Method for cleaning aluminum seamless can and rinse water

Abstract

To provide a method for cleaning aluminum seamless cans, which reduces environmental load, efficiently suppresses generation of sludge in waste water and does not damage productivity or economic efficiency.SOLUTION: A degreasing process, a first washing process, a surface treatment process, and a second washing process are provided at least in this order, with the cleaning water used in the first washing process being the discharge from the second washing process. In the degreasing process, a degreaser is used where the concentration of surfactant is 3500 ppm or less, the concentration of sulfate ions is 25000 ppm or less, and the concentration of iron ions is 300 ppm or higher. In the first washing process, regarding the cleaning water in the first washing process, the mass molar concentration (a) of iron compounds and iron ions from the degreasing process and the mass molar concentration (b) of aluminum compounds and aluminum ions are such that the molar concentration (c) of the chelating agent in the discharge from the second washing process supplied to the first washing process meets the condition (c) / ((a)+(b))=0.1 to 0.8.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for cleaning aluminum seamless cans, and more particularly to a cleaning method, cleaning water, and cleaning apparatus that can reduce the environmental load and reduce sludge in wastewater. [Background technology]

[0002] Conventionally, formed products such as rolled plates, cans, and containers made of aluminum or aluminum alloys (hereinafter, both may be collectively referred to as "aluminum") have been widely used, and since lubricants, aluminum powder (smut), etc. adhere to these formed products, they need to be degreased and cleaned after forming. In particular, seamless cans made of aluminum or aluminum alloy sheets are obtained by subjecting aluminum sheets to severe processing such as drawing and ironing, and are generally formed using lubricants and coolants. As a result, seamless cans (DI cans) after drawing and ironing are contaminated with aluminum powder as well as oily stains from the lubricants and coolants. In seamless cans with such lubricants or other substances adhering thereto, the lubricants or other substances must be removed before the can is subjected to the subsequent painting or printing processes. The quality of the degreasing and water washing processes significantly affects the quality of the subsequent surface treatment and painting processes.

[0003] Degreasing agents currently used industrially to degrease aluminum seamless cans include sulfuric acid, an aqueous sulfuric acid solution containing iron sulfate and a surfactant, etc. This has many advantages, such as the ability to form an oxide layer mainly composed of aluminum oxide or hydroxide, chemically inactivating the aluminum surface and preventing the occurrence of appearance defects known as brown spots (Patent Document 1).

[0004] In recent years, from the viewpoint of reducing the environmental load, there has been a demand to reduce carbon dioxide emissions and water consumption. In the cleaning of aluminum seamless cans, various measures have been taken, such as reducing the concentration of degreasers used in the degreasing step to facilitate cleaning in the subsequent water rinsing step and reduce the amount of water consumed, or increasing the iron ion content in the degreaser to enable degreasing at lower temperatures than before.

[0005] In the cleaning of aluminum seamless cans, the above-mentioned degreasing step and water-rinsing step (first water-rinsing step) are followed by a surface treatment step in which surface treatment such as phosphoric acid treatment, zirconium phosphate treatment, or zirconium treatment is performed, and a water-rinsing step (second water-rinsing step) in which a surface treatment agent used in the surface treatment step is removed is provided. From the viewpoint of reducing the amount of tap water or industrial water used, the cleaning water in the second water-rinsing step is recycled through a filter and a part of it is discharged depending on the degree of cleanliness, and this wastewater is used as cleaning water for the first water-rinsing step. This cleaning water contains phosphoric acid, which is a chemical component used in the surface treatment step. On the other hand, in the first water-rinsing step, the cleaning water is also recycled through a filter and a part of it is discharged depending on the degree of cleanliness, and since the first water-rinsing step is a step for cleaning aluminum seamless cans that have been subjected to the degreasing step, the wastewater from the first water-rinsing step contains aluminum ions and iron ions that have been attached to the can surface in the degreasing step. In reality, the concentrations of the aluminum ions and iron ions are about 1 / 200 to 1 / 1000 of the concentration of the degreasing agent, respectively. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5007482 Summary of the Invention [Problem to be solved by the invention]

