Improving recovery of iron using column flotation of iron ore slimes

In general, the industrial flowsheets for the beneficiation of itabirite iron ores from the Quadrilcitero Fernier degrees (Minas Gerais state) in Brazil involves grinding, desliming, magnetic separation and cationic reverse flotation using both mechanical and columns flotation cells. At Brazilian plants, it is estimated that Fe losses generated at the slimes stage range between 8% reaching values higher than 20%. Slimes generated at hydrocyclone containing particle sizes of approximately 99% < 45 mu m, 25% > 10 mu m, 45% < 5 mu m and 15% < 1 mu m, 3% of solids by weight and between 35% and 45% of Fe grade. This work aims at evaluating the technical feasibility of concentration of two slimes samples from two different plants in operation at the Quadrilcitero Fernier degrees using the column flotation technology without prior desliming. Despite the similarity in terms of mineralogy, grade and particle size distribution, the flotation results indicate a very distinct behavior considering similar process conditions, including variables such as collector type and dosage, depressant dosage, pH and circuit configuration. A final concentrate containing an Fe grade higher than 60%, 4% SiO2 and 3.1% Al2O3 with an Fe recovery up to 75% in rougher column flotation can be obtained from Sample 1 with 45.2% Fe, 28.6% SiO2 and 3.1% Al2O3, when a collector type amide-amine (Flotinor 5530) was used in substitution of a conventional amine collector. On the other hand, it was not possible to obtain a final concentrate containing an Fe grade higher than 55% from Sample 2 with 39.6% Fe, 33.4% SiO2 and 5.1% Al2O3, using both types of collector (amide-amine and amine) even when applying different types of column flotation circuits (rougher or rougher/cleaner). Based on literature review and the results obtained in this study, it can be observed the non-existence of a standard solution for an efficient slimes processing in the iron ore industry. Considering flotation as the most suitable technology for the treatment of such type of material, future research should focus on a deep fundamental study of the collector-depressant mechanism interaction with the iron-bearing and gangue minerals, especially in those ores with a high amount of alumina-containing minerals. Considerations about the effect of bubble generator device to flotation columns and its impact on the metallurgical performance are also discuss regarding to application at industrial scale to slimes concentration.