DFT study of coadsorption of fatty acid and kerosene on fluorapatite (001) surface

Abstract

The adsorption of fatty acid, kerosene and fatty acid-kerosene on fluorapatite (001) surface were investigated by density functional theory (DFT) calculations. The results showed that the single fatty acid could form stable chemisorption on fluorapatite (001) surface by the O of fatty acids bonding with Ca1 site. The single kerosene could not be stably adsorbed on fluorapatite (001) surface because the H of kerosene did not form hydrogen bond with the O of PO<sub>4</sub><sup>3-</sup> on (001) surface (O<sub>surf</sub>). For the coadsorption conformation, the chemisorption of fatty acid-kerosene on fluorapatite (001) surface was contributed by the interaction between O of fatty acids and Ca1, the H of kerosene did not bond with the O<sub>surf</sub>, but the carbon chain length of kerosene has a large influence on the coadsorption. Compared with the coadsorption of fatty acid-decane, the adsorption of butyric acid-tetradecane and octanoic acid-tetradecane on fluorapatite (001) surface have greater adsorption energies and overlapping region of DOS between O 2p and Ca 4d, indicating that there is a synergistic effect between fatty acid and tetradecane. Meanwhile, the collaborative effects exist between the molecules of fatty acids. The interpenetrating adsorption of fatty acid and kerosene on the fluorapatite surface could improve the adsorption strength and density. The flotation test further confirmed that the single kerosene could not collect fluorapatite, but it could be collected by the single fatty acid. Besides, the synergistic effect between fatty acid and kerosene could increase the flotation recovery of fluorapatite.

Application of Quantum Chemistry in the Study of Flotation Reagents

“…The interaction between 4-methylheptanoic acid and the fluorapatite surface is stronger than that between 6-methylheptanoic acid and the fluorapatite surface, indicating that the change in the substitution configuration of fatty acid has a great influence on the adsorption of fatty acid on fluorapatite. The co-adsorption mechanism of kerosene and fatty acid on the fluorapatite (001) surface was also studied by Du et al [263]. The results show that there is a synergistic effect of the chain-chain interaction between fatty acid molecules.…”

Flotation Behavior and Interface Characteristics of Apatite with Co-Depression by Sulfuric Acid and Phosphoric Acid

“…As shown in Figure 15, in general, with the increase in the initial concentration of sodium oleate in the slurry (from 0.16 to 1.60 mmol/L), the adsorption capacity of sodium oleate on the apatite surface also increases. This is because the fatty acid could form stable chemisorption on the apatite surface by the O of fatty acids bonding with the Ca1 site [27]. However, no matter how much the initial addition amount of sodium oleate changes (0.16-1.6 mmol/L), when the mixed acid is used as a depressant, the adsorption amount of sodium oleate on apatite surface is the lowest; this is because the hydrophilic substances CaSO 4 , CaHPO 4 /Ca(H 2 PO 4 ) 2 formed in the presence of the mixed acid and adsorbed on the surface of apatite hinder the adsorption of sodium oleate [28].…”