[0007] However, as described above, changing the composition of the degreaser to reduce the environmental impact caused a new problem in that the filter for filtering the tank circulating water in the first water-washing step and the filter for filtering the wastewater became clogged, increasing the frequency of cleaning and replacing the filters, thereby reducing productivity and cost efficiency. That is, the tank circulating water and wastewater from the first water washing step contain aluminum ions and iron ions, while the wastewater from the second water washing step contains phosphoric acid. Furthermore, as described above, when a degreasing agent with a high iron ion content and a reduced sulfate ion content is used, the wastewater from the first water washing step becomes nearly neutral. This makes it easier for the phosphoric acid in the wastewater from the first water washing step to react with the aluminum ions, or the iron ions to react with phosphoric acid, resulting in the precipitation of aluminum phosphate or iron phosphate. It was found that this precipitate (sludge) causes clogging of the filter for filtering the tank circulating water in the first water washing step and the filter for filtering the wastewater.

[0008] Therefore, an object of the present invention is to provide a method, washing water, and washing apparatus for washing aluminum seamless cans which can reduce the environmental load, effectively suppress the formation of sludge in wastewater, and does not impair productivity or cost efficiency. [Means for solving the problem]

[0009] According to the present invention, in a method for cleaning an aluminum seamless can, the method comprises at least a degreasing step (degreasing means), a first water-rinsing step (first water-rinsing means), a surface treatment step (surface treatment means), and a second water-rinsing step (second water-rinsing means) in this order, and the cleaning water used in the first water-rinsing step is wastewater from the second water-rinsing step. In the degreasing step, degreasing is performed using a degreaser having a surfactant concentration of 3500 ppm or less, a sulfate ion concentration of 25000 ppm or less, and an iron ion concentration of 300 ppm or more, The present invention provides a method for washing aluminum seamless cans, characterized in that the wash water in the first water-washing step is prepared by adding a chelating agent to wastewater from the second water-washing step so that the chelating agent has a mass molar concentration (c) of (c) / ((a)+(b))=0.1 to 0.8 relative to the sum of the mass molar concentration (a) of iron compounds and iron ions derived from the degreasing step as iron elements and the mass molar concentration (b) of aluminum compounds and aluminum ions as aluminum elements.

[0010] In the method for cleaning aluminum seamless cans of the present invention, (1) The chelating agent is a carboxylic acid, an aminocarboxylic acid, or a salt thereof; (2) The carboxylic acid and its salt are at least one of acetic acid, citric acid, and their salts; (3) The washing water used in the first washing step is obtained by adding a chelating agent to the wastewater from the second washing step. (4) The wastewater from the second washing step contains phosphoric acid, and 50 to 300 g / L of a chelating agent solution is added to the wastewater containing phosphoric acid to prepare washing water to be used in the first washing step. is preferred.

[0011] The present invention also provides washing water used in washing in a first water-washing step after a degreasing treatment of an aluminum seamless can, wherein a chelating agent has been added to the washing water so that a molar concentration (c) of the chelating agent in wastewater from the second water-washing step supplied to the first water-washing step satisfies (c) / ((a)+(b))=0.1 to 0.8 relative to the sum of a molar concentration (a) of iron compounds and iron ions derived from the degreasing step in terms of iron elements and a molar concentration (b) of aluminum compounds and aluminum ions in terms of aluminum elements.

[0012] The present invention further provides an aluminum seamless can cleaning apparatus comprising a degreasing means, a first water-washing means, a surface treatment means, and a second water-washing means, at least in this order, wherein the degreasing means performs a degreasing treatment using a degreasing agent having a surfactant concentration of 3500 ppm or less, an iron sulfate ion concentration of 25000 ppm or less, and an iron ion concentration of 300 ppm or more, and the first water-washing means cleans the aluminum seamless cans after the degreasing treatment using cleaning water to which a chelating agent has been added so that the mass molar concentration (c) of the chelating agent in the second water-washing wastewater supplied to the first water-washing step satisfies (c) / ((a)+(b))=0.1 to 0.8 relative to the sum of (a) the mass molar concentration of iron compounds and iron ions as iron elements derived from the degreasing step and (b) the mass molar concentration of aluminum compounds and aluminum ions as aluminum elements. In the aluminum seamless can washing apparatus of the present invention, it is preferable that the washing water is obtained by adding 50 to 300 g / L of a chelating agent solution to the wastewater discharged from the second water washing means. Effect of the Invention

[0013] According to the method for cleaning aluminum seamless cans of the present invention, it is possible to provide a method, cleaning water, and cleaning apparatus for cleaning aluminum seamless cans that can reduce the environmental load and effectively suppress the generation of sludge in wastewater without impairing productivity or economic efficiency.

