Controlling the elasticity of calcite suspensions by ionic species

Abstract

Calcite is an extremely widespread material that can be found naturally in rocks and is employed in many industrial fields such as paper filling, pharmaceutical, art or construction. Understanding the mechanical properties of calcite suspensions is a first step to improve the workability of the paste as well as the final properties of solid mineral materials. Here, we show how a macroscopic quantity of the calcite suspensions, namely the elasticity, measured by rheological measurements can be linked to microscopic interactions, via DLVO analysis. Our pure calcite pastes are weakly attractive systems, showing a typical colloidal gel behavior, and characterized by an elastic shear modulus and a critical strain (Liberto et al. 2017). We have tuned the interaction forces between particles by addition of simple ionic species (Ca2+ and OH-). Rheological measurements are compared to DLVO calculations, obtained by chemical speciations and ζ potential measurements on dense suspensions. Addition of calcium hydroxide improves the initial workability of the paste by lowering the elastic modulus of the paste, which is further recovered upon carbonation in contact with atmospheric carbon dioxide. The degree of carbonation is monitored through pH measurements. Besides, we observe a minimum in the initial elastic response for a pH close to 12, correlated to a maximum in the electrostatic repulsion in the DLVO potential. Below this pH, the main effect is a change in surface potential with calcium concentrations, while at high pH, modifications of the ionic strength and Debye lengths are dominant.