Influence of surface conductivity and Reynolds number on the zeta potential of calcite

Abstract : Calcite is one of the most common minerals on the earth’s surface and controls the chemical composition of ground and surface waters. Its reactivity in water is intimately related to the surface complexation reactions occurring in the electrical double layer (EDL) around the grains. The properties of the EDL cannot be directly measured, but they can be estimated using the zeta potential, which is the electrical potential at the shear plane between the grains and the surrounding water. The zeta potential of calcite is usually deduced from streaming potential experiments, but in dilute water (ionic strength < 0.1 mol L-1) and inertial laminar flow, the Helmholtz-Smoluchowski (HS) equation may considerably underestimate the intrinsic zeta potential because of surface conductivity and Reynolds effects. A triple layer model (TLM) is used to calculate the electrical potential and ions distribution at the calcite/water interface and the apparent zeta potential deduced from the HS equation is corrected for the surface conductivity of the Stern and diffuse layer and the Reynolds number. The corrected zeta potential corresponds to the electrical potential at the beginning of the diffuse layer computed by our TLM, confirming our calculations of intrinsic zeta potentials of larger magnitudes than apparent zeta potentials.