Mercury Extraction By The TRUEX Process Solvent: III. Extractable Species And Stoichiometry†

ABSTRACT

Mercury extraction from acidic aqueous solutions by the TRUEX process solvent, 0.2 M n-octyl(phenyl)N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), 1.4 M tributylphosphate (TBP) in n-dodecane, has not been extensively examined, Research is currently in progress at the Idaho Chemical Processing Plant to evaluate the TRUEX process for actinide removal from several acidic waste streams, including liquid sodium-bearing waste (SBW), which contains significant quantities of mercury. Reactions for two mercury species, HgCl₂ and HgCl₄ ^?2, are reported. Classical slope analysis techniques were utilized to evaluate the stoichiometric coefficients of each Hg species independently for both CMPO and TBP. The slope analysis results indicate that even the HgCl₄ ^?2 species extracts as HgCl₂. The results also indicate that 1.9 to 2.2 moles of CMPO and 1.5 to 1.81 moles of TBP are required per mole of HgCl₂ extracted. A generic equation for mercury extraction into CMPO or TBP has been shown to be:

where x = 2 or 4, y = 0 or ?2, E = CMPO or TBP, a = the experimentally determined CMPO or TBP stoichiometry, and over lines indicate organic species. Equilibrium constants for HgCl₂ species were determined to be 295 when extracted by CMPO and 18.2 when extracted by TBP. Equilibrium constants for the HgCl₄ ^?2 species were found to range between 5.8 and 12.0 for the CMPO reaction and 0.13 to 0.27 with TBP.     

SYNERGISTIC EXTRACTION OF Eu(III) AND Am(III) BY THENOYLTRIFLUOROACETONE AND NEUTRAL DONOR EXTRACTANTS: (CARBAMOYLMETHYL)PHOSPHINE OXIDE AND 2,6-BIS((DIPHENYLPHOSPHINO)METHYL)PYRIDINE N,P, P-TRIOXIDE

ABSTRACT

Solvent extraction of Eu(III) and Am(III) from weakly acidic solutions with octyl(phenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and 2,6-bis((diphenylphosphino)methyl)pyridine N, P, P-trioxide (NOPOPO) in 1,2-dichloroethane was studied on a comparative basis. NOPOPO was found to exhibit unusually high extractability for Eu(III) and Am(III), probably due to its trifunctional nature, sufficient steric flexibility and basicity of the functional groups. Both CMPO and NOPOPO demonstrated synergistic effects in extraction of Eu(III) and Am(III) when used in combination with thenoyltrifluoroacetone (HTTA). However, the stoichiometry of the extracted species with CMPO/HTTA and NOPOPO/HTTA was different under similar experimental conditions. The extractant dependencies of the synergistic extractions suggest that the extracted species are the adduct complexes, M(ClO₄)(TTA)₂(CMPO)₂ and M(ClO₄)₂(TTA)(NOPOPO)₂, respectively. It was also observed that CMPO and CMPO/HTTA in dichloroethane extracted Eu(III) and Am(III) equally well, with very similar extraction constants. However, NOPOPO and NOPOPO/HTTA in dichloroethane demonstrated a slight preference for Eu(III) over Am(III), with the extraction constants for Eu(III) more than one order of magnitude higher than that for Am(III).     

SYNERGISTIC SOLVENT EXTRACTION OF TRIVALENT LANTHANIDES AND ACTINIDE BY MIXTURES OF 1-PHENYL-3-METHYL-4-BENZOYL-PYRA2ALONE-5 AND NEUTRAL OXO-DONORS

ABSTRACT

The synergistic solvent extraction of trivalent lanthanides such as La, Eu and Lu and a trivalent actinide, Am, has been studied with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 (HPMBP) and bis(2-ethylhexyl) sulphoxide (B2EHSO) or octyl(phenyl)-N,N-di isobutylcarbamoylmethylphosphine oxide (CMPO) in xylene. The extraction data have been analysed by both graphical and theoretical methods by taking into account aqueous phase speciation and all plausible complexes extracted into the organic phase. With HPMBP alone all the trivalent metal ions form M(PMBP)₃.HPMBP type self adducts. With B2EHSO as a neutral donor, the synergistic adduct species are M(PMBP)₃.B2EHSO and M(PMBP)₃.2 B2EHSO (where M = La, Eu, Lu and Am), whereas with CMPO as a neutral donor the only complex extracted into the organic phase is M(PMBP)₃.CMPO. The synergistic extraction constants of the above species which were deduced by non-linear regression analysis are found to increase monotonically with decreasing ionic radii of these metal ions.     

ZIRCONIUM EXTRACTION INTO OCTYL(PHENYL)-N,N- DIISOBUTYLCARBAMOYLMETHYL PHOSPHINE OXIDE AND TRIBUTYL PHOSPHATE†

ABSTRACT

Classical slope analysis techniques were used to determine the octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) and nitrate stoichiometrics for the extraction of zirconium by CMPO diluted with diisopropylbenzene (DIPB). The equilibrium constant for the extraction of zirconium by CMPO was also determined using classical slope analysis techniques. The extraction of zirconium by TBP in n-dodecane was used as a control to verify the zirconium species as Zr⁺⁴, and to verify the experimental methodology. Equilibrium [CMPO]_org and [TBP]_org concentrations were determined by accounting for the extraction of HNO₃ into both TBP and CMPO solvents. Nitric acid dissociation and aqueous phase activity coefficients were also taken into consideration. Organic activity coefficients, Zr⁺⁴ activity coefficients, Zr⁺⁴ hydrolysis, and consumption of TBP or CMPO by water were neglected. Nitrate and CMPO dependencies for the extraction of zirconium have been determined from this work to be:

An equilibrium constant of 1.13 × 10⁵ ± 1.48 × 10⁴ at 25^° C was also determined for this reaction.     

Application of N,N-Dialkyl Aliphatic amides in the Separation of Some Actinides

Abstract

N, N-dialkyl substituted alkyl amides are known to be good extractants of some actinides such as U, Pu, and Th. Their stability is comparable to that of TBP, and their degradation products do not interfere as do the degradation products of TBP. On the other hand, the principal disadvantage of the amides is their tendency to form poorly soluble U adducts in organic diluents.

A systematic investigation has been carried out on the extractive behavior of two typical alkyl amides of different structures with respect to the actinide ions UO₂ ²⁺, Th⁴⁺, Np⁺⁴, Pu⁺⁴, NpO₄₊ ², PuO²⁺ ₂, Pu³⁺, and Am³⁺, as well as with respect to the most significant fission products. The results obtained have been compared with those obtained using TBP in the same experimental conditions, verifying the applicability of amides in the separation of U from Th.     

Comparative study on the extraction of trivalent americium and europium by CMPO in imidazolium-based ionic liquids and dodecane

The extraction of Am³⁺ and Eu³⁺ by octyl(phenyl)-N,N-diisobutyl carbamoylmethylphosphine oxide (CMPO) in eight imidazolium-based ionic liquids and in n-dodecane was studied and compared. Slope analysis indicates that the ligand/metal ratio in the extracted complexes in ionic liquids is much larger than that in n-dodecane. Nitric acid has different impacts on the extraction, depending greatly on the nature of the ionic liquids. A mixed-extraction mechanism, namely cation exchange plus the formation of neutral complexes (solvation), was proposed for the extraction in the ionic liquid systems. In addition, temperature was found to have a remarkable influence on the extraction. Highly exothermic enthalpy changes were obtained for the extraction in ionic liquid systems. This work provides further insight into the particular role played by the unique properties of ionic liquids in the extraction of metal ions from nitric acid media.     

TEMPERATURE EFFECT ON THE EXTRACTION OF Np(V) BY n-(OCTYLPHENYL)-N,N- DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE

ABSTRACT

The temperature effect on the solvent extraction of Np(V) by n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) from nitric acid solutions was studied. A slight decline of distribution ratio was observed at increasing temperature in the CMPO and CMPO-TBP systems, It was found that HNO₃ is extracted by CMPO with the following extraction stoichiometry:

Thermodynamic parameters of extraction of Np from 0.5M and 4.0M HNO₃ were determined. At ≤2M HNO₃, addition of TBP suppresses the distribution ratio of Np. However, at 4M HNO₃, relative to the CMPO alone, a mixture of 0.2M CMPO and 1.4M TBP shows a slight increase in distribution ratio of Np.     

Synergistic Extraction Studies Using n-Octyl(Phenyl) N,N-Diisobutylcarbamoyl-Methylphosphine Oxide

Abstract

The effectiveness of n-octyl(phenyl)-N,N′-diisobutylcarbamoyl-methylphosphine oxide, CMPO, as a neutral extractant for the trivalent actinides and lanthanides from strong acid media has been well established. This investigation characterized the use of CMPO as a synergistic agent in the extraction of Am(III) and Eu(III) by thenoyltrifluoroacetone (HTTA). The distributions of the metal ions were measured using radiotracer techniques as functions of HTTA concentration, CMPO concentration and pH. The results show that the presence of CMPO enhances the extraction of Eu(III) and Am(III) by 10⁸. The synergistic adduct was M(TTA)₃·CMPO with no indication of higher complexes being formed. Unlike previous studies, the extraction of Eu(III) was more strongly enhanced than that of Am(III). The results showed little, if any, enhancement in the extraction efficiency due to the bidentate nature of the CMPO.     

