CN1110583C - Process for treating waste liquid in surface treatment of aluminum materials - Google Patents

Abstract

The present invention relates to the surface treatment of aluminum materials, wherein the aluminum-containing waste liquid produced by treating the material with alkali or acid solution is neutralized and the slurry containing aqueous aluminum hydroxide gel is separated; a waste liquid treatment method is also provided, This includes separating the slurry at a high pH of 9.0 or above, using recovered low sulfate concentration slurry and recycling unrecovered aluminum to aluminum-containing waste liquor. The invention can efficiently and cost-effectively treat various aluminum-containing waste liquids produced in the surface treatment of aluminum materials, especially aged anodic oxidation liquid, waste liquid produced by moisture and waste liquid produced by washing water.

Description

Waste liquid treatment method for aluminum surface treatment

The present invention relates to the surface treatment of aluminum materials including aluminum and its alloys with alkali solution or with said alkali solution and acid solution; Approach.

Aluminum including aluminum and its alloys are used in ships, automobiles and machinery as well as construction materials such as window frames, electrical appliances and office consumer products. In these applications, aluminum is subjected to surface treatments, such as lye etching and acid anodizing, to clean the surface or to provide corrosion resistance or artistic graphics.

However, in the above surface treatment process, there are obvious problems of consumption of active ingredients in the treatment solution and accumulation of aluminum produced by the aluminum material in the treatment solution. When the consumption and accumulation exceed a certain limit, the treatment solution becomes the so-called aging etching solution or aging anodizing solution, which must be renewed. This aging solution becomes a waste solution containing a large amount of aluminum.

In addition, in the above-mentioned surface treatment using etching and anodizing, the waste liquid leaks in the form of moisture together with gases such as hydrogen generated during the treatment, and is absorbed in the discharge system or escaped as treatment waste. This is the so-called "waste from moisture". The surface-treated aluminum is washed with water, which generates a large amount of waste liquid from the washing water. These waste liquids obtained from moisture and wash water also contain aluminum and constitute aluminum-containing waste liquids.

A large amount of aluminum-containing waste liquid produced in the surface treatment of aluminum materials is usually collected and neutralized to a pH of 5-9, and the resulting aqueous aluminum hydroxide gel slurry is separated as much as possible, and the resulting neutral transparent liquid is discharged in the form of waste liquid Lose. Since no economical method is available for such reuse, the slurry is disposed of as waste, creating a huge waste.

In recent years, efforts are being made to minimize the generation of the aforementioned slurries and to maximize the recovery and utilization of valuable substances such as sodium and aluminum present in aluminium-containing waste liquids, a suitable example being the so-called regeneration and utilization of aluminum Aging solution in the corrosion of materials: the aging solution is discharged regularly or continuously, and crystal aluminum hydroxide [a Al(OH) ₃ , hydrated aluminum oxide] is added as a crystal seed, and the sodium aluminate in the aging solution is hydrolyzed, and a part of the aluminum Aluminum hydroxide precipitates out as industrially valuable crystalline crystals, while the spent sodium silicate liquor of the aluminum is recycled as regeneration liquor to the etching step where the sodium is reused.

However, no other economical use of aluminum-containing waste liquor has been available so far because of its low aluminum concentration or the presence of impurities. The waste liquid in question is still to be neutralized together, posing a problem of disposal of the slurry, and therefore research into reuse of the slurry is underway.

A typical example of this type of research is, for example, the method disclosed by Japan Kokai Tokkyo Koho No.Sho52-43,184 (1977) and Hei4-323,386 (1992): slurry is dissolved in sodium hydroxide solution or sodium aluminate solution ( Specifically, it is the above-mentioned regenerated sodium aluminate solution after hydrolyzing the aging etching solution), increasing the aluminum concentration, separating insolubles to remove alkaline components such as iron, magnesium, nickel and silicon, and using the purified solution Combined hydrolysis with aged etching solution to recover industrially useful crystalline aluminum hydroxide and alkali metals. The methods listed above are considered to be economical and easy to implement from the standpoint of slurry chemistry and equipment availability.

