Thermokinetic Model of Borosilicate Glass Dissolution: Contextual Affinity

1989 ◽  
Vol 176 ◽  
Author(s):  
T. Advocat ◽  
J.L. Crovisier ◽  
B. Fritz ◽  
E. Vernaz
Keyword(s):  
Experimental Data ◽  
Dissolution Rate ◽  
Rate Equation ◽  
Computer Code ◽  
Solution Chemistry ◽  
Glass Dissolution ◽  
Water Composition ◽  
Silica Activity ◽  
Short And Long Term

ABSTRACTShort and long-term geochemical interactions of R7T7 nuclear glass with water at 100°C were simulated with the DISSOL thermokinetic computer code. Both the dissolved glass quantity and the resulting water composition, saturation states and mineral quantities produced were calculated as a function of time. The rate equation used in the simulation was first proposed by Aagaard and Hegelson: v = k+.S.a(H+)-n(l - e-(A/RT)). It simulates a gradually diminishing dissolution rate as the reaction affinity diminishes. The best agreement with 1-year experimental data was obtained with a reaction affinity calculated from silica activity (Grambow's hypothesis) rather than taking into account the activity of all the glass components as proposed by Jantzen and Plodinec. The concept of residual affinity was introduced by Grambow to express the fact that the glass dissolution rate does not cease. We prefer to replace the term “residual affinity” by “contextual affinity”, which expresses the influence on the dissolution rate of three factors: the solution chemistry, the metastability of SiO2(m), and the possible precipitation of certain aluminosilicates such as zeolites.

Alteration of Basaltic Glass in Iceland as a Natural Analogue for Nuclear Waste Glasses: Geochemical Modelling with DISSOL

1988 ◽  
Vol 127 ◽  
Author(s):  
J. L. Crovisier ◽  
T. Advocat ◽  
J. C. Petit ◽  
B. Fritz
Keyword(s):  
Computer Code ◽  
Solution Chemistry ◽  
Iron Hydroxides ◽  
Basaltic Glass ◽  
Secondary Products ◽  
Glass Dissolution ◽  
Mineral Phases ◽  
Kinetic Effects ◽  
Good Agreement

ABSTRACTThe long term geochemical consequences of basaltic glass dissolution in fresh water at 0°C have been calculated with the computer code DISSOL. The clay minerals were represented by an ideal solid solution model (CISSFIT) able to describe variations in chemical composition of a clay phase in response to variations of the solution chemistry. The predicted mineral phases were iron hydroxides followed by kaolinite, TOT clays, chabazite and cli-noptilolite. These results are in reasonably good agreement with experimental results and observations of altered subglacial hyaloclastites from Iceland. The formation of secondary products are mainly controlled by thermodynamic constraints. Kinetic effects, such as diffusion in the near glass surface are not important.

scholarly journals Dissolution Rates of DWPF Glasses from Long-Term PCT

1996 ◽  
Vol 465 ◽  
Author(s):  
W. L. Ebert ◽  
S.-W. Tam
Keyword(s):  
Dissolution Rate ◽  
Surface Area ◽  
Spherical Particles ◽  
Dissolution Rates ◽  
Glass Dissolution ◽  
Dissolution Tests ◽  
Dissolution Model ◽  
Advanced Stages ◽  
Radionuclide Release

ABSTRACTWe have characterized the corrosion behavior of several Defense Waste Processing Facility (DWPF) reference waste glasses by conducting static dissolution tests with crushed glasses. Glass dissolution rates were calculated from measured B concentrations in tests conducted for up to five years. The dissolution rates of all glasses increased significantly after certain alteration phases precipitated. Calculation of the dissolution rates was complicated by the decrease in the available surface area as the glass dissolves. We took the loss of surface area into account by modeling the particles to be spheres, then extracting from the short-term test results the dissolution rate corresponding to a linear decrease in the radius of spherical particles. The measured extent of dissolution in tests conducted for longer times was less than predicted with this linear dissolution model. This indicates that advanced stages of corrosion are affected by another process besides dissolution, which we believe to be associated with a decrease in the precipitation rate of the alteration phases. These results show that the dissolution rate measured soon after the formation of certain alteration phases provides an upper limit for the long-term dissolution rate, and can be used to determine a bounding value for the source term for radionuclide release from waste glasses. The long-term dissolution rates measured in tests at 20,000 m−1 at 90°C in tuff groundwater at pH values near 12 are about 0.2,0.07, and 0.04 g/(m2•d) for the Environmental Assessment glass and glasses made with SRL 131 and SRL 202 frits, respectively.

scholarly journals Constraints on the Affinity Term for Modeling Long-Term Glass Dissolution Rates