Effect of phase modifiers TBP and iso-decanol on the extraction and complexation of Eu3+ with CMPO

The effect of tri-n-butyl phosphate (TBP) and iso-decanol as phase modifiers on the complexation of Eu³⁺ with octyl-phenyl N,N-diisobutyl carbamoyl methyl phosphine oxide (CMPO) was studied. On an increase of iso-decanol the extraction efficiency of Eu³⁺ decreases. The metal–ligand stoichiometry was found to be 1:3. The Eu complex of CMPO–TBP was more symmetric compared to CMPO–iso-decanol. The Eu³⁺ complex exhibited D_3h and C_3h symmetry for 30% and 5% iso-decanol, while that for TBP was C_6v. The radiative, non-radiative life time, electric and magnetic dipole transition probabilities, branching ratio, quantum efficiency etc. were evaluated. The covalency between Eu³⁺ and CMPO is as follows: CMPO–TBP < CMPO-5% iso-decanol < CMPO-30% iso-decanol.     

Novel rare earth free phosphors CsMg2P3O10: Mn2+ with efficient and ultra-broadband red emission for plant growth LEDs

An efficient and ultra-broadband red phosphor CsMg₂P₃O₁₀: Mn²⁺ (CMPO: Mn²⁺) is first synthesized toward indoor plant growth LEDs. The phase purity, element composition, crystal, and local electronic structure are explored to discuss the structure and photoluminescence properties. Structure refinement and series X-ray diffractometer (XRD) results show that CMPO: Mn²⁺ is well crystallized in an orthogonal crystal system. The diffuse reflection and excitation spectra show that CMPO: Mn²⁺ has strong absorption around near ultraviolet region, assigned to the [⁶A₁ → ⁴E(⁴D), ⁴T₂(⁴D), [⁴A₁(⁴G), ⁴E(⁴G)], and ⁴T₁(⁴G)] transitions of Mn²⁺, respectively. Upon 415 nm excitation, an efficient red emission centered at 647 nm with ultra-broad full width at half-maximum (FWHM ∼ 100 nm) and high quantum efficiency (IQE ∼ 44.3 %) is observed, and because of the ultra-broad FWHM, the red emission is well accordant with the absorption spectra band of phytochrome P_R and P_FR. The optimal doping contents, lifetime as well as interaction mechanism of CMPO: Mn²⁺ are discussed in detail. Finally, the excellent thermal stability (84.5% @ 140°C) and related thermal quenching mechanism of CMPO: Mn²⁺ are discussed. The above results indicate that CMPO: Mn²⁺ phosphors have great potential for application in plant growth LEDs.     

Electrode reaction of the Np3+/Np couple in LiCl–KCl eutectic melts

The electrochemical behaviour of the Np³⁺/Np couple in the LiCl–KCl eutectic salt was investigated by electromotive force measurements, cyclic voltammetry and chronopotentiometry in the temperature region between 723 and 823 K. The standard redox potential of the Np³⁺/Np couple vs Ag/AgCl (1.00 wt %) was measured and given by the equation, E _Np ³⁺ _/Np ^° = –2.0298 + 0.000706 T, where E is in V and T in K. The electrode reaction of the Np³⁺/Np couple was almost reversible under the conditions studied. The diffusion coefficient of Np³⁺, D _Np ³⁺, in the LiCl–KCl eutectic melts between 723 and 823 K was represented by the equation, D _Np ³⁺ = 2.22 × 10^–6 – 6.88 × 10^–9 T + 5.60 × 10^–12 T ² cm² s^–1. The adsorption and desorption peaks of Np at the Mo working electrode caused by underpotential deposition were also observed in the cyclic voltammograms, and the work function of Np was evaluated as 3.04 eV by peak analysis of the cyclic voltammograms.     

Extraction of some Hexavalent Actinide Ions from Nitric Acid Medium using Several Substituted Diglycolamides

Several substituted diglycolamides, namely TPDGA, THDGA, TODGA, and TDDGA, were evaluated in a comparative study on the extraction of hexavalent actinide ions such as UO₂²⁺, NpO₂²⁺, and PuO₂²⁺ from nitric acid medium. The acid extraction constants (K_H) for the diglycolamides were determined to be 3.8 ± 0.6, 1.6 ± 0.1, 4.1 ± 0.4, and 1.4 ± 0.2 for TPDGA, THDGA, TODGA, and TDDGA, respectively. Though metal ion extraction generally increased with increasing the feed acid concentration, the nature of the extracted species changed with aqueous-phase acidity. While complexes of the type MO₂(NO₃)₂·nL (where L is the diglycolamide extractant and n is 1 and 2) were found to be extracted at 1 M HNO₃, the average number of ligand molecules associated with the complex decreased to ?1 when the nitric acid concentration increased to 3 M. These results have great significance from the actinide separation point of view, as the actinides ions can be made virtually inextractable by adjusting their oxidation state. The thermodynamic parameters were also calculated, which indicated spontaneous reactions with large exothermicities.     

