Calcium sulfate occurence

Calcium sulfate occurs in large deposits throughout the world as its hydrate (gypsum CaS04-2H20). When heated at moderate temperatures, gypsum loses part of the water to form a semihydrate. 

Calcium Sulfate occurs as a fine, white to slightly yellow-white powder. It is anhydrous or contains two molecules of water of hydration. 

Calcium sulfate occurs in nature as the mineral gypsum, CaS04 2H20. 

Anhydrous calcium sulfate occurs naturally as the mineral anhydrite. The naturally occurring rock gypsum may be crushed and ground for use as the dihydrate or calcined at 150°C to produce the hemihydrate. A purer variety of calcium sulfate may also be obtained chemically by reacting calcium carbonate with sulfuric acid or by precipitation from calcium chloride and a soluble sulfate. 

Calcium. sulfate occurs naturally as its dihydrate, (natural gypsum) as anhydrous anhydrite and rarely as its hemihydrate in the form of the mineral bassanite. Only the deposits of natural gypsum and anhydrite are of economic interest. For applications in the construction industry only the hardenable modifications, calcium sulfate hemihydrate (a- and P-form) and anhydrite, which are manufactured by dehydrating the dihydrate, are important. The properties and formation conditions of the different calcium sulfate modifications are given in Table 5.3-11. 

Both the anhydrous and dihydrate forms of calcium sulfate occur naturally in the form of the minerals anhydrite, angelite, muriacite, and karstenite (CaS04) and gypsum (CaS04-2H20). These minerals have been known to humans and used by them for thousands of years. The method for converting natural gypsum to the hemihydrate (plaster of... 

Scaling is not always related to temperature. Calcium carbonate and calcium sulfate scaling occur on unheated surfaces when their solubiUties are exceeded in the bulk water. Metallic surfaces are ideal sites for crystal nucleation because of their rough surfaces and the low velocities adjacent to the surface. Corrosion cells on the metal surface produce areas of high pH, which promote the precipitation of many cooling water salts. Once formed, scale deposits initiate additional nucleation, and crystal growth proceeds at an accelerated rate. 

Gypsum [13397-24-5] CaSO 2H20, is a naturally occurring mineral found mainly in the western United States and eastern Canada (see Calcium COMPOUNDS, CALCIUM sulfate). The purer deposits require only minimal beneficiation to get a product pure enough for commercial appHcations. Other... 

Sulfates and Sulfites. Calcium sulfate [7778-18-9] occurs in large deposits as CaSO and as gypsum, CaSO -2H20. The dihydrate is a... 

Calcium sulfate [7778-18-9J, CaSO, ia mineral form is commonly called gypsum and occurs abundandy ia many areas of the wodd. In natural deposits, the main form is the dihydrate. Some anhydrite is also present ia most areas, although to a lesser extent. Mineral composition can be found ia Table 1. 

This time the trial product, 4 X 10-4, is greater than Klp = 2.4 X 10 s so a precipitate does form. Solid calcium sulfate, CaS04, will continue to form, lowering the concentrations [Ca+2] and [SO -2] until they are low enough that the ion product equals Kcp. Then equilibrium exists and no more precipitation occurs. 

The precipitation of anhydrite (anhydrous calcium sulfate, CaS04) may also occur. Under ambient temperatures, anhydrite is much more soluble than calcium carbonate, but because calcium sulfate, in common with other calcium salts such as calcium phosphate (also known as tricalcium phosphate [Ca3(P04)2]), has an inverse-temperature solubility, it deposits more rapidly on the hottest heat transfer surfaces. 

Sulfates in surface MU water sources usually are present at lower concentrations (typically 20-60 ppm) but this level may rise to several hundred ppm in subsurface waters. The maximum solubility of calcium sulfate is dependent on temperature but is in the range of 1,800 to 2,000 ppm in cold water. This rate is significantly less in hot BW where boiler deposits occur, the sulfate scale normally is present as anhydrite (CaS04). Sulfate scales are hard and very difficult to remove, so treatment programs employed must be carefully controlled to avoid risks of scaling. 

