Granular materials such as limestone and sand have been observed to exhibit an aptitude to aggregate with a hydrophobic phase, such as oil, thereby capturing substantial amounts of oil that floats on water surfaces. This unique phenomenon of selective positioning of the granular materials at the non-colloidal scale at the hydrophobic liquid-water interfaces is yet to be exhaustively studied and reported in the existing scientific literature. Consequently, it has therefore attracted profound interest as the comprehension of the granular particle behavior is needed for the possibility of utilizing readily available granular materials for capturing oil and curbing the mobility of floating oils as a treatment method.
In a recent paper published in Journal of Cleaner Production Daria Boglaienko and Berrin Tansel from the Department of Civil and Environmental Engineering at Florida International University proposed to analyze the observed variations in the positioning and behavior of the natural granular particles of limestone and quartz at the hydrophobic liquid-water interfaces. They also aimed at evaluating the dominant force impact on the particles behavior.
Foremost, experiments were carried out using dyed quartz and limestone particles with a 0.2-millimeter diameter for the fine particles and 0.5 millimeter for the medium sized particles. The researchers then used particles of different colors so that positioning of the particles with different sizes could be visually observed in the hydrophobic liquid water systems. They then selected silicon oil, tetradecane and crude oil for use as the hydrophobic liquid. Eventually, the researchers analyzed the behavior of the particles at the hydrophobic liquid and water interfaces through the application of the electrostatic image force theory.
By comparing theoretical and empirical results obtained, the researchers observed that the theoretical results did not support the assumption that the particle positioning at the liquid interface can be theoretically linked to gravitational force. The limestone which has active surface properties was observed to possess higher surface charge hence was able to cross the tetradecane-water interface abandoning the non-reactive tetradecane phase. They also observed that the zeta potentials of the aqueous limestone decreased upon addition of crude oil which explains why the limestone particles were held at the crude oil-water interface. These helped them conclude that the polar fractions of crude oil affected the surface charge and zeta potential of a particle.
The empirical observations have directed that the effects of the charge differences are more significant than the effect of the size difference in determining the position of a particle in a hydrophobic liquid, hydrophobic liquid-water interface and water phase. It is therefore important to note that slight differences in material composition affects surface characteristics thereby resulting in differences in the preferential positioning of the particles. The phenomenon presented here is of high interest and presents a new oil spills treatment technique which is inexpensive, simple and environmentally friendly.
Daria Boglaienko, Berrin Tansel. Preferential positioning and phase exposure of granular particles at hydrophobic liquid-water interface. Journal of Cleaner Production volume 142 (2017) pages 2629-2636.
Department of Civil and Environmental Engineering, Florida International University, Miami, FL, USA.
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