Method and device for removing oxalic acid and ferric oxalate complexes in molten liquid

Abstract

The invention discloses a method for removing oxalic acid and ferric oxalate complexes in a molten solution, which comprises the following steps: S1, carrying out UV illumination treatment on a solution containing target metabolic micromolecules, oxalic acid and ferric oxalate complexes at a low temperature of not higher than 77K, and then putting the solution into a dDNP spectrometer for polarization and melting to obtain the molten solution; s2, quickly adding a sodium hydroxide solution into the molten liquid, adjusting the pH value of the molten liquid to be alkaline, and starting to generate precipitates; s3, after the precipitation is completed, rapidly filtering to remove the precipitate to obtain a filtrate; s4, rapidly adding a hydrochloric acid solution into the filtrate, adjusting the pH value of the filtrate to be neutral, and starting to generate a precipitate; and S5, after the precipitation is completed, quickly filtering to remove the precipitation to obtain polarized clear liquid without oxalic acid and ferric oxalate complexes, and injecting the polarized clear liquid into the to-be-detected magnet of the dDNP spectrometer. Excessive sodium hydroxide and a pressure filtration type impurity removal device are introduced, and oxalic acid and oxalic acid complex iron in the molten liquid are successfully removed.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear magnetic resonance, and specifically relates to a method and device for removing oxalic acid and iron oxalate complexes from a molten solution. Background Art

[0002] The dissolution dynamic nuclear polarization technique (dDNP) can improve the detection sensitivity of nuclear magnetic resonance and plays a crucial role in the current field of nuclear magnetic resonance. In the process of realizing dDNP, the photosensitive free radical technique is an important method for generating the radical polarizer required in dDNP.

[0003] The Chinese invention patent "Application of Oxalic Acid and Iron Complexes in Dissolution Dynamic Nuclear Polarization" (Patent No. ZL202411085775.3) discloses that oxalic acid is used as a photosensitive free radical polarizer for dissolution dynamic nuclear polarization, and its UV spectral range is between 200 - 280 nm. Conventional available UV light sources can only excite oxalic acid to produce a very weak photosensitive reaction, and the generated radical concentration is very low. It is found in experiments that when adding iron oxalate complex as a photocatalyst to an oxalic acid solution, the yield of its photosensitive free radicals can be greatly increased, which can provide an appropriate concentration of unpaired radical electrons for dDNP and is expected to achieve a more efficient and faster electron-nuclear polarization transfer.

[0004] However, during subsequent radical removal, even if the generated photosensitive free radicals are quenched as the temperature rises, the presence of iron oxalate and oxalic acid in the polarized solution will still affect the use of the hyperpolarized molecular solution. Iron ions in iron oxalate complex as paramagnetic ions will accelerate the relaxation process and affect the observation of the results of polarized molecules. At the same time, too high content of oxalic acid will cause damage to organisms and thus affect the application of hyperpolarized molecules in metabolic tracing. Therefore, during the transfer of the dDNP molten solution to the magnet to be measured, quality control of the molten solution is required to remove oxalic acid and iron oxalate from the molten solution. Summary of the Invention

[0005] Based on the above-mentioned prior art, the present invention provides a method and device for removing oxalic acid and iron oxalate complexes from a molten solution. The present invention introduces an excessive amount of sodium hydroxide and a pressure filtration type impurity removal device, and successfully realizes the removal of oxalic acid and iron oxalate complex from the molten solution.

[0006] The technical solution adopted to achieve the above object of the present invention is as follows:

[0007] A method for removing oxalic acid and iron oxalate complexes from a molten solution, comprising the following steps:

[0008] S1. Subject the solution containing the target metabolic small molecule, oxalic acid, and iron oxalate complex to UV light treatment at a low temperature below 77K, and then place it in a dDNP spectrometer for polarization and melting to obtain a melted solution.

[0009] S2. Quickly add a sodium hydroxide solution to the melted solution to adjust the pH of the melted solution to alkaline, and precipitation begins to occur.

[0010] S3. After the precipitation is complete, quickly filter to remove the precipitate to obtain a filtrate.

[0011] S4. Quickly add a hydrochloric acid solution to the filtrate to adjust the pH of the filtrate to neutral, and precipitation begins to occur.

[0012] S5. After the precipitation is complete, quickly filter to remove the precipitate to obtain a polarized clear solution with oxalic acid and iron oxalate complex removed, and inject the polarized clear solution into the magnet to be detected in the dDNP spectrometer.

