Ecological Restoration and Transformation of Maoming Oil Shale Mining Area: Experience and Inspirations

Abstract

Oil shale is a kind of unconventional energy resource with abundant reserves, but its exploitation has a continuous negative impact on the environment, which has hindered the research and exploitation of oil shale under the international environmental consensus on issues such as climate change. Therefore, more attention should be paid to environmental problems as the side effect of oil shale exploitation. With the combination of field research, literature collection, and tracking survey, the oil shale open-pit exploitation and management process in Maoming, Guangdong, China, has been investigated, and its development and transformation model has been subsequently refined and summarized. The research results show that Maoming oil shale open-pit mine area has gone through four main stages: pre-exploitation stage, large-scale utilization stage, restoration stage, and green development stage. Through the management of mine pit treatment, vegetation restoration, ecological park construction, and tourism resource development, the abandoned open-pit mine has been transformed into an ecological park combining ecosystem, tourism, and cultural resources. In this process, this area has achieved the transformation from rough resource extraction to environment-friendly sustainable growth in its development mode. As a successful case of open-pit mine management in the world, the ecological restoration experience in Maoming can function as a reference for the smooth development and transformation of other oil shale mines in developing countries.

1. Introduction

Defined as a high-ash solid combustible organic rock, oil shale is typically a fine-grained sedimentary rock (usually shale) with a high kerogen content that is sufficient for fractionating a significant amount of oil [1,2,3]. It has more than 40% ash content and 3.5% oil content and is regarded as a typical unconventional oil and gas resource. With rich organic matter and complex micropore structure, oil shale can generate hydrocarbons during diagenetic evolution, and the hydrocarbon generation potential is very considerable [4,5,6]. The abundance of oil shale reserves and the feasibility of developing and utilizing the resource make it a very significant alternative energy in the 21st century [7,8]. Oil shale resources are widely distributed around the world [9,10], and the USA [11,12], China [13,14], Estonia [15,16], and other countries [17,18] have the largest reserves. In particular, Estonia enjoys a long history of oil shale exploitation and utilization, and China has also explored and developed some of its reserves. However, oil shale extraction can have a negative impact on the environment; together with the high development cost and international consensus on climate change, it hinders the research, development, and utilization of unconventional hydrocarbon resources, and it calls for the upgrading of green and clean relevant technologies [19,20]. Additionally, the ecological restoration and management of the oil shale extraction sites have also become an urgency [21,22].

Currently, the research and practice on this topic have been mainly conducted in Estonia and China, where the oil shale reserve is abundant and has experienced long-term exploitation. Specifically, in Estonia, afforestation has been regarded as the best approach to restoring the ecosystem of the oil shale post-mining areas due to the rough soil conditions [23,24,25]. The success of the ecological restoration of this method is greatly affected by the characteristics of the planted species and their responses to the climate and soil factors; therefore, the growth and survival responses of different species in different oil shale mining sites have been investigated and compared [26,27,28].

China also has a large oil shale potential, which is dispersed across a number of energy basins, including the Songliao Basin, Maoming Basin, and Fushun Basin [29]. Among them, the Maoming Basin in southern China with oil shale reserves of 5.515 billion tons has a long history in the development and utilization of this energy source and is the pioneer in carrying out ecological restoration and land-use transformation in China. Currently, the mining has stopped, and the ecological restoration and management there have yielded considerable results [30,31,32]. However, the systematic summarization of Maoming’s restoration strategies is still absent. The study of this successful example is beneficial for broadening the experience and providing a reference for other mines’ environmental restoration and development transformation [33,34]. Therefore, taking the oil shale mine in the Maoming Basin as the case area, this research has summarized the experience of the oil shale mine’s ecological restoration and management and then refined the mine area’s development model and transformation mechanism on the basis of ecological restoration, which can serve as the scientific grounds for the transformative development of other oil shale mines in developing countries. The aim of the present study is to (1) track the course of the exploitation and post-mining management in Maoming oil shale open-pit mines, (2) summarize the measures and effects of the post-mining management in Maoming, and (3) refine the model of Maoming oil shale post-mining management and promote the regional economic transformation and development.

