Impacts « multi-échelle » d'un échange (Mg,Ca)–Pb et ses conséquences sur l'augmentation de la perméabilité d'une bentonite

Abstract

Présenté par Georges Pédro Résumé L'article présente d'abord l'évolution structurale d'une bentonite mise en suspension dans des solutions de concentrations variées en nitrate de plomb. L'augmentation de perméabilité de la même bentonite compactée, lors la percolation d'une solution de nitrate de plomb, est ensuite décrite. En s'appuyant sur l'analyse des solutions, la diffusion des rayons X aux petits angles et la microscopie électronique à balayage, on présente les modifications structurales expliquant cette augmentation de perméabilité, de l'échelle nanométrique (diminution de taille des particules d'argile) à l'échelle micrométrique (microfisssuration des agrégats particulaires). Pour citer cet article : N.

Advanced Nano-biocomposites Based on Starch

“…7) (Hendricks 1942 4 , M y + for hectorite. The differences are mainly due to the isomorphic substitutions that take place inside the aluminum oxide layer (Jozja et al 2003). These substitutions induce a negative charge inside the silicate platelet, which is naturally counterbalanced by inorganic cations (Li + , Na + , Ca 2+ , K + , Mg 2+ , etc.)…”

Analytical Determination of Flow Patterns in a Double Porosity Medium Containing Ellipsoidal Occluded Macro-Voids

“…Therefore, if we look at pure clay at the mesoscopic scale after pollutant permeation, in the absence of quartz grains or other impurities (or if their proportion is negligible), clay aggregates and inter-aggregate voids co-exist. This arrangement creates a porous medium with two distinct length scales in it, while under the effect of inter-aggregate void development, the overall permeability measured on a macroscopic sample using Darcy's law is shown to increase notably (Jozja 2003;Jozja et al 2003;Souli et al 2008).…”

“…Owing to the high level of compaction pressures employed, the inter-particle pore space is of the same order of magnitude as the inter-layer spacing, and inter-aggregate voids are not present within the initial microstructure, prior to pollutant permeation. In contrast, after permeation of lead nitrate and zinc solutions under mechanical compaction, Scanning Electron Microscopy, using the technique of cryo-fracturing, has displayed the formation of inter-aggregate pores (of diameter > 1.5 μm), which may be connected or not depending on the initial degree of organization within the clay material considered (Jozja 2003;Jozja et al 2003;Souli et al 2008). Therefore, if we look at pure clay at the mesoscopic scale after pollutant permeation, in the absence of quartz grains or other impurities (or if their proportion is negligible), clay aggregates and inter-aggregate voids co-exist.…”

“…Clay is an heterogeneous and multi-scale material, and the observation of clay at the smallest scale displays stackings of nanometric montmorillonite lamellae and inter-layer water, lenticular porosity that form a clay particle (Jozja 2003;Pusch and Yong 2006;Pusch and Schomburg 1999). Assembling of clay particles and inter-particular porosity form clay aggregates of typical length about 10 −8 m. During laboratory permeability experiments performed by Jozja (2003), compaction pressures ranging from 0.5 to 5 MPa have been applied on samples of natural bentonites prior to water saturation, in order to study the effect of mechanical compaction as well as to cover an extended range of density.…”

“…Assembling of clay particles and inter-particular porosity form clay aggregates of typical length about 10 −8 m. During laboratory permeability experiments performed by Jozja (2003), compaction pressures ranging from 0.5 to 5 MPa have been applied on samples of natural bentonites prior to water saturation, in order to study the effect of mechanical compaction as well as to cover an extended range of density. The applied compaction is also intended to reproduce the mechanical state of compaction on site since the investigated bentonite is a potential candidate as a clay liner for use in a waste deposit.…”