Two microporous alumina filters are studied. The pore size distributions and porosities are obtained by an extended bubble point method, Some asymmetries are detected in their structures while the structural parameters and permeabilities are close to the nominal values. The frequency distributions are narrow and substantially Gaussian. The membranes are bathed by several diluted aqueous solutions of LiCl at 298 K. The equations of transport through these microporous membranes (Nernst-Planck, Navier-Stokes, Poisson, and charge and mass conservation laws) numerically solved, under the adequate limit conditions, are used to obtain the electrokinetic coefficients for an assumed mean pore size. The streaming potential is measured, making it possible to obtain the adsorbed surface charge density (adsorption isotherm) as a function of concentration. An heterogeneous adsorption mechanism has to be assumed. The corresponding Freundlich isotherm is corrected, in order to take into account the complex structure of the electrical double layer, allowing the calculation of the proper charge of the membrane. This proper charge seems to be negligible in our case, whereas, the average adsorption free energy and the maximum number of accessible sites are evaluated being relatively small, according to the hydrophillic character assumed for the membrane.