Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iiia metal or beryllium
Patent
1985-06-06
1986-09-30
Carter, H. T.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iiia metal or beryllium
423121, C01F 706
Patent
active
046146423
DESCRIPTION:
BRIEF SUMMARY
The invention, which is an improvement to patent application No. 82 12412 filed July 8, 1982, concerns a highly productive method of precipitating Al(OH).sub.3, from a super-saturated solution of alkali metal aluminate obtained by the Bayer process of alkaline action on bauxites, wherein the introduction of primer results in an aluminium trihydroxide of large, even particle size, where a maximum of 10% of the particles produced have their smallest dimension less than 45 microns.
The Bayer process, which has been widely described in the specialised literature and is well known in the art, is the essential technique for producing alumina designed to be converted to aluminium by igneous electrolysis. In this process the bauxite is treated hot with an aqueous solution of sodium hydroxide at an appropriate concentration, thus making the alumina soluble and producing a super-saturated solution of sodium aluminate. After separation of the solid phase, comprising the unattacked residue (red mud) of the ore, the super-saturated solution of sodium aluminate is generally seeded with aluminium hydroxide, hereinafter referred to as "primer", in order to bring about the precipitation of an aluminium trihydroxide.
It is well known in the art that there are several different industrial methods of producing aluminium trihydroxide by alkaline action on bauxites in the Bayer process; these are normally divided into two categories, one known as the European process and the other as the American process.
In the European process the aluminium trihydroxide is precipitated in the course of the operation known as decomposition of an aqueous solution of sodium aluminate with a high concentration of caustic Na.sub.2 O, generally containing from 130 to 170 grammes of Na.sub.2 O per liter of sodium aluminate solution to be decomposed. The expression "concentration of caustic Na.sub.2 O should be understood as referring to the total quantity of Na.sub.2 O expressed in grammes per liter in the sodium aluminate solution to be decomposed, in the bonded form of sodium aluminate and in the free form of sodium hydroxide. In this process a quantity generally ranging from 350 g/l to 600 g/l of Al(OH).sub.3 acting as primer is added to the sodium aluminate solution to be decomposed, decomposition generally taking place at a maximum temperature of 55.degree. C. A process of this type gives high alumina productivity, of up to 80 g of Al.sub.2 O.sub.3 per liter of sodium aluminate solution, but the aluminium trihydroxide thus produced generally has fine particles and, when calcined, gives an alumina of a fineness which at the present time is considered troublesome for igneous electrolysis.
In the American process the aluminium trihydroxide is precipitated by decomposing an aqueous solution of sodium aluminate with a low concentration of caustic Na.sub.2 O, not exceeding 110 g of Na.sub.2 O per liter of sodium aluminate solution to be decomposed. This is done by adding a smaller quantity than in the European process of Al(OH).sub.3 acting as primer to the sodium aluminate solution to be decomposed; the quantity is generally from 100 g/l to 200 g/l of the aluminate solution to be decomposed. On the other hand decomposition takes place at a higher temperature, such as 70.degree. C. All these operating conditions combined lead to the production of an aluminum trihydroxide of a larger particle size than that obtained by the European process; after grading and calcination it gives an alumina of a particle size known as "sandy coarse", which is at present required for igneous electrolysis. However, the operating conditions have the adverse effect of reducing Al.sub.2 O.sub.3 productivity, which is much lower than in the European process, generally about 50 g of Al.sub.2 O.sub.3 per liter of aluminate solution in the production of a sandy coarse alumina. Attempts to improve productivity by reducing the decomposing temperature and adding a larger quantity of Al(OH).sub.3 acting as primer to the sodium aluminate solution to be decomposed are known to have c
REFERENCES:
patent: 4049773 (1977-09-01), Mejdell et al.
patent: 4234559 (1980-11-01), Tschamper
patent: 4305913 (1981-12-01), Anjier
patent: 4311486 (1982-01-01), Yamasla et al.
patent: 4364919 (1982-12-01), Yamasla et al.
patent: 4511542 (1985-04-01), Anjier et al.
patent: 4512959 (1985-04-01), Pohland et al.
Cristol Benoit
Mordini Jacques
Aluminum Pechiney
Carter H. T.
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