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

Abstract

The invention 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 alkali adjustment, industrial tail gas softening and high-fiber turntable filtration. Wherein in the alkali adjusting step, the pH value of a high-hardness water body is adjusted to be alkaline, slightly-soluble hardness substances Ca (HCO3) 2 and Mg (HCO3) 2 in the water are converted into CaCO3 and MgCO3 precipitates, and meanwhile HCO3 <-> is prevented from being generated in the hydrolysis process of the industrial tail gas softening step; in the industrial tail gas softening step, Ca < 2 + > and Mg < 2 + > in the high-hardness water are converted into precipitates by CO3 <-> and SO3 < 2-> generated by hydrolysis through a method of introducing micro-nano industrial tail gas bubbles into the water; and the high-fiber turntable filtering step is to realize solid-liquid separation of the precipitate generated in the industrial tail gas softening step through a high-fiber turntable.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and specifically to a method for removing hardness ions in water by using micro-nano bubbles of industrial tail gas. Background Art

[0002] During the coal gasification process, the ash water usually has characteristics such as high hardness, high turbidity, and high alkalinity, and is prone to forming sediments, scaling, and corrosion inside the equipment, thus affecting the normal operation and service life of the equipment. Common hard removal methods mainly include chemical agent scale removal method, ultrasonic physical scale removal method, and electrochemical scale removal method. The traditional chemical agent scale removal method mainly removes hardness ions in water by directly adding sodium carbonate to convert them into precipitates. However, this method has disadvantages such as high chemical agent cost, serious corrosion to equipment (high introduction amount of sodium ions), and low automation degree (preparing chemical agents is manually operated).

[0003] Therefore, the present invention proposes a method for removing hardness ions in water by using micro-nano bubbles of industrial tail gas to solve the above problems. Summary of the Invention

[0004] The technical problem solved by the present invention is that the traditional chemical agent scale removal method mainly removes hardness ions in water by directly adding sodium carbonate to convert them into precipitates. However, this method has disadvantages such as high chemical agent cost, serious corrosion to equipment (high introduction amount of sodium ions), and low automation degree (preparing chemical agents is manually operated).

[0005] To solve the above technical problems, the present invention adopts the following technical solutions: A method for removing hardness ions in water by using micro-nano bubbles of industrial tail gas, and the specific method is as follows: 1) Alkalinity adjustment: Dropwise add an alkali solution to the high-hardness water body for alkalinity adjustment; 2) Industrial tail gas softening: Transport micro-nano bubbles containing industrial tail gas to the high-hardness water body after alkalinity adjustment to form precipitates; 3) High-fiber rotary disk filtration: Transfer the high-hardness water body after precipitation to a high-fiber rotary disk filter to intercept the precipitates and separate to obtain clear water.

