Cryolite

Cryolite (Na3AlF6, sodium hexafluoroaluminate) is an uncommon mineral identified with the once large deposit at Ivigtût on the west coast of Greenland, depleted by 1987.

Cryolite mine ivgtut greenland
The cryolite mine Ivigtut, Greenland, summer 1940

It was historically used as an ore of aluminium and later in the electrolytic processing of the aluminium-rich oxide ore bauxite (itself a combination of aluminium oxide minerals such as gibbsite, boehmite and diaspore). The difficulty of separating aluminium from oxygen in the oxide ores was overcome by the use of cryolite as a flux to dissolve the oxide mineral(s). Pure cryolite itself melts at 1012 °C (1285 K), and it can dissolve the aluminium oxides sufficiently well to allow easy extraction of the aluminium by electrolysis. Substantial energy is still needed for both heating the materials and the electrolysis, but it is much more energy-efficient than melting the oxides themselves. As natural cryolite is too rare to be used for this purpose, synthetic sodium aluminium fluoride is produced from the common mineral fluorite.

Cryolite-unit-cell-3D-polyhedra
Cryolite's unit cell. Sodium atoms are purple; fluorine atoms are pale green, arranged in octahedra around an aluminium atom.

Cryolite occurs as glassy, colorless, white-reddish to gray-black prismatic monoclinic crystals. It has a Mohs hardness of 2.5 to 3 and a specific gravity of about 2.95 to 3.0. It is translucent to transparent with a very low refractive index of about 1.34, which is very close to that of water; thus if immersed in water, cryolite becomes essentially invisible.[6]

Cryolite has also been reported at Pikes Peak, Colorado; Mont Saint-Hilaire, Quebec; and at Miass, Russia. It is also known in small quantities in Brazil, the Czech Republic, Namibia, Norway, Ukraine, and several U.S. states.

Cryolite was first described in 1798 by Danish veterinarian and physician Peder Christian Abildgaard (1740-1801);[7] it was obtained from a deposit of it in Ivigtut and nearby Arsuk Fjord, Southwest Greenland. The name is derived from the Greek language words κρυος (cryos) = ice, and λιθος (lithos) = stone.[8] The Pennsylvania Salt Manufacturing Company used large amounts of cryolite to make caustic soda at its Natrona, Pennsylvania works during the 19th and 20th centuries.

Due to its rarity it is possibly the only mineral on Earth ever to be mined to commercial extinction.[9]

Cryolite
816- Ivigtut - cryolite
Cryolite from Ivigtut Greenland
General
CategoryHalide mineral
Formula
(repeating unit)
Na3•AlF6
Strunz classification3.CB.15
Dana classification11.6.1.1
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/n
Unit cella = 7.7564(3) Å,
b = 5.5959(2) Å,
c = 5.4024(2) Å; β = 90.18°; Z = 2
Identification
Formula mass209.9 g mol−1
ColorColorless to white, also brownish, reddish and rarely black
Crystal habitUsually massive, coarsely granular. The rare crystals are equant and pseudocubic
TwinningVery common, often repeated or polysynthetic with simultaneous occurrence of several twin laws
CleavageNone observed
FractureUneven
TenacityBrittle
Mohs scale hardness2.5 to 3
LusterVitreous to greasy, pearly on {001}
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.95 to 3.0.
Optical propertiesBiaxial (+)
Refractive indexnα = 1.3385–1.339, nβ = 1.3389–1.339, nγ = 1.3396–1.34
Birefringenceδ = 0.001
2V angle43°
Dispersionr < v
Melting point1012 °C
SolubilitySoluble in AlCl3 solution, soluble in H2SO4 with the evolution of HF, which is poisonous. Insoluble in water.[1]
Other characteristicsWeakly thermoluminescent. Small clear fragments become nearly invisible when placed in water, since its refractive index is close to that of water. May fluoresce intense yellow under SWUV, with yellow phosphorescence, and pale yellow phosphorescence under LWUV. Not radioactive.
References[2][3][4][5][6]

Uses

Cryolite is used as an insecticide and a pesticide.[10] It is also used to give fireworks a yellow color.[11] Molten cryolite is used as a solvent for aluminium oxide (Al2O3) in the Hall–Héroult process, used in the refining of aluminium. It decreases the melting point of molten (liquid state) aluminium oxide to 900-1000 °C from 2000-2500 °C. Thus cryolite makes the extraction of aluminium profitable. Fluorspar (CaF2) is also added to the mixture.

