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Article

Non-Fuel Carbon-Neutral Use of Lignite: Mechanism of Bitumen and Humic Acid Interaction

by
Yuriy Prysiazhnyi
1,
Yurii Lypko
1,
Taras Chipko
1,
Denis Miroshnichenko
2,
Maryna Zhylina
3,4,5,
Mykhailo Miroshnychenko
2,
Hennadii Omelianchuk
2 and
Serhiy Pyshyev
1,*
1
The Department of Chemical Technology of Oil and Gas Processing, Lviv Polytechnic National University, 79013 Lviv, Ukraine
2
The Department of Oil, Gas and Solid Fuel Refining Technologies, National Technical University “Kharkiv Polytechnic Institute”, 61002 Kharkiv, Ukraine
3
Institute of Biomaterials and Bioengineering, Faculty of Natural Sciences and Technology, Riga Technical University, Paula Valdena Street 3, K-1, LV-1048 Riga, Latvia
4
Stende Research Centre, Institute of Agricultural Resources and Economics, Dizzemes, Dizstende, Libagu Parish, Talsu County, LV-3258 Talsi, Latvia
5
Institute of Materials and Surface Engineering, Faculty of Natural Sciences and Technology, Riga Technical University, Paula Valdena Street 7, LV-1048 Riga, Latvia
*
Author to whom correspondence should be addressed.
Clean Technol. 2025, 7(3), 81; https://doi.org/10.3390/cleantechnol7030081
Submission received: 12 June 2025 / Revised: 19 July 2025 / Accepted: 1 September 2025 / Published: 11 September 2025
Browse Figures
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Abstract

The study investigates the interaction of humic acids (HAs) with road petroleum bitumen to enhance its performance and resistance to technological aging. It addresses a critical gap in understanding the modification mechanisms. The research is motivated by the need for sustainable and effective bitumen modifiers to improve the durability of asphalt pavements. The primary objective was to characterize the interaction between HA and bitumen using advanced analytical techniques, including complex thermal analysis (DTA/DTG), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results demonstrated that adding two wt.% HA to bitumen BND 70/100 increased its thermal stability, raising the onset temperature of thermo-oxidative processes from 214 to 237 °C and reducing the mass loss rate during heating from 2.5 to 1.9%·min−1. FTIR analysis revealed chemical interactions between polar groups of humic acids (e.g., –COOH, –OH) and bitumen components, forming a denser structure. SEM images confirmed a more homogeneous microstructure with fewer microcracks in the modified bitumen. Practical improvements included a higher softening point (52.6 to 54 °C) and enhanced elastic recovery (17.5 to 28.7%). However, the study noted limitations such as reduced ductility (from 58 to 15 cm) and penetration (from 78 to 72 dmm), indicating increased stiffness. The findings highlight the potential of humic acids as eco-friendly modifiers to improve bitumen’s aging resistance and thermal performance, offering practical value for extending pavement lifespan. The effective use of HA will, in turn, allow the use of Ukrainian lignite, the balance reserves of which are estimated at 2.0–2.9 billion tons, in non-fuel technologies.

