Morphology and Mineral Composition of Humic Materials from Oxidized and Unoxidized Lignite

Oxidized and unoxidized samples of 2B lignite from the Tisul deposit of the Kansk-Achinsk coal basin are investigated. By means of a scanning electron microscope, the oxidized and unoxidized samples are shown to differ considerably in chemical and granulometric composition and also in particulate morphology of the humic and fulvic acids extracted from the lignite samples. These differences may be attributed to the chemical composition of the samples’ organic mass and mineral component. Oxidized lignite has a higher concentration of calcium (Ca), which binds predominantly with the organic mass; and iron (Fe), present as hematite. These elements pass mainly to the humic and fulvic acids, leading to the formation of particles that are denser and more amorphous. In contrast, the humic and fulvic acids from the unoxidized samples take the form of aggregates constituting a porous structure or sheet-like aggregates forming a laminar structure. Understanding the differences in chemical composition and morphology of the particles of humic and fulvic acids extracted from different forms of lignite is of great benefit for their practical application in fields such as ecology, agriculture, and the power industry.