Method for removing hardness ions in water by using industrial tail gas micro-nano bubbles

Abstract

The application discloses a method for removing hardness ions in water by using industrial tail gas micro-nano bubbles, and relates to the technical field of water treatment. The method comprises the steps of adjusting an alkali, industrial tail gas softening and high-fiber rotating disc filtration. In the step of adjusting an alkali, the pH of high-hardness water is adjusted to be alkaline, so that the slightly soluble hardness substances Ca(HCO3)2 and Mg(HCO3)2 in the water are converted into CaCO3 and MgCO3 precipitates, and the generation of HCO3 ‑ in the hydrolysis process of the step of industrial tail gas softening is prevented; in the step of industrial tail gas softening, micro-nano industrial tail gas bubbles are introduced into the water, CO3 ‑ and SO3 2‑ generated by hydrolysis are used to convert Ca 2+ and Mg 2+ in high-hardness water into precipitates; and in the step of high-fiber rotating disc filtration, the precipitates generated in the step of industrial tail gas softening are subjected to solid-liquid separation by a high-fiber rotating disc.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically a method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas. Background Technology

[0002] In coal gasification processes, ash water typically exhibits high hardness, high turbidity, and high alkalinity, easily forming deposits, scale, and corrosion inside equipment, thus affecting its normal operation and lifespan. Common descaling methods include chemical descaling, ultrasonic physical descaling, and electrochemical descaling. Traditional chemical descaling primarily involves directly adding sodium carbonate to convert hardness ions in the water into precipitates for removal. However, this method suffers from drawbacks such as high chemical costs, severe equipment corrosion (due to high sodium ion introduction), and low automation (chemical preparation is done manually).

[0003] Therefore, this invention proposes a method for removing hardness ions from water using micro-nano industrial exhaust gas bubbles to solve the above-mentioned problems. Summary of the Invention

[0004] The technical problem solved by this invention is that traditional chemical descaling methods mainly involve directly adding sodium carbonate to convert hardness ions in the water into precipitates for removal. However, this method has disadvantages such as high chemical costs, severe equipment corrosion (due to high sodium ion introduction), and low automation (chemical preparation is done manually).

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas is described below:

[0007] 1) Adjusting alkalinity: Add alkaline solution dropwise to water with high hardness to adjust the alkalinity;

[0008] 2) Industrial exhaust gas softening: Micro-nano bubbles containing industrial exhaust gas are introduced into the high-hardness water after alkali adjustment to form a precipitate;

[0009] 3) High-fiber rotary disc filtration: After sedimentation, the high-hardness water is directed to the high-fiber rotary disc filter to trap the sediment and separate it to obtain clean water.

[0010] Preferably, the concentration of the alkali solution is 30-50%; the dropping rate of the alkali solution is 6.5-7.0 mL / s, and the dropping time is 40-200 s;

[0011] Preferably, the alkaline solution is not limited to alkaline substances such as sodium hydroxide and potassium hydroxide;

[0012] Preferably, the pH of the high-hardness water after alkali adjustment is 10-14, which enables the slightly soluble hardness substances (Ca(HCO3)2, Mg(HCO3)2) in the water to be converted into CaCO3 and MgCO3 to undergo preliminary precipitation, while preventing the generation of HCO3 during the hydrolysis process in the industrial exhaust gas softening step. - ;

[0013] Preferably, the diameter of the micro-nano bubbles is 20-80μm; the ventilation rate of the industrial exhaust gas is 5-8L / min, and the ventilation time is 3-6min; depending on the hardness of the incoming water, the delivery volume of the industrial exhaust gas can be precisely controlled by adjusting the ventilation time to reduce the overflow of the industrial exhaust gas.

