A method and system for treating coal mine water by step softening and removing silicon in combination with membrane method

Abstract

The present application relates to the technical field of mine water treatment, and particularly relates to a method and system for step-by-step softening and silicon removal of coal mine water by a membrane method, comprising the following steps: A) coagulating and clarifying the coal mine water; B) removing calcium and softening and preliminarily removing silicon from the effluent obtained in step A); C) adjusting the pH value of the effluent obtained in step B) to 7.8-8.3 and then performing sterilization treatment; D) performing ultrafiltration and reverse osmosis desalination treatment on the effluent obtained in step C); E) removing magnesium and softening and deeply removing silicon from the reverse osmosis concentrated water obtained in step D); and F) performing filtration treatment on the effluent obtained in step E). The process adopted by the present application is short and efficient, calcium and magnesium ions can be recovered and utilized in steps, the softening and silicon removal effects are good, the membrane method treatment makes the system effluent reach the industrial and agricultural recycled water standards, and the subsequent combination with a deep treatment process can realize zero discharge of the coal mine water.

Description

Technical Field

[0001] This invention relates to the field of mine water treatment technology, and in particular to a method and system for stepwise softening and silica removal combined with membrane treatment of coal mine water. Background Technology

[0002] High-hardness, high-mineralization mine water is widely distributed, found in Shanxi, Shaanxi, Inner Mongolia, Xinjiang, and other regions. The salt content of this type of mine water is typically in the range of 1200–6000 mg / L, and the total hardness and calcium hardness are also very high, generally in the range of 800–2000 mg / L (calculated as calcium carbonate). Direct infiltration of high-salt, high-hardness wastewater into farmland will damage soil structure, causing soil salinization and leading to a decline in the yield and quality of agricultural products. Membrane technology has become a key research area in the field of zero-discharge mine water, as evidenced by Chinese patent applications 201821967438.7, 201811306485.1, and 202121863177.6. Commonly used membrane systems require a softening pretreatment process to remove calcium and magnesium hardness from the water to reduce the risk of scaling. However, current softening pretreatment processes mainly remove calcium and magnesium hardness simultaneously, requiring the addition of large amounts of flocculants and coagulants, resulting in high operating costs, unstable softening effects, and difficulty in achieving resource utilization of calcium and magnesium ions. In addition, enterprises need to pay additional industrial solid waste disposal costs.

[0003] Therefore, given the characteristics of mine water in coal mines with high hardness and high mineralization, it is of great practical significance to develop a synergistic treatment process with low investment and operating costs, short process flow, good softening and desiliconization effects, and the ability to recover and utilize calcium and magnesium ions. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a method and system for step-by-step softening and desiliconization combined with membrane treatment of coal mine water. The process is simple and efficient, the softening and desiliconization effects are relatively stable, calcium and magnesium ions can be recovered and reused in steps, and the combined membrane treatment enables the system water to meet the standards for industrial and agricultural reclaimed water.

[0005] This invention provides a method for step-by-step softening and desiliconization synergistic membrane treatment of coal mine moisture, comprising the following steps:

[0006] A) Clarify and coagulate coal mine water;

[0007] B) Perform calcium removal softening and preliminary silica removal on the effluent obtained in step A);

[0008] C) After adjusting the pH of the effluent obtained in step B) to 7.8–8.3, perform sterilization treatment;

[0009] D) Perform ultrafiltration and reverse osmosis desalination on the effluent obtained in step C);

[0010] E) Perform magnesium removal, softening, and deep silica removal on the reverse osmosis concentrate obtained in step D);

[0011] F) Filter the effluent obtained in step E).

[0012] Preferably, in step B), the pH value of the calcium removal softening and preliminary silicon removal is controlled at 9.0 to 9.3.

[0013] Preferably, in step B), the effluent obtained in step B) contains 0.5 to 1.0 mmol / L of carbonate.

[0014] Preferably, in step E), the pH value of the magnesium removal softening and deep silicon removal reaction is controlled at 10.8 to 11.3.

[0015] Preferably, in step E), after the magnesium removal softening and deep silicon removal, the process further includes:

[0016] The pH of the effluent after magnesium removal, softening, and deep silica removal is adjusted to 7.8–8.3.

[0017] This invention also provides a system for step-by-step softening and desiliconization synergistic membrane treatment of coal mine moisture, comprising:

[0018] A coagulation and clarification unit, wherein the coagulation and clarification unit is provided with a coal mine water inlet;

[0019] A calcium removal and softening unit connected to the outlet of the coagulation and clarification unit;

[0020] An ultrafiltration device connected to the outlet of the calcium removal and softening unit;

[0021] A reverse osmosis device connected to the outlet of the ultrafiltration device;

[0022] A magnetic coagulation high-efficiency sedimentation unit connected to the concentrate outlet of the reverse osmosis unit;

[0023] A filtration unit connected to the outlet of the magnetic coagulation high-efficiency sedimentation unit.

[0024] Preferably, the calcium removal and softening unit is equipped with a first online pH meter for monitoring pH value and an online alkalinity analyzer for monitoring carbonate ions;

[0025] The magnetic coagulation high-efficiency sedimentation unit is equipped with a second online pH meter for monitoring pH values.

[0026] Preferably, the coagulation and clarification unit is one or more of a mechanically stirred clarification tank, a high-density sedimentation tank, and a high-efficiency cyclone purifier.

[0027] Preferably, the calcium removal and softening unit is one or more of the following: chemical crystallization circulating granulation fluidized bed, high-density sedimentation tank, and mechanically stirred clarification tank.

[0028] Preferably, the filtration unit is one or more of a V-type filter, a fiber filter, and a variable porosity filter.

[0029] This application provides a method for stepwise softening and silica removal combined with membrane treatment of coal mine water, comprising the following steps: A) coagulating and clarifying the coal mine water; B) subjecting the effluent obtained in step A) to calcium removal softening and preliminary silica removal; C) adjusting the pH of the effluent obtained in step B) to 7.8–8.3 and then sterilizing it; D) subjecting the effluent obtained in step C) to ultrafiltration and reverse osmosis desalination; E) subjecting the reverse osmosis concentrate obtained in step D) to magnesium removal softening and deep silica removal; F) filtering the effluent obtained in step E). Calcium recovery and preliminary silica removal are performed in the calcium removal softening unit, while the reverse osmosis unit performs desalination and simultaneously concentrates and enriches magnesium ions in the water. The RO concentrate enters a magnetic coagulation high-efficiency sedimentation unit for magnetic coagulation-enhanced magnesium recovery and deep silica removal. In response to the characteristics of coal mine water with high hardness and high mineralization, the process adopted in this application is simple and efficient, with relatively stable softening and desiliconization effects. Calcium and magnesium ions can be recovered and reused in stages, and the synergistic membrane treatment enables the system's produced water to meet the standards for industrial and agricultural reclaimed water. Attached Figure Description

[0030] Figure 1 This is a system diagram of a step-by-step softening and desiliconization synergistic membrane treatment for coal mine moisture, provided as an embodiment of this application. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] This application provides a method for step-by-step softening and desiliconization synergistic membrane treatment of coal mine moisture, including the following steps:

[0033] A) Clarify and coagulate coal mine water;

[0034] B) Perform calcium removal softening and preliminary silica removal on the effluent obtained in step A);

[0035] C) After adjusting the pH of the effluent obtained in step B) to 7.8–8.3, perform sterilization treatment;

[0036] D) Perform ultrafiltration and reverse osmosis desalination on the effluent obtained in step C);

[0037] E) Perform magnesium removal, softening, and deep silica removal on the reverse osmosis concentrate obtained in step D);

[0038] F) Filter the effluent obtained in step E).

