Kaolin Mineral Processing Methods


At present, kaolin beneficiation and purification and processing methods mainly include aqueous medium floatation, classification, magnetic separation, flotation, chemical purification, microbiological method, bleaching, calcination processing, ultrafine grinding and surface modification. Because the genesis and types of kaolin mines in various places are different, the associated mineral impurities contained in them are different, so the methods of beneficiation and processing are different. Therefore, in the case of understanding the composition of mineral substances, the selection of mineral processing methods must be different, depending on the ore.

1. Water Medium Float-sink Method

Aqueous medium floating-sinking method refers to a beneficiation and purification processing method that uses water as a medium to separate useful minerals and impurity minerals by using the difference in the floating-sinking speed and solubility of various minerals in water. At present, this method is mainly used for the beneficiation and purification of sandy minerals such as quartz contained in kaolin ore. Many kaolin production enterprises in my country adopt this method.

This method is simple, easy to operate, and has low economic cost; however, this method mainly removes coarse-grained impurities such as quartz, feldspar, mica and other detrital minerals and rock debris, and can also remove part of iron-titanium minerals. Impurity minerals similar in density and solubility to kaolin cannot be removed, and the increase in whiteness is not obvious. It is suitable for the beneficiation and purification of relatively high-quality kaolin ore.

2. Classification

Classification is to use the difference in the size or density of mineral particles to separate minerals. According to different situations, the classification methods are different. If there is a big difference in the particle size of the minerals that make up the slurry, it is generally classified with a screen; if it is similar, it is sorted according to the difference in density. Commonly used grading equipment includes vibrating screens, water jets, hydrocyclones and centrifuges.

The role of classification is basically the same as that of the water medium float-sink method. It is mainly used to remove impurity minerals such as feldspar and quartz in kaolin ore, so that the purity of kaolin and calcined whiteness can be improved.

3. Magnetic Separation

Magnetic separation is a method of using magnetic force to remove magnetic metal impurities in materials. The application of magnetic separation is to use the magnetic difference of various ores or materials to carry out the separation process under the action of magnetic force and other forces. It is effective for removing high magnetic minerals such as magnetite and ilmenite, or iron filings mixed in during processing.

Almost all kaolin ore contains a small amount of iron and titanium minerals, mainly iron oxide, titanium oxide, ilmenite, siderite, pyrite, mica and tourmaline. These colored impurities usually have weak magnetic properties, so that these harmful impurities can be removed by magnetic separation.

4. Flotation

Flotation refers to the technical method of separating useful minerals from ore according to the different physical and chemical properties of the surface of mineral particles. The application of flotation to purify kaolin is very extensive, and the current technology and equipment are constantly being improved and updated, making the kaolin concentrate obtain higher whiteness, thereby meeting industrial needs.

The purpose of kaolin flotation is to remove colored minerals and improve its whiteness. Generally, it can be divided into carrier flotation and carrier-free flotation. The beneficiation method of kaolin was initially carrier flotation, and then the carrier-free flotation process was developed. The collectors used in kaolin flotation are mainly fatty acids such as dodecylamine, triethanolamine and pyridine. At present, hydroxamic acid is also used as a collector for kaolin flotation, and sodium or calcium lignosulfonate is used as a regulator. The pH value of the medium has a great influence. In an acidic medium (pH value less than 3), the grade of kaolin can reach more than 80%, and the recovery rate can reach 60%-68%. Ultrafine particle flotation can also be used. The purpose is to separate those fine particles that are difficult to be processed by foam flotation, that is, use carrier minerals less than 44μm to make the floatable particles adhere to the carrier mineral and separate with the foam product. The carrier mineral can be calcite, barite, sulfur, etc. There is no special reagent for ultra-fine flotation. Generally, the same flotation reagent is used to remove impurities in the raw ore, and water glass is used as a dispersant to improve the separation effect. At present, kaolin flotation at home and abroad has been widely used, and the effect is very good.

