Sonochemical dissolution of nanoscale ThO₂ and partial conversion into a thorium peroxo sulfate

The influence of the sample morphology and experimental conditions towards the sonochemical dissolution of nanoscale ThO₂ samples in sulfuric acid media is described. Significant sonochemical dissolution rates and yields are observed at 20 kHz under Ar/O₂ atmosphere in dilute 0.5 M H₂SO₄ at room temperature, contrasting with the generally-reported high refractory behavior for ThO₂. The dissolution of ThO₂ combines the physical effects driven by acoustic cavitation phenomenon, the complexing affinity of Th(IV) in sulfuric medium and the sonochemical generation of H₂O₂. These sonochemical conditions further allow the observation of the partial conversion of ThO₂ into a scarce Th(IV) peroxo sulfate with 1D morphology resulting from one or both following processes: dissolution/reprecipitation or formation of an intermediate Th(IV) surface complex.