Reduced-charge montmorillonite (RCM, cation exchange capacity (CEC)=7.5 cmol_c kg⁻¹) prepared by heating Li⁺-montmorillonite (CEC=98.1 cmol_c kg⁻¹) at 400°C for 2 h could be finely dispersed in a mixture of water, dimethylformamide, and ammonia, as confirmed by particle size distribution and atomic force microscopy measurements. Upon dispersion, the CEC of RCM increased to 51.8 cmol_c kg⁻¹, and about 50% of fixed Li⁺ ions was converted into exchangeable ones.

Cationic polymer of poly((N,N-dimethylamino)ethyl methacrylate) (PDMA) as flocculant was used for treating bentonite suspension with pH 3–11, and the effect of PDMA on sedimentation rate, the size of aggregates and floating bentonite ratio in supernatant was investigated. Furthermore, the PDMA amount in aggregates by thermogravimetry and d(001) of bentonite by X-ray diffraction were measured. When pH of the bentonite suspension decreased, the sedimentation rate of bentonite aggregates increased and the floating bentonite ratio in supernatant solution decreased with only a small amount of PDMA. However, when more than optimum amount of PDMA was added, the sedimentation rate decreased and the floating bentonite ratio increased. Also, bentonite aggregates became the largest by adding optimum amount of PDMA, while they became smaller by using an excessive amount of PDMA. These phenomena were explained by the interaction between PDMA and bentonite surface. That is, in the case of strong interaction, the size of bentonite aggregate was large and the sedimentation rate was fast. On the contrary, in the case of weak interaction, bentonite was difficult to aggregate and the sedimentation rate was slow.

The ultrasonic velocities in a colloidal solution and a thixotropic hydrogel containing imogolite are measured. Our original experimental setup can detect the change of ultrasonic velocity caused by the mixing of imogolite and maleic acid in pure water. Using this setup, the ultrasonic velocity is found to remain unchanged during the macroscopic solid/liquid transition and viscoelastic change of a thixotropic hydrogel consisting of imogolite and maleic acid, which is consistent with previous literatures. Thus, the ultrasonic velocity measurement proves to be effective for the detection of well-dispersed clay minerals in diluted state, regardless of the phase and viscoelastic change of substances.