1993 ◽  
Vol 333 ◽  
Author(s):  
William L. Bourcier ◽  
Susan A. Carroll ◽  
Brian L. Phillips
Keyword(s):  
Dissolution Rate ◽  
Expression Analysis ◽  
Experimental Results ◽  
Dissolution Rates ◽  
Saturation State ◽  
Glass Dissolution ◽  
Rate Expression ◽  
Quantitative Effect ◽  
Simple Analog

ABSTRACTPredictions of long-term glass dissolution rates are highly dependent on the form of the affinity term in the rate expression. Analysis of the quantitative effect of saturation state on glass dissolution rate for CSG glass (a simple analog of SRL-165 glass), shows that a simple (1-Q/K) affinity term does not match experimental results. Our data at 100°C show that the data is better fit by an affinity term having the form where σ =10.

scholarly journals Dissolution of simplified nuclear waste glass and formation of secondary phases

2021 ◽  
Vol 1 ◽  
pp. 143-144
Author(s):  
Felix Brandt ◽  
Martina Klinkenberg ◽  
Sébastien Caes ◽  
Jenna Poonoosamy ◽  
Wouter Van Renterghem ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Nuclear Waste ◽  
Borosilicate Glass ◽  
Glass Surface ◽  
Cementitious Materials ◽  
Solution Chemistry ◽  
Secondary Phases ◽  
Release Rates ◽  
Glass Dissolution ◽  
Safety Assessments

Abstract. Immobilization of high-level and intermediate-level nuclear wastes by vitrification in borosilicate glass is a well-established process. There is a consensus between the waste management agencies of many countries and many experts that vitrified nuclear waste should be disposed of in a deep geological waste repository and therefore its long-term behavior needs to be taken into account in safety assessments. In contact with water, borosilicate glass is metastable and dissolves. In static dissolution experiments, often a surface alteration layer (SAL) forms on the dissolving glass, and later sometimes secondary phases form. Based on boron or lithium release rates, commonly three stages of glass dissolution are defined as a function of the reaction progress: (I) initial dissolution, described by a congruent glass dissolution at the highest rate, (II) residual dissolution, characterized by a glass dissolution rate several orders of magnitude lower than the initial one, and (III) resumption of glass alteration with initial rates. Microscopically, the formation of a complex SAL has been identified as a prerequisite for the slower dissolution kinetics of stage II. Stage III is typically observed under specific conditions, i.e., high temperature and/or high pH driven by the uptake of Si and Al into secondary phases. Different glass dissolution models explaining the mechanisms of the SAL formation and rate-limiting steps have been proposed and are still under debate. In this article different aspects of glass dissolution from recent studies in the literature and our own work are discussed with a focus on the microscopic aspects of SAL formation, secondary phase formation and the resumption of glass dissolution. Most of the experiments in the literature were performed under near-neutral pH conditions and at 90 ∘C, following standard procedures, to understand the fundamental mechanisms of glass dissolution. The example of interaction of glass and cementitious materials as discussed here is relevant for safety assessments because most international concepts include cement e.g., as lining, for plugs, or as part of the general construction of the repository. The aim of the investigations presented in this paper was to study the combined effect of hyperalkaline conditions and very high surface area/volume ratios (SA/V=264000m-1) on the dissolution of international simplified glass (ISG) and the formation of secondary phases at 70 ∘C in a synthetic young cement water containing Ca (YCWCa). The new results show that the SA/V ratio is a key parameter for the dissolution rate and for the formation of the altered glass surface and secondary phases. A comparison with similar studies in the literature shows that especially on the microscopic and nanoscale, different SA/V ratios lead to different features on the dissolving glass surface, even though the SA-normalized element release rates appear similar. Zeolite and Ca-silicate-hydrate phases (CSH) were identified and play a key role for the evolution of the solution chemistry. A kinetic dissolution model coupled with precipitation of secondary phases can be applied to relate the amount of dissolved glass to the evolution of the solution's pH.

Measurement of Glass Corrosion in Boom Clay Disposal Conditions

2001 ◽  
Author(s):  
Karel Lemmens ◽  
Marc Aertsens ◽  
Véra Pirlet ◽  
Hélène Serra ◽  
Elie Valcke ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Kinetic Modeling ◽  
Dissolution Time ◽  
Dissolution Test ◽  
Dissolution Rates ◽  
Boom Clay ◽  
Glass Dissolution ◽  
Dissolution Tests ◽  
Environmental Materials

