Method for removing nitrate from wastewater in drill-and-blast tunnel construction

Abstract

This invention discloses a method for removing nitrates from wastewater generated during drill-and-blast tunnel construction, comprising the following steps: 1. Preparation of electrospun nanofibers: First, DMF is added to a container, and submicron-sized iron powder and submicron-sized calcium-based montmorillonite are added sequentially to the DMF solution and ultrasonically dispersed. Then, the mixture is stirred to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. PAN powder is weighed and added to the above solution, and stirred until the PAN is completely dissolved into a viscous liquid. The resulting solution is then placed in an electrospinning machine for electrospinning to prepare PAN nanofibers. 2. Removal of nitrates from the drill-and-blast tunnel construction wastewater: The prepared PAN nanofibers are completely immersed in the drill-and-blast tunnel construction wastewater. After immersion for a period of time, the PAN nanofibers are removed. This invention can efficiently and cost-effectively remove nitrates present in wastewater generated during drill-and-blast tunnel construction.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology in drill-and-blast tunnel construction, specifically relating to a method for removing nitrates from wastewater in drill-and-blast tunnel construction. Background Technology

[0002] The explosives used in tunnel drilling and blasting construction, such as emulsion explosives or TNT, mainly consist of NH4NO3 or 1,3,5-trinitrotoluene. This results in tunnel construction wastewater containing a certain amount of ammonia nitrogen and nitrate nitrogen, which is high in suspended solids (SS) and highly alkaline, making it slightly polluted water. Generally, the levels of ammonia nitrogen and nitrate nitrogen will not exceed the standards. However, in ecologically sensitive areas, when the discharge complies with the Class III standards in the "Surface Water Environmental Quality Standard" (GB3838-2002), the levels of ammonia nitrogen and nitrate nitrogen may exceed the standard requirements.

[0003] Because the concentration of organic matter in the wastewater is low, it is not suitable to rely on biological treatment processes to remove nitrate nitrogen, and the removal of nitrate is a major challenge.

[0004] Zero-valent metal reduction has advantages such as low cost, simple management, and high efficiency. However, this method may generate secondary pollutants that pollute water bodies. Therefore, it is necessary to develop an efficient and low-cost nitrate removal method. Summary of the Invention

[0005] The purpose of this invention is to provide a method for removing nitrates from wastewater generated during drilling and blasting tunnel construction, in order to solve the problem mentioned in the background art that nitrate nitrogen in wastewater generated during drilling and blasting tunnel construction may exceed the standard but there is a lack of efficient and low-cost removal methods.

[0006] To achieve the above objectives, the present invention provides a method for removing nitrates from wastewater generated during drill-and-blast tunnel construction, comprising the following steps:

[0007] Step 1: Preparation of electrospun nanofibers: Using DMF (N,N-dimethylformamide) as the solvent for the nanofiber precursor and PAN (polyacrylonitrile) as the electrospinning substrate material, DMF is first added to a container, and submicron-sized iron powder and submicron-sized calcium-based montmorillonite are added to the DMF solution in a mass ratio of 1 to 9:3. The mixture is then ultrasonically dispersed and stirred to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. PAN powder is weighed and added to the above solution, and stirred until the PAN is completely dissolved into a viscous liquid, thus obtaining the electrospinning precursor solution. The mass fraction of PAN in the electrospinning precursor solution is 5% to 15%. The obtained solution is then placed in an electrospinning machine for electrospinning to prepare PAN nanofibers. The prepared PAN nanofibers are dried to remove excess DMF and prevent PAN nanofiber adhesion.

[0008] Step 2: Remove nitrates from the wastewater from the drill-and-blast tunnel construction: Completely immerse the dried PAN nanofibers in the wastewater from the drill-and-blast tunnel construction. After soaking for a period of time, remove the PAN nanofibers.

