New Reagent Formulations for Selective Flotation of Scheelite from a Skarn Ore with Complex Calcium Minerals Gangue

International audienceThe approach using synergistic effects of the blend of carboxylic collectors was applied to process the Tabuaco tungsten skarn ores (Portugal) by flotation. However, a very complex mineral composition with high amounts of the fluorite (>10%) and apatite (3–5%), as well as the presence of more than 40% of vesuvianite, a silicate of calcium, implied that such separation is highly challenging. In this work, the influence of sodium silicate and sodium carbonate on the selective flotation of scheelite has been investigated. A study of depressants dosage allowed to reach a selective flotation of scheelite from calcium minerals at 1125 g/t, except from fluorite. The use of sodium carbonate with sodium silicate showed synergistic effects, increasing the WO3 grade from 6.6% to 11.2% without impacting the recovery. Collector formulations were created in the laboratory by mixing the commercial fatty acids, in which oleic and linoleic acid predominated, in various proportions with rosin acids while the ratio between oleic and linoleic acids was kept constant. The tungsten recovery increased significantly, up to 98%, with the amount of rosin acids in the mixture while the concentrate grade decreased from 16% WO3 grade to 10.5% WO3 grade impacting the selective flotation of scheelite from an ore with 0.9% WO3 grade. The optimal ratio of fatty and rosin acids was then experimentally set to 5/1-6/1. An unprecedented increase of the flotation selectivity between scheelite and fluorite was obtained when the saturated acids were introduced in the formulation. The concentrate grade reached 27% WO3 grade for the same ratio between anionic reagents. Thus, the new reagent formulation allowed to obtain a tungsten concentrate after only one cleaner stage without additional use of thermal treatment or activating heavy metals salts or specific depressants