16 results on '"Artas Migdisov"'
Search Results
2. Nature and coordination geometry of geologically relevant aqueous Uranium(VI) complexes up to 400 ºC: A review and new data
- Author
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Alexander Kalintsev, Qiushi Guan, Joël Brugger, Artas Migdisov, Barbara Etschmann, Rahul Ram, Weihua Liu, Yuan Mei, Denis Testemale, and Hongwu Xu
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Environmental Engineering ,Health, Toxicology and Mutagenesis ,Environmental Chemistry ,Pollution ,Waste Management and Disposal - Published
- 2023
3. Uranium carbonate complexes demonstrate drastic decrease in stability at elevated temperatures
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Artas Migdisov, Yifeng Wang, Carlos F. Jove-Colon, Florie Caporuscio, Robert Roback, Xiaofeng Guo, Hakim Boukhalfa, Edward N. Matteo, Robert A. Mayanovic, Joël Brugger, Jason Baker, Christopher Darrell Alcorn, Alexander Kalintsev, Nadib Akram, Hongwu Xu, and Hari S. Viswanathan
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inorganic chemicals ,chemistry.chemical_element ,Context (language use) ,complex mixtures ,Biochemistry ,Hydrothermal circulation ,law.invention ,chemistry.chemical_compound ,law ,Nuclear power plant ,Materials Chemistry ,Environmental Chemistry ,QD1-999 ,business.industry ,technology, industry, and agriculture ,Radioactive waste ,General Chemistry ,Uranium ,Nuclear power ,Uranium ore ,Chemistry ,chemistry ,Environmental chemistry ,Environmental science ,Carbonate ,business - Abstract
Quantitative understanding of uranium transport by high temperature fluids is crucial for confident assessment of its migration in a number of natural and artificially induced contexts, such as hydrothermal uranium ore deposits and nuclear waste stored in geological repositories. An additional recent and atypical context would be the seawater inundated fuel of the Fukushima Daiichi Nuclear Power Plant. Given its wide applicability, understanding uranium transport will be useful regardless of whether nuclear power finds increased or decreased adoption in the future. The amount of uranium that can be carried by geofluids is enhanced by the formation of complexes with inorganic ligands. Carbonate has long been touted as a critical transporting ligand for uranium in both ore deposit and waste repository contexts. However, this paradigm has only been supported by experiments conducted at ambient conditions. We have experimentally evaluated the ability of carbonate-bearing fluids to dissolve (and therefore transport) uranium at high temperature, and discovered that in fact, at temperatures above 100 °C, carbonate becomes almost completely irrelevant as a transporting ligand. This demands a re-evaluation of a number of hydrothermal uranium transport models, as carbonate can no longer be considered key to the formation of uranium ore deposits or as an enabler of uranium transport from nuclear waste repositories at elevated temperatures. Carbonate species may play a role in uranium transport in natural systems and nuclear waste repositories at high temperatures. Here uranyl carbonate species are shown to decrease in stability under hydrothermal conditions, suggesting that these species may not mediate transport after all.
- Published
- 2021
4. Thermodynamic non-ideality and disorder heterogeneity in actinide silicate solid solutions
- Author
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Artas Migdisov, Adel Mesbah, José Marcial, Emily T. Nienhuis, Nicolas Dacheux, Xiaofeng Guo, Jörg Neuefeind, Yang Zhang, X. Zhao, John S. McCloy, Stéphanie Szenknect, Liang Qi, J. Lin, Hongwu Xu, Rodney C. Ewing, Interfaces de Matériaux en Evolution (LIME), Institut de Chimie Séparative de Marcoule (ICSM - UMR 5257), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)
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Materials science ,Scattering ,Materials Science (miscellaneous) ,Thermodynamics ,Pair distribution function ,02 engineering and technology ,Actinide ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Stability (probability) ,Silicate ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Chemistry (miscellaneous) ,Materials Chemistry ,Ceramics and Composites ,TA401-492 ,[CHIM]Chemical Sciences ,Neutron ,0210 nano-technology ,Materials of engineering and construction. Mechanics of materials ,Mixing (physics) ,Solid solution - Abstract
Non-ideal thermodynamics of solid solutions can greatly impact materials degradation behavior. We have investigated an actinide silicate solid solution system (USiO4–ThSiO4), demonstrating that thermodynamic non-ideality follows a distinctive, atomic-scale disordering process, which is usually considered as a random distribution. Neutron total scattering implemented by pair distribution function analysis confirmed a random distribution model for U and Th in first three coordination shells; however, a machine-learning algorithm suggested heterogeneous U and Th clusters at nanoscale (~2 nm). The local disorder and nanosized heterogeneous is an example of the non-ideality of mixing that has an electronic origin. Partial covalency from the U/Th 5f–O 2p hybridization promotes electron transfer during mixing and leads to local polyhedral distortions. The electronic origin accounts for the strong non-ideality in thermodynamic parameters that extends the stability field of the actinide silicates in nature and under typical nuclear waste repository conditions.