[0009] In one specific embodiment, the method for removing nitrates from the wastewater of the drill-and-blast tunnel construction further includes step 3, recycling of PAN: the used PAN nanofibers are first soaked in dilute hydrochloric acid to remove excess iron powder, then dried in an oven, and then the dried PAN nanofibers are put into a ball mill for grinding. After the ball milling is completed, the PAN is separated and screened, thus completing the recycling of PAN.

[0010] In one specific embodiment, in step 1, the PAN nanofibers are dried at 80°C in an oven; in step 3, the used PAN nanofibers are dried at 80°C in an oven for 10 hours.

[0011] In one specific embodiment, in step 3, when the material is placed in a ball mill for grinding, the ball mill speed is set to 200-400 r / min, the ball-to-material ratio is set to 50-150:1, and the ball milling time is set to 5-15 min.

[0012] In one specific embodiment, in step 1, the mass ratio of DMF: iron powder: calcium-based montmorillonite is 17-19:1:1.

[0013] In one specific embodiment, in step 1, the mass ratio of the amount of PAN powder added to the sum of the masses of iron powder and calcium-based montmorillonite is 0.5 to 1.5:1.

[0014] In one specific embodiment, in step 1, the electrospinning machine is set with a voltage of 15-25kV, a feed speed of 0.01-0.03mL / min, a receiving distance of 10-20cm, and a roller speed of 200-500r / min.

[0015] In one specific embodiment, in step 1, after ultrasonic dispersion, the mixture is stirred for 0.5 to 2 hours, and after adding PAN powder, it is stirred for 4 to 16 hours.

[0016] In one specific implementation, the soaking time in step 2 is 6 to 18 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention can efficiently and cost-effectively remove ammonia nitrogen and total nitrogen from wastewater generated during drilling and blasting tunnel construction.

[0019] This invention ingeniously utilizes nanofiber materials, and employs an optimal mass ratio of iron powder and calcium-based montmorillonite in the preparation of the nanofiber materials to achieve the best removal effect on nitrate ions.

[0020] This invention creatively combines the adsorption of calcium-based montmorillonite with the reduction of zero-valent iron. Calcium-based montmorillonite adsorbs and enriches nitrate ions, and generates harmless nitrogen gas under the reduction of zero-valent iron, thereby reducing the nitrate concentration in water.

[0021] Compared with other methods for removing nitrates, this invention has the advantages of simple operation and low cost.

[0022] The PAN substrate material used in this invention can be recycled after being sieved into powder, further reducing costs.

[0023] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The present invention will now be described in further detail. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0025] Figure 1 This is a graph showing the nitrate removal rate of nanofibers containing iron powder and calcium-based montmorillonite at different mass ratios.

[0026] Figure 2 The graph shows the nitrate removal rate and PAN recovery rate for comparative and different embodiments;

[0027] Figure 3 This is a scanning electron microscope image of PAN nanofibers. Detailed Implementation

[0028] The embodiments of the present invention will be described in detail below. The specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0029] The present invention discloses a method for removing nitrates from wastewater generated during drill-and-blast tunnel construction, comprising the following steps:

[0030] Step 1: Preparation of electrospun nanofibers: Using DMF (N,N-dimethylformamide) as the solvent for the nanofiber precursor and PAN (polyacrylonitrile) as the electrospinning substrate material, DMF is first added to a container. Submicron-sized iron powder and submicron-sized calcium-based montmorillonite are added to the DMF solution in a mass ratio of 1 to 9:3, and then ultrasonically dispersed. The mixture is then stirred to ensure uniform dispersion of the iron powder and montmorillonite. PAN powder is weighed and added to the above solution, and stirred until the PAN is completely dissolved into a viscous liquid, thus obtaining the electrospinning precursor solution. The mass fraction of PAN in the electrospinning precursor solution is 5-15%. The obtained solution is then placed in an electrospinning machine for electrospinning to prepare PAN nanofibers. The prepared PAN nanofibers are dried to remove excess DMF and prevent PAN nanofiber adhesion.