[0014] Preferably, the micro-nano bubbles are added in small, multi-stage steps; this allows for more complete hydrolysis of carbon dioxide and sulfur dioxide in alkaline water, reducing the hardness of Ca2+ ions. 2+ Mg 2+ The conversion and precipitation are more thorough, and at the same time, the addition of small amounts in multiple stages can reduce the spillover of industrial exhaust gas into the environment;

[0015] Preferably, the working principle of the high-fiber disc filter is to use a negative pressure pump to trap hard ion precipitates when water passes through the high-fiber disc; the trapped ion precipitates are then removed from the high-fiber disc by centrifugal force driven by a motor; at the same time, high-pressure water is used to backwash the high-fiber disc to further remove the precipitates and regenerate the disc.

[0016] Preferably, the purified water obtained in step 3) is diverted to a fiber filter column for filtration; wherein the fiber filter column is filled with MOF-fiber composite material; wherein the preparation method of MOF-fiber composite material is as follows:

[0017] Step 1: Take chromium nitrate nonahydrate, cobalt nitrate hexahydrate, and 2-aminoterephthalic acid and place them in N,N-dimethylformamide. Stir for 2-3 hours, heat to react, centrifuge, wash, and dry to obtain MOF material;

[0018] Step 2: Dissolve polyacrylonitrile in N,N-dimethylformamide, add the MOF material prepared in Step 1, stir for 12 h to obtain composite spinning solution, perform electrospinning to obtain MOF-PAN fiber;

[0019] Step 3: Hydrolyze the MOF-PAN fiber, place it in sodium hydroxide solution, heat and reflux for 4 hours, immerse it in hydrochloric acid solution and stand for 2 hours, then take it out, wash and dry it, crosslink it, mix it with polyethyleneimine aqueous solution, heat and reflux for 1 hour, take it out and dry it, and repeat the first hydrolysis step and crosslinking step in sequence to obtain MOF-PAN-PEI fiber.

[0020] Step 4: Mix MOF-PAN-PEI fibers and chloroacetic acid, place them in deionized water, add sodium carbonate to adjust the pH, heat the reaction for 4-6 hours, remove the mixture, wash it, place it in hydrochloric acid solution and let it stand for 20-30 minutes, then transfer it to sodium hydroxide solution and soak it for 1-2 hours. Wash it with water and dry it to obtain MOF-fiber composite material.

[0021] Preferably, in step 1, the molar ratio of chromium nitrate nonahydrate, cobalt nitrate hexahydrate, and 2-aminoterephthalic acid is 1:2:3. The process conditions for the heating reaction in step 1 are: heating to 150-180°C within 5-6 hours and holding the reaction at that temperature for 24 hours.

[0022] Preferably, in step 2, the ratio of polyacrylonitrile, MOF material, and N,N-dimethylformamide is 1:(1-2):19; the electrospinning process is as follows: 10mL syringe, spinning voltage of 20-25kV, spinning speed of 0.0004-0.0008mm / s, and receiving distance of 20cm;

[0023] Preferably, in step 3, the heating reflux temperature is 100°C, the ratio of MOF-PAN fiber to polyethyleneimine aqueous solution in the crosslinking process is 1:50, and the mass fraction of polyethyleneimine in the polyethyleneimine aqueous solution is 1%.

[0024] Preferably, in step 4, the ratio of MOF-PAN-PEI fiber to chloroacetic acid is 2:(3-4), and the heating temperature is 50-60℃.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. In the alkali adjustment step of this invention, the pH of high-hardness water is adjusted by controlling the dropping rate and dropping time. This achieves the initial precipitation of slightly soluble hardness substances Ca(HCO3)2 and Mg(HCO3)2 in the water into CaCO3 and MgCO3, while preventing the generation of HCO3 during the hydrolysis process in the subsequent industrial tail gas softening step. - To quickly stabilize the pH of the system, the circulation pump was turned on during the addition of the alkali solution.

