A mechanism for the stable adhesion of bubbles and particles: The effect of particle surface properties

Shale gas fracturing flowback fluid (FFF) is characterized by complex composition, high generation volume, viscosity, chemical oxygen demand, and suspended solids content, which is harmful to the environment and needs to be reused after treatment. In the previous work, microbubble-enhanced flocculation can effectively treat the microfine particles in FFF by the trapping and bridging functions of microbubbles. The formation of stable bubble-particle adhesion throughout the microbubble-enhanced flocculation process is the key step to achieve efficient solid-liquid separation. In this work, the influence of particle surface interface properties, including surface hydrophobicity and roughness, on the stable adhesion was investigated. The results show that the more hydrophobic and rougher the particle surface is, the lower the three-phase contact (TPC) formation time (from 581 ms to 128 ms) and the number of collisions (from 10 to 4). The shorter TPC formation time and fewer collisions mean the faster the bubble forms a stable adhesion with the particle. The main reasons are the increase of hydrophobic gravitational force and the existence of "pinch" effect. In addition, the addition of surfactant can enhance the stability of the liquid film and weaken the deformation of the bubble, which increases the formation time of TPC. The above results provide a theoretical basis for the treatment of FFF by microbubbles-enhanced flocculation.