[0014] Furthermore, by containing a chelating agent in the washing water used in the water-rinsing step, even if the pH of the washing wastewater becomes neutral due to the reduction in the sulfuric acid concentration in the degreasing agent as described above, the aluminum ions and iron ions in the washing wastewater are chelated by the chelating agent, and are effectively prevented from reacting with phosphoric acid in the wastewater to generate sludge such as aluminum phosphate. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a flow chart showing an example of a process for cleaning aluminum seamless cans according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] (Cleaning method) In the method for cleaning aluminum seamless cans (hereinafter sometimes referred to as "aluminum cans") of the present invention, an example is shown in Fig. 1, in which aluminum cans formed in a can-making process such as drawing and ironing are continuously conveyed to a drying process through a preliminary cleaning process, a degreasing process, a first water-washing process, a surface treatment process, a second water-washing process, and a pure water rinsing process. In the example shown in the figure, the cleaning wastewater discharged from the second water-washing process is subjected to a filtration process (indicated by symbol F in Fig. 1) and then used as cleaning water in the first water-washing process, and the cleaning wastewater discharged from the first water-washing process is subjected to a filtration process and then used as cleaning water in the preliminary cleaning process. In the pure water rinsing process, the cleaning water is circulated and reused within this process through the filtration process. The washing steps shown in FIG. 1 are typical washing steps for aluminum cans. In the present invention, the degreasing step, the first water-rinsing step, the surface treatment step, and the second water-rinsing step are essential, and the preliminary washing step and the pure water rinsing step are not particularly limited.

[0017] A first important feature of the cleaning method of the present invention is that the degreasing agent used in the degreasing step has a surfactant concentration of 3500 ppm or less, a sulfate ion concentration of 25000 ppm or less, and an iron ion concentration of 300 ppm or more. As a result, as described above, cleaning in the subsequent first water washing step is facilitated, and the reduced sulfate ion content makes it possible to reduce the amount of neutralizing agent (caustic soda) used in wastewater treatment. A second important feature of the cleaning method of the present invention is that cleaning water containing a chelating agent is used as the cleaning water used in the first water-rinsing step. This makes it possible to chelate aluminum ions and iron ions generated during the degreasing treatment and contained in the cleaning wastewater from the first water-rinsing step, thereby effectively preventing the generation of sludge such as aluminum phosphate in the cleaning liquid.

[0018] [Seamless aluminum cans] In the cleaning method of the present invention, the aluminum can to be cleaned is not particularly limited, but is preferably an aluminum seamless can formed using a lubricant as a coolant during forming. Such an aluminum can is a seamless can formed by subjecting an aluminum plate made of known aluminum or aluminum alloy such as 3004 material, 3104 material, etc., to severe processing such as drawing, drawing / deep drawing, drawing / ironing, and drawing / bending / stretching / ironing, using a conventionally known lubricant such as mineral oil or synthetic oil.

[0019] [Degreasing process] Aluminum cans that have been subjected to the can-making process and have been coated with lubricating oil are continuously conveyed, bottom-up, to the degreasing process of the cleaning equipment. Before the degreasing process, a preliminary cleaning process is provided as necessary to remove smut and other contaminants, as shown in Figure 1. In the degreasing process, a degreasing agent, which is generally made of an alkali or acid, is used for degreasing treatment. As described above, the degreasing agent is sprayed onto the aluminum cans from above and below, and the surfactant removes the lubricant adhering to the surface of the aluminum can. At the same time, an etching agent dissolves the aluminum, removing the aluminum oxide film that has formed on the surface of the aluminum can. In the present invention, it is preferable to use, as the degreasing agent used in the degreasing step, a degreasing agent having a surfactant concentration of 3500 ppm or less, particularly in the range of 1000 to 2500 ppm, a sulfate ion concentration as an etching agent of 25000 ppm or less, particularly in the range of 10000 to 20000 ppm, and an iron ion concentration as an etching accelerator of 300 ppm or more, particularly in the range of 300 to 1000 ppm. As the surfactant, any of the cationic, anionic, nonionic and ionic surfactants used in degreasers for aluminum cans can be used without limitation, but it is particularly preferable to use a nonionic surfactant.

