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[Display omitted] • Acid surface pretreatment reinforced the flotation separation of ilmenite pre-absorbed by reagents. • Acid surface pretreatment increased distribution densities of main elements on ilmenite surfaces. • Original Fe and new Ti sites appeared on ilmenite surfaces after acid surface pretreatment. • Original Ca and Mg sites were unfound after acid surface pretreatment. Minerals in the unqualified ilmenite concentrate collected by flotation reagents appeared the similar surface hydrophobicity and floatability. In this work, acid surface pretreatment was applied to improve the difference in surface properties of ilmenite and gangue minerals pre-absorbed by reagents. Microflotation experiments showed that after ilmenite and titanaugite were treated with high concentrations of NaOL followed by acid surface pretreatment, their recovery differences increased from around 45% to stable 80% regardless of the collector dosage later. AFM and XPS analyses revealed that acid surface pretreatment strengthened the distribution densities of original Fe and new Ti sites and the strengths chemisorbed NaOL onto ilmenite surfaces, while it dissolved intrinsic Ca and Mg sites on titanaugite surfaces. These changes increased the differences in surface hydrophobicity and NaOL adsorption on ilmenite and titanaugite surfaces, which was certified by contact angle and zeta potential. Compared to conventional separation methods, the best result was obtained after rougher flotation concentrate was treated with acid surface pretreatment and three cleaning flotation stages, producing a concentrate with a TiO 2 grade of 47.68% and a TiO 2 recovery of 26.66%. Taken together, acid surface pretreatment is a potential and novel method to reinforce the separation of ilmenite flotation. [ABSTRACT FROM AUTHOR]