EXTRACTION OF HNO 3 AND SOME IONS WITH TRIBUTYL PHOSPHATE (TBP)-MIXED TRIALKYL PHOSPHINE OXIDES (TRPO)/KEROSENE

Tributyl phosphate (TBP) and trialkyl phosphine oxides (TRPO) are important extractants. They are widely used in industrial extraction processes, especially in the nuclear power industry. However, both TBP and TRPO suffer from several disadvantages. TBP has a low extractability for trivalent transuranium elements such as Am 3+ and Pu 3+ while TRPO has low loading capacity for HNO 3 and UO 2 2+ . The extraction of HNO 3 and 20 other ions of importance in the nuclear power industry was studied using TBP-TRPO/kerosene. The loading capacity of UO 2 2+ and HNO 3 in TBP-TRPO/kerosene was determined. The synergistic extraction characteristics of the mixture for Am 3+ and TcO 4 - were studied. the influence of high-concentration UO 2 2+ on the extraction of Am 3+ , Eu 3+ , Pu 4+ , and TcO 4 - was investigated. The experimental results show that TBP-TRPO/kerosene mixtures display both a high extractability for a number of ions and a high loading capacity for UO 2 2+ and HNO 3 .     

Back-extraction Of Pu4 + From 20% Tributyl Phosphate – 20% Mixed Trialkyl Phosphine Oxides/kerosene In The Presence Of

Back-extraction of Pu^4 +  from a mixture of 20% tributyl phosphate (TBP) and 20% mixed trialkyl phosphine oxides (TRPO) in kerosene in the presence of UO²⁺ ₂was studied. The back-extractants investigated may be divided into three groups: carboxylic acids and salts, amino polycarboxylates, and phosphonic acid. The distribution coefficients of both Pu^4 +  and UO²⁺ ₂using a number of different back-extractants were measured and compared. The results obtained suggest that the only practical back-extractants are carboxylic acids. Among the carboxylic acids tested, oxalic acid is suitable when the UO²⁺ ₂ concentration in the organic phase is less than 2 g/L. For UO²⁺ ₂concentrations between 2 and 10 g/L, oxalic acid-nitric acid mixtures may be used. For UO²⁺ ₂concentrations greater than 10 g/L, the only practical back-extractant is glycolic acid. The results obtained here may be used to further develop a new process for separation of Pu^4 +  and UO²⁺ ₂ from TBP-TRPO/kerosene mixture.     

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.     

Aqueous Biphase Systems for Liquid/Liquid Extraction of f-Elements Utilizing Polyethylene Glycols

Abstract

Aqueous biphasic systems formed by adding a H₂O soluble polymer (polyethylene glycol) to an aqueous salt solution ((NH₄)₂SO₄ or K₂CO₃) have been investigated for use in extracting aqueous Am³⁺, Pu⁴⁺, UO₂ ²⁺, and Th⁴⁺ ions into the polymer-rich phase. Extraction occurs only in the presence of complexing dyes which preferentially partition to the polymer-rich phase. Three such dyes, arsenazo III, alizarin complexone, and xylenol orange were investigated. Arsenazo III extracts all four metal ions from SO₄ ^2- media but not from CO₃ ^2- solutions. Alizarin complexone quantitatively extracts Th⁴⁺ and Pu⁴⁺ from SO₄ ^2- media, while Am³⁺ is the best extracted ion in CO₃ ^2- solution. Xylenol orange extracts only Am³⁺ from CO₃ ^2- media. In SO₄ ^2- solutions low concentrations of xylenol orange extract Th⁴⁺ and Pu⁴⁺, while Am³⁺ and UO₂ ²⁺ are extracted at higher concentrations of xylenol orange. H₂SO₄ can be used to strip the metal ions, while NH₄OH often but not always enhances the extraction.     

