The effective separation of magnetite (Fe₃O₄) and quartz (SiO₂) is essential for mineral purification in the field of mineral resource utilization. In this study, we examined the effects of Fe³⁺ and corn starch (CS) on the flotation separation of magnetite and quartz using micro-flotation experiments, solution chemistry calculations, Fourier transform infrared spectroscopy (FT-IR), zeta potential tests, contact angle tests, and scanning electron microscopy (SEM). The results of our micro-flotation experiment demonstrated that the combined depressant of CS and Fe3+ significantly depressed the flotation of magnetite. When the pH value was 10, the CS concentration was 8 mg/l, the Fe³⁺ concentration was 150 mg/l and the dodecamine concentration was 6 mg/l; approximately 19.30% of the magnetite and 72.01% of the quartz entered the foam product. In addition, the results of SEM and FT-IR analyses revealed that the addition of Fe³⁺ significantly enhanced the selective depressant effect of CS on magnetite. This effect was the result of Fe³⁺ undergoing hydrolysis reactions on the surface of magnetite, forming Fe(OH)₃ and Fe(OH)₂ precipitates, which both enhance the binding strength between CS and the mineral surface through chemical adsorption. Lastly, the zeta potential and contact angle test results further revealed that Fe³⁺ alters the charge distribution on the magnetite surface, reduces the absolute value of the potential, and weakens its surface hydrophobicity.