Graphical Abstract

1. Introduction

The modifiers of various natures are added to bitumen to provide the binder used to construct asphalt concrete pavements with the desired properties [1,2,3]. There is also a growing trend towards increased use of by-products of production, waste, bio-raw materials, etc., which increases the importance of “clean” technologies and the circular economy. Today, the list of these additives (traditional and alternative) is so extensive that, for convenience, it is more practical to classify them according to the raw materials from which they are produced. Thus, among the primary classes, the following can be distinguished: polymer and organic modifiers, mineral additives, surfactants (SAA), wax-based modifiers, and complex modifiers. Each of these groups of components is used for a specific purpose to impart unique properties to the binder [4,5,6,7,8,9,10,11,12,13].
Polymer modifiers are used to increase the hardness, elasticity, crack resistance, and durability of the pavement, as well as to improve the adhesion of bitumen to mineral materials and reduce the loss of properties due to aging. Mineral additives enhance the rheological properties of bitumen, providing it with thermal and water resistance. Various surfactants (SAA) improve the wetting of fillers and the adhesion of bitumen to stone materials. Wax-based additives help reduce energy consumption during the installation of asphalt concrete pavements. Complex modifiers combine several additives to achieve optimal binder characteristics [14,15,16,17,18,19].
It is proposed that lignite (brown coal), namely the humic acids extracted from it, be used as a potential resource for obtaining modifiers of road bitumen. Our research and analysis of the literature [20,21] have shown that humic acids or their salts (humates) are advisable to reduce road bitumen’s technological aging. In addition, humic acids can serve as a natural substitute for part of bitumen, since brown coal is a significantly cheaper raw material than oil, from which bitumen is produced: the average price for crude oil is 460/ton; the cost of lignite, depending on the conditions of occurrence, is 55–250 $/ton depending on the conditions of extraction and occurrence [22,23,24].
Potential brown coal reserves in Ukraine are estimated at 5.0 billion tons [25], and balance reserves are 2.0–2.6 billion tons [25,26,27]. The primary use of lignite is combustion in thermal power plants to produce electricity and heat. Today, green (carbon-neutral) technologies for using lignite are practically absent [28,29,30,31,32].
For the industrial production of bitumen modified with humic acids, it is necessary to comprehensively study the process of combining these two substances. In works [20,21], the influence of humic acids on the operational characteristics of road bitumen was established. At the same time, the nature of the interaction between humic acids and road petroleum bitumen remains unexplored. This is explained by the fact that the direction of using humic acids as modifiers of road bitumen is relatively new and poorly studied. Despite the positive influence of humic acids on several operational characteristics, the effective interaction (combination) of two substances, different in structure and state (solid humic acids with viscous liquid petroleum bitumen), raises many doubts and questions.
Today, numerous analysis methods are designed to determine the type of interaction between the modifier and the binder, and their effect on the performance characteristics of the resulting mixture. The most commonly used methods among these are [33,34,35,36]: Fourier-transform infrared spectroscopy (FTIR); MDSC analysis; structural-group analysis; scanning electron microscopy (SEM); SARA fraction separation; differential scanning calorimetry (DSC); gel permeation chromatography (GPC); quantum-chemical calculation; nuclear magnetic resonance (NMR); spectroscopy and microstructure analysis by atomic force microscopy (AFM); and complex thermal analysis (DTA/DTG).
Given the above, the study’s purpose was to establish the nature of the interaction of humic acids with road petroleum bitumen, making it possible to use the brown coal resource in a non-fuel technology for obtaining binders for road construction. For this purpose, the following analysis methods were used: complex thermal analysis (DTA/DTG), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).

2. Materials and Methods

2.1. Materials

Humic acids and oxidized road petroleum bitumen were used as raw materials for the experimental studies. The humic acids were extracted from a composite sample of Ukrainian-origin brown coal (Cherkasy region, Ukraine), Figure 1A. Humic acids were obtained according to the standard method [37], improved by the authors [38]. The extraction method involved crushing the brown coal (particle size ≤ 0.2 mm), extracting the humic substances with a sodium hydroxide solution, neutralizing the resulting solution with acid to precipitate the alkali-soluble fraction (humic acids), filtering, and drying. The output of HA was −87.60 wt.%. The obtained humic acids were mechanically crushed and classified using a sieve with a hole size of 0.14 mm. The qualitative and quantitative analysis of the obtained humic acid sample (fraction ≤ 0.14 mm) is presented in Table 1 and Figure 1B.
A sample of oxidized road petroleum bitumen of grade BND 70/100 was collected at the PJSC “Ukrtatnafta” oil refinery in Kremenchuk, Ukraine. The physicochemical characteristics of the original bitumen and the sample with the addition of humic acids are presented in Table 2.

