The Impact of Na—H+ Exchange on Long-Term Borosilicate Glass Corrosion: Experiments and Field Observations
Conference
·
OSTI ID:1024553
New insights from laboratory experiments coupled with field observations indicate that pore water solutions that eventually breach containment materials in disposal systems will interact with sodium-excess borosilicate waste glass in an unexpected way. Because many glass waste forms are relatively sodium-rich, they are especially vulnerable to Na+—H+ exchange (ion exchange or simply, IEX). Although the kinetics of this process has been previously investigated for early-stage glass reactions, the implications of IEX for long-term dissolution resistance have not yet been realized. Non-radioactive glass with major- and minor-element chemical compositions similar to Hanford high-Na waste glass were subjected to dissolution experiments to quantify the rates of matrix dissolution and IEX rates. Single-Pass Flow-Through (SPFT) tests quantified the IEX rate at 40°C pH = 8 and silica saturation and showed a dependence upon the fraction of excess sodium in the glass. The equation for the rate (in moles of sodium released per meter squared per second) dependence on excess sodium is: log10rate[mol/(m2∙s)] = 0.63R + (-11.0); r2 = 0.86 where R = molar Na+/(M3+). Further, rates of Na release are slower by ≥30% in D2O-based solutions compared to those in H2O. These results are the hallmark of IEX reactions. Our results are compared against those from a lysimeter field experiment consisting of glasses buried in Hanford sand and to dissolution experiments conducted with a Pressurized Unsaturated Flow (PUF) apparatus. These longer-term tests indicate an initial decrease in dissolution rate by a factor of 10×, and then a constant steady-state rate thereafter. Thus, these data show that IEX reactions are important at near-saturation conditions and effectively prevent dissolution rates from falling below a minimum value. In sum, IEX modifies the long-term behavior of glass dissolution and models cannot assume that dissolution of Na-rich borosilicate glass will decrease by a factor of 100× to 1000×, as argued for minerals and less sodic glasses.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1024553
- Report Number(s):
- PNNL-SA-64130; DF0961000
- Country of Publication:
- United States
- Language:
- English
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