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.     

PARAFFIN WAX - TOPO,AN EXTRACT ANT FOR ACTINIDES AND LANTHANIDES

ABSTRACT

Paraffin wax - TOPO has been used for the extraction of Eu³⁺, Pu⁴⁺, and U0₂ ²⁺ from HN0₃ solutions at 65^° C. The extraction of Eu³⁺ increased with increasing TOPO percent in the wax phase but it decreased with increasing HNO₃ or Eu³⁺ carrier concentrations. The extraction of Pu4+ at tracer and U022+ between 2 to 10 mg (U)/ml from 0.5 to 1.0 M HN0₃ was almost quantitative while using 10 or 15% TOPO/wax at an aqueous to wax phase ratio of 1:1. In presence of uranyl ion, the extraction of Eu³⁺ decreased under all conditions. The best possible condition has been established and a scheme has been proposed for the separation of trivalent actinides and lanthanides, Pu⁴⁺ and U0₂ ²⁺ from their mixtures in laboratory wastes by using non-preequilibrated 15% TOPO/wax. The metal ions were individually stripped using various reagents. The easy phase separation from use of paraffin wax as the diluent makes the separation technique very simple.     

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 Separation of Pu from Macro Concentration of Th in HNO3 Medium

Abstract

Sorption behavior of Th and Pu from anion‐ as well as cation‐exchange resin was investigated from nitric acid medium by both batch and column methods. The anion‐exchange studies involved anionic nitrate complexes of Pu⁴⁺ and Th⁴⁺ sorbed onto DOWEX 1x4 resin (50–100 mesh), and the cation‐exchange studies involved the sorption of Pu³⁺ and Th⁴⁺ onto BIORAD AG 50Wx8 (50–100 mesh) or DOWEX 50Wx4 (50–100 mesh) resin. The batch data gave a separation factor (K _d,Pu/K _d,Th) of 22 for the anion‐exchange method and 0.017 for the cation‐exchange method at 3 and 2 M HNO₃, respectively. A two‐stage ion‐exchange separation method was developed for the quantitative separation of Pu (8 g/L) from a macro amount of Th (200 g/L) in nitric acid medium. The first step involved the quantitative sorption of plutonium from the mixture while about 90% of Th could be washed in 6 column volumes. The plutonium, eluted (as Pu³⁺) using 0.5 M HNO₃ + 0.2 M hydrazinium nitrate (HN) + 0.2 M hydroxyl ammonium nitrate (HAN), and the residual (～10%) Th were subsequently loaded onto a cation‐exchange column in the second step. Greater than 99% Pu was recovered with 2 M HNO₃ (in ～8 column volumes) containing 0.2 M HN + 0.2 M HAN. The final elution of thorium from the cation‐exchange column was achieved in about 6 column volumes of 1 M α‐hydroxy isobutyric acid. A (Pu, Th)O₂ fuel scrap sample was dissolved in 16 M HNO₃ containing 0.005 M HF and was used subsequently as the feed for the anion‐exchange column. The eluted Pu was subsequently loaded onto a cation‐exchange column for final purification. The recovery of plutonium and thorium was found to be >99% and >98%, respectively, while the respective decontamination factors were estimated to be 215 and 292.     

Kilogram-Scale Purification of Americium by Ion Exchange

Abstract

Sequential anion and cation exchange processes have been used for the final purification of ²⁴¹Am recovered during the reprocessing of aged plutonium metallurgical scrap. Plutonium was removed by absorption on Dowex 1, X-3.5 (30–50 mesh) anion exchange resin from 6.5–7.5 M HNO₃ feed solution. Following a water dilution to 0.75–1.0 M HNO₃, americium was absorbed on Dowex 50W, X-8 (50–100 mesh) cation exchange resin. Final purification was accomplished by elution of the absorbed band down 3 to 4 successive beds of the same resin, preloaded with Zn²⁺, with an NH₄OH buffered chelating agent.

