Method and device for reducing sulfate hardness in coal mine well water based on core crystal granulation

Abstract

The application discloses a method and device for reducing sulfate hardness in coal mine well water based on nucleation granulation, wherein after removal of suspended solids, sulfate-specific seeds are added to the coal mine well water, and only the sulfate-specific seeds are added; calcium ions in the coal mine well water are used to make sulfate in the coal mine well water crystallize and precipitate on the surface of the sulfate-specific seeds to form granulation bodies, the granulation bodies are discharged outside, and synchronous removal of calcium ions and sulfate and solid-liquid separation are realized; a corresponding device comprises a sulfate nucleation granulation tank and a suspended solids tank arranged vertically; the sulfate-specific seeds added through a seed adding pipe and the coal mine well water from which the suspended solids are removed circulate in an outer cylinder and between the outer cylinder and the inner wall of the sulfate nucleation granulation tank in an axial direction to form the granulation bodies; and the sulfate in the coal mine well water can be removed at low cost, and the calcium ions can be synchronously removed.

Description

Technical Field

[0001] This invention belongs to the field of coal mine well water treatment technology, and specifically relates to a method for reducing sulfate hardness in coal mine well water based on nucleus crystal granulation. Background Technology

[0002] Coal mine water contains sulfate ions produced by the oxidation of pyrite, with sulfate concentrations ranging from several thousand to tens of thousands of ppm. Excessively high sulfate concentrations can lead to the release of toxic sulfides. Furthermore, sulfate ions can combine with calcium ions to form scale, increasing hardness and raising the operating and maintenance costs of equipment. Current methods for treating sulfate ions in coal mine water include reverse osmosis, biological reduction, and chemical precipitation. Acidic coal mine water is often treated using neutralization chemical precipitation, which involves adding alkaline agents or using limestone as filter media for neutralization. However, neutralization precipitation methods involve complex equipment, high noise levels, and severe secondary pollution. The reaction product, calcium sulfate, mixes with excess limestone, making treatment difficult. Membrane separation and concentration are often necessary for further sulfate precipitation, but this method requires large amounts of softening agents, resulting in high investment and operating costs, and the membrane modules are prone to fouling. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for reducing sulfate hardness in coal mine water based on nucleus crystal granulation, so as to remove sulfate ions from coal mine water at low cost and simultaneously remove calcium ions.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for reducing sulfate hardness in coal mine water based on nucleus crystal granulation involves adding only sulfate-specific seed crystals to the coal mine water after removing suspended solids. The calcium ions in the coal mine water cause the sulfate ions in the coal mine water to crystallize and precipitate on the surface of the sulfate-specific seed crystals to form granules. The granules are then discharged, achieving simultaneous removal of calcium ions and sulfate ions and solid-liquid separation.

[0006] In one embodiment, the calcium ion concentration in the coal mine water after removing suspended solids ranges from 200 to 500 mg / L, the sulfate concentration ranges from 6000 to 8000 mg / L, the amount of sulfate-specific seed crystals added is 0.3 to 1.8 g / L, the treatment time is more than 30 minutes, and the sulfate concentration in the treated coal mine water ranges from 2000 to 3000 mg / L.

[0007] In one embodiment, the sulfate-specific seed crystals are prepared by the following method: sucrose, calcium nitrate, and aluminum sulfate in a weight ratio of 1:1:1.5 to 1:1.2:2 are thoroughly ground until uniformly mixed. Then, concentrated sulfuric acid is added and stirred to obtain a carbonized precursor material. The precursor material is mixed with a sodium hydroxide solution of 1.5 to 2 mol / L at a solid-liquid ratio of 12 to 15 g / 100 mL. The mixture is stirred with a magnetic stirrer, allowed to stand, filtered with deionized water, centrifuged, and washed until no sulfate ions are detected in the washing liquid. The mixture is then dried in an oven and calcined at 550 to 600°C for 2.5 to 3 hours under a nitrogen atmosphere, followed by cooling for 8 to 10 hours to obtain sulfate-specific seed crystals whose main component is ettringite.

[0008] In one embodiment, hydraulic parameters are adjusted to suspend the sulfate-specific seed crystals in coal mine water after the removal of suspended solids.