2. Methodology and Study Area

2.1. Methodology

Despite the popularity of the post-mining ecosystem restoration brought about by environmental consensus on issues such as climate change, ecological treatment and recovery projects in mining areas are systematic and span a long time, which poses difficulties in tracing their effects. A systematic post-mining ecological treatment project involves the interaction and cooperation of various measures, including geological disaster management, water management, vegetation restoration and greening, landscape planning and construction, traffic planning, and building reconstruction and utilization. In addition, the project will also change the surrounding economy mode, which cannot be overlooked in the research on the transformation of mining areas. Therefore, the research on this topic is interdisciplinary basically and requires multiple methods to conduct comprehensive characterization and long-term tracking. The problems faced by this study include that (1) a long time span of tracking was needed due to the ecological management cycle; (2) interdisciplinary research was needed considering that the post-mining treatment and transformation combines many engineering measures and complex approaches; and (3) high multidisciplinary skills were needed for the team to conduct the field survey, literature analysis, geographic information (such as remote sensing) analysis, geological research, project management, and evaluation.

To solve the above problems, the team has designed a systematic package of research methods. First of all, the tracking of post-mining ecological management in Maoming has spanned the entire treatment cycle and was divided into several stages to fully compare the measures and effects, including before, during, and after the treatment. In this regard, the team has carried out field surveys several times in the past ten years to follow the progression. Secondly, a multidisciplinary research team has been specially established. The research team is composed of professional researchers in geology, geographic information, tourism management, architecture (solid waste direction), landscape design, and other fields. The team visited the Maoming oil shale open-pit mine and its surrounding areas five times in the years 2012, 2013, 2014, 2018, and 2022. During these visits, the team methodically tracked and gathered pertinent data, consulted with local experts in ecological restoration and mining, and collected remote sensing images of the area for comparative analysis. Through comparative study, the research aims to extract the design and implementation of the environmental management project in this area and track its effects. In addition, an effective information collection and communication channel was established between the research team and the relevant personnel and residents the team investigate and consult with to ensure the smooth collection of research data.

2.2. Study Area and Geological Features

Maoming basin is located in southwestern Guangdong (Figure 1). Organic-rich shale with a thickness of 20–40 m was developed in the Cenozoic Paleogene there. The Maoming mud shale deposit is located at the southwest edge of Maoming Basin extending in the southeast–northwest direction, with a total length of about 40 km and a maximum width of more than 10 km from north to south. Maoming Basin is a half-graben fault basin formed under the action of tension. The stratum in the basin is generally a syncline structure extending from northwest to southeast. The basin is based on the Sinian metamorphic series and covered by the multilayers of Late Cretaceous Shigu Group stratum, Eocene Shangdong Formation stratum, Oligocene Youganwo Formation stratum, Miocene Huangniuling Formation and Shangcun Formation stratum, Pliocene Laohuling Formation and Gaopeng Ridge Formation, and Quaternary Formation successively [35,36,37]. The well-developed mud shale in the basin is mainly from Youganwo Formation and Shangcun Formation. The Youganwo Formation developed during the period from the late Eocene to the early Oligocene. Without any surface outcrop, the Youganwo Formation is only found in open-pit mines and is mainly composed of dark brown shale with rich organic matter. Quaternary topsoil covering kaolin oil shale, coal, etc., is exposed in this area’s oil shale open-pit mines. Professional researchers in geology, geographic information, tourism management, architecture (solid waste direction), landscape design, etc., formed a team and conducted field research in Maoming oil shale open-pit mines 5 times in the years 2012, 2013, 2014, 2018, and 2022 to systematically collect the relevant data. The local miners and experts in ecological restoration were consulted, and remote sensing images were collected for comparative analysis. Through the comparative analysis, this research is aimed at summarizing the design and implementation of the Maoming ecological restoration project, and by tracking the restoration effect, the key problems, the design features, the implementation status of the project, and the project’s influence on the surrounding region’s economy are further investigated.

