Mechanisms of Dodecylamine Flotation of Quartz

Primary monoamines have been long used and studied as flotation collectors for quartz. In the past several mechanisms have been proposed to explain the manner in which the amines adsorb onto and render the mineral hydrophobic and, thus, floatable. From past data and proposed mechanisms and reinterpreting some of the past data it appears that somewhat different mechanisms account for amine function at different pH values. At low pH values the amine ions apparently adsorb as individual ions through coulombic interaction between the ion and the quartz surface. The surface coverage of amine ions is not great and only limited flotation takes place. As pH is raised adsorption of individual ions (monomers and dimere) increase. Thus it is suggested that at higher pH values, provided the Krafft lemperature is not exceeded (26° C for dodccylammonium chloride), the adsorption of ions increases with pH to a point where the amine solubility limit is exceeded within the quartz-solution interface. Surface precipitation takes place resulting in increased surface hydrophobicity and flotation. If the Krafft temperature is exceeded increased hydrophobicity and flotation will probably occur only after the critical micelle concentration (CMC) is exceeded within the quartz-solution interface. In both cases if pH is still further increased ultimately either the solubility or the CMC would be exceeded within the bulk of the solution provided the total amount of amine present is sufficient. Under such conditions flotation would become erratic and decrease. Ultimately, near pH 12 and above flotation does not occur.