Sulfate-based mine water concentrated solution hardness removal method and system

Abstract

The invention discloses a hardness removal method and system for a sulfate-based mine water concentrated solution, and the method comprises the following steps: sequentially introducing the sulfate-based mine water concentrated solution into a coagulating basin and a flocculation basin for chemical treatment, and allowing the treated mine water concentrated solution to enter a sedimentation basin for standing to obtain softened effluent; wherein lime or sodium hydroxide and a coagulant are put into the coagulating basin, and the coagulating basin is used for carrying out coagulating treatment on the mine water concentrated solution; sodium carbonate, a coagulant aid and an inducer seed crystal are put into the flocculation basin and used for carrying out flocculation treatment and precipitation reaction on the mine water concentrated solution subjected to coagulation treatment, the standing time of the flocculation basin is 14-45 minutes, the precipitation reaction time is 6-30 minutes, and the excessive amount of sodium carbonate is 1.5-2.5 mmol / L. According to the invention, the hardness of calcium in softened water can be lower than 20mg / L.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method and system for removing hardness from sulfate-based mine water concentrate. Background Technology

[0002] Mine water, as an unconventional water resource in my country, is subject to strategic requirements for zero-discharge construction, particularly in coal mines in the western region. Western mine water faces challenges such as large inflow volumes, high mineralization, complex composition, and stringent discharge requirements. Field investigations of mine water in the Xinjie Taige Temple and surrounding mining areas revealed that in some zero-discharge practices for mine water primarily composed of Na2SO4, softening units exhibited high chemical dosages and inadequate hardness removal. Furthermore, the softening effect after membrane concentration was hampered by scale inhibitors, resulting in unsatisfactory hardness removal. This necessitated frequent chemical cleaning of subsequent membrane concentration units, increasing operational complexity and maintenance costs. Calcium carbonate and calcium sulfate, formed from hardness ions in the membrane system, are the main forms of scaling. Currently, there are no clear standards for the influent water quality, but a general requirement is calcium <20 ppm.

[0003] The research foundation for industrial wastewater softening and hardening removal technology mainly revolves around coal chemical wastewater, desulfurization wastewater, seawater, and cooling circulating water. The essential difference between industrial wastewater and mine water lies in the different water quality types. Specifically, the salt type of mine water in western mining areas is mainly Na2SO4, with a high ratio of NaCl, even higher than 10:1. The existing pretreatment and hardening removal technology system is insufficient to support the pretreatment of mine water dominated by Na2SO4.

[0004] Patent CN114180756A discloses a softening and desalination device for high-salt, high-hardness wastewater. It employs a high-density sedimentation tank with a dosing device for pretreatment before membrane concentration. Calcium and magnesium ions in the wastewater are removed by adding NaOH, CaO, and Na2CO3, reducing the hardness. Then, a tubular microfiltration membrane achieves relatively complete solid-liquid separation, and the effluent meets the requirements for RO membrane inlet. However, this patent focuses on the high-density sedimentation tank dosing operation for pretreatment before membrane concentration, a routine procedure for pretreatment of mine water and industrial wastewater. It does not provide detailed discussion on controlling the residence time for different water qualities and is not suitable for softening concentrated mine water solutions primarily composed of Na2SO4, thus failing to achieve the desired hardness removal effect. Summary of the Invention

[0005] In view of this, the main objective of the present invention is to provide a method and system for hardening mine water concentrate with sulfate as the main component. After treatment by the method of the present invention, the calcium hardness of the effluent can be reduced to less than 20 mg / L, which meets the feed water requirements of downstream membrane and other processes, greatly reduces the scaling risk and cleaning and maintenance costs of membrane processes, and is conducive to the efficient resource utilization of mine water.

[0006] To achieve the above-mentioned objectives, the first aspect of this invention provides a method for removing hardness from sulfate-based mine water concentrate, comprising the following steps: sequentially passing a sulfate-based mine water concentrate into a coagulation tank and a flocculation tank for chemical softening treatment, followed by settling in a sedimentation tank to obtain softened effluent; wherein,

[0007] Lime or sodium hydroxide and coagulant are added to the coagulation tank for coagulation treatment of the concentrated mine water.

