Growth Behavior and Size Characterization of Metallic Iron Particles in Coal-Based Reduction of Oolitic Hematite-Coal Composite Briquettes

To reveal the growth behavior and size characterization of iron particles in coal-based reduction, we reduced oolitic hematite-coal composite briquettes at various temperatures, durations and ore size fractions. The degree of metallization and microstructure of the reduced briquettes and the characteristic of iron particle size were investigated through chemical composition analysis, scanning electron microscopy, energy dispersive spectroscopy, and Bgrimm process mineralogy analysis. Results showed that iron oxides in the oolitic hematite ore were reduced to metallic iron from outer to inner layers; these oxides gradually grew into quasi-spherical iron particles with random distribution in the gangue. As reduction continued, iron grains agglomerated occurred, and iron particle clusters were formed in the form of quasi-spherical, chained, blocky, and clavate when they were viewed in the cross section. The boundaries among the iron grains of the iron particle cluster continuously faded and disappeared, and an iron particle with increased size and homogeneity was finally produced. The reduction temperature, time, and ore size fraction influenced the reduction of composite briquettes and iron particle size. The degree of metallization increased as reduction temperature was increased, reduction time was extended, or ore size fraction was decreased until the equilibrium of reaction was achieved. Moreover, the iron particle size gradually increased as reduction temperature was increased, reduction time was extended, or ore size fraction was decreased.