The kaolin iron removal process is a critical step in producing some of the world’s finest ceramics and clays. Iron is the main impurity ore for the purification and whitening of kaolin. Its occurrence state is diverse, often in the form of hematite, pyrite, siderite, limonite, anatase, ilmenite and other mineral forms, and sometimes it also contains mica and tourmaline. Kaolin is difficult to purify and maintain due to iron impurities. Since iron removal is the main measure for kaolin whitening, further research to improve each step of the kaolin beneficiation process is necessary to improve efficiency and reduce costs.
The minerals contained in natural kaolin are mainly divided into clay and non-clay minerals.
- Clay minerals: mainly contain kaolinite minerals and a small amount of montmorillonite, mica and chlorite;
- Non-clay minerals: Mainly contain hydrates of feldspar, quartz and calcium. Iron minerals such as hematite, siderite, limonite, etc., titanium minerals such as rutile, and organic matter such as plant fibers.
Importance of Purifying Kaolin
Kaolin also called China clay, is a non-metallic hydrated aluminum silicate crystal mineral. It is a kind of clay and clay rock mainly composed of kaolinite minerals. Because it is white and delicate, it is also called dolomite.
Wide range of applications
Kaolin is an essential mineral component in producing paper, rubber, paints and many other products. It is also used to increase crop yields and purify drinking water.
Kaolin has long been used to make pottery, porcelain and other ceramic products. It is also used in industrial applications such as papermaking, paint pigments, and rubber processing. The first step in preparing kaolin for these uses is to remove its iron content. This can be done through various processes involving heat or chemical treatment. Sometimes, irons can be washed off with water or other liquids. When dealing with higher concentrations of iron in clay or other pollutants that need to be removed, it must be treated by beneficiation.
To use kaolin for its intended purpose, purifying kaolin is a simple but important process that ensures the highest quality kaolin for manufacturing.
Whiteness is one of the main parameters of kaolin’s process performance, and kaolin with high purity is white. The color of kaolin is mainly related to the metal oxides or organic matter it contains. For example: Generally, Fe2O3 is rose red and brownish yellow; Fe2+ is light blue or light green; MnO2 is light brown; organic matter is light yellow, gray, blue, black and other colors. The presence of these impurities reduces the natural whiteness of kaolin.
When calcined at high temperatures, it will turn into Fe2O3, causing the raw material to turn yellow or brick red, affecting the quality of kaolin products. Because the physical method is cost-effective and can be tailored to the specific requirements of each application. Therefore, physical beneficiation methods are becoming more attractive in removing iron impurities from kaolin. This article will discuss how to effectively remove iron impurities from kaolin to purify kaolin.
Methods Of Removal Iron Impurities from Kaolin
In order to minimize the iron content in kaolin and increase its whiteness. Physical beneficiation methods are usually used to enrich kaolin raw materials or separate harmful substances. The physical way is low-cost and has little impact on the environment. Firstly, most impurity minerals are sorted out to purify kaolin.
1. Magnetic separation methods
Magnetic separation is the primary physical iron removal method. Iron mineral impurities in kaolin usually have weak magnetic properties and can be removed by magnetic separation. The effect of removing iron by ordinary magnetic separation is remarkable for magnetic solid minerals such as magnetite and ilmenite. However, iron mineral impurities in kaolin are usually weakly magnetic, and high-gradient strong magnetic separation is mainly used. This method can remove weakly magnetic fine and colloidal particles in iron minerals and different micron-scale paramagnetic materials. It is also possible to roast the weakly magnetic minerals first to convert them into strong magnetic iron oxides, then remove them by magnetic separation.
Under the magnetic field strength of the high-gradient strong magnetic separation method, the surface of the stainless steel magnetic gathering medium can generate a high magnetic field gradient, which can separate weak magnetic materials at the micron or colloidal particle level.
The high-gradient superconducting magnetic separation will remove weakly magnetic minerals more effectively and without pollution and will not destroy the crystal structure of kaolin.
2. Flotation Separation methods
(1) Carrier flotation method
The adsorption flotation method uses the standard mechanical agitation flotation machine as the leading equipment. In the flotation process, sodium silicate is mainly used as a dispersant. Ammonium hydroxide and caustic soda act as pH adjusters. Tal oil, fatty acid and petroleum calcium sulfonate are used as collectors. Then complete the flotation and titanium removal operation.
Since the adsorption carrier affects iron in kaolin, it also has various functions, such as absorption, coagulation, coercion, and mixed crystal. In addition, factors such as the pH value of the slurry system, the adding time, and the carrier’s location also seriously affect the separation effect of adsorption flotation. This makes the application of adsorption flotation limited to some extent.
(2) Double liquid flotation method
The fatty acid is added into the kaolin slurry to stir, stand still, and layered to form a double-layer suspension of organic liquid and kaolin, then separated by gravity separation equipment. The method has a good iron removal effect and can also recycle and regenerate the organic solution, and the recycling effect is good.
(3) Selective flocculation method
The selective flocculation method adds a flocculant to the fully dispersed pulp. The free harmful iron impurities dispersed in the ore pulp are selectively flocculated through the bridging effect between the flocculant and the surface of the ore particles. Then the flocs are separated from the ore pulp.
The pulp concentration is lower than 20%, and there is a lot of water in the production of this method, which needs to be removed in the subsequent process.
3. Coagulation and flocculation
The kaolin coagulation or flocculation method mainly removes iron and titanium impurities in kaolin. The pulp concentration must be lower than 20%, so a large amount of water needs to be released in the subsequent process.
Kaolin is wide application but often contains iron impurities that detract from its effectiveness. Fortunately, there are ways to remove these iron impurities so that kaolin resources can be used efficiently. The Kaolin iron removal beneficiation process can better control product quality and improve efficiency. Due to the differences in the origin and types of kaolin ore, it is necessary to choose the best iron removal and purification scheme according to the occurrence state of iron elements in industrial practice. In addition, understanding the physical and chemical properties of kaolin and iron, JXSC custom ore beneficiation plant and equipment will help create a more efficient method.