Impacts of lithium on Magnox waste glass dissolution

Abstract

The safe storage of vitrified waste demands a thorough understanding of the effects of wasteform composition on chemical durability. One of the major compositional differences between UK glass and international glasses is the presence of Li. Based upon a 25 wt% loading UK Magnox waste glass, two seven-component analogues of molar Li:Na 1.0 and 1.5 were leached to investigate the effects of Li on chemical durability. A comprehensive 11B nuclear magnetic resonance study then took place to investigate the B network before and after dissolution. Here we show that the proportion of IIIB to IVB units did not evolve as the Li:Na ratio was varied; suggesting that Na preferentially charge compensates the B network. However, the B network was shown to leach incongruently at 90 °C. Despite Li being shown to be detrimental to durability during the earlier dissolution regimes, the residual rates of alteration implied excess Li contents had no long-term effects on chemical durability. The observed incongruent dissolution of the B network and initially decreased chemical durability could be attributed to Li preferentially modifying the Si network, thereby promoting glass hydration and B network dissolution whilst the Na compensated IVB units were less affected than IIIB units.