Concentration-polarization in nanofiltration of low concentration Cr(VI) aqueous solutions. Effect of operative conditions on retention

Nanofiltration of Cr(VI) has been modelled by using the Spiegler-Kedem theory modified to include concentration-polarization. This allowed us the simultaneous evaluation of the three characteristic parameters of the model: reflection coefficient σ, solute permeability P and mass transfer coefficient Km from rejection experiments. Both σ and P are shown to decrease with concentration and to reach a relatively high concentration plateau. Other methods habitually used to evaluate the mass transfer coefficient have also been compared showing, when applicable, similar results for Km.