New rare earth langbeinite phosphosilicates KBaREEZrP 2 SiO 12 (REE: La, Nd, Sm, Eu, Gd, Dy) for lanthanide comprising nuclear waste storage

Abstract

Abstract In contrast to the existing cubic langbeinite phosphates and sulphates, orthorhombic langbeinite phosphosilicates of the chemical formula KBaYMP2SiO12 (M: Zr, Sn), KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) and the wasteform KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12 have been synthesized by solution method. Powder X-ray diffraction analysis affirmed that the compounds were phase pure and crystallized in an orthorhombic structure with P212121 space group. Spectral analysis of the wasteform revealed the phase stability, thermal stability and chemical durability of the langbeinite structure. Chemical durability of the powder wasteform has been studied by a dynamic Soxhlet test. Elemental analysis of the leachates showed that the normalized mass losses of barium, zirconium and silicon were in the order of 10−3–10−2 g/m2, 10−5–10−4 g/m2 and 10−2–10−1 g/m2 respectively. Normalized mass losses of lanthanides, potassium and phosphorous were found to be below the instrumental detection limits.