Supported Extractant Membranes for Americium and Plutonium Recovery

Abstract

Solid supported liquid membranes(SLM) are useful in transferring and concentrating americium and plutonium from nitrate solutions. Specifically, DHDECMP (d ihexyl-N, N-diethylcarbamoyImethylphosphonate) supported on Accurel or Celgard polypropylene hollow fibers assembled in modular form transfers >95% of the americium and >70% of the plutonium from high nitrate (6.9 M), low acid (0.1 M) feeds into 0.25 M oxalic acid stripping solution. Membranes supporting TBP (tri-n-butylphosphate) also transfer these metal ions. Maximum permeabilities were observed to be 1 × 10^?3 cm sec^?1, similar to the values for other systems. The feed:strip volume ratio shows an inverse relationship to the fraction of metal ion transferred. Cation exchangers may be used to concentrate americium from the strip solution.     

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.     

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 neptunium was studied from the aspect of the extraction rate. For the solvent containing 0.5 M DIDPA and 0.1 M 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 0.73, which was 1.7 times larger than the value for the solvent irradiated in the absence of HNO₃.

In the experiment on the extraction of neptunium initially in the pentavalent state from the solution containing 0.5 M HNO₃ and 0.5 M H₂O₂, it was found that the extraction rete tas determined by the concentration of MIDPA forted by radiolysis when the solvent was irradiated with lower dose than 1 MGy in the absence of HNO₃. When the solvent absorbed higher dose or was irradiated in the presence of HNO₃, the extraction rate was influenced by the other radiolysis products. Even in this case, when the solvent contained TBP, the rate varied little until absorbed dose increased over 0.5 MGy.     

THE SEPARATION OF NEPTUNIUM AND PLUTONIUM FROM NITRIC ACID USING n-OCTYL(PHENYL)-N,N DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE EXTRACTION AND SELECTIVE STRIPPING†

The extraction of neptunium and plutonium in several oxidation states was studied as a function of nitric acid concentration for 0.1M n-octyl(phenyl)-N, N-diisobutylcarbamoyl -methylphosphine oxide in 1.4M tributylphosphate with dodecane diluent. Np(V) is only weakly extractable over the range of acid concentrations studied while Np(IV) and Np(VI) are highly extractable. Pu(IV) and Pu(VI) are also highly extractable while Pu(III) was extracted but with lower efficiency. An Fe(II) reductant was used to reduce neptunium to Np(IV) and plutonium to Pu(III) for the initial extraction. Pu(III) was then stripped with dilute HNO₃ in the presence of a holding reductant leaving the Np(IV) in the organic phase. Neptunium may then be recovered to an aqueous phase with one of a number of complexing agents.     

Sorption Capacity of Ferromagnetic Microparticles Coated with CMPO

Abstract

Magnetically assisted chemical separation (MACS) was developed at Argonne National Laboratory as a compact process for reducing the volume of high-level aqueous waste streams that exist at many U.S. Department of Energy sites. In the MACS process, ferromagnetic particles coated with solvent extractants are used to selectively separate transuranic nuclides and heavy metals from aqueous wastes. The contaminant-loaded particles are recovered from the waste stream by using a magnet. For the recovery of transuranic species the extractant used is octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in tri-n-butyl phosphate (TBP). To better understand the extraction chemistry of this solvent/particle system, europium was used to monitor the sorption capacity of the MACS particles for lanthanides and actinides. Europium concentrations varying from 10^?7 M to 10^?1 M were prepared with 3M NaNO₃ in 0.1M HNO₃. Neutron activation analysis was used to measure the concentration of europium. The sorption capacity was evaluated, along with the sorption isotherms to simulate multiple contact stages. The maximum absorption capacities obtained was 0.62 mmol/g. The adsorption models of Langmuir and Freundlich and the extended Langmuir model of Brunauer, Emmett, and Teller (BET) were fitted to the data. The best correlations were obtained from the Langmuir and BET models, a result that supports a monolayer adsorption mechanism. The Langmuir and BET models suggested a loading capacity of 0.33 mmol/g and 0.25 mmol/g, respectively. The Freundlich model results support favorable metal loading with a 1/n value of 0.3.