[0013] Furthermore, the target metabolic small molecule is selected from at least one of [1- 13 C]-pyruvic acid, 13 C-urea, and 15 N-glycine.

[0014] Furthermore, in step S2, adjust the pH of the melted solution to pH≥9.

[0015] Furthermore, the concentration of the sodium hydroxide solution is 1 M - 4 M.

[0016] Furthermore, the concentration of the hydrochloric acid solution is 0.05M - 0.15 M.

[0017] A device for removing oxalic acid and iron oxalate complex from a melted solution, comprising a first-stage removal mechanism, a second-stage removal mechanism, and a conveying mechanism for conveying the polarized clear solution to the magnet to be detected in the dDNP spectrometer.

[0018] The first-stage removal mechanism includes a first injection pump, an alkali solution injection pipeline, and a first filter. The downstream end of the melted solution injection pipeline is connected to the liquid chamber of the first injection pump. The outlet of the first injection pump is connected to the inlet of the first filter. The downstream end of the alkali solution injection pipeline is connected to the liquid chamber of the first injection pump. A first pH meter for detecting the pH of the liquid in the liquid chamber of the first injection pump is installed on the liquid chamber of the first injection pump.

[0019] The second-stage removal mechanism includes a second injection pump, a filtrate injection pipeline, an acid solution injection pipeline, and a second filter. The outlet of the first filter is connected to the upstream end of the filtrate injection pipeline. The downstream ends of the filtrate injection pipeline and the acid solution injection pipeline are respectively connected to the liquid chamber of the second injection pump. A second pH meter for detecting the pH of the liquid in the liquid chamber of the second injection pump is installed on the liquid chamber of the second injection pump. The outlet of the second injection pump is connected to the inlet of the second filter;

[0020] The conveying mechanism includes a buffer container for holding the polarized clear liquid and a conveying pipeline. The outlet of the second filter is connected to the buffer container, and the upstream end of the conveying pipeline is connected to the buffer container.

[0021] The molten solution injection pipeline includes a molten solution injection pipe and a first one-way valve. The first one-way valve is installed on the molten solution injection pipe. The downstream end of the molten solution injection pipe is connected to the liquid chamber of the first injection pump. The alkali solution injection pipeline includes an alkali solution bottle, an alkali solution injection pipe, a second one-way valve, and a first liquid pump. The upstream end of the alkali solution injection pipe is connected to the alkali solution bottle, and the downstream end of the alkali solution injection pipe is connected to the liquid chamber of the first injection pump. The second one-way valve and the first liquid pump are respectively installed on the alkali solution injection pipe.

[0022] The filtrate injection pipeline includes a filtrate injection pipe and a third one-way valve. The upstream end of the filtrate injection pipe is connected to the outlet of the first filter, and the downstream end of the filtrate injection pipe is connected to the liquid chamber of the second injection pump. The third one-way valve is installed on the filtrate injection pipe. The acid solution injection pipeline includes an acid solution bottle, an acid solution injection pipe, a fourth one-way valve, and a second liquid pump. The upstream end of the acid solution injection pipe is connected to the acid solution bottle, and the downstream end of the acid solution injection pipe is connected to the liquid chamber of the second injection pump. The fourth one-way valve and the second liquid pump are respectively installed on the acid solution injection pipe.

[0023] The conveying pipeline includes a conveying pipe and a third liquid pump. The upstream end of the conveying pipe is connected to the buffer container, and the third liquid pump is installed on the conveying pipe.

[0024] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0025] 1. The present invention adds an excessive amount of sodium hydroxide as a chemical treatment method. By utilizing the reaction between oxalic acid and sodium hydroxide to generate sodium oxalate precipitation and the characteristic that iron oxalate is insoluble in water under alkaline conditions, oxalic acid and iron oxalate complex in the molten solution can be removed simultaneously.

[0026] 2. The present invention introduces a pressurized filtration type impurity removal device, which can quickly remove the produced precipitate impurities through the filter and quickly inject the hyperpolarized molecular solution after removing oxalic acid and iron oxalate into the NMR magnet for metabolic tracing or detection. Description of the Drawings

[0027] Figure 1It is a schematic structural diagram of a device for removing oxalic acid and iron oxalate complexes in a melt solution.

