Laboratory assessment of semi-permeable properties of a natural sodium bentonite

2018 ◽  
Vol 55 (11) ◽  
pp. 1611-1631 ◽  
Author(s):  
Andrea Dominijanni ◽  
Nicolò Guarena ◽  
Mario Manassero
Keyword(s):  
Mechanistic Model ◽  
Effective Diffusion ◽  
Swelling Pressure ◽  
Solute Concentration ◽  
Transport Processes ◽  
Laboratory Assessment ◽  
Sodium Bentonite ◽  
Clay Particles ◽  
Chemical Osmosis ◽  
Multi Stage

The relevance of the semi-permeable properties of bentonites, which affect both their transport processes and mechanical behaviour, has been assessed through the experimental determination of three parameters: the reflection coefficient, ω; the osmotic effective diffusion coefficient, [Formula: see text]; and the swell coefficient, ϖ. Two multi-stage tests were conducted on a natural sodium bentonite, while varying both the specimen void ratio, e, and the solute concentration, cs, of the equilibrium sodium chloride (NaCl) solutions. The measured phenomenological parameters were interpreted through a mechanistic model, in which the electric charge of clay particles is taken into account via a single material parameter, [Formula: see text], referred to as the “solid charge coefficient”. A constant value of [Formula: see text] = 110 mmol/L was found to provide an accurate interpretation of the experimental data, at least within the investigated range of bentonite void ratios (3.33 ≤ e ≤ 4.18) and NaCl concentrations of the external bulk solutions (5 ≤ cs ≤ 90 mmol/L). The results support the hypothesis that both chemical osmosis and swelling pressure are macroscopic manifestations of the same interactions, which occur at the microscopic scale between the clay particles and the ions contained in the pore solution, and that both of them can be modelled through a single theoretical framework.

scholarly journals Thermodynamically Coupled Mass Transport Processes in a Saturated Clay

1984 ◽  
Vol 44 ◽  
Author(s):  
C. L. Carnahan
Keyword(s):  
Mass Transport ◽  
Solute Concentration ◽  
Transport Processes ◽  
Fluid Composition ◽  
Coupled Transport ◽  
Chemical Osmosis ◽  
Saturated Clay ◽  
Specific Discharge ◽  
Coupled Transport Processes ◽  
Waste Repositories

AbstractGradients of temperature, pressure, and fluid composition in saturated clays give rise to coupled transport processes (thermal and chemical osmosis, thermal diffusion, ultrafiltration) in addition to the direct processes (advection and diffusion). One-dimensional transport of water and a solute in a saturated clay subjected to mild gradients of temperature and pressure was simulated numerically. When full coupling was accounted for, volume flux (specific discharge) was controlled by thermal osmosis and chemical osmosis. The two coupled fluxes were oppositely directed, producing a point of stagnation within the clay column. Solute flows were dominated by diffusion, chemical osmosis, and thermal osmosis. Chemical osmosis produced a significant flux of solute directed against the gradient of solute concentration; this effect reduced solute concentrations relative to the case without coupling. Predictions of mass transport in clays at nuclear waste repositories could be significantly in error if coupled transport processes are not accounted for.

A model of hindered solute transport in a poroelastic shale

1994 ◽  
Vol 445 (1925) ◽  
pp. 679-692 ◽  
Keyword(s):  
Pore Pressure ◽  
Direct Effect ◽  
Swelling Pressure ◽  
Solute Concentration ◽  
Solute Diffusion ◽  
Permeable Membrane ◽  
Coupled Diffusion ◽  
Final Steady State ◽  
Thermodynamic Pressure ◽  
Osmotic Pressure Difference

Theories for the transport of solvent and solute through an imperfect semi-permeable membrane are used as the basis for a model of transport through shale. The flow of solute is reduced, relative to that of solvent, by a transmission coefficient λ ≼ 1. In this model, it is assumed that the chemical composition of the pore fluid has no direct effect upon the swelling of the shale, other than via the thermodynamic pressure p . Invasion is governed by a pair of coupled diffusion equations. There is an initial, rapid diffusion of pressure, leading to a swelling pressure (1-λ) RT ∆ x / V w , where RT ∆ x / V w is the van’t Hoff osmotic pressure difference due to a change in solute mole fraction ∆ x . A subsequent slow diffu­sion process, dominated by diffusion of the solute, then occurs. A change in solute concentration has been assumed to have no direct effect upon the rock, and ultimately has no effect upon the pore pressure and stress. Nevertheless, imperfect exclusion of solute can lead to transient changes in pore pressure which might destabilize the shale before the final steady state is achieved. This is demonstrated by a poroelastic analysis of pressure and solute diffusion into rock surrounding a wellbore.

