Abstract
Humic acid (HA) is a principal component of humic substances, which are the major organic constituents of soil, peat, coal, many upland streams, dystrophic lakes and ocean water. HA has an important impact on a variety of environment processes. This work aimed to characterize the HA extracted and purified from the Candiota coalfield (Brazil) by visible (VIS), Fourier transform infrared (FTIR), energy dispersive X-ray (EDX), inductively coupled plasma absorption emission (ICP-AES), and X-ray diffraction (XRD) spectroscopies, thermogra- vimetry (TG), differential thermal analysis (DTA), and scanning electron microscopy (SEM). The results of these analyses showed that Can- diota HA presents a high degree of humification, which is considered to be type A with a turbostratic structure. The elemental analysis (EDX/ ICP-AES) indicated the presence of low concentrations of heavy metals.
Highlights
The organic matter of soils can be divided into non-humic and humic substances
The purpose of this study is to characterize humic acids extracted from mineral coal from the Candiota coalfield (Rio Grande do Sul state, Brazil) using visible (VIS) absorbance, Fourier transform infrared (FTIR), energy dispersive X-ray (EDX), inductively coupled plasma absorption emission (ICP-AES), and X-ray diffraction (XRD) spectroscopies, thermogravimetry (TG); differential thermal analysis (DTA); and scanning electron microscopy (SEM)
The values of the E4/E6 ratio and the D log K coefficient for the CHA were 3.20 ± 0.10 and 0.42 ± 0.02, respectively, which are considered to be type A (D log K < 0.6 - high degree of humification), according to Kumada [14]. These results suggest that the Humic acid (HA)-C presents a high structural condensation and a large molecular size [17]
Summary
The organic matter of soils can be divided into non-humic and humic substances. Carbohydrates, amino acids, protein, lipids, nucleic acids, and lignins are non-humic substances that originate from plants and other organisms. HSs are major importers, exporters and transporters of solutes in soils and natural waters, and they play a much greater role than clays and minerals in this respect [5]. Based on their solubility properties, HSs are generally classified into the three following categories: humic acids (HAs), fulvic acids, and humin [6]. These three humic fractions are structurally similar and their properties differ, especially with respect to their molecular weight, their ultimate analysis, and the number of functional groups present [7]. The most important mineral coalfield in Brazil is the Candiota coalfield, which is located in the Rio Grande
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