Gypsum has a wide range of applications, mainly used in construction materials, can be used as a cement retarder, construction gypsum products and cementing materials, etc.; used as a soil conditioner, fertilizer and pesticide in agriculture; can also be applied to paper, paint, rubber, ceramics, plastics, textiles, food, arts and crafts, education and medicine, etc.; in the absence of other sulfur resources, but also as a manufacture of sulfuric acid, ammonium sulfate, ammonium sulfate, sulfuric acid and other raw materials. In the absence of other sulfur resources, it can also be used as raw material for manufacturing sulfuric acid and ammonium sulfate.
I. Main uses
1. Application in construction and building materials industry
Gypsum is the main raw material for the production of gypsum cementitious materials and gypsum building products, and it is also the retarder of silicate cement. The raw materials of cementitious materials include construction gypsum and anhydrous gypsum cementitious materials, high strength gypsum, filler gypsum, and calcareous gypsum cementitious materials. Construction gypsum is generated by calcining and dehydrating gypsum dihydrate to produce hemihydrate gypsum (cooked gypsum, with α, β two variants), which is quickly set and hardened after blending with water. High-strength gypsum is composed of α-hemihydrate gypsum as the main air-hard cementitious material, which is produced by processing gypsum dihydrate or heating gypsum dihydrate in certain aqueous solutions of salts in closed equipment with certain vapor pressure, and then dried and ground, which is characterized by high compressive strength. Hard gypsum cementitious material is obtained by calcined hard gypsum with hardening activator *** with grinding.
Gypsum in the cement industry as a silicate cement retarder: in the cement clinker by adding an appropriate amount of gypsum (allowed to be mixed into the maximum limit of SO3 in our country is set at 3.5%) can be lifted to cement fast solidification, improve the strength of the cement (especially the early strength), so that the dry shrinkage of the cement products in the air decreased by 30% to 50%, to improve the freezing resistance of cement, chemical resistance and stability. It can be used as cement ingredients to produce gypsum cement dihydrate, hard gypsum cement, common silicate cement, gypsum slag cement, fast-setting gypsum slag cement, gypsum alumina expansion cement, etc.
Gypsum building products, including lightweight wall materials gypsum board, gypsum wall objects. Characterized by light weight, earthquake resistance, low thermal conductivity, non-combustible, sound insulation, moisture absorption, low shrinkage, can be nailed or sawed. The use of construction gypsum production of building products are:
1) paper gypsum board: adding a small amount of construction gypsum adhesives, fibers, foam and other mixing agents and water, continuous pouring between two layers of protective paper, and then by the roller, solidification, cutting, drying and become. The thickness of the board is 9～25mm, dry weight 750～850kg/m3, good toughness, non-combustible, stable size, flat surface, can be sawed, easy to construct. Mainly used for internal partition walls, internal wall veneer, ceiling, acoustic panels, etc., but poor water resistance, should not be used in humid environments.
2)Fiber gypsum board: mixed with fibers and other additives in the construction of gypsum slurry, winding, filtering or roll pressure and other methods of molding, solidification, cutting, drying and become. Thickness is generally 8 ~ 12mm, and paper-faced gypsum board than its higher bending strength, without the face paper and adhesive, but the weight is larger, the use of the same as paper-faced gypsum board.
3)Decorative gypsum board: the preparation of building gypsum slurry, cast in the bottom mold with patterned mold frame, by smoothing, solidification, demolding, drying and become, the thickness of the board is about 10mm. In order to improve its sound-absorbing effect, can also be made with perforated and blind holes in the plate, commonly used as ceilings and decorative walls.
4)Gypsum hollow lath and gypsum blocks: the construction of gypsum slurry poured into the mold, vibration molding and solidification after demolding, drying and become. Thickness of hollow lath is generally 60 ~ 100mm, hole rate of 30% ~ 40%; block size is generally 600 × 600mm, thickness of 60 ~ 100mm, the perimeter of the mouth, and sometimes can be made into a hollow block with round holes. Hollow slats and blocks are special gypsum masonry, construction is convenient, commonly used for non-load-bearing internal partition walls.
2. Application in chemical industry
Production of sulfuric acid: CaSO4 in gypsum is decomposed into SO2 and CaO under the reducing effect of coke, the former is used to produce sulfuric acid, and the latter can be burned with clay raw materials into cement clinker.
3. Uses in agriculture
Production of ammonium sulfate fertilizer: ammonia and carbon dioxide into the suspension of gypsum powder and produced. It can also be used to improve the soil with gypsum dihydrate, burnt gypsum and hard gypsum.
