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Due to numerous and valuable properties of humic substances, preparations produced from alternative organic materials have been widely used in agriculture, bioremediations, dietary supplements and others. In addition to well-known humic acids, fulvic acids (FA) are a valuable product with a wide range of applications. The aim of performed examinations was to assess the thermal and physicochemical properties of FA obtained from lignite and peat using simplified conventional and ultrasound-assisted methods. DSC coupled with TG and MS, 13C NMR, FTIR spectroscopy and differential pulse voltammetry has been used to examine extracted FA. Depending on the source of FA and the extraction method applied, their structure and properties differ. Obtained FA fractions varied for both tested raw materials in terms of analyzed carbon structures, and the highest discrepancy was observed for carbonyl groups (20.2 pp) in fractions obtained by conventional extraction. The use of the ultrasound-assisted extraction (UAE), in comparison with the traditional method, lowered the ratio of carbon in carbonyl groups by 8.4 pp and increased the ratio of aromatic and aliphatic carbon by 3.5 and 4.9 pp, respectively, for FA obtained from lignite. As for FA obtained from peat, the UAE effect appeared to be less impactful in terms of structural changes. Thermal analysis showed that the products were thermally stable up to 100 °C, and the simplified extraction resulted in the creation of mineral-organic structures that decomposed at unusually high temperatures. Simplifying the extraction process, by excluding inorganic purification and protonation of obtained FA fractions, greatly affects product quality and limits its possible application. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the possibilities of using humic acids obtained from lignite in modern water treatment. The humic acids (HAs) were extracted from polish deposit of lignite – Sieniawa Lubuska by alkaline extraction using for this purpose following extractants: 0.1 M NaOH – HAs SN0.1 and 0.1 M Na4P2O7 – HAs SP0.1. In order to assess the impact of extractant on the sorption properties of the examined humic acids, their specific surface area and the content of active functional groups were determined. Thermo-oxidative behavior of examined humic substances was investigated employing the thermal analysis. The humic acids obtained from lignite were characterized also by 13C NMR spectroscopy. In addition to demonstrate the potential of examined humic acids as a low-cost reactive barrier material for environmental protection applications of toxic metals, sorption of Cr(VI) on the HAs was carried out using a batch method. The structure of obtained humic acids was undoubtedly influenced by the type of extractants used for their isolation. In structure of humic acids derived from lignite the aliphatic connections were dominated. Their participation in HAs obtained by using 0.1 M NaOH amounts to 78.9% and 58.5% for sample obtained using 0.1 M Na4P2O7. The highest content of all acidic functional groups - referred to total acidity (TA) is characterized by HAs obtained by extraction with 0.1 M Na4P2O7 and it was 7.69 mmol/g. In lignite humic acids the carboxylic groups, assigned to peak in the range of 160–190 ppm of 13C NMR spectra constituted for HAs SP0.1 – 3.54% and 2.40% for HAs SN0.1. The specific surface area for all humic acids samples was high from 370.0 to 394.4 m²/g and correlate with the results of humic acids acidity. The sorption of Cr(VI) on the surface of HAs depends strongly on the pH and Cr(VI) sorption increased with a decreasing pH. It was observed that the removal efficiency of Cr(VI) was the highest for SP0.1 and decreased from 79.8% to 66.5% with the rise of pH from 2 to 5. Therefore and because of the highly developed specific surface area of examined humic acids as well as the presence of hydrophilic functional groups resulting in their specific sorption and ion exchange properties can be an attractive and inexpensive option in the water treatment. [ABSTRACT FROM AUTHOR]