[0006] 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; Preferably, the alkali solution is not limited to alkaline substances such as sodium hydroxide and potassium hydroxide; Preferably, the pH of the high-hardness water body after alkalinity adjustment is 10 - 14, so as to convert slightly soluble hardness substances (Ca(HCO3)2, Mg(HCO3)2) in water into preliminary precipitates of CaCO3 and MgCO3, and at the same time prevent the generation of HCO3 during the hydrolysis process in the industrial tail gas softening step - ; Preferably, the diameter of the micro-nano bubbles is 20 - 80 μm; the ventilation volume of the industrial tail gas is 5 - 8 L / min, and the ventilation time is 3 - 6 min; according to the hardness of the incoming water, the delivery volume of the industrial tail gas can be accurately controlled by adjusting the ventilation time to reduce the overflow of the industrial tail gas. Preferably, the micro-nano bubbles are added in a small amount and multiple stages; this enables more complete hydrolysis of carbon dioxide and sulfur dioxide in the alkaline water body, and more complete conversion and precipitation of hardness ions Ca 2+ , Mg 2+ ; meanwhile, adding in small amounts and multiple stages can reduce the overflow of industrial tail gas into the environment. Preferably, the working principle of the high-fiber rotary disk filter is to use a negative pressure pump to intercept the hardness ion precipitates when water passes through the high-fiber rotary disk; the intercepted ion precipitates are driven by a motor to rotate the disk, and the precipitates are shed from the high-fiber rotary disk by centrifugal force; at the same time, the high-fiber rotary disk is backflushed with high-pressure water to further remove the precipitates and achieve disk regeneration. Preferably, the clear water separated in 3) is diverted to a fiber filter column for filtered water output; the fiber filter column is filled with MOF-fiber composite materials; the preparation method of the MOF-fiber composite materials is as follows: Step 1: Take chromium(III) nitrate nonahydrate, cobalt(II) nitrate hexahydrate, and 2-aminoterephthalic acid and place them in N,N-dimethylformamide. After stirring for 2 - 3 h, heat and react, then centrifuge, wash, and dry to obtain the MOF material. Step 2: Dissolve polyacrylonitrile in N,N-dimethylformamide, add the MOF material prepared in Step 1, stir for 12 h to obtain a composite spinning solution, and perform electrospinning to obtain MOF-PAN fibers. Step 3: Hydrolyze the MOF-PAN fibers, place them in a sodium hydroxide solution, heat under reflux for 4 h, then immerse them in a hydrochloric acid solution, let stand for 2 h, take them out, wash with water and dry, then perform crosslinking. Mix with an aqueous solution of polyethyleneimine, heat under reflux for 1 h, take them out and dry, and then repeat the first hydrolysis step and crosslinking step in sequence to obtain MOF-PAN-PEI fibers. Step 4: Mix the MOF-PAN-PEI fibers and chloroacetic acid, place them in deionized water, add sodium carbonate to adjust the pH, heat and react for 4 - 6 h, take them out, wash, then place them in a hydrochloric acid solution, let stand for 20 - 30 min, transfer them to a sodium hydroxide solution, soak for 1 - 2 h, wash with water and dry to obtain the MOF-fiber composite materials.

