Reduction behaviour of apatite in oolitic haematite ore using coal as a reductant

Abstract

An oolitic haematite ore containing 1.31% P was reduced in the presence of coal at temperatures ranging from 1473 to 1548 K. The reduction behaviour of apatite, which is the only P-containing mineral in the ore, was studied at different reduction conditions based on the thermodynamic analysis. Thermodynamic calculation showed that the SiO2, Al2O3 or SiO2–Al2O3 could decrease the standard Gibbs free energy and initial temperature of the apatite reduction significantly. The initial temperature of the apatite reduction decreased from above 1650 K to 1497, 1541 and 1419 K in the presence of SiO2, Al2O3 and SiO2–Al2O3, respectively. Experimental results indicated that the reduction conditions obviously affected the reduction behaviour of apatite. A higher reduction temperature, C/O molar ratio and a longer reduction time were favourable for the apatite reduction. The reduction degree of apatite reached 83.62% at 1548 K with a C/O molar ratio of 2.5 and after 60 min reduction. In addition, the reduction kinetics of apatite was investigated by common order reactions, and the corresponding kinetic parameters were computed according to the Arrhenius function. The results demonstrated that the most suitable mechanism for the apatite reduction was first-order reaction, and the apparent reaction rate of apatite reduction increased with increasing reduction temperature and C/O molar ratio. Furthermore, both the apparent activation energy and pre-exponential factor of apatite reduction decreased slightly with increasing C/O molar ratio.