References

  1. ^ CRC Handbook of Chemistry and Physics, 83rd Ed., p. 4-84.
  2. ^ Gaines, Richard V., et al (1997) Dana's New Mineralogy, Wiley, 8th, ISBN 978-0-471-19310-4
  3. ^ Cryolite: Cryolite mineral information and data. Mindat.org (2010-10-03). Retrieved on 2010-10-25.
  4. ^ Cryolite Mineral Data. Webmineral.com. Retrieved on 2010-10-25.
  5. ^ Cryolite, Handbook of Mineralogy. Retrieved on 2010-10-25.
  6. ^ a b Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7
  7. ^ See:
    • (Abildgaard) (1799) "Norwegische Titanerze und andre neue Fossilien" (Norwegian titanium ores and other new fossils [i.e., anything dug out of the earth]), Allgemeines Journal der Chemie, 2 : 502. From p. 502: "In der ordenlichen Versammlung der königl. Gesellschaft der Wissenschaften am 1. Februar dieses Jahres stattete Hr. Prof. Abildgaard einen Verricht über die Norwegischen Titanerze und über die von ihm mit denselben angestellten Analysen ab. Zugleich theilte er auch eine Nachricht von einer vor wenigen Jahren aus Grönland nach Dänemark gebrachten besonders weißen spathartigen Miner mit. Einer damit angestellten Untersuchung zu folge bestand sie aus Thonerde und Flußspathsäure. Eine Verbindung, von welcher noch kein ähnliches Beyspiel im Mineralreich vorgekommen ist. Sie hat den Namen Chryolit erhalten, weil sie vor dem Löthrohre wie gefrorne Salzlauge schmilzt." (At the ordinary session of the [Danish] Royal Society of Science on February 1st of this year, Prof. Abildgaard presented a report about Norwegian titanium ores and about the analysis of them undertaken by him. He also communicated a notice of an especially white, spar-like mineral that was brought several years ago from Greenland to Denmark. According to an investigation performed on it, it consists of alumina and hydrofluoric acid. A compound of which no similar example in the mineral realm has yet been found. It received the name "cryolite" because under a blowpipe, it melts like frozen brine.)
    • P. C. Abildgaard (1800) "Om Norske Titanertser og om en nye Steenart fra Grönland, som bestaaer af Flusspatsyre og Alunjord" (On Norwegian titanium ores and on a new mineral from Greenland, which consists of hydrofluoric acid and alumina), Det Kongelige Danske Videnskabers-Selskabs (The Royal Danish Scientific Society), 3rd series, 1 : 305-316. Abildgaard named cryolite on p. 312: "Han har kaldt denne grönlandske Steen Kryolith eller Iissteen formedelst dens Udseende, og fordi den smelter saa meget let for Blæsröret." (He has named this Greenlandic stone cryolite or ice stone on account of its appearance, and because it melts so easily under a blowpipe.)
  8. ^ Albert Huntington Chester, A Dictionary of the Names of Minerals Including Their History and Etymology (New York, New York: John Wiley & Sons, 1896), p. 68.
  9. ^ "Royal Society of Chemistry, Chemistry in its element: compounds - Cryolite". Archived from the original on 2016-04-18. Retrieved 2016-04-08.
  10. ^ EPA R.E.D. FACTS Cryolite http://www.epa.gov/oppsrrd1/REDs/factsheets/0087fact.pdf
  11. ^ http://chemistry.about.com/od/fireworkspyrotechnics/a/fireworkcolors.htm
Acuminite

Acuminite is a rare halide mineral of with chemical formula: SrAlF4(OH)·(H2O). Its name comes from the Latin word acumen, meaning "spear point". Its Mohs scale rating is 3.5.