[0007] Preferably, in Step 1, the molar ratio of chromium(III) nitrate nonahydrate, cobalt(II) nitrate hexahydrate, and 2-aminoterephthalic acid is 1:2:3; the process conditions for the heating reaction in Step 1 are: heat to 150 - 180 °C within 5 - 6 h and hold for 24 h. Preferably, in step 2, the dosage ratio of polyacrylonitrile, MOF material, and N,N-dimethylformamide is 1:(1 - 2):19; the electrospinning process is as follows: a 10 mL syringe, a spinning voltage of 20 - 25 kV, a spinning speed of 0.0004 - 0.0008 mm / s, and a receiving distance of 20 cm; Preferably, in step 3, the heating reflux temperature is 100 °C, the dosage ratio of MOF-PAN fibers and polyimide aqueous solution during crosslinking is 1:50, and the mass fraction of polyimide in the polyimide aqueous solution is 1%; Preferably, in step 4, the dosage ratio of MOF-PAN-PEI fibers and chloroacetic acid is 2:(3 - 4), and the heating temperature is 50 - 60 °C; Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the step of adjusting the alkali in the present invention, by controlling the dropping speed and dropping time, the pH of high-hardness water is adjusted, and the slightly soluble hardness substances Ca(HCO3)2 and Mg(HCO3)2 in water are converted into the preliminary precipitation of CaCO3 and MgCO3. At the same time, the hydrolysis process in the subsequent industrial tail gas softening step is prevented from generating HCO3 - ; In order to quickly stabilize the pH of the system, a circulation pump is turned on during the dropping of the alkali solution; 2. After adjusting the alkali, the present invention sets industrial tail gas to soften the water body. Through a micro-nano bubble generator, the industrial tail gas is transported into the high-hardness water body. The micro-nano bubbles have a large specific surface area and can quickly hydrolyze the industrial tail gas; according to the hardness of the water body, the ventilation time of the industrial tail gas is adjusted, and the transportation volume of the industrial tail gas is accurately controlled to reduce the overflow of the industrial tail gas and improve the utilization rate; among them, when the industrial tail gas micro-nano bubbles contact the high-hardness water body, carbon dioxide and sulfur dioxide are completely hydrolyzed to generate CO3 2- and SO3 2- , and react with the hardness ions Ca 2+ , Mg 2+ in the water to be converted into CaCO3 / CaSO3 and MgCO3 precipitates; the role of nitrogen is to stir the water body and accelerate the production of precipitates; the micro-nano bubbles are added in small amounts and multiple stages, so that CO2 and SO2 are hydrolyzed more fully in the alkaline water body, and the hardness ion conversion and precipitation are more complete. At the same time, adding in small amounts and multiple stages can reduce the overflow of industrial tail gas into the environment and reduce pollution; 3. After softening the industrial tail gas, the present invention sets a high-fiber rotating disk for filtration. Using a negative pressure pump, when the water body passes through the high-fiber rotating disk, the hardness ion precipitates generated during the industrial tail gas softening process are intercepted. The intercepted precipitates are removed from the high-fiber rotating disk by the motor driving the rotating disk using centrifugal force. At the same time, the high-fiber rotating disk can be backflushed with high-pressure water to further remove the precipitates and realize the regeneration of the high-fiber disk; 4. A fiber filter column is provided after the high-fiber rotary disk filtration in the present invention. In the fiber filter column, a composite material obtained by combining a metal-organic framework with PAN-PEI fibers is used for post-treatment. Among them, PAN-PEI forms iminodiacetic acid through carboxylation and has excellent adsorption properties for multivalent metal ions in plural. At the same time, due to the doping of the metal-organic framework, the stability of the spun fibers is improved, and more adsorption active sites are provided, further accelerating the realization of impurity removal in post-treatment. 5. Compared with traditional softening technologies, the present invention does not require the introduction of chemical agents such as sodium bicarbonate, does not produce secondary pollution, and the softening agent used is the tail gas discharged from industry, realizing waste recycling and reducing greenhouse gas emissions. Secondly, the operation is simple and efficient, without complex equipment and cumbersome technological processes. The micro-nano bubbles used accelerate the hydrolysis of industrial tail gas in water, realizing the hardness removal of large-volume water bodies in a short time. In addition, the equipment has a long service life and low maintenance costs. Most importantly, the recycling of industrial production water is realized, solving the problem of water shortage. 6. A method for removing hardness ions in water by using micro-nano industrial tail gas bubbles in the present invention is applicable to the hardening removal of high-hardness water bodies, especially large-volume and difficult-to-treat high-hardness water bodies such as the concentrated brine generated by reverse osmosis and the coal chemical ash water. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0009] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0010] In the experiment, the concentration of industrial tail gas is measured by the CO2 concentration; the average Mw of polyacrylonitrile is about 150,000, and the Mw of polyethyleneimine is 3,000. Example 1: This example provides a method for removing hardness ions in water by using micro-nano bubbles of industrial tail gas. The specific steps are as follows: Select the high-hardness influent water from a certain flame retardant material company. The water quality parameters are: pH = 7.7, hardness = 870 mg / L (calculated as calcium carbonate); the treated water volume is 100 L; the lye is 32% NaOH solution. 1) Add lye to the high-hardness water body for 45 s at a dropping rate of 6.8 mL / s, and a total of 306 mL of lye is added, that is, 1.0 g / L NaOH, and mix with a circulating pump for 5 min, and the measured pH is 10.3. 2) Introduce industrial tail gas micro-nano bubbles with an aeration rate of 6 L / min for 4 minutes, totaling 0.24 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 500 mg / L, with the hardness reduced by 42.6%.

[0011] Example 2: This example provides a method for removing hardness ions in water using industrial tail gas micro-nano bubbles. The specific steps are as follows: Select the high-hardness influent water from a certain flame retardant material company, with water quality parameters: pH = 7.7, hardness = 870 mg / L (calculated as calcium carbonate); the water treatment volume is 100 L; the lye is 32% NaOH solution; 1) Drop the lye into the high-hardness water body for 80 s at a dropping rate of 6.8 mL / s, with a total of 544 mL of lye dropped, that is, 1.85 g / L NaOH, and mix it with a circulation pump for 5 minutes, and measure the pH to be 11.1; 2) Introduce industrial tail gas micro-nano bubbles with an aeration rate of 6 L / min for 4 minutes, totaling 0.24 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 425 mg / L, with the hardness reduced by 51.1%.