However, the tentative application of this method to the slurry produced by the waste liquid treatment normally practiced today has caused problems related to the solubility of the slurry and the presence of a large amount of sulfate in the slurry, so it is difficult to use this method. The method was put into experimental application.

Generally speaking, for hydrolysis of sodium aluminate in aluminum-containing waste liquid, aluminum in the waste liquid should exist in a supersaturated state. In order to precipitate 30-50% dissolved aluminum at an economically viable decomposition rate, the Al/NaOH equivalence ratio must be about 0.4 or above in the 70-150 g/L NaOH solution typically used for etching.

However, the slurries of aqueous aluminum hydroxide gel produced by the conventional neutralization reaction in commonly surface-treated aluminum materials are less soluble in sodium hydroxide solutions than crystalline aluminum hydroxide (aluminox) due to its single crystal structure. Therefore, high temperature and pressure must be applied to dissolve the slurry in a NaOH solution of a concentration suitable for normal etching. Alternatively, a higher concentration NaOH solution must be used for dissolution at or below the boiling point at atmospheric pressure. These procedures are not necessarily easy to accept.

Sulphate radicals in aluminum-containing waste liquids will probably enter the slurry produced by neutralization, for example, by combining aged etching and anodizing solutions, neutralizing at pH 5-9 and drying at 105 °C (loss on drying 70 -75%) obtained slurry, which is composed of 25-35% aluminum, 10-17% sulfate (SO ₄ ^2- ) and 0.4-1.5% sodium, the sulfate content is several times that of sodium in terms of equivalent ratio .

The difficulty in removing sulphate from the slurry actually indicates that the sulphate was not reduced by repeated washing of the filter cake or repressurization, drying and heating to a temperature above that to remove the water of crystallization or further washing after the aforementioned drying, only It can only be removed by calcining the slurry at 800°C or above.

If sulfate is present in the slurry, it will neutralize and consume valuable sodium hydroxide during dissolution and hydrolysis of the slurry and subsequent recovery _of crystalline aluminum hydroxide and filtrate, the _Na2SO4 thus formed is The accumulation in the etching solution interferes with hydrolysis, significantly deteriorates the economics of alkali recovery, and adversely affects the product quality of aluminum after the etching results.

The present inventor has done extensive research on the treatment of aluminum-containing waste liquid produced in surface-treated aluminum materials, and found that before or after neutralizing this aluminum-containing waste liquid, the separation of slurry at pH 9.0 or above can achieve the best results. It is possible to prevent sulfate radicals from entering the recycled sludge, thus completing the present invention.

It is therefore an object of the present invention to provide a new method of cost-effectively treating a variety of aluminum-containing effluents generated in the surface treatment of aluminum materials, especially those effluents which have been found to be difficult to treat, such as aged anodized effluent, effluent from moisture and effluent from wash water.

Another object of the present invention is to provide a method for treating waste liquid produced in surface-treated aluminum materials, which prevents as far as possible the entry of sulfate radicals in the process of neutralizing the aluminum-containing waste liquid produced by surface-treated aluminum materials. Aqueous aluminum hydroxide gels and recycled slurries can be utilized.

Another object of the present invention is to provide a treatment method for waste liquid in surface-treated aluminum materials, which can be used to neutralize the hydrous aluminum hydroxide gel formed in the neutralization of aluminum-containing waste liquid produced by surface-treated aluminum materials. Industrially valuable crystalline aluminum hydroxide and alkali solution are recovered from the slurry.

Therefore, in the surface treatment of aluminum materials including aluminum and its alloys with alkaline solution or with the alkaline solution and acid solution (wherein the aluminum-containing waste liquid produced by the treatment with alkali or acid solution is neutralized and neutralized Formed hydrous aluminum hydroxide gel is separated from the neutralization liquid and carries out waste liquid treatment), the present invention relates to a kind of processing method of the waste liquid in the surface treatment aluminum material, and this method comprises separating described Pre-neutralize the pre-neutralization slurry present in the aluminum-containing waste liquid, after the separation of the pre-neutralization slurry, neutralize the remaining liquid to adjust the pH to 5-9, and separate the slurry of the hydrous aluminum hydroxide gel, And the post-neutralized slurry is recycled to the aluminum-containing waste liquor.

