Policies and Technical Status Quo of Large-Scale Backfilling with Bulk Solid Wastes
In the process of rapid industrial development, the output of bulk solid wastes continues to rise, and their disposal has become a key focus in the field of environmental protection. The use of bulk solid wastes for ecological backfilling not only effectively addresses problems such as land occupation by waste stockpiling and environmental pollution but also realizes the recycling of resources to a certain extent, promoting sustainable development. Based on a comprehensive review of literature and industry research, this article conducts an in-depth analysis of the policies and technical status quo of large-scale backfilling with bulk solid wastes.
01 Policy and Standard System
1.1 Policy Promotion at the National Level
The state has issued a series of policies to encourage the comprehensive utilization of bulk solid wastes, among which large-scale backfilling is one of the important application directions. The Guiding Opinions on the Comprehensive Utilization of Bulk Solid Wastes During the "14th Five-Year Plan" Period clearly states that efforts should be accelerated to promote the large-scale utilization of industrial solid wastes such as tailings in underground filling, ecological restoration, and other fields. In August 2024, the Notice of the General Office of the Ministry of Natural Resources on Strictly Adhering to the Policy Bottom Line for the Utilization of Soil and Stone Materials and Further Improving Incentive Measures for Mine Ecological Restoration emphasized promoting the ecological utilization of general mining solid wastes (such as tailings) generated from mining and beneficiation activities in ecological restoration projects. On the premise of strict pollution risk control, compliance with soil environmental quality requirements, and ensuring environmental safety, it encourages the use of such wastes for soil improvement. These policies provide clear guidance and support for the large-scale backfilling of bulk solid wastes.
1.2 Local Standards and Policies
Under the guidance of national policies, various localities have formulated local policies and standards in light of their actual conditions to further refine the implementation requirements for bulk solid waste backfilling.
In August 2022, the Inner Mongolia Autonomous Region approved and issued DB15/T 2763 Technical Specification for the Use of General Industrial Solid Wastes in Mine Pit Backfilling and Ecological Restoration, which details the implementation requirements for general solid waste backfilling and enhances operability.
In December 2022, Baotou City issued the Administrative Regulations of Baotou City on the Use of General Industrial Solid Wastes in Mine Pit Backfilling and Ecological Restoration, clarifying the collaborative governance and supervision responsibilities of various departments and units.
In July 2023, Anhui Province released the Technical Specification for the Disposal of General Industrial Solid Wastes and Ecological Restoration in Abandoned Open-Pit Mines, specifying the site selection, survey, design, stacking, ecological restoration, safety and environmental monitoring, and acceptance inspection for backfilling abandoned open-pit mines with general industrial solid wastes and ecological restoration projects.
In January 2025, Shanxi Province issued the Environmental Protection Technical Specification for Ecological Backfilling with Coal Gangue, providing a provincial-level technical standard for large-scale backfilling with coal gangue, aiming to address the problem of coal gangue, with an annual output of over 100 million tons and a historical stockpile exceeding 1 billion tons in the province.
In August 2025, Shandong Province issued the Pilot Plan for Backfilling with Bulk Industrial Solid Wastes in Shandong Province, proposing to select suitable areas such as surface excavation areas from open-pit mining, subsidence areas from underground mining, and natural depressions for backfilling applications on the premise of controllable environmental risks and site selection in line with territorial spatial planning. For the backfilling pilot projects, Class I general industrial solid wastes or Class II general industrial solid wastes that meet Class I standards after pretreatment shall be used.
These local standards and specifications provide a solid institutional guarantee for the implementation of large-scale bulk solid waste backfilling projects.
02 Analysis of Technical Status Quo
Backfilling technology has gone through three key stages of evolution.
In the early stage, simple landfilling was the main method, where bulk solid wastes were directly dumped into designated areas. However, this method had obvious drawbacks: harmful substances in the wastes were prone to leaching, polluting soil and groundwater, resulting in high environmental risks. Meanwhile, the resource recycling rate was extremely low, and a large amount of usable resources were wasted.
Between 2005 and 2015, modified backfilling technology gradually matured. This technology mainly involves pretreating bulk solid wastes by adding curing agents and stabilizing agents. For example, when treating tailings, adding curing agents such as cement can improve the strength and stability of the backfill; for solid wastes containing heavy metals, adding specific stabilizing agents can fix the heavy metals and reduce their leaching risk during backfilling, greatly improving the engineering performance and environmental safety of the backfill.
In recent years, ecologically functional backfilling has become a research and application hotspot. Researchers have deeply explored the potential value of industrial solid wastes such as phosphogypsum, red mud, and coal gangue, converting them into various renewable resources. Taking phosphogypsum as an example, after a series of complex processes, it can be made into bio-based backfilling materials. These materials not only realize the effective utilization of solid wastes but also provide certain nutrients for the soil and promote vegetation growth. Red mud can be processed through special technologies to become a raw material for green building materials, used in backfilling of building foundations and other fields. After treatment, coal gangue can be transformed into soil-like substrates, which are used for ecological restoration of abandoned mine lands, creating favorable conditions for vegetation rooting and contributing to the restoration and reconstruction of ecosystems.
2.1 Backfilling Materials
At present, the bulk solid wastes used for large-scale backfilling mainly include tailings, coal gangue, fly ash, smelting slag, industrial by-product gypsum, etc. Different solid wastes have different physical and chemical properties. When selecting backfilling materials, factors such as the composition, particle size, strength, stability, and environmental impact of the solid wastes should be comprehensively considered. For example, tailings are one of the commonly used backfilling materials due to their wide source and large output, but some tailings may contain harmful substances such as heavy metals, so their environmental risks need to be carefully evaluated.
