Main beneficiation and purification technologies and characteristics of kaolin
The purpose of purifying kaolin is to remove harmful dyeing impurities such as iron minerals, titanium minerals and organic matter to improve the whiteness of the product; on the other hand, to remove sandy minerals such as quartz and feldspar to improve Improve the quality of kaolin products, and then expand the breadth and depth of its application, and obtain better economic benefits while making full use of kaolin resources.
At present, the purification process of kaolin mainly includes gravity separation, magnetic separation, flotation, leaching, chemical bleaching and roasting.
1. Re-election
The gravity separation purification process mainly uses the difference in density and particle size between kaolin and gangue minerals to remove light organic matter and high-density impurities containing elements such as iron, titanium and manganese, so as to achieve the purpose of purifying kaolin and reduce or remove impurities. Negative impact on its whiteness.
2. Magnetic separation
The magnetic separation process is used to remove weak magnetic dyeing impurities such as hematite, siderite, pyrite and rutile in kaolin. Magnetic separation does not require the use of chemicals and has no pollution to the environment, so it is widely used in the purification process of non-metallic ores. The removal of weakly magnetic impurity particles in kaolin requires a high magnetic induction intensity and magnetic field gradient, and the development of magnetic separation technology and equipment upgrades have enabled the magnetic separation and purification of kaolin and other non-metallic minerals to be effectively realized.
3. Flotation
The flotation purification process can effectively remove iron, titanium and carbon impurities in kaolin, and realize the recovery and reuse of low-grade kaolin resources such as coal series kaolin. Kaolin has finer particles and is more difficult to float than gangue minerals. Therefore, reverse flotation is often used in the kaolin flotation purification process to achieve a better effect of removing impurities, such as reverse flotation carbon removal, desulfurization and iron removal. Kerosene is used as a collector, pine oil is used as a foaming agent, and water glass is used as an inhibitor. The flotation purification process is mostly used to treat kaolin raw ore with more impurities and lower whiteness, so as to realize the comprehensive utilization of low-grade kaolin resources.
4. Leaching
Leaching is a method of selectively dissolving and removing certain impurity components in kaolin through appropriate leaching agents, such as acid leaching and microbial leaching using hydrochloric acid or sulfuric acid. The leaching process is simple, energy-saving, can reduce production costs, and has good development potential. Using sulfuric acid with a concentration of 25% to acid-leach hard kaolin with high iron content for 5 hours, the iron removal rate can reach 37.67%. Because most of the iron in the raw ore exists in the form of pyrite, in order to achieve a better iron removal effect, oxidative acid leaching is carried out with H2O2 as the oxidizing agent. Coal series kaolin contains impurities such as pyrite, limonite and hematite. During the calcination process, pyrite will be oxidized into dark brown iron oxides, which will reduce the whiteness of kaolin. Thiobacillus ferrooxidans can decompose pyrite through catalytic oxidation, so it can be used to remove pyrite from kaolin.
5. Chemical bleaching
Ferric ions and their oxides are the main dyeing impurities that reduce the whiteness of kaolin. The method of removing these harmful impurities through chemical reagents is called chemical bleaching. The chemical bleaching method of kaolin is divided into oxidation method, reduction method and oxidation-reduction combined method.
The principle of the oxidation bleaching method is to oxidize the harmful coloring impurities in the reduced state into soluble substances, and then remove them. For example, oxidize pyrite into soluble ferrous sulfate, and then oxidize the organic matter and remove it by washing with water. Commonly used strong oxidants include sodium hypochlorite, potassium permanganate and hydrogen peroxide. The bleaching effect is affected by pH value, temperature, chemical dosage, pulp concentration and bleaching time.
The principle of the reduction bleaching method is to reduce the insoluble ferric oxide to soluble ferrous salt, so that the harmful element iron is converted into a soluble phase for dissolution, and then removed through the washing process. Commonly used reductive bleaching agents include sodium dithionite (Na2S2O4) and thiourea dioxide (HO2SC(NH)NH2).
6. Roasting
Roasting is also an important purification process to improve the whiteness of kaolin. Kaolin can remove carbon-containing impurities in it through roasting process, such as removing magnetic impurities through magnetization roasting and magnetic separation, and removing certain metal impurities through chlorination roasting.
Low-temperature roasting can remove surface and interlayer hydroxyl groups without destroying the kaolinite structure, and at the same time effectively decompose carbon-containing organic matter, so that the low-grade coal-measure kaolin can meet the requirements of glass fiber raw materials, and effectively realize the low-grade coal-measure kaolin resources. use.
Magnetization roasting converts iron-containing impurities in kaolin into strong magnetic or strong magnetic iron-containing minerals, and then removes impurities by magnetic separation. The purification effect of magnetization roasting on kaolin is better than that of traditional chemical bleaching methods.
Chlorination roasting is the addition of chlorinating agents during kaolin roasting to convert certain metal oxides and sulfide impurities into volatile chlorides to achieve the purpose of removing the metal elements.
7. Combined purification technology
It is difficult to obtain high-quality kaolin products by a single purification process, especially when dealing with low-grade coal-measure kaolin with large reserves in my country and kaolin with complex mineral composition. Different types of kaolin treatment processes are different, among which soft kaolin treatment process includes crushing, pulping, cyclone, selective flocculation, bleaching, centrifugation, peeling, magnetic separation; hard kaolin treatment process includes crushing, pulping, Cyclone, centrifuge, flaking, bleaching or crushing, roasting, pulping, cyclone, flaking, centrifuge; sandy kaolin treatment process includes pulping, spiral classifier, sedimentation, centrifuge, flaking, bleaching or raw ore , Pulping, Gravity Desanding, Blending, Flotation.
8. Stripping
Peeling is divided into mechanical peeling and chemical peeling, which is an important process of deep processing technology. It is necessary to peel kaolin into extremely thin sheets, and then go through magnetic separation to remove iron and bleach to meet the requirements of low wear and high whiteness. It is widely used in papermaking, Cosmetics, medicine, etc.