[0028] Among them, 1 - first injection pump, 2 - melt solution injection pipe, 3 - first one-way valve, 4 - lye bottle, 5 - lye injection pipe, 6 - second one-way valve, 7 - first liquid pump, 8 - first pH meter, 9 - first filter, 10 - second injection pump, 11 - second pH meter, 12 - filtrate injection pipe, 13 - third one-way valve, 14 - acid solution bottle, 15 - acid solution injection pipe, 16 - fourth one-way valve, 17 - second liquid pump, 18 - second filter, 19 - buffer container, 20 - delivery pipe, 21 - third liquid pump.

[0029] Figure 2 It is a comparison chart of the relaxation times of the supernatant obtained by adjusting different simulated melt solutions to different pH values and filtering.

[0030] Figure 3 It is an HPLC spectrum of the clear solution obtained after filtering when a 2 M oxalic acid solution is adjusted to neutral. Detailed implementation mode

[0031] For the convenience of those of ordinary skill in the art to understand and implement the present invention, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0032] The device of the present invention for removing oxalic acid and iron oxalate complexes in a melt solution will be described in detail below with reference to the accompanying drawings.

[0033] Example 1

[0034] The structure of the device for removing oxalic acid and iron oxalate complexes in a melt solution provided in this embodiment is as Figure 1 shown, including a first-stage removal mechanism, a second-stage removal mechanism, and a delivery mechanism for delivering the polarized clear solution to the magnet to be detected in a dDNP spectrometer.

[0035] The melt solution injection pipeline is an existing one for delivering the melt solution. The melt solution injection pipeline includes a melt solution injection pipe 2 and a first one-way valve 3, and the first one-way valve 3 is installed on the melt solution injection pipe 2.

[0036] The first - stage removal mechanism includes a first injection pump 1, an alkali - solution injection pipeline, and a first filter. The downstream end of the molten - solution injection pipe 2 is connected to the liquid chamber of the first injection pump 1. The alkali - solution injection pipeline includes an alkali - solution bottle 4, an alkali - solution injection pipe 5, a second one - way valve 6, and a first liquid pump 7. The upstream end of the alkali - solution injection pipe 5 is connected to the alkali - solution bottle 4, and the downstream end of the alkali - solution injection pipe 5 is connected to the liquid chamber of the first injection pump 1. The second one - way valve 6 and the first liquid pump 7 are respectively installed on the alkali - solution injection pipe 5. A first pH meter 8 is installed on the liquid chamber of the first injection pump 1, and the first pH meter 8 is used to detect the pH of the liquid in the liquid chamber of the first injection pump 1.

[0037] The outlet of the first injection pump 1 is connected to the inlet of the first filter 9 (diameter: 13 mm, pore size: 0.22 μm, material: polyethersulfone, Jinteng). The piston of the first injection pump 1 is quickly pushed to quickly push the mixed liquid with precipitate in the liquid chamber of the first injection pump 1 into the first filter 9 for filtration.

[0038] The second - stage removal mechanism includes a second injection pump 10, a filtrate injection pipeline, an acid - solution injection pipeline, and a second filter 18. The filtrate injection pipeline includes a filtrate injection pipe 12 and a third one - way valve 13. The upstream end of the filtrate injection pipe 12 is connected to the outlet of the first filter 10, and the downstream end of the filtrate injection pipe 12 is connected to the liquid chamber of the second injection pump 10. The third one - way valve 13 is installed on the filtrate injection pipe 12. The acid - solution injection pipeline includes an acid - solution bottle 14, an acid - solution injection pipe 15, a fourth one - way valve 16, and a second liquid pump 17. The upstream end of the acid - solution injection pipe 15 is connected to the acid - solution bottle 14, and the downstream end of the acid - solution injection pipe 15 is connected to the liquid chamber of the second injection pump 10. The fourth one - way valve 16 and the second liquid pump 17 are respectively installed on the acid - solution injection pipe 15. A second pH meter 11 is installed on the liquid chamber of the second injection pump 10, and the second pH meter 11 is used to detect the pH of the liquid in the liquid chamber of the second injection pump 10.

[0039] The outlet of the second injection pump 10 is connected to the inlet of the second filter 18. The piston of the second injection pump 10 is quickly pushed to quickly push the mixed liquid with precipitate in the liquid chamber of the second injection pump 10 into the second filter 18 for filtration.

[0040] The conveying mechanism includes a buffer container 19 (such as a buffer bottle, etc.) for holding the polarized clear liquid and a conveying pipeline. The outlet of the second filter 18 is connected to the buffer container 19, and the super - polarized molecular solution after removing oxalic acid and iron oxalate enters the buffer container 19. The conveying pipeline includes a conveying pipe 20 and a third liquid pump 21. The upstream end of the conveying pipe 20 is connected to the buffer container 19, and the third liquid pump 21 is installed on the conveying pipe 20. The polarized clear liquid is quickly pumped into the magnet to be detected of the dDNP spectrometer through the third liquid pump 21.