3. Utilization and Ecological Restoration of Oil Shale

3.1. Oil Shale Utilization History of Maoming Basin

Maoming Basin has witnessed a long history of extracting and utilizing oil shale, which can date back to the period of 1905–1924, when personnel from China and overseas made the preliminary geological exploration of Jintang oil shale in Maoming Basin. After 1954, systematic geological exploration was conducted on oil shale in Maoming Basin, which sparked the construction of open-pit mines and started the development and utilization of oil shale [38]. Specifically, the Maoming oil shale exploitation began in 1955 (Figure 2a) as a large shale oil plant was built with the approval of the National Reserves Committee. In 1970, the fourth furnace, which was known as the famous Maoming Garden Furnace, was put on the agenda with the designed capacity of refining 5 × 10⁴ t per furnace, and the actual production capacity of refining 19 × 10⁴ t in four furnaces. By 1980, the annual output of oil shale reached 4 million tons, and the highest actual annual output reached 6.44 million tons. By 1986, the open-pit shale mine with an annual output of 5 million tons and a shale refinery with an annual output of 200,000 tons was built. Fushun retort technology was used in the extraction, through which oil shale was crushed and sorted into a distillation furnace firstly, and then after being dried and preheated to 450~600 °C under the condition of air isolation, shale oil was cracked and released, and the remaining shale semi-coke underwent the vaporization process and began the oxidation–reduction reaction. Finally, the shale waste was discharged out of the oven. Despite the crucial role played by the Maoming oil shale exploitation and utilization in this period when China was confronted with an oil energy shortage, the open-pit mining and high-temperature retorting techniques used to extract shale oil exerted a great bad influence on the surrounding environment and came at a high economic cost. By the 1990s, Maoming oil shale mines turned to function as the oil shale power generator and incorporated other comprehensive utilizations. In 1991, 295.5 × 10⁴ t oil shale ores were produced. In 1992, the mining and refinery ended. In 1994, all furnaces were dismantled due to the limited oil content (5.94–8.37% on average), high water content (16–17% on average), low recovery rate of shale oil (60% on average, up to 64%), and high energy consumption (shale crushing, transport, retorting, cooling, etc.) in oil shale development. In 2011, the open-pit mining of associated resources such as kaolin and coal also ended, with a pit that needed treatment being outstanding. In 2013, the polluting enterprises were also closed due to environmental problems and high development costs, representing the conclusion of the oil shale utilization and the start of the environmental management. However, at the time when the open-pit mine was shut down, the mining volume only accounted for 2% of the total reserves, and other associated resources such as kaolin and coal were still underdeveloped in spite of their abundance. In the whole production operation from 1962 to 1992, the cumulative mining volume of the Maoming open-pit mine was nearly 200 million tons, among which 102 million tons was oil shale, and 2.92 million tons of shale oil was produced.

3.2. Environmental Problems Caused by Oil Shale Utilization

Large-scale oil shale exploitation in Maoming Basin has brought about environmental pollution problems. After 1992, although the exploitation of oil shale stopped, the exploitation of associated minerals kaolin and coal still continued. Due to the relatively backward mining technology and inadequate management, industrial waste and mine wastewater have caused serious damage to the local environment. A pit was formed in the oil shale open-pit mining area with a total volume of about 160 million cubic meters. After several years, it turned into a pit lake used for discharging industrial wastewater. Based on the field survey around the mine, we found that mining also led to the piling up of dumped topsoil and leftover waste residue caused by the oil extraction (Figure 3a,b). As a result, two refuse dumps were formed in the south and north. The south waste dump with an area of 3.31 km² was used to store topsoil. The north waste dump with an area of 6.93 km² was used to store waste residue with a pH value ranging from 3.2 to 4.5. The pH of its leachate was generally 3.2, indicating the strong acidity of the north waste dump and causing acidic underground water in the surrounding area of the waste dump and open pit. In addition, there are hidden hazards of geological disasters such as landslides, collapses, and debris flows in the slope around the mine (Figure 3a). In addition, after the accumulative leaching of the oil and sulfur from the oil shale, the water quality of the pit lake became significantly poor and acidified. In 1996, Guangdong Province carried out scientific and technological research on and made a plan for oil shale development and utilization, including the application of oil shale power generation and combustion technology. In 2001, the government’s concern for environmental protection led to the initiation of the “Ecological Restoration Study of Degraded Ecosystems in Oil Shale Dumps”. At the same time, kaolin and oil shale once covered by the topsoil were exposed (Figure 3c), and the vegetation was significantly scarce after years of decreasing. Since 2013, open-pit mining has been discontinued by the local government, and the Maoming oil shale mining area has progressively moved into a stage of ecological restoration and control except for the problems of illicit mining. From 2013 to 2016, a series of ecological restoration projects were initiated in the Maoming mining area (Figure 3b,d). Figure 3 shows the image of the research team’s survey in the area around the Maoming oil shale pit from 2012 to 2014. The team found that years of extensive and disorderly mining have caused serious damage to the surrounding environment. Specifically, the water and surrounding soil in the mining area are essentially unrecoverable. Damage to the biological habitat environment, a decline in biodiversity, and new issues with air, water, and soil pollution as well as geological dangers have all occurred. Figure 3e,f shows the comparison of the same parts in the mine before and after treatment.

