Development of chitosan and fly ash-based zeolite composites for water softening

Abstract

Hard water is the denomination adopted to refer to the water with high Ca²⁺ and Mg²⁺ content. Due to the elevated cationic exchange capacity of zeolites, these materials are used as water softeners. However, restrains imposed from their powder form, and modified-packed form of pellets affects severely their efficiency in Ca²⁺ and Mg²⁺ capture. Such difficulty can be surpassed via the hierarchization of zeolitic structure. This work targets the production of magnetic and non-magnetic fly ash-based zeolite NaA composites using the biopolymer chitosan as matrix, and their application in water softening. The zeolite NaA was prepared using coal fly ashes as the main source of silicon and aluminum, via hydrothermal route synthesis. The magnetic and non-magnetic composites were prepared through the dripping of chitosan solution containing the zeolite NaA crystals, and/or magnetic particles from fly ashes into alkaline coagulant solution to obtain the beads The obtained materials were characterized using X-ray diffractometry (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and magnetometry (VSM). Water softening tests were performed by the contact of the materials with aliquots of Ca²⁺ solution at a concentration of 100 ppm. The characterization indicates the well succeeded synthesis of fly ash-based zeolite NaA, with the effective preparation of the composites. The softening tests showed the complete removal of Ca²⁺ from the aqueous media, confirming great potential of these material in water treatment.