Fluorspars

The worldwide consumption of fluorine can be adduced from the consumption of fluorspar, since the contribution from the possible second fluorine source, hexafluorosilicic acid, which is a byproduct in the production of pho.sphate-containing fertilizers, has been minor up to now. Starting materials for the manufacture of industrial fluorochemicals are  

The total reserves of economically and marginally economically workable fluorspar is ca. 311 10 t. The quantities extracted worldwide were  

Although not easily detonated, ammonium nitrate will explode under confinement at high temperatures. When mixed with other nutrient-bearing compounds hazards vary but when combined with combustible materials (e.g., fuel oil), its strong oxidizing properties increase the likelihood of explosion. At lower concentrations and in the absence of combustibles the mixture presents only a limited hazard. 

Tankage comes from two sources the dried solid product of boiling the bones, skin, meat scraps, and other animal by-products from abattoirs and garbage treated with high-pressure steam and subsequently pressed. Both products are high in nitrogen, in the form of ammonia, and phosphorus as phosphoric acid, potash, and phosphates. Tankage can be flammable and presents a spontaneous combustion hazard. 

see Terminology, Inert, p.240 Inorganic, see Terminology, Inorganic, p.241 

Mixture, see Terminology, Mixture, p.243 Organic, see Terminology, Organic, p.244 Solution, see Terminology, Solutions, p.247 Tankage, see also Solid Bulk Materials, p.221 

Animal fabrics, oily Animal fibres, burnt, wet or damp Animal fibres, oily Bhusa, 

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Boron trifluoride is a colourless, reactive gas which can be prepared by heating boron tnoxide and fluorspar with concentrated sulphuric acid. 

The reaction is carried out in a lead retort one suitable for the laboratory can be made from a piece of lead piping, bent like a retort and closed at the shorter end. This is charged with fluorspar and the acid and heated, and the hydrogen fluoride is distilled into a polythene vessel. 

Calcium. Calcium is the fifth most abundant element in the earth s cmst. There is no foreseeable lack of this resource as it is virtually unlimited. Primary sources of calcium are lime materials and gypsum, generally classified as soil amendments (see Calcium compounds). Among the more important calcium amendments are blast furnace slag, calcitic limestone, gypsum, hydrated lime, and precipitated lime. Fertilizers that carry calcium are calcium cyanamide, calcium nitrate, phosphate rock, and superphosphates. In addition, there are several organic carriers of calcium. Calcium is widely distributed in nature as calcium carbonate, chalk, marble, gypsum, fluorspar, phosphate rock, and other rocks and minerals. 

Fluorine, which does not occur freely in nature except for trace amounts in radioactive materials, is widely found in combination with other elements, accounting for ca 0.065 wt % of the earth s cmst (4). The most important natural source of fluorine for industrial purposes is the mineral fluorspar [14542-23-5] CaF2, which contains about 49% fluorine. Detailed annual reports regarding the worldwide production and reserves of this mineral are available (5). A more complete discussion of the various sources of fluorine-containing minerals is given elsewhere (see Fluorine compounds, inorganic). 

M. M. Miller, Fluorspar, HnnualFeport, U.S. Dept, of Interior, Bureau of Mines, Washington, D.C., Sept. 1991. 

The names fluorine and fluorospar are derived from the Latin fluere meaning flow or flux. In 1529 the use of fluorspar as a flux was described. In 1670 the etching of glass by acid-treated fluorspar was reported. Elemental fluorine was isolated by Moissan ia 1886 (7). 

The ores of most importance are fluorspar, CaF2 fluorapatite, Ca (P0 2Fj cryoHte [15096-52-3], Na AlF. Fluorspar is the primary commercial source of fluoiine. Twenty-six percent of the world s high quaHty deposits of fluorspar are ia North America. Most of that is ia Mexico. United States production ia 1987—1991 was 314,500 metric tons, most of which occurred ia the Illinois-Kentucky area. Imported fluorspar ia 1990—1991 represented about 82% of U.S. consumption 31% of U.S. fluorspar imports were from Mexico and 29% from China compared to 66% from Mexico ia the 1973—1978 period. The majority of the fluorine ia the earth s cmst is ia phosphate rock ia the form of fluorapatite which has an average fluorine concentration of 3.5%. Recovery of these fluorine values as by-product fluorosiHcic acid from phosphate production has grown steadily, partially because of environmental requirements (see Phosphoric acid and THE phosphates). 

Production of hydrogen fluoride from reaction of Cap2 with sulfuric acid is the largest user of fluorspar and accounts for approximately 60—65% of total U.S. consumption. The principal uses of hydrogen fluoride are ia the manufacture of aluminum fluoride and synthetic cryoHte for the Hall aluminum process and fluoropolymers and chlorofluorocarbons that are used as refrigerants, solvents, aerosols (qv), and ia plastics. Because of the concern that chlorofluorocarbons cause upper atmosphere ozone depletion, these compounds are being replaced by hydrochlorofluorocarbons and hydrofluorocarbons. 

The steel (qv) iadustry is also an extremely large user of fluorspar which is added to slag to make it more reactive. Smaller amounts are also used ia the aluminum, ceramic, brick, cement, glass fiber, and foundry iadustries. 

Minerals Yearbooks Chapter on Fluorspar (aimual comprehensive reports but delayed approximately two years). 