ION EXCHANGE BEHAVIOUR OF CHELATING RESIN DOWEX A-1WITH ACTINIDES AND LANTHANIDES

Adsorption studies of several actinides and lanthanides have been carried out by chelating ion exchange resin Dowex A-1. The metal ions studied were Pu⁴⁺, Zr⁴⁺, UO₂ ⁺⁺, Am³⁺, Cm³⁺, Bk³⁺, Cf³⁺, Eu³⁺, and Tm³⁺. The separation factors between consecutive trivalent actinides and between Am(III) and Eu(III) have been evaluated. Mechanism of adsorption of actinides and lanthanides from different aqueous media has been discussed. An ion exchange procedure for the separation of Pu⁴⁺ and UO₂ ⁺⁺ has been developed using this resin.     

Extraction of Lanthanides(III) and Am(III) by Mixtures of Malonamide and Dialkylphosphoric Acid

Abstract

N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide, DMDOHEMA, and di‐n‐hexylphosphoric acid, HDHP, are the extractants of reference for the French DIAMEX–SANEX process for the separation of trivalent actinide ions from the lanthanide ions. In this work, the extraction of Eu³⁺ and Am³⁺ by the two extractants, alone or in mixtures, has been investigated under a variety of experimental conditions. The two cations are extracted by HDHP as the M(DHP · HDHP)₃ complexes with an Eu/Am separation factor of ～10. With DMDOHEMA, Eu³⁺ and Am³⁺ are extracted as the M(NO₃)₃(DMDOHEMA)₂ disolvate species with an Am/Eu separation factor of ～2. The metal distribution ratios measured with a mixture of the two reagents indicated that almost all lanthanides are extracted equally well. The extraction of Eu³⁺ and Am³⁺ by HDHP‐DMDOHEMA mixtures exhibits a change of extraction mechanism and a reversal of selectivity taking place at ～1 M HNO₃ in the aqueous phase. Below this aqueous acidity, HDHP dominates the metal extraction by the mixture, whereas DMDOHEMA is the predominant extractant at higher aqueous acidities. Some measurements indicated apparent modest antagonism between the two extractants in the extraction of Eu³⁺ and synergism in the extraction of Am³⁺. These data were interpreted as resulting from the formation in the organic phase of mixed HDHP‐DMDOHEMA species containing two HDHP and five DMDOHEMA molecules.     

Solvent extraction separation of titanium(IV), vanadium(V) and iron(III) from simulated waste chloride liquors of titanium minerals processing industry by the trialkylphosphine oxide Cyanex 923

The solvent extraction of magnesium(II), aluminium(III), titanium(IV), vanadium(V), chromium(III), manganese(II) and iron(III) from hydrochloric acid solutions has been investigated using the trialkylphosphine oxide Cyanex 923 (TRPO) in kerosene as extractant. The results demonstrate that titanium(IV), vanadium(V) and iron(III) are extracted into kerosene as TiOCl₂·2TRPO, VO₂Cl·TRPO and HFeCl₄·2TRPO, respectively. On the other hand magnesium(II), aluminium(III), chromium(III) and manganese(II) are not extracted with TRPO from hydrochloric acid solutions (1.0–4.0 mol dm^?3) under the experimental conditions. IR spectral studies of the extracted complexes were further used to clarify the nature of the extracted complexes. The effect of the diluent on the extraction of titanium(IV), vanadium(V) and iron(III) has been studied and correlated with the dielectric constant. The loading capacity of the TRPO system has been evaluated and the potential for the separation and recovery of titanium(IV), vanadium(V) and iron(III) from simulated waste chloride liquors of the titanium minerals processing industry has been assessed. Copyright © 2004 Society of Chemical Industry     

Third Phase Formation in the Extraction of Zirconium(IV) by TRPO in Kerosene

The third phase formation in the extraction of zirconium(IV) from nitric acid media by TRPO(trialkyl phosphine oxide)/kerosene was studied. The limiting organic concentrations (LOC) of Zr(IV) under various experimental conditions were determined. Low temperature and high nitric acid concentrations (> 3 M) were found to facilitate the third phase formation, while increasing the concentration of TRPO or adding phase modifier (TBP) into the organic phase resulted in increased LOC of Zr(IV). When the third phase appeared, the conductivity in the organic phase changed sharply, indicating the change of aggregating behavior in the organic phase. FT-IR spectra were used to illustrate the interaction of TRPO with HNO₃ or Zr(IV), and the composition of the two organic phases indicated by FT-IR spectra was consistent with a diluent-enriched light phase and a zirconium/TRPO-concentrated heavy phase.     

