Americium(III) capture using phosphonic acid-functionalized silicas with different mesoporous morphologies: adsorption behavior study and mechanism investigation by EXAFS/XPS.

Efficient capture of highly toxic radionuclides with long half-lives such as Americium-241 is crucial to prevent radionuclides from diffusing into the biosphere. To reach this purpose, three different types of mesoporous silicas functionalized with phosphonic acid ligands (SBA-POH, MCM-POH, and BPMO-POH) were synthesized via a facile procedure. The structure, surface chemistry, and micromorphology of the materials were fully characterized by (31)P/(13)C/(29)Si MAS NMR, XPS, and XRD analysis. Efficient adsorption of Am(III) was realized with a fast rate to reach equilibrium (within 10 min). Influences including structural parameters and functionalization degree on the adsorption behavior were investigated. Slope analysis of the equilibrium data suggested that the coordination with Am(III) involved the exchange of three protons. Moreover, extended X-ray absorption fine structure (EXAFS) analysis, in combination with XPS survey, was employed for an in-depth probe into the binding mechanism by using Eu(III) as a simulant due to its similar coordination behavior and benign property. The results showed three phosphonic acid ligands were coordinated to Eu(III) in bidentate fashion, and Eu(P(O)O)3(H2O) species were formed with the Eu-O coordination number of 7. These phosphonic acid-functionalized mesoporous silicas should be promising for the treatment of Am-containing radioactive liquid waste.

Solution speciation of plutonium and Americium at an Australian legacy radioactive waste disposal site.

During the 1960s, radioactive waste containing small amounts of plutonium (Pu) and americium (Am) was disposed in shallow trenches at the Little Forest Burial Ground (LFBG), located near the southern suburbs of Sydney, Australia. Because of periodic saturation and overflowing of the former disposal trenches, Pu and Am have been transferred from the buried wastes into the surrounding surface soils. The presence of readily detected amounts of Pu and Am in the trench waters provides a unique opportunity to study their aqueous speciation under environmentally relevant conditions. This study aims to comprehensively investigate the chemical speciation of Pu and Am in the trench water by combining fluoride coprecipitation, solvent extraction, particle size fractionation, and thermochemical modeling. The predominant oxidation states of dissolved Pu and Am species were found to be Pu(IV) and Am(III), and large proportions of both actinides (Pu, 97.7%; Am, 86.8%) were associated with mobile colloids in the submicron size range. On the basis of this information, possible management options are assessed.

Synergistic extraction of europium and americium into nitrobenzene by using hydrogen dicarbollylcobaltate and dodecaethylene glycol.

Extraction of microamounts of europium and americium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of dodecaethylene glycol (DDEG, L) has been investigated. The equilibrium data have been explained assuming that the species HL+, H2L2+, ML3+ and MH-1L2+ (M3+ = Eu3+, Am3+; L = DDEG) are extracted into the organic phase. The values of extraction and stability constants of the complex species in nitrobenzene saturated with water have been determined. It was found that in this nitrobenzene medium, the stability constant of the EuL3+ complex is comparable with that of AmL3+.

Separation techniques for quantification of radionuclides in environmental samples.

The reliable and quantitative measurement of radionuclides is important in order to determine environmental quality and radiation safety, and to monitor regulatory compliance. We examined soil samples from Podunajske Biskupice, near the city of Bratislava in the Slovak Republic, for the presence of several natural ((238)U, (232)Th, (40)K) and anthropogenic ((137)Cs, (90)Sr, (239)Pu, (240)Pu, (241)Am) radionuclides. The area is adjacent to a refinery and hazardous waste processing center, as well as the municipal incinerator plant, and so might possess an unusually high level of ecotoxic metals. We found that the levels of both naturally occurring and anthropogenic radionuclides fell within the expected ranges, indicating that these facilities pose no radiological threat to the local environment. During the course of our analysis, we modified existing techniques in order to allow us to handle the unusually large and complex samples that were needed to determine the levels of (239)Pu, (240)Pu, and (241)Am activity. We also rated three commercial techniques for the separation of 90Sr from aqueous solutions and found that two of them, AnaLig Sr-01 and Empore Extraction Disks, were suitable for the quantitative and reliable separation of (90)Sr, while the third, Sr-Spec Resin, was less so. The main criterion in evaluating these methods was the chemical recovery of (90)Sr, which was less than we had expected. We also considered speed of separation and additional steps needed to prepare the sample for separation.

A rapid method for the sequential separation of polonium, plutonium, americium and uranium in drinking water.

