Natural Mordenite Derived Zeolites: Synthesis,Formation,and Their Evaluation in Cr(III) Removal from Tannery Wastewater

Abstract

The synthesis of zeolites from natural mordenite, their subsequent forming process, and their evaluation in a Cr(III) removal process from tannery wastewater is presented. Mordenite is an abundant naturally occurring zeolite with relatively low cation exchange properties. Zeolite synthesis from mordenite was carried out in a larger reactor than commonly employed autoclaves. Synthesized products were identified by X-ray diffraction (XRD), and zeolite extrudates were characterized by their chromium exchange capacity (CrEC), mechanical, and textural properties, which were optimized as a function of binder composition. A FAU zeolite-rich product was obtained under controlled synthesis conditions. FAU-type zeolite is a nanoporous material (pore opening of ∼0.74 nm), which presents high cation exchange capacity. The use of silicate–urea-based binders enabled the production of FAU-type zeolite extrudates with CrEC (0.64 mEq · g⁻¹) and compressive strength (143 kg · m⁻²) appropriate for their use in Cr(III) removal processes from aqueous solution; these values were as high as those found for commercial zeolite extrudates (0.65 mEq · g⁻¹ and 66 kg · m⁻², respectively). Columns packed with the prepared zeolite extrudates, exhibited high performance for Cr(III) removal from synthetic and diluted tannery wastewater (pH 3.5). Thus, FAU-type zeolite extrudates obtained from natural mordenite appear as promising ion exchangers for tannery wastewater treatment and as a feasible alternative to the commercial ion exchangers.