Tungsten minerals flotation with 4-alkoxy benzohydroxamic acid: The structure-performance relationship of its C3 derivatives

To improve the flotation recovery of tungsten minerals, 4-alkoxy benzohydroxamic acids containing C3 alkyl (C3OBs), namely 4-propoxy benzohydroxamic acid (POB), 4-iso-propoxy benzohydroxamic acid (IPOB) and 4-allyloxy hydroxamic acid (AOB), were designed as scheelite and wolframite collectors. The micro-flotation results uncovered that C3OBs exhibited stronger collecting ability towards Pb(Ⅱ)-activated scheelite and wolframite than benzohydroxamic acid (BHA) and the collecting ability of C3OBs was in sequence of POB > IPOB > AOB. The density functional theory (DFT) calculation indicated that the alkoxy oxygen atom of C3OBs contributed to their highest occupied molecular orbital (HOMO), and the HOMO energy followed the order as IPOB > POB > AOB > BHA. The higher HOMO energy, the stronger electron-donating activity. Nevertheless, IPOB didn’t return the highest flotation recovery of tungsten minerals. On the other hand, the hydrophobicity of these four hydroxamate collectors was in sequence of POB > IPOB > AOB > BHA, corresponding to the results of contact angle, micro-flotation and adsorption capacity. Therefore, the hydrophobization of the four hydroxamate collectors played a key role in their flotation performance to the Pb(II)-activated scheelite and wolframite. Moreover, this work offered a new approach for developing superior collectors.