Surface oxidation promotes the flotation of ilmenite: a critical review

Due to its high efficiency, ease of operation, and superior selectivity, flotation separation has emerged as a promising technique for the extraction of ilmenite from natural resources. In light of the solution chemistry of ilmenite, it is widely accepted that ferrous ions and ferrous hydroxy compounds serve as the primary active sites for collector adsorption across a broad range of slurry pH values. The commonly used collectors like sodium oleate and hydroxamic acid are capable of chemical bonding with Fe2+ to form complexes and then enhance the floatability of ilmenite. However, Fe3+ ions perform a higher affinity to both collectors rather than Fe2+, the formed stronger complexes are advantageous for enhancing the hydrophobicity of ilmenite and increasing the probability for air bubble attachment, resulting in an improved ilmenite flotation recovery. Consequently, how to maximize the conversion efficiency of Fe2+ to Fe3+ and provide additional Fe3+ active sites on ilmenite surface for collector attachment have become the hot spot. Herein, this review aims to firstly analyze the crystal structure and solution chemistry of ilmenite and then provide a concise summary of recent advances in different oxidation technologies for promoting the conversion of Fe2+ to Fe3+, including hydroxyl radicals oxidation, direct chemical oxidation, and thermal oxidation, and the in-depth activation mechanisms are well illustrated. Also, current challenges and perspectives in this field are discussed. This review would benefit the development of next-generation flotation techniques for earth-abundant titanium resources.