Acid surface dissolution as a pretreatment method converts Fe2+ ions on the ilmenite surface to Fe3+ ions. XPS analysis showed that the content of Fe3+ increases from 48.5% to 59.8% after surface dissolution for 15 min in a solution of sulfuric acid with a concentration of 10%. This conversion, without any phase transformation, decreases the zeta potential of ilmenite in a wide pH range, resulting in a shift in IEP (Iso-Electric Point) from a pH of 5.4 to 2.3. FTIR spectra and zeta potential measurements showed that the increase of oleate ions adsorption on the ilmenite surface, resulting from the surface dissolution process, is insignificant. After surface dissolution, the formation of more ferric iron oleate species (Ksp = 10(-29.7)) being more stable than ferrous iron oleate (Ksp = 10(-15.5)) compounds yields an increase of ilmenite hydrophobicity and floatability in a wide pH range. Using 3.65 x 10(-4) M sodium oleate at a pH of 6.3, the maximum flotation recoveries are obtained as 73.5% and 92% for non-treated and acid pre-treated ilmenite, respectively. (C) 2016 Elsevier Ltd. All rights reserved.