Comparative study on the performance of two synthetic zeolite 4A on the removal of heavy metals from aqueous solution—effect of coal fly ash as Al and Si source

Pollution of water bodies from improper disposal of toxic metal contaminated effluents causes several problems for the environment. Several processes can be used to remove these metal ions from aqueous media, and the adsorption being the most efficient technique. In this process, a diversity of adsorbent materials is used, with the use of zeolite 4A emphasized in this study. This study aimed to evaluate the efficiency of zeolite 4A as an adsorbent material for the removal of Cu 2+ , Cd 2+ , Pb 2+ , and Zn 2+ from aqueous media. For this, zeolite 4A was synthesized by the hydrothermal route starting from two sources of precursors, one from standard reagents (ZA-P) and the other from coal fly ash (ZA), a residue from a thermoelectric industry plant in the state of Ceará (Brazil). Both materials were characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and cation exchange capacity techniques. The materials were subjected to batch adsorption tests with multi-element synthetic solutions of Pb 2+ , Cu 2+ , Zn 2+ , and Cd 2+ . The parameters investigated in the adsorption experiments were the dosage effect, contact time, and adsorption equilibrium. Flame atomic absorption spectroscopy was used for metal ion quantitation. The characterization results showed that both ZA-P and ZA yielded mainly the crystalline phase of zeolite 4A. In the dosage test, a weight of 100 mg promoted the best results for both ZA-P and ZA, with ZA achieving superior removal results. Pb 2+ was more efficiently removed at 95% for ZA and 93% for ZA-P. In addition, at the time of contact, it was observed that ZA reached equilibrium faster (10 min) than ZA-P (50 min). In the adsorption equilibrium, the Langmuir model was able to describe almost all results, only the Zn 2+ for ZA was modeled by the Freundlich isotherm. The affinity of metal ions for materials followed the order (Pb 2+ > Cd 2+ > Zn 2 > Cu 2+ ) for ZA-P and (Pb 2+ > Cd 2+ > Cu 2+ > Zn 2+ ) for ZA. Finally, it is concluded that both products have potential for application as metal adsorbents of Cu 2+ , Cd 2+ , Pb 2+ , and Zn 2+ in aqueous solutions and that coal fly ash can be recycled to obtain zeolite.