A method for removing suspended solids and hardness from negative marcasite mine water

Abstract

This disclosure relates to a method for removing suspended solids and hardness from negatively hard mine water. The method includes: S1, introducing the negatively hard mine water to be treated into a chemical mixing unit to contact with a hardening agent for hardening removal, thereby obtaining hardened mine water; wherein the hardening agent contains calcium hydroxide and / or sodium hydroxide, and the dosage of the hardening agent is 50-2000 mg relative to 1 L of the negatively hard mine water to be treated; S2, introducing the hardened mine water into an underground water purification unit for purification; wherein the underground water purification unit includes a closed space for water self-purification treatment, and the closed space contains collapsed rock masses from the goaf; the residence time of the hardened mine water in the closed space is more than 2 hours, and the purification distance in the direction of water flow is more than 20 m. This method, when used to treat negatively hard mine water with alkalinity higher than hardness, can simply and efficiently reduce the hardness of the mine water and remove suspended solids, offering advantages such as low treatment cost and good treatment effect.

Description

Technical Field

[0001] This application relates to the field of mine water treatment, and more specifically, to a method for removing suspended solids and hardness from negative hard mine water. Background Technology

[0002] High-mineralization mine water, also known as saline mine water or brackish water, refers to mine water with a dissolved solids content greater than 1000 mg / L, mainly containing calcium. 2+ Mg 2+ Na + K + SO4 2- HCO3 - Cl - The pH value is generally greater than 6.7. The key to achieving high recovery rates for this type of mine water is hardening removal. It also contains a large amount of dust particles, resulting in high suspended solids content. Without proper processes for removing suspended solids, turbidity, and hardening, the normal operation of subsequent deep desalination processes will be affected.

[0003] For mine water with high suspended solids and high hardness, the traditional method is to remove them in stages during pretreatment. The first step is suspended solids treatment, which typically uses coagulation and sedimentation. Enhanced treatment technologies include heavy medium rapid sedimentation and supermagnetic separation, all of which require the addition of PAC, PAM, magnetic powder, and other agents to accelerate the coagulation and flocculation process and speed up the settling of suspended solids. The second step is hardness treatment. Currently, effective methods for reducing water hardness include softening with chemical dosing, ion exchange, tubular membrane microfiltration, and crystallization granulation. Current surface-based staged treatment methods are characterized by high investment costs, long settling times, large land area requirements, and high reagent consumption.

[0004] To ensure effective sedimentation, actual engineering applications of mine water pretreatment often involve excessive addition of PAC (polyaluminum chloride) and PAM (polyacrylamide), resulting in prolonged coagulation and settling times. This necessitates large treatment equipment or spaces, such as high-density sedimentation tanks, for thorough solid-liquid separation. Residual chemicals can clog subsequent membrane filtration systems, which are difficult and irreversible to clean. Furthermore, the effluent from chemical sedimentation processes typically has a pH above 11.2, requiring significant amounts of alkaline chemicals. Deep treatment membrane elements, especially inorganic membrane filters, are susceptible to acid and alkali instability; therefore, the effluent from chemical sedimentation must be pH-adjusted before entering the membrane filtration system. This conditioning process often involves large quantities of chemicals, leading to significant waste.

[0005] CN109574361A discloses a wastewater softening pretreatment method, which involves adding a chemical agent to the wastewater in a reaction tank for a chemical reaction, while simultaneously adding magnetized water or a dispersant, controlling the reaction time to 5-30 minutes; controlling the pH value of the reaction to 10.5-12; and filtering the effluent after the reaction using a ceramic membrane. However, this method has problems such as small water treatment capacity per unit membrane area, incomplete membrane filtration leading to easy scaling and clogging of the system, large dosage of alkaline agents, and high system pH.

[0006] With the increasing importance of water resource utilization in mining areas, the improvement and innovation of mine water treatment technology has become an urgent task. Therefore, it is imperative to develop a new and efficient mine water turbidity and hardness removal technology. Summary of the Invention

[0007] The purpose of this disclosure is to provide a method for removing suspended solids and hardness from negative hard mine water. When the method of this disclosure is used to treat negative hard mine water with alkalinity higher than hardness, it can simply and efficiently reduce the hardness of the mine water and remove suspended solids in the water, and has the advantages of low treatment cost and good treatment effect.