The ecological condition of the mining area has significantly improved after several years of treatment. The analysis of Maoming oil shale development, utilization, and ecological restoration process shows that it is closely associated with China’s economic and social development and China’s demand for energy and can be divided into several stages (Figure 4). As can be seen from Figure 4, the process of oil shale utilization and environmental restoration in Maoming can be divided into four stages. Before 1954, the investigation of Maoming oil shale was mainly limited to geological theoretical research rather than actual exploitation, which can be regarded as the pre-exploitation stage. From 1954 to 2013, oil shale and its associated resources were developed in this area, which can be regarded as the large-scale utilization stage. From 2013 to 2018, ecological restoration was the theme in this stage, and relevant treatment projects were carried out centrally. After 2018, the ecological restoration achievements started to contribute to Maoming’s tourism and ecological economy and became an important link to reshaping the regional economic development model and creating a green growth system.

4. Ecological Restoration Measures for Maoming’s Oil Shale Mining Area

Through specialized treatment, the open-pit mine area in Maoming has been turned into an ecological park that has distinctive historical and cultural elements and integrates sightseeing and relaxation functions. The ecology of the damaged mining area was restored, and functional areas were further divided. On this basis, the ecological restoration project stimulated the growth of local rural tourism, ecological agriculture, and other industries in the neighboring villages and towns, and a new development force was created. Maoming’s experience can be regarded as a representative model of mining area governance and restoration, which includes modifying mine control measures to local conditions, transferring water to the pit lake to improve water quality, large-scale tree planting, reviving open-pit mines’ ecological and tourism resources, enhancing nearby traffic, and developing a “countryside complex” which integrates tourism and agriculture.

4.1. Treatment of Mining Pit

Selecting the treatment method is the first step of open-pit mine management, and the main methods include landfilling and transforming the pits into lakes, depending on the size of the pit. Considering Maoming oil shale’s long development history and large pit scale, the landfill of the mine pit is considerably expensive. After the discontinuation of the mining, a pit lake with a surface area of around 5.2 km² was formed as a result of rainwater accumulation and the discharge of acidic water from kaolin mining and washing. Considering the large scale of the mine pit and the acidic water problems, the lake transformation is a more economical choice. Therefore, a water quality improvement project was conducted. Specifically, a 950 m diversion canal, a 920 m dam, and a 1130 m flood discharge canal were established to divert the Jianjiang River into the open-pit lake and facilitate the water flow into the Xiaodong River. As a result, the mine pit lake was associated with the Gaozhou Reservoir, Jianjiang River, and Xiaodong River water systems. The continuing injection of fresh water greatly improved the mine pit lake water quality [39]. At the same time, the surrounding polluting enterprises (red brick plants, ore washing plants, small oil refineries, etc.) were shut down to strictly control the pollution sources and ensure the mining area was no longer polluted by domestic and industrial sewage. In 2016, the water diversion canal was completed and transformed the mine pit into a multifunctional water reservoir with a storage capacity of 160 million cubic meters and a water surface area of 6.8 km². The water quality of the mine lake was also greatly improved. The establishment of the multifunctional water reservoir has turned the seriously polluted abandoned mine pit into a man-made lake (Haoxin Lake) integrating ecology, irrigation, and landscape functions. Furthermore, it also facilitates solving the irrigation of surrounding farmland by improving the irrigation conditions of more than 5.8667 km² of nearby farmland. It also further contributes to improving the ecological environment of the Xiaodongjiang River basin.

