Gravity separation of ultra-fine iron ore in the Reflux classifier

The recovery and concentration of ultra-fine iron ore can provide significant economic benefits. Presently, there are limited options available given the low settling rates achieved by conventional gravity separation and the relatively poor performance of reverse flotation. The Reflux Classifier is a new water-based gravity separation technology that consists of a set of parallel inclined channels positioned above a vertical fluidised section. This arrangement promotes a powerful throughput advantage compared to conventional fluidisation and a highly selective hydrodynamic basis for achieving sharp separations. A high shear rate develops within the inclined channels, which generates sufficient hydrodynamic lift to convey the lower-density particles (even if they are relatively course) to overflow while retaining the high-density particles (even those that are ultra-fine) for discharge to the underflow. The technology has previously been used around the world on particle sizes in excess of 0.1 mm, The present work, however, is concerned with density-based separations down to much finer particle sizes approaching 0.01 mm.A major advantage of the Reflux Classifier technology is the achievement of simultaneous separation and desliming via a single-stage separation. A series of continuous experiments using an iron ore feed with head grade of 35 wt per cent FeT and nominal top size of 0.106 mm, with 59 wt percent being below 0.038 mm in size. At a low throughput of 1.5 t/(m2 h), the Reflux Classifier produced high-grade products at high recovery. For the entire feed, grades of 66.1 wt per cent FeT with Fe recoveries of 80 per cent were achieved in a single-stage separation. Within the 0.020-0.038 mm size fraction, grades of 68.8 per cent were achieved with iron recoveries of 94.7 per cent. Excellent recoveries of up to 57.0 per cent were achieved for the -0.020 mm size fraction. The ability of the inclined channels to retain the fine dense material further enhances the effectiveness of the Reflux Classifier by creating an autogenous dense medium effect within the vertical section. This helps to elevate large gangue particles up into the overflow