Growth Kinetics of Metallic Iron Phase in Coal-based Reduction of Oolitic Iron Ore

To understand the growth mechanism of metallic iron phase an oolitic iron ore was reduced isothermally by coal under various experimental conditions to examine the metallization process. The microstructural characteristics of metallic iron were investigated using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The grain size of metallic iron was measured by image analysis and the growth kinetics was analyzed based on the classical phenomenological kinetic theory. Experimental results showed that the metallization degree firstly increased and then gradually plateaued as reduction progressed. Metallic iron phase existed in the form of sphere-like grains inlaying in the slag phase. Reduction time and temperature had significant influence on the growth of metallic iron grain. The grain size of metallic iron increased with an increase in reduction time and temperature. The growth process of metallic iron grain was characterized by two stages with an inflection point at 30 min. The grain growth exponent and activation energy at the corresponding stage were determined, and the growth kinetics model was proposed to describe the metallic iron grain growth during coal-based reduction of oolitic iron ore. The metallic iron grain growth was controlled by chemical reaction of iron oxide minerals reduced to metallic iron at reduction time <= 30 min, and combined surface diffusion and metallic iron diffusion in the slag at reduction time >30 min.