[0008] Soda ash, coagulant aid, and seed crystals of inducing agent are added to the flocculation tank to perform flocculation treatment and precipitation reaction on the concentrated mine water after coagulation treatment. The residence time in the flocculation tank is 14-45 minutes, of which the precipitation reaction time is 6-30 minutes. The excess of soda ash is 1.5-2.5 mmol / L relative to the theoretical dosage.

[0009] Furthermore, the sulfate-based mine water concentrate has a concentration of 10,000-80,000 mg / L, an SO42-:Cl- content ratio ≥1:1, and a calcium hardness of 1-1,000 mg / L.

[0010] Furthermore, the coagulant is polyferric sulfate (PFS) or other reagents with similar coagulation effects, and the present invention does not limit the specific type of coagulant; and / or, the soda ash is sodium carbonate, and the coagulant aid is high-salt resistant polyacrylamide (PAM) or other reagents with similar effects, and the present invention does not limit the specific type of coagulant aid.

[0011] Furthermore, the inducing seed crystal is Fe. 3+ One or more of the following: seed crystals, calcium carbonate seed crystals, and calcium sulfate seed crystals.

[0012] Furthermore, the residence time in the flocculation tank includes the flocculation treatment time and the sedimentation reaction time, wherein the flocculation treatment time is 8 to 15 minutes.

[0013] Furthermore, the retention time in the coagulation tank is 0.5 to 2 minutes.

[0014] Furthermore, the sulfate-based mine water concentrate is a concentrate obtained by filtering and membrane concentration of mine water.

[0015] Furthermore, the method further includes: filtering and membrane concentrating the softened effluent to obtain recycled water.

[0016] Furthermore, the coagulation treatment, as well as the sedimentation reaction and flocculation treatment, are all carried out under a stirring state.

[0017] Furthermore, the calcium hardness of the softened water is less than 20 mg / L.

[0018] A second aspect of the present invention provides a mine water hardening system based on sulfate as the main component, comprising, in the order of mine water intake:

[0019] The first filter is used to receive mine water and filter out suspended solids and colloids in the water;

[0020] The first membrane concentration unit is used to receive the effluent from the first filter and treat it by reverse osmosis to obtain primary reverse osmosis permeate and concentrate.

[0021] A coagulation tank, in which lime or sodium hydroxide and a coagulant are added, is used to receive the concentrate and coagulate it.

[0022] A flocculation tank, in which soda ash, coagulant aid and seed crystals of inducer are added, is used to receive the effluent from the coagulation tank and to carry out sedimentation reaction and flocculation treatment.

[0023] Sedimentation tanks are used to receive effluent from flocculation tanks and allow it to settle, resulting in softened effluent.

[0024] The second filter is used to receive softened water and filter out suspended solids in the water.

[0025] The second membrane concentration unit is used to receive the effluent from the second filter and treat it by reverse osmosis to obtain secondary reverse osmosis permeate and concentrate.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] This invention provides a method for hardening sulfate-based mine water concentrate. The concentrate is sequentially passed through a coagulation tank and a flocculation tank for chemical treatment, then settled in a sedimentation tank to obtain softened effluent. In the coagulation tank, lime coagulant is added for coagulation treatment of the mine water concentrate. In the flocculation tank, soda ash, coagulant aid, and seed crystal inducer are added for precipitation and flocculation treatment of the coagulated mine water concentrate. Soda ash is added in excess at 1.5–2.5 mmol / L, and the residence time in the flocculation tank is 14–45 minutes, with the precipitation reaction time being 6–30 minutes.

[0028] This invention addresses the issue of high dosage and inadequate hardness removal in the chemical softening unit of Na2SO4-based concentrates used in zero-discharge mine water processes. Through the above steps, it focuses on chemical hardness removal of Na2SO4-based mine water concentrates or high-mineralization mine water in the process. It employs an integrated approach, including extending reaction time, scientifically determining dosage, and using seed-induced scale inhibitors to improve hardness removal efficiency. This results in softened effluent with a calcium hardness below 20 mg / L, meeting the feed water requirements of downstream membrane processes. This significantly reduces the scaling risk and cleaning / maintenance costs of membrane processes, facilitating the efficient resource utilization of mine water.

[0029] Other features and advantages of the present invention will be described in detail through the following specific embodiments. Attached Figure Description

[0030] Figure 1 This is a schematic flowchart of a method for removing hardness from sulfate-based mine water concentrate provided by the present invention.

