Effect of Potential-Determining Ions on Rheological Properties of Calcite Paste

The mechanical properties of calcite suspension are predominantly affected by different ions dissolved in solution. In this work, natural and synthetic calcites were employed to investigate the influence of potential-determining ions (PDIs) (Ca²⁺, Mg²⁺, OH^-, CO₃^2- and SO₄^2-) on the zeta potential and rheological behavior of calcite paste. Electric double layer (EDL) models were proposed to further interpret the ionic adsorption mode and zeta potential evolution. Experimental results show that moderate addition of the positive PDIs Ca²⁺ and Mg²⁺ significantly increases the positive charge of calcite and enhances paste flow. Calcite exhibits higher zeta potential in Ca(NO₃)₂ but lower viscosity in Mg(NO₃)₂, which is attributed to the different affinity of Ca²⁺ and Mg²⁺ for the calcite surface. As for the negative PDIs OH^-, CO₃^2- and SO₄^2-, they make the calcite negatively charged with the order of ξNa2CO3>ξNa2SO4>ξNaOH. The negatively charged calcite paste exhibits much higher viscosity, which is against the conventional DLVO (Derjaguin-Landau-Verwey-Overbeek) theory. Lattice site screening and specific attraction induced by negative PDIs may be the reason for the phenomenon. This work provides a comprehensive understanding on the correlation between ionic adsorption, surface charge and particle interactions. These theories are enlightening for calcite application in many areas such as paper manufacturing, wall coating and heritage conservation.