Flotation dynamics of metal and non-metal components in waste printed circuit boards.

Flotation is an effective and clean separation technology to realize the recovery of metal in waste printed circuit boards (WPCBs). The flotation kinetic of metal and non-metal components was concerned in this study. In addition, the loading of bubbles, the collision and shedding of particles and bubbles were used to assist in proving the particle dynamics results. By analyzing the force on the particles, the load of bubbles on particles was analyzed, and the appropriate volume ratio of bubbles to particles was 1.5-8.0, depending on the particle density. Moreover, Clift model and Schiller-Naumann model has high fitting accuracy for the final bubble velocity. In addition, metal particles have greater settling velocity, which results in shorter collision time with bubbles. In the process of bubble-particle rising, the shedding probability gradually decreases, and the shedding probability of metal particles is much higher than that of non-metal particles. The results of flotation kinetics show that the removal of impurity particles represented by silicon mainly occurs in the initial stage of flotation process. The loss of copper increases with flotation time and collector dosage. This study reveals the flotation kinetics of particles from the perspectives of bubble loading, bubble-particle collision and shedding.