Improvement to the bayer process for producing alumina...

Details Improvement to the bayer process for producing alumina... Improvement to the bayer process for producing alumina...

C - Chemistry, Metallurgy

01

F

C01F 7/14 (2006.01) B01D 29/00 (2006.01) C01F 7/06 (2006.01)

Patent

CA 2732529

Process for manufacturing alumina trihydrate by alkaline attack of bauxite, following the general steps of the Bayer process, and during which, after settling and before decomposition, the aluminate liquor undergoes a filtration, known as security filtration, so that at the end of the filtration it contains less than 10 mg/l of insoluble particles, characterized in that, during said security filtration, a filtration device is used that comprises a zone in which the liquor is subjected, after passing through said filtration media, to a pressure greater than 2 bar, preferably greater than 3 bar. Preferably, this device also comprises a zone in which the liquor is subjected, before passing through the filtration media, to a pressure greater than 5 bar, preferably greater than 6, typically in the vicinity of 7 bar. In this way, the aluminate liquor can be kept at a high temperature during the security filtration, typically greater than 130°C, preferably greater than 140°C, and be brought to a high degree of supersaturation Rp, typically greater than 1.25, without risk of reversion.

Procédé de fabrication de trihydrate d'alumine par attaque alcaline de bauxite, suivant les étapes générales du procédé Bayer, et au cours duquel, après décantation et avant décomposition, la liqueur d'aluminate subit une filtration, dite filtration de sécurité, de sorte qu'en sortie de filtration elle contienne moins de 10 mg/l de particules insolubles, caractérisé en ce que, au cours de ladite filtration de sécurité, on utilise un dispositif de filtration comprenant une zone dans laquelle la liqueur est soumise, après passage par ledit média de filtration, à une pression supérieure à 2 bars, de préférence supérieure à 3 bars. De préférence, ce dispositif comprend également une zone dans laquelle la liqueur est soumise, avant passage par le média de filtration, à une pression supérieure à 5 bars, de préférence supérieure à 6, typiquement voisine de 7 bars. De la sorte, la liqueur d'aluminate peut être maintenue à une température élevée au cours de la filtration de sécurité, typiquement supérieure à 130 °C, de préférence supérieure à 140 °C, et être portée à un taux de sursaturation R p important, typiquement supérieur à 1,25, sans risque de rétrogradation.

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