Ash limitation of physical coal beneficiation for medium–high ash coal—A geochemistry perspective

Nowadays the industrial coal beneficiation in China could only reduce the ash yield to about 10%, which could not meet the requirement or standard of environment protection. In this work, the possibility of reducing the ash yield was studied from the aspect of geochemistry. The channel samples were collected from two coal seams in Guizhou and Shanxi province, China and then conducted analysis by combining data from coals worldwide. The result reveals that the same coal seam or the coals deposited in the same peat swamp show a significantly positive correlation between ash yield and Al2O3 + SiO2 content, and the intercept of regression equation on the ash axis is always less than 5% (generally 2–5%). Overall, the coal from China is featured with a higher intercept compared with that in the other countries. The intercept of 2–5% on the ash axis indicates an original inorganic component in coal-forming peat. The research result also presents a theoretical limitation of coal ash by coal cleaning, because 2–5% of inorganic components in medium–high quality ash coal could hardly be separated by traditional physical coal beneficiation.