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1.
Environ Sci Technol ; 55(11): 7605-7614, 2021 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-33974404

RESUMO

Advanced materials and processes are required to separate halides and fission products from complex salt waste streams associated with the chemical reprocessing of used nuclear fuels and molten salt reactor technologies for immobilization into chemically durable waste forms. In this work, we explore an innovative concept using metal halide perovskites as advanced host phases to incorporate Cs and Cl with very high waste loadings. Wet chemistry-synthesized Cs2SnCl6 powders from CsCl salt solutions are successfully encapsulated into a silica matrix to form a composite using low-temperature spark plasma sintering with tunable Cs and Cl loadings up to 31 and 26 wt %, respectively. Chemical durability testing of the composite waste forms by semi-dynamic leaching experiments demonstrates that an incongruent leaching mechanism dominates the release of Cs and Cl. The metal halide perovskite-silica composite waste forms display exceptional chemical durability with the long-term release rates of Cs and Cl comparable to or outperforming the state-of-the-art waste form materials but with significantly higher waste loadings. The scalable synthesis of the metal halide perovskite from wet chemistry processes opens up new opportunities in designing advanced waste forms for salt wastes with very high waste loadings and exceptional chemical durability for the sustainable development of advanced fuel cycles and next-generation reactor technologies.


Assuntos
Cloretos , Dióxido de Silício , Compostos de Cálcio , Metais , Óxidos , Titânio
2.
Environ Sci Technol ; 51(15): 8635-8642, 2017 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-28695732

RESUMO

Technetium (Tc) remains a priority remediation concern due to persistent challenges, including mobilization due to rapid reoxidation of immobilized Tc, and competing comingled contaminants, e.g., Cr(VI), that inhibit Tc(VII) reduction and incorporation into stable mineral phases. Here Fe(OH)2(s) is investigated as a comprehensive solution for overcoming these challenges, by serving as both the reductant, (Fe(II)), and the immobilization agent to form Tc-incorporated magnetite (Fe3O4). Trace metal analysis suggests removal of Tc(VII) and Cr(VI) from solution occurs simultaneously; however, complete removal and reduction of Cr(VI) is achieved earlier than the removal/reduction of comingled Tc(VII). Bulk oxidation state analysis of the final magnetite solid phase by XANES shows that the majority of Tc is Tc(IV), which is corroborated by XPS measurements. Furthermore, EXAFS results show successful, albeit partial, Tc(IV) incorporation into magnetite octahedral sites. Cr XPS analysis indicates reduction to Cr(III) and the formation of a Cr-incorporated spinel, Cr2O3, and Cr(OH)3 phases. Spinel (modeled as Fe3O4), goethite (α-FeOOH), and feroxyhyte (δ-FeOOH) are detected in all reacted final solid phase samples analyzed by XRD. Incorporation of Tc(IV) has little effect on the spinel lattice structure. Reaction of Fe(OH)2(s) in the presence of Cr(III) results in the formation of a spinel phase that is a solid solution between magnetite (Fe3O4) and chromite (FeCr2O4).


Assuntos
Cromo/química , Poluentes Ambientais/química , Compostos Férricos/química , Tecnécio/química , Compostos de Ferro , Minerais , Oxirredução
3.
Environ Sci Technol ; 49(14): 8856-63, 2015 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-26111202

RESUMO

The kinetics of the feed-to-glass conversion affects the waste vitrification rate in an electric glass melter. The primary area of interest in this conversion process is the cold cap, a layer of reacting feed on top of the molten glass. The work presented here provides an experimental determination of the temperature distribution within the cold cap. Because direct measurement of the temperature field within the cold cap is impracticable, an indirect method was developed in which the textural features in a laboratory-made cold cap with a simulated high-level waste feed were mapped as a function of position using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The temperature distribution within the cold cap was established by correlating microstructures of cold-cap regions with heat-treated feed samples of nearly identical structures at known temperatures. This temperature profile was compared with a mathematically simulated profile generated by a cold-cap model that has been developed to assess the rate of glass production in a melter.


Assuntos
Temperatura Baixa , Resíduos Radioativos/análise , Vitrificação , Vidro/química , Modelos Teóricos , Espectrometria por Raios X , Difração de Raios X
4.
Environ Sci Technol ; 48(10): 5832-9, 2014 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-24779585

RESUMO

Powders of a Sn2S3 chalcogen-based aerogel (chalcogel) were combined with powdered polyacrylonitrile (PAN) in different mass ratios (SnS33, SnS50, and SnS70; # = mass% of chalcogel), dissolved in dimethyl sulfoxide, and added dropwise to deionized water to form pellets of a porous PAN-chalcogel hybrid material. These pellets, along with pure powdered (SnSp) and granular (SnSg) forms of the chalcogel, were then used to capture iodine gas under both dynamic (dilute) and static (concentrated) conditions. Both SnSp and SnSg chalcogels showed very high iodine loadings at 67.2 and 68.3 mass%, respectively. The SnS50 hybrid sorbent demonstrated a high, although slightly reduced, maximum iodine loading (53.5 mass%) with greatly improved mechanical rigidity. In all cases, X-ray diffraction results showed the formation of crystalline SnI4 and SnI4(S8)2, revealing that the iodine binding in these materials is mainly due to a chemisorption process, although a small amount of physisorption was observed.


Assuntos
Resinas Acrílicas/química , Géis/química , Adsorção , Iodo/análise , Radioisótopos do Iodo , Microscopia Eletrônica de Varredura , Pós , Espectrometria por Raios X , Termogravimetria , Fatores de Tempo , Difração de Raios X
5.
RSC Adv ; 14(27): 18978-19000, 2024 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-38873547

RESUMO

The synthesis methods, crystal structures, and properties of anhydrous monazite and xenotime (REPO4) crystalline materials are summarized within this review. For both monazite and xenotime, currently available Inorganic Crystal Structure Database data were used to study the effects of incorporating different RE cations on the unit cell parameters, cell volumes, densities, and bond lengths. Domains of monazite-type and xenotime-type structures and other AXO4 compounds (A = RE; X = P, As, V) are discussed with respect to cation sizes. Reported chemical and radiation durabilities are summarized. Different synthesis conditions and chemicals used for single crystals and polycrystalline powders, as well as first-principles calculations of the structures and thermophysical properties of these minerals are also provided.

6.
ACS Omega ; 9(17): 19395-19400, 2024 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-38708232

RESUMO

Electrochemical processing of spent nuclear fuel in molten chloride salts results in radioactive salt waste. Chlorine removal from the salt has been identified as an effective and efficient first step in the management of high-level waste. In this work, a simple salt was dechlorinated with a phosphoric acid phosphate precursor, resulting in a glassy dechlorinated product. The dechlorination efficacy was evaluated in air and argon environments. This work serves as an initial step to advance the Technological Readiness Level of H3PO4-based dechlorination step toward implementation of iron phosphate waste forms to immobilize electrochemical fuel reprocessing salt waste streams.

7.
Environ Sci Technol ; 47(13): 7540-7, 2013 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-23763706

RESUMO

The efficient capture of radionuclides with long half-lives such as technetium-99 ((99)Tc), uranium-238 ((238)U), and iodine-129 ((129)I) is pivotal to prevent their transport into groundwater and/or release into the atmosphere. While different sorbents have been considered for capturing each of them, in the current work, nanostructured chalcogen-based aerogels called chalcogels are shown to be very effective at capturing ionic forms of (99)Tc and (238)U, as well as nonradioactive gaseous iodine (i.e., a surrogate for (129)I2), irrespective of the sorbent polarity. The chalcogel chemistries studied were Co0.7Bi0.3MoS4, Co0.7Cr0.3MoS4, Co0.5Ni0.5MoS4, PtGe2S5, and Sn2S3. The PtGe2S5 sorbent performed the best overall with capture efficiencies of 98.0% and 99.4% for (99)Tc and (238)U, respectively, and >99.0% for I2(g) over the duration of the experiment. The capture efficiencies for (99)Tc and (238)U varied between the different sorbents, ranging from 57.3-98.0% and 68.1-99.4%, respectively. All chalcogels showed >99.0% capture efficiency for iodine over the test duration. This versatile nature of chalcogels can provide an attractive option for the environmental remediation of the radionuclides associated with legacy wastes from nuclear weapons production as well as wastes generated during nuclear power production or nuclear fuel reprocessing.