[0031] The submicron-sized iron powder has a particle size of 0.5–10 μm, and the submicron-sized calcium-based montmorillonite has a particle size of 2–8 μm, preferably with an average particle size of 4 μm. The preferred mass ratio of iron powder to montmorillonite is 1:1.

[0032] Step 2: Remove nitrates from the wastewater from the drill-and-blast tunnel construction: Completely immerse the dried PAN nanofibers in the wastewater from the drill-and-blast tunnel construction. After soaking for a period of time, remove the PAN nanofibers.

[0033] The method for removing nitrates from wastewater in tunnel construction using the drill-and-blast method also includes step 3, recycling of PAN: the used PAN nanofibers are first soaked in dilute hydrochloric acid to remove excess iron powder, then dried in an oven, and then the dried PAN nanofibers are put into a ball mill for grinding. After the ball milling is completed, the PAN powder is separated and sieved, thus completing the recycling of PAN.

[0034] In step 1, the PAN nanofibers are dried at 80°C in an oven; in step 3, the used PAN nanofibers are dried at 80°C in an oven for 10 hours.

[0035] In step 3, when grinding the material in a ball mill, the ball mill speed is set to 200-400 r / min, the ball-to-material ratio is set to 50-150:1, and the ball milling time is set to 5-15 min; preferably, the ball milling time is set to 10 min.

[0036] In step 1, the mass ratio of DMF: iron powder: calcium-based montmorillonite is 17-19:1:1.

[0037] In step 1, the mass ratio of the added PAN powder to the sum of the masses of iron powder and calcium-based montmorillonite is 0.5 to 1.5:1.

[0038] In step 1, the electrospinning machine is set with a voltage of 15-25kV, a feed speed of 0.01-0.03mL / min, a receiving distance of 10-20cm, and a roller speed of 200-500r / min; preferably, the electrospinning machine is set with a voltage of 20kV, a feed speed of 0.02mL / min, a receiving distance of 15cm, and a roller speed of 300r / min.

[0039] In step 1, the ultrasonic dispersion is followed by stirring for 0.5 to 2 hours, and then PAN powder is added and stirred for 4 to 16 hours; preferably, the ultrasonic dispersion is followed by stirring for 1 hour, and then PAN powder is added and stirred for 8 hours.

[0040] In step 2, the soaking time is 6 to 18 hours.

[0041] The wastewater from the drilling and blasting construction of a certain water conservancy tunnel had a total nitrogen (TN) concentration of 21.69 mg / L and a NO concentration of... 3- The concentration was 12.42 mg / L. This wastewater was treated using nanofibers with different mass ratios of iron powder and calcium-based montmorillonite. The nitrate removal rate was as follows: Figure 1 As shown.

[0042] Example 1

[0043] First, 9g of DMF was added to a beaker. Then, 0.5g of submicron-sized iron powder and 0.5g of submicron-sized calcium-based montmorillonite were added to the DMF solution sequentially and ultrasonically dispersed. The mixture was then stirred for 1 hour to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. 1g of white PAN powder was weighed and added to the above solution. The mixture was stirred for 8 hours until the PAN was completely dissolved into a viscous liquid, yielding an electrospinning precursor solution with a PAN mass fraction of 10%. The electrospinning precursor solution was then placed in an electrospinning machine for electrospinning. Electrospinning was performed for 12 hours under the conditions of 20kV voltage, a feed speed of 0.02mL / min, a receiving distance of 15cm, and a roller speed of 300r / min to prepare PAN nanofibers. The prepared PAN nanofibers were dried to remove excess DMF and prevent PAN nanofiber adhesion, thus completing the preparation of PAN nanofibers. The dried PAN nanofibers were completely immersed in the wastewater from the drill-and-blast tunnel construction to remove nitrates. The immersion time was 12 hours. After the reaction was completed, the PAN nanofibers were removed.