The recovery of mixed ²⁴¹Am?²⁴³Am from power reactor reprocessing waste has been demonstrated. Solvent extraction was used to recover a HNO₃ solution of mixed lanthanides and actinides from waste generated by the reprocessing of 13.5 tons of Shippingport Power Reactor blanket fuel. Sequential cation exchange band-displacement processes were then used to separate americium and curium from the lanthanides and then to separate ～60 g of ²⁴⁴Cm from 1000 g of mixed ²⁴¹Am-²⁴³Am.     

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.     

SELECTIVE SEPARATION OF URANYL ION FROM TRU'S IN A COMBINED SOLVENT EXTRACTION PROCESS USING TETRAHYDROFURAN-2,3,4,5-TETRACARBOXYLICACID

ABSTRACT

Selective partitioning of uranyl from transuranic elements in a solvent extraction system which employs a neutral organophosphorus extractant and an aqueous complexant has been demonstrated in a previous report. The extractant solution combines octyl(phenyl)-N,N-diisobutylcarbamoylrnethylphosphine oxide (CMPO), diamyt(amyl)phosphonate (or tributylphosphate), and di(t-butylcyclohexano)-18-crown-6 in Isopar L, and is designed for simultaneous removal of strontium, technetium, lanthanides and actinides from radioactive wastes. The aqueous complexant is tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA). In this report, the separation of UO₂ ²⁺ from Np(IV), Eu(III), Am(III), and Pu(IV) using the Combined Process Solvent has been optimized. Potentiometric titration and NMR spectroscopic results describe the distribution of THFTCA into the organic phase as a function of acidity and [THFTCA]. Further potentiometric titration experiments have determined the stoichiometry and stability of uranyl complexes in the aqueous phase. The thermodynamic data indicate that the uranyl complexes are anomalously weak which partially accounts for the selectivity. Ternary complexes involving, UO₂ ²⁺ CMPO, and THFTCA in the extractant phase also appear to play a role.     

Extraction of HNO3 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 Am³⁺ and Pu³⁺ while TRPO has low loading capacity for HNO₃ and UO₂ ²⁺. The extraction of HNO₃ and 20 other ions of importance in the nuclear power industry was studied using TBP-TRPO/kerosene. The loading capacity of UO₂ ²⁺ and HNO₃ in TBP-TRPO/kerosene was determined. The synergistic extraction characteristics of the mixture for Am³⁺ and TcO₄ m were studied. The influence of high-concentration UO₂ ²⁺ on the extraction of Am³⁺, Eu³⁺, Pu⁴⁺, and TcO₄ m 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 UO₂ ²⁺ and HNO₃.     

Solvent Extraction of Plutonium(IV), Uranium(VI), and Some Fission Products with Di-n-octylsulfoxide

Abstract

Extraction behavior of plutonium(IV), uranium(VI), and some fission products from aqueous nitric acid media with di-n-octylsulfoxide (DOSO) has been studied over a wide range of conditions. Both the actinides are extracted essentially completely, whereas fission product contaminants like Zr, Ru, Ce, Eu, and Sr show negligible extraction. The absorption spectra of sulfoxide extracts containing either Pu⁴⁺ or UO₂ ²⁺ indicate the species extracted from nitric acid into the organic phase to be Pu(NO₃)₄. 2DOSO and UO₂(NO₃)₂. 2DOSO, respectively. Extraction of these actinides decreases with increasing temperature, indicating the extraction to be exothermic. DOSO extracts plutonium and uranium better than di-n-hexylsulfoxide (DHSO) under all condition and is also more soluble in aromatic diluents than the latter. The effect of gamma radiation on the extraction properties of DOSO is found to be similar to that of DHSO.     