Acumenite has only been described from its type locality of the cryolite deposit in Ivigtut, Greenland.

Aluminium smelting

Aluminium smelting is the process of extracting aluminium from its oxide, alumina, generally by the Hall-Héroult process. Alumina is extracted from the ore bauxite by means of the Bayer process at an alumina refinery.

This is an electrolytic process, so an aluminium smelter uses prodigious amounts of electricity; they tend to be located very close to large power stations, often hydro-electric ones, and near ports since almost all of them use imported alumina. A large amount of carbon is also used in this process, resulting in significant amounts of greenhouse gas emissions.

Aluminium sulfate

Aluminium sulfate is a chemical compound with the formula Al2(SO4)3. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water and waste water treatment plants, and also in paper manufacturing.

The anhydrous form occurs naturally as a rare mineral millosevichite, found e.g. in volcanic environments and on burning coal-mining waste dumps. Aluminium sulfate is rarely, if ever, encountered as the anhydrous salt. It forms a number of different hydrates, of which the hexadecahydrate Al2(SO4)3•16H2O and octadecahydrate Al2(SO4)3•18H2O are the most common. The heptadecahydrate, whose formula can be written as [Al(H2O)6]2(SO4)3•5H2O, occurs naturally as the mineral alunogen.

Aluminium sulfate is sometimes called alum or papermaker's alum in certain industries. However, the name "alum" is more commonly and properly used for any double sulfate salt with the generic formula XAl(SO4)2·12H2O, where X is a monovalent cation such as potassium or ammonium.

Arcubisite

Arcubisite (Ag6CuBiS4) is a sulfosalt mineral occurring with cryolite in Greenland. Its named after its composition (ARgentum, CUprum, and BISmuth).

Berryite

Berryite is a mineral with the formula Pb3(Ag,Cu)5Bi7S16. It occurs as gray to blue-gray monoclinic prisms. It is opaque and has a metallic luster. It has a Mohs hardness of 3.5 and a specific gravity of 6.7.

It was first identified in 1965 using X-ray diffraction by mineralogist Leonard Gascoigne Berry (1914–1982). It is found in Park and San Juan counties in Colorado. It occurs in sulfide bearing quartz veins in Colorado and with siderite-rich cryolite in Ivigtut, Greenland.

Bluie

Bluie was the United States military code name for Greenland during World War II. It is remembered by the numbered sequence of base locations identified by the 1941 United States Coast Guard South Greenland Survey Expedition, and subsequently used in radio communications by airmen unfamiliar with pronunciation of the Inuit and Old Norse names of those locations. These were typically spoken BLUIE (direction) (number), with direction being east or west along the Greenland coast from Cape Farewell.

Bluie East One: Torgilsbu radio and weather station at 60°9′N 43°53′W on Prince Christian Sound

Bluie East Two: Ikateq airfield with radio and weather station at 65°56′43″N 36°39′45″W

Bluie East Three: Gurreholm radio and weather station at 70°30′N 25°00′W on Scoresby Sund

Bluie East Four: Ella Island radio, weather, and sledge patrol station at 72°51′N 25°00′W

Bluie East Five: Eskimonæs radio and weather station captured by German troops in 1943 and later reestablished at Myggbukta 73°29′28″N 21°32′26″W

Bluie West One: Narsarsuaq Air Base at 61°10′N 45°26′W

Bluie West Two: Kipisako unused alternative airfield location on Coppermine Bay

Bluie West Three: Simiutak HF/DF station at 60°41′N 46°34′W

Bluie West Four: Marrak Point radio and weather station at 63°27′N 51°11′W

Bluie West Five: Aasiaat radio and weather station at 68°42′35″N 52°52′10″W on Disko Island

Bluie West Six: Thule radio and weather station at 76°31′52″N 068°42′11″W

Bluie West Seven: Kangilinnguit base at 61°14′00″N 48°05′55″W to defend the Ivittuut cryolite mine

