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Iron removal and whitening can be said to be an important means to improve the added value and application effect of kaolin. Usually, the whiteness of natural kaolin is reduced due to various impurities. Common impurities mainly include organic matter, iron, titanium, dark minerals, etc. Iron is often the main impurity that affects the whiteness of kaolin and will change when calcined at high temperatures. It forms Fe2O3, causing the raw materials to turn yellow or brick red, affecting the quality of kaolin products.
For strongly magnetic minerals such as magnetite, the ideal effect can be achieved by using weak magnetic separation. For weakly magnetic minerals, a high-gradient strong magnetic field magnetic separation method is required. This method can effectively remove weakly magnetic fine particles and even colloidal particles from useful minerals, and at the same time separate micron-level paramagnetic materials.
In production, common kaolin chemical treatment and purification methods mainly include chemical leaching, chemical bleaching and roasting purification.
Certain impurities in kaolin can be selectively dissolved by leaching agents such as sulfuric acid, hydrochloric acid, and nitric acid to remove impurities. This method is mainly used for iron reduction and purification of low-grade kaolin, such as the removal of hematite, limonite, and siderite. Mine etc.
In the actual production process, polyphosphate, ethylenediamine acetate, oxalic acid, citric acid, etc. can be used to form stable water-soluble chelates with metal ions to achieve the purpose of iron removal and bleaching of kaolin mineral processing.
Impurities in kaolin are oxidized into soluble substances through bleaching, and then washed and removed to greatly improve the whiteness of kaolin products. For example, iron in a poorly soluble state is converted into soluble iron, which is removed through a washing process. However, the cost of chemical bleaching is relatively high and is usually used for kaolin concentrates that require further purification after impurity removal.
Iron-containing impurities, carbon-containing impurities, sulfides and other impurities in kaolin can be removed by utilizing the differences in chemical composition and reactivity between impurities and kaolin, and performing treatments such as magnetization roasting, high-temperature roasting or chloride roasting.
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