Leaching studies of natural and synthetic titanites using secondary ion mass spectrometry

Titanite (CaTiSiO5) has been proposed as the ceramic component of a glass-ceramic host for the immobilization of nuclear fuel reprocessing wastes. Central to this proposal is the argument that titanite can be in thermodynamic equilibrium with a range of natural groundwaters. In this paper, we discuss experimental evidence for the thermodynamic argument, obtained from SIMS depth profiles of natural and synthetic titanites after leaching in deionized water, Ca2+/Si4+ doped solutions and pure D2O. From the absence of any dissolution in equilibrium solutions and evidence of titanite regrowth on adjacent mineral surfaces leached within the titanite stability field, it is concluded that the thermodynamic approach is probably valid under these conditions. Geochemical evidence also indicates that titanite can nucleate and grow at low temperatures if Psub(CO2) is sufficiently low. (author)