A bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings and its application.

Abstract

This invention discloses a bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings and its application, belonging to the field of aquaculture wastewater treatment technology. The invention utilizes a self-made circular electrolytic cell, along with cation and anion exchange membranes, a bipolar membrane, a peristaltic pump, and ruthenium-iridium-titanium electrodes, to form a bipolar membrane electrodialysis device. From left to right, the bipolar membrane electrodialysis device consists of an anode chamber, a tailings leaching chamber, a wastewater chamber, and a cathode chamber. A bipolar membrane connects the anode chamber and the tailings leaching chamber, a cation exchange membrane connects the tailings leaching chamber and the wastewater chamber, and an anion exchange membrane connects the wastewater chamber and the cathode chamber. Under the influence of an electric field, the bipolar membrane electrodialysis device catalyzes the dissociation of water to generate H₂. + And enter the tailings leaching chamber to assist in the Mg removal of magnesium tailings. 2+ Leaching, Mg in the tailings leaching chamber 2+ and OH in the cathode chamber ‑ It enters the wastewater chamber under the influence of an electric field, where OH... ‑ Under suitable alkaline conditions, nitrogen and phosphorus in aquaculture wastewater in the wastewater chamber are effectively precipitated in the form of magnesium ammonium phosphate precipitate.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture wastewater treatment technology, specifically relating to a bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings and its application. Background Technology

[0002] With population growth and rising living standards, global demand for fish is constantly increasing, making aquaculture the fastest-growing segment of the global food supply chain. China has the largest freshwater aquaculture industry in the world, but this rapid development has also brought many environmental problems. Freshwater aquaculture typically requires ample water resources, but my country has long faced a water shortage. Aquaculture processes discharge large amounts of wastewater into water bodies, with nitrogen and phosphorus being the main pollutants. Excessive nitrogen and phosphorus can cause eutrophication, leading to aquatic environmental imbalance and exacerbating water resource depletion. Furthermore, phosphorus is a non-renewable resource, making its recycling crucial.

[0003] Currently, the main methods for treating aquaculture wastewater include ion exchange / adsorption, ozone oxidation, and biological treatment. However, these methods all have unavoidable drawbacks. Ion exchange / adsorption methods suffer from limited adsorption capacity, low efficiency, and the inability to remove nitrogen and phosphorus simultaneously. Ozone oxidation is easily affected by water quality and other factors, and residual ozone in the water can harm aquatic organisms. Biological treatment methods have long reaction processes and are easily affected by natural conditions. Furthermore, these methods cannot effectively recover nitrogen and phosphorus resources.

[0004] Magnesium ammonium phosphate precipitation is a type of chemical precipitation method that uses NH4+. + Mg 2+ and PO4 3- This method involves generating magnesium ammonium phosphate hexahydrate under alkaline conditions to remove nitrogen and phosphorus from water. The recovered magnesium ammonium phosphate precipitate is not only a high-quality slow-release fertilizer but can also be used as a flame retardant to reduce the risk of wildfires. The magnesium ammonium phosphate precipitation process often requires the addition of phosphorus and magnesium, making the selection of phosphorus and magnesium sources crucial. Given the large number of tailings ponds in my country and their high environmental risk, using magnesium tailings as a magnesium source can reduce resource waste, achieve resource recovery, and alleviate resource pressure.

[0005] Bipolar membrane electrodialysis technology is developed based on traditional electrodialysis technology, adding a special ion exchange membrane—the bipolar membrane—compared to the traditional electrodialysis process. Under the action of an external electric field, water in the middle layer of the bipolar membrane dissociates to produce H₂. + and OH-, H + OH- ions migrate through the cation exchange layer and anion exchange layer to both ends of the system, respectively, while the water consumed in the intermediate layer is replenished through free diffusion. Calculations based on the second Wien effect model show that the hydrolysis rate of the bipolar membrane is 10 times that of conventional water electrolysis. 7The theoretical energy consumption of bipolar membrane hydrolysis is only about 40% of that of water electrolysis. Bipolar membrane hydrolysis does not produce gas and can generate acids and bases in situ without the addition of foreign substances. Therefore, exploring a method that combines bipolar membrane electrodialysis technology with abundant magnesium tailings resources for the resource-based treatment and recovery of nitrogen and phosphorus from aquaculture wastewater has significant practical value and broad application prospects.

