Influence of the precursor and the calcination temperature on the dissolution of thorium dioxide

The effect of the precursor and temperature of calcination on the dissolution of thorium dioxide was carried out. The dissolution of crystallized ThO2 has been studied as a function of pH to evaluate the solubility product of a high temperature calcinated thorium oxide. However no equilibrium was reached after 4 months (at least in acidic media). Nevertheless, high temperature crystallized ThO2 is less soluble by two orders of magnitude than the amorphous hydrated ThO2. We have pointed out a correlation between the surface of the solid and its apparent leachability in acidic perchlorate solutions, resulting mainly in the thorium site concentration differences between the solids. The normalized dissolution rate of crystallized ThO2 which was found to be 1–3×10−6 g m−2 d−1 in 0.1 M acid solutions is independent of the way of synthesis of the solid.