( 2 ) superconducting magnetic separation As the kaolin ore body continues to be mined, the quality of the kaolin ore is gradually reduced, the size of the iron- titanium minerals present in the kaolin is getting smaller and smaller, and the high-gradient magnetic separator cannot separate the weak paramagnetic minerals at several micrometers. come out. According to reports, at present, more than 10 countries in foreign countries are engaged in the research on the removal of iron and titanium from kaolin by superconducting magnetic separator. The superconducting magnetic separator consists of three main parts. First, a superconducting magnet, which is made of titanium wire of niobium or niobium tin wire wounded; two cryogenic refrigeration system with liquid helium, liquid nitrogen cooling, niobium titanium or niobium tin magnet magnet reaches at 4.2K DC-free The superconducting state of the resistor; the third is the sorting pipe or sorting device, so that the ore or slurry to be sorted separates the magnetic mineral from the non-magnetic mineral in the superconducting magnetic field. Superconducting magnetic separator can be divided into two types: non-gradient superconducting magnetic separator and high gradient superconducting magnetic separator according to the presence or absence of medium and the gradient generated by it. Kaolin is more suitable for post-production. It can handle very weak paramagnetic minerals on the order of a few microns or submicron. Superconducting magnetic separation function long-term operation, as compared with conventional magnetic separator and reduce power consumption 80--90% alone can save $ 150,000 per year, which covers 34% of the original weight as the original 47% ; in addition, it also has rapid excitation and demagnetization capabilities, which can reduce the time required for sorting, demagnetizing and rinsing debris, thus greatly increasing the amount of mineral processing. The device has a processing capacity of 6t/h . 5 , flotation The flotation method is widely used in the purification of kaolin. At present, the process and equipment are continuously improved and updated, so that the kaolin concentrate can obtain higher whiteness and meet the industrial needs. The flotation methods, chemicals and equipment used are different due to the different impurities contained in the kaolin ore. Commonly used are froth flotation, carrying flotation, two-layer flotation and selective flocculation flotation. Froth flotation has little effect on the treatment of minerals below a few microns, especially for some difficult minerals, and is generally not commonly used. ( 1 ) Ultrafine flotation Super fine particles flotation (also known as bear flotation) capable of handling 100% less than 3 μ m, wherein 48% is less than 0.5 μ m minerals (such as anatase, quartz, tourmaline and iron oxide), a sorting One of the most effective processes for fine-grained minerals. This method is the use of oleic acid (tall oil, fuel oil) as collector, pine oil as a blowing agent, a soluble alkaline earth metal salt (calcium petroleum sulfonate) as co-agent selected from the group, adjusting the pH with ammonium hydroxide (typically around pH = 9) using --325 object of calcite, quartz, silica, fluorite, barite and the like as the carrier, to be sorted for trapping fine mineral impurities, essence of this method is to increase the carrier Collision rate and contact surface of minerals and bubbles. During the flotation process, the carrier of the adsorbent carrier carries the impurity particles to the foam layer, and the foam overflows, and the kaolin is the underflow product, so as to achieve the purpose of separation. Under normal circumstances, the reduction of the particle size of the carrier mineral and the increase of the stirring strength can significantly increase the collision rate of the carrier mineral and the fine-grained ore particles, which is very advantageous for improving the separation index, and the pre-hydrophobic treatment of the carrier mineral is improved. An essential measure of iron removal rate. The advantage of ultra-fine particle flotation is that ordinary equipment and flotation reagent can be used, and the sorting effect is good. Generally, 70% of iron-titanium impurities can be removed, and the whiteness can reach 90 or more. The disadvantage is that the process is complex. ( 2 ) Two-layer flotation method The two-layer flotation method is developed on the basis of ultrafine flotation. The method is to first add a dispersant to the kaolin slurry, adjust the pH between 5 and 11 , and then selectively wherein the trap of cation trapping agents of a mineral and carbon tetrachloride, and then with an organic liquid to reconcile, in the pulp pH = 8 - 12, the emulsified form of kaolin - impurities in the aqueous layer and - an organic liquid layers of two liquid layers, Finally, the former is