[0012] Example 3: This example provides a method for removing hardness ions in water using industrial tail gas micro-nano bubbles. The specific steps are as follows: Select the high-hardness influent water from a certain flame retardant material company, with water quality parameters: pH = 7.7, hardness = 870 mg / L (calculated as calcium carbonate); the water treatment volume is 100 L; the lye is 32% NaOH solution; 1) Drop the lye into the high-hardness water body for 95 s at a dropping rate of 6.8 mL / s, with a total of 646 mL of lye dropped, that is, 2.21 g / L NaOH, and mix it with a circulation pump for 5 minutes, and measure the pH to be 11.2; 2) Add industrial tail gas micro-nano bubbles in a small amount and multiple stages, with an aeration rate of 6 L / min: Aerate for 1 minute, totaling 0.06 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 460 mg / L, and the pH drops to 10.27; Aerate again for 1 minute, totaling 0.12 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 390 mg / L, and the pH drops to 9.69; Aerate again for 1 minute, totaling 0.18 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 380 mg / L, and the pH drops to 9.17; Ventilate again for 1 min, with a total of 0.24 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 375 mg / L, the pH drops to 8.68, and the hardness is reduced by 56.9%.

[0013] Example 4: This example provides a method for removing hardness ions in water by using industrial tail gas micro-nano bubbles. The specific steps are as follows: Select the high-hardness influent water from a flame retardant material company. The water quality parameters are: pH = 8.1, hardness = 1216 mg / L (calculated as calcium carbonate); the treated water volume is 100 L; the lye is 32% NaOH solution; 1) Drop the lye into the high-hardness water body for 180 s at a dropping rate of 6.8 mL / s, with a total of 1224 mL of lye dropped, that is, 4.19 g / L NaOH, and mix with a circulation pump for 5 min, and measure the pH to be 11.6; 2) Introduce industrial tail gas micro-nano bubbles in a small amount and multi-stage manner, with an aeration volume of 6 L / min: Aerate for 3 min, with a total of 0.18 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 750 mg / L, the pH drops to 10.31; Ventilate again for 1 min, with a total of 0.24 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 690 mg / L, the pH drops to 9.93; Ventilate again for 1 min, with a total of 0.30 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 630 mg / L, the pH drops to 9.57; Ventilate again for 1 min, with a total of 0.36 L CO2 / L; filter the water through a high-fiber rotary disk, take a sample, and measure the hardness to be 515 mg / L, the pH drops to 9.2, and the hardness is reduced by 57.6%.

[0014] Example 5: This example provides a method for removing hardness ions in water by using industrial tail gas micro-nano bubbles. The specific steps are as follows: Select the secondary reverse osmosis high-hardness influent water from a new material company. The water quality parameters are: pH = 7.9, hardness = 3350 mg / L (calculated as calcium carbonate); the treated water volume is 100 L; the lye is 45% NaOH solution; 1) Drop the lye into the high-hardness water body for 180 s at a dropping rate of 6.8 mL / s, with a total of 1224 mL of lye dropped, that is, 8.37 g / L NaOH, and mix with a circulation pump for 5 min, and measure the pH to be 12.7; 2) Introduce industrial tail gas micro-nano bubbles with an aeration rate of 6 L / min for 6 min, totaling 0.36 L CO2 / L; filter the water through a high-fiber rotary disk, take samples, and measure the hardness to be 0 mg / L, with a 100% reduction in hardness; the pH of the effluent remains at 12.5 - 12.6.

[0015] Example 6: This example provides a method for removing hardness ions in water using industrial tail gas micro-nano bubbles, and the specific steps are as follows: Select the secondary reverse osmosis high-hardness influent water from a certain new material company, with water quality parameters: pH = 7.9, hardness = 3350 mg / L (calculated as calcium carbonate); the treatment water volume is 100 L; the lye is 45% NaOH solution; 1) Drop the lye into the high-hardness water body for 150 s at a dropping rate of 6.8 mL / s, with a total of 1020 mL of lye dropped, that is, 6.98 g / L NaOH, and mix it with a circulation pump for 5 min, and measure the pH to be 12.3; 2) Add industrial tail gas micro-nano bubbles in a small amount and multi-stage manner, with an aeration rate of 6 L / min: Aerate for 2 min, totaling 0.12 L CO2 / L; filter the water through a high-fiber rotary disk, take samples, and measure the hardness to be 557 mg / L, and the pH remains at 12.2 - 12.3; Aerate again for 1 min, totaling 0.18 L CO2 / L; filter the water through a high-fiber rotary disk, take samples, and measure the hardness to be 0 mg / L, with a 100% reduction in hardness, and the pH of the effluent remains at 12.1 - 12.2.

