Effects of Aoueous Phase Composition on the Leach Behavior of Nuclear Waste Glasses

Abstract

AbstractA systematic matrix of leach tests on a Rest Valley waste glass composition is described. These tests are intended to provide quantitative systematic information on leachant composition effects. and accordingly elucidate the controlling orocesses in hiuh-solute media. e.g. silicate ground water. brine. etc. In order to separate the effects of the nature and concentration of solutes from pH effects. leach tests were first carried out on the glass in de-ionized water under highly interactive conditions (high surface to volume ratio) in a configuration which pre- vented lowering the pH due to the intrusion of CO:. After determination of the resulting pH. the leach behavior of the glass was characterized in a series of high-dilution tests in various leachants buffered at this pH value in order to quantify the effects of leachant composition and concen- trations on the leaching orocess. The high-dilution conditions were used at this stage to ensure that the leachant composition mould not be signifi- cantly affected by accumulation of leached glass components. It was concluded that increased ionic strength appears to depress the leach rates in near-neutral media but enhances the leach rates under moderately basic conditions.