2.2. Experimental Procedure

Modifying oxidized bitumen with humic acids was performed under the following conditions: temperature—120°C; modifier content—2.0 wt.%; mixing duration—1 h; and mixing intensity (Daihan Scientific HT-50 DX mixer, Wonju, Republic of Korea)—1000 rpm.
The numerical values of these modification parameters were selected based on studies that had previously been conducted, particularly [21]. It should be noted that the content of humic acids in bitumen at the level of 2.0 wt.% is optimal in terms of their effect on the performance characteristics of the binder. Therefore, the resulting sample (bitumen modified with 2.0 wt.% humic acids) was used for complex thermal analysis and Fourier-transform infrared spectroscopy.
However, to obtain a micrograph using scanning electron microscopy, the content of humic acids in the bitumen was increased to 12.0 wt.% to enable a more detailed visual assessment of the impact of humic acids on the structure of road bitumen (microphotographs of a bitumen sample modified with 2% by weight of humic acids practically did not differ from microphotographs of a sample of the original bitumen).
Thus, Table 3 lists the names of the studied samples and their affiliation to the research methods used.
The modification process was carried out according to a standard methodology. The road bitumen was heated to the specified modification temperature while continuously stirring. Once the target temperature was reached, the predetermined amount of modifier was added, and the blending process was continued for the specified duration.
Complex thermal analysis of the bitumen and humic acid samples was performed using a Q-1500 derivatograph of the “Paulik–Paulik–Erdey” system (Paulik–Paulik–Erdey system, Magyar Optikai Művek, Budapest, Hungary), connected to a personal computer (Linseis TA Software, version 2.3.3.150, evaluation module). The samples were heated in an air atmosphere up to 400 °C. The heating rate was 5 °C per minute, and the sample mass was 200 mg. Aluminum oxide was used as the reference material.
Micrographs of the binder and humic acid samples were obtained using scanning electron microscopy on a REMMA-102-02 scanning electron microscope and microanalyzer (Open Joint Stock Company “SELMI”, Sumy, Ukraine). This type of microscope enables non-destructive analysis of bulk samples and solid-phase microparticles, both specially prepared and in their natural state. Surface scanning is performed using an electron beam with a diameter of several nanometers and electron energies ranging from 0.2 to 40 kV. The magnification range is from 10 to 300, and the resolution is approximately 5.0 nm (as specified in the technical documentation).
IR spectra of bitumen and humic acid samples were recorded using a Spectrum Two spectrometer (PerkinElmer, Waltham, MA, USA) equipped with a single-reflection U-ATR diamond crystal. PerkinElmer Spectrum 10 software was used for spectrum construction. The spectra (16 scans per spectrum) were collected in the mid-infrared region, covering wavelengths from 4000 to 400 cm−1, with a spectral resolution of 4.0 cm−1. IR absorption bands were identified by [34,35].
For the IR spectra of the studied products, baseline correction was applied, and the heights of the absorption bands were measured relative to the corrected baselines. The band heights were normalized to relative values for approximate quantification and spectral comparison, with the total height of all bands considered 100%. Among all the bands, 16 were selected for confident interpretation by correlating specific bands with corresponding types of atomic vibrations and chemical bonds. The sum of the relative heights of these 16 bands ranged from 74 to 85%.
Two parallel tests were performed for each sample for the DTA/DTG and FTIR analysis methods (Table 3). The average values were determined for the results obtained, which are presented in the next part of the manuscript. For the SEM analysis method, for each sample (Table 3), 2 to 5 micrographs were taken at different locations on the surface. The most informative micrographs are presented in Section 3 of this manuscript.

