Interactions between fine and coarse hematite particles in aqueous suspension and their implications for flotation

•Effects of fine hematite particles on flotation performance were investigated.•Flotation recovery was related with the aggregation between fine and coarse hematite.•Interaction energies between fine and coarse hematite were calculated.•Effects of mass ratio between fine and coarse hematite on aggregation were studied.

The interactions between fine and coarse hematite particles were investigated, and their effects on the flotation of the hematite using sodium oleate as a collector were studied through micro-flotation tests, supplemented by optical microscopic analysis, extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theoretical analysis, and focused beam reflectance measurement (FBRM) particle/aggregate size analysis. The micro-flotation results show that the recovery of hematite from fine-coarse hematite mixtures did not decrease monotonously with increasing the fine hematite mass ratio. The highest recovery was obtained when the fine and coarse hematite were approximately equal in mass ratio, indicating that the interactions between fine and coarse hematite particles could promote the overall flotation recovery. The results of optical microscopy analysis, EDLVO calculation, and FBRM measurements showed that the interaction energies and aggregation tendencies between fine and coarse hematite particles were stronger than that among the fine hematite particles, and the aggregation would weaken when the coarse and fine fractions were mixed in extreme mass ratios, which explained the observed effects of different mixing ratios of fine and coarse hematite particles on their flotation.