[0008] To achieve the above objectives, this disclosure provides a method for removing suspended solids and hardness from negatively hard mine water, the method comprising: S1. The negative hard mine water to be treated is introduced into the chemical mixing unit to contact the hardening agent for hardening removal, and the hardened mine water is obtained. The hardening agent contains calcium hydroxide and / or sodium hydroxide, and the dosage of the hardening agent is 50-2000 mg relative to 1 L of the negative hard mine water to be treated. S2. The hardened mine water is introduced into the underground reservoir purification unit for purification. The underground water purification unit includes a closed space for water self-purification treatment, and the closed space contains collapsed rock masses from the goaf. The hardened mine water stays in the closed space for more than 2 hours, and the purification distance in the direction of water flow is more than 20m.

[0009] Optionally, in step S1, the amount of the hardening agent used is 200-1000 mg relative to 1 L of the hardened mine water to be treated; the pH value of the hardened mine water is 9.5-10.5.

[0010] Optionally, in step S1, the hardening is carried out under stirring conditions, the stirring speed is 100-500 r / min, and the stirring time is 5-30 min.

[0011] Optionally, in step S2, the enclosed space includes the outer framework formed by coal pillars and / or artificial dams.

[0012] Optionally, in step S2, the residence time of the dehardened mine water in the enclosed space is 2 hours to 60 days, and the purification distance in the direction of water flow is 100-5000m.

[0013] Optionally, the method further includes: introducing the negative hard mine water to be treated into a pre-sedimentation tank for sedimentation treatment, and then introducing it into the dosing and mixing unit.

[0014] Optionally, the method further includes: when the turbidity of the effluent from the outlet of the underground water purification unit is greater than a threshold ΔA and / or the hardness is greater than a threshold ΔB, introducing the hardness removal agent into the underground water purification unit through the dosing and mixing unit; wherein the threshold ΔA is 18-22 NTU and the threshold ΔB is 0.4-0.6 mmol / L.

[0015] Optionally, the amount of the hardening agent used is 50-2000 mg relative to 1 L of hardened mine water in the underground reservoir purification unit.

[0016] Optionally, the water storage coefficient of the collapsed rock mass in the goaf within the enclosed space is 0.05-0.3.

[0017] Optionally, the total hardness of the negative hard mine water to be treated is 0.5-20 mmol / L, the total alkalinity is 1-30 mmol / L, the turbidity is 0-10000 NTU, and the pH value is 6-9.

[0018] Through the above technical solution, the method disclosed herein removes hardness from mine water by adding a hardening agent containing calcium hydroxide and / or sodium hydroxide through a chemical mixing unit before introducing the mine water into the underground water reservoir purification unit. This solves the problems of complex traditional chemical precipitation softening processes, long reaction times, and the need for multiple types and large dosages of chemicals. Simultaneously, the subsequent purification process of the underground water reservoir purification unit removes suspended solids from the water. By utilizing the existing treatment space and purification advantages of underground water reservoirs and tunnels, the construction of underground equipment and pipelines is reduced, achieving the synergistic removal of hardness and suspended solids and lowering the overall cost of mine water treatment.

[0019] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic flowchart of a method for removing suspended solids and hardness from negatively hard mine water.

[0021] Figure 2 This is a schematic flowchart of the mine water hardening method used in Comparative Examples 1 and 2 of this disclosure. Detailed Implementation

[0022] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0023] like Figure 1 As shown, this disclosure provides a method for removing suspended solids and hardness from negatively hardened mine water. The method includes: S1, introducing the negatively hardened mine water to be treated into a chemical mixing unit to contact with a hardening agent for hardening removal, thereby obtaining hardened mine water; wherein the hardening agent contains calcium hydroxide and / or sodium hydroxide, and the dosage of the hardening agent is 50-2000 mg relative to 1 L of the negatively hardened mine water to be treated; S2, introducing the hardened mine water into an underground reservoir purification unit for purification; wherein the underground reservoir purification unit includes a closed space for water self-purification treatment, and the closed space contains collapsed rock masses from a mined-out area; the residence time of the hardened mine water in the closed space is more than 2 hours, and the purification distance in the direction of water flow is more than 20 m.

