Chemical and Spectroscopical Characterization of Humic Acids from two South Brazilian Coals of Different Ranks

Abstract

Ácidos húmicos (HA) extraídos de carvões de diferentes ranks, de suas amostras regeneradas e de uma amostra nitrada, foram caracterizados por análise elementar e por espectroscopia de infravermelho (FTIR), de ressonância magnética nuclear de 13 C no estado sólido (NMR) e de ressonância paramagnética eletrônica (EPR). O HA de carvão de baixo rank apresentou maiores valores de teor de C e razão C/N e menores valores de teor de O e razões H/C e O/C do que o de alto rank. Resultados de RMN mostraram que ambas amostras foram mais aromáticas e menos carboxílicas do que HA comuns em solos. Estas características podem limitar o uso de HA de carvão como condicionadores e fertilizantes adequados para solos. A regeneração não provocou alterações relevantes, exceto pelo decréscimo no teor de radicias livres determinados por espectroscopia de EPR. Provavelmente as condições e o tempo de regeneração não foram adequados para oxidar as amostras. Os espectros de FTIR obtidos foram semelhantes, excentuando-se aquele da amostra nitrada, onde a banda de absorção em 1533 cm -1 comprova a presença de grupos nitrogenados. A nitração aumentou o teor de N e reduziu a razão C/N a valores comparáveis aos observados em HA de solos, porém a aromaticidade permaneceu alta e o teor de carboxílicos diminuiu após o processo.Humic acids (HA) extracted from two coals of different ranks, from their regenerated samples and from a nitrated sample, were characterized by elemental analysis and by infra-red (FTIR), solid state 13 C nuclear magnetic resonance (NMR) and eletronic paramagnetic resonance (EPR) spectroscopies. The low rank coal HA presented higher C and lower O contents, higher C/N and lower H/C and O/C ratios than high rank coal HA. NMR results showed that both samples were more aromatic and less carboxylic than common soil HA. Those characteristics may limit the coal HA efficiency as an appropriate soil conditioner and fertilizer. The regeneration process did not produce major alterations in the coal HA, except a decrease of the free radical content as determined by EPR spectroscopy. Probably, the regeneration conditions and time were not adequate to oxidize the samples. The obtained FTIR spectra were much alike, except that from the nitrated sample, where the absorption band at 1533 cm -1 confirms the presence of nitrated groups. The nitration process increased the N content and reduced the C/N ratio to values comparable to those reported for soil HA, but the aromaticity still remained high and the carboxylic content was lowered after the procedure.

Impact of HNO3 Solution Treatment of South Brazil Coal Matrices on Their Chemical Composition and Humic Acids Yield

“…These values are consistent with the values usually observed for HA in soil. 30,31 The FTIR spectra of HA extracted from the nitrated matrices showed, in general, the same pattern as the spectra of the nitrated coal samples (Figure 3). The main differences were: a shift of the band of C=O stretching from 1703 to 1713 cm -1 and of the band of C=C stretching from 1603 to 1613 cm -1 .…”

“…The presence of the band in 1526 cm -1 shows that during treatment with 25% HNO 3 solution, the incorporation of NO 2 in the coal structure occurred in the HA fraction as already seen in other coals from Southern Brazil. 31,32 The values of relative intensities of HA were, in general, similar between samples R-FOR and RBC ( Table 8), indicating that after treatment with HNO 3 solution the HA of these samples showed a similar chemical composition. These results corroborate the C/N data ( Table 7).…”

Characterization of Humic Acids from Raised Bog Peat

“…In humic substances from peat, concentrations of carboxyl groups and phenolic hydroxyl groups are lower (Table 1), than in humic substances from other sources (waters, soils, sediments) [2,5,6,29].…”

Three-dimensional interpolation of soil data: fertility and pedomorphological features in southern Brazil

“…In the upper parts (better drained areas and lower OC content), the volume of lower H concentrations extended up to the surface soil. The functional groups of organic matter and pH-dependent variable charges of the clay fraction minerals (kaolinite and Fe-and Al-oxides) are main sources of covalent H -dissociation of carboxylic and phenol groups from humic substances (Dick et al, 2002;Novotny et al, 2006), and of silanol (-SiOH), aluminol (-AlOH) and the iron group (-FeOH) from clay fraction minerals (Tarì et al, 1999).…”