[0039] In step A):

[0040] Coagulation and clarification of coal mine water.

[0041] In this invention, the coal mine water is high-hardness, high-mineralization coal mine water. In some embodiments of this application, the turbidity of the coal mine water is 100–380 NTU, the salt content is 4200–4400 mg / L, the total hardness is 900–1200 mg / L, the total alkalinity is 4–5 mmol / L, the calcium ion content is 400–500 mg / L, the magnesium ion content is 40–55 mg / L, the sulfate content is 2600–3000 mg / L, the chloride content is 55–65 mg / L, and the total silica content is 10–20 mg / L. In some embodiments of this application, the turbidity of the coal mine water is 120-250 NTU, the salt content is 3600 mg / L, the total hardness is 1100-1500 mg / L, the total alkalinity is 4-5 mmol / L, the calcium ion content is 500-700 mg / L, the magnesium ion content is 60-75 mg / L, the sulfate content is 2150-2400 mg / L, the chloride content is 45-60 mg / L, and the total silicon content is 15-25 mg / L.

[0042] In some embodiments of the present invention, before coagulation and clarification of coal mine water, the method further includes:

[0043] The coal mine water undergoes water quality balancing and quantity regulation. Specifically, the coal mine water undergoes water quality balancing and quantity regulation in a regulating pond.

[0044] In some embodiments of the present invention, coagulation and clarification of coal mine water includes:

[0045] Coal mine water is mixed with coagulants to carry out a coagulation reaction. The coagulants include flocculants and coagulant aids. Specifically, the effluent from the equalization tank enters the coagulation and clarification unit, where it is mixed sequentially with flocculants and coagulant aids to carry out a coagulation reaction, thereby removing coal dust, colloids, and other substances from the coal mine water.

[0046] In some embodiments of this application, the flocculant includes, but is not limited to, one or more of polyaluminum chloride, polyaluminum sulfate, polyferric chloride, polyferric sulfate, polyaluminum silicate, polyferric silicate, polyaluminum phosphate chloride, polyferric phosphate chloride, and polyacrylamide. The coagulant aid includes, but is not limited to, one or more of sulfuric acid, phosphoric acid, lime, chlorine, polyacrylamide, activated silica, and sodium alginate. In some specific implementations, the flocculant is polyaluminum chloride, and the coagulant aid is polyacrylamide. This invention does not impose any special limitations on the amount of the flocculant and coagulant aid used; they can be selected according to the content of suspended particles and colloidal substances in the influent.

[0047] In some embodiments of the present invention, the coal slime obtained from coagulation and clarification is subjected to sedimentation and dewatering. The filtrate is recycled to the water quality equalization and quantity adjustment stage, specifically, to the equalization tank.

[0048] In step B):

[0049] The effluent obtained in step A) is subjected to calcium removal, softening, and preliminary silica removal.

[0050] In some embodiments of the present invention, before calcium removal, softening and preliminary silicon removal, the process further includes: passing the effluent obtained in step A) through a clarification tank before calcium removal, softening and preliminary silicon removal.

[0051] The methods for calcium removal, softening, and preliminary silicon removal are flocculation precipitation or crystallization.

[0052] In some embodiments of the present invention, a flocculation and sedimentation method is used for calcium removal, softening, and preliminary silica removal. The agents used for calcium removal, softening, and preliminary silica removal include sodium hydroxide, sodium carbonate, flocculant, and coagulant aid. Specifically, after the effluent obtained in step A) passes through a clarification tank, sodium hydroxide, sodium carbonate, flocculant, and coagulant aid are added sequentially, and a flocculation and sedimentation method is used for calcium removal, softening, and preliminary silica removal.

[0053] The flocculant includes, but is not limited to, one or more of polyaluminum chloride, polyaluminum sulfate, polyferric chloride, polyferric sulfate, polyaluminum silicate chloride, polyferric silicate sulfate, polyaluminum phosphate chloride, polyferric phosphate chloride, and polyacrylamide. The coagulant aid includes, but is not limited to, one or more of sulfuric acid, phosphoric acid, lime, chlorine, polyacrylamide, activated silica, and sodium alginate. In some specific implementations, the flocculant is polyferric sulfate, and the coagulant aid is polyacrylamide.

[0054] By adding sodium hydroxide and sodium carbonate, the pH value of the calcium removal softening and preliminary silicon removal processes is controlled to be 9.0–9.3, ensuring that the effluent obtained in step B) contains 0.5–1.0 mmol / L of carbonate ions. Calcium ions undergo a chemical reaction to form calcium carbonate precipitate. The calcium removal rate can reach over 95%, while a preliminary silicon removal reaction is carried out simultaneously, with a silicon removal rate of over 60%. Maintaining the reaction pH in a slightly alkaline range helps reduce the pressure of subsequent pH adjustment and decreases acid consumption.

[0055] The calcium removal and softening, as well as the preliminary desiliconization, are carried out in the calcium removal and softening unit. A portion of the sludge discharged after calcium removal, softening, and preliminary desiliconization is processed by the first sludge dewatering device to produce calcium carbonate sludge, which can be recycled. The purity of calcium carbonate in the calcium carbonate sludge is greater than 90%. Another portion of the sludge discharged after calcium removal, softening, and preliminary desiliconization is returned to the calcium removal and softening unit. The filtrate from the first sludge dewatering device is recycled to the equalization tank.

[0056] In some embodiments of the present invention, crystallization methods are used for calcium removal, softening, and preliminary silicon removal, such as chemical crystallization circulating granulation fluidized bed. The agents used for calcium removal, softening, and preliminary silicon removal include sodium hydroxide, sodium carbonate, and seed crystals. Specifically, after the effluent obtained in step A) passes through a clarification tank, sodium hydroxide, sodium carbonate, and seed crystals are added sequentially, and a chemical crystallization circulating granulation fluidized bed is used for calcium removal, softening, and preliminary silicon removal.

[0057] The seed crystals include, but are not limited to, calcium carbonate crystals, quartz sand, garnet, calcite, and karatite, with calcium carbonate crystals being preferred. By adding sodium hydroxide and sodium carbonate, the pH value of the calcium removal softening and preliminary silicon removal processes is controlled to be 9.0–9.3, so that the Ca... 2+ Ions undergo a chemical reaction to generate CaCO3 / SiO2 composite crystals, which adhere to the surface of the seed crystals, thereby removing calcium hardness and silicon from the water without producing difficult-to-treat sludge. After chemical crystallization and circulating granulation fluidized bed treatment, the calcium removal rate is over 95%, while the effluent contains 0.5–1.0 mmol / L of excess carbonate ions. Following chemical crystallization and circulating granulation fluidized bed treatment, the resulting calcium carbonate crystal particles are discharged; these particles have a particle size of 2–3 mm and a purity greater than 90%.

