Permeation data of cetyltrimethylammonium bromide (CTABr) in water by ultrafiltration (UF) through zircon membranes are reported as a first step in the knowledge of micellar enhanced ultrafiltration of heavy metals by cationic surfactants [1]. The experimental results are analysed using a model of diffusion in the membrane matrix based on the thermodynamics of irreversible processes (TIP). A comparison with the classical model of resistances in series indicates that these two approaches are consistent and that the TIP method leads to new insights into the observed resistances. The major insight relates to the understanding of the membrane resistance in terms of interactions membrane-permeants and permeants-permeants.