[0009] The present invention also provides a device for reducing sulfate hardness in coal mine water based on nucleus crystal granulation, comprising a vertically arranged sulfate nucleus crystal granulation tank and a suspension tank; the sulfate nucleus crystal granulation tank is connected to a seed crystal addition pipe, and an outer cylinder coaxial with the tank is provided in the tank, the upper and lower ends of the outer cylinder are open, and there is a distance between the outer cylinder and the top, bottom and wall of the tank.

[0010] The inlet of the suspension tank is connected to the inlet pipe, and the water in the suspension tank removes the suspended solids. The outlet of the suspension tank is connected to the sulfate nucleation granulation tank, and the sulfate nucleation granulation tank is equipped with an outlet pipe at the top.

[0011] Sulfate-specific seed crystals added through the seed crystal addition pipe circulate axially with coal mine water (after removing suspended solids) within the outer cylinder and between the outer cylinder and the inner wall of the sulfate nucleation granulation tank to form granules. A granule discharge port is provided at the bottom of the sulfate nucleation granulation tank.

[0012] In one embodiment, the suspension tank is disposed in the sulfate nucleation granulation tank and located inside the outer cylinder. The suspension tank is provided with an inner cylinder coaxial with the tank. The inner cylinder is open at both the top and bottom and is spaced away from the top, bottom and wall of the suspension tank. The coagulant and coal mine water circulate axially in the inner cylinder and between the inner cylinder and the inner wall of the suspension tank to remove suspended solids. A sludge discharge pipe is provided at the bottom of the suspension tank.

[0013] In one embodiment, a separation device is provided at the top of the suspended solids tank, a vertical central water supply pipe is provided in the tank, a rotating blade is provided on the central water supply pipe, the bottom end of the central water supply pipe is connected to the water inlet pipe, and the top end extends out of the suspended solids tank to the separation device.

[0014] The separation device is equipped with a first circulating water pipe at the bottom and a second circulating water pipe at the top. The outlet of the first circulating water pipe is connected to the suspended solids tank, and the outlet of the second circulating water pipe is connected to the sulfate nucleation granulation tank.

[0015] In one embodiment, there are multiple water inlet pipes distributed circumferentially and supplying water radially. The bottom end of the central water supply pipe is connected to each water inlet pipe through a vertical water supply pipe. The inner diameter of the vertical water supply pipe is larger than that of the central water supply pipe. Along the water flow direction, the end of the vertical water supply pipe or the beginning of the central water supply pipe is provided with a connecting structure that widens and then narrows at the cross-section. The inner diameter of the maximum cross-section of the connecting structure is larger than that of the vertical water supply pipe.

[0016] In one embodiment, the separation device consists of an upper isolation screen and a lower stirring blade. The isolation screen is fixed to the inner wall of the suspension tank, and the drive motor at the top of the separation device drives the stirring blade to rotate via the driving stirring shaft.

[0017] In one embodiment, both circulating water pipe one and circulating water pipe two are hollow water pipes used to connect the inlet and outlet areas of different regions; the outlet of circulating water pipe one is located directly above the space between the inner cylinder and the inner wall of the suspended solids tank; the outlet of circulating water pipe two is connected to the space between the outer cylinder and the inner wall of the sulfate nucleation granulation tank through the inlet pipe of the nucleation granulation area.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. This invention is based on nucleus crystal granulation technology, which can achieve simultaneous and efficient removal of sulfate and calcium ions in water without the need to add other reagents. The resulting crystal products have the characteristics of compact structure, low water content and high solid-liquid separation efficiency.

[0020] 2. This invention combines a sludge enrichment device and a granulation device, integrating suspended solids removal and nucleation granulation into one unit. It can simultaneously realize the sludge coagulation and sulfate reduction nucleation granulation process in coal mine water, thereby reducing treatment steps, lowering process costs, and improving treatment efficiency.

[0021] 3. This invention is based on nucleogranulation technology, producing only granules and no sludge. The reaction time and hydraulic retention time are short, requiring only about 10 minutes in a single-stage reactor (this invention can be designed as a three-stage reaction), significantly shorter than membrane treatment technology. The footprint, construction, and operating costs are also significantly lower than membrane treatment technology. The effluent has low turbidity, produces no sludge, and causes no secondary pollution. Furthermore, the treatment method is simple and easy to operate. The calcium sulfate crystals produced by this process, i.e., gypsum, can be used as a raw material in commercial industries, such as as a filler in the paint and paper industries, and in the manufacture of sulfuric acid and ammonium sulfate.

