Abstract: Direct-flotation separation of limonite from quartz and the effect of Fe³⁺ on floatability of limonite and quartz were studied in NaOl flotation system. The results showed that NaOl was a good collector for the separation of limonite from quartz; and Fe³⁺ showed strongly activation effect on quartz but less effect on limonite. Sodium hexametaphosphate (SHP) could reduce the effects of Fe³⁺ on the flotation of quartz, but has no effect on limonite in the pH range of 7~9. When sodium pyrophosphate was selected as the regulator, direct flotation separation of artificial mixed minerals was studied with 63 mg/L sodium oleate and 90 mg/L SHP at pH 8.5. The recovery of limonite was beyond 90%, and the content of TFe reached 52%. Mechanism study results showed that zeta potentials of quartz changed from negative to positive, and the electrostatic adsorption of Ol^- on the surface of quartz was enhanced when Fe³⁺ was adsorbed on quartz. The complex reaction of SHP with Fe³⁺ on quartz surface contributed to eliminating the Fe³⁺ effect on zeta potentials of quartz as well as its floatability.