Unraveling Interaction Mechanisms between Molybdenite and a Dodecane Oil Droplet Using Atomic Force Microscopy

Charge-Dipole Attraction as a Surface Interaction between Water Droplets Immersed in Organic Phases

The dynamic behavior of emulsion droplets during their interactions with one another or with solid surfaces plays a paramount role in their ultimate stability in various applications. While the interaction of oil droplets through a surrounding aqueous phase is well understood, recent studies on the interaction of water droplets through a surrounding pure organic phase showed the presence of an unexplained attraction between water droplets at relatively long ranges. In this research study, we propose fixed-surface-charge-bulk-dipole attraction as a new interaction force between water-in-oil droplets and then derive an equation for its disjoining pressure. The behavior of water droplets in the presence and absence of this charge-dipole interaction was numerically quantified using the Stokes-Reynolds-Young-Laplace model and compared to the experimental data. Numerically calculated net force curves are in excellent agreement with experimental data from the literature when charge-dipole attraction is included, while they deviate in its absence. In addition, the water droplet and thin oil film profiles in the presence and absence of charge-dipole attraction were calculated and compared. This research indicates that charge-dipole attraction can adequately explain the mysterious force observed in some studies, which demonstrates its unexplored potential to capture the physical properties and dynamic behavior of water droplets in organic phases with useful implications to unravel unidentified interactions between emulsion droplets in different industries.

Interfacial Adhesion between Fatty Acid Collectors and Hydrophilic Surfaces: Implications for Low-Rank Coal Flotation

Fatty acids, which are enriched in vegetable oil, have attracted much attention in low-rank coal flotation because of their unique chemical structure. In this study, density functional theory calculations, molecular dynamics simulations, and atomic force microscopy were employed to investigate the adsorption structure and forces between collectors and hydrophilic surfaces. The results show that fatty acids can be easily adsorbed onto surfaces through hydrogen bonds, and can cover the oxygen sites. The existence of hydration film on hydrophilic surfaces prevented nonpolar molecules from being able to adsorb, while polar fatty acids could adsorb and expel water molecules. The adhesion force between the RCOOH-terminated probe and the surface appeared in the retraction process, which differed significantly from that of the RCH₃-terminated probe, indicating that polar fatty acids are more suitable as flotation collectors for low-rank coal than nonpolar hydrocarbon oil. The simulation and AFM test revealed the mechanisms of polar fatty acids, and can provide guidance for low-rank coal flotation applications.

Effect of sodium citrate on asphaltene film at the oil-water interface

HYPOTHESIS

Sodium citrate (Na₃Cit) has been proven to improve the oil sands extraction recovery, but its mechanism is still unclear. Here we hypothesize that the presence of Na₃Cit affects the asphaltene behaviour at the oil-water interface, which enhances oil-water separation and, thereby, heavy oil recovery.

EXPERIMENTS

Na₃Cit-asphaltene interaction was first investigated on their interfacial shear rheology at one heptol-water interface. Na₃Cit-asphaltene interaction was further revealed by measuring the interaction forces between two heptol-water interfaces using the atomic force microscopy droplet technique combined with the Stokes-Reynolds-Young-Laplace (SRYL) model. Interfacial properties were further illustrated through interfacial tension, zeta potential, Langmuir trough, and FE-SEM.

FINDINGS

Na₃Cit was found to weaken the strength of the asphaltene film at the heptol-water interface. Moreover, Na₃Cit could diminish the adhesion forces observed between two asphaltene-in-heptol droplets in high salinity solutions. Besides, Na₃Cit also made the asphaltene-in-heptol droplet more negatively charged. These results collectively suggest that Na₃Cit-asphaltene interaction results in a looser and more elastic asphaltene interfacial network with the slow formation and reduces the adhesion between two interfaces, all of which are most likely the consequence of increased electrostatic repulsion between asphaltene interfacial nanoaggregates. Our study provided new understandings of Na₃Cit-asphaltene interactions at the interface.

Recent progress on research of molybdenite flotation: A review

Molybdenum is an important alloy element for metallurgical industry because of its high temperature stability. As the major mineral reserve for molybdenum, molybdenite (MoS₂) is commonly found in porphyry copper deposits. Molybdenite is naturally floatable and can be separated from copper sulfide mineral using froth flotation. Properties of molybdenite such as mineralogy, microstructure, surface wettability, zeta potential, etc. can have a great effect on its floatability. Organic and inorganic depressants and surface pre-treatment methods are applied to improve the recovery of molybdenite. Electrochemical potential measurements using different electrodes are used to monitor process conditions and enable processing parameter adjustments to improve flotation circuit performance and reduce operating costs. Cations like Ca²⁺ and Mg²⁺ are reported to have negative effects on the flotation of molybdenite in alkaline solution, and dispersants and oil collectors need to be added to restore the flotation of molybdenite. In addition, effects of gangue minerals, particle size, and oil collectors and surfactants on molybdenite recovery are also discussed in this manuscript.