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Surface Potential of Calcite in Aqueous Medium

Reactions at the calcite/aqueous electrolyte solution interface have an enormous impact on numerous natural processes. Contact of solid calcite particles or macroscopic calcite single crystal surfaces with aqueous electrolyte solutions results in the accumulation of ions at the interface and the formation of an electrical interfacial layer (EIL) [1]. Calcite single crystal electrodes (SCrEs) enable the evaluation of the inner surface potential (Ψ0) of defined (104)-oriented calcite single crystal surfaces [2]. These surfaces are the most stable one and they control the reactivity of natural calcite particles. In this study, the surface potential of the (104) calcite/electrolyte solution interface was investigated at different experimental conditions. For that purpose two types of calcite SCrE were constructed. The stability of the calcite SCrEs and the reproducibility of measurements with these systems were tested. Measurements of surface potentials were performed at non-equilibrium and equilibrium conditions of well-defined calcite/electrolyte solution/atmosphere systems. At non-equilibrium conditions, a series of potentiometric titrations was carried out to examine the surface potential of calcite in aqueous sodium chloride environment as a function of pH. Additionally, the influence of Ca2+ and CO32− concentration on the surface potential of calcite was investigated. Furthermore, the measurements of calcite SCrE potential at conditions where calcite dissolution is expected was used for monitoring the calcite dissolution process. The topography of the calcite single crystal surface used for surface potential measurements was examined by atomic force microscopy (AFM). Equilibrated aqueous suspensions of calcite were prepared in order to investigate the pH-dependency of the surface potential of calcite and at the same time avoiding or minimizing any possible dissolution or growth effects. Equilibrium conditions and composition of solutions required to achieve a certain pH and ionic strength were a priori calculated on the basis of thermodynamic modeling using PhreeqC 3.2 [3].

surface potential, calcite, surface complexation, electrical interfacial layer

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