This research is part of a cycle devoted to establishing scientific principles for the control of coal’s physicochemical state in the exploitation of beds using injective grouting of cracks by active suspensions. The deactivating mixtures are filtrates of lime suspensions with different concentrations. The samples to which these suspensions are applied consist of long-flame coal of limited metamorphic development, which is highly susceptible to oxidation and self-ignition. Change in its surface wettability is assessed by liquid filtration through a layer of coal powder in a soil model. Steeping coal with suspension filtrates of pH 12.5 is found to produce uniform passivation of the coal surface, with change in its oxidative properties. This is accompanied by increase in wettability and mineralization of the coal surface. That must be taken into account in choosing the parameters of the suspension and the methods of bed deactivation.

The influence of a gas atmosphere during sample preparation, granulometric composition, the duration of contact with air, and the stage of metamorphism on the sorption of oxygen by coals from the atmosphere was established. It was shown that sample preparation performed in an atmosphere of air led to the primary oxidation of the outer surface of coals, which introduced an error in the subsequent determination of the rate of oxygen sorption. Fine coal fractions (0–0.2 mm) with a more developed outer surface exhibited increased oxygen absorption activity. The rate of oxygen sorption was maximal at the initial moment of the interaction of native coals with air, and it decreased with the duration of contact. The least metamorphosed hard coals of the D brand with a high concentration of reactive functional groups and a developed porous structure were characterized by the greatest chemisorption activity.

Thermogravimetric analysis is used for preliminary assessment of how ozonation affects the yield of coal tar factions in distillation. Since the distillation temperature of light fractions matches the main peak of gas liberation in coal tar pyrolysis, the yield of tar fractions may be indirectly assessed by means of the intervals corresponding to the boiling points of standard tar fractions: <170°C, light; 170–210°C, phenol; 210–230°C, naphthalene; 230–300°C, absorbing fraction; 300–360°C, anthracene; and 360–1000°C, pitch. Treating tar with ozone in the absence of solvents does not significantly change the yield of the fractions. By contrast, ozonation of coal tar in the presence of benzene and chloroform lowers the yield of fractions boiling below 300°C and significantly increases the mass loss in the temperature ranges corresponding to the anthracene fraction and pitch.

The structure of coal tar pitch produced from industrial tar and pitch produced from tar modified by ozone is compared. The pitch structure is identified by standard analysis of pitch, IR and NMR spectroscopy, and elemental and thermogravimetric analysis. Modification of tar by ozone increases the yield of pitch, its content of the α fraction, the yield of volatiles, and the softening temperature.

The change in surface properties of long-flame coal of limited metamorphic development on steeping with mixtures based on Portland cement is considered. The passivating liquids employed are the filtrate and suspension of cement solution used in grouting the bottom of mine workings. Treatment of coal with mineralized cement mixtures transforms surface groups that may be oxidized to groups that cannot be oxidized. The mineral layer formed on the coal surface prevents the development of oxidation. The results indicate that cement suspensions may be used to reduce the oxidation of the coal’s contact surface in mine workings.

The properties and efficiency of a solid–liquid suspension based on ground blast furnace slag, which is used to deactivate the processes of oxidation and spontaneous combustion of coals, have been studied. It has been established that sequential impregnation of coal with water-soluble and thickened components of the slag suspension promotes uniform passivation and a decrease in the oxidative activity of the external contacting surface. The results obtained justify the effectiveness of using slag waste as a constituent of technological suspensions for the insulation plugging of a coal seam.

The chemical composition of low- and medium grade Russian coal (ranks G, DZh, and Zh) on first exposure to the air is analyzed. The changes in the coal’s organic matter are recorded by means of diffuse-reflection infrared (IR) spectroscopy, electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR) spectroscopy. The variation in the number of paramagnetic centers and functional groups shows that the most significant changes in the structural fragments and surface layer of the coal occur within hours of exposure. Without further disturbance, residence in air for several days is accompanied by slow accumulation and loss of the radicals and the formation of functional O groups. For coal of low and moderate metamorphic development, • CH alkyl radicals and CO • phenyl and alkyl ester radicals react most with atmospheric oxygen.

The article presents the results of toothed screw crushing of coal on a laboratory scale. The samples are the marketable coal from different deposits in Russia, Kazakhstan and Kyrgyzstan. From the analysis of change in the quantity outputs of grain sizes, it is found that irrespective of the coal field location and coal grade, the use of a toothed screw crusher in coal preparation for dressing leads to no overgrinding of coal.

