Next Article in Journal
Forging a Sustainable Future in G20 Economies: The Transformative Role of Technological Innovation, Green Finance and Higher Education Amid Globalization and Entrepreneurial Growth
Previous Article in Journal
Utilization of Phosphogypsum as Sustainable Adsorbent for Removal of Crystal Violet Dye from Wastewater: Kinetics, Thermodynamics, and Applications in Textile Effluent Treatment
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 17
Issue 8
10.3390/su17083318
sustainability-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Preparation of Coal Gangue-Based Artificial Soil and Investigation of the Mechanism of Aggregate Structure Formation

by
Weinan Gong
1,2,3,4,
Helong Hui
2,3,4,
Shuhua Ma
2,3,4,*,
Jianbing Ji
1 and
Hongtao Jiang
1,*
1
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
2
CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
3
Innovation Academy for Green Manufacture, Chinese Academy of Sciences, Beijing 100190, China
4
National Engineering Research Center of Green Recycling for Strategic Metal Resources, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
*
Authors to whom correspondence should be addressed.
Sustainability 2025, 17(8), 3318; https://doi.org/10.3390/su17083318
Submission received: 21 February 2025 / Revised: 4 April 2025 / Accepted: 6 April 2025 / Published: 8 April 2025
Browse Figures
Review Reports Versions Notes

Abstract

:
Coal gangue (CG) has become a critical environmental challenge in China, with nearly one billion tons produced annually. To address this challenge while simultaneously supplementing soil resources during mine ecological restoration, a novel process is proposed to convert CG into CG-based artificial soil (CGAS) using a microbial treatment method. This study examined the effects of local microbial agents (LMAs), commercial microbial agents (CMAs), and fly ash (FA) on key soil properties of CGAS, such as organic matter (OM) content, humic acid (HA) content, and water-holding capacity. Additionally, the mechanisms underlying aggregate formation in CGAS were investigated. The results showed that the synergistic effect of LMAs and FA significantly enhanced the essential quality properties of CGAS. In particular, the HA content increased by 2.06 times compared with untreated CG, the proportion of water-stable macroaggregates increased to 11.46%, and the bulk density decreased by 39.71%, achieving an optimal level of 1.30 g/cm3. Analysis of phase compositions, surface functional group characterization, and microstructural examination indicated that organic binders such as HA, inorganic binders such as calcium carbonate and gypsum, and the bonding effect of spherical particles of FA played significant roles in forming a stable and healthy soil structure in CGAS.

1. Introduction

Coal gangue (CG) is a type of solid waste material composed of rock fragments with an ash content exceeding 50% on a dry basis. It is generated at various stages of coal mining activities, including mine construction, development, excavation, extraction, and washing processes. Typically, CG production accounts for 10–25% of raw coal extracted [1]. As of 2023, China’s annual CG generation reached 830 million metric tons, with an accumulated total exceeding 7 billion tons. The accumulation of CG poses significant environmental risks, including land occupation, dust pollution, and landslides. [2]. Effectively utilizing CG as a resource is crucial for promoting sustainable economic, social, and environmental development. Currently, CG is widely used in construction materials [3,4], energy production [5], filling applications [6,7], and emerging materials [8]. However, as of 2023, the overall utilization rate of CG in China remains at approximately 70% [9], leaving a significant gap in its effective use. The large-scale accumulation of CG severely hinders the sustainable development of China’s economy and society, necessitating the development of new technologies to facilitate its large-scale utilization.
China’s primary coal-producing areas are located in the arid and semi-arid regions of the northwest, where ecological challenges such as land desertification and degradation are prevalent [10]. CG originates from rock layers surrounding coal seams and consists primarily of carbonaceous organic matter (OM) and inorganic minerals. The inorganic fraction primarily includes clay minerals (for example, kaolinite, feldspar, and mica), quartz, and calcium carbonate, which share similarities with healthy soils and serve as effective soil-forming matrices. Converting CG into soil-like material or soil-improving agents can support the ecological restoration of degraded lands while enabling large-scale in situ utilization of CG. Consequently, using CG to prepare CG-based artificial soil (CGAS) presents significant research potential in CG resource utilization.
The current research focuses on preparing artificial soil by mixing CG with external materials and activating plant-available nutrients. Studies have shown that artificial soil prepared by directly mixing CG with natural soil [11] or compounding it with straw [12], sludge [13], mushroom sludge, and organic fertilizers exhibits good water retention and sufficient nutrient conditions. However, the limited weathering of CG hinders the efficient release and utilization of its nutrients, necessitating external OM to supplement artificial soil. Consequently, CG utilization in these approaches remains relatively low. Despite its abundance of organic and inorganic nutrients, CG contains OM in highly solidified forms, restricting its bioavailability for plants. To fully utilize the nutrients of CG, researchers have explored mechanical [14], chemical [15], and microbial methods [16,17,18] to enhance the bioavailability of silicon, potassium, and phosphorus. Among these, microbial methods have garnered significant attention owing to their high efficiency, low energy consumption, and environmental benefits. However, current studies primarily focus on the activation of inorganic nutrients in CG, with fewer investigations into the activation of OM and the adaptation of nutrient-poor environment strains in CG. Additionally, studies on soil structure formation in CG-based artificial soils remain limited.
Soil aggregates are key indicators of soil structure and fertility. Improving soil aggregate structure enhances soil fertility and promotes plant growth. Soil aggregate formation is a complex process involving physical, chemical, and biological factors. Recent studies have proposed several theories, including the binding of clay particles to OM after being coated with iron oxide to promote microaggregate formation [19]. Soil aggregates also function as incubators for microbial evolution [20], and they play a role in phosphorus microcirculation within the soil [21]. Owing to the diversity of soil types and environmental conditions, the mechanisms underlying aggregate formation remain complex, and no unified theory has been established. Moreover, artificial soil derived from CG differs from naturally occurring healthy soil, particularly in soil structure and formation mechanisms, which have not been addressed in relevant studies.
Therefore, this study used CG as the primary raw material and employed a microbial method to prepare CGAS. Key physicochemical properties, including soil organic matter (SOM) content, humic acid (HA) concentration, water-holding capacity, aggregate structure, and bulk density, were analyzed. Additionally, this study evaluated the effectiveness of local microbial agents (LMAs), which were cultivated independently, in comparison with commercial microbial agents (CMAs). Furthermore, the role of supplementary materials, such as fly ash (FA), in CGAS formation and aggregate structure development was investigated.

2. Materials and Methods

2.1. Experimental Material

In this study, CG, obtained from a coal-washing plant in Yulin, Shanxi Province, was used as the primary raw material. The CG samples were subjected to crushing, fine grinding, and sieving, yielding particles smaller than 0.25 mm. Previous studies have indicated that FA plays a significant role in promoting the formation of aggregate structures in CG soil production [22]. Therefore, this study utilized FA as a supplementary material in preparing CGAS, specifically using FA samples with a particle size of less than 0.25 mm. The chemical compositions of the CG and FA raw materials, which mainly contain SiO2, Al2O3, and Fe2O3, are shown in Table 1. The SO3 and K2O contents of CG are higher than those of FA, whereas the CaO content of FA is higher than that of CG.
For the microbial treatment, LMA, extracted and screened from CG, was selected as the target microbial inoculant for CGAS production. CMA was included in a parallel comparison to evaluate the performance of LMA. LMA, which was isolated and enriched from CG in our laboratory, was characterized via 16S rRNA high-throughput sequencing, revealing the presence of dominant microbial genera including Ralstonia, Pseudomonas, Akkermansia, Latilactobacillus, Muribaculaceae, and Bacillus. CMA is a commercially available microbial agent purchased from Puyang Yuyi Jiayi Biotechnology Co., Ltd. (Puyang, China), mainly composed of Bacillus subtilis, Bacillus licheniformis, Lactobacillus spp., and nitrogen-fixing bacteria capable of solubilizing phosphate and potassium. The viable cell concentrations of both LMA and CMA, determined by plate counting, ranged from 5.35 × 108 to 9.00 × 108 cfu/g. To ensure the validity of comparative analyses, both microbial inoculants were applied at similar concentrations and inoculation rates in parallel experiments.

2.2. Experimental Design

The experimental design for preparing artificial soil from CG is shown in Table 2. The effects of FA and microbial agents were evaluated as independent variables, while the total sample weight was fixed at 500 g, with a moisture content of 25%. Based on previous studies, where CMA addition at 1% (w/w) was found to enhance soil aggregation, an optimal soil structure was achieved with 30% (w/w) FA addition. Therefore, this study adopted 30% (w/w) FA for subsequent experiments. The prepared CGAS samples were incubated at 30 °C with a humidity level of 45% for 35 d. Each set of experiments was conducted in triplicate to ensure reliability. During the incubation, the samples were turned every two days, and humidity was maintained using a weighing method. Untreated CG was used as the blank control to evaluate the effects of the treatments.

2.3. Methods of Analysis

2.3.1. Instrumental Characterization

The chemical compositions of the samples were analyzed using X-ray fluorescence spectrometry (XRF, AXIOS, PANalytical B.V., Almelo, The Netherlands). The physical phase compositions of the samples were determined using X-ray diffraction (XRD, X’Pert PRO MPD, PANalytical B.V., Almelo, The Netherlands). Fourier-transform infrared spectroscopy (FTIR) was performed using an FTIR spectrometer (TENSOR27, Bruker Corporation, Billerica, MA, USA) in the 4000–400 cm−¹ range to identify functional groups in the samples. A high-resolution X-ray tomograph (Xrada 520 Versa, Carl Zeiss Ltd., Cambridge, UK) was utilized to study soil porosity, operating at a scanning voltage of 80 kV and a resolution of 12 µm. Additionally, the morphology of the soil aggregates was examined using a thermal field-emission scanning electron microscope (JSM-7610F, JEOL Ltd., Tokyo, Japan).

2.3.2. Indicator Testing

The OM and HA in the CG were detected using the standard methods of NY/T 1121.6-2006 [23] and GB/T 11957-2001 [24], respectively. The calculations followed Equations (1) and (2):
O M ( g / k g ) = C × ( V 0 − V ) × 0.003 × 1.724 × 1.10 m × 1000
where V represents the volume of titrant used for filtrate titration (mL), V 0 represents the volume of titrant used for blank titration (mL), C represents the titrant concentration (mol/L), m represents the mass of the sample taken (g), 0.003 represents the millimolar mass of 1/4 carbon atoms (g), and 1.724 represents the organic carbon-to-OM conversion factor. The value 1.10 represents the oxidation correction factor, and 1000 represents conversion to gram per kilogram.
H A a d ( m g / g ) = 3 ( V 0 − V 1 ) C 0.62 × m × 1000 × a b × 1000
where V 1 represents the volume of titrant used for filtrate titration (mL), V 0 represents the volume of titrant used for blank titration (mL), C represents the concentration of the titrant, m represents the mass of the sample taken (g), 0.62 represents the carbon ratio of HA, a represents the total volume of the base extract (mL), b represents the volume of the sample taken during titration (mL), and 1000 represents conversion to mg per gram.
When preparing artificial soil samples by adding FA, the OM, and HA contents need to be adjusted based on the proportion of FA in the mixture. This adjustment is essential to ensure a fair comparison between samples, as FA contains minimal OM and HA.
The water-holding capacity of the soil samples was tested based on the NY/T 1121.22-2010 [25] standard. The water-stable aggregate content of artificial soil was determined based on the NY/T 1121.19-2008 [26] standard. The NY/T 1121.4-2006 [27] standard was used to test the volumetric weight of soil samples. The mean weight diameter (MWD) and geometric mean diameter (GMD) of soil water-stable aggregates were calculated using Equations (3) and (4).
M W D = ∑ i = 1 n W i X ¯ i
G M D = e x p ∑ i = 1 n W i · ln ⁡ X ¯ i
where X ¯ i represents the average diameter of the water-stabilized aggregates at the level i and W i represents the mass of the water-stabilized aggregates at the level i .

2.3.3. Statistical Analysis

Statistical tests were performed using SPSS 26.0 (IBM, Armonk, NY, USA). Figures with error bars were plotted using OriginPro 2021 (OriginLab Corporation, Northampton, MA, USA). Where applicable, p-values from ANOVA and Tukey tests are reported in Section 3 to support treatment comparisons.

3. Results and Discussion

3.1. Comparison of OM Content per Unit Mass of CG

SOM is a key indicator of soil health and significantly affects soil fertility, structure, water retention, and nutrient cycling. Figure 1 compares the OM content in CG after 35 d of incubation under various treatment conditions. In this figure, the dotted line represents the OM content of untreated CG. The addition of microbial agents increased the OM content in CG. Specifically, LMA increased OM by 4.69%, whereas CMA resulted in a 2.35% increase compared to untreated CG. These enhancements are likely due to microbial remnant accumulation. Studies have shown that the soil microbial remnant pool is 40 times larger than living biomass [28], and microbial remnants contribute more than 50% of soil organic carbon [29]. LMA is extracted and cultivated from CG, which may be more adapted to the environment of CG. Its biological activities, such as reproduction and metabolism, are more vigorous, promoting the production of residues and improving OM. Another possible reason for the increase in OM is the presence of autotrophic microorganisms in the artificial soil, which can convert inorganic carbon (e.g., CO2 or carbonates) into organic carbon through assimilation processes [30]. Additionally, Figure 1 shows that FA addition slightly increased the OM content in both CG + FA + LMA and CG + FA + CMA treatments compared to CG + LMA and CG + CMA. This could be attributed to FA’s loose and porous structure, which enhances soil respiration, creating conditions more conducive to microbial metabolism. This may, in turn, lead to higher microbial residue production and promote inorganic carbon conversion to organic carbon [31].

3.2. Comparison of HA Content per Unit Mass of CG

SOM primarily consists of humus, with HA being a key component essential for soil structure formation. Figure 2 illustrates the HA content in CG under different treatment conditions, with the dashed line representing the HA content of untreated CG. The results showed that adding LMA and CMA promoted HA formation, and LMA was significantly more effective in enhancing HA production compared to CMA (p = 0.0022). Improvement with LMA was 2.04 times greater than that with untreated CG (p = 0.0002). Moreover, FA addition further promoted HA production, with HA levels higher in the FA-amended samples than in those in the samples without FA (e.g., CG + FA vs. CG: p = 0.0348; CG + FA + LMA vs. CG: p = 0.0001), suggesting synergy between LMA and FA. The observed increase in HA content can be attributed to microbial metabolism. Microorganisms produce extracellular metabolites (e.g., organic acids and enzymes) that dissolve coarse coal particles [32], facilitating the conversion of complex OM in coal into HAs. Our previous analysis of functional groups in CG before and after microbial activity revealed that Bacillus sp. promotes the conversion of C–C/C=C bonds into C=O and COOH functional groups, leading to increased HA content [31]. This process likely involves microbial degradation of residual organic carbon within CG to low-molecular-weight compounds (e.g., phenols and organic acids). These intermediates may then undergo oxidative transformation, condensation, and polymerization, leading to the formation of humic-like macromolecules with abundant aromatic rings and carboxyl, hydroxyl, and quinone groups. During this transformation, extracellular enzymes secreted by the microbes, such as laccase and lignin peroxidase [33], probably play a catalytic role in promoting oxidative coupling and polymerization reactions, leading to HA formation. Moreover, FA addition may further enhance aeration in CG soil, thereby improving the microbial community structure by increasing the relative abundance of aerobic coal-degrading microorganisms such as Bacillus [34] and Pseudomonas [35]. This shift likely contributed to increased HA production.

3.3. Water-Holding Capacity (WHC) Test for Artificial Soils

WHC is a key indicator for soil water retention, with significant implications for plant growth, water management, and ecosystem health. Table 3 lists the WHC of the CGAS under different conditions. The results showed that microbial addition significantly improved WHC, with LMA performing slightly better than that of CMA. Additionally, FA addition further enhanced the WHC of artificial soil. Among all treatments, CG + FA + LMA samples exhibited the highest WHC, demonstrating a 16.41% increase compared with CG. This value exceeds the typical WHC range of clay loam soils (40–50%), indicating strong potential for improving soil water retention in the arid regions of Northwest China. Contact angle measurements between soil samples and water (Figure 3) revealed that microbial activity and FA addition increased the hydrophilicity of CG and enhanced the water adsorption capacity of the artificial soil. Microorganisms can fill soil pores by secreting extracellular polymers to reduce water evaporation [36] and increase micropore volume to improve the soil WHC through vital activities [37]. The porous structure of FA, with its capillary channels formed by microscopic particles, enhanced water adsorption and absorption, further boosting WHC.

3.4. Evaluation of Water-Stable Macroaggregates in Artificial Soils

Soil structure is a key parameter for measuring soil fertility and environmental conditions, and water-stable macroaggregates (≥0.25 mm) are an essential indicator for assessing soil WHC, permeability, and erosion resistance. Figure 4 shows the particle size distribution of the water-stable CGAS aggregates after 35 d of incubation.
The results indicated that the CGAS primarily consisted of water-stable microaggregates (with particle size smaller than 0.25 mm), which accounted for over 80% of the total composition. This was attributed to the smaller particle size of the raw materials (<0.25 mm) and the relatively short incubation period, which limited macroaggregate formation. The addition of microorganisms promoted the formation of water-stable macroaggregates, with LMA exhibiting a superior performance. The content of water-stable macroaggregates in the LMA treatment increased to 11.46%. The addition of FA enhanced the content of water-stable macroaggregates by approximately 40% compared to the system without FA. Microbial activity and FA addition facilitated the stepwise transformation of fine particles (<0.053 mm) into larger aggregate structures. A correlation analysis between water-stable macroaggregates, OM, and HA content (Figure 5) showed a positive relationship, suggesting that OM and HAs played a crucial role in macroaggregate stability.
The MWD and GMD of soil aggregates are key indicators of aggregate stability. Higher MWD and GMD values indicate greater structural stability, while lower values indicate increased susceptibility to water and nutrient loss. The results of the stability evaluation of artificial soil water-stable aggregates (Table 4) showed that both microbial agents and FA significantly increased the MWD and GMD values, enhancing the structural stability of water-stable aggregates. Among the treatments, the LMA and FA combination exhibited the most significant synergistic effect, leading to the highest MWD and GMD values. This suggests that the combined action of microbial agents and FA further improved the stability of water-stable CGAS aggregates.

3.5. Artificial Soil Bulk Weight

Soil bulk density is a measure of soil compactness, and its reduction helps to improve soil permeability, water retention capacity, and erosion resistance. Figure 6 compares the bulk density of artificial soil after 35 d of incubation under different treatment conditions. The dashed line in the figure represents the bulk density of untreated gangue raw material (2.09 g/cm3), which is higher than that of conventional sandy soil (1.2–1.8 g/cm3). Among the treatments, the LMA + FA combination (CG + FA + LMA) promoted the most significant reduction, decreasing the bulk density by 39.71% to a final value of 1.26 g/cm3, which falls within the typical bulk density range for loamy soils (1.2–1.4 g/cm3). This value was significantly lower than those of CG (1.76 g/cm3, p < 0.001), CG + FA (1.56 g/cm3, p = 0.015), and CG + CMA (1.50 g/cm3, p = 0.040), based on Tukey’s HSD test. This reduction was primarily attributed to aggregate formation, which decreased soil compaction. Microbial activity and FA addition facilitated the formation of aggregates and enhanced the soil pore structure, thereby reducing bulk density.
Furthermore, soil computed tomography scans were used to visualize the morphology of the soil. Figure 7 shows the two-dimensional slices of the untreated gangue, CG, and CG + FA + LMA-treated samples, with soil particles shown in blue and pores in black. The scanning sample area was a cylinder with a diameter of 12 mm and a height of 12 mm. Avizo software (version 2022.2) was used to remove the edge effects, retaining the image with an internal diameter of 11 mm and a height of 10 mm. The pores were extracted using threshold segmentation, and porosity was calculated. As shown in Figure 7a, untreated CG had a dense, fine-grained structure with low porosity. After 35 d of incubation (Figure 7b), the CG sample formed an overall structure with larger particle sizes. Quantitative analysis of the images showed that the average particle size increased from 51.72 μm for untreated CG (Figure 7a) to 178.11 μm for CG + FA (Figure 7b), with a slight reduction to 137.11 μm for CG + FA + LMA (Figure 7c); these results indicate the formation of more uniform and compact aggregates. It was inferred from the results of water-stable aggregates (Figure 4) that these large particles did not maintain an aggregate structure under water erosion and were not water-stable aggregates. After cultivation with FA and LMA (Figure 7c), the particle size distribution of the sample particles became more uniform, the number of micropores on the surface of the particles significantly increased, and most were water-stable aggregated particles (Figure 4). The results showed that the porosity of the raw gangue material was 12.02%. However, the porosities of the CG and CG + FA + LMA samples were 34.14% and 42.72%, respectively, which were 1.84 and 2.55 times higher than those of the raw gangue material. These results indicate that the formation of aggregates significantly increased soil porosity and decreased bulk density.

4. Analysis of Aggregate Formation Mechanisms

Soil aggregate formation involves the binding of fine particles by cementing materials, resulting in larger aggregates. This process is influenced by various factors such as soil diversity, OM content, and mineral composition. The mechanisms underlying aggregate formation are complex and are not yet fully understood. Studies have shown that the content of water-stable macroaggregates in artificial soils is positively correlated with the OM and HA levels. Additionally, these studies have highlighted the significant role of OM in the formation of water-stable microaggregates. In unconventional soil systems such as CGAS, where inorganic minerals are the primary components, the formation mechanisms of the aggregate structure can be preliminarily analyzed through the characterization of inorganic materials such as CG and FA.

4.1. Mineral Phase Analysis

Figure 8 shows the XRD spectra of artificial soil samples prepared by microbial treatment of gangue and FA additives. This comparison indicates that the main mineral composition of the gangue (remaining as quartz, muscovite, and kaolinite) before and after microbial action did not change; however, after microbial treatment, the soil samples exhibited a distinct gypsum phase. Gypsum microsolubilization facilitated the release of Ca2+, which has a strong positive charge. These ions interacted with negatively charged clay particles, promoting the formation and enlargement of soil aggregates through charge-neutralization mechanisms [38]. This phenomenon may partially explain the enhanced soil aggregate structure observed with FA addition. Furthermore, FA contains calcium carbonate, which is considered an effective soil binder. The “calcium bridge” effect of Ca2+ ions facilitated the interaction between minerals and OM, promoting aggregate formation. Additionally, calcium carbonate accumulated within or around newly formed aggregates, further stabilizing soil structure [39]. This mechanism likely contributed to the further enhancement of aggregate stability in FA-treated soils.

4.2. Surface Functional Group Analysis

To investigate the chemical changes in gangue and FA under moisture infiltration, a hydration reaction was simulated at a liquid-to-solid ratio of 20:1 by stirring the materials for 24 h at room temperature. The surface functional groups of the samples before and after treatment were determined. Figure 9 shows the infrared spectra of CG (a) and FA (b) before and after the hydration treatment. The transmission peaks observed at wavenumbers 3650–3590 cm−1 and 3500–3300 cm−1 are attributed to the free –OH stretching vibration peaks and hydrogen-bonded –OH stretching vibration peaks, respectively. As shown in Figure 9, the free −OH stretching vibration peaks of CG did not change significantly after the hydration treatment, whereas the intermolecular hydrogen bonding –OH telescopic vibration peaks of FA were enhanced significantly. This suggests that the hydration treatment increased the number of hydrophilic hydroxyl functional groups on the surface of FA. However, a large amount of active SiO2 and Al2O3 was produced during the formation process of FA after high-temperature activation treatment. Upon hydration, these compounds formed groups containing hydroxyl or oxygen atoms that interacted with polar functional groups in OM (such as hydroxyl, carbonyl, and carboxyl groups) through hydrogen bonding, resulting in stable aggregate structures [40,41]. Furthermore, the alkaline nature of the FA hydration products (approximately pH 9.1) is related to alkaline substances, such as CaHCO3 or Ca(OH)2, produced by the hydration treatment of the FA. These substances, together with the reactive SiO2 and Al2O3, may undergo a volcanic ash reaction to generate a gelling substance [42]. This process increases the adhesion between the FA and the soil particles and facilitates the formation of a macroaggregate structure. The increased number of hydroxyl functional groups also explains the observed reduction in water contact angles for artificial soils containing FA.

4.3. Characterization of Microstructure

Scanning electron microscopy was used to examine the microstructures of the artificial soils, and the results are shown in Figure 10. The primary components of CG include quartz and secondary clay minerals (such as muscovite and kaolinite), which typically exhibit a laminar structure. The untreated CG (Figure 10a) exhibited a distinct blocky and laminar structural distribution. However, after microbial treatment (Figure 10c), numerous scaly fragments and fine debris emerged, suggesting that microbial activity promoted the weathering of some primary or secondary minerals in CG, thereby producing smaller particles. Comparative analysis of Figure 10b,d revealed that the FA raw material has a smooth spherical structure, whereas in the CG + FA + LMA sample, particulate matter adheres to the surfaces of the spherical FA particles. These adhering substances may be weathered debris or fine CG particles. On a larger scale, as shown in Figure 10e, the spherical FA particles adhere to fine-weathered materials on their surfaces and also aggregate through the adhesion of larger mineral particles. Based on these observations, it is speculated that after microbial and hydration treatments, the spherical FA particles may form large soil aggregates by acting as bridging carriers that cement fine particles or adhere to larger particles through mechanisms such as charge neutralization, calcium bridging, and hydroxyl bonding.

4.4. Mechanism Diagram of the Formation of Artificial Soil Aggregate

Based on the theory of conventional soil aggregate structure formation and previous analyses, it can be concluded that the formation of soil macroaggregates in the new gangue-based artificial soil system primarily occurs through the following stages (Figure 11):
(1)
Microorganisms attach to mineral surfaces to form microstructural units while promoting the weathering of gangue minerals and releasing mineral ions [43].
(2)
The metabolites produced by microbial activity, including HA, other OM, and mineral particles, form an organic–mineral complex. At this stage, the CG and FA particles primarily serve as carriers in the formation of the complex. In particular, the gypsum phase formed by microbial treatment of CG and the calcium carbonate present in FA act as “cation bridges”, connecting the minerals and OM through the production of Ca2+ [39]. Additionally, the abundant iron and aluminum oxides in coal gangue and fly ash may carry a substantial positive charge in the weakly acidic microenvironment induced by water erosion or microbial metabolism. These oxides can serve as binding agents between clay particles and organic molecules, jointly promoting the formation of microaggregates [44].
(3)
The organic–mineral complexes aggregate to form microaggregates, which subsequently coalesce into macroaggregates. FA particles are primarily used as bridging carriers during the formation of both microaggregate and macroaggregate structures.

5. Conclusions and Future Outlook

(1)
Microorganisms can effectively activate OM in CG and promote the conversion of coal and other OM to HA, thereby improving the soil’s WHC, reducing bulk density, and promoting the formation of a stable macroaggregate structure. The LMA screened from the CG demonstrated significant advantages over the CMA in enhancing artificial soil properties.
(2)
Both FA and microbial agents showed similar trends in enhancing the quality of CGAS. Under the synergistic effect of microorganisms and FA, compared with the untreated gangue, the HA content increased by 2.06 times, the content of water-stable macroaggregates increased to 11.46%, and the bulk density decreased by 39.71% to 1.26 g/cm3. Additionally, the OM content and WHC of the soil were effectively improved.
(3)
The formation of soil macroaggregates in the new CGAS system involves four primary stages: the development of microstructural units, formation of organic–mineral complexes, aggregation into microaggregates, and growth into macroaggregates. The resulting soil exhibits good properties and a stable aggregate structure formed through the combined action of microorganisms, organic binders (such as HA), and inorganic binders (such as iron and aluminum oxides and calcium ions). The FA particles serve as carriers and bridging agents during the formation of the CGAS structure.
Overall, the laboratory-scale findings of this study demonstrated that CG, when combined with FA and beneficial microbial agents, can be transformed to a functional artificial soil (CGAS) with improved physical structure and water-holding capacity. These results underscore the potential of CGAS as a sustainable substrate for ecological restoration, particularly in arid and semi-arid mining areas. However, further research is needed to extend these findings to real field conditions.
In practical applications, environmental variables such as heterogeneous soil matrices, seasonal fluctuations in temperature and precipitation, and natural microbial competition may significantly influence the performance and stability of CGAS. Therefore, long-term field trials across diverse climatic zones are necessary to evaluate CGAS behavior under dynamic conditions, including its interactions with native vegetation, soil biota, and hydrological processes. Additionally, factors such as the sources and stability of CG and FA, large-scale processing challenges, and ecological considerations must be considered to enhance the performance, scalability, and environmental sustainability of CGAS.
Particular attention should be given to the environmental implications of using CG and FA, which may contain trace amounts of heavy metals or other potentially hazardous elements. Future studies should include the separation and removal of heavy metals and environmental risk evaluations to ensure the safety and long-term viability of CGAS-based reclamation strategies. These efforts will provide a deeper understanding of CGAS systems and promote their application in sustainable land reclamation.

Author Contributions

Conceptualization, H.H. and S.M.; methodology, H.H. and W.G.; Formal analysis, W.G. Investigation, W.G.; Writing-original draft, W.G.; Supervision, H.H., J.J. and H.J.; Funding acquisition, H.H. and S.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Shaanxi Provincial Key Research and Development Program under the project titled “Research on Key Technologies for the Comprehensive Utilization of Coal-based Solid Waste in Coordinated Ecological Restoration”, grant number 2024CY2-GJHX-92.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
CGCoal gangue
CGASCoal gangue-based artificial soil.
LMALocal microbial agent
CMACommercial microbial agent
FAFly ash
FTIRFourier transform Infrared spectroscopy
OMOrganic matter
HAHumic acid
WHCWater-holding capacity
MWDMean weight diameter
GMDGeometric mean diameter

