Stability constants of technetium(IV) oxalate complexes as a function of ionic strength

Xia, Yuanxian; Hess, Nancy J.; Felmy, Andrew R.

doi:10.1524/ract.2006.94.3.137

Cited by 29 publications

(29 citation statements)

References 8 publications

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“…gluconate, EDTA). This explanation for the increase in solubility agrees with published complexation studies, as Tc(IV) was shown to form soluble complexes with oxalic acid [15], acetate [16], and humic substances [17].…”

Section: Introductionsupporting

confidence: 91%

“…Our value for β 0 1,0,1 is much larger than stability constant for complexes with other carboxylic ligands, such as acetate [16] (log β 0 1,−1,1 = 2.8) and oxalate [15] (log β 0 1,0,1 = 7.2 ± 0.2) -an expected trend due to the larger number of carboxylate sites for EDTA. The stability constant for the EDTA complex with TcO 2+ determined in the present work is similar to that of free tetravalent vanadium: literature shows log β 1,0,1 = 18.7 at 0.1 M ionic strength for VO 2+ [30], while the present work reports log β 1,0,1 at 20.0 ± 0.4 and 17.1 ± 0.4, at 0 and 0.5 ionic strength, respectively, for TcO 2+ .…”

Section: Resultsmentioning

confidence: 57%

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

Boggs¹,

Islam²,

Dong³

et al. 2012

Radiochimica Acta

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The stability constant for Tc(IV)/EDTA complexes were determined using a solvent extraction technique at varying ionic strength (NaCl) and the specific ion interaction theory model allowed for calculating stability constants at zero ionic strength. The stability constants at zero ionic strength for the formation of the TcOEDTA2− and TcOHEDTA− complexes are 1020.0 ± 0.4 and 1025.3 ± 0.5, respectively. The modeled Tc(IV) solubility was calculated to be 3.9 × 10−7 M at near-neutral pH and in presence of 2.5 mM EDTA, a result found to be in good agreement with published solubility experimental data. Speciation calculations showed that TcOEDTA2− is the predominant species between pH 4 and 7.5 in presence of 0.171 mM EDTA, while TcO(OH)2 0 is predominant in basic solution. These studies show that EDTA has a very strong affinity for complexation with Tc(IV) and can increase the environmental mobility of Tc(IV).

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Section: Introductionsupporting

confidence: 91%

Section: Resultsmentioning

confidence: 57%

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

Boggs¹,

Islam²,

Dong³

et al. 2012

Radiochimica Acta

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“…The preponderance of evidence suggests, therefore, that strong interactions between technetium and organic matter either do not occur, or are very sensitive to the presence of oxygen. In very unusual chemical environments, such as those represented by tank waste, stronger interaction may occur, as demonstrated by Xia et al (2006). They found that strong Tc-oxalate complexes formed in solutions with high ionic strength.…”

Section: 14mentioning

confidence: 97%

The Geochemistry of Technetium: A Summary of the Behavior of an Artificial Element in the Natural Environment

Icenhower¹,

Qafoku²,

Martin³

et al. 2008

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“…The chemical form of technetium in the raw tank waste is usually pertechnetate, but lower valent complexes may be present in some tanks. [12][13][14][15][16] When the waste is incorporated into glass, the nitrate and nitrite will oxidize all of the organic compounds and will oxidize technetium to Tc(VII) (fused nitrate is an extremely powerful oxidizing agent). At the maximum temperature of the glass melt, Tc(VII) can lose oxygen and drop to a lower oxidation state, which likely will have a different solubility in the glass than Tc(VII).…”

Section: Introductionmentioning

confidence: 99%

Redox-dependent solubility of technetium in low activity waste glass

Soderquist

Schweiger

Kim

et al. 2014

Journal of Nuclear Materials

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The solubility of technetium was measured in a Hanford low activity waste glass simulant. The simulant glass was melted, quenched and pulverized to make a stock of powdered glass. A series of glass samples were prepared using the powdered glass and varying amounts of solid potassium pertechnetate. Samples were melted at 1000°C in sealed fused quartz ampoules. After cooling, the bulk glass and the salt phase above the glass (when present) were sampled for physical and chemical characterization. Technetium was found in the bulk glass up to 2000 ppm (using the glass as prepared) and 3000 ppm (using slightly reducing conditions). The chemical form of technetium obtained by x-ray absorption near edge spectroscopy can be mainly assigned to isolated Tc(IV), with a minority of Tc(VII) in some glasses and TcO 2 in two glasses. The concentration and speciation of technetium depends on glass redox and amount of technetium added. Solid crystals of pertechnetate salts were found in the salt cake layer that formed at the top of some glasses during the melt. BackgroundRadioactive waste from decades of plutonium production is currently stored in large underground tanks at the Hanford Site. This waste will be mixed with glass formers and then vitrified. 1 The Hanford tank wastes vary widely in composition, but are typically largely sodium nitrate, nitrite, and carbonate with a small amount of hydroxide.2; 3 Aluminum, iron and zirconium comprise 20% or more of the waste in some cases. Chromium and manganese may be present up to several percent. not recover all of the plutonium from the irradiated uranium, and a small amount of plutonium, uranium and americium are also found in the tanks. Many of the waste components do not incorporate well into silicate glasses. A number of ionic compounds such as sulfates have low solubility in silicate glasses and may form a separate salt phase.The current plan is to chemically separate the waste into a small volume of high-level waste, intensely radioactive from 90 Sr and 137 Cs, and a large volume of low-activity waste (LAW). 1 These two fractions will be vitrified separately. Technetium will report to the low-activity waste and will be vitrified in that fraction. Tc in LAW GlassPage 2 of 21Technetium incorporates poorly into silicate glass in traditional glass melting. Technetium readily evaporates during melting of glass feeds (waste + additives) and out of the molten glass, leading to low retention in a final glass product. [4][5][6][7] To effectively manage technetium retention in the Hanford LAW glass, it is critical to understand if the solubility of technetium is a controlling factor. The speciation of technetium in glass has been previously studied, and the technetium species present in waste glass have been previously reported; [8][9][10][11] however, the solubilities of these species are unknown.The solubility of technetium and many other waste constituents depends partly on their chemical forms.A particular constituent may be better incorporated into the glass if it is adde...

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Stability constants of technetium(IV) oxalate complexes as a function of ionic strength

Abstract: SummarySolvent extraction method was used to determine the stability constants of Tc(IV) with oxalate anions in NaCl solutions ranging in concentration from 0.5 M to 2.0 M. All experiments were conducted in an atmosphere-controlled chamber under Ar atmosphere (<1.0 ppm O

Cited by 29 publications

References 8 publications

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

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

The Geochemistry of Technetium: A Summary of the Behavior of an Artificial Element in the Natural Environment

Redox-dependent solubility of technetium in low activity waste glass

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