[0027] 2. This invention incorporates industrial waste gas to soften the water after alkali adjustment. A micro-nano bubble generator delivers the industrial waste gas to the high-hardness water. The micro-nano bubbles, with their extremely large specific surface area, rapidly hydrolyze the industrial waste gas. The aeration time of the industrial waste gas is adjusted according to the water hardness, precisely controlling the delivery volume, reducing waste gas overflow, and improving utilization. Specifically, upon contact with the high-hardness water, the micro-nano bubbles in the industrial waste gas completely hydrolyze carbon dioxide and sulfur dioxide to generate CO3. 2- and SO3 2- With the hardness ions Ca in the water 2+Mg 2+ The water is converted into CaCO3 / CaSO3 and MgCO3 precipitates. Nitrogen gas is used to stir the water and accelerate the precipitation. Micro-nano bubbles are added in small amounts and in multiple stages to make CO2 and SO2 hydrolyze more fully in alkaline water and hardness ions precipitate more thoroughly. At the same time, small amounts and multiple stages of addition can reduce the leakage of industrial exhaust gas into the environment and reduce pollution.

[0028] 3. In this invention, a high-fiber rotating disc is set up for filtration after the industrial exhaust gas is softened. A negative pressure pump is used to make the water body pass through the high-fiber rotating disc, and the hardness ions generated during the softening process of the industrial exhaust gas are precipitated and intercepted. The intercepted precipitate is removed from the high-fiber rotating disc by centrifugal force driven by a motor. At the same time, high-pressure water can be used to backwash the high-fiber rotating disc to further remove the precipitate and realize the regeneration of the high-fiber disc.

[0029] 4. This invention incorporates a fiber filter column after high-fiber rotary filtration. The fiber filter column uses a composite material obtained by combining a metal-organic framework with PAN-PEI fibers for post-treatment. PAN-PEI is carboxylated to form imine diacetic acid, which has excellent adsorption properties for complex multivalent metal ions. At the same time, the doping of the metal-organic framework improves the stability of the spun fibers and provides more adsorption active sites, further accelerating the post-treatment impurity removal process.

[0030] 5. Compared with traditional softening technologies, this invention does not require the use of chemical agents such as sodium bicarbonate, does not produce secondary pollution, and uses industrial exhaust gas as the softening agent, thus achieving waste recycling and reducing greenhouse gas emissions. Secondly, it is simple and efficient to operate, requiring no complex equipment or cumbersome processes. The micro-nano bubbles used accelerate the hydrolysis of industrial exhaust gas in water, achieving hardness removal from large volumes of water in a short time. In addition, the equipment has a long service life and low maintenance costs. Most importantly, it realizes the recycling of industrial production water, solving the water shortage problem.

[0031] 6. The present invention provides a method for removing hardness ions from water using micro-nano industrial exhaust gas bubbles, which is suitable for hardening high-hardness water bodies, especially large-volume, difficult-to-treat high-hardness water bodies such as concentrated brine produced by reverse osmosis and coal chemical ash water. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The concentration of industrial exhaust gas in the experiment was expressed as CO2 concentration; the average Mw of polyacrylonitrile was ~150,000, and the Mw of polyethyleneimine was 3,000.

[0035] Example 1: This example provides a method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas. The specific steps are as follows:

[0036] High-hardness incoming water from a flame retardant materials company was selected, with the following water quality parameters: pH=7.7, hardness=870mg / L (calculated as calcium carbonate); the treatment volume was 100L; the alkaline solution was 32% NaOH solution.

[0037] 1) Add alkaline solution to the high-hardness water body for 45 seconds at a dropping rate of 6.8 mL / s, for a total of 306 mL of alkaline solution, i.e. 1.0 g / L NaOH. Mix the solution with a circulating pump for 5 minutes and the pH is measured to be 10.3.

[0038] 2) Industrial exhaust gas was introduced into micro-nano bubbles at a flow rate of 6L / min for 4 minutes, totaling 0.24L CO2 / L; after passing through a high-fiber rotating disc filter, the water was sampled and the hardness was measured to be 500mg / L, a decrease of 42.6%.

