Encapsulation of polucite in magnesium phosphate cement (MKPC)

Pollucite, (Cs(Si2Al)O6·nH2O), has long been considered one of the most stable and suitable mineral forms for the immobilization of radioactive cesium over time, due to its good thermal stability, its low leaching rate (high resistance to leaching) and the fact that it has a dense and stable structure through its strong covalent bonds. But even if Cs is fixed in a chemically stable form (pollucite), this form is still classified as intermediate level waste (ILW) and must therefore be safely encapsulated in a cementitious matrix. For this purpose, magnesium phosphate cement pastes (MKPC) have been designed with the incorporation of pollucite, in a proportion of 0 and 10 %. The effect of the incorporation of the pollucite on the mineralogy and microstructure of the MKPC systems was analysed from the mechanical and mineralogical point of view. Mechanical compressive strengths (1, 7, 28 and 90 days), as well as mineralogical and microstructural changes in presence of pollucite (XRD, ATD/TG, Hg porosimetry and BSEM) were analysed. Finally, the confining capacity of this matrix has been determined after 90d of leaching (ANSI/ANS-16.1-2003).