Abstract: In the process of MAP formation, the influence and change of pH of solution were very obvious，and then, the effects of pH on MAP production, yield and crystal type were studied. In the range of pH8~11, with the formation of MAP crystals, the pH of the solution dropped sharply, and quickly dropped to about 7 after 8min of addition. However, when the pH increased to 12, the pH of the solution changed slowly, but the impurities in the precipitate increased significantly, and basically no MAP crystal was formed. The results of yield experiment show that pH10 was the best condition for MAP production, which yield was high to 2.52g, and the impurities in the precipitate are few, the component was mainly magnesium ammonium phosphate. The SEM and XRD analyses showed that the composition of the precipitate were different with pH. It was mainly magnesium ammonium phosphate at pH8~10, however, the compositions of the precipitates were more complex at pH11~12, which were mainly the mixture of magnesium phosphate, magnesium hydroxide and ammonium magnesium phosphate. These results showed that the pH of solution has a significant effect on the formation of magnesium ammonium phosphate crystals.
