Static Leaching and Alteration Mechanisms of Zirconium Alkali Resistant Glasses Containing Heavy Metals

Abstract

The aim of this study is to understand mechanisms that occur during leaching of alkali-resistant zirconium-containing glasses in acid and alkaline solutions. For this, we have developed 5 glass compositions: two alkali-resistant model glasses type CEMFIL, V1 (with zirconium and without heavy metals) and V2 (with zirconium and heavy metals), then three glasses of fly ashes V3 (without zirconium and with heavy metals), V4 (with 30 % of V3, zirconium and heavy metals) and V5 (with 60% of V3, zirconium and heavy metals). V4 and V5 are obtained using V3 as raw material and supplementing with SiO2, ZrO2 and Na2O to give them alkali-resistant properties. Glasses leaching in acidic and basic medium led to an important basification from the first times of alteration at pH = 4 when a basification decrease is observed for solutions initially at pH = 13. Normalized elementary mass losses results showed that, glass alteration  is higher for low-calcium glasses (V1 and V2) and V4 and V5 glasses have the lowest elemental mass losses at pH = 4 and 13. SIMS profiles made on glass alteration films permitted to observe behaviour of  H, Na, Ca, Si and Zr elements after  28 days at pH = 4 and 13 and understand the different  dissolution mechanisms involved. SIMS profiles showed that a hydrated film develops on glass surface characterized by hydrogen enrichment and sodium depletion irrespective of the glass. These glasses are also characterized by a surface enrichment of zirconium (except V3 which does not contain zirconium) whatever the pH. Hydrated film thickness confirm that V1, V2 and V3 glasses are more altered than V4 and V5 glasses. These results are confirmed by ICP-AES leachate analysis.