(59n) Ionic Transport in Reverse Osmosis Membrane

Nano-filtration membrane (NF)/ reverse osmosis membrane (RO) can be described by extended Nernst-Planck equation, where separation is a result of diffusion, convection and electro-migration of ionic species. Poisson-Boltzmann equation is used to describe potential profile. Ionic species are electro-neutrality everywhere in bulk of feed channel, and potential of solution is zero in this region. In electrical double layer region where is close to the charged membrane surface, negative static charged trends to repel co-ions and attracts counter-ions, and distinct ionic concentration distribution is formed. Co-ions and counter-ions would be balanced inside membrane, where potential change is assumed to be linear. We assume electro-migration effect in permeate site is minor. It is noticed from the numerical solution that the rejection of chloride was lower than the rejection of sodium throughout membrane. The rejection of both ions increased as the volumetric permeating flux based on membrane area increased. An extension to multiple species shows that fixed charged membrane has a priority to reject divalent, sulfate, ions more than monovalent, chloride .