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Schroeder, Norman C.; Radzinski, Susan D.; Ashley, Kenneth R.; Truong, Anh P.; Whitener, Glenn D.

doi:10.1023/a:1017927109400

Cited by 15 publications

(19 citation statements)

References 15 publications

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“…First, previous attempts to separate Tc from the liquid fraction of the tank waste using an ion-exchange processes specific to pertechnetate (TcO 4 -) met with limited success particularly for the wastes with high organic content. [7][8][9] This implies that a significant fraction of the soluble Tc is present as low-valent Tc (oxidation state < +7) due to the reductive conditions generated by the radiolysis products of water, nitrate, and other constituents and stabilized by the organic complexants present in the waste. Second, the presence of the low-valent Tc species has been confirmed by the direct Tc K-edge X-ray absorbance spectroscopic measurements of the Hanford tank waste samples; the obtained spectra could be reasonably fit to the spectrum of the gluoconate or hydroxide-coordinated [fac-Tc(CO) 3 ] + complex leading to their tentative identification as [fac-Tc(CO) 3 ] + (or possibly [fac-Tc(CO) 2 (NO)] 2+ ) derivatives.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Characterization of Aqua [fac-Tc(CO)₃]⁺ Complexes at High Ionic Strength

et al. 2018

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Understanding fundamental Tc chemistry is important to both the remediation of nuclear waste and the reprocessing of nuclear fuel; however, current knowledge of the electronic structure and spectral signatures of low-valent Tc compounds significantly lags behind the remainder of the d-block elements. In particular, identification and treatment of Tc speciation in legacy nuclear waste is challenging due to the lack of reference data especially for Tc compounds in the less common oxidation states (I-VI). In an effort to establish a spectroscopic library corresponding to the relevant conditions of extremely high ionic strength typical for the legacy nuclear waste, compounds with the general formula of [ fac-Tc(CO)(OH)(OH) ] (where n = 0-3) were examined by a range of spectroscopic techniques including Tc/C NMR, IR, XPS, and XAS. In the series of monomeric aqua species, stepwise hydrolysis results in the increase of the Tc metal center electron density and corresponding progressive decrease of the Tc-C bond distances, Tc electron binding energies, and carbonyl stretching frequencies in the order [ fac-Tc(CO)(OH)] > [ fac-Tc(CO)(OH)(OH)] > [ fac-Tc(CO)(OH)(OH)]. These results correlate with established trends of the Tc upfield chemical shift and carbonylC downfield chemical shift. The lone exception is [ fac-Tc(CO)(OH)] which exhibits a comparatively low electron density at the metal center attributed to the μ-bridging nature of the OH ligands causing less σ-donation and no π-donation. This work also reports the first observations of these compounds by XPS and [ fac-Tc(CO)Cl] by XAS. The unique and distinguishable spectral features of the aqua [ fac-Tc(CO)] complexes lay the foundation for their identification in the complex aqueous matrixes.

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Section: Introductionmentioning

confidence: 99%

Spectroscopic Characterization of Aqua [fac-Tc(CO)₃]⁺ Complexes at High Ionic Strength

et al. 2018

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“…25 Quantitative oxidation of non-pertechnetate was possible only after vigorous digestions with the repeated additions of the Ce(NH 4 ) 2 (NO 3 ) 2 -16 M HNO 3 reagent followed by evaporation of the digestate to incipient dryness. 28 The reported time required to process a batch of samples was 8 h, which would be excessive for a rapid automated analysis.…”

Section: Resultsmentioning

confidence: 99%

“…28,29 Oxidation of non-pertechnetate was possible in matrixes with stoichiometric excess of nitrite and total organic carbon relative to peroxydisulfate. In the aged nuclear waste samples, nitrite and organic species represent major sources of reducing capacity.…”

Section: Resultsmentioning

confidence: 99%

“…Microwaveassisted acidification and oxidation using peroxydisulfate successfully overcome previously documented challenges in controlling the 99 Tc speciation in such samples. 25,28,29 Development of reliable, rapid, automated sample treatment procedures for caustic aged nuclear waste samples is significant because it opens the possibility of developing integrated radionuclide analyzer instrumentation for monitoring nuclear waste processes in near real time, using previously described automated radiochemical separation and detection methods. 40,41 Development of the integrated radionuclide analyzer for automated radiochemical analysis of total 99 Tc in aged nuclear waste will be a subject of a subsequent publication.…”

