Nine bauxite samples from Brazil and one from Ghana were submitted to alkaline digestion at 145°C. All initial samples and their red muds were chemically analysed and characterised by X-ray diffraction and Mössbauer spectroscopy at 298 and 77 K. The settling rates of all red muds were also measured. It was observed that the presence of goethite in the bauxite has a profound effect on the settling rate of the red mud produced in the Bayer process. The goethite possess high Al-for-Fe substitution and/or nanometric crystallites, and decreases the settling rate. The dissolution of this goethite during the caustic digestion at 145°C was also observed, leading to the formation of hematite. Finally, the hematite in the red muds presents crystals with larger sizes in comparison with those in the original bauxites.
On a soumis à la digestion alcaline à 145°C, neuf échantillons de bauxite du Brésil et un échantillon du Ghana. On a analysé chimiquement tous les échantillons initiaux et leurs boues rouges et on les a caractérisés par diffraction des rayons x et par spectroscopie Mössbauer à 298 K et à 77 K. On a également mesuré la vitesse de sédimentation de toutes les boues rouges. On a observé que la présence de goethite dans la bauxite avait un effet important sur la vitesse de sédimentation de la boue rouge produite par le procédé Bayer. La goethite possède une substitution élevée d’Al pour le Fe et/ou des cristallites nanométriques, et elle diminue la vitesse de sédimentation. On a également observé la dissolution de cette goethite lors de la digestion caustique à 145°C, qui menait à la formation d’hématite. Finalement, l’hématite des boues rouges présente des cristaux de plus grandes tailles en comparaison à ceux des bauxites originales. 相似文献
In the present study, direct acid and active calcination–acid leaching processes were employed to remove K2O and Fe2O3 impurities from bauxite tailings. For direct acid leaching, the results indicated that Fe2O3 can be removed with the addition of 3?mol?L?1 HCL, whereas K2O cannot be removed even when the concentration of HCl is higher than 7?mol?L?1. As the bauxite tailings were calcined at 400–700°C, both K2O and Fe2O3 were removed at low HCl concentration (3?mol?L?1), which was ascribed to the removal of hydroxyls and increased K activity, derived from X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. 相似文献