The ammonia nitrogen recovery ratio from wastewater was investigated in the presence of NaOH plus Mg(OH)2 at the molar ratio of 1:1 during MAP pyrolysis, and the concentration of View the MathML source and Mg2+ residues in the supernatant were analyzed. Acidolysis was used during the MAP pyrolysate recycling to solve the problem of Mg2P2O7 and Mg3(PO4)2 accumulation. Characterization of magnesium hydrogen phosphate (MgHPO4), Mg2P2O7 and Mg3(PO4)2 was performed by FTIR, XRD, and the grain size of MAP was calculated using the Scherrer equation. Pyrolysis and formation of MAP derivatives were also visualized.