Immobilization of cesium into mineral-like matrices of tridymite, kosnarite, and langbeinite structure

Abstract

Cesium-containing phosphates CsMgPO4, CsZr2(PO4)3, and Cs2Mg0.5Zr1.5(PO4)3 of framework structure were synthesized. The chemical stability of the crystalline phosphates in neutral, acidic, and alkaline media was studied. Quantitative data on the chemical stability in a wide pH range and on the ion-exchange capacity of phosphates containing cesium, magnesium, and zirconium ions were obtained by potentiometric titration. The Cs leach rates from the ceramic samples upon long contact with water were from 3 × 10–4 to 4 × 10–6 g cm–2 day–1. The phosphates CsZr2(PO4)3 and Cs2Mg0.5Zr1.5(PO4)3 are thermally stable in the temperature range from–268 to 1000°C, and CsMgPO4 undergoes a low-temperature phase transition at–37°C without break of chemical bonds in the structure. The stability of ceramic and powdered samples of CsMgPO4, CsZr2(PO4)3, and Cs2Zr1.5Mg0.5(PO4)3 was studied in different aspects, and these materials proved to be promising for cesium consolidation. High cesium content of CsMgPO4 allows its use as a material of the active core of 137Cs/137mBa sources.