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

Abstract

SummarySeveral 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 RuO2,xH2O formed into process devices, without generating troublesome byproducts or secondary wastes. In this study, a three-phase solid-gas-liquid column was used for dissolution experiments where the ozone gas flow was contacted with RuO2,xH2O 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 RuO42-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 RuO2,xH2O 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.