NiSO4 as Additive Effect on the Carbothermal Reduction Process of Phosphate Rock and SiO2

This study aims to solve the problems related to the kiln method in which the slag phase melts at high temperature and the phosphorus reduction rate is reduced at low temperature. This study also intends to determine whether the carbothermal reduction reaction of phosphate rock would be catalyzed using coke-supported NiSO4. The reaction conditions were optimized at 1300 °C and 60 min, and the results were as follows: SiO2–CaO mass ratio, 1.1; optimum coke excess coefficient, 1.1; and NiSO4 support, 5% of the coke mass. When the reaction time was extended to 4 h, the reduction rate of the coke-supported NiSO4 system increased from 75.56% to 90.68%, an increase of 15.12%. Scanning electron microscopy analysis of the reaction slag indicated that with coke-supported NiSO4 at 1300 °C, the slag phase exhibited no morphological change. Kinetic analysis indicated that the reaction order was not changed by the coke-supported NiSO4 and remained in accordance with the first-order reaction law, and the activation energy decreased by 29.1 kJ/mol from 255.65 kJ/mol to 226.55 kJ/mol, compared with the unsupported system. XRD analysis of the reaction slag indicated that the reflection of the material was significantly reduced; however, no new substances was formed with coke-supported NiSO4, which suggested that NiSO4 only acted as a catalyst and caused no change in the reaction process.