[0022] 4. This invention is based on nucleus crystal granulation technology and does not require the addition of any other reagents. It only requires the addition of sulfate-specific seed crystals to induce sulfate crystallization and produce precipitates. The seed crystals are carried by the upward water flow to a fluidized bed state in the nucleus crystal granulation zone, which increases the contact area between the seed crystals and the solution, which is conducive to achieving rapid heterogeneous induced crystallization, forming large-particle crystal precipitates, reducing energy consumption and reagent dosage, and improving water treatment efficiency. It is suitable for the treatment of sulfate in large-volume coal mine well water. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the nucleus crystal granulation device of the present invention.

[0024] Figure 2 This is a SEM characterization image of the sulfate-specific seed crystals of this invention before granulation.

[0025] Figure 3 This is a SEM characterization image of the sulfate-specific seed crystals after granulation according to the present invention.

[0026] Figure 4 This invention relates to the effect of different initial sulfate concentrations on sulfate removal.

[0027] Figure 5 This invention relates to the effect of different seed crystal addition heights on sulfate removal.

[0028] Figure 6 This is a schematic diagram of the structure of the isolation screen of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] To effectively and cost-effectively address the problem of high sulfate hardness in coal mine water, this invention provides a method for reducing sulfate hardness in coal mine water based on nucleus crystal granulation. First, the coal mine water is pretreated to remove suspended solids. Then, sulfate-specific seed crystals are directly added. The existing calcium ions in the coal mine water cause the sulfate ions to crystallize and precipitate on the surface of the sulfate-specific seed crystals. Under the action of various chemical forces, dense and thick granules with a spherical structure of about 1 mm in diameter are formed. Finally, the granules are discharged, achieving simultaneous removal of calcium ions and sulfate ions and solid-liquid separation. After solid-liquid separation, filtration, and pH adjustment, clear water is obtained. Compared with existing technologies, this invention can reduce energy consumption and reagent dosage while improving water treatment efficiency, and is suitable for treating large volumes of sulfate in coal mine water.

[0031] The method of this invention eliminates the need for any reagents. It utilizes a special sulfate seed crystal and coexisting calcium ions in water to enhance sulfate removal, achieving simultaneous removal and solid-liquid separation of calcium ions and sulfate ions. The final granulated product is then discharged, thus removing sulfate ions. The granulated product of this invention consists of dense, thick calcium sulfate particles with a spherical structure, approximately 1 mm in diameter, formed by sulfate ions accumulating on the surface of a proprietary seed crystal through a nucleation granulation process.

[0032] In a preferred embodiment of the present invention, after removing suspended solids, the calcium ion concentration in the coal mine water ranges from 200 to 500 mg / L, and the sulfate concentration ranges from 6000 to 8000 mg / L. Based on the coal mine water, when the dosage of sulfate-specific seed crystals is 0.3 to 1.8 g / L and the treatment time is more than 30 minutes, the sulfate concentration in the treated coal mine water is controlled below 3000 mg / L, typically 2000 to 3000 mg / L, and the sulfate removal rate is approximately 60%.

[0033] One specific method for pretreatment to remove suspended solids is to add PAM (polyacrylamide) to coal mine water to remove suspended solids from the raw water through coagulation and sedimentation.

[0034] The sulfate-specific seed crystals of this invention are prepared by the following method: sucrose, calcium nitrate, and aluminum sulfate are thoroughly ground until uniformly mixed. Then, concentrated sulfuric acid is added and stirred to obtain a carbonized precursor material. The carbonized material is placed in a beaker, sodium hydroxide solution is added, and the mixture is stirred with a magnetic stirrer. After standing, it is filtered with deionized water, centrifuged, and washed until no sulfate ions are detected in the washing liquid. The mixture is then dried in an oven and calcined under a nitrogen atmosphere to obtain sulfate-specific seed crystals with a particle size of 200–450 μm, the main component of which is ettringite.

