Tail-end purification of americium from plutonium loading effluents using a mixture of octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide and tri-N-butyl phosphate

The tail-end purification of Am from Pu loading effluents in 7.5M HNO₃ containing 160 mg l^–1 Am and 1.2 mg l^–1 Pu has been carried out. With 0.2M CMPO+1.2M TBP in dodecane as the extractant and stripping by 0.04M HNO₃+0.05M NaNO₂, the Pu level is brought down to 31.2 g l^–1. When the acidity was reduced to 4.2M HNO₃, one contact with 20% TLA/dodecane and subsequent extraction by a mixture of CMPO and TBP and stripping with 0.04M HNO₃+0.05M NaNO₂ gave Am samples without any detectable amounts of Pu. The recovery of Am was 90% by the first procedure and 98% by the second one.     

Uptake of actinides and lanthanides from nitric acid by dihexyl-N,N-diethylcarbamoylmethylphosphonate adsorbed on chromosorb

Batchwise uptake of Am(III), Pm(III), Eu(III), U(VI) and Pu(IV) by dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP) adsorbed on chromosorb (CAC) at nitric acid concentrations between 0.01 to 6.0M has been studied. The difference between the uptake behavior of Pu(IV) as compared to other actinides and lanthanides is discussed. The Am(III) and U(VI) species taken up on CAC were found to be Am(NO₃)₃·3CMP and UO₂(NO₃)₂·2CMP, respectively. The equilibrium constants for the formation of these species have been evaluated and compared with those of similar species formed in liquid-liquid extraction. Batchwise loading of Pm(III) on CAC from 3.0M HNO₃ has also been studied.     

Extraction and extraction chromatographic separation of minor actinides from sulphate bearing high level waste solutions using CMPO

Bench-Scale studies on the partitioning and recovery of minoractinides from the actual and synthetic sulphate-bearing high level waste (SBHLW) solutions have been carried out by giving two contacts with 30% TBP to deplete uranium content followed by four contacts with 0.2M CMPO+1.2M TBP in dodecane. The acidity of the SBHLW solutions was about 0.3M. In the case of actual SBHLW, the final raffinate contained about 0.4% -activity originally present in the HLW, whereas with synthetic SBHLW the -activity was reduced to the background level.¹⁴⁴Ce is extracted almost quantitative in the CMPO phase,¹⁰⁶Ru about 12% and¹³⁷Cs is practically not extracted at all. The extraction chromatographic column studies with synthetic SBHLW (aftertwo TBP contacts) has shown that large volume of waste solutions could be passed through the column without break-through of actinide metal ions. Using 0.04M HNO₃>99% Am(III) and rare earths could be eluted/stripped. Similarly >99% Pu(IV) and U(VI) could be eluted.stripped using 0.01M oxalic acid and 0.25M sodium carbonate, respectively. In the presence of 0.16M SO ₄ ^2– (in the SBHLW) the complex ions AmSO ₄ ⁺ , UO₂SO₄, PuSO ₄ ²⁺ and Pu(SO₄)₂ were formed in the aqueous phase but the species extracted into the organic phase (CMPO+TBP) were only the nitrato complexes Am(NO₃)₃·3CMPO, UO₂(NO₃)₂·2CMPO and Pu(NO₃)₄·2CMPO. A scheme for the recovery of minor actinides from SBHLW solution with two contacts of 30% TBP followed by either solvent extraction or extraction chromatographic techniques has been proposed.     

Actinides selective extractants coated magnetite nanoparticles for analytical applications

N,N,N′,N′-tetraoctyl diglycolamide (TODGA) and bis(2-ethylhexy)phosphoric acid (HDEHP) were coated on Fe₃O₄ nanoparticles under different chemical conditions. The TODGA-coated magnetite nanoparticles (Fe₃O₄@TODGA) captured representative actinides Am(III) and Pu(IV) at 3–4 M HNO₃ with high efficiency. However, the HNO₃ induced pre-organization of TODGA, before coating on the magnetite nanoparticles, was found to be important for the sorption of Am(III) and Pu(IV) ions. The Fe₃O₄@HDEHP particles exhibited selectivity toward Pu(IV), and Am(III) did not sorb from 3 to 4 M HNO₃. The quantification of Pu(IV) preconcentrated on coated particles was carried out by removing the extractant coating in dioxane based scintillator, followed by liquid scintillation counting.

