How Gypsum is Processed | M&C - Mining & Construction

Definition of Gypsum

Gypsum ( CaSO4·2H2O) is a natural monoclinic minera, Its main chemical component is calcium sulfate hydrate, which is widely distributed in the salt lake sediments formed by evaporation and widely used as industrial materials and building materials.

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History of Gypsum

The English word for plaster is &#;Gypsum&#;, and German is &#;Gyps&#;. It all comes from the Greek γύψος (gypsos), and then the Latin word is &#;gypsus&#;. At that time, it didn&#;t mean gypsumin the modern sense, but meant something like moonstone.

Gypsum was used as a building material in the Neolithic Age and was used for interior decoration in Anatolia (now in Turkey) in BC. Evidence of the use of plaster was later found in Sumir and Babylon sites, such as Jericho in BC (now in Israel) and Uluk in BC (now in Iraq). The Pyramid of Khufu and the Sphinx, built in BC, used gypsum mortar as a cementitious material to bond and masonry stones.

Properties of Gypsum

Gypsum is a very common soft sulfate mineral, which can be easily identified by its hardness, cleavage and solubility in water:

Classification of Gypsum

Gypsum usually refers to two kinds of minerals: raw gypsum and anhydrite.

Raw Gypsum is calcium sulfate dihydrate ((Ca (SO4) 2H2O), also known as gypsum dihydrate, gypsum or gypsum, composition CaO (32.6%), SO3 (46.5%), H2O+ (20.9%), monoclinic system, crystal is plate-like, usually dense block or fiber, white or gray, red, brown, vitreous or silky luster, Mohs hardness is 2, density 2.3g/cm3.

Anhydrite is anhydrous calcium sulfate (Ca (SO4)), theoretical component CaO (41.2%), SSO3 (58.8%), orthorhombic system, crystal is plate, usually dense block or granular, white, grayish white, vitreous luster, Morse hardness is 3 &#; 3.5, density 2.8~3.0g/cm3.

Raw gypsum and anhydrite are often produced together, and anhydrite can be formed by calcining gypsum at 400 &#; 500 °C.

How is Gypsum Formed

Gypsum is a widely distributed mineral, which is mainly formed by sedimentation and weathering, and a few are found in hydrothermal sulphide deposits. Gypsum usually can be fond in the form of crystals or deposits beds.

Gypsum formed in sea basins and lake basins is formed by evaporation of brine or hydration of anhydrite; symbiosis with anhydrite, gypsum, etc. It is layered or lenticular in the interlayer of limestone, red shale, marl and sandy clay. The gypsum in the oxidation zone of sulphide deposits is mainly caused by sulfides.

Distribution of Gypsum

The world&#;s largest producer of gypsum is the United States. In the United States, gypsum deposits are distributed in 22 states with a total of 69 mines, with the largest producing area in Fort Dodge, Iowa, followed by Canada. France takes the lead in European gypsum production, followed by Germany, the United Kingdom and Spain.

Use of Gypsum

Gypsum is a widely used industrial material and building material. Gypsum (CaSO4 ·2H2O) can be calcined and grinded to obtain β-type hemihydrate gypsum (2CaSO4 ·H2O), that is, building gypsum, also known as cooked gypsum or plaster. The model gypsum can be obtained when the calcination temperature is 190 °C, and its fineness and whiteness are higher than that of building gypsum. If raw gypsum is calcined at 400 °C or above 800 °C, floor gypsum can be obtained, its setting and hardening are slow, but the strength, wear resistance and water resistance of hardened gypsum are better than that of ordinary building gypsum.

1. Building Gypsum: Mostly used in building mold ash, painting, masonry mortar and all kinds of gypsum products.
2. Model Gypsum: less impurities, white color, mainly used for ceramic culture process, a small amount for decorative relief.
3. Floor Gypsum: Mainly used for demanding mold ash engineering, decorative products and plasterboard.
4. Whitewash Gypsum: Made of cementing material with appropriate amount of retarder, water-retaining agent and other chemical admixtures.

In addition, gypsum can also be used in the manufacture of cement, sulfuric acid, soil improvers, food coagulants, pesticide diluents as well as medical and cosmetology.

How is Gypsum Processed

The raw material of gypsum powder is natural gypsum ore, and the production process of gypsum powder is mainly divided into 5 stages: crushing, screening, grinding, calcination, storage and transportation.