In addition, in the surface treatment of aluminum materials including aluminum and its alloys with alkaline solution or with the alkaline solution and acid solution (wherein the aluminum-containing waste liquid generated by the treatment with alkali or acid solution is neutralized and will be neutralized to form The aqueous aluminum hydroxide gel slurry is separated from the neutralization solution), the present invention relates to a treatment method for the waste liquid in the surface treatment aluminum material, the method comprises neutralizing the aluminum-containing waste liquid to make the pH Control within the range of 5-9, separate the slurry of the hydrous aluminum hydroxide gel formed by neutralization, discharge the clarified liquid, and control the pH of the solution coexisting with the balance of the post-neutralization slurry at 9.0 or higher. After pH control at said higher value the slurry of aqueous aluminum hydroxide gel is separated again and the separated liquid is recycled to the aluminium-containing waste liquor.

In addition, the present invention relates to a method for surface treatment of waste liquid in aluminum materials, the method comprising dissolving the above-mentioned slurry recovered by the method of the present invention in sodium hydroxide solution and/or sodium aluminate solution of low concentration aluminum , remove insoluble matter from the solution, add crystalline aluminum hydroxide as a seed crystal to the solution for hydrolysis, recover the precipitated crystalline aluminum hydroxide by filtration and reuse the filtrate as an alkaline solution.

In the method of the present invention, the target of waste liquid treatment is aluminum-containing waste liquid, and such waste liquids are not limited, as long as they are generated during surface treatment of aluminum materials and contain aluminum. Specifically, they include effluents for which no effective treatment method is available, such as effluents resulting from moisture and wash water from etching and aged anodes from moisture and wash water from anodizing solution and waste.

The first method of the present invention is implemented through the following steps: the pre-neutralization slurry is separated from the pre-neutralization aluminum-containing waste liquid (pH9.0 or above, preferably 9.4-11.0), and the pre-neutralization slurry After the separation, the remaining liquid is neutralized so that the pH is controlled within the range of 5-9, and the slurry of the hydrous aluminum hydroxide gel formed by neutralization is separated, and the neutralized slurry is returned to the aluminum-containing waste liquid and discharge the clarified liquid as waste water.

In carrying out the above-mentioned first method, in the case where the pre-neutralization aluminum-containing liquid is an alkaline solution with a pH of 9.0 or below or an acid solution with a pH controlled at 9.0 or above before separating the slurry, it is necessary to add sodium hydroxide. On the other hand, when the aluminum-containing waste liquid is an alkaline solution with a pH of 9.0-11.0, the slurry can be separated practically as it is.

Separation of slurries at high pH can be carried out by common methods such as filtration, settling and centrifugation, and this method can be combined with the addition of suitable coagulants or by means of pressurization.

In the process of separating the slurry, it is better to wash the recovered slurry with water of pH 9.0 or above or dry the slurry first and wash with water of pH 9.0 or above, and then use water of pH 6.0-3.0 as needed washing. After the washing step, it is preferable to combine the separation liquid with the washing liquid and use this mixture in the next neutralization treatment. Here, washing further reduces the sulphate remaining in the slurry to be recovered.

If necessary, the liquid separated from the above separation slurry is combined with the washing liquid of the slurry, and an acid solution is added to neutralize the pH to 5-9. The acid solution used for neutralization is basically aqueous sulfuric acid, and in some cases, aqueous hydrochloric acid may also be used.

The solid resulting from the above-mentioned neutralization, namely the slurry of aqueous aluminum hydroxide gel, is separated again by a suitable method, and the filtrate and clear supernatant are discharged as waste water. The slurry or the thick fraction containing a large amount of slurry is combined with the aluminum-containing waste liquid before being treated by the method of the present invention, and the waste liquid is treated again by the method of the present invention.

