A theoretical and experimental study of the effects of NaCl and the competitive chemisorption of ions at the surface sites in the context of galena flotation

In this study we have investigated the effects of increasing the NaCl concentration on the flotation of galena. Experiments were carried out using a Hallimond tube in NaCl solutions with concentrations of 1, 10 and 100 mM, at pH 9. It was found that the recovery of galena by collector-less flotation improved for higher NaCl concentrations. Zeta potential measurements made on galena particles conditioned in NaCl solutions were used to calibrate the parameters for describing a chemisorption model representing charge regulation at the galena binding sites. Our galena chemisorption model presented here is a “two-site/not amphoteric” surface complexation model. A chemisorption model representing the charge regulation process on the surface of an air bubble has also been applied. The zeta potentials calculated using these models were in agreement with the measured values, indicating that these models can be applied to predict the potentials on the surface of galena and an air bubble for a range of NaCl concentrations and pH. To investigate the mechanisms of particle-bubble interactions for each NaCl concentration, the total interaction free energy as a function of the separation distance between galena and an air bubble was determined. It was found that at a NaCl concentration of 1 mM, due to adsorption of ions at the galena surface, repulsion dominated the interaction, and the lowest galena recovery was reported. With an increase in NaCl concentration in solution to 100 mM, the total interaction between galena and an air bubble was represented by a purely attractive total interaction free energy curve. The theoretical predictions of the models supported the experimental results, with a stronger attraction predicted by the models at higher ionic concentrations, corresponding to a higher galena recovery during flotation.