Molecular dynamics simulations of adsorption behavior of DDAH, NaOL and mixed DDAH/NaOL surfactants on muscovite (001) surface in aqueous solution.

The adsorption mechanism of collectors on minerals is of fundamental importance in the research and development of flotation science and processing technology. To examine the effect of cationic dodecylamine hydrochloride (DDAH), anionic sodium oleate (NaOL) and mixed DDAH/NaOL surfactants with different molar ratios on the adsorption behavior on the muscovite (001) surface, the adsorption mechanism of DDAH, NaOL and their mixture on the muscovite (001) surface in neutral aqueous solution was investigated by molecular dynamics (MD) simulations. The results showed that the cationic DDAH molecules absorb on the muscovite (001) surface by electrostatic interactions and hydrogen bonding, whereas the anionic NaOL molecules cannot independently adsorb on the muscovite surface. Based on the analysis of the density distribution profile, radial distribution function (RDF) and interaction energy between surfactant molecules and muscovite surface, and the root mean square displacement (RMSD) of surfactants on water-muscovite interface, individual DDAH surfactant is a superior collector for the muscovite flotation. The molar ratio of DDAH/NaOL surfactants is found to be a key factor in the flotation response of muscovite. No significant adsorption of 1:2, 1:3 and 1:4 mixed DDAH/NaOL surfactants on the muscovite surface can be detected, while an effective adsorption was observed for the DDAH/NaOL mixture in molar ratios of 1:1, 2:1, 3:1 and 4:1. The cationic DDAH surfactant was determined to play a primary role in the adsorption of the mixed surfactants on the muscovite surface, while the anionic NaOL molecules co-adsorb with the DDAH molecules. The additional micro-flotation experiments under neutral aqueous conditions also showed that the flotation recovery of muscovite was the highest in the presence of DDAH surfactant, which was consistent with the findings derived from MD simulations.