References

  1. Xu, M.Y.; Mao, Y.C.; Yan, Z.L.; Zhang, M.Q.; Xiao, D. Coal and Gangue Classification Based on Laser-Induced Breakdown Spectroscopy and Deep Learning. ACS Omega 2023, 8, 47646–47657. [Google Scholar] [CrossRef] [PubMed]
  2. Shi, L.Q.; Peng, J.F.; Xu, D.J.; Tian, J.J.; Liu, T.H.; Jiang, B.B.; Zhang, F.C. Leaching Characteristics and Pollution Risk Assessment of Potentially Harmful Elements from Coal Gangue Exposed to Weathering for Different Periods of Time. Environ. Sci. Pollut. Res. 2023, 30, 63200–63214. [Google Scholar] [CrossRef]
  3. Gao, H.; Zhao, G.H.; Guo, L.H.; Zhou, L.Q.; Yuan, K.K. Utilization of Coal Gangue as Coarse Aggregates in Structural Concrete. Constr. Build. Mater. 2021, 268, 121212. [Google Scholar] [CrossRef]
  4. He, Z.X.; Zhao, X.; Ye, M.C.; Zuo, W.; Nie, X.X.; Zhao, J.J. Study on the Effect of Basalt Fiber Content and Length on Mechanical Properties and Durability of Coal Gangue Concrete. Sustainability 2024, 16, 9310. [Google Scholar] [CrossRef]
  5. Xu, Y.H.; Wu, H.J.; Dong, Z.F.; Wang, Q.Q.; Chen, X.Y. Life Cycle Energy Use Efficiency and Greenhouse Gas Emissions of Circulating Fluidized Bed Coal-Fired Plant with Coal Gangue and Coal Co-Combustion. Environ. Dev. Sustain. 2024, 26, 0049–0071. [Google Scholar] [CrossRef]
  6. Xie, S.R.; Pan, H.; Gu, W.Z.; Zhu, L.; Yue, D.; Chen, D.D.; Song, T.Q.; Jiang, Z.S. Technology and Engineering Test of Filling Goaf with Coal Gangue Slurry. Sci. Rep. 2023, 13, 20536. [Google Scholar] [CrossRef] [PubMed]
  7. Zhang, Z.T.; Xu, Y.X.; Liao, J.B.; Liu, S.K.; Liu, Z.; Gao, W.H.; Yi, L.W. Study on the Particle Strength and Crushing Patterns of Coal Gangue Coarse-Grained Subgrade Fillers. Sustainability 2024, 16, 5155. [Google Scholar] [CrossRef]
  8. Zheng, Y.S.; Zhou, J.X.; Ma, Z.J.; Weng, X.Y.; Cheng, L.; Tang, G.R. Preparation of a High-Silicon ZSM-5 Molecular Sieve Using Only Coal Gangue as the Silicon and Aluminum Sources. Materials 2023, 16, 4338. [Google Scholar] [CrossRef]
  9. Wu, C.L.; Wang, W.L.; Wang, X.J. Research Status and Innovative Utilization Strategy of Coal Gangue Resource in Building Material Field. Energy Environ. Prot. 2023, 37, 167–177. [Google Scholar]
  10. Peng, S.P.; Bi, Y.L. Strategic Consideration and Core Technology About Environmental Ecological Restoration in Coal Mine Areas in the Yellow River Basin of China. J. China Coal Soc. 2020, 45, 4. [Google Scholar]
  11. Li, S.Q.; Li, X.Q.; Qiang, X.L.; Zhao, Y.; Li, H.Y.; Sun, Z.J.; Li, Q.; He, J.; Han, L.; Zhao, N.X. Improving Saline–Alkaline Soil and Ryegrass Growth with Coal Gangue Treatments. Plants 2024, 13, 3419. [Google Scholar] [CrossRef] [PubMed]
  12. Du, T.; Wang, D.M.; Bai, Y.J.; Zhang, Z.Z. Optimizing the Formulation of Coal Gangue Planting Substrate Using Wastes: The Sustainability of Coal Mine Ecological Restoration. Ecol. Eng. 2020, 143, 105669. [Google Scholar] [CrossRef]
  13. Luo, C.; Li, S.H.; Ren, P.G.; Yan, F.; Wang, L.; Guo, B.; Zhao, Y.M.; Yang, Y.; Sun, J.; Ga, P.C.; et al. Enhancing the Carbon Content of Coal Gangue for Composting Through Sludge Amendment: A Feasibility Study. Environ. Pollut. 2024, 348, 123439. [Google Scholar] [CrossRef] [PubMed]
  14. Liu, Y.C.; He, X.M.; Hu, H.M.; Zhang, Q.W. Cogrinding with Alkaline Metal Salts to Enhance the Reactivity of Silicate Mineral to Serve as Silicon Fertilizer. Chem. Phys. Lett. 2020, 747, 137347. [Google Scholar] [CrossRef]
  15. Shao, S.; Ma, B.Z.; Wang, C.Y.; Chen, Y.Q. Extraction of Valuable Components from Coal Gangue through Thermal Activation and Hno3 Leaching. J. Ind. Eng. Chem. 2022, 113, 564–574. [Google Scholar] [CrossRef]
  16. Bi, Y.L.; Xiao, L.; Liu, R.R. Response of Arbuscular Mycorrhizal Fungi and Phosphorus Solubilizing Bacteria to Remediation Abandoned Solid Waste of Coal Mine. Int. J. Coal Sci. Technol. 2019, 6, 603–610. [Google Scholar] [CrossRef]
  17. Lv, Y.; Li, J.; Ye, H.P.; Du, D.Y.; Sun, P.; Ma, M.Y.; Zhang, T.C. Bioleaching of Silicon in Electrolytic Manganese Residue (Emr) by Paenibacillus mucilaginosus: Impact of Silicate Mineral Structures. Chemosphere 2020, 256, 127043. [Google Scholar] [CrossRef]
  18. Zhu, X.B.; Gong, W.H.; Li, W.; Bai, X.Y.; Zhang, C.X. Reclamation of Waste Coal Gangue Activated by Stenotrophomonas maltophilia for Mine Soil Improvement: Solubilizing Behavior of Bacteria on Nutrient Elements. J. Environ. Manag. 2022, 320, 115865. [Google Scholar] [CrossRef]
  19. Regelink, I.C.; Cathelijne, R.S.; Svetla, R.; Weng, L.P.; Georg, J.L.; Pavel, K.; Nikolaos, P.N.; Kercheva, M.; Banwart, S.; Comans, R.N.J. Linkages Between Aggregate Formation, Porosity and Soil Chemical Properties. Geoderma 2015, 247, 24–37. [Google Scholar] [CrossRef]
  20. Rillig, M.C.; Ludo, A.H.M.; Anika, L. Soil Aggregates as Massively Concurrent Evolutionary Incubators. ISME J. 2017, 11, 1943–1948. [Google Scholar] [CrossRef]
  21. Garland, G.; Bünemann, E.K.; Oberson, A.; Frossard, E.; Snapp, S.; Chikowo, R.; Six, J. Phosphorus Cycling Within Soil Aggregate Fractions of a Highly Weathered Tropical Soil: A Conceptual Model. Soil Biol. Biochem. 2018, 116, 91–98. [Google Scholar] [CrossRef]
  22. Cheng, Z.; Gaohang, C.; Zheng, Y.; Haohang, G.; Zening, G.; Daili, Z.; Chen, X. Improvement of the Salinized Soil Properties of Fly Ash by Freeze-Thaw Cycles: An Impact Test Study. Sustainability 2021, 13, 2908. [Google Scholar] [CrossRef]
