Uses and methods of washed kaolin

Washed kaolin has the characteristics of strong hiding power, high whiteness and uniform particle size distribution. It is widely used in the paper industry and can improve the printability, ink absorption and smoothness of paper. So what is washed kaolin? What are the purification methods and uses of washed kaolin?

What is Washed Kaolin?

Kaolin gets its name from the discovery of Gaoling Mountain in Jingdezhen, my country. Natural kaolin cannot be directly used in industries such as porcelain making, paper making, and coatings because it contains many impurities. Therefore, natural kaolin should be processed. According to different processing methods, it can be divided into washed kaolin and calcined kaolin. Therefore, washed kaolin is a kind of kaolin after deep processing.

Compared with calcined kaolin, washed kaolin has the characteristics of low processing cost and wide application, but its whiteness is slightly worse. Generally speaking, the whiteness of calcined kaolin will increase significantly, while the whiteness of washed kaolin will not increase significantly.

Purification method of washed kaolin

Washed kaolin purification process: After the raw ore is crushed, it is pounded, desanded, classified by a cyclone, peeled, classified by a centrifuge, magnetically separated (or bleached), concentrated, filtered, and dried.

1. Water selection method

The raw kaolin (rock) ore is made into mud, so that the minerals are dissociated in the form of granular monomers in water, and most of them are micron-sized fine particles. In order to remove the charge attraction on the particle interface, add an appropriate amount of dispersant to make the pulp concentration 5% to 14%, and the mineral particles in the pulp can be fully dispersed under the action of gravity. The principle is based on Stokes' law, that is, when a spherical object falls in a viscous body due to gravity, the falling speed is a constant and proportional to the square of the radius of the spherical object.

This method mainly removes clastic minerals such as quartz, feldspar, mica and relatively coarse-grained impurities such as cuttings. At the same time, it can also remove some iron and titanium minerals to improve the whiteness, but the increase is not large, generally not more than 90 %.

2. Flotation method

At present, the flotation processes applied to kaolin mainly include the following types.

(1) Selective flocculation

The process of selective flocculation is relatively simple. First, the solid particles in the suspension are fully dispersed, and then flocculants are added to selectively adsorb the target minerals (mineral particles or gangue fine mud). After the target minerals are flocculated, the flocculation is separated from the dispersed phase by means of flotation.

(2) Carrier flotation

Carrier flotation is to use the ore particles of general flotation particles as the carrier, so that the target mineral fine particles are covered on the carrier for flotation. Carrier flotation can reduce the TiO2 content to below 0.8%. The carrier can use the same kind of minerals or different kinds of minerals.

For xample, use sulfur as the carrier of fine-grained apatite flotation; use pyrite as the carrier to flotation fine-grained gold; use calcite as the carrier to flotation impurities such as anatase in kaolin; Choose Fe2O3 adsorbed in kaolin. Among them, calcite is a widely used carrier mineral, which has good buoyancy and is easy to remove in the form of foam.

(3) Double layer flotation

The principle of double-layer flotation is to use the difference in interfacial tension between solid (mineral particles)-liquid (water)-oil three-phase. Different mineral particles have different degrees of hydrophobicity between the three-phase interfaces, and they will enter different interfaces or phases. So as to achieve the purpose of separation.

The selective enrichment of ore particles at the oil-water interface is the theoretical basis of double-layer flotation. By adding a certain collector, the wettability of the mineral surface and the three-phase interfacial tension can be adjusted, and the fine minerals can be enriched at the oil-water interface, or the mineral particles can be extracted into the organic phase.

3. Magnetic separation

The dyed mineral impurities in kaolin (such as siderite, pyrite, limonite, hematite, ilmenite, rutile, etc.) have weak magnetic properties. Therefore, the kaolin after desanding is generally subjected to magnetic separation.

Because most of the iron and titanium minerals in kaolin are embedded with fine particle size, the general strong magnetic separation often has a low removal rate. Therefore, most of the industries currently use high-gradient magnetic separators for magnetic separation of kaolin. High-gradient magnetic separation refers to the selection of fine magnetic media under a relatively high background magnetic field (generally 1 to 2T) to generate a high magnetic field gradient (that is, a high magnetic force) on the surface, so as to achieve a level that cannot be achieved by general magnetic separation. purpose of magnetic separation.