New basis for adsorption of ionic pollutants onto modified zeolites

Abstract

This work presents studies of ions uptake from aqueous solutions by natural zeolites showing and validating techniques using pre-treated, modified, saturated zeolites and in the form of floc, with polymeric flocculants. Powdered zeolites (from Chile) were pre-treated with Na + ions (NaCl) following modification (adsorption by ionic exchange) with Ba 2+ ions. Batch adsorption studies of sulphate ions were performed with this treated material in the flocculated and powdered forms. Zeolites samples (approximately 48% clinoptilolite and 30% mordenite) were prepared and characterized by their particle size distribution ( d p: 25.4 μm), moisture (2.5%), porosity (0.89), specific surface area (80 m 2 g −1), specific mass (2.2 g cm −3), zeta potential (pie = pH about 1.8), cation-exchange capacity (1.08 meq NH 4 + g −1), microstructure and mineralogical composition. Adsorption studies showed that this natural zeolite does not adsorb sulphate ions, but after the treatment (with Ba 2+ ions) the zeolite (now Ba–Z) was able to uptake the sulphate significantly. The adsorption capacity was not influenced by the medium pH showing that the mechanism involved appear to be proceeding as a chemisorption reaction. Hence, sulphate ions adsorption showed high process kinetic (0.24 min −1) followed by a first-order reaction kinetic model and the data fitted a Langmuir isotherm model; q m and K parameters of 1.3 meq g −1 and 0.1 L meq −1, respectively. An interesting feature was the reuse of the saturated adsorbent materials as new adsorbents. Thus, the BaSO 4–Z (Ba–Z, loaded with sulphate ions) uptakes Ba 2+ ions again and this Ba 2+ bearing zeolite (BaSO 4–Ba–Z) showed, again, a high capacity of sulphate ions adsorption ( q m : 1.1 meq g −1). Moreover flocs of Ba–Z formed with a conventional flocculant (ionic polyacrylamide) showed high sulphate adsorption capacity ( q m : 1.1 meq g −1) and the results were not affected by the flocculant. Again, the saturated flocs were reused as adsorbents for Ba 2+ ions and subsequently for sulphate ions (last stage studied) showing a high adsorption capacity ( q m : 1.2 meq SO 4 g −1). It is believed that this new adsorption basis and reuse as pre-treated and modified zeolites, as powder or flocs form, broaden the applications in the area of adsorption of pollutants on natural zeolitic adsorbents.