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Calcium sulphates (or calcium sulfate) is an inorganic salt with the chemical formula CaSO4.
Calcium sulphates occurs in several hydrated forms; the anhydrous state (known as anhydrite) is a white crystalline solid often found in evaporite deposits.
Calcium sulphate is dihydrate form is the mineral gypsum, which may be dehydrated to produce bassanite, the hemihydrate state.
Gypsum occurs in nature as crystals (selenite) or fibrous masses (satin spar), typically colorless to white, though impurities can impart other hues.
All forms of calcium sulfate are sparingly soluble in water and cause permanent hardness when dissolved therein.
Chemical Name: CALCIUM SULFATE
Synonyms: CaSO;Calciumsulfat;anhydrite;anhydrouscalciumsulfate;CALCIUM SULFATE, POWDER;Drierite, with indicator;gibs;KH2PO24;thiolite;crysalba
CBNumber: CB7151358
Molecular Formula: CaSO4 Lewis structure
Molecular Weight: 136.14
MDL Number: MFCD00799067
MOL File: 7778-18-9.mol
MSDS File: SDS
TDS File: TDS
CALCIUM SULFATE Properties
Melting point: 1450 °C
Density: 2.960
refractive index: 1.575
storage temp.: Store at RT.
solubility: 2g/l
form: Powder
Specific Gravity: 2.96
color: White
Odor: wh. to sl. yel.-wh. powd. or crystals, odorless, tasteless
Water Solubility: Soluble in water.
Sensitive: Moisture Sensitive
Merck: 14,1706
Stability: Stable. Incompatible with aluminium, strong acids.
InChI: 1S/Ca.H2O4S/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2
InChIKey: OSGAYBCDTDRGGQ-UHFFFAOYSA-L
LogP: -1.031 (est)
CAS DataBase Reference: 7778-18-9(CAS DataBase Reference)
Substances Added to Food (formerly EAFUS): CALCIUM SULFATE, FDA UNII, E934B3V59H
EPA Substance Registry System: Calcium sulfate (7778-18-9)
UNSPSC Code: 41123003
NACRES: SB.52
Description
Calcium sulphates and its hydrates are important industrial compounds that have been used throughout history.
Calcium sulphates is obtained naturally from mined gypsum rock, but it also exists in mineral form.
Gypsum forms in beds as sedimentary rock when calcium sulfate, which is a natural component of seawater, is deposited as shallow marine water bodies evaporate.
Gypsum is a transparent, soft, white mineral and is the most common sulfate mineral.
History
Gypsum’s use dates back to prehistoric times.
Archeological evidence shows that it was mined from caves and used to paint ancient gravestones.
The earliest evidence of its use as a building material dates from 6000 b.c.e. in the southwest Asian areas of ancient Anatolia and Syria.
Egyptians used gypsum and plaster in their buildings and monuments, with both found in the Great Pyramids built around 3700 b.c.e.
Calcium sulphates has been used for more than 2,000 years in China to produce tofu.
The word gypsum comes from the Greek word for chalk, gypsos.
The Greek natural philosopher Theophrastus (371–286 b.c.e.) referred to gypsum in his writings.
Gypsum was extensively used in Roman times and throughout the Middle Ages.
In the 1700s, Paris was a leading plaster center, with most of its buildings made using plaster.
After the fire of London in 1666 destroyed 80% of the city, the king of France ordered all wooden houses in France to be covered with plaster as protection against fire.
The hemihydrate form got the name plaster of Paris from the extensive gypsum deposits quarried in the Montmartre district of Paris.
In 1765 and 1766, Antoine Lavoisier (1743–1794) presented papers to the French Academy of Science on gypsum that explained the setting of plaster.
Lavoisier determined that gypsum is a hydrated salt and that set plaster occurs when the hemihydrate form rehydrates back to gypsum.
Chemical Properties
White powder or granules.
Both Calcium sulphates and calcium sulphate dihydrate are white or offwhite, fine, odorless, and tasteless powder or granules.
Calcium sulphates forms white to clear crystals.
Calcium sulphates is commonly encountered in the anhydrous form or as the dihydrate.
Physical properties
Anhydrous Calcium sulphates 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/cm3; 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.
Hemihydrate is a white fine powder; sparingly soluble in water (3g/L at 25°C); combines with water, setting to a hard mass.
Dihydrate may occur as lumps or powder; density 2.32 g/cm3; partially loses water on heating at 100°C; slightly soluble in water (2.4 g/L at 25°C); KSP =2.4x10-5; almost insoluble in organic solvents.