[0016] Example 7: This example provides a method for removing hardness ions in water using industrial tail gas micro-nano bubbles, and the specific steps are as follows: Select the secondary reverse osmosis high-hardness influent water from a certain new material company, with water quality parameters: pH = 8.1, hardness = 4050 mg / L (calculated as calcium carbonate); the treatment water volume is 100 L; the lye is 45% NaOH solution; 1) Drop the lye into the high-hardness water body for 120 s at a dropping rate of 6.8 mL / s, with a total of 816 mL of lye dropped, that is, 5.58 g / L NaOH, and mix it with a circulation pump for 5 min, and measure the pH to be 12.0; 2) Add industrial tail gas micro-nano bubbles in a small amount and multi-stage manner, with an aeration rate of 6 L / min: Aerate for 2 min, totaling 0.12 L CO2 / L; filter the water through a high-fiber rotary disk, take samples, and measure the hardness to be 700 mg / L, and the pH remains at 11.6 - 11.7; Re-aerate for 1 min, with a total of 0.18 L CO2 / L; filter the effluent through a high-fiber rotary disk, take a sample, and measure the hardness to be 200 mg / L, with the pH maintained at 11.4 - 11.5; Re-aerate for 1 min, with a total of 0.24 L CO2 / L. Filter the effluent through a high-fiber rotary disk, take a sample, and measure the hardness to be 0 mg / L, a 100% reduction in hardness, and the effluent pH is maintained at 11.0 - 11.2.

[0017] Example 8: Referring to Example 2, a fiber filter column was installed after the effluent. Among them, the volume of the MOF-fiber composite material is 1.2 m 3 , and the bulk density is 0.15 kg / m 3 , and the specific steps are as follows: Select the high-hardness influent from a certain flame retardant material company, with water quality parameters: pH = 7.7, hardness = 870 mg / L (calculated as calcium carbonate); the treatment water volume is 100 L; the lye is 32% NaOH solution; 1) Drop the lye into the high-hardness water body for 80 s at a dropping rate of 6.8 mL / s, with a total of 544 mL of lye dropped, that is, 1.85 g / L NaOH, and mix with a circulation pump for 5 min, and measure the pH to be 11.1; 2) Add industrial tail gas micro-nano bubbles in a small amount and multi-stage manner, with an aeration rate of 6 L / min: Aerate for 4 min, with a total of 0.24 L CO2 / L; filter the effluent through a high-fiber rotary disk, take a sample, and measure the hardness to be 425 mg / L, a 51.1% reduction in hardness; 3) Connect the fiber filter column, take a sample after 10 min, and measure the hardness to be 153 mg / L, a 82.41% reduction in hardness; Among them, the preparation steps of the MOF-fiber composite material in the fiber filter column are as follows: Step 1: Take 4.00 g of chromium nitrate nonahydrate, 5.82 g of cobalt nitrate hexahydrate, and 5.43 g of 2-aminoterephthalic acid and place them in 100 g of N,N-dimethylformamide. After stirring for 2 h, load them into a reaction kettle, heat to 150 °C within 5 h, keep the temperature for reaction for 24 h, then centrifuge and wash, and dry to obtain the MOF material; Step 2: Dissolve 5 g of polyacrylonitrile in 95 g of N,N-dimethylformamide, add 5 g of the MOF material prepared in Step 1, stir for 12 h to obtain a composite spinning solution, load it into a 10 mL syringe for electrospinning, set the spinning voltage to 20 kV, the spinning speed to 0.0005 mm / s, and the receiving distance to 20 cm to obtain MOF-PAN fibers; Step 3: Hydrolyze the MOF-PAN fiber. Place it in a sodium hydroxide solution with a mass concentration of 0.1%, with a material-liquid ratio of 1:50. After heating to 100 °C and refluxing for 4 h, immerse it in a 1 mol / L hydrochloric acid solution. After standing for 2 h, take it out, wash it with water and dry it, and then carry out cross-linking. Mix it with an aqueous solution of polyethyleneimine with a mass fraction of 1%, with a material-liquid ratio of 1:50. After heating and refluxing for 1 h, take it out and dry it. Then repeat the first hydrolysis step and cross-linking step in sequence to obtain MOF-PAN-PEI fiber; Step 4: Mix 10 g of MOF-PAN-PEI fiber and 20 g of chloroacetic acid, place them in 1 L of deionized water, add sodium carbonate to adjust the pH to 9, heat to 60 °C and react for 5 h, then take it out, wash it, place it in a 1 mol / L hydrochloric acid solution and stand for 30 min, then immerse it in a sodium hydroxide solution with a mass concentration of 0.1% and soak for 2 h, wash it with water and dry it to obtain the MOF-fiber composite material.

