Strontianite

Strontian, town in Scotland) Isolated by Davey by electrolysis in 1808 however, Adair Crawford in 1790 recognized a new mineral (strontianite) as differing from other barium minerals. 

Strontium is found chiefly as celestite and strontianite. The metal can be prepared by electrolysis of the fused chloride mixed with potassium chloride, or is made by reducing strontium oxide with aluminum in a vacuum at a temperature at which strontium distills off. Three allotropic forms of the metal exist, with transition points at 235 and 540oC. 

Strontianite is the naturally occurring form of strontium carbonate. It has a theoretical strontium oxide content of 70.2%, but no economically workable deposits are known. There are some naturally occurring strontium—barium and strontium—calcium isomorphs, but none has economic importance. 

Strontium Carbonate. Strontium carbonate, SrCO, occurs naturally as strontianite in orthorhombic crystals and as isomorphs with aragonite, CaCO, and witherite, BaCO. There are deposits in the United States in Schoharie County, New York in WestphaUa, Germany and smaller deposits in many other areas. None is economically workable. Strontianite has a specific gravity of 3.7, a Mohs hardness of 3.5, and it is colorless, gray, or reddish in color. 

Strontium (thirty-eighth most abundant clement) is rather rare and is found principally as the mineral strontianite, SrC03. 

Blount, C.W. (1974) Synthesis of barite, celestite, anglesite, witherite, and strontianite from aqueous solutions. Am. Min., 59, 1209-1219. 

Adair Crawford (1748-1795) first distinguished strontium ore (strontianite) from barite and other barium ores. 

We then equilibrate the formation fluid, using data from Table 30.1. Since pH measurements from saline solutions are not reliable, we assume that pH in the reservoir is controlled by equilibrium with the most saturated carbonate mineral, which turns out to be witherite (BaCC U) or, for the Amethyst field, strontianite (SrC03). Using the Miller analysis, the procedure for completing the calculation is... 

Fig. 30.1. Volumes of minerals precipitated during a reaction model simulating the mixing at reservoir temperature of seawater into formation fluids from the Miller, Forties, and Amethyst oil fields in the North Sea. The reservoir temperatures and compositions of the formation fluids are given in Table 30.1. The initial extent of the system in each case is 1 kg of solvent water. Not shown for the Amethyst results are small volumes of strontianite, barite, and dolomite that form during mixing.

Mineral phases of geogenic origin, found in most of the investigated sediments, are barite (BaS04), strontianite (SrC03), rutile (Ti02), ilmenite (FeTi03),... 

Strong base anion exchangers, 74 395, 411 Strong inversion, in silicon-based semiconductors, 22 239 Strong nitric acid process, materials of construction for, 77 187-188 Strong phosphoric acids, equilibrium composition of, 78 827t Strontianite, 23 317, 321 Strontium (Sr) 23 316-325 chemical properties of, 23 318 economic aspects of, 23 320-321 effect of micro additions on silicon particles in Al-Si alloys, 2 311-312 in ferrites, 77 59... 

It may be noted that, since the distribution coefficient is smaller than unity, the solid phase becomes depleted in strontium relative to the concentration in the aqueous solution. The small value of D may be interpreted in terms of a high activity coefficient of strontium in the solid phase, /srco3 38. If the strontium were in equilibrium with strontianite, [Sr2+] 10 3-2 M, that is, its concentration would be more than six times larger than at saturation with Cao.996Sro.oo4C03(s). This is an illustration of the consequence of solid solution formation where with Xcaco3 /caC03 -1 ... 

Although equilibrium was not established, it was more closely approached in the KCl-KBr-H20 system than in carbonate systems. For example, in a similar analysis of the strontianite-aragonite solid solution system (4 ), it was found that the experimental distribution coefficient for Sr substitution from seawater into aragonite is 12 times larger than the expected equilibrium value. Most of the distribution coefficients for the KCl-KBr-H20 system are within a factor of two of the equilibrium value, but clearly not at equilibrium. Considerable caution should be exercised before reaching the conclusion that equilibrium is established at relatively low temperatures in other solid solution-aqueous solution systems. 

The calcium ion is of such a size that it may enter 6-fold coordination to produce the rhombohedral carbonate, calcite, or it may enter 9-fold coordination to form the orthorhombic carbonate, aragonite. Cations larger than Ca2+, e.g., Sr2+, Ba2+, Pb2+, and Ra2 only form orthorhombic carbonates (at earth surface conditions) which are not, of course, isomorphous with calcite. Therefore these cations are incapable of isomorphous substitution in calcite, but may participate in isodimorphous or "forced isomorphous" substitution (21). Isodimorphous substitution occurs when an ion "adapts" to a crystal structure different from its own by occupying the lattice site of the appropriate major ion in that structure. For example, Sr2+ may substitute for Ca2 in the rhombohedral lattice of calcite even though SrC03, strontianite, forms an orthorhombic lattice. Note that the coordination of Sr2 to the carbonate groups in each of these structures is quite different. Very limited miscibility normally characterizes such substitution. 

Occurrence. Strontianite (SrC03) and celestite (SrS04) are the only minerals of economic importance. 

Strontium - the atomic number is 38 and the chemical symbol is Sr. The name derives from Strontian, a town in Scotland . The mineral strontianite is found in mines in Strontian. The element was discovered by the Scottish chemist and physician Thomas Charles Hope in 1792 observing the brilliant red flame color of strontium. It was first isolated by the English chemist Humphry Davy in 1808. 