5. Chemical Purification

Chemical purification is a method that utilizes the acid-soluble or alkali-soluble characteristics of minerals that contain certain associated impurities, and uses acids or alkalis to remove them. Iron minerals and titanium minerals are the most common coloring substances in kaolin. Each type of kaolin has different degrees of distribution. Common iron and titanium minerals include: pyrite, limonite, hematite, siderite, and magnetite. Iron ore and titanium oxide, among which trivalent iron is the most common. These iron and titanium minerals will make kaolin show different degrees of gray, brown, pink, etc., and reduce the whiteness of kaolin.

Due to the different properties of iron and titanium minerals, different purification processes can be used. For kaolin with high iron and titanium content, reduction, oxidation-reduction, acid leaching, reduction complexation and other methods can be used for beneficiation, purification and whitening. Among them, the reduction complexation method is the most effective. Commonly used agents are sodium hypochlorite and hydrogen peroxide. , Potassium permanganate, hydrochloric acid, sulfuric acid and oxalic acid. At present, most of the purification and bleaching processes at home and abroad use chemical purification processes, which save costs and have higher purification whiteness than direct bleaching with bleaching agents. However, chemical purification still has a certain impact on the environment, and may affect the original properties of kaolin.

6. Microbiological Method

The microbial purification and processing technology of minerals is a relatively new subject of mineral processing. Its notable features are relatively low investment, low cost, low energy consumption, and low environmental pollution. The microbial processing and purification technology of minerals includes microbial leaching technology and microbial flotation technology. The microbial leaching technology of minerals is an extraction technology that uses the deep interaction between microorganisms and minerals. It is an extraction technology that destroys the crystal lattice of minerals, thereby dissolving useful components. Oxidized pyrite and other sulfide ore contained in kaolin can be purified and processed using microbial proposed technology. Commonly used microorganisms include Thiobacillus ferrooxidans and iron-reducing bacteria.

The microbiological method has low cost and low environmental pollution will not affect the physical and chemical properties of kaolin. It is a promising new purification and whitening method for kaolin mines.

7. Bleaching

The whiteness and brightness of kaolin used as pigments, fillers and coatings directly affect its value. The chemical bleaching method of kaolin is divided into oxidation method, reduction method and combined oxidation-reduction method. The chemical bleaching method can greatly increase the whiteness of kaolin products, but its production cost is relatively high, and it is mostly used to further purify the kaolin concentrate after impurity removal. The use of sodium dithionite and other chemicals will produce acidic waste gas and waste water, which will have a greater impact on environmental pollution. Therefore, environmental protection issues and economic rationality need to be considered when using this method. The future development trend should use cheaper and pollution-free bleaching agents.

8. Superfine Grinding

In order to meet the higher fineness requirements of kaolin in the papermaking, plastic and rubber products industries, it is necessary to increase the fineness of kaolin to improve the quality of the product. The superfine grinding process mainly includes grinding and stripping method, high pressure extrusion method, jet pulverization method and so on.

9. Calcining Processing

For coal series kaolin, calcination is required. Because calcination can remove carbon and improve whiteness, it is an indispensable process for beneficiation and a special processing method to improve the properties of kaolin. The use of calcined kaolin in the paper coating industry can increase the scattering power and coverage rate, and increase the ink adsorption speed. Used in cable filler to increase resistivity, in the synthesis of 4A zeolite, aluminum chloride and cryolite industry, calcination can increase the chemical activity of kaolin. High-temperature calcination can increase the whiteness and can partially replace the expensive titanium dioxide.

10. Surface Modification

In the application process of kaolin, modification is an important deep processing method. It is based on the active groups of kaolin (including aluminum alcohol groups, silanol functional groups, etc.), and changes the process characteristics of kaolin through mechanical, physical, chemical, etc. , To meet its application requirements in various fields and industries. At present, the most important modification method of kaolin is surface chemical modification. Commonly used surface modifiers mainly include silane coupling agent, silicone (oil) or silicone resin, surfactant and organic acid.

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