Abstract: Coal mine water is characterized by large volume and relatively light pollution, making it a potential unconventional water resource. However, the utilization rate of coal mine water is currently low. This paper analyzes the key issues hindering the resource utilization of coal mine water from three aspects: treatment technology, integrated utilization model, and standard system. For the treatment of water containing suspended solids, iron and manganese, high salinity, and acidity, the development direction of low-carbon and low-cost technologies such as enhanced coagulation sedimentation and microfiltration and ultrafiltration direct filtration for removing suspended solids, biological iron and manganese removal, and nanofiltration membrane desalination reuse are discussed and analyzed. The characteristics and progress of sludge reduction and resource utilization technologies in the process of mine water treatment are summarized. Addressing the issue of limited in-house consumption and unclear external utilization pathways for coal mine water, this paper explores an integrated resource utilization model combining internal and external enterprise utilization through a centralized treatment plant. The prospects and feasibility of preparing high-quality drinking water from mine water are also preliminarily analyzed. Based on clarifying the current status of the emission and comprehensive utilization standard system for coal mine water, this paper proposes the formulation of specific emission standards for coal mine water and suggests supplementing the technical specifications for the resource utilization and comprehensive utilization of coal mine water, sludge treatment and disposal, and resource utilization technologies.

 

The coal industry is a major source of national energy and an important pillar of the national economy. China's coal resources are unevenly distributed, exhibiting a pattern of "rich in the north and poor in the south, abundant in the west and scarce in the east." Northern coal resources are mainly concentrated in Shanxi, Inner Mongolia, Shaanxi, Henan, Gansu, and Ningxia provinces, accounting for about 68% of the national basic reserves. These areas are all typical water-scarce regions in Northwest China. It is noteworthy that a large amount of mine water is produced during coal mining, with approximately 2.0 m³ of water produced per ton of coal mined. The annual mine water production is about 7.1 billion m³, approaching the volume of the South-to-North Water Transfer Project. The characteristics of large water volume and relatively light water pollution in coal mine water create favorable conditions for its use as an unconventional water resource. However, in reality, the resource utilization rate of coal mine water is less than 25%. Theoretically, coal-rich areas should have both coal and water, but the reality is "rich in coal but poor in water."

To change the status quo of "rich in coal but poor in water" and achieve "win-win cooperation between coal and water," on February 23, 2024, the National Development and Reform Commission, the Ministry of Water Resources, the Ministry of Natural Resources, the Ministry of Ecology and Environment, the Ministry of Emergency Management, the State Administration for Market Regulation, the National Energy Administration, and the National Mine Safety Administration jointly issued the "Guiding Opinions on Strengthening the Protection and Utilization of Mine Water," which states: "By 2025, the utilization of mine water nationwide will continue to increase, and the utilization rate will continue to improve, with the Yellow River Basin striving to reach over 68%." The document emphasizes strengthening the protection of mine water sources; promoting graded treatment of mine water; and promoting the comprehensive utilization of mine water. It also calls for the formulation and revision of a series of standards and technical specifications for the use of mine water in various fields, and pilot programs for the development of emission standards for high-salinity mine water.

Shanxi Province is China's largest coal-producing province, and the issue of mine water resource utilization is particularly prominent. On October 9, 2023, the Shanxi Provincial Development and Reform Commission and the Shanxi Provincial Energy Bureau issued the "Implementation Plan for Carbon Peak in Shanxi's Coal Industry," which points out the need to strengthen the governance and comprehensive utilization of mine water, and to scientifically promote the optimization and upgrading of mine water treatment and utilization systems in accordance with national and provincial requirements for mine water management, reducing material and energy consumption in mine water treatment. The plan also calls for actively expanding the comprehensive utilization of mine water, comprehensively optimizing the water supply and drainage systems in mining areas, improving the comprehensive benefits of mine water reuse, and increasing the utilization rate of mine water.

