In China, a production capacity of one hundred million tonnes of coal culminates in the emission of approximately fourteen million tonnes of gangue. Within the coal purification sector, the refinement of an equivalent volume of coking coal results in the discharge of twenty million tonnes of gangue, whereas the laundering of the same amount of thermal coal contributes about fifteen million tonnes of gangue. Over the preceding triennium, the production of coal gangue has seen an uptick of approximately six hundred and fifty million tonnes. It is evident that coal gangue emerges as the primary solid waste derivative during the coal extraction process. Coal gangue refers to the mixture of non-coal materials that are extracted alongside coal from mines. It is primarily composed of rocks and minerals that are present in the coal seam and the layers above or below it, which are co-excavated during mining operations. This mixture can include various materials such as mudstone, shale, sandstone, clay, and other associated minerals. In addition to these inorganic components, coal gangue may also contain trace amounts of coal and organic matter. As a byproduct of coal mining, coal gangue typically accumulates in large heaps near mining sites, where it can pose environmental and disposal challenges. Its composition varies depending on the geographical location and geological conditions of the coal mine. This variability influences its physical and chemical properties, which are significant for understanding its environmental impact and potential reutilization.
Untended mounds of coal gangue have morphed into one of the dominant influencers of the ecological equilibrium and sustainable evolution of mining terrains(Bian et al., 2012). Inner Mongolia, a significant coal-generating region within China, contributes about one hundred and fifty million tonnes of coal gangue annually. National stipulations pertaining to land restoration specifically mandate that tailings (rock) disposal locales within mining zones are subject to land restoration and vegetation rehabilitation.
Historical precedents have elucidated that the dearth of topsoil reserves is a salient issue in the execution of ecological restoration initiatives within mining zones. Accessible topsoil reserves embody one of the constraining conditions for the execution of land restoration projects within mining zones and for botanical colonization.
Within a specific open-cast coal pit in the Eastern Mongolian mining region of Inner Mongolia, the prevalent coal gangue is carbonaceous shale, replete with organic matter and exhibiting minimal pollutant content(Erdenetsogt et al., 2009). With its extremely delicate stratification and plethora of rock fissures, this shale is readily weathered into soil. Investigations indicate that rocks exposed to atmospheric conditions are susceptible to progressive weathering and disintegration under the purview of physical, chemical, and biological influencers(Minyard et al., 2012; Chizhikova et al., 2016; Trudgill et al., 2022).
The physical weathering of rocks, marking the inception of soil genesis, is dictated by several influencers, with pH, temperature, humidity, salinity, and physical stress being paramount. Temperature and moisture emerge as the primary arbiters of the weathering rate(Luo et al., 2022). In frigid climes, characterized by significant day-night temperature variations, rocks are subjected to the simultaneous impacts of humidity and freeze-thaw cycles. Intrinsic pore water freezes and expands, catalyzing the deformation and dispersion of micro-cracks within the rock(Fantong et al., 2015; Shi et al., 2021). The ensuing stress reconfigures the stratified structure of the rock, accelerating its weathering decomposition and subsequent transmutation into soil(Shrestha and Lal, 2011).
Therefore, analyzing the weathering characteristics of coal gangue under the purview of humidity and freeze-thaw cycles is indispensable for comprehending the process and mechanism of soil genesis from coal gangue in cold mining zones. The findings of these probes will play a crucial role in broadening the source of topsoil for land restoration in mining zones(Zhang et al., 2021).
The existing mainstream technology for ecological restoration and remediation of coal gangue hills is based on soil covering methods which necessitate the use of natural soil resources (Krzyszowska Waitkus, 2022). However, natural soil is not only a crucial natural resource but also forms the foundation and a significant component of the ecosystem. As a result, natural soil resources are increasingly under stringent protection, and large-scale acquisition of natural soil will not only increase the costs but also become increasingly challenging, even impossible to implement. Therefore, the development of ecological restoration or remediation technology for coal gangue hills that does not depend on natural soil resources is a highly inherent demand. Preceding study has primarily concentrated on the physical, chemical, and biological attributes of coal gangue weathering by-products and their environmental ramifications(Cheng et al., 2020). Nevertheless, there exists a relative deficit in quantitative probes into coal gangue weathering decomposition and associated mechanisms, particularly in relation to coal gangue soil genesis in frigid regions and the factors dictating it(Koele et al., 2014; Tamamura et al., 2015; Xiao et al., 2015; Li et al., 2019).
In this study, detailed examination has been conducted on the effects of humidity fluctuation and freeze-thaw cycle treatments on the weathering disintegration rate of coal gangue in frigid mining regions. Through an in-depth investigation into the mechanism of coal gangue weathering, this study provides insight towards addressing the issue of topsoil scarcity in restoration initiatives within cold mining areas. This contributes both a theoretical foundation and practical guidance to the domain of land restoration in mining regions.