JP2000144490A - Surface treating method for aluminum material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treating method for an aluminum material reducing the amt. of gel-shaped aluminum hydroxide to be generated as much as possible while the burden of industrial chemicals for waste soln. neutralizing treatment is reduce, furthermore reducing sulfuric acid radicals in this gel-shaped aluminum hydroxide as much as possible and capable of facilitating its convertion into useful resources. SOLUTION: In a surface treating method for an aluminum material having an etching stage and an anodic oxidation stage, an acidic waste soln. in relation to the anodic oxidation stage is subjected to reverse osmosis treatment, a sulfuric acid concentrated soln. obtd by this reverse osmosis treatment is circulated to the anodic oxidation stage, furthermore, a permeation soln, obtd. by the reverse osmosis treatment is introduced into a waste soln. neutralizing stage together with an alkaline waste soln. in relation to the etching stage, neutralizing treatment and coagulating sedementation treatment are executed, the concentrated part obtd. by the coagulating sedementation treatment is subjected to modifying treatment under the alkaline condition, and, solid-liq. separation is executed to recover gel-shaped aluminum hydroxide low in sulfuric acid radicals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a surface of an aluminum material made of aluminum or an aluminum alloy, and more particularly to a method for reducing the amount of gel aluminum hydroxide inevitably generated while saving valuable industrial chemicals. The present invention relates to a method for recovering a gelled aluminum hydroxide in a state in which it is reduced and the amount of impurities is extremely easy to convert into a useful resource.

[0002]

2. Description of the Related Art Aluminum materials made of aluminum or an aluminum alloy are widely used in various fields such as various parts such as ships, vehicles, and machines, building materials such as sashes, other electric products, office supplies, and household goods. Has been used,
At that time, the aluminum material is subjected to various surface treatments for the purpose of cleaning the surface, imparting improvement in corrosion resistance and designability, and the like, and is used as a desired aluminum product.

[0003] As such a surface treatment, anodizing treatment for improving the durability of an aluminum material is most widely performed, and the treatment process is usually performed by washing with an acidic solution → washing with water → using a sodium hydroxide solution. Etching → washing with water → desmutting with acidic solution → acidic bath (usually sulfuric acid)
Anodic oxidation → water washing → sealing or painting.

[0004] Of these, the most basic steps are an etching step and an anodic oxidation step. In the processing liquid in these steps, the consumption of the effective component and the accumulation of aluminum derived from the aluminum material inevitably occur. If these exceed a certain limit, they become so-called etching aging baths or anodic oxidation aging baths and need to be renewed, and these aging baths become aluminum-containing waste liquids containing a large amount of aluminum.

Conventionally, aluminum-containing waste liquid generated by such surface treatment of aluminum material is collectively treated with a pH 6 solution.
~ 8, and the gelled aluminum hydroxide sludge generated at that time was separated as much as possible, and the neutral clarified liquid was used as waste water. , And waste disposal at a high cost.

In recent years, there has been proposed a method for suppressing the generation of sludge, which is troublesome in treatment, by recovering and effectively utilizing valuables such as sodium and aluminum in such aluminum-containing waste liquid. Various methods have been devised, and they have been implemented according to the location conditions of each.

For example, with respect to an aging bath generated during the etching treatment of an aluminum material, the aging bath is periodically or continuously extracted, and a crystalline aluminum hydroxide [α
Al (OH) ₃ , dibusite] as a seed, and hydrolyzes sodium aluminate in the aging bath to precipitate a part of aluminum as crystalline aluminum hydroxide which is industrially valuable. As a result, a so-called etching aging bath in which sodium is reused by recycling a sodium aluminate solution having reduced aluminum content as a regenerating etching treatment solution in the etching process, that is, a so-called etching aging bath is being effectively used.

In addition, since the aging bath generated during the anodizing treatment of the aluminum material usually contains a considerable amount of aluminum sulfate of about 120 g / liter, most of the free sulfuric acid is used for the dialysis method or the ion exchange method. After collecting in
BACKGROUND ART Useful resources are being used as industrial liquid aluminum sulfate, cement quick setting agents, and other raw materials for the chemical industry. As a result, the generation of gelled aluminum hydroxide sludge derived from the etching aging bath and the anodic aging bath has almost disappeared.

However, in the etching step and the anodic oxidation step, it is essential to wash with water after the surface treatment. At that time, a large amount of washing waste liquid is generated, and the etching step and the anodic oxidation step are performed. So-called "mist-derived waste liquid" which scatters around as mist with the gas such as hydrogen gas generated during surface treatment and is absorbed by the exhaust system, and leaks as other handling loss is generated. And waste liquids cannot be reused because of their low concentration, and in the past, waste liquid neutralization treatment was performed in which neutralization treatment was performed with other dilute waste liquid to recover the gelled aluminum hydroxide produced. I have.

In the surface treatment of such an aluminum material, the concentration of sodium hydroxide in the etching bath is about 3 N or less, the concentration of sulfate in the anodic oxidation bath is about 5 to 6 N, Therefore, the washing waste liquid from the etching step and the anodic oxidation step and the waste liquid derived from mist and the like are inevitably excessive in acid, and further, the acidic washing waste liquid in the pre-pickling step and desmutting step with other acidic solutions. , A large excess of acid will result. For this reason, in the waste liquid neutralization treatment, it is necessary to additionally use a large amount of valuable industrial sodium hydroxide for the neutralization, which is wasteful in terms of resources and, depending on the region, the total amount of sodium sulfate in the waste water. May be regulated, and in such a case, a treatment for recovering sodium sulfate in the wastewater is required.

