Rheological Behavior of Smectite Dispersions: The Influence of Suspension Concentration and Exchangeable Cation

الملخص EN

The mechanical behaviors of smectite materials in water are very sensitive to many parameters, such as concentration, particle size and morphology, exchangeable cation nature, and chemical environment (pH, ionic strength).

The literature usually provides general rules for sodium and calcium bentonites.

However, it appears that the quantitative results present a large range of values.

This study has established the relationships between the smectite nature (mineralogy, morphology, reactivity) and its rheological behavior according to the exchangeable cation.

To develop a complete rheological study, we need 800 g of montmorillonite purified and saturated with Na+ or Ca2+.

Huge production necessitates optimized process with accurate control of the powder quality and the chemical environment.

Smectite particles have been extracted from a natural bentonite and then saturated with sodium or calcium.

Then, each sample was characterized with classical methods like X-ray diffractometry (XRD), and laser granulometry but also cutting-edge technologies like scanning transmission electron microscopy on wet samples (Wet STEM).

The Na-smectite dispersion contains a lot of small units whereas the Ca-smectite dispersion contains a few large units.

Rheological study consists in flow curves obtained with a high-resolution rheometer.

Logarithmic representation of the rheograms permits detecting a yield stress, it separates solid and fluid behavior.

The rheological datas (viscosity, consistency, and yield stress) allow defining the limits depending on the concentration and on the saturation state.

A Newtonian law could be applied to around 4% for Na- and Ca-smectites.

Seaward of these concentrations, the dispersions are shear thinning and modelled by Ostwald law.

Finally a yield stress appears at 6% for Na-smectite and 11% for Ca-smectite, the flow curves could be modelled by Hershel-Bukley law.

Results are in accordance with the bibliography.