Bluie West Eight: Sondrestrom Air Base at 67°00′38″N 50°42′33″W

Bluie West Nine: Cruncher Island light and radio beacon at 66°03′N 53°36′W

Bluie West Seven

Bluie West 7 or Grondal was a major U.S. naval operating facility (naval base) near Ivigtut in Arsuk Fjord, Greenland. In some form, it was in operation from 1940 to 1951, although its formal establishment by the U.S. Navy was on 1 April 1943. After 1942, the proper name was Grønnedal (Danish), or Green Valley (English), but the base was also called Grondal ("groan dale") by Americans. Bluie was the military code name for Greenland. It was three miles east of the Ivigtut cryolite mine. The location's local name in use today is Kangilinnguit. The Arsuk Fjord approach is accessible by sea year-round, though with occasional ice-breaking assistance, and is known as an exceptionally scenic area.

Greenland in World War II

The fall of Denmark in April 1940 left the Danish colony of Greenland an unoccupied territory of an occupied nation, under threat of seizure by the United Kingdom or Canada. To forestall this, the United States acted to guarantee Greenland's position. However, with the entrance of the United States into the war in December 1941, Greenland became a combatant.

From 1941 until 1945, the United States established numerous and extensive facilities for air and sea traffic in Greenland, as well as radio beacons, radio stations, weather stations, ports, depots, artillery posts, and search-and-rescue stations. The United States Coast Guard also provided a considerable portion of the civilian resupply task up and down both coasts.

Economically, Greenland traded successfully with the United States, Canada, and Portugal, which, supplemented by the cryolite exports, caused a reanimation and permanent realignment of the island's economy.

Halide minerals

The halide mineral class include those minerals with a dominant halide anion (F−, Cl−, Br− and I−). Complex halide minerals may also have polyatomic anions in addition to or that include halides.

Examples include the following:

Atacamite Cu2Cl(OH)3

Avogadrite (K,Cs)BF

Bararite (ß)(NH4)2SiF6

Bischofite (MgCl2·6H2O)

Brüggenite Ca(IO3)2(H2O)

Calomel HgCl

Carnallite KMgCl3·6H2O

Carnallite KMgCl·6H2O

Cerargyrite/Horn silver AgCl

Chlorargyrite AgCl, bromargyrite AgBr, and iodargyrite AgI

Cryolite Na3AlF6

Cryptohalite (a)(NH4)2SiF6

Dietzeite Ca2(IO3)2CrO4

Eglestonite Hg4OCl2

Embolite AgCl+AgBr

Eriochalcite CuCl2·2H2O

Fluorite CaF2

Halite NaCl

Lautarite Ca(IO3)2

Marshite CuI

Miersite AgI

Nantokite CuCl

Sal Ammoniac NH4Cl

Sylvite KCl

Terlinguaite Hg2OCl

Tolbachite CuCl2

Villaumite NaF

Yttrocerite (Ca,Y,Ce)F2

Yttrofluorite (Ca,Y)F2

Many of these minerals are water-soluble and are often found in arid areas in crusts and other deposits as are various borates, nitrates, iodates, bromates and the like. Some, such as the fluorite group, are not water-soluble. All or most of simple halides of fluorine through iodine of all of the natural alkali metals and alkaline earth metals as well as numerous other metals and cations are found in some quantity at one or more locations. More complex minerals as shown below are also found.

Hall–Héroult process

The Hall–Héroult process is the major industrial process for smelting aluminium. It involves dissolving aluminium oxide (alumina) (obtained most often from bauxite, aluminium's chief ore, through the Bayer process) in molten cryolite, and electrolysing the molten salt bath, typically in a purpose-built cell. The Hall–Héroult process applied at industrial scale happens at 940–980°C and produces 99.5–99.8% pure aluminium. Recycled aluminum requires no electrolysis, thus it does not end up in this process.

Hexafluorosilicic acid

Hexafluorosilicic acid is an inorganic compound with the chemical formula (H3O)2SiF6 (also written as (H3O)2[SiF6]). It is a colorless liquid rarely encountered undiluted. Hexafluorosilicic acid has a distinctive sour taste and pungent smell. It is produced naturally on a large scale in volcanoes. It is manufactured as a coproduct in the production of phosphate fertilizers. The resulting hexafluorosilicic acid is almost exclusively consumed as a precursor to aluminum trifluoride and synthetic cryolite, which are used in aluminium processing. Salts derived from hexafluorosilicic acid are called hexafluorosilicates.