In order to solid-liquid separate the gelled aluminum hydroxide formed and precipitated, and to discharge the wastewater as it is, the pH of the neutralized liquid phase is usually adjusted to 5.5 to 8.5. Although it is necessary, a large amount of sulfate (SO ₄ / Al weight ratio of 0.3 to 0.7) is adsorbed in the gelled aluminum hydroxide formed under such conditions, and the amount thereof is adjusted to pH.
Depends heavily on

Further, when the wastewater is excessive in acid, the pH of the wastewater is adjusted to 5.0 when neutralization is performed by adding an alkali such as sodium hydroxide.
Dissolved aluminum ions are almost completely insolubilized when the pH is 5 or more. However, if the pH is increased further, the sulfate adsorbed on the gelled aluminum hydroxide consumes alkali. Requires a large amount of alkali. For example, in order to change the pH from 5.5 to 8.5, 0.2 g or more of sodium hydroxide is required per 1 g of aluminum.

For this reason, the neutralization treatment in the waste liquid neutralization step is usually performed at a pH of 5.5 to 8.5, but is preferably performed at a pH of 5.5 to 7.0 and further at a pH of 6.0 for economical convenience. ~
The fact is that the addition of alkali is stopped at 6.5. For this reason, the generated gelled aluminum hydroxide has
It will contain a large amount of sulfate groups with an O ₄ / Al weight ratio of 0.5 to 0.7, and besides very specific applications requiring sulfate groups together with aluminum, besides economical useful resources It is difficult at present.

[0014]

Therefore, the present inventors, when surface-treating an aluminum material, reduce the amount of gel-like aluminum hydroxide which is troublesome to treat as much as possible.
In addition, as a result of intensive studies on a method of removing sulfate groups (SO ₄ ^2- ) in the inevitably formed gelled aluminum hydroxide as much as possible to facilitate the use of useful resources, etching with a sodium hydroxide solution was carried out. When performing a surface treatment of an aluminum material having a step and an anodic oxidation step using sulfuric acid, a dilute waste liquid such as a cleaning waste liquid after anodic oxidation treatment and a waste liquid derived from mist, which occupies most of the acidic waste liquid, according to the conventional method. Concentration by reverse osmosis treatment without sending directly to the waste liquid neutralization process as
The obtained sulfuric acid concentrated solution is circulated to the anodic oxidation step, and the permeate obtained by the reverse osmosis treatment is introduced into the waste liquid neutralization step together with the alkaline waste liquid.
The waste liquid containing the gelled aluminum hydroxide produced by the neutralization treatment is subjected to coagulation sedimentation treatment, the dense portion obtained by the coagulation sedimentation treatment is modified by adding alkali, and then solid-liquid separated. The inventors have found that the object can be achieved, and have completed the present invention.

Accordingly, an object of the present invention is to provide an etching process including an alkali regenerating device for regenerating an etching aging bath by hydrolyzing sodium aluminate, and an anodic oxidation process provided with a device for recovering sulfuric acid from the anodic aging bath. In the surface treatment method of aluminum material having a, while reducing the burden of industrial chemicals for waste liquid neutralization treatment, while reducing the amount of gelled aluminum hydroxide as much as possible, and,
It is an object of the present invention to provide a surface treatment method for an aluminum material which can reduce a sulfate group in the gelled aluminum hydroxide as much as possible to facilitate its use as a useful resource.

[0016]

That is, the present invention comprises an etching step using a sodium hydroxide solution and an anodic oxidation step using sulfuric acid. In the etching step, an alkali regenerating apparatus by hydrolysis of sodium aluminate is used. In the surface treatment method of an aluminum material, which is provided with a sulfuric acid recovery device for recovering sulfuric acid from the anodic oxidation aging bath in the anodic oxidation process, a washing process for washing the aluminum material treated in the anodic oxidation process with water. Reverse osmosis treatment of the washing waste liquid from the step and the acidic waste liquid derived from mist etc. in the anodic oxidation step, and circulating the sulfuric acid concentrated solution obtained in this reverse osmosis treatment to the anodic oxidation step, obtained by the above reverse osmosis treatment The permeated liquid is used as a washing waste liquid and an etching step from a washing step of washing the aluminum material treated in the above etching step with water. Along with the alkaline waste liquid derived from the mist and the like, the waste liquid is introduced into a waste liquid neutralization step.In this waste liquid neutralization step, the waste liquid containing the gelled aluminum hydroxide produced by the neutralization treatment is subjected to coagulation sedimentation treatment. This is a surface treatment method for an aluminum material in which the obtained dense part is modified under alkaline conditions, and then solid-liquid separated to recover low sulfate gel aluminum hydroxide.

The present invention also provides a method for surface treating an aluminum material as described above, wherein the low sulfated gelled aluminum hydroxide is dissolved in a sodium hydroxide solution, and the obtained sodium aluminate solution is introduced into an alkali regenerating apparatus. It is.

In the surface treatment of the aluminum material according to the present invention, the aluminum material is preferably first washed with a 1 to 3 N acidic solution for surface activation in a pre-pickling step, and is usually 60 to 120 g / liter. Is used. After the acid cleaning, the acidic liquid (taken out) adhering to the surface of the aluminum material is washed with a large amount of water before being sent to the next etching step. At that time, a dilute acidic cleaning waste liquid (approximately pH 1.0) Occurs.

As described above, the aluminum material washed with acid and water is sent to an etching step for surface adjustment, and is etched with a sodium hydroxide solution. The etching treatment is usually performed using a sodium hydroxide solution of about 10% at 50 to 60 ° C. for several minutes.
It is dissolved as sodium aluminate at a rate of 35 g / m ³ .

