A pure manganese-based black phosphating solution for electrolytic manganese flake production and a preparation method thereof

Abstract

The present application relates to the technical field of metal surface treatment, and particularly relates to a pure manganese black phosphating solution for electrolytic manganese flake production and a preparation method thereof, which comprises phosphoric acid, nitric acid, electrolytic manganese, modified nickel-cerium-molybdenum coprecipitation compound, hydrogen peroxide and water. In the present application, the three active components of nickel, cerium and molybdenum in the modified nickel-cerium-molybdenum coprecipitation compound synergistically play a role under the phosphating working condition: the nickel component participates in the construction of the film layer crystal grains, and improves the film layer compactness; the cerium component is enriched at the film layer microdefects, and inhibits the autocatalytic corrosion induced by chloride ions; and the molybdenum component is adsorbed on the film layer defect sites, and enhances the chemical stability. The present application does not contain antimony and organic matter, and has low waste liquid treatment difficulty and a mild process.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically to a pure manganese-based black phosphating solution produced from electrolytic manganese sheets and its preparation method. Background Technology

[0002] Manganese phosphating is a common surface treatment technique for steel and electrolytic manganese flakes. It involves the reaction of phosphoric acid with metallic manganese at high temperatures to deposit a black chemical conversion film, primarily composed of Mn3(PO4)2, on the substrate surface. In electrolytic manganese flake production, black phosphating is often used industrially to improve product appearance and oxidation resistance, by introducing sulfur (Sb). 3+ Blackening agents give the film a uniform black color, which requires the use of organic complexing agents (such as citric acid, tartaric acid, etc.) to maintain Sb. 3+ Stability, to prevent hydrolysis and precipitation.

[0003] High concentrations of chloride ions are commonly found in the production environment of electrolytic manganese flakes. The main sources include: firstly, the electrolysis process often uses a manganese chloride system or an electrolyte containing ammonium chloride, leading to the introduction of chloride ions into the manganese flake substrate and pretreatment residues. - Secondly, in the black phosphating formulation, in order to inhibit Sb 3+ Hydrolysis introduces hydrochloric acid or chloride, further increasing the chloride ion concentration in the system.

[0004] When the above phosphating system is simultaneously subjected to high temperature (70-90℃) and high concentration of Cl... - Under conditions where organic complexing agents coexist, the carboxyl and hydroxyl groups in the complexing agent react with Mn. 2+ Strong coordination occurs, leading to free Mn 2+ The concentration decreased significantly. Free Mn 2+ The deficiencies directly interfere with the normal film formation process of manganese phosphate conversion membranes—an imbalance in the initial deposition rate prevents the membrane from growing uniformly and densely, ultimately resulting in a loose, porous structure with poor adhesion to the substrate. The loose phosphate membrane has a severely insufficient ability to block chloride ions. - After penetrating the micro-defects in the membrane and reaching the manganese substrate, MnCl2 reacts with the substrate under high temperature and acidic conditions. MnCl2 then hydrolyzes at the interface to produce hydrochloric acid, causing a sharp drop in the local pH. This hydrolysis reaction exhibits autocatalytic properties: the generated hydrochloric acid further accelerates the dissolution of the substrate, releasing more Mn. 2+ and Cl - This creates a vicious cycle of "MnCl2 generation - hydrolysis and acidification - accelerated matrix dissolution," which not only leads to localized film peeling and failure but also causes the deep pitting corrosion of the matrix to develop. Summary of the Invention

[0005] (1) Technical problems to be solved The purpose of this invention is to provide a pure manganese-based black phosphating solution produced by electrolytic manganese flakes and its preparation method, in order to solve the problem of the interaction between organic complexing agents and Mn under high temperature and high chlorine conditions. 2+ Strong coordination leads to a loose manganese phosphate membrane and Cl - It easily penetrates and induces self-catalytic corrosion due to the hydrolysis of MnCl2.

