Kinetics of UO2 (s) Dissolution in the Presence of Hypochlorite, Chlorite, and Chlorate Solutions

2008 ◽  
Vol 1107 ◽  
Author(s):  
Rosa Sureda ◽  
Ignasi Casas ◽  
Javier Giménez ◽  
Joan de Pablo
Keyword(s):  
Dissolution Rate ◽  
Continuous Flow ◽  
Empirical Equation ◽  
Uranium Concentration ◽  
Experimental Methodology ◽  
Dissolution Rates ◽  
Experimental Conditions ◽  
Flow Through ◽  
Kinetics Of ◽  
Hypochlorite Anion

AbstractThe influence of hypochlorite, chlorite and chlorate in the UO2 dissolution rate has been studied experimentally using a continuous flow-through reactor. Uranium concentration in each outflow solution was measured as a function of time and dissolution rates were determined once the steady-state was reached. The results obtained show that the influence of the hypochlorite anion concentration on the UO2 dissolution rate can be expressed by the following empirical equationrdiss = 10-8.7±0.1•[ClO-]0.28±0.04The dissolution rates obtained in this work were higher than those previously determined in presence of either oxygen or hydrogen peroxide using the same experimental methodology.In contrast, neither chlorate nor chlorite had any significant effect on the UO2 dissolution rates under the experimental conditions of this work.

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

2000 ◽  
Vol 88 (9-11) ◽  
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

Kinetics of MgO Dissolution and Buffering of Fluids in the Waste Isolation Pilot Plant (Wipp) Repository

1999 ◽  
Vol 556 ◽  
Author(s):  
Valerie Monastra ◽  
D. E. Grandstaff
Keyword(s):  
Dissolution Rate ◽  
Surface Area ◽  
Pilot Plant ◽  
Dissolution Rates ◽  
Waste Isolation Pilot Plant ◽  
Oxidizing Agents ◽  
Reducing Conditions ◽  
Kinetics Of ◽  
Gas Pressures

AbstractDOE has proposed to add MgO to backfill in the WIPP repository to stabilize pH and reduce gas pressures and spallation. Experiments show that MgO dissolution rates are proportional to surface area, nearly independent of pH, and decrease with increasing dissolved NaCl. The probable repository MgO dissolution rate will be ≤ 10 to 20 μmol m2 min−1. Simulations indicate that MgO dissolution will buffer pH and provide stabilizing cement; however, under highly reducing conditions MgO will not control total gas pressures. Adding oxidizing agents or materials containing oxidized species, for example anhydrite, to the backfill, might control gas pressures.

Effect of Temperature and Bicarbonate Concentration on the Kinetics of UO2(s) Dissolution Under Oxidizing Conditions

1996 ◽  
Vol 465 ◽  
Author(s):  
J. de Pablo ◽  
I. Casas ◽  
J. Giménez ◽  
M. Molera ◽  
M. E. Torrero
Keyword(s):  
Dissolution Rate ◽  
Solid Particles ◽  
Effect Of Temperature ◽  
Bicarbonate Concentration ◽  
Rate Laws ◽  
Carbonate Concentration ◽  
Hydrogen Carbonate ◽  
Different Temperatures ◽  
Flow Through ◽  
Kinetics Of

ABSTRACTThe dissolution rate of unirradiated UO2 (s) has been studied as a function of hydrogen carbonate concentration at three different temperatures (298.15 K, 313.15 K and 333.15 K) under oxidizing conditions in a continuous flow-through reactor with a thin layer of solid particles (particle size from 100 to 300 μm). From the results of these experiments, two different rate laws have been determined. At high temperature (313.15 K and 333.15 K), we obtained a dissolution rate proportional to hydrogen carbonate concentration while at 298.15 K, the rate almost depends on the square root of the hydrogen carbonate concentration. This indicates a different reaction mechanism depending on temperature which can be related to the oxidation step of the overall process. The apparent activation energy obtained was 41 kJ mo1−1.

