Studies on the thixotropy of ferric aluminum magnesium hydroxide/montmorillonite suspension

The study on the thixotropy of aqueous dispersion consisting of ferric aluminum magnesium Hydroxide(Fe-Al-Mg-MMH) possessing permanent positive charges and Na-montmorillonite(MT) possessing permanent negative charges is reported. It was found that the suspension studied may display positive thixotropy, negative thixotropy or complex thixotropy depending on the Fe-Al-Mg-MMH/MT mass ratio (R). Two kinds of complex thixotropy were found, one is that the system may display a positive thixotropic character and negative thixotropic character successively, and the other is that the system may display a negative thixotropic character and positive thixotropic character successively. In the studied range of R (0-0.091), with increasing R, the thixotropy of the suspension changes from positive thixotropy through complex thixotropy and then to negative thixotropy. The effects of rest time(t(s)) after cessation of high intensity and the low shear rate (D-L) used at measuring viscosity on the viscosity change for Fe-Al-Mg-MMH/MT suspension were examined. It was found that the suspension which shows negative thixotropy at low D-L may display complex thixotropy, first negative thixotropic character and then positive thixotropic character, at high D-L. The system which is negative thixotropy at low t(s) may display complex thixotropy at high t(s). The mechanism of the thixotropy is discussed, and the change process of "dispersed particles-steric continuous network structures over the whole system-densed floc units" and "dispersed particles-densed floc units-clusters of densed floc units" is proposed to explain the complex thixotropic phenomenon observed.