Pre-Concentration of Ultrafine Crushed Hematite Ores

Abstract

In this study, a lean hematite ore was crushed to produce ultrafine particles using a high pressure grinding roll and then pre-concentrated using a high gradient magnetic separator with a steel rod matrix to reduce the ore tonnage for milling and grinding energy consumption. Pilot test results showed that the primary concentrate grade was increased by 6.98 percentage points from the crude ore with 18.34% Fe at an optimum pre-concentration condition obtained using a matrix with a rod diameter and a rod gap that both measure 4 mm. The concentrate recovery reached a maximum of 86.13% with a tailings yield of 37.61%. Primary concentrates were separated further, and clean concentrates with a grade of 67.15% were obtained. In a magnetic field around a matrix rod, the magnetic capturing force on coarse hematite particles was increased, but such force on fine hematite particles was decreased as the matrix rod diameter increased at the same background magnetic field intensity. Considering gravity and viscous resistance of locked particles, the matrix with large diameter rods (e.g., 4 mm) could effectively and completely recover these particles. By contrast, the matrix with small diameter rods (e.g., 1 mm) could efficiently recover fine particles but not coarse particles such as lean-locked particles.