Kinetic Study of the Crystallized ThO2 and Solid Solutions Th1−xUxO2 Dissolution

2001 ◽  
Author(s):  
G. Heisbourg ◽  
N. Dacheux ◽  
G. Lagarde ◽  
S. Hubert ◽  
J. Ritt
Keyword(s):  
Dissolution Rate ◽  
Solid Solutions ◽  
Uranium Concentration ◽  
Nuclear Industry ◽  
Aqueous Corrosion ◽  
Thorium Dioxide ◽  
X Ray ◽  
Vegard’S Law ◽  
Fuel Reactor ◽  
Kinetics Of

Abstract Thorium dioxide is an important material for the nuclear industry. In the last decade, there has been a renewal of interest in studying the feasibility of thorium based fuel reactor to decrease the minor actinides production during the burn-up. Furthermore the resistance of the thorium dioxide to aqueous corrosion can make this material attractive for immobilizing tetravalent actinides. Leaching tests of powdered samples of thorium dioxide calcinated at 1300°C showed that the normalized dissolution rate is very low (between 10−6 and 10−7 g/(m2.d) in acidic media, and 10−9–10−10 g/(m2.d) after pH>3 when the formation of colloïdes occurs. Thorium dioxide which is isomorphic with the actinide dioxides such as UO2, PuO2 allows the formation of solid solutions whatever the concentration of the actinide. Several solid solutions Th1−xUxO2 were synthesized with mole-ratios Th/(U+Th) ranging from x = 0 to 1. X-ray powder diffraction data allowed to check that the Vegard’s law is respected in all the range, and specific surface area was also measured. The resistance of the solid-solution to aqueous corrosion was measured as a function of several parameters (leaching time, leachate acidity, uranium concentration) and the kinetics of solid solutions dissolution was determined as a function of the uranium concentration. The stoechiometry of the release of both actinides was verified, however due to the oxidization of U (IV) in U (VI) in contact with the leachate, the dissolution rate of both thorium and uranium increases with the thorium substitution in the solid by uranium (TV).

Effect of β-Radiation on the Non Irradiated UO2(s) Dissolution

2002 ◽  
Vol 757 ◽  
Author(s):  
F. Clarens ◽  
J. Giménez ◽  
J. de Pablo ◽  
I. Casas ◽  
M. Sevilla ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Continuous Flow ◽  
Spent Nuclear Fuel ◽  
Nitrogen Atmosphere ◽  
Dissolution Rates ◽  
Corrosion Rates ◽  
Ph Values ◽  
Oxygen Contamination ◽  
Bet Method ◽  
Flow Through

ABSTRACTIn this work, we studied the effect of β radiation (Sr90 source with an activity of 7 mCi) on the dissolution of non irradiated UO2, as a chemicalanalogue of the spent nuclear fuel, in different leaching solutions.The experiments were carried out using a specifically designed continuous flow-through reactor and in nitrogen atmosphere to avoid oxygen contamination. The solid used was a non irradiated uranium dioxide with a particle size of 100–320 μm, which specific surface are was determined by the BET method. The experiments were carried out in NaCl media at different pH values. Both pH and redox potential of the solutions were continuously monitored. In all the cases, blank experiments were performed in parallel.Dissolution rates obtained under the effect of β radiation were compared with dissolution rates determined in the presence of hydrogen peroxide (the main oxidizing species radiolitically formed by the β radiation according to the CHEMSIMUL code) and with electrochemically determined UO2 corrosion rates found in the literature.

scholarly journals Dissolution kinetics of hydrated calcium aluminates (AFm-Cl) as a function of pH and at room temperature

2017 ◽  
Vol 81 (5) ◽  
pp. 1245-1259 ◽  
Author(s):  
Nicolas C. M. Marty ◽  
Sylvain Grangeon ◽  
Catherine Lerouge ◽  
Fabienne Warmont ◽  
Olivier Rozenbaum ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Room Temperature ◽  
Dissolution Kinetics ◽  
Dissolution Rates ◽  
Ph Values ◽  
Surface Areas ◽  
Calcium Aluminates ◽  
Waste Repositories ◽  
Kinetics Of ◽  
Hydrated Calcium