Although aluminum gradually accumulates in the etching solution, the present invention is provided with an alkali regenerating device for regenerating the etching aging bath by hydrolyzing sodium aluminate. Without being discharged to the outside, the waste liquid related to the etching step is composed of a waste liquid derived from mist in the etching step and a cleaning waste liquid generated in a cleaning step of washing the aluminum material treated in the etching step with water.
Together, it becomes an alkaline waste liquid containing 4 to 10 g / l of sodium hydroxide and 2 to 4 g / l of aluminum. In the washing step of washing the aluminum material treated in the etching step with water, for example,
An AC washing method or the like in which washing is sequentially performed from the downstream side to the upstream side of the flow of washing water by a plurality of washing tanks connected in series is adopted.

In addition, a small amount of smut mainly derived from an intermetallic compound adheres to the surface of the aluminum material after the etching step, and if sent to the anodic oxidation step as it is, it hinders the formation of a uniform anodic oxide film, In addition, since the anodizing bath is contaminated, it is preferable to remove the smut by washing the aluminum material with an acidic solution (for example, H ₂ SO ₄ : 70 g / liter or more when using sulfuric acid) in the desmutting step. .

In the desmutting tank in the desmutting step, since almost no water is brought in by the aluminum material, the desmutting bath tends to be constantly diluted. Therefore, the acid concentration of the desmutting bath is adjusted to a predetermined concentration. In order to maintain the acid solution, it is necessary to replenish the acid solution. For this reason, an overflow corresponding to the volume of the replenished acid solution occurs to form a part of the acidic waste liquid. The aluminum material after the desmutting treatment does not need to be washed with water and can be directly sent to the anodizing step unless a different acid other than sulfuric acid is used in the desmutting bath.

The anodic oxidation step is usually performed using an anodic oxidation bath consisting of about 15% sulfuric acid aqueous solution. At this time, aluminum is dissolved from the surface of the aluminum material at a rate of 6 to 10 g / m ² and free sulfuric acid is dissolved. It is operated while constantly replenishing sulfuric acid. When the accumulated aluminum concentration (Al concentration) becomes approximately 20 g / liter, the bath is renewed as an aging bath. The anodic oxidation aging bath is usually or continuously withdrawn from the anodic oxidation bath so that the Al concentration is 18 to 22 g / liter,
At the same time, a new bath having the same volume as the anodized aging bath extracted is supplied.

If the components of the anodic oxidation bath remain on the aluminum material after the anodic oxidation step, the quality of the product after the subsequent sealing step, coloring step and coating step is deteriorated. The adhered components of are tightly regulated. For this reason, after the anodizing step, the aluminum material is sent to a washing step with washing water, where the adhered components on the surface are washed and removed by washing with water. For this reason, a large amount of diluted acidic washing waste liquid is generated in this washing step.

In the washing of the aluminum material in the above-mentioned washing step, generally, the aluminum material is sequentially transferred from the downstream washing tank to the upstream washing tank by a plurality of washing tanks connected in series. The countercurrent washing method of washing with water while moving it in a flowing manner is widely used, and the concentration of free sulfuric acid in the discharged washing waste liquid usually reaches 3 to 6 g / liter, depending on the amount of washing water. It contains 1/8 (weight ratio) of aluminum (Al).

According to the present invention, the washing waste liquid in the washing step after the anodizing step is not directed to the waste liquid neutralizing step as it is in the conventional method, but is reversed together with the acidic waste liquid containing Al derived from mist and the like in the anodizing step. Concentrate as much as possible by permeating. The degree of concentration in the reverse osmosis treatment depends on the properties (acid resistance and durability) of the osmosis membrane, but the concentration of free sulfuric acid in the concentrated solution is 45 g / l or more, preferably 50 g / l or more. It is preferred to concentrate to The concentration of free sulfuric acid in this concentrate is 4
If it is lower than 5 g / liter, the volume of the solution to be circulated to the anodizing step becomes excessively large, making it difficult to maintain the volume of the anodizing bath and the sulfuric acid concentration, and it is difficult to completely recover the acidic waste liquid containing aluminum. Become.

The concentrated solution obtained by the reverse osmosis treatment is added with sulfuric acid to form a new bath so that the volume of the anodizing bath and the sulfuric acid concentration thereof can be maintained at predetermined values. Recirculated to the process.

On the other hand, the permeated liquid obtained by the reverse osmosis treatment contains some leaked free sulfuric acid (H ₂ S).
Since O _{4 (} approximately 1 g / liter) contains only a trace amount of Al, this permeate is directly sent to the waste liquid neutralization step as an acid source for neutralizing the waste liquid. In addition, the permeate having a reduced acid concentration is again introduced into another reverse osmosis treatment, and the permeate is refluxed as washing water for the anodized material. The burden can be reduced.

As a result of the reverse osmosis treatment, Al in the cleaning waste liquid generated in the cleaning step after the anodizing step and the acidic waste liquid derived from mist and the like in the anodizing step are converted into useful resources through the anodizing step. It is discharged out of the system in an easy state. Therefore, the Al component directed to the waste liquid neutralization step is substantially a waste liquid related to the etching step, that is, a washing waste liquid from a washing step of washing the aluminum material treated in the etching step and an alkaline waste liquid derived from mist in the etching step. , The amount of gelled aluminum hydroxide sludge to be recovered is greatly reduced.

Further, sulfuric acid and free sulfuric acid bound to aluminum are discharged out of the system together with the Al content, so that the waste liquid sent to the waste liquid neutralization step becomes alkali excess as it is, but the recovered sulfuric acid is used for neutralization treatment. By using as an acid source, acid and alkali can be balanced.
For this reason, conventionally, in the waste liquid neutralization step, neutralization was performed using an alkali from the acid side in the waste liquid neutralization step. However, in the present invention, the neutralization can be performed from the alkali side using an acid.