[0006] Patent CN113025829A discloses a method for treating copper ore smelting waste using bipolar membrane electrodialysis. It combines an electrolytic cell with anion and cation exchange membranes and a bipolar membrane, using ruthenium-iridium-titanium plates as electrodes to form a bipolar membrane electrodialysis device for treating copper ore smelting waste. However, the main technical problem addressed by this patent is the harmless treatment and resource utilization of copper ore smelting waste, making it unsuitable for application in the field of aquaculture wastewater treatment. Patent CN113023845A discloses an electrochemical method for recovering low concentrations of nitrogen and phosphorus from wastewater using struvite. It connects a bipolar membrane electrodialysis system in series with a magnesium-air battery system, utilizing the bipolar membrane electrodialysis system to treat NH4 in wastewater. + and PO4 3 Separation, enrichment, and concentration were performed, and then the enriched NH4 was pumped out using a peristaltic pump. + and PO4 3 Pumped to the magnesium-air battery system, it reacts with the Mg generated spontaneously by the magnesium-air battery system. 2+ The reaction produces struvite, while simultaneously utilizing the OH generated by the bipolar membrane and the Ca enriched by bipolar membrane electrodialysis. 2+ The reaction produces Ca(OH)₂ precipitate, which is removed by filtration, reducing the amount of Ca. 2+ The method affects the purity of struvite and simultaneously generates electrical energy. However, it also involves the crystallization process of struvite, requiring a MAC system composed of a self-made cylindrical container, magnesium strips, titanium plates, resistors, and a multimeter. This system utilizes the spontaneously generated OH and Mg atoms from the MAC system. 2+ Provides Mg for struvite crystallization 2+ This method utilizes an alkaline environment to address the increased costs associated with the addition of magnesium sources and alkaline reagents during the traditional struvite crystallization process. Furthermore, it leverages the self-discharge process of MAC to generate electrical energy. Consequently, the apparatus involved in this method is quite complex, and the application requires stringent conditions. Summary of the Invention

[0007] The purpose of this invention is to provide a bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings and its application, wherein the bipolar membrane electrodialysis device catalyzes the dissociation of water to generate H2O. + And enter the tailings leaching chamber to assist in the Mg removal of magnesium tailings. 2+ Leaching, Mg in the tailings leaching chamber 2+Under the influence of the electric field, OH- ions in the cathode chamber enter the wastewater chamber. In the suitable alkaline environment provided by OH- ions, nitrogen and phosphorus in the aquaculture wastewater in the wastewater chamber are effectively precipitated in the form of magnesium ammonium phosphate precipitate.

[0008] The technical solution of the present invention is as follows:

[0009] One objective of this invention is to provide a bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings. Magnesium tailings powder is used as the magnesium source. NaNO3 solution, NaOH solution, HNO3 / NaNO3 mixed solution and aquaculture wastewater are added to the bipolar membrane electrodialysis device. After the solutions are mixed evenly, the device is connected to a DC constant current power supply. Under the action of an external electric field, the device is treated by bipolar membrane electrodialysis technology for 4-12 hours. Finally, the magnesium ammonium phosphate precipitate generated in the bipolar membrane electrodialysis device is recovered.

[0010] Furthermore, the amount of magnesium tailings powder added is 25g / L-250g / L.

[0011] Furthermore, the operating current of the DC regulated power supply is 0.469-5mA / cm. 2 .

[0012] Furthermore, the concentrations of both the NaNO3 solution and the NaOH solution are 0.3 mol / L.

[0013] Furthermore, the concentration of the HNO3 / NaNO3 mixed solution is 0.1-0.8 mol / L, wherein the ratio of HNO3 to NaNO3 is (0-0.4):(0-0.4), and is not both 0.