MineralIndusty Surveys on Fluorspar, quartedy, and aimual (less comprehensive but current). 

In addition, there are other methods of manufacture of cryoHte from low fluorine value sources, eg, the effluent gases from phosphate plants or from low grade fluorspar. In the former case, making use of the fluorosiHcic acid, the siHca is separated by precipitation with ammonia, and the ammonium fluoride solution is added to a solution of sodium sulfate and aluminum sulfate at 60—90°C to precipitate cryoHte (26,27) ... 

Boron trifluoride [7637-07-2] (trifluoroborane), BF, was first reported in 1809 by Gay-Lussac and Thenard (1) who prepared it by the reaction of boric acid and fluorspar at duU red heat. It is a colorless gas when dry, but fumes in the presence of moisture yielding a dense white smoke of irritating, pungent odor. It is widely used as an acid catalyst (2) for many types of organic reactions, especially for the production of polymer and petroleum (qv) products. The gas was first produced commercially in 1936 by the Harshaw Chemical Co. (see also Boron COMPOUNDS). 

Manufacture. Boron trifluoride is prepared by the reaction of a boron-containing material and a fluorine-containing substance in the presence of an acid. The traditional method used borax, fluorspar, and sulfuric acid. 

In the geochemistry of fluorine, the close match in the ionic radii of fluoride (0.136 nm), hydroxide (0.140 nm), and oxide ion (0.140 nm) allows a sequential replacement of oxygen by fluorine in a wide variety of minerals. This accounts for the wide dissemination of the element in nature. The ready formation of volatile silicon tetrafluoride, the pyrohydrolysis of fluorides to hydrogen fluoride, and the low solubility of calcium fluoride and of calcium fluorophosphates, have provided a geochemical cycle in which fluorine may be stripped from solution by limestone and by apatite to form the deposits of fluorspar and of phosphate rock (fluoroapatite [1306-01 -0]) approximately CaF2 3Ca2(P0 2 which ate the world s main resources of fluorine (1). 

On average, fluorine is about as abundant as chlorine in the accessible surface of the earth including oceans. The continental cmst averages about 650 ppm fluorine. Igneous, metamorphic, and sedimentary rocks all show abundances in the range of 200 to 1000 ppm. As of 1993, fluorspar was still the principal source of fluorine for industry. 

Fluorspar deposits ate commonly epigenetic, ie, the elements moved from elsewhere into the country rock. For this reason, fluorine mineral deposits ate closely associated with fault 2ones. In the United States, significant fluorspar deposits occur in the Appalachian Mountains and in the mountainous regions of the West, but the only reported commercial production in 1993 was from the faulted carbonate rocks of Illinois. 

Worldwide, large deposits of fluorspar ate found in China, Mongofla, France, Morocco, Mexico, Spain, South Africa, and countries of the former Soviet Union. The United States imports fluorspar from most of these countries (Table 1). 

Mining. Underground mining procedures are used for deep fluorspar deposits, and open-pit mines are used for shallow deposits or where conditions do not support underground mining techniques (see Mineral RECOVERY AND PROCESSING). 

Fluorspar occurs in two distinct types of formation in the fluorspar district of southern Illinois and Kentucky in vertical fissure veins and in horizontal bedded replacement deposits. A 61-m bed of sandstone and shale serves as a cap rock for ascending fluorine-containing solutions and gases. Mineralizing solutions come up the faults and form vein ore bodies where the larger faults are plugged by shale. Bedded deposits occur under the thick sandstone and shale roofs. Other elements of value associated with fluorspar ore bodies are zinc, lead, cadmium, silver, germanium, iron, and thorium. Ore has been mined as deep as 300 m in this district. 

Outside of the United States, there are six primary producers in China, France, Mexico, Morocco, South Africa, and Spain. Mines in Newfoundland, Canada, were closed in 1990. Both Mexico and South Africa have lost market share to China which has high grade, low cost fluorspar. China is expected to dominate world markets because reserves are vast and production cost is low. Table 3 (2) shows a Hst of world producers by country of fluorspar in the early 1990s. 

Economic Aspects. Pertinent statistics on the U.S. production and consumption of fluorspar are given in Table 4. For many years the United States has rehed on imports for more than 80% of fluorspar needs. The principal sources are Mexico, China, and the Repubflc of South Africa. Imports from Mexico have declined in part because Mexican export regulations favor domestic conversion of fluorspar to hydrogen fluoride for export to the United States. 

Table 4. United States Fluorspar Production and Consumption, t...

Consumer stocks (2) at the end of 1993 were 65,000 t. The National Defense Stockpile of fluorspar iaventory, at year end 1992, contained 809,000 t of acid-grade material, 281,000 t of metallurgical-grade material, 816 t of nonstockpile, acid-grade material, and 105,938 t of nonstockpile, metallurgical-grade material. 

The prices for acid-grade fluorspar dry basis from Mexico and the RepubHc of South Africa for 1993 were Mexican spar, fob Tampico,... 

Grades, Quality Control. Fluorspar is marketed ia several grades metallurgical fluorspar (metspar) is sold as gravel, lump, or briquettes. The minimum acceptable assay is 60% effective calcium fluoride. The effective value is determined by subtracting from the contained calcium fluoride 2.5% for every percent of Si02 found ia the complete analysis apparently based on the following stoichiometry (1) ... 

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