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Mechanisms of surface reactions and dissolution of fluorite (111) surface in aqueous electrolyte solution

Semi-soluble in water [1], easy available crystals and well define crystallographic planes [2] make fluorite a good system for simultaneous study of the surface reactivity and dissolution. In the contact with aqueous electrolyte solution, fluorite surface is charged, and electrical charging is influenced by calcium and fluoride ions [3]. However, indirectly, the pH also affects the fluorite surface equilibrium and rate of dissolution [4]. For that purpose, fluorite (111) single-crystal electrode [5] was constructed and the inner surface potential (Ψ0) as a function of pH, ionic strength and concentrations of Ca2+ and F– ions was examined. Inner surface potential directly affects the state of ionic species bound to certain surface plane and is thus essential parameter governing interfacial equilibrium [6]. The kinetics of dissolving (111) fluorite plane was investigated by monitoring the concentrations of Ca2+ and F– ions in solution for 24 hours of dissolution by in situ measurements with fluoride and calcium ion-selective electrode. Furthermore, the influence of dissolving on the morphology of (111) fluorite plane was examined by AFM. A model of the surface reactions and surface dissolution for the (111) fluorite/aqueous electrolyte solution interface was proposed.

fluorite, surface properties, dissolution kinetics, surface potential

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