[0014] Furthermore, the bipolar membrane electrodialysis device includes a cylindrical trough-shaped electrolytic cell, a peristaltic pump, and a wastewater external beaker connected in series. Inside the cylindrical trough-shaped electrolytic cell, bipolar membranes, cation exchange membranes, and anion exchange membranes are arranged vertically and parallel in sequence. An anode electrode is arranged on the side of the cylindrical trough-shaped electrolytic cell opposite to the bipolar membrane, and a cathode electrode is arranged on the side of the cylindrical trough-shaped electrolytic cell opposite to the anion exchange membrane. An anode chamber is formed between the anode electrode and the bipolar membrane, a tailings chamber is formed between the bipolar membrane and the cation exchange membrane, a wastewater chamber is formed between the cation exchange membrane and the anion exchange membrane, and a cathode chamber is formed between the anion exchange membrane and the cathode electrode.

[0015] Furthermore, the cylindrical trough-shaped electrolytic cell is made entirely of nylon or other acid and alkali resistant materials.

[0016] Furthermore, NaNO3 solution is added to the anode chamber, with the amount of NaNO3 solution added being 90% of the anode chamber volume; NaOH solution is added to the cathode chamber, with the amount of NaOH solution added being 90% of the cathode chamber volume; a mixed solution of HNO3 / NaNO3 and magnesium tailings powder is added to the tailings chamber, with the amount of magnesium tailings powder added being 90% of the tailings chamber volume; and aquaculture wastewater is added to the wastewater chamber.

[0017] Furthermore, both the anode and cathode electrodes of the bipolar membrane electrodialysis device are made of ruthenium-iridium-titanium electrodes.

[0018] The second objective of this invention is to provide a bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings, which can be applied to the recovery of nitrogen and phosphorus from aquaculture wastewater.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. This invention utilizes magnesium tailings as a magnesium source and employs bipolar membrane electrodialysis technology to recover nitrogen and phosphorus from wastewater via magnesium ammonium phosphate precipitation. This approach achieves high-value-added comprehensive utilization of the abundant magnesium resources in the magnesium tailings, while also generating Mg from the leaching process. 2+ This invention can react with nitrogen and phosphorus in aquaculture wastewater to form magnesium ammonium phosphate precipitate, thereby achieving recycling and maximizing the benefits of magnesium resources. On the other hand, this invention solves the problem of magnesium tailings solid waste storage and the environmental pollution it causes, promotes the development of the circular economy of industrial solid waste, and has great significance for the protection of the natural and production environments.

[0021] 2. The bipolar membrane electrodialysis device disclosed in this invention can generate acids and bases in situ, catalyzing the hydrolysis of water to produce H+. + Enter the tailings leaching chamber, in H + The action promotes the leaching of magnesium tailings to produce Mg 2+ Mg in the tailings leaching chamber 2+ Under the influence of an electric field, OH- ions in the cathode chamber enter the wastewater chamber. The presence of OH- ions provides a suitable alkaline environment for the formation of magnesium ammonium phosphate precipitate. This bipolar membrane electrodialysis method reduces the use of other chemical reagents in the process, lowers the treatment and recycling costs of aquaculture wastewater, and realizes the resource utilization of wastewater.

[0022] Figure Labels

[0023] Figure 1 This is a schematic diagram of the wastewater treatment unit of the self-made cylindrical trough-shaped electrolytic cell in the bipolar membrane electrodialysis device for recovering nitrogen and phosphorus from magnesium tailings according to the present invention.

[0024] The reference numerals in the attached diagram are as follows: 1. Cylindrical trough electrolytic cell; 2. Anode electrode; 3. Bipolar membrane; 4. Cation exchange membrane; 5. Anion exchange membrane; 6. Cathode electrode; 7. Wastewater outdoor inlet beaker; 8. Peristaltic pump;

[0025] Figure 2 The image shows the XRD pattern of magnesium ammonium phosphate precipitate recovered by the bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings in Example 1 of this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0027] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0028] In the quantitative experiments in the following examples, three replicate experiments were set up, and the average value of the results was taken.