[0006] (2) Technical solution To achieve the above objectives, on the one hand, the present invention provides a pure manganese-based black phosphating solution produced from electrolytic manganese sheets, comprising the following components by weight percentage: 25-33% phosphoric acid, 5-9% nitric acid, 6-15% electrolytic manganese, 1.5-3.5% modified nickel-cerium-molybdenum coprecipitation complex, 0.1-0.3% hydrogen peroxide, and water as the balance. The modified nickel-cerium-molybdenum coprecipitation complex is a complex obtained by hydrothermal coprecipitation crystallization of modified nickel nitrate, modified cerium nitrate, and sodium molybdate dihydrate; the modified nickel nitrate is nickel nitrate modified by tetramethoxysilane via sol-gel method; the modified cerium nitrate is cerium nitrate modified by KH550 via hydrothermal method.

[0007] Furthermore, the phosphoric acid has a mass percentage concentration of 85%; the nitric acid has a mass percentage concentration of 68%; and the electrolytic manganese has a purity of >99.7%.

[0008] Furthermore, the preparation method of the modified nickel nitrate includes the following steps: M11. Mix anhydrous ethanol and distilled water thoroughly, then add tetramethoxysilane; while stirring, adjust the pH with dilute nitric acid; then stir again to obtain a tetramethoxysilane hydrolysate. M12. Dissolve nickel nitrate hexahydrate in anhydrous ethanol to obtain a nickel nitrate solution; add the nickel nitrate solution dropwise to a tetramethoxysilane hydrolysate while stirring; continue stirring after the addition is complete to obtain a precursor solution; M13. Transfer the precursor solution to a sealed container and allow it to stand to gel; after gelation, age the gel to obtain the aged gel. M14. The aged gel was washed with anhydrous ethanol to remove residual methanol and uncondensed silanol molecules; after washing, it was dried to remove solvent and free water; after drying, it was ground to obtain modified nickel nitrate.

[0009] Furthermore, the volume ratio of anhydrous ethanol to distilled water is 3:1; the molar ratio of tetramethoxysilane to nickel nitrate hexahydrate is 4:1.

[0010] Furthermore, the preparation method of the modified cerium nitrate includes the following steps: M21. Dissolve KH550 in distilled water, add cerium nitrate hexahydrate, stir, and obtain mixture A; M22. Transfer mixture A to a reaction vessel; seal it and heat the reaction, then allow it to cool naturally to obtain a precipitate; M23. The precipitate was separated by centrifugation, washed successively with distilled water and anhydrous ethanol; dried, and ground to obtain modified cerium nitrate.

[0011] Furthermore, the mass ratio of KH550 to cerium nitrate hexahydrate is 1:2.

[0012] Furthermore, the preparation method of the modified nickel-cerium-molybdenum coprecipitation composite includes the following steps: M31. Modified nickel nitrate was added to deionized water and ultrasonically dispersed to obtain suspension A; modified cerium nitrate was added to deionized water and ultrasonically dispersed to obtain suspension B; M32. Dissolve sodium molybdate dihydrate in deionized water to obtain solution C; while stirring, add suspension A and suspension B dropwise to solution C in sequence; after the addition is complete, continue stirring to obtain mixture B; M33. Adjust the pH of mixture B with dilute nitric acid, then transfer mixture B to a reaction vessel to react and obtain a coprecipitated product; M34. After natural cooling, the coprecipitate is centrifuged and the supernatant is discarded. The obtained solid is washed successively with deionized water and anhydrous ethanol to remove unreacted ions and organic residues, and the washed solid is obtained. M35. The washed solid was dried and then ground to obtain a modified nickel-cerium-molybdenum coprecipitate composite.

[0013] Furthermore, the solid-liquid ratio of the modified nickel nitrate to deionized water is 1:20, with the mass-volume ratio unit being g / mL; the solid-liquid ratio of the modified cerium nitrate to deionized water is 1:20, with the mass-volume ratio unit being g / mL.

