Effect of ozone on ruthenium species in alkaline medium – Part I: Oxidative dissolution of ruthenium dioxide hydrate

Abstract

Ruthenium / Ozone / Solid dissolution / Ruthenate catalysis / Alkaline medium / Waste reprocessingSummary. Several ruthenium species compounds are typically encountered in waste management from nuclear fuel reprocessing operations. Ozone acting as a strong oxidizing agent in aqueous alkaline medium presents some advantages to dissolve rapidly solid deposits of RuO 2 , xH 2 O formed into process devices, without generating troublesome byproducts or secondary wastes. In this study, a three-phase solid-gasliquid column was used for dissolution experiments where the ozone gas flow was contacted with RuO 2 , xH 2 O solid particles suspended in sodium hydroxide solution. The analysis of reaction by-products, ruthenate and perruthenate ions, leads us to propose a reaction mechanism. It points out the autocatalytic effect of ruthenate RuO 4 2− in the dissolution reaction mechanism. Parametric experimental study has been performed. It shows that increase of oxidative dissolution kinetics is obtained: (i) with a particular RuO 2 , xH 2 O solid morphology, (ii) for an optimum sodium hydroxide concentration near 0.5 M, (iii) by increasing gas-liquid exchange surface area, (iv) by increasing ozone concentration in the gas and (v) by increasing ruthenium initial concentration.

Effect of ozone on ruthenium species in alkaline medium – Part III: Oxidative dissolution of ruthenium deposits onto stainless steel

“…In previous papers, we reported studies about the oxidative dissolution of ruthenium dioxide hydrate (Part I [22]) and oxidation of ruthenium nitrosyl complexes by ozone in an alkaline medium (Part II [23]). In particular an autocatalytic oxidative dissolution of RuO 2 ·xH 2 O was highlighted: ruthenium dioxide is first oxidized to give ruthenates ions, which are oxidized into perruthenates ions.…”

Oxidative dissolution of ruthenium deposits onto stainless steel by permanganate ions in alkaline medium

“…In a previous study [10], we showed that the rate of oxidative dissolution of RuO 2 ·xH 2 O particles was inversely related to the particle size. In this study, the RuO(OH) 2 ·xH 2 O deposits completely covered the stainless steel test specimen, and any variation in the quantity deposited simply implied different thicknesses but with the same reactive surface area: 100 cm 2 .…”

“…The variation in the solution potential then diminished on reaching the decontamination plateau. In a previous article [10] we showed that it was possible to monitor oxidative dissolution of RuO 2 ·xH 2 O suspensions by ozone in alkaline medium.…”

“…Nevertheless recent studies of Mun on this subject clearly demonstrate that this black ruthenium deposit corresponds to an oxyhydroxide of Ru(IV), namely RuO(OH) 2 [9], which will be considered in the following as RuO(OH) 2 ·xH 2 O. The available decontamination processes for equipment items often involve alkaline medium in which the formation of RuO 4 remains very limited [10,11], thereby limiting the transfer of contamination. To the best of our knowledge, relatively few studies have been carried out on the oxidative dissolution of fission product oxides [12][13][14][15][16][17][18][19] and only one example of complete oxidative dissolution of ruthenium oxides [20].…”

“…We therefore focused our investigation on the oxidative dissolution of RuO 2 ·xH 2 O in suspension or RuO(OH) 2 ·xH 2 O deposited on stainless steel surfaces by strong oxidizing agents in alkaline medium. In three previous articles [10,11,21] we described oxidative dissolution of RuO 2 ·xH 2 O suspensions and RuO(OH) 2 ·xH 2 O deposits by ozone and by perruthenate ions in alkaline medium. In this follow-up study we investigated oxidative dissolution of RuO(OH) 2 ·xH 2 O deposits on 304L stainless steel surfaces by permanganate ions in aqueous sodium hydroxide medium.…”