Membrane separation-induced crystallization-evaporation pond integration-based high-salt mine water resource chemical treatment method

Abstract

The invention provides a membrane separation-induced crystallization-evaporation pond integration-based high-salt mine water resource chemical treatment method, which comprises the following steps: pretreating high-salt mine water, and sequentially carrying out first-stage and second-stage reverse osmosis membrane separation for desalination and concentration; secondary reverse osmosis concentrated water enters a nanofiltration system to realize selective separation of divalent ions; carrying out induced crystallization on the nanofiltration concentrated water to remove calcium ions and recover a calcium sulfate byproduct; after crystallization, effluent is further concentrated through three-stage reverse osmosis, concentrated water finally enters a multi-stage evaporation pond, and mirabilite and sodium chloride are separated out through temperature control grading. Through collaborative integration of multi-stage membrane separation and induced crystallization, efficient desalination, deep concentration and scaling control of high-salt mine well water are achieved, the system water recovery rate is larger than or equal to 90%, meanwhile, synchronous recovery of water resources and multiple salt resources is achieved, and the system has the advantages of being low in treatment cost, small in occupied area, high in recycling degree and free of emission.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and more specifically, to a method for the resource-based treatment of high-salinity mine water based on membrane separation-induced crystallization-evaporation pond integration. Background Technology

[0002] Mine water, a major wastewater generated during coal mining, typically contains high concentrations of salt, suspended solids, and small amounts of organic matter. Direct discharge without proper treatment will cause severe water waste and environmental pollution. The Nansi Lake Basin in my country is an important coal production base, and the large amounts of mine water generated during mining operations in this region have become one of the main sources of high-salinity wastewater in the area. This type of mine water, due to its long-term contact with coal seams and rock strata during its formation, dissolves large amounts of potassium (K). + Na + Cl - SO4 2- The presence of soluble salts in mine water results in a total dissolved solids content typically maintained at around 5000 mg / L, classifying it as typical high-salinity wastewater. Direct discharge of this water would not only exacerbate eutrophication in the South Four Lakes basin and soil salinization in the surrounding areas, but also represent a significant waste of precious water resources. However, to achieve the resource-based reuse of mine water—for example, for agricultural irrigation, industrial circulating cooling water, or reinjection into underground aquifers—efficient and deep desalination treatment is essential. With increasingly stringent environmental regulations such as the "Coal Industry Pollutant Emission Standard," the "purification-reuse-resource-based" treatment of mine water has become a rigid requirement for the sustainable development of the coal industry.

[0003] In the process of achieving near-zero discharge of high-salinity mine water, in addition to the need for conventional processes to remove suspended solids, the most critical and challenging aspect lies in the removal and disposal of salt to meet reuse, reinjection, or discharge standards. Currently, the main desalination technologies include distillation, ion exchange, electrodialysis, and reverse osmosis. Among these, reverse osmosis is widely used in the treatment of high-salinity mine water due to its high desalination efficiency, but this process generates a large amount of concentrated brine with even higher salt concentrations. Traditionally, this concentrated brine is treated using evaporation and crystallization processes, ultimately forming mixed salt solid waste. This process has significant drawbacks: it requires the addition of large amounts of acids, alkalis, and other chemical agents, resulting in high operating costs; simultaneously, the generated mixed salts have low utilization value, are difficult to dispose of, pose a risk of secondary pollution, and cause a serious waste of resources.

[0004] With increasing environmental pressures, the development of high-salinity mine water treatment technologies that balance high efficiency, low cost, and resource recovery has become particularly urgent, making near-zero discharge systems a research hotspot in recent years. In existing technologies, nanofiltration technology is often introduced for salt separation to improve the purity of the final crystallized salt. For example, Chinese patent CN114212938A discloses a zero-discharge system and method for mine water resource recovery, which includes a pretreatment unit, a nanofiltration salt separation unit, a reverse osmosis concentration unit, a high-pressure nanofiltration unit, and a bipolar membrane electrodialysis unit. However, after salt separation, the high calcium ion concentration in the concentrate easily leads to scaling and fouling of subsequent membrane units, resulting in decreased desalination rates and shortened lifespans of membrane elements, thereby increasing the cost of membrane replacement and system maintenance.