  23. NY/T 1121.6-2006; Soil Testing—Part 6: Determination of Organic Matter. Ministry of Agriculture of the People’s Republic of China: Beijing, China, 2006.
  24. GB/T 11957-2001; Soil Quality—Determination of Particle Size Distribution. Standards Press of China: Beijing, China, 2001.
  25. NY/T 1121.22-2010; Soil Testing—Part 22: Determination of Available Potassium. Ministry of Agriculture of the People’s Republic of China: Beijing, China, 2010.
  26. NY/T 1121.19-2008; Soil Testing—Part 19: Determination of Available Phosphorus. Ministry of Agriculture of the People’s Republic of China: Beijing, China, 2008.
  27. NY/T 1121.4-2006; Soil Testing—Part 4: Determination of Soil pH. Ministry of Agriculture of the People’s Republic of China: Beijing, China, 2006.
  28. Liang, C.; Cheng, G.; Wixon, D.L.; Balser, T.C. An Absorbing Markov Chain Approach to Understanding the Microbial Role in Soil Carbon Stabilization. Biogeochemistry 2011, 106, 303–309. [Google Scholar] [CrossRef]
  29. Liang, C.; Amelung, W.; Lehmann, J.; Kästner, M. Quantitative Assessment of Microbial Necromass Contribution to Soil Organic Matter. Glob. Change Biol. 2019, 25, 3578–3590. [Google Scholar] [CrossRef]
  30. Ye, J.X.; An, N.; Chen, H.; Ying, Z.Y.; Zhang, S.H.; Zhao, J.K. Performance and Mechanism of Carbon Dioxide Fixation by a Newly Isolated Chemoautotrophic Strain Paracoccus denitrificans PJ-1. Chemosphere 2020, 252, 126473. [Google Scholar] [CrossRef] [PubMed]
  31. Liu, C.X.; Wang, X.H.; Ou, Y.J.; Du, H. Biodegradation of Organic Compounds in the Coal Gangue by Bacillus Sp. Into Humic Acid. Biodegradation 2023, 34, 125–138. [Google Scholar] [CrossRef]
  32. Li, S.Y.; Tan, J.F.; Wang, Y.; Li, P.P.; Hu, D.S.; Shi, Q.Z.; Yue, Y.J.; Li, F.; Han, Y.L. Extraction Optimization and Quality Evaluation of Humic Acids from Lignite Using the Cell-Free Filtrate of Penicillium ortum MJ51. RSC Adv. 2022, 12, 528–539. [Google Scholar] [CrossRef]
  33. Liang, C.; Lu, L.; Tao, X.; Kang, G.; Liu, Z.; Li, B. The Pseudomonas Ligninolytic Catalytic Network Reveals the Importance of Auxiliary Enzymes in Lignin Biocatalysts. Proc. Natl. Acad. Sci. USA 2025, 4, e2417343122. [Google Scholar] [CrossRef]
  34. Nuraly, A.; Digel, I.; Qiao, X.H.; Tastambe, K.; Zhubanova, A. Lignite Biosolubilization by Bacillus sp. RKB 2 and Characterization of its Products. Geomicrobiol. J. 2020, 37, 255–261. [Google Scholar]
  35. Hazrin, C.; Hazlin, N.; Marjo, C.E.; Theerthankar, D.; Anne, M.R.; Mike, M. Surface Analysis Reveals Biogenic Oxidation of Sub-Bituminous Coal by Pseudomonas fluorescens. Appl. Microbiol. Biotechnol. 2014, 98, 6443–6452. [Google Scholar] [CrossRef]
  36. Adessi, A.; Carvalho, R.C.D.; Philippis, R.D.; Branquinho, C.; Silva, J.M.D. Microbial Extracellular Polymeric Substances Improve Water Retention in Dryland Biological Soil Crusts. Soil Biol. Biochem. 2018, 116, 67–69. [Google Scholar] [CrossRef]
  37. Philippot, L.; Chenu, C.; Kappler, A.; Rillig, M.C.; Fierer, N. The Interplay Between Microbial Communities and Soil Properties. Nat. Rev. Microbiol. 2024, 22, 226–239. [Google Scholar] [CrossRef] [PubMed]
  38. Tirado-Corbalá, R.; Slater, B.K.; Dick, W.A.; Bigham, J.; Muñoz-Muñoz, M. Gypsum Amendment Effects on Micromorphology and Aggregation in No-Till Mollisols and Alfisols from Western Ohio, USA. Geoderma Reg. 2019, 16, e00217. [Google Scholar] [CrossRef]
  39. Pihlap, E.; Steffens, M.; Kögel-Knabner, I. Initial Soil Aggregate Formation and Stabilisation in Soils Developed from Calcareous Loess. Geoderma 2021, 385, 114854. [Google Scholar] [CrossRef]
  40. Wershaw, R.L.; Llaguno, E.C.; Leenheer, J.A. Mechanism of Formation of Humus Coatings on Mineral Surfaces 3. Composition of Adsorbed Organic Acids from Compost Leachate on Alumina by Solid-state 13C NMR. Colldid Surface A 1996, 108, 213–223. [Google Scholar] [CrossRef]
  41. Kleber, M.; Sollin, P.; Sutton, R. A Conceptual Model of Organo-Mineral Interactions in Soils: Self-Assembly of Organic Molecular Fragments into Zonal Structures on Mineral Surfaces. Biogeochemistry 2007, 85, 9–24. [Google Scholar] [CrossRef]
  42. Zeynali, Y.; Niroumand, H.; Moayed, R.Z. Stabilizing Cohesive Soils with Micro- and Nano- Fly Ash as Eco-Friendly Materials: An Experimental Study. Constr. Build. Mater. 2023, 399, 132490. [Google Scholar] [CrossRef]
  43. Ahmed, E.; Holmström, S.J.M. Microbe-Mineral Interactions: The Impact of Surface Attachment on Mineral Weathering and Element Selectivity by Microorganisms. Chem. Geol. 2015, 403, 13–23. [Google Scholar] [CrossRef]
  44. Zhe, L.; Huang, Z.G.; Liao, D.L.; Huang, W.X.; Huang, J.; Deng, Y.S. Effects of Soil Organic Matter Components and Iron Aluminum Oxides on Aggregate Stability During Vegetation Succession in Granite Red Soil Eroded Areas. J. Mt. Sci. 2022, 19, 2634–2650. [Google Scholar]
Sustainability 17 03318 g001
Figure 1. Comparison of OM content per unit mass of CG after 35 d of incubation.
Figure 1. Comparison of OM content per unit mass of CG after 35 d of incubation.
Sustainability 17 03318 g001
Sustainability 17 03318 g002
Figure 2. Comparison of HA content in unit CG after 35 d of incubation.
Figure 2. Comparison of HA content in unit CG after 35 d of incubation.
Sustainability 17 03318 g002
Sustainability 17 03318 g003