Strontium metal is not found in its elemental state in nature. Its salts and oxide compounds constitute only 0.025% of the Earths crust. Strontium is found in Mexico and Spain in the mineral ores of strontianite (SrCO ) and celestite (SrSO ). As these ores are treated with hydrochloric acid (HCl), they produce strontium chloride (SrCy that is then used, along with potassium chloride (KCl), to form a eutectic mixture to reduce the melting point of the SrCl, as a molten electrolyte in a graphite dish-shaped electrolysis apparatus. This process produces Sr cations collected at the cathode, where they acquire electrons to form strontium metal. At the same time, Cl anions give up electrons at the anode and are released as chlorine gas Cl T. 

In 1787 William Cruikshank (1745-1795) isolated, but did not identify, strontium from the mineral strontianite he examined. In 1790 Dr. Adair Crawford (1748—1794), an Irish chemist, discovered strontium by accident as he was examining barium chloride. He found a substance other than what he expected and considered it a new mineral. He named the new element strontium and its mineral strontianite after a village in Scotland. In 1808 Sir Humphry Davy treated the ore with hydrochloric acid, which produced strontium chloride. He then mixed mercury oxide with the strontium chloride to form an amalgam alloy of the two metals that collected at the cathode of his electrolysis apparatus. He heated the resulting substance to vaporize the mercury, leaving the strontium metal as a deposit. 

William Cruickshank in 1787 and Adair Crawford in 1790 independently detected strontium in the mineral strontianite, small quantities of which are associated with calcium and barium minerals. They determined that the strontianite was an entirely new mineral and was different from baryta and other barium minerals known at the time. In 1808, Sir Humphry Davy isolated strontium by electrolysis of a mixture of moist strontium hydroxide or chloride with mercuric oxide, using a mercury cathode. The element was named after the town Strontian in Scotland where the mineral strontianite was found. 

The two principal strontium minerals are its carbonate, strontianite, SrCOs, and the more abundant sulfate mineral celestite, SrS04. 

Strontium carbonate occurs in nature as mineral strontianite. The compound is used in pyrotechnics and ceramic ferrites. It also is used in making iridescent glass for color television tubes. Other uses are in refining sugar and preparing other strontium salts. 

Strontium carbonate occurs in nature as strontianite and can be mined from its deposit. It is, however, usually made from the mineral celestite. Celestite is fused with sodium carbonate at elevated temperatures or boiled with a solution of ammonium carbonate ... 

Carbonates Aragonite CaCOs, calcite CaCOs, cerussite PbCOs, magnesite MgCOs, strontianite SrCOs, witherite BaCOs... 

Dr. Crawford showed in this paper that the salt (strontium chloride) obtained by dissolving the new mineral in hydrochloric acid differs in several respects from barium chloride. It is much more soluble in hot water than in cold, the strontium salt is much the more soluble in water and produces a greater cooling effect, and these two chlorides have different crystalline forms. He concluded therefore that the mineral which is sold at Strontean [sic] for aerated terra ponderosa possesses different qualities from that earth, although at the same time it must be admitted that in many particulars they have a very near resemblance to each other. He also stated that it is probable that the Scotch mineral is a new species of earth which has not hitherto been sufficiently examined and that Mr. Babington. . . has for some time entertained a suspicion that the Scotch mineral is not the true aerated terra ponderosa. In 1790 Dr. Crawford sent a specimen of the new mineral (strontianite, strontium carbonate) to Richard Kirwan for analysis (50, 66). 

Near the close of 1791, Thomas Charles Hope of Edinburgh began an elaborate investigation of the Strontian spar, the results of which he presented to the College Literary Society of Edinburgh in March, 1792, and to the Royal Society of Edinburgh on November 4, 1793. In these experiments he made a clear distinction between witherite and strontian spar (strontianite) and proved conclusively that the latter contains a new earth strontites, or strontia (26, 30, 48). He noticed that strontia slakes even more avidly with water than does lime that, like baryta, it is much more soluble in hot water than in cold that its solubility in water is extremely great and that all its compounds, especially the chloride,... 

Strontium occurs chiefly as sulfate (celestite, SrSO,i) and carbonate (strontianite. SrCO ) although widely distributed in small concentration. The commercially exploited deposits are mainly in England. The sulfate or carbonate is transformed into chloride, and the electrolysis of die fused chloride yields strontium metal,... 

Strontium. Sr at no 38 at wt 87.62 valence 2 two important radioactive isotopes (out of 12), Sr-89 and Sr-90 four stable isotopes, 88 (82.56% abundance), 86 (9.86% abundance), 87 (7.02% abundance), 84 (0.56% abundance) silvery-white metal, face-centered cubic structure brief exposure to air results in the yel oxide mp 752°, 757°, 769° (separate values) bp 1366°, 1384°, 1390° (separate values) d 2.6g/cc. Sol in acids, ethanol and liq ammonia. CA Registry No [7440-24-6]. Occurs in nature as the sulfate celestine or the carbonate strontianite also found in small quantities associated with Ba, Ca, Pb or K minerals. Prepn is by a) electrolysis of molten Sr chloride in a graphite crucible with cooling of the upper cathodic space to isolate the Sr vapors, or b) thermal redd of the oxide... 

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