[0044] The PAN nanofibers that have adsorbed nitrate were first soaked in dilute hydrochloric acid to remove excess iron powder, and then dried in an oven at 80°C for 10 hours. The dried PAN nanofibers were then put into a ball mill for grinding, with a ball mill speed of 300 r / min, a ball-to-material mass ratio of 100:1, and a grinding time of 10 minutes. After the ball milling was completed, the PAN was separated and sieved through a 200-mesh sieve, thus completing the recycling of PAN.

[0045] like Figure 1 As shown, the addition of both calcium-based montmorillonite and iron powder is beneficial for the removal of nitrate ions, with the optimal mass ratio of iron powder to calcium-based montmorillonite being 1:1. Figure 2 It can be seen that the above method has a high nitrate removal rate in water, and also a high PAN recovery rate after recovery, indicating that the material prepared in Example 1 has good performance.

[0046] Comparative Example 1

[0047] First, 9.6g of DMF was added to a beaker. Then, 0.5g of submicron-sized iron powder and 0.5g of submicron-sized calcium-based montmorillonite were added to the DMF solution sequentially and ultrasonically dispersed. The mixture was then stirred for 1 hour to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. Next, 0.4g of white PAN powder was weighed and added to the above solution. The mixture was stirred for 8 hours until the PAN was completely dissolved into a viscous liquid, yielding an electrospinning precursor solution with a PAN mass fraction of 4%. The electrospinning precursor solution was then placed in an electrospinning machine for electrospinning. Electrospinning was performed for 12 hours under the conditions of 20kV voltage, a feed speed of 0.02mL / min, a receiving distance of 15cm, and a roller speed of 300r / min to prepare PAN nanofibers. The prepared PAN nanofibers were dried to remove excess DMF and prevent PAN nanofiber adhesion, thus completing the preparation of PAN nanofibers. The dried PAN nanofibers were completely immersed in the wastewater from the drill-and-blast tunnel construction to remove nitrates. The immersion time was 3 hours. After the reaction was completed, the PAN nanofibers were removed.

[0048] The PAN nanofibers that have adsorbed nitrate ions were first soaked in dilute hydrochloric acid to remove excess iron powder, and then dried in an oven at 80°C for 10 hours. The dried PAN nanofibers were then put into a ball mill for grinding, with a ball mill speed of 150 r / min, a ball-to-material mass ratio of 40:1, and a grinding time of 10 minutes. After the ball milling was completed, the PAN was separated and sieved through a 200-mesh sieve, thus completing the recycling of PAN.

[0049] This comparative example is basically the same as Example 1, except that:

[0050] In the preparation of PAN nanofibers, the amount of DMF added was 9.6g, and the amount of PAN white powder added was 0.4g, of which the mass fraction of PAN was 4%. After adding PAN, the soaking time was 3h during the nitrate removal process. During the PAN nanofiber recovery process, the ball-to-material ratio was 40:1, the ball milling speed was 150r / min, and the other conditions were the same as in Example 1.

[0051] like Figure 2 It can be seen that the nitrate removal rate and PAN recovery rate of Comparative Example 1 are both low. This is because the PAN mass fraction is low, the viscosity is low, and the diameter of the nanofibers is small, which leads to a reduction in the loading of iron powder and calcium-based montmorillonite. The soaking time is too short, which leads to a reduction in the nitrate removal rate in the water. During the PAN recovery process, the ball-to-material ratio and the ball mill speed are low, which prevents the PAN from being fully ground, resulting in a reduction in the PAN recovery rate.

