With the rapid depletion of relatively simple iron ores that can be readily beneficiated, agglomeration magnetic separation has been increasingly applied for recovery of fine iron minerals. In this study, the effects of stirring speed, pH, and fiocculant dosage on the recovery of fine hematite are investigated by floc-magnetic separation experiments in the presence of carboxymethyl starch (CMS). The experimental results show that the recovery of fine hematite is improved in the presence of CMS in the high-intensity magnetic separation (HIMS) with sufficient kinetic energy input and appropriate pulp pH value. Compared to the conventional RIMS, the concentrate recovery has increased by 7.03 percentage point in the presence of CMS under optimal conditions. Furthermore, the mechanism of the interaction between CMS and fine hematite is investigated through scanning electron microscopy, energy dispersive spectros-copy, and zeta potential and infrared spectrum measurements. The results of SEM-EDS and optical microscope tests indicate that CMS can adsorb on the surface of hematite, but not on the quartz surface. The results of the zeta potential and FUR measurement illustrate that electrostatic adsorption and hydrogen bond adsorption exist between hematite and CMS, but barely found between quartz and CMS. Therefore, the selective agglomeration of fine hematite particles is formed by the polymer bridging effect of CMS in the pulp. Subsequently, the collecting efficiency of fine hematite particles is improved in the HIMS. The model of selective flocculation of fine hematite is proposed and attributed to two processes: the sensitisation process and the collision process. While the former process is the selective adsorption of CMS on the surface of fine hematite particles through hydrogen bonds, the later process is the polymer-bridging flocculation performance with sufficient kinetic energy input at an appropriate pulp pH value. (C) 2018 Elsevier B.V. All rights reserved.