4. Application in traditional Chinese medicine
Drug effects:Relieve muscle heat, remove boredom and quench thirst. Indications:Treatment of fever, fever and feverishness, heartburn and dizziness, delirium, thirst and dry throat, lung heat and shortness of breath, sunstroke and spontaneous sweating, stomach fire and headache, toothache, heat and toxic congestion, macular rash, sores on the mouth and tongue. Calcined and applied to regenerate muscles and astringent sores. External treatment of carbuncle sores and ulcers, ulcers do not close the mouth, burns.
5. Other uses
Used in paints, rubber, plastics, textiles, paper, chalk, toothpaste, cosmetics, fillers, casting, ceramics, medical, educational and other industries in the mold, in food, arts and crafts, and other fields have a wide range of applications.
The structure of gypsum application in China is shown in Table 15-2.
Table 15-2 Structure of gypsum application in China Unit:%
Two, industrial requirements
There are different requirements on the type and content of gypsum for different purposes, and there are different restrictions on the accompanying elements contained in gypsum ore. For example, there are restrictions on the content of K, Na and Cl in paper-faced gypsum board; there are restrictions on the content of As, S, Se, Cr, F, Cl and MgCl2 in medical and food gypsum; there are restrictions on the content of MgO in gypsum and hard gypsum in special cement and sulphuric acid; there are restrictions on the content of radioactive elements in gypsum in construction, medical and food products.
1.General industrial indicators
Layered gypsum, hard gypsum deposits, the lowest industrial grade (CaSO4-2H2O + CaSO4) 55%. The recoverable thickness is ≥2m for open pit mining and ≥1m for pit mining.
Fibrous gypsum deposit, minimum industrial grade (CaSO4-2H2O) 95%. Minimum line inclusion rate of 14%. Fiber gypsum minimum recoverable single layer (vein) thickness of 2cm, the thickness of the ore body can be extracted: pit mining ≥ 1.7m, sandwiched between the stone culling thickness of pit mining for 1m.
Fiber gypsum and layered gypsum, hard gypsum deposits, fibrous gypsum CaSO4-2H2O content of 95%, layered gypsum, hard gypsum CaSO4-2H2O + CaSO4 content of 55%, the line ore content 14%. -Pegmatite gypsum rate is determined according to mineral processing test. Minable thickness:open pit ≥2m, sandwiched rock rejection thickness:open pit >2m.
Paper filler requires sand content of <3%. Paint filler with requirements for adsorption of water <2%, fineness should be through 1600 holes/cm2, 6400 holes/cm2 sieve residue does not exceed 2%.
Ceramic equipment for modeling materials, cooked gypsum, requires high SO3 content, can not be mixed with impurities, otherwise it will affect the quality of the product. Requirements for limited Fe2O3 content: special grade Fe2O3<0.1%; A grade Fe2O3<0.3%; B grade Fe2O3<0.4%.
2. Product quality standards
The national standard of the People's Republic of China (GB-5483-2008) divides all kinds of natural gypsum into 5 levels according to grade: special grade, first grade, second grade, third grade and fourth grade. In the form of mainly calcium sulfate dihydrate (CaSO4-2H2O) exists called gypsum; in the form of mainly anhydrous calcium sulfate (CaSO4) exists, and anhydrous calcium sulfate mass fraction and calcium sulfate dihydrate and anhydrous calcium sulfate and the ratio of the sum of the mass fractions is not less than 80% of called hard gypsum; in the form of mainly calcium sulfate dihydrate and anhydrous calcium sulfate exists, and anhydrous calcium sulfate mass In the form of mainly calcium sulfate dihydrate and anhydrous calcium sulfate exist, and the mass fraction of anhydrous calcium sulfate and calcium sulfate dihydrate and anhydrous calcium sulfate (CaSO4) and the ratio of the sum of the mass fraction of the mixed gypsum is called less than 80%. The block size of the product is not more than 400mm, and the attached water content shall not be more than 4%. For details, please refer to Table 15-3.
Table 15-3 Grade requirements for each natural gypsum product (GB-5483-2008)
China's relevant departments of the α hemihydrate gypsum, β hemihydrate gypsum, polyphase gypsum (containing β hemihydrate), a small amount of dihydrate gypsum and a part of the gypsum. Gypsum, β half-water gypsum, multi-phase gypsum (containing β half-water gypsum, a small amount of dihydrate gypsum and part of anhydrite gypsum), etc. The main physicochemical indexes of cooked gypsum powder are shown in Table 15-4, and the technical requirements of whitewash gypsum are shown in Table 15-5.
Table 15-4 Physicochemical indexes of cooked gypsum powder
(According to the Non-metallic Mineral Industry Handbook Editorial Committee, 1992)
Table 15-5 Technical requirements for whitewash gypsum (JC/T517-2004)