The dissolution of ThO₂(cr) in carbonate solutions and a granitic groundwater

ThO2(cr) was dissolved in the solutions containing various carbonate ion concentrations, and the results were compared with thorium solubility in a domestic granitic groundwater having very low ionic strength. The soluble thorium concentration excluding colloids after phase separation increased with increasing carbonate concentration. However, the thorium concentration in the real groundwater was remarkably greater than that in the carbonate-containing solutions with a similar concentration of carbonate and pH condition. This might be attributable to other species as well as Th(OH)(4)(aq) and Th(OH)(3)(CO3)(-). These species form colloids or precipitates, and their concentration can be reduced in the ultra-filtered solution by an aging effect.