4.2. Vegetation Restoration

The exploitation of oil shale in the Maoming region has caused great damage to the local ecosystem. Due to the long development history, the soil in the mining area was significantly polluted with the tendency of compaction and the production of ponding. Abandoned chemical hazardous waste and various kinds of garbage covered the surface of the mine’s surrounding area, and the soil was barren and acidic with the composition of kaolin ore and oil shale. Conventional plants were difficult to grow on the soil polluted by element leaching and oil seepage. Finally, Acacia auriculiformis, Acacia confusa, Paeonia suffruticosa, Handroanthus chrysanthus, Handroanthus impetiginosus, Campanula medium, Lagerstroemia speciosa, Cassia fistula, Bauhinia variegata L., etc., were selected after the trial planting of 30 species of trees for regreening [39]. Simultaneously, in the tree pits, large holes were dug to replace the original soil. The waste sludges from the Xiaodongjiang River and the city park were used as organic fertilizer to improve the soil in the mine areas ensure the survival of tree species. Over 6 km² of trees were planted and regreened, and roughly 500,000 trees were planted during the treatment time [39]. The soil’s physical and chemical characteristics were enhanced, and the overall number of soil microorganisms grew significantly. Effective changes were made to the mining area’s ecological surroundings. The regrowth of plants will also lessen the likelihood of desertification brought on by water and soil loss and assist in organically resolving the soil pollution issues in the mining area. With the closure of polluting businesses and the coverage of the surface-exposed sand, the area’s air quality has been greatly improved. In Maoming’s urban area, the concentrations of fine particulate matter (PM2.5) and inhalable particulate matter (PM10) declined from 39 μg/m³ and 58 μg/m³ in 2014 to 30 μg/m³ and 46 μg/m³ in 2016, respectively, according to the monitoring data.

4.3. Ecological Park and Tourism Resource Construction

Maoming’s oil shale open-pit mine area bears significant city memory and the local mining history and culture, therefore belonging to a typical industrial and mining relic resource. With a rich mining heritage, it has significant scientific significance. By using an abandoned factory building, the local government of Maoming constructed the first mineral site museum in Guangdong. It incorporated exhibition, science popularization, collection, and other multifunctional collections; preserved historical mining artifacts; and displayed the history of the development of the Maoming open-pit mine from the 1950s to the present. The construction of the museum is aimed to promote the learning and the passing down of Maoming’s mining culture and spirit as an oil industry city, and now the museum has become an important platform for publicizing the ecological restoration of open-pit mines. With the implementation of the traffic and road enhancement plan, approximately 40 km of roads have been enlarged or freshly build. The construction of the park’s outer ring road was completed, creating a network that runs both inside and outside of the perimeter of the mine pit and lake. The landscape, including green paths and water-friendly platforms, was also formed to match the road network. The enhanced traffic condition revitalized the open-pit mine’s ecological resources as well as its tourism and sightseeing resources. Mine lakes, mining sites, comprehensive museums, and the surrounding landscape made up an ecological park (Maoming Open-Pit Mine Ecological Park) with cultural, ecological, and tourism functions and the elements of mountains, water, garden, trees, and mines. In 2017, Guangdong National Park was approved as National Mine Park.

5. Discussion

5.1. Key Issues of Maoming Oil Shale Open-Pit Mine Treatment

In the exploitation process of the oil shale open-pit mine in the Maoming area, the surface of the oil shale and kaolin were exposed as a result of the excavation of mine pits (including oil shale mining and associated resource mining). The impact of the oil shale development, including the slope at the pit’s edge, the piling up of waste soil around the pit, the accumulation of waste residue from oil shale retorting, and the abandoned pits, contributed to specific geological risks and was a source of soil and water pollution.