     

Development and Testing of Srex Flowsheets for Treatment of Idaho Chemical Processing Plant Sodium-Bearing Waste Using Centrifugal Contactors

Abstract

Laboratory experimentation has indicated that the SREX process is effective for partitioning ⁹⁰Sr from acidic radioactive waste solutions located at the Idaho Chemical Processing Plant. A baseline flowsheet has been proposed for the treatment of sodiumbearing waste (SBW) which includes extraction of strontium from liquid SBW into the SREX solvent (0.15 M 4′,4′ (5′)-di-(tert-butyldicyclohexo)-18-crown-6 and 1.2 M TBP in Isopar L®), a 0.01 M nitric acid strip section to back-extract components from the loaded solvent, and a 2.0 M HNO₃ solvent acidification section to equilibrate the solvent with HNO₃ prior to recycle to the extraction section. The flowsheet was designed to provide a decontamination factor (DF) of >10³ which will reduce the ⁹⁰Sr activity in the waste solution to below the NRC Class A LLW limit of 0.04 Ci ⁹⁰Sr/m³. SREX flowsheet testing was performed using sixteen stages of 5.5-cm diameter centrifugal contactors. The behavior of stable Sr and other components which are potentially extracted by the SREX solvent were evaluated. Specifically, the behavior of the matrix components including Pb, K, Hg, Na, Ca, Zr, and Fe was studied. The described flowsheet achieved 99.98% Sr removal (DF=4250) with one cycle of SREX. Potassium and Zr were partially extracted into the SREX solvent with 35% and 21%, respectively, exiting in the strip product. Sodium, Ca, and Fe were essentially inextractable. Lead was determined to extract and accumulate in the SREX solvent and in the strip section. As a result, a Pb precipitate formed in the strip stages of the contactors. Mercury was also determined to extract and accumulate in the SREX solvent.     

Amides as Phase Modifiers for N,N′-Tetraalkylmalonamide Extraction of Actinides and Lanthanides from Nitric Acid Solutions

Abstract

The N,N′-tetraalkylmalonamides are a class of compounds under development for transuranic (TRU) separations under high nitric acid conditions. There are several issues that challenge the further development of these ligands. One is the development of improved synthetic procedures that lend themselves to commercial scale-up. Another major issue is the third-phase formation that occurs when the N,N′-tetraalkylmalonamides are contacted with medium-to-high nitric acid concentrations in hydrocarbon solvents. To address the synthesis issue we have developed a new synthetic approach for preparing these materials. Third-phase formation can be eliminated by addition of diluent modifiers such as tributylphosphate (TBP). TBP is inappropriate if a nonphosphate-containing process stream is required. Amides have been proposed as alternatives for TBP in a variety of applications because of their ease of synthesis and the variety of substituents that can be generated. We have been able to develop an amide phase-modified system that extends the working process range of alkylmalonamides (0.5 M) in dodecane (unbranched hydrocarbon) from 3.5 M to 7.5 M nitric acid and in Isopar H (branched hydrocarbon) from 4.0 M to 10.0 M nitric acid using 1.0 M di-2-ethylhexylacetamide/0.5 M alkylmalonamide. The K_d values were comparable to extraction with alkylmalonamide in Isopar H or hydrogenated tetrapropylene (TPH) solvents. The overall extraction system was more robust than the phase-unmodified system allowing for greater temperature and acid concentration fluctuations without third-phase formation.     