Slurries separated at the above high pH values usually contain 1.0% or less sulfate, occasionally as low as 0.6% or less, although the sulfate content varies with the pH of the separation process, and such slurries can be very Easy to use.

The second method of the present invention is preferably implemented through the following steps, namely: neutralizing the aluminum-containing waste liquid so that the pH is controlled within 5-9, and separating by settling the hydrous aluminum hydroxide gel slurry produced by the neutralization, Discharge the clarified supernatant as wastewater, control the pH of the thick part of the post-neutralization slurry to a high pH of 9.0 or more, and separate the hydrous aluminum hydroxide gel again after controlling the pH to the high value The slurry and the separated liquid is returned to the aluminum-containing waste liquid.

In the second method of the present invention, the pH is controlled at 5-9 by neutralizing the aluminum-containing waste liquid, and the neutralization is by using an acid solution such as sulfuric acid (when the aluminum-containing waste liquid is alkaline) or using sodium hydroxide solution (when the aluminum-containing waste liquid is acidic).

Although a variety of methods are suitable for separating the slurry of aqueous aluminum hydroxide gel produced by neutralization, sedimentation is preferred because of its simplicity and the addition of a suitable coagulant as needed.

The clarified supernatant obtained from the above separation was directly discharged as waste water, while the thick part of the slurry was controlled to a high pH of 9.0 or above by adding an aluminum hydroxide solution.

After the pH is controlled to the above-mentioned high value, the aqueous aluminum hydroxide slurry is separated and recovered again, and before being treated by the method of the present invention, the separated liquid is combined with the aluminum-containing waste liquid, and the mixture is processed by the method of the present invention Waste liquid treatment.

The slurries recovered here typically contain 1.0% or less sulfate, sometimes as low as 0.6% or less, although the sulfate content varies with the pH of the separation, and such slurries can be readily used.

In the above-mentioned second method of the present invention, the thick part of the slurry obtained by neutralization (pH 5-9) and then sedimentation is subjected to the processing step of adjusting the pH to a high value as it is by the currently widely used procedure. Environmentally important, this treatment essentially re-neutralizes the slurry resulting from neutralization with a high pH solution.

Therefore, the above-mentioned adjustment of the thick part of the slurry to a high pH can also be performed by a method other than the above-mentioned method. For example, according to one method, at a certain point on the conveying line from the bottom of the settling tank to the separator (such as a pressurized filter), sodium hydroxide solution can be continuously added to the thick part of the slurry and mixed with the conveying or The slurry in the conditioning tank immediately before the separator reacts so that the solution coexisting with the slurry assumes a pH of 9.0 or more immediately before the separator. According to another method, the filter cake of the slurry formed at pH 5-9 after neutralization is initially shaken with a small amount of sodium hydroxide solution and then with a washing solution of pH 9.0 or above, so that the pH of the washing solution becomes 9.0-11.0. According to another method, the filter cake of the slurry formed at pH 5-9 is reslurried with an alkaline solution so that the pH of the equilibrium solution is 9.0 or above.

The slurry recovered at high pH using the first or second method of the present invention has a low concentration of sulfate and can be used in a variety of ways. In general, the slurry in question is dissolved in sodium hydroxide solution and/or sodium aluminate solution with low aluminum concentration, the insolubles are separated, crystalline aluminum hydroxide is seeded into the resulting solution, and precipitates out due to hydrolysis The aluminum hydroxide is recovered by filtration, and the filtrate is reused as an alkaline solution.

The sodium hydroxide solution and/or the sodium aluminate solution with low aluminum concentration prepared for dissolving the slurry can be: a sodium hydroxide solution with a NaOH concentration of 70-150 g/L for normal etching, and a NaOH concentration of A sodium aluminate solution of 70-150 g/L, a make-up solution with a NaOH concentration of 300 g/L or more for etching, or a sodium aluminate solution with a NaOH concentration of 70-150 g/L and a NaOH concentration of 300 A mixture of supplementary solutions of sodium hydroxide in grams per liter or more.

