Environment-friendly low-slag low-consumption phosphating solution and preparation method thereof

Abstract

The invention discloses an environment-friendly low-slag low-consumption phosphating solution and a preparation method thereof, and belongs to the technical field of metal surface anti-rust treatment solutions. The corrosion inhibitor comprises the following chemical components in percentage by mass: 8-13% of zinc oxide, 8-12% of nitric acid, 17-25% of phosphoric acid, 0.5-0.8% of citric acid, 0.3-0.5% of hydroxylamine sulfate, 0.3-0.5% of sulfamic acid and the balance of water. The method comprises the steps of preparing zinc oxide turbid liquid; preparing a zinc salt solution; and preparing a finished product phosphating solution. The method has the advantages that invalid consumption of phosphate ions can be reduced from the source; the compactness and the anti-rust performance of the zinc-series phosphating film can be guaranteed, meanwhile, a large amount of sediment brought by nitric acid serving as a strong oxidant is avoided, and the total nitrogen content can be lower than 70 mg / L; the spontaneous precipitation of free zinc ions and phosphate ions can be inhibited, and the ion balance effect of the system can be well maintained.

Description

Technical Field

[0001] This invention belongs to the technical field of metal surface rust prevention treatment liquid, specifically relating to an environmentally friendly, low-slag, and low-consumption phosphating liquid, and also to its preparation method. Background Technology

[0002] In metal surface treatment processes, phosphating is widely used in processes such as metal pretreatment before coating, wire drawing pretreatment, cold drawing of steel pipes, precision rolling, and rust prevention of finished steel pipes. Phosphating is performed before coating to improve the adhesion of the coating and the corrosion resistance of the substrate.

[0003] Depending on the operating environment, phosphating solutions are classified into room temperature type (30-45℃), low temperature type (such as CN100443632A, which discloses "a low temperature zinc-based phosphating solution" <30-38℃>), medium temperature type (50-70℃), and high temperature type (80-90℃). Room temperature and low temperature phosphating have low energy consumption, but the phosphating time is long and the efficiency is low, making it difficult to meet the requirements of industrial-scale production. In order to promote the phosphating reaction, high concentrations of sodium nitrite are usually added as an accelerator, but this causes problems such as a large amount of sediment. High temperature phosphating has a shorter phosphating time, which is conducive to meeting the requirements of industrial production, but the energy consumption is high, and there is also a problem of a lot of sediment, which is not in line with the current social advocacy of energy-saving, economical, and environmentally friendly economic spirit.

[0004] The mechanism by which sodium nitrite, as an accelerator, is relied upon in room temperature and medium temperature zinc-based phosphating solutions is: the ferrous ions (Fe2+) generated during phosphating... 2+ ) is oxidized by sodium nitrite to trivalent iron ions (Fe) 3+ This process results in the formation of a large amount of water-insoluble ferric phosphate (FePO4) sludge in the phosphating solution, causing the solution to appear as a white liquid (known in the industry as "white phosphating"). In particular, sodium nitrite is restricted by the EU's REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) regulation, and is also listed as an acute poison and carcinogen in my country's "List of Hazardous Chemicals." Its high operational risks and stringent management requirements, coupled with its environmental impact, increase the cost of solid waste treatment.

[0005] Low-residue, especially residue-free, phosphating solutions are highly valued in the industry. For example, CN115725964A recommends "a low-temperature low-residue phosphating solution and its preparation method." However, this patent requires the addition of sodium dodecyl sulfate as a corrosion inhibitor, resulting in a complex system with many components and expensive specialized chemicals. Furthermore, the use of nickel acetate, organic peroxides such as benzoyl peroxide, and diethylene glycol leads to high raw material costs and still results in significant sludge production. Another example is CN103695881A, which provides "a room-temperature residue-free rapid phosphating solution and its preparation method." In this patent's formulation, sodium m-nitrobenzenesulfonate, used as a accelerator, is a toxic and difficult-to-degrade nitrobenzene derivative. EDTA, used as a chromium binding agent, is difficult to treat in wastewater and can cause heavy metal redissolution pollution in the water. The formulation contains 20-25% zinc nitrate, introducing a large amount of zinc ions and increasing the environmental burden. Sodium m-nitrobenzenesulfonate, as an oxidation accelerator, also promotes the removal of Fe... 2+ Oxidized to Fe 3+ It is known as slag-free, but it inevitably produces a large amount of iron phosphate sludge; although EDTA can strongly complex and inhibit sludge, once it is supersaturated and / or the pH changes, the sludge problem will recur; the price of zinc nitrate is much higher than that of zinc oxide and nitric acid alone; excessive complexation of EDTA affects the formation of crystal nuclei, resulting in an excessively thin film (phosphating film) or coarse crystals.