Glycolamide-functionalized ionic liquid: Synthesis and actinide ion extraction studies

A glycolamide-functionalized ionic liquid (G-FIL) was synthesized for the first time and was evaluated for the extraction of actinide ions such as Am³⁺, Pu⁴⁺ and UO₂²⁺ and fission product element ions such as Eu³⁺, Sr²⁺ and Cs⁺. The extraction of the trivalent metal ions was found to be exceptionally high at low acid concentrations, which rapidly decreased with increasing acidity. In view of the high viscosity of the G-FIL, the studies were carried out using its diluted solution in a commercial ionic liquid, viz. 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₄mim][Tf₂N]).     

Extraction of Actinide(III,IV, V,VI) Ions and TcO4 − by N,N,N′,N′‐Tetraisobutyl‐3‐Oxa‐Glutaramide

Abstract

The extraction behavior of U(VI), Np(V), Pu(IV), Am(III), and TcO₄ ^? with N,N,N′,N′‐tetraisobutyl‐3‐oxa‐glutaramide (TiBOGA) were investigated. An organic phase of 0.2 mol/L TiBOGA in 40/60% (V/V) 1‐octanol/kerosene showed good extractability for actinides (III, IV, V VI) and TcO₄ ^? from aqueous solutions of HNO₃ (0.1 to 4 mol/L). At 25°C, the distribution ratio of the actinide ions (D _An) generally increased as the concentration of HNO₃ in the aqueous phase was increased from 0.1 to 4 mol/L, while the D _Tc at first increased, then decreased, with a maximum of 3.0 at 2 mol/L HNO₃. Based on the slope analysis of the dependence of D _M (M=An or Tc) on the concentrations of reagents, the formula of extracted complexes were assumed to be UO₂L₂(NO₃)₂, NpO₂L₂(NO₃), PuL(NO₃)₄, AmL₃(NO₃)₃, and HL₂(TcO₄) where L=TiBOGA. The enthalpy and entropy of the corresponding extraction reactions, Δ_r H and Δ_r S, were calculated from the dependence of D on temperature in the range of 15–55°C. For U(VI), Np(V), Am(III) and TcO₄ ^?, the extraction reactions are enthalpy driven and disfavored by entropy (Δ_r H<0 and Δ_r S<0). In contrast, the extraction reaction of Pu(IV) is entropy driven and disfavored by enthalpy (Δ_r H>0 and Δ_r S>0). A test run with 0.2 mol/L TiBOGA in 40/60% 1‐octanol/kerosene was performed to separate actinides and TcO₄ ^? from a simulated acidic high‐level liquid waste (HLLW), using tracer amounts of ²³⁸U(VI), ²³⁷Np(V), ²³⁹Pu(IV), ²⁴¹Am(III) and ⁹⁹TcO₄ ^?. The distribution ratios of U(VI), Np(V), Pu(IV), Am(III) and TcO₄ ^? were 12.4, 3.9, 87, >1000 and 1.5, respectively, confirming that TiBOGA is a promising extractant for the separation of all actinides and TcO₄ ^? from acidic HLLW. It is noteworthy that the extractability of TiBOGA for Np(V) from acidic HLLW (D _Np(V)=3.9) is much higher than that of many other extractants that have been studied for the separation of actinides from HLLW.     