The process of the present invention is to separate the slurry at a high pH of 9.0 or above while utilizing the recovered slurry at a low sulfate concentration and recycling this aluminum not available in the high pH separation to the aluminium-containing waste liquor. Therefore, it is possible to effectively treat those difficult-to-treat aluminum-containing waste liquids, especially aged anodizing liquids, waste liquids from moisture and waste liquids from washing water, at low cost.

It is known that when the slurry is repeatedly washed and reslurried on the filter cake, when the slurry is dried and heated at a temperature higher than that at which the water of crystallization is removed, or when the slurry is further washed after the aforementioned heat treatment, The sulfate radicals in the slurry have not been eliminated. The reason why sulfate does not enter the slurries separated at high pH of 9.0 or above has not been verified, but plausible explanations are as follows:

Sulphate in the slurry of aqueous aluminum hydroxide gel produced by neutralizing aluminum-containing waste liquor is considered to satisfy the following equilibrium in a water-rich environment:

Therefore, sulfate groups cannot be removed only by washing with water, drying at low temperature or heating. A high pH aqueous solution can shift the above equilibrium to the right or perform a fast ion exchange reaction, only in this way is it possible to easily remove the sulfate group. The present invention utilizes this ion exchange reaction.

The method of the present invention can process various aluminum-containing waste liquids produced in the surface treatment of aluminum materials with low cost and high efficiency, especially aged anodic oxidation liquid, waste liquid produced by moisture and waste liquid produced by washing water , all these waste liquids were difficult to deal with before. In addition, this method prevents sulfate radicals from entering the slurry of the hydrous aluminum hydroxide gel as much as possible, making it possible to easily recover industrially valuable crystalline aluminum hydroxide and alkali from the slurry recovered from the treatment waste liquid. solution.

Fig. 1 is a flowchart showing the waste liquid treatment steps related to Embodiment 1 of the present invention.

Fig. 2 is a flowchart showing the waste liquid treatment steps related to Embodiment 3 of the present invention.

The present invention will be described in detail below with reference to the examples and the attached flow chart of waste liquid treatment. The symbol "%" in Examples and Comparative Examples is % by weight.

Example 1

50 liters of alkaline waste (NaOH, 8.4 g/L; Al, 2.4 g/L) and 130 _liters of acidic waste ( _H2SO4 , 5.7 g/L; Al, 0.4 g / liter) mixture is used as aluminum-containing waste liquid, and it is processed according to the waste liquid treatment process shown in Figure 1.

In this example 1, sodium hydroxide was added to the above-mentioned mixture whose pH was controlled at 9.5, and a polymer coagulant was added to the high-pH mixture to precipitate a slurry of hydrous aluminum hydroxide gel, and 12 liters were taken out The thick fraction containing high concentration slurry was filtered under pressure and the filter cake was washed by flowing 2 liters of water at pH 9.4 under pressure. The recovered slurry (76% water content) was about 2090 grams.

The supernatant, filtrate and washing liquid obtained in the above deposition and separation steps were combined, and neutralized with sulfuric acid to adjust the pH to 8.0.

The insolubles (i.e. the slurry of aqueous aluminum hydroxide gel) resulting from this neutralization step were allowed to settle, 180 liters of the clarified supernatant was discharged as wastewater, and the 20 liters thick fraction was mixed with the aluminum-containing waste to be disposed of below. liquid combined.

In this example, the slurry separated and recovered at the above mentioned high pH was found to have the following composition: Al, 8.0%; Na. 0.25%; _SO4 , 0.47%.

Comparative example 1

Add 131 grams of sodium hydroxide (100%) to neutralize the aluminum-containing waste liquid (the same mixture as in Example 1 above) to pH6.7, filter the whole liquid under pressure, and let 3 liters of water flow under pressure filter cake to wash the filter cake. The recovered slurry (76% water content) was about 2,240 grams and had the following composition: Al 7.5%; Na 0.2%; _SO4 3.4%.

