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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.

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