[0014] On the other hand, the present invention also provides a method for preparing pure manganese-based black phosphating solution produced by electrolytic manganese sheets, comprising the following steps: M1. Add deionized water to the reaction vessel, and add phosphoric acid and nitric acid in sequence while stirring, and continue stirring until well mixed; after the acid solution cools down, add hydrogen peroxide and continue stirring to obtain a mixed acid solution; M2. Electrolytic manganese is added to the mixed acid solution while stirring, and the reaction is cooled in a water bath. A small amount of nitrogen oxide gas is generated during the dissolution of electrolytic manganese. The tail gas is treated using a sodium hydroxide solution absorption device to obtain a transparent solution. M3. Add the modified nickel-cerium-molybdenum coprecipitation complex to the transparent solution, stir, and obtain the phosphating working solution; add the remaining deionized water, continue stirring, and obtain the pure manganese-based black phosphating solution.

[0015] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. This invention modifies nickel nitrate and cerium nitrate with tetramethoxysilane and KH550, respectively, and then constructs a modified nickel-cerium-molybdenum coprecipitation composite with sodium molybdate dihydrate via a hydrothermal reaction, replacing traditional organic complexing agents and antimony-based blackening agents. Under phosphating working temperature (83-87℃) and strong acid conditions, the composite matrix undergoes slow dissolution, allowing the dispersed nickel, cerium, and molybdenum active components to be continuously and controllably released into the working fluid: the nickel component participates in the grain formation of the manganese phosphate film, refining the grains and improving the film density; the molybdenum component, as an adsorption-type corrosion inhibitor, preferentially accumulates at film defect sites, enhancing the chemical stability of the film; the cerium component preferentially accumulates and deposits at micro-defects in the film, forming a protective oxide coating layer in the cathode region, effectively inhibiting the autocatalytic corrosion cycle of "MnCl2 generation - hydrolysis and acidification - accelerated matrix dissolution" induced by chloride ions. The synergistic release mechanism of the three components also avoids the problem of uneven film formation caused by a sudden increase in ion concentration, maintaining free Mn 2+ The stable concentration gives the membrane both physical barrier and electrochemical protection functions.

[0016] 2. This invention adds a small amount of hydrogen peroxide as an oxidation promoter, which moderately increases the redox potential of the system, accelerating the anodic dissolution process in the early stage of film formation. This facilitates the rapid formation of uniform manganese phosphate crystal nuclei on the manganese substrate surface and shortens the film induction period. This invention does not contain antimony or organic complexing agents, making wastewater treatment easy and meeting clean production requirements. The composite preparation is based on sol-gel and hydrothermal methods, which are mild, use readily available raw materials, and are well-suited to the high chlorine residues commonly found in electrolytic manganese sheet production environments. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: This example discloses a pure manganese-based black phosphating solution produced from electrolytic manganese sheets, comprising the following components by weight percentage: phosphoric acid 29%, nitric acid 7%, electrolytic manganese 11%, modified nickel-cerium-molybdenum coprecipitation complex 2.5%, hydrogen peroxide 0.2%, and water 50.3%; The modified nickel-cerium-molybdenum coprecipitation complex is a complex obtained by hydrothermal coprecipitation crystallization of modified nickel nitrate, modified cerium nitrate, and sodium molybdate dihydrate; the modified nickel nitrate is nickel nitrate modified by tetramethoxysilane via sol-gel method; the modified cerium nitrate is cerium nitrate modified by KH550 via hydrothermal method.

[0019] The phosphoric acid has a mass percentage concentration of 85%; the nitric acid has a mass percentage concentration of 68%; and the electrolytic manganese has a purity of >99.7%.

