Strontium carbonates

The Specification of Lime for Industrial Uses , The Chalk, Lime and Allied Industries Research Association, Information Note, IP 58,1966. 

Hansen, Limestone for Precipitated Calcium Carbonate (PCC) , Proc. International Lime Congress, Berlin, 1994. 

Gallone, Chlorine Oxides and Chlorine Oxygen Acids , Ullmann s . 

ASTM C911-94 Specification for Quicklime, Hydrated Lime and Limestone for Chemical Uses , 1994. 

Boynton, Chemistry and Technology of Lime and Limestone , John Wiley Sons, 1980, ISBN 0-471-02771-5. 

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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 has a valence of +2 and forms compounds that resemble the compounds of the other alkaline-earth metals (see Barium compounds Calcium compounds). Although many strontium compounds are known, there are only a few that have commercial importance and, of these, strontium carbonate [1633-05-2] SrCO, and strontium nitrate [10042-76-9], Sr(N03)2, are made in the largest quantities. The mineral celestite [7759-02-6], SrSO, is the raw material from which the carbonate or the nitrate is made. 

As of 1996, Solvay Barium Strontium GmbH was the world s largest producer of strontium carbonate at its combined barium—strontium plant at Bad Hunningen (Germany). Cia Minera La Valencia (Mexico) was the next largest producer, followed by Chemical Products Corporation of the United States, which has two plants, one in the United States and one in Mexico. Dachan Specialty Chemicals (South Korea) was another principal producer. Together these four companies accounted for almost 80% of world capacity. 

Strontium carbonate is the principal strontium compound consumed. Other commercial compounds include strontium nitrate and strontium hydrate. The latter is available in an anhydrous form or as the dihydrate or octahydrate form and is called strontium hydrate. 

There are two main processes for conversion of celestite, ie, strontium sulfate, to strontium carbonate. The principal process is the black ash process. Strontium nitrate is produced by dissolving celestite in nitric acid and purifying it. Most other strontium compounds are produced from strontium nitrate. To service this market, NOAH Technologies Corporation (San Antonio, Texas) has estabUshed a plant in Mexico to manufacture most commercial- and reagent-grade strontium compounds except strontium carbonate. 

Total exports of strontium carbonate have increased significantly in recent years, particularly those from Mexico. Between 1990 and 1993, Mexico... 

Uses. The United States and Japan account for about three quarters of the world demand for strontium carbonate, ca 150,000 t/yr. In 1993,... 

Health and Safety Factors. The strontium ion has a low order of toxicity, and strontium compounds are remarkably free of toxic hazards. Chemically, strontium is similar to calcium, and strontium salts, like calcium salts, are not easily absorbed by the intestinal tract. Strontium carbonate has no commonly recognized hazardous properties. Strontium nitrate is regulated as an oxidizer that promotes rapid burning of combustible materials, and it should not be stored in areas of potential fire hazards. 

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 carbonate is a colorless or white crystalline soHd having a rhombic stmcture below 926°C and a hexagonal stmcture above this temperature. It has a specific gravity of 3.70, a melting point of 1497°C at 6 MPa (60 atm), and it decomposes to the oxide on heating at 1340°C. It is insoluble in water but reacts with acids, and is soluble in solutions of ammonium salts. 

Production. In the commercial production of strontium carbonate, celestite ore is cmshed, ground, and stored in bins before it is fed to rotary kilns. As the ground ore is being conveyed to the kilns, it is mixed with ground coke. In the kilns, the celestite is reduced to strontium sulfide [1314-96-1J, known as black ash, according to the reaction ... 

The product stream from the kilns is collected in storage bins. Black ash from the bins is fine-ground in a ball mill and fed to a leacher circuit, which is a system of stirred tanks, where it is dissolved in water and the muds are separated by countercurrent decantation. The solution from the decantation is passed through filter presses the muds are washed, centrifuged, and discarded. The filtered product, a saturated solution containing 12—13 wt % strontium sulfide, is sent to an agitation tank where soda ash is added to cause precipitation of strontium carbonate crystals ... 