[0020] [First washing process] After the degreasing process, the aluminum cans are transported to the first water washing process, where the degreaser attached to the can surface is removed. The aluminum can surface contains aluminum ions dissolved by etching and iron ions derived from the degreaser. As described above, the washing water used in the first washing step is the washing wastewater from the second washing step described below, and therefore this washing wastewater contains phosphoric acid and the like, which are chemical components derived from the surface treatment agent. However, in the washing method of the present invention, in the washing step, the washing water in the first washing step is prepared by adding a chelating agent to the washing water in such a way that the chelating agent has a mass molar concentration (c) of the second washing step wastewater supplied to the first washing step is (c) / ((a)+(b))=0.1 to 0.8 relative to the total of the mass molar concentration (a) of the iron compounds and iron ions as iron elements derived from the degreasing step and the mass molar concentration (b) of the aluminum compounds and aluminum ions as aluminum elements. This prevents aluminum phosphate and iron phosphate from being formed during the first washing step, and effectively prevents the formation of sludge. If it is less than 0.1, the chelating effect is insufficient and the effect of suppressing the formation of sludge cannot be obtained. On the other hand, if it is more than 0.8, the effect of suppressing the formation of sludge can be obtained, but no further effect can be obtained, which is disadvantageous in terms of environmental load and economy.

[0021] The chelating agent contained in the cleaning water is not limited as long as it forms a chelate with aluminum ions, etc., but a carboxylic acid can be preferably used. Examples of the carboxylic acid include acetic acid, citric acid, gluconic acid, oxalic acid, and salts thereof, as well as EDTA, NTA, DTPA, HEDTA, TTHA, PDTA, HIDA, DHEG, GEDTA, CMGA, EDDA, ​​etc., and salts thereof, and among these, citric acid can be preferably used. When a carboxylic acid is used as the chelating agent, a carboxylic acid solution having a concentration of 5 to 30%, preferably 5 to 20%, may be added to the wastewater from the second washing step, which serves as the wash water for the first washing step, so that the molar concentration (c) of the chelating agent is adjusted to the desired concentration of the present invention.

[0022] [Surface treatment process / second washing process] The surface treatment step is carried out in order to improve the coating stability and corrosion resistance of the degreased aluminum seamless can, and can be carried out by a chemical conversion treatment using a conventionally known surface treatment agent. However, as described above, in the present invention, even if the cleaning water contains phosphoric acid or the like which reacts with aluminum ions and the like to form precipitates, the generation of sludge is effectively suppressed, and therefore the present invention is particularly useful when a surface treatment agent containing phosphoric acid or the like is used. Examples of such surface treatment agents include, but are not limited to, surface treatment agents containing phosphate compounds such as zirconium phosphate, sodium phosphate, and phosphoric acid, and fluorides such as aluminum fluoride, zirconium fluoride, and hydrofluoric acid. In particular, a surface treatment agent containing phosphoric acid capable of forming a chemically inactive treatment film on the surface of an aluminum can is preferred, and among these, phosphoric acid is preferably used. The surface treatment agent using phosphoric acid is not limited to this, but it is preferable that phosphoric acid is contained so that the phosphate ion concentration is 1 to 500 ppm, particularly 20 to 200 ppm.