[0024] This disclosed method involves adding a hardening agent containing calcium hydroxide and / or sodium hydroxide to the negatively hardened mine water in a dosing and mixing unit for pretreatment. The hardened mine water is then introduced into an underground reservoir purification unit. This effectively avoids the problems of clogging in the mine water treatment system caused by the complexity, long reaction time, and multiple types and dosages of traditional chemical precipitation and softening processes. Simultaneously, it utilizes the voids, fissures, and delamination spaces of the collapsed rock mass in the goaf area for the storage and utilization of mine water. The collapsed rock mass in the underground reservoir is used for self-purification treatment of the mine water through filtration, sedimentation, adsorption, and ion exchange. This tightly integrates mine water treatment with the underground space, reducing the construction of underground equipment and pipelines, and lowering the overall cost of mine water treatment. This disclosed method achieves synergistic removal of suspended solids and hardness, featuring underground source control, low system treatment cost, underground utilization of product water, and no discharge of pollutants from the well.

[0025] In this disclosure, the purification distance in the direction of water flow refers to the water flow distance in the goaf roadway.

[0026] According to this disclosure, such as Figure 1 As shown, the dosing and mixing unit of this disclosure includes a dosing device and a mixing device. The dosing device is used to add a hardening agent to the mine water to be treated, and the mixing device is used to mix and react the mine water to be treated and the hardening agent. The outlet of the mixing device is in fluid communication with the inlet of the underground water reservoir purification unit.

[0027] In one specific embodiment of this disclosure, in step S1, the amount of the hardening agent used is 20-1000 mg relative to 1 L of the hardened mine water to be treated; the pH value of the hardened mine water is 9.5-10.5. In this embodiment, the appropriate amount of hardening agent can more effectively reduce the hardness of the mine water. This disclosure does not impose specific limitations on the ratio of calcium hydroxide to sodium oxide in the hardening agent, and it can be selected according to actual needs.

[0028] To ensure thorough mixing and reaction between the mine water to be treated and the hardening agent, in one specific embodiment of this disclosure, step S1 involves hardening under stirring conditions. The stirring speed is 100-500 r / min, and the stirring time is 5-30 min.

[0029] According to this disclosure, the underground reservoir purification unit can be one or more. In one embodiment, in step S2, the enclosed space includes an outer framework formed by coal pillars and / or an artificial dam.

[0030] In one specific embodiment of this disclosure, in step S2, the residence time of the de-hardened mine water in the enclosed space is from 2 hours to 60 days, and the purification distance in the water flow direction is 100-5000m. The voids, fissures, and delamination spaces of the collapsed rock mass in the mined-out area within the enclosed space of the underground reservoir purification unit of this disclosure can store and utilize the mine water. The collapsed rock mass in the underground reservoir is used to filter, precipitate, adsorb, and exchange ions to achieve self-purification of the mine water. Under the above conditions, suspended matter in the mine water can be removed more thoroughly and effectively through the purification effect of the collapsed rock mass.

[0031] In one specific embodiment of this disclosure, the method further includes: introducing the untreated negative-hardness mine water into a pre-sedimentation tank for sedimentation treatment, and then introducing it into the chemical mixing unit to remove large particulate suspended matter in the untreated mine water in advance, thereby reducing the operating load of the underground reservoir and extending its service life. In a preferred embodiment, the hardness of the water effluent from the pre-sedimentation tank is detected by an online water quality monitoring device, and the detection results are fed back to the chemical mixing unit to control the dosage.

[0032] In one specific embodiment of this disclosure, the method further includes: when the turbidity of the effluent from the outlet of the underground water purification unit is greater than a threshold ΔA and / or the hardness is greater than a threshold ΔB, introducing the hardening agent into the underground water purification unit through the dosing and mixing unit; wherein the threshold ΔA is 18-22 NTU, and the threshold ΔB is 0.4-0.6 mmol / L; preferably, the threshold ΔA is 20 NTU, and the threshold ΔB is 0.5 mmol / L. In this embodiment, by monitoring the turbidity and hardness of the effluent from the outlet of the underground water purification unit, it is determined whether to add the hardening agent into the underground water purification unit (i.e., perform in-situ dosing) to further improve the mine water purification effect. In one specific embodiment of this disclosure, the dosage of the hardening agent is 50-2000 mg relative to 1 L of the hardened mine water in the underground water purification unit.