Feasibility of Using Di-Dodecyl-Di-Octyl Diglycolamide for Partitioning of Minor Actinides from Fast Reactor High-Level Liquid Waste

The unsymmetrical diglycolamide, di-dodecyl-di-octyl diglycolamide (D³DODGA) is a modifier-free extractant proposed for partitioning of trivalent actinides from nitric acid medium. D³DODGA has been evaluated for the feasibility of using it in the absence of a phase modifier, for the partitioning of minor actinides from fast reactor high-level liquid waste (FR-HLLW). The extraction behavior of various metal ions present in the simulated FR-HLLW was studied in a solution of 0.1 M D³DODGA/n-dodecane from nitric acid medium. The distribution ratio of about 20 metal ions was measured as a function of concentration of nitric acid and other interfering ion. The extraction was found to be strongly dependent on the oxidation state of the metal ion. The extraction of Am(III) from 3–4 M nitric acid medium was quantitative in a single contact. However, it was accompanied by the quantitative extraction of fission products such as trivalent lanthanides (Ln(III)), Y(III), and Zr(IV). The extraction of Sr(II), Pd(II), and Ru(III) in 0.1 M D³DODGA/n-dodecane was not insignificant, but quite low. The extraction of Ba(II), Ni(II), Mo(VI), and Fe(III) was marginal and the extraction of Co(II), Sb(III), Mn(II), and Cs(I) in 0.1 M D³DODGA/n-dodecane was negligible. Our results indicated that 0.1 M D³DODGA/n-dodecane is a promising candidate for the separation of trivalent actinides from fast reactor high-level liquid waste containing significant quantities of trivalent lanthanides and actinides.     

Use of Weak-Acid Cation-Exchange Resins Purolite C105 (H+) and Purolite C106 (H+) for the Adsorption of UO2+ 2

Abstract

The polyacrylic weak-acid cation-exchangers Purolite C105 (H⁺) and Purolite C106 (H⁺) have been used in batchwise adsorption of UO²⁺ ₂ from nitrate solutions containing 0.01 M of UO²⁺ ₂ at pH 3.2. The two resins, which have a saturation capacity up to about 1.24 mmol UO²⁺ ₂ g^?1 resin, showed rapid exchange kinetics. In addition, the resin Purolite C105 (H⁺) displayed high UO²⁺ ₂ loading in small-scale column operations and retained its capacity after five cycles. Adsorbed UO²⁺ ₂ was rapidly and quantitatively eluted from this resin with 0.1 N H₂SO₄.     

Bioaccumulation of lanthanum,uranium and thorium,and use of a model system to develop a method for the biologically-mediated removal of plutonium from solution

Removal of La³⁺, UO₂²⁺ and Th⁴⁺ from aqueous solution by a Citrobacter sp. was dependent on phosphatase-mediated phosphate release and the residence time in a plug-flow reactor (PFR) containing polyacrylamide gel-immobilized cells. In a stirred tank reactor (STR) lanthanum phosphate accumulated on the biomass rapidly, in preference to uranium or thorium phosphates. Thorium removal was not affected by the presence of uranium but was promoted in the presence of lanthanum. Analysis of the accumulated polycrystalline material by X-ray powder diffraction (XRD) analysis and proton induced X-ray emission (PIXE) suggested the formation of a mixed crystal of lanthanum and thorium phosphate. La³⁺, UO₂²⁺ and Th⁴⁺ are analogues of the corresponding species of Pu³⁺, PuO₂²⁺ and Pu⁴⁺. The La/U/Th model system was used to identify some potential problems in the bioremediation of wastes containing plutonium and to develop a method for the biologically-mediated removal of plutonium from solution, in a test solution of ²³⁹Pu ‘spiked’ with a ²⁴¹Pu tracer. © 1998 SCI.     

SYNERGISTIC SELECTIVE EXTRACTION OF ACTINIDES(III) OVER LANTHANIDES FROM NITRIC ACID USING NEW AROMATIC DIORGANYLDITHIOPHOSPHINIC ACIDS AND NEUTRAL ORGANOPHOSPHORUS COMPOUNDS

