Alumina production

Table 3. Composition of Bauxite Used for Alumina Production...

The large majority of activated alumina products are derived from activation of aluminum hydroxide, rehydrated alumina, or pseudoboehmite gel. Other commerical methods to produce specialty activated aluminas are roasting of aluminum chloride [7446-70-0], AIQ calcination of precursors such as ammonium alum [7784-25-0], AlH2NOgS2. Processing is tailored to optimize one or more of the product properties such as surface area, purity, pore size distribution, particle size, shape, or strength. 

The gel-based products have traditionally been the most expensive and highest performance activated alumina products. They have very good mechanical properties, high surface area, and their purity and ganima-aluniina stmcture make them somewhat resistant to thermal degradation. On the other hand, they are the most difficult to manufacture and disposal of by-product salts can present an environmental problem. 

Alumina Products and Technology, Product Data, Kaiser Chemicals Corporation, Baton Rouge, La., 1984. Note Kaiser is now owned by La Roche Chemicals Corporation. 

Alumina Product Data Bulletins L o. CHE920, CHE 922, Alcoa, Bauxite, Arkansas Alcoa Chemie, Lausanne, Switzerland Alcan Chemicals, Qeveland, Ohio Kaiser Chemicals, Cleveland, Ohio Malakoff Industries (Reynolds), Malakoff, Texas Baikowski, Charlotte, North Carolina Criceram (Pechiney), Cedex, Prance Union Carbide Specialty Powders, IndianapoHs, Indiana Sumitomo Aluminum Smelting, Tokyo, Japan Showa Alumina Industries SAL, Tokyo, Japan VAW Aluminum, Germany Martinswerke, Germany Pechiney, Prance Arco Specialty Chemicals, Newton Square, Pennsylvania. 

Table 5. Location and Capacities of Chemical Grade Alumina Production Facilities...

S. Yu. Gordienko and L. S. Lartseva. Plugging-solution—contains Portland cement, soda-sulphate waste from alumina production, glycerine and water and hardens at sub-zero temperatures. Patent SU 1760087-A, 1992. 

In the flowsheet of alumina production by the Bayer process, aluminum is precipitated from an aqueous solution as aluminum hydroxide. The hydroxide is dried in rotary furnaces. In recent times, fluidized-bed reactors have been deployed which yield practically nonhygroscopic alumina. The dissociation of aluminum hydroxide occurs in steps,... 

One major environmental problem is associated with the Bayer process for alumina production from bauxite. The residue (called red mud ) which is obtained in the process contains unextracted oxides (e.g., alumina, ferric oxide, titanium dioxide, silicon dioxide, calcium oxide) and various insoluble materials. This solid waste is washed and discharged into impoundment ponds or into the marine environment. 

Kaolinite, 2 345t 6 659-664, 686-687, 718 composition in bauxite used for alumina production, 2 346t structure and composition, 6 668 in unit layer mixtures, 6 671 Kaolins, 6 686. See also Kaolin dry process, 6 673-675 estimated total production, 6 683 grades for polymer applications, 6 694t properties relating to applictions, 6 686t uses, 6 686-696 wet process, 6 675-679 Kapok, 11 297... 

In Australia one alumina producer has started to specify membrane-only caustic soda for consumption in the process. Yields of alumina production can be increased if membrane caustic soda is used. 

Literature has revealed limited kinetic data on secondary nucleation of alumina trihydrate in the precipitator of the Bayer Process for alumina production. A batch agitated, isothermal, three litre crystallizer was used in the study. A Coulter-Counter was utilized as the particle sizing equipment. The effects of seed density, supersaturation and temperature on secondary nucleation were investigated. Maximum nucleation rates were found to occur at about 70 C and for any crystallization temperature, the nucleation rate passed through a maximum. The correlated equation for the effective secondary nucleation rate of alumina trihydrate is... 

Methanol, ethanol, n- and isopropyl alcohol and allyl alcohol were determined by gas chromatography on a 3-meter column packed with 15% Hallcomid on 60-80 mesh acid-washed Chromosorb. Methane, ethane, ethylene, and propylene were also determined by gas chromatography using a 3-meter column packed with 60-80 mesh activated alumina. Products were identified by comparing their retention times with those of pure standards. 

Currently Alcoa of Australia Limited imports almost 600,000 tonnes of 50% caustic soda solution, mainlyfrom Europeand North America, for its alumina production operations in Western Australia. This demand constitutes 20 deliveries per year of 30,000 tonnes each (3 ships involved). The ships unload their caustic soda at the Fremantle and Bunbury ports. 

Gardner H. J., Grjotheim K., Welch B. J., Proc. Int. ICSOBA Symposium on Alumina Production until 2000, Tilrany, Hungary, Oct. 1981, p. 27. 

Primary air flow, supplied at the bottom of the bed, is insufficient for complete combustion of the fuel. The zone below the elevation of secondary-air jets is endothermic, cracking oil to yield carbon and fuel gas species. These burned in the upper, exothermic zone. Alumina product is withdrawn from a standpipe receiving solid from the upper zone, and burn-off of carbon in this zone is sufficient to yield a product that is acceptably white. Fluidizing-gas velocity being lower in the primary combustion zone than in the secondary, density is higher. Provision of the two zones accomplishes two purposes (1) affording a sufficient solid residence time in the primary zone and (2) reducing horsepower needed for air compression. 

One of the industrial applications of hydrothermal precipitation is ordinary alumina production. The Bayer process is shown in Figine 1.7. T... 

Above 2000°F the authors observed the presence of beta-alumina. In the higher alumina products, the amount was still on the increase at the highest test temperature. Unexplainably the quantity of beta-alumina decreased above the 2300°F in the 70% alumina sample. Furthermore, a decrease in beta-alumina occurred above this temperature in the superduty product. This was due to the increased formation of glass. The magnitude of these decreases was not discussed by the authors. However, their plot of relative XRD peak intensity vs. temperature clearly indicates that the decrease is greater for the 70% alumina product than the superduty sample. 

The change in mineralogy is dependent on the alumina content of the sample. For the lower alumina products, the alpha alumina content remained essentially the same. However, a slight increase in the alumina content of certain samples, the superduty and the 60% alumina products, was observed at the lower test temperature. 

Because the details of processing in each class of CMCs (e.g., oxide, carbide, or nitride matrix) are slightly different, the appropriate thermochemical approach for each class may also be different. For example, in the formation of alumina matrix materials by directed metal oxidation, the alumina product grows from a molten aluminum alloy by reaction with an oxygen-containing gas phase. On the other hand, in the formation of platlet-reinforced zirconium carbide, the gas phase is not involved in the reaction at all, being inert to the reactants and products. Thus, a general approach to deal with the myriad of possible products formed by the... 

While the qualitative changes which occur during the dehydrations of aluminum hydroxides have been characterized, little quantitative information concerning the kinetics and mechanisms of these processes has been obtained. The surface textures and reactivities of the alumina products have been investigated, but little is known about the detailed changes which occur on heating the precursor phases. 

TABLE 12.3 Major World Producers of Alumina (Production in Thousands of Metric Tonnes)... 

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