EFFECTS OF THE NATURE OF THE EXCHANGEABLE CATION AND CLAY CONCENTRATION ON THE RHEOLOGICAL PROPERTIES OF SMECTITE SUSPENSIONS

摘要

The rheological characteristics of purified bentonite suspensions as a function of exchangeable cation (Ca~(2+), NH_4~+, 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 differ on 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.