Coal kaolin purification technology and research progress

　　Coal kaolin is a hard kaolin formed by deposition in the coal system, the main mineral composition is kaolinite and multi-water kaolinite, which is stored in the coal seam collusion and coexists with coal, which is unique to China. According to the different contents of coal-based kaolin Al2O3, SiO2 and Fe2O3, it can be applied to papermaking, rubber, chemical industry, metallurgy, ceramics, petroleum and other industries.

　　

　　With the expansion of demand for kaolin, mineral processing purification, acid leaching and calcination are the technical keys for the processing and utilization of coal-based kaolin. It is difficult to obtain high-quality kaolin products by a single process for coal-based kaolin purification, and a joint process combining multiple processes is required.

　　After 900°C calcination of coal-based kaolin, Zhu et al. leached 54.86% at a liquid-solid ratio of 1:3, a hydrochloric acid concentration of 2mol/L, and an iron leaching rate of 54.86%. Peng et al. used gravity separation to reduce the Fe2O3 and TiO2 content of coal-based kaolin by 48.57% and 59.57%, respectively.

　　Zhao Xuesong and others used the "first calcination and then bleaching" process to obtain a coal-based kaolin whiteness of 90.88%, which can be used for industrial rubber. Ren Ruichen et al. adopted the process of "purification - weak magnetism - high gradient magnetic separation - chemical bleaching - calcination" for the associated kaolin of the slime, and obtained a whiteness of 92.87% of the kaolin products, which met the requirements of the paper industry.

　　Using a coal-based kaolin in Sichuan as raw material, Ma Junhui et al. investigated the influence of grinding time, magnetic induction intensity, calcination temperature and other conditions on the purification effect, and the results showed that:

　　(1) Adopt the process of "ultra-fine grinding ore - tertiary magnetic separation - centrifugation - acid leaching - reduction calcination". The mass fraction of the grinding is 65%, the media filling rate is 50%, and the addition of 1% sodium hexametaphosphate ultra-fine stirring grinding ore is 190min, which can make the -2μm mass fraction account for 91.30%. Using a high-gradient strong magnetic separator, magnetic separation was made 3 times under the conditions of magnetic induction intensity of 1.4T, slurry flow rate of 1.0cm/s, and pulsation frequency of 400r/min; magnetic separation concentrate was centrifuged to extract 120min at 120min at 15% hydrochloric acid mass fraction and 90°C at 90°C, and calcined at 950°C. Finally, calcined kaolin concentrate products with calcined whiteness of 70.89% and 83.36% were obtained, and the iron removal rate reached 67.90% and 70.23% respectively, and the iron removal effect was obvious, which met the requirements of ceramic materials and had high product added value.

　　(2) High temperature calcination can remove the hydroxyl group to increase the whiteness, but the temperature should not be too high, and the temperature is too high, which will make kaolinite change to kaolinite and molai petrochemical, thereby reducing the whiteness.

　　Source: Ma Junhui, Ren Zijie, Gao Huimin, et al. Experimental study on kaolin purification of a coal system in Sichuan[J].Non-metallic Ore,2021,44(05):79-82", edited by [Powder Technology Network], please indicate the source!