Synergistic effects between fatty acids and non-ionic reagents for the selective flotation of scheelite from a complex tungsten skarn ore

•With single fatty acids, the flotation selectivity is always in favour of fluorite.•Mixing saturated and unsaturated fatty acids increase the selectivity for scheelite.•Isotridecanol further increases the selectivity towards scheelite.•A WO3 grade of 45.2% is attained in the cleaning concentrate. Tungsten skarns today represent >40% of the global tungsten reserves although their processing is usually difficult due to the fine textures, low grade, and complex mineralogical association. Notably, the selective flotation of scheelite from gangue calcium minerals, particularly fluorite, using fatty acids still remains an industrial and scientific challenge. In the present work, we investigated the influence of the pH, of the chain length and unsaturation degree, of mixing fatty acids with different structures, and of mixing fatty acids with non-ionic reagents on the flotation selectivity towards scheelite. Four different fatty acids were tested in micro-flotation on scheelite and fluorite, at an optimal pH of 9. We demonstrated that the short-length chain fatty acids do not afford a good floatability of scheelite while sodium oleate always exhibits a very good floatability of fluorite. Meanwhile, linoleate and stearate present more equilibrated properties. When fatty acids are mixed, particularly saturated and unsaturated fatty acids, the micro-flotation selectivity towards scheelite increases, which is, however, always in favour of fluorite in the whole studied range. However, the introduction of saturated fatty acids in non-commercial unsaturated-fatty-acid-based mixtures did not increase significantly the selectivity in flotation tests conducted on the Tabuaço complex tungsten skarn ore. Though, the use of tall oil fatty acids comprising saturated fatty acids provided a better selectivity between scheelite and fluorite compared to the classical formulations, although it was not enough to attain a satisfactory selectivity between scheelite and fluorite. Finally, the introduction of isotridecanol, a fatty alcohol, in commercial formulations afforded a significant increase in the flotation selectivity in favour of scheelite, which allowed attaining an unprecedented WO3 grade of 45.2% with 56.5% WO3 recovery in the flotation cleaning concentrate.