True flotation versus entrainment in reverse cationic flotation for the concentration of iron ore at industrial scale

The loss of iron-bearing minerals to the tailings, especially in the finest fractions (-44 mu m), is a problem that must be endured due to the depletion of deposits containing high-Fe hematite. The two main mechanisms for iron mineral loss in the froth in reverse cationic flotation are hydrodynamic dragging and true flotation. This last one being attributed to failures in the conditioning processes regarding the depression of iron mineral by starch. In this work, two industrial mechanical flotation circuits located in Minas Gerais-Brazil, namely Conceicao Itabiritos II and Pico, operating with mineralogically distinct iron minerals, had their tailings analyzed in order to attribute reasons for the iron-bearing minerals losses. Liberation studies excluded losses due to the presence of composite particles where hematite was combined to silica or goethite. The method known as two-liquid flotation was applied to the several particle fractions present in the tailings to evaluate the particles surfaces hydrophobicity/hydrophilicity. The results indicated that for Conceicao Itabiritos II, the loss of iron minerals was due to a combination of true flotation and hydrodynamic dragging. True flotation probably took place because of depression failure. For Pico, the results revealed that most of the iron-bearing particles were lost due to hydrodynamic dragging. The shape factor and terminal velocity, both obtained via permeametry, confirmed the two-liquid flotation results. Two-liquid flotation was shown to be a fast and simple method to qualitatively assess the hydrophobicity of particles in froth flotation, thus allowing quick improvements in the process.