Calcium sulfate hydrate

Calcium sulfate crystals were precipitated in a Continuous Mixed Suspension Mixed Product Removal (CMSMPR) crystallizer by mixing of calcium phosphate and sulfuric acid feed streams. The formed calcium sulfate hydrate (anhydrite, hemihydrate and dihydrate) mainly depends on the temperature and the solution composition. The uptake of cadmium and phosphate ions in these hydrates has been studied as a function of residence time and solution composition. In anhydrite, also the incorporation of other metal ions has been investigated. The uptake was found to be a function of both thermodynamics and kinetics. 

Water can be determined in solid samples by infrared spectroscopy. The water content of calcium sulfate hydrates is to be measured using calcium carbonate as an internal standard to compensate for some systematic errors in the procedure. A series of standard solutions containing calcium sulfate dihydrate and a constant known amount of the internal standard are prepared. The solution of unknown water content is also prepared with the same amount of internal standard. The absorbance of the dihydrate is measured at one wavelength ( sample) along with that of the internal standard at another wavelength (As,d). The following results were obtained. 

Fluorogypsum is not being used in any commercial applications however, it has been evaluated for use as a road base material, and in the production of impure plasterboard Phosphogypsum is a calcium sulfate hydrate that is pumped into ponds, eventually dewatered, and ultimately disposed of in large stockpiles called stacks. It has been recovered and reused with some success in stabilized road bases, unbound road bases, and roller-compacted concrete. It can be used for agricultural purposes, if the radium-226 concentration of the source material is less than 10 pCi/g... 

Table 2. Influence of K2SO4 to anhydrous calcium sulfate hydration...

Table 9. Lower line of sulfate concentration that hydrated sulfate crystallized from calcium sulfate hydration phase (mol/L)...

Wltkamp, G.J., van Rosmalen, G.M. Reduction of cadmium uptake In calcium sulfate hydrates by complexlng agents. In Industrial Crystallization 90 (ed. Mersmann, A.), p. 689, Munich 1990... 

Plaster of Paris Calcium sulfate -hydrate CaS04 1 H2O... 

A similar approach for the quantitative estimation of the calcium sulfate hydrates can be used with TGA analysis. 

The following empirical relationship was developed to predict the relative proportion of calcium sulfate hydrates. 

A diagram for one implementation of this process (61,62) is shown in Eigure 11. Recovered potassium sulfate is converted to potassium formate [590-29 ] by reaction with calcium formate [544-17-2] which is made by reacting hydrated lime, Ca(OH)2, and carbon monoxide. The potassium formate (mp 167°C), in hquid form, is recycled to the combustor at about 170°C. Sulfur is removed as soHd calcium sulfate by filtration and then disposed of (see... 

C265-91 Calcium Sulfate in Hydrated Portiand Cement ... 

Other reactions taking place throughout the hardening period are substitution and addition reactions (29). Ferrite and sulfoferrite analogues of calcium monosulfoaluminate and ettringite form soHd solutions in which iron oxide substitutes continuously for the alumina. Reactions with the calcium sihcate hydrate result in the formation of additional substituted C—S—H gel at the expense of the crystalline aluminate, sulfate, and ferrite hydrate phases. 

The composition of the Hquid phase during the early hydration of Portiand cements is controlled mainly by the solution of calcium, sulfate, sodium, and potassium ions. Very Httie alumina, siHca, or iron are present in solution. Calcium hydroxide, as calcium oxide, and gypsum, as calcium sulfate, alone have solubihties of about 1.1 and 2.1 g/L at 25°C, respectively. In the presence of alkaHes released in the first 7 min, the composition tends to be governed by the equiHbrium ... 

ASTM C845 Type E-I (K) expansive cement manufactured ia the United States usually depends on aluminate and sulfate phases that result ia more ettriagite formation duriag hydration than ia normal Portland cements. Type K contains an anhydrous calcium sulfoaluminate, C A SI. This cement can be made either by iategraHy burning to produce the desired phase composition, or by intergrinding a special component with ordinary Portland cement clinkers and calcium sulfate. 

Calcium sulfate, the substance used to absorb water in desiccators, provides an example of this temperature sensitivity. Anhydrous calcium sulfate absorbs water vapor from the atmosphere to give the hydrated salt. The reaction has a negative AS° because water molecules become more constrained when gaseous water molecules move into the solid state. The reaction also has a negative AH ° because of the electrical forces of attraction... 

Much building material has been derived from two monomineral sedimentary rocks gypsum (composed of hydrated calcium sulfate) and limestone, which consists of calcite (composed mostly of calcium carbonate). Freshwater and seawater contain dissolved calcium carbonate and calcium sulfate. Most limestone and gypsum are formed when, as a consequence of the evaporation of water, calcium sulfate and calcium carbonate precipitate out of the water solutions as either gypsum or limestone. Limestone is also formed as a result of the activity of living organisms. Many sea- and freshwater animals, such as snails, clams, and corals, as well as some water plants, draw... 

Likewise, the calcination of gypsum drives away water. Calcinating gypsum (composed of hydrated calcium sulfate) causes that part of the water combined with the calcium sulfate to evaporate, leaving a solid, friable residue usually known as plaster of Paris (composed of calcium sulfate hemihydrate) plaster of Paris is used as a cement and mortar as well as an efficient casting material (see Textbox 35). 

Plaster of Paris has long been used as a casting material, a cement, and a mortar. If mixed with water, plaster of Paris forms a very soft and pliable mixture. After a very short time, lasting only 5-8 minutes, the wet, pliable mixture sets, that is, it hardens into a stable, firm solid. The setting process entails the incorporation of water molecules (a process known as hydration) into the calcium sulfate hemihydrate and the consequent formation and crystallization of hydrated sulfate of calcium. In other words, when water is added to plaster of Paris, the two combine, again forming gypsum, which soon crystallizes into a hard solid mass ... 

There are several variants of the Dorr process which differ according to the treatment of the calcium sulfate. Some variants produce the dihydrate, gypsum, others produce the hemi-hydrate. The variants also differ in the concentration of the phosphoric acid produced, but it is never more than 43 percent. The basic process was patented by Lawes in England in 1842 but the presently used variant was developed by the Dorr-Oliver company in the 1930s. Stevens, H. M., Phosphorus and Its Compounds, Interscience, New York, 1961. 

Guillini A process for making gypsum from the waste product from the Wet Process for making phosphoric acid. The waste is heated with water in an autoclave this removes impurities and converts the calcium sulfate dihydrate to the hemi-hydrate. 

The experiment often uses hydrates of copper(II) sulfate, magnesium sulfate, calcium sulfate, or barium chloride. 

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. 

Calcium aluminate monosulfate hydrate CaNH4P04-8H20 Calcium sulfate hemihydrate CaS04 CaS04-2H20... 

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