     

Synthesis and application of a macroporous silica-based polymeric octyl(phenyl)-N,N-diisobutylcarbamoylmethylphoshine oxide composite for the chromatographic separation of high level liquid waste

Summary The Minor Actinides Recovery from HLW by Extraction Chromatography (MAREC) process was used mainly for the separation of minor actinides (MAs) and some specific fission products (FPs) from highly active liquid waste (HLW) by the composite CMPO/SiO₂-P of the macroporous silica based polymeric octyl(phenyl)-N,N-diisobutylcarbamoylmethylphoshine oxide (CMPO) and others. In this study a cascade of chromatographic separation was performed on a 3.0M HNO₃ solution containing 5.0 ^. 10^-3M of 13 elements, at 323 K. The cascade consisted of three columns the first and second ones were packed with CMPO/SiO₂-P and the third with SiO₂-P particles. The first column was employed to prepare various eluents containing saturated CMPO. The second column was used for separation into groups. The CMPO of CMPO/SiO₂-P was recovered from the effluent by the third column and a CMPO-free effluent containing minor actinides was obtained. The elements contained in the simulated HLW of 3.0M HNO₃ were separated into (1) a non-adsorption group (Sr, Cs, and Ru etc.), (2) a MA-hRE (heavy rare earth)-Mo-Zr group, and (3) a lRE (light rare earth) group by eluting with 3.0M HNO₃, 0.05M DTPA (diethylenetriaminepentaacetic acid) (pH 2.0) and HNO₃ (pH 3.5), respectively. The resultant MA-hRE-Mo-Zr mixture containing minor actinides was then separated into the groups (1) Pd-Ru, (2) MA-hRE, and (3) Mo-Zr by utilizing 3.0M HNO₃, distilled water, and 0.05M DTPA (pH 2.0) as eluents. More than 92% of CMPO in the MA-hRE containing effluent was adsorbed by SiO₂-P particles. The effectivity and technical feasibility of MAREC process were demonstrated.     

Americium and plutonium separation by extraction chromatography for determination by accelerator mass spectrometry

A simple method was developed to separate Pu and Am using single column extraction chromatography employing N,N,N′,N′-tetra-n-octyldiglycolamide (DGA) resin. Isotope dilution measurements of Am and Pu were performed using accelerator mass spectrometry (AMS) and alpha spectrometry. For maximum adsorption Pu was stabilized in the tetra valent oxidation state in 8 M HNO₃ with 0.05 M NaNO₂ before loading the sample onto the resin. Am(III) was adsorbed also onto the resin from concentrated HNO₃, and desorbed with 0.1 M HCl while keeping the Pu adsorbed. The on-column reduction of Pu(IV) to Pu(III) with 0.02 M TiCl₃ facilitated the complete desorption of Pu. Interferences (e.g. Ca²⁺, Fe³⁺) were washed off from the resin bed with excess HNO₃. Using NdF_3, micro-precipitates of the separated isotopes were prepared for analysis by both AMS and alpha spectrometry. The recovery was 97.7 ± 5.3% and 95.5 ± 4.6% for ²⁴¹Am and ²⁴²Pu respectively in reagents without a matrix. The recoveries of the same isotopes were 99.1 ± 6.0 and 96.8 ± 5.3% respectively in garden soil. The robustness of the method was validated using certified reference materials (IAEA 384 and IAEA 385). The measurements agree with the certified values over a range of about 1–100 Bq kg⁻¹. The single column separation of Pu and Am saves reagents, separation time, and cost.     

