Analysis of Surface Alteration after Leaching Test of Simulated Radioactive Waste Glass Forms

Leaching behavior is the major waste characteristic that is critical for a long-term assessment prior to disposal. The extent of leaching depends on the initial contact of the glass surface with leachant. There is a need to analyze the behavior of glass materials on surfaces altered after the leaching test to prove the leaching mechanism. Based on the results of SIMS, the postleaching penetration depth for sodium and lithium was larger than those of silicon and calcium while hydrogen concentration was gradually decreasing. Such analysis agreed with their grouping into two categories by leaching mechanisms, one by initial wash-off and diffusion control and another by dissolution associated with diffusion. Single and multilayer terraces on the surface of waste glass were found and characterized by SEM. In the XRD results, a crystallized precipitation layer was not detected. Results of a leaching mechanism model and EPMA measurements were also consistent in explaining the leaching behavior of glass materials. For sodium and lithium, diffusion was the dominant leaching mechanism, while dissolution associated with diffusion affects the leaching of silicon and calcium.