Search NASA⌕ Search

Engineering topics

Dembowski, Mateusz

Publications and source records attributed to Dembowski, Mateusz.

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Separation of rare earth element radioisotopes by reverse-phase high-speed counter-current chromatography

Analytical scale purification of rare earth element (REE) radioisotopes is typically accomplished using cation-exchange resins (e.g. AG 50W-X8) and high-performance liquid chromatography (HPLC). Despite the variety of improvements made since the development of this separation process in the 1950s, nearest neighbor separations remain a challenge, as does the issue of irreversible sample adsorption. Herein, we report a study that evaluates the potential of high-speed counter-current chromatography (HSCCC) as an alternative method for purifying REE elements, with specific reference to separations of fission product REE of interest to nuclear forensics. Complementary HSCCC REE separation experiments, one spiked with radiotracer and REE fission product activity, allowed for in depth analysis of resulting fractions from both an elemental (inductively coupled plasma atomic emission spectroscopy, ICP-AES) and radiological (gamma-ray spectrometry, beta counting) purity perspective. The highly reproducible nature of separation profiles generated from HSCCC instruments was leveraged to simplify work-up of samples containing radioisotopes. Subsequent radioanalytical evaluation revealed minimal carryover of Eu into neighboring Sm and Tb fractions (as indicated by presence of 150Eu), and trace contamination of the Tb fraction with Y (as indicated by presence of 91Y). Subtle differences in stationary phase retention across the two columns were reflected in significant variations in decontamination factors of duplicate parallel separations. Furthermore, these differences paired with obtained distribution of radioisotopes provided valuable insights into future improvements. Collectively, this study represents a significant step forward in development of HSCCC technology for task specific REE radioisotope purification.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2023

Shinkolobweite, from the Shinkolobwe Mine, Democratic Republic of Congo: A New Mineral Containing Uranium in the Rare Pentavalent Oxidation State

ABSTRACT Shinkolobweite, Pb1.333[U5+O(OH)(UO2)5O4.67(OH)5.33](H2O)5, is a new lead uranyl oxide-hydroxide hydrate mineral containing hexavalent and pentavalent uranium from the Shinkolobwe mine, Democratic Republic of Congo. Crystals of shinkolobweite are dark reddish-brown prisms up to 0.5 mm in length, occurring on a matrix of massive uraninite associated with fourmarierite, rutherfordine, soddyite, and sklodowskite. Crystals are translucent with subadamantine luster and light bronze-yellow streak, are flattened on {010}, are elongated on [001], and exhibit the forms {100}, {010}, {101}, and . The mineral is non-fluorescent under both longwave and shortwave ultraviolet illumination. It has a Mohs hardness of ∼2 and exhibits brittle tenacity with perfect cleavage on {010}, imperfect cleavage on {100}, and even fracture. The calculated density is 5.853 g/cm3 based on the empirical formula. Electron probe microanalysis provided the empirical formula Pb1.290U6+4.876U5+1.166O27H16.633 based on 27 O apfu and U5+:U6+ determined by X-ray photoelectron spectroscopy. Shinkolobweite is orthorhombic, superspace group Pnnm(0b0)000, a = 14.4808(4), b = 7.0681(8), c = 11.9423(3) Å, V = 1222.32(15) Å3, modulation wave vector [0 1/3 0], and Z = 2. The structure was refined from 8959 reflections to a final R1 = 0.0736 for all reflections. Uranyl oxide-hydroxide sheets in shinkolobweite adopt the β-U3O8 topology and possess (3 + 1) commensurately modulated ordering that results from the long-range ordering of U5+ and U6+ in the sheet, as well as the position and occupancy of interlayer Pb2+ cations. Observations of a topological transition between α-U3O8 and β-U3O8 type sheets in shinkolobweite supplements our understanding of U5+ mineral oxidation and stability.

