The influence of Ca2+/Mg2+ concentration on the rheological properties of kaolinite slurry: An experiment and DLVO calculation study

Abstract

This study researched into the underlying influence mechanism of Ca²⁺ and Mg²⁺ on the rheological properties of kaolinite slurry through rheological technique, turbidity analysis and DLVO theory calculation. The rheological results showed that both the viscosity and yield stress of kaolinite slurry were reduced under high Ca²⁺/Mg²⁺ concentration. The apparent viscosity of slurry containing Mg²⁺ was lower than that of slurry containing Ca²⁺, but the yield stress of slurry containing Mg²⁺ was higher than that of slurry containing Ca²⁺. Turbidity results showed that Ca²⁺ have a stronger turbidity removal effect on kaolinite suspension than Mg²⁺. The agglomeration of kaolinite in the presence of Ca²⁺ was greater than that in the presence of Mg²⁺. The DLVO theoretical calculation results indicated that there was strong attractive energy between silica face-alumina face, silica face-edge face and edge face-edge face under 1 mmol/L Ca²⁺/Mg²⁺. There were repulsive energy barriers between the silica face-silica face, as well as between the alumina face-alumina face and alumina face-edge face. However, there was an attractive energy between the alumina face-edge face under 1 mmol/L Mg²⁺. The kaolinite agglomeration was a basal face-basal face (F-F) structure with tight and large under 1 mmol/L Ca²⁺, but the kaolinite agglomeration was F-F and edge face-basal face (E-F) structure with loose and large under 1 mmol/L Mg²⁺. The E-F structure in the presence of Mg²⁺ caused high yield stress of kaolinite slurry. Under high ions concentration, there was a weak attraction or repulsion between basal faces of kaolinite, but there was an attractive effect between the edge faces. The kaolinite agglomerates were edge face-edge face (E-E) structure with small and even dispersed, resulting in a low viscosity of the slurry. The conclusion of this study provides a basis for regulating the rheological properties of rich-clay slurry during mineral processing.