Testing seismic noise caused by highly concentrated sediment flows in laboratory experiments

2020 ◽  
Author(s):  
Marco Piantini ◽  
Florent Gimbert ◽  
Alain Recking ◽  
Hervé Bellot
Keyword(s):  
Sediment Transport ◽  
Seismic Noise ◽  
Laboratory Experiments ◽  
River Flow ◽  
Mechanistic Model ◽  
Transport Processes ◽  
Sediment Flux ◽  
Extreme Floods ◽  
Starting Point ◽  
Grain Sorting

<p>Sediment transport processes and fluxes play a key role in fluvial geomorphology and hazard triggering. In particular, extreme floods characterized by highly concentrated flows set the pace of mountain landscape evolution, where the linkage between streams and sediment sources leads to strong solid inputs characterized by significant grain sorting processes. The main observation that river processes generate ground vibrations has led to the application of seismic methods for monitoring purposes, which provides an innovative system that overcomes traditional monitoring difficulties especially during floods. Mechanistic models have been proposed in the attempt to invert river flow properties such as sediment fluxes from seismic measurements. Although those models have recently been validated in the laboratory and in the field for low transport rates, it remains unknown whether they are applicable to extreme floods.</p><p>Here we carry a set of laboratory experiments in a steep (18% slope) channel in order to investigate the link between seismic noise and sediment transport under extreme flow conditions with highly concentrated sediment flows. The originality of this set-up is that instead of feeding the flume section directly as usually done, we feed with liquid and solid discharge a low slope storage zone connected to the upstream part of the steep channel. This allows us to produce sediment pulses of varying magnitude (up to the transport capacity) and granulometric composition, traveling downstream as a result of alternate phases of deposition and erosion occurring in the storage area. We measure flow stage, seismic noise, sediment flux and grain size distribution. We find that the previously proposed relationships between seismic power, sediment flux and grain diameter often do not hold in such sediment transport situations. We support that this is due to granular interactions occurring between grains of different sizes within the sediment mixture and leading to complex grain sorting processes. In particular, we observe that bigger grains do not directly impact the bed but rather roll over fines or smaller grains, such that observed seismic power is much lower than expected. These results constitute a starting point for the development of a new mechanistic model for seismic power generated by highly concentrated bedload sediment flows.</p>

scholarly journals Modeling of Carbon Dioxide Leakage from Storage Aquifers

Fluids ◽  
2018 ◽  
Vol 3 (4) ◽  
pp. 80 ◽  
Author(s):  
Parvaneh Heidari ◽  
Hassan Hassanzadeh
Keyword(s):  
Driving Forces ◽  
Mechanistic Model ◽  
Co2 Storage ◽  
Transport Processes ◽  
Saline Aquifers ◽  
Storage Site ◽  
Geological Storage ◽  
Co2 Leakage ◽  
Deep Saline Aquifers ◽  
The Impact

Long-term geological storage of CO2 in deep saline aquifers offers the possibility of sustaining access to fossil fuels while reducing emissions. However, prior to implementation, associated risks of CO2 leakage need to be carefully addressed to ensure safety of storage. CO2 storage takes place by several trapping mechanisms that are active on different time scales. The injected CO2 may be trapped under an impermeable rock due to structural trapping. Over time, the contribution of capillary, solubility, and mineral trapping mechanisms come into play. Leaky faults and fractures provide pathways for CO2 to migrate upward toward shallower depths and reduce the effectiveness of storage. Therefore, understanding the transport processes and the impact of various forces such as viscous, capillary and gravity is necessary. In this study, a mechanistic model is developed to investigate the influence of the driving forces on CO2 migration through a water saturated leakage pathway. The developed numerical model is used to determine leakage characteristics for different rock formations from a potential CO2 storage site in central Alberta, Canada. The model allows for preliminary analysis of CO2 leakage and finds applications in screening and site selection for geological storage of CO2 in deep saline aquifers.

scholarly journals Second ISSMGE R. Kerry Rowe Lecture: On the intrinsic, state, and fabric parameters of active clays for contaminant control

2020 ◽  
Vol 57 (3) ◽  
pp. 311-336 ◽  
Author(s):  
Mario Manassero
Keyword(s):  
Electric Charge ◽  
Solid Phase ◽  
Effective Diffusion ◽  
Swelling Pressure ◽  
Efficiency Coefficient ◽  
Solid Skeleton ◽  
Self Healing ◽  
Intrinsic State ◽  
Healing Efficiency ◽  
Charge Concentration

