Adsorption process and mechanisms of AEO-3/dodecane mixed collector on low-rank coal surface driven by water flow: A non-equilibrium molecular dynamics simulation study

Abstract

During coal slime flotation, the collector is adsorbed to the coal in the form of fine oil droplets in the turbulent slurry. And understanding the adsorption behavior of collector oil droplets on the coal surface is important for the development of efficient collector. In this study, the adsorption process and mechanism of triethylene glycol dodecyl ether (AEO-311triethylene glycol dodecyl ether.)/dodecane mixed collector oil droplet (MCOD22mixed collector oil droplet.) on the surface of low-rank coal driven by water flow were investigated by non-equilibrium molecular dynamics simulations. The changes of the mass center velocity of MCOD, contact area and interaction energy between MCOD and coal during the simulation were analyzed, and the adsorption process was divided into the adhesion stage, spreading stage and equilibrium stage. The kinetic reason for the adsorption of AEO-3 molecules at the interface was found. The pushing of oil droplet by the water flow caused the AEO-3 molecules to be slowly pressed into the contact interface between the oil droplet and coal, and the adsorption occurred. The presence of polar oxygen-containing functional groups on the AEO-3 molecule makes it much more strongly adsorbed on low-rank coal than dodecane. Water molecules play an important role in the adsorption process of AEO-3 with coal, and the bridging action of water molecules that enables indirect adsorption of collector with coal was proposed. The water molecule connects AEO-3 and coal molecules, which cannot form hydrogen bond due to the distance, through hydrogen bonding, and inserts between alcohol oxygen, ether oxygen and carbonyl oxygen, which are originally mutually exclusive, so that the three of them (OAEO-3, H2O and Ocoal) are connected together through hydrogen bonding (OAEO-3…H-O-H…Ocoal), and the stability of AEO-3 adsorption on coal surface is greatly enhanced. The presence of strong indirect electrostatic interactions between polar collector and coal generated by the bridging action of water molecules proves that it is the strong electrostatic interactions that are the reason for the strong flotation performance of polar collector on low-rank/oxidized coals.