Kaolin, especially ultra-fine calcined kaolin, as a very important inorganic non-metallic materials, by virtue of its excellent physical properties have been occupied a very important position in the paper industry. Calcined kaolin used in the paper industry is a porous structural features of high brightness material that is primarily used to replace expensive titanium white powder pigments and other advanced. The quality requirements of the calcined kaolin in the paper industry are mainly the requirements for the particle size, whiteness and hiding power, oil absorption rate, viscosity concentration, pH value and abrasion value of calcined kaolin. In recent years, the United Kingdom, the United States and other countries have successively developed and mass-produced some brand-name products with high whiteness, high fineness and high hiding power, and their product whiteness (F457) and fineness (with -2 micron particle content). All of them have exceeded 90% (the so-called "double 90" indicator). In the case of the ordinary washed kaolin market, which has been hit by heavy calcium carbonate and has been shrinking year after year, the market sales have prospered, and many manufacturers are competing to follow. Since the 1980s, found that a large number of coal-based kaolin (allegedly prospective reserves of over 10 billion tons), and due to the high quality of kaolin, and rarely harmful impurities, making the production of paper coating grade calcined kaolin ideal raw material . In recent years, many departments in China have taken “double 90†as their goal, and have made some attempts on the process development of using coal gangue to produce paper-grade coating grade kaolin and have made some progress. However, only a very small number of companies are currently able to produce qualified products. Most of the products have been unsatisfactory due to raw materials, processes and equipment. This paper intends to make an analysis and comparison of some existing processes, in order to obtain some inspiration.  A process principle The process for producing paper-coated grade kaolin from coal gangue mainly comprises two parts: pulverization ultrafine process and calcination whitening process.  1î€Crushing ultra-fine process The pulverizing ultrafine process is an important part of determining the quality of kaolin. The pulverized superfine of the coal-based kaolin is a fine kaolin pulverized (from 5 to 20 mm to 40 to 80 μm) and ultrafine (from 40 to 80 μm to -10 μm or -2 μm). Although the functions, fracture range, energy consumption, etc. of various equipments are not the same, according to the principle of crushing and crushing, the following can be summarized as follows: 1) Extrusion method: material crushing between two working faces due to pressure P; 2) Impact method: The material is crushed due to the impact force. The impact force is generated by: the impact of the moving working body on the material; the high-speed moving material impacts on the fixed working surface; the high-speed moving materials impact each other; the high-speed moving working body impacts on the suspended material; 3) grinding and stripping method: the shearing force applied when the material is rubbed against the movement of the material, or the shearing action when the materials are rubbed against each other to smash the material; 4) Splitting method: The material is crushed by the action of the wedge-shaped working body.  Different types of pulverizers smash materials in different ways. In a pulverizer, a single method is not used, and it is usually pulverized by combining two or more methods.  In the process of coarse and medium crushing of the existing kaolin pulverization ultrafine process, a pulverizing device mainly composed of an extrusion method or an impact method is generally used, and the equipment used in the ultrafine process is mainly a grinding and stripping method.  2î€ calcination whitening process In view of the diagenetic characteristics of coal-series kaolin, that is, it contains part of organic matter, the whiteness of its ore is only 6-40%, which is far from meeting the quality requirements of coating grade kaolin in the paper industry. Therefore, the process of calcination decarbonization and whitening must be adopted. . In the coal-based kaolin, the organic matter and the fixed carbon undergo the following reactions during the calcination and whitening process: CmHn (m 1/4n)O2→mCO2 1/2nH2O C O2→CO2 The above two forms of carbon generally react between 300 and 800 ° C, and can be completed after a certain period of time to achieve the purpose of decarburization. The thermal reaction history of kaolinite minerals is shown in Table 1 during the heating process. Table 1 Thermal reaction history of kaolinite minerals Temperature °C thermal reaction 100~110 remove physical water 400~800 remove structural water to form metakaolin Form 925 metakaolin conversion occurs, an aluminum spinel Si 1100 Al-Si spinel converted to pseudo-mullite 1300 pseudo-mullite converted to mullite Wherein the square formed mullite and silica at a temperature above 1000 ℃. In order to avoid the formation of harmful mineral crystal forms (mullite and cristobalite), in the process of producing paper grade kaolin, the calcination temperature is generally controlled below 1000 °C. According to the different requirements of kaolin quality, it can be divided into medium temperature calcined kaolin and high temperature calcined kaolin.  