An article to understand the kaolin processing technology and characteristics

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　　The quality of kaolin is mainly reflected in the three aspects of whiteness, purity and fineness, the higher the whiteness, the higher the purity, the finer the particle size, the better the quality, and the higher the price on the market. There are many factors affecting the quality of kaolin, mainly iron and titanium. According to the different properties of kaolin, its processing technology is mainly for the mineral processing and purification of kaolin, ultra-fine crushing and surface modification.

　　

　　1. Re-selection

　　Re-separation is mainly used in the beneficiation and purification of sand and soft kaolin, the process is to add kaolin, water and dispersant to the pulper to mix into a certain concentration of slurry, through the high-speed rotating impeller in the pulper to separate kaolin and other minerals, organic matter such as quartz, feldspar, etc., and the pulp after the pulp is then removed by centrifugal grading equipment such as spiral classifier and hydrocyclone group to remove fine sand in kaolin and further purified. After the purified product meets the requirements of use, it can be used as a kaolin product, and the quality of kaolin can also be improved by further iron removal and whitening.

　　2. Magnetic separation

　　The magnetic minerals present in kaolin mainly contain: (1) fine-grained ferro-titanium-containing oxides, such as magnetite, ilmenite, etc.; (2) iron-containing or iron-containing or iron in the lattice to enter the weak magnetic minerals in the form of lattice substitution, such as black mica.

　　There are two main methods for sorting weak magnetic minerals: high gradient magnetic separation and magnetization roasting, and high gradient magnetic separation is commonly used in industry. High-gradient magnetic separation differs from conventional magnetic separation in that it produces magnetic field strengths of up to 107 gauss/cm, enabling efficient capture of fine-grained, weakly magnetic mineral particles present in kaolin.

　　With the increasing demand for kaolin and mining, high-quality kaolin resources are less and less, most of them are low-grade and difficult to develop and utilize kaolin, ore impurity content is high and embedded in fine, high gradient magnetic separation can not do effective iron removal, therefore, the future by increasing the magnetic field strength to achieve the application of superconducting magnetic separation in industrial production is the trend of high gradient magnetic separation technology development.

　　3. Flotation

　　The flotation of kaolin is mainly the addition of flotation agents to make the fine-grained iron and titanium impurity minerals in kaolin enter the foam and be scraped out, so as to achieve the purpose of iron removal and whitening. Due to the good natural floatability of iron sulfide minerals, flotation separation can be achieved by adding a futation collector of sulfide minerals for foam flotation.

　　A foreign clay development company uses carrierless flotation technology to flotify iron removal of kaolin, activates the flotation process by adding Ca2+ in the flotation process, and at the same time performs high-intensity scrubbing of kaolin slurry to remove its surface pollutants, and achieves a good flotation effect.

　　4. Selective flocculation

　　Selective flocculation is based on the difference in properties between minerals, by adding a flocculant to selectively aggregate some fine particles of the slurry to form a flocculent with a larger particle size. The principle of selective flocculation of kaolin iron removal is mainly to floccinate and settle fine kaolin by adding a flocculant of kaolin, while the iron and titanium impurity minerals in kaolin are left in the upper suspension, and then supplemented by magnetic separation or flotation to remove iron and titanium impurity minerals to achieve the purpose of iron removal and whitening.

　　5. Chemical whitening

　　Chemical whitening is mainly through the addition of agents and kaolin in the reaction of impurities, and then removed by water washing. Commonly used methods include acid-soluble, oxidative bleaching, reductive bleaching, and oxidation-reduction bleaching.

　　The principle of acid solubility is to add acid to kaolin and react with insoluble impurities, and then wash and remove with water, the commonly used acids are mainly hydrochloric acid, sulfuric acid, oxalic acid.

　　The principle of reductive bleaching is to add a reducing agent in an acidic environment with a pH of 2 to 5 to convert the insoluble Fe3+ in kaolin into a soluble Fe2+, and then remove the soluble Fe2+ after washing, and the commonly used reducing agent is sodium dibisulfite (insurance powder), sodium thiosulfate, etc.

　　The principle of oxidative bleaching is similar to that of reductive bleaching, which is mainly by adding strong oxidants (such as hydrogen peroxide, potassium permanganate, chlorine, etc.) to the kaolin to oxidize insoluble impurities (such as FeS2 and organic matter, etc.), and then rinse with water to remove.

　　Many times the ore contains both insoluble trivalent iron and divalent iron, a single reduction bleaching or oxidative bleaching can not be effective in iron removal, at this time can be used oxidation - reduction combined bleaching method to remove iron. The principle is mainly to add an oxidant to oxidize the insoluble FeS2 to Fe3+, and then add a reducing agent to transform Fe3+ into Fe2+ that can be removed by water washing. Compared with a single reductive bleaching or oxidative bleaching, the iron removal effect of this method is significantly improved, but its process flow is more complicated.

　　6. Calcination and whitening

　　Chlorination roasting is a commonly used kaolin whitening process, the main principle is to add a solid chlorinator or chlorine in the process of kaolin calcination in the reducing environment to make it react with the iron and titanium impurities therein to form chloride and discharge, thereby improving whiteness. The coal-based kaolin raw ore itself contains a certain amount of carbon, which is conducive to the chlorination reaction, and the coal-based kaolin forging and decharization is one of the necessary processing processes, which combines carbonization with chlorination and iron removal and titanium. Therefore, the chlorination roasting method is widely used in the purification of coal-based kaolin.

　　7. Ultra-fine crushing

　　The particle size of kaolin is the key to measuring the quality of its products, and there are certain requirements for the particle size of kaolin in the field of papermaking, coatings, rubber and plastics, so it is necessary to crush kaolin ultra-fine.

　　Because kaolin has a lamellar structure, ultra-fine crushing of kaolin is also called stripping. Mainly through physical or chemical action to laminate kaolin grinding into a single layer of flakes, without destroying its lattice structure to reduce its particle size, commonly used equipment for stirring mill and ball mill and so on.

　　Nano kaolin has many properties unique to nanoparticles, such as surface effect, macroscopic quantum tunneling effect, etc., making it widely used in various fields, and can greatly improve the physicochemical properties of materials. With the development of science and technology, the nanolimization of kaolin will also become the main research direction of kaolin deep processing.

　　8. Surface modification

　　Kaolin surface modification is the use of physical or chemical means to treat the surface of kaolin, so that the whiteness, brightness, chemical activity and other physical and chemical properties of kaolin change. Kaolin surface modification methods mainly include coupling agent treatment, adsorption, surface coating, etc., of which the most widely used is coupling agent modification. The principle of coupling agent modification is mainly through the coupling agent interacting with the active group on the surface of kaolin, so that the physical and chemical properties of its surface change.

　　Source: Zhang Fan. Research on the processing and comprehensive utilization of a sandy kaolin in Jiangxi [D].Wuhan University of Technology, edited and sorted by [Powder Technology Network], please indicate the source when reprinting!