[0039] Example 2: This example provides a method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas. The specific steps are as follows:

[0040] High-hardness incoming water from a flame retardant materials company was selected, with the following water quality parameters: pH=7.7, hardness=870mg / L (calculated as calcium carbonate); the treatment volume was 100L; the alkaline solution was 32% NaOH solution.

[0041] 1) Add alkaline solution to the high-hardness water body for 80 seconds at a dropping rate of 6.8 mL / s, for a total of 544 mL of alkaline solution, i.e. 1.85 g / L NaOH. Mix the solution with a circulating pump for 5 minutes and the pH is measured to be 11.1.

[0042] 2) Industrial exhaust gas was introduced into micro-nano bubbles at a flow rate of 6L / min for 4 minutes, totaling 0.24L CO2 / L; after passing through a high-fiber rotating disc filter, the water was sampled and the hardness was measured to be 425mg / L, a decrease of 51.1%.

[0043] Example 3: This example provides a method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas. The specific steps are as follows:

[0044] High-hardness incoming water from a flame retardant materials company was selected, with the following water quality parameters: pH=7.7, hardness=870mg / L (calculated as calcium carbonate); the treatment volume was 100L; the alkaline solution was 32% NaOH solution.

[0045] 1) Add alkaline solution to the high-hardness water body for 95 seconds at a dropping rate of 6.8 mL / s, for a total of 646 mL of alkaline solution, which is 2.21 g / L NaOH. Mix the solution with a circulating pump for 5 minutes and the pH is measured to be 11.2.

[0046] 2) Industrial exhaust gas micro-nano bubbles are added in small batches and in multiple stages, with a ventilation rate of 6 L / min:

[0047] Aeration for 1 minute resulted in a total CO2 / L of 0.06 L; after filtration through a high-fiber rotating disc, water samples were taken and measured to have a hardness of 460 mg / L and a pH of 10.27.

[0048] After aeration for 1 minute, a total of 0.12 L CO2 / L was obtained. After filtration through a high-fiber rotating disc, the water was sampled and the hardness was measured to be 390 mg / L, and the pH dropped to 9.69.

[0049] After 1 minute of re-aeration, a total of 0.18 L CO2 / L was obtained. After filtration through a high-fiber rotating disc, the water was sampled and the hardness was measured to be 380 mg / L, and the pH dropped to 9.17.

[0050] After 1 minute of aeration, a total of 0.24 L CO2 / L was released. Water was filtered through a high-fiber rotating disc filter and sampled. The hardness was measured to be 375 mg / L, the pH dropped to 8.68, and the hardness decreased by 56.9%.

[0051] Example 4: This example provides a method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas. The specific steps are as follows:

[0052] High-hardness incoming water from a flame retardant materials company was selected, with the following water quality parameters: pH=8.1, hardness=1216mg / L (calculated as calcium carbonate); the treatment volume was 100L; the alkaline solution was 32% NaOH solution.

[0053] 1) Add alkaline solution to the high-hardness water body for 180 seconds at a dropping rate of 6.8 mL / s, for a total of 1224 mL of alkaline solution, which is 4.19 g / L NaOH. Mix the solution with a circulating pump for 5 minutes and the pH is measured to be 11.6.

[0054] 2) Industrial exhaust gas is introduced using a small-volume, multi-stage method with micro-nano bubbles, at a flow rate of 6 L / min:

[0055] After 3 minutes of aeration, a total of 0.18 L CO2 / L was obtained. After filtration through a high-fiber rotating disc filter, the water was sampled and the hardness was measured to be 750 mg / L, and the pH dropped to 10.31.

[0056] After 1 minute of re-aeration, a total of 0.24 L CO2 / L was obtained. After filtration through a high-fiber rotating disc, the water was sampled and the hardness was measured to be 690 mg / L, and the pH dropped to 9.93.

