Characterization of chemically modified zeolite-clay composite membranes using separation of trivalent cations

Three zeolite-clay composite membranes have been used for separation of chloride salts of trivalent cations (FeCl3 and AlCl3) in an unstirred batch cell. The membranes used are the unmodified analcime zeolite (Z1), the modified zeolite containing oxynitride groups (Z2) and the modified zeolite containing imine/amine groups (Z3). The experimental data has been analyzed by the irreversible thermodynamics approach and the concentration polarization is also taken into account in the model used. The calculations show that modification causes an increase in the intrinsic rejection (from ∼70% for the unmodified to ∼94% for the Z2 and ∼96% for the Z3 membrane in case of FeCl3 solution and from ∼84% for Z1 to 90% for both Z2 and Z3 membranes in the case of AlCl3 solution) of the membrane and a decrease in the solute permeability. The reflection coefficients of the modified membranes are found to be more than that of the unmodified membrane and that of Z3 membrane is found to increased to a value of about 1 (σ=0.978 for FeCl3 and σ=0.99 for AlCl3).