Interactions between coarse and fine galena and quartz particles and their implications for flotation in NaCl solutions

In this study we have investigated the interactions between coarse and fine galena and quartz particles and their implications for flotation in NaCl solutions. Tested were four different particle systems: (CC) Coarse galena/Coarse quartz, (CF) Coarse galena/Fine quartz, (FC) Fine galena/Coarse quartz and (FF) Fine galena/Fine quartz. The flotation experiments were carried out on the four particle systems in NaCl concentrations of 10 mM and 100 mM, at pH 9. It was found that the recovery was the highest for the CC particle system, and the lowest for the FF particle system. The experiments also indicated that the recovery improved for the higher NaCl concentration. As part of this study, we calculated the total interaction free energy as a function of separation distance for each pairwise combination of particles and bubbles, for each test condition. It was found that for all particle systems, galena/quartz interactions are dominated by repulsion. The interactions between two galena particles indicated attraction as the dominating force, while the interactions between quartz particles showed repulsion in 10 mM NaCl, which changed to attraction with an increase in NaCl concentration. Galena/air bubble interactions were controlled by repulsive electrostatic interactions in 10 mM NaCl, but these interactions became attractive in 100 mM NaCl salt solutions. On the other hand, the quartz/air bubble interactions were always repulsive, irrespective of the NaCl concentration. Based on these theoretical predictions, we postulate that the stronger repulsion of quartz particles away from the air bubbles could be the driving force for galena recovery.