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CaSO4 • 2H2O = CaSO4 • 0,5H2O + l, 5H2O.
Gypsum stone 140 -170 ° Closes a large amount of water at room temperature and turns into a semi-aqueous, fast-setting (CaSO4 • 0.5H2O) gypsum. Such a binder is sometimes also called alabaster.
Hence, the technical task set for the formation of building gypsum is to convert two molecules of aqueous gypsum into half-molecules of aqueous gypsum. Waste from the hydrochemical conversion of natural calcium phosphates into phosphoric acid and concentrated phosphorus fertilizers - phosphogypsum is a major source of raw materials for industry.
On the basis of specially developed methods, phosphogypsum can be obtained from a product made of the best quality natural raw materials, a ready-made binder.
Gypsum production.Construction gypsum is produced in three different ways:
1. Gypsum stone is powdered and baked.
2. Grind the gypsum stone and then grind.
3. Gypsum stone is crushed and processed in high-pressure water vapor.
Gypsum stone is mainly baked in mines and rotary kilns or in steam boilers. Gypsum stone for mine pits 70-300 mmfilled in large, rotating jars15 mmup to 25 for steam boilers.50 mmfilled in size; when baked in pots, gypsum-stone is filled with what appears to be a powder. The method of baking gypsum stone is first selected depending on the nature of the raw material, the demand for the product to be obtained.
Gypsum-stone is crushed in hammer crushers or in steel ball (grinding) mills. If it needs to be ground to a powdery level, it is first dried and then ground. Drying, grinding and baking of gypsum can be done in mines or wheel mills.
In practice, gypsum is widely used in so-called boiling pots. The pot, which consists of a steel cylinder and a guard mounted on a vertical axis, is filled with gypsum, which looks like powder. Four heating pipes were laid along the diameter of the boiler. They cook the raw gypsum that is being poured and the finished product falls into the gypsum collecting bunker through a sieve at the bottom of the pot.2 m3The capacity of the boiler is 2 hours1000 kgga teng. Cooking time of gypsum powder in the pot is 1 -1.5 hours.
A product called structural gypsum, which is mainly composed of semi-aqueous gypsum and is made by thermal processing of gypsum stone, can also be obtained from phosphogypsum. Semi-aqueous gypsum contains 38.63% CaO, 55.16% SO3 and 6.21% H2O.
According to its crystalline structure, gypsum has the following main types: dense gypsum with fine grains or coarse-grained gypsum (alabaster) that burns irregularly in the cavity; Plate-shaped gypsum in the form of a fine-grained, straight-layered fibrous rock consisting of silky crystals and layered flat transparent crystals.
Gypsum monoclinic, which contains two molecules of water, belongs to the syngony. Its crystal lattice consists of layers divided by layers of water molecules containing Ca2 + ions and SO42-sulfate tetrahedra. Ca2 + ions with a coordination number of 8 and SO42- ions are more strongly bound to each other than water molecules. When two molecules of aqueous gypsum are heated, the weaker bonds of the water molecule with the Ca2 + and SO42- ions are initially broken, and water disappears from the crystal lattice. Usually gypsum crystallizes in columnar and tablet-like forms, often forming double forks reminiscent of a swallow’s tail. Crystals with curved edges and a smooth surface are also typical for gypsum. Create dual separate systems two or more claw-shaped crystals are also found. Crystals sometimes coalesce into larger branched forms. Light refractive index of crystals: