Résumé
The solubility of the pure thorium phosphate-diphosphate, Th
4
(PO
4
)
4
P
2
O
7
, has been measured in 0.1 M NaClO
4
solutions by PERALS
spectrometry (photon electron rejecting alpha liquid scintillation), ICP-MS (inductively coupled plasma-mass spectrometry) and PIXE (particle induced X-ray emission). The results obtained by the three methods are in good agreement and show that the total concentration of thorium in solution is mainly controlled by the precipitation of two compounds: Th(HPO
4
)
2
in acidic media (pH 4.5) and Th(OH)
4
in basic and near-neutral media.