Gypsum powder

classification
Gypsum powder can be divided into phosphogypsum powder, desulfurized gypsum powder, citric acid gypsum powder and fluorogypsum powder according to different physical components.
Gypsum powder can be divided into red stone paste powder, yellow stone paste powder, green gypsum powder, bluestone paste powder, white gypsum powder, blue gypsum powder and color gypsum powder according to different colors.
Gypsum powder can be divided into dolomitic gypsum powder, clayey gypsum powder, chlorite gypsum powder, alabaster gypsum powder, talc gypsum powder, sandy gypsum powder and fiber gypsum powder according to different physical characteristics.
Gypsum powder can be divided into: gypsum powder for building materials, gypsum powder for chemical industry, gypsum powder for molds, gypsum powder for food and gypsum powder for casting.
Gypsum has been used for a long time, but in the early days, it was simply used to make chalk, putty, tofu and simple handicrafts, lacking in-depth research and development, so it did not attract people's attention. In the late 1970s, especially since the implementation of reform and opening up in China, with the rapid development of economy, the demand for gypsum in buildings, building materials and other related industries that consume a large amount of gypsum has increased sharply, and gypsum has attracted more and more attention. At present, a huge emerging industry has been formed.
China is rich in natural gypsum mineral resources, with a total reserve of nearly 60 billion tons, ranking the first in the world. It is also a major manufacturer of chemical gypsum. A large amount of chemical gypsum is produced every year: phosphogypsum alone is produced nearly 20 million tons every year, and the accumulation of phosphogypsum in some phosphate fertilizer plants is up to 10 million tons. Especially with the rapid development of China's economy and the attention paid to environmental protection in recent years, Desulfurization of power plants has become a necessary process link of power plants, producing a large amount of desulfurized gypsum. In addition, there are citric acid gypsum, fluorogypsum, salt gypsum and other chemical gypsum. Relying on abundant natural and artificial resources to carry out comprehensive utilization and develop gypsum industry is also the need of building a circular economy, and is also a new highlight of many investors.
In recent years, with the development of gypsum products industry, gypsum powder of various uses has been promoted one after another, especially in the building materials industry. With the continuous increase of high-rise buildings and the gradual deepening of the national wall reform work, gypsum powder has become a hot product in the building materials market. In 2005, the national gypsum powder consumption was about 120 million tons, the output was 85 million tons, and the gap was 35 million tons, which is far from meeting the market demand. Therefore, the processing and development of this project has a large market, high profits and good economic benefits.
At present, the production process and production line automation level of gypsum powder are not high, most of them are in manual operation or semi-automatic level, and the quality of gypsum powder products is in a low level and low quality state for a long time.
Fold and edit the production process of this section
The process of the construction gypsum powder production line project (raw materials: natural gypsum ore, desulfurized gypsum and phosphogypsum) is divided into four steps:
(1) Crushing link
(2) Pre grinding link
(3) Calcination
(4) Storage and transportation link
Fold and edit the chemical composition of this paragraph
Gypsum:
CaSO4 ˙ 2H2O
Crystal chemistry:
Theoretical composition (WB%): Cao 32.5, SO3 46.6, H2O + 20.9. The composition changes little. There are often mechanical mixtures such as clay and organic matter. Sometimes it contains impurities such as SiO2, Al2O3, Fe2O3, MgO, Na2O, CO2, Cl, etc.
Structure and form:
Monoclinic system, A0 = 0.568nm, B0 = 1.518nm, C0 = 0.629nm, β= 118.23'; Z=4。 The crystal structure is composed of [SO4] 2-tetrahedron and Ca2 + to form a bilayer of ‖ (010), and the bilayer is connected by H2O molecules. Its complete cleavage occurs in this direction. The coordination number of Ca is 8, and it is bound to 6 o and 2 H2O molecules in the adjacent 4 [SO4] tetrahedra. H2O molecules and O in [SO4] are linked by hydrogen bonds, and water molecules are linked by molecular bonds.
Rhombic columnar, c2h-2 / M (l2pc). The crystals are often developed into plate-like or granular. Ordinary simple form: parallel double-sided B, P, oblique column m, l, etc; Crystal plane and often have longitudinal grain; Sometimes lenticular. Double crystals are common, one is Gary double crystal or swallow tail double crystal with (100) as the double crystal plane, and the other is Paris double crystal or arrow double crystal with (101) as the double crystal plane. The aggregates are mostly dense granular or fibrous. Fine grained block is called alabaster; Fibrous aggregates are called fibrous gypsum. Rosette like aggregates formed by lenticular crystals are rare. There are also earthy and flaky aggregates.
