Exploring efficiency and regeneration of magnetic zeolite synthesized from coal fly ash for water treatment applications

This study investigates novel synthetic magnetic zeolites from coal fly ash (CFA) and laboratory-grade LTA zeolite enhanced with nano magnetite particles for the remediation of heavy metal ions (Pb²⁺, Cu²⁺, Zn²⁺, Ni²⁺) from wastewater. Utilizing a continuous flow system with a laboratory scale Wet High Intensity Magnetic Separator (WHIMS), heavy metal removal and magnetic particles’ recovery from the treated solution was investigated in a process that could be appropriate to real-world systems. The adsorption performance was investigated under various operational conditions, maintaining a consistent selectivity order of Pb > Cu > Zn > Ni, repeating the selectivity order found in previous study of magnetic CFA zeolite in batch systems. Moreover, magnetic CFA zeolite was shown to be a more effective adsorbent when compared to magnetic LTA zeolite. Thus, when tested in continuous flow system under selected conditions, magnetic CFA zeolite removed 63 % Pb, 37 % Cu, 13 % Zn, and 7 % Ni while magnetic LTA zeolite removed 25 % Pb, 16 % Cu, 6 % Zn, and 3 % Ni. Furthermore, treated solution that passed through WHIMS did not contain any zeolite particles, as they were successfully captured in the metal grid.

Additionally, regeneration of metal-laden magnetic zeolites through desorption experiments was investigated by enhancing the ion-exchange process using a saturated NaCl solution. The results indicated that Pb, Zn, and Ni ions were fully desorbed from magnetic zeolite, while approximately 70 % of the Cu remained to the sample. The Cu remained in the sample may be attributed to its partial adsorption onto the carbonized binder, a highly oxygenated graphenic structure, which does not readily release the adsorbed Cu ions. As these findings highlight the difference between adsorption and desorption selectivity order, further investigation into the topic would be beneficial.

This research underscores the operational advantages of using magnetic LTA and CFA zeolites in industrial water treatment applications, illustrating their high adsorption capacity and straightforward desorption processes.