Gravimetric determination of carbon in uranium carbide

Summary The results of the determination of combined carbon and free carbon in uranium carbide in oxygen by a differential temperature technique suggest the pre-mature oxidation of the free carbon due to the local heating of the sample caused by the exothermic decomposition of the carbide. However, it was found possible to overcome this difficulty employing air as supporting gas at controlled heating rates.

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Gravimetrische Bestimmung von Kohlenstoff in Urancarbid

Zusammenfassung Bei der Bestimmung von gebundenem und freiem Kohlenstoff in Urancarbid bei unterschiedlichen Temperaturen ergaben sich Fehler durch vorzeitige Oxidation von freiem Kohlenstoff infolge lokaler Erhitzung der Probe durch die exotherme Zersetzung des Carbids. Diese Schwierigkeit konnte jedoch durch den Einsatz von Luft als Trägergas bei kontrollierter Erhitzungsgeschwindigkeit überwunden werden.

     

A conductivity method for combined carbon and free carbon determination in uranium carbide

A conductivity method based on differential temperature oxidation of combined carbon and free carbon has been worked out for their determination in uranium carbide employing purified air for oxidation. The combined carbon determined at 550°C and free carbon at 900°C were found to be 4.58% and 0.27% with a precision of 2% and 11%, respectively. The free carbon determined by the present method and that by dissolution followed by conductivity method agreed within ±5%. Effect of temperature and time on the oxidation of free carbon /taken as graphite/ in air atmosphere was also studied.     

Coulometric determination of uranium in perchloric acid medium and its applications

Amorphous samples of a new inorganic ion exchanger, cerium(IV) selenite have been prepared under varying conditions. The material prepared by mixing 0.025M ceric sulfate and 0.025M sodium selenite in the ratio of 11 was studied in detail for its ion-exchange capacity, chemical stability, IR, thermogravimetry and K_d values. Separations of metal ions have been performed on columns of this ion exchanger.     

Simultaneous spectrophotometric determination of uranium, nitric acid and nitrous acid by least-squares method in PUREX process

Multi-wavelength linear regression spectrophotometry combined with method of least squares for simultaneous determination of uranium, nitric acid and nitrous acid in PUREX (Plutonium/URanium EXtraction) process was developed. The molar absorbance matrix was calibrated with absorbance data measured in the wavelength range of 350–500 nm for a series of standard solutions by linear least-squares regression. This method used information from the absorption spectra of U(VI)–nitrous acid–nitric acid solutions to determine U(VI), nitrous acid and nitric acid. In the range of 0.95–74.1 g/L U(VI), 5 × 10^?4–2 × 10^?3 mol/L nitrous acid and 3–5 mol/L aqueous nitric acid solution, the measuring precision for determination of U(VI), nitrous acid and nitric acid was 0.46, 4.09, and 0.68 % respectively. In the solution of 30 % TBP–kerosene, the measuring precision for determination of U(VI) and nitrous acid was 0.42 and 4.2 % respectively in the range of 0.95–74.1 g/L U(VI) and 5 × 10^?4–2×10^?3 mol/L nitrous acid. The spectrophotometric method can be valuable for monitoring and controlling of both species in PUREX process operation, thanks to its simplicity, efficiency and accuracy.     

Electrochemical reduction of uranium(VI) in nitric acid-hydrazine solution on glassy carbon electrode

Electrochemical reduction of U(VI) in nitric acid-hydrazine solution is greatly influenced by the concentration of nitric acid. In low acidity nitric acid solution such as 0.1M (M=mol/dm³) HNO₃, U(VI) was firstly reduced to U(V) and then partially reduced to U(IV). In high acidity nitric acid solution, e.g., 3-6M HNO₃, an electrode process of two-electron transfer was involved in the reduction of U(VI). A higher U(IV) yield could be achieved in nitric acid solution with higher concentration. Hydrazine was very effective in suppressing the reduction of concentrated nitric acid, and the optimal concentration of hydrazine added was 0.075 to 0.15M in 6M HNO₃ This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetic studies on the oxidation of uranium(IV) in nitric acid solution

The kinetics of oxidation of U(IV) in nitric acid solution by nitrous acid and air oxygen have been studied. The effects of concentrations of U(IV), nitric acid, hydrogen ion and nitrous acid in aqueous solution or oxygen in gas on the oxidation rate have been examined. The oxidation rate increases with increasing temperature and the activation energies are 47 kJ mol^–1 for nitrous acid and 91 kJ mol^–1 for oxygen. The mechanisms for both oxidation reactions are discussed.     

