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Kaolin is a deposit of natural minerals containing hydrated aluminum silicate. Widely known as white clay or china clay, these minerals have desirable properties that are crucial for industrial and commercial applications. Therefore, kaolin mining and processing steps take into account the nature of the raw deposit and the end use of the product.
The mining stage is the process of extracting ore from its original or original mineral environment. It usually involves drilling procedures carried out in open pit or underground mining types. Electric and diesel shovels as well as large draglines are used in mining practice. Trucks transport the extracted mineral deposits to processing plants.
After the mining phase, kaolin undergoes further dry or wet processing stages.
Kaolin clay undergoes a drying process such as crushing, drying, crushing and classification to purify the sediment. Roller crushers can crush large pieces of raw kaolin clay to the required size.
These crushed kaolin enter the rotary dryer for further drying, crushing and air flotation procedures. The purpose is to eliminate coarse grit particles. Only fine particles move to the collection chamber, while coarse particles return to the crusher.
The wet processing process also begins with the mining stage, for example, by using water jet mining to extract coarse kaolin clay. A coarse grinder grinds the white clay deposits into smaller pieces, which are then mixed with water. Chemical dissolving agents are also added to form a slurry.
A centrifugal pump or high-pressure pump pushes the slurry from the drum to the settling tank, where the sand removal process begins. Screens, hydrocyclones, and hydroseparators or barrels also exist to eliminate coarse "grit."
A centrifugal separator then separates the slurry into a fine fraction and a coarse fraction. Fine-grained kaolin undergoes the most challenging and innovative processing. In other words, the centrifugal classifier classifies - 325 mesh desanded clay to produce fine or ultra-fine fractions according to the needs of different markets.
The largest users of fine-grained grades are coated paper, high-gloss coatings, specialty ceramics, rubber and ink industries. Meanwhile, the coarse-grained grade is ideal for use as fillers in paints, plastics, paper coatings and adhesives.
Chemical bleaching methods are also used at this stage to refine the material and remove some of the iron color or coloration caused by iron impurities. Sulfuric acid acidifies the clay slurry to approximately pH 3.0 to dissolve the iron component. The addition of strong reducing agents such as sodium dithionite or zinc converts iron into soluble sulfate.
The leaching (whitening and brightening) process is followed by filtration and dewatering using a centrifuge, filter press, tube filter or rotary vacuum filter. The filter-dewatered slurry enters the drying stage in a rotary dryer, spray dryer or apron.
Pre-dispersed clay is produced by adding a chemical dispersant and performing a centrifugal dehydration process with the help of a spray dryer. The rotary filter will extrude the kaolin particles, which are apron dried, producing lump clay and powdered clay.
As for the filter press, water and dissolved impurities are removed to form kaolin cakes and noodles, and apron drying is performed to form powdered clay. Kaolin powder is processed into kaolin powder through natural drying and disc grinding. If the press cake is placed in a dispersing and drum dryer, pre-dispersed clay is produced.
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