separated and pure kaolin is recovered. The method is characterized in that instead of using a mineral carrier, the slurry is treated with a hydrophobic trapping agent capable of trapping impurities and a non-polar organic liquid, and the flotation process can be carried out in a hydrocyclone or a gravity sedimentation tank. Before the selection, the solid content of the slurry must be adjusted and appropriate dispersant added to obtain the best sorting effect. British Kaolin Company (ECC Corporation) using this method Isolation impurities tourmaline kaolin, clay added in the pulp and the alkali silicate as a dispersant, an industrial coal-conditioner as an oil, a fatty acid as the trapping agent, After stirring and mixing, the mixture was allowed to stand, and the two liquid layers were separated. The pure kaolin was recovered from the liquid phase, and the tourmaline was recovered from the oil phase. The used blending agent ( industrial kerosene ) can be reused after removing impurities. The disadvantages of this method are costly. ( 3 ) Selective flocculation floatation method In this method, kaolin is precipitated by using an anionic flocculant, other minerals are left in the suspension, and after standing for 10 minutes, the suspension is poured out, and the floc is stirred into a suspension in clear water and then further separated. The impurities dispersed in the kaolin slurry can also be flocculated, the kaolin is dispersed, and the kaolin slurry is separated from the flocculated impurities by siphoning or decantation. This method has been developed in the past 20 years and is considered to be one of the most promising effective processes in fine-grain dressing . The United States, the former Soviet Union, Britain, West Germany, the Czech Republic and other countries have adopted this process, which makes the kaolin Both the selection capacity and the beneficiation recovery rate have been improved. In the late 1970s , China began to study the selective flocculation and flotation of kaolin, mainly in addition to alum , and achieved certain results. In the test, water glass was used as dispersant, hydrolyzed polyacrylamide was used as flocculant, and Ca 2+ was used to activate the slurry. As a result, the desulfurization rate of ore reached 65.72% . Flocculant concentration of test 16 × 10ppm, the flocculant poly enamide degree of hydrolysis of 70%, the settling time is 180min, pH = 9.5 - 10, when the sodium silicate in an amount of 400ppm best. The addition of Ca 2+ to the slurry can produce different flocculation effects of kaolin and alum, and the flocculation of alum is obviously activated. When CaCl 2 reaches 40 ppm , the flocculation recovery rate of alum can reach 92% . 6 , bleaching The kaolin used as a pigment, filler and coating directly affects the value of its whiteness and brightness. The so-called bleaching is to increase the whiteness of kaolin by different means. Specific methods include magnetic separation bleaching, flotation bleaching, chemical bleaching, and the like. Magnetic separation bleaching and flotation bleaching have been previously described, with emphasis on pigmented bleaching and chemical bleaching. ( 1 ) coloring bleaching Coloring bleaching refers to the addition of an appropriate amount of white agent to kaolin. After sufficient agitation, the white agent covers the surface of the kaolin, thereby greatly increasing the whiteness of the kaolin. The agents used for the coloring bleaching include TiO 2 , CaSO 4 · 2H 2 O , CaCO 3 , CaSiO 3 · H 2 O, and Al(OH) 3 . Czech bleaching experts have made breakthroughs in this process research and are currently working on industrial applications. The results show that the best bleaching effect is obtained with TiO 2 as the covering agent, and Al(OH) 3 is the worst. However, TiO 2 is expensive, so it is recommended to use inexpensive CaSO 4 · 2H 2 O or CaSiO 3 , and other agents can be used to obtain the above-mentioned agents by reaction between them, followed by stirring and bleaching. For example, Ca(OH) 2 and Al 2 [ SO 4 ] 3 · 18H 2 O can be used , and both react to form CaSO 4 · 2H 2 O and Al(OH) 3 , both of which are white. The reaction formula is as follows: 3Ca(OH) 2 +Al 2 [ SO 4 ] 3 · 18H 2 O=3CaSO 4 · 2H 2 O+2Al(OH) 3 +12H 2 O Notable in this process is the fineness of the white medicinal agent and the mixing equipment used. Insufficient fineness of the medicinal agent or improper agitation speed will reduce the bleaching effect. ( 2 ) Chemical bleaching For some iron oxides that are firmly covered on the surface of kaolin particles, it is difficult to remove them by magnetic separation and flotation, which must be treated by chemical bleaching. The chemical bleaching method is to chemically dissolve the colored impurities such as iron and titanium and then rinse them out. The specific methods commonly used are: redox method, acid solution