A new sequential separation method for the determination of polonium and actinides (Pu, Am and U) in drinking water samples has been developed that can be used for emergency response or routine water analyses. For the first time, the application of TEVA chromatography column in the sequential separation of polonium and plutonium has been studied. This method utilizes a rapid Fe+3 co-precipitation step to remove matrix interferences, followed by plutonium oxidation state adjustment to Pu4+ and an incubation period of ~ 1 h at 50-60 °C to allow Po2+ to oxidize to Po4+. The polonium and plutonium were then separated on a TEVA column, while separation of americium from uranium was performed on a TRU column. After separation, polonium was micro-precipitated with copper sulfide (CuS), while actinides were micro co-precipitated using neodymium fluoride (NdF3) for counting by the alpha spectrometry. The method is simple, robust and can be performed quickly with excellent removal of interferences, high chemical recovery and very good alpha peak resolution. The efficiency and reliability of the procedures were tested by using spiked samples. The effect of several transition metals (Cu2+, Pb2+, Fe3+, Fe2+, and Ni2+) on the performance of this method were also assessed to evaluate the potential matrix effects. Studies indicate that presence of up to 25 mg of these cations in the samples had no adverse effect on the recovery or the resolution of polonium alpha peaks.

On the sequential separation and quantification of 237Np, 241Am, thorium, plutonium, and uranium isotopes in environmental and urine samples.

The implementation of the one-pass-through separation technique using two stacked chromatography columns of TEVA - TRU resins for the separation of 237Np, 241Am, thorium, plutonium and uranium from environmental and urine samples was investigated. The sequential separation technique proved to be successful and gave similar results to those obtained when using individual separations. The analysis time was considerably improved. The amount of chemical waste was also reduced by 50% and the use of HClO4 was avoided. The technique of ICP-MS was also investigated as a complementary technique to alpha-spectrometry.

Sequential determination of Pu and Am radioisotopes in environmental samples; a comparison of two separation procedures.

Two separation methods for the sequential determination of Am and Pu radionuclides are presented and the results obtained are compared. Analysis involves leaching the sample with concentrated nitric acid (HNO(3)), followed by radiochemical separation using extraction chromatographic resins (UTEVA, TRU) and anion exchange. Sources for alpha spectrometry were prepared by micro-precipitation on neodymium fluoride (NdF(3)). The chemical recoveries were determined using (242)Pu and (243)Am tracers. The methods were tested on reference materials and on two sediments. All the results were in good agreement with the reference values. The evaluation of uncertainty is also included.

Separation of Am3+ and Eu3+ using an extraction chromatographic resin containing bis(2,4,4-trimethylpentyl)dithiophosphinic acid as the stationary phase.

Sorption of Am3+ and Eu3+ onto an extraction chromatographic resin material, prepared by impregnating purified bis(2,4,4-trimethylpentyl)dithiophosphinic acid (commercially available as Cyanex 301) into Chromosorb W, was investigated. Separation factor (S.F. = K(d,Am)/K(d,Eu)) values tend to increase in the presence of complexing agents such as thiocyanate and nitrate. In presence of 1 M NaNO3 in the aqueous phase, a S.F. value of approximately 1000 was obtained. The nature of extracted species was ascertained by carrying out the sorption studies at different aqueous phase pH. A column made from 300 mg of the resin material was used for the separation of Am3+ and Eu3+. A synthetic solution containing 1x10(5) cpm each of Am3+ and Eu3+ when loaded on to the column, >99% Eu was eluted out in 60 mL of 1 M NaNO3 at a pH of 3.2 while Am was eluted out using 5 mL of 1 M HNO3. The performance of the resin material was found to be reasonably good even after three cycles.

Enzymically accelerated biomineralization of heavy metals: application to the removal of americium and plutonium from aqueous flows.

A biological process for the removal of heavy metals from the aqueous flows is described. Metals are precipitated on the surface of immobilized cells of a Citrobacter sp. as cell-bound metal phosphates. This uses phosphate liberated by the activity of a cell-bound phosphatase. Some radionuclides (e.g. 241americium) form metal phosphates readily; efficient removal of 241Am on a continuous basis is demonstrated. At low phosphatase activities, the efficiency of uranium removal correlates with enzyme activity. High phosphatase activities are not realised as an increase in metal removal, suggesting that chemical events become rate-limiting. Studies have suggested that maximal metal uptake occurs only after nucleation and the formation of precipitation foci. A model is presented to illustrate how nucleation and crystallization processes could enhance the removal of plutonium and neptunium from dilute solutions.

