Metallurgical and Materials Transactions B | 2021
Reaction Mechanism of Low-Grade Phosphate Ore During Vacuum Carbothermal Reduction
Abstract
The non-isothermal kinetic method was used in this manuscript to obtain the reaction models by fitting the reduction ratio of low-grade phosphate ore and the volatilization ratio of phosphorus. And the reaction mechanism of vacuum carbothermal reduction of low-grade phosphate was investigated by combining XRD, SEM, EDS, chemical analysis, and FactSage7.2. Ca5(PO4)3F first reacted with a small amount of SiO2 in the ore sample at 1080 °C to form Ca3(PO4)2, CaSiO3, and SiF4 (escaped in the form of gas). Then, Ca3(PO4)2 was reduced by C. When the temperature reached approximately 1300 °C, a large number of Ca5(PO4)3F in ore sample began to react with C to form CaO, P2(g), CO(g), and CaF2. Through the mutual verification of Coats-Redfern and Šatava-Šesták methods, it is concluded that the unitary reduction process was under the control of the shrinking core model, and the activation energy of unitary reduction was 74.54±10.39 kJ/mol. The volatilization of P was under the control of the 3-D diffusion (anti-Jander), and the activation energy was 416.43±1.81 kJ/mol.