Uses
The largest use of Calcium sulphates is in the construction industry, which accounts for more than 90% of its production.
Gypsum has hundreds of other applications outside the construction industry.
Calcium sulphates can be used agriculturally for several purposes: to supply calcium and sulfur to soils, to balance pH, and to condition soil.
Food grade calcium sulfate is used as a calcium supplement in enriched foods such as flour, cereals, and baked goods.
Calcium sulphates is used as a gelling and firming agent with canned vegetables.
Calcium sulphates is the most common tofu coagulant. The positively charged calcium ion in Calcium sulphates attracts the negatively charged groups in protein molecules, causing thermally denatured proteins to coagulate.
Anhydrous Calcium sulphates is used as a filler to whiten food and consumer products such as frostings, ice creams, paper, paints, and toothpaste.
Powdered gypsum can be used as a chalk for marking athletic fields and other large areas.
Pharmaceutic aid (tablet and capsule diluent).
The insoluble anhydrite is used in cement formulations and as a paper filler; the soluble anhydrite is used as a drying agent; the hemihydrate is used for wall plaster and wallboard; gypsum is used in manufacture of plaster of paris and portland cement.
The main use of calcium sulfate is to produce plaster of Paris and stucco.
These applications exploit the fact that calcium sulfate which has been powdered and calcined forms a moldable paste upon hydration and hardens as crystalline calcium sulfate dihydrate.
Calcium sulphates is also convenient that calcium sulfate is poorly soluble in water and does not readily dissolve in contact with water after its solidification.
Food industry
The Calcium sulphates hydrates are used as a coagulant in products such as tofu.
For the FDA, Calcium sulphates is permitted in cheese and related cheese products; cereal flours, bakery products, frozen desserts, artificial sweeteners for jelly & preserves, condiment vegetables, and condiment tomatoes, and some candies.
Calcium sulphates is known in the E number series as E516, and the UN's FAO knows calcium sulphates as a firming agent, a flour treatment agent, a sequestrant, and a leavening agent.
Dentistry
Calcium sulphates has a long history of use in dentistry.
Calcium sulphates has been used in bone regeneration as a graft material and graft binder (or extender) and as a barrier in guided bone tissue regeneration.
Calcium sulphates is a biocompatible material and is completely resorbed following implantation.
Calcium sulphates does not evoke a significant host response and creates a calcium-rich milieu in the area of implantation.
Desiccant
When sold at the anhydrous state as a desiccant with a color-indicating agent under the name Drierite, it appears blue (anhydrous) or pink (hydrated) due to impregnation with cobalt(II) chloride, which functions as a moisture indicator.
Definition
anhydrite:
An important rockforminganhydrous mineral form ofcalcium sulphate, CaSO4.
Calcium sulphates is chemicallysimilar to gypsum but isharder and heavier and crystallizes inthe rhombic form (gypsum is monoclinic).
Under natural conditions anhydriteslowly hydrates to formgypsum.
Calcium sulphates occurs chiefly in whiteand greyish granular masses and isoften found in the caprock of certainsalt domes.
Calcium sulphates is used as a raw materialin the chemical industry and inthe manufacture of cement and fertilizers.
Production Methods
Gypsum is mined throughout the world, with gypsum mines in 90 countries.
In addition to mined gypsum, gypsum is produced synthetically as a by-product of chemical processes. Most synthetic gypsum comes from flue gas desulfurization used to control sulfur emissions from electric power generation, especially coal-burning power plants.
In this process calcium carbonate reacts with sulfur dioxide to produce Calcium sulphates (CaSO3): CaCO3(s) + SO2(g) → CaSO3(s) + CO2(g).
Calcium sulphates is then oxidized to gypsum: 2CaSO3(s) + O2(g) + 4H2O(l) → 2CaSO42H2O(s).
The second major source of synthetic gypsum is acid neutralization.
Calcium sulphates production of titanium dioxide, TiO2, used as a whitener in many commercial products, yields gypsum as a by-product in the process of neutralizing acidic waste.
Gypsum is also generated from sugar and citric acid production.
In the latter, dilute citric acid (C6H8O7) is precipitated with calcium hydroxide as calcium citrate (Ca3(C6H5O7)2).
Solubility
The solubility of calcium sulfate decreases as temperature increases.
This behaviour ("retrograde solubility") is uncommon: dissolution of most of the salts is endothermic and their solubility increases with temperature.