[0058] In step C):

[0059] Adjust the pH of the effluent obtained in step B) to 7.8–8.3.

[0060] In some embodiments of the present invention, the pH value is adjusted to 7.8–8.3 by adding acid to the effluent obtained in step B). The acid includes, but is not limited to, sulfuric acid. Within this pH range, all excess carbonate ions in the original water are converted to bicarbonate ions, which helps reduce the risk of scaling in the subsequent membrane system.

[0061] In some embodiments of this application, the calcium hardness of the effluent obtained in step B) is less than 60 mg CaCO3 / L, the silicon content is less than 6 mg / L, and the turbidity is less than 2 NTU.

[0062] In some embodiments of this application, after adjusting the pH value, the process further includes sterilization. The present invention does not impose any special limitations on the methods and parameters of the sterilization process; sterilization methods and parameters well known to those skilled in the art can be used. Specifically, sodium hypochlorite or chlorine dioxide can be added.

[0063] In step D):

[0064] The effluent obtained in step C) is subjected to ultrafiltration and reverse osmosis desalination treatment.

[0065] Specifically, the effluent from the first softened water tank enters the ultrafiltration device for treatment.

[0066] In some embodiments of this application, the effluent turbidity of the ultrafiltration device is less than 0.1 NTU and the SDI is less than 3.

[0067] The ultrafiltration effluent is mixed with reverse osmosis antiscalant and reducing agent, and then desalinated in a reverse osmosis unit.

[0068] This invention does not impose any special restrictions on the type and source of the reverse osmosis antiscalant and the reverse osmosis reducing agent, which can be commercially available. This invention also does not impose any special restrictions on the amount of the reverse osmosis antiscalant and the reverse osmosis reducing agent used.

[0069] The desalination rate of the reverse osmosis treatment is above 98%.

[0070] To address the generally low magnesium content in coal mine water, membrane technology is used to concentrate and enrich magnesium ions. The reverse osmosis (RO) unit employs a single-stage, two-section (75%–80% recovery rate) or three-stage (85% recovery rate) configuration with inter-stage pressurization. Membrane concentration significantly increases the magnesium ion concentration in the RO concentrate (approximately 4–7 times that of the influent), providing higher concentration conditions for subsequent chemical precipitation. This overcomes the problems of low precipitation efficiency, poor sedimentation, and the need for additional magnesium additives due to the formation of fine magnesium hydroxide flocs at low concentrations. It ensures a synergistic effect between membrane treatment and chemical softening precipitation, contributing to efficient magnesium recovery and efficient silicon removal.

[0071] In step E):

[0072] The reverse osmosis concentrate obtained in step D) will be subjected to magnesium removal, softening, and deep silica removal.

[0073] Specifically, the reverse osmosis concentrate enters the magnetic coagulation high-efficiency sedimentation unit, where sodium hydroxide, magnetic media, and coagulant are added in sequence to carry out magnesium removal, softening, and deep silicon removal reactions.

[0074] In some embodiments of the present invention, the magnetic coagulation high-efficiency sedimentation unit includes a coagulation reaction tank and a sedimentation tank connected in sequence.

[0075] In some embodiments of the present invention, the pH value of the magnesium removal softening and deep silicon removal reaction is controlled at 10.8 to 11.3.

[0076] In some embodiments of this application, the magnetic medium is a soft magnetic micron-sized particle with stable chemical properties, commonly composed of iron(III) oxide (Fe3O4), with a particle size of 80-500 mesh, preferably 100-300 mesh, and a magnetic content of not less than 90%.

[0077] In some embodiments of this application, the coagulant aid includes, but is not limited to, one or more of sulfuric acid, phosphoric acid, lime, chlorine, polyacrylamide, activated silica, and sodium alginate. In some specific implementations, the coagulant aid is polyacrylamide. This invention does not impose any particular limitation on the amount of the coagulant aid used; it can be selected based on the content of suspended particles and colloidal substances in the influent.

[0078] In some embodiments of this application, after the magnesium removal softening and deep silicon removal, the process further includes:

[0079] The pH of the effluent after magnesium removal, softening, and deep silica removal is adjusted to 7.8–8.3.

[0080] The reagent used to adjust the pH value is an acid, including but not limited to sulfuric acid.

[0081] The sludge discharged from the sedimentation tank of the magnetic coagulation high-efficiency sedimentation unit undergoes deflocculation treatment, and then the magnetic media are separated. The separated sludge is dewatered, and the filtrate is recycled to the equalization tank. The separated magnetic media is returned to the magnetic coagulation high-efficiency sedimentation unit, specifically, it is refluxed to the coagulation reaction tank of the magnetic coagulation high-efficiency sedimentation unit.

[0082] In some embodiments of this application, the total hardness of the effluent after magnesium removal, softening, and deep silica removal is less than 50 mg / L, the turbidity is less than 1 NTU, and the silica content is less than 2 mg / L.

[0083] In step F):

[0084] The effluent obtained in step E) is then filtered.

[0085] This invention utilizes a strongly alkaline environment to induce flocculation and precipitation of high-concentration magnesium ions in reverse osmosis concentrate. The increased magnesium ion concentration reduces the actual amount of sodium hydroxide consumed, saving operating costs. Simultaneously, magnetic media are added during flocculation to accelerate floc formation, increase floc density, and accelerate sedimentation, enhancing separation efficiency and significantly improving overall sedimentation efficiency. Magnesium removal rate reaches over 95%, and silicon removal exceeds 90% due to the adsorption and co-precipitation effect of magnesium hydroxide flocs. The magnetic media can be recycled through subsequent recovery processes, typically with a recovery rate of no less than 97% and a replenishment amount of no more than 5 mg / L, resulting in low reagent costs. The application of magnetic coagulation enhanced separation technology also effectively solves problems such as poor flocculation and sedimentation effects of conventional flocculants at high pH and the risk of subsequent membrane system fouling due to excessive reagent dosage. The produced residual sludge has a magnesium hydroxide purity greater than 90%, achieving magnesium ion recovery and utilization.

[0086] This application also provides a system for implementing the above method, comprising:

[0087] A coagulation and clarification unit, wherein the coagulation and clarification unit is provided with a coal mine water inlet;

[0088] A calcium removal and softening unit connected to the outlet of the coagulation and clarification unit;

[0089] An ultrafiltration device connected to the outlet of the calcium removal and softening unit;

[0090] A reverse osmosis device connected to the outlet of the ultrafiltration device;

[0091] A magnetic coagulation high-efficiency sedimentation unit connected to the concentrate outlet of the reverse osmosis unit.

[0092] A filtration unit connected to the outlet of the magnetic coagulation high-efficiency sedimentation unit.

