The Improved Phosphorus Solubility of Mechanochemically Activated Phosphate Rock and Its Effect on Soil-Available Phosphorus in Weakly Acidic Soil

Mechanochemical treatment is an effective and ecological way to treat medium and low-grade phosphate rock (PR) for fertilizer. To explore the phosphorus (P) solubility mechanisms of mechanochemically activated phosphate rock (MAPR) and its P supply capacity, we investigated the chemical properties and infrared spectroscopy (IR) characteristics of different types of MAPR and soil-available P using the chemical extraction method (2% citric acid), IR analysis and soil incubation experiment in this study. The results showed that the P solubility of magmatic, metamorphic and sedimentary types of MAPR increased by 7.76-13.67, 0.6-1.64 and 0.91-2.68 times, respectively, compared with the initial PR. The IR analysis demonstrated that the isomorphous substitution (B-type of CO32- for PO43- and OH- for F-) occurred in the apatite and beta-Ca(PO3)(2) was generated with better P solubility. The dynamic changes in soil-available P (Bray and Kurtz method) treated by MAPR significantly increased by 3.81-6.57-, 2.49-5.4- and 4.98-8.39-fold, respectively, within 100 days in red soil (pH 5.94), compared with the initial PR. In conclusion, the significant increase in P solubility of MAPR and soil-available P in weakly acidic soil was due to the improved reactivity of MAPR during the process of mechanochemical activation.