Recovering ammonium by treated and untreated zeolitic mixtures: A comprehensive experimental and modelling study

The recovery of ammonium (NH4+) from aqueous solutions by zeolite is attractive. In this study, the physicalchemistry of NH4+ adsorption process from aqueous solution by two zeolitic mixtures, either treated or not treated with NaCl, was assessed. Results suggested that the zeolitic mixture richer in mordenite and with high specific surface area adsorbed more NH4+ than the one richer in clinoptilolite and heulandite showing a lower specific surface area. NaCl treatment increased the amount of NH4+ adsorbed by the zeolitic mixtures. The higher amount of NH4+ adsorbed by the zeolitic mixtures treated with NaCl was explained by the low/high density water model accounting for cation exchange among the two kosmotropic systems: Na-enriched zeolitic mixtures and NH4+-enriched aqueous solution. The adsorption kinetics were best approximated by the bimodal pseudo-first-order model. The two sorption kinetic constants, k1 and k2 were related to the adsorption (mediated by k1) and the ion exchange (mediated by k2) processes. The fitting of NH4+ data to Langmuir-Sips model suggested that the NaCl treatment increased the number of active sites only of the zeolitic mixture with the large amount of mordenite. Thus, it is conceivable that modulation of NaCl treatment of zeolitic mixtures can be applied to obtain new materials for water remediation from NH4+ contamination.