Kaolin, also called Chinese clay, is a soft white solid that is an essential element in the manufacture of porcelain and porcelain and is widely used in the manufacture of paper, rubber, paint and many other products.
The name is derived from a hill in China (Kao-ling) from which this material has been extracted for centuries. The prototypes were sent to different parts of Europe by the French as an example of the materials used by the Chinese in Chinese production.
It is mostly used in the coating industry and is washed with water to remove impurities. It has a clay structure, but unlike talc and mica, it is more valuable in the production of coatings than its contribution to its optical properties.
This product is an economic term used for almost white clay deposits. These deposits often contain kaolinite ore or products derived from it. In the past, the term Chinese soil was used as a synonym. The name is derived from the Chinese word meaning white hill, from which soil is extracted. this product is most used in the production of porcelain and ceramics. The United States, Russia, the Czech Republic and Brazil are the largest producers.
It is classified into two groups of soft and hard bonds according to its type of bonds. One of the most important industrial properties of kaolin is its neutral chemical nature. Kaolin is stable under industrial chemical conditions.
Thin crystal plates provide go
g power and are better for coating on paper and paint. This product is often used in industrial processes as a liquid or water polymer suspension. The viscosity of these liquid slides is important. Basically, the value of it is high in solid percentages due to its very low viscosity. This property is in contrast to the property of bentonite.
The minerals of this group are: dikite, nacrite and halosite. It is the most abundant mineral in this group. The chemical composition of all of them is the same and is the most abundant mineral in this group and is crystallized in the triclinic system, and dikite and nacrite are crystallized in the monoclinic system.
The structure of it can be depicted as a layer of silica rings connected to a layer of alumina octagon by common oxygen. In nature, these plates are placed in categories that show different degrees of order of accumulation.
Because a single particle has an oxygen surface on one side and a hydroxyl surface on the other, hydrogen is strongly attached to its upper and lower plates. This makes peeling more difficult than other silicate, talc and mica fillers. It is hydrophilic so it disperses easily in water. For non-aqueous applications, the compatibility of the matrix with the surface operation is improved.
The best kaolins have up to 20% of impurities that are processed in different ways to reduce these impurities and in each method a specific type of this substance is obtained and each has its own consumption that in addition to specific genetic traits, the type of processing is also a product. Distinguishes from each other. reserves are divided into the following types: aerated reserves, hydrothermal reserves, transported reserves, diagenetic reserves.
Natural type usually contains varying amounts of other minerals such as muscovite, quartz, feldspar and anatase. In addition, crude type is often found with yellow iron hydroxide pigments. It is often necessary to whiten the clay to remove the iron pigment and wash it with water to remove other minerals to prepare it for commercial use.
It is with the name of kaolinite mineralogy Its color is yellowish white and sometimes a little green or blue and it tastes like soil and when it is wet, it gives a strong smell of soil. This mineral is often plastic and is practically soluble in water, cold and dilute acids, hot and concentrated hydrochloric acid and sulfuric acid, and insoluble alkaline hydroxides.
Most of these deposits are formed by weathering and decomposition of volcanic rocks containing aluminum silicate. Granite rocks, gneisses, quartz, porphyries as well as sediments containing feldspars, mica and zeolite are suitable for the formation, which due to weathering and chemical decomposition of alkalis and quartz and other associated minerals remain as a combination.
Large deposits in the Cornwall area of England are found in the outermost parts of the hydrothermal system, associated with granite batholiths, which have formed several kilometers deep.
It is less orderly than Nakrit-Dickite, and therefore the size of the crystal and particles is smaller than that of the rest. This product is formed in aerated zones and alteration of igneous and metamorphic rocks, especially feldspars.
Ball clay is a type of sedimentary rock that contains kaolinite and small amounts of illite, chlorite, quartz and montmorionite. Kaolinite particles in ball clay are smaller than other clay sources. The amount of ball is 20 to 95%, quartz is 10 to 70% and illite and chlorite is 5 to 45%. Organic matter, montmorionite, iron compounds, titanium oxide and soluble salts are among the impurities in the clay. Ball clay is mostly associated with coal seams, and since it contains fine particles of clay minerals, its formability is very good.