[0033] In one specific embodiment of this disclosure, the water storage coefficient of the collapsed rock mass in the goaf within the enclosed space is 0.05-0.3. In this disclosure, the water storage coefficient of the collapsed rock mass in the goaf within the enclosed space is also referred to as porosity. The method for measuring the water storage coefficient is well known to those skilled in the art and will not be elaborated here. Excessive packing density of the collapsed rock mass in the goaf may cause poor water flow, while insufficient packing density may result in poor purification and digestion of the water by the rock mass. In this embodiment, the voids, fissures, and abscission spaces of the collapsed rock mass within the enclosed space of the underground reservoir serve to store and utilize mine water. Under the aforementioned packing density conditions, sufficient contact between the mine water and the collapsed rock mass can be achieved to realize self-purification treatment such as filtration, sedimentation, adsorption, and ion exchange.

[0034] According to this disclosure, the effluent from the outlet of the underground reservoir purification unit can be reused at the point of use or in the post-treatment unit, thereby improving the degree of resource utilization.

[0035] According to this disclosure, the method is particularly suitable for purifying negative hard mine water with alkalinity higher than hardness. In one specific embodiment of this disclosure, the negative hard mine water to be treated has a total hardness of 0.5-20 mmol / L, a total alkalinity of 1-30 mmol / L, a turbidity of 0-10000 NTU, and a pH of 6-9.

[0036] In this disclosure, the chemical dosing and mixing unit is located above ground, and the underground water purification unit is located underground. The de-hardened mine water obtained by the chemical dosing and mixing unit is pumped into the underground water purification unit, and the effluent from the underground water purification unit is drawn out by a water pump.

[0037] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0038] The calcium hydroxide and sodium hydroxide used in the examples were commercially available.

[0039] The negative hard mine water treated in Examples 1-2 below had a calcium hardness of 2.5 mmol / L, a magnesium hardness of 0.74 mmol / L, a bicarbonate alkalinity of 7.05 mmol / L, a turbidity of 370 NTU, and a pH of 7.6.

[0040] Example 1 A method for removing suspended solids and hardness from negative hard mine water, the method comprising: S1. The negative-hard mine water to be treated is introduced into the pre-sedimentation tank for sedimentation treatment, and then introduced into the chemical mixing unit to contact with the hardening agent for hardening removal, resulting in hardened mine water. The hardening agent contains calcium hydroxide, and the dosage is 304 mg per 1 L of negative-hard mine water. The pH of the hardened mine water is 9.9, and the total hardness is 0.95 mmol / L. Hardening removal is carried out under stirring conditions at a speed of 300 r / min for 15 min.

[0041] S2. The de-hardened mine water is introduced into the underground water purification unit for purification. After 7 days of system operation, the turbidity of the effluent from the underground water purification unit is 19 NTU and the hardness is 0.43 mmol / L. The underground water purification unit includes a closed space for water self-purification treatment. The closed space includes an outer framework formed by coal pillars and artificial dams. The closed space contains collapsed rock mass from the goaf, and the water storage coefficient of the collapsed rock mass is 0.2. The residence time of the de-hardened mine water in the closed space is 168 hours, and the purification distance in the direction of water flow is 150m.

[0042] The total hardness of the purified mine water was 0.43 mmol / L, with an average hardness removal rate of 89.5%; the total alkalinity was 0.21 mmol / L, with an average alkalinity removal rate of 97%; the turbidity was 19 NTU; and the pH value was 9.9.

[0043] Example 2 The negative hard mine water was purified using the same method as in Example 1, except that in step S1, the amount of hardening agent used was 190 mg relative to 1 L of the negative hard mine water to be treated, and the pH value of the hardened mine water was 9.2 and the total hardness was 0.188 mmol / L; in step S2, the residence time of the hardened mine water in the enclosed space was 100 hours, and the purification distance in the direction of water flow was 80 m.

