Some Methodological Modifications of Determination of Diffusion Coefficients in Compacted Bentonite

2006 ◽  
Vol 932 ◽  
Author(s):  
Dušan Vopálka ◽  
Helena Filipská ◽  
Antonín Vokál
Keyword(s):  
Diffusion Coefficients ◽  
Effective Porosity ◽  
Diffusion Method ◽  
Dry Density ◽  
Diffusion Cell ◽  
Compacted Bentonite ◽  
Method Of Evaluation ◽  
Exclusion Effect ◽  
Positively Charged

ABSTRACTThe results of 3H, 36Cl and 137Cs diffusion experiments through compacted bentonite using a new design of diffusion cell and a new methodology of diffusion coefficients evaluation are presented. The diffusion cell was made from the stainless steel and enables to connect it directly to the input and/or output reservoirs without any tubing. The evaluation of diffusion coefficients utilizes a compartmental model developed in the environment of the GoldSim transport code. It enables to determine diffusion coefficients for various types of boundary conditions, including also input and output filters. The influence of the diffusion through filters on the determined values of both effective (De) and apparent (Da) diffusion coefficients was numerically demonstrated for the through diffusion method. This effect is most important for Da, the value of which would be underestimated using standard ways of evaluation for neutral and positively charged species, mainly in the case of high effective porosity.The comparison of standard and the newly developed method of evaluation of diffusion coefficients showed a significant influence of diffusion in filters for HTO. Contrary to the standard method of evaluation, the evaluation taking into account filters showed here no difference between total and effective porosity. The effect of filter resistance was negligible for Cl-, especially at high dry density of compacted bentonite, due to the anion exclusion effect. The numerical model developed enabled to determine Da values of Cs+ from the concentration change in the inlet reservoir.

Zu Stofftransport und Hydrodynamik der Pulsationsdiffusion

1974 ◽  
Vol 29 (7) ◽  
pp. 1045-1049
Author(s):  
H. Beßerdich ◽  
E. Kahrig ◽  
Fr. Lange
Keyword(s):  
Diffusion Coefficients ◽  
Ternary Mixtures ◽  
Diffusion Method ◽  
Periodic Flow ◽  
Matter Transport ◽  
Binary And Ternary Mixtures ◽  
Transfer Parameters ◽  
Diffusion Separation ◽  
Separation Problems

The pulsation diffusion method is used successfully for the determination of diffusion coefficients in different systems (selfdiffusion, binary and ternary mixtures) and in connection with diffusion separation in liquids. The main advantage is the enhancement of matter transport by periodic flow e. g. in a capillary. Adapting a computation by P. L. Kapiza it is reported on a general treatment for the special conditions in a pulsation diffusion apparatus. Transport behavior depends strongly on hydrodynamic and mass transfer parameters. The results are important for the application of the pulsation method for measuring diffusion coefficients and for separation problems.

Diffusion of Gases in Porous Solids. I. Theoretical Background and Experimental Method

1974 ◽  
Vol 52 (15) ◽  
pp. 2684-2691 ◽  
Author(s):  
K. R. Weller ◽  
N. S. Stenhouse ◽  
Harry Watts
Keyword(s):  
Diffusion Coefficients ◽  
Experimental System ◽  
Theoretical Background ◽  
Porous Solids ◽  
Diffusion Cell ◽  
Improved Method ◽  
Method Of Calculation ◽  
The Past ◽  
Concentration Changes

In the past, some authors have not defined the diffusion coefficient appropriate to their experimental system, consequently, valuable data have been lost. We discuss the various diffusion coefficients referred to all possible frames of reference in relation to the choice of a suitable experimental system for the determination of gaseous diffusion coefficients in porous media. A modified Ney and Armistead type diffusion cell is described with an improved method of calculation of results from continuously monitored concentration changes in the diffusion cell.

Distribution Coefficients and Apparent Diffusion Coefficients of Cesium in Compacted Bentonites

1999 ◽  
Vol 556 ◽  
Author(s):  
Akiko Okamoto ◽  
Kazuya Idemitsu ◽  
Hirotaka Furuya ◽  
Yaohiro Inagaki ◽  
Tatsumi Arima
Keyword(s):  
Diffusion Coefficients ◽  
Distribution Coefficients ◽  
Dry Density ◽  
Apparent Diffusion Coefficients ◽  
Compacted Bentonite ◽  
Apparent Diffusion ◽  
Tracer Solution ◽  
Cesium Concentration ◽  
Penetration Profile ◽  
Very High

AbstractDistribution coefficients and apparent diffusion coefficients of cesium in some compacted bentonites were determined by the penetration profile method. Cylindrical compacted bentonites with the dry density of 0.8 to 1.6 Mg/m3 were contacted with tracer solutions containing 1000, 100 or 10 ppm of cesium. The apparent diffusion coefficients were obtained from the concentration profiles of cesium in compacted bentonites. The distribution coefficients were obtained concurrently by dividing the intercepts of the profiles by the concentration of the tracer solution. The apparent diffusion coefficients of cesium in compacted bentonite were obtained in the range of 0.42 to 9.6· 10−12 m2/s. The apparent diffusion coefficients in the compacted bentonite contacted with three different concentrations of cesium tended to decrease with increasing dry density of the specimen; but, they had no dependence on cesium concentration within a factor of 3 at the same dry density. The distribution coefficient of cesium for the specimens contacted with three different concentrations of cesium were obtained in the range of 0.3 to 90 L/kg and had little dependence on dry density. The distribution coefficients obtained in the compacted bentonites were dependent on pH of the solution rather than concentration of cesium. These distribution coefficients obtained in the compacted bentonites were 10 to 1000 times smaller than those obtained by batch experiments. The data suggest that not all sorption sites for cesium are available in highly compacted bentonite. It is necessary to consider surface diffusion as a significant migration mechanism of cesium through the compacted bentonites at very high pH condition such as 12.

The Dependence of the Diffusion Coefficients of 3H and Cs on Grain Size in Compacted Montmorillonite

1997 ◽  
Vol 506 ◽  
Author(s):  
Mamoru Nakajima ◽  
Tamotsu Kozaki ◽  
Hiroyasu Kato ◽  
Seichi Sato ◽  
Hiroshi Ohashi
Keyword(s):  
Grain Size ◽  
Diffusion Coefficients ◽  
Dry Density ◽  
Formation Factor ◽  
Apparent Diffusion Coefficients ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Apparent Diffusion ◽  
Different Grain Size ◽  
High Level

ABSTRACTCompacted bentonite is a candidate buffer material in geological disposal of high-level radioactive waste. The transport of radionuclides in compacted bentonite is dominated by diffusion, because of its very low permeability. In this study, we focused on the grain size of clay mineral, which is considered to be closely related to the formation factor in the pore water diffusion model[1,2]. The apparent diffusion coefficients (Da) of HTO and cesium ions in compacted clays were determined using montmorillonite samples with different grain size and dry density, and the effect of the grain size on diffusion behavior was discussed.

scholarly journals Note: Determination of effective gas diffusion coefficients of stainless steel films with differently shaped holes using a Loschmidt diffusion cell

2010 ◽  
Vol 81 (4) ◽  
pp. 046104 ◽  
Author(s):  
N. G. C. Astrath ◽  
J. Shen ◽  
F. B. G. Astrath ◽  
J. Zhou ◽  
C. Huang ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Diffusion Coefficients ◽  
Gas Diffusion ◽  
Diffusion Cell

Determination of Methane Diffusion Coefficients in Live Oils for Tight Reservoirs at High Pressures

2021 ◽  
Author(s):  
Yibo Yang ◽  
Teresa Regueira ◽  
Hilario Martin Rodriguez ◽  
Alexander Shapiro ◽  
Erling Halfdan Stenby ◽  
...  
Keyword(s):  
High Pressure ◽  
Diffusion Coefficients ◽  
High Pressures ◽  
Diffusion Method ◽  
Pressure Diffusion ◽  
Reservoir Conditions ◽  
Tight Reservoirs ◽  
Methane Diffusion ◽  
Live Oil

Abstract Molecular diffusion plays a critical role in gas injection in tight reservoirs such as liquid-rich shale. Despite recent efforts on measuring diffusion coefficients at high pressures, there is a general lack of the diffusion coefficients in live oil systems at reservoir conditions relevant to the development of these tight reservoirs. The reported diffusion coefficients often differ in orders of magnitude, and there is no consensus on the reliability of the common correlations for liquid phase diffusion coefficients, such as the extended Sigmund correlation. We employed the constant volume diffusion method to measure the high-pressure diffusion coefficients in a newly designed high-pressure tube. The experimental method was first validated using methane + hexadecane and methane + decane, and then used to measure the methane diffusion coefficients in two live oils at reservoir conditions. The obtained data were processed by compositional simulation to determine the diffusion coefficients. The diffusion coefficients measured for methane + hexadecane and methane + decane are in agreement with the existing literature data. For methane + live oil systems, however, the diffusion coefficients estimated by the extended Sigmund correlation are much lower than the measured results. An over ten times adjustment is needed to best fit the pressure decay curves. A further check reveals that for live oil systems, the reduced densities are often in the extrapolated region of the original Sigmund model. The curve in this region of the extended Sigmund correlation has a weak experimental basis, which may be the reason for its large deviation. The estimates from other correlations like Wilke-Chang and Hayduk-Minhas also give very different results. We compared the diffusion coefficients in high-pressure oils reported in the literature, showing a large variation in the reported values. All these indicate the necessity for further study on accurate determination of high-pressure diffusion coefficients in live oils of relevance to shale and other tight reservoirs.

