Chemical demineralization/desulphurization of high sulphur coal using sodium hydroxide and acid solutions

Demineralization and desulphurization of high sulphur coal from Assam (Makum Coal fields), India was investigated using aqueous sodium hydroxide followed by hydrochloric acid treatment. Compared to the alkali and acid alone, successive treatments with the alkali and acid resulted in significant removal of mineral matters and sulphur from the coal. Demineralization and desulphurization were found to increase with the increase in alkali concentration. Alkali treatment resulted in formation and precipitation of sodium aluminosilicate, which subsequently undergoes decomposition and solubilization in presence of acid. It is possible to remove 43–50% of the ash, total inorganic sulphur and around 10% organic sulphur from the coal by treatment with 16% sodium hydroxide solution followed by 10% hydrochloric acid.