3. Results

Table 4 and Figure 2, Figure 3, Figure 4, Figure 5 and Figure 6 presents the results of the complex thermal analysis of humic acid samples and the original and modified bitumen. It should be noted that the nature of the curves of the starting materials is similar to that of similar studies of bitumen and HA [52,53].
The mass loss (11.48%) of the humic acid sample in the temperature range of 20–170 °C corresponds to the release of moisture Figure 2. This process is accompanied by a gradual mass loss from the sample and the appearance of an endothermic effect on the DTA curve. Subsequently, a significant mass loss (11.84%) in the temperature range of 170–334 °C corresponds to the initiation of thermo-oxidative processes. On the DTA curve of the sample in this temperature range, an apparent exothermic effect appears, with its maximum occurring at 300 °C. At temperatures above 334 °C, active destructive and thermo-oxidative processes begin to develop in the humic acid sample, corresponding to a mass loss and a sharp exothermic effect on the DTA curve.
The gradual mass loss (1.69%) of the bitumen sample in the temperature range of 214–303 °C, which is accompanied by a deviation of the DTA curve into the region of exothermic effects, corresponds to the initiation of thermo-oxidative processes Figure 3. The sharp mass loss of the bitumen sample (20.06%) in the temperature range of 303–393 °C corresponds to intense thermo-oxidative processes, accompanied by a rapid exothermic effect on the DTA curve, with a maximum at 382 °C, and a distinct extremum on the DTG curve. The maximum mass loss rate at this stage is 2.5% per minute.
On the DTA curve of the bitumen sample modified with humic acids, a shallow endothermic effect appears in the temperature range of 75–200 °C, which is not accompanied by the release of volatile components. This effect corresponds to the softening of the modified bitumen. The gradual mass loss (1.50%) of the modified bitumen sample in the temperature range of 237–305 °C, which is accompanied by a deviation of the DTA curve into the region of exothermic effects, corresponds to the initial thermo-oxidative processes in the sample. The sharp mass loss of the bitumen sample (17.83%) in the temperature range of 305–389 °C corresponds to intense thermo-oxidative processes, accompanied by a rapid exothermic effect, with a maximum at 376 °C, and a distinct extremum on the DTG curve. The maximum mass loss rate at this stage is 1.9% per minute.
Based on the comprehensive thermal analysis results, the modified bitumen sample exhibits higher heat resistance and thermal stability, unlike the original bitumen sample. The softening of the bitumen sample modified with humic acids in the low-temperature range is accompanied by a shallow endothermic effect, indicating the formation of a denser structure during the modification process, as shown in Figure 4.
The thermo-oxidative processes in the modified bitumen sample begin at higher temperatures (237 °C), compared to the original bitumen sample (214 °C). A less rapid mass loss accompanies these processes in the modified bitumen sample than in the original bitumen Figure 5. The maximum mass loss rate of the modified bitumen sample is 1.9%·min−1. In comparison, the maximum mass loss rate of the original bitumen sample is 2.5%·min−1.
The higher thermal stability of the bitumen modified with humic acids compared to the unmodified bitumen, indicated by the shallow endothermic effect during the softening of the bitumen samples at lower temperatures, and its higher thermal stability at increased temperatures, may result from two types of processes:
  • The bitumen chemically interacts with the humic acids, forming new compounds with a denser structure that are more heat resistant than unmodified bitumen.
  • As a result of intensive dispersion of solid humic acid particles within the bitumen, through intermolecular interactions of a physical nature, complex structural units (micelles) with a denser structure are formed with some of the bitumen’s hydrocarbons or their groups, which are more heat resistant than unmodified bitumen.
Infrared spectroscopic studies were conducted to confirm or refute these hypotheses. The obtained results are presented in Figure 7 and Table 5. It should be noted that the nature of the IR curves is similar to that of similar studies of HA [54].
Based on IR studies, bitumen contains aromatic, aliphatic, and cycloalkane structures. The aromatic structures of bitumen (unlike humic acids) contain side chains (peaks 813–745 cm−1). Bitumen can also include a few reactive oxygen-containing structures (mainly acids and methoxyl esters). Lignite humic acid’s most pronounced absorption bands are peaks corresponding to methoxyl, carboxyl, ether, and ether groups (contained in bitumen in much smaller quantities or absent), coinciding with similar studies [34,35]. In addition, the studied humic acids can include organometallic compounds (peaks 532, 465 cm−1), which are most likely humates (products of the interaction of the organic and mineral parts of coal). After mixing humic acids with bitumen, some peaks characteristic of reactive oxygen and organometallic groups disappear (1169, 1007, 912, 532, 465 cm−1). Based on this, it is possible to hypothesize about a partial chemical interaction of humic acids, lignite, and bitumen even at a temperature of 532, 465 cm−1.
The microstructural changes in bitumen BND 70/100 after modification with humic acids, as shown in Figure 8, Figure 9 and Figure 10, significantly impact its physicochemical properties. Humic acids (Figure 8) are characterized by a fine-dispersed structure with particle sizes ranging from 20 to 200 μm (mainly 20–50 μm), which is confirmed by their high specific surface area and the presence of inorganic inclusions (ash content 7.90% by mass). Their non-branching morphology indicates their ability to disperse effectively in bitumen.
