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

A. Muhammad Syahren and N.C. Wong

Abstract

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.

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