Abstract
In this study, for the first time, a comprehensive investigation of the thermal behavior and decomposition kinetics of humic acids (HAs) extracted from lignites of the Kumyskuduk and Kuznetsk deposits was conducted using thermogravimetric analysis. Kinetic analysis showed that the decomposition of the organic matrix requires lower activation energy than the final stage of carbon structure stabilization. The Kissinger-Akahira-Sunose (KAS) and Friedman methods demonstrated good consistency. It was shown that HAs from the Kumyskuduk deposit exhibit greater thermal stability, as reflected in the higher activation energy at the first stage of decomposition compared to the Kuznetsk samples. These differences may be related to the geological conditions of humic acid formation, including variations in mineral composition, degree of aromaticity, and functional group content.