Based on an analysis of the key issues hindering the improvement of the resource utilization efficiency of coal mine water, this paper proposes suggestions and countermeasures for improving the resource utilization efficiency of coal mine water from the aspects of treatment technology progress, resource utilization model, and standard system. This can provide reference and guidance for the low-carbon and sustainable development of the coal industry.

 

01

Key Issues in Coal Mine Water Treatment and Resource Utilization

 

 

Mine water is generated during coal mine construction and mining due to factors such as underground water inflow, surface infiltration water, and underground production drainage (external drainage for dust prevention, grouting, equipment cooling, etc.). According to water quality characteristics, coal mine water can be divided into mine water containing suspended solids, high salinity, iron and manganese, acidity, and other types of pollutants (Table 1).

 

Table 1 Classification and Water Quality Characteristics of Coal Mine Water

 

The water quality of coal mine water is generally dominated by inorganic pollutants, similar to groundwater quality, providing a basis for its use as an unconventional water resource. At the same time, the large volume of coal mine water provides a sufficient water resource basis. A technical promotion and application framework system that integrates and drives treatment technology, models, and standards is necessary to fundamentally solve the problem of resource utilization of coal mine water.

1) Optimize and develop low-carbon and low-cost treatment and resource utilization technologies for coal mine water.

For the treatment of mine water containing suspended solids, high salinity, iron and manganese, and acidity, conventional technologies such as coagulation sedimentation, multi-stage chemical oxidation for iron and manganese removal, reverse osmosis desalination, and neutralization have been used for many years. Significant progress has been made in exploring the treatment and resource utilization of coal mine water to meet emission standards. However, there are generally high operating costs and carbon emissions, and large sludge production. It is necessary to learn from and apply advanced water treatment technologies to achieve cost reduction, quality improvement, and efficiency enhancement in the treatment and resource utilization of coal mine water.

2) Develop an integrated resource utilization model for coal mine water that combines internal and external enterprise utilization.

Currently, the resource utilization of coal mine water mainly focuses on internal reuse within enterprises, including for miscellaneous water use and coal washing. However, mine water is continuously produced in large quantities, and internal reuse cannot accommodate all of it, making a "zero-discharge" wastewater model difficult to implement. It is necessary to explore an open integrated utilization model that combines internal enterprise utilization and external output, expanding the resource utilization pathways for the continuously generated mine water and achieving economical and reasonable reuse and comprehensive utilization.

3) Improve the emission and resource utilization standard system for coal mine water.

The inability of coal mining enterprises to completely utilize mine water internally inevitably leads to the problem of mine water discharge. Currently, there are no specific standards for the discharge of coal mine water. High-salinity mine water previously followed the "Emission Standard for Pollutants in the Coal Industry" (GB 20426—2006). In recent years, in order to strictly control mine water discharge, some local environmental protection departments have stipulated that mine water discharge should meet the Class III standard of the "Surface Water Environmental Quality Standard" (GB 3838—2002). There are problems with the mine water discharge control standards, such as inconsistencies and large differences in the indicator system and limit values, high difficulty in meeting standards, and unclear requirements for direct and indirect discharge. Moreover, technical standards for the resource utilization and comprehensive utilization of mine water are limited to directional technical guidelines and lack technical procedures and specifications for guiding engineering practice.

 

 

02

Progress in Coal Mine Water Treatment Technology

 

 

2.1 Treatment of Mine Water Containing Suspended Solids

Treatment methods for mine water containing suspended solids are similar to those for water treatment to remove turbidity, employing traditional processes such as coagulation, sedimentation, and filtration. Engineering practice has proven their effectiveness in removing turbidity and suspended solids. Enhanced coagulation and sedimentation techniques are widely used in the treatment of mine water with high suspended solids. For example, by adding inert high-density microparticles (magnetic seeds, fine sand, etc.) as flocculation nuclei to form a heavy-medium coagulation sedimentation, promoting floc formation; at the same time, the heavy-medium powder also plays a ballasting or weighting role, significantly accelerating the sedimentation process. High-efficiency cyclone technology separates impurities in water through the centrifugal force generated during rotation, suitable for separating high concentrations of coal powder and rock powder suspended solids in coal mine water, with the significant advantages of short reaction time and small footprint.

