Structural studies of natural zeolites and optimizations for water hardness softening media

Abstract

This study was aimed at investigating the mineralogical composition and structural features of natural zeolites using XRF, XRD, TGA, FT-IR and SEM. Natural zeolites were subjected to acid-activation and subsequently with NaCl salt to enhance surface area for water hardness softening applications. Peaks around 3560 and 1650 cm^-1 belongs to O–H stretching and O–H bending vibrations which confirmed the presence of moisture within zeolite structures. This result was further supported by evolution of moisture above 108°C from thermogravimetric analysis. Fibrous structures which are full of rough texture were examined by SEM. The XRD pattern confirmed Stellerite and Barrerite compositions were dominant crystal structures. The mineralogical analysis determined by XRF showed SiO₂, Al₂O₃ and CaO were dominant oxides. The specific surface area of raw and acid-activated zeolites was estimated by the Sears’ method and hence, the experimental values are 10.2 m²Â·g^-1 and 35.8 m²Â·g^-1, respectively. Batch adsorption parameters such as contact time, pH, adsorbent dose and initial concentrations were studied and optimized. Maximum adsorption capacity (8.04 mg·g^-1) was recorded at optimum conditions. The experimental data was fitted-well with Freundlich isotherm model.