THE EXTRACTION OF Am(III) FROM NITRIC ACID BY OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE - TRI-n-BUTYL PHOSPHATE MIXTURES

Abstract

The extraction behavior of Am(III) from nitric acid by octy1(phenyl)-N,N-diisobutylcarbamoyl methyphosphine oxides, OØD[IB]CMPO, in the presence of tributylphosphate, TBP, has been studied using diethylbenzene, decalin, and normal aliphatic hydrocarbon diluents. Relative to ØD[IB]CMPO alone, mixtures of TBP and OØD[IB]CMPO show a slight enhancement in the extraction of Am(III) from nitric acid solution above 2 M and a moderate decrease in extraction for lower acid concentrations. The net effect of TBP addition to OØD[IB]CMPO (as well as other selected carbamoyl methylphosphoryl extractants) is a relative insensitivity of the distribution ratio of Am(III) to HNO₃ concentration in the range of 0.5 M to 6 M and facilitated stripping of Am(III) with dilute acid. Since a continuous variation study of Am(III) extraction using mixtures of ØOD[IB]CMPO and TBP at a fixed total concentration revealed no evidence of a mixed complex, the TBP appears to be behaving primarily as a phase modifier

The most significant benefit gained from addition of TBP to ØD[IB]CMPO is the increased metal ion loading capacity and extractant compatibility with alicyclic and aliphatic diluents. The use of TBP to overcome phase compatibility with other bifunctional extractants of the carbamoylmethylphosphoryl type and the use of other phase modifiers with ØD[IB]CMPO have also been investigated.     

Recovery of Uranium from Seawater

Abstract

Seawater contains various elements in solution. Deuterium, lithium, and uranium are the important ingredients for energy application at present and in the future. This paper deals with the recovery of uranium from seawater, with emphasis on the development of an adsorbent with high selectivity and rate of adsorption for uranium.

Polyacrylamidoxime chelating resins were synthesized from various co-polymers of acrylonitrile and cross-linking agents. The resulting resins with the chelating amidoxime group showed selective adsorption for uranium in seawater. The amount of uranium adsorbed from seawater at room temperature reached 3.2 mg/g resin after 180 days.

Polyacrylamidoxime fiber, which was prepared from polyacrylo-nitrile fiber and hydroxylamine, showed a high rate of adsorption for uranium. The polyacrylamidoxime fiber conditioned with 1 M HCl and 1 M NaOH adsorbed 4 mg U/g fiber from seawater in ten days.     

Degradation of Methyl β-D-Ribopyranoside and Methyl β-D-Xylopyranoside by Oxygen in Aqueous Sodium Hydroxide Solution

Methyl β-D-ribopyranoside (1) and methyl β-D-xylopyranoside (2) were degraded by oxygen (0.682 MPa partial pressure) in 1.25 M sodium hydroxide at 120°C. The degradations of 1 and 2 were similar to the previously reported degradations of 1,5-anhydroribitol (3) and 1,5-anhydroxylitol (4), respectively.⁴ Both hydrogen peroxide and stable organic peroxides were detected in the reactions of 1 and 2. The riboside 1 degraded faster than the xyloside 2. This difference in reactivity is proposed to be a function of the relative acidity of the glycosides. Ionization of hydroxyl groups is postulated to be favored in 1, thus facilitating the initiation of the free radical degradation. The degradations of both 1 and 2 exhibited complex kinetics indicating autoinhibited reactions. In spite of the differences in reactivity, glycosidic bond cleavage occurred in approximately 60% of the degradations for both 1 and 2. C-1 radicals, resulting from abstraction of the anomeric hydrogen atom, are proposed to cause the observed autoinhibition via termination reactions with α-hydroxyhydroperoxyl radicals. However, decomposition of the glycosides via C-1 radicals is not believed to constitute a major degradation pathway since the reactivities of 1 and 2 were essentially the same as the analogous 1,5-anhydroalditols, i.e. 3 and 4, respectively. The major acidic degradation products of 1 and 2 were identical, but were formed in different relative ratios. The major acidic products were methoxyacetic acid, lactic acid, glycolic acid, glyceric acid, a methyl 3-C-carboxyfuranoside, and two isomeric 2-C-carboxyfuranosides.     