Abstract To estimate the life-time of vitrified high level waste (HLW-glass) in geological disposal conditions in Boom Clay, the dissolution behaviour of waste glass has been studied in experiments in surface laboratories and in the HADES underground research facility of SCK•CEN since the 1980’s. The programme consists mainly of dissolution tests. The purpose of these tests is to understand the basic glass dissolution mechanisms, and to demonstrate realistic long-term dissolution rates. The main experimental variables are glass composition, environmental materials, temperature, and test duration. The studied glasses are the COGEMA glass R7T7, and the PAMELA glasses with SM539, SM527 and SM513 glass frit. The environmental materials comprise Boom Clay, metallic corrosion products and engineered barrier materials. Dissolution tests have been performed at temperatures from 40 to 190°C, for test durations from days to several years. The tests are performed with inactive glasses, which can be doped with radionuclides of interest. Because of the importance of silica sorption by the environmental materials, the dissolution test programme was extended with silica diffusion- and sorption tests in Boom Clay and FoCa clay. The interpretation of the experimental results is supported by geochemical and kinetic modeling. In the area of kinetic modeling, both analytical and Monte Carlo codes are applied. The dissolution tests have demonstrated that, although the presence of Boom Clay initially increases the glass dissolution rate, the long-term dissolution rate decreases for diluted clay / clay water slurries. This decrease has not yet been demonstrated for the R7T7 glass in compact Boom Clay, but is expected to occur here also on the long term. The dissolution rate decreases faster after sufficient addition of glass powder to the medium. This was tested in experiments with the R7T7 glass at relatively high clay concentration (2000 g of humid Boom Clay per liter clay water, this is about half the solid/liquid ratio of compact Boom Clay), at 40 and 90°C. Linear interpolation of the long-term mass losses resulted in dissolution rates of ∼ 0.01 g.m−2.day−1. The statistical uncertainties on the dissolution test results did not allow to demonstrate smaller rates. The minimum statistically significant dissolution rate depends on the test conditions. Therefore, the present SCK•CEN programme includes dissolution tests at long-term near-field conditions (this is at 30°C, with compact Boom Clay and FoCa clay), which are considered more representee for the long-term situation. In view of the uncertainties on the experimental long-term dissolution rates and on the long-term dissolution mechanisms, rates smaller than 0.01 g.m−2.day1 (about 1 μ/year) should not be used as best estimate in the present performance assessment studies for disposal in Boom Clay. A constant dissolution rate of 0.01 g.m−2.day−1 would correspond to a dissolution time for a R7T7 glass package of approximately 150 000 years. The minimum dissolution time is of the order of 104 years.

Dissolution Mechanism of Soda-Lime Silicate Glass and of PNL 76-68 in the Presence of Dissolved Mg

1993 ◽  
Vol 333 ◽  
Author(s):  
Jing C. Sang ◽  
Yan Guo ◽  
Alisa Barkatt ◽  
M.A. Adel-Hadadi ◽  
Gwendolyn S. Marbury ◽  
...  
Keyword(s):  
Experimental Data ◽  
Dissolution Rate ◽  
Silicate Glass ◽  
Soda Lime ◽  
Sodium Borate ◽  
Dissolution Mechanism ◽  
Square Root ◽  
Glass Dissolution ◽  
Real Change ◽  
Soda Lime Silicate Glass

ABSTRACTLeaching studies were performed on powdered PNL 76-68 glass in de-ionized water in the presence of Mg solute. The results showed that the presence of Mg in the leachant greatly reduced the rate of glass dissolution. The equation Q=krα was used to express the experimental data. In the absence of Mg, α was about 1, i.e., the amount of glass dissolved was linear with time. In the presence of Mg, α was close to 0.5, i.e. the extracted amount was proportional to the square root of time. Therefore, the reduction of the dissolution rate of PNL 76-68 glass in the presence of Mg solute could be explained as a result of a change in the glass dissolution mechanism.Comparative leaching studies on bulk soda-lime silicate glass in a sodium borate buffered system (pH 8.1) showed the same results. The presence of Mg in the leachant reduced the rate of glass dissolution. In the absence of Mg, α was about 1, while in the presence of Mg, α was 0.5. This change in α was not caused by changes in pH, and it represents a real change in the glass dissolution mechanism.

Geochemical Simulation of Dissolution of West Valley and Dnpf Glasses in J-13 Water at 90°C

1987 ◽  
Vol 112 ◽  
Author(s):  
Carol J. Bruton
Keyword(s):  
Waste Product ◽  
Computer Code ◽  
Yucca Mountain ◽  
Solution Chemistry ◽  
Complexing Agent ◽  
The West ◽  
Glass Dissolution ◽  
J 13 ◽  
Aqueous Species ◽  
Solution Changes