[0031] Labeling description: First filter 1, First membrane concentration device 2, Coagulation tank 3, Flocculation tank 4, Sedimentation tank 5, Second filter 6, Second membrane concentration device 7. Detailed Implementation

[0032] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0033] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] Unless otherwise specified, all reagents or instruments used in this invention are commercially available products.

[0035] This invention provides a method for hardening mine water concentrate containing sulfate as the main component, comprising the following steps: passing the sulfate-containing mine water concentrate sequentially into a coagulation tank and a flocculation tank for chemical softening treatment, followed by settling in a sedimentation tank to obtain softened effluent; wherein...

[0036] Lime or sodium hydroxide and coagulant are added to the coagulation tank for coagulation treatment of the concentrated mine water.

[0037] Soda ash, coagulant aid, and seed crystals of inducing agent are added to the flocculation tank to perform flocculation treatment and precipitation reaction on the concentrated mine water after coagulation treatment. The residence time in the flocculation tank is 14-45 minutes, of which the precipitation reaction time is 6-30 minutes. The excess of soda ash is 1.5-2.5 mmol / L relative to the theoretical dosage.

[0038] The inventors of this invention have discovered that, for the chemical softening treatment of sulfate-based mine water concentrate, longer coagulation and flocculation times are not necessarily better. This is because, under sulfate-based water conditions, extending the treatment time can lead to calcium ion re-dissolution, which is detrimental to improving the hardness removal effect. In addition, extending the sedimentation reaction time in industrial applications results in a longer residence time in the reactor, requiring a larger reactor per unit volume of water treated, thus increasing costs.

[0039] When adding sodium carbonate to mine water with sodium sulfate as the main component, this invention also needs to comprehensively consider various factors. For example, in mine water systems with high sodium sulfate concentrations, sulfate ions will effectively combine with calcium ions, increasing the difficulty of calcium carbonate precipitation. Therefore, this invention uses an excess of soda ash of 1.5–2.5 mmol / L, such as excesses of 1.6 mmol / L, 1.7 mmol / L, 1.8 mmol / L, 1.9 mmol / L, 2.0 mmol / L, 2.1 mmol / L, 2.2 mmol / L, 2.3 mmol / L, and 2.4 mmol / L.

[0040] In summary, this application employs a flocculation tank retention time of 14–45 minutes (e.g., 15, 16, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, or 42 minutes, etc.) with an excess of 1.5–2.5 mmol / L of soda ash and a precipitation reaction time of 6–30 minutes (e.g., 8, 10, 12, 15, 18, 20, 22, 25, or 28 minutes, etc.) under the condition of 1.5–2.5 mmol / L excess of soda ash, and a precipitation reaction time of 6–30 minutes (e.g., 8, 10, 12, 15, 18, 20, 22, 25, or 28 minutes, etc.). The combination of these parameters can achieve better hardness removal effect in sulfate-based mine water concentrate.

[0041] In some embodiments, the sulfate-based mine water concentrate has a concentration of 10,000-80,000 mg / L, an SO42-:Cl- content ratio ≥1:1, and a calcium hardness of 1-1,000 mg / L.

[0042] In some embodiments, the coagulant is polyferric sulfate (PFS); and / or, the soda ash is sodium carbonate, and the coagulant aid is high-salt resistant polyacrylamide (PAM).

[0043] In some embodiments, based on the liquid system treated in the coagulation tank, the dosage of coagulant such as PFS is 10-200 mg / L, and based on the liquid system treated in the flocculation tank, the dosage of coagulant aid such as PAM is 1-2 mg / L.

[0044] In this invention, the amount of lime added is calculated as follows:

[0045] Ca(OH)2=37x(CO2+A+HMg+α)÷ε1(mg / L)

[0046] Where: A -- Total alkalinity of raw water (H) (mmol / L)

[0047] CO2 -- The content of free carbon dioxide in raw water (mmol / L)

[0048] HMg -- Magnesium hardness of raw water (1 / 2Mg) 2+ (calculated) (mmol / L)

[0049] ε1 -- Purity of lime

[0050] α--Lime (Ca(OH)2) in excess, typically 0.2-0.4 mmol / L.

[0051] 37--1 / 2 Ca(OH)2 molar mass (mmol / L).

