Leaching behaviour of rhyolite glass

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Glass has long been recognised as a potentially suitable matrix for diluting and stabilising nuclear waste1–5. Most of the glasses which have been studied are borosilicates1–3. One notable exception is the aluminosilicate nepheline syenite glass, used in the pioneering Canadian study4 that showed much lower apparent leach rates than for borosilicates4,5. The natural aluminosilicate volcanic glass, rhyolite, has existed in some natural environments for millions of years6,7; and, as Mendel has pointed out1, it could be adopted as a model against which other glasses could be compared for nuclear waste disposal. We report here results on the hydrothermal leaching and recrystallisation of rhyolite at temperatures up to 300 C, using not only the classical leach monitors of weight loss and solution analyses, but also modern surface probes such as SEM (scanning electron microscopy), ESCA (electron spectroscopy for chemical analyses) and SIMS (secondary ion mass spectroscopy). These surface techniques are especially valuable for gaining a more complete understanding of hydrothermal reactions of glasses or minerals8–10.