Method for removing a metal coating from an article having a steel substrate.
Patent Information
- Application Number
- JP2026504668
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-07-27
- Filing Date
- 2024-07-26
- Publication Date
- 2026-08-18
AI Technical Summary
【0014】 発明の説明 本発明の1つ以上の目的は、鋼基材を有する物品から金属コーティングを選択的に除去する方法であって、トリクロロ酢酸(TCA)またはメタンスルホン酸(MSA)を含む水溶液を準備する工程、および、物品を水溶液中に浸漬する工程を含む方法を提供することにより達成される。TCAおよびMSAは両方とも比較的強い有機酸であり、これらは、電流および加熱の適用を必要とすることなく金属コーティングを容易に溶解し得る。さらに、驚くべきことに、両酸は、鋼と比較して金属コーティングに対して極めて高い選択性を有することが見出された。したがって、自己制御型プロセス(self-regulating process)が得られ、金属コーティングは、鋼基材から選択的に除去され得る。物品は、金属コーティングの溶解が実質的に完了するまで、水溶液中に保持される。金属コーティングが完全に溶解した後、反応は自発的に停止するため、水溶液中における鉄の溶解は防止され得るか、または、少なくとも鉄の溶解の発生は無視できるレベル(insignificant level)である。可能な一実施形態において、水溶液は、水と、トリクロロ酢酸(TCA)およびメタンスルホン酸(MSA)のうちの1種とから本質的に構成される。したがって、水溶液中の他の物質による鉄の溶解のリスクが防止され得る。
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for selectively removing a metal coating from an article having a steel substrate.
Background Art
[0002] Steel recycling saves resources and reduces CO2 emissions, energy consumption, and water usage. However, steel waste usually contains various metal elements derived from metal coatings formed by coating or plating the steel substrate for the purpose of improving corrosion resistance, adhesion, or appearance. The coating material and the steel substrate must be properly separated from each other for recovery and reintroduction into the manufacturing cycle. For example, tinplate, which consists of a steel substrate coated with a thin layer of tin, is widely used in the food and beverage industries. As a result of high usage and efficient waste recovery, a significant amount of steel waste is generated, and thus, tinplate recycling is inevitable for the realization of a sustainable world. However, while tin has an advantageous effect as a tin layer on the steel substrate, it has an adverse effect on the properties of the steel substrate and the steelmaking process. Also, since tin is not easily removed from molten steel in the steelmaking process, it is important to remove tin from steel waste before reusing the steel waste in the steelmaking process. Therefore, before using the steel substrate as clean scrap in the steelmaking process, tinplate scrap is subjected to a detinning process for removing tin from the tin-coated steel substrate.
[0003] US4164542(A) discloses one conventional detinning method. This method rapidly removes tin from tinned scrap metal to produce a detinned base metal with a shiny metallic surface, and includes immersing the scrap metal in a container containing an aqueous detinning solution essentially comprising 18-30% sodium hydroxide and 2-10% sodium nitrate or sodium nitrite for up to about 20 minutes to completely dissolve the tin plating from the base metal. The solution is heated to a temperature above 110°C to enhance the initial effect of dissolving the tin plating. At this relatively high concentration and temperature, the tin reacts with the sodium salt in the solution to form sodium stannate, which precipitates from the solution and is continuously separated by a centrifuge or filter press. The detined scrap is washed with water as it is removed from the detinning bath, and the used wash water is discharged into the detinning bath.
[0004] However, this process cannot selectively remove tin from tinplate because some of the steel substrate also dissolves in the liquid bath during the process. Furthermore, this process is inefficient from a cost and energy standpoint because it requires maintaining the liquid bath temperature above 110°C.
[0005] Steel scrap may have lacquer and paint layers that need to be removed from the steel substrate before the steel can be recycled. EP0105551(B1) discloses a method for detinting painted tin waste, in which the waste is placed as the anode in a bath containing NaOH and subjected to electrolytic treatment. In this method, the tin waste is compressed and then placed in a bath solution with a NaOH concentration of 6-15% to achieve substantial softening of the paint. The softening of the paint is carried out at a temperature of 70-90°C for 12-16 hours. After that, electrolytic treatment is performed to remove tin from beneath the paint film. However, this process also requires a large amount of energy to heat the alkaline solution. Furthermore, this process is time-consuming.
[0006] In addition to tin, various other metals such as Zn, Al, and Mg are also widely used as coating / plating materials on steel substrates, depending on the requirements of each industrial sector. It is extremely important to remove these metals from the steel substrate before using it in the steelmaking process.
