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Titanium valorization: From chemical milling baths to air depollution applications

Abstract : Titanium metal is widely used in the aeronautical sector for its specific properties and corrosion resistance. The design of titanium workpieces is based on chemical milling: a fast, precise, low cost technique popular in the aerospace industry. Material is removed from selected areas of a part by immersing it in a strong chemical reagent. This process produces shallow cavities on plates and sheets or removes shallow layers of materials from large aircraft components to optimize the strength/weight ratio. However, it leads to large volumes of wasted acid baths, which are harmful to the environment and have to be sent to an approved waste facility. The objective of this paper is to highlight a cleaner production process based on the circular economy concept, i.e. reduce, reuse and recycle to limit environmental pollution and operating costs. Waste from chemical milling baths used in the design of titanium parts was recovered with the aim of synthesizing titanium dioxide and using it for air depollution applications. The waste consisted of hexafluorotitanate compounds. Various processing techniques to synthesize titanium dioxide from hexafluorotitanate compounds were tested and resulted in powders having different physicochemical characteristics. The synthesis parameters studied were the nature of the decomplexing agent, the dehydration temperature and the heating period. Photocatalytic coatings were then formulated on the basis of the synthesized powders. They were applied to a mortar surface to evaluate their efficiency to degrade nitric oxide under two UV lighting intensities, 5 and 20 W/m2. Depending on the synthesis process conditions, the concentration and crystal form of titanium dioxide particles varied, leading to more or less efficient photocatalytic coatings. The proportions of anatase and rutile phases in the synthesized powders were between 3 and 13%, and 5 and 30%, respectively. Concerning the particle size distribution, the variations observed were dependent on the D-values. D10% was quite similar for all powders. However, D50% and D90% differed by a factor of two for some powders, notably because of the presence of impurities or remaining decomplexing agent particles. NO degradation varied depending on the photocatalytic dispersions and could reach 7% under an irradiation of 20 W/m2. This article highlights the possible valorization of a massive industrial waste for specific applications provided that the conditions of processing techniques are optimized.
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Submitted on : Monday, March 2, 2020 - 3:20:38 PM
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Julie Hot, Ariane Dasque, Jivko Topalov, Vanessa Mazars, Erick Ringot. Titanium valorization: From chemical milling baths to air depollution applications. Journal of Cleaner Production, Elsevier, 2020, 249, pp.119344. ⟨10.1016/j.jclepro.2019.119344⟩. ⟨hal-02495816⟩



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