After precipitation is complete, the slurry is pumped to vacuum dmm filters where a nearly complete Hquid-soHds separation is accompHshed. The hquid is dilute sodium sulfide solution, which is concentrated by evaporation to a flaked 60 wt % sodium sulfide product. The filter cake is a 60 wt % strontium carbonate soHd which is fed to a carbonate dryer. After drying, the strontium carbonate product is cooled, ground, and screened for packaging. 

Strontium carbonate also precipitates from strontium sulfide solution with carbon dioxide. Hydrogen sulfide is generated as a by-product of this reaction and reacts with sodium hydroxide to produce sodium hydrosulfide, which is sold as by-product. The abiUty of the black ash process to produce a product exceeding 95% strontium carbonate, from ores containing <85% strontium sulfate, has led to its predorninance. 

In another process, strontium sulfate can be converted to strontium carbonate direcdy by a metathesis reaction wherein strontium sulfate is added to a solution of sodium carbonate to produce strontium carbonate and leave sodium sulfate in solution (6). Prior to this reaction, the finely ground ore is mixed with hydrochloric acid to convert the calcium carbonates and iron oxides to water-soluble chlorides. 

Strontium Hexaferrite. Strontium hexaferrite [12023-91 -5] SrO-6 Fe2 03, is made by combining powdered ferric oxide, Fe203, and strontium carbonate, SrCO, and calcining the mixture at ca 1000°C in a rotary kiln (9). The material is cmshed, mixed with a binder, and pressed or extmded into... 

Strontium Halides. Strontium haUdes are made by the reactions of strontium carbonate with the appropriate mineral acids. They are used primarily in medicines as replacements for other bromides and iodides. 

Strontium Oxide, Hydroxide, and Peroxide. Strontium oxide, SrO, is a white powder that has a specific gravity of 4.7 and a melting point of 2430°C. It is made by heating strontium carbonate with carbon in an electric furnace, or by heating celestite with carbon and treating the sulfide formed with caustic soda and then calcining the product (10). It reacts with water to form strontium hydroxide [18480-07-4] and is used as the source of strontium peroxide [1314-18-7],... 

Strontium Titanate. Strontium titanate [12060-59-2], SrTiO, is a ceramic dielectric material that is insoluble in water and has a specific gravity of 4.81. It is made from strontium carbonate and is used in the form of 0.5-mm thick disks as electrical capacitors in television sets, radios, and computers. 

Most barium compounds are prepared from reactions of barium carbonate [513-77-9] BaCO, which is commercially manufactured by the "black ash" process from barite and coke ki a process identical to that for strontium carbonate production. Depending on the co-product, soda ash and/or carbon dioxide are also consumed. 

Strontium carbonate was produced by the carbonation of strontium hydroxide (Yagi etal., 1988), as... 

The product crystals were agglomerates of needles or dendrites. Loose floes of dendroid strontium carbonate are compacted by agitation, which is an important factor in controlling the habit of product particles. Semi-batch operation produces larger particles compared to batch or continuous operation. 

Strontium metal is responsible for the red color in fireworks. Fireworks manufacturers use strontium carbonate, which can be produced by combining strontium metal, graphite (C), and oxygen gas. The formation of one mole of SrC03 releases 1220 X 103 k) of energy. 

The radiation hazard associated with fallout from nuclear weapons testing arises from radioactive isotopes such as these. One of the most dangerous is strontium-90. In the form of strontium carbonate, SrC03, it is incorporated into the bones of animals and human beings, where it remains far a lifetime. 

Both carbonates decompose to their oxides with the evolution of carbon dioxide. The decomposition temperature for calcium carbonate is in the temperature range 650-850 °C, whilst strontium carbonate decomposes between 950 and 1150°C. Hence the amount of calcium and strontium present in a mixture may be calculated from the weight losses due to the evolution of carbon dioxide at the lower and higher temperature ranges respectively. This method could be extended to the analysis of a three-component mixture, as barium carbonate is reported to decompose at an even higher temperature ( 1300 °C) than strontium carbonate. 

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