Method and device for recycling mine water

Abstract

The invention belongs to the technical field of water treatment and resource utilization, and particularly relates to a method and device for resource treatment of mine water. The method for recycling the mine water comprises the following steps: pre-treating the mine water to obtain pre-treated water; performing primary reverse osmosis treatment on the pretreated water to obtain primary reverse osmosis fresh water and primary reverse osmosis concentrated water; carrying out nanofiltration treatment on the primary reverse osmosis concentrated water to obtain nanofiltration fresh water and nanofiltration concentrated water; performing secondary reverse osmosis treatment on the nanofiltration fresh water to obtain secondary reverse osmosis fresh water and secondary reverse osmosis concentrated water; carrying out evaporative crystallization treatment on the secondary reverse osmosis concentrated water to obtain monovalent salt crystals; softening the nanofiltration concentrated water, and concentrating the nanofiltration concentrated water by using three-stage reverse osmosis to obtain three-stage reverse osmosis fresh water and three-stage reverse osmosis concentrated water; and performing bipolar membrane electrodialysis treatment on the third-stage reverse osmosis concentrated water, and converting divalent salt in the third-stage reverse osmosis concentrated water into corresponding acid and alkali.

Description

Technical Field

[0001] This invention belongs to the field of water treatment and resource utilization technology, specifically relating to a method and apparatus for the resource utilization of mine water. Background Technology

[0002] Mine water is groundwater generated during coal mining. It is produced in large quantities and has complex quality, containing a large amount of dissolved salts, including monovalent ions (such as Na+, K+, Cl-) and divalent ions (such as Ca2+, Mg2+, SO42-). Direct discharge not only wastes water resources but also pollutes surrounding water bodies and soil. If recycled, its high salt content leads to severe scaling problems in subsequent treatment processes, especially in reverse osmosis systems. Scaling reduces membrane permeate flux and separation efficiency, increasing operating costs and maintenance complexity.

[0003] Currently, commonly used technologies for mine water concentration treatment include multi-stage reverse osmosis and evaporation crystallization. However, when treating high-salinity mine water, single reverse osmosis technology poses a significant risk of scaling in the second and subsequent reverse osmosis units due to the high hardness of the feed water (high content of divalent ions), requiring the addition of large amounts of scale inhibitors. This not only increases treatment costs but may also introduce new pollutants. On the other hand, directly using evaporation crystallization to treat mine water results in extremely high energy consumption and poor economic efficiency due to the large water volume and relatively low salt concentration.

[0004] Nanofiltration, a membrane separation technology situated between ultrafiltration and reverse osmosis, exhibits a high rejection rate for divalent ions but a lower rejection rate for monovalent ions, enabling effective separation of these two types of ions. Bipolar membrane electrodialysis, on the other hand, can directly convert salt solutions into corresponding acids and bases, offering advantages such as being green and highly efficient. Rationally coupling these technologies with reverse osmosis and evaporative crystallization holds promise for solving scale inhibition problems in mine water concentration processes and achieving efficient recovery and utilization of salt resources. However, mature and systematic technical solutions for this coupling process have not yet been developed. Summary of the Invention

[0005] This application provides a method and apparatus for the resource-based treatment of mine water, aiming to solve the shortcomings of existing mine water concentration processes, such as high scaling risk, high treatment cost, and low resource water recovery rate.

[0006] The first aspect of this application provides a method for the resource-based treatment of mine water, comprising the following steps: (1) Pre-treat the mine water to obtain pre-treated water; (2) The pretreated water is subjected to primary reverse osmosis treatment to obtain primary reverse osmosis desalinated water and primary reverse osmosis concentrate; (3) The first-stage reverse osmosis concentrate is subjected to nanofiltration treatment to obtain nanofiltration desalinated water and nanofiltration concentrate; (4) The nanofiltration desalinated water is subjected to two-stage reverse osmosis treatment to obtain two-stage reverse osmosis desalinated water and two-stage reverse osmosis concentrate; (5) The concentrated water from the secondary reverse osmosis is evaporated and crystallized to obtain monovalent salt crystals; (6) The nanofiltration concentrate is softened and then concentrated using three-stage reverse osmosis to obtain three-stage reverse osmosis desalinated water and three-stage reverse osmosis concentrate. (7) The concentrate from the third-stage reverse osmosis is treated by bipolar membrane electrodialysis to convert the divalent salts in the concentrate into the corresponding acids and bases.

[0007] According to some embodiments of the method for resource-based treatment of mine water described in this application, in step (1), the salt content of the mine water is ≥1500mg / L.

[0008] According to some embodiments of the mine water resource treatment method described in this application, the pretreatment includes coagulation, sedimentation, filtration, and disinfection.

[0009] According to some embodiments of the mine water resource treatment method described in this application, the pressure of the first-stage reverse osmosis treatment is 1.5-2.5 MPa, the temperature is 20-30℃, and the water recovery rate is 60%-70%.

[0010] According to some embodiments of the mine water resource treatment method described in this application, the reverse osmosis membrane used in the primary reverse osmosis treatment is a spiral wound reverse osmosis membrane.

[0011] According to some embodiments of the mine water resource treatment method described in this application, the salt concentration of the primary reverse osmosis concentrate obtained from the primary reverse osmosis treatment is 5000-20000 mg / L; According to some embodiments of the mine water resource treatment method described in this application, the salt concentration of the first-stage reverse osmosis freshwater obtained from the first-stage reverse osmosis treatment is ≤70mg / L.

[0012] According to some embodiments of the method for mine water resource treatment described in this application, in step (3), the pressure of the nanofiltration treatment is 0.8-1.5 MPa, the temperature is 20-30℃, and the water recovery rate is 70%-80%.

[0013] According to some embodiments of the mine water resource treatment method described in this application, the nanofiltration treatment has a rejection rate of ≥95% for divalent ions and a rejection rate of ≤30% for monovalent ions.

[0014] According to some embodiments of the method for mine water resource treatment described in this application, in step (4), the pressure of the secondary reverse osmosis treatment is 2.0-3.0 MPa, the temperature is 20-30℃, and the water recovery rate is 75%-85%.

[0015] According to some embodiments of the mine water resource treatment method described in this application, the content of monovalent ions in the secondary reverse osmosis desalination obtained by the secondary reverse osmosis treatment is ≤100mg / L.

[0016] According to some embodiments of the mine water resource treatment method described in this application, in step (5), the temperature of the evaporation crystallization is 80-120℃, and the intensity of the evaporation crystallization is 10-20 kg / (m²). 2 •h).

[0017] According to some embodiments of the method for mine water resource utilization described in this application, in step (6), the softening treatment includes removing scale-causing ions from nanofiltration concentrate using chemical precipitation.

[0018] According to some embodiments of the mine water resource treatment method described in this application, in step (7), the voltage of the bipolar membrane electrodialysis treatment is 20-50V, and the current density is 50-100A / m. 2 .

[0019] According to some embodiments of the mine water resource treatment method described in this application, the concentration of acid obtained by the bipolar membrane electrodialysis treatment is 0.5-2.0 mol / L, and the concentration of alkali is 0.5-2.0 mol / L.

[0020] This application also provides a mine water resource treatment device, including a pretreatment system, a primary reverse osmosis device, a nanofiltration device, a secondary reverse osmosis device, a tertiary reverse osmosis device, a concentrate softening treatment system, a bipolar membrane electrodialysis system, and a crystallization system; The outlet of the pretreatment system is connected to the inlet of the first-stage reverse osmosis unit, the concentrate outlet of the first-stage reverse osmosis unit is connected to the inlet of the nanofiltration unit, the desalination outlet of the nanofiltration unit is connected to the inlet of the second-stage reverse osmosis unit, and the concentrate outlet of the second-stage reverse osmosis unit is connected to the inlet of the crystallization system. The concentrate outlet of the nanofiltration unit is connected to the inlet of the concentrate softening system, the outlet of the concentrate softening system is connected to the inlet of the three-stage reverse osmosis unit, and the concentrate outlet of the three-stage reverse osmosis unit is connected to the inlet of the bipolar membrane electrodialysis system.

[0021] According to some embodiments of the mine water resource treatment device described in this application, the pretreatment system includes a coagulation tank, a sedimentation tank, a filtration device, and a disinfection tank connected in series.

[0022] According to some embodiments of the mine water resource treatment device described in this application, the filtration device includes a quartz sand filter and / or an activated carbon filter.

[0023] The beneficial effects of this application include: the mine water resource treatment method described in this application achieves effective separation of monovalent and divalent ions through a coupled process of "first-stage reverse osmosis concentrate - nanofiltration - second-stage reverse osmosis", reducing the scaling risk of second-stage reverse osmosis. At the same time, it combines evaporation crystallization and bipolar membrane technology to realize the resource utilization of salt resources. It has the characteristics of reasonable process, stable operation, good economy, and environmental protection and high efficiency.

[0024] The mine water resource treatment device described in this application has a simple structure, is easy to operate, and its various units work together. It is highly adaptable and can be applied to the treatment of mine water with different salt contents, thus having broad application prospects. Attached Figure Description

[0025] Figure 1 This application presents a schematic diagram of the structure of the mine water resource treatment device.

[0026] In the diagram: 1. Concentrate softening system; 2. First-stage reverse osmosis unit; 3. Nanofiltration unit; 4. Second-stage reverse osmosis unit; 5. Third-stage reverse osmosis unit; 6. Bipolar membrane electrodialysis system; 7. Crystallization system. Detailed Implementation

[0027] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0029] This application provides a method for the resource-based treatment of mine water, including the following steps: (1) Pre-treat the mine water to obtain pre-treated water; (2) The pretreated water is subjected to primary reverse osmosis treatment to obtain primary reverse osmosis desalinated water and primary reverse osmosis concentrate; (3) The first-stage reverse osmosis concentrate is subjected to nanofiltration treatment to obtain nanofiltration desalinated water and nanofiltration concentrate; (4) The nanofiltration desalinated water is subjected to two-stage reverse osmosis treatment to obtain two-stage reverse osmosis desalinated water and two-stage reverse osmosis concentrate; (5) The concentrated water from the secondary reverse osmosis is evaporated and crystallized to obtain monovalent salt crystals; (6) The nanofiltration concentrate is softened and then concentrated using three-stage reverse osmosis to obtain three-stage reverse osmosis desalinated water and three-stage reverse osmosis concentrate. (7) The concentrate from the third-stage reverse osmosis is treated by bipolar membrane electrodialysis to convert the divalent salts in the concentrate into the corresponding acids and bases.

[0030] The mine water resource treatment method described in this application achieves effective separation of monovalent and divalent ions in the first-stage reverse osmosis concentrate by adding a nanofiltration unit between the first-stage and second-stage reverse osmosis. The nanofiltration desalinated water mainly contains monovalent ions, which significantly reduces the scaling risk of the second-stage reverse osmosis system. It eliminates the need for large amounts of scale inhibitors, reduces treatment costs, extends the service life of the reverse osmosis membrane, and improves the stability of system operation.

[0031] The method for mine water resource treatment described in this application further concentrates nanofiltration desalinated water using a two-stage reverse osmosis process. The concentrated second-stage reverse osmosis concentrate is then evaporated and crystallized to recover monovalent salt resources. The nanofiltration concentrate is softened and then concentrated again using a three-stage reverse osmosis process. The three-stage reverse osmosis concentrate is then used for acid and alkali preparation via bipolar membrane electrodialysis. This method achieves the fractional recovery and efficient utilization of salt resources in mine water, improving resource recovery rates, turning waste into treasure, and demonstrating good economic benefits. The reverse osmosis desalinated water can be combined and recycled, and the steam generated by evaporation and crystallization can also be used as recycled water after condensation, improving water resource utilization. The acids and alkalis prepared by the bipolar membrane can be reused for softening treatment of nanofiltration concentrate or other industrial processes, achieving resource recycling, reducing pollutant emissions, and demonstrating good environmental benefits.

[0032] In some embodiments of this application, in step (1), the salt content of the mine water is ≥1500mg / L.

[0033] In some embodiments of this application, the pretreatment includes coagulation, sedimentation, filtration, and disinfection; pretreatment of mine water removes suspended solids, colloids, organic matter, and microorganisms. The main scale-causing ions in the pretreated water include Ca. 2 + SO4 2- CO3 2- wait.

[0034] In some embodiments of this application, the pressure of the first-stage reverse osmosis treatment is 1.5-2.5 MPa, such as 1.5 MPa, 2.0 MPa, 2.2 MPa, 2.5 MPa, etc., the temperature is 20-30°C, and the water recovery rate is 60%-70%, such as 60%, 63%, 65%, 68%, 70%, etc.

[0035] In some embodiments of this application, the salt concentration of the primary reverse osmosis concentrate obtained from the primary reverse osmosis treatment is 5000-20000 mg / L, such as 5000 mg / L, 8000 mg / L, 9800 mg / L, 10000 mg / L, 12000 mg / L, 16000 mg / L, 20000 mg / L, etc. The reverse osmosis membrane used in the primary reverse osmosis treatment in the embodiments of this application is a spiral wound reverse osmosis membrane.

[0036] In some embodiments of this application, the salt concentration of the first-stage reverse osmosis desalinated water obtained from the first-stage reverse osmosis treatment is ≤70mg / L, such as 70mg / L, 68mg / L, 63mg / L, 51mg / L, 47mg / L, 41mg / L, 38mg / L, 30mg / L, etc.

[0037] In some embodiments of this application, in step (3), the pressure of the nanofiltration treatment is 0.8-1.5 MPa, for example 0.8 MPa, 0.9 MPa, 1.0 MPa, 1.2 MPa, 1.5 MPa, etc., the temperature is 20-30℃, and the water recovery rate is 70%-80%, for example 70%, 72%, 75%, 80%, etc. Utilizing the high rejection rate of divalent ions and low rejection rate of monovalent ions of the nanofiltration membrane, nanofiltration desalinated water and nanofiltration concentrate are obtained; the nanofiltration desalinated water mainly contains monovalent ions, and the nanofiltration concentrate mainly contains divalent ions.

[0038] In some embodiments of this application, the nanofiltration process achieves a rejection rate of ≥95% for divalent ions, such as 95%, 98%, 100%, etc., and a rejection rate of ≤30% for monovalent ions. The nanofiltration membrane used in the embodiments of this application is a high ion-selective nanofiltration membrane.

[0039] In some embodiments of this application, in step (3), the nanofiltration membrane used in the nanofiltration process is a high ion selectivity nanofiltration membrane.

[0040] In some embodiments of this application, in step (4), the pressure of the secondary reverse osmosis treatment is 2.0-3.0 MPa, the temperature is 20-30°C, and the water recovery rate is 75%-85%; for example, 75%, 78%, 80%, 83%, 85%, etc.

[0041] In some embodiments of this application, the content of monovalent ions in the secondary reverse osmosis desalination obtained by the secondary reverse osmosis treatment is ≤100mg / L.

[0042] In some embodiments of this application, the reverse osmosis membrane used in the secondary reverse osmosis treatment is a disc tube reverse osmosis membrane. Because the content of divalent ions in nanofiltration desalination water is extremely low, the risk of scaling in the secondary reverse osmosis system is significantly reduced, and stable operation can be achieved without the need for additional scale inhibitors or with only a small amount of scale inhibitor.

[0043] In some embodiments of this application, in step (5), the evaporation crystallization temperature is 80-120℃, for example 80℃, 85℃, 98℃, 100℃, 110℃, 120℃, etc., and the evaporation crystallization strength is 10-20 kg / (m²). 2 •h), for example 10kg / (m 2 •h), 12kg / (m 2 •h), 15kg / (m 2 •h), 18kg / (m 2 •h), 20kg / (m 2 •h) etc. The concentrate from the secondary reverse osmosis is evaporated and crystallized to obtain monovalent salt crystals (such as sodium chloride and potassium chloride), realizing the recycling of monovalent salt resources; the steam generated during the evaporation and crystallization process can be used as recycled water after condensation.

[0044] In some embodiments of this application, in step (6), the softening process includes removing scale-causing ions from nanofiltration concentrate using chemical precipitation.

[0045] In some embodiments of this application, in step (7), the bipolar membrane used in the bipolar membrane electrodialysis treatment includes a cation exchange layer, an anion exchange layer, and a hydrolysis layer sandwiched therebetween. Through the hydrolysis effect of the bipolar membrane and the selective permeability of the ion exchange membrane, divalent salts in the nanofiltration concentrate are converted into corresponding acids and bases; the obtained acids and bases can be reused in mine water pretreatment or other industrial production processes, realizing the recycling of resources.

[0046] In some embodiments of this application, in step (7), the voltage of the bipolar membrane electrodialysis treatment is 20-50V, such as 20V, 25V, 33V, 38V, 43V, 50V, etc., and the current density is 50-100A / m. 2 For example, 50A / m 2 56A / m 2 63A / m 2 71A / m 2 86A / m 2 95A / m 2 100A / m 2 wait.

[0047] In some embodiments of this application, the concentration of acid obtained by the bipolar membrane electrodialysis treatment is 0.5-2.0 mol / L, such as 0.5 mol / L, 1.5 mol / L, 5.7 mol / L, 8.6 mol / L, 10.2 mol / L, 15.7 mol / L, 20 mol / L, etc., and the concentration of alkali is 0.5-2.0 mol / L, such as 0.5 mol / L, 1.5 mol / L, 5.7 mol / L, 8.6 mol / L, 10.2 mol / L, 15.7 mol / L, 20 mol / L, etc.

[0048] The second aspect of this application provides a mine water resource treatment device, including a pretreatment system, a primary reverse osmosis device, a nanofiltration device, a secondary reverse osmosis device, a tertiary reverse osmosis device, a concentrate softening treatment system, a bipolar membrane electrodialysis system, and a crystallization system; The outlet of the pretreatment system is connected to the inlet of the first-stage reverse osmosis unit, the concentrate outlet of the first-stage reverse osmosis unit is connected to the inlet of the nanofiltration unit, the desalination outlet of the nanofiltration unit is connected to the inlet of the second-stage reverse osmosis unit, and the concentrate outlet of the second-stage reverse osmosis unit is connected to the inlet of the crystallization system. The concentrate outlet of the nanofiltration unit is connected to the inlet of the concentrate softening system, the outlet of the concentrate softening system is connected to the inlet of the three-stage reverse osmosis unit, and the concentrate outlet of the three-stage reverse osmosis unit is connected to the inlet of the bipolar membrane electrodialysis system. The crystallization system used in this embodiment includes a multi-effect evaporator crystallizer or an MVR evaporator crystallizer.

[0049] In some embodiments of this application, the pretreatment system includes a coagulation tank, a sedimentation tank, a filtration device, and a disinfection tank connected in series. As a preferred embodiment, the coagulant used in the coagulation process can be polyaluminum chloride or polyferric sulfate, with a dosage of 20-50 mg / L; the sedimentation time is 1-2 hours; filtration uses quartz sand filtration or activated carbon filtration, with a filtration rate of 5-10 m / h; and disinfection uses sodium hypochlorite, with a dosage of 1-3 mg / L.

[0050] The technical solution of this application will be further described below with reference to specific embodiments.

[0051] This application provides a mine water resource treatment device, including a pretreatment system, a primary reverse osmosis device 2, a nanofiltration device 3, a secondary reverse osmosis device 4, a tertiary reverse osmosis device 5, a concentrate softening treatment system 1, a bipolar membrane electrodialysis system 6, and a crystallization system 7. The pretreatment system described in this application embodiment includes a coagulation tank, a sedimentation tank, a filtration device, and a disinfection tank connected in series. In a preferred embodiment, the filtration device includes a quartz sand filter. The outlet of the pretreatment system is connected to the inlet of the first-stage reverse osmosis unit 2. The concentrate outlet of the first-stage reverse osmosis unit 2 is connected to the inlet of the nanofiltration unit 3. The desalination outlet of the nanofiltration unit 3 is connected to the inlet of the second-stage reverse osmosis unit 4. The concentrate outlet of the second-stage reverse osmosis unit 4 is connected to the inlet of the crystallization system 7. The concentrate outlet of the nanofiltration device 3 is connected to the inlet of the concentrate softening system 1, the outlet of the concentrate softening system 1 is connected to the inlet of the three-stage reverse osmosis device 5, and the concentrate outlet of the three-stage reverse osmosis device 5 is connected to the inlet of the bipolar membrane electrodialysis system 6.

[0052] Example 1 A method for the resource-based treatment of mine water includes the following steps: Step 1: Mine water pretreatment A sample of mine water from a coal mine was taken. Its water quality indicators were: suspended solids 85 mg / L, CODcr 62 mg / L, total hardness (as CaCO3) 1200 mg / L, and total salt content 3500 mg / L, of which Na... + 500mg / L, K + 80 mg / L, Ca 2+ 250 mg / L, Mg 2+ 120 mg / L, Cl - 650 mg / L, SO4 2- 850 mg / L. Polyaluminum chloride coagulant was added to the mine water at a dosage of 30 mg / L. After thorough stirring, the water was allowed to settle in a sedimentation tank for 1.5 hours. The effluent from the sedimentation tank was then filtered through a quartz sand filter at a filtration rate of 8 m / h. The filtered effluent was then placed in a disinfection tank and disinfected with sodium hypochlorite at a dosage of 2 mg / L, resulting in pretreated effluent with a suspended solids content ≤5 mg / L and a COD of 0.5 mg / L. cr ≤20mg / L, the microbial indicators meet the Class I water quality standards of the "Surface Water Environmental Quality Standard".

[0053] Step 2: First-stage reverse osmosis treatment The pretreated effluent obtained in step 1 is fed into a primary reverse osmosis system using spiral wound reverse osmosis membrane elements. The operating pressure is 2.0 MPa, the temperature is 23℃, and the water recovery rate is 65%, yielding primary reverse osmosis desalinated water and primary reverse osmosis concentrate. The total salt content of the primary reverse osmosis desalinated water is ≤70 mg / L, and it can be directly used as recycled water in coal mine production. The total salt content of the primary reverse osmosis concentrate is 9800 mg / L, of which Na... + 1350mg / L, K + 210 mg / L, Ca2+ 680 mg / L, Mg 2+ 320 mg / L, Cl - 1750 mg / L, SO4 2- 2300mg / L.

[0054] Step 3: Nanofiltration separation The first-stage reverse osmosis concentrate obtained in step 2 was fed into a nanofiltration system using a high ion-selective nanofiltration membrane. The operating pressure was 1.2 MPa, the temperature was 23°C, and the water recovery rate was 75%. Separation was performed to obtain nanofiltration desalinated water and nanofiltration concentrate. Analysis showed that the nanofiltration desalinated water mainly contained monovalent ions, including Na+. + 1300mg / L, K + 200 mg / L, Ca 2+ 25 mg / L, Mg 2+ 15 mg / L, total divalent ion content 40 mg / L; nanofiltration concentrate mainly contains divalent ions, including Ca 2+ 2000 mg / L, Mg 2+ 930 mg / L, SO4 2- 6800 mg / L, total divalent ion content 9730 mg / L.

[0055] Step 4: Secondary Reverse Osmosis Deep Concentration The nanofiltration desalinated water obtained in step 3 is fed into a secondary reverse osmosis system using disc tube reverse osmosis membrane elements. The operating pressure is 6.5 MPa, the temperature is 23℃, and the water recovery rate is 80%, yielding secondary reverse osmosis desalinated water and secondary reverse osmosis concentrate. The total salt content of the secondary reverse osmosis desalinated water is ≤100 mg / L, and it can be combined with the primary reverse osmosis desalinated water as recycled water. Due to the extremely low divalent ion content in the nanofiltration desalinated water, no scaling occurred during the operation of the secondary reverse osmosis system, and no scale inhibitor was required. The total salt content of the secondary reverse osmosis concentrate is 90,000-100,000 mg / L, mainly consisting of monovalent salts.

[0056] Step 5: Resource Utilization of Secondary Reverse Osmosis Concentrate Evaporation and Crystallization The secondary reverse osmosis concentrate obtained in step 4 is fed into an MVR evaporator crystallizer at an operating temperature of 95℃ and an evaporation rate of 15 kg / (m²). 2 •h), by evaporation and crystallization, a mixed crystal of sodium chloride and potassium chloride is obtained with a crystal purity of ≥98%, which can be used as industrial salt; the steam generated during the evaporation and crystallization process is condensed to obtain condensate water with a total salt content of ≤50mg / L, which can be used as recycled water.

[0057] Step 6: Soften and then concentrate the nanofiltration concentrate. The nanofiltration concentrate obtained in step 3 is fed into a concentrate softening treatment system. After the scale-causing ions are removed from the permeate, it is concentrated again using a three-stage reverse osmosis unit.

[0058] Step 7: Bipolar membrane acid and alkali production Water concentrated by a three-stage reverse osmosis unit is fed into a bipolar membrane electrodialysis system. The membrane stack uses a combination of homogeneous ion exchange membranes and bipolar membranes, with an operating voltage of 35V and an operating current density of 80A / m³. 2 By utilizing the water dissociation effect of bipolar membranes and the selective permeability of ion exchange membranes, divalent salts such as calcium sulfate and magnesium sulfate in nanofiltration concentrate are converted into sulfuric acid and a mixed alkaline solution of calcium hydroxide and magnesium hydroxide. The resulting sulfuric acid concentration is 1.2 mol / L, and the concentration of the calcium hydroxide-magnesium hydroxide mixed alkaline solution is 1.0 mol / L. The sulfuric acid can be reused for pH adjustment in the pretreatment unit, and the mixed alkaline solution can be reused for coagulation auxiliary treatment of mine water, thus realizing the recycling of resources.

[0059] Example 2 A method for the resource-based treatment of mine water includes the following steps: Step 1: Mine water pretreatment A sample of mine water from a coal mine was taken. Its water quality indicators were: suspended solids 120 mg / L, CODcr 85 mg / L, total hardness (as CaCO3) 1800 mg / L, and total salt content 5200 mg / L, of which Na... + 750mg / L, K + 120 mg / L, Ca 2+ 380 mg / L, Mg 2+ 180 mg / L, Cl - 950 mg / L, SO4 2- 1250 mg / L. Add polyferric sulfate coagulant at a dosage of 40 mg / L to the mine water, stir thoroughly, and then allow it to settle in a sedimentation tank for 2 hours. The effluent from the sedimentation tank is then filtered through an activated carbon filter at a filtration rate of 6 m / h. The filtered effluent is then placed in a disinfection tank and disinfected with sodium hypochlorite at a dosage of 3 mg / L. The resulting pretreated effluent has a suspended solids content ≤5 mg / L, a CODcr ≤25 mg / L, and meets the microbiological standards.

[0060] Step 2: First-stage reverse osmosis treatment The pretreated effluent obtained in step 1 is fed into a primary reverse osmosis system using spiral wound reverse osmosis membrane elements. The operating pressure is 2.5 MPa, the temperature is 25℃, and the water recovery rate is 70%, yielding primary reverse osmosis desalinated water and primary reverse osmosis concentrate. The total salt content of the primary reverse osmosis desalinated water is ≤70 mg / L, and it can be directly used as recycled water in coal mine production. The total salt content of the primary reverse osmosis concentrate is 17300 mg / L, of which Na... + 2500 mg / L, K + 400 mg / L, Ca 2+ 1260 mg / L, Mg 2+600mg / L, Cl - 3150 mg / L, SO4 2- 4100mg / L.

[0061] Step 3: Nanofiltration separation The first-stage reverse osmosis concentrate obtained in step 2 was fed into a nanofiltration system using a high ion-selective nanofiltration membrane. The operating pressure was 1.5 MPa, the temperature was 25°C, and the water recovery rate was 80%. Separation was performed to obtain nanofiltration desalinated water and nanofiltration concentrate. Analysis showed that the nanofiltration desalinated water mainly contained monovalent ions, including Na+. + 2400mg / L, K + 380 mg / L, Ca 2+ 35 mg / L, Mg 2+ 20 mg / L, total divalent ion content 55 mg / L; nanofiltration concentrate mainly contains divalent ions, including Ca 2+ 4900 mg / L, Mg 2+ 2320 mg / L, SO4 2- 16200 mg / L, total divalent ion content 23420 mg / L.

[0062] Step 4: Secondary Reverse Osmosis Deep Concentration The nanofiltration desalinated water obtained in step 3 is fed into a secondary reverse osmosis system using disc tube reverse osmosis membrane elements. The operating pressure is 6.0 MPa, the temperature is 25℃, and the water recovery rate is 85%, yielding secondary reverse osmosis desalinated water and secondary reverse osmosis concentrate. The total salt content of the secondary reverse osmosis desalinated water is ≤120 mg / L, and it can be combined with the primary reverse osmosis desalinated water as recycled water. During the operation of the secondary reverse osmosis system, only a small amount of antiscalant (5 mg / L) is added, which allows it to operate stably without significant scaling. The total salt content of the secondary reverse osmosis concentrate is 95000 mg / L, mainly consisting of monovalent salts.

[0063] Step 5: Resource Utilization of Secondary Reverse Osmosis Concentrate Evaporation and Crystallization The secondary reverse osmosis concentrate obtained in step 4 is fed into a multi-effect evaporator crystallizer at an operating temperature of 110℃ and an evaporation rate of 18 kg / (m³). 2 •h), sodium chloride crystals are obtained by evaporation and crystallization, with a crystal purity of ≥99%, which can be used as food-grade salt raw material; the steam generated by evaporation and crystallization is condensed to obtain condensate water with a total salt content of ≤60mg / L, which can be used as recycled water.

[0064] Step 6: Soften and then concentrate the nanofiltration concentrate. The nanofiltration concentrate obtained in step 3 is fed into a concentrate softening treatment system. After the scale-causing ions are removed from the permeate, it is concentrated again using a three-stage reverse osmosis unit.

[0065] Step 7: Bipolar membrane acid and alkali production Water concentrated by a three-stage reverse osmosis unit is fed into a bipolar membrane electrodialysis system. The membrane stack uses a combination of homogeneous ion exchange membranes and bipolar membranes, with an operating voltage of 50V and an operating current density of 100A / m³. 2 The process converts divalent salts in nanofiltration concentrate into a mixed alkaline solution of sulfuric acid, calcium hydroxide, and magnesium hydroxide. The resulting sulfuric acid has a concentration of 1.8 mol / L, and the calcium hydroxide-magnesium hydroxide mixed alkaline solution has a concentration of 1.5 mol / L. The sulfuric acid can be used in the production of surrounding chemical enterprises, and the mixed alkaline solution can be used as an auxiliary treatment for coagulation in mine water pretreatment, thus realizing the recycling of resources.

[0066] Example 3 The only difference between the mine water resource treatment method described in Example 3 and Example 1 is that the pressure of nanofiltration during the mine water resource treatment process in Example 3 is 0.95 MPa.

[0067] Example 4 The difference between the mine water resource treatment method in Example 4 and Example 1 is that the nanofiltration pressure in the mine water resource treatment process in Example 4 is 1.30 MPa. Example 5 The difference between the mine water resource treatment method in Example 5 and Example 1 is that the nanofiltration pressure in the mine water resource treatment process in Example 5 is 1.45 MPa. Example 6 The difference between the mine water resource treatment method in Example 6 and Example 1 is that the nanofiltration temperature in the mine water resource treatment process in Example 6 is 28°C. Example 7 The difference between the mine water resource treatment method in Example 7 and Example 1 is that the nanofiltration temperature in the mine water resource treatment process in Example 7 is 22°C. Example 8 The difference between the mine water resource treatment method in Example 8 and Example 1 is that the nanofiltration temperature in the mine water resource treatment process in Example 8 is 30°C. Example 9 The method for mine water resource utilization in Example 9 differs from that in Example 1 only in that the nanofiltration recovery rate during the mine water resource utilization process in Example 9 is 70%. Example 10 The difference between the mine water resource treatment method in Example 10 and Example 1 is that the water recovery rate of nanofiltration in the mine water resource treatment process in Example 10 is 85%. Example 11 The method for mine water resource utilization in Example 11 differs from that in Example 1 only in that the water recovery rate of nanofiltration during the mine water resource utilization process in Example 11 is 75%. The effects of the mine water resource treatment methods described in Examples 1-11 of this application were studied, and the results are shown in Table 1.

[0068] Table 1

[0069] As can be seen from Table 1, the method for mine water resource treatment described in this application has a high recovery rate of both mine water and salt resources, and the stable operation of the secondary reverse osmosis system reaches 8 months, demonstrating significant economic, environmental and social benefits.

[0070] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for the resource-based treatment of mine water, characterized in that, Includes the following steps: (1) Pre-treat the mine water to obtain pre-treated water; (2) The pretreated water is subjected to primary reverse osmosis treatment to obtain primary reverse osmosis desalinated water and primary reverse osmosis concentrate; (3) The first-stage reverse osmosis concentrate is subjected to nanofiltration treatment to obtain nanofiltration desalinated water and nanofiltration concentrate; (4) The nanofiltration desalinated water is subjected to two-stage reverse osmosis treatment to obtain two-stage reverse osmosis desalinated water and two-stage reverse osmosis concentrate; (5) The concentrated water from the secondary reverse osmosis is evaporated and crystallized to obtain monovalent salt crystals; (6) The nanofiltration concentrate is softened and then concentrated using three-stage reverse osmosis to obtain three-stage reverse osmosis desalinated water and three-stage reverse osmosis concentrate. (7) The concentrate from the third-stage reverse osmosis is treated by bipolar membrane electrodialysis to convert the divalent salts in the concentrate into the corresponding acids and bases.

2. The method for resource-based treatment of mine water according to claim 1, characterized in that, In step (1), the salt content of the mine water is ≥1500mg / L; And / or, the pretreatment includes coagulation, sedimentation, filtration and sterilization; And / or, the pressure of the first-stage reverse osmosis treatment is 1.5-2.5 MPa, the temperature is 20-30℃, and the water recovery rate is 60%-70%; And / or, the reverse osmosis membrane used in the first-stage reverse osmosis treatment is a spiral wound reverse osmosis membrane; And / or, the salt concentration of the primary reverse osmosis concentrate obtained from the primary reverse osmosis treatment is 5000-20000 mg / L; And / or, the salt concentration of the first-stage reverse osmosis desalinated water obtained from the first-stage reverse osmosis treatment is ≤70mg / L.

3. The method for resource-based treatment of mine water according to claim 1, characterized in that, In step (3), the nanofiltration treatment is carried out at a pressure of 0.8-1.5 MPa, a temperature of 20-30℃, and a water recovery rate of 70%-80%. And / or, the nanofiltration process has a rejection rate of ≥95% for divalent ions and a rejection rate of ≤30% for monovalent ions.

4. The method for resource-based treatment of mine water according to claim 1, characterized in that, In step (4), the pressure of the secondary reverse osmosis treatment is 2.0-3.0 MPa, the temperature is 20-30℃, and the water recovery rate is 75%-85%. And / or, the content of monovalent ions in the secondary reverse osmosis desalination obtained from the secondary reverse osmosis treatment is ≤100mg / L.

5. The method for resource-based treatment of mine water according to claim 1, characterized in that, In step (5), the evaporation crystallization temperature is 80-120℃, and the evaporation crystallization strength is 10-20 kg / (m²). 2 •h).

6. The method for resource-based treatment of mine water according to claim 1, characterized in that, In step (6), the softening treatment includes removing scale-causing ions from nanofiltration concentrate using chemical precipitation.

7. The method for resource-based treatment of mine water according to claim 1, characterized in that, In step (7), the voltage of the bipolar membrane electrodialysis treatment is 20-50V, and the current density is 50-100A / m. 2 .

8. The method for resource-based treatment of mine water according to claim 1, characterized in that, The concentration of acid obtained by the bipolar membrane electrodialysis treatment is 0.5-2.0 mol / L, and the concentration of alkali is 0.5-2.0 mol / L.

9. A mine water resource treatment device, characterized in that, It includes a pretreatment system, a primary reverse osmosis unit, a nanofiltration unit, a secondary reverse osmosis unit, a tertiary reverse osmosis unit, a concentrate softening system, a bipolar membrane electrodialysis system, and a crystallization system; The outlet of the pretreatment system is connected to the inlet of the first-stage reverse osmosis unit, the concentrate outlet of the first-stage reverse osmosis unit is connected to the inlet of the nanofiltration unit, the desalination outlet of the nanofiltration unit is connected to the inlet of the second-stage reverse osmosis unit, and the concentrate outlet of the second-stage reverse osmosis unit is connected to the inlet of the crystallization system. The concentrate outlet of the nanofiltration unit is connected to the inlet of the concentrate softening system, the outlet of the concentrate softening system is connected to the inlet of the three-stage reverse osmosis unit, and the concentrate outlet of the three-stage reverse osmosis unit is connected to the inlet of the bipolar membrane electrodialysis system.

10. The mine water resource treatment device according to claim 9, characterized in that, The pretreatment system includes a coagulation tank, a sedimentation tank, a filtration device, and a disinfection tank connected in series. Preferably, the filtration device includes a quartz sand filter and / or an activated carbon filter.

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