[0029] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0030] Example 1

[0031] This embodiment provides a bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings.

[0032] The wastewater to be treated (containing ammonia nitrogen: 0.03 mol / L, phosphorus: 0.015 mol / L) is introduced into... Figure 1 In the wastewater chamber of the bipolar membrane electrodialysis device shown, 0.3 mol / L NaNO3 solution is added to the anode chamber, 0.3 mol / L NaOH solution is added to the cathode chamber, and a 0.6 mol / L HNO3 / NaNO3 (0.3 / 0.1) mixed solution and 95 g / L magnesium tailings powder are added to the tailings chamber. Then, the peristaltic pump, mechanical stirrer, and power supply are turned on, and the DC constant current power supply is controlled at 3.6 mA / cm². 2 After 6 hours of treatment, the ammonia nitrogen removal rate in the wastewater was 58.85%, and the phosphorus removal rate was 99.34%. Simultaneously, magnesium ammonium phosphate precipitate was formed in the wastewater, and its XRD pattern is shown below. Figure 1 As shown.

[0033] Example 2

[0034] This embodiment provides a bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings.

[0035] The wastewater to be treated (containing ammonia nitrogen: 0.03 mol / L, phosphorus: 0.015 mol / L) is introduced into... Figure 1In the wastewater chamber of the bipolar membrane electrodialysis device shown, 0.3 mol / L NaNO3 solution is added to the anode chamber, 0.3 mol / L NaOH solution is added to the cathode chamber, and a 0.8 mol / L HNO3 / NaNO3 (0.4 / 0.2) mixed solution and 250 g / L magnesium tailings powder are added to the tailings chamber. Then, the peristaltic pump, mechanical stirrer, and power supply are turned on, and the DC constant current power supply is controlled to operate at 5 mA / cm². 2 After 12 hours of treatment, the ammonia nitrogen removal rate in the wastewater was 59.51%, the phosphorus removal rate was 95.19%, and magnesium ammonium phosphate precipitate was formed in the wastewater.

[0036] Example 3

[0037] This embodiment provides an application of a bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings.

[0038] The wastewater to be treated (containing ammonia nitrogen: 0.03 mol / L, phosphorus: 0.015 mol / L) is introduced into... Figure 1 In the wastewater chamber of the bipolar membrane electrodialysis device shown, 0.3 mol / L NaNO3 solution is added to the anode chamber, 0.3 mol / L NaOH solution is added to the cathode chamber, and a 0.4 mol / L HNO3 / NaNO3 (0.2 / 0.2) mixed solution and 155 g / L magnesium tailings powder are added to the tailings chamber. Then, the peristaltic pump, mechanical stirrer, and power supply are turned on, and the DC constant current power supply is controlled at 2.3 mA / cm². 2 After 8 hours of treatment, the ammonia nitrogen removal rate in the wastewater was 58.33%, the phosphorus removal rate was 86.63%, and magnesium ammonium phosphate precipitate was formed in the wastewater.

[0039] Example 4

[0040] This embodiment provides an application of a bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings.

[0041] The wastewater to be treated (containing ammonia nitrogen: 0.03 mol / L, phosphorus: 0.015 mol / L) is introduced into... Figure 1 In the wastewater chamber of the bipolar membrane electrodialysis device shown, 0.3 mol / L NaNO3 solution is added to the anode chamber, 0.3 mol / L NaOH solution is added to the cathode chamber, and a 0.1 mol / L HNO3 / NaNO3 (0.3 / 0.4) mixed solution and 25 g / L magnesium tailings powder are added to the tailings chamber. Then, the peristaltic pump, mechanical stirrer, and power supply are turned on, and the DC constant current power supply is controlled at 0.469 mA / cm². 2 After 4 hours of treatment, the ammonia nitrogen removal rate in the wastewater was 37.96%, the phosphorus removal rate was 99.34%, and magnesium ammonium phosphate precipitate was formed in the wastewater.