[0052] Example 2

[0053] First, 9.2g of DMF was added to a beaker. Then, 0.5g of submicron-sized iron powder and 0.5g of submicron-sized calcium-based montmorillonite were added to the DMF solution sequentially and ultrasonically dispersed. The mixture was then stirred for 1 hour to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. Next, 0.8g of white PAN powder was weighed and added to the above solution. The mixture was stirred for 8 hours until the PAN was completely dissolved into a viscous liquid, yielding an electrospinning precursor solution with a PAN mass fraction of 8%. The electrospinning precursor solution was then placed in an electrospinning machine for electrospinning. Electrospinning was performed for 12 hours under the conditions of 20kV voltage, a feed speed of 0.02mL / min, a receiving distance of 15cm, and a roller speed of 300r / min to prepare PAN nanofibers. The prepared PAN nanofibers were dried to remove excess DMF and prevent PAN nanofiber adhesion, thus completing the preparation of PAN nanofibers. The dried PAN nanofibers were completely immersed in the wastewater from the drill-and-blast tunnel construction to remove nitrates. The immersion time was 12 hours. After the reaction was completed, the PAN nanofibers were removed.

[0054] The PAN nanofibers that have adsorbed nitrate were first soaked in dilute hydrochloric acid to remove excess iron powder, and then dried in an oven at 80°C for 10 hours. The dried PAN nanofibers were then put into a ball mill for grinding, with a ball mill speed of 300 r / min, a ball-to-material mass ratio of 100:1, and a grinding time of 10 minutes. After the ball milling was completed, the PAN was separated and sieved through a 200-mesh sieve, thus completing the recycling of PAN.

[0055] This embodiment is basically the same as Embodiment 1, except that:

[0056] In the preparation of PAN nanofibers, 9.2 g of DMF and 0.8 g of PAN white powder were added, with PAN having a mass fraction of 8%.

[0057] Depend on Figure 2 It can be seen that the nitrate removal rate is low. The low PAN mass fraction and low viscosity of the precursor solution during electrospinning result in a smaller diameter of nanofibers and a lower loading of calcium-based montmorillonite and iron powder, which in turn leads to a lower nitrate removal rate.

[0058] Example 3

[0059] First, 8.5g of DMF was added to a beaker. Then, 0.5g of submicron-sized iron powder and 0.5g of submicron-sized calcium-based montmorillonite were added to the DMF solution sequentially and ultrasonically dispersed. The mixture was then stirred for 1 hour to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. 1.5g of white PAN powder was weighed and added to the above solution. The mixture was stirred for 8 hours until the PAN was completely dissolved into a viscous liquid, yielding an electrospinning precursor solution with a PAN mass fraction of 15%. The electrospinning precursor solution was then placed in an electrospinning machine for electrospinning. Electrospinning was performed for 12 hours under the conditions of 20kV voltage, a feed speed of 0.02mL / min, a receiving distance of 15cm, and a roller speed of 300r / min to prepare PAN nanofibers. The prepared PAN nanofibers were dried to remove excess DMF and prevent PAN nanofiber adhesion, thus completing the preparation of PAN nanofibers. The dried PAN nanofibers were completely immersed in the wastewater from the drill-and-blast tunnel construction to remove nitrates. The immersion time was 12 hours. After the reaction was completed, the PAN nanofibers were removed.

[0060] The PAN nanofibers that have adsorbed nitrate were first soaked in dilute hydrochloric acid to remove excess iron powder, and then dried in an oven at 80°C for 10 hours. The dried PAN nanofibers were then put into a ball mill for grinding, with a ball mill speed of 300 r / min, a ball-to-material mass ratio of 100:1, and a grinding time of 10 minutes. After the ball milling was completed, the PAN was separated and sieved through a 200-mesh sieve, thus completing the recycling of PAN.

[0061] This embodiment is basically the same as Embodiment 1, except that:

[0062] In the preparation of PAN nanofibers, 8.5g of DMF and 1.5g of PAN white powder were added, with PAN having a mass fraction of 15%.

[0063] like Figure 2It is known that the nitrate removal rate is low. Due to the increase in the mass fraction of PAN during electrospinning, the viscosity of the solution increases, resulting in a larger diameter of the electrospinned nanofibers. Iron powder and calcium-based montmorillonite are encapsulated inside the nanofibers, and the iron powder and calcium-based montmorillonite cannot fully contact the water, leading to a decrease in the nitrate removal rate.