Hallucite is a type of kaolin that is found in both aqueous and anhydrous forms, and the composition of the aqueous form is similar to the others and has only two additional molecules of water (2SiO2.Al2O3.4H2O).
Detection of hallucinations is possible with the help of X-ray diffraction. Halosite is mostly found in alteration zones and rarely in saprolyte weathered zones. Its main uses are in the production of Portland cement and refractories and ceramics.
Dicket is a type of kaolin that crystallizes in the monoclinic system and is mainly formed in alteration zones.
Most refractory clays are composed of kaolinite, kaolin was crystallized well in it and there is a good order in its network. In addition to kaolin, refractory clay also contains aluminum oxides and hydroxides. Any type of soil that can withstand temperatures above 1,500 ° C and has significant AL2O3 levels is known as refractory clay. Refractory clay is divided into ductile, semi-ductile and amorphous types. Refractory clay is mostly found in the lower horizons of coal seams.
The main use of this soil is in the preparation of firebricks, which are known as chamotte. Other uses are in the manufacture of furnace components, boilers and refractory tiles.
Kaolin reserves are divided into the following types: aerated reserves, hydrothermal reserves, transported reserves, diagenetic reserves. Kaolin deposits are formed according to how they are formed, both primary and secondary:
Kaolin reserves are large enough to meet the mineral needs over the coming years and are estimated at about 20 billion tons worldwide. Georgia, South Carolina belt reserves in the United States are estimated at 5 to 10 billion tons. India, Brazil, China, the United Kingdom and Ukraine have huge reserves.
Iran has less than 1% of the world’s kaolin reserves among the world with a reserve of about 40 million tons. At present, the potential reserves of kaolin in the country are estimated at more than 230 million tons and are scattered in acidic igneous rocks from Precambrian to Miocene in Fars, Isfahan, Azerbaijan, Zanjan, Khorasan, Markazi, Qazvin and Tehran provinces.
Iran’s main consumption in fireclay bricks is the inner lining of furnaces, heating boilers and tiles.
Kaolin deposits and clays are divided into the following 4 groups based on geographical location:
Aluminum-rich rocks such as shales, alkali-rich feldspars, feldsparite igneous rocks (nepheline syenite), calc-alkaline and alkaline basalts, super-aluminum granites and… in hot and humid climates are exposed to chemical weathering and surface weathering. There are many changes in their chemical and mineralogical composition. Adequate water and proper temperature cause plants to. The stability of minerals formed in rocks is different and their type of changes are not the same.
Important and effective factors in the formation of aerated kaolin reserves are: humid climate, decrease in water pH, aluminum-rich mother rock, high porosity, seams and fractures in the rock, low groundwater level, sufficient time, high water flow in the rock and washing Show and carry cations.
Under the right conditions, most rock minerals, with the exception of quartz, are exposed to chemical weathering and convert to other compounds. Potassium feldspar is converted to kaolinite or illite.
If all KOH is washed away, kaolinite will form (low groundwater levels will cause more cations to be completely washed away). If the groundwater level is high in this case illite and smectite will be formed.
The effect of hydrothermal solutions (whose pH is acidic) on rocks containing aluminous silicate minerals (such as feldspar, feldspar, mica, etc.) is formed under suitable conditions of kaolinite. Hydrothermal deposits are often located in fault zones, except in porphyry deposits (tin-molybdenum and tungsten type) which cover a wide area. Kaolinite forms part of the alteration zones of hydrothermal deposits.
The origins of deposits are classified into three groups: in situ, sedimentary and hydrothermal. Most of Iran’s deposits are due to the alteration of igneous rocks and mainly in the volcanic belts of the third period, especially in the Eocene. Zenoz Kaolin, Nusrat Kushk and Kazan Raghi mines are of this type.
It is first processed dry, which includes crushing, drying and softening, the product of which is kaolin used in ceramics, paints and rubber. Wet processing, or rinsing with water, separates non-kaolin minerals from the conductive liquid, at which point is obtained as a filler and coating.