Example 2

The slurry (2,150 g) isolated at high pH in the same manner as in Example 1 was dried at 105°C for 3 hours to obtain 510 g of dry flakes. The dried tablet was washed by dispersing it in 2 liters of water of pH 9.5, filtered under pressure, and further washed with 1 liter of water. The recovered slurry (30% water content) was approximately 740 grams and had the following composition: Al 23.3%; Na 0.9%; _SO4 0.8%.

Comparative example 2

The slurry obtained in the same manner as in Comparative Example 1 above was dried at 105°C and washed with water as in Example 2 above. The recovered slurry had the following composition: Al 22.5%; Na 0.4%; _SO4 9.3%.

Example 3

[50 liters of alkaline waste liquid (NaOH 8.4 grams/liter; Al 2.4 grams/liter) and 130 liters of acidic waste liquid are processed according to the waste liquid treatment flow process shown in Figure 2. (H ₂ SO ₄ total 5.7 g/l; Al 0.4 g/l)].

In Example 3, 131 grams of sodium hydroxide (100%) was added to neutralize the mixture, and the pH was adjusted to 6.7.

Add polymer coagulant to the neutralized mixture to precipitate a slurry of hydrous aluminum hydroxide gel, discharge 164 liters of clear supernatant as it is, recover 16 liters of thick part from the lower part, transfer to separator and mix with 185ml of 25% sodium hydroxide solution was mixed, and the pH was adjusted to a high value of 10.0.

After the pH was adjusted to the high value, the slurry was pressure filtered and the filter cake was washed by passing first 2 liters of pH 9.4 water and then 2 liters of pH 6.9 water down the filter cake under pressure.

The recovered slurry (76% water content) was approximately 2,280 grams and had the following composition: Al 7.9%; Na 0.3%; _SO4 0.2%.

The filtrate from the high pH separation slurry and the slurry wash are combined and added to the aluminum-containing spent liquor to be treated next.

Example 4

2,100 g of slurry (Al 8.0%; Na 0.25%; SO ₄ 0.47%) obtained in the same manner as in Example 1 above was used in an existing pipeline comprising an etching step and an anodizing step for surface-treated aluminum Add it to 21.56 liters of etching solution (NaOH 89.0 g/L; Al 17.9 g/L) regenerated after alkali recovery. The resulting mixture was kept at 50°C for 20 minutes and filtered under reduced pressure, and the residue was washed with 0.02 liter of water.

The filtrate and washings totaled approximately 23.31 liters and had the following composition: NaOH 82.2 g/l; Al 23.7 g/l; _{Na2SO4 0.6} g/l. The reclaimed filter cake (water content 50%) is about 28 grams.

The results showed that when the slurry was added to the aged etchant, 98.5% of the Al in the slurry was recovered in the filtrate and washes.

The above filtrate and washes containing dissolved slurry were combined with 77.30 liters of aged etchant (NaOH8 7.0 g/L; Al 25.0 g/L) and recycled to the unit for immersion caustic recovery to give 100.61 liters of solution (NaOH 85.9 g/l; Al 24.7 g/l; _{Na2SO4 0.15} g/l). The solution was mixed with 6,000 g of alumina as a seed crystal and stirred at 45° C. for 24 hours for hydrolysis. The crystals were separated by filtration and washed with water to obtain 2,340 g of crystalline aluminum hydroxide (aluminum, water content 8%).

_The recovered filtrate and washings totaled about 99.42 liters and had the following composition: NaOH 86.8 g/l; Al 17.5 g/l; _Na2SO4 0.5 g/l.

The results showed that 98.5% of the aluminum in the slurry was recovered as useful crystalline aluminum hydroxide.

Part of the filtrate and wash solution from which the above-mentioned crystalline aluminum hydroxide is recovered is used to dissolve the slurry, and the remainder makes up alkali and is recycled to the aluminum etching step as regenerated etching solution. The accumulation _{of Na2SO4} in this line does not exceed 3.0 g/L.