[0064] Example 4

[0065] First, 9g of DMF was added to a beaker. Then, 0.5g of submicron-sized iron powder and 0.5g of submicron-sized calcium-based montmorillonite were added to the DMF solution sequentially and ultrasonically dispersed. The mixture was then stirred for 1 hour to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. 1g of white PAN powder was weighed and added to the above solution. The mixture was stirred for 8 hours until the PAN was completely dissolved into a viscous liquid, yielding an electrospinning precursor solution with a PAN mass fraction of 10%. The electrospinning precursor solution was then placed in an electrospinning machine for electrospinning. Electrospinning was performed for 12 hours under the conditions of 20kV voltage, a feed speed of 0.02mL / min, a receiving distance of 15cm, and a roller speed of 300r / min to prepare PAN nanofibers. The prepared PAN nanofibers were dried to remove excess DMF and prevent PAN nanofiber adhesion, thus completing the preparation of PAN nanofibers. The dried PAN nanofibers were completely immersed in the wastewater from the drill-and-blast tunnel construction to remove nitrates. The immersion time was 6 hours. After the reaction was completed, the PAN nanofibers were removed.

[0066] The PAN nanofibers that have adsorbed nitrate were first soaked in dilute hydrochloric acid to remove excess iron powder, and then dried in an oven at 80°C for 10 hours. The dried PAN nanofibers were then put into a ball mill for grinding, with a ball mill speed of 300 r / min, a ball-to-material mass ratio of 100:1, and a grinding time of 10 minutes. After the ball milling was completed, the PAN was separated and sieved through a 200-mesh sieve, thus completing the recycling of PAN.

[0067] This embodiment is basically the same as Embodiment 1, except that:

[0068] In the process of removing nitrates from water using nanofiber materials, the soaking time is 6 hours.

[0069] like Figure 2 It can be seen that the reduced nitrate removal effect is mainly due to the short soaking time, which results in a short contact time between the nanofibers and the water, and thus cannot effectively remove nitrate ions.

[0070] Example 5

[0071] First, 9g of DMF was added to a beaker. Then, 0.5g of submicron-sized iron powder and 0.5g of submicron-sized calcium-based montmorillonite were added to the DMF solution sequentially and ultrasonically dispersed. The mixture was then stirred for 1 hour to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. 1g of white PAN powder was weighed and added to the above solution. The mixture was stirred for 8 hours until the PAN was completely dissolved into a viscous liquid, yielding an electrospinning precursor solution with a PAN mass fraction of 10%. The electrospinning precursor solution was then placed in an electrospinning machine for electrospinning. Electrospinning was performed for 12 hours under the conditions of 20kV voltage, a feed speed of 0.02mL / min, a receiving distance of 15cm, and a roller speed of 300r / min to prepare PAN nanofibers. The prepared PAN nanofibers were dried to remove excess DMF and prevent PAN nanofiber adhesion, thus completing the preparation of PAN nanofibers. The dried PAN nanofibers were completely immersed in the wastewater from the drill-and-blast tunnel construction to remove nitrates. The immersion time was 18 hours. After the reaction was completed, the PAN nanofibers were removed.

[0072] The PAN nanofibers that have adsorbed nitrate were first soaked in dilute hydrochloric acid to remove excess iron powder, and then dried in an oven at 80°C for 10 hours. The dried PAN nanofibers were then put into a ball mill for grinding, with a ball mill speed of 300 r / min, a ball-to-material mass ratio of 100:1, and a grinding time of 10 minutes. After the ball milling was completed, the PAN was separated and sieved through a 200-mesh sieve, thus completing the recycling of PAN.

[0073] This embodiment is basically the same as Embodiment 1, except that:

[0074] In the process of removing nitrates from water using nanofiber materials, the soaking time is 18 hours.

