Influence of surface conductivity on the apparent zeta potential of calcite

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 HelmholtzSmoluchowski (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.

Modeling the evolution of complex conductivity during calcite precipitation on glass beads

“…A geochemical code written in Matlab was developed to compute the surface complexation model of Heberling et al (2014) (Li et al 2016). The details of the calculation procedure are written in Li et al (2016).…”

“…The details of the calculation procedure are written in Li et al (2016). The program combines aqueous complexation, surface complexation equilibria, surface charge density and mass balance conditions (Vancappellen et al 1993;Hiemstra & VanRiemsdijk 1996).…”

“…Table 3 summarizes, in matrix form, the set of equations relative to the calculation of surface and solution speciation for fixed values of pH and partial pressure of CO 2 (pCO 2 ). The value of the capacitance C 1 between the 0-plane and beta-plane is equal to 1.24 F m −2 (Li et al 2016).…”

“…The cementation exponent of the calcite particles and the porosity of the glass beads pack were taken initially as m = 1.35 and φ = 0.3, respectively. The cementation exponent of dispersed calcite crystals is typically between 1.3 and 1.5 (Guichet et al 2006;Li et al 2016). The parameter values of the complex conductivity model are summarized in Table 6.…”

“…In this study, a mechanistic model for the induced polarization of calcite is proposed, which depends on the surface charge density and ion mobility in the Stern layer, electrical potential at the onset of the diffuse layer, particle size distribution and shape. Our SIP model is combined with a basic Stern model (BSM) of the calcite/water interface (Li et al 2016). After a short review of the grain polarization model of Leroy et al (2008), the complex conductivity model is generalized to the polarization of different monovalent and multivalent counter-ions in the Stern and diffuse layers according to Lyklema et al (1983).…”