Solvent extraction of Eu3+ with 4-oxaheptanediamide into ionic liquid system

ABSTRACT

Liquid–liquid extraction of Eu³⁺ from aqueous solution with 4-oxaheptanediamides (OHAs) as extractant into room temperature ionic liquids (RTILs) of 1-alkyl-3-methylimidazolium hexafluorophosphate (C_nmim⁺PF₆^–, n = 4, 6 and 8) was investigated. The strong affinity of OHAs to Eu³⁺ was observed in the present C_nmim⁺PF₆^– system. The extraction was assumed to proceed by cation-exchange mechanism and formed a 4:1 complex of the OHA extractants and Eu³⁺ in C₄mim⁺PF₆^– system. The preferable composition of extracted species was presumed to be Eu(OHA)₄(H₂O)₄(PF₆)₃ by ESI-MS.     

Extraction of Eu(III) and Am(III) by 1-phenyl-3-methyl-4-acetylpyrazol-5-one (HPMAP) and tri-n-octylphosphine oxide (TOPO) in a room-temperature ionic liquid

Extraction behaviour of trivalent americium and europium was investigated with 1-phenyl-3-methyl-4-acetyl-5-pyrazolone (HPMAP) and tri-n-octylphosphine oxide (TOPO) in a room-temperature ionic liquid, 1-methyl-3-octyl-imidazolium bis(trifluoromethylsulphonyl) imide (C₈mim·Tf₂N). In select cases, comparison was made using xylene, a molecular diluent. For binary extraction studies involving only PMAP, Eu³⁺ was marginally better extracted than Am³⁺ and the species extracted into C₈mim·Tf₂N conformed to species of the type M(PMAP)₃ (where M = Am or Eu). On the other hand, cationic species were extracted for the ternary extraction systems involving HPMAP and TOPO. Luminescence spectroscopic studies suggested no inner-sphere water molecules in the extracted species. The luminescence decay lifetime showed mono-exponentials, suggesting the extraction of single species.     

EFFECT OF ANIONS ON THERMODYNAMICS OF EXTRACTION OF Am(III) AND Eu(III) WITH OCTYL(PHENYL)-N,N-DIISOBUTYL-CARBAMOYLMETHYLPHOSPHINE OXIDE

The extraction of Am(III) and Eu(III) by octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in xylene from aqueous media containing 1.0 M NH₄NO₃, NH₄SCN, NH₄ClO₄ or a mixture of 0.3 M NH₄NO₃ + 0.7 M NH₄ClO₄ at pH 2.70 and at the temperatures of 15, 25, 35 and 45±0.1 °C has been studied. At all the temperatures, the species extracted were ML₃ · 3CMPO (M = Am(III) or Eu(III), L = NO₃ ^?, SCN^? or ClO₄ ^?) and M(NO₃)(ClO₄)₂ · 3CMPO. The thermodynamic parameters of the extraction reactions have been evaluated using the temperature coefficient method. The ?ΔG values follow the order SCN^? > NO₃ ^? + ClO₄ ^? > NO₃ ^? ≈ ClO₄ ^?, whereas the ?ΔH values an order NO₃ ^? + ClO₄ ^? > SCN^? > NO₃ ^? ≈ ClO₄ ^?. The effect of these anions on the thermodynamic parameters have been discussed employing compensation effects and also on the basis of the energy associated with the transfer of these anions from aqueous to the extractant phase.     

THERMODYNAMICS OF EXTRACTION OF Am(III) AND Eu(III) FROM NITRATE AND THIOCYANATE MEDIA WITH OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE

ABSTRACT

The extraction of Am(III) and Eu(III) from 1.0 M NH₄NO₃ and NHS₄SCN at pH 2.60 into octyl(pheriyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in n-dodecane has been studied in the temperature range 15.0 to 45.0°C. Under all conditions, the species ML₃·CMPO is the dominant extracted complex. The extraction equilibrium constants are at least 10₃ higher in the SCN^- systems than in the NO₃ ^- systems. This difference is attributed to the relative energy associated with transfer of the anions from the aqueous to the: extractant phase. Extraction enthalpies and entropies have been calculated in each system from the temperature dependence of K_ex. Enthalpies are considerably more exothermic in the thiocyanate system for both metal ions. Comparison of ΔH_Am ^SCN with ΔH_EU ^SCN gives a possible indication of enhanced Am-SCN bond strength in the extracted complex.     