The current calcination process can be divided into a molding calcination process and a powder calcination process, and each has its own characteristics.  Introduction and discussion of the process and characteristics of the second process  According to the super-fine process is the wet process or the dry process and the sequence of the ultra-fine process and the calcination process, the production process can be combined into four, namely (1) wet first Method after superfine calcination process (2) first dry method ultra-fine post-calcination process (3) first calcination after wet superfine process (4) first calcination after dry superfine process. Because people have different understandings of ultra-fine materials, the process routes selected in different enterprises are not the same. The author intends to carry out a simple analysis of different routes:  1) After the calcination, the wet superfine process The process flow diagram of the process is: Raw ore→crushing→crushing→calcining→wet superfine→dry→dispersion→product The advantages of the process are as follows: (1) The amount of ultrafine material is small, and the theoretical loss on ignition of calcined kaolin from kaolin is 13î€96%, considering the combustion and volatilization of organic matter and fixed carbon during calcination and in the calcination process. The mechanical loss in the process, the yield of calcined kaolin in the actual production process is only about 80%, the ultra-fine process is a process that consumes more energy, and the energy consumption is reduced from one side due to the reduction of the amount of treated material. (2) The ultra-fine material is easy to be dried and dispersed. Due to the viscous property of the kaolin itself, it is difficult to reduce the material into a dry powder after being ultra-fine before burning, so that the material is easily bonded from the initial state during the calcination process. It becomes sintered, especially when the content of fusible minerals in the material is high, the sintering situation is more serious, which is extremely unfavorable for the dispersion of the materials after burning, so it is still necessary to superfine the ultra-fine equipment after burning; This can be avoided after the calcination process. This is because the calcined kaolin itself no longer has cohesiveness and is easily dispersed after drying.  3 countries 3 trees 3 fat 3 in 3 lines big 0 force 0 god 0 cloud 0 stone 0 glue The disadvantages of this process are as follows: (1) The wet superfine grinding medium is difficult to solve. The grinding medium selected for the wet superfine equipment is generally glass beads, corundum balls, porcelain balls or zirconium corundum balls, which are superfine according to the wet method. The hardness requirement of the grinding medium is greater than the hardness of the material. The hardness of the kaolin before burning is 3-4, and the hardness after burning is about 7, so when using the above medium as the grinding medium, it is easy to cause large wear. It is not even possible to complete the grinding task. When the wear is large, the scraper wear value of the product may not reach the index due to excessive introduction of impurities. When using expensive zirconium corundum balls, production costs are difficult to reduce. (2) The quality of kaolin needs to be high. Because of the dry coarse crushing and medium crushing process before calcination, the harmful impurities are not effectively removed, so that harmful impurities such as iron and titanium directly affect the quality (whiteness) of the calcined product. Therefore, only the use of higher grade raw materials for calcination can achieve better whiteness. (3) A separate drying and dispersing equipment is needed in the process to complete the processing of the wet superfine material, so that the drying equipment has high quality requirements to prevent the material from being contaminated three times.  2) Dry superfine process after calcination The process flow diagram of the process is as follows: Raw ore → crushing → crushing → calcining → dry superfine → product The main advantages of the process are: short process flow; less material for ultra-fine treatment; low energy consumption.  The main disadvantages of this process are: high quality requirements for raw materials; difficulty in producing ultra-fine products with -2μm up to 90%; high requirements for abrasive bodies for ultra-fine equipment; only airflow mills can be used.  At the current level of equipment, this process is not yet a viable production process because there is currently no suitable ultra-fine pulverizer.  