[0052] In this invention, the theoretical dosage of soda ash is calculated as follows:

[0053] Na₂CO₃ = 53(Hy + β) ÷ ε² (mg / L)

[0054] Among them: H Y --Permanent hardness of raw water (1 / 2Ca) 2+ +1 / 2Mg 2+ (calculated) (mmol / L)

[0055] β--Excess soda ash (calculated as 1 / 2 Na2CO3) (mmol / L), the theoretical dosage is taken as 0 mmol / L, but the process of this invention generally uses 1.5-2.5 mmol / L.

[0056] ε2 -- Purity (%) of industrial soda ash

[0057] 53--Molar mass of 1 / 2 Na₂CO₃ (mmol / L)

[0058] In some embodiments, the flocculation treatment time is preferably 8 to 15 minutes.

[0059] In some implementations, the retention time in the coagulation tank is 0.5 to 2 minutes, such as 1 minute, 1.5 minutes, or 2 minutes.

[0060] In some embodiments, the inducing seed crystal is Fe. 3+ One or more of calcium carbonate and calcium sulfate seed crystals are added, based on the liquid system being treated in the flocculation tank, with a seed crystal dosage of 10–100 g / L.

[0061] Chemical softening (hardness removal) of mine water is performed after the membrane concentration process. Scale inhibitors are required during membrane concentration, especially in concentrate systems primarily composed of sodium sulfate, where scale inhibitors are typically present. Scale inhibitors themselves disperse sparingly soluble inorganic salts in water and prevent or interfere with their precipitation and scaling on metal surfaces. Residual scale inhibitors, however, can inhibit softening. This invention involves adding Fe to the flocculation tank. 3+ Calcium carbonate and calcium sulfate seed crystals can reduce the softening and inhibiting effect of scale inhibitors. Other wastewaters, such as industrial wastewater, are generally softened and dehardened before concentration, with less consideration given to the presence of scale inhibitors. Therefore, the above-mentioned seed crystal addition is an effective method to improve hardening removal efficiency based on specific sodium sulfate-based mine water concentrates.

[0062] In some embodiments, the sulfate-based mine water concentrate is a concentrate obtained by filtration and membrane concentration of mine water.

[0063] In some embodiments, the method further includes: filtering and membrane concentrating the softened effluent to obtain recycled water.

[0064] In some embodiments, the coagulation treatment, sedimentation reaction, and flocculation treatment are all carried out under stirring conditions. The specific stirring parameters are the same as those in conventional processes and will not be described in detail here.

[0065] In some embodiments, the calcium hardness of the softened effluent is less than 20 mg / L.

[0066] The following will describe the mine water concentrate hardening method and system of the present invention in a nested manner. It should be understood that the mine water concentrate hardening method and system of the present invention can be used in combination or exist independently of each other, and are not limited by the nested description method.

[0067] Reference Figure 1 The mine water concentrate hardening system of the present invention includes, in the order of mine water intake, the following components: a first filter 1, a first membrane concentration device 2, a coagulation tank 3, a flocculation tank 4, a sedimentation tank 5, a second filter 6, and a second membrane concentration device 7.

[0068] In this invention, mine water is sent to the first filter 1 to remove suspended solids and colloids from the water, and the produced water meets the reverse osmosis membrane feed water quality requirements (SDI<5). The first filter 1 can be an iron removal filter or an ultrafiltration membrane, etc.

[0069] In this invention, the mine water treated by the first filter is sent to the first membrane concentration device 2 for primary concentration of the mine water to obtain primary reverse osmosis permeate and concentrate. The primary reverse osmosis permeate enters the finished product water tank.

[0070] In this invention, the concentrate from the first membrane concentration device 2 is sequentially sent to the coagulation tank 3 and the flocculation tank 4 for chemical softening treatment to remove calcium, magnesium hardness and suspended matter, and then enters the sedimentation tank 5 for settling.

[0071] In some embodiments, a dosing device and a mixing mixer are provided in the coagulation tank 3. The dosing and water quality reaction, as well as the mixing, accelerate the reaction time and the flocculation state.

[0072] In some embodiments, a flow guide tube is installed in the flocculation tank 4 to divide the flocculation reaction into two parts, each with different flocculation energy. The flocculation speed inside the flow guide tube is fast, and it is stirred by an axial flow impeller. The plugging condition between the outer wall of the flow guide tube and the tank wall results in slow flocculation, ensuring the increase and density of the floc.

