№ 5 (2023)

Humic substances (HSs) extracted from brown coal, peat, and other sources are considered as an
efficient and affordable sorbent used to trap and bind heavy metal ions, which are hazardous to the environment.
This paper provides an overview of modern works on this subject matter. Typical structural characteristics
and properties of HSs and methods for their extraction from brown coal, peat, swamp waters, and other
media are described, and quantitative results of a wide range of experiments on the sorption of metal ions by
HSs are presented. Significant fluctuations in the measured sorption capacity of HSs in different experiments
probably arise not so much due to variations in the elemental composition and structure of HSs extracted
from different sources, but they are associated with experimental conditions, such as the acidity (pH) of solution,
ionic strength, concentration of metal ions, and concentration of HSs in the solution. In terms of the
order of magnitude, the maximum sorption capacity of HSs is comparable to the total concentration of surface
carboxyl and hydroxyl groups, and it amounts to several millimoles of metal ions per gram of HSs

The colloid-chemical properties of humic acids (HAs) were studied depending on the mechanochemical
modification of their structure. An increase in the amount of acidic ionogenic groups and hydrophilic
fragments in the composition of modified HAs facilitated a decrease in the excess energy of surface
molecules. In an alkaline solution, two types of colloids characterized by a decrease in the energy of adsorption and the constant of adsorption equilibrium were formed as the concentration of HAs was increased.

Experimental studies were carried with coal–water suspensions (CWSs) based on brown coal (grade 2B) with the addition of woody biomass of different types (pine sawdust and pine needles) in various concentrations (2, 4, and 6 wt %) on a fuel basis with a water content of 50%. It was shown that the addition of woody biomass to the coal–water suspensions is promising. An increase in the weight concentration of biomass in the CWSs significantly decreased the volume of anthropogenic emissions generated upon fuel combustion.

The dependence of the temperature of minimum electrical resistivity on the size of the mosaic blocks of artificial graphite of GMZ grade based on isotropic coke was calculated. A chain model of the electrical connection of lamellar structural elements (graphite flakes) was used. Compliance of the calculated results with Mason’s empirical formula was shown. Two cases were considered: the case of independence of the dimensions of mosaic blocks and the anisometry of the lamellar structural elements and the case when the dimensions of the mosaic blocks were proportional to the anisometry of the lamellar structural elements.

The characteristics of thermal decomposition and combustion processes on the heating of fine particles (100–200 m) of Chernogorsky coal, larch wood, and mixtures based on them, including the concentrations of the main components of flue gases (CO, CO2, NOx, and H2S + SO2), were determined using modern
techniques, analytical instrumentation, and experimental equipment. The biomass contents of the fuel mixtures based on coal were 10, 20, and 30 wt %. The temperatures at which the ignition of the coke residue occurred and the combustion process was completed were established using the synchronous thermal analysis of individual solid fuels and their mixtures. Larch sawdust was more reactive than Chernogorsky coal due to the lowest temperature at which the carbon residue was ignited; therefore, the addition of even 10% biomass to coal had a positive effect on the reactivity of the mixture. Under conditions of fuel heating in a flow of air at temperatures of 500–800C, the ignition delay times were determined using a hardware–software complex for high-speed video recording of fast processes. Based on the results of the experimental studies, it was found that the ignition delay times of the test fuels in a flow of heated air varied in a range from 0.02 to 0.22 s, and the addition of 10–30 wt % biomass to coal shortened the ignition delay times of fuel mixtures by up to 50%. The analysis of flue gases upon the combustion of solid fuels made it possible to establish the concentrations of the main anthropogenic emissions; the use of biomass as an additive to coal reduced the emissions of carbon
dioxide, nitrogen oxides, and sulfur compounds (H2S + SO2) by 2.2–13.5, 6.2–28.9, and 18.2–33.3%, respectively.