[0007] In conclusion, selectively removing metal coatings from steel substrates and recovering both the iron and coating metal elements in a reusable quality is important from both an environmental and economic standpoint. [Overview of the project] [Problems that the invention aims to solve]
[0008] The present invention provides additional improvements, additional advantages, or alternatives to the prior art.
[0009] Purpose of the invention The object of the present invention is to provide a method for selectively removing a metal coating from an article having a steel substrate.
[0010] Another object of the present invention is to provide a method for selectively, energy-efficiently, and cost-efficiently removing a metal coating from an article having a steel substrate.
[0011] Another object of the present invention is to provide a method for recovering steel by selectively removing a metal coating from an article having a steel substrate.
[0012] Another object of the present invention is to provide a method for recovering coating metal elements by selectively removing the metal coating from an article having a steel substrate.
[0013] Another object of the present invention is to provide an aqueous solution for use in a method for selectively removing a metal coating from an article having a steel substrate. [Means for solving the problem]
[0014] Description of the Invention One or more objects of the present invention are achieved by providing a method for selectively removing a metal coating from an article having a steel substrate, comprising the steps of preparing an aqueous solution containing trichloroacetic acid (TCA) or methanesulfonic acid (MSA), and immersing the article in the aqueous solution. Both TCA and MSA are relatively strong organic acids that can readily dissolve metal coatings without the need for the application of electric current and heating. Furthermore, surprisingly, both acids have been found to have extremely high selectivity for metal coatings compared to steel. Thus, a self-regulating process is obtained, and the metal coating can be selectively removed from the steel substrate. The article is held in the aqueous solution until the dissolution of the metal coating is substantially complete. After the metal coating is completely dissolved, the reaction spontaneously stops, so that the dissolution of iron in the aqueous solution can be prevented, or at least the occurrence of iron dissolution is at an insignificant level. In one possible embodiment, the aqueous solution essentially consists of water and one of trichloroacetic acid (TCA) and methanesulfonic acid (MSA). Therefore, the risk of iron dissolution by other substances in the aqueous solution can be prevented.
[0015] In this method, distilled water, deionized water, or tap water may be used to obtain an aqueous solution. In one possible embodiment of the present invention, the temperature of the aqueous solution is 5 to 50°C, preferably 15 to 30°C, and more preferably 18 to 25°C. Since the entire process can be carried out at room temperature without heating the aqueous solution, a cost-effective and energy-efficient method is obtained.
[0016] In one possible embodiment, the aqueous solution contains methanesulfonic acid (CH3SO3H). The following reaction occurs between tin and methanesulfonic acid: 2CH3SO3H+Sn→Sn 2+ +2CH3SO3 - +H2
[0017] Methanesulfonic acid (MSA) has a pKa of -1.9 and acts as a strong acid due to its sulfonate group, readily dissolving metal coatings. MSA is a widely available industrial agent and can provide a cost-effective method. The concentration of MSA in the aqueous solution is 15% to 70% by weight, preferably 40% to 60% by weight, more preferably 45% to 55% by weight, and most preferably 50% to 55% by weight, based on the total weight of the aqueous solution.
[0018] In one possible embodiment, the aqueous solution contains trichloroacetic acid (CCl3COOH). The following reaction occurs between tin and trichloroacetic acid: 2CCl3COOH + Sn → Sn 2+ +2Cl3COO - +H2
[0019] Trichloroacetic acid (TCA), with a pKa value of 0.7, is also a relatively strong acid. TCA has the advantage of being able to dissolve metal coatings at much lower concentrations than MSA. In one possible embodiment, the concentration of TCA in the aqueous solution is 3% to 25% by weight, preferably 5% to 20% by weight, more preferably 7% to 15% by weight, and most preferably 10% to 15% by weight, based on the total weight of the aqueous solution.
[0020] In one possible embodiment, the metal coating comprises one or more of Sn, Zn, Al, or Mg. The metal coating may also comprise a metal alloy of Sn, Zn, Al, or Mg. Preferably, the metal coating comprises tin. The metal coating can serve various purposes such as corrosion resistance, paint adhesion, magnetism, hardness, conductivity, surface roughness, or decoration. The above metal elements or other suitable elements may be selected or preferred depending on environmental, technical, and / or economic constraints. These metals may be applied to the steel substrate by plating, coating, or other suitable methods. The article may have multiple metal coating layers. In one possible embodiment of the present invention, the steel substrate is made of carbon steel. Preferably, the steel substrate is made of mild steel (also known as plain-carbon steel and low-carbon steel). In one possible embodiment of the present invention, the article is tinplate. The tinplate may be painted or unpainted. Tinplate can be derived from tin cans, tin can scraps, tin can waste, or combinations thereof. Furthermore, articles may include metal coatings containing elements such as Mg, Zn, Al, or combinations / alloys thereof. For example, an article could be an automobile part. Alternatively, an article could be a component of a household appliance or a building component (e.g., a profile, panel, or drainage system).