[0006] With the significant enhancement of environmental awareness and the awareness of economic conservation and energy saving throughout society, how to effectively eliminate residual zinc oxide, reduce or inhibit sludge, help reduce consumption, and facilitate production control have become technical issues that manufacturers developing and using phosphating solutions are concerned about and hope to solve effectively as soon as possible.

[0007] CN100443632A (a low-temperature zinc phosphating solution) is environmentally unfriendly due to the use of nickel sulfate and offers no insights into sludge suppression; CN102703889A (a low-temperature single-component zinc phosphating solution) uses hydroxylamine sulfate and citric acid, but also contains nickel nitrate (a heavy metal), sodium m-nitrobenzenesulfonate (which may decompose to produce nitrites), and sodium chlorate (a highly hazardous chemical); CN104313557A (a low-temperature phosphating solution for cold-drawn tubes) The patent mainly focuses on the ratio of total acidity to free acidity; CN105951084A (a low temperature metal passivation phosphating solution) contains sodium chlorate, which is an explosive and highly hazardous chemical; CN104250742A (a phosphating solution for pretreatment of cold-rolled steel pipes) contains nickel sulfate, which is a harmful substance and not environmentally friendly, and hydrogen peroxide, which is used as an accelerator in the formula, is unstable and easily decomposes, which can damage the life of the bath solution; CN1847455A (zinc-nickel-manganese ternary phosphating solution) is neither environmentally friendly nor safe. Summary of the Invention

[0008] The objective of this invention is to provide an environmentally friendly, low-slag, low-consumption phosphating solution that helps eliminate residual zinc oxide, inhibits sludge formation and avoids excessive total nitrogen, significantly reduces the ineffective consumption of phosphate ions from the source, facilitates production control to achieve ideal film-forming performance and bath stability, and achieves energy conservation and emission reduction.

[0009] The present invention also aims to provide a method for preparing an environmentally friendly, low-residue, and low-consumption phosphating solution. This method has simple process steps, does not rely on complex equipment, does not pose a safety risk to operators during the preparation process, and fully realizes the technical effects of the prepared environmentally friendly, low-residue, and low-consumption phosphating solution.

[0010] The objective of this invention is to provide an environmentally friendly, low-residue, and low-consumption phosphating solution, the chemical composition of which, by mass percentage, is: 8-13% zinc oxide, 8-12% nitric acid, 17-25% phosphoric acid, 0.5-0.8% citric acid, 0.3-0.5% hydroxylamine sulfate, and 0.3-0.5% aminosulfonic acid, with the remainder being water.

[0011] In a specific embodiment of the present invention, an environmentally friendly, low-slag, and low-consumption phosphating solution has the following chemical composition by mass percentage: 13% zinc oxide, 8% nitric acid, 20% phosphoric acid, 0.6% citric acid, 0.3% hydroxylamine sulfate, and 0.4% aminosulfonic acid, with the remainder being water.

[0012] In another specific embodiment of the present invention, an environmentally friendly, low-slag, and low-consumption phosphating solution has the following chemical composition by mass percentage: 11% zinc oxide, 10% nitric acid, 17% phosphoric acid, 0.8% citric acid, 0.4% hydroxylamine sulfate, and 0.5% aminosulfonic acid, with the remainder being water.