[0035] Preferably, the sulfate seed crystals obtained by the present invention are washed with ultrapure water and dried in an oven before use to remove impurities.

[0036] Preferably, by adjusting hydraulic parameters and / or the amount of seed crystals added, sulfate-specific seed crystals can be suspended in the coal mine water after removing suspended solids. The purpose of suspending the sulfate-specific seed crystals in the coal mine water after removing suspended solids is to increase the contact area between the seed crystals and water, thereby increasing the reaction rate. Specifically, the influent flow rate can be adjusted to 5-20 m³ / h. 3 / h, with an influent pH of 6.5–7.5, for example, an influent flow rate of 5m³ / h can be selected. 3 / h, 12.5m 3 / h, 20m 3 / h, with influent pH values ​​of 6.5, 7, and 7.5 respectively; by adjusting the influent flow rate between fluidization velocity and carry-out velocity, the difference between the actual flow velocity of the fluid in the bed and the settling velocity of the crystal-inducing carrier caused by gravity in the vertical direction is ensured to be greater than zero, thereby allowing the crystal-inducing carrier to suspend for nucleation granulation.

[0037] This invention also provides a device for reducing sulfate hardness in coal mine water based on nucleus crystal granulation, combining a sludge enrichment device and a granulation device to reduce processing steps, lower process costs, and improve processing efficiency. Figure 1 As shown, the system includes a vertically arranged sulfate nucleation granulation tank 1 and a suspension tank 2. The sulfate nucleation granulation tank 1 is connected to a seed crystal addition pipe 5, through which sulfate-specific seed crystals are added. The sulfate nucleation granulation tank 1 has an outer cylinder 21 coaxial with the tank, open at both ends. The cylinder wall is fixed by a bracket or iron plate 25, and the outer cylinder 21 is at a certain distance from the top, bottom, and walls of the sulfate nucleation granulation tank 1. The inlet of the suspension tank 2 is connected to the inlet pipe 3, and the incoming water is coal mine water. The outlet of the suspension tank 2 is connected to the sulfate nucleation granulation tank 1. After the coal mine water has suspended solids removed in the suspension tank 2, it enters the sulfate nucleation granulation tank 1. In the sulfate nucleation granulation tank 1, together with the sulfate-specific seed crystals added through the seed crystal addition pipe 5, it circulates axially within the outer cylinder 21 and between the outer cylinder 21 and the inner wall of the sulfate nucleation granulation tank 1 to form granules. The upper part of the sulfate nucleation granulation tank 1 is equipped with an outlet pipe 15 to discharge the finally treated coal mine water. The bottom of the sulfate nucleation granulation tank 1 is equipped with a granule discharge outlet 23 to discharge the finally treated granules.

[0038] In a further embodiment of the present invention, the suspension tank 2 is disposed within the sulfate nucleation granulation tank 1, specifically within the outer cylinder 21 of the sulfate nucleation granulation tank 1, and preferably coaxially disposed. An inner cylinder 22, coaxial with the tank, is disposed within the suspension tank 2. The inner cylinder 22 is open at both ends, and its wall is fixed by a bracket or iron plate 25. The inner cylinder 22 is at a certain distance from the top, bottom, and wall of the suspension tank 2. The coagulant and coal mine water circulate axially within the inner cylinder 22 and between the inner cylinder 22 and the inner wall of the suspension tank 2 to remove suspended solids. A sludge discharge pipe 10 is disposed at the bottom of the suspension tank 2 for discharging the sludge formed by coagulation.

[0039] In a further embodiment of the present invention, a separation device 19 is provided at the top of the suspension tank 2. The separation device 19 is used to separate impurities, large suspended solids, or suspended solids combined with coagulants in the water. A vertical central water supply pipe 12 is provided in the suspension tank 2. A rotating blade 11 is provided on the central water supply pipe 12. The bottom end of the central water supply pipe 12 is connected to the water inlet pipe 3, and the top end extends out of the suspension tank 2 to the separation device 19. That is, the raw water in the water inlet pipe 3 goes directly upward to the separation device 19 through the central water supply pipe 12, and the initial removal of impurities and suspended solids is completed in the separation device 19.

