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

Coexisting ammonium (NH-N) and phosphate (PO-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/CA), which was constructed by incorporating Mg into cement-based material CA via solid-state reaction, was employed in the simultaneous removal of NH-N and PO-P. Considering the wastewater with unbalanced N/P ratio and fluctuant pH, the effect of multiple factors (Mg/CA 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 NH removal by Mg/CA was: temperature > Mg/CA dosage > initial NH concentration > pH > initial PO concentration; the impact order on the PO removal was: initial PO concentration > Mg/CA dosage > temperature > pH > initial NH concentration. The maximum removal amount of NH (54.13 mg g) and PO (56.47 mg g) were obtained at: Mg/CA dosage = 3 g L, initial NH concentration = 160 mg L, initial PO concentration = 160 mg L, temperature = 308 K, and pH = 7. In addition, the possible interactive influence mechanisms were elucidated in depth. Mg played a major role in the PO removal by forming struvite (MgNHPO·6HO) and newberyite (MgHPO·3HO). OH released from Mg/CA hydration mainly contributed to NH removal. This work showed that Mg-rich CA is a promising candidate for simultaneous removal of NH and PO, shedding light on practical water remediation.