Dissolution kinetics of C–S–H gel: Flow-through experiments

Environmental context. Uranium-phosphate minerals have been identified as a long-term controlling phase that limit the mobility of uranium to groundwater in many contaminated subsurface environments. Complex, coupled processes confound the ability to isolate the rates attributed to individual processes. Results of this investigation provide the necessary information to refine current prediction on the release and long-term fate of uranium in subsurface environments. Abstract. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to (1) quantify the effect of temperature (23–90°C) and pH (6–10) on meta-torbernite dissolution; (2) compare the dissolution of meta-torbernite to other autunite-group minerals; and (3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100× over the pH interval of 6 to 10, irrespective of temperature. The power law coefficient for meta-torbernite, η = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, η = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m–2 s–1) = –4.7 × 10–13 + 4.1 × 10–10[PO43–].

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Experimental Determination of the Dissolution Kinetics of Plutonium- and Uranium-Bearing Ceramics at 90°C

MRS Proceedings ◽

10.1557/proc-713-jj11.38 ◽

2002 ◽

Vol 713 ◽

Cited By ~ 1

Author(s):

J. P. Icenhower ◽

B. P. McGrail ◽

D. M. Strachan ◽

R. D. Scheele ◽

V. L. Legore ◽

...

Keyword(s):

Radiation Damage ◽

Dissolution Kinetics ◽

Solution Rate ◽

Release Rates ◽

Solution Ph ◽

Bearing Materials ◽

Flow Through ◽

Effects Of Radiation ◽

Kinetics Of

ABSTRACTAs a first step toward understanding the effects of radiation damage on element release rates from Ti-bearing waste forms, we performed single-pass flow-through (SPFT) experiments with 239Pu- and 238U-bearing ceramics over a solution pH-interval of 2 to 10 at 90°C. The ceramics tested are chemically complex and are dominated volumetrically by betafite (Ti-pyrochlore) (ABTi2O7) (A = Ca2+, Gd3+, B = Gd3+, Hf4+, Pu4+, U4/6+). The 239Pu-bearing specimens contained 11.9 mass% PuO2 and 23.7 mass% UO2. In addition, a 238Pu-bearing (11.8 and 23.9 mass% PuO2 and UO2, respectively) specimen was tested at pH = 2, 90°C. The 239Pu-bearing specimens slowly released Pu to solution (rate = 7.6x10-6 g m-2 d-1), even at pH = 2. Release of elements across the pH interval investigated exhibits a weak amphoteric behavior. Compared to results from the 239Pu-bearing materials, the 238Pu-bearing specimen released Pu >1000X faster (rate = 9.3x10-3 g m-2 d-1) at pH = 2. Release rates of U, Gd, and Hf are also faster from the 238Pu-bearing ceramic compared to the specimen containing 239Pu. Although preliminary, the data can be interpreted to indicate that accumulation of radiation damage may result in faster release of Pu and U to solution than previously suspected.

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Dissolution kinetics of struvite pellets grown in a pilot-scale crystallizerA paper submitted to the Journal of Environmental Engineering and Science.

Canadian Journal of Civil Engineering ◽

10.1139/s08-049 ◽

2009 ◽

Vol 36 (3) ◽

pp. 550-568 ◽

Cited By ~ 7

Author(s):

M.I.H. Bhuiyan ◽

D.S. Mavinic ◽

R.D. Beckie

Keyword(s):

Batch Reactor ◽

Dissolution Kinetics ◽

Theoretical Models ◽

Pilot Scale ◽

Reactor System ◽

Alkaline Ph ◽

Rate Of Dissolution ◽

Flow Through ◽

Experimental Values ◽

Kinetics Of

Dissolution kinetics of struvite are important for optimizing intentional struvite crystallization, as well as for ensuring the efficient use of the crystallized products. Dissolution experiments were carried out for struvite pellets grown in a pilot-scale fluidized bed reactor. To determine the kinetics and mechanism of the dissolution process in a batch reactor system, two different theoretical models were tested. The experimental values were found to fit well with both models. In a mixed flow-through reactor system, the constituents release became stoichiometric when the input solution had an alkaline pH. The dissolution rates for struvite pellets were found to decrease with increasing pH due to proton promoted dissolution. After a transition from around 7.5 to 8, the rate of dissolution increased with the increase in pH, because of the hydroxyl promoted dissolution.

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Dissolution Kinetics of UO2. I. Flow-Through tests on UO2.00 Pellets and Polycrystalline Schoepite Samples in Oxygenated, Carbonate/Bicarbonate Buffer Solutions at 25°C

MRS Proceedings ◽

10.1557/proc-257-339 ◽

1991 ◽

Vol 257 ◽

Cited By ~ 6

Author(s):

Son N. Nguyen ◽

Homer C. Weed ◽

Herman R. Leider ◽

Ray B. Stout

Keyword(s):

Fission Products ◽

Dissolution Kinetics ◽

Spent Fuel ◽

Bicarbonate Buffer ◽

Buffer Solutions ◽

Flow Through ◽

High Level ◽

Radionuclide Release ◽

Kinetics Of

ABSTRACTThe modelling of radionuclide release from waste forms is an important part of the performance assessment of a potential, high-level radioactive waste repository. Since spent fuel consists of UO2 containing actinide elements and other fission products, it is necessary to determine the principal parameters affecting UO2 dissolution and quantify their effects on the dissolution rate before any prediction of long term release rates of radionuclides from the spent fuel can be made.

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Dissolution Kinetics of Titanium Pyrochlore Ceramics at 90°C by Single-Pass Flow-Through Experiments

MRS Proceedings ◽

10.1557/proc-608-373 ◽

1999 ◽

Vol 608 ◽

Cited By ~ 7

Author(s):

J. P. Icenhower ◽

B. P. Mcgrail ◽

H. T. Schaef ◽

E. A. Rodriguez

Keyword(s):

Dissolution Kinetics ◽

Single Pass ◽

Flow Through ◽

Kinetics Of

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Aqueous dissolution kinetics of pyrochlore, zirconolite and brannerite at 25, 50, and 75 °C

Radiochimica Acta ◽

10.1524/ract.2000.88.9-11.539 ◽

2000 ◽

Vol 88 (9-11) ◽

Cited By ~ 33

Author(s):

S. K. Roberts ◽

W.L. Bourcier ◽

H.F. Shaw

Keyword(s):

Activation Energy ◽

Apparent Activation Energy ◽

Dissolution Rate ◽

Dissolution Kinetics ◽

Kcal Mole ◽

Dissolution Rates ◽

Flow Through ◽

Kinetics Of ◽

Total Dissolution ◽

Calculated Average

We measured the rates of dissolution of pyrochlore, zirconolite, and brannerite in pH-buffered solutions of pH 2, 4, 6, 8, 10, and 12 at temperatures of 25, 50, and 75 °C in flow-through reactors. The dissolution rates for all phases show a minimum near pH 8. Zirconolite dissolves the slowest of the three phases, with a slightly higher rate for pyrochlore and a much higher dissolution rate for brannerite. Brannerite dissolves as much has 30 times faster than zirconolite. The rates increase with temperature, but the magnitude of the increase varies with pH. The calculated average apparent activation energy for dissolution is 6±3 kcal/mole. Dissolution is non-stoichiometric at all pHs. Ti and Hf are released most slowly, and are often below detection limits (1 ppb for Ti, 0.2 ppb for Hf). Releases of Ca, U, Gd, and Ce appear to be stoichiometric below pH 8. At pH 8 and above only U is measurable in solution. Dissolution rates are slow under all conditions, and commonly in the range of 1-100 nm total dissolution/year (between 10

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