Studies on the Effects of Particle Size in Direct Reduction Roasting of Limonite Ores

A series of direct reduction roasting - magnetic separation tests were carried out with refractory limonite ore in two different particle size compositions. The effect of particle size in the grade and recovery of direct reduced iron (DRI) at different roasting time, temperature and reductant dosages was investigated, and the mineralogical transformations of DRI obtained at different roasting time were analyzed using scanning electron microscopy (SEM-EDS). The results demonstrate that direct reduction roasting with limonite ore in large particle size (100% -20mm) was feasible, and the reducibility of limonite ore in large particle size increased with increasing reductant dosage and roasting time. The optimum reduction roasting - magnetic separation parameters of 100%-20mm limonite ore were proposed as the following: roasting at 1200 degrees C for 120min with 40% reductant, and milling 30min followed by low intensity magnetic separation, which resulted in the DRI with TFe grade of 90.2% and recovery of 89.3%.