Natural Anhydrite

Anchoic acid. See/ zelaic acid Anesthetic ether. See Ethyl ether Anhydrite (natural forn. See Calcium sulfate 3,6-Anhydro-d-galactan. See Carrageenan (Chondrus crispus) 1,4-Anl dro-D-glucitol, 6-hexadecanoate. See Sorbitan palmitate Anhydro-d-ghicitol monooctadecanoate. See Sorbitan stearate Anhydrohexhol s uioleate. See Sorbitan sesquioleate Anhydrosorhitol dioleate. See Sorbitan dioleate Anhydrosorhitol monolaurate. See Sorbitan laurate Anhydrosorhitol monooleate. See Sorbitan oleate Anhydrosorhitol monostearate. See Sorbitan stearate... 

Synonyms Anhydrite (natural form) Anhydrous calcium sulfate Anhydrous gypsum Calcium sulfate (1 1) Calcium sulfonate Gypsum Plaster of Paris Sulfuric acid, calcium salt Sulfuric acid, calcium salt (1 1) Classification Inorganic salt Empirical CaOjS Formula Ca H2O4S... 

Sulfur constitutes about 0.052 wt % of the earth s cmst. The forms in which it is ordinarily found include elemental or native sulfur in unconsohdated volcanic rocks, in anhydrite over salt-dome stmctures, and in bedded anhydrite or gypsum evaporate basin formations combined sulfur in metal sulfide ores and mineral sulfates hydrogen sulfide in natural gas organic sulfur compounds in petroleum and tar sands and a combination of both pyritic and organic sulfur compounds in coal (qv). 

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. 

Anhydrite also has several common classifications. Anhydrite I designates the natural rock form. Anhydrite 11 identifies a relatively insoluble form of CaSO prepared by high temperature thermal decomposition of the dihydrate. It has an orthorhombic lattice. Anhydrite 111, a relatively soluble form made by lower temperature decomposition of dihydrate, is quite unstable converting to hemihydrate easily upon exposure to water or free moisture, and has the same crystal lattice as the hemihydrate phase. Soluble anhydrite is readily made from gypsum by dehydration at temperatures of 140—200°C. Insoluble anhydrite can be made by beating the dihydrate, hemihydrate, or soluble anhydrite for about 1 h at 900°C. Conversion can also be achieved at lower temperatures however, longer times are necessary. 

Some mechanisms of anhydrite deposition in Kuroko deposits. Shikazono et al. (1983) considered the depositional mechanism of anhydrite based on the mode of occurrence, texture, Sr content, nature of the contained fluid inclusions and isotopic composition of Sr, S and O in anhydrite together with the mineralogy of the sekko ore, combined with their experimental study on the patitioning of Sr between coexisting anhydrite and aqueous solution. The following is their discussion on the depositional mechanism of anhydrite. 

As a test of our ability to calculate activity coefficients in natural brines, we consider groundwater from the Sebkhat El Melah brine deposit near Zarzis, Tunisia (Perthuisot, 1980). The deposit occurs in a buried evaporite basin composed of halite (NaCl), anhydrite (CaSC>4), and dolomite [CaMg(CC>3)2]. The Tunisian government would like to exploit the brines for their chemical content, especially for the potassium, which is needed to make fertilizer. 

In contrast to the fate of silicates, a catchment exhibiting a small area of so-called Biindner Schiefer, a sandy-marly schist containing soluble anhydrite or gypsum, will produce a remarkably high weathering rate for the entire basin. This effect arises in the alpine catchments of the Ticino, Rhine, and Rhone. The occurrence of Biindner Schiefer also causes sulfate concentrations in the range of 0.5-1 mmol in rivers. Natural and anthropogenic atmospheric sulfur... 

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. 

The use of natural anhydrite (CaS04) as a substitute or partial replacement for gypsum (CaS04.2H20) in the... 

The soluble sulfate versus time curve for the cement containing the natural anhydrite is radically changed when CLS is present [130, 131]. The rate of solution of natural anhydrite, which is much slower than that of gypsum or calcium sulfate hemihydrate, is further retarded in the presence of chemical admixtures, which leads to a sulfate-starved system in the concrete, often producing rapid set and an increase in rate of concrete slump loss (Fig. 7.42). Apparently the adsorption of the lignosulfonate by the natural anhydride plus the rapid reaction between the soluble SO3 and the... 

Fig. 7.42 SO3 solubilities of gypsum and natural anhydrite in saturated lime water with and without CLS admixture (Dodson [127]).

Anhydrite is a calcium sulfate, CaS04, with an orthorhombic structure (mmm) where sulfur atoms, which are at the centers of tetrahedra of oxygens, and calcium atoms he on the lines of intersection of mirror planes (100) and (010). In nature, REE and Mn can easily substitute for Ca, becoming luminescence... 

The natural anhydrite in our study consisted of five samples from a variety of geologic environments. Concentrations of potential luminescence impurities in one sample are presented in Table 4.9. 

Luminescence of trivalent Eu was not detected in natural barite yet, but the possible emission maybe seen on artificially activated BaS04 (Eig. 5.15). The Sr addition generates the appearance of an additional Eu " " luminescence center compared with BaS04. The luminescence of Eu " " and Eu " is well known in anhydrite (Tarashchan 1978 Gaft et al. 1985 Baumer et al. 1997). They are also found in time-resolved spectra under excitation at 266 nm (Eig. 4.17). 

Luminescence of in synthetic alkaline earth sulfates is well known (Folk-erts et al. 1995). In this study, CaS04 Pb shows an emission band with a maximum at 235 nm at 300 K, while the excitation maximum is at 220 nm. The decay curve of the emission is single exponential with a decay time of 570 ps at 4.2 K. The emission spectrum of BaS04 Pb demonstrates a broad band peaking at 340 nm with an excitation maximum at 220 nm, while in SrS04 Pb the luminescence band has a maximum at 380 nm. hi natural barite and anhydrite samples we detected several narrow UV bands, which may be connected with Pb emission, but for confident conclusion additional study is needed. In any case, Pb participation in natural sulfates liuninescence has to be taken into consideration. 

If soluble anhydrite is desired, firing is maintained until a second boil occurs accompanied by a second temperature plateau at about 190°C. Virtually all the water of crystallization has been removed at 215°C. Soluble salts are impurities that increase the vapor pressure within the kettle. Aridized stucco refers to ketde-calcined hemihydrate that has been made with the intentional addition of 0.55—1.1 kilograms of NaCl or CaCl per metric ton of land plaster. The stucco characteristic of lower water demand permits higher density and higher strength casts. The hygroscopic nature of the chlorides prevents the use of aridized stucco for some applications. 

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