Vermiculite gelation: structural and textural evolution

Abstract--The swelling of n-butylammonium vermiculite in water was investigated as a function of the sol concentration (r), the salt concentration (c) and the temperature (T).The interlayer spacing in the gel phase was investigated as a function of r and c by neutron diffraction and by laboratory experiments which measured how many times its own volume a crystal would absorb. The salt concentration was found to be the stronger variable with the interlayer spacing decreasing proportional to c~ which is consistent with previous results and with the Coulombic attraction theory. The sol concentration was found to affect the swelling for two reasons, the salt fractionation effect and the trapped salt effect. Both of these cause the salt concentration in the supernatant fluid to be greater than that originally added to the crystals and so reduce the swelling.A new method was used for extracting the solution from inside the gels by collapsing the gels by the addition of potassium hydrogen carbonate. The Volhardt titration was carried out on the extracted and supernatant solutions from about 250 gels. The ratio of the external to the internal chloride concentration was found to be approximately constant across the range of salt concentrations. Its average value was equal to 2.6, again in agreement with Coulombic attraction theory and showing the surface potential to be constant at about 70 mV.The (r, c, T) boundary of the two phase colloid region was investigated by three methods. A plot of log c against Tc was linear within experimental accuracy, with a gradient of 0.077 K-~ or 13 K per log unit. This shows that the surface potential varies by only 1 mV per decade in the salt concentration. The system is therefore governed by the Dirichlet boundary condition and not by the Nernst equation.

Section: Introductionmentioning

confidence: 92%

The Sol Concentration Effect in n-Butylammonium Vermiculite Swelling

Williams¹,

Moody

Smalley

et al. 1994

“…The mechanism leading to the appearance of these properties is linked with the interlamellar swelling of clay in contact with an ionic solution (Mdring 1946;Barshad 1953;Norrish 1954;Quirk 1968;Van Olphen 1977;Pons 1980;Saez-Aunon et al 1983;Tessier 1984;Raussel-Colom et al 1989). One problem occurring during drilling is to control the swollen states and their total or partial reversibility under the action of different physicochemical parameters and different stresses to which the clay can be subjected (chargebalancing cation, salt concentration of the solution, temperature).…”

Section: Introductionmentioning

confidence: 99%

Structural Organization of Na- and K-Montmorillonite Suspensions in Response to Osmotic and Thermal Stresses

Faisandier

1998

Abstract--In order to understand the influence of salt concentration and temperature on the behavior and properties of clays used in drilling muds, we studied montmorillonite supensions (4 g clay/100 g solution) in 0.1, 0.5 and 1 M NaC1 and KC1 solutions. A fraction of each sample was heated to 200 ~ in a closed vessel for 7 d, then cooled at room temperature (RT, 25 ~ Small-angle X-ray scattering (SAXS) spectra were recorded, for all the samples, at RT. The structure of the clay particles was determined by comparing the experimental intensity with the theoretical intensity computed from a model that took into account the number of layers per particle, the hydration state of the layers (0, l, 2, 3 or 4 water layers) and the order in the succession of these states. With this set of parameters, we can compute the mean statistical parameters ~/ (mean number of layers per particle), cl (mean interlayer distance) and g2/~ (parameter describing the disorder of the distribution of interlayer distances). The evolution of these parameters shows that: 1) At low concentration (0.1 M NaC1 or KC1), the samples do not consist of particles but of isolated layers (M = 1). The suspensions form gel-like structures. The difference between Na and K suspensions, or between heated and nonheated samples, is unnoticeable at the studied scale (5-500 ,~).2) An increase in salt concentration (from 0.1 to 0.5 M) brings the sample in a granular state: we notice the appearance of particles at 0.5 M (~7/ ~ 25). Differences appear between NaC1 and KC1 suspensions, and the temperature effect becomes visible. Thus, we noticed that in NaC1 suspensions, particles are composed of hydrated layers (1, 2, 3 or 4 water layers) and internal porositYo(d > 30 A), whereas suspensions in KC1 are characterized by the presence of interlayer distances of 10 A, that is, of collapsed layers. Particles in the KC1 suspensions are much thicker than in the NaCI corresponding ones, and also less hydrated at the interlayer level as well as at the internal porosity level. Further increase in salt concentration (0.5 to 1 M) amplifies this effect. As far as temperature is concerned, its effect is to promote the clay dispersion by breaking up the particles, dehydrating and disordering them. This effect is more important for low salt concentration, that is, when the system is less stressed.

“…The phenomenon of osmotic swelling occurs only with vermiculite. This effect was observed by Garret and Walker (1962) for short chain alkylammonium vermiculite and by Rausell-Colom et al (1989) for ornithine-vermiculite. The swelling of BAvermiculite has recently been reported by several workers (Smalley et al 1989;Crawford et al 1991;Lee and Solin 1991;Fan et al 1992;Williams et al 1994).…”

Section: Introductionmentioning

confidence: 78%

Stability of n-Butylammonium Vermiculite in Powder and Flake Forms

Haro

1998

Abstract--Interaction between n-butylammonium (BA) chloride and vermiculite from Santa Olalla (Spain) has been studied in large flake (5 • 5 • 0.1 ram) or ground powder (~<80 txm) samples. The differences in adsorption and decomposition of BA ions in both particle sizes have been established. In the interlamellar space, the BA ion remains unaltered in powder samples, but is degraded in flakes. The experimental results suggest decomposition of the BA in the interlamellar space of vermiculite flakes by breaking of the C-N bond. The degradation of BA takes place over a short period. The variety with BA in the interlamellar space is transformed into a new one, due to the degradation of alkylammonium. The transformation occurs through an interstratified phase formed between BA-vermiculite and NH:vermiculite, and finally a phase appears in which only ammonium is present in the interlamellar space. Due to the many industrial applications of alkylammonium-clays, determination of the stability of alkylammonium in the interlamellar space of clay minerals is of great importance.