Extraction of uranium(VI) from nitric acid solution by N,N-dibutyldodecanamide

The partition of uranium(VI) between nitric acid solutions and solutions of N,N-dibutyldodecanamide (DBDA) in kerosene has been investigated at varying concentrations of nitric acid, extractant, salting-out agent LiNO₃ and at different temperatures. The mechanism of extraction is discussed in the light of the results obtained.     

Analysis of uranium in dissolver solution of fast reactor carbide fuel reprocessing

Uranium in simulated dissolver solution of FBTR mixed carbide fuel containing fission products is analyzed by modified Davies–Gray method. The uranium is analyzed after the sample is evaporated with 1 M H₂SO₄ and followed all the steps carried out by Davies–Gray method. The proposed method assures analysis of uranium in dissolver solution of FBTR fuel can be titrated directly without prior separation of fission products.     

Quantitative analysis of neodymium, uranium, and palladium in nitric acid solution by reflection absorption spectrophotometry

Quantitative analysis of Nd, U, or Pd in 3 mol dm^?3 (M) HNO₃ was performed by reflection absorption spectrophotometry at ultraviolet–visible–near-infrared (UV/Vis/NIR) region. A sample chamber with optics for reflection measurement was designed and attached to a UV/Vis/NIR spectrophotometer by optical fibers. The reflection absorbance showed linear relations with concentrations of Nd, U, and Pd at the absorbance region less than 0.1. The quantitative analysis was found to be possible for 3 M HNO₃ solutions containing [Nd] ~0.2 M, [U] ~0.04 M, or [Pd] ~0.01 M.     

Thermodynamics of uranium extraction from nitric acid solution by TBP loaded on inert supporting material

Thermodynamic investigation of the extraction of both uranium(VI) and uranium(IV) from nitric acid solutions using tri-n-butyl phosphate (TBP) loaded on polyacrylic acid polymer (SM-7) as an inert supporting material has been done using batch technique. The effect of temperature on the equilibrium extraction values has been utilized to evaluate the change in standard thermodynamic quantities (viz. DH, DS, and DG). The Freundlich isotherm was successfully applied to the extraction data of both metal ions. The Dubinin-Radushkevich (D-R) isotherm was found to be valid only in case of U(IV) extraction. Based on the D-R expression, the maximum extraction capacity of loaded TBP and the mean free energy of U(IV) extraction have been determined.     

Extraction of uranium(VI) from nitric acid solution with hexyloctylsulfoxide (HxOSO)

The thermodynamic extraction of uranium(VI) with hexyloctylsulfoxide (HxOSO) has been studied. It was found that the distribution ratio increases with increasing nitric acid concentration up to 2.3 mol/l and then decreases. The distribution ratio also increases with increasing extractant concentration. The extracted species appears to be UO₂(NO₃)₂ ^.2HxOSO. The influences of temperature, sodium nitrate and oxalate concentrations on the extraction were also investigated, and the thermodynamic functions of the extraction reaction were obtained.     

X-ray fluorescence determination of uranium and neighbouring elements in solution

A method of energy dispersive X-ray fluofescence analysis of U, Np, Pu contents in solution has been developed for application in the field of VVER spent nuclear fuel reprocessing. Precision is 0.4% in the range of the U contents 0.2–2‰, and the detection limit is 0.15 ppm. Preliminary dilution is required for solutions with hihg U contents (>3‰). Spectra treatment program for a minicomputer has been developed and the method of corrections for non-linearity of concentration curves was checked.     

Organic quantitative analysis. XL — Conductometric micro and ultramicro determination of carbon

Summary A rapid method is described for the determination of 0.3–3 mg of carbon in organic samples by catalytic combustion in the presence of Co₃O₄, and conductometric measurement of the amount of carbon dioxide produced. Interfering elements are dealt with in the usual way, and the carbon dioxide is absorbed in a specially designed absorption vessel. The accuracy and precision of the method are practically constant over the whole range of 0.3–3 mg carbon, and are at least as good as those of the gravimetric micro methods; the method is therefore particularly useful since it gives excellent results with both micro and ultramicro sample weights.