Figure 3. Static contact angle of water on the surfaces of the (a) CG, (b) CG + LMA, (c) CG + CMA, (d) CG + FA, (e) CG + FA + LMA, and (f) CG + FA + CMA sample slices. Green curves represent fitted droplet profiles; purple lines indicate the tangent angles at the contact points; the yellow line shows the solid surface baseline.
Figure 3. Static contact angle of water on the surfaces of the (a) CG, (b) CG + LMA, (c) CG + CMA, (d) CG + FA, (e) CG + FA + LMA, and (f) CG + FA + CMA sample slices. Green curves represent fitted droplet profiles; purple lines indicate the tangent angles at the contact points; the yellow line shows the solid surface baseline.
Sustainability 17 03318 g003
Sustainability 17 03318 g004
Figure 4. Particle size distribution of water-stable aggregates in artificial soil after 35 d of incubation.
Figure 4. Particle size distribution of water-stable aggregates in artificial soil after 35 d of incubation.
Sustainability 17 03318 g004
Sustainability 17 03318 g005
Figure 5. Correlation analysis between water-stable macroaggregate content, OM, and HA in coal gangue-based artificial soil. Blue circles (●) represent OM content (g/kg coal gangue); green triangles (▲) represent HA content (mg/g coal gangue). The blue and green lines indicate the corresponding linear regression fits.
Figure 5. Correlation analysis between water-stable macroaggregate content, OM, and HA in coal gangue-based artificial soil. Blue circles (●) represent OM content (g/kg coal gangue); green triangles (▲) represent HA content (mg/g coal gangue). The blue and green lines indicate the corresponding linear regression fits.
Sustainability 17 03318 g005
Sustainability 17 03318 g006
Figure 6. Bulk density of artificial soil after 35 d of incubation. The dashed vertical line represents the bulk density of the untreated gangue raw material (2.09 g/cm³).
Figure 6. Bulk density of artificial soil after 35 d of incubation. The dashed vertical line represents the bulk density of the untreated gangue raw material (2.09 g/cm³).
Sustainability 17 03318 g006
Sustainability 17 03318 g007
Figure 7. Two-dimensional slices of (a) untreated CG, (b) CG, and (c) CG + FA + LMA samples in the natural state.
Figure 7. Two-dimensional slices of (a) untreated CG, (b) CG, and (c) CG + FA + LMA samples in the natural state.
Sustainability 17 03318 g007
Sustainability 17 03318 g008
Figure 8. Mineral phases of some artificial soil samples and FA raw materials.
Figure 8. Mineral phases of some artificial soil samples and FA raw materials.
Sustainability 17 03318 g008
Sustainability 17 03318 g009
Figure 9. Infrared spectra of (a) CG and (b) FA before and after hydration treatment.
Figure 9. Infrared spectra of (a) CG and (b) FA before and after hydration treatment.
Sustainability 17 03318 g009
Sustainability 17 03318 g010
Figure 10. Scanning electron micrographs of the samples under different treatment conditions. (magnification 20,000×: (a) untreated CG, (b) FA, (c) CG + LMA, (d) CG + FA + LMA; magnification 5000×: (e) CG + FA + LMA).
Figure 10. Scanning electron micrographs of the samples under different treatment conditions. (magnification 20,000×: (a) untreated CG, (b) FA, (c) CG + LMA, (d) CG + FA + LMA; magnification 5000×: (e) CG + FA + LMA).
Sustainability 17 03318 g010
Sustainability 17 03318 g011
Figure 11. Mechanism of formation of CGAS aggregate.
Figure 11. Mechanism of formation of CGAS aggregate.
Sustainability 17 03318 g011
Table 1. Chemical composition of CG and FA.
Table 1. Chemical composition of CG and FA.
SampleChemical Composition (wt%)
SiO2Al2O3SO3Fe2O3K2OTiO2MgOCaONa2OP2O5
CG57.0322.304.145.133.741.901.252.891.230.12
FA46.2134.701.775.150.922.490.996.480.550.23
Table 2. Experimental program.
Table 2. Experimental program.
Sample NameCG (%)FA (%)Microbial Agents (%)
CG10000
CG + LMA10000.1
CG + CMA10000.1
CG + FA70300
CG + FA + LMA70300.1
CG + FA + CMA70300.1
Table 3. Comparison of water-holding capacity of artificial soils.
Table 3. Comparison of water-holding capacity of artificial soils.
Sample NameWHC (%)
CG38.47
CG + LMA49.44
CG + CMA46.50
CG + FA49.41
CG + FA + LMA54.88
CG + FA + CMA51.95
Table 4. Stability evaluation of water-stable aggregates in artificial soil.
Table 4. Stability evaluation of water-stable aggregates in artificial soil.
Sample NameMWDGMD
CG0.140.11
CG + LMA0.240.20
CG + CMA0.200.16
CG + FA0.180.13
CG + FA + LMA0.360.24
CG + FA + CMA0.310.22
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Gong, W.; Hui, H.; Ma, S.; Ji, J.; Jiang, H. Preparation of Coal Gangue-Based Artificial Soil and Investigation of the Mechanism of Aggregate Structure Formation. Sustainability 2025, 17, 3318. https://doi.org/10.3390/su17083318

AMA Style

Gong W, Hui H, Ma S, Ji J, Jiang H. Preparation of Coal Gangue-Based Artificial Soil and Investigation of the Mechanism of Aggregate Structure Formation. Sustainability. 2025; 17(8):3318. https://doi.org/10.3390/su17083318

Chicago/Turabian Style

Gong, Weinan, Helong Hui, Shuhua Ma, Jianbing Ji, and Hongtao Jiang. 2025. "Preparation of Coal Gangue-Based Artificial Soil and Investigation of the Mechanism of Aggregate Structure Formation" Sustainability 17, no. 8: 3318. https://doi.org/10.3390/su17083318

APA Style

Gong, W., Hui, H., Ma, S., Ji, J., & Jiang, H. (2025). Preparation of Coal Gangue-Based Artificial Soil and Investigation of the Mechanism of Aggregate Structure Formation. Sustainability, 17(8), 3318. https://doi.org/10.3390/su17083318

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop