Etude de la repartition de l'eau dans des argiles saturees Mg²⁺ aux fortes teneurs en eau

Abstract

RI~SUMI~: Des poudres d'6chantillons de smectites satur6es Mg 2+ ont 6t6 r6hydrat6es jusqu'h obtention d'une hydratation maximale. Les microscopies 61ectroniques ~t balayage et ~ transmission ont permis de caract6riser l'organisation des argiles, en particulier l'arrangement, la taille et la structure cristalline des particules. La diffusion aux petits angles des rayons X a 6t6 utilis6e pour quantifier la microstructure des mat6riaux. Les r6sultats obtenus montrent que les teneurs en eau atteintes/t saturation ne sont pas directement reli6es ?a des variations de la distance interfoliaire. Le m6canisme de l'hydratation est en revanche correl6 ~ la taille des particules et ~ celle des agr6gats de particules. I1 est montr6 que l'extension des feuillets dans le plan a, b joue un r61e direct sur la taille et la forme aussi bien des particules que des agr6gats de particules, lnfine, il apparaSt que pour mieux comprendre le m6canisme du gonflement maximal des argiles, il devient n6cessaire de prendre en compte tousles niveaux d'organisation et que la contribution de l'espace interfoliaire dans l'6valuation de l'eau totale peut &re, pour les smectites-Mg relativement faible.A B S T R ACT: Powdered 2:1 Mg-clay samples were rehydrated up to the maximum hydration. Both scanning and transmission electron microscopy were used to characterize their structural organization i.e. particle arrangement, texture and crystal structure. Low-angle X-ray scattering experiments were carried out to quantify the microstructure of the system. The results showed that sample water contents reached at saturation are not directly related to changes in layer distance. The hydration mechanism is rather correlated to particle size and particle aggregate size. It is also shown that the a, b plane extension of the layers influences particle size and shape. Finally, it appears that for a better understanding of clay swelling mechanisms, at high water contents, it is necessary to take into account all organization levels and that the contribution of interlayer space to the total water content, for Mg-smectites, is small.

Use of X-Ray Transmission Diffractometry for the Study of Clay-Particle Orientation at Different Water Contents

“…These three clays were relatively pure and have crystallites of significant size, which was confirmed by the specific-surface area data and TEM data. The number of layers in the coherent domains of Ca-rich montmorillonite is estimated at >8 with faceto-face stacking of these coherent domains (--50 layers) (Tessier and P6dro, 1987;Touret et al, 1990). In kaolinite, there were ~ 100 layers per crystallite (Vasseur et al, 1995) whereas, in illite, there were three to four layers, which is in agreement with the specific surface area (Dj6ran-Maigre et al, 1998).…”

Acid-Gangue Interactions in Heap Leach Operations: A Review of the Role of Mineralogy for Predicting Ore Behaviour

“…-Advanced argillic alteration, on the other hand, generated percolation problems, and returned poor copper recovery, which the authors ascribed to the presence of smectite, holding acid in inner sheet structures, and capturing copper from solution through ion exchange [22]. Acid may also be held in outer sheet structures of clays [23]. -Brecciated rocks in the deposit showed better porosity than the plutonic rocks, which leads to more pervasive fluid attack, more clay mineral formation, and later percolation problems.…”

“…Worth noting is that clay minerals, particularly those of the smectite group, whether as ore alteration products or products of gangue-acid reaction in the heap, have the potential to hold acid in their structures [22,23]. Whilst not strictly acid consumption, the capacity for adsorbing acid makes these minerals important as acid is then not available for reaction with the Cu minerals.…”

Morphology, Texture, and Microstructure of Halloysitic Soil Clays as Related to Weathering and Exchangeable Cation

“…The decrease in particle frequency from increasing soil weathering can be related to a decrease in the layer charge of the clay minerals from SN5 to MK1, as inferred from Table 1. In strongly hydrated systems made of pure homoionic 2:1 swelling clays, it is established that the number of particles per unit area decreases with decreasing layer charge Tessier and Pedro, 1987;Touret et al, 1990). Table 3.…”

“…These hydration properties distinguish smectites from kaolinites and illites sensu stricto 1987). As far as homoionic 2:1 swelling clays are concerned, water content and dispersion at low suctions increase with decreasing layer charge, i.e., from vermiculite to low charge smectite (Touret et al, 1990).…”