Sulphoxide ligands inbicyclooctanium based ionic liquid: Novel solvent systems for the extraction of f-elements

The extraction of Pu⁴⁺, PuO₂²⁺, Am³⁺, and Eu³⁺ by structurally modified sulphoxides in 1-hexyl-1,4-diaza [2.2.2] bicyclooctanium Bis(trifluoromethylsulfonyl)imide was investigated at 25 ± 2 °C in an aqueous acidic medium. The extraction process followed ‘cation exchange’ mechanism. The phenyl substituted ligands showed higher extraction efficiency due to steric and electronic factors and followed the trend: Allyl phenyl sulphoxide (APSO) > Benzyl phenyl sulphoxide (BPSO) > Benzyl methyl sulphoxide (BMSO). The extraction process was thermodynamically spontaneous and only one ligand was found to coordinate in the extracted species for all the metal ions. Oxalic acid was found suitable for Pu⁴⁺ stripping. PuO₂²⁺, Am³⁺, and Eu³⁺ were efficiently back extracted by the Na₂CO₃ solution. APSO-IL system showed excellent radiolytic stability and all the three solvent systems were found highly selective.     

Optical Spectroscopic Investigation of Hexavalent Actinide Ions in n-Dodecane Solutions of Tri-butyl Phosphate

ABSTRACT

The extraction of hexavalent actinides An(VI) by tri-butyl phosphate (TBP) was investigated by electronic absorption and vibrational spectroscopies. Through a series of spectral subtractions, vibrational spectra associated with TBP, TBP–HNO₃ adducts, and An(VI)–TBP complexes could be isolated. Investigation of U(VI) extracts indicated spectral features consistent with the formation of the expected [UO₂(NO₃)₂(TBP)₂] complex, but spectral features of other species were clearly evident. Likewise, multiple species were evident in the electronic absorption and vibrational spectra of TBP phases generated by extraction of Pu(VI). Although definitive characterization of the additional species formed could not be achieved in this work, it is hypothesized that they contain 3:1 TBP-to-An(VI) stoichiometry.     

PERTECHNETATE REMOVAL BY MACROPOROUS POLYMER IMPREGNATED WITH 2-NITROPHENYL OCTYL ETHER (NPOE)

ABSTRACT

The loading kinetics of TcO₄ ^? from water and 1?M NaOH solution to macroporous polymer (MPP) impregnated with 2-nitrophenyl octyl ether (NPOE) are reported. The loading process can be simply expressed as: -ln (1 - [TcO₄ ^?]_MPP / [TcO₄ ^?]_MPP,e) =k t +A, where [TcO₄ ^?]_MPP and [TcO₄ ^?]_MPP,e respectively refer to the pertechnetate concentration in the MPP phase at time t and the equilibrated value, and A is a constant. With TcO₄ ^? in water and in 1?M NaOH as loading solutions, the overall mass transfer coefficients k are estimated to be 0.058?min^?1 and 0.067?min^?1 and the saturated loading capacities of TcO₄ ^? are 8.0 × 10^?8?mol/g wet MPP and 5.6 × 10^?8?mol/g wet MPP, respectively. TcO₄ ^? can be easily stripped from loaded MPP by >1?M HNO₃ solution. Loading-stripping cycling and breakthrough experiments demonstrate a good performance of NPOE-impregnated MPP, in particular with TcO₄ ^?-containing water as the loading feed.     

Complexation of Eu(III) with Dibutyl Phosphate and Tributyl Phosphate

Abstract

The complexation of Ln(III) with tributyl phosphate (TBP) in the presence of dibutyl phosphate (HDBP) is of importance for the smooth operation of the plutonium uranium refining extraction (PUREX) process. The time resolved laser‐induced fluorescence spectroscopy (TRLFS) and extraction experiments were employed to study the complexation of Eu(III) with TBP or HDBP and their mixture. The emphasis was on the inner‐sphere hydration numbers and emission spectra of the Eu(III) extracted complexes. The results show that the HNO₃ loading in the organic phase influences not only the distribution ratio but also the emission spectra, as well as the hydration numbers of the complexes. For the Eu‐TBP complexes, one water molecule remained at low HNO₃ loading in the organic phase, and it would be removed at enhanced HNO₃ loading. For the Eu‐HDBP complexes, one water molecule remained at low or high HNO₃ loading. For the Eu‐HDBP/TBP or Eu‐HDBP/30%TBP, more than one species formed and third phase with different chemical form appeared at low HNO₃ loading. The possible species of Eu(III) complexes formed under various conditions were proposed and discussed.     

