The considerable increase in worldwide demand for iron ore requires more studies for efficiency of silicate gangue flotation. New reagents and synergistic mixtures have been pursued to tackle this technological problem. Although there are several studies of collector mixtures in the literature, very few were dedicated to mixtures of cationic collectors. To fill such gap, the interaction between ethermonoamine (M) and etherdiamine (D) was evaluated using bench flotation tests with a typical Brazilian iron ore, solution chemistry analysis and density functional theory calculations (DFT) for the first time in literature. The combined use of these collectors in the proportion 3 D: 1 M, w/w, at pH 10.5, provided the best recovery and selectivity, showing synergism. The iron recovery was 83.9% with a rougher concentrate presenting an iron and silica content of 64.0% and 4.6%, respectively. Differences in the pKa values of primary and secondary amino groups point to minimization of electrostatic repulsion between adsorbed collectors. Interaction free energy values indicate that the complexes M(0)-D(+) (−8.29 kcal/mol), D(0)-D(+) (−7.74 kcal/mol) and M(+)-D(0) (−8.66 kcal/mol) are the most thermodynamically favored and, therefore, confirm the experimental results and explain the nature of the favorability, which is related to the reorganization of the collectors in order to minimize ether-ether and cation-cation repulsion and maximize ether-amine or amine–amine neighbors, especially when the amino group is protonated.
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