[0057] After aeration for 1 minute, a total of 0.30 L CO2 / L was obtained. After filtration through a high-fiber rotating disc, the water was sampled and the hardness was measured to be 630 mg / L, and the pH dropped to 9.57.

[0058] After 1 minute of aeration, a total of 0.36 L CO2 / L was obtained. After filtration through a high-fiber rotating disc, the water was sampled and the hardness was measured to be 515 mg / L, the pH dropped to 9.2, and the hardness decreased by 57.6%.

[0059] Example 5: This example provides a method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas. The specific steps are as follows:

[0060] High-hardness influent from a secondary reverse osmosis system of a new materials company was selected. The water quality parameters were: pH=7.9, hardness=3350mg / L (calculated as calcium carbonate); the treatment volume was 100L; and the alkaline solution was 45% NaOH solution.

[0061] 1) Add alkaline solution to the high-hardness water body for 180 seconds at a dropping rate of 6.8 mL / s, for a total of 1224 mL of alkaline solution, which is 8.37 g / L NaOH. Mix the solution with a circulating pump for 5 minutes and the pH is measured to be 12.7.

[0062] 2) Industrial exhaust gas was introduced into micro-nano bubbles at a flow rate of 6L / min for 6 minutes, resulting in a total CO2 / L of 0.36L. After passing through a high-fiber rotating disc filter, the water was sampled and the hardness was measured to be 0mg / L, indicating a 100% reduction in hardness. The pH of the effluent was maintained at 12.5~12.6.

[0063] Example 6: This example provides a method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas. The specific steps are as follows:

[0064] High-hardness influent from a secondary reverse osmosis system of a new materials company was selected. The water quality parameters were: pH=7.9, hardness=3350mg / L (calculated as calcium carbonate); the treatment volume was 100L; and the alkaline solution was 45% NaOH solution.

[0065] 1) Add alkaline solution to the high-hardness water body for 150 seconds at a dropping rate of 6.8 mL / s, for a total of 1020 mL of alkaline solution, i.e. 6.98 g / L NaOH. Mix the solution with a circulating pump for 5 minutes and the pH is measured to be 12.3.

[0066] 2) Industrial exhaust gas micro-nano bubbles are added in small batches and in multiple stages, with a ventilation rate of 6 L / min:

[0067] Aeration for 2 minutes resulted in a total CO2 / L concentration of 0.12 L. After passing through a high-fiber rotating disc filter, water samples were taken and the hardness was measured to be 557 mg / L, with the pH maintained between 12.2 and 12.3.

[0068] After 1 minute of aeration, a total of 0.18 L CO2 / L was obtained. The water was filtered through a high-fiber rotating disc and sampled. The hardness was measured to be 0 mg / L, which represents a 100% reduction. The pH of the effluent was maintained at 12.1~12.2.

[0069] Example 7: This example provides a method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas. The specific steps are as follows:

[0070] High-hardness influent from a secondary reverse osmosis system of a new materials company was selected. The water quality parameters were: pH=8.1, hardness=4050mg / L (calculated as calcium carbonate); the treatment volume was 100L; and the alkaline solution was 45% NaOH solution.

[0071] 1) Add alkaline solution to the high-hardness water body for 120 seconds at a dropping rate of 6.8 mL / s, for a total of 816 mL of alkaline solution, i.e. 5.58 g / L NaOH. Mix the solution with a circulating pump for 5 minutes and the pH is measured to be 12.0.

[0072] 2) Industrial exhaust gas micro-nano bubbles are added in small batches and in multiple stages, with a ventilation rate of 6 L / min:

[0073] Aeration for 2 minutes resulted in a total CO2 / L of 0.12 L; after filtration through a high-fiber rotating disc filter, water samples were taken and the hardness was measured to be 700 mg / L, with the pH maintained at 11.6~11.7.

[0074] After aeration for 1 minute, a total of 0.18 L CO2 / L was obtained. The water was filtered through a high-fiber rotating disc filter, and a sample was taken. The hardness was measured to be 200 mg / L, and the pH was maintained at 11.4~11.5.

