| 摘要 |
In both the European and American versions of the Bayer alumina process, precipitation of alumina trihydrate from the caustic solution is limited to about one-half of the alumina in solution, in order to obtain a product of commercial specification grade. The partly-spent caustic is recycled to the digestion state. In the process of this invention, the partly-spent liquor is further cooled to intentionally precipitate very fine particles of alumina hydrate. This is separated from the spent liquor which is recycled to digestion. The fine alumina is dissolved in a reheated sidestream of the clarified pregnant liquor to provide a hot, saturated liquor which is combined with the remaining clarified pregnant liquor, enriching it in alumina. More than 50 percent of the alumina in this richer liquor is recovered from precipitation as specification grade alumina. The recycled spent liquor has a correspondingly greater capacity to dissolve alumina from the bauxite ore due to its lower alumina content. The smaller volume of recycle liquor compared to bauxite digested therein also aids desilication, and proportionately lessens evaporation and filtration loads. The process of the invention can be used in existing European or American Bayer process plants and, with slight modification in processing steps and conditions, essentially any type of bauxite ore can be treated.
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