Enhancing nutrient efficient recovery and utilization: Preparation of water-soluble polyphosphate ammonium from urea phosphate mother liquor and its release behavior, leaching characteristics

• APP slow-release fertilizer was prepared by urea phosphate mother liquor. • The prepared APP can effectively reduce the pH value of alkaline soil. • Acidity and high temperature will accelerate the hydrolysis of prepared APP. • The prepared APP can reduce nitrogen loss to a certain extent. Ammonium Polyphosphate (APP) is a novel water-soluble slow-release fertilizer. However, the current production cost of low water-soluble APP is relatively high. In this study, water-soluble APP was successfully prepared by using urea phosphate mother liquor as raw material and urea as a condenser through the processes of purification, concentration, drying, pulverization, and polymerization. Under the optimal conditions, the resulting product had a phosphorus pentoxide (P 2 O 5 ) content of 51.70%, a total nitrogen content of 19.46%, a polymerization rate of 94.21% and an average polymerization degree of 3.79. XRD analysis confirmed that the product APP exhibited an amorphous structure. In addition, the prepared APP was applied in various soils, and the results indicated that APP could effectively reduce the pH value of alkaline soils . The available phosphorus content of alkaline soil is 22.75% and 29.46% higher than that of acidic soil, respectively. Acidity and high temperature will accelerate the hydrolysis of APP, resulting in more phosphorus being fixed by soil. The percentages of total nitrogen loss in urea, monoammonium phosphate (MAP), commercially available APP and self-made APP for forty days were 73.10%, 74.20%, 55.55% and 56.71%, respectively. APP can reduce nitrogen loss to a certain extent compared with traditional fertilizers. In general, the preparation of APP from urea phosphate mother liquor is conducive to the high-value utilization of urea phosphate mother liquor, and opens up a new way for low-cost preparation of APP.