Recent R&D Studies Related to Coprocessing of Spent Nuclear Fuel Using N,N-Dihexyloctanamide

Abstract

The PUREX process has undergone several modifications to address the issues of high burn up, fewer solvent extraction cycles, and reduced waste arisings. Advanced fuel cycle scenarios have led to a renewed international interest in the development of separation schemes for co-recovering U/Pu from spent fuels. Completely incinerable N,N-dihexyloctanamide (DHOA) has been identified as a promising candidate for the reprocessing of spent fuels. Batch extraction studies were carried out to evaluate DHOA and TBP for the coprocessing (co-extraction and co-stripping) of U and Pu from spent fuel under varying concentrations of nitric acid and of uranium as well as under simulated pressurized heavy water reactor spent fuel feed conditions. At 50 g/L U in 4 M HNO₃, D_Pu values for 1.1 M DHOA and 1.1 M TBP solutions in n-dodecane were 7.9 and 3.8, respectively. In contrast, significantly lower D_Pu value at 0.5 M HNO₃ (4 × 10^?3) for DHOA as compared to TBP (4 × 10^?2) suggested that it was a better choice for coprocessing of spent nuclear fuel. This behavior was attributed to the change in stoichiometry of extracted species at lower acidity vis-a-vis the higher acidity. These studies suggest that plutonium fraction can be enriched with respect to uranium contamination in the product stream. DHOA displays better extraction behavior of plutonium and stripping behavior of uranium under simulated feed conditions. DHOA appears distinctly better than TBP with respect to fission product/structural material decontamination of U/Pu.     

Synergistic Extraction of Dysprosium and Aggregate Formation in Solvent Extraction Systems Combining TBP and HDBP

During treatment of nuclear fuel in the Plutonium/URanium EXtraction (PUREX) process, the extractant tri-n-butyl phosphate (TBP) is known to degrade to dibutylphosphoric acid (HDBP), which increases the extraction of metal ions, thereby inhibiting their stripping from the organic phase. To better understand this phenomenon, we investigated how mixtures of TBP and HDBP influenced the extraction of metal, nitric acid, and water, and correlated the results to aggregated structures in the organic phase. The mole ratios of TBP-HDBP mixtures had a non-linear effect on the extraction of Dy³⁺ and water from 0.2 M HNO₃, indicating synergism. In 2 M HNO₃, the TBP:HDBP mole ratio had a more linear relation to Dy³⁺ and water extraction, so the synergistic effect was less pronounced than in the low acid system. The extraction of nitric acid showed no synergistic effect and follows closely what would be expected in a system using TBP only. The small-angle X-ray scattering (SAXS) data of the 0.2 M acid system showed maximum contrast at a TBP:HDBP mole ratio of 0.25, so that the synergistic mixture is also the most aggregated at 0.2 M acid. The 2 M acid system also showed that the mixed system is more aggregated than the end members, although this does not result in peak extraction. Previous studies of synergistic extraction of metal cations explain the enhanced extraction by increased dehydration of the metal ion. Although our data do not rule out the formation of mixed complexes according to the classical mechanism of synergism, our evidence of increased water extraction and aggregate formation in systems combining TBP and HDBP are complementary to the metal-centric dehydration aspects of the process. The findings in this study give insights into the complex chemistry of solvent extraction, providing a possible link between formation of aggregates in the organic phase and synergistic extraction.     