[0013] In another specific embodiment of the present invention, an environmentally friendly, low-slag, and low-consumption phosphating solution is provided, with the following chemical composition by mass percentage: 8% zinc oxide, 12% nitric acid, 25% phosphoric acid, 0.5% citric acid, 0.5% hydroxylamine sulfate, and 0.3% aminosulfonic acid, with the remainder being water.

[0014] In another specific embodiment of the present invention, the zinc oxide has a purity greater than 98-99.7%; the nitric acid has a mass percentage concentration of 65-68%; the citric acid is a white translucent crystal or powder with a main content of greater than 99.5%; the hydroxylamine sulfate is a chemically pure grade colorless or white crystal or crystalline powder with a main content of 99%; and the aminosulfonic acid is an industrial grade aminosulfonic acid with a purity greater than 99.5%.

[0015] Another objective of this invention is achieved by providing a method for preparing an environmentally friendly, low-slag, and low-consumption phosphating solution, comprising the following steps: S1. To prepare a zinc oxide suspension, add 8-13% zinc oxide by mass percentage to a stirring container filled with water and equipped with a stirrer, and control the stirring temperature, stirring time and stirring speed to obtain a zinc oxide suspension. S2. To prepare a zinc salt solution, 8-12% nitric acid and 17-25% phosphoric acid by mass percentage are added sequentially to the stirring container described in step S1, and the zinc oxide suspension is stirred until the zinc oxide is completely dissolved. The stirring temperature is kept at a medium temperature, and the stirring time and speed are controlled to obtain the zinc salt solution. S3. To prepare the finished phosphating solution, 0.5-0.8% citric acid, 0.3-0.5% hydroxylamine sulfate, and 0.3-0.5% aminosulfonic acid by mass percentage are added sequentially to the zinc salt solution described in step S2, followed by stirring, and the stirring temperature, stirring time, and stirring speed are controlled to obtain an environmentally friendly, low-slag, and low-consumption phosphating solution.

[0016] In another specific embodiment of the present invention, the water mentioned in step S1 is deionized water or reverse osmosis water; the control of stirring temperature, stirring time and stirring speed is to control the stirring temperature to room temperature, the stirring time to 20-30 min and the stirring speed to 80-100 rpm.

[0017] In a more specific embodiment of the present invention, the temperature of the medium temperature mentioned in step S2 is 60-80°C, and the stirring time and stirring speed are controlled as follows: the stirring time is controlled to be 20-40 min, and the stirring speed is controlled to be 85-110 rpm.

[0018] In a further specific embodiment of the present invention, the control of the temperature, time and speed of subsequent stirring in step S3 is to control the temperature of subsequent stirring to room temperature, the time of subsequent stirring to 30-60 min, and the speed of subsequent stirring to 80-100 rpm.

[0019] In yet another specific embodiment of the present invention, the pH value of the environmentally friendly, low-slag, and low-consumption phosphating solution in step S3 is less than 1.

[0020] The technical advantages of the solution provided by this invention are as follows: By eliminating substances such as nickel, nitrite, and sodium chlorate based on reasonable raw material selection and proportions, and employing a ternary synergistic system of environmentally friendly hydroxylamine sulfate, citric acid, and sulfamic acid, citric acid, as a complexing agent, forms a stable and soluble complex with the ferrous ions generated during phosphating, preventing the oxidation of ferrous ions to form ferric phosphate sludge, thereby reducing the ineffective consumption of phosphate ions at the source. Hydroxylamine sulfate, as a reduction promoter, ensures the density and rust prevention performance of the zinc phosphating film while avoiding a large amount of sludge caused by strong oxidizing agents such as nitric acid and keeping the total nitrogen below 70 mg / L. Sulfamic acid, as a stabilizer, stabilizes the pH and ion activity of the bath solution, thus inhibiting the spontaneous precipitation of free zinc ions and phosphate ions and effectively maintaining the ion balance of the system. Attached Figure Description

