Structural integrity of Cs and Sr immobilized lacunar apatite phosphate simulated ceramic wasteform Na0.9Cs0.1Pb3Sr(PO4)3 under heat and aqueous flow

Abstract

Lacunar apatite host, NaPb4(PO4)3was converted into a ceramic wasteform with the incorporation of Cs and Sr ions. The systematic substitution yielded the wasteform composition Na0.9Cs0.1Pb3Sr(PO4)3 with 8.52 wt% of Strontium and 1.29 wt% of caesium. The wasteform was subjected to continuous heating in the temperature range 298–973 K and aqueous flow to study the thermal stability and chemical durability respectively. The wasteforms response was studied by powder X-Ray diffraction analysis (Room temperature and High temperature), electron microscopic & elemental analysis and normalized mass loss (NLi) & leach rate (LRi) calculations. The average thermal expansion coefficient (αavg) value of 14.4 ± 1.1 × 10−6 K−1 and the leach rates of immobilised Cs, LRCs (10−6–10−8 gm−2d−1) and Sr, LRSr (10−3–10−4 gm−2d−1) demonstrate the structural integrity of the phase. The anisotropic nature of thermal expansion and the mechanistic feature of leaching are discussed.