[0020] The method for preparing the modified nickel nitrate includes the following steps: M11. Mix 90 mL of anhydrous ethanol with 30 mL of distilled water until homogeneous, then add 20 mL of tetramethoxysilane; while stirring, adjust the pH to 3.0–4.0 with dilute nitric acid; then stir at room temperature for 40 minutes to obtain a tetramethoxysilane hydrolysate. M12. Dissolve 9.7 g of nickel nitrate hexahydrate in 10 mL of anhydrous ethanol to obtain a nickel nitrate solution; add the nickel nitrate solution dropwise to the tetramethoxysilane hydrolysate at a rate of 1-2 mL / min while stirring continuously; continue stirring for 1.5 hours after the addition is complete to obtain a precursor solution. M13. Transfer the precursor solution to a sealed container and let it stand at room temperature for 36 hours to allow it to gel; after gelation, age it at room temperature for 24 hours to obtain the aged gel. M14. The aged gel was washed three times with anhydrous ethanol to remove residual methanol and uncondensed silanol molecules; after washing, it was dried at 70°C for 18 hours to remove solvent and free water; after drying, it was ground to obtain modified nickel nitrate.

[0021] The method for preparing the modified cerium nitrate includes the following steps: M21. Dissolve 2.21g of KH550 in 45mL of distilled water, add 4.34g of cerium nitrate hexahydrate, and stir continuously for 30 minutes to obtain mixture A; M22. Transfer mixture A to a 100mL hydrothermal reactor, with a filling volume not exceeding 80mL; seal and react at 140℃ for 24h, then allow to cool naturally to room temperature to obtain a precipitate; M23. The precipitate was separated by centrifugation, washed three times with distilled water and twice with anhydrous ethanol, dried under vacuum at 45°C for 8 hours, and then ground to obtain modified cerium nitrate.

[0022] The preparation method of the modified nickel-cerium-molybdenum coprecipitation composite includes the following steps: M31. Add 1.0 g of modified nickel nitrate to 20 mL of deionized water and sonicate for 30 minutes to obtain suspension A; add 0.5 g of modified cerium nitrate to 10 mL of deionized water and sonicate for 30 minutes to obtain suspension B. M32. Dissolve 0.48 g of sodium molybdate dihydrate in 20 mL of deionized water to obtain solution C; while stirring, add suspension A and suspension B dropwise to solution C at a rate of 1-2 mL / min; after the addition is complete, continue stirring for 1 hour to obtain mixture B; M33. Adjust the pH of mixture B to 4.0-5.0 with dilute nitric acid, then transfer mixture B to a 100mL polytetrafluoroethylene-lined hydrothermal reactor and react at 140℃ for 18 hours to obtain a coprecipitated product; M34. After naturally cooling to room temperature, centrifuge the coprecipitate (8000 rpm, 10 minutes) and discard the supernatant; wash the obtained solid three times with deionized water (20 mL each time) and twice with anhydrous ethanol (15 mL each time) to remove unreacted ions and organic residues, and obtain the washed solid. M35. After washing the solid, it was vacuum dried at 70°C for 10 hours and then ground evenly with an agate mortar to obtain a modified nickel-cerium-molybdenum coprecipitate complex.

[0023] The method for preparing pure manganese-based black phosphating solution produced from electrolytic manganese sheets includes the following steps: M1. Add 1 / 3 of the total amount of deionized water to the reactor, and add phosphoric acid and nitric acid in sequence while stirring. Continue stirring until the mixture is homogeneous. After the acid solution temperature cools to below 25°C, add hydrogen peroxide and continue stirring for 10-20 minutes to obtain a mixed acid solution. M2. Add electrolytic manganese to the mixed acid solution while stirring. Cool the reaction in a water bath. A small amount of nitrogen oxide gas will be generated during the dissolution of electrolytic manganese. Use a sodium hydroxide solution absorption device to treat the tail gas until the electrolytic manganese is completely dissolved and a transparent solution is obtained. M3. Add the modified nickel-cerium-molybdenum coprecipitation complex to the transparent solution and stir for 60 minutes to obtain the phosphating working solution; add the remaining deionized water and continue stirring for 60 minutes to obtain the pure manganese-based black phosphating solution.

[0024] Example 2: This example is based on Example 1, but differs from Example 1 in that it includes the following components by weight percentage: 25% phosphoric acid, 5% nitric acid, 6% electrolytic manganese, 1.5% modified nickel-cerium-molybdenum coprecipitation complex, 0.1% hydrogen peroxide, and 62.4% water; other components and preparation methods are the same as in Example 1.