[0021] In one possible embodiment, the method includes a step of recovering the dissolved metal coating from an aqueous solution by electroplating. Specifically, if the article contains tin, the dissolved tin can be recovered from the aqueous solution by electroplating. Thus, by using the aqueous solution as the electrolyte source for electroplating after and / or during the removal of the metal coating from the article, material waste can be minimized.
[0022] According to yet another aspect of the present invention, the method includes a step of recovering steel by taking out the steel substrate from the aqueous solution after the dissolution of the metal coating is substantially complete. After being taken out from the aqueous solution, the steel substrate is washed with water in preparation for melting in a furnace.
[0023] According to yet another aspect of the present invention, before immersing the article in the aqueous solution, the article is heated. Thereby, by decomposing, burning and / or volatilizing the organic substances on the article, the article can be thermally cleaned. The organic substances can be polymers, plastics, paper labels, oils, paint residues, residues or other organic contaminants. In one possible embodiment, before immersing the article in the aqueous solution, the article is heated in air. In one possible embodiment, the temperature of the heat treatment is 400°C to 540°C, preferably 450°C to 500°C, more preferably 470°C to 490°C, and most preferably about 480°C. In one possible embodiment of the present invention, the time of the heat treatment is 10 to 60 minutes, preferably 20 to 45 minutes, more preferably 25 to 35 minutes. The time of the heat treatment is most preferably 30 minutes.
[0024] The article may have additional layers such as lacquer, varnish, polymer, paint layer, etc. In one possible embodiment of the present invention, the method includes a step of removing the lacquer, varnish, polymer or paint layer of the article by applying a solvent before immersing the article in the aqueous solution. Thereby, the efficiency of the method can be increased. The solvent can be applied by immersing the article in a bath containing a solvent-based paint stripper. The article can be held in the bath until the additional layer is completely or almost completely removed. Then, the article is taken out of the bath, washed and immersed in another bath containing the aqueous solution. The solvent can be methyl ethyl ketone (MEK) or ethyl acetate.
[0025] Furthermore, one or more objects of the present invention are achieved by an aqueous solution for use in the above method, said aqueous solution containing trichloroacetic acid (TCA) or methanesulfonic acid (MSA). In one possible embodiment, the aqueous solution consists essentially of water and one of trichloroacetic acid (TCA) and methanesulfonic acid (MSA).
[0026] In one possible embodiment, the aqueous solution contains trichloroacetic acid (TCA). The concentration of TCA in the aqueous solution is 3% to 25% by weight, preferably 5% to 20% by weight, more preferably 7% to 15% by weight, and most preferably 10% to 15% by weight, based on the total weight of the aqueous solution.
[0027] According to yet another aspect of the present invention, the aqueous solution contains methanesulfonic acid (MSA). The concentration of MSA in the aqueous solution is 15% to 70% by weight, preferably 40% to 60% by weight, more preferably 45% to 55% by weight, and most preferably 50% to 55% by weight, based on the total weight of the aqueous solution.
[0028] Each embodiment disclosed herein can be combined with other embodiments disclosed herein, provided there are no technical constraints.
Brief Description of the Drawings
[0029] [Figure 1] Figure 1 shows the weight loss of the tinplate and the tin amounts on the front and back surfaces as a function of time. [Figure 2] Figure 2 shows the weight loss of the tinplate and the tin amounts on the front and back surfaces as a function of time.
Examples
[0030] Example 1 Four different 50×50mm pure metal plates, each made from one of the following materials: Sn, Fe, Cu, or Ni, were prepared. These metal plates were immersed in an aqueous solution containing methanesulfonic acid (MSA). The concentration of MSA in the aqueous solution was 50% by weight, based on the total weight of the solution.
[0031] The temperature of the aqueous solution was 20°C. The weight of the metal plate was measured periodically to determine the weight loss of the metal plate.
[0032] Table 1 shows the weight loss of the metal plates as a function of time. On the one hand, MSA effectively dissolved tin, while on the other hand, little dissolution of other metals was observed. Table 1 clearly shows that MSA has high selectivity for tin compared to other metals.
[0033] [Table 1]
[0034] Example 2 A 50 x 50 mm tinplate was prepared and immersed in an aqueous solution containing methanesulfonic acid (MSA). The tinplate was obtained from manufacturing scrap, and the tin content differed on each side of the plate. The concentration of MSA in the aqueous solution was 50% by weight, based on the total weight of the solution.
