A ceramic Supported crosslinked polystyrene composite membrane has been prepared from its monomers using a dual initiator System. The nonionic hydrophobic membrane so prepared has been chemically modified by a low temperature (50 degrees C), single step reaction with chloroacetic acid. The carboxylated membrane has functional groups oil its surface making it negatively acid charged and highly hydrophilic in nature. The membranes (unmodified and carboxylated) have been used for the separation of hazardous chromium (VI) salt solution where observed and intrinsic rejection has been studied as a function of pressure and concentration of the feed solution. The intrinsic rejection has been determined by calculating the concentration at the membrane surface (C) using Speigler-Kedam model and osmotic pressure model. The observed rejection for the chemically modified membrane decreases with increasing pressure but the intrinsic rejection is found to be more than 80%, for all concentrations in the range of study. The experimental results have been fitted using Space-Charge model to obtain the membrane wall potential and the membrane surface concentration which are difficult to measure directly. The transport through the membrane capillaries has been described by the two dimensional model using Nernst-Planck equation for ion transport, Navier-Stokes equation and Poisson-Boltzmann equation for the radial distribution of potential. We have then presented a semianalytical series solution to the highly nonlinear Poisson-Boltzmann equation to reduce the computational time required to solve the Set Of Coupled differential equations. The effective wall potential of the carboxylated membrane was found to be -28.07 mV. (C) 2008 Wiley Periodicals, Inc.