Leach bulk glass

Bulk glass leach rates based on various isotopes were calculated by the equation ... 

The leach rates seen here can be compared to those from a similar test on simulated waste glass of the same composition. The leach rates for cesium and strontium from the fully radioactive Rlass were the same as the leach rates of the simulated glass. Although both tests were done on bulk glass samples, they differed in configuration. The fully radioactive samples were disks cm (height) x 3.5 cm (diameter)], and the... 

Under low-pH conditions lead will be leached from the glass. The rate of the reaction depends on the concentration gradient between the bulk glass and the acid solution, and the diffusion coefficient through the reacted layer. 

Under certain circumstances components may be leached out of the bulk of the glass to leave a new material. 

Studies on hot water tank enamelsin media of varying pH demonstrate a minimum corrosion rate at pH value of 4. In citric acid (pH 2), IR measurements indicate that ion exchange is the principal mode of corrosion. Distilled water (pH 7) showed evidence of a bulk dissolution mechanism with no silica enrichment of the surface layer. In neutral solutions, the first stage of attack is leaching of alkali ions, raising the pH of solution, which subsequently breaks down the glass network of the acidic oxides. 

There are multiple applications of fluoridated bioceramics, essentially as bone and tooth substitutes (Table 1), involving bulk ceramics, glasses, composite materials and coatings for medical devices and surface treatments. In some cases, fluoride ions can leach out of the material inducing a direct biological effect in a soluble form. However, considering the affinity of fluoride ions for apatite... 

Gross dissolution of the waste can be measured from the loss of weight of the sample or by determination of the appearance in the leaching medium of the major matrix constituent e.g. glass). However, the selective leaching of important fission product elements has been observed in this work to be significantly different from that of the bulk waste matrix. The units normally used to describe leach rates, g/cm day, appear to imply... 

The glass was crushed, sieved, and leached for 24 hr with boiling distilled water in a Soxhlet-type extractor. Although there are variations, the values reported (Table X) would be reduced two to three orders of magnitude at ambient temperature, and the glasses would then have an acceptably low leach rate. Our program now is to determine the temperature dependence of leach rates and to correlate weight loss data with bulk leach rates based on specific elements. 

In equation 2, M is the total amount of Mg leached out, V5 volume of the bulk liquid phase, Q time, and K a characteristic constant which is dependent on the concentration of magnesium at the solid surface, total surface area of glass, temperature, and dlffusivity of magnesium ion in water. In logarithmic form. Equation 2 becomes (Cb Mg concentration in bulk liquid phase.)... 

The reaction proces.ses can be described by a combination of results from leach tests and SIMS. The nominal composition and leach rates (g in - d" ) of a glass formulation, PNL 76-68 (Pacific North-West Laboratories), used as the. standard high-level nuclear waste glass matrix [4], are shown in Table 4. The definition of leach rate u.sed normalizes the loss (in g) to the proportion of that element in the nominal bulk composition. It will be seen that the leach rates for Cs, Na, Mo, Si and B exceeded the overall rate of mass loss from the gla.ss surface, whereas the elements Fe, Zn and Ti did not show significant loss to solution under these conditions. There were also several elements, e.g.. Ca. Ba, Cd and Sr, that were neither rapidly leached nor apparently retained in the surface layers. Studies described in the above-mentioned reviews, using XPS, FTIR, SIMS, SEM and dissolution rates, have established clearly that the primary reaction occurring in solution is the bond-breaking attack by OH at Si (or Al and... 

The Kristallin-1 assessment assumes that, following failure, the canister offers no retardation to radionuclides leaching out of the vitrified waste. In reality, of course, failure of the canister will be localized and the resultant crack or hole may be the only route from the glass to the bentonite. This will be a beneficial effect (compared to the assumptions made in Kristallin-1) as the crack will offer transport resistance to the leached radionuclides (Smith Curti 1995), but a possible detrimental effect would be the release of oxidants produced by the radiolysis of water in contact with the vitrified waste. If the radiolytic oxidants were to pass through a crack in the canister which was coated by non-porous ferric oxides, so minimizing reaction with the bulk of the canister steel, the oxidants could penetrate to the bentonite so leading to a loss of reducing conditions in the bentonite pore waters... 

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