When a sodium hydroxide solution containing aluminum (sodium aluminate solution) containing aluminum is neutralized with sulfuric acid, the formation of insoluble gelled aluminum hydroxide is generally almost completed at pH 9.0 to 8.5. Subsequent addition of sulfuric acid is mainly consumed in the following ion-exchange adsorption reaction. AlO-OH → AlO-1 / 2 SO ₄

Therefore, the pH is slightly to weakly alkaline, for example, pH
If the gelled aluminum hydroxide is separated in 9 to 10, S
Although very high quality gelled aluminum hydroxide containing almost no O ₄ ^2- can be obtained, the alkaline waste liquid from which it is separated cannot be discharged as waste water as it is on the alkaline side. It needs to be neutralized. However, a small amount of Al is dissolved in such an alkaline waste liquid, and if this is neutralized, an insoluble precipitate (SS) is further generated, and equipment for solid-liquid separation such as coagulation sedimentation treatment and filtration is provided. Doubly needed.

Therefore, in the present invention, attention is paid to the ion exchange property of the gelled aluminum hydroxide, and the operation in the waste liquid neutralization step is performed as follows. That is, first, the entire amount or most of the alkaline waste liquid is discharged with an acidic waste liquid, and sulfuric acid is added, if necessary, to the liquid phase to such an extent that the discharge is not hindered (for example, pH 5 to 9, preferably pH 5.5 to 5.5).
8.5, more preferably pH 6 to 8) to completely insolubilize the dissolved aluminum in the alkaline waste liquid. Next, the waste liquid containing the gelled aluminum hydroxide formed is subjected to coagulation and sedimentation treatment, and then the supernatant liquid is directly used as waste water, and a part of the alkaline waste liquid and / or water is placed in the dense part where the volume is reduced as much as possible. Sodium oxide is added to make the solution slightly alkaline, for example, at pH 9.0 to 10 (usually pH 9 to 9.5 is sufficient) to release the adsorbed SO ₄ ²⁻ in the gelled aluminum hydroxide, and to release almost SO ₄ ²⁻ It is modified into a gelled aluminum hydroxide containing no SO ₄ / Al having a weight ratio of 0.1 or less, and then solid-liquid separation is performed to recover a low sulfated gelled aluminum hydroxide having improved quality. At this time, the slightly alkaline filtrate separated into solid and liquid needs to be further neutralized in order to be discharged as wastewater. Therefore, the filtrate is returned to the initial neutralization treatment and circulated.

As a source of alkali used for reforming the dense portion obtained by the above-mentioned coagulation sedimentation treatment, it is desirable to use a part of inevitably generated alkaline waste liquid as resources. Since the concentration of the alkaline waste liquid is not high, the amount of the alkaline waste liquid added becomes large, and as a result,
If a disadvantage arises in terms of cost due to an increase in volume in the heat treatment in the reforming treatment or the subsequent solid-liquid separation, a small amount of a concentrated sodium hydroxide solution may be used.

This reforming treatment is usually performed within 20 minutes at room temperature, for example, for about 10 to 15 minutes.
It is preferable that the heating is performed at a temperature of at least 40 ° C, preferably 40 to 80 ° C. By heating, there is an advantage that the reforming treatment is performed more completely and quickly, and that the separation property of the gelled aluminum hydroxide after the reforming treatment is improved, that is, the water content is reduced.

Since the gelled aluminum hydroxide thus recovered contains almost no sulfate, it can be used as a useful resource for chemical industry, ceramics and metallurgy, which could not be used conventionally due to the presence of sulfate. Becomes possible.

In particular, in order to effectively utilize the aluminum content,
The low sulfate gel aluminum hydroxide after the reforming treatment is reacted with sodium hydroxide to obtain a high-quality, high-concentration industrially useful sodium aluminate solution. When conventional gelled aluminum hydroxide is used, a large amount of sodium hydroxide is wasted due to coexisting sulfate groups, and only a low concentration of sodium aluminate solution can be obtained due to high water content. There was a problem,
Such a problem does not occur when the low sulfate gel aluminum hydroxide obtained in the present invention is used.

Further, the low sulfated gelled aluminum hydroxide thus modified is dissolved in a sodium hydroxide solution supplied in the etching step of the aluminum material surface treatment, and the obtained insoluble matter is separated. The purified sodium aluminate solution is introduced into an alkali regenerating apparatus, hydrolyzed together with an etching aging bath in the etching step, and then solid-liquid separated to recover the regenerated sodium hydroxide solution and industrially useful crystalline aluminum hydroxide. Occasionally, there is no danger of sodium sulfate accumulating in the etching solution in the etching step, and almost no gelled aluminum hydroxide sludge can be generated while recovering useful industrial aluminum hydroxide.

[0039]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an etching step using a sodium hydroxide solution provided with an alkali regenerating apparatus for hydrolysis of sodium aluminate, and an anodizing step provided with a sulfuric acid recovery apparatus for recovering sulfuric acid from an anodic oxidation aging bath. 5 is a flowchart showing a method for surface treatment of an aluminum material having the following.

In this method for treating the surface of an aluminum material, an acidic waste liquid related to the anodizing step, that is, a washing waste liquid from the washing step after the anodizing step and an acidic waste liquid derived from mist or the like in the anodizing step are reverse osmosis. The sulfuric acid concentrate obtained by the reverse osmosis treatment is circulated to the anodizing step, and the sulfuric acid is recovered from the anodizing aging bath, and the permeate obtained by the reverse osmosis treatment is removed after the etching step. Introduce into the waste liquid neutralization step together with the washing waste liquid from the washing step and the alkaline waste liquid derived from the mist in the etching step, and in this waste liquid neutralization step, the waste liquid containing the gelled aluminum hydroxide generated by the neutralization treatment is removed. Coagulation sedimentation treatment, while discharging the supernatant obtained in this coagulation sedimentation treatment as a waste liquid, the dense part is modified by adding alkali, Ide well as solid-liquid separation to recover a small amount of high-quality low sulfate radicals gel aluminum hydroxide, is returned to the neutralization treatment again for alkaline waste.