Development of novel composite sorbents for the removal of actinides from environmental and analytical solutions

A novel approach to preparing granular sorbents for the separation of actinides has been developed, where the extractant is directly immobilized in an inert matrix. This allows substantially higher extractant loadings in the sorbent than for conventional extraction chromatography resins. This approach utilizes polyacrylonitrile (PAN) as the inert matrix material. The well-known actinide extractant octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) has been loaded into sorbent granules at extractant loadings from 20 to 33 wt.% CMPO. The porosity of the PAN matrix allows the active material to have rapid and complete access to the solution containing the impurities, resulting in improved kinetics and higher sorption capacities. Sorbents containing CMPO were prepared using PAN as a binding matrix, and tested against commercially available actinide extraction chromatography resins. Direct comparative batch contact tests performed with TRU-Resin^Ò and CMPO-PAN using an INEEL tank waste simulant, resulting in distribution coefficient (K _d) values for Am approximately 2-90 times higher for CMPO-PAN than for TRU-Resin. Batch distribution coefficient (K _d) values for Pu were approximately 60-150 times higher for CMPO-PAN than for the TRU-Resin. Acid dependency curves were generated for Am and Pu with CMPO-PAN over a concentration range of 1 mM to 5M HNO₃.     

210Pb and210Po in tobacco-with a special focus on estimating the doses of210Po to man

Studies have been carried out on the solubility of Pu(III) oxalate by precipitation of Pu(III) oxalate from varying concentrations of HNO₃/HCl (0.5–2.0M) solutions and also by equilibrating freshly prepared Pu(III) oxalate with solutions containing varying concentrations of HNO₃/HCl, oxalic acid and ascorbic acid. Pu(III) solutions in HNO₃ and HCl media were prepared by reduction of Pu(IV) with ascorbic acid. 0.01–0.10M ascorbic acid concentration in the aqueous solution was maintained as holding reductant. The solubility of Pu(III) oxalate was found to be a minimum in 0.5M–1M HNO₃/HCl solutions containing 0.05M ascorbic acid and 0.2M excess oxalic acid in the supernatant.     

Influence of ionic liquids on actinides extraction by diphenyl(dibutyl)carbamoylmethylphosphine oxide in different solvents from nitric acid solution

Influence of ionic liquids (ILs) addition (1?C50 wt%) on extraction efficiency of actinides by diphenyl(dibutyl)carbamoylmethylphosphine oxide (Ph₂Bu₂) from 3 M HNO₃ has been studied. Am(III) distribution ratios in two-phase systems 0.1 M Ph₂Bu₂ in either DCE or CHCl₃?C3 M HNO₃ depending on the nature of additional ionic liquids: imidazolium-based ILs: [C₄mim][PF₆], [C₄mim][BF₄] and phosphonium-based ILs: PPF₆, PBF₄ and PCl were determined. The highest value of Am(III) extraction ratio change (1040) was found on addition of PPF₆ to Ph₂Bu₂ in CHCl₃. Extraction of Pu(IV) and U(VI) by 0.001 M Ph₂Bu₂ in the presence of [C₄mim][PF₆] in DCE, CHCl₃ or meta-nitrobenzotrifluoride (NBTF) have been investigated. The greatest enhancement of extraction efficiency was observed using CHCl₃, the least polar studied solvent. Using a mixture of conventional solvent and ionic liquid as a solvent for extractant enables one to increase distribution ratios and reduce viscosity of organic phase as compared with ionic liquid viscosity. The marked increase of Am(III), Pu(IV) and U(VI) extraction extent by Ph₂Bu₂ on addition of ionic liquids to the extent of 10 wt% permit one essentially to diminish amounts considerably more expensive carbamoylmethylphosphine oxide(the general name is CMPO) used in TRUEX process.     

