Influence of particle shape on the interaction processes of coal particles and bubbles in saline solution

Abstract

Understanding the role of coal particle shape in the flotation process is helpful in achieving a clean usage of coal slime flotation. In this investigation, the anthracite coal surface was modified using a chlorinated salt solution containing Na+, Ca2+, or Fe3+. Coal particles with four surface shapes were prepared: angular coal particles (ARPs), prismatic coal particles (PCPs), flat coal particles (FTPs), and spherical coal particles (SLPs). The ARPs were subdivided into five kinds of curvature: 3π/2, 21π/20, 7π/11, π/3, and π/10, and the PCPs were subdivided into five kinds of dihedral angles: 30°, 60°, 90°, 120°, and 150° according to the surface flatness of the ARPs and PCPs. Six ion concentrations, of 0, 5, 10, 20, 40, and 80 mmol/L, were examined. We tested the liquid film drainage time (LDT), maximum repulsive force (MRF), and maximum attractive force (MAF) between these coal particles and bubbles. The results show that at a constant solution concentration for a particular particle shape, the MRFs and LDTs increase in the order of Fe3+<Ca2+<Na+, and the MAFs decrease in the order of Fe3+>Ca2+>Na+. This indicates that Fe3+ enhances the adhesion probability and stability of anthracite particles and bubbles by the greatest extent, followed by Ca2+ and Na+. For a particular shape of coal particles, an increase in the ion concentration reduces the LDT and MRF and increases the MAF. When the curvature of the ARPs is 3π/2 and the dihedral angle of PCPs is 30°, the order of the LDTs of coal particles and bubbles is ARP < PCP < SLP < FTP. With a decrease in the curvature of ARPs and an increase in the dihedral angles of PCPs, their LDTs gradually approaches that of the FTP. The results for MRF and MAF are consistent with the LDT. Therefore, the ARPs with larger curvature and PCPs with smaller dihedral angles easily attach to air bubbles, and the decrease of the curvature and the increase of dihedral angles hindered the detachment. Adhesion and detachment experiments were conducted to confirm these results. The coal particles had a tendency to contact the bubbles with their available tips while sliding on the surfaces of bubbles to induce liquid film rupture. In addition, regardless of the coal particle shape, increasing ion concentration changes the detachment position of coal particles. These findings are consistent with the results of LDT, MRF, and MAF measurements. In this study, the role of coal particle shape in saline solution were systematically investigated, which provides a possible solution for the problems caused by the presence of ions in the flotation process using saline as the water source.