Nanofiltration is a membrane process which is used to separate charged molecules such as ions. Even if this process is well known, there is no mean to predict the performances of a given separation. The aim of this paper is to present a two-dimensional model called "pore and polarization transport model" which includes all the steps of the ions transfer. The membrane transport modeling is based on the classical one-dimensional vision coupling the Donnan, steric, and dielectric exclusions with the extended Nernst-Planck transport equation. But the originality of this study comes from the modeling of the transport through the polarization layer. The model used in this study is an improvement of the previous version, which includes an electrical gradient within the polarization layer allowing the prediction of polarization layer establishment even for ionic mixtures. The purpose of this article is to describe the model accurately before validating it with various ionic solutions. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 985-995, 2011