[0023] Aluminum cans that have gone through the surface treatment process are washed in the second water washing process. As shown in Figure 1, tap water or industrial water is used for washing in the second water washing process, and the washing water is recycled through a filter in the second water washing process, or discharged depending on the cleanliness, and the washing wastewater from the second water washing process contains surface treatment agents such as phosphoric acid. As mentioned above, the washing wastewater from the second water washing process is filtered before being supplied to the first water washing process. In the example shown in FIG. 1, the aluminum cans washed in the second water washing step are further washed in a pure water rinsing step, but the pure water rinsing step may not be essential depending on the washing condition of the aluminum cans.

[0024] [Drying process] After the pure water rinsing process, the aluminum cans are transported to the drying process, where they are dried in an oven or other dryer at a temperature of 170-210°C for 60-100 seconds, and then transported to the painting and printing process.

[0025] (Washing water) The washing water used for washing in the first water-washing step after the degreasing treatment of the aluminum can of the present invention is preferably such that the mass molar concentration (c) of the chelating agent in the wastewater from the second water-washing step supplied to the first water-washing step satisfies (c) / ((a)+(b))=0.1 to 0.8 relative to the sum of the mass molar concentration (a) of the iron compounds and iron ions derived from the degreasing step as iron elements and the mass molar concentration (b) of the aluminum compounds and aluminum ions as aluminum elements. As described above, in the first water-washing step, aluminum ions and iron ions are attached to the surface of the aluminum can by the degreasing treatment, and the washing water contains a chelating agent in the above range, which forms a chelate with these ions, and thus it is possible to effectively suppress the generation of sludge even if the washing water contains phosphoric acid. The carboxylic acid contained in the washing water is as described above, and citric acid is particularly preferably used.

[0026] (Cleaning Equipment) The aluminum seamless can cleaning apparatus of the present invention is equipped with a degreasing means, a first water-washing means, a surface treatment means, and a second water-washing means, at least in this order. An important feature of the aluminum seamless can cleaning apparatus of the present invention is that the degreasing means performs a degreasing treatment using a degreasing agent having a surfactant concentration of 3500 ppm or less, a sulfate ion concentration of 25000 ppm or less, and an iron ion concentration of 300 ppm or more, and the first water-washing means cleans the aluminum seamless cans after the degreasing treatment using cleaning water to which a chelating agent has been added so that the mass molar concentration (c) of the chelating agent in the second water-washing step drainage water supplied to the first water-washing step satisfies (c) / ((a)+(b))=0.1 to 0.8 relative to the sum of (a) the mass molar concentration of iron compounds and iron ions as iron elements derived from the degreasing step and (b) the mass molar concentration of aluminum compounds and aluminum ions as aluminum elements.

[0027] As described above, the washing wastewater from the second washing means is used as the washing water for the first washing means, and since the washing wastewater from the second washing means contains phosphoric acid and the like derived from the surface treatment agent, it is preferable to add 50 to 300 g / L of a chelating agent solution to the washing wastewater discharged from the second washing means to make the washing water into which the phosphoric acid and the like have been chelated, and to supply the washing water as the washing water for the first washing means. Furthermore, since the washing wastewater from the first washing means contains components derived from the degreasing agent, it is supplied to the preliminary washing means after being subjected to neutralization treatment and filtration treatment as necessary.

[0028] The cleaning apparatus of the present invention is not limited to the above-described embodiment, and depending on the condition of the aluminum cans or the use of the aluminum cans, the preliminary cleaning means, the surface treatment means, the second water washing means, or the pure water rinsing means may be omitted. EXAMPLES