Multi-podant diglycolamides and room temperature ionic liquid impregnated resins: An excellent combination for extraction chromatography of actinides.

Extraction chromatography resins, prepared by impregnating two multi-podant diglycolamide ligands, viz. diglycolamide-functionalized calix[4]arene (C4DGA) and tripodal diglycolamide (T-DGA) dissolved in the room temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (RTIL: C4mimTf2N) on Chromosorb-W (an inert solid support), gave excellent results for the removal of trivalent actinides from acidic waste solutions. Distribution coefficient measurements on several metal ions showed selective sorption of Am(III) over hexavalent uranyl ions and other fission product elements such as strontium and cesium. The sorbed metal ions could be efficiently desorbed with a complexing solution containing guanidine carbonate and EDTA buffer. The sorption of Am(III) on both resins followed pseudo-second order rate kinetics with rate constants of 1.37×10(-6) and 6.88×10(-7)g/cpmmin for T-DGA and C4DGA resins, respectively. The metal sorption on both resins indicated the Langmuir monolayer chemisorption phenomenon with Eu(III) sorption capacities of 4.83±0.21 and 0.52±0.05mg per g of T-DGA and C4DGA resins, respectively. The results of column studies show that these resins are of interest for a possible application for the recovery of hazardous trivalent actinides from dilute aqueous solutions.

Decorporation of Pu/Am Actinides by Chelation Therapy: New Arguments in Favor of an Intracellular Component of DTPA Action.

Diethylenetriaminepentaacetic acid (DTPA) is currently still the only known chelating drug that can be used for decorporation of internalized plutonium (Pu) and americium (Am). It is generally assumed that chelation occurs only in biological fluids, thus preventing Pu/Am deposition in target tissues. We postulate that actinide chelation may also occur inside cells by a mechanism called "intracellular chelation". To test this hypothesis, rats were given DTPA either prior to (termed "prophylactic" treatment) or belatedly after (termed "delayed" treatment) Pu/Am injection. DTPA decorporation efficacy was systematically tested for both plutonium and americium. Both prophylactic and delayed DTPA elicited marked decreases in liver Pu/Am. These results can be explained by chelation within subcellular compartments where DTPA efficacy increased as a function of a favorable intracellular DTPA-to-actinide molar ratio. The efficacy of intracellular chelation of liver actinides decreased with the delay of treatment. This is probably explained by progressive actinide binding to the high-affinity ligand ferritin followed by migration to lysosomes. Intracellular chelation was reduced as the gap between prophylactic treatment and contamination increased. This may be explained by the reduction of the intracellular DTPA pool, which declined exponentially with time. Skeletal Pu/Am was also reduced by prophylactic and delayed DTPA treatments. This decorporation of bone actinides may mainly result from extracellular chelation on bone surfaces. This work provides converging evidence for the involvement of an intracellular component of DTPA action in the decorporation process. These results may help to improve the interpretation of biological data from DTPA-treated contamination cases and could be useful to model DTPA therapy regimens.

Orally administered DTPA di-ethyl ester for decorporation of (241)Am in dogs: Assessment of safety and efficacy in an inhalation-contamination model.

PURPOSE: Currently two injectable products of diethylenetriaminepentaacetic acid (DTPA) are U.S. Food and Drug Administration (FDA)-approved for decorporation of (241)Am; however, an oral product is considered more amenable in a mass casualty situation. The di-ethyl ester of DTPA, named C2E2, is being developed as an oral drug for treatment of internal radionuclide contamination. MATERIALS AND METHODS: Single-dose decorporation efficacy of C2E2 administered 24-h post contamination was determined in beagle dogs using a (241)Am nitrate inhalation contamination model. Single and multiple dose toxicity studies in beagle dogs were performed as part of an initial safety assessment program. In addition, the genotoxic potential of C2E2 was evaluated by the in vitro bacterial reverse mutation Ames test, mammalian cell chromosome aberration cytogenetic assay and an in vivo micronucleus test. RESULTS: Oral administration of C2E2 significantly increased (241)Am elimination over untreated controls and significantly reduced the retention of (241)Am in tissues, especially liver, kidney, lung and bone. Daily dosing of 200 mg/kg/day for 10 days was well tolerated in dogs. C2E2 was found to be neither mutagenic or clastogenic. CONCLUSIONS: The di-ethyl ester of DTPA (C2E2) was shown to effectively enhance the elimination of (241)Am after oral administration in a dog inhalation-contamination model and was well tolerated in toxicity studies.

A remarkable enhancement in Am³âº/Eu³âº selectivity by an ionic liquid based solvent containing bis-1,2,4-triazinyl pyridine derivatives: DFT validation of experimental results.