[0075] After 1 minute of aeration, a total of 0.24 L CO2 / L was released. The water was filtered through a high-fiber rotating disc filter and sampled. The hardness was measured to be 0 mg / L, indicating a 100% reduction in hardness. The pH of the effluent remained between 11.0 and 11.2.

[0076] Example 8: Referring to Example 2, a fiber filter column was added after the water outlet, wherein the volume of the MOF-fiber composite material was 1.2 m³. 3 The bulk density is 0.15 kg / m³. 3 The specific steps are as follows:

[0077] High-hardness incoming water from a flame retardant materials company was selected, with the following water quality parameters: pH=7.7, hardness=870mg / L (calculated as calcium carbonate); the treatment volume was 100L; the alkaline solution was 32% NaOH solution.

[0078] 1) Add alkaline solution to the high-hardness water body for 80 seconds at a dropping rate of 6.8 mL / s, for a total of 544 mL of alkaline solution, i.e. 1.85 g / L NaOH. Mix the solution with a circulating pump for 5 minutes and the pH is measured to be 11.1.

[0079] 2) Industrial exhaust gas micro-nano bubbles are added in small batches and in multiple stages, with a ventilation rate of 6 L / min:

[0080] After 4 minutes of aeration, a total CO2 / L was obtained; water samples were taken from the high-fiber rotary filter and the hardness was measured to be 425 mg / L, representing a 51.1% reduction in hardness.

[0081] 3) After connecting to the fiber filter column and taking a sample 10 minutes later, the hardness was measured to be 153 mg / L, and the hardness decreased by 82.41%.

[0082] The preparation steps of the MOF-fiber composite material in the fiber filter column are as follows:

[0083] Step 1: Take 4.00g of chromium nitrate nonahydrate, 5.82g of cobalt nitrate hexahydrate, and 5.43g of 2-aminoterephthalic acid and place them in 100g of N,N-dimethylformamide. After stirring for 2 hours, put them into a reaction vessel and heat them to 150℃ within 5 hours. After keeping the temperature at 150℃ for 24 hours, centrifuge, wash, and dry to obtain MOF material.

[0084] Step 2: Dissolve 5g of polyacrylonitrile in 95g of N,N-dimethylformamide, add 5g of the MOF material prepared in Step 1, stir for 12h to obtain the composite spinning solution, load it into a 10mL syringe for electrospinning, set the spinning voltage to 20kV, the spinning speed to 0.0005mm / s, and the receiving distance to 20cm to obtain MOF-PAN fibers;

[0085] Step 3: Hydrolyze the MOF-PAN fiber and place it in a 0.1% sodium hydroxide solution at a material-to-liquid ratio of 1:50. Heat to 100℃ and reflux for 4 hours. Then immerse it in a 1 mol / L hydrochloric acid solution, let it stand for 2 hours, remove it, wash it with water, dry it, and crosslink it. Mix it with a 1% polyethyleneimine aqueous solution at a material-to-liquid ratio of 1:50. Heat to reflux for 1 hour, remove it, and dry it. Repeat the first hydrolysis step and crosslinking step in sequence to obtain MOF-PAN-PEI fiber.

[0086] Step 4: Mix 10g MOF-PAN-PEI fiber and 20g chloroacetic acid, place in 1L deionized water, add sodium carbonate to adjust pH to 9, heat to 60℃ and react for 5h, then remove, wash and place in 1mol / L hydrochloric acid solution to stand for 30min, then immerse in 0.1% sodium hydroxide solution for 2h, wash with water and dry to obtain MOF-fiber composite material.

[0087] Example 9: Referring to Example 3, a fiber filter column was added after the water outlet, wherein the volume of the MOF-fiber composite material was 1.2 m³. 3 The bulk density is 0.15 kg / m³. 3 The specific steps are as follows:

[0088] High-hardness incoming water from a flame retardant materials company was selected, with the following water quality parameters: pH=7.7, hardness=870mg / L (calculated as calcium carbonate); the treatment volume was 100L; the alkaline solution was 32% NaOH solution.