AbstractThe determination of reliable weathering/dissolution rates for cement phases is of fundamental importance for the modelling of the temporal evolution of both radioactive waste repositories and CO2 geological storage sites (e.g. waste matrix, plug in boreholes). Here, the dissolution kinetics of AFm-Cl (hydrated calcium aluminates containing interlayer Cl) has been studied using flow-through experiments conducted at pH values ranging from 9.2 to 13. Mineralogical (XRD) and chemical (EPMA, TEM) analyses have been performed to determine the evolution of the phases during the dissolution experiments. For pH values between 10 and 13, the dissolution of AFm-Cl is congruent (i.e. Ca/Al ratios close to 2 both for solids and outlet concentrations). In contrast, the precipitation of amorphous Al-phases and possibly amorphous mixed Al/Ca phases is observed at pH 9.2, leading to Ca/Al ratios in the outlet solutions higher than those of the initial solid. Therefore, at pH 9.2, even if Cl–/OH– exchange occurs, estimation of dissolution rate from released Cl appears to be the best proxy. Dissolution rates were normalized to the final specific surface areas (ranging from 6.1 to 35.4 m2 g−1). Dissolution rate appears to be pH-independent and therefore the far-from-equilibrium dissolution rate at room temperature is expressed as: logR(mol m–2 s–1) = –9.23 ± 0.18

Kinetics of Oxygen Delignification of High-Kappa Pulp in a Continuous Flow-Through Reactor

2014 ◽  
Vol 53 (20) ◽  
pp. 8385-8394 ◽  
Author(s):  
Vahid Jafari ◽  
Herbert Sixta ◽  
Adriaan van Heiningen
Keyword(s):  
Continuous Flow ◽  
Oxygen Delignification ◽  
Flow Through ◽  
Kinetics Of

Carbon tetrachloride biodegradation in a fixed-biofilm reactor and its kinetic study

1998 ◽  
Vol 38 (8-9) ◽  
pp. 155-162 ◽  
Author(s):  
G. Jin ◽  
A. J. Englande
Keyword(s):  
Carbon Tetrachloride ◽  
Continuous Flow ◽  
Model Comparison ◽  
Biofilm Reactor ◽  
Pseudomonas Cepacia ◽  
Initial Concentration ◽  
Biphasic Model ◽  
Providencia Stuartii ◽  
Kinetics Of ◽  
Fixed Biofilm

Kinetics of Carbon Tetrachloride biodegradation are evaluated in a continuous-flow fixed-biofilm reactor with controlled initial redox potential. The column was seeded with a mixed culture of indigenous microorganisms Pseudomonas cepacia and Providencia stuartii. The fixed biofilm reactor exhibited 98%–99.9% biodegradation of CT introduced into the reactor at an initial concentration of about 200 μg/l for retention times of 1 to 4 days respectively. Four models were employed to evaluate the kinetics of CT biodegradation. These included: Eckenfelder (1989), Arvin (1991), Bouwer and McCarty (1985) and a biphasic model. Comparison of calculated results with observed results between these models agreed very closely to each other (0.968 < R2 < 0.999). Predicted performance was best described by the model of Bouwer and McCarty (1985). However, the biphasic and Eckenfelder models provided excellent correlations and were much simpler to apply. The biphasic model yielded very good correlations of the data for all detention times evaluated; whereas, the Eckenfelder model effected comparable results only at the longer retention times studied.

Biosolids Reuse: Continuous Flow-Through Column Testing of Biosolids-Derived Biochar to Sorb Micropollutants

2017 ◽  
Vol 2017 (1) ◽  
pp. 302-305
Author(s):  
L.K Kimbell ◽  
Y Tong ◽  
A Avila ◽  
B. K Mayer ◽  
P. J McNamara
Keyword(s):  
Continuous Flow ◽  
Column Testing ◽  
Flow Through
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