Complexation of Tc(IV) with EDTA at varying ionic strength of NaCl

Boggs, Mark A.; Islam, Mohammed; Dong, Wenyi; Wall, Nathalie A.

doi:10.1524/ract.2013.2000

Cited by 25 publications

(11 citation statements)

References 24 publications

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“…On the other hand, EDTA is a useful chemical substance exhibiting both reducing and complexing reactivities. Among the latter, its ability to complex divalent and trivalent metal ions as a polydentate ligand is noteworthy.…”

Section: Introductionmentioning

confidence: 99%

Two Rate Constant Kinetic Model for the Chromium(III)–EDTA Complexation Reaction by Numerical Simulations

Perez‐Benito

2017

Int J of Chemical Kinetics

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The complexation reaction of Cr(III) ion in the presence of a large excess of ethylenediaminetetraacetic acid (EDTA) does not follow a pseudo–first‐order kinetics as sometimes suggested. There are two causes for the deviation from this simple behavior: the involvement of a long‐lived intermediate, precluding the application of the steady‐state approximation, and the autoinhibition provoked by the release of hydrogen ions from the organic ligand to the medium as the final Cr(III)–EDTA violet complex is formed. Numerical simulations have allowed obtaining for each kinetic experiment the values of two rate constants, k1 (corresponding to the formation of the long‐lived intermediate from the reactants) and k2 (corresponding to the formation of the final complex product from the long‐lived intermediate), as well as the number of hydrogens liberated per molecule of final complex product formed (Hkin). The results indicate that k1 is associated with a fast step (Ea = 87 ± 4 kJ mol−1) and k2 to a slow step (Ea = 120 ± 2 kJ mol−1), whereas the number of hydrogen ions lies within the range 0 < Hkin < 2 in all the kinetic runs. A mechanism in accordance with the experimental data has been proposed.

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Section: Introductionmentioning

confidence: 99%

Two Rate Constant Kinetic Model for the Chromium(III)–EDTA Complexation Reaction by Numerical Simulations

Perez‐Benito

2017

Int J of Chemical Kinetics

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“…Tc(IV), can be complexed with citrate (Wall et al, 2013), ethylenediaminetetraacetic acid (EDTA) 8 (Boggs et al, 2013;Gu et al, 2011), oxalate (Xia et al, 2006), acetate (Boggs et al, 2010) and 9 humic substances (Boggs et al, 2011;Gu et al, 2011), increasing the solubility of TcO 2 (s) (Gu et 10 al., 2011). The solubility of Re(IV)-EDTA complexes was also found to be higher than that of 11 Re(VII) (Corkhill et al, 2013).…”

Section: Introduction 10mentioning

confidence: 99%

Re(VII) diffusion in bentonite: Effect of organic compounds, pH and temperature

Wang

et al. 2016

Applied Clay Science

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In order to understand the diffusion properties of anionic radionuclides (RN) in 10 bentonite in the presence of organic compounds with chelating and reducing properties, the effect 11 of humic acid (HA), citrate, oxalate and formate on Re(VII) diffusion were investigated by a 12 through-diffusion method under different pH (pH 7.0 and 10.0) and temperature conditions (10 ~ 13 65 C). When the molar ratio of oxalate to Re(VII) was higher than 1:1, the accumulated mass and 14 flux were observed to decrease drastically as a function of time. It can be explained by 15 photocatalytic impact of Fe(III) on the reduction of Re(VII) to insoluble Re(IV) by oxalate. Thus, 16 the diffusion of Re(VII) was also observed to decrease in the presence of minor citrate, oxalate 17 and formate. Effective diffusion coefficient (D e) values decreased from 8.7  10-11 m 2 /s to (5.1 ~ 18 5.9)  10-11 m 2 /s. In contrast, HA had no significant impact on Re(VII) diffusion. The D e values of 19 1.54  10-11 and 6.5  10-12 m 2 /s were obtained at pH 7.0 and 10.0, respectively. HA thus neither 20

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“…Indeed, complexing ligands, including organic matter, influence both the ability to sequester Tc as a sulfide, and subsequent reoxidation mechanisms due to the formation of Tc(IV) complexes. 81,82 As discussed above, Wharton et al 51 conducted experiments in which mackinawite was co-precipitated with a TcS 2 -like phase. Upon oxidation of the mackinawite in air to form goethite, Tc remained reduced but in a Tc(IV)O 2 -like environment with six O atoms at ∼2 Å, rather than a TcS 2 environment, suggesting that oxidation of the FeS is not immediately accompanied by oxidation of the Tc(IV) to Tc(VII).…”

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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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Complexation of Tc(IV) with EDTA at varying ionic strength of NaCl

Cited by 25 publications

References 24 publications

Two Rate Constant Kinetic Model for the Chromium(III)–EDTA Complexation Reaction by Numerical Simulations

Two Rate Constant Kinetic Model for the Chromium(III)–EDTA Complexation Reaction by Numerical Simulations

Re(VII) diffusion in bentonite: Effect of organic compounds, pH and temperature

Technetium Stabilization in Low-Solubility Sulfide Phases: A Review

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