[0021] Figure 1 The image shows a photograph of the phosphate film crystal structure observed under a high-power microscope on the surface of a steel pipe after phosphate treatment, as described in an embodiment of the present invention. Figure 2 This is a photographic image showing the thickness of the phosphate film layer formed on the surface of a steel pipe after phosphate treatment with the environmentally friendly, low-slag, and low-consumption phosphate solution obtained in the embodiments of the present invention, measured using the eddy current thickness measurement method. Detailed Implementation

[0022] Example 1: The preparation method of the environmentally friendly, low-residue, and low-consumption phosphating solution of the present invention includes the following steps: S1. To prepare a zinc oxide suspension, add 13% zinc oxide by mass percentage to a stirring container filled with water and equipped with a stirrer. Stir at room temperature for 30 minutes and at a stirring speed of 80 rpm to obtain the zinc oxide suspension. The purity of the zinc oxide in this step is 99.7%. Deionized water or reverse osmosis water is preferred. The purity of the zinc oxide in this step is greater than 99.7%. S2. To prepare a zinc salt solution, 8% nitric acid and 20% phosphoric acid, by mass percentage, are added sequentially to the stirring vessel described in step S1, and the zinc oxide suspension is stirred until the zinc oxide is completely dissolved. The stirring temperature is controlled at 70°C, the stirring time is controlled at 20 minutes, and the stirring speed is controlled at 110 rpm to obtain the zinc salt solution. In this step, the mass percentage concentration of nitric acid is 68%. S3. To prepare the finished phosphating solution, 0.6% citric acid, 0.3% hydroxylamine sulfate, and 0.4% aminosulfonic acid by mass percentage are added sequentially to the zinc salt solution described in step S2. The solution is then stirred at room temperature for 60 minutes at a stirring speed of 80 rpm to obtain the finished phosphating solution, which is an environmentally friendly, low-slag, and low-consumption phosphating solution with a pH value of less than 1. The citric acid in this step is a white, semi-transparent crystal with a main content of greater than 99.5%, the hydroxylamine sulfate is a colorless or white crystal of chemical purity of 99%, and the aminosulfonic acid is an industrial-grade aminosulfonic acid with a purity of greater than 99.5%.

[0023] Example 2: The preparation method of the environmentally friendly, low-residue, and low-consumption phosphating solution of the present invention includes the following steps: S1. To prepare a zinc oxide suspension, add 11% zinc oxide by mass percentage to a stirring container filled with water and equipped with a stirrer. Stir at room temperature for 25 minutes and at a stirring speed of 90 rpm to obtain the zinc oxide suspension. The purity of the zinc oxide in this step is 99.7%. Deionized water or reverse osmosis water is preferred, and the purity of the zinc oxide in this step is greater than 98%. S2. To prepare a zinc salt solution, 10% nitric acid and 17% phosphoric acid, by mass percentage, are added sequentially to the stirring container described in step S1, and the zinc oxide suspension is stirred until the zinc oxide is completely dissolved. The stirring temperature is controlled at 60°C, the stirring time is controlled at 40 minutes, and the stirring speed is controlled at 85 rpm to obtain the zinc salt solution. In this step, the mass percentage concentration of nitric acid is 65%. S3. To prepare the finished phosphating solution, 0.8% citric acid, 0.4% hydroxylamine sulfate, and 0.5% aminosulfonic acid by mass percentage are added sequentially to the zinc salt solution described in step S2. The solution is then stirred at room temperature for 30 minutes at a stirring speed of 90 rpm to obtain the finished phosphating solution, which is an environmentally friendly, low-slag, and low-consumption phosphating solution with a pH value of less than 1. The citric acid in this step is a white, semi-transparent powder with a main content of more than 99.5%, the hydroxylamine sulfate is a colorless or white crystal of chemical purity of 99%, and the aminosulfonic acid is an industrial-grade aminosulfonic acid with a purity of more than 99.5%.

