PNNL

Abstract

Calculations have been performed to determine why, in static dissolution tests, the experimentally observed formation of a zeolite, such as analcime, causes a rapid increase in the dissolution rate for some glasses but not for others. The results of these calculations with a series of simple glasses show that there is a strong dependence on the Al content of the glass. For ratios of Si/(Si+Al) < 0.7, the amount of glass that has to dissolve for analcime to cause the dissolution rate to increase is 100 to 1000 times less than for glasses with higher ratios of Si/(Si+Al). Other glass components such as Na, Ca, B and Li are less effective at changing the rate of dissolution, although a minimum amount of Na needs to be present in the glass for analcime to form. These effects may be calculated for multi-component glasses by use of a simple six-component glass, although experimental verification is necessary to show that a six-component glass can be used. We also discuss the reasons why the effect of analcime precipitation on the silicon concentration in solution may be experimentally difficult to determine.