[0041] The method for removing oxalic acid and iron oxalate complex in the melt according to the present invention will be described in detail below in conjunction with the above-mentioned device.

[0042] Example 2

[0043] 1. Load 2 M sodium hydroxide solution into the alkali solution bottle 4, and load 0.1 M hydrochloric acid solution into the acid solution bottle 14.

[0044] 2. A 150 μL sample solution containing 2 M oxalic acid, 15 mM iron oxalate, and [1- 13 C]-pyruvate is subjected to UV light irradiation at a temperature of 77K, and then placed in a dDNP spectrometer for polarization and melting to obtain a melt.

[0045] 3. Open the first one-way valve 3, and the melt enters the liquid chamber of the first syringe pump 1 through the melt injection tube 2. After the melt injection is completed, close the first one-way valve 3. Then open the second one-way valve 6 and the first liquid pump 7, and the sodium hydroxide solution in the alkali solution bottle 4 is quickly injected into the liquid chamber of the first syringe pump 1 and mixed with the melt in the liquid chamber of the first syringe pump 1. Sodium oxalate and iron oxalate precipitates begin to appear in the liquid chamber of the first syringe pump 1. Adjust the pH of the melt to 9 according to the first pH meter 8, and then close the second one-way valve 6 and the first liquid pump 7.

[0046] 4. After the precipitation is complete, open the third one-way valve 13, and at the same time quickly push the piston of the first syringe pump 1 to quickly push the mixed liquid in the first syringe barrel 1 into the first filter 9 for rapid filtration to quickly remove the sodium oxalate and iron oxalate precipitates. The filtrate is injected into the liquid chamber of the second syringe pump 10 through the filtrate injection tube 12.

[0047] 5. After the filtrate injection is completed, close the third one-way valve 13. Open the fourth one-way valve 16 and the second liquid pump 17, and the hydrochloric acid solution in the acid solution bottle 14 is quickly injected into the liquid chamber of the second syringe pump 10 and mixed with the filtrate in the liquid chamber of the second syringe pump 10. Precipitates begin to appear in the liquid chamber of the second syringe pump 10. Adjust the pH of the filtrate to 7 according to the second pH meter 11, and then close the fourth one-way valve 16 and the second liquid pump 17.

[0048] 6. After the precipitation is complete, quickly push the piston of the second syringe pump 10 to quickly push the mixed liquid in the liquid chamber of the second syringe pump 10 into the second filter 18 for rapid filtration to quickly remove the precipitates, and the obtained polarized clear liquid enters the buffer container 19.

[0049] 7. After the polarized clear liquid completely enters the buffer container 19, turn on the third liquid pump 21 to pump the polarized clear liquid in the buffer container 19 to the magnet to be detected in the dDNP spectrometer.

[0050] Experiment 1: Changes in Relaxation Time of Oxalic Acid, Iron(III) Oxalate, and Oxalic Acid - Iron(III) Oxalate Solutions at Different pH Values

[0051] Experimental Method:

[0052] S1. Dissolve oxalic acid in water to prepare an oxalic acid solution with an oxalic acid concentration of 2 M. Dissolve iron(III) oxalate hexahydrate (Fe2(C2O4)3·6H2O) in a 1.6 wt% hydrochloric acid solution to prepare an iron(III) oxalate solution with an iron(III) oxalate concentration of 15 mM. Dissolve oxalic acid and iron(III) oxalate hexahydrate in water to obtain an oxalic acid - iron(III) oxalate mixed solution, where the concentration of oxalic acid is 2 M, the concentration of iron(III) oxalate is 15 mM, and the actual concentration of iron(III) oxalate is 15 mM * (11% - 12.5%). Dissolve sodium hydroxide in water to prepare a sodium hydroxide solution with a concentration of 2 M. Dilute concentrated hydrochloric acid with water to prepare a hydrochloric acid solution with a concentration of 0.1 M.