The leaching of waste residue and exposed oil shale around the pit resulted in the acidification of ponding water in the pit. Coupled with discharged industrial sewage, the water pollution problem around the pit emerged. The water pollution problem further aggravated the soil pollution problem and water and soil loss problem [40]. During the mining in 1985, the topsoil around the mine pit was exposed seriously (Figure 5), which directly or indirectly damaged the surface vegetation, changed the vegetation restoration process through soil acidification pollution, and negatively influenced the agricultural economy of the surrounding area. In addition, another issue to deal with was the remaining sites of industrial plants that were established to process and utilize the mining resources. Although mining can promote the local economy, its extensive development mode proved unsustainable at the expense of the ecological environment.

In summary, with a long mining history, Maoming was confronted with many pollution problems. Therefore, ecological restoration should take into account elements including waterbody, soil, atmosphere, vegetation, and geological factors. A larger-scale treatment project is required on the basis of the accurate identification of ecological problems in the mining area, as well as the clarification of core issues in restoring the open-pit mine environment and transferring regional economic development mode [41]. Through the geological investigation and comprehensive analysis, water and vegetation are the core issues of ecological management in the Maoming mining area, while introducing sustainable development concepts and construction as well as revitalizing ecological and tourism resources on the basis of ecological restoration were the primary concerns of innovating the economic development model of the area.

5.2. Experience and Inspirations from the “Maoming Model”

The experience of Maoming showed that the open-pit mine management and economic development mode transformation were deliberate projects. Through pit and slope management, water treatment, vegetation restoration, traffic improvement, pollution source shutdown, industrial site transformation, and the targeted design and transformation of the mine area landscape, the new infrastructure system was initially built. It consisted of a multipurpose reservoir, an interconnected water network, large-scale vegetation restoration, an improved traffic network, new landscape facilities, enhanced agricultural conditions, and renovated mining site sightseeing facilities. In particular, the mine pit was transformed into an ecological sightseeing lake and multifunctional reservoir, the mining-related facilities were converted into cultural and tourism facilities, and the area around the mine pit that had been environmentally damaged was transformed into an ecological restoration location suitable for developing agriculture and sightseeing tourism. As a result, the revitalization of ecological, transportation, and cultural resources was realized, and a new development system supported by tourism and agricultural resources on the basis of the restoration of oil shale open-pit ecological conditions was built (Figure 6). After the completion of the treatment project in 2018, the number of tourists visiting the scenic area of the mine pit grew rapidly, and the area became the first choice of popular scenic spots in Maoming. The construction of the multifunctional reservoir and the development of tourism resources also provided opportunities for sightseeing, agriculture, etc. Rural tourism projects were also promoted. Youganwo village adjacent to the mine pit lake has built farms and ecological picking gardens. Some villages have launched “garden village” initiatives to attract tourists, representing a new path for integrating agriculture and tourism based on the Maoming ecological restoration projects [42]. Currently, the open-pit mining area has been turned into an open ecological park, and the historical relics of the mining industry are still visible throughout the ecological landscape. The Chinese news media has given extensive attention to the Maoming open-pit mine management. The mainstream media source People’s Daily reported on Maoming’s experience, commenting that Maoming’s ecological restoration of open-pit mines serves as a “national model” for mine environmental management and should thus be promoted [39].

Maoming has likewise optimized its industries at the same time. The best businesses in the area, such as Maoming Petrochemical, have retained their competitiveness in the industry even though the mining of the basin’s rich oil shale has been discontinued. They developed the mid- and downstream petrochemical industry chain, and based on it, green chemical and new material industry clusters were created. With the advantageous resources of ports, petrochemicals, and bays, Maoming has concentrated on the development of the “marine economy” and expedited the concentration of port logistics, port manufacturing, and green chemical industries. The green chemical and hydrogen industries are developing particularly rapidly. The ecological development of the industry ensures the continuation of the region’s economic and social level, while the ecological restoration and treatment of mines pay the environmental debts from historical mining and help Maoming to complete the green transformation.