[0035] The temperature of the aqueous solution was 20°C.
[0036] Figure 1 shows the weight loss of tinplate and the amount of tin on the front and back surfaces as a function of time. To measure the weight loss of tinplate, the weight of the tinplate was measured periodically. The amount of tin on both sides was measured using an X-ray fluorescence analyzer (XRF). During XRF measurement, the coated article was exposed to X-rays emitted from the XRF, resulting in the production of fluorescent X-rays. These fluorescent X-rays were counted by the XRF device, and their intensity correlates with the thickness and material of the coating layer. The tin mass per unit area on both sides was calculated from the fluorescence intensity using a tinplate calibration curve and is shown in Figure 1.
[0037] As shown in Figure 1, the dissolution of tin on both the front and back surfaces was completed in a short time. Furthermore, as is evident from the total weight loss, the dissolution of iron is significantly suppressed in the method of the present invention.
[0038] Example 3 Four different 50×50mm pure metal plates, each made from one of the following materials: Sn, Fe, Cu, or Ni, were prepared. These metal plates were immersed in an aqueous solution containing trichloroacetic acid (TCA). The concentration of TCA in the aqueous solution was 10% by weight, based on the total weight of the solution.
[0039] The temperature of the aqueous solution was 20°C. The weight of the metal plate was measured periodically to determine the weight loss of the metal plate.
[0040] Table 2 shows the weight loss of the metal plates as a function of time. Dissolution of metals other than tin was hardly observed or was limited. Therefore, Table 2 clearly shows that TCA has high selectivity for tin compared to other metals.
[0041] [Table 2]
[0042] Example 4 A 50 x 50 mm tinplate was prepared and immersed in an aqueous solution containing trichloroacetic acid (TCA). The tinplate was obtained from manufacturing scrap, and the tin content differed on each side of the plate. The concentration of TCA in the aqueous solution was 10% by weight, based on the total weight of the solution.
[0043] The temperature of the aqueous solution was 20°C.
[0044] Figure 2 shows the weight loss of the tinplate and the tin content on the front and back surfaces as a function of time. The tin content on both surfaces was measured using an X-ray fluorescence analyzer (XRF) in the same manner as in Example 2. The weight of the tinplate was measured periodically to determine the weight loss of the tinplate.
[0045] As shown in Figure 2, the dissolution of tin on both the front and back surfaces was completed in a short time. Furthermore, as is evident from the total weight loss, the dissolution of iron is significantly suppressed in the method of the present invention.
Claims
1. A method for selectively removing a metal coating from an article having a steel substrate, A step of preparing an aqueous solution containing trichloroacetic acid (TCA) or methanesulfonic acid (MSA), and Steps to immerse the article in the aqueous solution. The method, including the method described above.
2. The method according to claim 1, wherein the temperature of the aqueous solution is 5 to 50°C, preferably 15 to 30°C, and more preferably 18 to 25°C.
3. The method according to claim 1 or 2, wherein the concentration of TCA in the aqueous solution is 3% to 25% by weight, preferably 5% to 20% by weight, and more preferably 7% to 15% by weight, based on the total weight of the aqueous solution.
4. The method according to claim 1 or 2, wherein the concentration of MSA in the aqueous solution is 15% to 70% by weight, preferably 40% to 60% by weight, and more preferably 45% to 55% by weight, based on the total weight of the aqueous solution.
5. The method according to any one of claims 1 to 4, wherein the metal coating comprises one or more of Sn, Zn, Al, or Mg.
6. The method according to any one of claims 1 to 5, wherein the method includes a step of recovering the metal coating dissolved in the aqueous solution by electroplating.
7. The method according to any one of claims 1 to 6, wherein the method includes a step of recovering the steel by removing the steel substrate from the aqueous solution after the dissolution of the metal coating is substantially completed.
8. The method according to any one of claims 1 to 7, wherein the article is tinplate.
9. The method according to claim 8, wherein the method includes a step of recovering dissolved tin from the aqueous solution by electroplating.
10. The method according to any one of claims 1 to 9, wherein the method includes the step of heating the article before immersing the article in the aqueous solution.
11. The method according to any one of claims 1 to 10, wherein the method includes a step of removing a lacquer, varnish, polymer, or paint layer from the article by applying a solvent before immersing the article in an aqueous solution.
12. The method according to any one of claims 1 to 11, wherein the steel substrate is made of carbon steel.
13. An aqueous solution for use in the method according to any one of claims 1 to 12, comprising trichloroacetic acid (TCA) or methanesulfonic acid (MSA).