Quantifying bubble-scheelite interaction under the effect of sodium oleate

Scheelite (CaWO4) is mainly collected through froth flotation. It has significant applications in the manufacturing of alloys and steels. To better understand bubble-scheelite attachment mechanisms, we probed the interaction force between a bubble and a scheelite surface using an atomic force microscope (AFM) and investigated the way in which sodium oleate and calcium ions affected how the bubble attached. The results showed that the electrical double layer (EDL) force was the main repulsive force that inhibited the scheelite-bubble attachment. Adding 0.01 mM of sodium oleate (NaOl) to the solution could hydrophobize the scheelite surface, allowing the hydrophobic attraction to dominate bubble-scheelite interaction. Increasing the NaOl concentration from 0.01 mM NaO1 to 0.02 mM made the scheelite and bubble's zeta potential more negative, resulting in a stronger EDL repulsion. Increasing the NaOl concentration also reduced the interfacial tension of the bubble, which could inhibit the bubble-scheelite attachment; accordingly, the air bubble cannot attach to the scheelite surface when NaOl concentration was 0.02 mM. Adding calcium ions significantly reduced the magnitude of the scheelite and bubble's zeta potential, which was increased by adding the NaOl. Reducing the magnitude weakened the EDL repulsive force and facilitated the bubble attachment. The interfacial tension for the air bubble was significantly increased from 39.5 to 69.8 mM/m, when the calcium ions concentration was only 1 mM, which could increase the Laplace pressure and benefit the bubble attachment. The weakened repulsive force and the increased interfacial tension led to the scheelite-bubble attachment. Micro-flotation tests also verified that the excessive NaOl concentration was detrimental for scheelite flotation and that the adverse effects could be eliminated by adding calcium ions. This study yielded quantitative data on the interaction forces between a scheelite surface and a bubble, providing a better understanding of the fundamental interaction mechanisms for bubble-scheelite attachment in mineral flotation.