Kaolin dry and wet beneficiation process

Kaolin is a general term for a group of clay minerals. Its basic composition is kaolinite group and kaolinite group. It is mainly composed of kaolinite and halloysite. The content is over 90%, followed by hydromica . there are pyrite, limonite, anatase, quartz, chalcedony, alum, and sometimes a small amount of organic matter. Kaolin is widely used in ceramics, paper, rubber, plastics and refractory industries due to its excellent processability such as plasticity, cohesiveness, sinterability and fire resistance. There are three main types of genesis of kaolin deposits: weathering, sedimentary and hydrothermal alterations.

The processing of kaolin ore depends on the nature of the ore and the end use of the product. There are two processes used in industrial production: dry process and wet process. Usually, hard kaolin is produced by dry process, and soft kaolin is produced by wet process.

 

Dry beneficiation process

The dry process is a simple and economical process. The produced ore is crushed to 25.4 mm by a hammer crusher and fed into the crusher to reduce the particle size to 6.35 mm. The hot air in the crusher reduces the moisture of the kaolin from about 20% of the produced to about 10%. The crushed ore is further ground by a ball mill equipped with a centrifugal separator and a cyclone. This process removes most of the sand and the product is commonly used in low-cost fillers in the rubber, plastics and paper industries. When used in the paper industry, the product can be used as a filler in the filler layer with an ash content of less than 10% or 12%. At this time, the brightness of the product is not high.

When the dry method requires high whiteness of the product, the product produced by the ball mill must be subjected to dry iron removal. The dry process has the advantages of eliminating the product dehydration and dry process, reducing the loss of ash powder, short process flow, low production cost, and is suitable for drought and water shortage areas. However, in order to obtain high-purity high-quality kaolin, it is necessary to rely on the wet process.

Wet beneficiation process

The wet process includes three stages: ore preparation, beneficiation processing and product processing. The preparation phase includes operations such as batching, crushing and mashing. The mash is to mix the kaolin ore with water and dispersant in the pulverizer. The mashing operation can disperse the ore. Prepare the appropriate fine kaolin slurry for the sorting operation, and remove the large sand at the same time. The beneficiation stage may include hydraulic grading, flotation, selective flocculation, magnetic separation, chemical treatment (bleaching), etc. to remove different impurities. The prepared slurry is firstly removed by a sputum washing tank, a float classifier or a cyclone, and then divided into two parts by a continuous centrifuge, a hydrocyclone, a hydraulic sorter or a vibrating fine screen (325 mesh). Two grades of thickness. The fine-grained grade of the classifier is fed into HGMS (high-gradient magnetic separator) to remove iron-titanium impurities. The product is detached by stirring and scouring and then leached by iron oxide. The clay which is high enough in brightness and has good coating properties can be magnetically removed. Stripped and sent directly to the leaching operation. After leaching, alum is added to the slurry to coagulate the clay minerals to facilitate dehydration. The bleached clay is dewatered using a high speed centrifuge, a rotary vacuum filter or a filter press. Dewatering by filter or filter press. The filter cake was redispersed into a slurry of 55% to 65% solids and then spray dried to make a loose dry product. Some of the dry product was mixed into the dispersed slurry to make 70% solids and shipped to the paper mill.

The final product, which is not selected, has low brightness and can only be obtained by magnetic separation, froth flotation or selective flocculation in the process. However, these independent operations have their own advantages and disadvantages, so the industry usually uses a combined process of two or three of these processes for the comprehensive utilization of clay resources.

 

High gradient magnetic separation

The dyed impurities in kaolin (such as hematite, etc.) have weak magnetic properties and can be removed by a high gradient magnetic separator. In the United States, the PEM-84 wet high gradient magnetic separator can reduce Fe2O3 in kaolin ore from 0.9% to 0.6%, and Ti2O3 from 1.8% to 2.0% to 0.8%. This high-gradient magnetic separator uses stainless steel wool as a medium. When the field strength is 1.5 to 2.0T, it consumes 270-500kw. China has carried out wet research on Hunan acid, Lingyang, Boluo and Hengling soils [3-6], and all of them have obtained good test results, especially the removal of iron and titanium in kaolin by vibration high gradient magnetic separation. Very good test indicators. According to the comparison test results of China's CLY500 vibrating high gradient magnetic separator and the US PEM-84 high gradient magnetic separator, the high gradient magnetic field of China is seen from the content of iron and titanium impurities and whiteness. The machine performance is better than the United States.

