The influence of coal particle shapes on the interaction behavior of air bubbles and coal particles

In order to study the influence of coal particle shape on the interaction behavior of air bubbles and coal particles, coal particles were divided into three types according to the contact region with air bubbles. They were angular coal particles (ARP) in point contact, prismatic coal particles (PCP) in line contact, and flat coal particles (FTP) in surface contact. Spherical coal particles (SLP) were used as a reference to compare the above three coal particles. We tested the acting time and force of coal particles with air bubbles using an instrument designed by us. For a systematic study, according to the angle of the contact location with the air bubble, the ARP and the PCP were subdivided into 5 types. By comparing the difference in the drainage time (DT) of the liquid film, the three-phase contact-line (TPCL) expansion time, the maximum repulsive force (MRF), and the maximum attractive force (MAF) during the acting process, the influence of the coal particle shape on the interaction process was systematically explored. The research results show that the order of DT, MRF, and MAF of the liquid film caused by the interaction of coal particles with bubbles is angular < prismatic < spherical < flat shape, while the order of TPCL expansion time is the opposite. As the angle of ARP and PCP increases, the DT, MRF, and MAF of the liquid film increase, the MAF of SLP and FTP are 54.50 μN and 104.99 μN, respectively, while the TPCL expansion time decreases with the increase of the angle. The MRF of SLP is similar to that of PCP of 120°, which are −43.42 μN and −41.84 μN, respectively. We further studied the adhesion and detachment processes. The results show that 95% of the coal particles will collide with the bubbles in thier sharp tip regions, and only 5% of the coal particles can collide with the bubbles in their plane regions when attachment is achieved. When the liquid film is induced to rupture, the irregularly shaped coal particles tend to contact the bubbles with their tips; when detachment occurs, the sharp tips of the coal particles will be dominant locations of detachment from the bubbles. Therefore, the shape of coal particles greatly affects the interacting process. This study provides a theoretical basis for effectively improving the flotation performance by changing the shape of coal particles in the process of coal flotation.