In different types of sieves, hydro cyclones and liquid clay can be concentrated up to 30% solid in the sedimentation tank and by centrifugation, 75% of particles with a size of 2 micrometers can be separated from it, large particles are dropped by ultra flotation and then delamination steps. It is screened, filtered and dried and sometimes calcined.
In the other case, the kaoliner liquid is divided into two groups, small and large, by centrifugation, hydrocyclone or separation with water, and then the ferrous iron compounds are washed from it. After evaporation by evaporation, rotary or compression suction filter, kaolin cake can be removed and dried or transferred to the material with 70% solid for trade.
In decontamination, Its particles are mechanically separated into light and thin particles and calcined at 500 ° C to form a distinct crystal structure. This action increases the brightness and opacity.
Even the best type in the world has about 20% impurities. Therefore, they should be concentrated and its alkalinity should be reduced to less than 1.5%.
Consumed type must have the following specifications:
1- The percentage of Al2O3 should be more than 30%.
2- The amount of Fe2O3 iron oxides should not exceed 1%.
3- The amount of titanium oxide TiO2 should be reduced to 0.2%.
4- Alkaline oxides should not exceed 2%.
5- The maximum amount of CaO is 0.2% and MgO is 0.3%.
6- Increasing the amount compared to other available minerals causes the quality of kaolin.
7- Kaolin melting delay should be around 1700 degrees Celsius.
The most used kaolin in fillers, coatings with special polish and bleach, expanders, abrasion resistant, diluent, hardener in petrochemical industry, surface softener and as a catalyst in various industries, paper, ceramics, Composites and paints, refractories, plastics, rubber, pharmaceuticals, fiberglass, refractory industries, building materials, insecticides, adsorbents, detergents, foodstuffs, pharmaceuticals, agricultural industries and chemical fertilizers.
In Iran, this mineral is used in fireclay bricks, interior coatings of furnaces, heating boilers and tiles. About 50% of kaolin is used in papermaking as a filler and coating (surface coating), 20% in ceramic and refractory industries, 10% in rubber manufacturing as a filler and 20% in plastic dyeing. Composite adsorption strength and coating Good advantages and filling of uneven surfaces of paper with cellulose paste and creating transparency in the paper are the advantages of using kaolin in the paper industry.
Kaolin is known in the pharmaceutical industry for its combination with hydrated aluminum silicate. This mineral is used in the preparation of anti-diarrheal drugs, which are consumed once every 4 hours in the amount of 2 to 6 grams. It is used to prepare pain relievers, reduce inflammatory pain, and treat gastrointestinal diseases.
composite drugs include: pectin syrup, children’s syrup, morphine syrup, syrup and kaolin ointment.
Medications containing kaolin may have side effects such as hypersensitivity to symptoms of hypotension, urticaria, fever, joint pain, measles blisters, gastrointestinal upset, nausea, headache, and disappear with discontinuation of the drug.
Kaolin, which is used as a pigment, is divided into fillers and paper coatings based on their luminosity, particle size and viscosity. It is a cheap, white or near-white filler mineral that is neutral in a wide range of pH. Non-abrasive and small particle size but fable control, low thermal and electrical conductivity and good luminosity, used in paper, plastic, paint, rubber and glue.
Its chemical composition is not critical except that it affects the color, and its oil or petroleum absorption is especially important for the paint or rubber. The above properties along with the grain shape, viscosity and pH allow it to be used as a paper coating pigment. Brightness, smoothness and acceptance of ink in printing and writing papers are artistic.
In plastics, kaolin is used to create a smooth surface, stability in various directions and resistance to chemicals.
The use of kaolin in paper making will make the paper softer, and the absorption of ink, luminosity, cheapness and proper coating are other advantages of using kaolin in the paper industry.
The paper is not suitable for use in modern printing processes, even if the gaps between its cellulosic fibers are filled with mineral filler, as long as it does not have a surface coating. The use of filler in the pulp fills some of the gaps and seams between the cellulose fibers, so many of the fine composite printing points are not placed properly in these areas. The surface coating is printed on Ba’ath paper for the softness, luster and absorbency of the ink. Proper coverage increases the use of paper.