Adsorption behavior of Me2-CA-BTP/SiO2-P adsorbent toward MA(III) and Ln(III) in nitrate solution

A porous Me₂-CA-BTP/SiO₂-P adsorbent was prepared to separate MA(III) from Ln(III) in high level liquid waste (HLLW). The adsorption behavior of Me₂-CA-BTP/SiO₂-P toward ²⁴¹Am(III) and Ln(III) in 0.01 M HNO₃-NaNO₃ solution was studied. Me₂-CA-BTP/SiO₂-P showed high adsorption and selectivity toward ²⁴¹Am(III) over Ln(III) fission products with the separation factor (SF) reaching to 557, 2355, 1952, 1082, 214, 105, 86, 14 for Y, La, Ce, Nd, Sm, Eu, Gd and Dy respectively in 0.01 M HNO₃-0.99 M NaNO₃ solution. The adsorption kinetics of both Dy(III) and Eu(III) on Me₂-CA-BTP/SiO₂-P was studied and followed pseudo-second-order rate equation indicating chemical sorption as the rate-limiting step of the adsorption, and the adsorption isotherm of Dy(III) and Eu(III) matched better with the Langmuir isotherm than the Freundlich isotherm with the adsorption amount around 0.22 and 0.20 mmol/g respectively. Thermodynamic study revealed that the adsorption of both Dy(III) and Eu(III) on Me₂-CA-BTP/SiO₂-P was spontaneous and endothermic processes with a positive entropy at 298, 308, 313 K.     

Reversed-phase partition chromatographic separation of minor actinides with bis(2-ethylhexyl) sulfoxide from acidic nitrate PUREX waste solutions

The uptake behavior of U(VI), Pu(IV), Am(III) and a few long-lived fission products from nitric acid media by bis(2-ethylhexyl) sulfoxide (BESO) adsorbed on Chromosorb has been studied U(VI), Pu(IV) and Zr(IV) are taken up appreciably as compared to trivalent actinides/lanthanides including some coexisting fission product contaminants which are weakly sorbed on the column. Chromosorb could be loaded with (1.12±0.03) g of BESO per g of the support. Maximum sorption is observed around 4–5 mol·dm^–3 HNO₃ for both U(VI) and Pu(IV), which are sorbed as their disolvates. The elution of (U(VI) and Pu(IV) from the metal loaded sorbent has also been optimized. Desorption of U(VI) is easily accomplished with dilute nitric acid (ca. 0.01 mol·dm^–3)while Pu(IV) is reductively stripped with 0.1 mol·dm^–3 NH₂OH·HCl. Effective sequential separation of U(VI), Pu(IV) and Am(III) from their several admixtures could be readily achieved from real medium and low level active acidic process raffinates.     

Recovery of neptunium from highly radioactive waste solutions of PUREX origin using CMPO

The partitioning and recovery of²³⁷Np from three types of simulated high level waste solutions originating from PUREX processing of spent nuclear fuels such as sulfate bearing high level waste (SB-HLW), HLW from a pressurised heavy water reactor (PHWR-HLW) and from a fast breeder reactor (FBR-HLW) have been carried out using a mixture of 0.2M CMPO and 1.2M TBP in dodecane. Quantitative extraction of neptunium was possible by either oxidizing it to the hexavalent state keeping K₂Cr₂O₇ at 0.01M concentration or by reducing it to tetravalent state keeping Fe²⁺ at 0.02M concentration. Stripping of neptunium was carried out using different reagents, such as dilute nitric acid, oxalic acid and sodium carbonate. Almost quantitative recovery of neptunium has been achieved during these studies.     

Chromatographic separation of americium from europium using bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl) pyridine

The separation of americium(III) from europium(III) was achieved utilizing a bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl) pyridine (CA-BTP) chromatographic resin. The extraction chromatographic materials were prepared using various concentrations of CA-BTP. This new, hydrolytically stable extractant was impregnated on an inert polymeric support at 40% loading. The uptake of Am(III) and Eu(III) by this material from 0.1 to 4.0 M aqueous HNO₃ solutions was measured. The resulting dry weight distribution ratios, D _w , indicated a strong preference for Am(III) with little affinity for Eu(III). These results are similar to recently reported solvent extraction studies indicating a maximum uptake of Am(III) in the 0.5–1.0 M HNO₃ range. The resin preparation, performance, and characterization of the Am/Eu separation are reported herein.

