A novel magnesium-rich tricalcium aluminate for simultaneous removal of ammonium and phosphorus: Response surface methodology and mechanism investigation

Abstract

Coexisting ammonium (NH₄⁺-N) and phosphate (PO₄^3--P) in wastewater is one of the main causes of eutrophication, which poses severe risks to aquatic ecosystem and human health worldwide. Herein, magnesium-rich tricalcium aluminate (Mg/C₃A), which was constructed by incorporating Mg into cement-based material C₃A via solid-state reaction, was employed in the simultaneous removal of NH₄⁺-N and PO₄^3--P. Considering the wastewater with unbalanced N/P ratio and fluctuant pH, the effect of multiple factors (Mg/C₃A dosage, pH, initial contaminant concentration, and temperature) on the removal of both ions were systematically investigated by employing response surface methodology technique. The results demonstrated that the impact order of the factors on the NH₄⁺ removal by Mg/C₃A was: temperature > Mg/C₃A dosage > initial NH₄⁺ concentration > pH > initial PO₄^3- concentration; the impact order on the PO₄^3- removal was: initial PO₄^3- concentration > Mg/C₃A dosage > temperature > pH > initial NH₄⁺ concentration. The maximum removal amount of NH₄⁺ (54.13 mg g^-1) and PO₄^3- (56.47 mg g^-1) were obtained at: Mg/C₃A dosage = 3 g L^-1, initial NH₄⁺ concentration = 160 mg L^-1, initial PO₄^3- concentration = 160 mg L^-1, temperature = 308 K, and pH = 7. In addition, the possible interactive influence mechanisms were elucidated in depth. Mg²⁺ played a major role in the PO₄^3- removal by forming struvite (MgNH₄PO₄·6H₂O) and newberyite (MgHPO₄·3H₂O). OH^- released from Mg/C₃A hydration mainly contributed to NH₄⁺ removal. This work showed that Mg-rich C₃A is a promising candidate for simultaneous removal of NH₄⁺ and PO₄^3-, shedding light on practical water remediation.

Keywords: Ammonium (NH(4)(+)); Magnesium-rich tricalcium aluminate (Mg/C(3)A); Phosphate (PO(4)(3−)); Response surface; Simultaneous removal.