Kaolin disperses rapidly in water (even in hard water) and is thinly coated on paper by modern coating machines. Kaolin is a suitable coating for high-gloss papers, light papers with LWC coating and suitable gravure papers by rolling (offset) method.
In the paper industry, it is used must be rapidly suspended in water. Particle size and granulation are of particular importance. The amount of viscosity and the percentage of particles smaller than 2 microns are more important.
First-class coating kaolin has 92% of its particles less than 2 microns and a luminosity of at least 87%. Second-class coating kaolin has 80% of its particles less than 2 microns and its luminosity is at least 85.5%.
In summary, the following properties can be considered for use in the paper industry:
A- Transparency: The minimum transparency for as a filler is 80% and for clay as a coating is 85%, which is determined in comparison with the transparency standard.
D- Residue of sieve: 325 mesh is used as abrasive material or residue of sieve. The practical method is to crush 100 grams of the sample and mix it well and disperse it by chemicals. The weight then measures the percentage of solids in the mixture, weighs the total remaining on the sieve, and calculates the percentage.
The use of kaolin in plastic paint helps to control viscosity. 10% kaolin is used in dyeing and increases the power of coating, lubrication and dispersion of dye. In dyeing, high quality and pure kaolin is used as a dye and filler. In water-washable paints, coarse-grained kaolin form opaque and fine-grained kaolin form glassy ones.
The position of the paint industry in the consumption of this product has been similar to that of the rubber industry in recent years. The highest growth rate of kaolin consumption in the paint industry was in the United States and Europe, which is estimated at about two percent per year.
It is predicted that in general and in the near future, the growth rate of kaolin consumption in this industry will be one percent. Of course, if there is economic growth in Asian countries as in the past, this growth will reach 1.5 percent.
Consumption of kaolin in the paint industry in the United States increased from 228,000 tons in 1991 to 329,000 tons in 1997 and decreased to 268,000 tons in 1998. Since paint production in the United States is about 30% of total world production. Therefore, the consumption of kaolin in the paint industry in the world in 1998 was estimated at 840 thousand tons.
It is basically used as an expander and the main white material as an alternative to titanium oxide in the production of paint. Calcined kaolin is the main used in the dye industry. Light color, while opaque, is one of the characteristics of kaolin used in the dye industry and has a special resemblance to kaolin used in the paper industry.
The smooth surfaces of kaolinite, especially in the paint industry, are placed on top of each other with a special cosmetic, which makes the paint sheet durable and gives it a long life. The biggest demand for kaolin in the paint industry is the manufacture of matte interior paints. The US Bureau of Standards recommends using at least 20 percent for home paints.
It can usually be added up to 10% by weight of glossy paints. It is used in dyeing should be light in color and have a minimum of impurities. It has a high suspension coefficient in water and its soluble salts are low. In terms of luminosity between 90-80% and its particles are 80-70% below 2 microns.
In the rubber industry, it is also used as a filler. Kaolin increases its wear resistance and rigidity. Pure and soft type is used in soft tires such as rubber tiles and impure kaolin is used in the production of hard tires such as heels and soles in shoes and car tires.
Consumption of kaolin in the rubber industry in 1998 was equal to 1.08 million tons. Between 1990 and 1998, global tire consumption increased from 2.52 million tonnes in 1991 to 61.6 million tonnes in 1998, reflecting an average annual growth of 3.9% during the 1990s. According to Roskill, annual growth of 1% is forecast for the near future for the consumption of kaolin in this industry. Consumption of kaolin in the plastics industry reduces the price of rubber.
Because kaolin is much cheaper than natural rubber or elastomer. Kaolin used in the rubber industry is not of good quality kaolin. In the United States, the kaolin used in this industry is air-concentrated. In industries where coarse particles are disturbed, such as in the rubber industry, which are formed by extrusion. Calcined kaolin is also used as a coating in the rubber industry. One of the main characteristics of kaolin used in the rubber industry is that 99.5% of the particles must be below 44 microns.