First, a reverse osmosis treatment is performed on the washing waste liquid generated in the washing step of washing the aluminum material treated in the anodizing step with water and the acidic waste liquid derived from mist and the like in the anodizing step. As the reverse osmosis membrane used for the concentration in the reverse osmosis treatment, various types of reverse osmosis membranes are currently on the market, and any known acid proof membrane can be used.

In the case of the waste liquid as described above, the concentration of free sulfuric acid in the concentrated liquid is preferably higher, but the degree of concentration in the reverse osmosis treatment is preferably determined in consideration of the balance with the membrane life. . The higher the degree of concentration, the easier the liquid around the anodizing tank becomes, and the true value of the present invention can be exhibited. For example, the free H ₂ SO _4: 7~8g / liter, Al: 1 g
/ Free liter of waste liquid H ₂ SO _4: If concentrated to 6-7 times so as to be 50 g / liter, the permeate obtained, leakage free H ₂ SO _4: 1g / liter or less,
Al: 0.05 g / liter or less.

The permeate obtained by the reverse osmosis treatment is as follows:
Since it contains almost no aluminum, it can be sent as it is as an acid source for the neutralization treatment in the waste liquid neutralization step. If necessary, sulfuric acid (industrial concentrated sulfuric acid) and / or sulfuric acid recovered from an anodizing aging bath by a sulfuric acid recovery device are added to the sulfuric acid concentrated solution obtained by the reverse osmosis treatment, and the sulfuric acid is concentrated in the anodizing step. A new bath having approximately the same volume as that of the anodic oxidation aging bath extracted from the anodic oxidation bath is constructed and refluxed to the anodic oxidation bath.

In the present invention, the anodizing aging bath extracted from the anodizing tank in the anodizing step is different from the conventional method in that the amount of the anodizing aging bath is increased by an amount of reflux of the acidic waste liquid derived from the aluminum material and mist. 40%). From the anodizing aging bath, free sulfuric acid is mainly used for recovering sulfuric acid used as an acid source for the neutralization treatment in the waste liquid neutralization step, and for making the anodizing aging bath easily a useful resource. Collected. The recovery of the free sulfuric acid can be performed by any known method such as a dialysis method and an ion exchange method, and the concentration of the recovered sulfuric acid is 70% or more (100 g / liter or more) of the free sulfuric acid concentration in the anodic aging bath. But it is convenient for draining.

A part of the recovered sulfuric acid is used as an anodizing bath instead of the anodizing aging bath extracted in the anodizing step, and a part is sent to a desmutting step.
A part of the recovered sulfuric acid that has passed through the desmutting step is used for a pre-pickling step before the etching step, and then sent to a waste liquid neutralization step, and the remaining recovered sulfuric acid that has passed through the desmutting step is directly used as a waste liquid. It is sent to the neutralization step. Therefore, the sulfuric acid recovery is performed so that the acidic waste liquid sent to the waste liquid neutralization step and the alkaline waste liquid unavoidably generated are balanced without excess and deficiency, and particularly, neutral wastewater can be obtained without adding a large amount of acid or alkali. It is desirable to do. Depending on the concentration of the recovered sulfuric acid and the control concentration of the desmutting bath in the desmutting step, the recovered sulfuric acid may be distributed to both the desmutting step and the pre-pickling step before the etching step.

In the waste liquid neutralizing step in the method for treating a surface of an aluminum material of the present invention, first, a cleaning waste liquid from a washing step of washing the aluminum material treated in the etching step and an alkaline waste liquid derived from mist and the like in the etching step are: Neutralization treatment can be performed with the permeate obtained by the above reverse osmosis treatment, the acidic waste liquid in the washing step after the preliminary pickling step and the desmutting step, and sulfuric acid added as necessary.

After the neutralization treatment, the waste liquid containing the gelled aluminum hydroxide produced is subjected to coagulation sedimentation treatment, and the clarified liquid obtained after the dense portion obtained by the coagulation sedimentation treatment is discharged as waste water. The pH at the time of the neutralization treatment is controlled within the pH control of the discharged water. In addition, pH at the time of neutralization treatment
The higher the water content, the lower the amount of SO ₄ ^2- adsorbed and held in the gelled aluminum hydroxide, and the easier the subsequent elution treatment (reforming treatment), so that it can be discharged as wastewater. in the highest possible it is good, pH during the neutralization process may be the prospect of between 7.5 and 8.5.

The slurry after the neutralization treatment is prepared by a conventional method.
For example, a coagulation sedimentation treatment is performed by adding a coagulant. Also,
As the coagulant used at that time, any known organic polymer coagulant for neutral liquid can be used.

The supernatant liquid of the neutral clarification after the coagulation and sedimentation treatment can be used as waste water, and the dense part obtained by the coagulation and sedimentation treatment is subjected to a reforming treatment. It is sent to a tank, where a part of the alkaline waste liquid is added to make it slightly alkaline, preferably, for example, pH 9.0 to 10.0 to elute the adsorbed sulfate.

This reforming treatment is usually performed in a short time (within 10 minutes) like an ion exchange reaction.
Heating to ° C. can be done more quickly and completely. The heating method is not particularly limited by a method such as direct heating or indirect heating, but steam blowing is simple and convenient.

The above-mentioned reforming treatment is preferably carried out with a volume as small as possible for the sake of the subsequent solid-liquid separation operation. However, since the alkaline waste liquid added for the reforming treatment has a low alkali concentration, the volume of the waste water is low. When it is necessary to reduce the increase in the amount of alkaline waste liquid, or when it is desired to increase the reaction rate, industrial sodium hydroxide, for example, 25%
Alternatively, 50% sodium hydroxide may be used.

