Kaolin is a general term for a group of clay minerals. Its basic composition is kaolinite group and halloysite group, mainly composed of kaolinite and halloysite, with a content of more than 90%, followed by hydromica, often mixed There are pyrite, limonite, anatase, quartz, chalcedony, alum, etc., and sometimes a small amount of organic matter.
The processing technology of kaolin raw ore depends on the nature of the raw ore and the final use of the product. There are two kinds of processes used in industrial production: the dry process and the wet process, usually hard kaolin is produced by the dry process, and soft kaolin is produced by the wet process.
The dry process is simple and economical. The mined raw ore is crushed to 25.4mm by a hammer crusher and then fed into a cage crusher to reduce the particle size to 6.35mm. The hot air in the cage crusher reduces the moisture content of kaolin from 20% mined to About 10%. The crushed ore is further ground by an air-blown Raymond mill equipped with a centrifugal separator and a cyclone dust collector. This process can remove most of the sand, and the product is usually used as a low-cost filler in the rubber, plastic, and paper industries. When used in the paper industry, this product can be used as a filler where the ash content of the filler layer is less than 10% or 12%, and the brightness of the product is not required at this time.
When the dry method has high requirements on the whiteness of the product, it is necessary to perform dry iron removal on the product produced by the Raymond mill. The advantage of the dry process is that it can save the product dehydration and dry operation process, reduce the loss of ash powder, the process flow is short, the production cost is low, and it is suitable for drought and water shortage areas. However, obtaining high-purity and high-quality kaolin depends on wet processing.
The wet process includes three stages ore preparation, mineral processing, and product treatment. The preparation stage includes operations such as batching, crushing, and mashing. Squeezing is mixing kaolin raw ore with water and dispersant in a pulping machine to make pulp. The mashing operation can disperse the raw ore, prepare kaolin slurry with appropriate fineness for sorting operations, and remove large grains of sand and stones at the same time.
The beneficiation stage may include hydraulic classification, flotation, selective flocculation, magnetic separation, chemical treatment (bleaching), and other operations to remove different impurities. The prepared pulp is first desanded by rake washing box, floating tank classifier, or cyclone, and then divided into two grades of thickness and fineness.
The fine-grained grade of the classifier is sent to HGMS (High Gradient Magnetic Separator) to remove iron and titanium impurities. After the product is stirred, scrubbed, and peeled off, iron oxide is leached. For clay with sufficient brightness and good coating performance, magnetic separation and Stripped and sent directly to leaching operations. After leaching, alum is added to the pulp to agglomerate the clay minerals and facilitate dehydration.
The bleached clay is dewatered with a high-speed centrifuge, rotary vacuum filter, or filter press. Filter or filter press for dehydration. The filter cake is redispersed into a 55% to 65% solid slurry, and then spray-dried to make a loose dry product. Part of the dry product is mixed into dispersed pulp to make 70% solids and shipped to the paper mill.
The final product without sorting has low brightness, and only by configuring magnetic separation, froth flotation, or selective flocculation in the process can clay products with high brightness be obtained. However, these independent operations have their advantages and disadvantages, so the industry usually adopts a joint process of two or three of these processes for the comprehensive utilization of clay resources.
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