Hydrolysis Mechanism of Water-Soluble Ammonium Polyphosphate Affected by Zinc Ions

Ammonium polyphosphate (APP) as a chelated and controlled-release fertilizer has been widely used in agriculture, and its hydrolysis process is of significance for its storage and application. In this study, the hydrolysis regularity of APP affected by Zn²⁺ was explored systematically. The hydrolysis rate of APP with different polymerization degrees was calculated in detail, and the hydrolysis route of APP deduced from the proposed hydrolysis model was combined with the conformation analysis of APP to reveal the mechanism of APP hydrolysis. The results show that Zn²⁺ decreased the stability of the P-O-P bond by causing a conformational change in the polyphosphate due to chelation, which in turn promoted APP hydrolysis. Meanwhile, Zn²⁺ caused the hydrolysis of polyphosphates with a high polymerization degree in APP to be switched from a terminal chain scission to an intermediate chain scission or various coexisting routes, affecting orthophosphate release. This work provides a theoretical basis and guiding significance for the production, storage, and application of APP.