[0029] Example 1 A 100 g / L aqueous solution of citric acid was prepared as a chelating agent, and this aqueous solution of citric acid was added to the washing wastewater from the second washing means in the washing step shown in Figure 1 so that the molar concentration of the washing water in the first washing step was 0.021 mmol / L, and this was used as the washing water for the first washing means. The production speed was 1500 cpm, and the washing water flow rate was 90 L / min. In addition, a degreaser containing 2000 ppm of a nonionic surfactant, 17000 ppm of sulfate ions, 550 ppm of iron ions, and 1000 ppm of aluminum ions was used as the degreaser in the degreasing treatment means, and an aqueous phosphoric acid solution of 50 ppm in terms of phosphate ions was used as the surface treatment agent in the surface treatment means. In this cleaning step, the dilution ratio of the degreasing agent in the first water-washing step was 500 times, and the molar concentrations of the iron compounds and iron ions derived from the degreasing step in the first water-washing step, in terms of iron elements, were 0.020 mmol / L, and the molar concentrations of the aluminum compounds and aluminum ions, in terms of aluminum elements, were 0.074 mmol / L. Uncleaned aluminum DI cans (diameter 66 mm × height 124 mm) formed by drawing and ironing a JISA3004 alloy aluminum plate were used as test materials. The desmutting ability of the aluminum DI cans was evaluated by the following method. Furthermore, the appearance of the aluminum cans was evaluated by the L value (appearance whiteness) by the following method. In addition, to prevent performance degradation due to the introduction of SO4 ions into the surface treatment process, the concentration of SO4 ions contained in the first washing solution was evaluated by the following method as the contamination level of the first washing process.

[0030] Example 2 A 100 g / L aqueous solution of gluconic acid was prepared as a chelating agent, and this aqueous solution of gluconic acid was added to the washing wastewater from the second water-washing means in the washing step shown in FIG. 1 so that the molar concentration of the washing water in the first water-washing was 0.007 mmol / L, and this was used as the washing water for the first water-washing means. The aluminum DI cans were cleaned in the same manner as in Example 1, except that a degreaser containing 1500 ppm of a nonionic surfactant, 24000 ppm of sulfate ions, 300 ppm of iron ions, and 640 ppm of aluminum ions was used as the degreaser in the degreasing treatment means, and an aqueous phosphoric acid solution containing 30 ppm, calculated as phosphate ions, was used as the surface treatment agent in the surface treatment means.

[0031] Example 3 An aqueous solution of oxalic acid with a concentration of 50 g / L was prepared as a chelating agent, and this aqueous solution of oxalic acid was added to the washing wastewater from the second water washing means in the washing step shown in FIG. 1 so that the molar concentration of the first washing water became 0.08 mmol / L, and this was used as the washing water for the first water washing means. The aluminum DI cans were cleaned in the same manner as in Example 1, except that a degreaser containing 3500 ppm of a nonionic surfactant, 1500 ppm of sulfate ions, 1000 ppm of iron ions, and 860 ppm of aluminum ions was used as the degreaser in the degreasing treatment means, and an aqueous phosphoric acid solution having a concentration of 30 ppm, calculated as phosphoric acid, was used as the surface treatment agent in the surface treatment means.

[0032] Comparative Example 1 Aluminum cans were washed in the same manner as in Example 1, except that the wastewater from the second water-washing step was used as the wash water for the first water-washing means without adding an aqueous citric acid solution. The desmutting ability and the appearance of the surface of the aluminum DI cans were evaluated in the same manner as in Example 1.

[0033] Comparative Example 2 As the degreasing agent in the degreasing treatment means, a degreasing agent containing 3000 ppm of a nonionic surfactant, 1350 ppm of sulfate ions, 75 ppm of iron ions, and 1000 ppm of aluminum ions was used, and as the cleaning water for the first water washing means, the cleaning wastewater from the second cleaning water washing means was not mixed with a chelating agent, and aluminum DI cans were washed in the same manner as in Example 1.

[0034] Comparative Example 3 As the degreasing agent in the degreasing treatment means, a degreasing agent containing 3500 ppm of a nonionic surfactant, 35000 ppm of sulfate ions, 75 ppm of iron ions, and 1000 ppm of aluminum ions was used, and as the cleaning water for the first water washing means, the cleaning wastewater from the second cleaning water washing means was not mixed with a chelating agent, and aluminum DI cans were washed in the same manner as in Example 1.