[0040] A circulating water pipe 13 is installed below the separator 19. The outlet of the circulating water pipe 13 is connected to the suspended solids tank 2. The pre-separated water to be treated after separation by the separator 19 falls into the suspended solids tank 2 through the circulating water pipe 13 for circulation. Specifically, it circulates to the space between the tank wall and the inner cylinder 22 of the suspended solids tank 2, flows down along this space, and then rises from the inner cylinder 22 to complete the circulation, thus better combining with the coagulant during circulation. The space inside the inner cylinder 22 and between the tank wall and the inner cylinder 22 forms a sludge enrichment zone. During the upward movement, the action of the rotating blades 11 allows this part of the water to re-enter the separator 19.

[0041] A second circulating water pipe 16 is installed above the separation device 19. The outlet of the second circulating water pipe 16 is connected to the sulfate nucleation granulation tank 1. The deeply separated water to be treated after separation by the separation device 19 falls into the sulfate nucleation granulation tank 1 through the second circulating water pipe 16 for circulation. Specifically, it circulates to the space between the tank wall and the outer cylinder 21 of the sulfate nucleation granulation tank 1, flows down along this space, and then rises from the space between the outer cylinder 21 and the tank wall of the suspended solids tank 2 to complete the circulation. During the circulation, granulation is better achieved under the action of sulfate-specific seed crystals. The space inside the outer cylinder 21 and between the tank wall and the outer cylinder 21 of the sulfate nucleation granulation tank 1 forms the nucleation granulation zone. Under the pressure of the inlet water, the crystalline particles generated in the sulfate nucleation granulation tank 1 are continuously impacted and thrown up by the water pressure, overflowing from the top of the outer cylinder 21, and then sinking down along the space between the outer cylinder 21 and the inner wall of the tank. In this cycle, the crystalline particles gradually grow larger, and the larger particles sink to the crystalline particle discharge outlet 23 for discharge. Furthermore, the end of the circulating water pipe 16 is connected to the inlet pipe 14 of the nucleation granulation area. The inlet pipe 14 of the nucleation granulation area is a curved pipe, which can better guide the treated water into the corresponding area.

[0042] After centrifugation to separate large suspended solids, separation device 19 uses a filter medium to trap and remove small suspended solids. Water passes through the separation device, and suspended solids and other impurities are trapped in the separation device. The medium in the separation device is activated carbon, sand filter, ceramic membrane, etc.

[0043] With this separation device 19, the present invention can achieve solid-liquid separation during granulation, and obtain clean water after adjusting the pH.

[0044] In a further embodiment of the present invention, the separation device 19 may specifically consist of an upper isolation screen 29 and a lower rotating blade 11, wherein the isolation screen 29 is fixed to the inner wall of the suspension tank 2, and the drive motor 17 at the top of the separation device 19 drives the rotating blade 11 to rotate by driving the stirring shaft 20.

[0045] like Figure 6 As shown, the separation device 19 is equipped with an isolation screen 29, which has several holes 28. After treatment, the wastewater in the suspended solids tank 2 enters the separation device 19 for further separation, passes through the holes 28 and enters the circulating water pipe 16. A bushing 27 is provided at the center of the isolation screen 29. The stirring shaft 20 passes through the bushing 27 and can rotate in it. The rotating blade 11 is installed on the stirring shaft 20 and is driven to rotate by the stirring shaft 20.

[0046] In a further embodiment of the present invention, there are multiple inlet pipes 3, distributed circumferentially and allowing water to enter radially. A coagulant dosing device 4 and a flow meter 26 can be installed on each inlet pipe 3. The flow meter 26 is located after the coagulant dosing device 4, adding coagulant to the raw water via the coagulant dosing device 4. The flow meter 26 controls the raw water inflow and the final hydraulic parameters. The bottom end of the central water supply pipe 12 is connected to each inlet pipe 3 via a vertical water supply pipe 24, the inner diameter of which is larger than that of the central water supply pipe 12. Since the outer side of the central water supply pipe 12 is a rotating blade 11, the diameter of the central water supply pipe 12 is reduced to increase the blade speed and improve processing efficiency, while the larger inner diameter of the vertical water supply pipe 12 facilitates flow control. Along the water flow direction, the end of the vertical water supply pipe 24 or the beginning of the central water supply pipe 12 is provided with a connecting structure that widens and then narrows at the cross-section. The inner diameter of the maximum cross-section of the connecting structure is larger than the inner diameter of the vertical water supply pipe 24, which plays a buffering role in the water flow and prevents equipment damage caused by excessive changes in pipe diameter.

