Fluorine minerals

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. 

Eluorspar assay may be completed by fluoride determination alone, because the mineralogical grouping rarely iacludes fluorine minerals other than fluorite. Calcium can be determined as oxalate or by ion-selective electrodes (67). SiUca can be determined ia the residue from solution ia perchloric acid—boric acid mixture by measuriag the loss ia weight on Aiming off with hydrofluoric acid. Another method for determining siUca ia fluorspar is the ASTM Standard Test Method E463-72. 

The most abundant fluorine mineral is fluorite—calcium fluoride (CaF )— which is often found with other minerals, such as quartz, barite, calcite, sphalerite, and galena. It is mined in... 

Fluorine never occurs as a free element in nature. The most common fluorine minerals are fluorspar, fluorapatite, and cryolite. Apatite is a complex mineral containing primarily calcium, phosphorus, and oxygen, usually with fluorine. Cryolite is also known as Greenland spar. (The country of Greenland is the only commercial source of this mineral.) It consists primarily of sodium aluminum fluoride (Na3ALF6). The major sources of fluorspar are China, Mexico, Mongolia, and South Africa. In 2008 in the United States, fluorspar was produced as a by-product of limestone quarrying in Illinois. The United States imports most of the fluorspar it needs from China and Mexico. 

Fluorine occurs widely in nature as insoluble fluorides. Calcium fluoride occurs as jluospar or fluorite, for example in Derbyshire where it is coloured blue and called bluejohn . Other important minerals are cryolite NajAlFg (p. 141) and Jluorapatite CaFjSCaj (P04)2. Bones and teeth contain fluorides and some natural water contains traces. 

Normally, a slight excess of sulfuric acid is used to bring the reaction to completion. There are, of course, many side reactions involving siHca and other impurity minerals in the rock. Fluorine—silica reactions are especially important as these affect the nature of the calcium sulfate by-product and of fluorine recovery methods. Thermodynamic and kinetic details of the chemistry have been described (34). 

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). 

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). 

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. 

Analytical Methods. Fluorite is readily identified by its crystal shape, usually simple cubes or interpenetrating twins, by its prominent octahedral cleavage, its relative softness, and the production of hydrogen fluoride when treated with sulfuric acid, evidenced by etching of glass. The presence of fluorite in ore specimens, or when associated with other fluorine-containing minerals, may be deterrnined by x-ray diffraction. 

Fluorinated Acids. This class of compounds is characterized by the strength of the fluorocarbon acids, eg, CF COOH, approaching that of mineral acids. This property results from the strong inductive effect of fluorine and is markedly less when the fluorocarbon group is moved away from the carbonyl group. Generally, their reactions are similar to organic acids and they find apphcations, particularly trifluoroacetic acid [76-05-1] and its anhydride [407-25-0] as promotors in the preparation of esters and ketones and in nitration reactions. 

Mineral Feed. Mineral feed supplements for domestic animals and fowl usually contain a pure form of pulverized limestone. In fact, some state laws require the supplement to be at least 35% available calcium. Other sources of calcium are bone meal and dicalcium phosphate. Use as mineral feed has been a steadily growing market for limestone. The material is ground to 90% minus 0.15 mm (100 mesh) or 80% minus 0.9074 mm (200 mesh), is low in silica, and has strict tolerances on arsenic and fluorine (see Feeds and feed additives). 

Under unusual circumstances, toxicity may arise from ingestion of excess amounts of minerals. This is uncommon except in the cases of fluorine, molybdenum, selenium, copper, iron, vanadium, and arsenic. Toxicosis may also result from exposure to industrial compounds containing various chemical forms of some of the minerals. Aspects of toxicity of essential elements have been pubhshed (161). 

Tin does not react directly with nitrogen, hydrogen, carbon dioxide, or gaseous ammonia. Sulfur dioxide, when moist, attacks tin. Chlorine, bromine, and iodine readily react with tin with fluorine, the action is slow at room temperature. The halogen acids attack tin, particularly when hot and concentrated. Hot sulfuric acid dissolves tin, especially in the presence of oxidizers. Although cold nitric acid attacks tin only slowly, hot concentrated nitric acid converts it to an insoluble hydrated stannic oxide. Sulfurous, chlorosulfuric, and pyrosulfiiric acids react rapidly with tin. Phosphoric acid dissolves tin less readily than the other mineral acids. Organic acids such as lactic, citric, tartaric, and oxaUc attack tin slowly in the presence of air or oxidizing substances. 