[0024] Example 3: The preparation method of the environmentally friendly, low-residue, and low-consumption phosphating solution of the present invention includes the following steps: S1. To prepare a zinc oxide suspension, add 8% zinc oxide by mass percentage to a stirring container filled with water and equipped with a stirrer. Stir at room temperature for 20 minutes and at a stirring speed of 100 rpm to obtain the zinc oxide suspension. The purity of the zinc oxide in this step is 99.7%. Deionized water or reverse osmosis water is preferred, and the purity of the zinc oxide in this step is greater than 99%. S2. To prepare a zinc salt solution, 12% nitric acid and 25% phosphoric acid, by mass percentage, are added sequentially to the stirring container described in step S1, and the zinc oxide suspension is stirred until the zinc oxide is completely dissolved. The stirring temperature is controlled at 80°C, the stirring time is controlled at 30 minutes, and the stirring speed is controlled at 100 rpm to obtain the zinc salt solution. In this step, the mass percentage concentration of nitric acid is 66%. S3. To prepare the finished phosphating solution, 0.5% citric acid, 0.5% hydroxylamine sulfate, and 0.3% aminosulfonic acid by mass percentage are added sequentially to the zinc salt solution described in step S2. The solution is then stirred at room temperature for 45 minutes at a stirring speed of 100 rpm to obtain the finished phosphating solution, which is an environmentally friendly, low-slag, and low-consumption phosphating solution with a pH value of less than 1. The citric acid in this step is a white, semi-transparent powder with a main content of more than 99.5%, the hydroxylamine sulfate is a chemically pure, colorless or white crystalline powder with a main content of 99%, and the aminosulfonic acid is an industrial-grade aminosulfonic acid with a purity of more than 99.5%.

[0025] Please see Figure 1 and Figure 2 After the steel pipe is phosphated with the environmentally friendly, low-slag, and low-consumption phosphating solution obtained in Example 1, the phosphate film formed on the surface of the steel pipe, as observed under a high-power microscope, has a crystal structure consisting of... Figure 1 As shown, since the crystalline structure of the phosphating film in Examples 2 and 3 is basically similar to that in Example 1, it is not shown in the corresponding figures. The thickness of the phosphating film layer formed on the surface of the steel pipe after phosphating treatment with the environmentally friendly, low-slag, and low-consumption phosphating solution of the present invention in Example 1 was measured to be 8.6 µm by eddy current thickness measurement method. Since the thicknesses of the phosphating film layers in Examples 2 and 3 are 8.45 µm and 8.5 µm respectively, they are not shown in the other figures.

[0026] Although aminosulfonic acid is a common chemical raw material, this invention adds it as a stabilizer to the phosphating solution formulation, achieving multiple benefits such as eliminating residual zinc oxide, reducing precipitation, assisting in reducing consumption, and facilitating production control. Because this invention eliminates heavy metal nickel and highly hazardous and explosive sodium chlorate, it solves environmental and long-standing safety hazards in the phosphating industry. Regarding the performance of the phosphating film, citric acid refines crystallization, and hydroxylamine sulfate accelerates film formation; the synergistic effect makes the film denser and has better adhesion. Since the low-slag content approaches zero slag, it reduces tank cleaning and maintenance costs, extends tank life, and saves on tank replacement costs. The absence of hazardous chemicals reduces storage and risk costs, truly embodying low consumption and low cost.

[0027] In summary, the environmentally friendly, low-slag, and low-consumption phosphating solution of this invention forms a phosphating film on the metal surface, which plays a crucial role in lubrication, supporting saponification, rust prevention, and enhancing coating adhesion. Especially in the field of cold working, it can significantly improve the wear resistance, pressure resistance, and fatigue resistance of workpieces, making it a key pretreatment measure for improving process efficiency and product quality.

[0028] In summary, the technical solution provided by this invention makes up for the shortcomings of the prior art, successfully completes the invention task, and accurately realizes the technical effects described by the applicant in the above-mentioned technical effects column.

Claims

1. An environmentally friendly, low-residue, and low-consumption phosphating solution, characterized in that: Its chemical composition by mass percentage is as follows: zinc oxide 8-13%, nitric acid 8-12%, phosphoric acid 17-25%, citric acid 0.5-0.8%, hydroxylamine sulfate 0.3-0.5%, and aminosulfonic acid 0.3-0.5%, with the remainder being water.