Comparative example 3

For comparison, the slurry obtained in Comparative Example 1 was treated by keeping the mixture at 100°C for 30 minutes in the same manner as in Example 4 above. The recovery of Al in the slurry added to the aged etchant and recovered in the filtrate and washes was only 72%.

If the filtrate is recycled as it is, the accumulation of Na ₂ SO ₄ in the etching solution is calculated to be 16 g/l.

Example 5

In an existing pipeline comprising an etching step and an anodizing step for surface-treated aluminum, 721 g of slurry (Al 23.3%, Na 0.9%; SO _0.8 %) obtained in the same manner as in Example 2 above Add it to a part or 21.52 liters of the aging etching treatment solution after hydrolysis and regenerate the etching solution (NaOH 89.0 g/L; Al 17.9 g/L), the resulting mixture was kept at 100 °C for 1 hour, filtered under reduced pressure, and the residue was used 0.02 liters of water for washing.

The filtrate and washings totaled about 22.07 liters and had the following composition: NaOH 86.7 g/l, Al 24.9 g/l; _{Na2SO4 0.4} g/l. The recovered residue (50% water content) was about 27 g.

The results showed that when the slurry was added to the regenerated etching solution, 98.3% of the Al in the slurry was recovered in the filtrate and washes.

The above filtrate and washes in which the slurry was dissolved were combined with 77.30 liters of aged etching solution (NaOH 87.0 g/l; Al 25.0 g/l) to be recycled to the unit for etchant caustic recovery to obtain 99.37 liters solution (NaOH 86.9 g/L; Al 25.0 g/L; _{Na2SO4 0.09} g/L). The solution was mixed with 6,000 g of alumina as a seed crystal and stirred at 45°C for 24 hours for hydrolysis. The crystals were separated by filtration and washed with water to obtain 2,340 g of crystalline aluminum hydroxide (aluminum, water content 8%).

The recovered filtrate and washings totaled about 98.18 liters and had the following composition: NaOH 87.9 g/l; Al 17.7 g/l; _{Na2SO4 0.9} g/l.

The results showed that 98.3% of the aluminum in the slurry was recovered as useful crystalline aluminum hydroxide.

Part of the filtrate and wash solution from which the above-mentioned crystalline aluminum hydroxide is recovered is used to dissolve the slurry, and the rest is supplemented with alkali and recycled to the aluminum material etching solution as a regenerated etching solution. The accumulation _{of Na2SO4} in this line does not exceed 2.0 g/L.

Example 6

The slurry obtained in the same manner as in Example 1 (Al 8%; Na 0.25%; SO _0.47 %) (2,100 grams) was added to 846 grams (553 ml) of supplementary hydroxide for the etching solution for surface treatment of aluminum materials Sodium solution (50% strength), the mixture was stirred at 100° C. for 30 minutes until dissolution occurred.

The resulting solution was filtered under reduced pressure, the filter cake was washed with 0.02 liter of water, and 2.35 liters of filtrate and washing liquid (NaOH 178.4 g/L; Al 70.3 g/L; Na ₂ SO ₄ 6.2 g/L) and 28 g of filter cake were recovered.

The recovered filtrate and washes were combined with 88.60 liters of aged etching solution (NaOH 87.0 g/L; Al 25.0 g/L) to obtain 90.94 liters of solution (NaOH 89.4 g/L; Al 26.2 g/L; Na ₂ SO ₄ 0.16 g/L; Al 26.2 g/L; Na ₂ SO ₄ 0.16 g/L), which was mixed with 6,000 g of gibbsite seeds and stirred at 45° C. for 30 hours for hydrolysis.

The crystallized aluminum hydroxide was filtered and washed with 0.35 liters of water to obtain 2341 grams of crystalline aluminum hydroxide (water content 8%) and 89.80 liters of filtrate and washings (NaOH 90.3 g/l; Al 18.2 g/l; Na ₂ SO ₄ 0.16 g/L). As a regenerated etching solution, the filtrate and washes are recycled to the etching step and used again for the etching of aluminum.

