mechanisms of their distribution are described. It was shown that from 1 to 3 M HC1 solutions. complexes such as (R₂NH₂)₂PdCl₄ solvated by molecules of dioctvlamine chloride are extracted. With increasing the initial concentrations of palladium or decreasing acidity of the aqueous phase, a direct coordination takes place, first of one and then two molecules of amine to atom of palladium with the formation of extracted compounds such as HC1 solutions by salts of amines, diamines and QAB ionic associates such as (AmH)₂PdCl₄, (AmH)₂)PdCl₄ and (R₄N)₂PdCl₄, respectively, are recovered into the organic phase. In systems containing trioctylamine, tetraoctylalkylenediamines (n = 4, 6) and QAB. ionic associates containing the dimeric complex anion, Pd₂Cl₆ ^2-, are also formed. When primary (n-octylaniline - OA) and secondary amines are used as extractants the formation of dimeric species in the organic phase is not observed.

The extraction of palladium from weakly acidic and neutral solutions can proceed through a combination of anion-exchange and coordination mechanisms with the formation of (AmH)[Pd(Am)Cl₃] in systems with primary and secondary amines, and through a coordination mechanism with the formation of complexes such as Pd(Am)₂Cl₂ in systems with primary, secondary and tertiary amines. When palladium is extracted by diamines with a short hydrocarbon chain (n=2) the formation of coordination compounds also takes place.