Mutual separation of trivalent actinide (An(3+)) and lanthanide (Ln(3+)) using several soft (N) donor ligands (bis(5,6-dialkyl-1,2,4-triazinyl)pyridine (R-BTP)) is attempted for the first time in room temperature ionic liquid (RTIL) medium. The results indicate a spectacular enhancement in the selectivity as compared to that in molecular diluents with a separation factor (S.F.) of >3000 for Am(3+) over Eu(3+) using the methyl derivative (Me-BTP) in RTIL medium using [C(n)mim]·[NTf2] as the diluents (where n = 2, 3, 4, 6 or 8). Such a high S.F. value has never been reported before with any of the R-BTP derivatives in molecular diluents. An opposite trend in the distribution ratio values of both Am(3+) and Eu(3+) with the increasing size of the alkyl (R) group is observed in RTIL medium when compared with that in molecular diluents. The differences in the extraction behaviour of R-BTPs in RTILs vis-à-vis molecular diluents are explained on the basis of the difference in the nature of complexes extracted in these two distinctly different media as supported by the time resolved fluorescence (TRFS) study. An unusually high extractability and selectivity for Am(3+) over Eu(3+) with Me-BTP was attributed to the formation of a 1 : 4 complex for Am(3+), which was never reported earlier with any of the R-BTP derivatives in molecular diluents. DFT studies indicated higher metal 'd' and 'f' orbital participation (covalence) in the bonding with R-BTP in the case of Am(3+) complexes as compared to that in the case of Eu(3+) complexes, which resulted in the selectivity of these classes of ligands. The observed results may have a great significance in the radioactive waste management involving the partitioning and transmutation strategy.

Species-dependent chelation of (241)Am by DTPA Di-ethyl ester.

Diethylenetriaminepentaacetic acid (DTPA) is an FDA-approved chelating agent for enhancing the elimination of transuranic elements such as americium from the body. Early access to therapy minimizes deposition of these radionuclides in tissues such as the bone. Due to its poor oral bioavailability, DTPA is administered as an IV injection, delaying access. Therefore, a diethyl-ester analog of DTPA, named C2E2, was synthesized as a means to increase oral absorption. As a hexadentate ligand, it was hypothesized that C2E2 was capable of binding americium directly. Therefore, the protonation constants and americium stability constant for C2E2 were determined by potentiometric titration and a solvent extraction method, respectively. C2E2 was shown to bind americium with a log K of 19.6. The concentrations of C2E2, its metabolite C2E1, and DTPA required to achieve effective binding in rat, beagle, and human plasma were studied in vitro. Dose response curves for each ligand were established, and the 50% maximal effective concentrations were determined for each species. As expected, higher concentrations of C2E2 were required to achieve the same degree of binding as DTPA. The results indicated that chelation in beagle plasma is more representative of the human response than rats. Finally, the pharmacokinetics of C2E2 were investigated in beagles, and the data was fit to a two-compartment model with elimination from the central compartment, along with first-order absorption. Based on the in vitro data, a 100 mg kg dose of C2E2 can be expected to have an effective duration of action of 3.8 h in beagles.

241Am removal by DTPA vs. occurrence of skeletal malignancy.

Beagle dogs injected with 241Am and treated subsequently with DTPA exhibited a reduced occurrence of skeletal malignancies and increased lifespans when compared to corresponding untreated animals also given 241Am. Whereas 92% of dogs given about 11 kBq 241Am kg(-1) and not treated with DTPA developed bone cancer (skeletal dose about 5.9 Gy), skeletal malignancy was seen in only 40% and 27%, respectively, among two groups of DTPA-treated animals injected with 11 kBq kg(-1) (doses of 5.7 and 1.7 Gy). The median lifespan among the untreated dogs was 1,728 d, but the median lifespans in the DTPA-treated groups were 2,478 and 3,654 d, respectively. Untreated dogs with a skeletal dose averaging about 2 Gy had 53% bone cancer occurrence and a median lifespan of 3,227 d. These data did not enable us to address the question of whether the reduction in cancer occurrence was proportional to, greater than, or less than the reduction in skeletal dose, but the third possibility seems unlikely.

Assessment of the global fallout of plutonium isotopes and americium-241 in the soil of the central region of Saudi Arabia.