[0018] Example 9: Refer to Example 3. A fiber filter column was installed after the water outlet. Among them, the volume of the MOF-fiber composite material is 1.2 m 3 , and the bulk density is 0.15 kg / m 3 , and the specific steps are as follows: Select the high-hardness influent water from a certain flame retardant material company. The water quality parameters are: pH = 7.7, hardness = 870 mg / L (calculated as calcium carbonate); the treated water volume is 100 L; the lye is 32% NaOH solution; 1) Drop the lye into the high-hardness water body for 95 s at a dropping rate of 6.8 mL / s, with a total of 646 mL of lye dropped, that is, 2.21 g / L NaOH, and mix it with a circulation pump for 5 min, and the measured pH is 11.2; 2) Add industrial tail gas micro-nano bubbles in a small amount and multi-stage manner, with an air flow rate of 6 L / min: Ventilate for 1 min, with a total of 0.06 L CO2 / L; filter the water through a high-fiber rotary disk and take a sample. The measured hardness is 460 mg / L and the pH drops to 10.27; Ventilate again for 1 min, with a total of 0.12 L CO2 / L; filter the water through a high-fiber rotary disk and take a sample. The measured hardness is 390 mg / L and the pH drops to 9.69; Ventilate again for 1 min, with a total of 0.18 L CO2 / L. Filter the water through a high-fiber rotary disk and take a sample. The measured hardness is 380 mg / L and the pH drops to 9.17; Ventilate again for 1 min, with a total of 0.24 L CO2 / L. Filter the water through a high-fiber rotary disk and take a sample. The measured hardness is 375 mg / L and the pH drops to 8.68, and the hardness is reduced by 56.9%; 3) Connect to the fiber filter column. After sampling 10 minutes later, the measured hardness is 130 mg / L, and the hardness has decreased by 85.06%; Among them, the preparation steps of the MOF-fiber composite material in the fiber filter column are as follows: Step 1: Take 4.00 g of chromium nitrate nonahydrate, 5.82 g of cobalt nitrate hexahydrate, and 5.43 g of 2-aminoterephthalic acid and place them in 100 g of N,N-dimethylformamide. After stirring for 2 h, load them into a reaction kettle, heat to 150 °C within 5 h, keep the temperature for reaction for 24 h, then centrifuge and wash, and dry to obtain the MOF material; Step 2: Dissolve 5 g of polyacrylonitrile in 95 g of N,N-dimethylformamide, add 10 g of the MOF material prepared in Step 1, stir for 12 h to obtain a composite spinning solution, load it into a 10 mL syringe for electrospinning, set the spinning voltage to 20 kV, the spinning speed to 0.0005 mm / s, and the receiving distance to 20 cm to obtain MOF-PAN fibers; Step 3: Hydrolyze the MOF-PAN fibers, place them in a sodium hydroxide solution with a mass concentration of 0.1%, with a material-liquid ratio of 1:50, heat to 100 °C and reflux for 4 h, then immerse them in a 1 mol / L hydrochloric acid solution, take them out after standing for 2 h, wash and dry, and then crosslink. Mix with a 1% polyethyleneimine aqueous solution, with a material-liquid ratio of 1:50, heat and reflux for 1 h, take them out and dry, and then repeat the first hydrolysis step and crosslinking step in sequence to obtain MOF-PAN-PEI fibers; Step 4: Mix 10 g of MOF-PAN-PEI fibers and 20 g of chloroacetic acid, place them in 1 L of deionized water, add sodium carbonate to adjust the pH to 9, heat to 60 °C and react for 5 h, then take them out, wash, place them in a 1 mol / L hydrochloric acid solution and stand for 30 min, then immerse them in a sodium hydroxide solution with a mass concentration of 0.1% and soak for 2 h, wash and dry to obtain the MOF-fiber composite material.