[0042] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A bipolar membrane electrodialysis method for recovering nitrogen and phosphorus using magnesium tailings, characterized by, The magnesium tailing powder is used as a magnesium source, NaNO3 solution is added into the anode chamber of the bipolar membrane electrodialysis device, the HNO3 / NaNO3 mixed solution and the magnesium tailing powder are added into the tailing chamber, the aquaculture wastewater is added into the wastewater chamber, NaOH solution is added into the cathode chamber, then the direct current stabilizing power supply of the device is connected, the bipolar membrane electrodialysis technology is used for treatment under the action of the external electric field for 4-12 h, and finally the generated magnesium ammonium phosphate precipitate in the bipolar membrane electrodialysis device is recovered; The bipolar membrane electrodialysis device comprises a cylindrical slot-shaped electrolytic cell, a peristaltic pump and a wastewater chamber connected with a beaker in series; the cylindrical slot-shaped electrolytic cell is internally provided with a bipolar membrane, a cation exchange membrane and an anion exchange membrane arranged in sequence and vertically in parallel; the side surface of the cylindrical slot-shaped electrolytic cell opposite to the bipolar membrane is provided with an anode electrode, and the side surface of the cylindrical slot-shaped electrolytic cell opposite to the anion exchange membrane is provided with a cathode electrode; the anode electrode and the bipolar membrane form an anode chamber, the bipolar membrane and the cation exchange membrane form a tailing chamber, the cation exchange membrane and the anion exchange membrane form a wastewater chamber, and the anion exchange membrane and the cathode electrode form a cathode chamber.

2. A bipolar membrane electrodialysis process for recovering nitrogen and phosphorus from magnesium tailings according to claim 1, characterized in that, The magnesium tailing powder is added in an amount of 25 g / L-250 g / L.

3. A bipolar membrane electrodialysis process for recovering nitrogen and phosphorus from magnesium tailings according to claim 1, characterized in that, The direct current stabilized power supply operating current is 0.469-5 mA / cm 2 .

4. A bipolar membrane electrodialysis process for recovering nitrogen and phosphorus from magnesium tailings according to claim 1, characterized in that, The concentrations of the NaNO3 solution and the NaOH solution are both 0.3 mol / L.

5. A bipolar membrane electrodialysis process for recovering nitrogen and phosphorus from magnesium tailings according to claim 1, characterized in that, The concentration of the HNO3 / NaNO3 mixed solution is 0.1-0.8 mol / L, the ratio of HNO3 to NaNO3 is (0-0.4):(0-0.4), and the ratio is not 0 at the same time.

6. A bipolar membrane electrodialysis process for recovering nitrogen and phosphorus from magnesium tailings as claimed in claim 1, wherein, The cylindrical slot-shaped electrolytic cell is made of nylon or other acid and alkali resistant materials.

7. A bipolar membrane electrodialysis process for recovering nitrogen and phosphorus from magnesium tailings as claimed in claim 1, wherein, The NaNO3 solution is added into the anode chamber, the addition amount of the NaNO3 solution is 90% of the volume of the anode chamber, the NaOH solution is added into the cathode chamber, the addition amount of the NaOH solution is 90% of the volume of the cathode chamber, the HNO3 / NaNO3 mixed solution and the magnesium tailing powder are added into the tailing chamber, the addition amount of the magnesium tailing powder is 90% of the volume of the tailing chamber, and the aquaculture wastewater is added into the wastewater chamber.

8. A bipolar membrane electrodialysis process for recovering nitrogen and phosphorus from magnesium tailings as claimed in claim 1, wherein, The anode electrode and the cathode electrode of the bipolar membrane electrodialysis device are both made of ruthenium iridium titanium electrodes.

9. Application of the bipolar membrane electrodialysis method for recovering nitrogen and phosphorus from magnesium tailings according to any one of claims 1 to 8 to recovery of nitrogen and phosphorus in aquaculture wastewater.

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