     

Bleeding evaluation of the stationary phase from a few novel macroporous silica-substrate polymeric materials used for radionuclide partitioning from HLLW in MAREC process

Summary To separate minor actinides from HLLW by extraction chromatography, a few novel silica-based di(2-ethylhexyl)phosphoric acid (HDEHP), 4,4¢,(5¢)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6), octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), and N,N,N¢,N¢-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) polymeric adsorption materials (HDEHP/SiO₂-P, DtBuCH18C6/SiO₂-P, CMPO/SiO₂-P, and TODGA/SiO₂-P) were synthesized by impregnating HDEHP, DtBuCH18C6, CMPO, and TODGA into the pores of porous SiO₂-P particles, which were the new kind of inorganic/organic composites consisted of macroporous SiO₂ and copolymer. The bleeding behavior of these composites was investigated by examining the effect of contact time and HNO₃ concentration. It was found that in the tested HNO₃ concentration range, a noticeable quantity of DtBuCH18C6, at least 600 ppm, leaked out from DtBuCH18C6/SiO₂-P because of the protonation of DtBuCH18C6 with hydrogen ion, while the others were lower and basically equivalent to the solubility of HDEHP, CMPO, or TODGA in corresponding acidities solutions. Based on the batch experiment, the bleeding of CMPO/SiO₂-P and TODGA/SiO₂-P, the main adsorbents used in MAREC process for HLLW partitioning, was evaluated by column operation in 0.01M HNO₃ and 3M HNO₃. The quantity of CMPO leaked was ~48 ppm in 0.01M HNO₃ and ~37 ppm in 3.0M HNO₃. The bleeding of TODGA decreased from 23.2 ppm to 7.27 ppm at the initial stage and then basically kept constant. An actual bleeding of TODGA was evaluated by the separation of Sr(II) from a 2.0M HNO₃ solution containing 5.0 ^. 10^-3M of 6 typically simulated elements.     

Plutonium oxidation state distribution in natural clay and goethite

Distribution of Pu(IV) and Pu(V) oxidation states at trace initial concentrations (10^?10–10^?11 mol L^?1) was studied in a liquid- and solid-phase of natural clay and goethite systems. Experiments showed an increase in the concentration of Pu(III) up to 11% at pH 5 in solids of the natural clay ?0.1 mol L^?1 NaNO₃ system containing Pu(IV) after 7-day contact. A kinetic sorption/reduction experiment with goethite suspensions (0.01 mol L^?1 NaNO₃ containing Pu(V)) indicated the presence of Pu(III) in the solids up to 15%.     

Extraction of U(VI), Pu(IV), Am(III) and some fission products by 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester immobilized polyvinyl alcohol hydrogels

Cross-linked hydrogel matrices immobilized with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HA), were prepared to investigate their application in the recovery of radionuclide from acidic waste solutions. Gamma-radiation was used to produce HA immobilized polyvinyl alcohol (PVA) hydrogels (HA-gel). The hydrogels with different characteristics such as: degree of cross-linking (by varying radiation dose) and quantity of extractant immobilized (by starting with aqueous PVA solution containing different amounts of HA), were synthesised. These HA-gels were investigated for solid-liquid phase extraction of U(VI), Pu(IV), Am(III) and some fission products, under various experimental conditions. The concentration of HNO₃ in the aqueous phase was found to play an important role in the extraction of these radionuclei. Extraction of U(VI) was more favourable at lower concentration of HNO₃ (∼0.001 to 0.5M), while at higher concentrations (∼0.5 to 3M HNO₃), more than 90% of Pu(IV) present in the aqueous phase, could be extracted by the HA-gel. The extraction of Am(III) was also found predominant only at lower acidities (at pH∼2 and above). Under optimized conditions, maximum metal loading capacities obtained were 19±0.8 mg, 8±0.4 mg and 11±0.5 mg per gram of swollen HA-gel, for U(VI), Pu(IV) and Am(III), respectively. Under the experimental conditions, extractions of Cs(I) and Sr(II) were observed to be negligible. No leaching out of HA from the HA-gel particles was noted even after its repetitive use for the studied ten cycles of extraction and stripping experiments, as evident from its unchanged extraction efficiency.     

