Solvent extraction of neptunium(IV) from nitric acid solutions by sulphoxides and their mixtures

Studies have been performed on the liquid-liquid extraction of neptunium from nitric acid solutions by di-n-hexylsulphoxide (DHSO) di-no-octylsulphoxide (DOSO) and di-iso-amylsulphoxide (DISO) and their mixtures over a wide range of conditions. At a given strength of the extractant, extraction of Np(IV) increases initially rapidly with increase in the acid concentration; at high acidities, above 8M HNO₃, the extraction decreases. Under otherwise identical conditions, extraction increases with an increase in the extractant concentration. The species extracted would appear to be Np(NO₃)₄·2(R₂SO). A mixture of two extractants extracts more than the sum of the extractions due to the individual components at concentrations corresponding to those of the mixture. After loading the organic phase with uranium(VI), extractability of Np(IV) becomes considerably lower. The diminution in extraction with increase in temperature is small. A comparison of the extraction behaviour of Np(IV) with those of Pu(IV), U(VI) and some associated fission products has been made.     

A synergetic effect in nitrous acid formation by sonolysis of nitric acid in the presence of nitrous oxide

A synergetic effect is found in the sonochemical formation of HNO₂ in HNO₃ solution in the presence of an N₂O–Ar gaseous mixture. The maximum rate of HNO₂ formation is observed at an N₂O : Ar ratio of 15 : 85 (v/v). During the sonolysis of 4 M HNO₃ solutions, the rate of HNO₂ formation increases multifold due to the synergetic effect. The rate of sonochemical hydrazine decomposition in nitrate solutions also increases considerably in the presence of N₂O.     

Polarography of hexavalent molybdenum in hypophosphorous acid solutions

The polarographic behaviour and determination of Mo(VI) in hypophosphorous acid solutions of concentrations varying from 0.1 to 5.0 mol l^?1 andT=25±0.1 °C have been investigated. It was shown that reduction of MoO ₄ ^2? takes place along a single or two waves depending upon the acid concentration. Microcoulometric experiments have been performed at the limiting region of the different waves obtained at different acid concentrations. A scheme for the mechanism of reduction occuring at theDME has been deduced. A method for analytical determination of Mo(VI) on both the micro- and macro-scales in hypophosphorous acid solutions has been reported. Analysis of a binary mixture Mo(VI)/Cd(II) and a tertiary mixture Mo(VI)/Cd(II)/Zn(II) in mol l^?1 hypophosphorous acid has been investigated.     

Kinetics of benzene nitration by nitric acid

The kinetics of benzene mononitration in excess of 45–70 wt % nitric acid in a homogeneous liquid phase was studied. The data on the effects of temperature and nitric acid concentration on the reaction rate were obtained.     

Kinetics of iron(II) oxidation in pyrrhotine leaching with acid sulfate solutions in the presence of nitrous acid

Variation of the ratio between the concentrations of Fe²⁺and Fe³⁺ ions in leaching of pyrrhotine with acid sulfate solutions containing HNO₂ was studied for the example of the oxidation of iron(II) with molecular oxygen, which widely occurs in the nature and is widely used in hydrometallurgy.     

Kinetics and mechanism of the oxidation of nitrous acid by bromine in aqueous sulfuric acid

The kinetics and mechanism of the reaction between nitrous acid and bromine are studied in dilute sulfuric acid medium, using both the stopped‐flow method and conventional spectrophotometry. The partial reaction order with respect to Br₂ moderately differs from 1, showing a saturation at a higher concentration of bromine. The second order of the reaction towards nitrous acid has been observed. Hydrogen and bromide ions significantly suppress the rate of reaction. Despite the apparent simplicity, the mechanism is rather complex, with two reaction pathways proposed. The first one is represented by the reaction of bromine with the intermediate dinitrogen trioxide. A direct nucleophilic attack of NO₂⁻ ion towards the bromine molecule is suggested as the second pathway. The proposed mechanism accounts for the observed behavior; in almost all cases a satisfactory quantitative agreement with the experiments is obtained. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 279–285, 2000     

Kinetics of hexachloroplatinic acid reduction

The kinetics of hexachloroplatinic acid reduction with hydrogen have been studied at several temperatures by determining the rate of hydrochloric acid formation. The kinetic parameters are reported and discussed.

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Kinetics of oxidation of ascorbic acid by methylene blue in acid solutions

We propose a kinetic scheme for reduction of methylene blue by ascorbic acid, characterized by the existence of two pathways: outer-sphere reduction of methylene blue according to a second-order reaction, and reduction through formation of a 11 complex with ascorbic acid.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 5, pp. 424–429, September–October, 1993.     

Electrochemical and spectroelectrochemical properties of neptunium(VI) ions in nitric acid solution

A benchmark study was carried out to verify whether MCNP is useful in the design stage of a PGNAA facility for large samples up to 1 m length and 0.15 m diameter, using a 2.54 cm diameter thermal neutron beam. For this facility neutron self-shielding and gamma-attenuation correction methods have to be developed. The relative spatial neutron-density distributions within three samples with different macroscopic scattering and absorption cross sections were studied in a comparison between an MCNP simulation and an irradiation experiment using copper wires as neutron monitors. The neutron density in the sample was within statistical agreement between experiment and simulation. Typically the relative spatial neutron-density distributions agreed to within 1%. Therefore, MCNP can be used in design studies for the development of a large sample PGNAA facility as specified. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of the oxidation of nitrous acid by tetrachloroaurate(III) inHCl

Summary The kinetics of the reaction between nitrous acid and gold(III) in an HCl medium was studied. The reaction was first order with respect to [Au^III] and [HNO₂]·H⁺ and Cl^- ions inhibit the rate and alkali metal ions have specific effects on the rate. The reaction appears to involve different gold(III) species, viz. AuCl _inf4 ^sup– , AuCl₃(OH₂) and AuCl₃(OH)^–, which undergo a two-equivalent reduction to gold(I) leading to the formation of NO _inf2 ^sup+ which under-goes rapid hydrolysis to give nitric acid.     

Oxidation of benzyl alcohols by nitrous and nitric acids in strong sulfuric acid media

We have studied the oxidation of benzyl alcohols by nitrous and nitric acid in sulfuric acid media. The oxidation by nitrous acid is rapid and has an activation energy of 10.6 ± 0.8 kcal mol^?1. A Hammett plot of logk₂ vs. σ⁺ is linear with a ρ value of ?1.4. The oxidation by nitric acid in sulfuric acid media is autocatalytic. From the kinetic and product analyses, it is concluded that a common oxidant, the nitrosonium ion is involved when either nitrous or nitric acid is used. A mechanism is proposed which involves the abstraction of hydride from the alcohols as the rate determining step. It is demonstrated that the autoxidation of the alcohols is catalyzed by nitrous acid or nitric oxide.     

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.     

Kinetics and mechanism of the reaction betweencis-dichlorobisbipyridineruthenium(II) and nitric acid in water-methanol solutions

Summary The kinetics of the reaction betweencis-dichlorobisbipyridineruthenium(II) and nitric acid have been investigated spectrophotometrically in the 25°–40° range in the presence of 0.03 to 0.2 mol dm^–3 HNO₃. The reaction proceeds with the stepwise formation of monoaqua and diaqua products. Only the formation of the monoaqua intermediate was followed as this species could not be obtained in a pure state. Aquation proceeds through a dissociative process. The second order rate constants are 11.8 (25°), 17.5 (30°); 30.0 (35°) l mol^–1 s^–1. Activation parameters are H 52±3 kJ mol^–1; S–108±8 JK^–1 mol^–1.     

Study of reactivity of neptunium ions toward oh radicals in perchloric acid solutions by pulse radiolysis method

Conclusions The rate constants for the reactions of OH radicals with Np(IV) and Np(V) ions in aqueous perchloric acid solutions are practically independent of the acidity of the medium and are quite high, in order to exclude the recombination of the OH radicals in the presence of these ions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 940–942, April, 1982.