Extraction of Uranyl Ion Using 2-Thenoyltrifluoro Acetone (HTTA) in Room Temperature Ionic Liquids

The extraction of UO₂²⁺ ion was studied using six different solvent systems containing 2-thenoyltrifluoroacetone (HTTA) in room temperature ionic liquids such as [C_nmim][X] (where, n = 4, 6, or 8 and X^? = PF₆^? or NTf₂^?) from low to moderate pH solutions for the first time. The extraction kinetics studies indicated rather slow attainment of equilibrium which in some cases improved if the solutions were pre-equilibrated with the aqueous phase prior to the actual experiments. The D_U values were found to increase with increasing pH and leading to a plateau like profile at higher pH values. The D values were quite high as compared to that obtained with molecular diluents. The nature of the extracted species was ascertained by slope analysis method which suggested species of the type: UO₂(TTA)⁺_IL, UO₂(TTA)_2,IL, and UO₂(TTA)₂(HTTA)_IL in different ionic liquid based solvents. Temperature variation studies on UO₂²⁺ ion extraction were also carried out and the thermodynamic parameters were calculated which indicated high endothermicity of the reactions with large positive entropy values.     

NMR STUDY OF LANTHANIDE(III) NITRATE-CMPO EXTRACTION SYSTEM (I) STRUCTURE OF EXTRACTEDCHEMICAL SPECIES

ABSTRACT

Octyl(phenyl)-N,N-dtisobutylcarbamoylmethylphosphine oxide used in the TRUEX process is a new extractant for TRU elements. NMR measurements were carried out to study the coordination structure of lanthanide(III)-CMPO complexes. By analyzing Lan- thanide-Induced-Shifts(LIS) data It was found that CMPO molecule locates in the equatorial region with respect to the principal magnetic Z axis. From the NMR longitudinal relaxation time measurements for Ce(N0₃)₃· 3CMPO, the distance of Ce³⁺-P, Ce³⁺- C(bridging methylene carbon) and Ce³⁺-C(carbonyl carbon) were estimated to be 3.3, 3.1 and 3.1 Å, respectively, suggesting that CMPO coordinates to the central Ce³⁺ ion in a bidentate manner with the phosphoryl and carbonyl groups. This is consistent with the low frequency shifts of phosphoryl and carbonyl stretching frequencies observed in the IR spectrum of Ce(N0₃)₃·3CMPO. Moreover, from the dependence of ³¹P-NMR spectra for Nd(N0₃)₃·3CMPO and Er(N0₃)₃·2CMPO on temperature, lanthanide(IH) -CMPO complexes exist as several isomers in CDC1₃ and a rapid intramolecular interconversion occurs at higher temperature region.     

The Radiation Chemistry of CMPO: Part 1. Gamma Radiolysis

Octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) was irradiated using ⁶⁰Co γ-rays, and post-irradiation samples were analyzed for the decrease in CMPO concentration, the appearance of degradation products, and the effects on americium solvent extraction. The –G-value for the radiolytic degradation of CMPO depends on the presence of nitric acid and oxygen during irradiation, with both providing protection from radiolytic degradation. The –G-value does not depend on the γ-ray dose rate or the CMPO concentration. Effects on solvent extraction performance were independent of the change in CMPO concentration, but rather related to the nature of the degradation products. The main products were identified by ESI-MS and were different for irradiation in the presence of nitric acid.     

Highly efficient extraction of tetra- and hexavalent plutonium using DGA functionalized pillar[5]arene in RTIL: Understanding speciation,thermodynamics and radiolytic stability

DGA functionalized pillar[5]arene (P5DGA) in ionic liquid was demonstrated as highly efficient system for the extraction of plutonium from acidic aqueous solution in tetravalent and hexavalent oxidation state. The extraction followed ‘cation-exchange’ mechanism via [Pu.P5DGA]⁴⁺ and [PuO₂.P5DGA]²⁺, as extracted species for Pu⁴⁺ and PuO₂²⁺, respectively. Evaluation of thermodynamic parameters (ΔG, ΔH and ΔS) showed the feasibility and spontaneity of the extraction process. The process was exothermic and primarily ‘enthalpy driven’, since entropy change was found negative. P5DGA-RTIL solvent system showed good radiolytic stability even at 1000 kGy of gamma dose.