Modeling of separation of aqueous solutions of FeCl 3 and AlCl 3 by zeolite–clay composite membranes using a space-charge model

Abstract

In our earlier work, we reported the separation of FeCl 3 from its aqueous solution and AlCl 3 from its aqueous solution by analcime zeolite ( Z 1) membrane and its nitrated ( Z 2 membrane) and aminated ( Z 3 membrane) forms. Experimental data on the separation of aqueous solutions of FeCl 3 and AlCl 3 by zeolite–clay composite membranes has been simulated using the two-dimensional space-charge model. The computational requirement of the model has been considerably reduced by first obtaining a series solution of the nonlinear Poisson–Boltzmann equation. The effective pore radius of the membrane is taken as the one that gives the best fit to the experimental data, while the pore length is determined from the SEM photograph of the cross-sectional view of the membrane. The effective pore radii of the Z 1, Z 2, and Z 3 membranes for FeCl 3 solute are found to be 8.0, 7.0, and 5.0 nm, respectively, while for AlCl 3 they are 4.5, 2.5, and 2.5 nm, respectively. These values are much less than the average of the pore size range values determined independently in an earlier work using the bubble point method and indicate partial blocking of the pores by these salts. The effective pore radius is larger for FeCl 3 as compared to AlCl 3 and decreases on modification. The intrinsic rejection is also found to decrease on modification. The permeate flux calculated from the model matches very well with the experimental values.