AbstractDissolution of West Valley and Defense Waste Product Facility (DWPF) glasses in J-13 water at 90°C at the candidate Yucca Mountain, Nevada repository was simulated using the EQ316 computer code package. The objectives of the study were to attempt to predict the concentrations of radionuclides and other glass components in solution resulting from glass dissolution, and to identify potential precipitates that sequester glass components.Modified projected inventories of 10,000 year-old Nest Valley and DNPF SRL-165 frit glasses were used as starting glass compositions. J-13 water was considered to be representative of groundwater at Yucca Mountain. A total of 10 grams of each glass was assumed to dissolve congruently into a kilogram of J-13 water in a closed system. No inhibitions to precipitation, except for crystalline SiO2 polymorphs, were assumed to exist. Radiolysis and materials interactions were not considered.Simulation results predict that radionuclides and other glass components precipitate predominantly in the form of oxides and hydroxides, together with carbonates, silicates and phosphates. Precipitates appear to be effective in limiting the concentrations of radionuclides and other elements in solution. The general compositional trends in precipitates and solution chemistry are the same in the West Valley and DMPF simulations, except for variations arising from differences in glass chemistry.Concentrations of elements released from glass increase until the solution reaches saturation with respect to solids that contain these elements. Elemental concentrations are then predicted to remain constant, increase or decrease depending on: 1) whether the reaction between the dominant aqueous species of the element in solution and its precipitate is pH and/or Eh-dependent; 2) whether the species distribution of the element in solution changes significantly in response to changes in pH, Eh, or other factors; and 3) the competition with other phases for elements required to form the precipitate. pH increases from 7.3 to 9.8 and from 7.2 to 10 in the West Valley and DWPF simulations, respectively. Eh decreases abruptly from about 0.5 to 0.3 volts after dissolution of 3.4 and 5.8 grams of glass in the Nest Valley and DMPF simulations, respectively, because of depletion of dissolved oxygen in solution. Complexing of aqueous species has a significant impact on radionuclide concentrations in solution; predicted concentrations of U in solution, for example, are controlled by the presence or absence of P in solution because H2PO4 is an extremely effective complexing agent for U.

Long-Term Behavior of Embiez Archaeological Glass: Results after 1800 Years of Alteration in a Marine Environment

2006 ◽  
Vol 932 ◽  
Author(s):  
Stéphane Gin ◽  
Jean-Louis Chouchan ◽  
Danièle Foy
Keyword(s):  
Dissolution Rate ◽  
Surface Area ◽  
Marine Environment ◽  
Morphological Similarity ◽  
Preliminary Results ◽  
Glass Dissolution ◽  
Internal Surfaces ◽  
Different Temperatures ◽  
Long Term Behavior

ABSTRACTAn archaeological glass initially fractured and altered for 1800 years in a marine environment is now being examined by the CEA because of its strong morphological similarity to the nuclear glasses used for immobilization of long-lived radionuclides (i.e. the presence of fractures and cracks formed during cooling, which significantly increase the surface area accessible to water). The issue concerns glass alteration by water, and in particular the different behavior of the external surfaces in contact with a solution highly renewed and the internal surfaces, which constitute a much more confined medium.The preliminary results of this study are discussed. The cracks in the archaeological glass have been filled by crystallized alteration products formed jointly by elements from the glass and elements dissolved in seawater. The glass is distinctly less altered (by a factor of 10 to 100) on the internal surfaces generated by the cracks than on the external surfaces. The forward glass dissolution rate was measured at different temperatures on pristine glass samples and under conditions that allowed us to estimate the dissolution rate of the external surfaces under realistic conditions at about 200 μm in 1800 years. The implications of this study are then discussed.

scholarly journals Overview of Chemical Modeling of Nuclear Waste Glass Dissolution

1990 ◽  
Vol 212 ◽  
Author(s):  
William L. Bourcier
Keyword(s):  
Dissolution Rate ◽  
Experimental Tests ◽  
Model Parameters ◽  
Dissolution Mechanism ◽  
Short Term ◽  
Chemical Modeling ◽  
Glass Dissolution ◽  
Dissolved Species ◽  
Computer Codes

ABSTRACTGlass dissolution takes place through metal leaching and hydration of the glass surface accompanied by development of alteration layers of varying crystallinity. The reaction which controls the long-term glass dissolution rate appears to be surface layer dissolution. This reaction is reversible because the buildup of dissolved species in solution slows the dissolution rate due to a decreased dissolution affinity. Glass dissolution rates are therefore highly dependent on silica concentrations in solution because silica is the major component of the alteration layer.Chemical modeling of glass dissolution using reaction path computer codes has successfully been applied to short term experimental tests and used to predict long-term repository performance. Current problems and limitations of the models include a poorly defined long-term glass dissolution mechanism, the use of model parameters determined from the same experiments that the model is used to predict, and the lack of sufficient validation of key assumptions in the modeling approach. Work is in progress that addresses these issues.

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