PNNL

Abstract

According to an empirical sulfur solubility model developed from over 200 simulated low-activity waste (LAW) glasses, chlorine and chromium show strong effects on lowering sulfur solubility in glass. This work was aimed at understanding the mechanism behind the negative effect of chlorine and chromium on sulfur solubility. A simplified LAW glass was prepared and saturated by sodium sulfate, sodium chloride, and sodium chromate salts as single components and as mixtures with different ratios at 25 mol%, 50 mol%, and 75 mol% of sulfate mixed with chloride or chromate. A crucible-scale salt-saturation was performed by mixing the crushed glass powder with an excess amount of salts, melting at 1150 °C for one hour, and quenching. Three mixing-melting-quenching cycles were applied to determine saturation concentrations of sulfur, chromium, and chlorine incorporated into the simplified LAW glass. The glass compositions were analyzed by inductively coupled plasma–atomic emission spectroscopy, ion chromatography, and X-ray emission spectroscopy. It is proposed that the negative effect of chlorine and chromium on sulfur solubility can be explained based on the simple hypothesis that sulfur, chlorine, and chromium are present in the glass as anions competing for the voids or interstitial sites of the glass matrix, and that their solubility strongly depends on the effective size of corresponding anions.