The following picture shows the process flow of an annual production capacity of 30,000 tons of calcined kaolin in a kaolin company in China.
The process is briefly described as follows: the raw materials are crushed to less than 30 mm by a jaw crusher and then smashed into 4 JSM ultra-fine self-grinding mills , and the pulverized materials are finely classified by 4 air classifiers; (d97≤10μm) is directly fed into a flame-type rotary kiln for calcination. The coarse powder is pulped and then fed into a grinding and stripping machine for wet superfine grinding; the ultrafine slurry after grinding (d93≤2μm) is spray dried. After disintegration and depolymerization, two flame-spinning rotary kiln are calcined; some products after calcination of the fine powder are surface-modified with SLG continuous powder surface modification machine; wet-grinding-spray drying-calcination The powder fraction is further classified by a fine classifier to remove a small amount of coarse particles to obtain an ultrafine calcined kaolin having a fineness of -2 μm and a content of 86% ± 2%; and the other part is subjected to wet depolymerization and flash drying by a grinding and stripping machine. After drying, a paper-making grade superfine calcined kaolin having a fineness of -21 μm and a content of 92% ± 2% was obtained.
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.
1. Wet Process 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). thickness of two size fractions. 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, the clay mineral alum aggregation facilitate dewatering in the pulp. 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.
2. Dry Process The dry process is a simple and economical process. The produced ore is crushed to 25.4mm by a hammer crusher and fed into the cage crusher to reduce the particle size to 6.35mm. The hot air in the cage crusher reduces the moisture of the kaolin from 20% of the produced water. About 10%. The crushed ore is further ground by a blown Raymond mill equipped with a centrifugal separator and a cyclone [2]. 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 and the like, the product produced by Raymond 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.
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