Gravity separation of fine itabirite iron ore using the Reflux Classifier – Part I – Investigation of continuous steady state separations across a wide range of parameters

High grade iron ore resources are becoming depleted in Brazil, with relatively low-grade ores requiring more intensive concentration to achieve a premium product. Accordingly, a typical industrial itabirite concentration circuit includes desliming in hydrocyclones and concentration via reverse flotation, product thickening and filtration, with the slimes sent to tailings thickeners, and onto tailings storage facilities. This work examined the potential for applying a vastly simpler approach, a single stage of gravity separation using the Reflux Classifier. Here the classified feed, 90 % finer than 0.150 mm, is sent directly to the Reflux Classifier, leading immediately to a high-grade concentrate at high solids concentration. Part I describes the findings from a comprehensive series of experiments covering the effects of bed density set point, feed pulp density, throughput, fluidisation water rate and lamella channel spacing. The main program, based on an ore with 8 % goethite and 45 % hematite, achieved a feed upgrade from 37 % to 65.6+/−0.4 % iron and iron recovery of 72.9+/−0.4 % at 9 t/m2/h. A second feed with 1 % goethite and 57 % hematite was upgraded from 41 % to 66.3+/−0.4 % iron at an iron recovery of 84.7+/−0.5 % at 10 t/m2/h. (The grade of pure hematite is 69.9 % iron). It was essential to run the Reflux Classifier at a sufficient volumetric rate to achieve shear induced inertial lift of the coarse silica within the closely spaced inclined channels, to reject the gangue minerals from the high-grade product. The results demonstrate the technical feasibility of applying the Reflux Classifier to upgrade itabirite feeds.