Employment of 31P MAS NMR for the Identification of Amorphous Precipitation Products Obtained from the MAP Process

Abstract

Abstract In order to recover aqueous ammonium (NH4+) and phosphate (PO43−) from wastewater, these ions were immobilized with MgO and MgCl2 into an insoluble solid. Analysis by X-ray diffraction (XRD) showed that the insoluble solid was a single phase of ammonium magnesium phosphate (Mg(NH4)PO4·6H2O: MAP). Therefore, the present process has been commonly known as the MAP process. However, analysis by the solid-state 31P magic-angle spinning nuclear magnetic resonance (31P MAS NMR) of the insoluble solid revealed that the solid contained various phosphate compounds together with crystalline MAP. The results indicated that the solids obtained from the MAP process should be carefully identified, since they are considered to be utilized as a slow-acting fertilizer.