Foam Flotation The purpose of flotation operations is to float titanium impurities from kaolin . Since the impurity particles are extremely fine, a carrier flotation process is usually employed. The carrier mineral may be calcite or silica sand (-325 mesh), and the amount of the carrier mineral is generally 10% to 20% by weight of the kaolin, and a part of the carrier may be reused. The agents used in the flotation process include: dispersant sodium silicate, pH adjuster amine hydroxide and caustic soda collector Tal oil, fatty acid and calcium petroleum sulfonate. However, flotation has many disadvantages. The hydrophobicization of the carrier requires a large amount of chemicals. The flotation process can only be effective at a lower concentration of the slurry, thereby increasing the cost of dewatering. The loaded body must be removed from the clay product as much as possible. Recycling in the product for recycling. Chemicals and carrier minerals remaining in the clay are detrimental to the final product. Cundy and Yong et al. studied a flotation process that does not require a carrier and floats anatase directly from kaolin, which is characterized by the presence of dispersants (such as sodium silicate) and pH adjusters (usually amine hydroxide). under conditions of high pulp density (40% to 60% solids) scrub, surface clean, while also scrub hematite and anatase away from the kaolin mineral in solution, a small amount of activator and then capturing fatty acids The slurry is added together with the slurry, and the anatase covered by the collector forms a selective agglomeration under high shear stirring conditions, so that the particle size is significantly increased, and the slurry after high shear stirring and slurry mixing is diluted to 15%-20. The % solid is floated and the alum in the kaolin can also be removed by flotation.
Selective coagulation / flocculation when pH8 ~ 11, was added to the kaolin slurry in Ca2 +, Mg2 + and other alkaline earth metal ions can be observed selectively flocculating the iron-titanium impurities, and then selectively flocculated by a polyelectrolyte weak anion. The process requires that the slurry concentration be less than 20%, so there must be a large amount of water to be removed in the subsequent operations, and the residual flocculant also has an impact on the quality of the final product. Selective flocculation of kaolin with high-molecular flocculant, the kaolin particles flocculate to the bottom, and the iron-titanium impurities are reddish brown in the suspension in the upper part due to the fine particles, and the upper suspension can be removed. Most of the iron-titanium impurities are removed and processed by other operations (such as magnetic separation) to obtain high-quality kaolin. Suzhou Kaolin Company has achieved good indicators by adopting a new process of selective flocculation. The use of selective flocculation and high gradient magnetic separation to treat kaolin also obtained satisfactory indicators. Leaching Leaching is carried out in the presence of a reducing agent (NaS2O4) in a weakly acidic solution (pH 3 to 4) to keep the dissolved iron in the Fe2+ state, avoiding the formation of Fe(OH)3, and washing it with water to separate it from the kaolin. In order to remove the dark organic matter, it can be bleached with a strong oxidizing agent (hydrogen peroxide, sodium hypochlorite, etc.), and the Suzhou Kaolin Company has obtained high-quality kaolin products by oxidative bleaching. It has been reported that treatment of kaolin with microorganisms can significantly improve the quality of the product.
Dehydration The selected clay is stored in a slurry tank for 6-8 hours, and the pH is adjusted to 3-4, which is close to the zero point of the clay, so that the clay particles are easily agglomerated. The addition of alum to the pulp contributes to the agglomeration of the clay particles and promotes dehydration. The cylinder filter is a commonly used dewatering device which increases the slurry concentration to 55% to 60%. One of the important functions of the filtration operation is to remove chemicals from the clay. To enhance this work, water spray is often used. Spray drying has become a very effective process in the clay industry, but it is expensive. In recent years, a new filtration process utilizing the electrophoretic properties of charged particles in an electric field has emerged. The kaolin particles are negatively charged at pH > 3 and are surrounded by an oppositely charged ion mist to form an electric double layer. In the electric field, the clay particles move toward the anode, and the counter ions in the ion mist move toward the cathode. When the particles reach the anode, they are used to protect the filter cake formed on the anode film of the electrode. The anode filter cake is further dehydrated by electroosmosis, and the excess water is pumped through the negatively charged filter cake capillary by the electroosmotic principle. The dehydrating agent is used to agglomerate the kaolin particles into large particles, which can accelerate the precipitation rate of the particles, facilitate the dehydration, and reduce the kaolin loss of the fine particles. Therefore, the development of the new high-efficiency dehydrating agent for kaolin is also one of its research directions.
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