JP2010222159A - Processing method of aluminum hydroxide-containing solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a processing method of aluminum hydroxide sludge, recoverable of crystalline aluminum hydroxide excellent in handling property with good operability and preventing an increase in the amount of a liquid in the system during processing. <P>SOLUTION: In the processing method of an aluminum hydroxide-containing solution, a first recovering step and/or a second recovering step of crystalline aluminum hydroxide are introduced into the processing step of an aluminum hydroxide-containing solution. In the first recovering step, an aluminum hydroxide-containing solution is neutralized from the alkaline dissolution region of aluminum hydroxide to precipitate the crystalline aluminum hydroxide. In the second recovering step, an acid is added to the aluminum hydroxide-containing solution to prepare an acidic solution, which is neutralized from the acidic dissolution region of aluminum hydroxide to precipitate the crystalline aluminum hydroxide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for treating an aluminum hydroxide-containing solution containing aluminum hydroxide produced in the surface treatment step of an aluminum material made of aluminum or an aluminum alloy, and in particular, aluminum hydroxide sludge produced in the surface treatment step of the aluminum material. In addition, the present invention relates to a method for treating an aluminum hydroxide-containing solution capable of efficiently recovering crystalline aluminum hydroxide in a treatment process of aluminum hydroxide waste liquid.

  Aluminum materials are used in many fields such as various parts such as ships, vehicles, machines, etc., thin foil electrical related products for electrolytic capacitors, building materials such as aluminum sashes, office supplies, etc. In the manufacturing process, various surface treatments such as an etching treatment with an alkaline solution and an anodizing treatment with an acidic solution are performed for the purpose of cleaning the surface of the aluminum material, increasing the surface area, imparting corrosion resistance and design properties, and the like.

  However, in any case, for the treatment liquid used in these surface treatments, consumption of active ingredients in the treatment liquid and dissolution of aluminum from the aluminum material occur, and inevitably an excess of aluminum content after a certain period of time. Accumulation occurs. In this way, if the accumulation of aluminum exceeds a certain limit and becomes excessive, so-called liquid aging occurs in the processing liquid, requiring renewal. The aged processing liquid (aging bath) contains a large amount of aluminum. It becomes the aluminum-containing waste liquid to be contained, and it becomes necessary to dispose of it after processing.

  In addition, in the surface treatment of aluminum materials as described above, during the treatment such as the etching treatment or anodizing treatment, it is scattered around as a mist together with a gas such as hydrogen gas generated during the treatment and absorbed in the exhaust system. In addition, so-called “waste liquid derived from mist” that leaks as other handling loss occurs, or after these surface treatments, it is essential to wash with water, and a large amount generated at that time Although waste water derived from washing water is also generated, waste liquid derived from mist and the like and waste liquid derived from washing water also contain an aluminum component and become an aluminum-containing waste liquid.

  And, various aluminum-containing waste liquids generated by the surface treatment of such aluminum materials are normally neutralized to pH 5-9 in a lump, and the gelled aluminum hydroxide sludge generated at that time The neutral clarified liquid is separated as much as possible, and the recovered aluminum hydroxide sludge is not economically used as a resource. ing.

By the way, in recent years, in order to suppress the generation of such sludge as much as possible and to recover and effectively use valuable materials such as sodium and aluminum present in the aluminum-containing waste liquid, As for the aging bath that occurs in the process, it is extracted regularly or continuously, and crystalline aluminum hydroxide [αAl (OH) ₃ , dibsite] is added as seeds to hydrolyze sodium aluminate in the aging bath. Then, a part of aluminum is precipitated as crystalline aluminum hydroxide, which is industrially valuable, and the sodium aluminate solution with a reduced aluminum content is circulated in the etching process as a regenerative etching treatment liquid. Recycling effective use of so-called etching aging bath that reuses sodium Are we.

  However, other aluminum-containing waste liquids are not economically used due to their low aluminum concentration and impurities, and the method of neutralizing them at the same time is still adopted, and the sludge generated at that time is treated. In addition, for example, aluminum hydroxide sludge generated when neutralizing water drainage from condenser manufacturing plants contains a relatively large amount of phosphorus components derived from phosphoric acid used in the surface treatment process. Since it is included and phosphorus and aluminum hydroxide cannot be easily separated, their treatment and reuse are also problematic.

  In addition, crystalline aluminum hydroxide produced by the method as described above has a very small particle size of around 0.01 μm and is difficult to dehydrate by filtration or the like, and has a high water content after dehydration. A large amount of moisture is handled when transporting the equipment to the facility and processing the equipment, which requires a great deal of cost. In addition, in order to recycle these high water content aluminum hydroxides, it is necessary to evaporate the water content to reduce the water content, and a large amount of energy is required for the drying process.

  By the way, regarding the method of recovering useful crystalline aluminum hydroxide by treating aluminum hydroxide sludge, there have been some proposals so far. For example, Patent Document 1 discloses a surface treatment process of an aluminum material. When the gelled aluminum hydroxide sludge generated from the generated waste liquid is treated, the gelled aluminum hydroxide sludge is dissolved in a sodium hydroxide-containing solution, and calcium hydroxide or the like is added to the obtained sludge solution. The impurities such as various metal elements contained in the sludge are separated and removed efficiently by adding the alkaline earth metal hydroxide and then solid-liquid separation as seeds in the collected separation liquid Crystals formed by adding crystalline aluminum hydroxide to hydrolyze sodium aluminate in the separation liquid, and then solid-liquid separation With the recovery of aluminum hydroxide, a reduced sodium aluminate aqueous solution of aluminum concentration is recovered, a method of circulating the etching process has been proposed a reduced sodium aluminate aqueous solution of the aluminum concentration as reproduction etching solution.

  In Patent Document 2, a phosphorus component and an aluminum component are extracted with an extract containing sodium hydroxide from sludge incineration ash containing a high concentration of a phosphorus component and an aluminum component, and this extract is treated to obtain a phosphorus component. Recover calcium aluminate and aluminum components as sodium aluminate and aluminum hydroxide, respectively, and recycle sodium aluminate and aqueous sodium hydroxide solution obtained by hydrolyzing this sodium aluminate as an extract of sludge incineration ash. A method of using it has been proposed.

  However, in any of these methods, it is not always sufficient to obtain crystalline aluminum hydroxide having a low moisture content, excellent crystallinity, and excellent handling properties, and still has a high moisture content, and solid-liquid separation is difficult. Development of a method for treating aluminum hydroxide sludge that can recover crystalline aluminum hydroxide with excellent handling properties has not been solved. Was requested.

Japanese Unexamined Patent Publication No. 08-318,282 Japanese Patent Laid-Open No. 2004-203,641

Therefore, the present inventors have intensively studied a method for treating aluminum hydroxide sludge that can solve such conventional problems and recover crystalline aluminum hydroxide excellent in handling properties with good operability. When the crystalline aluminum hydroxide is recovered by treating the aluminum hydroxide-containing solution containing aluminum hydroxide generated in the surface treatment step, the aluminum hydroxide-containing solution is included in the aluminum hydroxide-containing solution treatment step. Crystalline aluminum hydroxide is added as seeds to precipitate crystalline aluminum hydroxide, the precipitated crystalline aluminum hydroxide is recovered and an aluminum-containing separation liquid containing aluminum is recovered, and then the aluminum-containing separation liquid is recovered. Neutralize and part or all of the resulting neutralization solution Crystalline aluminum hydroxide to drain the neutral separation liquid with water to aluminum hydroxide gel is dissolved in the aluminum hydroxide-containing solution: first step of recovering [gibbsite alpha Al (OH) _3], and / or, An acid is added to the aluminum hydroxide-containing solution or the balance of the neutralizing solution in the first step to prepare an acidic solution in which aluminum hydroxide is dissolved in the acidic solution, and an alkali is added to the acidic solution. The crystalline aluminum hydroxide is neutralized from the acidic dissolution region side of the aluminum hydroxide, and the generated crystalline aluminum hydroxide is dehydrated and recovered [dibsite: αAl (OH) ₃ or pseudo boehmite: AlO (OH)]. Introducing the second recovery step, the aluminum hydroxide-containing solution by the first recovery step of crystalline aluminum hydroxide, depending on the type of aluminum hydroxide-containing solution In addition to effectively preventing an increase in the amount of liquid in the system during the treatment process, it is possible to recover crystalline aluminum hydroxide with excellent handling properties by the second recovery process of crystalline aluminum hydroxide. It has been found that the object can be achieved by the first recovery step and / or the second recovery step of aluminum hydroxide, and the present invention has been completed.

