Propriedades superficiais da dolomita e hematita: um estudo teórico aplicado à flotação

Abstract

In iron ore mining, dolomitic itabirite ore is classified as waste rock due to the difficulty of selectively separating hematite and dolomite by flotation. The chemical reactivity of these minerals was investigated using Density Functional Theory (DFT) calculations to explore the geometric and electronic properties of their surfaces and their chemical reactivity toward water, amidodiol and amidoalcohol collectors, and a TEOS-derived compound used as a passivating agent. The structural properties estimated by DFT are consistent with experimental values. Dolomite exhibits a predominantly ionic character (c% ≈ 85), whereas hematite shows a higher covalent character (c% ≈ 66). PDOS and band structure analyses confirm the insulating nature of dolomite and the semiconducting nature of hematite. The calculated cleavage energies indicate that the most stable surfaces are (104) (γ = 0.25 J m⁻²) for dolomite and (001) (γ = 0.81 J m⁻²) for hematite. The adsorption mechanism of water on dolomite is molecular, whereas on hematite it is dissociative. The adsorption energy of water on the hematite (001) surface was estimated as E_ads ≈ –100 kJ mol⁻¹, while for the dolomite (104) surface it was E_ads ≈ –79 kJ mol⁻¹. The most favorable dissociative mechanism for hematite suggests that its surface is covered by hydroxyl ions, promoting interactions with the collectors through hydrogen bonding. In contrast, for dolomite, water displacement favors the interaction of the collector with the acidic Ca²⁺ and Mg²⁺ sites. Calculations involving amidodiol, amidoalcohol, and the TEOS-derived compound show predominant chemisorption on the Ca²⁺ and Mg²⁺ sites of dolomite, with amidodiol exhibiting the strongest adsorption energy (E_ads ≈ –163.25 kJ mol⁻¹). The partial results indicate that both collectors and the modifier may also adsorb onto hematite through interactions between Fe³⁺ sites and (C=O) (OH) groups, but the competition between minerals and the effects of the aqueous medium are expected to favor selectivity in the dolomite/hematite flotation process. This work establishes the conditions under which the collectors interact with hematite and dolomite surfaces, providing a foundation for future molecular dynamics simulations aimed at capturing relevant dynamic effects—such as the influence of the collectors’ hydrophobic fragments on adsorption processes, as well as solvent effects, pH, and molecular reorientation. The results obtained provide valuable insights for the development of more efficient collectors for the selective separation of hematite and dolomite by flotation.