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Tungsten recovery from a skarn with a low separation contrast : Contribution of molecular modelling in the flotation of calcium minerals

Abstract : Nowadays, skarns represent more than 40% of the global resources in tungsten, which has been classified as a critical raw material in the European Union. In particular, the Tabuaço deposit constitutes an archetype of tungsten skarns and contains high amounts of calcium minerals, including fluorite, apatite, and vesuvianite, in close association with scheelite (CaWO4). According to their similar surface properties, the separation of these minerals by flotation with fatty acids is significantly difficult and, therefore, remains a scientific challenge. In this study, which has been conducted within the framework of the FAME H2020 European project, an economic, environment friendly, and transferable process has been developed for the Tabuaço ore to demonstrate the feasibility of the tungsten skarns processing. In the froth flotation process, the Na2CO3/Na2SiO3 system has exhibited the best efficiency in terms of gangue minerals depression due to considerable synergistic effects that have been subsequently described by statistical, spectroscopic, and atomistic methods. Meanwhile, the influence of the ratios between different carboxylic acids in the collector formulations (Tall Oil Fatty Acids) has been assessed to improve the flotation selectivity. In addition, the enhanced gravity separation (Falcon centrifuge concentrator) has been investigated, optimised, and combined with the flotation to produce a marketable scheelite concentrate assaying 63% WO3 with 59% recovery. Besides, to gain understanding in the molecular mechanisms involved in the flotation process, the fluorite and scheelite interfaces have been modelled using the density functional theory. This study has allowed to characterise the hydration state of these minerals, which display different affinities for water molecules. Furthermore, the adsorption of fatty acids on fluorite has been studied to unravel the adsorption mechanisms of these molecules on calcium minerals, confirmed by experimental investigations.
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https://hal.univ-lorraine.fr/tel-02510942
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Submitted on : Wednesday, March 18, 2020 - 12:29:02 PM
Last modification on : Thursday, March 19, 2020 - 1:32:17 AM

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  • HAL Id : tel-02510942, version 1

Citation

Y. Foucaud. Tungsten recovery from a skarn with a low separation contrast : Contribution of molecular modelling in the flotation of calcium minerals. Earth Sciences. Université de Lorraine, 2019. English. ⟨NNT : 2019LORR0149⟩. ⟨tel-02510942⟩

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