- Published
- 2021
5. Retaining Geochemical Signatures during Aragonite-Calcite Transformation at Hydrothermal Conditions
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Padmanava Dash, Jac J. Varco, Anh Nguyen, Angel Jimenez, R. I. Gabitov, Brenda L. Kirkland, Alberto Pérez-Huerta, Varun Paul, Andrew Dygert, and Artas Migdisov
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Calcite ,hydrothermal ,Materials science ,Mineral ,Stable isotope ratio ,Aragonite ,Analytical chemistry ,Geology ,engineering.material ,Geotechnical Engineering and Engineering Geology ,Mineralogy ,Hydrothermal circulation ,aragonite–calcite transformation ,Crystal ,Mg/Ca ,chemistry.chemical_compound ,Sr/Ca ,Isotope fractionation ,chemistry ,engineering ,stable isotope ,Electron backscatter diffraction ,QE351-399.2 - Abstract
Transformation of aragonite, a mineral phase metastable at Earth’s surface, to calcite widely occurs in both sedimentary and metamorphic systems with the presence of an aqueous phase. The transformation process can affect geochemical signatures of aragonite (a protolith). This study focused on quantification of the retention of Mg/Ca and Sr/Ca ratios, and δ18O during the transformation process as well as evaluation of the transformation rate. To investigate the effect of transformation from aragonite to calcite on elemental and stable isotope ratios, we conducted a series of experiments in NaCl solutions at temperatures between 120 and 184 °C. Two additional experiments at 250 °C were conducted to estimate the transformation rate of aragonite to calcite. Protolith materials consist of (1) synthetic (Mg, Sr-bearing or non-Mg, Sr bearing) needle-shaped microcrystals of aragonite (<, 5 µm in size) and (2) larger chips (>, 100 µm in size) of natural aragonite. X-ray diffraction (XRD) showed that microcrystals successfully transformed to calcite within 30 h and scanning electron microscopy (SEM) yielded a change in the crystal size to >, 10 µm in rhombohedral shape. Electron backscatter diffraction (EBSD) of the larger aragonite chips showed that transformation to randomly oriented calcite occurred at the rims and along the cracks while the core retained an aragonite crystal structure. Isotope-ratio mass spectrometry (IRMS) analyses showed that calcite δ18O was controlled by temperature and δ18O of the solution. The obtained calibration curve of isotope fractionation factor versus temperature is consistent with other studies. Inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses showed that calcite partially or completely retained Mg/Ca and Sr/Ca ratios through the transformation.