[0089] 1) Add alkaline solution to the high-hardness water body for 95 seconds at a dropping rate of 6.8 mL / s, for a total of 646 mL of alkaline solution, which is 2.21 g / L NaOH. Mix the solution with a circulating pump for 5 minutes and the pH is measured to be 11.2.

[0090] 2) Industrial exhaust gas micro-nano bubbles are added in small batches and in multiple stages, with a ventilation rate of 6 L / min:

[0091] Aeration for 1 minute resulted in a total CO2 / L of 0.06 L; after filtration through a high-fiber rotating disc, water samples were taken and measured to have a hardness of 460 mg / L and a pH of 10.27.

[0092] After aeration for 1 minute, a total of 0.12 L CO2 / L was obtained. After filtration through a high-fiber rotating disc, the water was sampled and the hardness was measured to be 390 mg / L, and the pH dropped to 9.69.

[0093] After 1 minute of aeration, a total of 0.18 L CO2 / L was obtained. The water was filtered through a high-fiber rotating disc filter and sampled. The hardness was measured to be 380 mg / L and the pH dropped to 9.17.

[0094] After aeration for 1 minute, a total of 0.24 L CO2 / L was released. The water was then filtered through a high-fiber rotating disc filter and sampled. The hardness was measured to be 375 mg / L, the pH dropped to 8.68, and the hardness decreased by 56.9%.

[0095] 3) After connecting to the fiber filter column and taking a sample 10 minutes later, the hardness was measured to be 130 mg / L, and the hardness decreased by 85.06%.

[0096] The preparation steps of the MOF-fiber composite material in the fiber filter column are as follows:

[0097] Step 1: Take 4.00g of chromium nitrate nonahydrate, 5.82g of cobalt nitrate hexahydrate, and 5.43g of 2-aminoterephthalic acid and place them in 100g of N,N-dimethylformamide. After stirring for 2 hours, put them into a reaction vessel and heat them to 150℃ within 5 hours. After keeping the temperature at 150℃ for 24 hours, centrifuge, wash, and dry to obtain MOF material.

[0098] Step 2: Dissolve 5g of polyacrylonitrile in 95g of N,N-dimethylformamide, add 10g of the MOF material prepared in Step 1, stir for 12h to obtain the composite spinning solution, load it into a 10mL syringe for electrospinning, set the spinning voltage to 20kV, the spinning speed to 0.0005mm / s, and the receiving distance to 20cm to obtain MOF-PAN fibers;

[0099] Step 3: Hydrolyze the MOF-PAN fiber and place it in a 0.1% sodium hydroxide solution at a ratio of 1:50. Heat to 100°C and reflux for 4 hours. Then immerse it in a 1 mol / L hydrochloric acid solution, let it stand for 2 hours, remove it, wash it with water, dry it, and crosslink it. Mix it with a 1% polyethyleneimine aqueous solution at a ratio of 1:50. Heat and reflux for 1 hour, remove it, and dry it. Repeat the first hydrolysis step and crosslinking step in sequence to obtain MOF-PAN-PEI fiber.

[0100] Step 4: Mix 10g MOF-PAN-PEI fiber and 20g chloroacetic acid, place in 1L deionized water, add sodium carbonate to adjust pH to 9, heat to 60℃ and react for 5h, then remove, wash and place in 1mol / L hydrochloric acid solution to stand for 30min, then immerse in 0.1% sodium hydroxide solution for 2h, wash with water and dry to obtain MOF-fiber composite material.

[0101] Conclusion: This invention provides a method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas. It mainly utilizes maintaining a high pH environment, controlling the amount of industrial exhaust gas delivered, and fiber adsorption to reduce water hardness. In the experiment, good technical results were achieved for different water quality conditions.