[0047] In a further embodiment of the present invention, both circulating water pipe 13 and circulating water pipe 16 are hollow water pipes used to connect the inlet and outlet water areas of different regions. Circulating water pipe 13 connects the suspended solids tank 2 and the separation device 19, while circulating water pipe 16 connects the inlet pipe 14 of the separation device and the sulfate nucleation granulation tank 1. Specifically, the outlet of circulating water pipe 13 is located directly above the space between the inner cylinder 22 and the inner wall of the suspended solids tank 2; the outlet of circulating water pipe 16 communicates with the space between the outer cylinder 21 and the inner wall of the sulfate nucleation granulation tank 1 through the inlet pipe 14 of the nucleation granulation area.

[0048] To facilitate the discharge of sludge and granules, the bottom of both the sludge enrichment zone and the nucleation granulation zone of this invention is designed as a conical bucket shape.

[0049] To protect the entire device, the present invention provides a top cover 18 on the top of the sulfate nucleation granulation tank 1, and a drive motor 17 is arranged inside the tank, connecting the stirring shaft 20 and the central water supply pipe 12, driving the central water supply pipe 12 and the rotating blades 11 on it to rotate.

[0050] Because the nucleus crystal granulation device is small in size, it can be installed on a vehicle and the vehicle can be driven to the site where sulfate treatment is required in coal mine water, thus having good mobility.

[0051] Figure 2 and Figure 3 SEM images of the sulfate-specific seed crystals prepared in Example 1 of this disclosure before and after performance testing.

[0052] like Figure 2 As shown, the sulfate-specific seed crystals before nucleation granulation have a particle size of approximately 215 μm and a hexagonal star shape. After the nucleation granulation reaction, calcium sulfate precipitates adhere to the seed crystal surface, increasing the particle size to approximately 650 μm, and the shape becomes uniformly distributed, dense granules. Figure 3 As shown, the results indicate that the sulfate-specific seed crystals successfully formed dense granules after the reaction.

[0053] Reference effect of the nucleogranulation process of this invention on the removal rate of sulfate in coal mine water Figure 4 and Figure 5 .

[0054] Figure 4 The graphs show the removal effect of the prepared sulfate-specific seed crystals on sulfate in water (the bar graph represents turbidity, and the line graph represents sulfate removal rate). Figure 4 It can be seen that, under the enrichment effect of sulfate on the surface of the sulfate-specific seed crystals, sulfate forms a local supersaturated state on the seed crystal surface, and finally adheres and precipitates on the seed crystal surface in the form of calcium sulfate. After treatment by nucleation granulation reaction, the effluent sulfate concentration in wastewater with an initial sulfate concentration of 80 mM is reduced to below 4000 mg / L, with a sulfate removal rate of approximately 50% and a turbidity of approximately 8 NTU; in wastewater with an initial sulfate concentration of 120 mM, the effluent sulfate concentration is reduced to below 5000 mg / L, with a sulfate removal rate of approximately 60% and a turbidity of approximately 7 NTU; in wastewater with an initial sulfate concentration of 160 mM, the effluent sulfate concentration is reduced to below 6000 mg / L, with a sulfate removal rate of approximately 60% and a turbidity of approximately 6 NTU. Figure 5 The graph shows the effect of the filling height of the prepared sulfate-specific seed crystals on the removal of sulfate ions in water (the bar graph represents turbidity, and the line graph represents the sulfate removal rate). Figure 5It can be seen that when the filling height of the special seed crystals is 10%, 20%, and 30%, the removal rate of sulfate gradually increases to 30%, 35%, and 40%, respectively, while the turbidity of the effluent gradually decreases to 15, 14, and 11, respectively. These results indicate that the composite seed crystals prepared in this invention can effectively remove sulfate from wastewater. The low turbidity of the effluent indicates that sulfate ions precipitate and adhere to the seed crystals, forming granules. The special seed crystals prepared in this invention are beneficial for further wastewater treatment and are environmentally friendly.