- Published
- 2021
6. Long-term stability of dithionite in alkaline anaerobic aqueous solution
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Katherine Telfeyan, Velimir V. Vesselinov, Paul W. Reimus, Sachin Pandey, and Artas Migdisov
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Aqueous solution ,Chemistry ,Ion chromatography ,Inorganic chemistry ,010501 environmental sciences ,010502 geochemistry & geophysics ,Dithionite ,01 natural sciences ,Pollution ,Redox ,Decomposition ,Sodium dithionite ,chemistry.chemical_compound ,Iodometry ,Geochemistry and Petrology ,Environmental Chemistry ,Stoichiometry ,0105 earth and related environmental sciences - Abstract
Closed-system experiments were conducted to investigate the decomposition of sodium dithionite in aqueous solutions under varying pH and starting concentrations to simulate the deployment of dithionite as an in-situ redox barrier. Co-determination of dithionite and its degradation products was conducted using UV–Vis spectrometry, iodometric titration, and ion chromatography. In unbuffered solutions, dithionite reacted rapidly, whereas in near-neutral solutions (pH ∼7), it persisted for ∼ 50 days and in alkaline solution (pH ∼9.5) for >100 days. These are the longest lifetimes reported to date, which we attribute to not only excluding oxygen but also preventing outgassing of H2S. Thoroughly constraining the reaction products has led to the following hypothesized reaction: 4 S2O42− + H2O → HS− + SO32−+2 SO42− + S4O62− + H+ which represents relatively rapid degradation at near-neutral pH values. At the more alkaline pH, and over longer time scales, the reaction is best represented by: 3 S2O42− + 3 H2O → 2HS- + SO32−+3 SO42−+ 4 H+ the following kinetic rate law was developed for the pH range studied: dC i dt = S i 10 − 4.81 { H + } 0.24 { S 2 O 4 2 - } , where dC i dt is the rate of change of the i t h chemical component in the simplified equation (mole L−1 s−1) and Si is the stoichiometric coefficient of the ith chemical. The kinetic rate law was used to calculate a pseudo first order half-life of 10.7 days for near-neutral pH and 33.6 days for alkaline pH. This work implies that if hydrogen sulfide is contained within the system, such as in the case of a confined aquifer below the water table, dithionite decomposes more slowly in alkaline aqueous solution than previously thought, and thus it may be more cost-effectively distributed in aquifers than has been previously assumed.
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- 2019
7. Uranium Uptake by Apatite at Hydrothermal Conditions
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Todd E. Mlsna, Artas Migdisov, Robert Roback, R. I. Gabitov, Chanaka M. Navarathna, Anh Nguyen, Daniel Makowsky, Angel Jimenez, and Varun Paul
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Chemistry ,visual_art ,visual_art.visual_art_medium ,chemistry.chemical_element ,Uranium ,Hydrothermal circulation ,Apatite ,Nuclear chemistry - Published
- 2021
8. Energetics of La, Nd-Containing Hydroxylbästnasite (La1-xNdxCO3OH) Solid Solutions
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Xiaofeng Guo, Artas Migdisov, Chris J. Benmore, Vitaliy G. Goncharov, Haylea Nisbet, Hongwu Xu, and Andrew C. Strzelecki
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Materials science ,Energetics ,Thermodynamics ,Solid solution - Published
- 2021
9. Role of water and hydroxyl groups in the structures of stetindite and coffinite, MSiO4 (M = Ce, U)
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Hongwu Xu, Jason Baker, Nicolas Dacheux, Paul Estevenon, Adel Mesbah, Thomas Barral, Vitaliy G. Goncharov, Rodney C. Ewing, Artas Migdisov, Andrew C. Strzelecki, Jianming Bai, Xiaofeng Guo, Stephanie Szenknect, and Nicolas Clavier
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Crystallography ,Chemistry ,Coffinite - Published
- 2021
10. Revisit the thermodynamics of orthosilicates for actinide waste form
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Artas Migdisov, Rodney C. Ewing, Adel Mesbah, Xiaofeng Guo, Andrew C. Strzelecki, Hongwu Xu, Nicolas Dacheux, José Marcial, John S. McCloy, Stéphanie Szenknect, and Paul Estevenon
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Materials science ,Thermodynamics ,Actinide - Published
- 2021
11. Numerical simulation of Au-Cu-Ag-Mo vapor-transport applied to magmatic-hydrothermal ore formation
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Nicole C. Hurtig, Artas Migdisov, and Anthony E. Williams-Jones
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Materials science ,Computer simulation ,Chemical engineering ,Hydrothermal circulation - Published
- 2021
12. Challenging the thorium-immobility paradigm
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Hongwu Xu, Anthony E. Williams-Jones, Vincent J. van Hinsberg, Haylea Nisbet, Robert Roback, and Artas Migdisov
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Nuclear fuel cycle ,021110 strategic, defence & security studies ,Economic geology ,Multidisciplinary ,Aqueous solution ,lcsh:R ,0211 other engineering and technologies ,Geochemistry ,Thorium ,chemistry.chemical_element ,lcsh:Medicine ,Crust ,02 engineering and technology ,Actinide ,010502 geochemistry & geophysics ,01 natural sciences ,Hydrothermal circulation ,Article ,chemistry ,lcsh:Q ,Solubility ,lcsh:Science ,Earth (classical element) ,0105 earth and related environmental sciences - Abstract
Thorium is the most abundant actinide in the Earth’s crust and has universally been considered one of the most immobile elements in natural aqueous systems. This view, however, is based almost exclusively on solubility data obtained at low temperature and their theoretical extrapolation to elevated temperature. The occurrence of hydrothermal deposits with high concentrations of Th challenges the Th immobility paradigm and strongly suggests that Th may be mobilized by some aqueous fluids. Here, we demonstrate experimentally that Th, indeed, is highly mobile at temperatures between 175 and 250 °C in sulfate-bearing aqueous fluids due to the formation of the highly stable Th(SO4)2 aqueous complex. The results of this study indicate that current models grossly underestimate the mobility of Th in hydrothermal fluids, and thus the behavior of Th in ore-forming systems and the nuclear fuel cycle needs to be re-evaluated.
