Sodium tripolyphosphate and polyphosphate as dispersing agents for kaolin suspensions: rheological characterization

The aim of the present work is to evaluate the effectiveness of some commercial dispersing agents employed for maximizing the solid loading of kaolin suspensions. Two commercially available deflocculants were used—a sodium tripolyphosphate and a sodium polyphosphate. Rheological tests were carried out at 25±0.1 °C by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device MV1P with serrated surfaces. The tests were performed under both continuous and oscillatory flow conditions. As for sodium tripolyphosphate, a shear-thinning behavior is found for all dispersant concentrations in the whole range of the shear rates investigated. In the case of the polyphosphate, a shear-thickening behavior is made evident above a critical dispersant concentration before attaining the stabilization of the dispersion. pH measurements were accomplished in order to clarify the mechanism of particle stabilization. In the light of the results achieved, the sodium polyphosphate proved to be more effective as dispersant for kaolin suspensions.