[0055] Under the enrichment effect of sulfate ions on the surface of sulfate-specific seed crystals, sulfate ions form a local supersaturated state on the seed crystal surface, and finally adhere and precipitate on the seed crystal surface in the form of calcium sulfate. After nucleation granulation reaction, the removal rate of sulfate ions in water is about 60%, and the turbidity is below 20 NTU. Moreover, the removal efficiency increases significantly with the increase of seed crystal dosage, indicating that sulfate-specific seed crystals have a good removal effect on sulfate ions.

[0056] The technical principle of this invention is:

[0057] In the nucleation crystallization device, seed crystals are added to induce the crystallization of sulfate and calcium ions in a saturated state, producing precipitates and achieving rapid crystallization of sulfate in water, thus realizing rapid solid-liquid separation. The seed crystals are carried by the upward water flow into a fluidized bed state in the nucleation crystallization zone, increasing the contact area between the seed crystals and the solution, facilitating rapid heterogeneous induced crystallization, forming large-particle crystal precipitates that are discharged, thereby removing sulfate from coal mine water. The final treated water sulfate concentration is controlled below 3000 mg / L.

[0058] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0059] Example 1

[0060] The coal mine water of a certain coal mine enterprise has a pH of 2.2–3.8. The dosage of sulfate seed crystals is 0.8 g / L, and the adjusted pH is 6–7. The residence time in the nucleation granulation zone is 15 min, and the flow rate is 15 m³ / L. 3 / h.

[0061] SO4 before raw water treatment 2- =18000mg / L, after a week of stable operation, the SO4 in the effluent was... 2- =2800mg / L, and the final dense granules have a particle size of 800-900μm.

[0062] Example 2

[0063] The coal mine water of a certain coal mine enterprise has a pH of 3.1–4.2. The dosage of sulfate seed crystals is 1.0 g / L, and the adjusted pH is 6–7. The residence time in the nucleation granulation zone is 12 min, and the flow rate is 10 m³ / L. 3 / h.

[0064] SO4 before raw water treatment 2- =12000mg / L, after a week of stable operation, the SO4 in the effluent was... 2- =2500mg / L, the final dense granules have a particle size of 700-850μm.

[0065] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above operational steps, that is, it does not mean that the present invention must rely on the above operational steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for reducing sulfate hardness in coal mine well water based on core granulation, characterized in that, The sulfate special seed is added in the coal mine well water after removing the suspended solids, and only the sulfate special seed is added, the calcium ions in the coal mine well water are used to make the sulfate in the coal mine well water crystallize and precipitate on the surface of the sulfate special seed to form granules, the granules are discharged outside, the synchronous removal and solid-liquid separation of calcium ions and sulfate are realized; wherein the sulfate special seed is prepared by the following method: sucrose, calcium nitrate and aluminum sulfate with a weight ratio of 1:1:1.5~1:1.2:2 are fully ground and mixed uniformly, then concentrated sulfuric acid is added and stirred to obtain a carbonized precursor material, the precursor material is mixed with a sodium hydroxide solution with a concentration of 1.5~2 mol / L according to a solid-liquid ratio of 12~15 g / 100 mL, and is placed in a magnetic stirrer for stirring, then after standing, it is filtered, centrifuged and washed with deionized water until no sulfate ions are detected in the washing liquid, then it is placed in an oven for drying, calcined at 550~600 ℃ for 2.5~3 h under a nitrogen atmosphere, and then cooled for 8~10 h, to obtain the sulfate special seed with the main component of calcium aluminate.

2. The method for reducing sulfate hardness in coal mine water based on the nucleation granulation according to claim 1, characterized in that, The concentration of calcium ions in the coal mine well water after removing the suspended solids is 200~500 mg / L, the concentration of sulfate is 6000~8000 mg / L, the adding amount of the sulfate special seed is 0.3~1.8 g / L, the treatment time is more than 30 min, and the concentration of sulfate in the treated coal mine well water is 2000~3000 mg / L.

3. The method of claim 1, wherein the method is characterized by, The water power parameters are regulated to make the sulfate special seed suspended in the coal mine well water after removing the suspended solids.

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