Ivittuut

Ivittuut, formerly Ivigtût (Kalaallisut: "Grassy Place",) is an abandoned mining town near Cape Desolation in southwestern Greenland, in the modern Sermersooq municipality on the ruins of the former Norse Middle Settlement.

Ivittuut is one of the few places in the world so far discovered to have naturally occurring cryolite (Na3AlF6, sodium aluminum fluoride), an important agent in modern aluminum extraction.

Ivittuut Municipality

Ivittuut Greenlandic pronunciation: [ɪvɪtːuːt̚], (old spelling Ivigtût) was a municipality (from 1951 until 2008), located on the coast of Arsuk fjord in southern Greenland. With an area of just 100 km² (600 km² according to other sources), it was the smallest municipality of Greenland, bordering on the former Narsaq municipality in the north, east, and south, and on the west by the Labrador Sea. It has been integrated into the new Sermersooq municipality. Due its small size, the land of the municipality is all ice free, as it does not extend inward to the ice sheet of Greenland.

The town of Ivittuut is abandoned, and the only settlement of the municipality is the naval base Kangilinnguit (Grønnedal) which is to stay. The municipality only existed de jure and was about to be absorbed by Narsaq when the 2009 municipal reform took place.

Kangilinnguit is the Danish naval headquarters of Greenland. The base was originally established to protect the important cryolite mine of Ivittuut.

Kesterite

Kesterite is a sulfide mineral with a formula Cu2(Zn,Fe)SnS4. In its lattice structure, zinc and iron atoms share the same lattice sites. Kesterite is the Zn-rich variety whereas the Zn-poor form is called ferrokesterite or stannite. Owing to their similarity, kesterite is sometimes called isostannite. The synthetic form of kesterite is abbreviated as CZTS (from copper zinc tin sulfide). The name kesterite is sometimes extended to include this synthetic material and also CZTSe, which contains selenium instead of sulfur.

Marlan (fabric)

Marlan is a registered trademark for inherent flame retardant fabric (UNE EN 11612) used in protective clothing for foundries.

It was developed in 1997 and marketed by Marina Textil since 1998 conceived to protect against molten metal splashes including aluminium, cryolite, iron, steel, copper, magnesium, glass etc.

Marlan is a blend of different fibers, which includes wool and FR (flame retardant) cellulose fiber.

Origin and occurrence of fluorine

Fluorine is relatively rare in the universe compared to other elements of nearby atomic weight. On earth, fluorine is essentially found only in mineral compounds because of its reactivity. The main commercial source, fluorite, is a common mineral.

Simmonsite

Simmonsite is a halide mineral, being a tertiary light metal fluoride, with formula Na2LiAlF6. It was first discovered in nature in Mineral County in the Gillis Range of Nevada, U.S.A. The mineral is found intergrown with cryolite, cryolithionite and trace elpasolite. The mineral has a monoclinic structure of P2 or P2/m. The ideal chemical formula for simmonsite is Na2LiAlF6. The mineral has a no visible cleavage, Mohs hardness of 2.53, a pale white color with a white streak and feels somewhat greasy. Simmonsite was named for the Professor of Mineralogy and Petrology at the University of New Orleans, William B. Simmons.

Sodium hexafluoroaluminate

Sodium aluminium hexafluoride is the inorganic compound with the formula Na3AlF6. This white solid, discovered by José Bonifácio de Andrada e Silva, occurs naturally as the mineral cryolite and is used extensively in the industrial production of aluminium metal. The compound consists of the sodium (Na+) salt of hexafluoroaluminate (AlF63−).

Thomsenolite

Thomsenolite is a mineral with formula: NaCaAlF6·H2O. It is an alteration product of cryolite.It was discovered in 1868 in Ivigtut, Greenland and named for Hans Peter Jorgen Julius Thomsen (1826–1909).

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