The retrograde solubility of calcium sulphates is also responsible for its precipitation in the hottest zone of heating systems and for its contribution to the formation of scale in boilers along with the precipitation of calcium carbonate whose solubility also decreases when CO2 degasses from hot water or can escape out of the system.
Production Methods
Anhydrous Calcium sulphates occurs naturally as the mineral anhydrite.
The naturally occurring rock gypsum may be crushed and ground for use as the dihydrate or calcined at 1508℃ to produce the hemihydrate.
A purer variety of Calcium sulphates may also be obtained chemically by reacting calcium carbonate with sulfuric acid or by precipitation from calcium chloride and a soluble sulfate.
General Description
Odorless, white powder or colorless, crystalline solid.
Crystals sometimes have a blue, gray or reddish tinge or can be brick red.
Density: 2.96 g cm-3.
Health Hazard
Calcium sulfate is considered to be a nuisance dust.
There have been no reports of adverse effects in humans exposed to calcium sulfate.
Excessive concentrations would be expected to cause reduced visibility and skin and upper respiratory tract irritation.
1 One report on gypsum miners attributed adverse effects to respirable quartz rather than calcium sulfate.
Agricultural Uses
Anhydrite is a naturally occurring, solid, white mineral called anhydrous calcium sulphate (CaSO4).
Calcium sulphates differs from gypsum in hardness and in hydration.
Calcium sulphates is used as a raw material in the chemical industry and in the manufacture of fertilizers and cement.
Pharmaceutical Applications
Calcium sulphates dihydrate is used in the formulation of tablets and capsules.
In granular form it has good compaction properties and moderate disintegration properties.
Calcium sulphates hemihydrate, is used in the preparation of plaster of Paris bandage, which is used for the immobilization of limbs and fractures; Calcium sulphates should not be used in the formulation of tablets or capsules.
Anhydrous Calcium sulphates is hygroscopic and is used as a desiccant.
The uptake of water can cause the tablets to become very hard and to fail to disintegrate on storage.
Therefore, anhydrous Calcium sulphates is not recommended for the formulation of tablets, capsules, or powders for oral administration.
Therapeutically, calcium sulphates is used in dental and craniofacial surgical procedures.
Safety
Calcium sulfate dihydrate is used as an excipient in oral capsule and tablet formulations. At the levels at which it is used as an excipient, it is generally regarded as nontoxic. However, ingestion of a sufficiently large quantity can result in obstruction of the upper intestinal tract after absorption of moisture.
Owing to the limited intestinal absorption of calcium from its salts, hypercalcemia cannot be induced even after the ingestion of massive oral doses.
Calcium salts are soluble in bronchial fluid. Pure salts do not induce pneumoconiosis.
Potential Exposure
Calcium sulfate is used as a pigment; in Portland cement, in tiles and plaster; in polishing powders, a filler in paints and paper coatings; in the drying of gases and liquids; a soil conditioner; in molds and surgical casts; in wallboard, and many others.
First aid
If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids.
Seek medical attention immediately.
If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water.
Seek medical attention immediately.
If this chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped.
Transfer promptly to a medicalfacility.
When this chemical has been swallowed, get medical attention.
Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.
storage
Calcium sulfate is chemically stable.
Anhydrous calcium sulfate is hygroscopic and may cake on storage.
Store in a well-closed container in a dry place, avoiding heat.
Shipping
Calcium sulphate is a “NONREGULATED MATERIAL.”
Incompatibilities
In the presence of moisture, calcium salts may be incompatible with amines, amino acids, peptides, and proteins, which may form complexes.
Calcium salts will interfere with the bioavailability of tetracycline antibiotics.
Calcium sulphate is also anticipated that calcium sulfate would be incompatible with indomethacin, aspirin, aspartame, ampicillin, cephalexin, and erythromycin since these materials are incompatible with other calcium salts.
Calcium sulphate may react violently, at high temperatures, with phosphorus and aluminum powder; Calcium sulphate can react violently with diazomethane.
Incompatibilities
Contact with diazomethane, aluminum, phosphorus, and water may cause explosions.
Note: Hygroscopic material (i.e., absorbs moisture from the air). Reacts with water, forming gypsum and plaster of Paris.
Waste Disposal
Landfilling
Regulatory Status
GRAS listed.
Accepted for use as a food additive in Europe.
Included in the FDA Inactive Ingredients Database (oral capsules, sustained release, tablets).
Included in nonparenteral medicines licensed in the UK and Europe.
Included in the Canadian List of Acceptable Non-medicinal Ingredients.
