1,721,351 research outputs found
The second ISSMGE Kerry Rowe Lecture: On the intrinsic, state and fabric parameters of active clays for contaminant control
Full text linkThe 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,Csk,0 . 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, D*s ; 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.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Steady-state analysis of pollutant transport to assess landfill liner performance
Full text linkNew analytical solutions are presented for the assessment of the impact of contaminant transport through landfill liners on groundwater quality under steady-state conditions. These solutions can be applied to evaluate the equivalency and the effectiveness of landfill liners, even those that include a geomembrane, taking into account the presence of a natural attenuation layer interposed between the engineered barrier and the underlying aquifer. The impact of a contaminant on groundwater quality is quantified through the determination of the contaminant concentration along the horizontal direction of the groundwater flow for the case of thin aquifers that are only a few meters thick. For the case of thick aquifers, both a closed-form analytical solution and a step-by-step numerical solution are provided for the calculation of the variations in the contaminant concentration in horizontal and vertical directions within the aquifer
Modellazione dei fenomeni di trasporto dei soluti nei mezzi porosi in presenza di osmosi chimica
No full text
Influenza delle condizioni al contorno nella valutazione dei parametri di dispersione-diffusione ed assorbimento da prove di laboratorio in colonna filtrante
No full textThe role of diffusion induced electro-osmosis in the coupling between hydraulic and ionic fluxes through semipermeable clay soils
Full text linkMost of the experimental research conducted to date has provided evidence on the semipermeable membrane behaviour of smectite-rich clay soils, the extent of which is typically quantified through the reflection coefficient, when the permeant (electrolyte) solution contains a single monovalent or divalent salt. Under such conditions, the osmotic flow of solution is controlled to a great extent by the different accessibility of ions and water molecules to the soil porosity, which is referred to as the chemico-osmotic effect. However, theoretical simulations of coupled solute and solvent transport suggest that, when two or more cations that diffuse in water at different rates are present simultaneously in the permeant solution, the electro-osmotic effect, which stems from the condition of null electric current density through the porous medium, can be enhanced compared to the case of a single salt to such an extent that it becomes comparable to or even greater than the chemico-osmotic effect. An original closed-form analytical solution to the problem of calculating the diffusion potential, which in turn controls the magnitude of the electro-osmotic effect, is here illustrated, and the relative importance of the aforementioned contributions to multi-electrolyte systems is examined through the interpretation of laboratory test results from the literature pertaining to a bentonite amended clay soil in equilibrium with aqueous mixtures of potassium chloride (KCl) and hydrochloric acid (HCl). The proposed mechanistic model is shown to be able to quantitatively capture the impact of both chemico-osmosis and electro-osmosis on the measured reflection coefficient of smectite clays, thereby breaking new ground in the experimental and theoretical research on the osmotic properties of engineered clay barriers in contact with mixed aqueous electrolyte solutions
The role of chemico-osmosis in the performance assessment of bentonite-based contaminant barriers
Full text linkAlthough conservative estimates of the containment performance of bentonite-based barriers can be obtained from the classical advective-diffusive transport theory, the semipermeable properties of the bentonite component can determine a significant reduction in the migration rate of contaminants at low salt concentrations (< 100 mM). After introducing the transport equations for a semipermeable porous medium, the paper presents the laboratory testing apparatuses and procedures that allow the chemico-osmotic efficiency coefficient, ω, and the osmotic effective diffusion coefficient, D ∗ω, of bentonites to be experimentally assessed. Finally, the advantages that derive from the ability to model the semipermeable behaviour of bentonites in the design of geoenvironmental barriers are discussed with the aid of a calculation example, which considers the use of geosynthetic clay liners for the bottom lining of waste disposal facilities
- …