method, chlorination method and the like. ( I ) reduction method   The essence of the method is to reduce the poorly soluble Fe 3+ in the kaolin to soluble Fe 2+ and then remove it by washing, thereby increasing the whiteness of the kaolin. This is the traditional method of removing iron in the kaolin industry. Before the bleaching, the slurry flows into the mixer and is stirred, and after flocculation is added, the bleaching is carried out. Commonly used reducing agents are: sodium dithionite ( also known as insurance powder ) , sodium thiosulfate, zinc sulfite, etc., the main reaction of the reduction is as follows: Fe 2 o 3 +Na 2 S 2 O 4 +3H 2 SO 4 =Na 2 SO 4 +2FeSO 4 +3H 2 O+2SO 2 There are many factors affecting the bleaching effect, such as the characteristics of the ore, temperature, pH , dosage, slurry concentration, bleaching time, and stirring strength. If the impurities in the ore are star-shaped, dip-dyed, and the content is low, a better bleaching effect can be obtained, and the whiteness is remarkably improved. If the ore contains organic matter and high impurity content, the bleaching effect is poor and the whiteness is not increased. The temperature during the bleaching process should generally be too high at normal temperature. Although the bleaching speed can be accelerated, the heat consumption is large, the decomposition rate of the agent is too fast, causing waste and polluting the environment; too low, the reaction is slow, and the production capacity is lowered. When the pH of the pulp is adjusted to 2 - 4 , the bleaching effect is best. In terms of dosage, generally, with the increase of the dosage, the bleaching speed is accelerated, and the whiteness is also increased, but when it reaches a certain level, the whiteness is no longer increased. Pulp concentration 12-- preferably 15%. The bleaching time should not be too long or too short. It takes too much time to waste the agent and reduce the quality of the kaolin. The oxygen in the air causes the oxidation of Fe 2+ to Fe 3+ . Too short, the whiteness does not meet the requirements. . After the reaction is completed, it should be filtered and washed immediately, otherwise the surface will gradually yellow. For products yellowing problem, there 70s U.S. Patent describes the added phosphate avoid reversion, i.e. the specific method is: first add sodium dithionite reduction bleaching, after certain time, added phosphate. The bleached product has been proven to achieve permanent bleaching. The bleaching of kaolin with dithionite can significantly increase the whiteness and brightness of kaolin to a certain extent, but the nature of the reducing agent is extremely unstable and can be decomposed by heat, moisture or exposure to air. In the bleaching process, a considerable amount of Na 2 S 2 O 4 is consumed in its own decomposition reaction. In order to avoid such waste, several improved methods have been developed in recent years, such as zinc powder bleaching method and sodium borohydride bleaching method. The sulfur dioxide electrolysis method, etc., are similar in that: Na 2 S 2 O 4 is generated instantaneously in the bleaching process , thereby avoiding waste of the medicament, reducing the cost, and obtaining a better bleaching effect. Oxidative bleaching is generally used for pyrite-containing or organic kaolin. Even if the pyrite in the reduced state is oxidized to soluble ferrous sulfate and ferric sulfate, the organic matter is oxidized to become a colorless oxide which is easily washed away. . According to the data, a redox combined bleaching has been adopted abroad, and it has been proved by experiments that this method is better than pure reduction or oxidative bleaching. For example, in the United States, the Asian kaolin soil, the original soil < 2 μ m content of 80% , whiteness of 70.2% , made 20% of the mud, added with a reducing agent (Na 2 S 2 O 4 ) bleaching, whiteness increased to 72. 0 % , obviously, this effect is not satisfactory. If hydrogen peroxide is first added to the mud to completely react the colored impurities in the kaolin, and then added with Na 2 S 2 O 4 bleaching, the whiteness can be increased to 85.0% . ( II ) The acid-soluble acid-dissolving method is to treat the kaolin with an acid solution ( hydrochloric acid, sulfuric acid, oxalic acid, etc. ) , and convert the insoluble compound into a soluble compound, and separate from the kaolin. Kaolin treated with hydrochloric acid required in 90-- Table 2    Leaching test results of hydrochloric acid with different mineral samples Sample number  index X-1 D-1 X-2 Y-1 L-1 W-1 X-3 SX-1 White degree Before bleaching 53.1 56.1 52.8 58.8 70.4 67.3 57.3 53.1 After bleaching 84.9 87.3 83.3 83.7 72.4 84.5 83.3 87.0 Processing Aid Acr,Acr Processing Aid,Acr 401 Pvc Processing Aid,Pvc Processing Aid Acr Hebei Xiongfa New materials Technology Development Co.,LTD , https://www.xiongfa-tech.com