[0025] Example 3: This example is based on Example 1, but differs from Example 1 in that it includes the following components by weight percentage: 33% phosphoric acid, 9% nitric acid, 15% electrolytic manganese, 3.5% modified nickel-cerium-molybdenum coprecipitation complex, 0.3% hydrogen peroxide, and 39.2% water; other components and preparation methods are the same as in Example 1.

[0026] Comparative Example 1: This comparative example differs from Example 1 in that unmodified nickel nitrate is used instead of modified nickel nitrate. The amounts of the remaining components and the preparation methods are the same as in Example 1.

[0027] Comparative Example 2: This comparative example differs from Example 1 in that unmodified cerium nitrate is used instead of modified cerium nitrate. The amounts of the remaining components and the preparation methods are the same as in Example 1.

[0028] Comparative Example 3: This comparative example differs from Example 1 in that modified nickel-cerium-molybdenum coprecipitate complex is not added. The amounts of other components and the preparation methods are the same as in Example 1.

[0029] Comparative Example 4: This comparative example differs from Example 1 in that modified cerium nitrate is not added to the modified nickel-cerium-molybdenum coprecipitate composite. The amounts of the remaining components and the preparation methods are the same as in Example 1.

[0030] Comparative Example 5: This comparative example differs from Example 1 in that modified nickel-cerium-molybdenum coprecipitation complex is not supplemented with modified nickel nitrate or modified cerium nitrate. In this comparative example, the preparation method of the modified nickel-cerium-molybdenum coprecipitation complex is adjusted from Example 1 as follows: only 0.48 g of sodium molybdate dihydrate is dissolved in 20 mL of deionized water, the pH is adjusted to 4.0–5.0, and then hydrothermal treatment is performed directly. The amounts and preparation methods of the remaining components are the same as in Example 1.

[0031] Comparative Example 6: This comparative example differs from Example 1 in that sodium molybdate dihydrate is not added to the modified nickel-cerium-molybdenum coprecipitate composite. In this comparative example, the preparation method of the modified nickel-cerium-molybdenum coprecipitate composite is adjusted from Example 1 as follows: only suspension A and suspension B are mixed and then directly subjected to hydrothermal treatment. The amounts of other components and the preparation methods are the same as in Example 1.

[0032] Comparative Example 7: This comparative example differs from Example 1 in that industrial manganese carbonate (Mn content ≥44%) is used instead of electrolytic manganese. The amounts of the remaining components and the preparation methods are the same as in Example 1.

[0033] Comparative Example 8: This comparative example differs from Example 1 in that the modified nickel-cerium-molybdenum coprecipitation complex is not added, while the amounts of the remaining components and the preparation methods are the same as in Example 1.

[0034] Comparative Example 9: This comparative example differs from Example 1 only in that the modified nickel-cerium-molybdenum coprecipitation complex is replaced with citric acid (2.3%) and tartaric acid (0.7%), while the amounts of the remaining components and the preparation methods are exactly the same as in Example 1.

[0035] Experimental verification: I. Experimental Preparation 1. Test piece: Electrolytic manganese sheet (purity ≥99.7%), size 50mm×50mm×1mm, polished with 400# and 800# sandpaper in sequence, degreased with acetone, rinsed with deionized water, and dried with cold air for later use.

[0036] 2. Phosphating solution: Prepared according to Examples 1-3 and Comparative Examples 1-9. Each phosphating solution is freshly prepared. Before use, the total acidity and free acidity are measured and adjusted to the process range (total acidity 25-35 points, free acidity 3-5 points).

[0037] 3. Heat each phosphating solution to 85±2℃, immerse the pretreated test pieces vertically in the solution for 10 minutes. After removal, rinse with deionized water, dry with cold air, and place in a desiccator for 24 hours before performance testing.

[0038] II. Performance Testing All the following tests used three parallel test pieces, and the results were averaged.