Synthesis,characterization, and antimicrobial activity of chitosan hydrazide derivative

A series of modified chitosan derivatives 1–4 has been synthesized. Modification process of chitosan was achieved through a sequence of four reactions starting by protection of its amino group with benzaldehyde (derivative 1), followed by reaction with epichlorohydrine (derivative 2), then reaction with benzhydrazide (derivative 3), and finally restoring the free amino groups on the chitosan by removing of benzaldehyde molecules (derivative 4). These four derivatives were characterized by elemental analyses, FTIR, and X-ray. The four chitosan derivatives showed better antibacterial and antifungal activities than that of chitosan. Derivative 4 exhibited the highest antimicrobial activity relative to the other derivatives.     

Extraction of Actinides from a Chloride Medium Using Pentaalkylpropanediamides

Abstract

Pyrometallurgical processes for the purification of plutonium for defense create waste solutions containing actinides, mainly americium, in chloride medium. Studies have been undertaken to study the extraction of actinides in a chloride medium (hydrochloric acid mixed with concentrated salts such as LiCl, CaCl₂, MgCl₂, KCl) using pentaalkylpropanediamides as extractants. Plutonium(IV) is very easily extracted, but Am(III) needs a salting-out agent such as LiCl. Back extraction of trivalent cations is easy in HCl <5 M . Plutonium(IV) and (VI) can be stripped by reduction either with ascorbic acid or hydroxylammonium salts in a weak-acid medium. Several diluents can be used (aromatic, chlorinated, or even aliphatic) with addition of decanol to prevent third-phase formation. In conclusion, diamides can be used for declassification of various wastes, they are potentially completely incinerable, and, as the synthesis has been optimized, they appear to be promising extractants.     

Preparation of a Macroporous Silica-Based Multidentate Soft-Ligand Material and its Application in the Adsorption of Palladium and the Others

To separate Pd(II), a macroporous silica-based soft-ligand 2,6-bis(5,6-di(iso-butyl)-1,2,4-triazine-3-yl)pyridine (BDIBTP) material, BDIBTP/SiO₂-P, was synthesized by vacuum treatment. It was a multidentate chelating composite prepared by impregnation and immobilization of BDIBTP and 1-octanol molecules into the pores of the macroporous SiO₂-P particles with a mean diameter of 50 µm. 1-Octanol was used to modify BDIBTP through intermolecular interaction force. The adsorption of some typical fission products Zr(IV), Pd(II), La(III), Y(III), Ru(III), Rh(III), and Mo(VI) contained in highly active liquid waste (HLW) onto the BDIBTP/ SiO₂-P materials was investigated. It was carried out by examining the effects of contact time and the concentration of HNO₃ in the range of 0.3 M?7.0 M. BDIBTP/SiO₂-P showed excellent adsorption ability and high selectivity for Pd(II) over all of the tested metals. It was ascribed to the effective complexation of Pd(II) with BDIBTP/SiO₂-P. Consideration of the complexation of BDIBTP for minor actinides MAs(III), the possibility and feasibility of effective partitioning of Pd(II) and MAs(III) simultaneously from a simulated HLW were discussed. A new concept process entitled MPS for the MA(III) and Pd(II) Separation has been proposed.     

Effects of Cα -Oxidation in the Fungal Metabolism of Lignin

C_α-Oxidation (benzyl alcohol oxidation) is a prominent reaction in the degradation of lignin by white-rot fungi. This study showed that such oxidation markedly retards metabolism of a nonphenolic β-O-4 model compound, 1-(3-methoxy-4-ethoxyphenyl)-2-(o-methoxyphenoxy)propane-1,3-diol, by cultures of Phanerochaete chrysosporium Burds. Surprisingly, however, selective chemical C_α -oxidation of spruce lignins enhanced their depolymerization by the cultures. Thus the decrease in intrinsic degradability of substructures is more than compensated by another effect of C_α-oxidation in lignin. One possibility is that the oxidation increases the accessibility of the lignin to enzymes by decreasing its steric complexity. This study also revealed that the β-O-4 model, like lignin in wood, is degraded in part via C_α-oxidation by P. chrysosporium. Reduction of the α-carbonyl groups thus formed does not occur. Addition of L-glutamate to ligninolytic cultures completely suppresses their competence to degrade the model compound, as it does their ability to oxidize lignin to CO₂. This result strengthens past evidence indicating that substructure models are metabolized by the same enzyme system as lignin.     