Further, the agglomerates after the neutralization treatment in the preceding step are in a state of dispersion of ultrafine particles by the modification treatment for elution of SO ₄ ²⁻ under the slight alkalinity of the gelled aluminum hydroxide. Since separation becomes difficult, it is advisable to introduce the coagulant into the coagulation tank again to perform coagulation. As the coagulant in this case, for example, an alkali-resistant polyacrylamide-based or a weak anion-based is effective.
It is preferably about 50 to 100 ppm based on the slurry.
In addition, in order to further simplify the operation, the dense portion after the neutralization treatment may be subjected to the coagulation treatment by automatically controlling the addition of alkali and the heating in the liquid feed pipe, and directly leading it to the coagulation tank.

Since the slurry after the reforming treatment is originally treated in the dense part after the neutralization treatment, the slurry concentration is relatively high, and the slurry can be separated into solid and liquid by filtration (usually using a pressurized filter). . However, sedimentation treatment may be performed in advance depending on the volume or other reasons. By this solid-liquid separation, the gelled aluminum hydroxide from which the sulfate groups have been drastically reduced is recovered, and the slightly alkaline filtrate is discharged for effective use of alkali and prevention of insoluble precipitate (SS) for neutralization. It is preferable that the solution is returned to the neutralization treatment without any treatment, and the neutralization treatment is repeated together with the new waste liquid.

In addition, a pre-pickling step and a water-washing step before etching, an etching step, an alkali regenerating apparatus, a water-washing step after the etching step, a desmutting step, an anodizing step, a water-washing step after the anodizing step, an anodizing aging bath Any known method and apparatus for recovering sulfuric acid from sulfuric acid can be used and do not depart from the spirit of the present invention.

Hereinafter, based on Test Examples, Examples and Comparative Examples,
Next, the method of the present invention will be specifically described. Test example Surface treatment factory (13000m daily)^Two), In waste liquid
Dense slurry from coagulation sedimentation basin after neutralization treatment in summing process
(PH 6.5, solid content concentration: 20 g / liter, solid content
Composition: Al: 29.8%, Na: 0.67%, S
O_Four ^2-: 16.6%, Si: 0.58%, Fe: 0.3
6%, Mg: 0.16%).
Sodium luminate solution (NaOH: 6 g / liter,
Al: 1.5 g / liter) until the desired pH is reached
20 minutes later, a pressure filter [manufactured by Koshinri Chemical Co., Ltd.]
KS-100-150] and a pressure of 6.5 kg / c.
m^TwoThe mixture was subjected to pressure filtration for solid-liquid separation. S in the cake at that time
O_FourFIG. 4 shows the / Al weight ratio. However, unaggregated gel
Aluminum hydroxide is difficult to wash, so it contains SO_Four ^2-
Na determined from the Na content_TwoSO_FourConsiderable SO_Four
^2-Adsorbed SO _Four ^2-And the ratio to the Al content
I asked.

[0057] As seen from this result, SO ₄ ^2-and OH of the gel in aluminum hydroxide ^- exchange reaction is, pH
Is remarkable at 9.0 or more. Further, it can be seen that the heating (50 ° C.) further completes the elution of SO ₄ ^2- , and conversely, when the pH is further increased, Na is adsorbed.

In the following Examples and Comparative Examples, the results of an experiment using a 400-liter experimental device were converted to a scale of 15,000 m ² / day in order to make it easier to understand the industrial effect.

Example 1 An aluminum material was subjected to a surface treatment according to the flow shown in FIG. Recovery of sulfuric acid from the anodizing aging bath was performed by a diffusion dialysis method. In the etching step, NaOH: 100
g / litre, Al: 26 g / litre, a bath solution was continuously withdrawn at a rate of 43 m ³ / day from the etching bath in the etching step, sent to an alkali regenerating apparatus, and treated with crystalline aluminum hydroxide. (Jibsite) Hydrolysis is carried out in the presence of seeds, while producing 1072 kg (10% moisture) of industrial aluminum hydroxide as a by-product, in addition to the loss of aluminum materials, loss due to mist, etc.,
NaOH: 339 kg including the by-product aluminum hydroxide accompanying component and neutralization loss of sulfuric acid carry-in from the previous process
/ Day of industrial sodium hydroxide (28% solution), and refluxed into the etching tank.

At this time, the washing waste liquid from the washing step for washing the aluminum material treated in the etching step with water and the alkaline waste liquid derived from mist and the like in the etching step are combined, and NaOH: 5.5 g / L, Al: 2.1 g
/ L alkaline waste 60 m ³ containing sent to waste neutralization step.

The washing waste liquid from the washing step of washing the aluminum material treated in the anodic oxidation step with water and the acidic waste liquid derived from mist and the like in the anodic oxidation step are combined together to form 37 m.
³ acidic waste liquid (total H ₂ SO ₄ : 12.6 g / liter,
Al: 1.0 g / liter, free H ₂ SO ₄ : 7.3 g
/ L, Al: 1.0 g / l).
The total H ₂ SO ₄ (total sulfuric acid) indicates the total of free sulfuric acid and sulfuric acid bound to aluminum.

The dilute sulfuric acid waste liquid containing aluminum is
Reverse osmosis device [Ace Engineering Co., Ltd. SW-4
Reverse osmosis treatment under the conditions of a water supply pressure of 20 kg / cm ² and a concentrated solution of 4 m ³ (free H ₂ SO ₄ : 57.
9 g / liter, Al: 8.7 g / liter) and 33
m ³ permeate (free H ₂ SO ₄ : 1.16 g / l, Al: 0.03 g / l) was recovered. The recovered concentrate is circulated to the anodizing step as a part of a new bath for replenishing the anodizing aging bath drawn out of the system, and the recovered permeate is directly passed to the waste liquid neutralization step. sent.