[0019] Conclusion: The present invention provides a method for removing hardness ions in water by using industrial tail gas micro-nano bubbles, mainly using maintaining a high pH environment, controlling the industrial tail gas delivery volume, and fiber adsorption to reduce the hardness of water bodies. In the experiment, good technical effects have been achieved for different water quality conditions.

[0020] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

Claims

1. A method for removing hardness ions in water by using micro-nano bubbles of industrial tail gas, characterized in that, The specific method is as follows: 1) Adjusting alkalinity: Adding an alkali solution dropwise to the high-hardness water body to adjust the alkalinity; 2) Softening industrial tail gas: Conveying micro-nano bubbles containing industrial tail gas into the high-hardness water body after alkalinity adjustment to form a precipitate; 3) High-fiber rotary disk filtration: Turning the high-hardness water body after precipitation to a high-fiber rotary disk filter to intercept the precipitate and separate to obtain clear water.

2. The method for removing hardness ions in water by utilizing micro-nano bubbles of industrial tail gas according to claim 1, characterized in that: The alkali solution is one of sodium hydroxide and potassium hydroxide; 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.

3. According to the method for removing hardness ions in water by using micro-nano bubbles of industrial tail gas described in claim 1, the pH of the high-hardness water body after alkalinity adjustment is 10-14.

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

5. A method for removing hardness ions in water by using industrial tail gas micro-nano bubbles according to claim 1, characterized in that, Turn the clear water separated in 3) to a fiber filter column for filtered water output; wherein the fiber filter column is filled with MOF-fiber composite material.

6. The method for removing hardness ions in water by using industrial tail gas micro-nano bubbles according to claim 5, characterized in that, 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. After stirring for 2-3 h, heat and react, then centrifuge, wash, and dry to obtain the MOF material; Step 2: Dissolve polyacrylonitrile in N,N-dimethylformamide, add the MOF material prepared in Step 1, stir for 12 h to obtain a composite spinning solution, and perform electrospinning to obtain MOF-PAN fibers; Step 3: Hydrolyze the MOF-PAN fibers, place them in a sodium hydroxide solution, heat and reflux for 4 h, then immerse them in a hydrochloric acid solution and let stand for 2 h, then take them out, wash with water and dry, and then perform crosslinking. Mix with an aqueous solution of polyethyleneimine and heat and reflux for 1 h, then take them out and dry. Then repeat the first hydrolysis step and crosslinking step in sequence to obtain MOF-PAN-PEI fibers; Step 4: Mix the MOF-PAN-PEI fibers and chloroacetic acid, place them in deionized water, add sodium carbonate to adjust the pH, heat and react for 4-6 h, then take them out, wash, place them in a hydrochloric acid solution and let stand for 20-30 min, then transfer them to a sodium hydroxide solution and soak for 1-2 h, wash with water and dry to obtain the MOF-fiber composite material.

7. A method for removing hardness ions in water by using industrial tail gas micro-nano bubbles according to claim 6, 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 °C within 5-6 h and holding for 24 h.

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

9. The method for removing hardness ions in water by using industrial tail gas micro-nano bubbles according to claim 6, characterized in that, In Step 3, the heating reflux temperature is 100 °C, the dosage ratio of MOF-PAN fiber to polyimide aqueous solution in crosslinking is 1:50, and the mass fraction of polyimide in the polyimide aqueous solution is 1%; in Step 4, the dosage ratio of MOF-PAN-PEI fiber to chloroacetic acid is 2:(3-4), and the heating temperature is 50-60 °C.

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