Claims
- 1. A process for producing alumina from gibbsitic bauxite by mixing the bauxite with a sodium hydroxide-sodium aluminate digestion liquor, having an A/C ratio digesting in a digestion reactor the bauxite in said liquor at a temperature of 100.degree.-180.degree. C. to form a resulting slurry having a liquid phase, of sodium aluminate liquor and red mud, diluting the slurry, separating the red mud therefrom, precipitating alumina hydrate from the thus-obtained sodium aluminate liquor through cooling and agitation, and calcining the precipitated alumina hydrate into alumina, the improvement characterized by so controlling the process that, in the liquid phase of the slurry leaving the digestion reactor, maintaining a reactive hydroxide ion concentration below about 6 g/l, said reactive hydroxide ion concentration, AH, being defined by the following formula ##EQU3## where C.sub.Al.sbsb.2.spsb.O.sub.3,gi is the equilibrium solubility of Al.sub.2 O.sub.3 for gibbsite, in g/l.
- C.sub.Al.sbsb.2.spsb.O.sub.3 is the actual concentration of Al.sub.2 O.sub.3, in g/l. and
- C.sub.SiO.sbsb.2 is the actual concentration of SiO.sub.2, in g/l,
- and wherein the A/C ratio of the digestion liquor is below about 0.45, and the SiO.sub.2 concentration of the liquor is less than about 1 g/l.
- 2. The process of claim 1 wherein said A/C ratio is less than about 0.4, and the SiO.sub.2 concentration is less than about 0.6 g/l.
- 3. The process of claim 1, wherein the digestion liquor contains a maximum of 135 g/l Al.sub.2 O.sub.3.
- 4. The process of claim 1, wherein the Al.sub.2 O.sub.3 concentration is maximum of about 100 g/l, and the sodium expressed as Na.sub.2 CO.sub.3 has a concentration between from about 150 and about 300 g/l.
- 5. The process of claim 1, further characterized by the reactive hydroxide ion concentration being maintained at a level between about 0 and about 2 g/l.
- 6. The process of claim 1, wherein the bauxite has a ratio to the digestion liquor, further characterized by the reactive hydroxite ion concentration being maintained by controlling the ratio of bauxite to the digestion liquor.
- 7. The process of claim 1, further characterized by the bauxite being mixed with at least 10% of the digestion liquor, and the resulting slurry being held before digestion at a temperature of from about 80.degree. to about 100.degree. C. for about 0.5 to about 20 hours.
- 8. The process of claim 7, further characterized by said resulting slurry, while being held before digestion, being agitated using agitating power of from about 0.03 to about 0.2 kw per cubic meter of slurry.
- 9. The process of claim 1, wherein the slurry has an electrical conductivity, further characterized by the reactive hydroxide ion concentration being controlled by measurement of the electric conductivity of the slurry.
- 10. The process according claim 1, there being a difference between the actual concentration of Al.sub.2 O.sub.3 and the equilibrium solubility thereof, and wherein said digestion reactor has an outlet, further characterized by the digesting being carried out so that the difference between the actual concentration of Al.sub.2 O.sub.3 and the equilibrium solubility thereof, in the slurry at the outlet of the digestion reactor, is not greater than 18 g/l.
Priority Claims (1)
Number |
Date |
Country |
Kind |
5601/88 |
Oct 1988 |
HUX |
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Parent Case Info
This application is a continuation-in-part of Ser. No. 317,778 filed Mar. 2, 1989, now abandoned.
US Referenced Citations (12)
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
317778 |
Mar 1989 |
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