Technetium sulfide – formation kinetics, structure and particle speciation

German, K. É.; Shiryaev, A. A.; Safonov, Alexey; Obruchnikova, Ya.A.; Ильин, В. А.; Tregubova, V. E.

doi:10.1515/ract-2014-2369

Cited by 11 publications

(8 citation statements)

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“…Tc sulfide formation kinetics and solubility were studied by German et al (2015) in the presence of Na 2 S in phosphate buffer. The pH of the solution was maintained at 8-12 as lower pH values resulted in sulfide hydrolysis.…”

Section: Formation Stability and Decomposition Of Technetium Sulfidementioning

confidence: 99%

“…Figure 10. Reaction scheme for Tc(VII) with sulfide according to Lukens et al (2005) and German et al (2015).…”

Section: Formation Stability and Decomposition Of Technetium Sulfidementioning

confidence: 99%

“…The solution was centrifuged, and the solubility of Tc 2 S 7 in water was measured to be 6.1 × 10 −4 mol/L, with dissolution proposed to occur according to eq 10: However, issues associated with partitioning of H 2 S into the vapor phase and/or oxidation to sulfide/hydrosulfide anions, in addition to the possible presence of Tc in a chemical form other than TcO 4 − , preclude the extraction of thermodynamic data from this measurement. 1,69 Tc-sulfide formation kinetics and solubility were studied by German et al 120 The product of this reaction then trimerizes to form the Xray amorphous trinuclear Tc(IV) polydisulfide Tc 3 (μ 3 -S)-(S 2 ) 3 S 6 (Figure 9), which has a Tc:S ratio of 2:6.7. The stability of Tc 3 S 13 in solution, and thus the solubility, was found to be dependent on the Na 2 S concentration, with Tc-sulfide solubility found to be described by C(Tc − .…”

Section: Formation Stability and Decomposition Of Technetium Sulfide ...mentioning

confidence: 99%

“…The stability of Tc 3 S 13 in solution, and thus the solubility, was found to be dependent on the Na 2 S concentration, with Tc-sulfide solubility found to be described by C(Tc − . 120 As this demonstrates, a significant amount of experimental work is still required to develop a thermodynamically sound understanding of Tc-sulfide chemistry. 1…”

Section: Formation Stability and Decomposition Of Technetium Sulfide ...mentioning

confidence: 99%

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Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Pearce

Icenhower²,

Asmussen

et al. 2018

ACS Earth Space Chem.

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Technetium (Tc) contamination remains a major environmental problem at nuclear reprocessing sites, e.g., the Hanford Site, Washington State, USA. At these site, Tc is present in liquid waste destined for immobilization in a waste form or has been released into the subsurface environment. The high environmental risk associated with Tc is due to its long half-life (213,000 years) and the mobility of the oxidized anionic species Tc(VII)O 4-. Under reducing conditions, TcO 4 is readily reduced to Tc(IV), which commonly exists as a relatively insoluble and therefore immobile, hydrous Tc oxide (TcO 2 •nH 2 O). The stability of Tc(IV) sequestered as solid phases depends on the solubility of the solid and susceptibility to re-oxidation to TcO 4-, which in turn depend on the (bio-geo)chemical conditions of the environment and/or nuclear waste streams. Unfortunately, the solubility of crystalline TcO 2 or amorphous TcO 2 •H 2 O is still above the maximum contaminant level (MCL) established by the US EPA (900 pCi/L), and the kinetics of TcO 2 oxidative dissolution can be on the order of days to years. In addition to oxygen, sulfur can form complexes that significantly affect the adsorption, solubility and re-oxidation potential of Tc, especially Tc(IV). The principal technetium sulfides areTcS 2 and Tc 2 S 7 but much less is known about the mechanisms of formation, stabilization and re-oxidation of Tc sulfides. A common assumption is that sulfides are less soluble that their oxyhydrous counterparts. Determination of the molecular structure of Tc 2 S 7 in particular has been hampered by the propensity of this phase to precipitate as an amorphous substance. Recent work indicates that the oxidation state of Tc in Tc 2 S 7 is Tc(IV), in apparent contradiction to its nominal stoichiometry. Technetium is relatively immobile in reduced sediments and soils, but in many cases the exact sink for Tc has not been identified. Experiments and modeling have demonstrated that both abiotic and biologic mechanisms can exert strong controls on Tc mobility and that Tc binding or uptake into sulfide phases can occur. These and similar investigations also show that extended exposure to oxidizing conditions results in transformation of sulfide-stabilized Tc(IV) to a Tc(IV)O 2-like phase without formation of measurable dissolved TcO 4-, suggesting a solid-state transformation in which Tc(IV)-associated sulfide is preferentially oxidized before the Tc(IV) cation. This transformation of Tc(IV) sulfides to Tc(IV) oxides may be the main process that limits remobilization of Tc as Tc(VII)O 4-. The efficacy of the final waste form to retain Tc also strongly depends on the ability of oxidizing species to enter the waste and convert Tc(IV) to Tc(VII). Many waste form designs are reducing (e.g., cementitious waste forms such as salt stone), therefore, attempt to restrict access of oxidizing species such that diffusion is the ratelimiting step in remobilization of Tc.

