Rare earth (RE) chlorides are essential compounds used for production of the RE metals, their alloys and compounds, also as catalysts in organic synthesis and polymerization. Because in vicinity of room temperature the RE chlorides crystalize from aqueous solutions as hydrates, it was essential to know the phase relations in this region. The corresponding literature was compiled and critically evaluated what allowed to select the most reliable solubility results (liquidus line) and the equilibrium solid phases of the RE chlorides in water. The selected solubility data do not change much near room temperature whereas at elevated temperatures typical strong bends of the liquiduses are observed reflecting tendencies of the systems to immiscibility. The water-rich parts of the RE chloride - water phase diagrams were constructed for majority of the systems. Shapes of the phase diagrams showed evolutional changes of the invariant points and phase stabilities through the RE series. This fact allowed to predict the phase diagrams of the HoCl₃-H₂O and TmCl₃-H₂O systems (which were not investigated) as well as of the PmCl₃-H₂O system (which due to the high radioactivity cannot be treated experimentally at proper concentrations of PmCl₃). Dehydration reactions of the RE chloride hydrates at higher temperatures, decreased pressures and using strong dewaterers are multistage processes, however there are some discrepancies in an uniform description of the reaction stages.

(partly based on achievements of late Tomasz Mioduski)

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