[0073] In some implementations, a sludge scraper is installed in the sedimentation tank 5 to promote sludge settling and thickening. The thickening zone can be divided into two layers: one above the conical circulation cylinder and one below the conical circulation cylinder. Part of the thickened sludge is extracted from the thickening tank and pumped back to the inlet at the bottom of the guide cylinder, while the remaining thickened sludge is discharged to the sludge treatment system as excess sludge.

[0074] In this invention, the softened effluent from the sedimentation tank is filtered through a second filter 6 to remove suspended solids, and then enters a second membrane concentration device 7 for secondary concentration to obtain secondary reverse osmosis permeate and concentrate. The secondary reverse osmosis permeate enters the finished water tank. The second filter 6 can be an iron removal multi-media filter or an ultrafiltration membrane, etc.

[0075] In some embodiments, the concentrated water obtained from the second membrane concentration unit 7 is sent to a weak acid cation bed for secondary hardening removal; the permeate from the weak acid cation bed enters the first membrane concentration unit 2 for tertiary concentration; the permeate from the tertiary reverse osmosis enters the finished water tank; the concentrated water is sent to the evaporation crystallization unit; the water in the finished water tank is then pumped by the finished water lift pump to the production fire water tank for coal mine production, domestic water use, or comprehensive external use.

[0076] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0077] Example 1

[0078] The primary membrane concentrate has a mineralization of 15000 mg / L, an SO42-:Cl- content ratio of 9:1, and a calcium hardness of 2000 mg / L (calculated as CaCO3). Lime and coagulant PFS (100 mg / L) are added to the coagulation tank, with a residence time of 2 minutes. Soda ash and coagulant PAM (1.5 mg / L) are added to the flocculation tank. The concentrate contains a scale inhibitor, a reverse osmosis membrane-specific acidic phosphorus-containing scale inhibitor used on-site. In addition to sodium carbonate and high-salt-tolerant PAM, 10 g / L of calcium carbonate crystals are added to the flocculation tank, with an excess of 2 mmol / L of sodium carbonate. The residence time in the flocculation tank (including flocculation time and sedimentation reaction time) is 30 minutes, and the sodium carbonate precipitation reaction time is 15 minutes. ICP testing shows the calcium ion concentration is 4.5 mg / L in the effluent from the chemical softening system.

[0079] In this embodiment, the precipitation reaction time is extended from 5 minutes in the traditional process to 15 minutes, and the residence time in the flocculation tank is extended to 30 minutes (the precipitation reaction occurs in the flocculation tank). Sodium carbonate is added in excess at 2 mmol / L, and an inducing agent is added simultaneously, resulting in the best hardening removal effect.

[0080] Example 2

[0081] Similar to Example 1, except that: the concentrate with a mineralization of 10000 mg / L in the primary membrane concentrate has an SO42-:Cl- content ratio of 5:1 and a calcium hardness of 1000 mg / L (calculated as CaCO3).

[0082] The retention time in the flocculation tank (including flocculation time and sedimentation reaction time) is 25 minutes, the sodium carbonate sedimentation reaction time is 10 minutes, and the excess sodium carbonate is 1.5 mmol / L. The calcium hardness of the effluent from the chemical softening system is 8.4 mg / L.

[0083] Example 3

[0084] Similar to Example 1, except that: the concentrate with a mineralization of 50,000 mg / L in the primary membrane concentrate has an SO42-:Cl- content ratio of 5:1 and a calcium hardness of 1,000 mg / L (calculated as CaCO3).

[0085] The retention time in the flocculation tank (including flocculation time and sedimentation reaction time) is 30 minutes, the sodium carbonate sedimentation reaction time is 15 minutes, the excess sodium carbonate is 2.0 mmol / L, the calcium sulfate seed crystals are added at 50 g / L, and the calcium hardness of the effluent from the chemical softening system is 8.2 mg / L.

[0086] Example 4

[0087] Similar to Example 1, except that: the concentrate with a mineralization of 80,000 mg / L in the primary membrane concentrate has an SO42-:Cl- content ratio of 5:1 and a calcium hardness of 1,000 mg / L (calculated as CaCO3).

[0088] The retention time in the flocculation tank (including flocculation time and sedimentation reaction time) is 45 minutes, the sodium carbonate sedimentation reaction time is 30 minutes, the excess sodium carbonate is 2.5 mmol / L, the calcium sulfate seed crystals are added at 70 g / L, and the calcium hardness of the effluent from the chemical softening system is 6.6 mg / L.

