Low temperature oxidation of coals of different rank and different sulphur content☆

Five coals of different rank and of different content of sulphur were subjected to oxidation by peroxyacetic acid (PAA), 5% nitric acid, by oxygen in 0.5N Na2CO3 aqueous solution and the air oxidation for 7 days at 125 °C. The processes of oxidation were carried out for coal samples demineralised by the Radmacher method, and additionally for the pyrite-free coal samples. Proximate, elemental and spectral analyses of the initial coals and the products obtained from them were made. The most effective oxidising agents were 5% HNO3 and PAA. As a result of oxidation, a significant part of the organic components of coal is converted into acid soluble products. Depending on the oxidising agent, the loss of sulphur in the solid oxidation products was different and the highest for the coal samples oxidised with HNO3 and PAA. Formation of oxidised sulphur species (SO and –SO2) was detected by IR spectroscopy. FTIR data also provide useful information on evolution of the molecular structure of different rank coals on oxidation, in particular in the carbonyl and aliphatic ranges (1800–1500 and 3500–2800 cm−1).