A phenomenological mass transfer approach in nanofiltration of halide ions for a selective defluorination of brackish drinking water

Our article deals with the possibility to treat high fluorinated brackish drinking water using nanofiltration (NF). Our approach is based on the phenomenological model of Spiegler, Kedem and Katchalsky (SKK) under dilute solution condition and neglects the charges carried by the membrane used (denoted NF45 from Dow, USA). We have calculated the phenomenological parameters σ (the membrane reflection coefficient) and Ps (the solute permeability), and observed that σ can be linked linearly to the hydration energy of the halide ions. Furthermore, Ps was appeared to be linked to the type of electrolyte. The σ values are highly dependent on the anion present in the salty solutions. If NF is generally used for elimination of divalent ions, the present work describes its potential to selectively separate the following single halide salts: NaF, NaCl, NaI, LiF and LiCl. We have observed for the first time that a selective defluorination can occur using a NF membrane. Furthermore, we have developed a very simple method, following the permeate salt concentration versus the reverse of the permeate flux, to quantify separately both parts of the mass transfer occurring in NF: convection and/or solution–diffusion.