mica and dodecylamine

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.

Topics: Adsorption; Aluminum Silicates; Amines; Molecular Dynamics Simulation; Surface-Active Agents; Water

In this work, molecular dynamics simulation was used to examine the effect of solution pH on the adsorption behavior and self-aggregation of dodecylamine hydrochloride (DDA) on the muscovite (0 0 1) surface. The properties of surfactants are assessed in terms of density profiles in the direction perpendicular to the muscovite surface. Results show that although DDA can adsorb at muscovite at all pH we discussed, the self-aggregation of DDA varies significantly at different pH values. At pH 10, a compact hydrophobic monolayer forms on the muscovite surface. At pH 3, hemi-micelle aggregated structure forms with several DDA cations far away from muscovite surface. At pH 12, it has been confirmed that adsorption of DDA neutral molecules occurs with only a few DDA molecules adsorbing on muscovite directly and acting as a bridge linking the rest DDA molecules, which exists nearby muscovite surface irregularly. Density profiles revealed that at pH 10, DDA cations play a dominant role in the interaction between DDA surfactants and muscovite. While DDA molecules have difficulty in forming a hydrogen bond with the oxygen atom on the muscovite surfaces, and they co-adsorb onto muscovite through the electrostatic interactions with muscovite and hydrophobic force with DDA cations. Therefore, the hydrophobization of muscovite in the presence of DDA are higher at pH 10 than that at pH 3 and pH 12. Our results indicate that molecular dynamics simulation can be a power tool in charactering adsorption behavior of surfactants onto mineral surfaces at different pH values.

Topics: Adsorption; Aluminum Silicates; Amines; Cations; Hydrogen-Ion Concentration; Minerals; Models, Molecular; Molecular Dynamics Simulation; Solutions; Surface Properties; Surface-Active Agents; Water