Assuntos
Iodo/química , Poluentes Radioativos/química , Pertecnetato Tc 99m de Sódio/química , Sulfetos/química , Compostos de Urânio/química , Calcogênios/química , Recuperação e Remediação Ambiental , Géis/química
8.
J Hazard Mater ; 446: 130644, 2023 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-36587601

RESUMO

The capture of long-lived radioactive iodine (129I) from oxidizing off-gasses produced from reprocessing used nuclear fuel is paramount to human health and environmental safety. Bismuth has been investigated as a viable iodine getter but the phase stability of bismuth-based sorbents in an oxidizing environment have not yet been researched. In the current work, bismuth nanoparticle-based sorbents, as free particles (Bi-NPs) and embedded within silica xerogel monoliths made with a porogen (TEO-5), were exposed to I2(g) before and after aging in 1 v/v% NO2 at 150 °C. For unaged sorbents, BiI3 was the dominant phase after iodine capture with 8-30 mass% BiOI present due to native Bi2O3 on the surface of the unaged nanoparticles. After 3 h of aging, 82 mass% of the Bi-NPs was converted to Bi2O3 with only a small amount of iodine captured as BiOI (18 mass%). After aging TEO-5 for 3 h, iodine was captured as both BiI3 (26 %) and BiOI (74 %) and no Bi2O3 was detected.". Additionally, bismuth lining the micrometer-scale pores in the TEO-5 led to enhanced iodine capture. In a subsequent exposure of the sorbents to NO2 (secondary aging), all BiI3 converted to BiOI. Thus, direct capture of iodine as BiOI is desired (over BiI3) to minimize loss of iodine after capture.


Assuntos
Iodo , Nanopartículas , Neoplasias da Glândula Tireoide , Humanos , Bismuto , Dióxido de Nitrogênio , Dióxido de Silício , Radioisótopos do Iodo , Envelhecimento
9.
Environ Sci Technol ; 46(22): 12616-22, 2012 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-23101883

RESUMO

The immobilization of technetium-99 ((99)Tc) in a suitable host matrix has proven to be a challenging task for researchers in the nuclear waste community around the world. In this context, the present work reports on the solubility and retention of rhenium, a nonradioactive surrogate for (99)Tc, in a sodium borosilicate glass. Glasses containing target Re concentrations from 0 to 10,000 ppm [by mass, added as KReO(4) (Re(7+))] were synthesized in vacuum-sealed quartz ampules to minimize the loss of Re from volatilization during melting at 1000 °C. The rhenium was found as Re(7+) in all of the glasses as observed by X-ray absorption near-edge structure. The solubility of Re in borosilicate glasses was determined to be ~3000 ppm (by mass) using inductively coupled plasma optical emission spectroscopy. At higher rhenium concentrations, additional rhenium was retained in the glasses as crystalline inclusions of alkali perrhenates detected with X-ray diffraction. Since (99)Tc concentrations in a glass waste form are predicted to be <10 ppm (by mass), these Re results implied that the solubility should not be a limiting factor in processing radioactive wastes, assuming Tc as Tc(7+) and similarities between Re(7+) and Tc(7+) behavior in this glass system.


Assuntos
Recuperação e Remediação Ambiental/métodos , Vidro/química , Resíduos Radioativos/análise , Rênio/química , Silicatos/química , Oxirredução , Resíduos Radioativos/prevenção & controle , Solubilidade , Espectrofotometria Atômica , Tecnécio/química , Vitrificação , Espectroscopia por Absorção de Raios X , Difração de Raios X
10.
Front Chem ; 10: 976781, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36186603

RESUMO

Reactions between phosphoric acid [H3PO4] or ammonium hydrogen phosphates [i.e., NH4H2PO4, (NH4)2HPO4] and halide salts can be used to dehalogenate (remove halides from) salt-based waste streams, where the process of removing halides yields products that have more efficient disposal pathways for repository storage. In this context, the term efficiency is defined as higher waste loadings and simplified immobilization processes with potential for recycle of certain salt components (e.g., 37Cl as H37Cl or NH4 37Cl). The main streams identified for these processes are nuclear wastes generated during electrochemical reprocessing of used nuclear fuel as well as used halide salts from molten salt reactor operation. The potential byproducts of these reactions are fairly consistent across the range of halide species (i.e., F, Cl, Br, I) where the most common are hydrogen halides [e.g., HCl(g)] or ammonium halides (e.g., NH4Cl). However, trihalide compounds (e.g., NCl3), nitrogen triiodide ammine adducts [NI3·(NH3) x ], and ammonium triiodide (NH4I3) are also possible. Several of these byproducts (i.e., NCl3, NBr3, NI3, and NH4I3) are shock-sensitive contact explosives so their production in these processes must be tracked and carefully controlled, which includes methods of immediate neutralization upon production such as direct transport to a caustic scrubber for dissolution. Several benefits arise from utilizing H3PO4 as the phosphate additive during dehalogenation reactions for making iron phosphate waste forms including more oxidized iron (higher Fe3+:Fe2+ ratios), higher chemical durabilities, and the avoidance of trihalides, but the byproducts are hydrogen halides, which are corrosive and require special handling.

