Abstract

ZHANG, L.; ZHOU, Y.; WANG, H.  and  MO, C.. Studies on fluorination of Fe₃O₄ (magnetite) by NH₄HF₂. J. S. Afr. Inst. Min. Metall. [online]. 2022, vol.122, n.12, pp.705-714. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/1639/2022.

Fluorination of magnetite (Fe₃O₄) by NH₄HF₂ was investigated using simultaneous thermogravimetry and differential thermal analysis (TG-DTA), and observing the morphology and phase changes using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffractometry (XRD). The results indicate that fluorination with the involvement of oxygen begins at room temperature, peaks at 1784ºC, and is completed at 200ºC with the formation of only (NH₄)₃FeF₆. On heating, (NH₄)₃FeF₆ gradually releases NH₄F by the formation of NH₄FeF₄ at 259ºC, then (NH₄)_0.l8FeF₃ at 327ºC, and finally FeF₃ with minor FeF₂ at 400ºC due to the partial reduction of Fe (III) to Fe (II). At 550ºC, FeF₃ is oxidized to FeOF/Fe₂O₃.

Keywords : Ammonium bifluoride; fluorination; thermal decomposition; FeF₃; XRD.

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