[0089] Comparative Example 1

[0090] The concentrate with a mineralization of 15000 mg / L in the primary membrane concentrate has a Cl-:SO42- content ratio of 9:1 and a calcium hardness of 2000 mg / L (calculated as CaCO3). The sodium carbonate in the flocculation tank is in excess at 1 mmol / L, the flocculation tank residence time is 20 minutes, and the sodium carbonate precipitation reaction time is 5 minutes. The calcium hardness of the effluent from the chemical softening system is 7.5 mg / L.

[0091] In this comparative example, the mine water, which is mainly composed of sodium chloride, achieved a good hardness removal effect with a relatively short precipitation reaction time of 5 minutes and an excess of 1 mmol / L of sodium carbonate.

[0092] Comparative Example 2

[0093] The concentrate from the primary membrane has a mineralization of 15000 mg / L, an SO42-:Cl- content ratio of 9:1, and a calcium hardness of 2000 mg / L (calculated as CaCO3). Lime and coagulant PFS (100 mg / L) are added to the coagulation tank, with a residence time of 2 minutes. Soda ash and coagulant aid PAM (1.5 mg / L) are added to the flocculation tank. Sodium carbonate is added in excess at 1 mmol / L in the flocculation tank, with a residence time of 20 minutes and a sodium carbonate precipitation reaction time of 5 minutes. The effluent from the chemical softening system has a calcium hardness of 25.5 mg / L.

[0094] In this comparative example, the mine water, which is mainly composed of sodium sulfate, did not achieve ideal hardness removal even with an excess of 1 mmol / L of sodium carbonate and a precipitation reaction time of 5 minutes.

[0095] Comparative Example 3

[0096] The concentrate with a mineralization of 15000 mg / L in the primary membrane concentrate had an SO42-:Cl- content ratio of 9:1 and a calcium hardness of 2000 mg / L (calculated as CaCO3). The flocculation tank contained an excess of 1 mmol / L of sodium carbonate. The flocculation tank retention time (including flocculation time and sedimentation reaction time) was 30 minutes, and the sedimentation reaction time was 15 minutes. The addition of lime, coagulant, and coagulant aid was the same as in Comparative Example 2. The calcium ion concentration was determined by ICP testing, and the calcium hardness of the effluent from the chemical softening system was 14.5 mg / L.

[0097] The sedimentation reaction time in this comparative example was extended from 5 minutes in the traditional process to 15 minutes, and the residence time in the flocculation tank was extended to 30 minutes, which significantly improved the hardening removal effect compared with comparative example 2.

[0098] Comparative Example 4

[0099] The concentrate with a mineralization of 15000 mg / L in the primary membrane concentrate had an SO42-:Cl- content ratio of 9:1 and a calcium hardness of 2000 mg / L (calculated as CaCO3). The sodium carbonate in the flocculation tank was in excess at 2 mmol / L. The residence time in the flocculation tank was 30 minutes, and the sodium carbonate precipitation reaction time was 15 minutes. The addition of lime, coagulant, and coagulant aid was the same as in Comparative Example 2. The calcium hardness of the effluent from the chemical softening system was 10.6 mg / L.

[0100] In this example, the precipitation reaction time was extended from 5 minutes in the traditional process to 15 minutes, and the residence time in the flocculation tank was extended to 30 minutes (the precipitation reaction occurred in the flocculation tank). At the same time, an excess of sodium carbonate of 2 mmol / L was added, which further improved the hardening removal effect compared with Comparative Example 3.

[0101] Comparative Example 5

[0102] The concentrate from the primary membrane has a mineralization of 15000 mg / L, an SO42-:Cl- content ratio of 9:1, and a calcium hardness of 2000 mg / L (calculated as CaCO3). The concentrate contains a scale inhibitor, specifically an acidic phosphorus-containing scale inhibitor for reverse osmosis membranes used on-site. The addition of lime, coagulant, and coagulant aid is the same as in Comparative Example 2. The residual Ca in the effluent from the chemical softening system... 2+ The concentration is 96 mg / L.

[0103] This comparative example illustrates that residual scale inhibitors in the system can affect the hardening effect.