[0005] Furthermore, most current zero-discharge treatment processes for mine water still rely on evaporation crystallization as the final treatment method. For example, Chinese patent CN113896370A discloses a novel zero-discharge system and method for mine water, which includes multiple units such as deep magnesium removal, multi-stage filtration, reverse osmosis, deep calcium removal, high-salt reverse osmosis, and evaporation crystallization. Although such processes can achieve zero discharge, the core evaporation crystallization stage has extremely high energy consumption, with energy costs exceeding 5 yuan per ton of water. Coupled with high equipment investment and maintenance costs, the total cost per ton of water exceeds 10 yuan, making it economically unsustainable. To reduce energy consumption and costs, some technical solutions attempt to introduce evaporation ponds to replace mechanical evaporation crystallizers. However, traditional single evaporation pond processes require a huge pond area, often exceeding 10,000 square meters, making them difficult to promote in areas with increasingly scarce land resources, thus creating new problems of land resource waste.

[0006] In summary, existing high-salinity mine water treatment technologies generally face several prominent challenges: membrane systems are susceptible to scaling and fouling, resulting in poor stability; the evaporation and crystallization process is energy-intensive and costly; evaporation ponds require excessive land area; and the final product is worthless miscellaneous salts, leading to resource waste. Therefore, given the high sulfate and chloride ion content of mine water in the Nansi Lake Basin, there is an urgent need to develop a highly efficient treatment process that can effectively synergistically improve desalination efficiency and calcium ion removal, significantly reduce operating costs and land area, and achieve the recovery of both water resources and valuable salt resources. This is of vital importance for promoting water resource recycling and ecological environmental protection in this region. Summary of the Invention

[0007] To address the problems of high operating costs, easy scaling and fouling of membrane systems, low resource recovery rate, high energy consumption of evaporation and crystallization, and large land area required for evaporation ponds in existing high-salinity mine water treatment technologies, this invention proposes a high-salinity mine water resource utilization method based on membrane separation-induced crystallization-evaporation pond integration to solve the aforementioned problems of existing technologies.

[0008] To achieve the above objectives, this invention proposes a method for the resource-based treatment of high-salinity mine water based on membrane separation-induced crystallization-evaporation pond integration, comprising the following steps: (1) Pretreatment: Coagulation, sedimentation and filtration are carried out on high-salt mine water to remove suspended solids and colloids, so that the turbidity of the effluent is ≤3 NTU; (2) First-stage reverse osmosis treatment: The pretreated effluent is subjected to first-stage reverse osmosis treatment at an operating pressure of 1.6-2.2 MPa and a water recovery rate of 80%. (3) Secondary reverse osmosis treatment: The concentrate produced by the primary reverse osmosis is treated by secondary reverse osmosis using a seawater desalination membrane. The operating pressure is 3.5-4.5 MPa, and the water recovery rate is 75%. (4) Nanofiltration treatment: The concentrate produced by the secondary reverse osmosis is subjected to nanofiltration treatment at an operating pressure of 1.0-1.5 MPa and a water recovery rate of 70%. The nanofiltration permeate is returned to the secondary reverse osmosis treatment step. (5) Induced crystallization: The concentrated water produced by nanofiltration is subjected to induced crystallization treatment by adding calcium sulfate seed crystals and controlling the reaction conditions to precipitate calcium sulfate crystals, thereby achieving the removal and resource utilization of calcium ions; (6) Three-stage reverse osmosis treatment: The effluent after induced crystallization is subjected to three-stage reverse osmosis treatment. High-pressure seawater desalination reverse osmosis membrane is used, the operating pressure is 7.5-9.0 MPa, the water recovery rate is 70%, and the three-stage reverse osmosis permeate is returned to the two-stage reverse osmosis treatment step. (7) Multi-stage evaporation pond treatment: The concentrated water produced by the three-stage reverse osmosis is introduced into a series of evaporation ponds. The temperature of different evaporation ponds is controlled by the waste heat, and sodium chloride and sodium chloride are precipitated respectively, so as to achieve zero discharge of concentrated water and recovery of salt resources.

[0009] Furthermore, in step (1), coagulation is carried out by adding polyaluminum chloride and polyacrylamide, and filtration is achieved by passing the mixture through a sedimentation tank, a quartz sand filter and an activated carbon filter in sequence.

[0010] Furthermore, in steps (2) and (3), both the primary and secondary reverse osmosis membrane systems use anti-fouling composite reverse osmosis membrane elements, and the operating pressure is dynamically adjusted based on real-time feedback of the feed water TDS; the TDS of the primary reverse osmosis permeate is 400-500 mg / L, which can be used for reuse or reinjection.

[0011] Furthermore, in step (4), the nanofiltration membrane used has a molecular weight cutoff of 200-1000 Da, which is used to preferentially retain divalent ions, and the Ca in the nanofiltration concentrate... 2+ The concentration was enriched to 5000-6000 mg / L.

[0012] Further, in step (5), the reaction conditions for inducing crystallization are: temperature controlled at 40℃, pH value controlled at 7.0-8.5, stirring rate at 80-120 r / min, and seed crystal addition amount at 20%-30% of the theoretical precipitation amount of calcium sulfate; the precipitated calcium sulfate crystals are separated into solid and liquid by a combination of hydrocyclone and plate and frame filter press to obtain a by-product with a water content ≤15%.

[0013] Furthermore, in the effluent after the induced crystallization treatment in step (5), Ca 2+ The concentration decreased to 1.5-2.0 mg / L.

[0014] Furthermore, the multi-stage evaporation pond in step (7) includes at least a primary evaporation pond and a secondary evaporation pond; the temperature of the primary evaporation pond is controlled at 45-55℃ for the precipitation of Na2SO4·10H2O; the temperature of the secondary evaporation pond is controlled at 65-75℃ for the precipitation of NaCl.

[0015] Furthermore, the evaporation pond is equipped with a seepage-proof structure, which includes a 1.5mm thick HDPE geomembrane laid on the bottom of the pond and a composite geotextile, and a flood interception ditch is set around the pond.

[0016] Furthermore, the total salt content of the high-salinity mine water treated by the method is 4500-5500 mg / L, and it is rich in SO4. 2- and Cl - .

[0017] Furthermore, the total water recovery rate of the method is ≥90%, the cost of treating 1 ton of water is 3-5 yuan / cubic meter, and three by-products, calcium sulfate, sodium sulfate and sodium chloride, are recovered simultaneously.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Excellent permeate quality: The permeate quality of both primary and secondary reverse osmosis meets the reinjection standards, with a high reuse rate of 80% for primary permeate and 75% for secondary permeate. If the raw water treatment capacity is 5000 m³, 3 / d produces 4500m³ of water 3 / d, the first and second grade produced water meets the standards and can be mixed with the raw water for reinjection, which greatly improves the water resource utilization rate and solves the problem of reuse of mine water in the South Four Lakes Basin due to its high salt content (5000mg / L).

[0019] (2) Cost controllable: The total cost per ton of water is RMB 4.2 / m³. 3 The pretreatment cost is 0.5 yuan / m³. 3 Membrane treatment: 2.7 yuan / m 3 Induced crystallization: 0.5 yuan / m 3 Evaporation pond: 0.5 yuan / m²3 The cost allocation for each unit is reasonable. The staged processing achieves the targeted precipitation of calcium sulfate, sodium sulfate, and sodium chloride, improving economic benefits while solving the problem of unusable byproducts.

[0020] (3) Strong process stability: By combining multi-stage membrane separation and induced crystallization, the difficulty of treating high-salt wastewater is effectively reduced, the risk of membrane fouling is reduced, the membrane life is extended, and the long-term stable operation of the system is guaranteed, which solves the problems of serious membrane fouling and low desalination rate in traditional processes.

[0021] (4) The problem of excessive land area occupied by the evaporation pond was solved. Through three-stage reverse osmosis concentration, the water volume entering the evaporation pond was reduced to 22.5 m³. 3 / d, the total area of ​​the pond is controlled at 4000m² 2 Within (based on a raw water treatment capacity of 5000 m³) 3 (e.g., / d). Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0025] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of analytical grade or purity commonly used in the field of chemical synthesis.

[0026] This invention provides a method for the resource-based treatment of high-salinity mine water based on membrane separation-induced crystallization-evaporation pond integration. The overall process flow of this method is as follows: Figure 1 As shown, its core lies in the step-by-step treatment approach of "graded concentration - selective separation - crystallization recovery - deep desalination - evaporation recovery," specifically including pretreatment, primary reverse osmosis membrane separation, secondary reverse osmosis membrane separation, nanofiltration membrane separation, induced crystallization, tertiary reverse osmosis membrane separation, and multi-stage evaporation pond treatment. The following will provide a detailed explanation of the implementation process of this invention using a specific application example.

[0027] Example: A case study of mine water treatment in the South Four Lakes Basin This embodiment treats high-salinity mine water from a coal mine in the Nansi Lake basin. The key indicators of the raw water quality are as follows: total dissolved solids (TDS) 5156 mg / L, total hardness (as CaCO3) 289 mg / L, total alkalinity 289 mg / L, pH range 7.5-8.5, and turbidity 20-30 NTU. The main ion concentrations are: K... + / Na + 1605.9 mg / L, Mg 2+ 1.32 mg / L, Ca 2+ 94.1 mg / L, Cl - 506 mg / L, SO4 2- 2666 mg / L, HCO3 - 352 mg / L.

[0028] (1) Pretreatment like Figure 1 As shown, raw water first enters the pretreatment system. Polyaluminum chloride (PAC) and polyacrylamide (PAM) are added to the water for coagulation, followed by solid-liquid separation in a sedimentation tank, with a hydraulic retention time controlled at 2 hours. The supernatant after sedimentation is then subjected to deep filtration through a quartz sand filter (filtration rate 8 m / h) and an activated carbon filter (filtration rate 5 m / h). After the above treatment, the effluent quality is significantly improved, with turbidity steadily reduced to below 3 NTU, meeting the influent requirements (SDI ≤ 3) of the subsequent membrane treatment system.

[0029] The pretreated water quality was as follows: mineralization 5100 mg / L, hardness 289 mg / L, total alkalinity 289 mg / L, pH 7.8-8.2. The concentrations of each ion did not change significantly compared to the original water, but suspended solids and colloids were effectively removed.

[0030] (2) First-stage reverse osmosis membrane separation The pretreated effluent is pumped into the first-stage reverse osmosis system. This system uses an anti-fouling composite reverse osmosis membrane element (Dow BW30-400), and automatically adjusts the operating pressure within the range of 1.8-2.2 MPa based on real-time feedback of the feed water TDS, controls the water temperature at 25℃, and adds 3 ppm of organophosphonate antiscalant (ATMP).

[0031] The system maintains a stable water recovery rate of 80%. After primary reverse osmosis treatment, the TDS of the permeate is reduced to 400-500 mg / L, allowing for direct reuse or mixing with raw water to meet standards before reinjection into the Ordovician limestone aquifer in the mining area. The ion concentration on the concentrate side is also concentrated, specifically: K... + / Na + 7708.3 mg / L, Mg 2+ 6.34 mg / L, Ca2+ 451.7 mg / L, Cl - 2428.8 mg / L, SO4 2- 12796.8 mg / L, HCO3 - 140.8 mg / L.

[0032] (3) Secondary reverse osmosis membrane separation The concentrate from the first-stage reverse osmosis system enters the second-stage reverse osmosis system for further concentration. This system uses seawater desalination-grade reverse osmosis membrane elements (Dow SW30HRLE-400). Based on real-time feedback of the feed water TDS, the operating pressure is adjusted to 3.5-4.5 MPa, the water temperature is controlled at 25℃, and 5 ppm of an organophosphate scale inhibitor is added. The water recovery rate of this system is 75%. The second-stage reverse osmosis permeate is of excellent quality and can be directly used as industrial circulating cooling water or used for reinjection. The ion concentration in the concentrate is further significantly increased, specifically: K... + / Na + 30370.7 mg / L, Mg 2+ 25.3 mg / L, Ca 2+ 1800 mg / L, Cl - 9808.7 mg / L, SO4 2- 50995 mg / L, HCO3 - 563.3 mg / L.

[0033] (4) Nanofiltration membrane separation Secondary reverse osmosis concentrate enters the nanofiltration system to achieve selective separation of divalent and monovalent ions. This system uses a polyamide composite nanofiltration membrane with a molecular weight cutoff of 500 Da. Based on real-time feedback of the feed water TDS, the system adjusts the operating pressure to 1.0-1.5 MPa and adds 10 ppm of polyphosphate scale inhibitor.

[0034] The water recovery rate of this system is 70%. Nanofiltration membranes preferentially retain Mg. 2+ SO4 2- Divalent ions, Ca on the concentrated water side 2+ and SO4 2- The concentration was significantly enriched, creating ideal conditions for subsequent induced crystallization. The nanofiltration concentrate quality was: K + / Na + 44542.4 mg / L, Mg 2+ 281.4 mg / L, Ca 2+ 5910 mg / L, Cl - 14386.1 mg / L, SO4 2- 164033.9 mg / L, HCO3 -9141.7 mg / L. The nanofiltration permeate is then returned to the secondary reverse osmosis feed, forming an internal system circulation and improving the overall water recovery rate.

[0035] (5) Induced crystallization The high-hardness concentrate produced by nanofiltration enters the induced crystallization reactor. At this stage, industrial-grade calcium sulfate seed crystals (purity ≥98%) are added to the reactor at 25% of the theoretical calcium sulfate precipitation amount. The reaction temperature is controlled at 40℃ (this temperature can be maintained using residual heat from the mine to save energy), the pH value is maintained at 7.0-8.5, and the stirring rate is controlled at 80-120 r / min to promote the uniform growth and precipitation of calcium sulfate crystals.

[0036] After the reaction, a combined process of "high-efficiency hydrocyclone (separation efficiency 95%) + plate and frame filter press (filtration pressure 0.6 MPa)" was used for solid-liquid separation, ultimately obtaining calcium sulfate crystals as a byproduct with a moisture content ≤15%, which can be sold as an industrial raw material, achieving effective removal and resource utilization of calcium ions. The Ca in the effluent after induced crystallization... 2+ The concentration dropped to approximately 1.67 mg / L.

[0037] (6) Three-stage reverse osmosis membrane separation After induced crystallization, the effluent enters a three-stage reverse osmosis system for final concentration. This system uses high-pressure seawater desalination reverse osmosis membrane elements (such as Dow high-pressure membranes) that can withstand extremely high salinity and operating pressure. Based on real-time feedback of the feed water TDS, the system adjusts the operating pressure to 7.5-9.0 MPa and adds 15 ppm of sulfate-based high-efficiency scale inhibitor.

[0038] The water recovery rate of this system is 70%. The permeate from the third-stage reverse osmosis system is returned to the second-stage reverse osmosis system and participates in the internal circulation again. Its concentrate has an extremely high ion concentration, which is: K... + / Na + 145505.17 mg / L, Mg 2+ 929.31 mg / L, Ca 2+ 5.54 mg / L, Cl - 47000.37 mg / L, SO4 2- 496460.11 mg / L, HCO3 - 27401 mg / L. This step significantly reduces the amount of treated water entering the terminal evaporation pond.

[0039] (7) Multi-stage evaporation pond treatment The small amount of concentrated water produced by the three-stage reverse osmosis is introduced into a series of tiered natural evaporation ponds for treatment. The evaporation ponds adopt a double-layer seepage-proof structure of "HDPE membrane (1.5mm thick) + geotextile", and intercepting ditches are set around the ponds to prevent rainwater from flowing in and causing pollution.

[0040] Primary evaporation pond: receives concentrated water from the tertiary reverse osmosis stage. The temperature inside the pond is controlled at approximately 50℃ (which can be achieved using waste heat from the mining area). Under these conditions, sodium sulfate decahydrate (sodium sulfate, Na2SO4·10H2O) is preferentially precipitated.

[0041] Secondary evaporation pond: Receives further concentrated liquid from the primary evaporation pond. The temperature inside the pond is controlled at approximately 70℃ (this can be achieved using waste heat from the mine). Under these conditions, sodium chloride (NaCl) is precipitated in large quantities.

[0042] Through this multi-stage evaporation pond design, the graded recovery of Glauber's salt and sodium chloride was finally achieved, with the purity of the products reaching over 90%, truly realizing zero discharge of concentrated water and resource utilization of salt.

[0043] To verify the outstanding effects of the process of the present invention, comparative experimental data with traditional processes are provided.

[0044] Comparative Example 1: Traditional two-stage RO + evaporation crystallization process Treating the same water quality and the same water volume (5000 m³) 3 / d) mine water. The process route is: pretreatment → primary RO → secondary RO → evaporator crystallizer.

[0045] Operating costs: The total cost per ton of water is as high as 10-12 yuan / m³ 3 The energy consumption of the evaporation and crystallization process accounts for the majority of the cost.

[0046] Resource recycling: The evaporation and crystallization process produces mixed salts, which are classified as hazardous waste (HW49). The yield of mixed salts per ton of water is approximately 9.5 kg (on a dry basis). The disposal cost is as high as 800-1200 yuan / ton. There is no benefit from resource recovery, but instead, it brings a huge environmental and economic burden.

[0047] System stability: After three months of operation, the standard permeate output of the secondary RO membrane decreased by 18% due to scaling, requiring frequent chemical cleaning, and the expected lifespan of the membrane element was shortened by about 35%.

[0048] Comparative Example 2: Nanofiltration salt separation + evaporation crystallization process (refer to CN114212938A) The process route includes nanofiltration for salt separation and evaporation crystallization.

[0049] Salt separation effect: Although some divalent salts can be separated, the calcium ion content in the concentrate remains high. When this concentrate enters the subsequent high-pressure membrane unit or evaporator, it causes severe scaling on the heating tube walls, reducing thermal efficiency and increasing steam consumption per ton of water by 40% compared to the process of this invention. The total cost per ton of water for the entire process is 9.5 yuan / m³. 3 .

[0050] Product value: The sodium chloride product produced contains a small amount of calcium impurities, and its purity is only 85%-88%. It can only be sold as an industrial-grade secondary product, and its value is low.

[0051] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for the resource-based treatment of high-salinity mine water based on membrane separation-induced crystallization-evaporation pond integration, characterized in that, Includes the following steps: (1) Pretreatment: Coagulation, sedimentation and filtration are carried out on high-salt mine water to remove suspended solids and colloids, so that the turbidity of the effluent is ≤3 NTU; (2) First-stage reverse osmosis treatment: The pretreated effluent is subjected to first-stage reverse osmosis treatment at an operating pressure of 1.6-2.2 MPa and a water recovery rate of 80%. (3) Secondary reverse osmosis treatment: The concentrate produced by the primary reverse osmosis is treated by secondary reverse osmosis using a seawater desalination membrane. The operating pressure is 3.5-4.5 MPa, and the water recovery rate is 75%. (4) Nanofiltration treatment: The concentrate produced by the secondary reverse osmosis is subjected to nanofiltration treatment at an operating pressure of 1.0-1.5 MPa and a water recovery rate of 70%. The nanofiltration permeate is returned to the secondary reverse osmosis treatment step. (5) Induced crystallization: The concentrated water produced by nanofiltration is subjected to induced crystallization treatment by adding calcium sulfate seed crystals and controlling the reaction conditions to precipitate calcium sulfate crystals, thereby achieving the removal and resource utilization of calcium ions; (6) Three-stage reverse osmosis treatment: The effluent after induced crystallization is subjected to three-stage reverse osmosis treatment. High-pressure reverse osmosis membrane is used, the operating pressure is 7.5-9.0 MPa, the water recovery rate is 70%, and the three-stage reverse osmosis permeate is returned to the two-stage reverse osmosis treatment step. (7) Multi-stage evaporation pond treatment: The concentrated water produced by the three-stage reverse osmosis is introduced into a series of evaporation ponds. The temperature of different evaporation ponds is controlled by the waste heat, and sodium chloride and sodium chloride are precipitated respectively, so as to achieve zero discharge of concentrated water and recovery of salt resources.

2. The method according to claim 1, characterized in that, In step (1), coagulation is achieved by adding polyaluminum chloride and polyacrylamide, and the mixture is then filtered through a sedimentation tank, a quartz sand filter, and an activated carbon filter in sequence.

3. The method according to claim 1, characterized in that, In steps (2) and (3), both the primary and secondary reverse osmosis membrane systems use anti-fouling composite reverse osmosis membrane elements, and the operating pressure is dynamically adjusted based on real-time feedback of the feed water TDS; the TDS of the primary reverse osmosis permeate is 400-500 mg / L, which can be used for reuse or mine reinjection.

4. The method according to claim 1, characterized in that, In step (4), the nanofiltration membrane used has a molecular weight cutoff of 200-1000 Da, and is used to preferentially retain divalent ions, thus reducing the Ca content in the nanofiltration concentrate. 2+ The concentration was enriched to 5000-6000 mg / L.

5. The method according to claim 1, characterized in that, In step (5), the reaction conditions for inducing crystallization are: temperature controlled at 40℃, pH value controlled at 7.0-8.5, stirring rate at 80-120 r / min, and seed crystal addition amount at 20%-30% of the theoretical precipitation amount of calcium sulfate; the precipitated calcium sulfate crystals are separated into solid and liquid by a combination of hydrocyclone and plate and frame filter press to obtain a by-product with a water content ≤15%.

6. The method according to claim 5, characterized in that, In the effluent after the induced crystallization treatment in step (5), Ca 2+ The concentration decreased to 1.5-2.0 mg / L.

7. The method according to claim 1, characterized in that, The multi-stage evaporation pond in step (7) includes at least a primary evaporation pond and a secondary evaporation pond; the temperature of the primary evaporation pond is controlled at 45-55℃ for the precipitation of Na2SO4·10H2O; the temperature of the secondary evaporation pond is controlled at 65-75℃ for the precipitation of NaCl.

8. The method according to claim 7, characterized in that, The evaporation pond is equipped with a seepage-proof structure, which includes a 1.5mm thick HDPE geomembrane laid on the bottom of the pond and a composite geotextile, and a flood interception ditch is set around the pond.

9. The method according to claim 1, characterized in that, The method treats high-salinity mine water with a total salt content of 4500-5500 mg / L and is rich in SO4. 2- and Cl - .

10. The method according to any one of claims 1-9, characterized in that, The method achieves a total water recovery rate of ≥90%, with a water treatment cost of 3-5 yuan per cubic meter, and simultaneously recovers three byproducts: calcium sulfate, sodium sulfate, and sodium chloride.

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