[0102] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas, characterized in that, The specific method is as follows: 1) Adjusting alkalinity: Add alkaline solution dropwise to water with high hardness to adjust the alkalinity; 2) Industrial exhaust gas softening: Micro-nano bubbles containing industrial exhaust gas are introduced into the high-hardness water after alkali adjustment to form a precipitate; 3) High-fiber rotary disc filtration: After sedimentation, the high-hardness water is diverted to the high-fiber rotary disc filter to trap the sediment and separate it to obtain clean water; The purified water obtained from separation in step 3) is then diverted to a fiber filter column for filtration; the fiber filter column is filled with MOF-fiber composite material. The preparation method of the MOF-fiber composite material is as follows: Step 1: Take chromium nitrate nonahydrate, cobalt nitrate hexahydrate, and 2-aminoterephthalic acid and place them in N,N-dimethylformamide. Stir for 2-3 hours, heat to react, centrifuge, wash, and dry to obtain MOF material; Step 2: Dissolve polyacrylonitrile in N,N-dimethylformamide, add the MOF material prepared in Step 1, stir for 12 h to obtain composite spinning solution, perform electrospinning to obtain MOF-PAN fiber; Step 3: Hydrolyze the MOF-PAN fiber, place it in sodium hydroxide solution, heat and reflux for 4 hours, immerse it in hydrochloric acid solution and stand for 2 hours, then take it out, wash and dry it, crosslink it, mix it with polyethyleneimine aqueous solution, heat and reflux for 1 hour, take it out and dry it, and repeat the first hydrolysis step and crosslinking step in sequence to obtain MOF-PAN-PEI fiber. Step 4: Mix MOF-PAN-PEI fibers and chloroacetic acid, place them in deionized water, add sodium carbonate to adjust the pH, heat the reaction for 4-6 hours, remove the mixture, wash it, place it in hydrochloric acid solution and let it stand for 20-30 minutes, then transfer it to sodium hydroxide solution and soak it for 1-2 hours. Wash it with water and dry it to obtain MOF-fiber composite material.

2. The method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas according to claim 1, characterized in that, The alkaline solution is either sodium hydroxide or potassium hydroxide; the concentration of the alkaline solution is 30-50%; the dropping rate of the alkaline solution is 6.5-7.0 mL / s, and the dropping time is 40-200 s.

3. The method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas according to claim 1, characterized in that, The pH of high-hardness water after alkali adjustment is 10-14.

4. The method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas according to claim 1, characterized in that, The diameter of the micro-nano bubbles is 20-80μm; the ventilation rate of industrial exhaust gas is 5-8L / min, and the ventilation time is 3-6min.

5. The method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas according to claim 1, characterized in that, In step 1, the molar ratio of chromium nitrate nonahydrate, cobalt nitrate hexahydrate, and 2-aminoterephthalic acid is 1:2:

3. The process conditions for the heating reaction in step 1 are: heating to 150-180℃ within 5-6 hours and holding the reaction at that temperature for 24 hours.

6. The method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas according to claim 1, characterized in that, In step 2, the ratio of polyacrylonitrile, MOF material, and N,N-dimethylformamide is 1:(1-2):19; the electrospinning process is as follows: 10mL syringe, spinning voltage of 20-25kV, spinning speed of 0.0004-0.0008mm / s, and receiving distance of 20cm.

7. The method for removing hardness ions from water using micro-nano bubbles from industrial exhaust gas according to claim 1, characterized in that, In step 3, the heating reflux temperature is 100℃, the ratio of MOF-PAN fiber to polyethyleneimine aqueous solution in crosslinking is 1:50, and the mass fraction of polyethyleneimine in the polyethyleneimine aqueous solution is 1%; in step 4, the ratio of MOF-PAN-PEI fiber to chloroacetic acid is 2:(3-4), and the heating temperature is 50-60℃.

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