Oxalate Complexation in Dissolved Carbide Systems

Choppin, R.; Bokelund, H.; Valkiers, S.

doi:10.1524/ract.1983.33.4.229

Cited by 17 publications

(5 citation statements)

References 10 publications

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“…The conditional equilibrium constant K 1H,cond is obtained from the spectrophotometric equilibrium measurements, and K 1H from eqn (1). 40 If reaction (C) takes place, the value of K 1H should be the same for solutions with different pH, corrected for ionic strength effects (vide infra). This condition is fulfilled, as demonstrated below (SIT treatment of equilibrium constants).…”

Section: Concentration Stability Constantsmentioning

confidence: 99%

Thermodynamics for complex formation between palladium(ii) and oxalate

2014

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Complex formation between [Pd(H2O)4](2+) and oxalate (ox = C2O4(2-)) has been studied spectrophoto-metrically in aqueous solution at variable temperature, ionic strength and pH. Thermodynamic parameters at 298.2 K and 1.00 mol dm(-3) HClO4 ionic medium for the complex formation [Pd(H2O)4](2+) + H2ox ⇄ [Pd(H2O)2(ox)] + 2H3O(+) with equilibrium constant K1,H (in mol dm(-3)) are log10K1,H = 3.38 ± 0.08, ΔH = -33 ± 3 kJ mol(-1), and ΔS = -48 ± 11 J K(-1) mol(-1), as determined from spectrophotometric equilibrium titrations at 15.0, 20.0, 25.0 and 31.0 °C. Thermodynamic overall stability constants β (in (mol dm(-3))(-n), n = 1,2) for [Pd(H2O)2(ox)] and [Pd(ox)2](2-) at zero ionic strength and 298.2 K, defined as the equilibrium constants for the reaction Pd(2+) + nox(2-) ⇄ [Pd(ox)n](2-2n) (water molecules omitted) are log10β = 9.04 ± 0.06 and log10β = 13.1 ± 0.3, respectively, calculated by use of Specific Ion Interaction Theory from spectrophotometric titrations with initial hydrogen ion concentrations of 1.00, 0.100 and 0.0100 mol dm(-3) and ionic strengths of 1.00, 2.00 or 3.00 mol dm(-3). The values derived together with literature data give estimated overall stability constants for Pd(ii) compounds such as [Pd(en)(ox)] and cis-[Pd(NH3)2Cl2], some of them analogs to Pt(ii) complexes used in cancer treatment. The palladium oxalato complexes are significantly more stable than palladium(ii) complexes with monodentate O-bonding ligands. A comparison between several different palladium complexes shows that different parameters contribute to the stability variations observed. These are discussed together with the so-called chelate effect.

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Section: Concentration Stability Constantsmentioning

confidence: 99%

Thermodynamics for complex formation between palladium(ii) and oxalate

2014

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“…Enhanced Drei values are attained much faster at the lower acidity; similarly the absorbance at 400 nm is attenuated and the CO2 evolution is accelerated. The concentration of oxalic add is lower in the 4 M HNO3 solutions than in the case of 8 M HNO3 dissolutions [3,4], a fact which may account for this behaviour. The Observation is also in agreement with that of WEISS [15], who found the photolytic decomposition of H2C2O4 to be strongly inhibited by strong acids, in that the concentration of the anion HC2 OJ was decreased in such cases: A.…”

Section: Extractability Of Plutoniummentioning

confidence: 99%

“…Oxalic acid and mellitic acid are the predominant species among the partly unidentified carbonaceous byprbducts of the reaction between carbide, inadiated or uninadiated, and nitric add [2,3]. In a recent study [4] of the distribution of plutonium between 30% TBP/ndodecane and nitric acid in the presence of these org^c adds the influence on the extraction equilibria was shown to be due to oxalic acid.…”

Section: Introductionmentioning

confidence: 99%

A Photochemical Head-end Step in Carbide Fuel Reprocessing

Bokelund¹,

Caceci²,

Müller³

1983

Radiochimica Acta

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U, Pu corbides IReprocessing of nuclear fuels /Photochemistry / Oxidation of organic Compounds/Th? extraction Summaty A photochemical oxidation process is discussed in the context of the reprocessing of mixed uranium, plutonium carbide fuels. The organic Compounds formed in the Solution of the dissolved carbides can be removed by photolysis in a head-end treatment prior to the PUREX extraction process.The course of the photochemical oxidation of the carbonaceous by-products as a function of nitric acid molarity is foUowed by measurements of the formation of CO,, by the changes in the absorption spectrum of the Solution and by the Variation in the extractability of plutonium with 30% TBP.Dissolution in a circulation set-up with the concomitant exposure to light is the most efficient.

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“…The Fast Breeder Test Reactor at Kalpakkam, India, uses a mixed carbide of uranium and plutonium (U 0 . 3 Pu 0 . 7 )-C as the driver fuel.…”

Section: Introductionmentioning

confidence: 99%

“…He suggested that the direct dissolution of carbide fuels may serve as the best head-end step to get a suitable feed solution for solvent extraction. However, the direct dissolution of the carbides yields, apart from carbon dioxide, a host of organic compounds including oxalic acid and mellitic acid, which affect the extraction of plutonium into TBP [2,3]. Additional steps are therefore required to destroy these organic species.…”

Section: Introductionmentioning

confidence: 99%

Chemical Head-end Steps for Aqueous Reprocessing of Carbide Fuels

1990

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The organic compounds formed during the dissolution of carbide fuels in nitric acid adversely affect the extraction of plutonium by tributyl phosphate. This work was undertaken as a preliminary study of the effect of refluxing the dissolver solutions obtained by dissolution of uranium carbide in 13 Μ nitric acid on the subsequent solvent extractions steps. The extraction of plutonium from carbide dissolver solutions by 30% TBP in ndodecane and the subsequent stripping and partitioning of Pu from the organic phase loaded with uranium and plutonium were studied. The results obtained were compared with those obtained with control solutions containing uranyl nitrate and plutonium(IV) nitrate with concentrations of uranium, plutonium and nitric acid similar to those of the dissolver solutions. The distribution ratios obtained with the dissolver solution and the control solution were comparable, indicating that the dissolver solution obtained after refluxing for 20h may give a feed solution suitable for PUREX process. Similarly, extraction and partitioning experiments were carried out with (U, Pu)C dissolver solutions and the results were similar to the results obtained with uranium carbide dissolver solutions.As an alternative chemical route for the destruction of carbonaceous materials in the UC dissolver solution, the effectiveness of sodium dichromate as an oxidizing agent was also investigated in terms of the percentage carbon remaining after treatment of the dissolver solution with sodium dichromate. The treatment resulted in destruction of nearly 97% of the initial carbon present in the carbide fuel.

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Oxalate Complexation in Dissolved Carbide Systems

Cited by 17 publications

References 10 publications

Thermodynamics for complex formation between palladium(ii) and oxalate

Thermodynamics for complex formation between palladium(ii) and oxalate

A Photochemical Head-end Step in Carbide Fuel Reprocessing

Chemical Head-end Steps for Aqueous Reprocessing of Carbide Fuels

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