- Published
- 2019
13. Uptake of uranium by carbonate crystallization from reduced and oxidized hydrothermal fluids
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Robert Roback, Anh Nguyen, Hongwu Xu, Florie Caporuscio, Aleksey Sadekov, Alberto Pérez-Huerta, Jason Baker, Kirsten B. Sauer, R. I. Gabitov, Varun Paul, Noah Van Hartesveldt, and Artas Migdisov
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Calcite ,010504 meteorology & atmospheric sciences ,Inorganic chemistry ,chemistry.chemical_element ,Geology ,Uranium ,010502 geochemistry & geophysics ,01 natural sciences ,Chloride ,Redox ,Hydrothermal circulation ,law.invention ,chemistry.chemical_compound ,chemistry ,Geochemistry and Petrology ,Mineral redox buffer ,law ,medicine ,Carbonate ,Crystallization ,0105 earth and related environmental sciences ,medicine.drug - Abstract
This work evaluated the immobilization of uranium (U) through incorporation into calcite under reduced and oxidized conditions. We investigated how much U could be entrapped by calcite crystallizing in chloride solutions in autoclaves at temperatures from 162 to 300 °C. The oxidation state of U was set by controlling oxygen fugacity via redox buffers. Uranium was introduced into calcite growth media as a solid oxide compound or U aliquot. We found the uptake of tetravalent U by calcite is higher than that of hexavalent U by up to four orders of magnitude. We estimate that crystallization of a few mg of calcite immobilizes all dissolved U when 1 kg of solution is saturated with UO2 under reduced hydrothermal conditions.
- Published
- 2021
14. Experiments to determine the suitability of sodium dithionite treatment for a Cr(VI) groundwater plume in a deep aquifer of the United States Southwest
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Katherine Telfeyan, Artas Migdisov, and Paul W. Reimus
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geography ,geography.geographical_feature_category ,Chemistry ,Process Chemistry and Technology ,Aquifer ,02 engineering and technology ,010501 environmental sciences ,021001 nanoscience & nanotechnology ,Dithionite ,01 natural sciences ,Pollution ,Redox ,Plume ,Sodium dithionite ,chemistry.chemical_compound ,Environmental chemistry ,Chemical Engineering (miscellaneous) ,Hexavalent chromium ,Leaching (agriculture) ,0210 nano-technology ,Waste Management and Disposal ,Groundwater ,0105 earth and related environmental sciences - Abstract
Legacy industrial waste has left groundwater plumes of hexavalent Cr (Cr(VI)) that requires treatment, predominantly by reduction to Cr(III) and subsequent precipitation. One promising technology is the injection of a strong reducing agent, sodium dithionite, to create an in-situ redox barrier, but implementation requires a comprehensive understanding of the reactions occurring with dithionite injection. Batch and column experiments were conducted with aquifer sediments to determine both the significant reactions and efficacy of sodium dithionite treatment for a groundwater plume of hexavalent chromium. The batch experiments demonstrate consumption of dithionite over the experiment (disappearance by 43 d) concurrent with leaching of about 1 mM Fe from the sediments. Reactions deduced from batch experiments were incorporated into a 1-D numerical model to simulate reactions occurring during the column injection. The treatment was able to successfully reduce approximately 30 pore volumes of groundwater containing 800 µg kg−1 Cr(VI). The experiments also demonstrate that although mineral forms of Fe are important phases in the reduction of Cr(VI), Fe alone cannot account for the entire reduction capacity imparted to the sediments. Rather, the correlation between Cr and reduced S retained in the columns, combined with Scanning Electron Microscopy (SEM) of treated sediments, suggest that formation of reduced S phases contributes to the prolonged reduction capacity.
