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

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.