The unmodified bitumen (Figure 9) has a typical structure for oxidized bitumens: the viscous maltenic phase (olive components) forms a dispersion medium, in which asphaltenes and resins (the dispersed phase) are uniformly distributed. After introducing 12% by mass of humic acids (Figure 10), a denser and more homogeneous structure is observed, with fewer microcracks than the unmodified bitumen. This is due to the formation of strong intermolecular bonds between the polar groups of humic acids (–COOH, –OH) and the functional groups of bitumen, which is confirmed by the increase in the temperature of the onset of thermooxidation from 214 to 237 °C Table 3.
The micrographs (Figure 8, Figure 9 and Figure 10) visually demonstrate the morphological changes in bitumen after modification with humic acids (HAs), such as a denser, more homogeneous structure with fewer microcracks. Still, they do not directly reveal the chemical or molecular interaction mechanisms. The study instead relies on FTIR spectroscopy and thermal analysis to infer the mechanism, concluding that polar groups (e.g., –COOH, –OH) in HAs likely form strong intermolecular bonds with bitumen components. While micrographs confirm structural improvements, the interaction mechanism is deduced from complementary analytical techniques rather than imaging alone.
Additionally, the mass loss rate during heating decreases (from 2.5 to 1.9%·min−1), indicating an improvement in thermal stability. These structural changes correlate with enhanced performance indicators: the softening point increases from 52.6 to 54 °C, elastic recovery rises from 17.5 to 28.7% (Table 2), and the sensitivity to technological aging decreases (softening point change after RTFOT decreases from 6.8 to 5.4 °C). At the same time, a slight decrease in penetration (from 78 to 72 dmm) and elongation (from 58 to 15 cm) is observed, indicating an increase in the stiffness of the modified bitumen.
Thus, when integrated into the bitumen matrix, humic acids form a more stable and stronger structure, which ensures improved resistance to temperature loads and oxidation, a key factor for the durability of asphalt concrete pavements.
Our study on humic acid (HA)-modified bitumen demonstrated significant improvements in thermal stability and aging resistance, aligning with the findings of references [55], where HAs were used to enhance biodegradable polymers and hydrogels. Similar to these studies, we observed that HAs increased the thermal stability of bitumen, raising the onset temperature of thermo-oxidative degradation from 214 to 237 °C, comparable to the enhanced thermal resistance reported for HA-modified hydrogels. FTIR analysis confirmed chemical interactions between HA polar groups (e.g., –COOH, –OH) and bitumen components, paralleling the hydrogen bonding and structural reinforcement observed in HA-polymer composites [33]. SEM results revealed a denser, more homogeneous microstructure in modified bitumen, analogous to the uniform morphologies reported for HA-blended films [36]. However, while references [33,34,35,36] emphasized improvements in flexibility and biodegradability for biomedical or packaging applications, our study focused on bitumen’s mechanical performance for road construction, noting trade-offs such as increased stiffness (reduced ductility from 58 to 15 cm) alongside superior aging resistance. This distinction highlights the material-specific effects of HA modification: in polymers, HAs often enhance elasticity, whereas in bitumen, they promote rigidity and durability. Despite these differences, both research streams underscore HAs’ versatility as eco-friendly modifiers capable of tailoring material properties through interfacial interactions. Our work extends the applicability of HAs to bitumen, addressing oxidative aging (a critical challenge in pavement engineering) while studies [33,34,35,36] showcase their potential in sustainable biomaterials. Together, these works illustrate the broad utility of HAs in enhancing material performance across diverse fields, from construction to biodegradable technologies.
Understanding the interaction mechanism between HA and lignite will increase the likelihood of developing an industrial technology for modifying bitumen with coal processing products. The content of humic acids in Ukrainian brown coal is predicted at 30–50 wt.% (per analytical sample) [56]. With an average content of 40 wt.% and the amount of lignite balance reserves of 2.0 billion tons, obtaining 800 million tons of humic acids is possible. According to [57,58], in the last 2–3 years, the consumption of road bitumen in Ukraine has not exceeded 500 thousand tons/year. The optimal amount of humic acids added to bitumen to inhibit aging is 2.0 wt.% (per mixture) [20,21]. Thus, using humic acids as a modifier of road bitumen, it will be possible to increase bitumen production by 10 thousand tons/year (500,000 × 2.0/100 = 10,000 tons). For this, the extraction of 25,000 tons/year of lignite of any quality is sufficient.
In addition, it should be noted that, as predicted in Section 1, humic acids and/or humates can be significantly cheaper than bitumen: the cost of road bitumen of the 70/100 grade is USD 380–400/ton; HA—USD 90–140/ton (with open-pit mining of lignite in the form of leonardite) [59,60,61]. Modified bitumens with improved indicators (relative to the original oxidized bitumen) are usually 6–8% more expensive [59,60].