A radiochemical technique for determination of plutonium isotopes and 241Am in soil samples is tested against IAEA-standard reference materials to determine its accuracy and precision for reliable results. The technique is then used in the investigation of topsoil samples, collected from the natural environment of the central region of Saudi Arabia, to assess the effect of fallout accumulation of these radionuclides in the region. Plutonium and americium were sequentially separated from all other components of the sample by anion-exchange chromatography and co-precipitated with Nd3+ as fluorides. The precipitates were mounted on membrane filters and measured using a high-resolution alpha-spectrometer. The results of the analysis of the reference materials showed satisfactory sensitivity and precision of the technique. The results of the analyzed soil samples show activity levels ranging from < LLD to 0.089 and from

Method for actinides and Sr-90 determination in urine samples.

The primary goal of radiation protection in decommissioning and decontamination of the old nuclear facilities of the CIEMAT is to monitor and minimize exposure of personnel. Monitoring programs include determination of actinides and 90Sr in biological samples. A technique for the sequential measurement of low levels of 239Pu, 241Am and 90Sr in urine samples has been developed. The method involves coprecipitation of these radionuclides as phosphates from bulk urine sample. Separation of Plutonium is carried out using a conventional anion exchange technique. Americium and strontium isolations are achieved sequentially by chromatographic extraction (Tru.Spec and Sr.Spec columns) from the load and rinse solutions coming from the anion exchange column. Plutonium and Americium measurements are performed by alpha spectrometry. The mean recovery obtained is 80% and the detection limit for 24 h urine sample (1.41) is 0.6 mBq L-1. 90Sr determination is made by liquid scintillation counting. The detection limit in this case is 1.1 E-01 Bq/L.

New purification protocol for actinide measurement in excreta based on calixarene chemistry.

The determination of actinides concentration level in excreta, mainly urine is currently carried out to monitor people potentially exposed to alpha emitters. To measure actinides in such samples, specific analytical protocols have been set up. The chemical purification uses different chromatographic columns to selectively separate the actinides and each fraction, after electroplating, is measured by alpha spectrometry. To reach 1 mBq l(-1) of U, Pu or Am using these protocols, 6 days equally distributed between the chemical purification and the measurement are necessary. The protocol proposed here is based on a single extractant, the 1,3,5-trimethoxy-2,4,6-tricarboxy-p-tert-butylcalix[6]arene, used to selectively separate U, Pu and Am from the urinary matrix prior to be measured. Using this analytical protocol, U and Pu are quantitatively and selectively recovered in two different acidic backextraction solutions whereas Am is quantitatively and selectively recovered in the organic phase. Furthermore, the purification stage is considerably shortened. The uranium and plutonium amounts are measured in aqueous phases using alpha spectrometry or inductively coupled plasma-mass spectrometry, whereas Am is measured in the organic phase using alpha liquid scintillation (photon/electron-rejecting alpha liquid scintillation).

Determination of 241Am in sediments by isotope dilution high resolution inductively coupled plasma mass spectrometry (ID HR ICP-MS).

Trace levels (pg kg(-1)) of 241Am in sediments were determined by isotope dilution high resolution inductively coupled plasma mass spectrometry (ID HR ICP-MS) using a microconcentric nebulizer. 241Am was isolated from major elements like Ca and Fe by different selective precipitations. In further steps. Am was first separated from other transuranic elements and purified by anion exchange and extraction chromatography prior to the mass spectrometric measurements. The ID HR ICP-MS results are compared with isotope dilution alpha spectrometry.

Nano-cerium vanadate: a novel inorganic ion exchanger for removal of americium and uranium from simulated aqueous nuclear waste.

Cerium vanadate nanopowders were synthesized by a facile low temperature co-precipitation method. The product was characterized by X-ray diffraction and transmission electron microscopy and found to consist of ∼25 nm spherical nanoparticles. The efficiency of these nanopowders for uptake of alpha-emitting radionuclides (233)U (4.82 MeV α) and (241)Am (5.49 MeV α, 60 keV γ) has been investigated. Thermodynamically and kinetically favorable uptake of these radionuclides resulted in their complete removal within 3h from aqueous acidic feed solutions. The uptake capacity was observed to increase with increase in pH as the zeta potential value decreased with the increase in pH but effect of ionic strength was insignificant. Little influence of the ions like Sr(2+), Ru(3+), Fe(3+), etc., in the uptake process indicated CeVO4 nanopowders to be amenable for practical applications. The isotherms indicated predominant uptake of the radioactive metal ions in the solid phase of the exchanger at lower feed concentrations and linear Kielland plots with positive slopes indicated favorable exchange of the metal ions with the nanopowder. Performance comparison with the other sorbents reported indicated excellent potential of nano-cerium vanadate for removing americium and uranium from large volumes of aqueous acidic solutions.