Calcium fluoride minerals

FLUORITE. Fluorite is a calcium fluoride mineral CaFi crystallizing in the isometric system, often in superb cubic crystals. Twinned crystals are common, usually as cubic penetration twins. It is found in many diverse... 

Klemm, W. A., Jawed, L, and Holub, K.J. (1979) Effect of calcium fluoride mineralization on silicate and melt formation in Portland cement clinker. Cement and Concrete Research 9,489-496. 

Only one calcium halide is known to have been used as a pigment, die calcium fluoride mineral fluorite q.v.). However, it has been suggested that bone (widely known as a pigment and used eidier as a white calcination product or a black coke) is to be considered a fluorinated calcium phosphate, fluorapatite (qq.v.). 

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. 

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). 

Using the density of calcium fluoride (CaF2, found in nature as the mineral fluorite), which is known to be... 

Imatra Also called the Solid Lime Process. A method for desulfurizing steel made by an electric arc process. Additions are made of burnt lime (calcium oxide), fluorspar (mineral calcium fluoride), and ferro-silicon. 

In his first paper3 , Stokes called the observed phenomenon dispersive reflexion, but in a footnote, he wrote I confess I do not like this term. I am almost inclined to coin a word, and call the appearance fluorescence, from fluorspar, as the analogous term opalescence is derived from the name of a mineral. Most of the varieties of fluorspar or fluorspath (minerals containing calcium fluoride (fluorite)) indeed exhibit the property described above. In his second paper7, Stokes definitely resolved to use the word fluorescence (Scheme 1.2). 

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... 

Calcium fluoride occurs in nature as the mineral fluorspar or fluorite. It is used as a flux in ferrous metallurgy to enhance the fluidity of the slag. An important application of this compound is in the manufacture of fluorine and hydrofluoric acid, starting materials for producing many fluoroorganics. It also is used in glass and ceramics. Pure crystals are used in lasers, optics, and electronics. Other applications are in high temperature, dry-film lubricants ... 

More recently, it has been shown that topical fluoride preparations do not lead to fluoridation of the hydroxyapatite crystal [181]. Rather they form a calcium fluoride-like substance that is deposited onto the tooth surface and dissolves when the local pH is lowered [182]. The resulting dissolution adjacent to the tooth surface provides a source of soluble fluoride that can be incorporated into the mineral structure, and thus augment remineralisation. 

The overall mode of action of fluoride varnishes is the same as gels, namely that they deposit soluble fluoride as calcium fluoride. When local pH adjacent to this deposit falls, fluoride is solubilised and then proceeds to become incorporated into the tooth mineral as fluorapatite [196]. 

Apatite, a natural calcium fluoride phosphate, can adsorb low to moderate levels of dissolved metals from soils, groundwater, and waste streams. Metals naturally chemically bind to the apatite, forming extremely stable phosphate phases of metal-substituted apatite minerals. This natural process is used by UFA Ventures, Inc., and is called phosphate-induced metals stabilization (PIMS). The PIMS material can by used in a packed bed, mixed with the contaminated media, or used as a permeable barrier. The material may be left in place, disposed of, or reused. It requires no further treatment or stabilization. Research is currently being conducted on using apatite to remediate soil and groundwater contaminated with heavy metals, and the technology may also be applicable to radionuclides. The technology is not yet commercially available. 

The fluorite structure is named after the mineral form of calcium fluoride, CaF2, which is found in the U.K. in the famous Derbyshire Blue John mines. The structure is illustrated in Figure 1.39. It can be described as related to a ccp array of calcium ions with fluorides occupying all of the tetrahedral holes. There is a problem with this as a description because calcium ions are rather smaller than fluoride ions, and so, physically, fluoride ions would not be able to fit into the tetrahedral holes of a calcium ion array. Nevertheless, it gives an exact description of the relative positions of the ions. The diagram in Figure 1.39(a) depicts the fourfold tetrahedral coordination... 

Using the density of calcium fluoride (CaF2, found in nature as the mineral fluorite), which is known to be 3.180 g-cm-3, and the information given in Exercise 5.34, calculate (a) the edge length a of the unit cell and (b) the Ca-F separation in fluorite. 

A reliable method of measuring the mineral matter content of a coal is an acid demineralization procedure. The method depends on the loss of weight of a sample when treated with 40% hydrofluoric acid at 50 to 60°C (122 to 140°F). Treatment of the sample with hydrochloric acid before and after treatment with hydrofluoric acid helps prevent the retention of insoluble calcium fluoride (CaF2) in the coal. Pyrite is not dissolved in the treatment, consequently, pyrite and a small amount of retained chloride must be determined separately. Since two-thirds of the mass of the pyrite (FeS2) is accounted for by the presence of ferric oxide (Fe203) in the residual ash, the mineral matter content is then given by the formula... 

A rich source of minerals, including calcium, fluoride, iodine, iron, and zinc... 

The raw minerals mined from natural deposits comprise mixtures of different specific minerals. An early step in mineral processing is to use crushing and grinding to free these various minerals from each other. In addition, these same processes may be used to reduce the mineral particle sizes to make them suitable for a subsequent separation process. Non-ferrous metals such as copper, lead, zinc, nickel, cobalt, molybdenum, mercury, and antimony are typically produced from mineral ores containing these metals as sulfides (and sometimes as oxides, carbonates, or sulfates) [91,619,620], The respective metal sulfides are usually separated from the raw ores by flotation. Flotation processes are also used to concentrate non-metallic minerals used in other industries, such as calcium fluoride, barium sulfate, sodium and potassium chlorides, sulfur, coal, phosphates, alumina, silicates, and clays [91,619,621], Other examples are listed in Table 10.2, including the recovery of ink in paper recycling (which is discussed in Section 12.5.2), the recovery of bitumen from oil sands (which is discussed further in Section 11.3.2), and the removal of particulates and bacteria in water and wastewater treatment (which is discussed further in Section 9.4). 

The F content in recent bone or dentine apatite is normally less than 0.1 wt.%. For ancient specimen, F is known to diffuse during burial into bone material. Its enrichment is generally a part of many complex diagenetic changes of bone and tooth, which remains after their deposit. Fluorine can react with the bone and dentine mineral phase to form calcium fluoride compounds. It usually substitutes for hydroxyl ions in hydroxyapatite, leading to the less soluble fluorapatite compound (Ca10(PO4)6(F)2, FAP). 

What explanation can you give of the fact that calcium fluoride, CaFj, (the mineral fluorite), is a crystalline substance with high melting point, whereas stannic chloride, SnCl, is an easily volatile liquid ... 

Cleaning Up Combine all reaction mixtures, remove the mineral oil from the top, and place it in the organic solvents container. The aqueous solutions, after diluting with about 50 volumes of water, can be flushed down the drain. Solutions containing fluoride ion are very toxic and should not be placed in the sewer system but neutralized and treated with excess calcium chloride to precipitate calcium fluoride. The latter is separated by filtration and put in the nonhazardous solid waste container. 

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