Dissolution kinetics of meta-torbernite under circum-neutral to alkaline conditions

2009 ◽  
Vol 6 (6) ◽  
pp. 551 ◽  
Author(s):  
Dawn M. Wellman ◽  
Bruce K. McNamara ◽  
Diana H. Bacon ◽  
Elsa A. Cordova ◽  
Ruby M. Ermi ◽  
...  
Keyword(s):  
Dissolution Kinetics ◽  
Coupled Processes ◽  
Effect Of Temperature ◽  
Subsurface Environments ◽  
Alkaline Conditions ◽  
Flow Through ◽  
Uranium Phosphate ◽  
The Stability ◽  
Kinetics Of

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–].

Smectite Dissolution Kinetics in High-Alkaline Conditions

2003 ◽  
Vol 807 ◽  
Author(s):  
Hiroshi Ohmoto ◽  
Kathryn R. Spangler ◽  
Yumiko Watanabe ◽  
Gento Kamei
Keyword(s):  
Dissolution Kinetics ◽  
Silica Content ◽  
Alkaline Solutions ◽  
Initial Silica ◽  
Alkaline Conditions ◽  
Short And Long Term ◽  
Stock Solutions ◽  
Aqueous Complexes ◽  
Kinetics Of

ABSTRACTTo determine the initial rates and effects of silica in solution on the dissolution kinetics of smectite, short- and long-term batch experiments (0.5 hour to 30 days) were completed at three temperatures (T = 25, 50, and 75°C) using stock solutions pH adjusted by NaOH (pH = 12, 13, and 13.5) with varying initial silica concentrations (0, 30, 60, and 100 ppm). The following important characteristics were observed at pH = 12: (1) The concentrations of Al, Si, Mg, Fe, and Ti in solutions increase rapidly during the first ∼2 hours and reach steady state (equilibrium) within ∼5 days. (2) The concentration ratios of Al, Si, Fe, Mg, and Ti in solutions during the early (<2 hours) reaction phase differ significantly from those of smectite, indicating initial dissolution proceeds non-stoichiometrically; Al dissolves much faster than Si, Mg, Fe, and Ti. (3) Further dissolution of smectite proceeds nearly stoichiometrically, including Fe and Ti. (4) The high solubility of Ti in highly alkaline solutions may be due to the formation of aqueous complexes, such as TiO(OH)3− and TiO2(OH)22−, similar to aqueous silica species. (5) The initial rate of smectite dissolution increases with increasing pH, T, and initial silica content of solution. (6) The silica in solution acts as a promoter and a catalyst, rather than an inhibitor, of smectite dissolution in high-alkaline solutions. This role is easily recognizable when the solubility of smectite and amorphous silica are very high, i.e., at pH >∼9.

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

1991 ◽  
Vol 257 ◽  
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.

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

2014 ◽  
Vol 70-71 ◽  
pp. 17-31 ◽  
Author(s):  
Ana Trapote-Barreira ◽  
Jordi Cama ◽  
Josep M. Soler
Keyword(s):  
Dissolution Kinetics ◽  
Flow Through ◽  
Kinetics Of

In situmonitoring of powder reactions in percolating solution by wet-cell X-ray diffraction techniques

2003 ◽  
Vol 36 (3) ◽  
pp. 948-949 ◽  
Author(s):  
Laurence N. Warr ◽  
Heiko Hofmann
Keyword(s):  
Open Systems ◽  
Reaction Chamber ◽  
Solution Chemistry ◽  
X Ray Diffraction ◽  
X Ray ◽  
Standard Powder ◽  
Flow Through ◽  
Kinetics Of

This note describes how the kinetics of powder reactions in percolating solution can be studied by X-ray diffraction using a wet-cell flow-through reaction chamber. The device can be routinely moved between diffractometer and controlled laboratory (pressure, temperature) conditions with the ease of a standard powder holder. Short-termin situmeasurements and long-termquasiin situmonitoring of dissolution and crystallization reactions are possible with a minimum of sample preparation and little disturbance of the system. Measuring time-dependent changes in the concentration of crystalline reactants and products provides information for quantifying reaction kinetics and for determining dissolution and crystal growth mechanisms. Results can be compared with changes in solution chemistry of the collected eluate, enabling a more complete reconstruction of heterogeneous crystal–solution reactions in open systems.

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

2002 ◽  
Vol 713 ◽  
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.

Sign in / Sign up

Export Citation Format

Share Document