Efficient removal behaviors and correlation rules of Na from Zhundong coal with low concentration organic acids

The effects on the removal of Na from Zhundong coal were investigated systemically using ten organic acids including seven aliphatic saturated acids and three aromatic acids as well as two inorganic acids of low con-centration. The results show that the structure and concentration of acids, leaching temperature and time are the main factors influencing Na removal from coal. The removal rate of Na, if only deionized water (DI) is used for leaching, is 52.03% resulting from water-soluble inorganic Na. When the acid concentration is 0.01 mol/L, the removal rate of total Na can reach 88.67-99.18% for aliphatic saturated acids, 85.26-89.38% for aromatic acids and 99.28-99.35% for HCl and H2SO4, indicating that the most organic Na can be removed by ion exchange between H+ and Na+ except for water-soluble inorganic Na. The removal amount of both total Na and organic Na increases basically linear with the increase of inorganic or organic acids until nearly the highest removal amount for different acids. The theoretical removal amount of Na and the optimum acid addition can be quantitatively calculated based on the correlation rules between the Na removal and the different acids, for example, ytotal Na (mmol/g) = 0.39xacid(mmol/g) + 0.099 for acetic acid (AA) and ytotal Na(mmol/g) = 0.56xacid(mmol/g) + 0.097 for HCl. The removal differences for various organic acids are mainly due to the difference in acidity and the molecular structure of organic acids. The Na2O content in coal ash decreases greatly from 6.21% for raw coal and 2.77% for water leaching coal to 0.22-0.95% for low concentration organic acids treated coal and ca. 0.21% for low concentration HCl and H2SO4 treated coal.