Study on the thixotropy of magnesium ferric hydroxide - Montmorillonite suspension

The thixotropy of suspension, the rheological properties change with the shear time, is a complicated rheological phenomenon. The shear - thinning and the shear - thickening phenomena, i.e., positive thixotropy and negative thixotropy, respectively were observed in the previous studies. Recently we found a novel thixotropic phenomenon, described as "complex thixotropy", during studying the thixotropic phenomenon of magnesium aluminum hydroxide - montmorillonite suspension. In this paper, the study of thixotropy of the aqueous suspension consisting of magnesium ferric hydroxide (Mg - Fe - MMH) possessing permanent positive charges and Na - montmorillonite (MT) possessing permanent negative charges is reported. The suspensions studied may display positive thixotropy or negative thixotropy, depending on the Mg - Fe - MMH/MT ratios. The complex phenomenon is also observed. In the range of Mg - Fe - MMH/MT ratio 0 similar to 0. 5 examined in this work, with increasing the Mg - Fe - MMH/MT ratio, the thixotropy of suspension changes from negative passing through positive, complex, then back to negative again. The effect of electrolyte NaCl on the thixotropy of the suspension was investigated, which showed that in the studied range of 0 similar to 0.10 mol/L of NaCl concentration the thixotropic type of the suspension did not change. The mechanism of the thixotropy is discussed and the change process of "dispersed particles - steric continuous net - work structures over the whole system - densed floc units" is purposed to explain the complex thixotropic phenomenon observed.