| Flotation deepend the differences of coupling degrees of each phase in three-phase flow of gas liquid and solid. Hydrophobic particles enter the bubbles and are flotated because it estranged water and intimate gas; hydrophilic particles are left in water because it intimate water. We have been devoted to realize the automatic control of flotation process. We found flotation mechanism is the key of the algorithm design of automatic control. The coupling relationship of particles-bubbles and the coupling relationship of particles-particles are the core of the flotation mechanism.At present, the coupling relationship of particles-particles is considered to be that non-polar molecules avoid the water to gather together, which changes the arrangement of water molecules around it, so that the system entropy is changed. The change of entropy promotes the hydrophobic attraction. However, the range of the hydrophobic attraction calculated by the theory of the change of water molecular arrangement is very short. The actual range of the hydrophobic attraction is much larger than that. The coupling relationship of particles-bubbles(the adhesion phenomenon of hydrophobic particle to bubble) has been considered to be the results of electrostatic force, namely, the surface charge of the particle and bubble are respectively opposite. However, none of experiment can absolutely prove the polarity of surface charge of any hydrophobic particle is opposite to that of any bubble. Therefore, the mechanism of attraction of particles-particles and particles-bubbles is uncleary.The gas dissolved in water can be adsorbed at a hydrophobic interface are recent discoveries in condensed matter physics. A hypothesis was inferred based on this phenomenon,the hydrophobic attractions are triggered by nanobubble bridges caused by the adsorbed gas, which generate the aggregation of particles- particles and the adhesion of particles-bubbles. However, few studies verify this hypothesis, and the specific process of the formation of the nanobubble bridge was unclear. Therefore, the purposes of this paper as follow.Firstly, the detailed process of gas adsorption and accumulation, the energy changes of gas adsorption and accumulation, the necessary conditions of gas adsorption and accumulation, the final morphology of gas adsorption and accumulation, the stability of gas adsorption and accumulation, the mobility of the adsorbed gas were studied intensively. The gas density distribution, water density distribution, the change of the density distribution of the system, the track of molecules of each phase and the change of the speed of molecules of each phase were analyzed. The results of the study showed that the gas dissolved in water can indeed be adsorbed at a hydrophobic interface and accumulates thereon and the process as follows. Initially, a water depletion layer appears on the hydrophobic interface. Gas molecules then enter the depletion layer and form a high-density gas-enriched layer. Finally, the gas-enriched layer accumulates and forms a nanobubble. The radian of the nanobubble increases with time until equilibrium is reached. The equilibrium state is arised by two mechanisms. The one is Brenner-Lohse dynamic equilibrium mechanism, the diffusive outflux is compensated by an influx near the contact line. The other one is that a high viscosity gas-liquid mixing layer coated on the nanobubble inhibits the gas diffusion of the nano bubbles.Secondly, the effects of adsorbed gas on the contact angle of the hydrophobic surface were studied. The results showed that the contact angle of the hydrophobic surface increased because the gas adsorption, and when the thickness of adsorption is greater than two gas layer, the contact angle will remain unchanged.Thirdly, the effects of adsorbed gas on the attraction of hydrophobic surfaces were studied by studing the interactions of two sheets of graphene in water with and without gas dissolved. During the simulation, the change of density distribution of each phase, the change of the phase diagram and the change of the potential of mean force are analyzed. The results showed that the attractions of two sheets of graphene in water with and without dissolved gas were all caused by Nanobubble Bridges.When the distance of hydrophobic surfaces is less then approximate 0.5 nm, hydrophobic attraction is triggered by vacuum nanobubble bridge no matter with or without gas phase in water. When the distance is greater than approximate 0.5 nm, the hydrophobic attraction without gas in water is triggered by the nanobubble bridge of vapor, the hydrophobic attraction with gas in water is triggered by the nanobubble bridge of the gas.Fourthly, the effects of adsorbed gas on the attraction of hydrophobic surface and bubble were studied by studing the interactions of one sheet of graphene and a bulk of gas in water with gas dissolved. The results also showed that the attractions of a sheet of graphene and bubbles in water with gas dissolved were caused by Nanobubble Bridge. When the graphene approach the bubble to a certain distance, the gas adsorbed on the graphene will connect with the gas in the bubble and form a bubble bridge, the bridge will suck the graphene into the bubble gradually. When the graphene leave the bubbles, the bridge will prevent them apart.Finally, Interaction principles of hydrophobic particles-particles and hydrophobic particles-bubbles can be interpreted as follows. When the distances of hydrophobic particles are closer enough, the gas adsorbed on the their surface will connect each other and form IV nanobubble-bridges; similarly, when the the distances of hydrophobic particles-bubbles are closer enough, the gas adsorbed on the surface of particles will also connect with gas inside the bubble and form nanobubble bridges, which is the source of attraction of hydrophobic particles-particles and hydrophobic particles-bubbles. The mechanism can explain the phenomena well in flotation experiments and flotation plant. Layout of the nozzle of agentia device is proposed to rearrange according to the mechanism... |
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