ABSTRACT

New aromatic dithiophosphinic acids (R₂PSSH) with R = C₆H_5?, ClC₆H_4?, FC₆H_4? and CH₃C₆H_4? were synthesized, characterized and tested as potential separating agents for trivalent actinides over lanthanides. The extraction of Am(III), Eu(III) and other lanthanides was carried out from nitric acid medium with mixtures of R₂PSSHS and neutral organophosphorus compounds. There was no detectable extraction when R₂PSSHS were used alone as extractants for either Am(III) or Eu(III) (D_AM,EU.< 10^?3) under the experimental conditions used in this study. High separation factors (D_AM/D_EU > 20) with D_AM > 1 were achieved in the nitric acid range 0.1-1 mol/L by means of a synergistic mixture of bis(chloro-phenyl)dithiophosphinic acid + tributylphosphate (TBP), irioctylphosphine oxide (TOPO) or tributylphosphine oxide (TBPO). The high radiation resistance (up to 10⁶ Gy absorbed γ-doses) of the extractants was also demonstrated.     

Synthesis and study of the chelating properties of 3-carboxy-4-hydroxyacetophenone-formaldehyde resins

3-Carboxy-4-hydroxyacetophenone (CHAP) was polycondensed with various proportions of formaldehyde using alcoholic alkali as catalyst. The resin samples, designated as CHAP-F, have been characterized by elemental analyses and IR spectroscopy, by estimation of their number average molecular weights (M?_n), by measurement of intrinsic viscosity, and by TGA. Polymeric metal chelates of one CHAP-F sample with Cu²⁺, Fe³⁺, Co²⁺, Ni²⁺, and UO₂²⁺ ions have been prepared and characterized. Ion-exchanging properties of one CHAP-F resin sample for Fe³⁺, Cu²⁺, and Ni²⁺ metal ions are studied by the application of the batch-equilibration method.     

Solvent Extraction and Fluorescence Spectroscopic Investigation of the Selective Am(III) Complexation with TS-BTPhen

An americium(III) selective separation procedure was developed based on the coextraction of trivalent actinides (An(III)) and lanthanides (Ln(III)) by TODGA (N,N,N′,N′-tetraoctyl-diglycolamide), followed by Am(III) selective stripping using the hydrophilic complexing agent TS-BTPhen (3,3′,3?,3?′-[3-(1,10-phenanthroline-2,9-diyl)-1,2,4-triazine-5,5,6,6-tetrayl]tetrabenzenesulfonic acid). Distribution ratios were found at an acidity of 0.65 mol L^?1 nitric acid that allowed for the separation of Am(III) from Cm(III) (D_Cm > 1; D_Am < 1), giving a separation factor between curium and americium of SF_Cm/Am = 3.6 within the stripping step. Furthermore, Am(III) was readily separated from the lanthanides with the lowest selectivity for the Ln(III)/Am(III) separation being lanthanum with a separation factor of SF_La/Am = 20. The influence of the TS-BTPhen concentration on Am(III) distribution ratios was studied, giving a slope (logD vs. log[TS-BTPhen]) of approximately ?1 for the stripping of An(III) with TS-BTPhen from the TODGA-based organic phase. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements of curium(III) were used to analyze the speciation of Cm(III)-TS-BTPhen complexes. Both 1:1 and 1:2 complexes were identified in single-phase experiments. The formation of the 1:1 complex was suppressed in 0.5 mol L^?1 nitric acid but it was significantly present in HClO₄ at pH 3. Conditional stability constants of the complex species were calculated from the TRLFS experiments.     

Solvent Extraction Separation of Some Actinides and Lanthanides with 2-Thenoyltifluoroacetone

Abstract

Solvent extraction behavior of Th(IV) and U(VI) and some lanthanides [Ce(III), Nd(III), Eu(III), Tb(III), and Yb(III)] from thiocyanate medium into sulfoxides and/or 2-thenoyltrifluoroacetone has been studied. The actinides are found to be favorably extracted by both the extractants. The alkyl sulfoxides extract Th(IV) and U(VI) as Th(SCN)₄·3DPSO, Th(SCN)₄·3DOSO, UO₂ (SCN)₂·2DPSO, and UO₂(SCN)₂·3DOSO. The chelate extracts the metals in the following order: U(VI) < Th(IV) < Eu(IV) < Tb(III) < Tb(III) < Ce (III) or Nd(III).     

