Sulfate Gypsum

CHEMICAL NAME = calcium sulfate calcium sulfate dihydrate  

MELTING POINT = decomposes at 1,450°C becomes hemihydrate at 128°C BOILING POINT = decomposes at 1,450°C becomes anhydrous at 160°C DENSITY = 2.96 g/cm3 2.32 g/cm3 

Calcination forms the hemihydrate type of calcium sulfate by the reaction CaS04 2H20 —-— CaS04 2 H20 + 2 H20. Various calcining methods have been used throughout history to 

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Calcium sulfate (gypsum) may be added to reduce the carbonate to required levels. The reaction is as follows ... 

Scmbbers for removing sulfur dioxide from smelter off-gases have been under development for many years. They are widely used in Japan. The calcium sulfate (gypsum) obtained from this process is suitable feed for waUboard production (see Calcium compound, calcium sulfate Sulfur removal and recovery). 

The scale may consist of calcium carbonate, barium sulfate, gypsum, strontium sulfate, iron carbonate, iron oxides, iron sulfides, and magnesium salts [943]. There are monographs (e.g.. Corrosion and Scale Handbook [159]) and reviews [414] on scale depositions available in the literature. 

So far, the techniques to recover sulfur have all related to sulfur in the form of H2S. Consider now how sulfur in the form of S02 can be dealt with. Sulfur dioxide can be reacted with limestone to produce solid calcium sulfate (gypsum), according to the equations11 ... 

The product, Ca(H2P04)2, is more soluble than the phosphate. Sulfuric acid is produced in the largest quantity of any compound, with production that approaches 100 billion pounds annually. Approximately two-thirds of this amount is used in the production of fertilizers. The mixture containing calcium dihydrogen phosphate and calcium sulfate (gypsum) is known as superphosphate of lime, and it contains a higher percent of phosphorus than does calcium phosphate. 

Gypsum A mineral form of calcium sulfate. Gypsum is a common component of evaporites, and... 

Traditionally, citric acid is recovered from fermentation broth via a Ume and sulfuric acid process. In this process, filtered fermentation broth is treated with lime to precipitate calcium citrate. This precipitate is washed and acidified with sulfuric acid to convert the calcium citrate to solid calcium sulfate (gypsum) and... 

Other Aluminosilicates - Mica, Feldspar, Chlorite, Quartz Sulfate - Fe Sulfate, Gypsum Carbonate - Calcite, Siderite, Dolomite Fe Altered - Oxides, Sulfate... 

Etherton, D.L., "Experimental Study of Calcium Sulfate (Gypsum) Crystallization from Stack-Gas Liquors," M.S. Thesis, University of Arizona, Tucson (1980). 

Sulfates Gypsum Anhydrite CaS04-2H20 CaS04 Congruent dissolution in H20... 

This is easier than pretreatment of the fuel, but the waste is calcium sulfite which, unlike the more familiar sulfate (gypsum, Plaster of Paris), is quite toxic to plants and is therefore difficult to dispose of safely. 

Buffering of pH during the early heavier precipitation of calcite and sepiolite is clear and is reflected in a near constancy of HCCV and CO32. However, after Ca2+ and Mg2+ are substantially reduced, the pH again rises with further concentration. Because the Sierra waters are so low in sulfate, gypsum does not precipitate abstraction of Ca2+ as calcite never permits the solubility product of gypsum to be exceeded. 

You have already seen on p. 122 in Table 8.2 that salts are useful substances. Some of the salts shown in that table occur naturally and are mined, for example calcium sulfate (gypsum) and calcium carbonate (limestone). Many of the others must be made by the chemical industry, for example ammonium nitrate, iron(n) sulfate and silver bromide. 

Calcium sulfates (gypsum and anhydrite) CaS04-2H20, CaS04 <1-6 Boyle and Jonasson (1973)... 

There is no current commercial biologic process for the production of succinic acid. In past laboratory systems, when succinic acid has been produced by fermentation, lime is added to the fermentation medium to neutralize the acid, yielding calcium succinate (2). The calcium succinate salt then precipitates out of the solution. Subsequently, sulfuric acid is added to the salt to produce the free soluble succinic acid and solid calcium sulfate (gypsum). The acid is then purified with several washings over a sorbent to remove impurities. The disposal of the solid waste is both a directly economic and an environmental concern, as is the cost of the raw materials. Some key process-related problems have been identified as follows (1) the separation of dilute product streams and the related costs of recovery, (2) the elimination of the salt waste from the current purification process, and (3) the reduction of inhibition to the product succinic acid on the fermentation itself. Acetic acid is also a byproduct of the fermentation of glucose by Anaerobiospirillium succiniciproducens almost 1 mol of acetate will be produced for every 2 mol of succinate (3). Under certain cultivation conditions by a mutant Escherichia coli, lesser amounts of acetate can be produced (4,5). This byproduct will also need to be separated. 

Lack of evaporitic sulfate (gypsum, anhydrite) and salt (halite, sylvite) deposits in sedimentary rocks older than 800 million years. 

The most popular thin layer is silica gel, and it is estimated that about 90% of TLC separations are performed on standard TLC silica plates a common size is 20 cm square and 250 g,m thick. Binders, in amounts up to 15%, are usually used to produce a stable layer and good adherence to the backing plate, but plates can be made without binders. Calcium sulfate (gypsum, designated with a G in the name, e.g., silica gel G) and polyvinyl alcohol (PVA) are most common. The PVA plates are very stable and will withstand rather rough handling. While it is not difficult to make one s own plates, most laboratories prefer commercially prepared plates, especially those made with PVA. It must not be forgotten, however, that both binders will modify the adsorption properties of the silica and can produce somewhat different separations. 

Sulfate Gypsum (satin spar, alabaster) CaS042H20... 

An important technology for removal of S02 is Flue Gas Desulfurization (FGD), carried out in units known as scrubbers. Most scrubbers contact the flue gas with a slurry of lime or limestone to capture the sulfur oxides and produce a sludge containing calcium sulfite and calcium sulfate. However, disposal of sludge is another environmental problem, and some scrubbers include oxidation to convert all the calcium sulfite to sulfate (gypsum), which can be used for wallboard manufacture. Fluidized-bed combustion units add a sulfur... 

Figure 3. SEM photomicrograph of same bone as Figure 2 cut parallel to blood vessels (dark areas). The thin bright area along the edge of the voids left by the blood vessels are calcium sulfate (gypsum or anhydrite).

In the future, it seems likely that most processes that currently entail the discharge of SO2 will have to be adapted with the introduction of scrubbers . Two main methods can be employed for this either the reduction of SO2 to snllur using the Claus process or, alternatively, neutralization nsing milk of lime (equation 18) to give either calcium sulfite or, with complete oxidation, calcium sulfate (gypsum). 

Calcium hydroxide (slaked lime) calcium oxide (quicklime) calcium carbonate (calcite, aragonite, marble, limestone) calcium sulfate (gypsum, plaster of Paws). 

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