Bauxite, synthetic

High Alumina Refractories. The desired alumina content, from 100% to just above 45%, is obtained by adding bauxites, synthetic aluminosihcates, and synthetic aluminas to clay and other bonding agents. These refractories are used in kilns, ladles, and furnaces that operate at temperatures or under conditions for which fireclay refractories are not suited. Phosphate-bonded alumina bricks have exceptionally high strength at low to intermediate temperatures and are employed in aluminum furnaces. High alumina and mullite are used in furnace roofs and petrochemical apphcations. 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

Cracking catalysts include synthetic and natural sihca-alumina, treated bentonite clay, fuller s earth, aluminum hydrosUicates, and bauxite. These catalysts are in the form of beads, pellets, and powder, and are used in a fixed, moving, or fluidized bed. The catalyst is usually heated and hfted into the reactor area by the incoming oil feed which, in mrn, is immediately vaporized upon contact. Vapors from the reactors pass upward through a cyclone separator which removes most of the entrained catalyst. The vapors then enter the fractionator, where the desired products are removed and heavier fractions are recycled to the reactor. 

Bauxitic Kaolins andMullites. Deposits of bauxitic kaolins, kaolins having aluminous minerals, have been discovered that have alumina contents between 50 and 70%. These materials are made into refractory aggregates called calcines, grog, clinker, or grain. In addition to sdectivdy mined deposits, synthetic compositions can be prepared from kaolin and alumina and other minerals to produce compositions of desired alumina and mineralogical content. These synthetic mullites are readily available in the form of sintered and fused aggregates. 

The production of flame retardant quahty aluminium hydroxide has recently been reviewed [98]. Various crystal forms of aluminium hydroxide exist, but that used for polymer appHcations is Gibbsite. This occurs widely in nature, usually in the rock bauxite, but the natural form is usually not suitable for direct use and synthetic products are nearly always employed. Most aluminium hydroxide is manufactured through the Bayer process used to make alumina for refractory applications. 

The most conventional catalytic material since the work of Bergius has been iron sulfide in various types. Pyrite, pyrrhotite, and various nonstoi-chiometric sulfides are known, and pyrrotite is postulated as the active form. Its precursors are red mud, residue of bauxite after the separation of alumina, iron ores of various sources, synthetic and natural pyrites, fine iron particles, iron dust from converters, iron sulfate, iron hydroxide, etc. (32, 33). 

Accurate production figures for natural and synthetic iron oxide pigments are difficult to obtain, because statistics also include nonpigmentary oxides (e.g., red mud from bauxite treatment, intermediate products used in ferrite production). World production of synthetic iron oxides in 1995 was estimated to be 600000 t ... 

Fluorine occurs in nature in the form of the minerals fluorite, CaF2, cryolite, Na3AlF6, and fluoroapatite, Ca5(P04)3F, and one commercial source of natural cryolite is Greenland. Both of the other minerals are widespread in nature, although the major use of fluoroapatite is in the production of fertilizers, not as a primary source of fluorine. Extensive fluorite deposits are found in Southeastern Illinois and Northwestern Kentucky. From the standpoint of fluorine utilization, both cryolite and fluorite are extremely important minerals. Cryolite is used as the electrolyte in the electrochemical production of aluminum from bauxite, and fluorite is used as a flux in making steel. Today, most of the cryolite used is synthetic rather than the naturally occurring mineral. 

Catalyst-manufacturing methods can be classified into two broad categories. In one, a naturally occurring solid material is treated to alter its physical or chemical properties. The treated solids are sometimes referred to as natural catalysts. These include the Filtrol activated clays and the bauxite Cycloversion catalyst. In the other category of methods, the solid catalyst is produced synthetically by interaction of aqueous solutions of the raw materials. 

When intended for use in ceramics, kyanite has to be calcined, not necessarily with the other two forms owing to the smaller volume change involved in their conversion to mullite. In place of natural raw materials from the sillimanite group, use is sometimes made of synthetic mullite produced by high-temperature reaction from a mixture of clay with bauxite, or in some cases from pure oxides. 