[0075] like Figure 2 It is known that the removal rate of nitrate is low. If the soaking time is too long, the nitrate ions adsorbed on the surface of calcium-based montmorillonite will detach and enter the water. Moreover, the iron powder in the nanofiber is easily oxidized, which prevents it from reacting with nitrate ions in time. The excessive soaking time leads to a decrease in the removal rate of nitrate by the nanofiber.

[0076] Example 6

[0077] First, 9g of DMF was added to a beaker. Then, 0.5g of submicron-sized iron powder and 0.5g of submicron-sized calcium-based montmorillonite were added to the DMF solution sequentially and ultrasonically dispersed. The mixture was then stirred for 1 hour to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. 1g of white PAN powder was weighed and added to the above solution. The mixture was stirred for 8 hours until the PAN was completely dissolved into a viscous liquid, yielding an electrospinning precursor solution with a PAN mass fraction of 10%. The electrospinning precursor solution was then placed in an electrospinning machine for electrospinning. Electrospinning was performed for 12 hours under the conditions of 20kV voltage, a feed speed of 0.02mL / min, a receiving distance of 15cm, and a roller speed of 300r / min to prepare PAN nanofibers. The prepared PAN nanofibers were dried to remove excess DMF and prevent PAN nanofiber adhesion, thus completing the preparation of PAN nanofibers. The dried PAN nanofibers were completely immersed in the wastewater from the drill-and-blast tunnel construction to remove nitrates. The immersion time was 12 hours. After the reaction was completed, the PAN nanofibers were removed.

[0078] The PAN nanofibers that have adsorbed nitrate ions were first soaked in dilute hydrochloric acid to remove excess iron powder, and then dried in an oven at 80°C for 10 hours. The dried PAN nanofibers were then put into a ball mill for grinding, with a ball mill speed of 200 r / min, a ball-to-material mass ratio of 50:1, and a grinding time of 10 minutes. After the ball milling was completed, the PAN was separated and sieved through a 200-mesh sieve, thus completing the recycling of PAN.

[0079] This embodiment is basically the same as Embodiment 1, except that:

[0080] During the PAN nanofiber recycling process, the ball-to-material ratio was 50:1 and the ball mill speed was 200 r / min.

[0081] like Figure 2 It can be seen that the recovery rate of PAN is low, mainly because the ball material is relatively low and the ball mill speed is low, which cannot completely crush the nanofibers. During the sieving process, a large amount of electrospun substrate material PAN cannot pass through the sample sieve, resulting in a decrease in the recovery rate of PAN.

[0082] Example 7

[0083] First, 9g of DMF was added to a beaker. Then, 0.5g of submicron-sized iron powder and 0.5g of submicron-sized calcium-based montmorillonite were added to the DMF solution sequentially and ultrasonically dispersed. The mixture was then stirred for 1 hour to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. 1g of white PAN powder was weighed and added to the above solution. The mixture was stirred for 8 hours until the PAN was completely dissolved into a viscous liquid, yielding an electrospinning precursor solution with a PAN mass fraction of 10%. The electrospinning precursor solution was then placed in an electrospinning machine for electrospinning. Electrospinning was performed for 12 hours under the conditions of 20kV voltage, a feed speed of 0.02mL / min, a receiving distance of 15cm, and a roller speed of 300r / min to prepare PAN nanofibers. The prepared PAN nanofibers were dried to remove excess DMF and prevent PAN nanofiber adhesion, thus completing the preparation of PAN nanofibers. The dried PAN nanofibers were completely immersed in the wastewater from the drill-and-blast tunnel construction to remove nitrates. The immersion time was 12 hours. After the reaction was completed, the PAN nanofibers were removed.