11.
Front Chem ; 10: 969303, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36118311

RESUMO

Methods for preventing radioiodine from entering the environment are needed in processes related to nuclear energy and medical isotope production. The development and performance of many different types of sorbents to capture iodine have been reported on for decades; however, there is yet to be a concise overview on the important parameters that should be considered when selecting a material for chemically capturing radioiodine. This paper summarizes several criteria that should be considered when selecting candidate sorbents for implementation into real-world systems. The list of selection criteria discussed are 1) optimal capture performance, 2) kinetics of adsorption, 3) performance under relevant process conditions, 4) properties of the substrate that supports the getter, and 5) environmental stability and disposition pathways for iodine-loaded materials.

12.
Front Chem ; 10: 1043653, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36618856

RESUMO

Radioiodine capture and immobilization is not only important to consider during the operation of reactors (i.e., I-131), during nuclear accidents (i.e., I-131 and I-129) or nuclear fuel reprocessing (i.e., I-131 and I-129), but also during disposal of nuclear wastes (i.e., I-129). Most disposal plans for I-129-containing waste forms (including spent nuclear fuel) propose to store them in underground repositories. Here, iodine can be highly mobile and, given its radiotoxicity, needs to be carefully managed to minimize long-term environmental impacts arising from disposal. Typically, any process that has been used to capture iodine from reprocessing or in a reactor is not suitable for direct disposal, rather conversion into a wasteform for disposal is required. The objectives of these materials are to use either chemical immobilization or physical encapsulation to reduce the leaching of iodine by groundwaters. Some of the more recent ideas have been to design capture materials that better align with disposal concepts, making the industrial processing requirements easier. Research on iodine capture materials and wasteforms has been extensive. This review will act as both an update on the state of the research since the last time it was comprehensively summarized, and an evaluation of the industrial techniques required to create the proposed iodine wasteforms in terms of resulting material chemistry and applicability.

13.
ACS Appl Mater Interfaces ; 14(16): 18439-18452, 2022 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-35412785

RESUMO

This study evaluated zeolite-based sorbents for iodine gas [I2(g)] capture. Based on the framework structures and porosities, five zeolites, including two faujasite (FAU), one ZSM-5 (MFI), one mesoMFI, one ZSM-22 (TON), as well as two mesoporous materials, were evaluated for I2(g) capture at room temperature and 150 °C in an iodine-saturated environment. From these preliminary studies, the three best-performing zeolites were ion-exchanged with Ag+ and evaluated for I2(g) capture under similar conditions. Energy-dispersive X-ray spectroscopy data suggest that Ag-FAU frameworks were the materials with the highest capacity for I2(g) in this study, showing ∼3× higher adsorption compared to Ag-mordenite (Ag-MOR) at room temperature, but X-ray diffraction measurements show that the faujasite structure collapsed during the adsorption studies because of dealumination. The Ag-MFI zeolites are decent sorbents in real-life applications, showing both good sorption capacities and higher stability. In-depth analyses and characterizations, including synchrotron X-ray absorption spectroscopy, revealed the influence of structural and chemical properties of zeolites on the performance for iodine adsorption from the gas phase.

14.
J Hazard Mater ; 425: 127779, 2022 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-34823954

RESUMO

This study investigates the impacts of Ni doping on technetium-99 (Tc) sequestration in aqueous solutions through transformation of Fe(OH)2(s) to iron spinel (magnetite) under alkaline conditions. Extensive solid characterization was performed for the mineral phases produced, as well as the Tc/Ni speciation and distribution within these phases. X-ray diffraction results show that iron spinel was the dominant mineral product without detectable Ni incorporation. The doped Ni ions mainly precipitated as fine Fe/Ni oxide/hydroxide particles, including strongly reduced nanometer-sized spheroidal Ni-rich and metallic Ni phases. High-resolution analytical scanning transmission electron microscopy using energy dispersive X-ray spectroscopy and electron energy loss spectroscopy on the produced solid samples (focused ion beam-prepared specimens) revealed three Tc distribution domains dominated by nanocrystals and, especially, a Tc-rich metallic phase. Instances of metallic Tc were specifically found in spheroidal, Ni-rich and metallic nanoparticles exhibiting a core/shell microstructure that suggests strong reduction and sequential precipitation of Ni-Tc-Ni. Mass balance analysis showed nearly 100% Tc removal from the 4.8 × 10-4 M Tc solutions. The finding of the metallic Tc encapsulation indicates that Tc sequestration through Ni-doped Fe(OH)2(s)-to-iron spinel transformation process likely provides an alternative treatment pathway for Tc removal and could be combined into further waste treatment approaches.

