Radiolysis of nitric acid solution : L.E.T. effects

Abstract

The radiolysis of nitric acid solutions was investigated using gamma, beta and alpha radiation. Solutions were gamma-irradiated under various conditions and analyzed for all stable products. Solutions that were alpha-or beta-irradiated were analyzed for nitrite ion only.Nitrite ion, the major radiolysis product, was determined as a function of nitric acid concentration. A nitrite scavenger, p-nitroaniline, was added to prevent the nitrite ion from reacting prior to analysis. The nitrite yields from alpha irradiation were appreciably lower than the yields from gamma and beta irradiations at lower acid concentrations but continually increased with increasing acid concentration. The nitrite yields from gamma or beta irradiation increased with increasing acid concentration up to about 1 M but then decreased. Similarity of the gamma and beta yields substantiated this unusual trend. Previous investigations of neutral nitrate solutions have always shown an increase in yields at the higher nitrate concentrations. A mechanism, based on L.E.T. effects on three radiolytic reactions, has been postulated to explain the differences in yields between alpha and gamma (or beta) irradiation.The radiation chemistry of the aqueous nitrate system has been the subject of much s t~d y . l -~ However, most of the investigations have been in neutral or slightly basic solutions. The only reported works in acidic solutions have been by Savel'ev et al.,5 Mahlman,6 and Vashman et al . ' Savel'ev et al., using alpha radiation, were the only investigators to analyze for all of the stable radiation products. Mahlman analyzed directly only for hydrogen and oxygen yields from gamma irradiation, and Vashman et al. examined only OH, NO2, and NO3 radical formation in alpha-irradiated frozen nitric acid solutions by electron paramagnetic resonance.One reason for the lack of information in nitric acid solutions is the difficulty of analysis of the major radiolysis products, nitrite ion and hydrogen peroxide. Nitrite ion, or HN02, not only reacts with H202 but decomposes in acid solutions. In order to prevent these reactions and obtain meaningful analytical results, an analytical reagent was added to the solutions to react with or " scavenge" the nitrite ion as it is formed. p-Nitroaniline was the reagent used although other amines have been previously used.s* The reactions of Hz02 were not prevented prior to its analysis so that H202 yields were determined only in dilute acid solutions, and are not reported here.In this study, nitric acid solutions of varying concentrations were gamma-, alpha-and beta-irradiated. Solutions that were alpha-or beta-irradiated were analyzed for nitrite only ; solutions that were gamma-irradiated were irradiated under various conditions and analyzed for all stable products. The linear energy transfer (L.E.T.) effects on the mechanism of nitrite production are discussed and the interpretations may lead to greater understanding of the radiation chemistry of the aqueous nitrate system." Nitrite " will be used in this repor...

Alpha radiolysis of nitric acid and sodium nitrate with 4He2+ beam of 13.5MeV energy

“…For sufficient high nitrate ion concentrations (from 0.5 to 1.0 mol L À 1 ), direct radiolysis has an effect on the nitrate ions (Faraggi et al, 1971;Kazanjian et al, 1970;Mahlman, 1963). Direct radiolysis mechanism implies two supplementary reactions (Katsumura et al, 1991;Mahlman, 1963):…”

“…However, in order to correlate the G(H 2 O 2 ) and G(HNO 2 ) radiolytic yields to the oxidation state modifications of actinides in the nitric acid solutions under ionizing radiation, the chemical yields of H 2 O 2 and HNO 2 independently from reaction (11) need to be determined. Only a few studies have quantified HNO 2 produced in solution, by adding a specific solute species blocking reaction (11) (Bhattacharyya and Saini, 1973;Kazanjian et al, 1970;Savel'ev et al, 1967).…”

Physico chemical properties of irradiated i-SANEX diluents

“…Preliminary, it is vital to understand the radiolysis effects on the diluents because it is prevalent in the literature that radiation damage mainly affects the diluents and, indirectly, the extractants [1]. With this regard, in the last decades a great deal of effort has been devoted to understand the radiolysis mechanism of nitric acid, in terms of possible by-products identifi cation and of formation yields evaluation [14][15][16][17], so as to assess their impact on the actinides chemistry [7,18,19]. Moreover, the composite system concentrated HNO 3 -organic diluent was studied with particular attention to degradation products impact on PUREX process safety [8][9][10].…”

“…In fact, this anion reacts with water by-products leading to the formation of nitrous anion [16,17], which plays a critical role in the redox chemistry of actinides, and thus on the effi ciency of the separation process [12,22]. Since nitrous anion immediately decomposes in acidic solutions, nitrate ion concentration was monitored [16].…”

Molecular modeling and electrochemical investigations of the corrosion inhibition of nickel using some thiosemicarbazone derivatives

“…Addition of thiosemicarbazone derivatives retards the anodic dissolution and cathodic reduction reactions that occur on nickel surface in 1.0 M HNO 3 . Thiosemicarbazone derivatives destroy completely nitrous acid which is always present in small amounts in nitric acid [40] and which increases by the reduction of nitric acid. The values of the corrosion current density (i corr ) for nickel corrosion reaction without and with thiosemicarbazone derivatives were determined by extrapolation of the cathodic Tafel lines to the corrosion potential (E corr ).…”