Dissolution of Borosilicate Waste Glass: Effect of Al and B Coordination on Alkali Ion Exchange
EMSL Project ID
14592
Abstract
Borosilicate glass will be used to immobilize nuclear waste located at several U. S. Department of Energy sites. Currently at Hanford, immobilized low-activity waste (ILAW) will be produced using the Waste Treatment Plant (WTP) and placed into a near-surface disposal system located on the Hanford Site. Before the ILAW can be placed into the disposal system, DOE must approve a performance assessment (PA), which is a document that describes the long-term impact of the disposal facility on public health and environmental resources. A critical component of the PA will be to provide quantitative estimates of radionuclide release rates from the engineered portion of the disposal facilities (source term). Previous studies have illustrated a major factor controlling the radionuclide release rates is the dissolution rate of the vitrified matrix (McGrail et al. 2001a; Pierce et al. 2004). Therefore, to provide these estimates fundamental information on the reaction kinetics of glass is required.The reaction kinetics of glass is controlled by matrix dissolution, and alkali-hydrogen ion exchange (IEX.
These processes are directly correlated to the structural characteristics of glass. Our discussion here will focus on one aspect of the glass/water interaction, IEX. The exchange of alkalis contained in glass for hydrogen contained in solution is a widely recognized process in the initial stages of the glass-water interactions. This process eventually causes the breakdown of the glass network and dissolution into the aqueous phase. The rate by which this process occurs has been directly correlated with non-bridging oxygen (NBO) sites using simple four component glasses (McGrail et al. 2001b). Non-bridging oxygen sites have also been observed in ILAW glass formulations. The presence of NBO sites causes network depolymerization and therefore decreases the overall glass durability. Therefore, to gain a more detailed understanding of the relationship between the local coordination geometry around aluminum, boron, and silicon atoms and the effect these network former element have on glass dissolution, magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was collected for two prototypic LAW glass formulations; LAW-A44 and -B45.
Project Details
Project type
Capability Research
Start Date
2005-10-01
End Date
2007-07-18
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members