Kinetics of the reaction of Np(VI) with iminodiacetic acid

The stability of Np(VI) in 5–200 mM iminodiacetic acid (H₂IDA) solutions at 23.5–55°С was studied by spectrophotometry. In a solution with pH 2 and excess Np(VI), 1 mol of H₂IDA reduces 2 mol of Np(VI) to Np(V). In 1 and 0.5 M HClO₄ solutions containing 200 mM H₂IDA and 1 mM Np(VI), no more than 36 and 65% of Np(VI), respectively, is reduced at 44.5°С. Complete reduction of Np(VI) is observed in solutions containing 0.2 M HClO₄ and less. In the examined ranges of H2IDA concentrations and temperatures, Np(VI) is consumed in accordance with the first-order rate law. The reduction mechanism involves formation of a Np(VI) iminodiacetate complex, which is followed by intramolecular charge transfer. The generated radical reduces Np(VI). The activation energy is 107 ± 3 kJ mol^–1.     

Oxidation of Np(V) with Xenon Trioxide in an HClO<Subscript>4</Subscript> Solution

Oxidation of Np(V) to Np(VI) with xenon trioxide in a 0.5–1.4 M HClO₄ solution was studied by spectrophotometry. The reaction rate is described by the equation–d[Np(V)]/dt = k[Np(V)][XeO₃], where k = 4.6 × 10^–3 L mol^–1 s^–1 in 1 M HClO₄ at 92°С. The activation energy is close to 92 kJ mol^–1. The activated complex is formed in contact of NpO ₂ ⁺ and ХеО₃ without participation of Н⁺ ions. The activated complex transforms into NpO ₂ ²⁺ and the products: ОН, Хе, and О₂. The ОН radical oxidizes Np(V). Admixtures of Со²⁺ and especially Fe³⁺ accelerate the Np(V) oxidation.     

A Study of the Kinetics of Decarbonization of Magnesite Concentrated by Flotation

The kinetics of decarbonization of magnesite concentrated by the method of flotation is studied in a laboratory under various conditions (stationary unblown layer, fluidized layer, layer mixed in a rotary furnace). Typical features of the process of decarbonization of magnesite are determined (constancy of the temperature of the material up to a decarbonization of 80 – 90%, self-fluidizing of the roasted material due to intense emission of CO₂ gas, etc.).     

Mechanism of Pu(VI) and Pu(V) autoreduction in aqueous solutions

Published data on the stability of Pu(VI) and Pu(V) in solutions of mineral and organic acids and their salts are analyzed. The hypothesis that Pu(VI) in acid solutions disappears owing to the disproportionation to Pu(VII) and Pu(V) cannot be accepted because of high redox potential of the Pu(VII)/(VI) couple. Plutonium( VI) is reduced owing to radiation-chemical reactions induced by its α-radiation and to the formation of a dimer (so-called excimer) by an excited Pu(VI) ion with an unexcited Pu(VI) ion, which rapidly decomposes to Pu(V) and H₂O₂. Plutonium(V) disappears owing to disproportionation and radiation-chemical processes.     

Precipitation of Am(III) and REE peroxides from alkaline solutions containing complexing agents

Precipitation of Am(III) and REE peroxides from alkaline-citrate solutions was studied spectrophotometrically. Hydrogen peroxide (0.25–0.4 M) quantitatively precipitates Am(III) and Nd(III) ions from a solution containing 0.1 M NaOH and 0.2–0.4 M citrate. After H₂O₂ decomposition, the precipitates formed are dissolved in the mother liquor. At lower alkali concentration, 4f and 5f metal ions are precipitated incompletely. In the systems studied, Am and Nd form citrate and hydroxo-citrate complexes in a solution and peroxides in the solid phase.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 524–526.Original Russian Text Copyright © 2004 by Gogolev, Nikonov, Tananaev, Myasoedov.     

On the Highest Oxidation States of Plutonium in Alkali Solutions in the Presence of Ozone

During ozonation of Pu(VI) alkaline solutions, the highest oxidation state of Pu is formed in an oscillatory reaction. This plutonium species is reduced with Pu(VI) or Fe(III). Ferrate ion is also reduced with Pu(VI). It was assumed that in alkali solution plutonium is partially oxidized with ozone to Pu(VIII).