Influence of surface conductivity on the apparent zeta potential of calcite

TL;DR

This study investigates how surface conductivity affects the measurement of calcite's zeta potential, revealing that traditional methods underestimate it, especially in dilute solutions, and proposes a corrected model for accurate estimation.

Contribution

The paper introduces a streaming potential model that accounts for surface conductivity, improving the accuracy of zeta potential measurements for calcite.

Findings

HS equation underestimates calcite zeta potential in dilute solutions

Surface conductivity significantly influences streaming potential measurements

Basic Stern model accurately predicts corrected zeta potential

Abstract

Zeta potential is a physicochemical parameter of particular importance in describing the surface electrical properties of charged porous media. However, the zeta potential of calcite is still poorly known because of the difficulty to interpret streaming potential experiments. The Helmholtz-Smoluchowski (HS) equation is widely used to estimate the apparent zeta potential from these experiments. However, this equation neglects the influence of surface conductivity on streaming potential. We present streaming potential and electrical conductivity measurements on a calcite powder in contact with an aqueous NaCl electrolyte. Our streaming potential model corrects the apparent zeta potential of calcite by accounting for the influence of surface conductivity and flow regime. We show that the HS equation seriously underestimates the zeta potential of calcite, particularly when the electrolyte is diluted (ionic strength < 0.01 M) because of calcite surface conductivity. The basic Stern model successfully predicted the corrected zeta potential by assuming that the zeta potential is located at the outer Helmholtz plane, i.e. without considering a stagnant diffuse layer at the calcite-water interface. The surface conductivity of calcite crystals was inferred from electrical conductivity measurements and computed using our basic Stern model. Surface conductivity was also successfully predicted by our surface complexation model.