Synthesis of zirconium-modified Merlinoite from fly ash for enhanced removal of phosphate in aqueous medium: Experimental studies supported by Monte Carlo/SA simulations

Elevated concentrations of nutrient in wastewater discharge can lead to severe imbalance water-ecosystems due to eutrophication, therefore, efficient and cost-effectiveness remediation strategies are urgently required. This work reports the feasibility of using zirconium-modified Merlinoite (Zr@Merl) obtained from Mexican coal fly ash (CFA) for the removal of phosphate ions from aqueous solutions. Direct method and soft reaction conditions were employed to synthesis Merlinoite (Merl) in more than 100% yield related to CFA. Further, the Merl surface was modified by ZrO2+ through the microwave-assisted process at 130 degrees C for 5 min. Inductively coupled plasma confirmed the increase of Zr(IV) content up to 7.07 wt% while the potassium concentration decreased from 11.53 to 5.66 wt%, indicating the successful exchange in the Merl surface. The pristine Merl and its Zr@Merl were physicochemically characterized. X-ray photoelectron spectroscopy analysis before and after phosphate ions adsorption was done to elucidate the involved adsorption mechanism. The adsorption behavior was explained by pseudo-second-order and Freundlich models. The maximum adsorbed amount was 67.72 mg g(-1). The results proved that the involved mechanisms for the phosphate sorption onto Zr@Merl were electrostatic attractions followed by coordination reactions. Further, a theoretical study using Monte Carlo/SA simulations was applied to get insight into the interaction between Merl and Zr@Merl surface groups and H2PO4- ions. The simulation results demonstrate the favorable adsorption, more stable and spontaneous, onto Zr@Merl than Merl. Overall, Zr@Merl could serve as a cost-effective and reusable adsorbent material for the phosphate recovery from aqueous effluents.