Section: Conclusion and Summarymentioning

confidence: 99%

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Microwave-Assisted Sample Treatment in a Fully Automated Flow-Based Instrument: Oxidation of Reduced Technetium Species in the Analysis of Total Technetium-99 in Caustic Aged Nuclear Waste Samples

2004

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An automated flow-based instrument for microwave-assisted treatment of liquid samples has been developed and characterized. The instrument utilizes a flow-through reaction vessel design that facilitates the addition of multiple reagents during sample treatment and removal of the gaseous reaction products and enables quantitative removal of liquids from the reaction vessel for carryover-free operations. Matrix modification and speciation control chemistries that are required for the radiochemical determination of total (99)Tc in caustic aged nuclear waste samples have been investigated. A rapid and quantitative oxidation procedure using peroxydisulfate in acidic solution was developed to convert reduced technetium species to pertechnetate in samples with high content of reducing organics. The effectiveness of the automated sample treatment procedures has been validated in the radiochemical analysis of total (99)Tc in caustic aged nuclear waste matrixes from the Hanford site.

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“…Furthermore, SCHROEDER and * Author for correspondence. co-workers [7][8][9] have shown that the complexes are difficult to separate on an anion-exchange column and are difficult to selectively oxidize back to pertechnetate. BLANCHARD and co-workers 10 obtained X-ray absorption near edge spectroscopy (XANES) data suggesting that the low-valent complexes are Tc(IV) species.…”

Section: Introductionmentioning

confidence: 99%

The autoreduction of pertechnetate in aqueous, alkaline solutions

Berning

Schroeder

Chamberlin

2005

J Radioanal Nucl Chem

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The autoreduction of pertechnetate (99 TcO 4-) to Tc(IV/V) alkoxide complexes in aqueous, alkaline, solutions is described. Solutions of sodium pertechnetate (0.01M) reacted with nitrogen and oxygen donor ligands (1.0M) in 2M sodium hydroxide. Solutions containing nitrogen donor ligands (e.g., EDTA) showed the initial formation of lightly colored complexes followed by rapid decomposition in air. In contrast, stable, reduced complexes were formed within minutes of mixing pertechnetate with mono-and disaccharides in strong base, as indicated by a persistent color change. Chemical yields of these reactions were determined by thin layer chromatography or paper chromatography and radiochemically assayed with a Bioscan imaging scanner. Analysis by UV-vis spectroscopy suggested that Tc(IV) or Tc(V) complexes were produced, with the oxidation state dependent on the reducing ligand. These experiments may help explain the reduction of pertechnetate to the soluble complexes that have been found in the Hanford nuclear waste tanks.

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Cited by 15 publications

References 15 publications

Spectroscopic Characterization of Aqua [fac-Tc(CO)₃]⁺ Complexes at High Ionic Strength

Spectroscopic Characterization of Aqua [fac-Tc(CO)₃]⁺ Complexes at High Ionic Strength

Microwave-Assisted Sample Treatment in a Fully Automated Flow-Based Instrument: Oxidation of Reduced Technetium Species in the Analysis of Total Technetium-99 in Caustic Aged Nuclear Waste Samples

The autoreduction of pertechnetate in aqueous, alkaline solutions

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Untitled

Cited by 15 publications

References 15 publications

Spectroscopic Characterization of Aqua [fac-Tc(CO)3]+ Complexes at High Ionic Strength

Spectroscopic Characterization of Aqua [fac-Tc(CO)3]+ Complexes at High Ionic Strength

Microwave-Assisted Sample Treatment in a Fully Automated Flow-Based Instrument: Oxidation of Reduced Technetium Species in the Analysis of Total Technetium-99 in Caustic Aged Nuclear Waste Samples

The autoreduction of pertechnetate in aqueous, alkaline solutions

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Spectroscopic Characterization of Aqua [fac-Tc(CO)₃]⁺ Complexes at High Ionic Strength

Spectroscopic Characterization of Aqua [fac-Tc(CO)₃]⁺ Complexes at High Ionic Strength