[0039] 1. Membrane weight determination: According to GB / T 9792-2003 standard, weigh the phosphated sample (m1), immerse it in a stripping solution containing 20 g / L chromic anhydride for 15 min at room temperature (20±5℃), remove, clean, dry, and weigh (m2). Membrane weight (g / m) 2 = (m1-m2) / area.

[0040] 2. Adhesion test: After phosphating, the same batch of epoxy primer (dry film thickness 20±2μm) was rolled onto the surface of the test piece. After curing at room temperature for 48h, the adhesion was tested according to the cross-cut test method (cross-cut spacing 1mm) of GB / T 9286-2022 to evaluate the overall bonding status between the phosphating conversion film and the subsequent coating system. The rating was 0 to 5 (0 is the best, no peeling; 5 is the worst, large-area peeling). The worst value among three parallel test pieces was used for the rating.

[0041] 3. Neutral salt spray resistance test: Conducted according to GB / T 10125-2021, with continuous spraying, and record the time (h) when rust (red rust) area on the surface of the test piece reaches 5%.

[0042] 4. Chloride ion corrosion immersion test (weight loss method): Corrosive medium preparation: Simulating the high-concentration acidic conditions of chloride ions in the electrolytic manganese production environment, a chloride-containing medium was prepared. - A corrosive solution of 1000 ppm (as NaCl) and pH=3.0 (adjusted with dilute hydrochloric acid). Test steps: (1) Dry the phosphated sample at 105℃ for 1 h, cool it and weigh it, and record the initial mass W0 (accurate to 0.1 mg); (2) Immerse the sample completely in the corrosive medium, seal it and place it in a 70℃ constant temperature water bath for 120 h; (3) After soaking, take out the sample, gently brush the surface corrosion products with a soft brush in running water, and then rinse it with deionized water; (4) Dry the sample at 105℃ for 1 h, cool it and weigh it, and record the mass W1 after corrosion. Calculation formula: Corrosion weight loss per unit area ∆W (mg / cm²) = (W0-W1) / S; where S is the total surface area of ​​the sample (cm²).2 The smaller the ∆W value, the stronger the film's affinity for Cl. - The stronger the barrier properties, the better the corrosion resistance.

[0043] Table 1 Performance test results:

[0044] As shown in Table 1, Examples 1-3 outperformed the comparative examples in terms of film weight, adhesion, salt spray time, and resistance to chloride ion weight loss, proving that the synergistic effect of the nickel, cerium, and molybdenum components is indispensable. Comparative Examples 3, 4, and 6 performed worse than the examples, with Comparative Example 5 showing the worst performance among Comparative Examples 1-6, confirming that single or dual components cannot achieve effective protection. Although Comparative Example 7 had a slightly higher film weight, the impurities caused a porous film layer, resulting in inferior corrosion resistance compared to the examples, demonstrating the necessity of high-purity electrolytic manganese. Comparative Example 8 showed the worst performance among the comparative examples; Comparative Example 9, using an organic complexing agent, exhibited higher resistance to chloride ion weight loss than the examples, collectively verifying the decisive contribution of the composite material and the technical advantages of replacing organic complexing agents.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pure manganese-based black phosphating solution produced from electrolytic manganese sheets, characterized in that, It includes the following components by weight percentage: phosphoric acid 25-33%, nitric acid 5-9%, electrolytic manganese 6-15%, modified nickel-cerium-molybdenum coprecipitate complex 1.5-3.5%, hydrogen peroxide 0.1-0.3%, and water as the balance; The modified nickel-cerium-molybdenum coprecipitation complex is a complex obtained by hydrothermal coprecipitation crystallization of modified nickel nitrate, modified cerium nitrate, and sodium molybdate dihydrate; the modified nickel nitrate is nickel nitrate modified by tetramethoxysilane via sol-gel method; the modified cerium nitrate is cerium nitrate modified by KH550 via hydrothermal method.

2. The pure manganese-based black phosphating solution produced from electrolytic manganese sheets according to claim 1, characterized in that, The phosphoric acid has a mass percentage concentration of 85%; the nitric acid has a mass percentage concentration of 68%; and the electrolytic manganese has a purity of >99.7%.

