Аннотация
The relevance of the topic is driven by the need to develop efficient and environmentally safe technologies for processing brown coal to obtain modified humic substances with tailored properties. This work investigates the effect of ultrasonic treatment on the physicochemical properties and molecular structure of humic acids derived from brown coal of the Oy-Karagay deposit (Republic of Kazakhstan). The study aims to substantiate and optimize the time parameters of mechanoacoustic treatment for the targeted production of physiologically active and bioavailable humic substances. Ultrasonic treatment of brown coal was performed in a specialized sealed container using a "UZV-1.3 Sapphire" ultrasonic bath (frequency: 35 kHz, power: 50 W) within a time interval of 15-90 minutes. Humic acids were isolated from the coal via aqueous alkaline extraction with sodium hydroxide, followed by precipitation in an acidic medium. The dynamics of technical composition changes were investigated using a MOC63u (Shimadzu) automatic analyzer and according to GOST 11022-95. The transformation of functional groups and the molecular framework was evaluated by Fourier-transform infrared spectroscopy (Bruker Tensor II), followed by the calculation of fundamental spectral indices. It was found that cavitation effects on the coal matrix proceed through a maximum and trigger coupled processes of ballast aliphatic periphery destruction and deep oxidation of the coal organic matter. Acoustic treatment for 45 minutes was shown to be optimal. This mode provides maximum hydrophilization of the matrix (sorption moisture increase up to 11.52%) and peak values of efficiency indices: aromaticity (Iar/al = 3.15), hydrophilicity (Ihyd = 1.48), and carboxylation (Icarb = 0.56). This indicates maximum structural saturation with active groups (–COOH, –OH) that form chelating and biostimulating capacity. Extending the treatment time beyond 60 minutes is impractical due to decarboxylation and secondary particle reagglomeration. The results obtained can be applied in technological schemes for the comprehensive processing of solid fossil fuels to produce highly effective organomineral growth stimulants and environmentally safe fertilizers for agriculture.