A COUNTER CURRENT EXPERIMENT FOR THE SEPARATION OF TRIVALENT ACTINIDES AND LANTHANIDES BY THE SETFICS PROCESS

ABSTRACT

The SETFICS process, a variation of TRUEX process, was developed for the recovery of Am and Cm from acidic waste solution and the separation of actinides (III) and light lanthanides. The process uses the general TRUEX solvent as the extracting reagent and a DTPA-sodium nitrate solution for selective stripping of actinides(III). The basic flow sheet is composed of four steps: extraction-scrubbing; acid stripping; actinide(III) stripping; and lanthanide stripping.

To demonstrate the usefulness of the SETFICS process, a counter current experiment was conducted using a real TRUEX product solution. Americium and curium were successfully recovered with a solution of 0.05 M DTPA-4 M NaNO₃ (pH 2.0). Although the actinide(III) product solution contained Sm and Eu, the decontamination factor of ¹⁴⁴Ce/²⁴¹Am was 72, and most of the light lanthanides, specifically La, Ce, Pr, Nd, were removed. At least 80 % of the lanthanides were separated from the Am and Cm end products. In order to minimize the acidity in the actinide(III) stripping step, the nitric acid which extracted with the trivalent metals was previously removed with a solution of 0.5 M NaNO₃ (pH 2.0) in the “acid stripping” step.     

A TBP/BTBP-based GANEX Separation Process. Part 1: Feasibility

Abstract

A GANEX (Group ActiNide EXtraction) separation system for transmutation has been developed. In this separation process the actinides should be extracted as a group from the lanthanides and the fission and corrosion/activation products. This can be achieved by combining BTBP (bis-triazine-bipyridine) with TBP (tri-butyl phosphate) in cyclohexanone. From 4M nitric acid this organic system extracts the actinides (log(D_Am) = 2.19, log(D_Pu) = 2.31, log(D_U) = 1.03, log(D_Np) = 0.53) and also separates them from the lanthanides (log(D_La) = ?2.0, log(D_Ce) = ?1.72, log(D_Nd) = ?1.05, log(D_Sm) = ?0.18, log(D_Eu) = ?0.02). One problem encountered is that some of the fission and corrosion products are also extracted. The new system however still looks feasible.     

Water Soluble PDCA Derivatives for Selective Ln(III)/An(III) and Am(III)/Cm(III) Separation

The synthesis and solvent extraction behavior of dipicolinic acid (pyridine-2,6-dicarboxylic acid, PDCA) and their derivatives have been studied for possible use in selective back-extraction of actinides, especially americium. The extraction was performed from an organic phase containing a mixture of trivalent actinides and lanthanides pre-extracted with N,N,N’,N’-tetraoctyl diglycolamide (TODGA). The efficiency of the back-extraction was enhanced when the picolinate platform was used in a heterocyclic decadentate ligand called h₄tpaen. Beyond selective An/Ln extraction, the aqueous soluble h₄tpaen ligand seemed a potential reagent for an intra-group Am(III)/Cm(III) separation with a separation factor SF_Cm/Am of about 3.5.     

Separation of americium from complex radioactive mixtures using a BTPhen extraction chromatography resin

Extraction chromatography (EC) resins are widely used in analytical radiochemical separations, in particular for actinide separation. However, there is currently limited choice for separation of americium using EC, with DGA (N,N,N′,N′-tetra-n-octyldiglycolamide) resin being the preferred option. Here, we describe preparation and testing of a covalently-linked EC resin utilising a triazine soft N-donor (Me₄BTPhen) extractant for americium extraction. The resin was generated by conjugation of a Me₄BTPhen derivative with poly(vinylbenzyl) chloride to generate PVB–Me₄BTPhen. PVB–Me₄BTPhen was shown to extract americium from a complex matrix simulating nuclear forensic samples, and containing lanthanides, actinides and matrix elements with high Am (III) recovery (>90%) and low extraction of other elements, and provides an alternative to the currently used BTPhen liquid–liquid separation process for Am (III) extraction.