[0044] The total hardness of the purified mine water was 1.02 mmol / L, with an average hardness removal rate of 76%; the total alkalinity was 2.6 mmol / L, with an average alkalinity removal rate of 63.1%; the turbidity was 51 NTU; and the pH value was 9.2.

[0045] Example 3 The mine water treatment capacity of a certain mine in Shendong is 200m³. 3 / h, Ca in water 2+ The concentration was 2.84 mmol / L, Mg 2+ The concentration was 1.5 mmol / L, the bicarbonate alkalinity was 9.5 mmol / L, and the turbidity was 344 NTU.

[0046] S1. The negatively hardened mine water to be treated is introduced into the chemical mixing unit and contacted with sodium hydroxide for hardening removal. The mixture is stirred for 20 minutes at a stirring speed of 300 r / min to obtain the de-hardened mine water. The amount of sodium hydroxide used is 482 mg relative to 1 L of the negatively hardened mine water to be treated. The pH value of the de-hardened mine water is 10, and the total hardness is 1.21 mmol / L.

[0047] S2. The de-hardened mine water is introduced into an underground reservoir purification unit for purification. The underground reservoir purification unit includes a closed space for water self-purification treatment. The closed space includes an outer framework formed by coal pillars and artificial dams. The closed space contains collapsed rock masses from the goaf, and the water storage coefficient of the collapsed rock masses is 0.3. The residence time of the de-hardened mine water in the closed space is 5 hours, and the purification distance in the direction of water flow is 23m.

[0048] The total hardness of the purified mine water was 0.47 mmol / L, with an average hardness removal rate of 89%; the total alkalinity was 0.796 mmol / L, with an average alkalinity removal rate of 91.6%; the turbidity of the effluent was 19 NTU; and the pH value was 10.1.

[0049] Example 4 The mine water treatment capacity of a certain mine in Shendong is 500m³. 3 / h, Ca in water 2+ The concentration was 2 mmol / L, Mg 2+ The concentration was 0.63 mmol / L, the bicarbonate alkalinity was 5.9 mmol / L, and the turbidity was 546 NTU.

[0050] S1. The negatively hardened mine water to be treated is introduced into the dosing and mixing unit and contacted with calcium hydroxide for hardening removal. The mixture is stirred for 20 minutes at a stirring speed of 300 r / min to obtain the de-hardened mine water. The amount of calcium hydroxide used is 559 mg relative to 1 L of the negatively hardened mine water to be treated. The pH value of the de-hardened mine water is 10, and the total hardness is 1.08 mmol / L.

[0051] S2. The de-hardened mine water is introduced into an underground reservoir purification unit for purification. The underground reservoir purification unit includes a closed space for water self-purification treatment. The closed space includes an outer framework formed by coal pillars and artificial dams. The closed space contains collapsed rock masses from the goaf, and the water storage coefficient of the collapsed rock masses is 0.3. The residence time of the de-hardened mine water in the closed space is 168 hours, and the purification distance in the direction of water flow is 150m.

[0052] The total hardness of the purified mine water was 0.38 mmol / L, with an average hardness removal rate of 86%; the total alkalinity was 0.65 mmol / L, with an average alkalinity removal rate of 89%; the turbidity of the effluent was 11 NTU; and the pH value was 10.

[0053] Comparative Example 1 A mine water treatment facility in Shendong has a capacity of 200m³. 3 / h, Ca in water 2+ The concentration was 8.4 mmol / L, Mg 2+ The concentration was 1.5 mmol / L, the bicarbonate alkalinity was 9.5 mmol / L, and the turbidity was 344 NTU. The following method was used: Figure 2 The system shown is used for mine water treatment, and the specific method is as follows: After adding polyaluminum chloride (PAC) and polyacrylamide (PAM) to the mine water to be treated for heavy medium rapid sedimentation, the total amount of PAC and PAM used is 25 mg relative to 1 L of mine water to be treated. The effluent is then introduced into a high-density sedimentation tank where sodium hydroxide, sodium carbonate, PAC, and PAM are added to control the pH of the tank at 11.2. The total amount of sodium hydroxide, sodium carbonate, PAC, and PAM used is 725 mg relative to 1 L of mine water in the high-density sedimentation tank.

