Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iiia metal or beryllium
Patent
1993-06-07
1994-05-17
Straub, Gary P.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iiia metal or beryllium
423121, 423266, 423625, 423629, 23300, 23305A, C01F 702
Patent
active
053126033
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP91/02251 filed Nov. 28, 1991, now WO 92/10426, published Jun. 25, 1992.
FIELD OF THE INVENTION
This invention relates to a process for the production of aluminum oxide trihydrate crystals by the Bayer process.
STATEMENT OF RELATED ART
The Bayer process is a process for obtaining aluminum hydroxide from bauxite {Buchner, Schliebs, Sinter, Buchel, Industrielle anorganische Chemie [Title in English: Industrial Inorganic Chemistry] (VCH Weinheim 1984), pages 259 and 260; Ullmanns Encyclopadie der technischen Chemie [Title in English: Ullmann's Encyclopedia of Industrial Chemistry], 4th Edition, Vol. 7 (VCH Weinheim 1982) pages 305 et seq.} The process comprises the following main steps: temperatures of 140.degree. to 200.degree. C. to form soluble sodium aluminate, stirring and seeded with a large quantity of aluminum hydroxide ("stirring-out"), a large part of the dissolved aluminum hydroxide accumulating as gibbsite, substantially freed from aluminum hydroxide is returned to the process.
Crystallization of the aluminum hydroxide is kinetically inhibited to a considerable extent, so that the precipitation phase is carried out with a gradual reduction in temperature, 10.degree. C. for example, over a period of 24 to 48 h, during which a large quantity of crystal nuclei are added. In addition to crystallization of the aluminum hydroxide, the agglomeration of fine particles to build up relatively large crystal agglomerates is of considerable importance during the stirring-out process. Most of the aluminum hydroxide thus obtained is then calcined to aluminum oxide in another process step.
According to Aluminumtaschenbuch [Title in English: Aluminum Handbook], 14th Edition, 1988, page 11, by far the largest part of the oxide produced is processed to metal in aluminum works. A relatively small proportion, including the hydroxide form, is used for various applications in chemistry, ceramics and other fields. The metallurgical oxide has to meet particularly stringent requirements. A moderately calcined oxide having an alpha-Al.sub.2 O.sub.3 content of less than 30% and very few fines smaller than 45 .mu.m in size in particularly preferred. Because of this requirement, stringent demands are imposed on the crystallization process, which can be influenced by impurities in the crystallization solution. The impurities in question are, above all, the salts of huminic acids and degradation products thereof, such as sodium oxalate (see DE-A-36 09 662). Sodium oxalate is particularly troublesome because it shows crystallization behavior similar to that of aluminum hydroxide and can even act as a crystallization nucleus. This leads on the one hand to a less pure hydroxide and, on the other hand, to distinctly smaller crystals.
Numerous efforts have been made in the prior art to improve the crystallization of aluminum hydroxide in order to obtain coarser crystals.
U.S. Pat. No. 4,608,237 (DE-A-36 09 662) describes the use of polymers or copolymers of acrylic or methacrylic acid derivatives to influence the crystallization of aluminum hydroxide. U.S. Pat. No. 4,737,352 describes the use of fatty acids in an oil carrier in the Bayer process, which is said to give coarser crystals.
It is known from Chemical Abstracts 92 (12), Abstract 96203s, that glycerine distinctly inhibits the crystallization of aluminum hydroxide.
DESCRIPTION OF THE INVENTION
Object of the Invention
Against this background, the problem addressed by the present invention was to improve the known process for the formation of aluminum oxide trihydrate crystals by the Bayer process by making available new crystallization aids for precipitation of the aluminum hydroxide.
SUMMARY OF THE INVENTION
It has surprisingly been found that, even in relatively low concentrations in the crystallization liquor, polyglycerines lead to an aluminum hydroxide precipitate having a distinctly coarser degree of crystallinity compared with the prior art.
In a first embodiment, therefore, the present invention relates to a process for
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Chemical Abstracts, vol. 92, No. 12, Mar. 24, 1980, Columbus, Ohio, US; Abstract No. 96203 S, "Crystallization of homogeneously precipitated alumina hydrate gelts in aqueous solutions of various organic reagents", p. 111.
Ullmanns Encyklopadie der technischen Chemie, 4. Auflage, Band 7, VCH Weinheim 1982, S. 305 ff.
Buchner, Schliebs, Winter, Buchel, Industrielle anorganische Chemie, VCH Weinheim 1984, pp. 259-260.
Ullmann's Encyclopedia of Industrial Chemistry, vol. A1 (1985), "Aluminum Oxide", p. 557.
Bunte Reinhard
Foell Juergen
Hachgenei Johannes
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Nguyen N. M.
Straub Gary P.
Szoke Ernest G.
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