Mineralogy↗
DOE OSTI2022

R-Value Measurements Performed on Actinide Targets Irradiated using the GODIVA IV Critical Assembly in FY22

The separation and characterization of two irradiated uranium targets, a depleted uranium (DU) and a highly enriched uranium (HEU) target as well as a plutonium (Pu) target, was conducted in April of 2022. The three targets were assembled at Los Alamos National Laboratory (LANL) and irradiated using the GODIVA critical assembly at the National Criticality Experiments Research Center (NCERC). Splits of the dissolved targets were received by Pacific Northwest National Laboratory (PNNL) after which the PNNL and LANL teams chemically separated the solutions using independent separation schemes and analyzed the separated fractions for short lived actinides and fission products. Chemical separations were traced with stable or radioactive tracers to allow for the determination of chemical yields, analyzing using either inductively coupled plasma optical emission spectroscopy (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS) or gamma emission analysis (GEA) depending on the nature of the tracer. The Pu target solution was traced with stable elements at LANL to follow elemental fractionation during a Pu removal step. Many analytical techniques were used by PNNL including kinetic phosphorescence analysis (KPA), ICP-OES, ICP-MS, GEA, and thermal ionization mass spectrometry (TIMS) depending on the analyte’s need.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Rare earth element separations by high-speed counter-current chromatography

We report that following the initial development of High-Speed Counter-Current Chromatography (HSCCC) in the 1960s, several studies have explored its applicability in the separation of rare earth elements (REEs). More recently, however, HSCCC publications have transitioned towards the separation of natural products or pharmaceuticals, leaving the application for REEs largely unexplored from a practical standpoint. Herein, we expand upon prior work in this field by evaluating the suitability of HSCCC to separation of a subset of non-radioactive REEs (Nd, Sm, Eu, Tb, and Y) at 10 -4 mol levels using di-(2-ethylhexyl)phosphoric acid (HDEHP) in n-heptane as the stationary phase and hydrochloric acid as the mobile phase. First, the effect of flow rate on the stationary phase volume retention ratio and resolution of Nd/Sm/Eu subgroup was evaluated followed by optimization of step-gradient elution profiles resulting in additional recovery of Tb and Y within a seven-hour window. The five REEs were separated at the baseline resolution level or above. Elution profiles obtained from multiple runs across two independently operated columns and across independent runs were cross analyzed. Reproducibility in elution profiles point to future applications in radioelement separation chemistry, where both chemical and radiochemical purity are of importance.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Column separation of tetravalent cerium fission products from trivalent rare earth radio-isotopes

Rapid and efficient isolation of individual rare earth element (REE) radioisotopes from complex mixtures is necessary to support the fields of nuclear forensics, medical isotope production and nuclear physics measurements. The separations must be robust and generate sufficiently high purity samples for subsequent radiological analysis. Current methodologies utilize a laborious two step Ce(IV)-iodate precipitation followed by Ce(IV)-nitrate di-(2-ethylhexyl)phosphoric acid/n-heptane extraction. This work reports an alternative method to isolate Ce fission product isotopes equilibrated with milligrams of cold carrier, from the remaining REE’s using a Ce(IV)/LN-resin (Eichrom Technologies) based separation. Optimization of Ce(IV) loading, REE(III) elution volume and subsequent Ce(III) stripping step utilized 166m Ho tracer. Mixed fission product experiments provided a further test of this LN-resin method, with analysis of purified 141/144 Ce, 147 Nd and 91 Y. Overall, while decontamination factors were lower for the LN-resin method, (vs. the combined precipitation/extraction) the simplicity of the technique and the satisfactory fission product analysis results point to the efficacy of this method.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Isotopic Substitution Reveals the Importance of Aluminate Diffusion Dynamics in Gibbsite (Al(OH) 3 ) Crystallization from Alkaline Aqueous Solution

