Space-charge model has been used for the analysis of separation of chromic acid by the charge zeolite-clay composite membranes. A series solution of the Poisson-Boltzmann equation for symmetrical electrolytes has been developed in this work and it leads to considerable reduction in the computation load. A new scheme for the solution of space-charge model has been introduced in which solute concentration at the membrane surface, effective pore radius and wall potential are taken as adjustable parameters to fit experimental data. The effective pore size and pore-wall potential of the membrane is determined by fitting the experimental data on the separation of chromic acid using the space-charge model. The pore length is estimated from the cross sectional SEM photograph and the experimentally determined porosity value is used in the simulation. Effective pore size value thus, determined lie inside the pore size range determined using the independent bubble point method. The permeate flux calculated from the model matches very well with the experimental values. (C) 2004 Elsevier B.V. All rights reserved.