Dodecylamine collector - pH effect on mica flotation and correlation with thin aqueous foam film and surface force measurements

This paper correlates data collected from several different fundamental measuring techniques in order to develop an improved understanding of the surface chemical nature of the flotation of mica in dodecylamine collector. Free equilibrium foam film experiments enabled the stability, thickness and interfacial potentials at the air/dodecylamine solution interface to be determined. Also, the batch flotation response of mica in dodecylamine solution was measured in a Clausson Flotation cell. These results were compared with surface force data, as reported in an earlier publication by Rutland et al., in which the interaction and hydrophobic adhesion (pull-off force) between molecularly smooth mica sheets in the amine collector solution was determined. Also the surface potential and thickness of the adsorbed collector layer were reported, together with the equilibrium contact angles on the smooth mica surface. All these data covered a range of pH values. It was found that maximum flotation occurred at pH 8 but this did not correspond to the minimum in the double-layer repulsive interaction between the mica and the bubble. However, it was shown that this critical pH value could be equated to a tightly packed organized collector monolayer which gave maximum hydrophobicity to the mica surface. In addition, it was demonstrated that both the bubble and mica had about the same magnitude of positive charge (+65 mV) at this optimum pH. Finally, from the extended DLVO theory, it was shown that heterocoagulation between the bubble and the mica could only occur, providing there was a long range hydrophobic interaction force to counterbalance the repulsive Van der Waals and electrostatic forces. A possible explanation for this long range attraction was spontaneous cavity formation or micro-bubbles caused by dissolved air.