What are the mining and processing steps of kaolin?

Kaolin is a natural mineral deposit containing hydrated aluminum silicate. These minerals are widely known as white clay or china clay. Due to its excellent plasticity, cohesiveness, sinterability and refractory properties, kaolin is widely used in industries such as ceramics, papermaking, rubber, plastics and refractory materials. Kaolin mining and processing steps take into account the nature of the original deposit and the end use of the product.

1. Dry beneficiation process

Kaolin goes through a dry process of crushing, drying, pulverizing and grading to purify the sediment. The roll crusher breaks the bulky raw kaolin into the desired size. These crushed kaolin go into the rotary dryer for further drying, crushing and air flotation procedures. The purpose is to eliminate coarse grains. Only fine particles are moved to the collection chamber, while coarse sand is returned to the pulverizer.

2. Wet processing process

The process also begins at the mining stage, for example, by extracting coarse kaolin using water jet mining. White clay mineral deposits are ground into smaller pieces and mixed with water and a chemical dissolver is added to create a slurry or mud.

A centrifugal or high pressure pump pushes the slurry from the piston into the settling tank to start the desanding process. Screens, hydrocyclones and hydroclassifiers are also used to remove coarse material known as "grit".

The centrifugal separator then separates the slurry into fines and coarses. Fine-grained kaolin clay undergoes the most challenging and innovative processing. In other words, centrifugal classifiers classify negative 325 mesh desanded clays to produce fine superfine fractions required by different markets.

The largest users of fine particles are industries such as coated paper, high-gloss coatings, special ceramics, rubber and ink. At the same time, the coarse-grained grade is ideally suited as a filler in paints, plastics, paper coatings and adhesives.

This stage also uses chemical bleaching to refine the material and remove some rust or coloration due to iron impurities. Sulfuric acid acidifies the clay slurry to approximately pH 3.0 to dissolve the iron component. Addition of strong reducing agents such as sodium dithionite or zinc converts iron to soluble sulfate.

After the leaching (whitening and brightening) process, it is filtered and dewatered using centrifuges, filter presses, tube filters or rotary vacuum filters. The filtered dewatered slurry material is subjected to a drying stage in a rotary dryer, spray dryer or apron.

The centrifugation process with the addition of chemical dispersants and the aid of a spray dryer will produce pre-dispersed clay. The spin filter will extrude the kaolin noodles and pass through the apron drying to get lumpy clay and powdery clay.

As for the filter press, water and dissolved impurities are removed to form kaolin cakes and noodles, which are then dried through an apron to form powdered clay. Kaolin noodles become kaolin powder through natural drying and disc milling. If the press cake is put into a disperser and tumble dryer it will produce pre-dispersed clay.

If you have any questions about kaolin purification, welcome to inquire or consult online customer service.