From the anodizing tank (anodizing step), an aging bath solution containing free H ₂ SO ₄ : 150 g / l, Al: 20 g / l and total H ₂ SO ₄ : 259 g / l was 5.98 m ³ / l. The sample was taken out at a rate of one day, and treated using a diffusion dialysis device (Asahi Glass, T-III W type) while supplying pure water, free H ₂ SO ₄ : 125.4 g / liter, Al: 0. 5.36 recovered sulfuric acid containing 6 g / l
m ³ and an acidic aluminum sulfate solution 6.24m ³ (free H
₂ SO ₄ : 36.0 g / liter, Al: 18.6 g /
Liters).

1.5 m of the recovered sulfuric acid^ThreeAnd said reverse osmosis
1261 kg of sulfuric acid (98% H_TwoSO_Four:
0.7m^Three) And water, and 6.28m new bath^ThreeAs yang
It was supplied to the extreme oxidation tank. The remaining 3.86m of recovered sulfuric acid
^ThreeTo the desmutting tank (desmutting process)
The recovered sulfuric acid passed through the mat tank is free H_TwoSO_Four: 90.
1 g / liter, Al: 0.48 g / liter waste liquid
3.86m^ThreeIt became. And 1.5 of the waste liquid
m^ThreeTo the pre-pickling process before the etching process,
2.36m ^ThreeWas sent to a waste liquid neutralization step.

In the pickling tank (pre-pickling step), while continuously adding 1.5 m ³ of the waste liquid from the desmutting step, the dried aluminum material is immersed to activate the surface, and then the washing is performed. The aluminum material pickled in the process is washed with water, and the cleaning waste liquid 33 m generated in the washing process
³ (total H ₂ SO ₄ : 4.03 g / liter, Al: 0.
02 g / l) was sent to the waste liquid neutralization step.

In the present invention, it is essential that the acidic waste liquid be balanced with the alkaline waste liquid inevitably generated by appropriately selecting the concentration of the acidic waste liquid derived from the anodizing step and the sulfuric acid recovery rate from the anodizing aging bath. However, in consideration of some fluctuations, the waste liquid neutralization step was provided with an acid and alkali addition device.

In the waste liquid neutralization step, the alkaline waste liquid 60 m
Of the ^three, mixed acid waste liquid 56m ^3, the sodium hydroxide 2kg addition, after a pH 7.5, manufactured by aggregating agent [Dia floc (Ltd.) AP410C: acrylamide
Sodium acrylate copolymer type weak anion type] 10 ppm was added to the mixture and sent to a coagulation sedimentation tank (coagulation sedimentation treatment) and allowed to stay for 24 hours, and the supernatant was used as wastewater.

Next, in the gel modification treatment, the solid content is about 20 g.
/ M ³ , the remaining 4 m ³ of the alkaline waste liquid was added to the dense part of about 20 m ³ to adjust the pH to 9.3, and the coagulant (AP
410C) was added in an aggregating tank to cause coagulation in the coagulation tank, and the dense portion was filtered under pressure to recover 1180 kg (67% water) of gelled aluminum hydroxide, and the filtrate was refluxed to a neutralization tank (neutralization treatment). I was sorry.

At this time, the amounts of H ₂ SO ₄ and NaOH used, the amount of the acidic aluminum sulfate solution discharged from the anodizing aging bath, the amount of the formed gelled aluminum hydroxide sludge and the water content, and 105 ° C. And the composition of the dried product was examined. Table 1 shows the results.

Comparative Example 1 A surface treatment of an aluminum material was performed according to the flow shown in FIG. Preliminary San'araiso (preliminary pickling step) H ₂ SO ₄ concentration of 90 g / l in addition to the H ₂ SO ₄ concentration in desmutting tank (desmutting step) was 90 g / liter,
Other processing and cleaning processing were performed in the same manner as in Example 1.
At this time, the amounts of H ₂ SO ₄ and NaOH used, the amount of the acidic aluminum sulfate solution discharged from the anodizing aging bath, the amount of the recovered gelled aluminum hydroxide sludge and the water content, and the same as in Example 1 And the composition of the dried product was examined. Table 1 shows the results.

[0071]

[Table 1]

Example 2 One liter of industrial 50% sodium hydroxide (1529)
g) The gelled aluminum hydroxide recovered in Example 1
(Adhered water: 67%, Al: 10.8%, Na: 0.1
%, SO_Four ^2-: 0.6%, Fe: 0.12%, Mg:
(0.08%, Si: 0.2%)
The mixture was stirred at 5 ° C for 3 hours to perform a dissolution treatment, and solid-liquid separation was performed.
Filter, NaOH: 230 g / liter, Al: 92 g / liter
Turtle, Na _TwoSO_Four: 25 g / l of aluminate
3.24 liters of sodium and filter cake (50% moisture) 66
g was obtained.

Under the same conditions, the flow shown in FIG.
Therefore, 339 kg of sodium hydroxide in the etching process
/ Day instead of industrial 50% sodium hydroxide 0.45
8m ^ThreeThe gelled aluminum hydroxide is dissolved in
After separation, it is led to an alkali regeneration tank (alkali regeneration device),
Alkali regeneration along with the aging bath (etching process)
After treatment, gelled aluminum hydroxide 1180k
g of crystalline aluminum hydroxide 40 that is industrially useful
4 kg was obtained, and the filter residue and sodium hydroxide required for the neutralization treatment were obtained.
Um loss was 8 kg. In the etching tank (D
Na of the etching step)_TwoSO_Four3g increase in equilibrium concentration
/ Liter or less.