15.
ACS Omega ; 6(47): 32239-32252, 2021 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-34870044

RESUMO

This paper describes an apparatus used to remove chlorine from chloride salt-based nuclear wastes from electrochemical reprocessing and/or chloride-based molten salt reactors (MSRs) through dechlorination by reacting the salts with ammonium dihydrogen phosphate (NH4H2PO4 or ADP) at temperatures up to 600 °C to produce NH4Cl as a byproduct. The benefits of removing the Cl from these salts include 37Cl recovery from Cl-based MSR salts, formation of UCl3 from the NH4Cl, as well as removal of Cl from the salts and conversion of the salt cations to oxides to allow for immobilization in a chemically durable iron phosphate waste form. This generation-2 system is an improvement over the generation-1 system and provides a means for scaling up salt throughput as well as NH4Cl recovery. The generation-2 system includes a five-zone furnace so the temperature of the four-zone gradient furnace can be tailored to control the location of NH4Cl condensation on a four-piece fused quartz off-gas system. Both ADP and NH4Cl decomposition reactions include the production of NH3 and acids (i.e., H3PO4 and HCl, respectively), so careful temperature control is needed during the ADP-salt reactions to maximize the NH4Cl production and minimize NH4Cl decomposition. In two sets of experiments run in the generation-1 and generation-2 apparatuses, NH4Cl yields were ≥5.5-fold higher for the new system compared to the original prototype system and the batch sizes can be ≥2.5-fold higher. In addition, some thermodynamic experiments evaluating the reactions of ADP + KCl as well as decomposition of pure NH4Cl were performed to assess the temperatures of the reactions and identify off-gas products.

16.
ACS Omega ; 6(17): 11628-11638, 2021 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-34056318

RESUMO

Various radionuclides are released as gases during reprocessing of used nuclear fuel or during nuclear accidents including iodine-129 (129I) and iodine-131 (131I). These isotopes are of particular concern to the environment and human health as they are environmentally mobile and can cause thyroid cancer. In this work, silver-loaded heat-treated aluminosilicate xerogels (Ag-HTX) were evaluated as sorbents for iodine [I2(g)] capture. After synthesis of the base NaAlSiO4 xerogel, a heat-treatment step was performed to help increase the mechanical integrity of the NaAlSiO4 gels (Na-HTX) prior to Ag-exchanging to create Ag-HTX xerogels. Samples were characterized by powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis, gravimetric iodine loading, nanoindentation, and dynamic mechanical analysis. The structural and chemical analyses of Ag-HTX showed uniform distribution of Ag throughout the gel network after Ag-exchange. After I2(g) capture, the AgI crystallites were observed in the sorbent, verifying chemisorption as the primary iodine capture mechanism. Iodine loading of this xerogel was 0.43 g g-1 at 150 °C over 1 day and 0.52 g g-1 at 22 °C over 33 days. The specific surface area of Ag-HTX was 202 m2 g-1 and decreased to 87 m2 g-1 after iodine loading. The hardness of the Na-HTX was >145 times higher than that of the heat-treated aerogel of the same starting composition. The heat-treatment process increased Young's modulus (compressive) value to 40.8 MPa from 7.0 MPa of as-made xerogel, demonstrating the need for this added step in the sample preparation process. These results show that Ag-HTX is a promising sorbent for I2(g) capture with good iodine loading capacity and mechanical stability.