Since some impurities in kaolin portion of iron is present in the form of silicates, very weak magnetism, and titanium present in the form of rutile, the magnetic separation method is difficult to work, so the flow is usually accompanied by flotation, selective flocculation, etc. Other jobs to improve the quality of the product. In recent years, superconducting magnetic separators have been successfully applied to kaolin sorting, which not only reduces energy consumption, but also greatly increases the field strength, and the quality of kaolin concentrate is also higher. The Eriez superconducting magnetic separator features rapid magnetization and achieves the highest design field strength (5T) in 60 seconds with a short degaussing time, which greatly reduces the time required to flush magnetic impurities from the magnet during load cycling. Its energy consumption is low, about 80% less than conventional magnetic separator, and the processing capacity is large, up to 100t/h. The United Kingdom has tested a reciprocating spiral superconducting magnetic system that is similar in design to a conventional can magnetic magnetic filter, except that it retains the superconducting magnet in an excited state during the duty cycle without switching control. Continuous operation. The 3048mm, superconducting and high gradient magnetic separator designed by Humboldt Company of Germany has simple structure, low operation and maintenance cost and good stability.

Foam flotation

The purpose of the flotation operation is to float titanium impurities from the kaolin. Since the impurity particles are extremely fine, a carrier flotation process is usually employed. The carrier mineral may be calcite or silica sand (-325 mesh), and the amount of the carrier mineral is generally 10% to 20% by weight of the kaolin, and a part of the carrier may be reused. The agents used in the flotation process include: dispersant sodium silicate, pH adjuster amine hydroxide and caustic soda collector Tal oil, fatty acid and calcium petroleum sulfonate. However, flotation has many disadvantages. The hydrophobicization of the carrier requires a large amount of chemicals. The flotation process can only be effective at a lower concentration of the slurry, thereby increasing the cost of dewatering. The loaded body must be removed from the clay product as much as possible. Recycling in the product for recycling. Chemicals and carrier minerals remaining in the clay are detrimental to the final product. Cundy and Yong et al. studied a flotation process that does not require a carrier and floats anatase directly from kaolin, which is characterized by the presence of dispersants (such as sodium silicate) and pH adjusters (usually amine hydroxide). Under high conditions, the high pulp concentration (40% to 60% solids) is scrubbed to remove surface dirt. At the same time, the scrubbing also disintegrates the anatase and hematite from the kaolin minerals, and then traps a small amount of activators and fatty acids. The slurry is added together with the slurry, and the anatase covered by the collector forms a selective agglomeration under high shear stirring conditions, so that the particle size is significantly increased, and the slurry after high shear stirring and slurry mixing is diluted to 15%-20. The % solid is floated and the alum in the kaolin can also be removed by flotation.

 

Characteristics of kaolin mineral processing technology

The comprehensive kaolin mineral processing technology in the country has the following characteristics:

1 The raw ore mined from the mine is coarsely selected on site, and a large amount of tailings are discarded in the mine. This not only solves the filling of the goaf, but also reduces the stockpiling and transportation of the ore in the ore dressing plant. Concentrates of each roughing plant;

2 Pipeline transportation is generally used between mines and selected plants. Since 1939, kaolin slurry has been transported by pipeline;

3 high-concentration pulping, adding dispersing agent to the pulp during the sorting process, adding flocculating agent during the dehydration process, and the filter press or vacuum filter product can be sold as a product without drying;

4 In addition to the hydrocyclone classification, the beneficiation operation also adopts centrifugal classifier, sand mill, high gradient magnetic separator and flotation machine to improve product fineness and reduce impurities such as iron, titanium and sulfur.

5 The chemical bleaching process is commonly used in major kaolin producing countries such as the United States, the United Kingdom, and the former Soviet Union to produce high-whiteness kaolin products, but the cost is high;

6 Gaoling products are sold in bulk, coarse powder, fine powder and paste form. The manufacturer supplies different products according to the requirements of the users. There are many types of drying equipment for the products, but the most applications are spray drying, because the cost is relatively low;

7 Concentrators not only have large production capacity, but also many varieties, and are standardized products. Can meet the needs of different users. China Kaolin Company has four major categories and 34 varieties. These products are widely used in paper fillers and coatings, ceramic industry raw materials, rubber and plastic fillers and reinforcing agents, white cement oil felts, roofing coatings and waterproofing agents, glass fiber ingredients, ink pigments, cosmetics and soaps. Fillers, carriers of pesticides and fertilizers, binders for abrasive materials, synthetic molecular sieves, petroleum catalysts, atomic energy reactors, etc.

The ore dressing method of kaolin depends on the type of impurities in the ore, the state of occurrence, the size of the inlay and the required product quality index. For kaolin with less impurities in raw ore, higher whiteness, less iron impurities and main impurities such as sand (quartz, feldspar, etc.), it can be removed by simple pulverization and wind classification (ie dry beneficiation). For kaolin with more impurities, lower whiteness, higher content of sandy minerals and iron minerals, re-election (desanding), strong magnetic separation or high gradient magnetic separation (except for sale of iron, titanium minerals), chemical bleaching (mineral iron and ferric iron is reduced to ferrous iron), flotation (aluminum alunite separation or removal of mineral anatase) or the like containing such other; a high content of organic matter for kaolin In addition to the foregoing methods, methods such as sieving and calcination after beating are also employed.

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