Kaolin processing technology-several methods of removing iron from kaolin

Kaolin is widely used in ceramic industry, paper making, rubber and plastic industry, chemical industry, paint industry and many other sectors. According to different uses, there are different requirements for the whiteness of kaolin.

For example, in the paper industry, it is required that the whiteness of coated kaolin must be greater than 83%, while in the ceramic industry, the raw materials used to manufacture high-grade porcelain require Fe2O3 <015%.

During kaolin processing, the application of traditional mineral processing technologies (conventional gravity separation, magnetic separation, flotation) cannot remove the impurity iron in kaolin fine powder and ultrafine powder to the standard content. Therefore, mineral processing personnel have another way to find a new non-traditional method of removing iron from kaolin, which greatly reduces the impurity iron content in kaolin, realizes the deep processing of kaolin and greatly improves the economic value. Here are several methods to remove impurity iron and improve the whiteness of kaolin.

Adsorption flotation method: In finely ground kaolin (fineness -43Lm, containing 0.72% Fe2O3), using carrier limestone powder and limestone powder as adsorbent, Fe2O3 is adsorbed from the slurry to the carrier of limestone powder. The carrier can rely on its hydrophobicity and that of the collector to adhere to the bubbles. An iron-containing carrier foam product and a kaolin concentrate-containing product are obtained. Therefore Fe2O3 can be separated from kaolin.

The equipment used for adsorption flotation is a conventional mechanical agitation flotation machine. The collector used was tall oil. Ammonium sulfate is used to inhibit kaolin. Sodium carbonate was used to adjust the pH and sodium silicate was used as a slurry dispersant. Since the adsorption of the carrier is the effect of adsorption, absorption, mixing, entrainment, etc., the pH value of the medium, the time and place of adding the carrier have a great influence on the adsorption flotation.

The double liquid flotation method is to transfer kaolinite to a certain concentration of aqueous slurry, add a pH regulator to adjust to the required pH value, mix for a certain period of time, add a suitable flotation agent, and continue to adjust the slurry for a certain period of time. After adding the organic solution and stirring for a suitable time, the organic phase product is obtained by static layering and separation.

The basic reaction of sodium bisulfite to remove iron is as follows: Fe2O3 + Na2S2O4 + 2H2SO4W2NaHSO3 + 2FeSO4 + H2O

The reaction reduces ferric iron to soluble ferrous iron, which is removed by filtration and washing. The reaction is reversible and requires immediate filtration and washing to prevent the oxidation of Fe2O3 to Fe2O3 in the air, which brings great difficulties to industrial production and it is difficult to achieve the expected iron removal index. However, an appropriate amount of chelating agent was added during iron removal with Na2S2O4. The chelating group and Fe2+ form a stable chelate, and the water-soluble functional group of the chelating agent promotes the hydrophilicity of the chelate, thus forming a stable water-soluble chelate. After kaolin minerals go through the bleaching process, the iron-containing chelate in the filtrate and the filtrate are removed, so as to remove the iron element in kaolin.

  In the process of selective flocculation and high-gradient magnetic separation, flocculants are added to kaolin slurry, so that the fine ore particles in the slurry are affected by polymer flocculants and linked into loose flocculant groups. After the high flocculation magnetic separator is separated, the iron content of the single flocculation product is reduced from 1.18% to 0.69% of Fe2O3, and then the final product containing Fe2O3 is reduced to 0.49%. The Fe2O3 content is 0.61%, and the Fe2O3 content in the secondary separation product is 0.52%, which cannot meet the requirement of Fe2O3 <0.5% for high-quality kaolin products. . Through the combination of selective flocculation and high gradient magnetic separation, the content of Fe2O3 in the product can be reduced to less than 0.5%. The method can greatly improve the quality of refractory kaolin with low iron content and high iron content, and find a new way for the raw material source of high-grade porcelain.