Effects of Roasting Conditions on the Microstructure and Grindability of Direct Reduction Products from High-Phosphorus Oolitic Hematite

High-phosphorus oolitic hematite is a refractory iron resource, and reduction roasting followed by grinding and magnetic separation is an important utilization route. The roasting stage determines the size and morphology of metallic iron in direct reduction products (DRPs), thereby affecting subsequent grinding. In this study, a high-phosphorus oolitic hematite was reduced with anthracite and limestone. The effects of reductant dosage (22–25%), reduction temperature (1150–1300 °C), and reduction time (40–130 min) on iron particle size, phosphorus occurrence, and relative grindability were investigated by SEM, XRD, SEM-EDS, and grinding tests. Increasing the reductant dosage refined the iron particles (D50: 209.2 to 62.7 μm) and increased the relative grindability from 0.876 to 1.107. Raising the temperature coarsened the particles (D50: 131.7 to 966.0 μm) and decreased the relative grindability from 1.214 to 0.695; EDS detected phosphorus signals in iron-rich regions at 1250 °C and above, although the form of phosphorus could not be resolved. Extending the time increased D50 from 171.3 to 468.5 μm and decreased the relative grindability from 1.086 to 0.847. LOI varied little and was affected by coal ash and residual carbon, so it was not used to quantify reduction extent. These results show that roasting conditions govern grinding behavior indirectly through iron particle size and phosphorus distribution, indicating that direct reduction and grinding should be considered as an integrated system. A condition of 23% reductant, 1200 °C, and 70 min is recommended as a practical compromise for subsequent separation studies. Future work should verify the recommended condition through metallization and magnetic separation tests.