[0104] Comparative Example 6

[0105] The concentrate from the primary membrane has a mineralization of 15000 mg / L, an SO42-:Cl- content ratio of 9:1, and a calcium hardness of 2000 mg / L (calculated as CaCO3). The concentrate contains a scale inhibitor, specifically an acidic phosphorus-containing scale inhibitor for reverse osmosis membranes used on-site. In addition to sodium carbonate and high-salt tolerant PAM, 10 g / L of calcium carbonate crystals as an inducer are added to the flocculation tank. The retention time in the flocculation tank is 30 minutes, and the sodium carbonate precipitation reaction time is 15 minutes. The addition of lime, coagulant, and coagulant aid is the same as in Comparative Example 2. The residual Ca in the effluent from the chemical softening system... 2+ The concentration was 23.2 mg / L.

[0106] In this example, the sedimentation reaction time was extended from 5 minutes in the traditional process to 15 minutes, and the residence time in the flocculation tank was extended to 30 minutes (the sedimentation reaction takes place in the flocculation tank). At the same time, the addition of an inducing agent can also improve the hardening removal effect.

[0107] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are within the spirit and scope of the present invention.

Claims

1. A method for removing hardness from sulfate-based mine water concentrate, characterized in that, The process includes the following steps: A concentrated mine water solution, primarily containing sulfates, is sequentially passed through a coagulation tank and a flocculation tank for chemical softening treatment, and then sent to a sedimentation tank for settling to obtain softened effluent; wherein, Lime or sodium hydroxide and coagulant are added to the coagulation tank for coagulation treatment of the concentrated mine water. Soda ash, coagulant aid, and seed crystals of inducing agent are added to the flocculation tank to perform flocculation treatment and precipitation reaction on the concentrated mine water after coagulation treatment. The residence time in the flocculation tank is 14-45 minutes, of which the precipitation reaction time is 6-30 minutes. The excess of soda ash is 1.5-2.5 mmol / L relative to the theoretical dosage.

2. The method for removing hardness from mine water concentrate according to claim 1, characterized in that, The sulfate-based mine water concentrate has a concentration of 10,000-80,000 mg / L, an SO42-:Cl- content ratio ≥1:1, and a calcium hardness of 1-1,000 mg / L.

3. The method for removing hardness from mine water concentrate according to claim 1, characterized in that, The coagulant is polyferric sulfate; and / or, the soda ash is sodium carbonate, and the coagulant aid is high-salt resistant polyacrylamide.

4. The method for removing hardness from mine water concentrate according to claim 1, characterized in that, The inducing agent seed crystal is Fe. 3+ One or more of the following: seed crystals, calcium carbonate seed crystals, and calcium sulfate seed crystals.

5. The method for removing hardness from mine water concentrate according to claim 1, characterized in that, The retention time in the flocculation tank includes the flocculation treatment time and the sedimentation reaction time, wherein the flocculation treatment time is 8 to 15 minutes; and / or, the retention time in the coagulation tank is 0.5 to 2 minutes.

6. The method for removing hardness from mine water concentrate according to claim 1, characterized in that, The sulfate-based mine water concentrate is a concentrate obtained by filtering and membrane concentration of mine water.

7. The method for removing hardness from mine water concentrate according to claim 1, characterized in that, The method further includes: filtering and membrane concentration of the softened effluent to obtain recycled water.

8. The method for removing hardness from mine water concentrate according to any one of claims 1-7, characterized in that, The coagulation treatment, as well as the sedimentation reaction and flocculation treatment, are all carried out under stirring conditions.

9. The method for removing hardness from mine water concentrate according to any one of claims 1-8, characterized in that, The calcium hardness of the softened water is less than 20 mg / L.

10. A sulfate-based mine water hardening system, characterized in that, According to the order of mine water intake, the following are included in sequence: The first filter is used to receive mine water and filter out suspended solids and colloids in the water; The first membrane concentration unit is used to receive the effluent from the first filter and treat it by reverse osmosis to obtain primary reverse osmosis permeate and concentrate. A coagulation tank, in which lime or sodium hydroxide and a coagulant are added, is used to receive the concentrate and coagulate it. A flocculation tank, in which soda ash, coagulant aid and seed crystals of inducer are added, is used to receive the effluent from the coagulation tank and to carry out sedimentation reaction and flocculation treatment. Sedimentation tanks are used to receive effluent from flocculation tanks and allow it to settle, resulting in softened effluent. The second filter is used to receive softened water and filter out suspended solids in the water. The second membrane concentration unit is used to receive the effluent from the second filter and treat it by reverse osmosis to obtain secondary reverse osmosis permeate and concentrate.

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