Extraction and chemical characteristics of nitro-humic acids from coals and composts.

Yield of humic acids (HA) extracted from Mukah coals and different types of compost using potassium hydroxide (KOH) extraction method was low even under optimized extraction environment. However, when the coals were initially subjected to nitric acids (HNO3) oxidation followed by KOH extraction, nitrohumic acids (NHA) yield were 5–6 times higher than the HA equivalent. The amount of NHA extracted from composts was higher than the HA equivalent, although the increase was moderate. Mukah sub-bituminous coal produced the highest NHA (7 .50–88. 2%) yield using 3 M HNO3 at 50 °C while the Kapit bituminous coal required higher temperature i.e. 90 oC to obtain high NHA yield of slightly more than 60%. Mukah lignite yielded best at about 70% NHA using M HNO3 at 25 °C. The chemical characteristics of NHA were different from those of HA extracted from the same materials. NHA has lower C but higher O, H, N, total acidity, CEC, carboxylic and phenolic groups. Fourier Transform Infrared Spectroscopy (FTIR) spectra indicated that HNO3 oxidation had incorporated nitro (-NO2) group into NHA at ,540 cm – and nitroso (NO) group at ,364 cm-1 adsorption bands respectively. The HNO3 used in the oxidation process could be recycled without affecting the performance of the oxidation process of coals by adjusting its acidity to its desired strength after each oxidation event. Introduction Previous study of yield recovery of humic acids (HA) extracted from coals and compost (Asing et al. 2005) using strong alkali was disappointingly low at about 0%. However, oxidation of coals with various oxidation agents is well known to produce high yield of nitro-humic acids (NHA) (Hayashi and Nagai 96 ; Hansen and Schnitzer 967; Won 968; Green and Manahan 979; Patti et al. 992; Sim et al. 2006). The oxidation process degrades the complex coal molecule and humus substances in the compost into smaller alkali soluble humic substances. This procedure also mimics the long natural oxidation process of coals into HA rich oxidized coal called ‘Leonardite’. In principle, alkaliinsoluble high rank coals can be rendered soluble by oxidation which increases acidic groups in the coal molecule (Lawson and Stewart 989). NHA has similar chemical structure to HA but with additional nitro (–NO2) and nitroso (-NO) groups introduced into the NHA molecule during the nitration process