Comparative Example 2 The gelled aluminum hydroxide recovered in Comparative Example 1 (attached water: 75%, Al: 7.5%, Na: 0.1%, SO
₄ ^2- : 4.0%, Fe: 0.08%, Mg: 0.05
%, Si: 0.13%), it was attempting to dissolution treatment in an industrial 50% sodium hydroxide solution, because of large amount of water and neutralizing loss due large amount of SO ₄ ^2-, when dissolved stable aluminate In order to obtain a sodium acid solution, only 3.3 kg of gelled aluminum hydroxide can be treated in 1 liter of a 50% sodium hydroxide solution, and the obtained sodium aluminate solution contains NaOH: 176 g / liter, A
l: 65 g / l, Na ₂ SO ₄ : 53 g / l.

Under the same conditions, when sodium hydroxide for replenishment in the etching step was carried out with sodium aluminate, 0.523 m ^{3 of} 50% sodium hydroxide for industrial use was obtained.
Required, gelled aluminum hydroxide sludge 2120k
Of the g, 1720 kg (equivalent to 80%) was treated to obtain 367 kg of industrially useful crystalline aluminum hydroxide. Mainly, the loss of sodium hydroxide required for the neutralization treatment was 59 kg, and was in the etching tank (etching step).
Had an equilibrium concentration of Na ₂ SO _{4 of} about 30 g / liter or more, which was impractical in terms of bath management and economy.

[0076]

According to the present invention, in a method for treating an aluminum material having an etching step with a sodium hydroxide solution and an anodic oxidation step using sulfuric acid, a washing step of washing the aluminum material treated in the anodic oxidation step with water. The acidic waste liquid containing aluminum, which is mainly the washing waste liquid from, can be used as a useful resource. As a result, without wasting valuable sodium hydroxide for neutralization treatment,
At the same time, it greatly reduces the amount of gelled aluminum hydroxide that is troublesome to treat, and is practically useful in the environment and industry, because it is very easy to use as a high-quality, useful resource that contains almost no unnecessary sulfate groups. High gelled aluminum hydroxide.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of an embodiment of a method for surface treating an aluminum material according to the present invention.

FIG. 2 is a flowchart illustrating an example of a conventional surface treatment method for an aluminum material according to Comparative Example 1.

FIG. 3 is a flowchart illustrating a surface treatment method for an aluminum material according to a second embodiment of the present invention.

FIG. 4 is a graph showing the results obtained in a test example of the present invention. A sodium hydroxide solution is added to a gelled aluminum hydroxide slurry produced by ordinary neutralization, and the solution is slightly alkaline. it is a graph showing the relationship between the SO ₄ / Al weight ratio of pH and gel form in the aluminum hydroxide when modified.

Continuing on the front page (72) Inventor Shoji Asahara 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Inside the Nippon Light Metal Co., Ltd. Group Technology Center (72) Inventor Yasushi Egami 1-3-34 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture No. 1 Nippon Light Metal Co., Ltd. Group Technology Center (72) Inventor Yoshiro Tanaka 2-2-20 Higashishinagawa, Shinagawa-ku, Tokyo F-term in Japan Light Metal Co., Ltd. 4D006 GA03 KA62 KA72 KB13 KB14 KB30 KE12P KE13P KE14Q MB12 PA04 PB08 PB25 PB27 PC80 4D062 BA19 BA24 BB05 CA20 DB02 DC08 EA14 EA16 FA01 FA03 FA12 FA17 FA19 FA28 FA29

Claims (7)

[Claims] 1. An etching step using a sodium hydroxide solution and an anodic oxidation step using sulfuric acid. The etching step is provided with an alkali regenerating device by hydrolysis of sodium aluminate. Is a method for surface treatment of aluminum material provided with a sulfuric acid recovery device for recovering sulfuric acid from the anodic oxidation aging bath, wherein a cleaning waste liquid from a cleaning step of washing the aluminum material treated in the anodic oxidation step with water and an anodizing step. Reverse osmosis treatment with acidic waste liquid derived from mist etc., and circulating the sulfuric acid concentrated solution obtained by this reverse osmosis treatment to the anodic oxidation step, and treating the permeate obtained by the above reverse osmosis treatment in the above etching step Cleaning wastewater from the washing process of washing the aluminum material with water and alkaline wastewater derived from mist etc. in the etching process Both are introduced into a waste liquid neutralization step. In this waste liquid neutralization step, the waste liquid containing the gelled aluminum hydroxide produced by the neutralization treatment is subjected to coagulation sedimentation treatment, and the dense part obtained by this coagulation sedimentation treatment is alkalinized. A surface treatment method for an aluminum material, comprising reforming under conditions and then solid-liquid separation to recover a low sulfate gel aluminum hydroxide. 2. A modification treatment in which a washing waste liquid from a washing step of washing the aluminum material treated in the etching step with water and an alkaline waste liquid derived from mist or the like in the etching step are added to the dense portion obtained by the coagulation sedimentation treatment. The surface treatment method for an aluminum material according to claim 1. 3. The dense part obtained by the coagulation sedimentation treatment is adjusted to pH
The surface treatment method for an aluminum material according to claim 1 or 2, wherein the modification treatment is performed under an alkaline condition in a range of 9.0 to 10.0. 4. The dense part obtained by coagulation and sedimentation is treated at 40 ° C.
The surface treatment method for an aluminum material according to any one of claims 1 to 3, wherein the reforming treatment is performed while heating at the above temperature. 5. The surface treatment method for an aluminum material according to claim 1, wherein the weight ratio of SO ₄ / Al in the recovered low sulfate group gelled aluminum hydroxide is 0.1 or less. 6. The low sulfate group gelled aluminum hydroxide is dissolved in a sodium hydroxide solution, and the obtained sodium aluminate solution is introduced into an alkali regenerating apparatus.
The surface treatment method for an aluminum material according to any one of the above. 7. A sodium aluminate solution obtained by dissolving a low sulfate group gelled aluminum hydroxide recovered by the method according to claim 1 in a sodium hydroxide solution.