Evaluation of Factors Affecting Diffusion in Compacted Bentonite

AbstractThe information available from the open literature and our studies on exclusion, sorption and diffusion mechanisms of ionic and neutral species in bentonite has been compiled and re-examined in relation to the microstructure of bentonite. The emphasis is placed on a more thorough understanding of the diffusion processes taking place in compacted bentonite. Despite the scarcity of experiments performed with neutral diffusants, these imply that virtually all the pores in compacted bentonite are accessible to neutral species. Anion exclusion, induced by the overlap of electrical double layers, may render the accessible porosity for anions considerably less than the porosity obtained from the water content of the clay. On the basis of the compiled data, it is highly probable that surface diffusion plays a significant role in the transport of cations in bentonite clays. Moreover, easily soluble compounds in bentonite can affect the ionic strength of porewater and, consequently, exclusion, equilibrium between cations, and surface diffusion.

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Coupled Chemical and Diffusion Model for Compacted Bentonite

MRS Proceedings ◽

10.1557/proc-353-253 ◽

1994 ◽

Vol 353 ◽

Cited By ~ 1

Author(s):

M. Olin ◽

J. Lehikoinen ◽

A. Muurinen

Keyword(s):

Ion Exchange ◽

Surface Diffusion ◽

Diffusion Model ◽

Chemical Equilibrium ◽

Equilibrium Model ◽

Binding Constants ◽

Compacted Bentonite ◽

Monovalent Ions ◽

And Diffusion ◽

Chemical Equilibrium Model

AbstractA chemical equilibrium model has been developed for ion-exchange and to a limited extent for other reactions, such as precipitation or dissolution of calcite or gypsum, in compacted bentonite water systems. The model was successfully applied to some bentonite experiments, especially as far as monovalent ions were concerned. The fitted log-binding constants for the exchange of sodium for potassium, magnesium, and calcium were 0.27, 1.50, and 2.10, respectively. In addition, a coupled chemical and diffusion model has been developed to take account of diffusion in pore water, surface diffusion and ion-exchange. The model was applied to the same experiments as the chemical equilibrium model, and its validation was found pardy successful. The above values for binding constants were used also in the coupled model. The apparent (both for anions and cations) and surface diffusion (only for cations) constants yielding the best agreement between calculated and experimental data were 3.0×10-11 m2/s and 6.0×10-12m2/s, respectively. These values are questionable, however, as experimental results good enough for fitting are currently not available.

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Comparison of Sr Transport in Compacted Homoionous Na and Ca Bentonite Using a Planar Source Method Evaluated at Ideal and Non-Ideal Boundary Condition

Water ◽

10.3390/w13111520 ◽

2021 ◽

Vol 13 (11) ◽

pp. 1520

Author(s):

Lucie Baborová ◽

Eva Viglašová ◽

Dušan Vopálka

Keyword(s):

Diffusion Coefficient ◽

Surface Diffusion ◽

Effective Diffusion Coefficient ◽

Effective Diffusion ◽

Ideal Boundary ◽

Batch Sorption ◽

Compacted Bentonite ◽

Source Method ◽

Planar Source ◽

And Diffusion

With the aim to determine the influence of dominant interlayer cation on the sorption and diffusion properties of bentonite, diffusion experiments with Sr on the compacted homoionous Ca- and Na-forms of Czech natural Mg/Ca bentonite using the planar source method were performed. The bentonite was compacted to 1400 kg·m−3, and diffusion experiments lasted 1, 3 or 5 days. Two methods of apparent diffusion coefficient Da determination based on the analytical solution of diffusion equation for ideal boundary conditions in a linear form were compared and applied. The determined Da value for Ca-bentonite was 1.36 times higher than that for Na-bentonite sample. Values of Kd were determined in independent batch sorption experiments and were extrapolated for the conditions of compacted bentonite. In spite of this treatment, the use of Kd values determined by batch sorption experiments on a loose material for the determination of effective diffusion coefficient De values from planar source diffusion experiments proved to be inconsistent with the standard Fickian description of diffusion taking into account only the pore diffusion in compacted bentonite. Discrepancies between Kd and De values were measured in independent experiments, and those that resulted from the evaluation of planar source diffusion experiments could be well explained by the phenomenon of surface diffusion. The obtained values of surface diffusion coefficients Ds were similar for both studied systems, and the predicted value of total effective diffusion coefficient De(tot) describing Sr transport in the Na-bentonite was four times higher than in the Ca-bentonite.

