Recent developments in the synthetic chemistry of technetium disulfide

Ferrier, Maryline G.; Kerlin, William M.; Poineau, Frédéric; Sattelberger, Alfred P.; Czerwinski, Kenneth R.

doi:10.1039/c3dt52079j

Cited by 7 publications

(9 citation statements)

References 24 publications

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“…In our system, the Tc K ‐edge shift was consistent with the presence of a Tc IV species (shift of –6.5 to –10.5 eV relative to TcO 4 – ). As suggested in a previous study, the position of the Tc K ‐edge is lower in TcS 2 than in TcO 2 due to the difference in electronegativity between O and S ligands 4. Based on the presented data and discussed literature, the existence of a Tc VII species with the formula Tc 2 S 7 is considered unlikely.…”

Section: Resultssupporting

confidence: 53%

“…Concerning technetium binary sulfides, only two compounds have been reported: TcS 2 and Tc 2 S 7 . Only technetium disulfide has been unambiguously characterized 2,4. Even though colloidal technetium heptasulfide is used in radiopharmaceuticals applications,5,6 and has been proposed as an immobilization process for environmental technetium,7 its exact structure and composition are still unclear 8,9…”

Section: Introductionmentioning

confidence: 99%

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Speciation of Technetium in Sulfuric Acid/Hydrogen Sulfide Solutions

et al. 2014

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The reaction between TcVII and H2S(g) in 12 M H2SO4 has been studied. This reaction produced a black solid and a brown supernate. The solid was analyzed by energy dispersive X-ray (EDX) and X-ray absorption fine structure (XAFS) spectroscopy and the results were consistent with the presence of Tc2S7. The speciation of technetium in the supernate was performed by UV/Visible and XAFS spectroscopy. Experiments showed that in 12 M H2SO4 an intermediate TcV sulfate complex was formed. Analysis indicated that the final complex present in solution was a polymeric species with a Tc-O-Tc core coordinated to sulfate ligands. Density Functional Theory (DFT) calculations showed that the proposed complexes were stable and that the theoretical structure was in good agreement with XAFS data

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Section: Resultssupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

Speciation of Technetium in Sulfuric Acid/Hydrogen Sulfide Solutions

et al. 2014

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“…Study of the TcS 2 has always been hampered by the small quantities of materials yielded by traditional synthesis routes. Three new synthesis routes for TcS 2 were also recently reported (Ferrier et al, 2013). These new synthesis routes allow one to obtain larger yields of technetium sulfides at lower temperatures.…”

Section: Technetium Sulfidesmentioning

confidence: 99%

“…Three new synthesis routes for TcS 2 were also recently reported. 27 These new synthesis routes allow one to obtain larger yields of technetium sulfides at lower temperatures. More routine synthesis of larger batches of TcS 2 will lead to better experiments exploring the efficacy of using TcS 2 as a waste form (see below).…”

Section: Technetium Sulfidesmentioning

confidence: 99%

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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“…Previous studies have also shown that pertechnetate can be readily bioreduced to Tc(IV)O 2 ⋅ x H 2 O (Istok et al, 2004; Fredrickson et al, 2009), a precipitate that can be quickly and nearly completely reoxidized. In contrast, Tc(IV) precipitated with sulfide (TcS 2 or TcS x ) oxidizes more slowly (Livens et al, 2004; Lukens et al, 2002, 2005; Ferrier et al, 2013). In addition, Tc(IV) incorporates into slower dissolving phases including Fe sulfides (Fan et al, 2013), sodalite (Wharton et al, 2000), and goethite (Livens et al, 2004).…”

mentioning

confidence: 99%

Remediation of Technetium in Vadose Zone Sediments Using Ammonia and Hydrogen Sulfide Gases

Szecsody

Truex

Zhong

et al. 2015

Vadose Zone Journal

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Technetium-99 is a mobile, long-lived radionuclide and environmental risk driver at some nuclear waste sites. The feasibility of decreasing 99 Tc mobility in vadose zone sediments using H 2 S and NH 3 gases was evaluated in laboratory experiments. In untreated sediments, 75 to 95% of the 99 Tc was leachable. Using combinations of H 2 S and NH 3 gases, the 99 Tc mobility was reduced to 14 to 48%. Individual H 2 S or NH 3 gas treatment of sediments had little lasting effect. For the combined gas treatment, the H 2 S gas created reducing conditions at the pore water-mineral interface, which temporarily reduced and precipitated 99 Tc, while the NH 3 gas created alkaline pore water that caused mineral dissolution. As the pH neutralized, subsequent aluminosilicate precipitation probably coated 99 Tc precipitates and rendered them less mobile. Surface phase analysis showed that 99 Tc was associated with weathered basalt clasts and S, possibly from the precipitation of TcS x . Treatment performance was nearly the same at different 99 Tc concentrations (1.3-240.5 Bq g −1 ), water contents (1-8%), and gas injection rates but was sensitive to gas concentrations. Low gas concentrations (<3%) had insufficient reductant or slower mineral dissolution. High gas concentrations (>30%) formed an NH 4 SH precipitate. The 14 to 48% mobile 99 Tc remaining after gas treatment may have been caused by the limited time for aluminosilicates to precipitate in our experiments. Degradation of added NH 3 was not observed during the 3-mo experiment. Overall, this study showed that combined H 2 S and NH 3 gas treatment of low-water-content sediments can be applied to significantly decrease 99 Tc mobility.

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Recent developments in the synthetic chemistry of technetium disulfide

Cited by 7 publications

References 24 publications

Speciation of Technetium in Sulfuric Acid/Hydrogen Sulfide Solutions

Speciation of Technetium in Sulfuric Acid/Hydrogen Sulfide Solutions

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

Remediation of Technetium in Vadose Zone Sediments Using Ammonia and Hydrogen Sulfide Gases

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