  Accordingly, an object of the present invention is to recover aluminum hydroxide sludge capable of recovering crystalline aluminum hydroxide excellent in handling properties with good operability and preventing an increase in the amount of liquid in the system during the treatment process. It is to provide a processing method.

That is, in the present invention, when recovering crystalline aluminum hydroxide by treating an aluminum hydroxide-containing solution containing aluminum hydroxide generated in the surface treatment step of an aluminum material made of aluminum or an aluminum alloy,
Introducing a first recovery step and / or a second recovery step of crystalline aluminum hydroxide during the treatment step of the aluminum hydroxide-containing solution,
In the first recovery step of the crystalline aluminum hydroxide, the aluminum hydroxide-containing solution is introduced into the precipitation tank and the crystalline aluminum hydroxide is added as seeds to the aluminum hydroxide-containing solution. A portion of the slurry solution containing the precipitated crystalline aluminum hydroxide is extracted from the precipitation tank and dehydrated, and the crystalline aluminum hydroxide is recovered and the filtrate is returned to the precipitation tank. The aluminum-containing separation liquid containing aluminum obtained by sedimentation and separation is recovered, then the aluminum-containing separation liquid is neutralized with an acid, and a part or all of the obtained neutralization treatment liquid is dehydrated and water. The aluminum oxide gel and the neutral separation liquid are recovered, and the recovered aluminum hydroxide gel is dissolved in the aluminum hydroxide-containing solution. Drained neutral separation liquid with dissolved during the addition,
In the second recovery step of the crystalline aluminum hydroxide, an acid is added to the remaining portion of the aluminum hydroxide-containing solution or the neutralization treatment liquid obtained by the neutralization treatment in the first step, so that the aluminum hydroxide is an acidic solution. Prepare an acidic solution dissolved in the solution, introduce the acidic solution into a neutralization tank and add an alkali to the acidic solution to neutralize the acidic solution from the acidic solution region side of aluminum hydroxide. Further, the method for treating an aluminum hydroxide-containing solution is characterized in that crystalline aluminum hydroxide is added as a seed at the time of neutralization, and then the precipitated crystalline aluminum hydroxide is settled, dehydrated and recovered.

  Further, the present invention provides a sludge solution derived from the aluminum hydroxide sludge produced in the aluminum material surface treatment step, wherein the aluminum hydroxide-containing solution is a phosphorus-containing water containing a phosphorus component. In the case of aluminum oxide sludge, the sludge solution is introduced into the phosphorus recovery step before being introduced into the first recovery step and / or the second recovery step of crystalline aluminum hydroxide. This is a treatment method for an aluminum hydroxide-containing solution in which calcium hydroxide is added to precipitate crystalline calcium phosphate, and then precipitated and separated, dehydrated, and the phosphorus component in the sludge solution is recovered as crystalline calcium phosphate.

[Aluminum hydroxide-containing solution to be treated]
In the present invention, the aluminum hydroxide-containing solution to be treated includes aluminum hydroxide generated in the surface treatment process of the aluminum material, and its origin is particularly limited as long as it is a solution that requires treatment. Rather, for example, a waste liquid derived from mist generated during the etching process, a waste liquid derived from washing water, a waste liquid derived from an aging bath generated during anodizing treatment, a leaked waste liquid derived from mist, or a cleaning water Aluminum hydroxide waste liquids containing various types of aluminum hydroxide, such as waste liquids, washing waste water from condenser manufacturing plants, and cleaning waste liquids for tools and dies used for extrusion of aluminum profiles, and these aluminum hydroxides The aluminum hydroxide sludge generated when the waste liquid is neutralized is treated by the sludge dissolution process described below. Sludge solution can be exemplified, also, for these aluminum hydroxide effluent and sludge solution may contain a phosphorus component.

[Sludge dissolution process]
When the aluminum hydroxide-containing solution to be treated is a sludge solution derived from the aluminum hydroxide sludge generated in the surface treatment process of the aluminum material, first, the aluminum hydroxide sludge is introduced into the sludge dissolution process, and the sludge In the dissolution step, the above aluminum hydroxide sludge is dissolved in an alkali solution to prepare a sludge solution containing sodium aluminate, but the alkali solution used in this sludge dissolution step is not particularly limited. For example, a virgin / alkali solution composed of an aqueous sodium hydroxide solution can be used. From the viewpoint of reusing as much as possible sodium hydroxide used for dissolving aluminum hydroxide sludge, crystalline aluminum hydroxide is preferable. Recovered in the first recovery step The aluminum-containing separated liquid back to the sludge dissolving process as part or all of the alkaline solution, it is preferable to use as alkali solution or a part thereof by dissolving aluminum hydroxide sludge is prepared sludge solution.

  In addition, regarding the amount of sodium hydroxide used to prepare a sludge solution by dissolving aluminum hydroxide sludge in an alkaline solution, the aluminum hydroxide in the aluminum hydroxide sludge reacts with sodium hydroxide. In order to become sodium aluminate, 1 mol of sodium hydroxide is required for 1 mol of aluminum hydroxide, and since the produced sodium aluminate is stably present in the sludge solution, 0.7-1 It is necessary to coexist with about 7 mol of free sodium hydroxide. Furthermore, when phosphate ion is present in aluminum hydroxide sludge, 3 mol of sodium hydroxide is required for 1 mol of phosphate ion. In addition, when sulfate ion is present in aluminum hydroxide sludge, Since 2 mol of sodium hydroxide is required, the aluminum concentration of the treated aluminum hydroxide sludge, phosphate ion concentration, sulfate ion, etc. are used by circulating from the first recovery step of crystalline aluminum hydroxide. It is determined in consideration of the amount of free sodium hydroxide in the aluminum-containing separation liquid.

  In this sludge dissolution step, the aluminum hydroxide sludge has a dissolution temperature of 20 ° C. or more and 105 ° C. or less, preferably 50 ° C. or more and 80 ° C. or less, and a dissolution time of 5 minutes or more and 120 minutes or less, preferably 30 minutes or more and 60 minutes or less. The composition of the sludge solution obtained after dissolution in an alkaline solution under a dissolution condition of less than or equal to minutes is, for example, a total sodium hydroxide concentration (T-NaOH concentration) of 40 grams / liter (g / L). ) 100 g / L or less, preferably 60 g / L or more and 80 g / L or less, and the aluminum concentration (Al concentration) is 12 g / L or more and 45 g / L or less, preferably 24 g / L or more and 36 g / L or less, The molar ratio (T-NaOH / Al) of total sodium hydroxide (T-NaOH) to aluminum (Al) is 1.0 or more and 2.3 or less, preferably 1.5 or more and 1.7 or less.

[Phosphorus recovery process]
When the aluminum hydroxide sludge to be treated is a phosphorus-containing aluminum hydroxide sludge containing a phosphorus component, the sludge solution thus prepared contains a phosphorus component as a result. Before introducing the dissolved solution into the first recovery step and / or the second recovery step of crystalline aluminum hydroxide, calcium hydroxide is added to the sludge solution to precipitate crystalline calcium phosphate, followed by settling and dehydration. Then, the phosphorus component in the sludge solution is introduced into a phosphorus recovery step for recovering it as crystalline calcium phosphate.

  In this phosphorus recovery step, it is preferable to use a thickener with a stirring function as means for precipitating crystalline calcium phosphate while performing the sludge dissolution step, including the crystalline calcium phosphate generated in the thickener with stirring function. The slurry solution is settled and extracted, and dehydrated to recover crystalline calcium phosphate, and the obtained filtrate is returned again into the thickener with stirring function, and the supernatant of the thickener with stirring function is extracted, This clarified solution is introduced as a solution of aluminum hydroxide sludge gel into the next first recovery step of crystalline aluminum hydroxide. By using a thickener with a stirring function as a means of crystalline calcium phosphate in this way, it is possible to combine both functions in a single tank rather than separately installing a precipitation tank and a thickener, reducing the installation area and manufacturing costs. And seed addition are unnecessary (because seeds are always accumulated inside the tank).

In this phosphorus recovery step, for example, the molar ratio (Ca / P) between calcium (Ca) and phosphorus (P) is 1.5 or more and 2.0 or less, preferably 1.5 or more and 1.6 or less. In addition, calcium hydroxide [Ca (OH) ₂ ] is added to the sludge solution, preferably crystalline calcium phosphate [Ca ₃ (PO ₄ ) ₂ · 2H ₂ O] as a seed is 100 g / L or more and 400 g / L or less, preferably Is added in the range of 200 g / L or more and 300 g / L or less, and is operated under the precipitation conditions of a precipitation temperature of 80 ° C. or more and 105 ° C. or less and a precipitation time of 4 hours or more and 8 hours or less. Crystalline calcium phosphate [Ca ₃ (PO ₄ ) ₂ · 2H ₂ O] having a water content of 50 to 60% is recovered, and the clarified liquid obtained by this sedimentation has a phosphorus content (P content) of 0. Reduced to 3 g / L or less. The recovered calcium phosphate can be used for applications such as fertilizers, phosphoric acid production raw materials, and activated sludge nutrients.

In this phosphorus recovery step, calcium hydroxide [Ca (OH) ₂ ] added to the sludge solution must be dissolved for reaction with phosphate ions, Since calcium hydroxide has low solubility, it is preferably added as a 10 to 20% by weight aqueous solution thereof, and in an aqueous solution of less than 10% by weight, the amount of liquid added increases and the amount of liquid in the system increases. On the other hand, when the aqueous solution exceeds 20% by weight, it is difficult to pump with a pump, and it is difficult to handle it because it tends to be clogged in the pipe.

  Further, when the aluminum hydroxide waste liquid contains a phosphorus component, the same phosphorus recovery as described above is performed before the aluminum hydroxide waste liquid is introduced into the first recovery step and / or the second recovery step of crystalline aluminum hydroxide. Introduced into the process, the phosphorus component can be recovered as crystalline calcium phosphate.

[First recovery step of crystalline aluminum hydroxide]
In the first recovery step of this crystalline aluminum hydroxide [dibsite: αAl (OH) ₃ ], firstly, the sludge prepared in the above-described sludge dissolution step and, if necessary, the phosphorus component removed in the above-described phosphorus recovery step. The aluminum hydroxide gel recovered in the first recovery step is introduced into the solution and the aluminum hydroxide-containing solution such as the above-mentioned aluminum hydroxide waste liquid, and the aluminum concentration (Al concentration) of the aluminum hydroxide-containing solution is introduced. Is increased.

  The aluminum hydroxide gel is dissolved in the aluminum hydroxide-containing solution, for example, when the aluminum hydroxide-containing solution and the aluminum hydroxide gel are dissolved at a temperature of 20 ° C. or higher and 105 ° C. or lower, preferably 50 ° C. or higher and 80 ° C. or lower The dissolution time is 5 minutes to 120 minutes, preferably 30 minutes to 60 minutes, and the composition of the aluminum hydroxide-containing solution obtained after the dissolution is usually 40 g / T. L to 100 g / L, preferably 60 g / L to 80 g / L, and the Al concentration is 27 g / L to 45 g / L, preferably 24 g / L to 36 g / L. The molar ratio (T-NaOH / Al) between sodium oxide (T-NaOH) and aluminum (Al) is 1.0 or more and 2.3 or less, preferably 1.5 or more and 1.7 or less.

Next, the sludge solution with an increased Al concentration is introduced into the precipitation tank, and crystallized aluminum hydroxide [dibsite: αAl (OH) ₃ ] is added to the sludge solution as seeds for crystallization. A portion of the slurry solution containing the precipitated crystalline aluminum hydroxide is extracted from the precipitation tank and dehydrated, and the crystalline aluminum hydroxide is recovered and the separated liquid is returned to the precipitation tank. Further, an aluminum-containing separation liquid containing aluminum obtained by settling and separating the slurry liquid is recovered.

  Here, as a precipitation tank for depositing crystalline aluminum hydroxide, any precipitation tank can be used. Preferably, a thickener with a stirring function is preferably used, and the crystallinity generated in the thickener with a stirring function is used. The slurry solution containing aluminum hydroxide is withdrawn and dehydrated to recover crystalline aluminum hydroxide, and the obtained separated liquid is returned again into the thickener with stirring function, and the supernatant of the thickener with stirring function is clarified. The liquid (the clarified liquid obtained by the sedimentation separation of the slurry solution) is extracted, and this clarified liquid is recovered as an aluminum-containing separation liquid, introduced into the next neutralization process, and returned to the sludge dissolution process as necessary for hydroxylation. It is good to use as an alkaline solution for dissolving aluminum sludge or a part thereof. In this first recovery step of crystalline aluminum hydroxide, the use of a thickener with a stirring function as a precipitation tank eliminates the need to install a thickener as a separation tank separately from the precipitation tank. The advantage of cost reduction is obtained.

  As for seeds used for depositing crystalline aluminum hydroxide in the precipitation tank, crystalline aluminum hydroxide recovered by dehydrating the slurry solution obtained in the precipitation tank may be used, as well as crystals described later. Crystalline aluminum hydroxide obtained in the second recovery step of crystalline aluminum hydroxide may be used, and the dehydration of the slurry solution containing the crystalline aluminum hydroxide is performed by pressure filtration, vacuum filtration, and centrifugal separation. However, it is preferable to use vacuum filtration or centrifugation because the filter cake can be easily washed with water.

  For the recovered aluminum-containing separation liquid, the amount of liquid in the system based on the sodium hydroxide concentration, aluminum concentration, total soluble substance (TDS) concentration, total organic carbon (TOC) concentration, etc. of the aluminum-containing separation liquid In consideration of this, a part or all of it is introduced into the neutralization tank, and used in this neutralization tank, for example, hydrochloric acid etching waste liquid (aluminum chloride waste liquid) used in the aluminum surface treatment process, degreasing process or electrolysis process Using a waste sulfuric acid solution (waste sulfuric acid: aluminum sulfate) or a dialysis waste acid (aluminum chloride, aluminum sulfate, etc.) separated from the above waste acid with an ion exchange resin, an ion exchange membrane, etc., usually pH 5 to pH 9, preferably Is neutralized to pH 5.8 or more and pH 8.6 or less, and part or all of the neutralized solution obtained by this neutralization treatment is dehydrated to obtain aluminum hydroxide. Recovered and Umugeru and neutral separation liquid, the recovered aluminum hydroxide gel to drain the neutral separation liquid with dissolved sludge lysates as described above. By dissolving the aluminum hydroxide gel thus recovered in the sludge solution, the Al concentration of the sludge solution introduced in the first recovery step of this crystalline aluminum hydroxide is increased, and the crystalline aluminum hydroxide is increased. In addition, it is possible to easily control the increase in the amount of liquid in the entire process of treating aluminum hydroxide sludge having a high water content by draining the neutral separation liquid. In addition, since organic substances and salts contained in the neutral separation liquid are also discharged, the concentration of organic substances and / or salts in the system can be adjusted.

  Here, as a method for controlling the increase in the amount of liquid in the system other than the above neutralization method, the aluminum hydroxide sludge is dried with a fluid dryer or the like, and the water content is dried to 10% by weight or less to increase the liquid amount There is a method for controlling the concentration and the method for concentrating and controlling the amount of the increased liquid with an evaporator, etc., but each method not only consumes a large amount of heat energy but also an organic substance, hydrochloride, sulfuric acid dissolved in alkali. Since salts such as salts and nitrates are also concentrated, it eventually becomes a factor that inhibits precipitation of aluminum hydroxide. In addition to the neutralization method described above, there is an adsorption method using activated carbon adsorption or the like for organic substance removal, and salt removal using an ion exchange membrane such as an electrodialysis method or salt exchange using an ion exchange resin. Although there are adsorption methods, the initial cost and the running cost are high as compared with the neutralization method described above.

  The method for separating and recovering the aluminum hydroxide gel produced after neutralizing the aluminum-containing separation liquid and the neutral separation liquid is not particularly limited. For example, the aluminum-containing separation liquid The neutralized product may be introduced into a sludge tank, dissolved and concentrated, and then separated into aluminum hydroxide gel and neutral separation solution by a dehydrator, and the neutralized product of the aluminum-containing separation solution may be settled and separated. Sludge may be dehydrated.

[Second recovery step of crystalline aluminum hydroxide]
In the second recovery step of crystalline aluminum hydroxide, first, the remaining portion of the above-described aluminum hydroxide-containing solution or the neutralization treatment liquid obtained by the neutralization treatment in the first step is introduced into a neutralization tank. In this neutralization tank, an acid is added to the aluminum hydroxide-containing solution or the remainder of the neutralization treatment solution to prepare an acidic solution in which aluminum hydroxide is dissolved in the acidic solution. As the acid used in this case, the same acid as that used in the neutralization treatment of the aluminum hydroxide-containing separation liquid in the first recovery step can be used, and the pH value of the prepared acidic dissolution liquid can be used. Is preferably in the range of pH 4.2 ± 0.2, more preferably in the range of pH 4.2 ± 0.1. When the pH value of the acidic solution is out of this range, there arises a problem that the acidic solution becomes cloudy.

  The acidic solution thus prepared is then neutralized from the acidic dissolution region side of aluminum hydroxide with alkali in the presence of crystalline aluminum hydroxide as a seed to precipitate crystalline aluminum hydroxide. However, for this neutralization operation, the concentration of the alkali used is preferably a concentration that is approximately equimolar (about 1 mol) with the concentration of the acidic solution, and the acid solution and the alkali are placed in the neutralization tank. It is better to add and mix at the same time and mix to neutralize, thereby suppressing the pH distribution in the neutralization tank and controlling it within the desired pH value range, that is, pH 4.5 ± 0.2. can do. At this time, the neutralization operation is carried out under normal temperature to 60 ° C., preferably 50 ° C. to 60 ° C. temperature mixing. Hereinafter, the simultaneous addition and neutralization of an acidic solution and an alkali at substantially equimolar concentrations as described above is referred to as “simultaneous addition neutralization”.

  As the alkali used for neutralization of the acidic solution, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, etc. can be used, but strong alkaline alkali has better pH controllability than weak alkaline alkali. Sodium hydroxide is preferred.

  In addition, during the simultaneous addition neutralization operation, a part of the slurry obtained in this operation is directly or dehydrated and added as a precipitation seed (crystalline aluminum hydroxide seed) to the simultaneous addition neutralization step. By doing so, new crystalline aluminum hydroxide produced in the step of neutralization at the same time is deposited on the seed surface and agglomerates, and the produced particles gradually grow larger. Then, by adding the alkali and crystalline aluminum hydroxide seeds and repeating the simultaneous neutralization operation of the acidic solution several times, preferably in the range of 2 to 3 times, the precipitated crystallinity The water content can be reduced as much as possible by increasing the size of aluminum hydroxide particles as much as possible.

  The slurry obtained by the above-described simultaneous addition neutralization operation is then subjected to solid-liquid separation. For the recovered crystalline aluminum hydroxide, if necessary, the first recovery step of crystalline aluminum hydroxide and / or the second For the filtrate of pH 4.5 ± 0.2, which is used as seeds in the recovery process or used as the crystalline aluminum hydroxide of the product, when the liquid temperature falls below room temperature, the pH is 5. It becomes 0 to 5.5, and the pH is easily adjusted in the filtrate pipe. Further, the pH is adjusted to about 6.8 by adding alkali, preferably sodium hydroxide, and is discharged as neutral discharge water. The

  The crystalline aluminum hydroxide obtained in the second recovery step usually has a crystal size of 1 to 60 μm, preferably 2 to 40 μm, and a 50% cumulative particle size of 10 μm or more. And vacuum filtration can be performed if necessary. In addition, the sedimentation rate is 10 cm / Hr or more, preferably 15 cm / Hr or more, gelation is prevented, sedimentation and dehydration are excellent, filterability by vacuum filtration, pressure filtration, etc. is good, and water content is also included. The rate is also 80% by weight or less, preferably 75% by weight or less, and the operability of this second recovery step is remarkably improved, and higher quality crystalline aluminum hydroxide is recovered. Moreover, if it is within the above-mentioned particle size range, when the flocculant is added, the sedimentation speed becomes 10 m / Hr or more, and the amount of the flocculant used is only about one-fourth of the normal amount. Can also be obtained.

Further, in this second recovery step of crystalline aluminum hydroxide, pseudoboehmite [AlO (OH)] can be easily generated and recovered by changing the pH value and temperature conditions in the simultaneous addition neutralization operation. You can also. Here, the pseudo boehmite is that of alumina monohydrate _{(Al 2 O 3 · H 2} O), good cohesion than conventional alumina trihydrate _{(Al 2 O 3 · 3H 2} O) Easy to coarsen. As a result, since sedimentation and filterability are better, it can be recovered more efficiently and is advantageous in that it is expensive. If necessary, the recovery of crystalline aluminum hydroxide and the recovery of pseudo boehmite can be performed, and the recovery process can be carried out more efficiently.

  That is, an acidic solution in which the pH value in the neutralization tank is preferably adjusted to a range of pH 4.2 ± 0.2, more preferably a range of pH 4.2 ± 0.1, and substantially the same as the acidic solution. A molar concentration of alkali is continuously added at the same time and mixed and neutralized, whereby the acidic solution is neutralized from the acidic dissolution region side of aluminum hydroxide to a pH range of 7 ± 0.5. At this time, the temperature is mixed at 80 ° C. or higher and 100 ° C. or lower, preferably 90 ° C. or higher and 95 ° C. or lower, and heat-aged for 7 hours or longer, preferably 7 hours or longer and 24 hours or shorter.

  In the second recovery step of crystalline aluminum hydroxide, in the case of the simultaneous addition neutralization operation in which neutralization is performed from the acidic dissolution region side of aluminum hydroxide to the range of pH 7 ± 0.5, the pH 4.5 ± 0 described above is used. Unlike the case of the simultaneous addition neutralization operation for neutralizing to the range of 2, if the crystalline aluminum hydroxide as the seed is first added to the neutralization tank, then the slurry extracted from the neutralization tank It is not necessary to add the crystalline aluminum hydroxide obtained by dehydrating a part of this to the neutralization tank as seeds for precipitation, and ripening is completed once.

  In addition, also in the case of generating pseudo boehmite, the same alkali as described above can be used, and for the crystalline aluminum hydroxide to be added as a seed first when neutralizing the acidic solution. The crystalline aluminum hydroxide obtained in the second recovery step of crystalline aluminum hydroxide is preferable.

  The pseudo boehmite obtained in the second recovery step has a crystal size of usually 1 μm or more and 60 μm or less, preferably 2 μm or more and 40 μm or less, and a 50% cumulative particle size of 10 μm or more. Further, the sedimentation rate is 10 cm / Hr or more, preferably 15 cm / Hr or more, gelation is prevented, the sedimentation property and the dehydrating solid-liquid separation property are excellent, and the filterability by vacuum filtration or pressure filtration is good. Further, the water content is not more than 50% by weight, and the operability of the second recovery step is remarkably improved, and more excellent pseudo boehmite is recovered.

  In the present invention, an aluminum hydroxide-containing solution such as the above sludge solution or aluminum hydroxide waste liquid is introduced into the first recovery step and / or the second recovery step of crystalline aluminum hydroxide, Therefore, it is possible to efficiently precipitate crystalline aluminum hydroxide while easily controlling the increase in the amount of liquid in the entire processing process, and in the second recovery process, it is possible to deposit crystalline aluminum hydroxide crystals. As much as possible, the sedimentation and dehydration properties of the crystalline aluminum hydroxide can be improved, the operability of the second recovery process and the quality of the crystalline aluminum hydroxide can be improved. By adopting a phosphorus recovery step, the phosphorus component can be recovered as useful crystalline calcium phosphate from the aluminum hydroxide sludge containing the phosphorus component.

  Therefore, in the present invention, the first recovery step and / or the second recovery step, and further the phosphorus recovery step are applied according to the properties of the aluminum hydroxide sludge to be treated, and the aluminum hydroxide is industrially advantageous. Sludge treatment can be performed.

  According to the present invention, dibsite crystal aluminum hydroxide can be produced in the first recovery step of crystalline aluminum hydroxide, and dibsite crystal or pseudoboehmite crystal aluminum hydroxide can be produced in the second step. By using these first recovery process and second recovery process in combination, the price of crystalline aluminum hydroxide and the transportation cost between the manufacturing plant and the customer are taken into account. Of aluminum hydroxide and pseudo-boehmite crystalline aluminum hydroxide can be produced at an arbitrary production ratio.

  According to the method for treating aluminum hydroxide sludge of the present invention, crystalline aluminum hydroxide having excellent handling properties can be recovered with good operability, and an increase in the amount of liquid in the system during the treatment process can be prevented. It is possible to provide a method for treating aluminum hydroxide sludge that can be produced.

FIG. 1 is a flowchart showing a typical treatment process of an aluminum hydroxide-containing solution of the present invention.

FIG. 2 is a flowchart showing the treatment process of the aluminum hydroxide-containing solution according to Example 1 of the present invention.

FIG. 3 is a flowchart showing a treatment process of an aluminum hydroxide-containing solution according to Example 2 of the present invention.

FIG. 4 is a flowchart showing the treatment process of the aluminum hydroxide-containing solution according to Example 3 of the present invention.

FIG. 5 is a flowchart showing a treatment process of an aluminum hydroxide-containing solution according to Example 4 of the present invention.

FIG. 6 is a flowchart showing a treatment process of an aluminum hydroxide-containing solution according to Example 5 of the present invention.

FIG. 7 is a flowchart showing a treatment process of an aluminum hydroxide-containing solution according to Example 6 of the present invention.

  Hereinafter, based on the treatment process of the representative aluminum hydroxide-containing solution of the present invention shown in FIG. 1, a mode for carrying out the invention will be specifically described.

  FIG. 1 is a flowchart showing a typical treatment process of an aluminum hydroxide-containing solution when the aluminum hydroxide-containing solution is derived from aluminum hydroxide sludge. In FIG. 1, the aluminum hydroxide sludge is sludge. It introduce | transduces into the 1st dissolution tank of a process process, is melt | dissolved in alkaline solutions, such as a sodium hydroxide solution, in this 1st dissolution tank, and is set as the sludge solution (aluminum hydroxide containing solution) containing sodium aluminate.

  When the sludge solution obtained in this sludge treatment step is, for example, phosphorus-containing aluminum hydroxide sludge generated in an aluminum chemical polishing manufacturing factory, an aluminum die-cast coating manufacturing factory, etc. The sludge solution is introduced into the first precipitation / separation tank (thickener with stirring function) in the phosphorus recovery process, and calcium hydroxide is added to the first precipitation / separation tank to precipitate crystalline calcium phosphate. The slurry solution containing calcium phosphate is settled and extracted, dehydrated with a first dehydrator, washed with cake washing water to recover crystalline calcium phosphate as a product, and the filtrate is put into the first precipitation / separation tank. Return it.

  The clarified liquid (sludge solution after dephosphorization) of the first precipitation / separation tank (thickener with stirring function) in the phosphorus recovery step is then introduced into the first recovery step of crystalline aluminum hydroxide. In the first recovery step of crystalline aluminum hydroxide, the sludge solution (clarified solution) is first introduced into the second dissolution tank, where the aluminum hydroxide gel described later is dissolved and the aluminum concentration (Al Concentration) and then introduced into the second precipitation / separation tank (thickener with stirring function), and crystalline aluminum hydroxide (dibsite) is added as seeds to this second precipitation / separation tank, Crystalline aluminum hydroxide is precipitated.

  From this second precipitation / separation tank (thickener with stirring function) in the first recovery step of crystalline aluminum hydroxide, the slurry solution is extracted, then dehydrated with a second dehydrator, and washed with cake washing water. Crystalline aluminum hydroxide (dibsite) is recovered as a product, and the filtrate is returned to the second precipitation / separation tank.

  Moreover, about the clarified liquid (aluminum containing separation liquid) collect | recovered from this 2nd precipitation and separation tank, it introduce | transduces into a collection tank, and the one part or all part is the 1st neutralization tank of the neutralization process of an aluminum containing separation liquid In the first neutralization tank, neutralization treatment is performed using waste sulfuric acid or the like, and the neutralization treatment solution obtained by this neutralization treatment is adjusted to a pH range of 5.8 to 8.6. Part or all of the neutralized solution obtained by this sum treatment is then introduced into a sludge tank to form a slurry containing aluminum hydroxide gel, and further dehydrated by a dehydrator to neutralize aluminum hydroxide gel and neutral separation. It is recovered as a liquid. The recovered aluminum hydroxide gel is introduced into the second dissolution tank and used to increase the aluminum concentration (Al concentration) of the sludge solution (clarified solution). In order to suppress an increase in the amount of internal liquid, it is drained as discharge water.

  Here, when a part of the aluminum-containing separation liquid is introduced into the first neutralization tank of the aluminum-containing separation liquid, the remainder of the aluminum-containing separation liquid is the second in the second recovery step of crystalline aluminum hydroxide. It introduce | transduces into a two neutralization tank, or introduce | transduces into the 1st dissolution tank of the said sludge process process as an alkaline solution for melt | dissolving aluminum hydroxide sludge as needed. Moreover, when a part of neutralization process liquid is introduce | transduced into a sludge tank, the remainder of this neutralization process liquid is introduce | transduced into the following 2nd collection | recovery process of crystalline aluminum hydroxide.

  In addition, in the second neutralization tank of the second recovery step of crystalline aluminum hydroxide, the filtrate from the first dehydrator of the phosphorus recovery step is used as the aluminum hydroxide-containing solution in addition to the remainder of the neutralization treatment liquid. If the aluminum hydroxide sludge does not contain phosphorus, the sludge solution obtained in the first dissolution tank of the sludge dissolution step may be introduced as it is as an aluminum hydroxide-containing solution. Further, if the aluminum hydroxide waste liquid does not contain phosphorus, this aluminum hydroxide waste liquid may be introduced as it is as an aluminum hydroxide-containing solution.

  In the second recovery step of crystalline aluminum hydroxide, first, the remaining part of the neutralization treatment liquid introduced into the second neutralization tank is adjusted to pH 4.2 ± 0.2 with waste sulfuric acid to dissolve acidic sludge. Then, this acidic sludge solution is introduced into the third neutralization / precipitation tank, where water is added in the presence of crystalline aluminum hydroxide as seeds by the simultaneous addition neutralization method. An alkali such as sodium oxide is added and neutralized from the acidic dissolution region side of aluminum hydroxide to pH 4.5 ± 0.2 to precipitate crystalline aluminum hydroxide (dibsite).

  The slurry solution containing crystalline aluminum hydroxide produced and extracted in this third neutralization / precipitation tank is dehydrated with a third dehydrator to recover the crystalline aluminum hydroxide as a product, and the filtrate Is introduced into the fourth neutralization tank, further neutralized to pH 6.8 with an alkali such as sodium hydroxide, and discharged as discharge water. Moreover, about the crystalline aluminum hydroxide collect | recovered here, the one part is added to the said 2nd precipitation / separation tank of said 3rd neutralization / precipitation tank or the said 1st collection process of crystalline aluminum hydroxide. It may be used as a seed.

  Hereinafter, preferred embodiments of the present invention will be specifically described based on examples shown in the accompanying drawings.

Example 1 (sludge dissolution process, phosphorus recovery process, first recovery process, and second recovery process)
In Example 1, phosphorus-containing aluminum hydroxide sludge generated at a condenser manufacturing plant or the like is used as aluminum hydroxide sludge, and crystalline aluminum hydroxide (dibsite) is converted as follows according to the flow shown in FIG. It collect | recovered at the 1st collection process and the 2nd collection process.

[Sludge dissolution process]
In the flow shown in FIG. 2, 1000 kg of phosphorus-containing aluminum hydroxide sludge (Al: 28% by weight, P: 8% by weight, water content: 79% by weight) is transferred to the first dissolution tank, and 25 wt% -sodium hydroxide solution Add 303 kg and 2.1 m ³ of recovery liquid from the recovery tank as an alkaline solvent, dissolve aluminum hydroxide sludge in the first dissolution tank at a dissolution temperature of 80 ° C. and a dissolution time of 30 minutes, and add all sodium hydroxide and aluminum And a sludge solution having a molar ratio (T · NaOH / Al) of 1.7.

[Phosphorus recovery process]
The sludge solution obtained in the above sludge dissolving step is introduced into the first precipitation / separation tank, and in this first precipitation / separation tank, calcium phosphate 200 g / liter (g / L) is used as a seed in the sludge solution. In addition, 403 kg of 20 wt% -calcium hydroxide was added, and calcium phosphate was precipitated at a precipitation temperature of 80 ° C. for a precipitation time of 4 hours. And separated.

In this phosphorus recovery step, the concentration of phosphorus remaining in the filtrate tank was 0.3 g / L, and the phosphorus separation efficiency was 94% by weight. Calcium phosphate is washed with 0.3m ³ of washing water, and 235kg of calcium phosphate (Ca: 37% by weight, P: 14% by weight, moisture content: 50% by weight) is recovered as a product, and the washing wastewater is neutralized in the subsequent process. Liquid.

[First recovery step of crystalline aluminum hydroxide]
The clarified liquid (sludge solution after phosphorus recovery treatment) in the first precipitation / separation tank is transferred to the second dissolution tank, and the aluminum hydroxide gel recovered in the subsequent process is dissolved in the sludge solution in this second dissolution tank. Further, this sludge solution is transferred to the second precipitation / separation tank, and 200 g / L of crystalline aluminum hydroxide is added as seeds to the sludge solution, and the crystalline hydroxide is deposited at a precipitation temperature of 50 ° C. and a precipitation time of 24 hours. Aluminum was deposited. The hydrolysis rate of aluminum in this second precipitation / separation tank was 61% by weight.

The aluminum hydroxide crystals precipitated in the second precipitation / separation tank are separated by a centrifugal separator (second dehydrator) and then washed with 0.2 m ³ of washing water to obtain 190 kg of crystalline aluminum hydroxide (containing water). Rate: 15% by weight). The separation liquid from the centrifuge was returned to the second precipitation / separation tank through a filtration tank.

On the other hand, 4.35 m ³ of the clarified liquid separated in the second precipitation / separation tank is sent to the recovery tank, and in this recovery tank, as an alkaline solvent for dissolving the phosphoric acid-containing aluminum hydroxide sludge of the next lot, The recovered liquid 2.1 m ³ was circulated in the sludge dissolving step, and the surplus recovered liquid 2.26 m ³ was sent to the first neutralization tank.

In the first neutralization tank, 300 g / L of sulfuric acid was gradually added to adjust the pH to 8.0 to neutralize the surplus recovered liquid to obtain a neutralized liquid. The sulfuric acid required for neutralization was 0.29 m ³ .

Next, 2.25 m ³ of the neutralized solution neutralized in the first neutralization tank is sent to the sludge tank, and the remaining 0.3 m ³ is sent to the second neutralization tank (crystalline aluminum hydroxide). To the second recovery step).

  The neutralized liquid sent to the sludge was sludge treated in this sludge tank and then transferred to a filter press (dehydrator) where it was separated into filtrate and aluminum hydroxide gel. The separated aluminum hydroxide gel 409 kg (Al: 34% by weight, water content: 70% by weight) was returned to the second dissolution tank, and the filtrate was drained.

[Second recovery step of crystalline aluminum hydroxide]
In the second neutralization tank, 300 g / L sulfuric acid is gradually added to the neutralization treatment solution, and the pH is adjusted to 4.2 ± 0.2 to obtain an acidic sludge solution. It was sent to the neutralization / precipitation tank. In this third neutralization / precipitation tank, 49.8 kg of crystalline aluminum hydroxide having an average particle size of 10 μm is added, and 40 g / L of sodium hydroxide (NaOH) is gradually added to adjust the pH to 4.5 ± 0.00. The solution was neutralized by adjusting the pH until 2 was reached.

  The precipitation and agglomeration reaction of aluminum hydroxide in the third neutralization / precipitation tank were completed quickly together with the neutralization reaction, and crystalline aluminum hydroxide with good filterability was obtained. The aluminum hydroxide particle-containing liquid obtained in the third neutralization / precipitation tank is separated into crystalline aluminum hydroxide particles and dehydrated liquid by a drum filter (third dehydrator), and 133 kg of crystalline aluminum hydroxide particles is obtained. was gotten.

Part of the obtained crystalline aluminum hydroxide is taken out as a product (66.6 kg, Al content: 34% by weight, moisture content: 52% by weight), and the remainder is third neutralized and precipitated. Returned to the tank. The filtrate had a sufficiently low aluminum concentration (Al concentration) of 7 mg / L, and was further added with NaOH 40 g / L in the fourth neutralization tank, neutralized to pH 6.8 and drained.
The aluminum recovery rate for recovering crystalline aluminum hydroxide from the aluminum content in the aluminum hydroxide sludge was 97% by weight.

Example 2 (sludge dissolution step, phosphorus recovery step, and first recovery step)
[Sludge dissolution process]
In the flow shown in FIG. 3, 1000 kg of phosphorus-containing aluminum hydroxide sludge (Al: 28% by weight, P: 8% by weight, moisture content: 79% by weight) generated at a condenser manufacturing plant or the like is transferred to the first dissolution tank. Add 353 kg of 25wt% -sodium hydroxide solution and 1.78m ³ of recovery liquid from the recovery tank as an alkaline solvent, and dissolve aluminum hydroxide sludge in the first dissolution tank at a dissolution temperature of 80 ° C and a dissolution time of 30 minutes. A sludge solution with a molar ratio of total sodium hydroxide to aluminum (T · NaOH / Al) of 1.7 was obtained.

[Phosphorus recovery process]
The sludge solution obtained in the above sludge dissolving step is introduced into the first precipitation / separation tank, and in this first precipitation / separation tank, 200 g / L of calcium phosphate is added as a seed to the sludge solution, 411 kg of 20 wt% -calcium hydroxide was added to precipitate calcium phosphate at a precipitation temperature of 80 ° C. and a precipitation time of 4 hours, and the precipitated calcium phosphate-containing liquid was separated into calcium phosphate and filtrate by a centrifuge (first dehydrator).

In this phosphorus recovery step, the concentration of phosphorus remaining in the filtrate tank was 0.3 g / L, and the phosphorus separation efficiency was 94% by weight. Calcium phosphate is washed with 0.3m ³ of washing water, and 240kg of calcium phosphate (Ca: 37% by weight, P: 14% by weight, moisture content: 50% by weight) is recovered as a product. Liquid.

[First recovery step of crystalline aluminum hydroxide]
The clarified liquid (sludge solution after phosphorus recovery treatment) in the first precipitation / separation tank is transferred to the second dissolution tank, and the aluminum hydroxide gel recovered in the subsequent process is dissolved in the sludge solution in this second dissolution tank. Further, this sludge solution is transferred to the second precipitation / separation tank, and 200 g / L of crystalline aluminum hydroxide is added as seeds to the sludge solution, and the crystalline hydroxide is deposited at a precipitation temperature of 50 ° C. and a precipitation time of 24 hours. Aluminum was deposited. The hydrolysis rate of aluminum in this second precipitation / separation tank was 63% by weight.

The aluminum hydroxide crystals precipitated in the second precipitation / separation tank are separated with a centrifugal separator (second dehydrator) and then washed with 0.3 m ³ of washing water to produce 198 kg of crystalline aluminum hydroxide (containing water). Rate: 15% by weight). The aluminum content recovery rate for recovering crystalline aluminum hydroxide from the aluminum content in the phosphorus-containing aluminum hydroxide sludge was 99% by weight.
Moreover, the separation liquid from the centrifugal separator was returned to the second precipitation / separation tank through a filtration tank.

On the other hand, 3.18 m ³ of the clarified liquid separated in the second precipitation / separation tank is sent to the recovery tank, and in this recovery tank, as an alkaline solvent for dissolving the phosphoric acid-containing aluminum hydroxide sludge of the next lot, The recovered liquid 1.78 m ³ was circulated to the sludge dissolving step, and surplus recovered liquid 1.4 m ³ was sent to the first neutralization tank.

  In the first neutralization tank, the excess recovery liquid is neutralized by gradually adding 300 g / L of sulfuric acid and adjusting the pH to 8.0, and the total amount of the obtained neutralization liquid is sent to the sludge tank. It was. The neutralized liquid sent to the sludge tank was sludge treated in the sludge tank and then separated into filtrate and aluminum hydroxide gel by a filter press (dehydrator). The total amount of the separated aluminum hydroxide gel 149 kg (Al: 34% by weight, moisture content: 70% by weight) was returned to the second dissolution tank, and the filtrate was drained as effluent water.

Example 3 (sludge dissolution step, caustic sludge separation step, first recovery step, and second recovery step)
[Sludge dissolution process]
In the flow shown in FIG. 4, 1000 kg of aluminum hydroxide sludge (Al: 28% by weight, S: 6% by weight, moisture content: 75% by weight) generated at an alumite manufacturing plant or the like is transferred to the first dissolution tank, and 25 wt% -Add 418 kg of sodium hydroxide solution and 3.09 m ³ of recovery liquid from the recovery tank as an alkaline solvent, dissolve aluminum hydroxide sludge in the first dissolution tank at a dissolution temperature of 80 ° C. and a dissolution time of 30 minutes, A sludge solution having a molar ratio of sodium hydroxide to aluminum (T · NaOH / Al) of 1.7 was obtained.

[Caustic sludge separation process]
The sludge solution obtained in the above sludge dissolution process is transferred to the first flocculation / separation tank, and 10 mg / L of the polymer flocculant (sodium polyacrylate) aqueous solution is added to the sludge solution in the first flocculation / separation tank. It was added and stirred gently to form flocculated ants from the sludge solution, followed by solid-liquid separation into a clear solution and sludge. Sludge is separated into caustic sludge and filtrate by a filter press (first dehydrator), and the filtrate is returned to the first flocculation separation tank. Further, 36 kg of recovered caustic sludge (Al: 18% by weight, Mg: 16% by weight, water content: 65% by weight) was disposed of as industrial waste.

[First recovery step of crystalline aluminum hydroxide]
The clarified liquid from the first flocculation / separation tank (sludge solution after separation of caustic sludge) is transferred to the second dissolution tank, and the aluminum hydroxide gel recovered in the subsequent process is dissolved in the sludge solution by this second dissolution tank. Further, this sludge solution is transferred to the second precipitation / separation tank, and 200 g / L of crystalline aluminum hydroxide is added as seeds to the sludge solution, and the crystalline hydroxide is deposited at a precipitation temperature of 50 ° C. and a precipitation time of 24 hours. Aluminum was deposited. The hydrolysis rate of aluminum in this second precipitation / separation tank was 59% by weight.

The aluminum hydroxide crystals precipitated in the second precipitation / separation tank are separated by a centrifugal separator (second dehydrator) and then washed with 0.2 m ³ of washing water to obtain 223 kg of crystalline aluminum hydroxide (containing water). Rate: 15% by weight).

On the other hand, 4.23 m ³ of the clarified liquid separated in the second precipitation / separation tank is sent to the collection tank, and in this collection tank, as an alkaline solvent for dissolving the phosphoric acid-containing aluminum hydroxide sludge of the next lot, the recovered solution 3.09M ³ together is recycled to the sludge dissolving process, sending the recovered solution 1.14 ³ became excessive to the first neutralization tank.

In the first neutralization tank, 300 g / L of sulfuric acid was gradually added to adjust the pH to 8.0 to neutralize the surplus recovered liquid to obtain a neutralized liquid. The sulfuric acid required for neutralization was 0.29 m ³ .
Next, 1.25 m ³ of the neutralized solution neutralized in the first neutralization tank is sent to the sludge tank, and the remaining 0.24 m ³ is sent to the second neutralization tank (crystalline aluminum hydroxide). To the second recovery step).

  The neutralized liquid sent to the sludge tank was sludge treated in this sludge tank and then transferred to a filter press (dehydrator) where it was separated into filtrate and aluminum hydroxide gel. The separated aluminum hydroxide gel (106 kg, Al: 34% by weight, moisture content: 70% by weight) was returned to the second dissolution tank, and the filtrate was drained.

[Second recovery step of crystalline aluminum hydroxide]
In the second neutralization tank, 300 g / L sulfuric acid is gradually added to the neutralization treatment solution, and the pH is adjusted to 4.2 ± 0.2 to obtain an acidic sludge solution. It was sent to the neutralization / precipitation tank. In this third neutralization / precipitation tank, 49.8 kg of crystalline aluminum hydroxide having an average particle size of 10 μm is added, and 40 g / L of sodium hydroxide (NaOH) is gradually added to adjust the pH to 4.5 ± 0.00. The solution was neutralized by adjusting the pH until 2 was reached.

  The aluminum hydroxide particle-containing liquid obtained in the third neutralization / precipitation tank is separated into crystalline aluminum hydroxide particles and dehydrated liquid by a drum filter (third dehydrator), and 116 kg of crystalline aluminum hydroxide particles are obtained. was gotten.

Part of the resulting crystalline aluminum hydroxide is taken out as a product (Al content: 34% by weight, moisture content: 52% by weight), and the remainder is the third neutralization / precipitation Returned to the tank. The filtrate had a sufficiently low aluminum concentration (Al concentration) of 7 mg / L, and was further added with NaOH 40 g / L in the fourth neutralization tank, neutralized to pH 6.8 and drained.
The aluminum recovery rate for recovering crystalline aluminum hydroxide from the aluminum content in the aluminum hydroxide sludge was 97% by weight.

Example 4 (sludge dissolution step, caustic sludge separation step, and first recovery step)
[Sludge dissolution process]
In the flow shown in FIG. 5, 1000 kg of aluminum hydroxide sludge (Al: 28% by weight, S: 6% by weight, moisture content: 75% by weight) generated at an alumite manufacturing plant or the like is transferred to the first dissolution tank, and 25 wt% -Add 435 kg of sodium hydroxide solution and 3.02 m ³ of recovery liquid from the recovery tank as an alkaline solvent, dissolve aluminum hydroxide sludge in the first dissolution tank at a dissolution temperature of 80 ° C and a dissolution time of 30 minutes, A sludge solution having a molar ratio of sodium hydroxide to aluminum (T · NaOH / Al) of 1.7 was obtained.

[Caustic sludge separation process]
The sludge solution obtained in the above sludge dissolution process is transferred to the first flocculation / separation tank, and 10 mg / L of the polymer flocculant (sodium polyacrylate) aqueous solution is added to the sludge solution in the first flocculation / separation tank. It was added and stirred gently to form flocculated ants from the sludge solution, followed by solid-liquid separation into a clear solution and sludge. Sludge is separated into caustic sludge and filtrate by a filter press (first dehydrator), and the filtrate is returned to the first flocculation separation tank. Further, 36 kg of recovered caustic sludge (Al: 18% by weight, Mg: 16% by weight, water content: 65% by weight) was disposed of as industrial waste.

[First recovery step of crystalline aluminum hydroxide]
The clarified liquid from the first flocculation / separation tank (sludge solution after separation of caustic sludge) is transferred to the second dissolution tank, and the aluminum hydroxide gel recovered in the subsequent process is dissolved in the sludge solution by this second dissolution tank. Further, this sludge solution is transferred to the second precipitation / separation tank, and 200 g / L of crystalline aluminum hydroxide is added as seeds to the sludge solution, and the crystalline hydroxide is deposited at a precipitation temperature of 50 ° C. and a precipitation time of 24 hours. Aluminum was deposited. The hydrolysis rate of aluminum in this second precipitation / separation tank was 60% by weight.