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Zusammenfassung Ein rasches Verfahren für die Bestimmung von 0,3 bis 3 mg Kohlenstoff in organischen Substanzen durch katalytische Verbrennung über Co₃O₄ und konduktometrische Messung des Kohlendioxids wurde beschrieben. Störende Elemente werden wie üblich behandelt. Das Kohlendioxid absorbiert man in einem speziellen Gefäß. In dem angegebenen Bereich ist die Genauigkeit des Verfahrens praktisch gleichbleibend gut und dem gravimetrischer Mikromethoden vergleichbar. Das Verfahren ist besonders deswegen nützlich, weil es sowohl mit Mikro- wie mit Ultramikroeinwaagen ausgezeichnete Ergebnisse liefert.

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Résumé On décrit une méthode rapide pour le dosage de 0,3 à 3 mg de carbone dans les échantillons organiques par combustion catalytique en présence de Co₃O₄ et mesure conductimétrique de la quantité de gaz carbonique produite. Les éléments qui interfèrent sont éliminés de la manière habituelle et le gaz carbonique est absorbé dans un vase à absorption spécialement conçu. L'exactitude et la précision de la méthode sont pratiquement constantes dans tout le domaine de 0,3–3 mg de carbone et sont au-moins aussi bonnes que celles des micro-méthodes gravimétriques; la méthode est donc particulièrement utile puisqu'elle donne d'excellents résultats avec des poids d'échantillon micro et ultramicro.

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XXXIX: Chemický prmysl, to be published.     

Conductometric determination of the concentration of acid centers on functionalized materials

The potentialities of conductometric titration were investigated for the study of protolytically active groups using organosilicas with immobilized acid groups of different types as an example. The methods of conductometric and pH-metric titration were compared in determining the concentrations of these groups. It was found that pH metry was mainly applicable to the determination of strongly acid groups of organosilicas, whereas conductometric titration can be applied to the determination of all types of test materials. It was shown that conductometry is a promising method for estimating the energetic heterogeneity of the immobilized layer and the concentration of functional groups on the surface of organosilicas.     

Extraction of uranium(VI) and thorium(IV) from nitric acid solution by N-alkylcaprolactam

Extraction of uranium(VI), thorium(IV) from nitric acid has been studied with N-octylcaprolactam and N-(2-ethyl)hexylcaprolactam. Distribution coefficients of U(VI), Th(IV) and HNO₃ as a function of aqueous NHO₃ concentration, extractant concentration and temperature have been studied. The compositions of extracted species, thermodynamic parameters of extraction have been evaluated. Third phase formation in extraction of U(VI) has been studied. Back extraction behavior of U(VI) and Th(IV) from the organic phase has also been tested. The results obtained are compared with those obtained by using TBP under the same experimental conditions.     

Simultaneous determination of uranium carbide dissolution products by capillary zone electrophoresis

Separation and simultaneous determination of a number of organic acid anions (oxalate, mellitate, trimellitate and benzoate) and U(VI) with direct UV detection is developed for analysis of uranium carbide (UC) dissolution products by capillary zone electrophoresis (CZE). Reverse polarity mode is used. It is found that complex formation of U(VI) with carbonate, used as a carrier electrolyte, allows U(VI) to be determined, as negatively charged species, in a single run with organic acid anions. Some parameters such as pH value, composition of electrolyte and detection wavelength are optimized. Under the chosen conditions (carbonate buffer (ionic strength of 100 mM), pH 9.8, 0.15 mM tetradecyltrimethylammonium bromide (TTAB)) a complete separation is achieved. Calibration plots are linear in two ranges of concentration for U(VI) (∼1 × 10⁻⁵ to 1 × 10⁻³), mellitate and trimellitate (∼5 × 10⁻⁶ to 5 × 10⁻⁴), and about one range (∼1 × 10⁻⁴ to 5 × 10⁻³) for oxalate and benzoate. Accuracy of the procedure is checked by the “added-found” method in standard mixture solutions. Relative standard deviation is within the range of 2–10% and the recovery is in the range of 90–110%. This method is applied for the analysis of real UC dissolution samples.