Effects of acidic oxidation on the porosity of coal waste-derived chars Original Research Article

The effects of acidic oxidation and carbonisation temperature on the pore structures of chars from coal reject were studied in this work. The oxidation reactions were carried out by refluxing coal reject samples in nitric acid solutions under various conditions. Treated and untreated samples were then carbonised at 600°C. Acid concentration, residence time and reaction temperature were varied to investigate their effects on the pore structure of the resulting chars. The porosity of the carbonised coal reject samples was significantly enhanced by acidic pre-treatment. It is found that an increase in the severity of pre-oxidation (mainly by increasing the acid concentration) enhanced the pore structure of the chars significantly. It was also found that the chemistry of the nitrogen containing functional groups, brought about by acid pre-treatments, was dependent on the carbonisation temperature rather than the pre-treatment conditions.