The regional development mode of ecological restoration and management and the transformation of oil shale open pits were summarized in the analysis above, and the route is illustrated in Figure 7. Although initial results have been achieved in Maoming’s management of oil shale mining, further construction and improvement are still required in many aspects. According to another field survey of the area around the Maoming oil shale open-pit mine conducted by the research team in 2022, a green development synthesis based on the existing achievements can be created. Specifically, the functional zoning of the open-pit mine perimeter area can be further optimized in accordance with the regional territorial spatial planning, general urban planning, and general land use planning of the adjacent area. It is necessary to carry out ongoing optimization work compatible with the green growth route by methodically leveraging the cultural significance of mining sites and the expertise in ecological restoration and management of open-pit mines. For instance, the traffic pattern requires improvement. The improvement status of water and soil pollution needs to be monitored and studied over time. Every functional entity and village in the area needs to have its industrial location indicated. Based on the architecture and qualities already present, each village’s attractiveness has to be improved. The ecological restoration and treatment of the Maoming oil shale open-pit mine and surrounding mining areas not only improved and restored the ecological conditions, but also exploited the cultural treasures of the industrial site. Opportunities for changing the economic development model from relying on energy resources to building a green and sustainable growth pattern in the economy have been presented by the ecological restoration of the mine region. In terms of mine management and the transition to a green economy, Maoming’s experience is symbolic of the entire world. As many developing nations have downplayed the environmental significance of the mining industry throughout the past century and left problems unattended, the Maoming model can serve as a helpful guide for improving the ecological conditions at mines in these nations and regions.

In light of the Maoming Basin’s availability of oil shale and related resources, these resources are still valuable for development under the introduction of green development technologies such as in situ conversion [43] and carbon emission reduction in the exploitation and utilization process. In recent years, the Maoming government has released “Maoming Oil Shale Power Generation Industry Plan (2005–2020)”, which states that the development of the oil shale power generation industry will be promoted under the premise of “scaling-up, high-efficiency, less pollution, and ecological preservation”. At the same time, the maximum depth of oil shale in the Maoming Basin is suitable for the formation of biogenic shale gas, indicating the potential for biogenic gas exploration in this area. The promotion of the regional economy’s sustainable growth is only possible through the achievement of green and low-carbon energy resource exploitation, as well as through the growth of the industries such as specialized tourism and ecological agriculture [44].

6. Conclusions

In the past few centuries, fossil energy, as an important industrial resource, has effectively promoted the development of society and the economy, but at the same time, it also left environmental problems calling for solutions. Different regions feature different post-mining measures and models, and the study of a typical region will provide a reference and scientific basis for the design of future projects. Maoming oil shale had a long exploitation history and also experienced systematic treatment after the mining was stopped, making it a representative case of ecological restoration and management in oil shale mining areas. Summarizing its treatment model and studying the experience not only is beneficial for the oil shale ecological governance, but also can inspire the innovative management of other raw materials. The following conclusions were obtained in this study:

• The development and treatment of oil shale open-pit mines in the Maoming area have undergone four main stages, namely the pre-exploitation stage, large-scale utilization stage, restoration stage, and green development stage. During these stages, a shift from the model of extensive energy resource development to the model of green and sustainable development was realized. In the achievement of the transition, rigorous governance is the most crucial factor.
• The Maoming oil shale open-pit mine’s ecological restoration and treatment mostly entail pit treatment, vegetation restoration, ecological park and tourism resource construction, etc. Specific measures include pit treatment, slope treatment, water treatment, vegetation restoration, traffic improvement, pollution source discontinuation, industrial site renovation, and landscape design and construction. A system of infrastructure has been developed, including multipurpose reservoirs, a connected water network, extensive regreening of the vegetation, an enhanced traffic network, new landscape facilities, improved farming conditions, and renovated mining site sightseeing facilities.
• Based on the construction of the new infrastructure system, cultural and tourism resources such as mining culture, mining industry sites, and agricultural tourism have been exploited to achieve the integration of ecological, transportation, and cultural resources and to build a green economic development model based on the ecological restoration of oil shale open-pit mines.
• The ecological restoration and management of the Maoming oil shale open-pit mine have realized the transformation of the economic development model. This case study serves as an example for the management as well as the transformative development in open-pit mine areas, providing a scientific guide for the ecological restoration of mines in developing countries.