[0093] Figure 1This is a system diagram of a stepwise softening and silica removal synergistic membrane treatment method for coal mine water according to an embodiment of this application. In the diagram, 1 is an equalization tank, 2 is a first flocculant dosing device, 3-1 is a first coagulant aid dosing device, 3-2 is a second coagulant aid dosing device, 3-3 is a third coagulant aid dosing device, 4 is a coagulation and clarification unit, 5 is a coal slime tank, 6 is a coal slime dewatering machine, 7 is a clarified water tank, 8-1 is a first sodium hydroxide dosing device, 8-2 is a second sodium hydroxide dosing device, 9 is a sodium carbonate dosing device, 10 is a second flocculant dosing device, 11 is a calcium removal and softening unit, 12 is a first sludge dewatering device, and 13-1 is a first... Acid addition device, 13-2 is the second acid addition device, 14 is the sodium hypochlorite dosing device, 15 is the first softening water tank, 16 is the ultrafiltration device, 17 is the ultrafiltration product water tank, 18 is the reverse osmosis antiscalant dosing device, 19 is the reducing agent dosing device, 20 is the reverse osmosis device, 21 is the fresh water tank, 22 is the concentrated water tank, 23 is the magnetic media dosing device, 24 is the magnetic coagulation high-efficiency sedimentation unit, 25 is the deflocculator, 26 is the magnetic media separator, 27 is the second sludge dewatering device, 28 is the filtration unit, and 29 is the second softening water tank.

[0094] The system provided in this application includes a regulating tank 1. High-hardness, high-mineralization coal mine water enters the regulating tank for water quality balancing and quantity regulation.

[0095] The regulating tank is equipped with a mine water inlet, a supernatant inlet, a filtrate water inlet, a first sludge dewatering and recovery port, a second sludge dewatering and recovery port, and a water outlet.

[0096] The system provided in this application also includes a coagulation and clarification unit 4. The coagulation and clarification unit is provided with a coal mine water inlet, a water outlet, and a coal slime outlet.

[0097] The coal mine water inlet of the coagulation and clarification unit 4 is connected to the outlet of the regulating tank.

[0098] In some embodiments of this application, the system further includes a first flocculant dosing device 2 and a first coagulant aid dosing device 3-1, which are respectively connected to the coagulation and clarification unit 4 and are used to add flocculant and coagulant aid to the coagulation and clarification unit 4.

[0099] The effluent from the equalization tank enters the coagulation and clarification unit, where flocculants and coagulants are added to carry out the coagulation reaction.

[0100] In some embodiments of this application, the coagulation and clarification unit is one or more of a mechanically stirred clarification tank, a high-density sedimentation tank, and a high-efficiency cyclone purifier, which removes coal powder, colloids, and other substances from mine water based on the principle of chemical coagulation + high-efficiency clarification or cyclone separation.

[0101] The system provided in this application also includes a clarification tank 7. The clarification tank 7 is provided with a mine water inlet, a backwash wastewater inlet, and an outlet.

[0102] The mine water inlet of the clarification tank is connected to the outlet of the coagulation clarification unit. The clarified water separated by the coagulation clarification unit enters the clarification tank. This application does not impose any special restrictions on the structure or type of the clarification tank, as long as it can store the clarified water separated by the coagulation clarification unit.

[0103] In some embodiments of this application, the system further includes a coal slurry tank 5. The coal slurry tank 5 is provided with a coal slurry inlet, a slurry outlet, and a supernatant outlet.

[0104] The coal slime inlet of the coal slime pond is connected to the coal slime outlet of the coagulation and clarification unit. The coal slime outlet is located at the bottom of the coagulation and clarification unit. The coal slime at the bottom of the coagulation and clarification unit is discharged into the coal slime pond for settling. This application does not impose any special restrictions on the type and structure of the coal slime pond, as long as it can store coal slime.

[0105] In some embodiments of this application, the system further includes a coal slime dewatering machine 6. The coal slime dewatering machine 6 is provided with a coal slime inlet, a coal slime outlet, and a filtrate water outlet.

[0106] The coal slime inlet of the coal slime dewatering machine is connected to the sludge discharge outlet of the coal slime tank. Sludge discharged from the coal slime tank enters the coal slime dewatering machine for dewatering. This application does not impose any special restrictions on the type and structure of the coal slime dewatering machine; any coal slime dewatering machine well-known to those skilled in the art can be used.

[0107] The supernatant outlet of the coal slime tank is connected to the supernatant inlet of the equalization tank. The filtrate outlet of the coal slime dewatering machine is connected to the filtrate inlet of the equalization tank.

[0108] In this application, the supernatant from the coal slime pond and the filtrate from the coal slime dewatering machine are recycled to the equalization tank.

[0109] The system provided in this application also includes a calcium removal and softening unit 11. The calcium removal and softening unit is provided with a mine water inlet, a sludge discharge outlet, and a water outlet.

[0110] The mine water inlet of the calcium removal and softening unit is connected to the outlet of the clarification pool.

[0111] The calcium removal and softening unit is one or more of the following: chemical crystallization circulating granulation fluidized bed, high-density sedimentation tank, and mechanically stirred clarification tank.

[0112] In some embodiments of this application, the calcium removal and softening unit is a high-density sedimentation tank. In this specific embodiment, flocculation sedimentation is used for calcium removal, softening, and preliminary silica removal. The agents used for calcium removal, softening, and preliminary silica removal include sodium hydroxide, sodium carbonate, flocculant, and coagulant aid. The treatment system also includes a sodium hydroxide dosing device 8, a sodium carbonate dosing device 9, a second flocculant dosing device 10, and a second coagulant aid dosing device 3-2. The sodium hydroxide dosing device 8, sodium carbonate dosing device 9, second flocculant dosing device 10, and second coagulant aid dosing device 3-2 are respectively connected to the calcium removal and softening unit 11 and are used to add sodium hydroxide, sodium carbonate, flocculant, and coagulant aid to the calcium removal and softening unit 11.

[0113] In some embodiments, the calcium removal and softening unit is provided with a sludge return inlet.

[0114] In some embodiments of this application, the calcium removal and softening unit is a chemical crystallization circulating granulation fluidized bed. In this specific embodiment, crystallization is used for calcium removal, softening, and preliminary silicon removal. The agents used for calcium removal, softening, and preliminary silicon removal include sodium hydroxide, sodium carbonate, and seed crystals. The processing system further includes a sodium hydroxide dosing device 8, a sodium carbonate dosing device 9, and a seed crystal dosing device, which are respectively connected to the calcium removal and softening unit 11 and are used to add sodium hydroxide, sodium carbonate, and seed crystals to the calcium removal and softening unit 11.

[0115] In some embodiments of this application, the calcium removal softening unit is equipped with a first online pH meter and an online alkalinity analyzer. This allows for timely feedback and adjustment of the dosage of sodium hydroxide and sodium carbonate based on real-time changes in the hydroxide and carbonate concentrations of the effluent from the clarification tank, thereby stabilizing the calcium hardness of the softened water while simultaneously ensuring an excess carbonate content of 0.5–1.0 mmol / L. The pH value within the calcium removal softening unit is controlled between 9.0 and 9.3.