In the modern version of this process, aluminum metal is obtained by electrolysis of aluminum oxide, which is refined from bauxite ore (AI2O3 2H2O). The aluminum oxide is dissolved at 1000°C in molten synthetic cryolite (Na3AlFg), another aluminum compound. The cell is lined with graphite, which forms the cathode for the reaction. Another set of graphite rods is immersed in the molten solution as an anode. The following half-reaction occurs at the cathode. 

Other synthetic processes to ammonia have been tested and found to be impractical for large scale commercial exploitation. Eor example, the Erench Serpek process for purifying alumina also formed aluminum nitride as a byproduct from the heating of bauxite in nitrogen [5] (Eq. 11.2). 

N. V. Y. Scarlett, I. C. Madsen, F. M. D. Cranswick, T. Fwin, E. Groleau, G. Stephenson, M. Aylmore and N. Agron-Olshina, Outcomes of the International Union of Crystallography Commission on powder diffraction round robin on quantitative phase analysis Samples 2, 3, 4, synthetic bauxite, natural granodiorite and pharmaceuticals, J. Appl. Crystallogr., 2002, 35, 383 00. 

Synthetic mullite is commonly used, and can be made by heating a mixture of pure AI2O3 or bauxite with clay or sillimanite. Mullite is a common constituent of fired pottery bodies and refractories and, under the microscope, appears as long prism-shaped crystals of nearly square cross-section. 

The electrolytic production of aluminium is more complex. Hall and Heroult developed the current process independently in 1886. In this process, alumina, AI2O3, is dissolved in molten sodium aluminium fluoride (Na3AlF6) and electrolysed (Figure 9.22). Originally, the aluminium oxide was derived directly from the mineral bauxite, and the sodium aluminium fluoride was used in the form of the naturally occurring mineral cryolite. These days, synthetic cryolite is used, and the aluminium oxide is produced from a wider variety of mineral sources, consisting of aluminium oxide-hydroxides. 

The high-specific-surface-area supports (10 to 100 m /g or more) are natural or manufactured materials that normally are handled as fine powders. When processed into the finished catalyst pellet, these materials often give rise to pore size distributions of the macro-micro type mentioned previously. The micropores exist within the powder itself, and the macropores are created between the fine particles when they are compressed together in a pellet press. Diatomaceous earth and pumice (or cellular lava) are naturally occurring low-cost materials that are representative of this class of catalyst support. Among the synthetic carriers that can be created by modem technology are those derived from clays, bauxite, activated carbon, and xerogels of silica gel and alumina gel. 

Some of the earliest major applications of adhesives in civil engineering involved the use of resins for abrasion resistant and non-slip surfaces to heavy duty floors and roads. This was achieved by the use of synthetic anti-skid grits, such as calcined bauxite, set in a resin base. Both epoxy and polyester resins have been used, applied either by trowel or in slurry form by squeegee. Trowelled systems are usually heavily filled mortars with an aggregate resin ratio of the order of 6 1 and as such usually require a priming... 

Jaw crushers These are used to break up substances with medium to extreme hardness ratings as well as brittle to tough materials, such as bakelite, bauxite, concrete, dolomite, ores, feldspar, ferroalloys, granite, glass, limestone, gravel, coal, coke, corundum, synthetic resins, quartz, salts, slag, silicates, sintered products, and many other substances. 

Synthetic materials made by sintering of bauxite and kaolinite clay. After processing, the final material mineralogical composition consists of a mixture of mullite and corundum. Sometimes less common ceramics are also used, e.g., carborundum, stabilized cubic zirconia, other oxides, and silicates. 

Karl Bayer first separated alumina from bauxite ore. This method, known as the Bayer process, is stiU used to purify alumina. In 1893, Edward Goodrich Acheson, an American chemist, electronically fused carbon and clay to create carborundum, also known as synthetic silicon carbide, a highly effective abrasive. 

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