Design and process regulation of CaO-SiO2-MgO-P2O5 based glass fertilizer from direct thermal activation of low-grade phosphate ore and phosphate tailings

A large number of low-grade phosphate ore have not been utilized, and applying them to fertilizer production can solve these problems. In this work, a process was developed for the production of fertilizer by phosphate tailings, and a system of CaO-SiO₂-MgO-P₂O₅ based on the composition of raw ore was built. The phase diagram of the system was calculated using thermodynamic software, the composition with respect to P, Ca, Mg, and Si as the basic components was explored and the melting properties of the materials in the phosphate system were determined. The high-temperature activation process of low-grade phosphorus ores and flux under different process conditions was studied, using the atmosphere lifting furnace to simulate the production process of glass fertilizer to carry out thermal activation experiments. Under the conditions of 1480 °C, melting time of 10 min and 2% K₂O high-activity glass fertilizer containing various nutrients can be obtained with reduced energy consumption, with the activation rates of P, Ca, Mg, and Si in glass fertilizer reaching 94.51%, 92.53%, 93.79%, and 95.04%, respectively. The influence of K₂O on the glass structure was determined and analyzed by XPS, SEM, and surface element solution characterization. The addition of K₂O changed the composition of oxygen and significantly lowered the polymerization degree of the structure.