Gypsum powder is one of the five major gel materials, which is processed through crushing, grinding and other processes. It is widely used in construction, building materials, industrial molds and art models, chemical industry and agriculture, food processing, medicine and beauty and other applications. It is an important industrial raw material.

Gypsum has good sound insulation, thermal insulation, and fire resistance characteristics. In China, natural gypsum reserves are abundant and have been used for a long time. With the improvement of economic and technological levels, gypsum powder production equipment and processes also have more choices and more scientific configuration plans.

White and colorless transparent crystals are usually referred to as transparent gypsum, and sometimes they become gray, light yellow, light brown, and other colors due to impurities.

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How do you manufacture gypsum powder? In order to ensure the quality and quantity of gypsum powder in production, many factories have chosen gypsum powder production lines that can be intelligently and automatically completed. From the different application fields of gypsum powder, the gypsum powder production line is mainly divided into construction gypsum production line and desulfurization gypsum production line.

Gypsum powder-making process

According to the process requirements, the construction gypsum production line is usually divided into five parts, including crushing system, storage conveying system, grinding system, calcining system, and electric control system.

STEP1. crushing system

The size and specifications of gypsum ores are different after mining, and the applicable crushing equipment is selected for preliminary crushing treatment according to the actual situation, and the particles with particle size not greater than 35mm are broken.

STEP2. storage conveying system

The crushed gypsum raw material is transported to the storage bin by the elevator. The storage bin is designed according to the requirements of the material storage time to ensure the stable supply of materials. At the same time, all parts of the material turnover are using lifts to reduce the floor area.

STEP3. grinding system

• The grinding process is the core process of gypsum powder production. The gypsum raw material in the storage bin enters the grinding machine through the vibration feeder for finishing. The electromagnetic vibration feeder is set under the storage bin, which is interlocked with the mill to adjust the supply of materials in time according to the running condition of the mill.
• The material is uniformly and continuously fed into the mill by the electromagnetic vibration feeder for grinding.
• The pulverized gypsum powder is blown out by the air flow from the mill blower and graded by the analytical machine above the main engine. The powder with the fineness meeting the specifications enters the large cyclone collector with the air flow, and is discharged as the finished product through the powder outlet pipe after collection.
• The finished product falls into the screw conveyor and is transported to the next system for calcining. The air flow flows from the return duct of the cyclone collector into the blower. The whole air path system is closed circulation and flows under negative pressure. Due to the water contained in the ground raw materials and the evaporation into gas during the grinding process, resulting in an increase in the air volume in the circulating air path, the increased air volume is introduced from the pipe between the large cyclone collector and the blower to the bag dust collector, and then discharged into the environment to ensure that the environment is clean.
• The particle size of the material through the grinding system is changed from 0-30mm to 80-120 mesh, which meets the requirements of the fineness of gypsum powder.

STEP4. calcining system

After grinding is completed, the pulverized gypsum powder is sent to the rotary kiln for calcining by the powder separator, the plaster of Paris is sent to the storage storage by the elevator, and the materials that do not meet the requirements are continued to be returned to the mill for grinding; The system mainly includes lifting machine, boiling furnace, electrostatic dust removal, Roots fan and other equipment.

STEP5. electrical control system

The electrical control system adopts the current advanced centralized control, DCS control or PLC control, and the control components are selected internationally well-known brand products

gypsum powder making machine

Crushing System: jaw crusher and impact crusher

jaw crusher has feed particle size of &#; mm, a discharge particle size is 10-350mm, and the production capacity can reach 1-t/h. Suitable for coarse crushing of large gypsum blocks, with strong crushing ability and high crushing ratio; Impact crusher feed particle size &#;mm, production capacity in 30-t/h, suitable for small hardness, Mohs hardness of 2 grade gypsum for fine crushing processing, and the discharge particle type is very good, uniform particle size.

Grinding System: Raymond mill, bucket elevator and vibrating feeder.

The grinding process of gypsum generally selects Raymond mill for processing operations. Raymond mill is good at high fineness grinding of non-flammable and explosive materials with Mohs hardness not greater than 9.3 and humidity below 6%. The feed particle size of Raymond mill is &#;25-&#;30&#;, the discharge particle size is 0.044-0.173&#;, and the class production is about 8-176t.

Calcination System: Rotary kiln

Rotary kiln and related equipment is used in calcination section of gypsum powder production line.

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