A. Yu. Garnov

Catalytic Decomposition of Organic Anions in Alkaline Radioactive Waste: 1. EDTA Oxidation

Decomposition of ethylenediaminetetraacetate in alkaline solutions with H2O2, Na2S2O8, NaClO, and NaBrO was studied titrimetrically. EDTA is oxidized in solutions heated above 60°C in the presence of cobalt salts at stepwise addition of excess H2O2. The reaction between persulfate and EDTA has an induction period decreasing with increasing NaOH concentration and temperature and with decreasing initial EDTA content or with adding AgNO3, K4Fe(CN)6, or NaNO2. The process involves thermal dissociation of the persulfate ions into radical ions and the subsequent development of a chain reaction. Hypochlorite ions oxidize EDTA in 0.5-5.0 M NaOH at 25-60°C. The process efficiency can be improved by fractional addition of the oxidant in the presence of Co(II) or Ni(II) salts. EDTA is oxidized in alkaline solutions with hypobromite ions only on heating to 95°C. Salts of Co(II), Ni(II), and Cu(II) accelerate the process.

Catalytic decomposition of organic anions in alkaline radioactive waste: III. Oxidation of oxalate and glycolate

Decomposition of oxalate and glycolate ions in alkaline solutions under the action of O3, H2O2, and Na2S2O8 was studied spectrophotometrically and titrimetrically. At 20°C, ozone slowly decomposes oxalate in 0.05 M NaOH. In 1 M NaOH, heating at 90°C is required to oxidize oxalate with ozone. Glycolate is readily oxidized with ozone at 20°C in 0.05–1 M NaOH, predominantly into oxalate. Hydrogen peroxide is ineffective reagent for oxalate and glycolate decomposition. Persulfate oxidizes oxalate ion in 0.5–5 M NaOH at 90°C. The reaction of persulfate with glycolate proceeds at 50°C and higher temperatures and is characterized by an induction period, which shortens with increase in concentration of S2O82−, OH−, and temperature, or in the presence of AgNO3 and K4Fe(CN)6. Oxidation involves thermal dissociation of persulfate ions into radical ions followed by a chain reaction.

Synthesis and Structure of Complexes of Np(V) Perchlorate and Np(V) Chloride with Urea

The crystal structure of [NpO2{OC(NH2)2}5]ClO4·H2O and [NpO2Cl{OC(NH2)2}4] was studied by X-ray diffraction. The electronic absorption spectra of these complexes were recorded. The coordination polyhedron of Np in both complexes is a distorted pentagonal bipyramid. There is no cation-cation interaction of neptunyl cations in these complexes.

Catalytic decomposition of organic anions in alkaline radioactive waste: II. oxidation of N-(2-Hydroxyethyl)ethylenediaminetriacetate

Decomposition of N-(2-hydroxyethyl)ethylenediam inetriacetate (HEDTA) in alkaline solutions containing H2O2, S2O82−, and ClO− and under the action of ozone was studied titrimetrically. HEDTA decomposes in the presence of cobalt or copper salts at stepwise addition of H2O2. In the reaction between HEDTA and persulfate ion, an induction period was observed. It shortens with increasing alkali concentration, or temperature, or with decreasing the initial HEDTA concentration. Nitrite ion does not affect the complexone decomposition. The process is initiated by thermal dissociation of persulfate ions into radical ions followed by chain reaction. Hypochlorite ions effectively decompose HEDTA. Porducts of HEDTA decomposition are oxidized by ozone and persulfate mainly to oxalate and carbonate.

Kinetics and kinetic isotope effect in pentavalent plutonium disproportionation activated by power ultrasound

A kinetic isotope effect in Pu(V) disproportionation has been observed in nitric acid solution under the effect of power ultrasound with intensity 0.9W·cm−2 and frequency 22 kHz. The isotope separation coefficient α for242Pu/239Pu isotopes was found to be 1.0081 at 20°C. Without sonication the k.i.e. was not observed. The rate constant of Pu(V) disproportionation was found to be accelerated under sonication. The rate constant determined was (5.7±0.6)·10−3 12·mol−2·s−1 atl=0.9 W·cm−2,v=22 kHz, [HNO3]=0.5 mol·l−1 andT=20°C. It is supposed that the acceleration of Pu(V) disproportionation and the kinetic isotope effect are due to the activation of plutonoyl groups in the interface between the cavitation bubble and the bulk solvent.