Fold and edit the physical and chemical properties of this paragraph
English Name: gypsum or stucco
Chinese alias: dihydrate gypsum, gypsum, gypsum, raw gypsum, chemical name: calcium sulfate dihydrate
Molecular weight: 172.17
Refractive index: 1.52
Mohs hardness: 1.5 ~ 2
Solubility: slightly soluble in water, soluble in acid, ammonium salt, sodium thiosulfate and glycerol
Stability: when heated to 150 ℃, 1.5H2O is lost to form hemihydrate (plaster of Paris), and when heated to 163 ℃, all crystal water is lost to become anhydrous
Toxicity: non toxic
Application: used as filler of sealant or inorganic adhesive
Under polarizer: colorless. Biaxial crystal (+). 2V=58。 Ng=1.530，Nm=1.523，Np=1.521。 2V decreases with the increase of temperature, and 2V is zero at about 90 ℃.
There are three stages of discharging crystal water during heating: 105 ~ 180 ℃, one water molecule is discharged first, and then half of the water molecule is discharged immediately, which is transformed into calcined gypsum, also known as plaster of Paris or hemihydrate gypsum. At 200 ~ 220 ℃, the remaining half water molecules are discharged and transformed into type III anhydrite. At about 350 ℃, it is transformed into type II gypsum CA [SO4]. At 1120 ℃, it is further transformed into type I anhydrite. The melting temperature is 1450 ℃.
The microporous structure and heating dehydration of gypsum and its products make it have excellent sound insulation, heat insulation and fire resistance.
Fold and edit the occurrence and combination of this section
It is mainly the product of chemical sedimentation and often forms a huge ore bed or lens. It occurs in limestone, red shale, sandstone, marl and clay rock series and often coexists with anhydrite and rock salt. The anhydrite layer is transformed into gypsum under the action of surface water due to the reduction of external pressure near the surface; At the same time, the volume increases by about 30%, causing the destruction of the gypsum layer.
Identification features: low hardness, a group of extremely complete cleavage, and various characteristics of morphology can be identified. Dense block gypsum can be distinguished from carbonate by its low hardness and non foaming in acid.
Folding editing: main application fields of this paragraph
1. Building materials and buildings
a: Anhydrite cement and cementitious materials: anhydrite cement or cementitious materials can be produced by adding an appropriate amount of activator. It is suitable for the reinforcement of soft soil foundation, wall painting, mechanical model, tunnel support and production of fiber pressure plate.
b: Used as cosolvent and purifier in glass production process.
c: It is used as filler in the industrial production of plastics, rubber, coatings, asphalt, linoleum, etc.
d: Main raw materials of concrete expansion agent, anti crack agent and self leveling mortar.
e: Cast in place pile and deep mixing pile are used as large expansion materials to increase friction resistance.
f: Used as compound mineralizer in special cement production
2. Chemical industry
a: It produces sulfuric acid and light cement.
b: It produces ammonium sulfate and light calcium carbonate.
3. Agriculture
a: Improve the soil, adjust the pH, and apply to the improvement of saline alkali land, red soil land and other soil.
b: In the cultivation of edible fungi, it is used as calcium and sulfur compound mineral fertilizer to adjust the pH of the culture medium.
c: It is used as compound mineral feed additive in poultry and livestock feed.
Anhydrite powder is packed in plastic woven composite bags, with a specification of 50 ± 1kg, and can be packaged in bulk and other specifications according to user requirements.
Anhydrite powder shall be stored under ventilated and dry conditions.
4. Cathodic protection
And is used as one of the filler components for the sacrificial anode. The general proportion is as follows: 75% gypsum powder, 20% bentonite and 5% sodium sulfate.
Benefits of folding and editing this paragraph
In the food industry, its official name is called "food additive calcium sulfate", commonly known as "edible gypsum". It can only be produced with natural gypsum, and chemical gypsum is strictly prohibited. Its application in food has a history of thousands of years. The initial application in China is the familiar point tofu. With the development of society, the safe and non-toxic food additive calcium sulfate (edible gypsum), which has been strictly tested by practice, is more and more widely used in the food industry.
The uses of calcium sulfate in food include: nutritional agent, yeast activator, dough property modifier, curing agent, chelating agent, gelling agent, baking powder, carrier, filler, pH regulator, abrasive. Among these uses, it is mainly used in baked goods. As a curing agent, it is used in canned potatoes, tomatoes, carrots, beans and pepper. Calcium sulfate is also used as an ingredient in candies, ice cream and other frozen desserts. Calcium sulfate is also used in beer brewing, adding this product during malt processing to increase the content of calcium ions in water. Calcium sulfate is used as an abrasive in cleaning agents for contact with food. Calcium sulfate is also used in cosmetics and toothpaste.