scholarly journals Density - A contentious issue in the evaluation and determination of Resources and Reserves in coal deposits

2021 ◽  
Vol 121 (5) ◽  
Author(s):  
L. Roux
Keyword(s):  
Accurate Determination ◽  
Integrated Approach ◽  
Volatile Matter ◽  
Core Sample ◽  
Effective Porosity ◽  
Raw Material ◽  
Dry Density ◽  
Coal Deposit ◽  
Reserve Estimation

SYNOPSIS The initial evaluation of a coal deposit often raises uncertainty with regard to the accuracy of the reported Resources and Reserves. Reconciliation of results from mining and beneficiation with the original raw field data highlights deficiencies in original estimations. Credible Resource and Reserve estimation forms the basis on which an entire mining enterprise is motivated, initiated, funded, and established as a commercially viable proposition. This is required for sustainable extraction purposes and to support vital downstream industries such as power generation. Accurate determination of the density of the matrix of the material being evaluated is the key to credible values being obtained for Resources and Reserves. Losses between 15% and 20% of the Resource/Reserve can be realized if incorrect densities are applied to the tonnage derivation. Coal plies and particles have different relative densities, determined by the maceral composition, rank, and mineral and moisture content. These factors in turn contribute to the moisture, volatile matter, ash and carbon contents of a coal, which affect the overall density of the raw coal. More specifically, the relationship of ash to density and the effective matrix porosity were found to be critical in solving the greater majority of the problems in predictive calculations. A major deficiency identified is the inability to determine effective porosity, allowing absorption of adventitious moisture and altering the mass of the core sample. Although the volume of the raw material is altered through crushing, the change in mass after controlled air-drying, used with the original geometrical volume of the raw material, provides a credible air-dry density and allows the determination of the volumetric change related to effective porosity. This parameter can be validated through the evaluation of proximate ash using the ash-adjusted algorithm and a correction for the inherent moisture applied to also give a credible relative density value for an air-dried sample. A combination of theoretical, empirical, and reconciliatory evaluations of the available data, taken from the exploration phase through the mining process to final production, has shown that an integrated approach using the ash-adjusted density (AAD) methodology, in conjunction with other evaluative techniques, provides credible results with a considerably higher degree of accuracy than is currently possible. Keywords: coal, deposit evaluation, Resources, Reserves, density determination, ash-adjusted density.

Diffusion Behavior for Se and Zr in Sodium-Bentonite

1994 ◽  
Vol 353 ◽  
Author(s):  
Haruo Sato ◽  
Mikazu Yui ◽  
Hideki Yoshikawa
Keyword(s):  
Diffusion Coefficients ◽  
Dominant Species ◽  
Atmospheric Condition ◽  
Aerobic Condition ◽  
Diffusion Method ◽  
Dry Density ◽  
Sodium Bentonite ◽  
Apparent Diffusion Coefficients ◽  
Anion Exclusion ◽  
Apparent Diffusion

AbstractApparent diffusion coefficients for Se and Zr in bentonite were measured by in-diffusion method at room temperature using water-saturated sodium-bentonite. KunigelVl® * containing 50wt% Na-smectite as a major mineral was used as the bentonite material. The experiments were carried out in the dry density range of 400–1800kg/m3. Bentonite samples were immersed with distilled water and saturated before the experiments. The experiments for Se were carried out under N2 atmospheric condition (O2: 2.5ppm). Those for Zr were carried out under aerobic condition. The apparent diffusion coefficients decrease with increasing density of the bentonite. Since dominant species of Se in the pore water is predicted SeO32-, Se may be retarded by anion-exclusion because of negative charge on the surface of the bentonite and little sorption. The dominant species of Zr in the porewater is predicted Zr(OH)5- or HZrO3-. Distribution coefficient measured for Zr on the bentonite was about 1.0m3/kg from batch experiment. Therefore, the retardation may be caused by combination of the sorption and the anion-exclusion. A modelling for the diffusion mechanisms in the bentonite were discussed based on an electric double layer theory. Comparison between the apparent diffusion coefficients predicted by the model and the measured ones shows a good agreement.

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