3. The pure manganese-based black phosphating solution produced from electrolytic manganese sheets according to claim 1, characterized in that, The method for preparing the modified nickel nitrate includes the following steps: M11. Mix anhydrous ethanol and distilled water thoroughly, then add tetramethoxysilane; while stirring, adjust the pH with dilute nitric acid; then stir again to obtain a tetramethoxysilane hydrolysate. M12. Dissolve nickel nitrate hexahydrate in anhydrous ethanol to obtain a nickel nitrate solution; add the nickel nitrate solution dropwise to a tetramethoxysilane hydrolysate while stirring; continue stirring after the addition is complete to obtain a precursor solution; M13. Transfer the precursor solution to a sealed container and let it stand; after gel formation, age the gel to obtain the aged gel. M14. The aged gel was washed with anhydrous ethanol; dried after washing; and ground after drying to obtain modified nickel nitrate.

4. The pure manganese-based black phosphating solution produced from electrolytic manganese sheets according to claim 3, characterized in that, The volume ratio of anhydrous ethanol to distilled water is 3:1; the molar ratio of tetramethoxysilane to nickel nitrate hexahydrate is 4:

1.

5. The pure manganese-based black phosphating solution produced from electrolytic manganese sheets according to claim 1, characterized in that, The method for preparing the modified cerium nitrate includes the following steps: M21. Dissolve KH550 in distilled water, add cerium nitrate hexahydrate, stir, and obtain mixture A; M22. Transfer mixture A to a reaction vessel; seal it and heat the reaction, then allow it to cool naturally to obtain a precipitate; M23. The precipitate was separated by centrifugation, washed successively with distilled water and anhydrous ethanol; dried, and ground to obtain modified cerium nitrate.

6. The pure manganese-based black phosphating solution produced from electrolytic manganese sheets according to claim 5, characterized in that, The mass ratio of KH550 to cerium nitrate hexahydrate is 1:

2.

7. The pure manganese-based black phosphating solution produced from electrolytic manganese sheets according to claim 1, characterized in that, The preparation method of the modified nickel-cerium-molybdenum coprecipitation composite includes the following steps: M31. Modified nickel nitrate was added to deionized water and ultrasonically dispersed to obtain suspension A; modified cerium nitrate was added to deionized water and ultrasonically dispersed to obtain suspension B; M32. Dissolve sodium molybdate dihydrate in deionized water to obtain solution C; while stirring, add suspension A and suspension B dropwise to solution C to obtain mixture B. M33. Adjust the pH of mixture B with dilute nitric acid, then transfer mixture B to a reaction vessel to react and obtain a coprecipitated product; M34. After natural cooling, the coprecipitate is centrifuged and the supernatant is discarded; the obtained solid is washed successively with deionized water and anhydrous ethanol to obtain the washed solid. M35. The washed solid was dried and then ground to obtain a modified nickel-cerium-molybdenum coprecipitate composite.

8. The pure manganese-based black phosphating solution produced from electrolytic manganese sheets according to claim 7, characterized in that, The solid-liquid ratio of the modified nickel nitrate to deionized water is 1:20, and the mass-volume ratio is expressed in g / mL; the solid-liquid ratio of the modified cerium nitrate to deionized water is 1:20, and the mass-volume ratio is expressed in g / mL.

9. A method for preparing a pure manganese-based black phosphating solution produced from electrolytic manganese sheets according to any one of claims 1 to 8, characterized in that, Includes the following steps: M1. Add deionized water to the reaction vessel, and add phosphoric acid and nitric acid in sequence while stirring, and continue stirring until well mixed; after the acid solution cools down, add hydrogen peroxide and continue stirring to obtain a mixed acid solution; M2. Electrolytic manganese is added to the mixed acid solution while stirring, and the reaction is cooled in a water bath to obtain a transparent solution; M3. Add the modified nickel-cerium-molybdenum coprecipitation complex to the transparent solution, stir, and obtain the phosphating working solution; add deionized water and continue stirring to obtain the pure manganese-based black phosphating solution.

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