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

Abstract

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 β-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.