[0053] S2. To simulate the dissolution process during melting polarization, add 150 μL of the iron(III) oxalate solution to 6.5 mL of water to obtain a simulated melt solution. Then, use a 2 M sodium hydroxide solution to adjust the pH of the simulated melt solution to 6 to obtain a sample solution. Take 2 mL of the sample solution, filter it using a filter to obtain a clear solution A1. Continue to use a 2 M sodium hydroxide solution to adjust the pH of the remaining sample solution to 9, filter it to obtain a clear solution A2. Take 2 mL of A2 and adjust the pH to around 7 using a 0.1 M hydrochloric acid solution, filter it to obtain a clear solution A3. Clear solutions A1, A2, and A3 are used for subsequent determination of relaxation time.

[0054] S3. Treat the oxalic acid solution according to the method in step S2 to obtain clear solutions B1, B2, and B3. Treat the oxalic acid - iron(III) oxalate mixed solution according to the method in step S2 to obtain clear solutions C1, C2, and C3.

[0055] S4. Use time - domain NMR technology to measure the relaxation times of clear solutions A1, A2, A3, B1, B2, B3, C1, C2, and C3, and compare them with the relaxation time of pure water.

[0056] Experimental Results:

[0057] The relaxation times of the above nine clear solutions and the relaxation time of pure water are as Figure 2 shown. From Figure 2It can be seen that when the simulated molten solutions simulated by iron(III) oxalate, oxalic acid, and oxalic acid - iron(III) oxalate are adjusted to pH = 6 using sodium hydroxide solution, the relaxation times of the clear solutions A1, B1, and C1 are all relatively short at this time. The clear solutions A1 and C1 are affected by iron ions, and the relaxation times are even shorter. When the pH is adjusted to pH = 9, the relaxation times of the clear solutions A2, B2, and C2 are similar to that of pure water, indicating that the oxalic acid and / or iron(III) oxalate in the simulated molten solution are almost completely removed at this time. Subsequently, when the pH of the clear solutions A2, B2, and C2 is adjusted to pH = 7, it is observed that the relaxation times of the solutions of the clear solutions A3, B3, and C3 decrease slightly, which may be caused by the re - dissolution of a small amount of iron(III) oxalate precipitate that has not been completely filtered, but the clear solutions A3, B3, and C3 still maintain long relaxation times at this time. This proves that introducing an excessive amount of sodium hydroxide and a pressure - filtration type impurity removal device can effectively remove oxalic acid and iron oxalate complex in the molten solution.

[0058] Experiment 2: Determination of the oxalic acid content in the oxalic acid - iron(III) oxalate solution when adjusted to neutral

[0059] Test method:

[0060] S1. Dissolve 2 M oxalic acid and 15 mM iron(III) oxalate hexahydrate in water to obtain an oxalic acid - iron(III) oxalate mixed solution, where the actual concentration of iron(III) oxalate is 15 mM*(11% - 12.5%). Dissolve sodium hydroxide in water to prepare a 2 M sodium hydroxide solution. Dilute concentrated hydrochloric acid with water to prepare a 0.1 M hydrochloric acid solution.

[0061] S2. Take 150 μL of the oxalic acid - iron(III) oxalate mixed solution and add it to 6.5 mL of water to obtain a simulated molten solution. Then use a 2 M sodium hydroxide solution to adjust the pH of the simulated molten solution to 9, and filter to obtain a filtrate. Use a 0.1 M hydrochloric acid solution to adjust the pH of the filtrate to about pH = 7, and filter to obtain a supernatant for subsequent determination of the oxalic acid content.

[0062] S3. Take 0.12174 g of the supernatant and make up the volume to 10 mL, with a dilution factor of 2 times. Determine the peak area of oxalic acid in the clear solution by HPLC and convert it to obtain the oxalic acid content in the clear solution.

[0063] Test results:

[0064] The HPLC chromatogram of the clear solution is as Figure 3 shown. After converting the peak area of the HPLC chromatogram, it can be known that after removing the oxalic acid and iron(III) oxalate in the simulated molten solution, the oxalic acid content in the supernatant is 0.4 wt%, and the oxalic acid concentration at this time is the human safety concentration. This shows that by introducing an excessive amount of sodium hydroxide and a pressure - filtration type impurity removal device to remove oxalic acid and iron oxalate complex in the molten solution, the residual oxalic acid concentration in the obtained polarized clear solution will not affect organisms.