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Diffusion of Innovation and Role of Opinion Leaders

Global Observations of the Influence of Culture on Consumer Buying Behavior - Advances in Business Strategy and Competitive Advantage ◽

10.4018/978-1-5225-2727-5.ch005 ◽

2018 ◽

pp. 83-93

Author(s):

Dayane Gabriele Alves Silveira

Keyword(s):

Diffusion Of Innovation ◽

Decision Process ◽

Diffusion Processes ◽

Opinion Leaders ◽

Innovation Networks ◽

Factors Affecting ◽

New Strategy ◽

Micro Level ◽

And Diffusion

The purposes of this study were: (1) examine the literature about innovation diffusion; (2) conduct a literature review on the innovation-decision process; (3) identify factors affecting the success of an innovation; (4) to determine a new strategy for diffusion of innovation. A structured search of the internet was undertaken to identify and appraise direct relationship between opinion leaders and diffusion of innovation. Models for describing the pattern of the diffusion processes for innovations are used by researchers. The present study went beyond the global structure of network to understand the actual position of the actors within the innovation networks. To do this, a strategy was needed that went to understand from the macro to the micro level, and then returned to the macro level to explain the structure of the authorship in innovation networks.

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Meridional Circulation, Turbulence, and Diffusion Processes in Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100080477 ◽

1976 ◽

Vol 32 ◽

pp. 109-116 ◽

Cited By ~ 1

Author(s):

S. Vauclair

Keyword(s):

Convection Zone ◽

Diffusion Processes ◽

Meridional Circulation ◽

Diffusion Time ◽

Work In Progress ◽

First Results ◽

Stellar Envelopes ◽

And Diffusion ◽

Turbulence And Diffusion ◽

Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

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NMR-Study of Structure and Diffusion Processes in Li3N

Le Journal de Physique Colloques ◽

10.1051/jphyscol:1980607 ◽

1980 ◽

Vol 41 (C6) ◽

pp. C6-28-C6-31 ◽

Cited By ~ 2

Author(s):

R. Messer ◽

H. Birli ◽

K. Differt

Keyword(s):

Diffusion Processes ◽

Nmr Study ◽

And Diffusion

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Effect of cluster-gradient architecture of nanostructured topocomposites on features of tribointeraction with heterophased material

10.36652/1813-1336-2020-16-3-130-135 ◽

2020 ◽

pp. 130-135

Author(s):

D.N. Korotaev ◽

K.N. Poleshchenko ◽

E.N. Eremin ◽

E.E. Tarasov

Keyword(s):

Wear Resistance ◽

Titanium Alloy ◽

Energy Dissipation ◽

Phase Structure ◽

Diffusion Processes ◽

Structural Phase ◽

High Wear Resistance ◽

Wear Characteristics ◽

And Diffusion

The wear resistance and wear characteristics of cluster-gradient architecture (CGA) nanostructured topocomposites are studied. The specifics of tribocontact interaction under microcutting conditions is considered. The reasons for retention of high wear resistance of this class of nanostructured topocomposites are studied. The mechanisms of energy dissipation from the tribocontact zone, due to the nanogeometry and the structural-phase structure of CGA topocomposites are analyzed. The role of triboactivated deformation and diffusion processes in providing increased wear resistance of carbide-based topocomposites is shown. They are tested under the conditions of blade processing of heat-resistant titanium alloy.

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Certain Problems with the Application of Stochastic Diffusion Processes for the Description of Chemical Engineering Phenomena. Diffusional Change of Solid Particle Size

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19960536 ◽

1996 ◽

Vol 61 (4) ◽

pp. 536-563

Author(s):

Vladimír Kudrna ◽

Pavel Hasal

Keyword(s):

Particle Size ◽

Solid Particle ◽

Chemical Engineering ◽

Diffusion Processes ◽

Granular Systems ◽

Size Distributions ◽

Particle Size Distributions ◽

Diffusion Term ◽

Population Balances ◽

And Diffusion

To the description of changes of solid particle size in population, the application was proposed of stochastic differential equations and diffusion equations adequate to them making it possible to express the development of these populations in time. Particular relations were derived for some particle size distributions in flow and batch equipments. It was shown that it is expedient to complement the population balances often used for the description of granular systems by a "diffusion" term making it possible to express the effects of random influences in the growth process and/or particle diminution.

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Electrokinetics of polymeric fluids in narrow rectangular confinements

Soft Matter ◽

10.1039/d1sm00537e ◽

2021 ◽

Author(s):

Aditya Natu ◽

Uddipta Ghosh

Keyword(s):

Cross Section ◽

Rectangular Cross Section ◽

Double Layers ◽

Polymeric Fluids ◽

Polymeric Liquids ◽

Electrical Double Layers

Flow of polymeric liquids in narrow confinements of rectangular cross section, in the presence of electrical double layers is analyzed here. Our analysis is motivated by the fact that many...

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