The Additive Effect of K 2 CO 3 -NiSO 4 on the Carbothermal Reduction Process of Phosphate Rock and SiO 2

In this study, K 2 CO 3 and NiSO 4 were used for doping the carbothermal reduction system of phosphate rock, and the effect of a K-Ni composite catalyst on the carbothermal reduction of phosphate rock was studied. The effects of the SiO 2 -CaO mass ratio, carbon excess coefficient, and the mass ratio of K 2 CO 3 -NiSO 4 loading on the carbothermal reduction of phosphate rock were investigated. At the temperature of 1300 °C and the reducing time of 90 min, the optimal reaction conditions were as follows: SiO 2 -CaO mass ratio, 1.1; coke excess factor, 1.1; mass of the supporting K 2 CO 3 -NiSO 4 , 10% of coke mass, and the mass ratio of K 2 CO 3 -NiSO 4 loading of 6/4. The maximum values of phosphorus conversion were 66.45% and 65.34%, when single components K 2 CO 3 and NiSO 4 were added, respectively, and the composite dopants increased phosphorus conversion by 4.5% and 5.61%, respectively, indicating that composite dopants compared with single dopants have certain advantages. Kinetic analysis indicated that the reaction order was not changed by the coke-supported K 2 CO 3 -NiSO 4 and remained in accordance with the first-order reaction law, and the activation energy decreased by 39.49 kJ/mol from 253.58 kJ/mol to 214.09 kJ/mol, compared with the unsupported system. In order to ensure that the conversion of phosphorus meets the requirements, the residence time of reactants in yellow phosphorus production by an electric furnace method is generally 4 h, and the residence time of general materials is more than 4 h in the existing industrial production of the kiln phosphoric acid process. Therefore, the reaction time was increased to 4 h, and the actual kiln process for phosphate production was simulated. Finally, at 1300 °C for 4 h, SEM analysis were used to determine whether the slag phase was discharged in the form of solid sintering and whether it met the slag discharge requirements for the kiln method.