Separation of neptunium, plutonium, americium and curium from uranium with di-(2-ethylhexyl)-phosphoric acid (HDEHP) for radiometric and ICP-MS analysis

The possibility of using di-(2-ethylhexyl)-phosphoric acid (HDEHP) in solvent extraction for the separation of neptunium, plutonium, americium and curium from large amounts of uranium was studied. Neptunium, plutonium, americium and curium (as well as uranium) were extracted from HNO₃, whereafter americium and curium were back-extracted with 5M HNO₃. Thereafter was neptunium back-extracted in 1M HNO₃ containing hydroxylamine hydronitrate. Finally, plutonium was back-extracted in 3M HCl containing Ti(III). The method separates²³⁸Pu from²⁴¹Am for α-spectroscopy. For ICP-MS analysis, the interferences from²³⁸U are eliminated: tailing from²³⁸U, for analysis of²³⁷Np, and the interference of²³⁸UH⁺ for analysis of²³⁹Pu. The method has been used for the analysis of actinides in samples from a spent nuclear fuel leaching and radionuclide transport experiment.     

An improved rapid method for the determination of actinides in water

A new rapid method has been developed for the determination of Th, Pu, Np, U, Am and Cm isotopes in water samples of about 1 L. Actinides are pre-concentrated by co-precipitation with Ca phosphate, sequentially separated on stacked TEVA and TK221 cartridges and measured by alpha spectrometry. The TK221 extraction chromatographic resin contains i.e. CMPO and DGA extractants. It has been characterized by measuring the weight distribution ratios (D_w) of actinides which are higher than 1000 for all actinides in 3 M HNO₃. The method has been optimized, applied for the analysis of tap and seawater samples and validated by participating in an IAEA proficiency test. Chemical recoveries for all actinides are better than 50%. The method can be performed within one day.

     

Use of alcoholic solutions for the isolation and purification of americium and curium with anion-exchangers

The sorption of transplutonium (TPE), rare-earth (RE) and other elements by anion-exchangers (Dowex 1 type) from aqueous alcoholic solutions of nitric acid and ammonium thiocyanate was investigated. This investigation allowed the development of simple and effective methods of americium—curium separation from frradiated plutonium. Plutonium, TPE (in a +3 oxidation state) and RE are firmly sorbed by the anion-exchanger from 1 M HNO₃ in 90% alcohol, Fe, Al and fission products Cs, Sr, Nb, Zr, and Ru pass through the column under these conditions. The RE separation from TPE is achieved by washing the column with 0.5M NH₄SCN in 80% alcohol. The column is then washed with 0.5 M HNO₃ in 85% alcohol, and americium—curium separation proceeds. Use of this method for recovery of an irradiated plutonium target containing 100 mg Pu, Am and Cm is described.     

Synthesis of N,N’-dimethyl-3-oxa-glutamic acid and application in the simplification of TRPO process

To simplify TRPO process, a novel ligand, N,N’-dimethyl-3-oxa-glutaramic acid (DMOGA), was synthesized and used for stripping of An(III, IV) from 30% TRPO-kerosene. The distribution ratios for transuranium elements, including Np(IV), Pu(IV), Am(III), and some fission products, including Eu(III), Fe and Zr between 30% TRPO-kerosene and various HNO₃-DMOGA solutions were measured. An(III, IV) and Ln(III) extracted to TRPO from simulated high level liquid waste could be recovered with an efficiency of 99.9% above in one stream with a 3-stage crosscurrent strip experiment with 0.2M DMOGA in HNO₃ solution. Using this new agent, the back extraction of TRU elements from loaded TRPO phase becomes more simple and practical. Therefore, the original TRPO process could be simplified.