Experimentally determined dissolution kinetics of Na-rich borosilicate glass at far from equilibrium conditions: Implications for Transition State Theory

Journal Article · Mon Apr 14 00:00:00 EDT 2008 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/j.gca.2008.02.026· OSTI ID:939012

Icenhower, Jonathan P. ^[1]; McGrail, B. Peter ^[1]; Shaw, Wendy J. ^[1]; Pierce, Eric M. ^[1]; Nachimuthu, Ponnusamy ^[2]; Shuh, David K. ^[3]; Rodriguez, Elsa A. ^[1]; Steele, Jackie L. ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of Nevada, Las Vegas, NV (United States)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Abstract—The dissolution kinetics of five chemically complex and two chemically simple borosilicate glass compositions (Na-B-Si±Al) were determined over a range of solution saturation values by varying the flow-through rates (1 to 100 mL d^-1) in a dynamic single-pass flow-through (SPFT) apparatus. The chemically complex borosilicate glasses are representative of prospective hosts for radioactive waste disposal and are characterized by relatively high molar Si/(Si+Al) and Na/(Al+B) ratios (>0.7 and >1.0, respectively). Analysis by x-ray absorption spectroscopy (XAS) indicates that the fraction of ivB to iiiB (N₄) varies from 0.66 to 0.70. Despite large differences in bulk chemistry, values of δ ²⁹Si peak shift determined by MAS-NMR varies only by about 7 ppm (δ²⁹Si = -94 to -87 ppm), indicating small differences in polymerization state for the glasses. Forward rates of reaction measured in dynamic experiments converge (average log10 rate [40°C, pH 9] = -1.87±0.79 [g/(m²•d)]) at high values of flow-rate (q) to sample surface area (S). Dissolution rates are independent of total Free Energy of Hydration (FEH) and this model appears to overestimate the impact of excess Na on chemical durability. For borosilicate glass compositions in which molar Na > Al + B, further addition of Na appears to stabilize the glass structure with respect to hydrolysis and dissolution. Compared to other borosilicate and aluminosilicate glasses, the glass specimens from this study dissolve at nearly the same rate (0 to ~55×) as the more polymerized glasses, such as vitreous reedmergnerite (NaBSi3O8), albite, and silica. Dissolution of glass follows the order: boroaluminosilicate glass > vitreous reedmergnerite > vitreous albite > silica glass, which is the same order of increasingly negative ²⁹Si chemical shifts. The chemical shift of ²⁹Si is a measure of the extent of bond overlap between Si and O and correlates with the forward rate of reaction. Thus, dissolution appears to be rate-limited by rupture of the Si—O bond, which is consistent with the tenants of Transition State Theory (TST). Therefore, dissolution at far from equilibrium conditions is dependent upon the speed of the rate-controlling elementary reaction and not on the sum of the free energies of hydration of the constituents of boroaluminosilicate glass.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 939012
• Report Number(s): PNNL-SA-56660; GCACAK; 14592; DF0961000; TRN: US0806077
• Journal Information: Geochimica et Cosmochimica Acta, Vol. 72, Issue 12; ISSN 0016-7037
• Publisher: The Geochemical Society; The Meteoritical Society
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
ABSORPTION SPECTROSCOPY
BOROSILICATE GLASS
CHEMICAL SHIFT
CHEMISTRY
DISSOLUTION
FELDSPARS
FLOW RATE
FREE ENERGY
GLASS
HYDRATION
HYDROLYSIS
KINETICS
POLYMERIZATION
RADIOACTIVE WASTE DISPOSAL
RUPTURES
SATURATION
SILICA
SURFACE AREA
VELOCITY
borosilicate glass
dissolution kinetics
Free Energy of Hydration model
Si-29 NMR spectroscopy
experimental
Environmental Molecular Sciences Laboratory