The osmotic, hydraulic and self-healing efficiency of bentonite-based barriers for the containment of subsoil pollutants is governed not only by the intrinsic chemicophysical parameters of the bentonite, i.e., the solid phase density, ρsk; the total specific surface, S; the surface density of the electric charge, σ; and the Stern layer thickness, dStern, and fraction, fStern, but also by the chemicomechanical fabric parameters that quantify the structure or texture of the solid skeleton, such as the micro, em, and nano, en, void ratios; the average number of platelets or lamellae per tactoid, Nl,AV; and the solid skeleton effective electric charge concentration, [Formula: see text]. In turn, the fabric parameters are controlled by state parameters, such as the total void ratio, e; and the salt concentration of the equilibrium solution, cs. A theoretical framework has been developed to describe the relationships between the aforementioned intrinsic, state, and fabric parameters for a bentonite barrier and its performance parameters: the hydraulic conductivity, k; the effective diffusion coefficient, [Formula: see text]; the chemico-osmotic efficiency coefficient, ω; and the osmotic swelling pressure, usw. The proposed theoretical hydrochemicomechanical model has been validated through comparison with a large amount of experimental results.

scholarly journals Calibration of the Dermal Advanced REACH Tool (dART) Mechanistic Model

2019 ◽  
Vol 63 (6) ◽  
pp. 637-650 ◽  
Author(s):  
Kevin McNally ◽  
Jean-Philippe Gorce ◽  
Henk A Goede ◽  
Jody Schinkel ◽  
Nick Warren
Keyword(s):  
Mass Transport ◽  
Mechanistic Model ◽  
Contextual Information ◽  
Measurement Data ◽  
Dermal Exposure ◽  
Transport Processes ◽  
Data Set ◽  
Mixed Effect ◽  
Model Estimate ◽  
Liquid Products

Abstract The dermal Advanced REACH Tool (dART) is a Tier 2 exposure modelling tool currently in development for estimating dermal exposure to the hands (mg min−1) for non-volatile liquid and solids-in-liquid products. The dART builds upon the existing ART framework and describes three mass transport processes [deposition (Dhands), direct emission and direct contact (Ehands), and contact transfer (Thands)] that may each contribute to dermal exposure. The mechanistic model that underpins the dART and its applicability domain has already been described in previous work. This paper describes the process of calibrating the mechanistic model such that the dimensionless score that results from encoding contextual information about a task into the determinants of the dART can be converted into a prediction of exposure (mg min−1). Furthermore, as a consequence of calibration, the uncertainty in a dART prediction may be quantified via a confidence interval. Thirty-six experimental studies were identified that satisfied the conditions of: (i) high-quality contextual information that was sufficient to confidently code the dART mechanistic model determinants; (ii) reliable exposure measurement data sets were available. From these studies, 40 exposure scenarios were subsequently developed. A non-linear log-normal mixed-effect model was fitted to the data set of Dhands,   Ehands, and    Thands scores and corresponding measurement data. The dART model was shown to be consistent with activities covering a broad range of tasks [spray applications, activities involving open liquid surfaces (e.g. dipping, mixing), handling of contaminated objects, spreading of liquid products, and transfer of products (e.g. pouring of liquid)]. Exposures resulting from a particular task were each dominated by one or two of the identified mass transport processes. As a consequence of calibration, an estimate of the uncertainty associated with a mechanistic model estimate is available. A 90% multiplicative interval is approximately a factor of six. This represents poorer overall precision than the (inhalation) ART model for dusts and vapours, although better than the ART model for mists. Considering the complexity of the conceptual model compared with the ART, the wide variety of exposure scenarios considered with differing dominant routes, and the particular challenges that result from the consideration of measurement data both above and beneath a protective glove, the precision of the calibrated dART mechanistic model is reasonable for well-documented exposure scenarios coded by experts. However, as the inputs to the model are based upon user judgement, in practical use, the reliability of predictions will be dependent upon both the competence of users and the quality of contextual information available on an exposure scenario.

Experiment on Water Infiltration and Solute Migration in Porous and Fractured Media

2014 ◽  
Vol 955-959 ◽  
pp. 1993-1997 ◽  
Author(s):  
Jing Wen Song ◽  
Ming Yu Wang ◽  
Da Wei Tang
Keyword(s):  
Porous Media ◽  
Water Flow ◽  
Solute Concentration ◽  
Transport Processes ◽  
Fractured Media ◽  
Water Infiltration ◽  
Typical Structure ◽  
Fracture Structure ◽  
Flow Features ◽  
And Migration

The experiments were performed by considering the upper loose porous media and lower fractured media as a typical structure of vadose zones, and by constructing the corresponding physical model to simulate water flow and solute transport processes in order to investigate water flow features and migration mechanism. It has been indicated that in the porous and fractured complex media, if the lower fracture structure remains unchanged, the structure and permeability of the porous media offer considerable impact on infiltration processes. Additionally, if the structure and permeability of the porous media remain unchanged, the overall permeability and flow features of the fracture structure are significantly controlled by fracture configurations. Furthermore, for the fracture structures with different fracture configurations, it is indicated that increasing of the density of the vertical fractures results in much more enhancement of the solute concentration decay rate than that caused by increasing the density of the horizontal ones. This investigation was expected to be of scientific significance and practical value for effective groundwater protection.

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