Chemical and environmental stability of monazite-cheralite solid solutions Ln1-2Ca Th PO4 (Ln = Pr, Nd; x = 0–0.15): A thermodynamic study

Monazite-cheralite ceramics are a promising waste form for actinides. To elucidate the long-term behavior of this matrix in aqueous solutions, study measured thermodynamic data Th-rhabdophanes Ln1-2xCaxThxPO4·nH2O (with Ln = Pr, Nd; x 0–0.15) and associated anhydrous monazite-cheralites Ln1-2xCaxThxPO4. Solubility experiments at 298 K high temperature oxide melt solution calorimetry were combined calculation ΔGf°, ΔHf° Sm° monazite-cheralites. Standard solubility constants employed geochemical simulation using PHREEQC software, results which confirmed chemical stability monazite-cheralite phases supported their use as specific conditioning immobilization