Identification of Saturating Solid Phases in the System Ce2(SO4)3-H2O from the Solubility Data

Saturating solid phases, Ce₂(SO₄)₃·hH₂O, with hydrate numbers h equal to 12, 9, 8, 5, 4 and 2, have been identified by critical evaluation of the solubility data in the system Ce₂(SO₄)₃—H₂O over the temperature range 273–373 K. The results are compared with the respective TG—DTA—DSC and X-ray data. The solubility smoothing equations, transition points and solution enthalpy estimators of the identified hydrates are given. The stable equilibrium solid phases are concluded to be only Ce₂(SO₄)₃·9H₂O at 273–310 K, Ce₂(SO₄)₃·4H₂O at 310–367 K and Ce₂(SO₄)₃·2H₂O at 367–373 K. Divergencies of up to 185% in the reported solubility data are mainly due to a variety of metastable equilibria involved in the close crystallization fields, and incorrect assignments of the saturating solid phases. Since a similar variety of the hydrate numbers exists for the analogous La(III) system, it most probably also occurs for the corresponding Pu(III), Np(III) and U(III) systems. This revised version was published online in July 2006 with corrections to the Cover Date.