Thermodynamics and stability of rhabdophanes, hydrated rare earth phosphates REPO4 · n H2O

Anna Shelyug, Adel Mesbah, Stéphanie Szenknect, Nicolas Clavier, Nicolas Dacheux, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


Rare earth phosphates comprise a large family of compounds proposed as possible nuclear waste disposal forms. We report structural and thermodynamic properties of a series of rare earth rhabdophanes and monazites. The water content of the rhabdophanes, including both adsorbed and structural water, decreases linearly with increase in ionic radius of the rare earth. The energetics of the transformation of rhabdophane to monazite plus water and the enthalpy of formation of rhabdophane from the constituent oxides was determined by high temperature drop solution calorimetry. The former varies linearly with the ionic radius of the lanthanide, except for cerium. By combining the enthalpy of formation determined by high temperature drop solution calorimetry and the free energy of formation determined previously by solubility experiments, a complete set of thermodynamic data was derived for the rhabdophanes. They are thermodynamically metastable with respect to the corresponding monazites plus water at all temperatures under ambient pressure conditions. This conclusion strengthens the case for monazites being an excellent nuclear waste form.

Original languageEnglish (US)
Article number604
JournalFrontiers in Chemistry
Issue numberDEC
StatePublished - 2018
Externally publishedYes


  • Enthalpy
  • Entropy
  • Free energy of formation
  • Lanthanides
  • Monazites
  • Rhabdophanes
  • Stability

ASJC Scopus subject areas

  • Chemistry(all)


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