- Published
- 2021
15. Rigorous analysis of non-ideal solubility of sodium and copper chlorides in water vapor using Pitzer-Pabalan model
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Artas Migdisov, Kirill A. Velizhanin, Christopher Darrell Alcorn, and Robert P. Currier
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Work (thermodynamics) ,Vapor pressure ,General Chemical Engineering ,Gaussian ,FOS: Physical sciences ,General Physics and Astronomy ,Salt (chemistry) ,Thermodynamics ,02 engineering and technology ,01 natural sciences ,Quantum chemistry ,symbols.namesake ,020401 chemical engineering ,Physics - Chemical Physics ,Molecule ,Physics - Atomic and Molecular Clusters ,0204 chemical engineering ,Physical and Theoretical Chemistry ,Solubility ,Chemical Physics (physics.chem-ph) ,chemistry.chemical_classification ,010405 organic chemistry ,Chemistry ,0104 chemical sciences ,symbols ,Atomic and Molecular Clusters (physics.atm-clus) ,Water vapor - Abstract
Gaseous mixtures of water vapor and neutral molecules of salt (e.g., NaCl, CuCl etc.) can be highly non-ideal due to a strong attractive interaction between salt and water molecules. In particular, this can result in high solubility of salts in water vapor and a strong dependence of solubility on vapor pressure. The analysis of salt solubility in water vapor can be done using the Pitzer-Pabalan model, which is based on the thermodynamic theory of imperfect gases. The original Pitzer-Pabalan work demonstrated that one can reproduce experimental data for NaCl solubility in vapor. No analysis was performed on the reliability of their original fits, which we believe has contributed to the lack of applications of the Pitzer-Pabalan model despite the apparent success of the original paper. In this work, we report our recent progress in developing a rigorous fitting procedure to parameterize the Pitzer-Pabalan model using experimental data. Specifically, we performed fitting of the experimental results obtained elsewhere for NaCl and CuCl. We investigate the degree of underfitting/overfitting and the sensitivity of the fitting quality to variations in the resulting fitting parameters. The results, as represented by the thermodynamic parameters describing the energetics of formation of salt-bearing water clusters, were successfully benchmarked against Gaussian 16 ab initio quantum chemistry calculations. The resulting rigorous fitting procedure presented here can now be applied to other systems.
- Published
- 2020
16. REE Incorporation into Calcite Individual Crystals as One Time Spike Addition
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Aleksey Sadekov, R. I. Gabitov, and Artas Migdisov
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Calcite ,lcsh:Mineralogy ,lcsh:QE351-399.2 ,010504 meteorology & atmospheric sciences ,rare earth ,calcite ,partitioning ,LA-ICP-MS ,Rare earth ,Mineralogy ,Geology ,010502 geochemistry & geophysics ,Geotechnical Engineering and Engineering Geology ,01 natural sciences ,Lower limit ,Crystal ,Partition coefficient ,chemistry.chemical_compound ,chemistry ,La icp ms ,0105 earth and related environmental sciences - Abstract
Experiments on the incorporation of trace elements into calcite were performed, and rare earth elements (REE) were used to mark the growth zones of individual crystals. Experiments were conducted at different pH (7.7 to 8.8) and temperatures (2 °C to 24.6 °C) in NH4Cl + CaCl2 solutions, where REE were rapidly consumed by growing calcite. LA-ICP-MS line-scans yielded the distribution of (REE/Ca)calcite within individual crystals in a manner consistent with the addition of REE into fluid. A sharp decrease of (REE/Ca)calcite toward the crystal edge suggests the fast depletion of (REE/Ca)fluid due to strong REE consumption by growing calcite. An attempt was made to estimate the lower limit of the partition coefficients between calcite and fluid using selected REE/Ca data within individual calcite crystals and the amount of REE added into fluid.
- Published
- 2017
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