As for the aluminum content of the slurry, the aluminum recovered from the slurry dissolved in the make-up sodium hydroxide solution and the aged etchant had a recovery rate of 98.5%, or 48.9% of the slurry recovered in one hydrolysis process (i.e., 48.2% of the aluminum in the slurry), the circulation of the solution can actually utilize all the aluminum in the slurry recovered in the aged etching solution, and the final utilization rate of the aluminum in the slurry is about 98.5%.

Comparative example 4

For proportion, 2,240 grams of slurry (Al7.5%; Na 0.2%; SO _3.4 %) obtained in the same manner as Comparative Example 1 were dissolved in 846 g of 50% sodium hydrogen hydride solution (553 ml, 423 grams of NaOH), and The insolubles were pressure filtered and washed to obtain 1,030 g of filter residue and 2.20 liters of filtrate and washings.

The composition of the filtrate and washings thus obtained was 166.5 g/l NaOH, 41.1 g/l Al and 51.1 g/l _Na2SO4 , the recovery of Al in the slurry dissolved in 50% NaOH solution and _recovered The rate is only 54%.

Claims (9)

1. A method for treating waste liquid in surface-treated aluminum materials, wherein said surface treatment of aluminum materials comprising aluminum and its alloys is carried out with alkali solution or said alkali solution and acid solution, and waste liquid treatment is carried out by using alkali or Neutralization of aluminum-containing waste liquid resulting from said treatment with an acid solution and separation of a slurry of aqueous aluminum hydroxide gel formed by neutralization from the neutralized liquid, characterized in that the process comprises neutralization of aluminum-containing waste liquid The pH of the waste liquid is adjusted to 5-9, the slurry of the hydrous aluminum hydroxide gel formed by neutralization is separated, the clarified liquid is discharged, and the pH of the solution coexisting with the post-treatment neutralized slurry equilibrium is adjusted to 9.0 or more, After the pH is adjusted to said high value, the slurry of aqueous aluminum hydroxide gel is separated again and the separated liquid is returned to the aluminum-containing waste liquid. 2. The waste liquid treatment method according to claim 1, wherein the slurry of the hydrous aluminum hydroxide gel formed by neutralization is separated by sedimentation, the clarified supernatant is discharged, and the thickened slurry after neutralization is Partially adjusted to a high pH of 9.0 or above. 3. The waste liquid treatment method according to claim 1 or 2, wherein the slurry separated at high pH is further washed with water having a pH of 9.0 or above. 4. The waste liquid treatment method according to claim 1 or 2, wherein the slurry separated at high pH is dried and further washed with water having a pH of 9.0 or above. 5. The waste liquid treatment method according to claim 4, wherein the slurry separated at high pH is washed with water of pH 9.0 or above, and then washed with water of pH 6.0-8.0. 6. The waste liquid treatment method in the surface-treated aluminum material according to any one of claims 3-5, the method comprises dissolving the described slurry separated at high pH and then cleaned in sodium hydroxide and/or low aluminum concentration In the sodium aluminate solution, the insoluble matter is removed from the solution, the solution is hydrolyzed by adding crystalline aluminum hydroxide as a seed crystal, the crystalline aluminum hydroxide precipitated by hydrolysis is recovered by filtration, and the filtrate is reused as an alkali solution. 7. The waste liquid treatment method according to claim 6, wherein said sodium hydroxide and/or sodium aluminate solution to be dissolved in the slurry has a concentration of 70-150 grams of NaOH per liter. 8. The waste liquid treatment method according to claim 6, wherein said sodium hydroxide solution to be dissolved in the slurry is a sodium hydroxide solution used in the etching step, and its NaOH concentration is 300 per liter or more. 9. The waste liquid treatment method according to claim 6, wherein the slurry is dissolved with a sodium aluminate solution having a NaOH concentration of 70-150 g per liter and a sodium hydroxide make-up solution having a NaOH concentration of 300 g per liter or more.