4. Conclusions

The comprehensive thermal analysis of bitumen, humic acids, and their mixture showed that the modified bitumen sample, in contrast to the original bitumen sample, has higher thermal stability. The softening of the bitumen sample modified with humic acids in the low-temperature range is accompanied by a shallow endothermic effect, indicating the formation of a denser structure during the modification process. Thermo-oxidative processes in the modified bitumen sample begin to develop at higher temperatures (237 °C), compared to the original bitumen sample (214 °C). The maximum mass loss rate of the modified bitumen sample is 1.9%/min, while the maximum mass loss rate of the original bitumen sample is 2.5%·min−1. All this indicates possible chemical connections between bitumen and humic acids. In addition, the higher thermal stability and the decreased mass loss of the modified bitumen (compared to the original bitumen) indicate its lower susceptibility to aging.
IR studies show that after mixing humic acids with bitumen, some peaks characteristic of reactive oxygen and organometallic groups disappear (1169, 1007, 912, 532, 465 cm−1). Based on this, it is also possible to hypothesize a partial chemical interaction of humic acids with lignite and bitumen even at 120 °C.
The microphotographs of the studied samples showed that after adding humic acids to the road bitumen, a more dense and homogeneous bitumen structure was formed with fewer microcracks. This is due to strong intermolecular bonds between the polar groups of humic acids (–COOH, –OH) and the functional groups of bitumen. It is confirmed by the increase in the onset temperature of thermo-oxidation from 214 to 237 °C.
The results will expand the range of road bitumen modifiers using humic acids derived from lignite. An equally important aspect of adding humic acids to road bitumen is that this direction of their use corresponds to the basic principles of sustainable development and valorization of the circular economy, in particular, the efficient use of available resources: reduction in the amount of oil raw materials used for bitumen production and development of a new non-fuel and environmentally friendly direction of using low-quality solid combustible minerals, particularly brown coal (the decarbonization of the coal industry). In addition to the restoration of lignite mining and the increase in bitumen production, the proposed direction of HA application can reduce the cost of the obtained bitumen by 1.5% and simultaneously increase the price of the final product by 5% due to the increase in its quality. Based on the data presented in Section 3, with an average price for bitumen of USD 390/ton and HA of USD 135/ton, it is possible to predict a profit of USD 15/ton of bitumen. In Ukraine, an average of 300,000 tons/year is consumed, so the total profit can reach USD 4.5 million/year (excluding the costs of compounding bitumen and HA). At the same time, the authors understand that the previous and present studies in this work are not enough to create an industrial “clean” technology for using lignite to produce binders. Therefore, the purpose of further research in this direction will be rheological tests (using a dynamic shear rheometer (DSR)), assessment of storage stability (according to the EN 13399 standard), studying the possibility of increasing HA in bitumen, as well as conducting a comprehensive statistical analysis of the repeatability of test results.

Author Contributions

Y.P.: Conceptualization, Methodology, Formal analysis, Data curation, Writing—original draft, Project administration; Y.L.: Conceptualization, Methodology, Visualization, Writing—original draft; T.C.: Methodology, Resources, Investigation; D.M.: Validation, Formal analysis, Writing—review and editing; M.Z.: Data curation, Writing—review and editing; M.M.: Resources, Validation; H.O.: Resources, Validation; S.P.: Conceptualization, Formal analysis, Data curation, Writing—original draft, Writing—review and editing, Supervision. All authors have read and agreed to the published version of the manuscript.

Funding

The authors acknowledge the financial support of this paper by the Ministry of Education and Science of Ukraine under grant (Zeltech/0124U000516).

