IPC분류정보
국가/구분 |
United States(US) Patent
등록
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국제특허분류(IPC7판) |
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출원번호 |
US-0613701
(1984-05-24)
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발명자
/ 주소 |
- Anjier Joseph L. (Baton Rouge LA) Roberson Morris L. (Baton Rouge LA) Atchison William E. (Greenwell Springs LA)
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출원인 / 주소 |
- Kaiser Aluminum & Chemical Corporation (Oakland CA 02)
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인용정보 |
피인용 횟수 :
12 인용 특허 :
4 |
초록
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An improved precipitation system is provided for the Bayer process production of alumina hydrate. In order to produce coarse and strong alumina hydrate at high yield, supersaturated Bayer process sodium aluminate liquor is seeded with a relatively small seed charge in a first precipitator at a relat
An improved precipitation system is provided for the Bayer process production of alumina hydrate. In order to produce coarse and strong alumina hydrate at high yield, supersaturated Bayer process sodium aluminate liquor is seeded with a relatively small seed charge in a first precipitator at a relatively low temperature and the produced slurry is transferred to a second precipitator where without additional seeding, the solids content of the slurry is allowed to increase to about 250-700 g/l by accumulating solids in the line until the desired solids content is reached. After a suitable residence time, a coarse, strong product hydrate can be recovered in yields of or exceeding 80 g/l based on the alumina (Al2O3) content of the supersaturated sodium aluminate liquor subjected to precipitation. The process not only produces the desired product at high yield but also, due to the use of a single, small seed charge, the precipitation system requires fewer precipitators and classifiers for a given residence time. Additionally, it allows significant energy savings by eliminating the need for cooling during the precipitation cycle due to the lower than conventional temperatures which can be utilized in the first precipitator.
대표청구항
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In the process of producing alumina hydrate from supersaturated Bayer process sodium aluminate liquors, the liquors being derived from the digestion of bauxite at elevated temperatures and pressures with a caustic medium, by seeding the liquors with an alumina hydrate seed charge to initiate precipi
In the process of producing alumina hydrate from supersaturated Bayer process sodium aluminate liquors, the liquors being derived from the digestion of bauxite at elevated temperatures and pressures with a caustic medium, by seeding the liquors with an alumina hydrate seed charge to initiate precipitation of alumina hydrate from the supersaturated liquors, the improvement which comprises: (a) introducing a supersaturated sodium aluminate liquor into one or more precipitation vessels defined as first precipitation stage, the liquor being characterized by an alumina (Al2O3) to caustic weight ratio (A/C) from about 0.575 to about 0.700, wherein the caustic concentration, expressed in grams/liter Na2CO3, is in the range from about 165 to about 300 grams/liter; (b) seeding the liquor with an alumina hydrate seed charge characterized by a particle size distribution wherein up to about 50% by weight of the seed charge consists of particles having a particle size below about 44 microns, the quantity of the seed charge being so selected as to establish a seed charge surface area in relation to the liquor to be seeded within the range from about 1 to about 3 m2/liter of liquor; (c) maintaining the seeded liquor at a temperature below about 68°C. (155°F.) for an average time period from about 90 to about 300 minutes to allow precipitation of alumina hydrate and the generation of a slurry having a solids content in the range from about 30 to about 40 g/l; (d) transferring the slurry into a second precipitation stage, where the slurry solids content is allowed to increase to about 250-700 g/l, without additional seeding, by accumulating solids from the first precipitation stage and maintaining the slurry of increased solids content in the second precipitation stage for a time period sufficient to allow agglomeration and growth of the solids within the temperature range from about 40°to about 55°C. (105°-131°F.); (e) subjecting the slurry, having the significantly increased solids content, to a separation treatment to recover product alumina hydrate from the slurry, the product being characterized by an average particle size distribution wherein at least about 95% by weight of the particles have a size in excess of 44 microns, and a fine fraction, characterized by a particle size distribution wherein up to about 50% by weight of the particles have a size below about 44 microns and a liquor having an A/C ratio of about 0.375 or less; (f) recovering the separated product alumina hydrate in a yield of about 80 g/l and above, based on the dissolved alumina (Al2O3) content of the supersaturated liquor subjected to precipitation in the first precipitation line and subjecting the fine fraction to a washing step to remove adhered impurities and recycling the washed fraction to the first precipitation stage as seed charge. In the process of producing alumina hydrate from supersaturated Bayer process sodium aluminate liquors, the liquors being derived from the digestion of bauxite at elevated temperatures and pressures with a caustic medium, by seeding the liquors with an alumina hydrate seed charge to initiate precipitation of alumina hydrate from the supersaturated liquors, the improvement which comprises: (a) introducing a supersaturated sodium aluminate liquor into one or more precipitation vessels defined as first precipitation stage, the liquor being characterized by an alumina (Al2O3) to caustic weight ratio (A/C) from about 0.575 to about 0.700, wherein the caustic concentration, expressed in grams/liter Na2CO3, is in the range from about 165 to about 300 grams/liter; (b) seeding the liquor with an alumina hydrate seed charge characterized by a particle size distribution wherein up to about 50% by weight of the seed charge consists of particles having a particle size below about 44 microns, the quantity of the seed charge being so selected as to establish a seed charge surface area in relation to the liquor to be seeded within the range from about 1 to about 3 m2/liter of liquor; (c) maintaining the seeded liquor at a temperature below about 68°C. (155°F.) for an average time period from about 90 minutes to about 300 minutes to allow precipitation of alumina hydrate and the generation of a slurry having a solids content in the range from about 30 to about 40 g/l; (d) transferring the slurry into a second precipitation stage, where the solids content of the slurry is allowed to accumulate to about 250-700 g/l and introducing additional seed into the slurry, the additional seed charge being so selected as to establish a seed surface area in relation to the slurry to be seeded within the range from about 5 to about 10 m2/liter of slurry; (e) maintaining the slurry for a time sufficient to allow agglomeration, growth, and cementation of the solids within the temperature range from about 40°to about 68°C.; (f) subjecting the slurry to a size classification stage to separate product alumina hydrate, characterized by a particle size distribution wherein at least about 95% by weight of the particles have a size in excess of 44 microns, and a fine fraction which is subjected to a further classification stage to recover a relatively coarse alumina hydrate fraction which is employed as seed charge in the second precipitation stage and a fine fraction dispersed in the slurry; (g) introducing the slurry containing the fine fraction into a clarifier-settler to provide a fine seed product which after washing is used as seed in the first precipitation stage and a spent liquor which is recycled to the Bayer process.
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