Claims

1. A method for removing oxalic acid and ferric oxalate complex in a melt, characterized in that It includes the following steps: S1. Perform UV light irradiation treatment on the solution containing the target metabolite small molecule, oxalic acid, and iron oxalate complex at a low temperature not higher than 77K, and then put it into a dDNP spectrometer for polarization and melting to obtain a melted solution; S2. Quickly add a sodium hydroxide solution to the melted solution, adjust the pH of the melted solution to alkaline, and precipitation starts to occur; S3. After the precipitation is complete, quickly filter to remove the precipitate to obtain a filtrate; S4. Quickly add a hydrochloric acid solution to the filtrate, adjust the pH of the filtrate to neutral, and precipitation starts to occur; S5. After the precipitation is complete, quickly filter to remove the precipitate to obtain a polarized clear solution from which oxalic acid and iron oxalate complex are removed, and inject the polarized clear solution into the magnet to be detected in the dDNP spectrometer.

2. The method for removing oxalic acid and ferric oxalate complex in the melt according to claim 1, characterized in that: The target metabolic small molecule is selected from at least one of [[1- 13 C]-pyruvic acid, 13 C-urea, and 15 N-glycine.

3. The method for removing oxalic acid and ferric oxalate complex from the melt according to claim 1, characterized in that: In step S2, the pH of the melted solution is adjusted to pH≥9.

4. The method for removing oxalic acid and ferric oxalate complex in the melt according to claim 1, wherein: The concentration of the sodium hydroxide solution is 1 M - 4 M.

5. The method for removing oxalic acid and ferric oxalate complex in the melt according to claim 1, characterized in that: The concentration of the hydrochloric acid solution is 0.05M - 0.15 M.

6. An apparatus for removing oxalic acid and ferric oxalate complex in a melt, characterized in that: It includes a first-stage removal mechanism, a second-stage removal mechanism, and a conveying mechanism for conveying the polarized clear solution to the magnet to be detected in the dDNP spectrometer, The first-stage removal mechanism includes a first injection pump, an alkali solution injection pipeline, and a first filter. The downstream end of the melted solution injection pipeline is connected to the liquid chamber of the first injection pump. The outlet of the first injection pump is connected to the inlet of the first filter. The downstream end of the alkali solution injection pipeline is connected to the liquid chamber of the first injection pump. A first pH meter for detecting the pH of the liquid in the liquid chamber of the first injection pump is installed on the liquid chamber of the first injection pump; The second-stage removal mechanism includes a second injection pump, a filtrate injection pipeline, an acid solution injection pipeline, and a second filter. The outlet of the first filter is connected to the upstream end of the filtrate injection pipeline. The downstream ends of the filtrate injection pipeline and the acid solution injection pipeline are respectively connected to the liquid chamber of the second injection pump. A second pH meter for detecting the pH of the liquid in the liquid chamber of the second injection pump is installed on the liquid chamber of the second injection pump. The outlet of the second injection pump is connected to the inlet of the second filter; The conveying mechanism includes a buffer container for holding the polarized clear solution and a conveying pipeline. The outlet of the second filter is connected to the buffer container. The upstream end of the conveying pipeline is connected to the buffer container.

7. The device for removing oxalic acid and ferric oxalate complex in the melt according to claim 6, wherein: The melted solution injection pipeline includes a melted solution injection tube and a first one-way valve. The first one-way valve is installed on the melted solution injection tube. The downstream end of the melted solution injection tube is connected to the liquid chamber of the first injection pump. The alkali solution injection pipeline includes an alkali solution bottle, an alkali solution injection tube, a second one-way valve, and a first liquid pump. The upstream end of the alkali solution injection tube is connected to the alkali solution bottle. The downstream end of the alkali solution injection tube is connected to the liquid chamber of the first injection pump. The second one-way valve and the first liquid pump are respectively installed on the alkali solution injection tube.

8. The device for removing oxalic acid and iron oxalate complex in the melt according to claim 6, characterized in that: The filtrate injection pipeline includes a filtrate injection tube and a third one-way valve. The upstream end of the filtrate injection tube is connected to the outlet of the first filter. The downstream end of the filtrate injection tube is connected to the liquid chamber of the second injection pump. The third one-way valve is installed on the filtrate injection tube. The acid solution injection pipeline includes an acid solution bottle, an acid solution injection tube, a fourth one-way valve, and a second liquid pump. The upstream end of the acid solution injection tube is connected to the acid solution bottle. The downstream end of the acid solution injection tube is connected to the liquid chamber of the second injection pump. The fourth one-way valve and the second liquid pump are respectively installed on the acid solution injection tube.

9. The device for removing oxalic acid and ferric oxalate complex in the melt according to claim 6, characterized in that: The described conveying pipeline includes a conveying pipe and a third liquid pump. The upstream end of the conveying pipe is connected to a buffer container, and the third liquid pump is installed on the conveying pipe.

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