2. The environmentally friendly, low-slag, and low-consumption phosphating solution according to claim 1, characterized in that: Its chemical composition by mass percentage is as follows: zinc oxide 13%, nitric acid 8%, phosphoric acid 20%, citric acid 0.6%, hydroxylamine sulfate 0.3%, and aminosulfonic acid 0.4%, with the remainder being water.

3. The environmentally friendly, low-slag, and low-consumption phosphating solution according to claim 1, characterized in that: Its chemical composition by mass percentage is as follows: 11% zinc oxide, 10% nitric acid, 17% phosphoric acid, 0.8% citric acid, 0.4% hydroxylamine sulfate, and 0.5% aminosulfonic acid, with the remainder being water.

4. The environmentally friendly, low-slag, and low-consumption phosphating solution according to claim 1, characterized in that: Its chemical composition by mass percentage is as follows: 8% zinc oxide, 12% nitric acid, 25% phosphoric acid, 0.5% citric acid, 0.5% hydroxylamine sulfate, and 0.3% aminosulfonic acid, with the remainder being water.

5. The environmentally friendly, low-slag, and low-consumption phosphating solution according to claim 1, characterized in that: The zinc oxide has a purity greater than 98-99.7%; the nitric acid has a mass percentage concentration of 65-68%; the citric acid is a white, semi-transparent crystal or powder with a content greater than 99.5%; the hydroxylamine sulfate is a chemically pure grade colorless or white crystal or crystalline powder with a content of 99%; and the aminosulfonic acid is an industrial grade aminosulfonic acid with a purity greater than 99.5%.

6. A method for preparing an environmentally friendly, low-residue, and low-consumption phosphating solution as described in claim 1, characterized in that: Includes the following steps: S1. To prepare a zinc oxide suspension, add 8-13% zinc oxide by mass percentage to a stirring container filled with water and equipped with a stirrer, and control the stirring temperature, stirring time and stirring speed to obtain a zinc oxide suspension. S2. To prepare a zinc salt solution, 8-12% nitric acid and 17-25% phosphoric acid by mass percentage are added sequentially to the stirring container described in step S1, and the zinc oxide suspension is stirred until the zinc oxide is completely dissolved. The stirring temperature is kept at a medium temperature, and the stirring time and speed are controlled to obtain the zinc salt solution. S3. To prepare the finished phosphating solution, 0.5-0.8% citric acid, 0.3-0.5% hydroxylamine sulfate, and 0.3-0.5% aminosulfonic acid by mass percentage are added sequentially to the zinc salt solution described in step S2, followed by stirring, and the stirring temperature, stirring time, and stirring speed are controlled to obtain an environmentally friendly, low-slag, and low-consumption phosphating solution.

7. The method for preparing environmentally friendly, low-slag, and low-consumption phosphating solution according to claim 6, characterized in that: The water mentioned in step S1 is deionized water or reverse osmosis water; the control of stirring temperature, stirring time and stirring speed is to control the stirring temperature to room temperature, the stirring time to 20-30 min and the stirring speed to 80-100 rpm.

8. The method for preparing environmentally friendly, low-residue, and low-consumption phosphating solution according to claim 6, characterized in that: In step S2, the medium temperature is 60-80℃, and the stirring time and speed are controlled as follows: the stirring time is controlled to be 20-40 minutes, and the stirring speed is controlled to be 85-110 rpm.

9. The method for preparing environmentally friendly, low-slag, and low-consumption phosphating solution according to claim 6, characterized in that: The control of the temperature, time, and speed of subsequent stirring in step S3 refers to controlling the temperature of subsequent stirring to room temperature, controlling the time of subsequent stirring to 30-60 minutes, and controlling the speed of subsequent stirring to 80-100 rpm.

10. The method for preparing environmentally friendly, low-residue, and low-consumption phosphating solution according to claim 6, characterized in that: The pH value of the environmentally friendly, low-slag, and low-consumption phosphating solution described in step S3 is less than 1.

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