Understanding molecular-scale factors governing the precipitation of aluminum hydroxides, such as gibbsite, under alkaline conditions is important for the formation of laterite deposits, as well as aluminum processing. However, mechanisms enabling tetrahedral aluminate ions to assemble into octahedral sites of the gibbsite lattice remain unclear. Formation of oligomeric complexes has been hypothesized as a critical intermediate step. Here, we report a study of gibbsite solubility in highly alkaline solutions using deuterium substitution to probe equilibrium and kinetic factors that could affect oligomeric intermediate formation, including the reactivity and the diffusivity of aluminate ions. When substituting sodium hydroxide with sodium deuteroxide, solution analysis shows a nearly 40% and 50% increase in gibbsite solubility in 2.4 and 3.3 mol·kg –1 total sodium solutions, respectively. Raman spectroscopy indicated that monomeric aluminate ions are the predominant species in solution irrespective of deuteration. However, both 27 Al and 23 Na nuclear magnetic resonance (NMR) spectroscopy revealed significant differences in chemical shifts in deuterated solutions, and analysis of 1 H, 23 Na, and 27 Al diffusion coefficients with pulsed-field gradient, stimulated echo NMR spectroscopy shows a decrease in ion diffusivity with increasing total deuterium in solution, consistent with the notion of increasing strength in the hydrogen/deuterium bonding network. In conclusion, because the relative change in 1 H diffusion coefficients are commensurate with the difference in apparent solubility constants, there is evidence for an oligomeric intermediate whose steady-state concentration is maintained by the collision frequency of aluminate ions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

The controlling role of atmosphere in dawsonite versus gibbsite precipitation from tetrahedral aluminate species

In highly alkaline solution, aluminum speciates as the tetrahedrally coordinated aluminate monomer, Al(OH)4- and/or dimer Al2O(OH)62-, yet precipitates as octahedrally coordinated gibbsite (Al(OH)3). This tetrahedral to octahedral transformation governs Al precipitation, which is crucial to worldwide Al production, and to the processing of caustic high-level radioactive wastes. Despite its significance, the transformation pathway remains unknown. Here we explore the roles of atmospheric water and carbon dioxide in mediating the transformation of the tetrahedrally coordinated potassium aluminate dimer salt (K2Al2O(OH)6) to gibbsite versus potassium dawsonite (KAl(CO3)(OH)2). A combination of in-situ attenuated total reflection infrared spectroscopy, ex-situ micro X-ray diffraction, and multivariate curve resolution-alternating least squares chemometrics analysis reveals that humidity plays a key role in the transformation by limiting the amount of alkalinity neutralization by dissolved CO2. Lower humidity favors higher alkalinity and incorporation of carbonate species in the final Al product to form KAl(CO3)(OH)2. Higher humidity enables more acid generation that destabilizes dawsonite and favors gibbsite as the solubility limiting phase. Because the transformation was restricted to occur in thin water films, the results suggest that transition from tetra- to octahedrally coordinated Al does not have to occur in bulk solution, as has often been hypothesized, but may instead appear on the source mineral surface.

Dembowski, Mateusz↗
DOE OSTI2021

Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species

Aluminate salts precipitated from caustic alkaline solutions exhibit a correlation between the anionic speciation and the identity of the alkali cation in the precipitate, with the aluminate ions occurring either in monomeric (Al(OH) 4 – ) or dimeric (Al 2 O(OH) 6 2– ) forms. The origin of this correlation is poorly understood as are the roles that oligomeric aluminate species play in determining the solution structure, prenucleation clusters, and precipitation pathways. Characterization of aluminate solution speciation with vibrational spectroscopy results in spectra that are difficult to interpret because the ions access a diverse and dynamic configurational space. To investigate the Al(OH) 4 – and Al 2 O(OH) 6 2– anions within a well-defined crystal lattice, inelastic neutron scattering (INS) and Raman spectroscopic data were collected and simulated by density functional theory for K 2 [Al 2 O(OH) 6 ], Rb 2 [Al 2 O(OH) 6 ], and Cs[Al(OH) 4 ]·2H 2 O. These structures capture archetypal solution aluminate species: the first two salts contain dimeric Al 2 O(OH) 6 2– anions, while the third contains the monomeric Al(OH) 4 – anion. Here, comparisons were made to the INS and Raman spectra of sodium aluminate solutions frozen in a glassy state. In contrast to solution systems, the crystal lattice of the salts results in well-defined vibrations and associated resolved bands in the INS spectra. The use of a theory-guided analysis of the INS of this solid alkaline aluminate series revealed that differences were related to the nature of the hydrogen-bonding network and showed that INS is a sensitive probe of the degree of completeness and strength of the bond network in hydrogen-bonded materials. Results suggest that the ionic size may explain cation-specific differences in crystallization pathways in alkaline aluminate salts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Cluster defects in gibbsite nanoplates grown at acidic to neutral pH

