The rheological characteristics of purified bentonite suspensions as a function of exchangeable cation (Ca2+, NH4+, Li+) are studied at three different clay concentrations (40 gL-1,60 gL-1,80 gL-1). A Herschel-Bulkley model is used to determine rheological parameters such as yield value, consistency and fluidification index. The flow curves are typical for shear thinning fluids but differo n two points; presence of yield stress and/or thixotropy.The Li suspensions are not yield stress fluid, and the thixotropy is weakly expressed only for the 80 gL-1 suspension. On the contrary, Ca-clay suspension flow curves always present yield stress and a large thixotropic area. The NH 4-clay suspensions exhibit an intermediate behavior as there is no thixotropy, but a yield stress appears for the most concentrated suspension. These differences in macroscopic mechanical properties are discussed with reference to the suggested microscopic clay organization in suspension.
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