Surface characterization of molybdenite, bismuthinite, and pyrite to identify the influence of pH on the mineral floatability

Researchers in most of the published works paid a great attention in the effects of pH on the flotation behavior of minerals, where most of which ignored the influences of pH on the surface properties. Herein, the detailed surface analyses of several typical sulfide minerals, namely, molybdenite, bismuthinite, and pyrite, were conducted to identify the effect of pH on the mineral surface property. As observed, all these minerals exhibited excellent hydrophobicity under highly acid conditions. The surface chemical composition of molybdenite and bismuthinite remained relatively steady as pH increased, but the decrease in surface hydrophobicity of bismuthinite was more serious than that of molybdenite under the alkaline conditions. Pyrite was more affected by the pH value. At pH below 4.0, FeS2 was the dominate species at pyrite surface. With the increase in alkalinity, the pyrite was gradually oxidized and the surface became hydrophilic. As the pH further increased to12.0, the hydrophobicity of pyrite almost vanished due to the deposition of hydrophilic oxidation products (e.g., Fe-2(SO4)(3), Fe(OH)(3), and FeOOH) on its surface. The differences in the surface characteristics of molybdenite, bismuthinite, and pyrite at different pH values can be used to design the flotation process for separation of these sulfide minerals.