Static filtration of purified sodium bentonite clay suspensions. Effect of clay content

• Published in: Applied clay science 2001-07, Vol.19 (1), p.103-120
• Main Authors: Benna, M, Kbir-Ariguib, N, Clinard, C, Bergaya, F
• Format: Article
• Language: English
• Subjects: Cake thickness; Clay; Earth sciences; Earth, ocean, space; Exact sciences and technology; Filtration properties; Mineralogy; Permeability; Silicates; Sol–gel transition; Water loss
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/S0169-1317(01)00050-3

The effect of clay content on the static filtration properties of purified Na-montmorillonite suspensions was studied at two different pressures. The results of filtering parameters are as expected. When the clay percentage increases, the thickness ( e) of the obtained cake increases, leading to the decrease of water loss (WL), and consequently, to the decrease of permeability ( k). These decreases of WL and k are more important for the low applied pressure than for the high one. The differences between values of the different experimental parameters (WL and e) obtained at applied pressures of 5.7×10 5 and 1.5×10 5 Pa, as a function of clay content in the initial samples, show some singular points. At the clay content corresponding to the sol–gel transition (SGT), already determined by rheological measurements, ΔWL presents a change in concavity and Δ e shows a maximum. Localisation of this maximum seems to be a simple way to detect the SGT by performing static filtration experiments of two series' of clay suspensions at two different pressures. According to the water contents obtained at the two pressures, all the cakes were localised in region (2), defined by Norrish (1954) as the “macroscopic” swelling paste of Na-montmorillonite. At low applied pressure, the texture of the cakes is identified by transmission electron microscopy (TEM). Generally, at low magnification, all samples are globally homogeneous. However, they present some regions more dense than others. At high magnification, the number of layers per particle seems to depend on SGT. Indeed, in the cake corresponding to 1% w/w of clay in the initial suspension, isolated layers are most frequent and particles with two to four layers per particle are scarce. In the cake obtained from the gel (3% w/w of clay) the most frequent stacking is about three layers per particle, and isolated layers almost disappear. In the cake obtained from gel, at the SGT (5.5% w/w of clay) which is the less oriented sample, the most frequent stacking is statistically also around three layers per particle but with a greater number of particles, some isolated layers appear again. After the sol–gel transition, in the cake obtained from the 7% sample (which is the most oriented sample), the number of particles increases but the number of layers in each particle decreases (two layers per particle most frequently occurs), and the number of isolated layers again rises. The frequent distances between the aggregates and particl