Synthesis method of kaolin

Synthesis method of kaolin

(1) In order to separate quartz, feldspar, mica, iron mineral, titanium mineral and other non Clay mineral and organic matter from kaolin, and produce kaolin products that can meet the needs of various industrial fields, in addition to purification and impurity removal of kaolin by gravity separation, flotation, magnetic separation, etc., kaolin is sometimes treated by chemical bleaching, ultra-fine flaking, calcination, surface modification and other deep processing methods. The beneficiation and processing of kaolin can be divided into two processes: dry process and wet process.

(1) The dry method generally involves crushing the extracted raw ore through a crusher to around 25mm and feeding it into a cage crusher to reduce the particle size to around 6mm. The crushed ore is further ground by a blown Raymond mill equipped with a centrifugal separator and cyclone dust collector. This process can remove most of the sand and is suitable for processing ores with high whiteness, low sand and gravel content and suitable particle size distribution. The production cost of dry processing is low, and the products are usually used as low-cost fillers in industries such as rubber, plastic, and paper.

(2) The wet processing process generally involves crushing the raw ore and then passing through the processes of pulping, sand removal, cyclone grading, peeling, centrifuge grading, magnetic separation (or bleaching), concentration, pressure filtration, and drying. The resulting product can be used for ceramic or papermaking coatings. If preparing filler grade or paper coating grade kaolin, it is necessary to increase the calcination process, including raw ore crushing, slurry compaction, cyclone classification, peeling, centrifugal classification, concentration, pressure filtration, internal steam drying, calcination, depolymerization, etc.

(3) The calcination method is a widely used method for producing special kaolin products. It has four calcination temperature ranges: 500~700 ℃, 925 ℃, 1000 ℃, and 1400 ℃. Calcined at different temperatures, the resulting products have different application ranges. Calcined kaolin, which only removes hydroxyl groups, is used as a filler for cable plastic and rubber sealing rings; Kaolin calcined at 1000 ℃ can replace TiO2 as a paper filler; Kaolin, which has been calcined at 1300~1525 ℃, can be used as a filler for refractory products and as a lining for optical glass crucibles.

(4) In order to produce coating grade kaolin products, thick layered kaolin must be peeled into thin slices using wet grinding, extrusion, and chemical soaking methods The wet grinding method prepares kaolin into a slurry with a solid gas content of about 40%. After adding a dispersant, a grinding medium (such as quartz sand, ceramic beads, glass beads, nylon polyethylene beads, etc.) is added to a grinding machine. After grinding for a certain time, it is sieved, and then precipitated and graded to obtain The extrusion method sends kaolin slurry into a high-pressure homogenizer, pressurizes the high-pressure homogenizer to 20-35Mpa, and then sprays it out through a nozzle. Due to the sudden decrease in pressure, the kaolin crystal layers become "loose". The high-speed sprayed slurry is sprayed onto the impeller, suddenly changing the direction of movement, causing the loose crystal layers to peel off The chemical soaking method involves soaking kaolin powder in a saturated solution of urea, heating it to 30-80 ℃, and then adding a small amount of dispersant to fully disperse the kaolin. High speed stirring is carried out to peel off the crystal layers. Urea can also be replaced by Benzidine, acetamide, etc. Mix a neutral aqueous solution of AlCl3 with Na2SiO3 in a ratio of 1:0.75 to 1:5 to produce precipitation. Drying at 110 ℃ yields Al2O3 · 2SiO2 · 2H2O.

(5) The kaolin is ground, washed and desanded, treated with Mineral acid, washed to near neutral, and dehydrated above 3300 ℃