Laboratory-Scale Counter-Current Centrifugal Contactor Demonstration of an Innovative-SANEX Process Using a Water Soluble BTP

In this paper the development and laboratory-scale demonstration of a novel “innovative-SANEX” (Selective Actinide Extraction) process using annular centrifugal contactors is presented. In this strategy, a solvent comprising the N,N,N’,N’-tetraoctyldiglycolamide (TODGA) extractant with addition of 5 vol.-% 1-octanol showed very good extraction efficiency of Am(III) and Cm(III) together with the trivalent lanthanides (Ln(III)) from simulated Plutonium Uranium Refining by Extraction (PUREX) raffinate solution without 3^rd phase formation. Cyclohexanediaminetetraacetic acid (CDTA) was used as masking agent to prevent the co-extraction of Zr and Pd. An(III) and Ln(III) were co-extracted from simulated PUREX raffinate, and the loaded solvent was subjected to several stripping steps. The An(III) were selectively stripped using the hydrophilic complexing agent SO₃-Ph-BTP (2,6-bis(5,6-di(sulfophenyl)-1,2,4-triazin-3-yl)pyridine). For the subsequent stripping of the Ln(III), a citric acid based solution was used. A 32-stage process flow-sheet was designed using computer-code calculations and tested in annular miniature centrifugal contactors in counter-current mode. The innovative SANEX process showed excellent performance for the recovery of An(III) from simulated High Active Raffinate (HAR) solution and separation from the fission and activation products. ≥ 99.8% An(III) were recovered with only low impurities (0.4% Ru, 0.3% Sr, 0.1% Ln(III)). The separation from the Ln(III) was excellent and the Ln(III) were efficiently stripped by the citrate-based stripping solution. The only major contaminant in the spent solvent was Ru, with 14.7% of the initial amount being found in the spent solvent. Solvent cleaning and recycling therefore has to be further investigated. This successful spiked test demonstrated the possibility of separating An(III) directly from HAR solution in a single cycle which is a great improvement over the former multi-cycle strategy. The results of this test are presented and discussed.     

Development of a New Flowsheet for Co-Separating the Transuranic Actinides: The “EURO-GANEX” Process

A flowsheet for a novel GANEX (Grouped ActiNide EXtraction) process has been tested in a spiked flowsheet trial in a 32 stage plutonium-active centrifugal contactor rig with a simulant feed that contained 10 g/L plutonium as well as some fission products and other transuranic actinides. The solvent system used was a combination of 0.2 mol/L N,N,N’,N’-tetraoctyl diglycolamide (TODGA) and 0.5 mol/L N,N’-(dimethyl-N,N’-dioctylhexylethoxy-malonamide (DMDOHEMA) in a kerosene diluent that co-extracted actinides and lanthanides. Actinides were subsequently selectively co-stripped away from the lanthanides using a sulphonated and, therefore, hydrophilic bis-triazinyl pyridine (BTP) complexant in conjunction with acetohydroxamic acid (AHA). Plutonium and americium recoveries were high with decontamination factors across the strip contactors of ?14,000 and ?390, respectively. However, approximately 30% of neptunium was lost to the aqueous raffinate which was due to recycling within the first extract-scrub section causing a large build-up of neptunium. Some accumulation of strontium was also observed but in this case it was fully directed to the raffinate stream. In the stripping section, a small fraction of europium (taken as a model lanthanide ion), ca. 7%, was found in the actinide product stream. Modelling of selected data using the PAREX code has shown that even with a relatively simplistic treatment, reasonable agreement between modelling and experiment can be obtained, giving confidence in the use of modelling to refine the GANEX flowsheet design prior to further testing with irradiated fast reactor fuel.     