Modeling of Liquid-Liquid Extraction (LLE) Equilibria Using Gibbs Energy Minimization (GEM) for the System TBP–HNO3–UO2–H2O–Diluent

Liquid-liquid extraction (LLE) is a widely used separation method for an extensive range of metals including actinides. The Gibbs energy minimization (GEM) method is used to compute the complex chemical equilibria for the LLE system HNO₃–H₂O–UO₂(NO₃)₂–TBP plus diluent at 25°C. The nonelectrolyte phase is treated as an ideal mixture defined by eight tri-n-butyl phosphate (TBP) complexes plus the inert diluent. The Pitzer method is used to capture nonidealities in the concentrated electrolyte phase. The generated extraction isotherms are in very good agreement with reported experimental data for various TBP loadings and electrolyte concentrations demonstrating the adequacy of this approach to analyze complex multiphase multicomponent systems. The model is robust and yet flexible allowing for expansion to other LLE systems and coupling with computational tools for parameter analysis and optimization.     

Quaternary ammonium-based task-specific ionic liquid: An efficient and ‘green’ separation for ‘f block’ elements

Functionalized ionic liquid based on quaternary ammonium salt was investigated for the specific task of the efficient extraction of f block elements in different oxidation states. It deals with the investigation of extraction efficiency, mechanism, speciation and associated kinetics and thermodynamics. The extracted species of Pu⁴⁺, PuO₂²⁺, Am³⁺, Eu³⁺ were found to be Pu(Hptha)(H₂O)₆³⁺, PuO₂(Hptha)(H₂O)₂⁺, Am(Hptha)(H₂O)₇²⁺, Eu(Hptha)(H₂O)₇²⁺, respectively where (Hptha)^? is the anionic part of the ionic liquid. Effect of radiation exposure on the performance of the ionic liquid was also investigated. The suitable back extraction procedure from the ionic liquid phase was developed using aqueous soluble complexing agents.     

Competitive Equilibria in the System: Water,Nitric Acid,Tri-n-Butyl Phosphate,and Amsco 125-82

Alternative mass action models were assumed to study competitive equilibria for nitric acid and water extraction in the range of 0-8.4 M nitric acid. Those models yielding the best data fits suggest that tri-n-butyl phosphate (TBP) and hydrocarbon phases contain several complexes. Four complexes appear to result from the association of nitric acid and water with the TBP dimer: [TBP]₂[H₂0]O] ₄ [TBP] ₂ HN0₃H₂O, [TBP] ₂[HNO₃] ₂[H₂O] ₂, and [TBP] ₂ HNO₃ [H₂O] ₃. One complex, TBP HNO₃, apparently predominates from the association of nitric acid with the TBP monomer. The TBP monomer primarily coordinates with nitric acid. The TBP dimer appears to coextract nitric acid and water together. This model gives an excellent fit to nitric acid extraction data in this concentration range and does well at predicting water extraction.     

EXTRACTION OF SOME LANTHANIDES AND ACTINIDES BY 15-CROWN-5 THENOYLTRIFLUOROACETONE MIXTURE IN CHLOROFORM

The extraction of Eu³⁺, Tm³⁺, and Yb³⁺ by a mixture of thenoyltrifluoroacetone (HTTA) and 15-Crown-5 (15C5) in chloroform from a 0.1-ionic strength acetate buffer was investigated. Large enhancement in the extraction for these lanthanides was obtained when a mixture of the two extractants was used. Experimental data indicated that this enhancement is a result of the formation of a lanthanide adduct in the organic phase of the type Ln(TTA) ³° 2CE, where CE refers to a crown ether. The synergistic factors (S.F.), mixed extraction constants and formation constants of the different adducts in the organic phase were found to take the sequence Eu³⁺ > Tm³⁺ > Yb³⁺.

Using 12-Crown-4 (12C4), no enhancement in the extraction was observed. This was explained in terms of the small cavity size of 12C4 relative to 15C5.

The same system comprising HTTA-15C5 was also studied for the extraction of Pu⁴⁺, Am³⁺, Nd³⁺, and Er³⁺. Moderate enhancement was obtained for the extraction of Am³⁺ while no increase in the extraction was found for Pu⁴⁺.The metal concentration in the aqueous phase was found to largely affect the S.F. values for Nd³⁺ and Er³⁺.