Kaolin, also known as dolomite, is a clay mineral commonly found in nature. Kaolin is a useful mineral for making white pigments, and whiteness is the main performance parameter that affects the value of kaolin. Kaolin often contains harmful impurities such as iron, organic matter, and dark substances. These harmful impurities will cause kaolin to show different colors and affect its whiteness. Therefore, kaolin must be removed before using it.
Common kaolin purification methods include gravity separation, magnetic separation, flotation, chemical treatment, etc. Below, this article will introduce common kaolin purification methods:
1. Kaolin Gravity Separation
The gravity separation method mainly uses the density difference between gangue mineral and kaolin to remove high-density impurities such as light organic matter, quartz, feldspar and iron-titanium-manganese, thereby reducing the effect of impurities on whiteness. Centrifugal concentrators are usually used to remove high-density impurities. The hydrocyclone group can also be used to complete the washing and screening operations in the process of sorting kaolin, which can not only achieve the purpose of washing and classification, but also remove some impurities, which has good application value.
However, it is difficult to obtain kaolin products that meet the requirements by the re-selection method. In the end, the final qualified products still need to be obtained by magnetic separation, flotation, and calcination.
2.Kaolin Magnetic Separation
Almost all kaolin raw ore contains a small amount of iron minerals, generally 0.5% -3%, mainly including colored impurities such as magnetite, ilmenite, siderite, and pyrite. The magnetic separation method mainly uses these magnetic differences between gangue minerals and kaolin to remove these colored impurities.
For ferromagnetic minerals such as magnetite and ilmenite or iron filings mixed in the process, it is more effective to use magnetic separation to separate kaolin. For weakly magnetic minerals, there are two main methods: one is to roast first to change the mineral to ferromagnetic iron oxide, and then perform magnetic separation; the other method is to use a high gradient strong magnetic field magnetic separation method Magnetic separation. Because the magnetic separation method does not require the use of chemicals, it will not cause pollution to the environment, so it is widely used in non-metal beneficiation processes. The magnetic separation method effectively solves the problem of the development and utilization of low-grade kaolin that is not commercially valuable due to the high iron ore content. The superconducting magnetic separator has the characteristics of high field strength, energy saving, and high productivity, and can be directly processed. Kaolin with more impurities.
3. Kaolin Flotation
The flotation method mainly uses the difference in physical and chemical properties of the surface between gangue minerals and kaolin to treat kaolin raw ore with more impurities and lower whiteness, and removes its iron, titanium and carbon impurities to achieve low grade kaolin Comprehensive utilization of resources.
Kaolin is a typical clay mineral. Impurity minerals such as iron and titanium are often embedded between kaolin particles. Therefore, the raw ore must be ground to a certain degree of fineness, and the particle size mostly belongs to the mud-level particles mentioned in the flotation process. The commonly used flotation methods of kaolin are ultra-fine particle flotation method, double liquid layer flotation method and selective flocculation flotation method.
The flotation method can effectively improve the whiteness of kaolin, but its disadvantages are the need to add chemical agents, resulting in increased production costs and easy environmental pollution.
4. Kaolin Chemical Treatment
Chemical leaching: Some impurities in kaolin can be selectively dissolved by leaching agents such as sulfuric acid, hydrochloric acid, and nitric acid to remove impurities. This method can be used for the removal of hematite, limonite, and siderite from low-grade kaolin.
Chemical bleaching: Impurities in kaolin can be oxidized into solubles by bleaching, and then washed and removed to improve the whiteness of kaolin products. However, the cost of chemical bleaching is relatively high, and it is usually used for kaolin concentrate that needs further purification after impurity removal.
Roasting and purifying: By using the difference in chemical composition and reactivity between impurities and kaolin, magnetization roasting, high temperature roasting or chlorination roasting can be used to remove iron-containing impurities, carbon-containing impurities, sulfides, etc. Impurities. The method can improve the chemical reaction activity of the roasted product, greatly improve the whiteness of kaolin, and obtain high-grade kaolin products. However, the disadvantage of roasting purification is that the energy consumption is large and it is easy to cause environmental pollution.