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Section: Formation Stability and Decomposition Of Technetium Sulfidementioning

confidence: 99%

“…Figure 10. Reaction scheme for Tc(VII) with sulfide according to Lukens et al (2005) and German et al (2015).…”

Section: Formation Stability and Decomposition Of Technetium Sulfidementioning

confidence: 99%

Section: Formation Stability and Decomposition Of Technetium Sulfide ...mentioning

confidence: 99%

Section: Formation Stability and Decomposition Of Technetium Sulfide ...mentioning

confidence: 99%

See 2 more Smart Citations

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Pearce

Icenhower²,

Asmussen

et al. 2018

ACS Earth Space Chem.

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“…However, identification of the chemical structure of the insoluble fraction remains challenging. One possible reason for the formation of the insoluble fraction is the formation of insoluble polydisulfide [Tc 3 (μ 3 – S)(S 2 ) 3 (S 2 ) 3/3 ] n by the trimerization of insoluble sulfide Tc(IV)S 2 [ 21 ] . The chemical structure of [ 99m Tc]Tc-gluconate is two gluconate molecules forming a complex with Tc(V)O.…”

Section: Discussionmentioning

confidence: 99%

Imaging Hydrogen Sulfide in Hypoxic Tissue with [99mTc]Tc-Gluconate

et al. 2020

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Hydrogen sulfide (H2S) is the third gasotransmitter and is generated endogenously in hypoxic or inflammatory tissues and various cancers. We have recently demonstrated that endogenous H2S can be imaged with [99mTc]Tc-gluconate. In the present study, we detected H2S generated in hypoxic tissue, both in vitro and in vivo, using [99mTc]Tc-gluconate. In vitro uptake of [99mTc]Tc-gluconate was measured under hypoxic and normoxic conditions, using the colon carcinoma cell line CT26, and was higher in hypoxic cells than that in normoxic cells. An acute hindlimb ischemia-reperfusion model was established in BALB/c mice by exposing the animals to 3 h of ischemia and 3 h of reperfusion prior to in vivo imaging. [99mTc]Tc-gluconate (12.5 MBq) was intravenously injected through the tail vein, and uptake in the lower limb was analyzed by single-photon emission computed tomography/computed tomography (SPECT/CT). SPECT/CT images showed five times higher uptake in the ischemic limb than that in the normal limb. The standard uptake value (SUVmean) of the ischemic limb was 0.39 ± 0.03, while that of the normal limb was 0.07 ± 0.01. [99mTc]Tc-gluconate is a novel imaging agent that can be used both in vitro and in vivo for the detection of endogenous H2S generated in hypoxic tissue.

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