Oxygen is by far the most abundant element in cmstal rocks, composing 46.6% of the Hthosphere (4). In rock mineral stmctures, the predominant anion is, and water (H2O) itself is almost 90% oxygen by weight. The nonmetaUic elements fluorine, sulfur, carbon, nitrogen, chlorine, and phosphoms are present in lesser amounts in the Hthosphere. These elements aU play essential roles in life processes of plants and animals, and except for phosphoms and fluorine, they commonly occur in earth surface environments in gaseous form or as dissolved anions. 

The principal applications of these plastics arose from their very good chemical resistance, as they are resistant to mineral acids, strong alkalis and most common solvents. They were, however, not recommended for use in conjunction with oxidising acids such as fuming nitric acid, fuming sulphuric acid or chlorosulphonic acid, with fluorine or with some chlorinated solvents, particularly at elevated temperatures. 

Fluorinated rubbers, copolymers of hexafluoropropylene and vinylidene-fluorides, have excellent resistance to oils, fuels and lubricants at temperatures up to 200°C. They have better resistance to aliphatic, aromatic and chlorinated hydrocarbons and most mineral acids than other rubbers, but their high cost restricts their engineering applications. Cheremisinoff et al. [54] provide extensive physical and mechanical properties data on engineering plastics. A glossary of terms concerned with fabrication and properties of plastics is given in the last section of this chapter. 

The fluorine industry is intimately related to aluminum production. Aluminum oxide, (AljOj) is electrolyzed to metallic aluminum with a flux of sodium fuoroaluminate (Na AlF,), called cryolite - a rare mineral found in commercial quantities only in Greenland with other uses glass, enamels, and as a filler for resin-bonded grinding wheels. 

Synthetic cryolite solved the supply problem, but synthetic cryolite requires fluorine which is actually more abundant in the Earth s crust than chlorine, but dispersed in small concentrations in rocks. Until the 1960s, fluorspar (CaFj) a mineral long known and used as a flux in various metallurgical operations was the source. A source is phosphate rock that contains fluorine i.s 3% quantity,... 

Hydrogen fluoride is maiiufaetured by the reaetion with sulfurie aeid of fluorspar, a fluorine-eontaining mineral. 

Fluorine is the thirteenth element in order of abundance in crustal rocks of the earth, occurring to the extent of 544 ppm (cf. twelfth Mn, 1060 ppm fourteenth Ba, 390 ppm fifteenth Sr, 384 ppm). The three most important minerals are... 

The processing of tantalum and niobium begins with the fluorination of the raw material, which always consists of complex oxide compounds containing tantalum and niobium. The main types of tantalum- and niobium-containing minerals are discussed in Chapter 1, and typical compositions of such minerals are presented in Table 2. 

Nevertheless, Ta5+ and Nb5+ interact with aqueous media containing fluorine ions, such as solutions of hydrofluoric acid. On the other hand, as was clearly shown by Majima et al. [448 - 450], the increased hydrogen ion activity can also significantly enhance the dissolution rate of oxides. The activity of hydrogen ions can be increased by the addition of mineral salts or mineral acids to the solution. 

Fluorine comes from the minerals fluorspar, CaF, cryolite, Na3AlF6 and the fluorapatites, Ca,F(P04)3. The free element is prepared from HF and KF by electrolysis, but the HF and KF needed for the electrolysis are prepared in the laboratory. Chlorine primarily comes from the mineral rock salt, NaCl. The pure element is obtained by electrolysis of liquid NaCl. Bromine is found in seawater and brine wells as the Br ion it ts also found as a component of saline deposits the pure element is obtained by oxidation of Br (aq) by Cl,(g). Iodine is found in seawater, seaweed, and brine wells as the I" ion the pure element is obtained by oxidation of I (aq) by Cl,(g). 

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