  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.
