Anhydrite CaSO

Fluoride production consists on reacting fluorspar mineral (CaF ) with H SO (cc) to form HF and calcium sulphate. However, reactions do not achieve 100 % yield, so fluorogypsum or anhydrite (CaSO ) obtained contains small amounts of fluoride as CaF in its stmcture. The application of this kind of subproduct is well-known as constmction material, so that the flouride content has to be controlled. 

Finally, sulfur occurs in many localities as the sulfates of electropositive elements (see Chapters 4 and 5) and to a lesser extent as sulfates of Al, Fe, Cu and Pb, etc. Gypsum (CaS04.2H20) and anhydrite (CaSO ) are particularly notable but are little used as a source of sulfur because of high capital and operating costs. Similarly, by far the largest untapped source of sulfur is in the oceans as the dissolved sulfates of Mg, Ca and K. It has been estimated that there are some 1.5 x 10 cubic km of water in the oceans of the world and that 1 cubic km of sea-water contains approximately 1 million tonnes of sulfur combined as sulfate. 

Quartz (SiCL), calcilc (CaCO,). kyanile (ALSiOo. anhydrite (CaSO.,), cnstalile (MgSiO,), gehlenile (Ca Al>Si07)... 

XRD analysis has revealed the presence of several different types of carbonate minerals in liquefaction residues from a number of coals. Minerals identified included vaterite and calcite (two polymorphs of CaCO,) dolomite (CaMg[C03]2) and in the residue from a high sulfur coal (2.26 db), anhydrite (CaSO,) was identified. The types of mineral deposits formed depend not only on the coal but also on the reaction conditions. Our data indicates that whilst vaterite forms at low temperatures (380°C), as the temperature increases, the vaterite becomes progressively converted to calcite, the more stable form. After further increases in temperature, particularly at long reaction times, dolomite begins to form. 

ABSTRACT A rapid and precise X-ray fluorescence method has been developed for the multielement analysis of gypsum and gypsum products. Gypsum specimens are calcined at IOOO°C and then fused with sodium tetraborate flux into flat and transparent disks. The choice of a suitable flux system for the specimen preparation is critical because of a rapid decomposition of anhydrite. CaSO,. in lithium ba fluxes at temperatures above 95O C. This decomposition causes not only visible imperfections in the didi surface but also alters considerably the concentrations of the major elements, calcium and sulfur. The procedure used for a fast setup of ten element analysis of gypsum on the Philips PW-1400 spectrometer utilizing synthetic standards and off-line calculated alpha coefficients is presented. Calibrations carried out with chemically analyzed specimens and their mixtures are compared lo those performed with synthetic standards prepared by blending pure chemicals and anhydrite into the flux. 

The exceptionally light carbonates (5 C= i8.9%o) in the Medjounes structure result from sulfate reduction by sulfate-reducing bacteria in the presence of hydrocarbons, leading eventually to the formation of elemental (native) sulfur. In view of the presence of thick layers of gypsum (CaSO x zH O) and anhydrite (CaSO ) in the succession at the above-mentioned site (sample 27a), a potential for the presence of a native sulfur deposit is indicated. 

Calcium sulfate (anhydrite, CaSO C 3rcmains in the clinker in free form at SO3 contents in the raw meal higher than those needed to convert the existing AI2O3 into C,A,S,... 

The content of calcium sulfate in the cement is typically 10-15 wt%. It may be introduced either as anhydrite (CaSO ) or as gypsum (CaS04.2H20). 

DH, dihydrate (CaS0. 2H20) HH, hemihydrate (CaSO /iH ) A =anhydrite (CaSO ). 

A form termed the right rkomMe prism is fenned by the oonr-bination of the three terminal planes, and is found in nature as Anhydrite, CaSO, By oontinning tiie vratioal axis of the rhombic octohedra to the distance oe, we get tiie vertical prisms as follows ... 

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