Removal of trivalent chromium contaminant from aqueous media using FAU-type zeolite membranes

This study demonstrates the rejection (>95%) of a toxic contaminant in tannery wastewater-Cr(III) from aqueous solutions by Faujasite (FAU)-type zeolite membranes. FAU membranes are hydrothermally grown from ZSM-2 seeds coated on both as prepared and mesoporous silica-coated porous supports (α-alumina disks and stainless steel tubular supports) and subsequently evaluated for Cr(III) removal from aqueous solutions by reverse osmosis (RO) process. The Cr(III) ions initially undergo ion exchange with the extra-framework Na⁺ ions in the membrane until saturation is realized. The subsequent entry of the ions is apparently prevented by the pore blocking effect of the sizably hydrated Cr(III) ions associated with the zeolite pores, thus enabling the membranes to serve as effective RO filters for the Cr(III) ions in the feed solution. In addition to this favorable ion filtration effect, the hydrophilic nature of the membranes simultaneously maintains a high flux of water through the membranes.