Experimental Approach for the Characterization of Low-Grade Phosphate Ore Performance in Isothermal Conditions

摘要

The vacuum carbothermal reduction behavior of low-grade phosphate ore was examined using coke powder as a reducing agent. The findings show that the reduction ratio of phosphate ore and the volatilization ratio of P increased with increasing temperature and holding time, of which the reduction temperature had a more significant influence on the reduction degree compared with the holding time. Above 1250 degrees C, the reaction rate was very high, but after 30 min, the rate of reaction began to slow. At 1080 degrees C, Ca-5(PO4)(3)F first reacted with a small amount of SiO2 in the ore sample to form Ca-3(PO4)(2), CaSiO3, and SiF4 (escaped in the form of gas), and Ca-3(PO4)(2) was subsequently reduced by C. When the temperature reached 1300 degrees C, a large amount of Ca-5(PO4)(3)F in the phosphate rock started to react with C to produce CaO, P-2 (g), CO (g), and CaF2. Via the mutual verification trial-and-error method, it was concluded that the unitary reduction process was under the control of the shrinking core model and diffusion, and the activation energies of the unitary reduction were 124.67 kJ/mol and 265.9 kJ/mol. Meanwhile, the volatilization of P was under the control of the diffusion and shrinking core model, and the activation energies were 604.77 kJ/mol and 339.49 kJ/mol.