Data Availability Statement

The original contributions presented in this study are included in the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Raw material and products of humic acid extraction: (A) lignite; (B) humic acids.
Figure 1. Raw material and products of humic acid extraction: (A) lignite; (B) humic acids.
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Figure 2. Thermogram of humic acids.
Figure 2. Thermogram of humic acids.
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Figure 3. Thermogram of bitumen BND 70/100.
Figure 3. Thermogram of bitumen BND 70/100.
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Figure 4. Thermogram of bitumen BND 70/100 + 2.0 wt.% humic acids.
Figure 4. Thermogram of bitumen BND 70/100 + 2.0 wt.% humic acids.
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Figure 5. Comparison of DTA curves for the samples of unmodified and modified bitumen. (1) Bitumen BND 70/100; (2) bitumen BND 70/100 + 2.0 wt.% humic acids.
Figure 5. Comparison of DTA curves for the samples of unmodified and modified bitumen. (1) Bitumen BND 70/100; (2) bitumen BND 70/100 + 2.0 wt.% humic acids.
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Figure 6. Comparison of DTG curves for the samples of unmodified and modified bitumen. (1) bitumen BND 70/100, (2) bitumen BND 70/100 + 2.0 wt.% humic acids.
Figure 6. Comparison of DTG curves for the samples of unmodified and modified bitumen. (1) bitumen BND 70/100, (2) bitumen BND 70/100 + 2.0 wt.% humic acids.
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Figure 7. IR spectra A—bitumen BND 70/100; B—humic acids; C—bitumen BND 70/100 + 2.0 wt.% humic acids.
Figure 7. IR spectra A—bitumen BND 70/100; B—humic acids; C—bitumen BND 70/100 + 2.0 wt.% humic acids.
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Figure 8. Microphotographs of humic acids.
Figure 8. Microphotographs of humic acids.
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Figure 9. Microphotographs of bitumen BND 70/100.
Figure 9. Microphotographs of bitumen BND 70/100.
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Figure 10. Microphotographs of bitumen BND 70/100 + 12.0 wt.% humic acids.
Figure 10. Microphotographs of bitumen BND 70/100 + 12.0 wt.% humic acids.
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Table 1. Qualitative and quantitative analysis of humic acids.
Table 1. Qualitative and quantitative analysis of humic acids.
No.IndexUnit of MeasurementValueMethods and Standards
1Moisture content (Wa)wt.%9.60[39]
2Ash content (Ad)wt.%7.90[40]
3Volatile matter yield (Vdaf)wt.%52.30[41]
4Total sulfur content (Std)wt.%3.90[42]
5Carbon content (Cdaf)wt.%62.34[43]
6Hydrogen content (Hdaf)wt.%4.63
7Nitrogen content (Ndaf)wt.%0.77
8Oxygen content (Oddaf)wt.%28.36
Table 2. Physico-chemical characteristics of bitumen.
Table 2. Physico-chemical characteristics of bitumen.
№ з/пIndexValue
BND 70/100BND 70/100 + Humic AcidsMethods and Standards
1Penetration at 25 °C, dmm7872[44]
2Softening point (SP), °C52.654[45]
3Ductility at 25 °C, cm5815[46]
4Elastic recovery at 25 °C, %17.528.7[47]
5Solubility in organic solvent, %99.95–[48]
6Adhesion to gravel, mark3.53.5[49]
7Adhesion to glass, %6560[49]
8Resistance to hardening at 163 °C (RTFOT method): [50]
Mass change, wt.%0.0860.156
Softening point after RTFOT, °C59.659.4
Penetration at 25 °C after RTFOT, dmm3948
Softening point change, °C6.85.4
Retained penetration, %50.068.6
9Homogeneity–No clumps or particles of humic acids are observed[51]
Table 3. Names of the samples studied and their affiliation with the research methods used.
Table 3. Names of the samples studied and their affiliation with the research methods used.
Sample NameResearch Methods
Humic acidsDTA/DTG, FTIR, SEM
Bitumen BND 70/100DTA/DTG, FTIR, SEM
Bitumen BND 70/100 + 2.0 wt.% humic acidsDTA/DTG, FTIR
Bitumen BND 70/100 + 12.0 wt.% humic acidsSEM
Table 4. Results of complex thermal analysis of humic acid samples, original, and modified bitumen.
Table 4. Results of complex thermal analysis of humic acid samples, original, and modified bitumen.
SampleTemperature Range, °CMass Loss, %
Humic acids20–17011.48
170–33411.84
Bitumen BND 70/10020–214–
214–3031.69
303–39320.06
Bitumen BND 70/100 + 2.0 wt.% humic acids20–237-
237–3051.50
305–38917.83
Table 5. Characteristic differences and typical peak values of IR spectra for samples of bitumen BND 70/100, humic acids, and bitumen BND 70/100 + 2.0 wt.% humic acids.
Table 5. Characteristic differences and typical peak values of IR spectra for samples of bitumen BND 70/100, humic acids, and bitumen BND 70/100 + 2.0 wt.% humic acids.
№ Wavenumber,
cm−1		BitumenHumic AcidsBitumen+ 2.0 wt.% Humic AcidsStructural Fragment of the MoleculeAtom Groups
Absorbance, a.u. *Relative, %Absorbance, a.u. *Relative, %Absorbance, a.u. *Relative, %
130470.00510.53----CH3ν(C–H) asymmetric
22919–29170.289729.920.01282.780.285530.94–CH2–ν(C–H) asymmetric
32850–28490.205521.220.00901.950.202921.99CH3 and CH2
or
−O−CH3		ν(C–H) symmetric
41603–16020.01021.050.03407.380.01391.51Ar
or
–COO-		ν (C=C) aromatic ring
or
ν (C–O) asymmetric, symmetric
51461–14300.09509.810.01182.550.099510.78–C–H (CH3)
–C–H(CH2)
or
Ar		δ (CH3) asymmetric
δ (CH2) asymmetric
or
ν (C=C) aromatic ring
61376–13750.04464.610.00992.150.05215.64–C–H (CH3)δ (CH3) symmetric
71169--0.00962.08--R–COO–R`–
81035–10290.00740.770.053211.560.01441.56−O−CH3δ (C–O) methoxyl group
91007--0.055312.01--O-containing compoundsν (C–O–C, O–O, etc.) asymmetric, symmetric
10912--0.01783.87--
11872–8710.01741.80--0.01731.87Arδ (C–H) in aromatic ring
12819–8100.02262.330.00080.170.02602.82Ar (–CH=CH–)δ (C–H) outside of the area of aromatic ring (mainly in the presence of alkyl substituents)
13749–7450.03053.150.00350.760.02893.13Ar (–CH=CH–)δ (C–H) outside of the area of aromatic ring (mainly in the presence of alkyl substituents)
147200.04274.41--0.04154.49Ar
(–CH=CH–)		δ (C–H) outside of the area of aromatic ring (mainly in the presence of alkyl substituents)
15532--0.053211.56--Me(CH3)xρ (Me–C)
16465--0.070915.40--
Total0.770779.600.341774.220.782084.73––
The rest of the IR bands0.197620.400.118725.780.141015.27––
* a.u.—absorption units.
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Prysiazhnyi, Y.; Lypko, Y.; Chipko, T.; Miroshnichenko, D.; Zhylina, M.; Miroshnychenko, M.; Omelianchuk, H.; Pyshyev, S. Non-Fuel Carbon-Neutral Use of Lignite: Mechanism of Bitumen and Humic Acid Interaction. Clean Technol. 2025, 7, 81. https://doi.org/10.3390/cleantechnol7030081