[0116] In some embodiments of this application, the system further includes a first sludge dewatering device 12. The first sludge dewatering device is provided with a sludge inlet, a filtrate water outlet, and a sludge outlet.

[0117] The sludge inlet of the first sludge dewatering device is connected to the sludge outlet of the calcium removal and softening unit. A portion of the sludge discharged from the calcium removal and softening unit is processed by the first sludge dewatering device to produce calcium carbonate sludge, which can be recycled. The purity of calcium carbonate in the calcium carbonate sludge is greater than 90%. Another portion of the sludge discharged from the calcium removal and softening unit is returned to the unit, entering through the return sludge inlet.

[0118] The filtrate outlet of the first sludge dewatering device is connected to the first sludge dewatering recovery port of the equalization tank. The filtrate from the first sludge dewatering device is recovered to the equalization tank.

[0119] In some embodiments of this application, the first sludge dewatering device is a plate and frame filter press.

[0120] The system provided in this application also includes a first softening water tank 15. The first softening water tank is provided with a mine water inlet and an outlet.

[0121] The mine water inlet of the first softening water tank is connected to the outlet of the calcium removal softening unit.

[0122] In some embodiments of this application, the effluent from the calcium removal softening unit contains 0.5 to 1.0 mmol / L of excess carbonate.

[0123] In some embodiments of this application, the system further includes a first acid addition device 13-1 and a sodium hypochlorite dosing device 14, which are respectively connected to the outlet of the calcium removal and softening unit 11 and are used to add acid and sodium hypochlorite to the outlet of the calcium removal and softening unit 11.

[0124] Acid is added to the effluent from the calcium removal softening unit to adjust the pH, and sodium hypochlorite is added for sterilization before it enters the first softening tank. Acid is added to the effluent from the calcium removal softening unit to adjust the pH to 7.8–8.3. Within this pH range, excess carbonate ions in the water are completely converted to bicarbonate ions, which helps reduce the risk of scaling in subsequent membrane systems.

[0125] In some embodiments of this application, the effluent from the first softening water tank has a calcium hardness of less than 60 mg CaCO3 / L, a silicon content of less than 6 mg / L, and a turbidity of less than 2 NTU.

[0126] This application does not impose any special restrictions on the structure and type of the first softening water tank, as long as it can store the clean water treated by the calcium removal softening unit.

[0127] The system provided in this application also includes an ultrafiltration device 16. The ultrafiltration device is provided with a mine water inlet, a mine water outlet, and a backwash wastewater outlet.

[0128] The mine water inlet of the ultrafiltration device is connected to the outlet of the first softened water tank. The effluent from the first softened water tank enters the ultrafiltration device for deep filtration. This invention does not impose any special restrictions on the type or source of the ultrafiltration device; it can be commercially available.

[0129] In some embodiments of this application, the effluent turbidity of the ultrafiltration device is less than 0.1 NTU and the SDI is less than 3.

[0130] In some embodiments of this application, the backwash wastewater outlet of the ultrafiltration device is connected to the backwash wastewater inlet of the clarification tank.

[0131] The system provided in this application also includes an ultrafiltration permeate tank 17. The ultrafiltration permeate tank is provided with a mine water inlet and an outlet. The mine water inlet of the ultrafiltration permeate tank is connected to the outlet of the ultrafiltration device. The effluent from the ultrafiltration device enters the ultrafiltration permeate tank. This application does not impose any special restrictions on the type and structure of the ultrafiltration permeate tank, as long as it can store ultrafiltration permeate.

[0132] The system provided in this application also includes a reverse osmosis unit 20. The reverse osmosis unit is provided with an ultrafiltration permeate inlet, a desalination outlet, and a concentrate outlet.

[0133] The ultrafiltration permeate inlet of the reverse osmosis unit is connected to the outlet of the ultrafiltration permeate tank.

[0134] The recovery rate of the reverse osmosis unit is 75%–85%.

[0135] In some embodiments of this application, the reverse osmosis device employs a single-stage two-stage (75% recovery rate) or three-stage (85% recovery rate) system with inter-stage pressurization.

[0136] In some embodiments of this application, a reverse osmosis antiscalant dosing device 18 and a reducing agent dosing device 19 are provided on the pipeline between the ultrafiltration permeate tank and the reverse osmosis unit.

[0137] Reverse osmosis antiscalant and reducing agent are added to the effluent from the ultrafiltration permeate tank before it enters the reverse osmosis unit for desalination treatment.

[0138] The system provided in this application also includes a freshwater tank 21. The freshwater inlet of the freshwater tank is connected to the freshwater outlet of the reverse osmosis unit.

[0139] The system provided in this application also includes a concentrate tank 22. The concentrate tank is provided with a concentrate inlet, a backwash water inlet, and a water outlet.

[0140] The concentrate inlet of the concentrate tank is connected to the concentrate outlet of the reverse osmosis unit.

[0141] The RO permeate enters the freshwater tank, and the concentrate enters the concentrate tank. Testing shows that the RO permeate meets industrial and agricultural reuse standards.

[0142] This application does not impose any special restrictions on the type and structure of the freshwater tank and the concentrate tank, as long as they can store RO permeate and reverse osmosis concentrate.

[0143] The system provided in this application also includes a magnetic coagulation high-efficiency sedimentation unit 24. The magnetic coagulation high-efficiency sedimentation unit is provided with a concentrate inlet, a sludge outlet, and a water outlet.

[0144] The concentrate inlet of the magnetic coagulation high-efficiency sedimentation unit is connected to the outlet of the concentrate tank.

[0145] In some embodiments of this application, the magnetic coagulation high-efficiency sedimentation unit includes a coagulation reaction tank and a sedimentation tank connected in sequence.

[0146] In some embodiments of this application, the system further includes a third coagulant dosing device 3-3, a magnetic medium dosing device 23, and a second sodium hydroxide dosing device 8-2; the third coagulant dosing device 3-3, the magnetic medium dosing device 23, and the second sodium hydroxide dosing device 8-2 are respectively connected to the coagulation reaction tank of the magnetic coagulation high-efficiency sedimentation unit 24, and are used to add coagulant, magnetic medium, and sodium hydroxide to the coagulation reaction tank of the magnetic coagulation high-efficiency sedimentation unit 24.

[0147] In some embodiments of this application, a second online pH meter is provided within the magnetic coagulation high-efficiency sedimentation unit.

[0148] The pH value of the magnetic coagulation high-efficiency sedimentation unit is controlled at 10.8 to 11.3, and the pH value of the effluent is adjusted to 7.8 to 8.3.

[0149] In some embodiments, the coagulation reaction tank of the magnetic coagulation high-efficiency sedimentation unit is equipped with a magnetic medium recovery port.

[0150] The effluent from the concentrate tank enters the magnetic coagulation high-efficiency sedimentation unit, where sodium hydroxide, magnetic media, and coagulant are added sequentially to the coagulation reaction tank to carry out magnesium removal and deep silicon removal reactions enhanced by magnetic coagulation.

[0151] In some embodiments of this application, the system further includes a deflocculator 25. The inlet of the deflocculator is connected to the sludge outlet of the sedimentation tank of the magnetic coagulation high-efficiency sedimentation unit. The sludge discharged from the sedimentation tank of the magnetic coagulation high-efficiency sedimentation unit enters the deflocculator for processing. The deflocculator is a device for breaking down magnetic media sludge, realizing the separation of the magnetic media from the coagulated flocs. The deflocculator is commercially available.

[0152] In some embodiments of this application, the system further includes a magnetic media separator 26. The magnetic media separator is a device that recovers magnetic media using methods such as magnetic fields. The magnetic media separator 26 is provided with a sludge inlet, a magnetic media outlet, and a sludge outlet.

[0153] The sludge inlet of the magnetic media separator is connected to the outlet of the deflocculator.

[0154] The sludge discharged from the sedimentation tank of the magnetic coagulation high-efficiency sedimentation unit undergoes deflocculation treatment, and then the magnetic media are separated. The separated sludge is dewatered, and the filtrate is recycled to the equalization tank. The separated magnetic media is returned to the magnetic coagulation high-efficiency sedimentation unit, specifically, it is refluxed to the coagulation reaction tank of the magnetic coagulation high-efficiency sedimentation unit.

[0155] In some embodiments of this application, the magnetic media separator is a commercially available product.

[0156] In some embodiments of this application, the system further includes a second sludge dewatering device 27. The second sludge dewatering device is provided with a sludge inlet, a water outlet, and a sludge outlet.

[0157] The sludge inlet of the second sludge dewatering device is connected to the sludge outlet of the magnetic media separator.

[0158] The filtrate outlet of the second sludge dewatering device is connected to the second sludge dewatering recovery port of the equalization tank. The filtrate from the second sludge dewatering device is recovered to the equalization tank.

[0159] In some embodiments of this application, the second sludge dewatering device is a plate and frame filter press.

[0160] After being processed by the deflocculator, the magnetic media sludge enters the magnetic media separator for separation. The magnetic media is returned to the coagulation reaction tank of the magnetic coagulation high-efficiency sedimentation unit. The remaining sludge is discharged to the second sludge dewatering device for treatment to produce magnesium hydroxide sludge, which can be recycled. The filtrate water from the second sludge dewatering device is recycled to the equalization tank.

[0161] The system provided in this application also includes a filtration unit 28. The filtration unit is provided with a water inlet, a filtered water outlet, and a backwash water outlet.

[0162] The inlet of the filtration unit is connected to the outlet of the sedimentation tank of the magnetic coagulation high-efficiency sedimentation unit.

[0163] The backwash water outlet of the filtration unit is connected to the backwash water inlet of the concentrate tank.

[0164] In some embodiments of this application, a second acid addition device 13-2 is provided at the outlet of the sedimentation tank of the magnetic coagulation high-efficiency sedimentation unit. This application does not impose any special restrictions on the type or structure of the second acid addition device 13-2, as long as it can achieve acid addition. This application also does not impose any special restrictions on the location and manner in which the second acid addition device 13-2 is installed, as long as it can achieve acid addition.

[0165] In some embodiments of this application, the filtration unit is one or more of a V-type filter, a fiber filter, and a variable porosity filter.

[0166] The system provided in this application also includes a second softening water tank 29. The inlet of the second softening water tank is connected to the filtered water outlet of the filtration unit.

[0167] The effluent from the sedimentation tank of the magnetic coagulation high-efficiency sedimentation unit is adjusted to pH 7.8–8.3 by adding acid before entering the filtration unit. After filtration, the effluent enters the second softening water tank. The backwash wastewater from the filtration unit is recycled to the concentrate tank.

[0168] In some embodiments of this application, the total hardness of the effluent from the second softened water tank is less than 50 mg / L, the turbidity is less than 1 NTU, and the silica is less than 2 mg / L.

[0169] This application does not impose any special restrictions on the structure and type of the second softening water tank, as long as it can store the clean water treated by the magnetic coagulation high-efficiency sedimentation unit.

[0170] The effluent from the second softening tank can then enter the subsequent advanced treatment system.

[0171] This invention involves sequentially adding sodium hydroxide, magnetic media, and coagulant aid to a coagulation reaction tank to conduct a magnetic coagulation enhancement reaction, followed by magnesium removal, softening, and deep silica removal in a sedimentation tank. The magnetic media sludge discharged from the sedimentation tank enters a magnetic media recovery device (i.e., a deflocculator + magnetic media separator). After treatment by the deflocculator, it enters the magnetic media separator for separation, and the magnetic media is returned to the coagulation reaction tank. The remaining sludge is discharged to a second sludge dewatering device for treatment, producing magnesium hydroxide sludge which is then recovered. The filtrate is returned to the equalization tank. The sedimentation tank effluent is acidified for pH adjustment before entering the filtration unit. After filtration, it enters the second softening water tank. The backwash wastewater from the filtration unit is recycled to a concentrate tank.

[0172] In this application, the stepwise softening and desiliconization synergistic membrane treatment achieves a relatively stable softening and desiliconization effect, and calcium and magnesium ions can be recovered and reused in steps. At the same time, the water produced by the reverse osmosis membrane system meets the standards for industrial and agricultural reclaimed water, and it is expected to achieve zero discharge of mine water when combined with a deep concentration process in the future.

[0173] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available.

[0174] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method and system for stepwise softening and desiliconization synergistic membrane treatment of coal mine water provided by the present invention, but it should not be construed as a limitation on the scope of protection of the present invention.

[0175] Example 1

[0176] Adopting such Figure 1 The system shown is used for treating mine water in coal mines.

[0177] A large coal mine has a mine water treatment capacity of 1800 m³. 3 / h, influent turbidity 100-380 NTU, salt content approximately 4300 mg / L, total hardness 900-1200 mg / L, total alkalinity 4-5 mmol / L, calcium ion 400-500 mg / L, magnesium ion 40-55 mg / L, sulfate 2600-3000 mg / L, chloride 55-65 mg / L, total silica 10-20 mg / L.

[0178] The mine water from the coal mine, after its flow rate and quality are adjusted in the equalization tank, enters a high-efficiency cyclone purifier. Flocculation occurs through the addition of polyaluminum chloride (PAC) (8–10 mg / L) and polyacrylamide (PAM) (0.3–0.5 mg / L). The clarified water after cyclone separation enters a clarification tank, while the bottom coal sludge is discharged into a coal sludge tank for sedimentation. The sludge from the coal sludge tank is then dewatered by a coal sludge dewatering machine. The supernatant from the coal sludge tank and the water removed by the dewatering machine are returned to the equalization tank. The effluent from the clarification tank enters a high-density sedimentation tank for calcium and preliminary silicon removal reactions. Sodium hydroxide (200–230 mg / L), sodium carbonate (660–750 mg / L), polyferric sulfate (PFS) (15–18 mg / L), and polyacrylamide (PAM) (0.4–0.6 mg / L) are added sequentially. The resulting CaCO3 sludge has a purity greater than 90% and is discharged to the first set of plate and frame filter presses for dewatering and recycling. The filtrate is returned to the equalization tank. The pH of the high-density sedimentation tank is controlled at 9.0–9.3 and is equipped with an online pH meter and an online alkalinity analyzer. Calcium removal rate is above 95%, and the effluent contains 0.5–1.0 mmol / L of excess carbonate. After adjusting the pH to 7.8–8.3 with sulfuric acid, sodium hypochlorite is added for sterilization before the effluent enters the first softening tank. The first softening tank water has a calcium hardness of less than 60 mg CaCO3 / L, silicon of less than 6 mg / L, turbidity of less than 2 NTU, and magnesium ion concentration of 35–50 mg / L. It then enters a ceramic membrane ultrafiltration unit for deep filtration, with an effluent turbidity of less than 0.1 NTU and an SDI of less than 3. The effluent from the ceramic membrane ultrafiltration unit enters the ultrafiltration permeate tank and then the reverse osmosis unit for desalination. The reverse osmosis unit is a two-stage, single-stage system with an 80% recovery rate. Permeate enters the desalination tank, and concentrate enters the reverse osmosis concentrate tank. The reverse osmosis concentrate treatment capacity is 360 m³ / L. 3The water concentration is approximately 210 mg / L for magnesium ions and 25 mg / L for silicon. The reverse osmosis concentrate enters a magnetic coagulation high-efficiency sedimentation water treatment facility (comprising a coagulation reaction tank and a sedimentation tank connected in sequence) for magnesium removal, softening, and deep silicon removal. Sodium hydroxide (800–850 mg / L), magnetic media (3–4 mg / L), and polyacrylamide (PAM) (0.3–0.5 mg / L) are added sequentially to the coagulation reaction tank, controlling the reaction pH at 10.8–11.3. The magnetic media sludge discharged from the sedimentation tank enters a magnetic media recovery device (comprising a deflocculator and a magnetic media separator connected in sequence). After treatment by the deflocculator, it enters the magnetic media separator for separation, and the magnetic media is returned to the coagulation reaction tank. The remaining sludge with a magnesium hydroxide purity greater than 95% is discharged to a second set of plate and frame filter presses for dewatering and recovery, and the filtrate is returned to the equalization tank. After the effluent from the sedimentation tank is adjusted to a pH of 7.8–8.3 with sulfuric acid, it enters a variable porosity filter and then a second softening tank. The water in the second softening tank has a total hardness of less than 50 mg / L, a turbidity of less than 1 NTU, and a silica content of less than 2 mg / L. Finally, the coal mine water undergoes a stepwise softening and silica removal combined with a membrane process. The softening and silica removal effect is relatively stable, and calcium and magnesium ions can be recovered and reused in stages. At the same time, the water produced by the reverse osmosis membrane system meets the standards for industrial and agricultural reclaimed water, and further integration with advanced treatment processes can achieve zero discharge of mine water.

[0179] Example 2

[0180] Adopting such Figure 1 The system shown is used for treating mine water in coal mines.

[0181] A large coal mine has a mine water treatment capacity of 1600m³. 3 / h, influent turbidity 120-250 NTU, salt content 3600 mg / L, total hardness 1100-1500 mg / L, total alkalinity 4-5 mmol / L, calcium ion 500-700 mg / L, magnesium ion 60-75 mg / L, sulfate 2150-2400 mg / L, chloride 45-60 mg / L, total silica 15-25 mg / L.

[0182] The mine water, after being regulated in a regulating tank for both volume and quality, enters a mechanically accelerated stirring clarification tank. Flocculation occurs through the addition of polyaluminum chloride (PAC) (7–9 mg / L) and polyacrylamide (PAM) (0.3–0.5 mg / L). The clarified water then enters a clarification tank, while the bottom coal sludge is discharged into a coal sludge tank for settling. The sludge from the coal sludge tank is then dewatered by a dewatering machine. The supernatant from the coal sludge tank and the water removed by the dewatering machine are returned to the regulating tank. The effluent from the clarification tank enters a chemical crystallization circulating granulation fluidized bed for calcium removal, softening, and preliminary silicon removal. Sodium hydroxide (190–220 mg / L), sodium carbonate (800–950 mg / L), and calcium carbonate seed crystals are added sequentially. The reaction produces CaCO3 crystal particles (2–3 mm, purity greater than 90%), which are then recycled. The pH of the chemical crystallization circulating granulation fluidized bed is controlled at 9.0–9.3, and it is equipped with an online pH meter and an online alkalinity analyzer. The calcium removal rate is over 95%, and the effluent contains 0.5–1.0 mmol / L of excess carbonate. The softened effluent after fluidized bed separation is first adjusted to pH 7.8–8.3 with sulfuric acid, then sterilized with chlorine dioxide before entering the first softening tank. The water in the first softening tank has a calcium hardness of less than 70 mg CaCO3 / L, silicon of less than 8 mg / L, turbidity of less than 3 NTU, and magnesium ion concentration of approximately 55–65 mg / L. It then enters a hollow fiber membrane ultrafiltration unit for deep filtration, resulting in an effluent turbidity of less than 0.1 NTU and an SDI of less than 3. The effluent from the hollow fiber membrane ultrafiltration unit enters the ultrafiltration permeate tank, and then proceeds to a reverse osmosis unit for desalination. The reverse osmosis unit is a two-stage, single-stage system with an 80% recovery rate. Permeate enters the desalination tank, and concentrate enters the reverse osmosis concentrate tank. The reverse osmosis concentrate treatment capacity is 320m³. 3The water contains approximately 250 mg / L of magnesium ions and 35 mg / L of silicon per hour. The reverse osmosis concentrate enters a magnetic coagulation high-efficiency sedimentation water treatment facility (comprising a coagulation reaction tank and a sedimentation tank connected in sequence) for magnesium removal, softening, and deep silicon removal. Sodium hydroxide (900–950 mg / L), magnetic media (4–5 mg / L), and polyacrylamide (PAM) (0.4–0.6 mg / L) are added sequentially to the coagulation reaction tank, controlling the reaction pH at 10.8–11.3. The magnetic media sludge discharged from the sedimentation tank enters a magnetic media recovery device (comprising a deflocculator and a magnetic media separator connected in sequence). After treatment by the deflocculator, it enters the magnetic media separator for separation, and the magnetic media is returned to the coagulation reaction tank. The remaining sludge with a magnesium hydroxide purity greater than 95% is discharged to a second set of plate and frame filter presses for dewatering and recovery, and the filtrate is returned to the equalization tank. Sulfuric acid is added to the sedimentation tank effluent to adjust the pH to 7.8–8.3 before it enters a fiber filter, and after filtration, it enters the second softening water tank. The second softening tank has a total hardness of less than 50 mg CaCO3 / L, a turbidity of less than 1 NTU, and a silica content of less than 2 mg / L. Finally, the coal mine water undergoes a stepwise softening and silica removal synergistic membrane treatment. The softening and silica removal effect is relatively stable, and calcium and magnesium ions can be recovered and reused in stages. Simultaneously, the reverse osmosis membrane system produces water that meets industrial and agricultural reuse standards, and further integration with advanced treatment processes can achieve zero discharge of mine water.

[0183] Comparative Example 1

[0184] In Example 2, the chemical crystallization circulating granulation fluidized bed treated 1600 m³ of water. 3The effluent has a calcium hardness of less than 70 mg CaCO3 / L, a silicon content of less than 8 mg / L, a turbidity of less than 3 NTU, and a magnesium ion content of 50–60 mg / L. The fluidized bed effluent enters a high-density sedimentation tank, where sodium hydroxide (350–400 mg / L), flocculant PFS (20–25 mg / L), and coagulant aid PAM (1.0–1.5 mg / L) are added sequentially for magnesium removal and softening. Additionally, to achieve deep silicon removal, magnesium-containing agents such as magnesium chloride (approximately 100 mg / L) are added. The reaction pH is controlled at 10.8–11.3, and sludge return and an online pH meter are provided. Magnesium-rich sludge enters a sludge tank, where it is further dewatered and recycled using a sludge dewatering device. Due to the low magnesium ion content in the influent and the large volume of water being treated, the generated fine magnesium hydroxide flocs have low sedimentation efficiency, are difficult to settle, and have poor silica removal effects. To achieve a certain sedimentation effect and effluent quality, large amounts of flocculant PFS (20-25 mg / L), coagulant aid PAM (1.0-1.5 mg / L), and even additional magnesium (approximately 100 mg / L) need to be added, resulting in high reagent consumption. The hardness of the effluent from the high-density sedimentation tank is 70-100 mg / L, the turbidity is greater than 2 NTU, generally between 2-5 NTU, and the silica exceeds 2 mg / L, generally between 3-5 mg / L. The magnesium hydroxide purity in the sludge does not reach 95%, generally between 88%-92%. In addition, due to the excessively high residual iron ions and PAM in the effluent from the high-density tank, it often causes severe membrane fouling when entering the subsequent ultrafiltration and reverse osmosis treatment system.

[0185] Comparative Example 2

[0186] The difference from Example 1 is as follows:

[0187] The high-density sedimentation tank can treat approximately 1800 m³ of water. 3 Add sodium hydroxide (400-450 mg / L), sodium carbonate (660-750 mg / L), polyferric sulfate (PFS) (18-22 mg / L), and polyacrylamide (PAM) (0.4-0.6 mg / L) in sequence per hour. The pH value of the high-density sedimentation tank is controlled at 10.8-11.3.

[0188] Calcium removal rate is above 95%, magnesium removal rate is above 75%, and the effluent contains 0.5–1.0 mmol / L of excess carbonate. The sludge generated is a calcium-magnesium mixed sludge, classified as industrial solid waste with low utilization value. After adjusting the pH to 7.8–8.3 with sulfuric acid, sodium hypochlorite is added for sterilization before the effluent enters the first softening tank. The first softening tank water has a calcium hardness of less than 50 mg CaCO3 / L, silicon of less than 5 mg / L, turbidity of less than 2 NTU, and magnesium ion concentration of approximately 10–15 mg / L. It then enters a ceramic membrane ultrafiltration unit for deep filtration, achieving an effluent turbidity of less than 0.1 NTU and an SDI of less than 3. The effluent from the ceramic membrane ultrafiltration unit enters the ultrafiltration permeate tank and then the reverse osmosis unit for desalination. The reverse osmosis unit is a two-stage, single-stage system with an 80% recovery rate. Permeate enters the desalination tank, and concentrate enters the reverse osmosis concentrate tank. The reverse osmosis concentrate treatment capacity is 360 m³ / L. 3 The water contains approximately 50 mg / L of magnesium ions and 20 mg / L of silicon per hour. The reverse osmosis concentrate enters a magnetic coagulation high-efficiency sedimentation water treatment facility (comprising a coagulation reaction tank and a sedimentation tank connected in sequence) for deep hardening and silicon removal. Sodium hydroxide (300–350 mg / L), magnetic media (approximately 5 mg / L), and polyacrylamide (PAM) (1.0–1.5 mg / L) are added sequentially to the coagulation reaction tank, controlling the reaction pH at 10.8–11.3. Additionally, to achieve deep silicon removal, a magnesium agent such as magnesium chloride (approximately 100 mg / L) is added. The magnetic media sludge discharged from the sedimentation tank enters a magnetic media recovery device (comprising a deflocculator and a magnetic media separator connected in sequence). After treatment by the deflocculator, it enters the magnetic media separator for separation, and the magnetic media is returned to the coagulation reaction tank. The remaining sludge, with approximately 60% magnesium hydroxide purity, is discharged to a second set of plate and frame filter presses for dewatering and recovery, and the filtrate is returned to the equalization tank. After the effluent from the sedimentation tank is adjusted to a pH of 7.8–8.3 with sulfuric acid, it enters the variable porosity filter and then the second softening tank. The total hardness of the water in the second softening tank is less than 50 mg CaCO3 / L, the turbidity is less than 1 NTU, and the silica content exceeds 5 mg / L, generally between 6 and 8 mg / L.

[0189] The experimental results show that the present invention can achieve stepwise recovery of calcium and magnesium ions in coal mine water and achieve deep silicon removal effect. At the same time, it significantly saves the consumption of reagents such as sodium hydroxide, flocculant, coagulant aid, magnesium agent, and acid, and is not likely to cause significant pollution to the membrane system. When combined with advanced treatment processes, it can achieve zero discharge of mine water.

[0190] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for step-by-step softening and desiliconization synergistic membrane treatment of coal mine moisture, comprising the following steps: A) Clarify and coagulate coal mine water; B) The effluent obtained in step A) is subjected to calcium removal softening and preliminary silica removal; the agents used for calcium removal softening and preliminary silica removal are sodium hydroxide, sodium carbonate, flocculant and coagulant aid; or the agents used for calcium removal softening and preliminary silica removal are sodium hydroxide, sodium carbonate and seed crystals; the pH value of calcium removal softening and preliminary silica removal is controlled at 9.0~9.3; the effluent obtained in step B) contains 0.5~1.0 mmol / L of carbonate ions; C) After adjusting the pH of the effluent obtained in step B) to 7.8~8.3, perform sterilization treatment; D) The effluent obtained in step C) is subjected to ultrafiltration treatment; the turbidity of the ultrafiltration effluent is less than 0.1 NTU and the SDI is less than 3; the ultrafiltration effluent is mixed with reverse osmosis antiscalant and reducing agent, and then desalinated in a reverse osmosis unit. E) The reverse osmosis concentrate obtained in step D) enters the magnetic coagulation high-efficiency sedimentation unit, where sodium hydroxide, magnetic media, and coagulant are added in sequence to carry out magnesium removal, softening, and deep desiliconization reactions. The pH value of the magnesium removal softening and deep desiliconization reaction is controlled at 10.8~11.3; after the magnesium removal softening and deep desiliconization, the process further includes: adjusting the pH value of the effluent after the magnesium removal softening and deep desiliconization to 7.8~8.3; F) Filter the effluent obtained in step E).

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