Comparison between etheramine and amidoamine (N-[3-(dimethylamino)propyl]dodecanamide) collectors: Adsorption mechanisms on quartz and hematite unveiled by molecular simulations

• Amidoamine N-[3-(dimethylamino)propyl]dodecanamide has a higher affinity for quartz than for hematite . • The steric hindrance impairs the adsorption of N-[3-(dimethylamino)propyl]dodecanamide on the surface of hematite-(D2). • The collector-collector interaction energy contributes to organize the amidoamine on the quartz surface. This work describes, at a molecular level, the adsorption differences between etheramine and amidoamine N-[3-(dimethylamino)propyl]dodecanamide, a conventional silicate collector and one not yet used in industrial iron ore flotation, respectively. The molecular dynamics simulations showed that the adsorption of this amidoamine on the quartz surface, regarding the quartz-hematite system, tends to be more selective than etheramine. The explanation for this behavior is related to the combination of the water coordination at hematite-(D2) surface and the bulky head group of the amidoamine. Regarding the neutral molecules of etheramine and amidoamine, the coordination of water on the surface of hematite-(D2) acts as a shield, making it difficult for collector adsorption. In relation to protonated collector molecules, the combination of the amidoamine head group (with methyl bonded to nitrogen in the tertiary amine) with the water on the hematite-(D2) surface causes steric hindrance, impairing the amidoamine adsorption, while the etherammonium cations manage to adsorb on this hematite surface anyway. Also, the amide group favors hydrogen-bonding between collectors in the adsorption layer, which brings stability to the layer.