Limestone is the cheapest basic product (0.20/lb in 1968 0.40/kg). However, it can become coated with calcium sulfate, which can almost stop neutralization from occurring. Some kind of scouring may be necessary to prevent this. Lime may be used, but it also can become coated and rendered ineffective. Soda ash and caustic soda are other alternatives, but they cost 8 to 10 times as much as limestone.35 Sometimes limestone or lime is used to raise the pH to between 4.0 and 5.0, and the more expensive but more easily controllable soda ash or caustic soda is used to obtain the desired final pH. The only equipment needed is storage tanks for the acids and bases and mixing tanks, equipped with the proper controls. 

The use of the perchlorate as desiccant in a drybag where contamination with organic compounds is possible is considered dangerous [1], Magnesium perchlorate ( Anhydrone ) was inadvertently used instead of calcium sulfate (anhydrite) to dry an unstated reaction product before vacuum distillation. The error was realised and all solid was filtered off. Towards the end of the distillation, decomposition and an explosion occurred, possibly owing to the presence of dissolved magnesium perchlorate, or more probably to perchloric acid present as impurity in the salt [2]. 

Gypsum. Hydrated calcium sulfate (CaSO4-2H20). It occurs naturally and - is used as a source of sulfur, as a drying agent, an organic liquid precursor, and in polishes. 

The second important factor, called the hardness factor for simplicity, includes contributions from Ba, F, hardness. Mg, TDS, Sr, and sulfate. This factor characterizes the upper aquifer waters. One may rationalize the distinction between upper and lower aquifers by hypothesizing a natural "softening" in the lower aquifer where ion-exchange of calcium, magnesium and sulfate occurred with sodium and fluoride. It is Interesting to note that fluoride occurs in both factors and it alone provides a good aquifer identifier. 

The compound occurs in nature as the mineral, berlinite. Also, it occurs in nature in minerals, amblygonite, [NaAl(P04)(0H)j augelite, [Al2(P04)(0H)3] lazulite, [(Mg,Fe)Al2(P04)2(0H)2] variscite [(Al,Fe3+)(P04) 2H20] andwavel-lite, [Al3(0H)3 (P04)2 5H20]. It is used as flux for ceramics as cement in combination with calcium sulfate and sodium silicate and in the manufacture of special glasses. It is also used in dried gel and therapeutically as an antacid. 

Both the anhydrous calcium sulfate and dihydrate occur in nature, the former as the mineral, anhydrite, and the latter as gypsum. Gypsum is widely distributed in nature. It has been known since ancient times. 

Anhydrous calcium sulfate is a crystalline substance orthorhombic the color may vary as white, gray, blue or brick-red occurs as insoluble anhydrite or porous soluble anhydrite density 2.96 g/cm hardness 3.5 Mohs insoluble anhydrite is practically insoluble in water (0.21% at 20°C) soluble anhydrite readily absorbs moisture and is soluble in water. 

Calcium sulfate exhibits high thermal stability. At elevated temperatures, it occurs in anhydrous form. The dihydrate loses its water molecules upon strong heating. When ignited with charcoal, it is reduced to calcium sulfide ... 

In order for normal set to occur in Portland cement paste, mortar, or concrete, calcium sulfate must be present in the cement-water system. In today s cements, most of the calcium sulfate introduced into the system as a component of the cement, can be present in one or more forms gypsum (CaS04.2H20), hemihydrate (CaS04.1/2... 

Gypsum (Calcium Sulfate Dihydrate, Alabaster), CaSO4.2H20 raw 172.17, sp gr 2.31-2.33, white substance, mp loses 3/2HaO by 128° and rest by 167° hardness 1.5 to 2. Occurs naturally in the USA, Canada, England, France, Sicily, Switzerland etc si sol in w sol in acids, glycerin and aqueous Na3S2Oa and ammonium salts... 

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