Effect of electrolyte addition on flotation response of coal

In this study, the flotation of naturally hydrophobic coal particles in salt solutions with different cations (Na+, Ca2+, and Al3+) was investigated to clarify the flotation enhancement mechanism. The surface chemistry aspects were examined using the zeta potential measurements and bubble-particle attachment time experiments. The results of the flotation experiments showed that the presence of electrolytes in the flotation system clearly enhanced the flotation performance in a manner dependent on the type and concentration of the electrolytes. In the experiments, the AlCl3 and NaCl solutions showed the highest and the lowest flotation performance improvements, respectively. The zeta potential measurements showed that AlCl3 had a stronger influence on the surface charge of coal particles than CaCl2 or NaCl did. The induction time measurements indicated that the attachment decreased with increasing salt concentration and ionic valency state. In addition, abundant fine bubbles were generated in higher concentration salt solutions, particularly for the AlCl3 solutions, which prevented from the bubble coalescence and increased froth stability. It is concluded that the addition of salt solutions to a flotation system enhances the coal flotation performance, particularly for high-valence electrolyte solutions, which is attributed to the abundance of finer bubbles in the froth phase, depending on the type and concentration of the electrolyte