Synthesis and characterisation of pure zeolite A from fly ash for removal of lead and cadmium

ABSTRACT

The primary objective of the present study is synthesis a highly crystalline zeolite A of pure phase using fly ash obtained from a thermal power station located in South India. The mineral composition of fly ash promotes the synthesis of zeolites, which are subsequently used in the treatment of wastewater. The composition of fly ash namely SiO₂, Al₂O_3, and Na₂O are enhanced to 88.01% through pre-treatment of original fly ash using HCl of 20% wt. and solid/liquid ratio of 20 during zeolite synthesis. The pre-treated fly ash was effectively converted to zeolite A by adjusting varying synthesis parameters including silica/alumina (Si/Al) ratio (0.8–1.2), hydrothermal synthesis time (3–12 h), and sodium hydroxide to fly ash (NaOH/FA) ratio (0.64–1.2). The fusion-assisted hydrothermal synthesis technique was employed to successfully transform fly ash into a pure phase zeolite A with a crystallinity of 95.01% by optimising the synthesis parameters. X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), Burner-Emmett -Teller (BET), and Fourier transform infrared spectroscopy (FTIR) methods were used for characterisation of synthetic zeolite samples. The findings unveiled a single-phase zeolite A with an excellent cation exchange capacity (CEC) of 218.66 meq/g and a high BET surface area of 108.59 m²/g. The efficacy of zeolite A towards heavy metal removal was investigated using Pb⁺² and Cd⁺² ions through batch experiments. The adsorption of Pb⁺² and Cd⁺² obeyed pseudo-second-order kinetics and the Langmuir model was found to provide a better description of adsorption isotherm. Synthetic zeolite A exhibited remarkable removal capacities of 277.78 mg/g and 87.729 mg/g for lead and cadmium, respectively. The experimental findings of the present study showcased the conversion of fly ash into a potent zeolite material with significant potential for the remediation of heavy metal-contaminated wastewater.

KEYWORDS:

• Adsorption kinetics
• fly ash
• heavy metal removal
• synthesis optimisation
• zeolite

Disclosure statement

No potential conflict of interest was reported by the author(s).