Abstract: International audience ; This work addresses the specific interactions between titania membrane and fluoride anions during ultrafiltration operation. In general, the salt transmission increases with salt concentration when pure salt-water solutions are ultrafiltrated, except for fluoride-based salts observed in our study, for which transmission decreased at low concentrations. This phenomenon was only observed with titanium dioxide membrane. A numerical tool based on a physical description of ionic mass transfer in porous material (generalized Nernst-Planck approach) was used to explore the modification-induced changes due to fluoride anions. Numerical investigations showed a modification of the electric charge of the membrane surface in the pore at low fluoride concentrations. This phenomenon screened the electric effect in a completely reversible way, and then enhanced the ion mass transfer through the porous membrane. These modifications can be explained by the substitution of oxygen atom (providing the surface electric charge) with a fluoride ion which was screening the electric charge and facilitated the ion transfer.
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