Mechanism of growth of metallic phase in direct reduction of iron bearing oolites

Abstract

The direct reduction of oolites involves progressive growth of the metallic phase with temperature. Two orders of magnitude increase in particle size are observed at 1100 °C followed by the formation of a continuous metallic phase at 1250 °C. Two growth mechanisms were identified: below 1050 °C particle coarsening, and above 1050 °C the formation of phosphorus rich iron melt. It is shown that particle coarsening can be related to the formation of fayalite and hercynite bridges between particles of different sizes. Finally, the direct reduction and growth mechanisms were correlated to the oolite internal shell structure, spacing of goethite particles, and pore content and size distribution, using electron microscopy, mercury porosimetry, and image analysis.