The hydration of borosilicate waste glass in liquid water and steam at 200 °C

• Published in: Waste management (Elmsford) 1991, Vol.11 (4), p.205-221
• Main Authors: Ebert, W.L., Bates, J.K., Bourcier, W.L.
• Format: Article
• Language: English
• Subjects: 052002 - Nuclear Fuels- Waste Disposal & Storage; Applied sciences; BOROSILICATE GLASS; CHEMICAL ANALYSIS; CHEMICAL COMPOSITION; COMPUTERIZED SIMULATION; DATA; DISSOLUTION; Exact sciences and technology; EXPERIMENTAL DATA; GLASS; HIGH-LEVEL RADIOACTIVE WASTES; HYDRATION; INFORMATION; LEACHING; MANAGEMENT; MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; MATERIALS; NUMERICAL DATA; Other wastes and particular components of wastes; PHASE STUDIES; Pollution; RADIOACTIVE MATERIALS; RADIOACTIVE WASTE MANAGEMENT; RADIOACTIVE WASTE STORAGE; RADIOACTIVE WASTES; SEPARATION PROCESSES; SIMULATION; SOLVATION; STORAGE; WASTE FORMS; WASTE MANAGEMENT; WASTE STORAGE; WASTES
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/0956-053X(91)90068-G

Simulated borosilicate waste glass was hydrated in steam at 200 °C for times up to 40 days to assess the effect of a very high glass surface area/leachant volume (SA/V) ratio on the reaction. The reactions in steam attained an SA/V in excess of 4000 m −1 due to the limited amount of water that was available to condense on the glass surface. Experiments in liquid water were performed at an SA/V of 40 m −1 for comparison. A solid reaction layer formed on the glass surface in both environments, and the thickness of this layer was used as a measure of the reaction progress. Other secondary phases formed on top of (and within) the layer on the steam-reacted samples after a few days of reaction but not on samples reacted in liquid water. The rate (layer thickness/time) measured in experiments with liquid water slows with time while the reaction in steam is very slow initially but then proceeds at a high rate after secondary phases form. The secondary phases are believed to increase the reaction rate by lowering the solution concentrations of glass species (probably most importantly silicon) which control the reaction affinity. The glass reaction is accelerated in a steam environment relative to liquid environment because, in steam, the small solution volume becomes saturated and precipitates are formed after much less glass has reacted. The experimental technique described allows secondary phases to be generated within short time periods at elevated temperatures in a steam environment. Knowledge of the phases formed is necessary to predict the long-term reaction rate. Precipitates formed on the steam-reacted samples were identified using SEM/EDS analysis and XRD. The EQ3/6 computer code was used to predict secondary phases formed at 200 °C for comparison to the observed phases. Differences in the assemblage predicted by the computer simulation and that produced in the experiments are attributed to the limited data base use by the simulation.