For mine water with low suspended solids content, the traditional three-stage process of coagulation, sedimentation, and filtration can be changed to a single-stage micro-coagulation filtration process. After adding flocculant, simple mixing in the pipeline and waiting for the flocs to grow moderately, then directly entering the filter for filtration.

Compared with the traditional process, the micro-coagulation filtration process can save two units of coagulation and sedimentation, and the flocculant dosage, investment, and operating costs are lower. The flocs produced after dosing in the micro-coagulation process are all intercepted by the filter, so it is necessary to ensure that the filter media has a high dirt-holding capacity to avoid frequent backwashing and high water consumption. In engineering applications, uniform filter media with uniform particle size can be used to avoid the problem that the backwashing hydraulic grading significantly reduces the dirt-holding capacity of the upper filter layer.

In addition, soft and elastic filter media such as fiber balls can be used. Compared with conventional quartz sand filter media, this soft and elastic filter media has higher porosity, specific surface area, and dirt-holding capacity, which can significantly reduce the filter layer resistance and extend the operating cycle; during operation, the dirt-holding capacity of the filter layer gradually increases, and the elastic filter layer is gradually compacted, which is not easy to penetrate. At the same time, the soft and elastic filter media will not run away during air-water backwashing.

The fine pores of microfiltration and ultrafiltration can effectively intercept suspended particles in water, showing good application prospects in the field of mine water treatment containing suspended solids. China's microfiltration and ultrafiltration membrane preparation and mass production technology are relatively mature. Its application form is direct filtration, which can further shorten the process flow and footprint of suspended solids removal. Using poly-ceramic microfiltration membrane direct filtration technology to treat mine water, without the addition of any chemicals, the effluent suspended solids and turbidity can be stably below 1.0 mg/L and 1.0 NTU respectively. Hydraulic backwashing and regular chemical cleaning can effectively control membrane fouling, with advantages such as short process, energy efficiency, and easy automation. Compared with microfiltration, ultrafiltration has higher retention accuracy. Using submersion-free ultrafiltration to directly purify coal mine water, stable membrane flux can be obtained through cross-flow operation and online cleaning. In the integrated system of coal mine water comprehensive utilization, ultrafiltration is often used as a pretreatment for reverse osmosis or nanofiltration desalination to ensure the safe operation of terminal reverse osmosis or nanofiltration membranes with higher retention accuracy. Obtaining low-pressure operating conditions and more efficient membrane fouling control to reduce operating costs and extend membrane life remains a future development direction for microfiltration and ultrafiltration technology for coal mine water.

2.2 Treatment of iron and manganese-containing mine water

The treatment of iron and manganese-containing mine water is similar to that of iron and manganese-containing groundwater. In the early days, the combined process of oxidation, pH adjustment, coagulation, and sedimentation was used. First, an oxidant was added to oxidize Fe ²⁺ and Mn ²⁺ to Fe ³⁺ and Mn ⁴⁺ , and then a coagulant was added to form a precipitate for removal. The remaining low amount of iron and manganese in the effluent was further removed by the filter. This process has a long flow, large amount of chemicals and sludge production; at the same time, because the oxidation-reduction potential of Mn ²⁺ is higher than that of Fe ²⁺ , the pH needs to be increased to above 9.0 to obtain a higher Mn ²⁺ oxidation rate.

In the 1980s, an active filter membrane with autocatalytic function was discovered in the iron and manganese removal filter, which developed the groundwater iron and manganese removal technology into a simple process, contact oxidation method for iron and manganese removal without the addition of chemicals, simultaneously triggering the innovation of iron and manganese removal technology for mine water with similar water quality. For water with coexisting iron and manganese, in the contact oxidation filter, due to the competition between Fe ²⁺ with lower oxidation-reduction potential and Mn ²⁺ with higher oxidation-reduction potential for dissolved oxygen (DO) in water, the presence of Fe ²⁺ interferes with the removal of Mn ²⁺ . Therefore, a contact oxidation combined process for graded removal of iron and manganese, with primary iron removal and secondary manganese removal, was proposed. In the 1990s, the biological oxidation of Mn ²⁺ was further discovered in the contact oxidation iron and manganese removal filter, providing theoretical and practical feasibility for simultaneous removal of iron and manganese in a primary filter.

Biological iron and manganese removal represents a high-efficiency and low-consumption development direction. Previous research has mainly focused on groundwater iron and manganese removal. Compared with groundwater as a water source, coal mine water has higher suspended solids and mineralization; at the same time, under the low-temperature conditions in northern winter, there is a potential problem that the activity of dominant iron and manganese removal microorganisms is inhibited. It is necessary to combine mine water treatment engineering practice to clarify the influence of the above factors on biological iron and manganese removal.

2.3 Treatment of high-mineralization mine water

For the treatment and reuse of high-mineralization mine water, membrane desalination is often used to reduce its salinity to meet the salinity requirements of industrial, agricultural, and miscellaneous water before reuse. Reverse osmosis membranes are commonly used in engineering practice, with high desalination degree, almost completely removing the salinity in water. However, the reuse of mine water for industrial, agricultural, and domestic miscellaneous purposes often does not require complete desalination, only meeting the TDS and total salt content indicators required for various reuse purposes. The high operating pressure and energy consumption of reverse osmosis complete desalination are common problems. Nanofiltration membranes have the characteristics of low operating pressure and partial desalination, making them more suitable for the treatment of high-mineralization mine water. According to the TDS and total salt content reuse requirements, nanofiltration membranes with different desalination rates can be flexibly selected to minimize operating pressure and operating costs. The research and development of nanofiltration membranes in China started in the 1990s, and a large amount of research has been carried out in membrane material research and development, membrane performance characterization, and membrane fouling control, but compared with the manufacturing and technological research and development of foreign nanofiltration membrane modules, the overall start is relatively late, and high-quality nanofiltration membranes still mainly rely on imports, and there is insufficient engineering practice in mine water treatment and resource utilization. Substantial breakthroughs are urgently needed in the independent research and development and optimization application of high-strength anti-pollution and low-pressure membrane materials.

In the membrane desalination process, membrane concentrate is inevitably produced, and high salt content is its typical characteristic. Currently, the "Surface Water Environmental Quality Standard" (GB 3838—2002) Class III standard and the "Coal Industry Pollutant Discharge Standard" (GB 20426—2006) implemented for coal mine water discharge do not have clear salinity requirements; however, on October 30, 2020, the Ministry of Ecology and Environment, the National Development and Reform Commission, and the National Energy Administration jointly issued the "Notice on Further Strengthening the Environmental Impact Assessment Management of Coal Resource Development", which stipulates: "If there is still surplus mine water after full utilization and it needs to be discharged, the water quality factor values after treatment should meet or be better than the corresponding values of the surface water environmental quality specified in the environmental functional zoning of the receiving water body, the salt content should not exceed 1000 mg/L, and it should not affect the water function needs of the upstream and downstream river sections." The discharge of membrane concentrate not only faces further desalination problems but also potential problems of exceeding the standard of organic pollutants. Under the high-salt matrix conditions of membrane concentrate, the use of biological and advanced oxidation methods to remove organic matter faces the problems of salt inhibition of organisms and quenching of free radicals. Many studies have been conducted on efficient biological and advanced oxidation methods for removing organic matter under high-salt conditions. In the future, it is necessary to further understand the mechanism, process, and operating parameters in combination with the characteristics of mine water quality to guide engineering practices.

In the currently proposed "zero-emission" model, not only membrane desalination but also membrane concentrate evaporation and crystallization are involved. The complex and high cost of waste salt disposal is a common problem. Through nanofiltration membrane salt separation followed by crystallization, theoretically, salt separation and resource utilization of the concentrate can be achieved. The resource utilization path of using high-grade waste heat from coal enterprises for evaporation, crystallization, and separation and recovery of monovalent and divalent salts is technically and economically feasible.

2.4 Treatment of Acidic Mine Water

The treatment of acidic mine water uses neutralization methods. Adding inexpensive lime to adjust the pH of mine water is a feasible method in engineering practice. The main problem with lime neutralization is the large amount of physicochemical sludge; in addition, the increase in mineralization after neutralization also causes subsequent desalination problems, which are discussed in section 2.3. Regarding the problem of a large amount of sludge, the author has explored the recycling path of hydrothermal treatment of sludge for reuse in neutralization, and found that the hydrothermally treated sludge can raise the pH of the raw water from 3.5 to 7.8~7.9, which can be reused to replace some of the added lime; the reuse of hydrothermally alkalized sludge can reduce the amount of lime added and the final sludge yield. According to current research, under hydrothermal conditions, sludge undergoes a series of complex chemical reactions such as decarboxylation, dehydration, depolymerization, and aromatization. Abundant hydroxyl (-OH) and amino (-NH ₂ ) and other alkaline functional groups are generated on the surface of the hydrothermal product, which can combine with H ⁺ in water, increasing the pH of the solution. Mine water sludge is mainly composed of inorganic matter, and its specific alkalization process in hydrothermal reactions needs further research.

In addition to the active treatment method of adding chemical agents to neutralize acidic mine water, a passive restoration system of natural neutralization can also be used with natural media (such as limestone). Iron and manganese elements in the stratum and iron and sulfur elements in coal pyrite (FeS ₂ ) leach out to form acidic mine water containing iron and manganese. Acidic mine water containing iron and manganese first needs to adjust the pH through neutralization, and then combined with aeration and oxygenation, iron and manganese removal filtration, which undoubtedly increases the complexity and cost of the process. Developing a short-process treatment technology for acidic mine water containing iron and manganese is the future direction of development. It is worth noting that sulfuric acid, metals, and rare earth elements in acidic mine water are potential resources that can be utilized. Integrating the resource utilization of sulfuric acid, metals, and rare earth elements based on water reuse can fully exert the benefits of mine water treatment, but it is necessary to focus on researching economically feasible resource extraction technologies without secondary pollution.

2.5 Sludge Treatment, Disposal, and Resource Utilization

A large amount of precipitated or flocculated physicochemical sludge is produced during the treatment of mine water containing suspended solids, iron and manganese, and acidic mine water. Although there is no exact data on the sludge quality and composition characteristics, theoretically, the composition of coal mine mine water sludge is mainly inorganic.

Coal mine mine water primary sedimentation or coagulation sludge is mainly reduced in volume through concentration and dehydration. Pressure filtration or centrifugal dehydration can reduce the water content of sludge to about 80%, while high-pressure plate-and-frame dehydration can reduce the water content of sludge to 60%~70%, and thermal drying can reduce the water content of sludge to a low level of 30%, greatly reducing the amount of sludge. The cost of thermal drying mainly lies in the consumption of heat sources. If high-grade waste heat from coal mine gas power plants, air compressors, and other sources is used for sludge thermal drying, low-carbon reduction of sludge can be achieved.

Sludge resource utilization is an important direction for sludge treatment and disposal. Mine water pre-sedimentation or coagulation sludge containing suspended solids often contains a large amount of coal slag and coal powder, which can be recycled and utilized as low-grade fuel. For the sludge produced in the subsequent coagulation and sedimentation treatment of iron and manganese-containing or acidic mine water after the recovery of coal slurry in primary sedimentation or coagulation sedimentation pretreatment, the calorific value is low and it is difficult to incinerate or co-incinerate as low-grade fuel. Its large output makes landfill also face the problem of no land available. According to current research, the resource utilization paths of inorganic coagulation sludge mainly include building material utilization, preparation of environmental functional materials, and soil utilization.

The heavy metal content of mine water coagulation sludge is relatively low. When used to make roadbed materials, ecological porous bricks, and pavement bricks and other non-residential civil building materials, high-strength solidification treatment is not required, which can reduce the production cost. Mine water coagulation sludge containing iron, manganese, and aluminum oxides can improve the consolidation degree of soil and adsorb and enrich heavy metals through the flocculation process. The ceramsite material prepared by sintering coagulation sludge can be used in wastewater biological filter pools to enhance nitrogen and phosphorus removal. Exploring mine water sludge resource utilization methods and approaches suitable for regional characteristics and needs is the key measure to improve the efficiency of sludge resource utilization.

 

 

03

Discussion on Coal Mine Mine Water Treatment and Resource Utilization Model

 

 

Mine water has a large volume and light water pollution, and can be used as an important supplement to unconventional water resources in water-scarce areas. Therefore, the treatment of mine water should follow the technical route of "giving priority to comprehensive utilization and supplementing discharge".

On-site utilization within the enterprise after mine water treatment is currently the main comprehensive utilization model for coal mine mine water. It must be emphasized that the mine water inflow is large and continuously generated, and on-site reuse within the enterprise is difficult to completely absorb, leading to a large amount of treated mine water that cannot be stored and can only be discharged in the end; at the same time, the path of mine water resource utilization for external industrial and agricultural use and miscellaneous water use is still unclear. The above factors make it difficult to improve the resource utilization rate of mine water, and also make it difficult to realize the "zero-emission" model in engineering applications.

To address the issue of a large amount of newly mined mine water that is difficult to completely utilize within enterprises and unclear external utilization pathways, it is necessary to explore the concept of a centralized treatment plant using mine water as the raw water. The construction and operation model of the centralized treatment plant is similar to that of a water treatment plant, with government-led construction and operation, and a market-oriented operation model. Coal mining enterprises will transport mine water that is difficult to be resourcefully utilized in situ within the enterprise to the centralized treatment plant, where it will be treated, then qualitatively and categorically transported, and resourcefully used as needed for external industrial and agricultural purposes, miscellaneous water use, irrigation, etc. Establish a market operation model and system between the enterprise, the centralized treatment plant, and external users, using a "疏导" (疏导 - to dredge, to guide) approach to solve the practical problem of mine water being "壅堵" (壅堵 - blocked, congested) within the enterprise.

Coal mine water has a large volume, and clean coal mine water from closed strata has a low pollution level, basically containing no organic matter or heavy metals, and contains calcium and magnesium, which are beneficial minerals for the human body. It has the characteristics of water volume and quality suitable for preparing high-quality drinking water. For a long time, the engineering community has carried out a large number of explorations and practices of drinking water treatment projects using coal mine water as the raw water. For example, in January 2006, China's largest mine water treatment project for drinking water was put into operation, with a design treatment capacity of 50,000 m³ ³ /d, which can be used for various purposes such as domestic drinking water, boiler water, and power plant water. To obtain high-quality and safe drinking water, reverse osmosis combined technology is often used to prepare drinking water from coal mine water.

It is undeniable that reverse osmosis deionization technology can ensure water safety, but it has significant problems of high operating pressure and energy consumption. The practice of high-quality drinking water treatment in currently economically developed regions can provide reference for the construction of high-quality drinking water treatment plants using mine water as a water source. The overall process of high-quality drinking water treatment projects uses a combination of coagulation sedimentation, ozone biochar, and nanofiltration membrane separation. This not only removes toxic and harmful substances in the water but also uses the partial desalination characteristics of the nanofiltration membrane to retain some mineral elements in the treated water, which generally meets the requirements of healthy drinking water; the operating pressure and power consumption of the nanofiltration membrane are much lower than those of the reverse osmosis membrane, which can reduce water production costs.

Given the different pollution characteristics of coal mine water, when it is used as a drinking water source, it is necessary to strictly identify, screen, and demonstrate its feasibility as a drinking water source, and fully demonstrate the technical and economic feasibility of the treatment process. At the same time, low-cost high-quality drinking water preparation technology and the construction of supporting water supply pipe network systems, as well as a perfect market-oriented operation model for the water supply system, are sustainable operation guarantees for mine water replacing drinking water sources.

 

 

04

Suggestions for the Resource Treatment and Technical Standard System of Coal Mine Water

 

 

A complete standard system for the discharge and resource utilization of coal mine water is the theoretical and technical support for the scientific management of coal mine water. After years of practice and summary, coal mine water treatment has made some progress in discharge standards and comprehensive utilization technical guidelines, but future work still needs to strengthen and improve the standard system construction.

1) Improve the mine water discharge index system, study the economic feasibility of stable and up-to-standard technologies, and formulate specific discharge standards applicable to coal mine water.

4.4.1 of the "Emission Standard for Pollutants in Coal Industry" (GB 20426—2006) stipulates: "For high-mineralization coal mining wastewater, in addition to complying with the limit values in Table 2, deep processing and comprehensive utilization should also be carried out according to the actual situation. When high-mineralization coal mining wastewater is used for farmland irrigation, it should meet the limit value requirements stipulated in GB 5084." In order to strictly control the discharge of mine water, some local ecological environment management departments currently stipulate that the discharge of mine water shall comply with Class III standard of the "Surface Water Environmental Quality Standard" (GB 3838—2002). For example, the Shanxi Provincial local standard "Green Mine Construction Specification Coal Mine" (DB 14∕T 2976—2024) 9.4.2 clearly stipulates: "Mine water should be treated completely, and after treatment, it should be reused completely. If it needs to be discharged, it should be treated to meet the Class III surface water standard."

Comparing the above-mentioned relevant standards, the following problems exist: ① The control indicators of nitrogen, phosphorus, and Class I pollutants are unclear. The "Emission Standard for Pollutants in Coal Industry" (GB 20426—2006) only involves high-mineralization coal mining wastewater and only includes 6 indicators such as pH, SS, COD, petroleum, total iron, and total manganese. It does not involve nitrogen, phosphorus, and Class I pollutants that have a greater impact on the aquatic ecological environment. The index system is imperfect and cannot fully reflect the safety of the discharged water quality; at the same time, the nitrogen and phosphorus indicators in Class III standard of the "Surface Water Environmental Quality Standard" (GB 3838—2002) have high requirements (TN≤1.0 mg/L, TP≤0.2 mg/L), and the technical and economic feasibility of achieving the standard discharge is unclear. ② The differences in indicator limits are large. Comparing the "Emission Standard for Pollutants in Coal Industry" (GB 20426—2006) and Class III standard of the "Surface Water Environmental Quality Standard" (GB 3838—2002), there are significant differences in the indicators of COD, petroleum, total iron, and total manganese, and Class III standard of the "Surface Water Environmental Quality Standard" (GB 3838—2002) does not specify the limit value for SS. ③ Direct and indirect discharge is unclear. The currently implemented "Emission Standard for Pollutants in Coal Industry" (GB 20426—2006) and Class III standard of the "Surface Water Environmental Quality Standard" (GB 3838—2002) are applicable to direct discharge in situ; for the concentrated liquid produced by desalination of mine water, the difficulty and cost of direct discharge are high. If zero discharge is implemented for the concentrated liquid by evaporation and crystallization, there are problems such as the difficulty of completely utilizing the recycled water and the disposal of a large amount of waste salt. The indirect discharge path, feasibility, and standard limit values need to be further explored.

2) Strengthen the research on feasible models, paths, and technical solutions for mine water resource utilization, supplement and develop technical specifications for the resource utilization and comprehensive utilization of coal mine water, and scientifically guide the full resource utilization of coal mine water.

Currently formulated technical specifications for the resource utilization and comprehensive utilization of mine water include "Classification of Coal Mine Water" (GB/T 19223—2015), "Technical Guidelines for the Utilization of Coal Mine Water" (GB/T 31392—2022), "Technical Guidelines for the Treatment and Reuse of High-Mineralization Mine Water" (GB/T 37758—2019), "Technical Guidelines for the Treatment and Reuse of Acid Mine Water" (GB/T 37764—2019), and "Technical Guidelines for the Comprehensive Utilization of Mine Water" (GB/T 41019—2021), etc.

The above-mentioned standards, as the higher-level standards for the comprehensive utilization of mine water resources, indicate the principles, directions, and reference water quality requirements for reuse. However, for specific project implementation, it is difficult to determine the specific comprehensive utilization model and technical route, treatment process, and parameters based on the above standards. It is necessary to further supplement and formulate lower-level standards such as technical regulations and specifications for the comprehensive utilization of mine water resources, and to scientifically guide and guide enterprises to formulate comprehensive utilization technical models and plans, treatment processes and parameters, clarify the amount of recycled water and the ways of utilization, achieve the matching of water production and recycled water, treatment process and recycled water quality, and propose practical engineering technical solutions.

3) Strengthen the analysis of the mud component characteristics of mine water coagulation sludge, build a technical system and model for sludge resource utilization, and formulate technical specifications for sludge treatment, disposal, and resource utilization.

Currently, various sludge standards have been formulated for different resource utilization pathways of sludge, including "Sludge for landscaping and greening in urban sewage treatment plants" (GB/T 23486—2009), "Sludge for co-disposal in urban sewage treatment plants" (GB/T 23485—2009), "Sludge for land improvement in urban sewage treatment plants" (GB/T 24600—2009), "Sludge for incineration in urban sewage treatment plants" (GB/T 24602—2009), "Sludge for brick making in urban sewage treatment plants" (GB/T 25031—2010), "Control Standard for Pollutants in Agricultural Sludge" (GB 4284—2018), "Sludge ceramsite" (JC/T 2621—2021), and "Quality Control Standard for Land Use Sludge in Urban Sewage Treatment Plants" (DB 5301/T 86—2023).

From the analysis of the source of mine water coagulation sludge, the components are mainly inorganic. However, there is currently a lack of scientific definition and analysis of the sludge components, making it difficult to determine the applicable resource utilization pathway for mine water coagulation sludge. At the same time, the determination of feasible pathways and models for sludge resource utilization should be combined with local conditions to determine the absorption capacity and feasible resource utilization pathways. Formulating corresponding technical specifications for the treatment, disposal, and resource utilization of mine water sludge is the technical cornerstone for scientifically guiding the multi-pathway resource utilization of mine water sludge, including the use in building materials, land use, the preparation of functional materials, and co-incineration.

 

05

Conclusion

 

 

Many major coal-producing provinces in China are located in water-scarce northern regions, and coal mining produces a huge amount of mine water. Although the water quality of coal mine water is relatively less polluted, the rate of resource utilization is low, resulting in a huge contrast of "rich coal, poor water" in the coal industry and coal-producing provinces and regions, seriously restricting the sustainable development of the coal industry.

The low resource utilization rate of mine water is due to multiple factors, including technology, models, and standards. To change the status quo of "rich coal, poor water" and achieve "win-win coal and water", it is necessary to link and drive innovation in key areas such as the research and development of low-carbon and low-cost resource comprehensive utilization technologies, the exploration of open resource utilization pathways and models, and the construction of emission and comprehensive utilization standard systems, in order to fundamentally change the current low resource utilization rate of coal mine water. At the same time, it is necessary to continuously track the strategic needs of the national coal industry development, promote the continuous optimization and improvement of low-carbon governance technologies and resource comprehensive utilization models for coal mine water, and proactively maintain the long-term leading role of the standard system, which is an important measure for the scientific governance and resource utilization of coal mine water.

(Source: Industrial Water Treatment, 2025, Issue 1 First/Corresponding Author: Xue Gang, Donghua University)