Multifunctional Tailoring of Fertilizer Composites Directly Derived From Phosphate Rock

To address the critical challenges of depleting high-grade phosphate reserves and underutilization of calcium (Ca) and magnesium (Mg) resources in low-grade phosphate rock (LPR), herein, a novel phosphorus-sulfur mixed acid with urea (PSU) activation system for LPR to fabricate multifunctional fertilizer composites (MFCs) is developed. It is found that under optimized conditions, the activation efficiencies for P, Ca, and Mg reached 78.5%-98.3%. The characterization results including particle size analysis, scanning electron microscopy, and nitrogen adsorption-desorption isotherms indicated that after activation, MFCs possessed porous structures, endowing it with great adsorption capacity for nutrients. In this regard, MFCs exhibited superior slow-release properties, significantly reducing Ca and Mg leaching to 27.6% and 73.9%, respectively. In contrast to conventional fertilizers, MFCs substantially increased Chinese cabbage biomass by 11.5%-23.4% in pot experiments. Furthermore, the MFCs are shown to be environmentally friendly, posing no risk of heavy metal contamination to either soil or crops. Overall, this novel activation method developed in this study not only facilitated minimizing the discharge of industrial phosphorus by-products, but also remediating soil acidity and nutrient deficits caused by long-term NPK fertilization, offering a sustainable paradigm for integrated nutrient management and acidic soil amelioration.