Extraction and Characterization of Humic Acid Based on Brown Coal from Kuznetsk Deposit
Abstract
The scientific novelty of this study lies in a comprehensive analysis of the physical and chemical properties of brown coal of the Kuznetsk deposit using modern research methods. Data on elemental composition, ash content, moisture and volatile matter yield of this coal are systematized and presented. Particular attention was paid to the study of the influence of functional groups on the reactivity of coal, which had not previously been studied in such a detailed form for this deposit. This research uniquely unveils and details the chemical structures of humic acids, offering a more comprehensive understanding of their makeup and functional aspects. The resulting activation energies ranged from 35.65 to 143.9 kJ/mol, with an average of approximately 73.3 kJ/mol, indicating the moderate thermal stability of humic acids derived from the feedstock. Optimal extraction conditions were achieved by treating brown coal from the Kuznetsk deposit with a 4% NaOH solution at 80°C for 2 hours, yielding up to 7% humic acids. Ultrasonic treatment enhanced the physicochemical characteristics of the coal, particularly by increasing the number of oxygen-containing functional groups, as confirmed by IR spectroscopy. The presence of hydroxyl groups was observed in the 3800–3550 cm⁻¹ range, while absorption bands between 1600–1250 cm⁻¹ indicated aromatic structures, suggesting a significant content of stable carbon bonds. The coal exhibited a microporous structure, with pore diameters around 5 nanometers, supporting its high adsorption capacity for gases and liquids. Additionally, nanoparticles approximately 1 nanometer in size were identified, possibly originating from organic matter decomposition or interactions between coal and mineral components, potentially affecting its reactivity. Thus, the research results obtained are a significant contribution to the field of coal chemistry and ecology, and can also serve as the basis for further research and development in the field of the use of humic acids as environmentally friendly additives and sorbents.