[0054] The total hardness of the purified water was 0.7 mmol / L, with an average hardness removal rate of 83.9%; the total alkalinity was 1.2 mmol / L, with an average alkalinity removal rate of 87%; and the turbidity of the purified water was 30 NTU.

[0055] Comparative Example 2 The mine water treatment capacity of a certain mine in Shendong is 200m³. 3 / h, Ca in water 2+ The concentration was 8.4 mmol / L, Mg 2+ The concentration was 1.5 mmol / L, the bicarbonate alkalinity was 9.5 mmol / L, and the turbidity was 344 NTU.

[0056] Adopting such Figure 2 The system shown is used for mine water treatment, and the specific method is as follows: After adding polyaluminum chloride (PAC) and polyacrylamide (PAM) to the mine water to be treated for heavy medium rapid sedimentation, the total amount of PAC and PAM used is 21 mg relative to 1 L of mine water to be treated. The effluent is then introduced into a high-density sedimentation tank where calcium hydroxide, sodium carbonate, PAC, and PAM are added to control the pH of the tank at 8.8. The total amount of calcium hydroxide, sodium carbonate, PAC, and PAM used is 300 mg relative to 1 L of mine water in the high-density sedimentation tank.

[0057] The total hardness of the purified water was 1.5 mmol / L, with an average hardness removal rate of 65%; the total alkalinity was 4.1 mmol / L, with an average alkalinity removal rate of 57%; and the turbidity of the purified water was 130 NTU.

[0058] As can be seen from the above, the method disclosed herein uses a small amount of reagent and can effectively remove suspended solids from mine water and reduce water hardness.

[0059] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0060] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0061] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for removing suspended solids and hardness from negatively hard mine water, characterized in that, The method includes: S1. The negative hard mine water to be treated is introduced into the chemical mixing unit to contact the hardening agent for hardening removal, and the hardened mine water is obtained. The hardening agent contains calcium hydroxide and / or sodium hydroxide, and the dosage of the hardening agent is 50-2000 mg relative to 1 L of the negative hard mine water to be treated. S2. The hardened mine water is introduced into the underground reservoir purification unit for purification. The underground water purification unit includes a closed space for water self-purification treatment, and the closed space contains collapsed rock masses from the goaf. The hardened mine water stays in the closed space for more than 2 hours, and the purification distance in the direction of water flow is more than 20m.

2. The method according to claim 1, wherein, In step S1, the amount of the hardening agent used is 200-1000 mg relative to 1 L of the hardened mine water to be treated; the pH value of the hardened mine water is 9.5-10.

5.

3. The method according to claim 1, wherein, In step S1, the hardening is carried out under stirring conditions, the stirring speed is 100-500 r / min, and the stirring time is 5-30 min.

4. The method according to claim 1, wherein, In step S2, the enclosed space includes the outer framework formed by coal pillars and / or artificial dams.

5. The method according to claim 1, wherein, In step S2, the residence time of the dehardened mine water in the enclosed space is 2 hours to 60 days, and the purification distance in the direction of water flow is 100-5000m.

6. The method according to claim 1, wherein, The method further includes: introducing the negative hard mine water to be treated into a pre-sedimentation tank for sedimentation treatment, and then introducing it into the dosing and mixing unit.

7. The method according to claim 1, wherein, The method further includes: when the turbidity of the effluent from the outlet of the underground water purification unit is greater than the threshold ΔA and / or the hardness is greater than the threshold ΔB, introducing the hardness removal agent into the underground water purification unit through the dosing and mixing unit; Wherein, the threshold ΔA is 18-22 NTU, and the threshold ΔB is 0.4-0.6 mmol / L.

8. The method according to claim 7, wherein, The amount of the hardening agent used is 50-2000 mg relative to 1 L of hardened mine water in the underground reservoir purification unit.

9. The method according to claim 1, wherein, The water storage coefficient of the collapsed rock mass in the goaf within the enclosed space is 0.05-0.

3.

10. The method according to claim 1, wherein, The total hardness of the negative hard mine water to be treated is 0.5-20 mmol / L, the total alkalinity is 1-30 mmol / L, the turbidity is 0-10000 NTU, and the pH value is 6-9.

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