3) First dry method, ultra-fine calcination process The process flow diagram is:  Raw ore→crushing→crushing→dry superfine→calcining→product The advantages of this process are that (1) the process is short, and the main equipment required for the whole process is only three to four. If the ultra-fine equipment of Xianyang is used, only three equipments are needed, namely: crusher , superfine crusher, calcination. Furnace, convenient for overall management and reasonable dispatch; (2) Reasonable energy utilization, the process of placing the ultra-fine process of materials before the calcination process to avoid the problem of consuming more energy due to the material after crushing. If the powder calcination process is used, it can be regarded as a full dry process. In terms of technology alone, energy use is more reasonable.  The shortcomings of this process are as follows: (1) Product grades are difficult to improve. As mentioned above, there are no dry superfine equipments at home and abroad that can produce ultra-fine products with a particle size of -2μm and 90% in the papermaking industry. Due to the coarser particles of the final product, the particle size, scraper wear, and viscosity concentration of the product may not meet the quality requirements of the coating industry for the knife coating grade kaolin; (2) the requirements for the fusible mineral content in the product are strictly required. In order to avoid the occurrence of sintering, bonding, etc. in the reasonable calcination temperature range of kaolin, the content of K, Na, Ca, Mg, Fe, Cl, S and other components in the ore should be strictly controlled to avoid the formation of eutectic. Because there is no post-burning material re-grinding in the process. The author believes that the process is a process for producing low-grade paper-making fillers using high-quality raw materials, and is suitable for a start-up process for enterprises with resource advantages but not with financial strength.  4) First wet superfine calcination process The process flow diagram is:  Raw ore→crushing→crushing→wet superfine→drying→calcining→reduction→product The advantages of this process are: (1) The ultra-fine position problem is better solved. Because the hardness of the coal-based kaolinite is between 3 and 5, which is much lower than the hardness of the kaolin after calcination, the energy consumption for ultra-fine pulverization is low, and the grinding medium is easy to select; (2) the wet superfine process is adopted. It is easy to make the product particle size reach -2 μm at a level of 90%. At present, the dry superfine process at home and abroad can not reach this level; (3) the technology is reliable; (4) it is easy to solve the problem of impurities such as iron and titanium.ä¸»è¦ The main disadvantages of this process are (1) long process flow and (2) the need for a reduction process.  After many years of exploration, Shanxi Xidi Fine Chemical Co., Ltd. adopts the first wet-process ultra-fine calcination process to produce calcined kaolin in line with the requirements of the paper industry at the domestic rate, and transfers the technology together with Xidi's calcination technology to Shanxi. Yangquan Jingrui Chemical Co., Ltd. enabled the company to use only half a year for construction and trial production, which facilitated the successful production of high-standard calcined kaolin products in July 1998 and passed provincial appraisal in October.  Twenty-seven meters of building materials network including wood flooring, famous wood flooring brand, wood floor supermarket, new building materials website Three conclusions The use of coal-based kaolinite to produce coating grade calcined kaolin for paper industry is undoubtedly an effective way to make rational use of coal gangue. It should be noted that the appropriate process route should be selected according to local resources and funds. According to the previous analysis, the author believes that: (1) The wet superfine recalcination process is long, but the adaptability to the raw materials is strong, and the product quality can meet the needs of the paper industry; (2) Calcination and rewetting method Ultra-fine process generally requires special configuration of drying equipment and dispersing equipment. The process has weak adaptability to raw materials, but can produce products demanded by the paper industry; (3) The dry superfine recalcination process and the first calcination and dry process ultrafine processes cannot produce kaolin for papermaking industry (because of superfine equipment), and the quality of raw materials is high.  Xidi Company is willing to share its lessons and successful experiences in its explorations with its counterparts who are or are preparing to use coal-based kaolinite to produce calcined kaolin. Leaders at all levels are welcome to provide guidance to experts and scholars at home and abroad. TC Bolts, Tension Control Bolts, A325 TC Bolts, A490 TC Bolts, High Tension Bolts Ningbo Brightfast Machinery Industry Trade Co.,Ltd , https://www.brightfastener.com
Technology for producing calcined kaolin from coal-series kaolinite