[0084] The PAN nanofibers that have adsorbed nitrate ions were first soaked in dilute hydrochloric acid to remove excess iron powder, and then dried in an oven at 80°C for 10 hours. The dried PAN nanofibers were then put into a ball mill for grinding, with a ball mill speed of 400 r / min, a ball-to-material mass ratio of 150:1, and a grinding time of 10 minutes. After the ball milling was completed, the PAN was separated and sieved through a 200-mesh sieve, thus completing the recycling of PAN.

[0085] This embodiment is basically the same as Embodiment 1, except that:

[0086] During the recycling of PAN nanofibers, the ball-to-material ratio was 150:1, and the ball mill speed was 400 r / min.

[0087] like Figure 2 It can be seen that, compared with Example 1, the recovery rate of PAN is reduced. The high ball-to-material ratio and high rotation speed cause the PAN nanofibers to stick together severely during the ball milling process, making them difficult to separate, which leads to a decrease in the recovery rate of PAN.

[0088] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions and substitutions can be made without departing from the inventive concept, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for removing nitrates from wastewater generated during drill-and-blast tunnel construction, characterized in that, Includes the following steps: Step 1: Preparation of electrospun nanofibers: Using DMF (N,N-dimethylformamide) as the solvent for the nanofiber precursor and PAN (polyacrylonitrile) as the electrospinning substrate material, DMF is first added to a container. Submicron-sized iron powder and submicron-sized calcium-based montmorillonite are then added to the DMF solution sequentially, with a mass ratio of DMF:iron powder:calcium-based montmorillonite of 17-19:1:

1. The mixture is ultrasonically dispersed and then stirred to ensure uniform dispersion of the iron powder and calcium-based montmorillonite. PAN powder is weighed and added to the above solution, and stirred until the PAN is completely dissolved into a viscous liquid, thus obtaining the electrospinning precursor solution. The mass fraction of PAN in the electrospinning precursor solution is 5-15%. The resulting solution is then placed in an electrospinning machine for electrospinning to prepare PAN nanofibers. The prepared PAN nanofibers are dried to remove excess DMF and prevent PAN nanofiber adhesion. The mass ratio of PAN powder to the sum of the masses of iron powder and calcium-based montmorillonite is 0.5-1.5:

1. Step 2: Remove nitrates from the wastewater from the drill-and-blast tunnel construction: Immerse the dried PAN nanofibers completely in the wastewater from the drill-and-blast tunnel construction for a period of time, and then remove the PAN nanofibers. Step 3, PAN recycling: First, soak the used PAN nanofibers in dilute hydrochloric acid to remove excess iron powder, then dry them in an oven, and then put the dried PAN nanofibers into a ball mill for grinding. After the ball milling is completed, the PAN powder is separated and sieved, thus completing the recycling of PAN.

2. The method for removing nitrates from wastewater in drill-and-blast tunnel construction according to claim 1, characterized in that, In step 1, the PAN nanofibers are dried at 80°C in an oven; in step 3, the used PAN nanofibers are dried at 80°C in an oven for 10 hours.

3. The method for removing nitrates from wastewater in drill-and-blast tunnel construction according to claim 1, characterized in that, In step 3, when grinding the material in a ball mill, the ball mill speed is set to 200~400 r / min, the ball-to-material ratio is set to 50~150:1, and the ball milling time is set to 5~15 min.

4. The method for removing nitrates from wastewater in drill-and-blast tunnel construction according to claim 1, characterized in that, In step 1, the electrospinning machine is set with a voltage of 15~25kV, a feed speed of 0.01~0.03 mL / min, a receiving distance of 10~20cm, and a roller speed of 200~500r / min.

5. The method for removing nitrates from wastewater in drill-and-blast tunnel construction according to claim 1, characterized in that, In step 1, the mixture is ultrasonically dispersed and stirred for 0.5 to 2 hours, and then PAN powder is added and stirred for 4 to 16 hours.

6. The method for removing nitrates from wastewater in drill-and-blast tunnel construction according to claim 1, characterized in that, In step 2, the soaking time is 6 to 18 hours.

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