| 摘要 |
A method for processing trihydrate alumina bauxite with a low reactive silica content by subjecting said bauxite milled at atmospheric pressure to Bayer method alkaline etching is described, being characterised in that a desilication or pre-desilication process is conducted prior to etching the milled bauxite for a period of at least 30 minutes at a temperature of not more than 108 DEG C in the presence of a spent liquor aliquot with a non critical sol Al2O3 g/l to caust Na2O g/l concentration ratio (Rp) of 0.5 to 0.7, with a concentration of caustic soda of 140 to 170 g Na2O/l, to obtain a desilicated suspension with a dry matter concentration of at least 0.7 tons per m<3> of suspension, and in that, directly after the suspension is subjected to etching at atmospheric pressure by the remaining spent liquor with a non critical Rp of around 0.5 to 0.7 and with a caustic soda concentration set to 180 to 220 g Na2O/litre, a second desilication or post-desilication process is conducted for a period of at least 2 hours at a temperature of not more than 108 DEG C, generally of 95 to 195 DEG C, on the entire amount of suspension resulting from the etching, which then has an Rp of 1.05 to 1.17, prior to which the caustic soda concentration is adjusted by diluting to 140 to 180 g Na2O/litre.
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