17.
Data Brief ; 39: 107460, 2021 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-34841015

RESUMO

Samples of ∼1 µm films of CeO2 doped with 2 wt% Mo, 1.5 wt% Ru, 0.75 wt% Pd, 0.5 wt% Re and 0.25 wt% Rh grown with pulsed laser deposition were irradiated with I2+ ions (610 °C and 730 °C, 1016 and 5 × 1016 I2+/cm2). For selected samples post-irradiation heat treatment was conducted (900 °C, 1100 °C). The specimens were sectioned with focused ion beam milling and characterized in a transmission electron microscope with energy-dispersive x-ray spectroscopy, and with atom-probe tomography. Energy-dispersive x-ray spectroscopy was used to obtain elemental maps showing the distribution of dopants in the specimen after exposure. Some of these maps are discussed in detail in our companion article "Formation of multicomponent alloy particles in doped ceria under I2+ ion irradiation and thermal annealing" in the Journal of Nuclear Materials [1]. Advanced computational analysis could be used to more accurately quantify local compositions. Data is provided for additional regions of interest and one additional irradiation condition. The doped ceria film that was heat treated at 1100 °C delaminated from the substrate in most places. Samples were extracted from the underside of a delaminated piece and analyzed with atom-probe tomography. The resulting data show ceria and a Mo-rich particle and demonstrate that this approach is feasable in principle to study local compositions in a sample exposed to such extreme conditions.

18.
J Hazard Mater ; 401: 123279, 2021 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-32629351

RESUMO

Cs3Bi2I9, a defect perovskite derivative, is a potential host phase to immobilize iodine and cesium with high waste loadings. In this work, two strategies were explored to form Cs3Bi2I9-silica composites and a core-shell structure in order to improve chemical durability of waste form materials meanwhile maintaining high waste loadings. Cs3Bi2I9 loadings as high as 70 wt.% were incorporated into a silica matrix to form silica-ceramic composites, and 20 wt.% Cs3Bi2I9 was encapsulated into silica to form a core-shell structure by low temperature spark plasma sintering. Chemical durability of the composite and core-shell waste forms was evaluated by semi-dynamic leaching experiments, and Cs and I were incongruently released from waste form matrices. A BiOI alteration layer formed, acting as a passivation layer to reduce the release of radionuclides. The long-term iodine release rate was low (30 mg m-2 day-1) for the 70 wt.% Cs3Bi2I9-silica composite leached in deionized water at 90 °C, which can be further reduced to 5 × 10-3 mg m-2 day-1 for the 20 wt.% core-shell structure. This work highlights a robust way to immobilize the highly mobile radionuclides with high waste loadings through encapsulation into durable matrices and a surface passivating mechanism that can greatly reduce the elemental transport from waste form materials and significantly enhance their chemical durability.

19.
Glob Chall ; 4(10): 2000013, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-33033626

RESUMO

Several different types of aerogels and xerogels are demonstrated as effective sorbents for the capture and/or immobilization of radionuclides and other contaminants in gaseous form [e.g., Hg(g), I2(g), Xe, Kr] as well as ionic form (e.g., Cd2+, Ce4+, Cs+, Cu2+, Fe2+, Hg2+, I-, IO3 -, Kr, Pb2+, Rb+, Sr2+, 99Tc7+, U6+, Zn2+). These sorbents have unique properties, which include high specific surface areas, high pore volumes, a range of pore sizes, and functionalities that provide methods for binding radionuclides and other contaminants, generally through physisorption, chemisorption, or a combination thereof. This combination of properties and functionalities makes these types of materials ideal for use as sorbents for capturing radionuclides. The primary base materials that will be discussed in this paper include Ag0-functionalized silica aerogels, Ag+-impregnated aluminosilicate aerogels, Ag0-functionalized aluminosilicate aerogels, metal-impregnated (non-Ag) aluminosilicate aerogels and xerogels, sulfide-based aerogels, and carbon-based aerogel composites. For the capture of I2(g), the materials reported herein show some of the highest iodine loadings ever reported for inorganic sorbents. For the capture of ionic species, these materials also show promise as next-generation materials for active radionuclide remediation. This progress report describes materials fabrication, general properties, and environmental remediation applications.

20.
Acta Crystallogr E Crystallogr Commun ; 76(Pt 5): 621-624, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32431920

RESUMO

Terbium oxychloride, TbOCl, was synthesized via the simple heat-treatment of TbCl3·6H2O and its structure was determined by refinement against X-ray powder diffraction data. TbOCl crystallizes with the matlockite (PbFCl) structure in the tetra-gonal space group P4/nmm and is composed of alternating (001) layers of (TbO) n and n Cl-. The unit-cell parameters, unit-cell volume, and density were compared to the literature data of other isostructural rare-earth oxychlorides in the same space group and showed good agreement when compared to the calculated trendlines.

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