20% kaolin is one of the basic materials in the tile, porcelain and ceramics industries. Kaolin is a type of aluminum refractory in which the amount of Al2O3 varies depending on the type. Low-alumina types of calcined kaolin, flint (35-45%) and high-alumina types such as andalusite, kyanite and sillimanite (40-60%).
The oldest and perhaps the most common method of using this product in industry is the use of this ore in the manufacture of various ceramic products. Porcelain flower has been used in making ceramics for more than four thousand years. In the ceramics industry, a set of methods of material formulation, forming, heating and firing methods are used.
Therefore, the range of changes in the type of kaolin consumed is wide, in other words, it determines the type of product and the production method of kaolin.
Due to its special chemical composition, kaolin is used in the ceramic industry. In the face of heat, its glass state does not change and creates a special radiance and transparency in the product. In the preparation of ceramics, the most important factor is the mixing ratio of kaolin, silica and melting aid (Flux) in the body of ceramics.
The characteristic of it used in the ceramic industry is generally related to the harmful impurities in it, which cause the color of the product to change after firing. The most important and harmful impurities are iron oxide. Other harmful elements include copper, chromium and manganese.
This problem occurs when these materials are finely placed in the clay, in which case it appears as the body of the product after baking, and in baking biscuits if the amount of oxygen in the oven decreases. Cavities form around the stain.
The permissible amount of 3O2Fe in ceramics is between 0.6 and 0.7 percent. Iron oxide in kaolin to make porcelain should be less than 0.5% because titanium reacts with iron in the ceramic body and reduces transparency. The degree of alkalinity has a special effect on the glassiness of the product, because it makes the ceramic body porous. Kaolin used in porcelain Potash should be less than 1.5% and the amount of titanium and silica should be minimal.
Although global kaolin production has been on the rise in recent years, the average very low growth rate of 0.01% indicates relative stability and equilibrium in terms of production, supply and demand. The main reasons for this stability can be considered the following:
2- Due to the fact that Brazil produces kaolin cheaper than the United States, Latin American countries supply their consumed kaolin from Brazil, and this in itself increases Brazil’s production and decreases the production of the United States of America (as the largest producer of kaolin). World) has been.
3- With the development of mining technology in the Far East, these countries have been able to meet the needs of their paper and ceramics factories by increasing the production of kaolin, which has increased the production of the Far East and reduced the production of the United States.
A change in any of the above can be seen in a fluctuation in the amount of kaolin production in the world, which can be a decrease or increase.
In addition to the economic and political issues of the world, the supply and demand debate also has a significant impact on global mineral production.
The average global production is 21,780 thousand tons with an average growth rate of 0.01% increase from 21,400,000 tons in 1997 to 22,000 thousand tons in 2001.
Among the producers of kaolin, the United States of America is in the first place with an average annual production of 8998 thousand tons. The country’s production with an average growth rate of 2.4% has decreased from 9280 thousand tons in 1997 to 8110 thousand tons in 2001.
The United Kingdom is in second place with an average annual production of 2327.2 thousand tons. The country’s production with an average growth rate of 66% has decreased from 2360 thousand tons in 1997 to 2204 thousand tons in 2001.
Brazil is in the third place with an average annual production of 1665.8 thousand tons. The country’s production with an average growth rate of 28.7% has increased from 1349 thousand tons in 1997 to 2000 thousand tons in 2001. China and South Korea are next.
The main producers of refined types are the United States, Britain, Brazil, Australia, Germany, the Czech Republic and Slovakia, which are the main exporters of high quality kaolin used in paint, paper and plastics. Low-quality kaolin used in refractories, ceramics, etc. is controlled by Colombia, South Korea, Uzbekistan, and Ukraine. Meanwhile, according to Raskel reports, Iran’s production is 500,000 tons per year.
There are 65 kaolin and refractory mines in operation in the country, which produce an average of 1.2 million tons of kaolin and refractory soil per year, of which about 1 million tons were sold. In general, the production trend is upward, but in some years it has fluctuated.
Production in 1380 has increased by more than 12% compared to 1376, while sales show a growth of about 26%. According to these figures, it can be said that the number or capacity of consumers has increased over the years.