HYDROGEN PEROXIDE OR NITRIC ACID.Low-rank coals are an important source of humic acids, which are important in retention processes of water and nutrients in plants.In this study coal samples of Montelibano, Colombia, were oxidized with air at different temperatures and subsequently with H 2 O 2 and HNO 3 .The materials were characterized by FTIR, proximate and elemental analysis, and quantification of humic acids.The oxidation process led to an increased content of oxygenated groups and humic acids in the carbonaceous structure.The solid oxidized with air at 200 °C for 12 h and re-oxidized with HNO 3 for 12 h showed the highest percentage of humic acids (85.3%).