AMA Style

Prysiazhnyi Y, Lypko Y, Chipko T, Miroshnichenko D, Zhylina M, Miroshnychenko M, Omelianchuk H, Pyshyev S. Non-Fuel Carbon-Neutral Use of Lignite: Mechanism of Bitumen and Humic Acid Interaction. Clean Technologies. 2025; 7(3):81. https://doi.org/10.3390/cleantechnol7030081

Chicago/Turabian Style

Prysiazhnyi, Yuriy, Yurii Lypko, Taras Chipko, Denis Miroshnichenko, Maryna Zhylina, Mykhailo Miroshnychenko, Hennadii Omelianchuk, and Serhiy Pyshyev. 2025. "Non-Fuel Carbon-Neutral Use of Lignite: Mechanism of Bitumen and Humic Acid Interaction" Clean Technologies 7, no. 3: 81. https://doi.org/10.3390/cleantechnol7030081

APA Style

Prysiazhnyi, Y., Lypko, Y., Chipko, T., Miroshnichenko, D., Zhylina, M., Miroshnychenko, M., Omelianchuk, H., & Pyshyev, S. (2025). Non-Fuel Carbon-Neutral Use of Lignite: Mechanism of Bitumen and Humic Acid Interaction. Clean Technologies, 7(3), 81. https://doi.org/10.3390/cleantechnol7030081

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