[0035] The treatment conditions for the examples and comparative examples are shown in Table 1. [Table 1]

[0036] (1) Appearance evaluation After the drying process, the outer surface of the DI can was measured at eight points using a handheld colorimeter (NR-12A) and the average value was calculated. The evaluation criteria were as follows: 〇: L value brightness 30 or more (excellent), ×: L value brightness lower than 30 (poor)

[0037] (2) Anti-smut property After the drying process, cellophane tape (manufactured by Nichiban Co., Ltd.) was applied to the inside surface of the DI can in three places, and then peeled off. After peeling, the tape was applied to a blank piece of paper, and the brightness of the five places was measured using a handy colorimeter (NR-12A), and the average value was obtained. The evaluation criteria are as follows. 〇: L value brightness 85 or more (excellent), ×: L value brightness lower than 85 (poor)

[0038] (3) Sludge generation prevention The time it took for the filter (18 mesh) installed before the pump suction port in the first water washing step to become clogged was used for evaluation. The evaluation criteria were as follows: 〇: No clogging for over a day (Excellent), ×: Clogging occurred within a day (Poor)

[0039] (4) Degree of contamination in the first washing process The degreaser was evaluated based on the concentration of sulfate ions when it was diluted 500 times. The evaluation criteria are as follows: 〇: Sulfate ion concentration: 50 ppm or less (excellent), ×: sulfate ion concentration: 50 or more (poor)

[0040] The evaluation results are shown in Table 2.

[0041] [Table 2]

Claims

1. A method for cleaning aluminum seamless cans, comprising at least a degreasing step, a first water-rinsing step, a surface treatment step, and a second water-rinsing means (second water-rinsing step) in this order, wherein cleaning water used in the first water-rinsing step is wastewater from the second water-rinsing step, In the degreasing step, degreasing is performed using a degreasing agent having a surfactant concentration of 3,500 ppm or less, a sulfate ion concentration of 25,000 ppm or less, and an iron ion concentration of 300 ppm or more; a first water-washing step using washing water obtained by adding a chelating agent to wastewater from a second water-washing step to be supplied to the first water-washing step such that a molar concentration (c) of the chelating agent is (c) / ((a)+(b))=0.1 to 0.8 relative to a total of a molar concentration (a) of iron compounds and iron ions derived from the degreasing step as iron elements and a molar concentration (b) of aluminum compounds and aluminum ions as aluminum elements.

2. 2. The method for cleaning aluminum seamless cans according to claim 1, wherein the chelating agent is a carboxylic acid, an aminocarboxylic acid, or a salt thereof.

3. 3. The method for cleaning aluminum seamless cans according to claim 2, wherein the carboxylic acid is at least one of acetic acid, citric acid and salts thereof.

4. 3. The method for washing aluminum seamless cans according to claim 1 or 2, wherein wastewater from the second water-washing step contains phosphoric acid, and 50 to 300 g / L of a chelating agent solution is added to the wastewater containing phosphate ions to prepare wash water for the first water-washing step.

5. A cleaning water used for cleaning in a first water-washing step after a degreasing treatment of an aluminum seamless can, the cleaning water being characterized in that a chelating agent has been added to the cleaning water such that a molar concentration (c) of the chelating agent in the washing wastewater from a second water-washing step supplied to the first water-washing step satisfies (c) / ((a)+(b))=0.1 to 0.8 relative to a sum of a molar concentration (a) of iron compounds and iron ions derived from the degreasing step as iron elements and a molar concentration (b) of aluminum compounds and aluminum ions as aluminum elements.

6. An aluminum seamless can cleaning apparatus comprising a degreasing means, a first water-rinsing means, a surface treatment means, and a second water-rinsing means, at least in this order, the degreasing means performs a degreasing treatment using a degreasing agent having a surfactant concentration of 3,500 ppm or less, a sulfate ion concentration of 25,000 ppm or less, and an iron ion concentration of 300 ppm or more; a first water-washing means for washing the aluminum seamless cans after the degreasing process using washing water to which a chelating agent has been added so that a mass molar concentration (c) of the chelating agent in the washing wastewater from the second water-washing process to be supplied to the first water-washing process satisfies (c) / ((a)+(b))=0.1 to 0.8 relative to a sum of a mass molar concentration (a) of iron compounds and iron ions derived from the degreasing process as iron elements and a mass molar concentration (b) of aluminum compounds and aluminum ions as aluminum elements.

7. 7. The aluminum seamless can washing apparatus according to claim 6, wherein the washing water in the first washing means is obtained by adding 50 to 300 g / L of a chelating agent solution to the wastewater discharged from the second washing means.

Images