Surface Alteration of Sintered Product of Strontium Aluminum Silicate Under Hydrothermal Conditions

Abstract

AbstractThe surface alteration of strontium aluminum silicate has been studied under hydrothermal conditions in connection with the leachability of Sr from solidified radioactive wastes. Samples exposed to a 3 M NaCl solution at 300°C produced a precipitated layer of analcime (NaAISi2O6) with high crystallinity. The normalized leach rates for Sr in 3 M NaCl and 3 M KC1 solutions were found to be less than 10-3 g/cm2.d, yielding high resistance to leaching in these solutions.On exposure to the CaCl2 solution at 300°C, anorthite (CaAl2Si2O8) was formed on the surface, indicating the replacement of Sr with Ca through isomorphous substitution. In the case of MgCl2 solution, a thick precipitated layer of clinochlore (Mg5Al(Si3Al)O10(OH)8) built up on the outermost surface. This layer serves to depress the migration of Sr, resulting in the deposition of SrCl2 salts in the altered layer.