NOTE: EXTRACTIVE SEPARATIONS WITH HYDROTROPES

Hydrotropic substances, such as, sodium P-toluene sulfonate, potassium P -toluene sulfonate, sodium P -xylene sulfonate, potassium P-xylene sulfonate, sodium benzoate, potassium benzoate, etc., in aqueous solutions, at relatively high concentrations, have been used successfully to separate mixtures of close boiling point substances like 2,6-xylenol/P-cresol, pheno1/o-chlorophenol, P -chlorophenol/2,4-dichlorophenol, and o-cresol76-chloro-o-cresol, dissolved in a suitable solvent. Very high values of separation factor in the range of 10 to 66 have been realised and this novel method appears to be promising for industrial utilization.     

The Truex Process and the Management of Liquid Tru Uwaste

Abstract

The TRUEX (TRansUranium Extraction) process is a new generic actinide extraction/recovery process for the removal of all actinides from acidic nitrate and chloride nuclear waste solutions. A brief review of the relevant chemistry of the TRUEX process and a summary of the current status of development and deployment of TRUEX process flowsheets to treat specific acidic waste solutions at several U.S. DOE sites is presented.     

NEW STRATEGIES IN SEPARATION OF CLOSE BOILING(SOLID)MIXTURES : EXTRACTION INTO MICELLAR AND MICROEMULSION MEDIA

Aqueous solutions of various surfactants, such as, sodium lauryl sulphate, lauryl alcohol-7-ethoxylate, cetyl pyridinium chloride, cetyl trimethylammonium bromide, etc., at concentrations above their critical micelle concentration values, known as micellar solutions, and microemulsion solutions consisting of these surfactants and a co-surfactant, n-butanol, have been used successfully to separate mixtures of isomeric/non-isomeric close boiling substances like o-nitrochlorobenzene/ p-nitrochlorobenzene, o-nitrotochlorbenzene, p-nitrotoluene, 2,6-xylenol/ p-cresol, -2,4-dichloro-phenol/2,4,6-trichlorophenol, o-isopropylphenol/ p-isopropylphenol, from their solid mixtures. Exceptionally high values for the separation factor have been realized and these novel methods appear to be promising for industrial utilization.     

Hydrogen Isotope Separation by Catalyzed Exchange Between Hydrogen and Liquid Water

Abstract

The discovery, at Chalk River Nuclear Laboratories, of a simple method of wetproofing platinum catalysts so that they retain their activity in liquid water stimulated a concentrated research program for the development of catalysts for the hydrogen-water isotopic exchange reaction. This paper reviews 10 years of study which have resulted in the development of highly active platinum catalysts which remain effective in water for periods greater than a year.

The most efficient way to use these catalysts for the separation of hydrogen isotopes is in a trickle bed reactor which effects a continuous separation. The catalyst is packed in a column with hydrogen and water flowing countercurrently through the bed. The overall isotope transfer rate measured for the exchange reaction is influenced by various parameters, such as hydrogen and water flow rates, temperature, hydrogen pressure, and platinum metal loading. The effect of these parameters as well as the improved performance obtained by diluting the hydrophobic catalyst with inert hydrophilic packing are discussed.

The hydrophobic catalysts can be effectively used in a variety of applications of particular interest in the nuclear industry. A Combined Electrolysis Catalytic Exchange - Heavy Water Process (CECE-HWP) is being developed at Chalk River with the ultimate aim of producing parasitic heavy water from electrolytic hydrogen streams. Other more immediate applications include the final enrichment of heavy water and the extraction of tritium from light and heavy water. Pilot plant studies on these latter processes are currently in progress.