Characterization of nanofiltration membranes used for the separation of aqueous dye-salt solutions

The process of desalination of aqueous dye-salt solutions by polymeric nanofiltration membranes using commercially available modules was studied. The influence of dye and salt concentration on the salt rejection and flux as well as comparison of individual NF membranes used for desalting purposes are presented. An extended Spiegler-Kedem model including the Donnan exclusion mechanism and the term of concentration dependence of salt permeability was used for predicting salt rejection. The experimental results reveal a negative salt rejection during desalination and the influence of this phenomenon on permeate flux. It is also shown that the model can sufficiently predict salt rejection even at high concentration typical of desalting process.