Continuous float–sink density separation of lump iron ore using a dry sand fluidized bed dense medium

Abstract

A continuous separator based on float–sink density separation using a gas–solid fluidized bed dense medium was used to upgrade iron ore. The separator has three devices for (A) conveying floaters, (B) recovering floaters, and (C) conveying and recovering sinkers. The optimum speeds of these devices were investigated using density adjusted spheres of the diameter=30mm in the range of 2400–3300kg/m3 in density increments of 100kg/m3. A mixture of zircon sand and iron powder was used as the fluidized medium to adjust the fluidized bed density to produce a separation density=2850kg/m3, a typical separation density for lump iron ore wet separation. The recovery of the spheres as floaters or sinkers depended on the speed of the devices, because the recovery was affected by the number density of spheres directly under the feeder, the local fluidized bed density, and flow currents in the medium derived from the movement of the devices. The optimum speeds were determined to be 3.5cm/s for (A), 2.0rpm for (B) and 1.0cm/s for (C), respectively. Continuous separation experiments were conducted on lump iron ore particles in the size range of +11.1–31.5mm in the fluidized bed with medium density of 2850kg/m3 and feed rate of 200kg/h. Comparison of the feed rate and the recovery rate indicated that the feed and the recovery were in equilibrium after 10min of operation. The experiments resulted in nearly perfect separation; 98.4% of the ore with density greater than 2850kg/m3 was recovered. The Fe, Al and Si content of the feed ore particles (before the separation) and the floaters and sinkers (after the separation) was measured using inductively coupled plasma spectrometry. The separator produced an upgrade in iron content of 3.3wt% and reduced the Al and Si content by 44%.