2.2 Pretreatment Processes
To meet backfilling requirements and reduce environmental risks, it is often necessary to pretreat bulk solid wastes. Pretreatment technologies include crushing, screening, grinding, mixing, solidification/stabilization, etc. For solid wastes containing harmful substances, solidification/stabilization technology is particularly important. By adding curing agents or stabilizing agents, harmful substances are fixed inside the solid wastes, reducing their leaching risk during backfilling. For instance, using curing agents such as cement and lime to solidify tailings containing heavy metals, so that they meet the environmental protection standards for backfilling.
2.3 Backfilling Processes and Technical Parameters
Common backfilling processes for bulk solid wastes include dry backfilling, hydraulic filling, and paste filling.
Dry backfilling involves directly transporting pretreated massive or granular solid wastes to the backfilling area for landfilling. This process is simple to operate but may have problems such as insufficient compaction and high porosity.
Hydraulic filling uses pipelines to transport the slurry (mixed with solid wastes and water) to the backfilling site, and the solid wastes are deposited and accumulated in the backfilling area by hydraulic action. Its advantages are long transportation distance and high filling efficiency, but it is prone to water waste and environmental pollution.
Paste filling mixes solid wastes with cement and other cementitious materials to make a paste with certain fluidity and stability, which is transported to the backfilling area by pumping or other methods. This process can effectively control the strength and stability of the filling body and reduce environmental impact, making it a relatively advanced backfilling process at present.
In different backfilling processes, there are some key technical parameters that need to be strictly controlled. Taking paste filling as an example, the concentration of the slurry is an important parameter affecting the filling effect. Generally, the mass concentration of the paste slurry is required to be between 70% and 85% to ensure good fluidity and sufficient strength. The dosage of cementitious materials is also crucial, which is usually determined according to the properties of the solid wastes and the designed strength of the filling body, generally accounting for 3% to 10% of the mass of the solid wastes. In addition, parameters such as filling speed and filling pressure need to be optimized and adjusted according to actual conditions to ensure the smooth progress of backfilling operations and the quality of filling.
2.4 Environmental Monitoring Technologies
During and after the large-scale backfilling of bulk solid wastes, long-term monitoring of the surrounding environment is required to keep track of changes in environmental quality in a timely manner. The indicators of environmental monitoring mainly include soil quality, water quality (surface water and groundwater), air quality, and the status of the ecosystem. Common monitoring technologies include on-site sampling and analysis, online monitoring, and remote sensing monitoring.
On-site sampling and analysis can obtain accurate environmental data, but the monitoring frequency is limited.
Online monitoring can conduct real-time and continuous monitoring of environmental parameters, enabling timely detection of abnormal situations.
Remote sensing monitoring can monitor the ecological environment of large areas from a macro perspective, helping to understand information such as vegetation coverage and changes in land use.
03 Challenges and Prospects
3.1 Faced Challenges
Although a variety of backfilling technologies are available at present, some technologies still have problems such as high cost, low efficiency, and poor adaptability. For example, although the paste filling process has good effects, it requires large equipment investment and high operating costs, which limits its application in some small mines or economically underdeveloped areas. At the same time, for bulk solid wastes with complex components, the existing pretreatment and solidification/stabilization technologies cannot fully meet environmental protection requirements, requiring further R&D and innovation.
In addition, although the state and local governments have issued a series of policies to support the large-scale backfilling of bulk solid wastes, in the actual implementation process, there are problems such as inadequate policy implementation and supervision loopholes. To reduce costs, some enterprises may violate relevant regulations by not conducting necessary pretreatment or environmental monitoring during backfilling, posing potential risks to the environment.
3.2 Future Prospects
(1) Technological Innovation and Development
With the continuous advancement of science and technology, more investment will be made in the R&D of bulk solid waste backfilling technologies in the future to promote technological innovation. More efficient and low-cost pretreatment technologies and backfilling processes will be developed to improve the utilization rate of solid wastes and the effect of backfilling. For example, new types of curing agents and stabilizing agents will be developed to realize the harmless treatment of solid wastes with complex components; technologies such as artificial intelligence and big data will be used to optimize the parameter control in the backfilling process and the operation and management of equipment, improving production efficiency and safety.
(2) Policy Improvement and Strengthened Supervision
Relevant policies and regulations will be further improved, the detailed implementation rules of policies will be refined, and the supervision and inspection of policy implementation will be strengthened to ensure that policies can be truly implemented. A sound multi-department collaborative supervision mechanism will be established to strengthen communication and cooperation among departments such as ecological environment, natural resources, and emergency management, forming a joint supervision force. Illegal and irregular behaviors will be severely cracked down to ensure the environmental safety of bulk solid waste backfilling projects.
(3) Enhancing Public Awareness and Participation
Through popular science publicity activities and information disclosure, the public's awareness of bulk solid waste backfilling technologies and their environmental impacts will be improved, and public understanding and support for related projects will be enhanced. The public will be encouraged to participate in the supervision and evaluation of projects, and a public feedback mechanism will be established to respond to public concerns in a timely manner, promoting the sustainable development of large-scale bulk solid waste backfilling projects.
Source：https://mp.weixin.qq.com/s/7lVZHRpd68SqfPIwDSgrsA