Sodium polyacrylate mediated dispersion of calcite

Abstract

The stabilising action of sodium polyacrylate (NaPA) on colloidal dispersions of calcite has been investigated through measurement of viscosity, electrophoretic mobility and solution ion concentration. The dose of NaPA was in the range 0 to 28 mg per g of calcite and the dispersions were prepared at a solids content of 70% (by weight). The ionic strength of the dispersions increased with dose and was in the range ca. 5 to 500 mmol dm⁻³.

The stabilising action of the NaPA was evident from the sharp fall in viscosity observed at low levels of addition, and the invariance of this low viscosity throughout the remainder of the dose range.

Electrophoretic mobility was converted into zeta potential using the mathematical procedures of O’Brien and White; in this conversion the colloid particles were treated as spheres with a number average radius of 193 nm.

The stability of the dispersion at low levels of NaPA addition was quantified by DLVO theory and readily attributed to electric double layer repulsion. However, at higher levels of addition, and with the encumbent double layer compression, the DLVO theory was found inadequate.

Recent calculations have shown that the acknowledgements of an interparticle steric repulsion can generate increasing colloidal stability at higher NaPA doses and so reconcile theory with experiment.