Gibbsite [α-Al(OH) 3 ] is the solubility limiting phase for aluminum across a wide pH range, and it is a common mineral phase with many industrial applications. The growth mechanism of this layered-structure material, however, remains incompletely understood. Synthesis of gibbsite at low to circumneutral pH yields nanoplates with substantial interlayer disorder. Here we examine defects in this material in detail, and the effects of recrystallization in highly alkaline sodium hydroxide solution at 80 °C. We employed a multimodal approach, including scanning electron microscopy, magic-angle spinning nuclear magnetic resonance (MAS-NMR), Raman and infrared spectroscopies, X-ray diffraction (XRD), and X-ray total scattering pair distribution function (XPDF) analysis to characterize the ageing of the nanoplates over several days. Additionally, XRD and XPDF indicate that gibbsite nanoplates precipitated at circumneutral pH contain dense, truncated sheets imparting a local difference in interlayer distance. These interlayer defects appear well described by flat Al 13 aluminum hydroxide nanoclusters nearly isostructural with gibbsite sheets present under synthesis conditions and trapped as interlayer inclusions during growth. Ageing at elevated temperature in alkaline solutions gradually improves crystallinity, showing a gradual increase in H-bonding between interlayer OH groups. Between 7 to 8 vol% of the initial gibbsite nanoparticles exhibit this defect, with the majority of differences disappearing after 2–4 hours of recrystallization in alkaline solution. The results not only identify the source of disorder in gibbsite formed under acidic/neutral conditions but also point to a possible cluster-mediated growth mechanism evident through inclusion of relict oligomers with gibbsite-like topology trapped in the interlayer spaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Prediction of Solution Behavior via Calorimetric Measurements Allows for Detailed Elucidation of Polyoxometalate Transformation

The solution behavior of a polyoxometalate cluster, LiNa-U 24 Pp 12 (Li 24 Na 24 [(UO 2 O 2 ) 24 (P 2 O 7 ) 12 ]) that consists of 24 uranyl ions, peroxide groups, and 12 pyrophosphate linkers, was successfully predicted based on new thermodynamic results using a calorimetric method recently described for uranyl peroxide nanoclusters (UPCs), molybdenum blues, and molybdenum browns. The breakdown of LiNa-U 24 Pp 12 and formation of U 24 (Li 24 [UO 2 O 2 OH] 24 ) was monitored in situ via Raman spectroscopy using a custom heating apparatus. A combination of analytical techniques confirmed the simultaneous existence of U 24 Pp 12 and U 24 midway through the conversion process and U 24 as the single end product. The application of a molecular weight filter resulted in a complete and successful separation of UPCs from solution and, in conjunction with DOSY results, confirmed the presence of large intermediate cluster building blocks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Nitrate and Nitrite Incompatibility with Hydroxide Ions in Concentrated NaOH Solutions: Implications for Hydroxide and Gibbsite Reactivity in Alkaline Nuclear Waste