Many technological processes occurred upon the extraction and primary processing of coal (dust suppression, grouting, hydraulic fracturing, wet enrichment, etc.) depend on the wettability of the coal surface, determined by the physicochemical properties of the interacting media. The filtration properties of a fractured-porous coal massif significantly depend on the wettability of the surface. We present the results of studying the wettability of the coal surface with water and its filtration through a layer of coal powder. It is shown that the increased humidity of coal contributes to an increase in the wetting and filtration properties of the coal layer in relation to water due to the creation of a hydrate shell at the contact surface. It is revealed that the method of coal sample preparation significantly affects the functional composition and hydrophilicity of the outer surface of coal particles. Grinding coal in the presence of oxygen in air contributes to the formation of polar oxygen groups (hydroxyl, carboxyl) on the surface of coal particles, which leads to an increase in the hydrophilicity and filtration properties of coal. The results obtained can be used to predict the wettability of coals with process fluids, to improve technologies for mining, enrichment and processing of coals.

The method of liquid filtration through a layer of coal powder was used for a comprehensive characterization of surface wettability in conjunction with the determination of the contact angle. The effect of the degree of chemical maturity (metamorphism) of coal on the filtration characteristics of a layer with fractured porous properties was evaluated. Different activity of coal surfaces to water wettability upon a change from the native state to the surface-oxidized one was established. It was shown that the wetting and filtration properties of the coal surfaces increased from native to surface-oxidized coals and decreased as the degree of metamorphism increased from low to medium metamorphosed coals.

In a laboratory experiment, samples of SS coal prepared in an inert atmosphere (nitrogen) and by standard methods in air are compared. The surface changes of the coal particles are studied by IR spectral analysis and chemical analysis of functional oxygen groups. The wetting properties of the coal are assessed by complementary methods: determination of the limiting wetting angle for a liquid drop; liquid filtration through a layer of coal powder; and reagent flotation. Exposure of the coal surface to air during sample preparation perceptibly changes the function composition and hence the natural hydrophobic properties of the coal particles. The results may be used to refine estimates of the properties of undisturbed coal in beds and to improve methods of sample preparation and coal enrichment and processing.

Data on the analysis of the chemical composition and physicochemical properties of native low-metamorphosed coal at the initial moment of its contact with the air are presented. Diffuse reflectance IR spectroscopy, EPR spectroscopy, NMR spectroscopy, gas chromatography, chemical analysis of oxygen-containing groups, and the determination of the specific surface area and wettability of the contacting surface were used to identify changes in the organic matter of coal. The dynamics of changes in the numbers of paramagnetic centers and functional groups showed that the most intense transformations in the surface layer occurred in the first day of coal exposure to air. Next, oxidation at room temperature proceeded in a periodic mode of the accumulation and consumption of radicals and functional O groups. After four days, the process of low-temperature oxidation passed from the accessible outer surface into the diffusion region of the porous space of coal and gradually slowed down.

Ozone may be used to accelerate the oxidation of coal and hence to permit more rapid determination of its susceptibility to self-heating and self-ignition. In the present research, the coal is oxidized at 25°C, with low ozone concentrations (~10 mg/L), so as to moderate the destructive effect of secondary oxidative processes. The influence of the size and specific surface of the coal particles on the reactivity with ozone is assessed.

The susceptibility of coal to oxidation with stimulation by low concentrations of ozone (~10 mg/L) is considered. The influence of the coal’s metamorphic stage and its specific surface on its oxidation rate is assessed. For coal with a developed surface (low-metamorphic long-flame coal and high-metamorphic lean coal), the rate of ozone absorption and the degree of oxidation of the organic matter are greater.

The change in surface wettability of long-flame coal with little metamorphic development on first contact with air is analyzed. The wetting liquids considered are filtrates of cement suspensions of different concentrations, which are used to seal the external contour of mine workings. Wetting by water and cement solutions is better for surface-oxidized coal. The results indicate that cement suspensions may be used to reduce the oxidative activity of the coal bed's external contact surface.

The effect of ozonizing spent mineral oil on the dispersion of the emulsion during emulsification by blade impellers is considered. The disperse composition of the emulsion is determined by laser diffraction analysis. Optimal conditions are selected for dispersion of the emulsion and ozonization of the spent oil. Emulsified ozonized spent oils prove effective in intensifying coal flotation.

Ozone is employed to accelerate oxidation and hence shorten experiments regarding the susceptibility of coal to oxidation and self-ignition. To avoid profound oxidative destruction of the coal sample, experiments are conducted at 25°C and low ozone concentrations (~10 mg/L). The influence of the sample’s moisture content on the reactivity of coal with ozone is assessed. The oxidation rate declines when excess moisture is removed.