Electrolyte solutions in alkaline nuclear waste contain aluminate, hydroxide, nitrate and nitrite with sodium as the predominant counterion. The salts of these ions are highly soluble, so the liquids are highly concentrated. This study found that there is a substantial incompatibility between the hydroxide and nitrate and/or nitrate ions. This was determined by the observations that adding just one molal of NaNO2 or NaNO3 to saturated NaOH solution precipitation of 12 moles of NaOH·H2O salt, whereas the common ion effect would have expected only about 1 mole to precipitate. Further analysis indicates that the presence of nitrate and nitrite drastically increases the reactivity of sodium hydroxide ions in solution, which likely influences the reactivity of other hydroxide-mediated reactions. This enhanced reactivity is likely because it disrupts large Na+-OH- ion networks because nitrate and nitrite do not fit in those ion networks similarly to how some ions cannot substitute into a foreign crystal lattice. In contrast, the aluminate ion did not have the same large incompatibility with hydroxide.

Nitrite, Nitrate, Aluminate, NaOH*H2O, Ion-aggrega↗
DOE OSTI2020

Mechanisms of Al3+ dimerization in alkaline solutions

The molecular speciation of aluminum (Al3+) in alkaline solutions is fundamental to its precipitation chemistry within a number of industrial applications that include ore renement and industrial processing of Al wastes. Under these conditions, Al3+ is predominantly Al(OH) {4 , while at high [Al] dimeric species also known to form. To date, the mechanism of dimer formation remains unclear and it is likely infuenced by complex ion ion interactions. In the present work, we investigate the role of ion pairing and a suite of potential dimerization pathways using a three-pronged approach that consists of density functional theory-based molecular dynamics (DFTMD), static DFT calculations (sDFT) and semi-empirical density functional tight binding molecular dynamics (SEMD). Specic cation eects imparted by the background electrolyte cations Na+, Li+ and K+ have been examined. Our simulations predict that when the Al species are ion paired with either cation the formation of the oxo-bridged Al2O(OH) 2{6 is favored with respect to the dihydroxo-bridged Al2(OH) 2{8 , in agreement with previousspectroscopic work. The formation of both dimers rst proceeds by bridging of two monomeric units via one hydroxo ligand, leading to a labile Al2(OH) 2{8 isomer. The eect of contact ion pairing of Li+ and K+ on the dimerization energetics is distinctly more favorable than that of Na+, which may have an impact on further ligomerization.

Pouvreau, Maxime↗
DOE OSTI2020

Influence of soluble oligomeric aluminum on precipitation in the Al-KOH-H2O system

The role of oligomeric aluminate (Al(OH)4-) species in the precipitation of aluminum phases such as gibbsite (a-Al(OH)3) from aqueous hydroxide solutions remains unclear and difficult to probe directly, despite its importance to developing accurate predictions of Al solubility in highly alkaline systems. Precipitation in this system entails a transition from predominantly tetrahedrally coordinated Al species in solution to octahedrally coordinated Al in gibbsite. Here we report a quantitative study of dissolved Al in the Al-KOH-H2O system using a combination of molecular spectroscopies. We established a relationship between changes in 27Al NMR chemical shifts and the relative intensity of Raman vibrational bands, indicative of variations in the ensemble speciation of Al in solution, and the formation of unique contact ion pair interactions with the aluminate dimer, Al2O(OH)62 . A strong correlation between the extent of Al oligomerization and the amount of solvated Al was demonstrated by systematically varying the KOH:Al molar ratio. The concentration of dissolved oligomeric Al in solution also directly impacted the particle size and morphology of gibbsite; high concentrations of dimeric Al2O(OH)62-, yielded smaller and more numerous anhedral to subhedral gibbsite particles, while low concentrations yielded fewer and larger euhedral gibbsite platelets. The collective observations suggest a key role of the Al2O(OH)62- dimer in promoting gibbsite precipitation from solution, where the potassium ion-paired dimer possibly catalyzes a more rapid transformation of Al coordination from tetrahedral in solution to octahedral in gibbsite.

Dembowski, Mateusz↗