The aluminum hydroxide crystals precipitated in the second precipitation / separation tank are separated by a centrifugal separator (second dehydrator) and then washed with 0.3 m ³ of washing water to obtain 231 kg of crystalline aluminum hydroxide (containing water). Rate: 15% by weight).
The aluminum recovery rate for recovering crystalline aluminum hydroxide from the aluminum content in the aluminum hydroxide sludge was 97% by weight.

On the other hand, 4.26 m ³ of the clarified liquid separated in the second precipitation / separation tank is sent to the recovery tank, and in this recovery tank, as an alkaline solvent for dissolving the phosphoric acid-containing aluminum hydroxide sludge of the next lot, While the recovered liquid 3.02 m ³ was circulated in the sludge dissolving step, the surplus recovered liquid 1.24 m ³ was sent to the first neutralization tank.

  In the first neutralization tank, the excess recovery liquid is neutralized by gradually adding 300 g / L of sulfuric acid and adjusting the pH to 8.0, and the total amount of the obtained neutralization liquid is sent to the sludge tank. It was. The neutralized liquid sent to the sludge tank was sludge treated in the sludge tank and then separated into filtrate and aluminum hydroxide gel by a filter press (dehydrator). The separated aluminum hydroxide gel 131 kg (Al: 34% by weight, moisture content: 70% by weight) was entirely returned to the second dissolution tank, and the filtrate was drained as effluent water.

Example 5 (Second recovery step of crystalline aluminum hydroxide)
In FIG. 6, 1 m ³ of aluminum hydroxide waste liquid (so-called dice cleaning waste liquid, Al: 100 g / L) generated at an aluminum extruded shape manufacturing factory is transferred from the receiving tank to the second neutralization tank, and the sulfuric acid concentration is 200 g / L. An alumite treatment waste liquid containing 15 g / L of aluminum concentration (Al concentration) was gradually added to adjust the pH to 4.2 ± 0.2 to make the reaction liquid acidic. The alumite waste liquid required for this was 3.68 m ³ . This reaction solution was sent to the third neutralization / precipitation tank.

  In the third neutralization / precipitation tank, 102 kg of crystalline aluminum hydroxide having an average particle size of 10 μm and a water content of 52% by weight is added, and 40 g / L of sodium hydroxide (NaOH) is gradually added to adjust the pH to 4.5. The solution was neutralized by adjusting the pH until it reached ± 0.2. The precipitation and agglomeration reaction of aluminum hydroxide were completed quickly with the neutralization reaction, and crystalline aluminum hydroxide with good filterability was obtained.

The aluminum hydroxide particle-containing liquid obtained in the third neutralization / precipitation tank is separated from the crystalline aluminum hydroxide particles and the dehydrated liquid with a drum filter (third dehydrator), and the crystalline aluminum hydroxide particles 722. 1 kg was obtained.
The aluminum recovery rate for recovering crystalline aluminum hydroxide from the aluminum content in the aluminum hydroxide waste solution was 99% by weight.

  The water content of the obtained crystalline aluminum hydroxide was 52% by weight, a part was returned as seeds to the third neutralization / precipitation tank, and the rest was recovered as a product. The filtrate in the drum filter had a low Al concentration of 7 mg / L, neutralized by adding a sodium hydroxide solution in the fourth neutralization tank, and drained to pH 6.8.

Example 6 (Second recovery step of crystalline aluminum hydroxide)
In FIG. 7, 1 m ³ of aluminum hydroxide waste liquid (so-called dice cleaning waste liquid, Al: 100 g / L) generated at an aluminum extruded shape manufacturing plant is transferred from the receiving tank to the second neutralization tank, and the sulfuric acid concentration is 200 g / L. An alumite treatment waste liquid containing 15 g / L of aluminum concentration (Al concentration) was gradually added to adjust the pH to 4.2 ± 0.2 to make the reaction liquid acidic. The alumite waste liquid required for this was 3.68 m ³ . This reaction solution was sent to the third neutralization / precipitation tank.

  In the third neutralization / precipitation tank, 400 kg of crystalline aluminum hydroxide having an average particle size of 10 μm and a water content of 52% by weight was added, and the reaction solution was heated to 90 ° C. The heated reaction liquid was maintained at 90 ° C. to promote the aggregation and precipitation of aluminum hydroxide on the charged seeds, and almost all of the aluminum hydroxide in the liquid was precipitated after 5 hours. During this time, since free sulfate ions were released with the precipitation of aluminum hydroxide, the pH gradually decreased. In order to prevent this, pH 4.5 to pH 7 was maintained while adding NaOH.

The aluminum hydroxide particle-containing liquid obtained in the third neutralization / precipitation tank is separated from the crystalline aluminum hydroxide particles and the dehydrated liquid with a drum filter (third dehydrator) to obtain 335 kg of crystalline aluminum hydroxide particles. Obtained.
The crystalline aluminum hydroxide obtained in this step was crystalline aluminum hydroxide (pseudo boehmite) with good filterability. Further, the recovery rate of the aluminum content obtained by recovering the crystalline aluminum hydroxide from the aluminum content in the aluminum hydroxide waste liquid was 99% by weight.

  The water content of the obtained crystalline aluminum hydroxide was 52% by weight, a part was returned as seeds to the third neutralization / precipitation tank, and the rest was recovered as a product. The filtrate in the drum filter had a sufficiently low Al concentration of 7 mg / L, neutralized by adding a NaOH solution in the fourth neutralization tank, and drained to pH 6.8.

Claims (12)

When recovering crystalline aluminum hydroxide by treating an aluminum hydroxide-containing solution containing aluminum hydroxide produced in the surface treatment step of an aluminum material made of aluminum or an aluminum alloy,
Introducing a first recovery step and / or a second recovery step of crystalline aluminum hydroxide during the treatment step of the aluminum hydroxide-containing solution,
In the first recovery step of the crystalline aluminum hydroxide, the aluminum hydroxide-containing solution is introduced into the precipitation tank and the crystalline aluminum hydroxide is added as seeds to the aluminum hydroxide-containing solution. A portion of the slurry solution containing the precipitated crystalline aluminum hydroxide is extracted from the precipitation tank and dehydrated, and the crystalline aluminum hydroxide is recovered and the filtrate is returned to the precipitation tank. The aluminum-containing separation liquid containing aluminum obtained by sedimentation and separation is recovered, then the aluminum-containing separation liquid is neutralized with an acid, and a part or all of the obtained neutralization treatment liquid is dehydrated and water. The aluminum oxide gel and the neutral separation liquid are recovered, and the recovered aluminum hydroxide gel is dissolved in the aluminum hydroxide-containing solution. Drained neutral separation liquid with dissolved during the addition,
In the second recovery step of the crystalline aluminum hydroxide, an acid is added to the aluminum hydroxide-containing solution or the balance of the neutralization treatment liquid obtained by the neutralization treatment of the first step to make the aluminum hydroxide acidic. Prepare an acidic solution dissolved in the solution, introduce this acidic solution into the neutralization tank and add an alkali to the acidic solution to neutralize the acidic solution from the acidic solution region side of aluminum hydroxide. Further, a method for treating an aluminum hydroxide-containing solution, wherein crystalline aluminum hydroxide is added as a seed at the time of neutralization, and the precipitated crystalline aluminum hydroxide is then separated, dehydrated and recovered.   The aluminum hydroxide-containing solution introduces aluminum hydroxide sludge containing aluminum hydroxide generated in the surface treatment process of the aluminum material into the sludge dissolving process, and in this sludge dissolving process, the aluminum hydroxide sludge is dissolved in the alkaline solution. An acid sludge obtained by adding an acid to the aluminum hydroxide-containing solution derived from the aluminum hydroxide sludge or the remainder of the neutralizing solution in the first step. The method for treating an aluminum hydroxide-containing solution according to claim 1, which is a solution.   3. The method for treating an aluminum hydroxide-containing solution according to claim 2, wherein, in the second recovery step of crystalline aluminum hydroxide, an alkali is added to the acidic sludge solution to neutralize to pH 4.5 ± 0.2.   When the aluminum hydroxide sludge is a phosphorus-containing aluminum hydroxide sludge containing a phosphorus component, the sludge solution is introduced into the phosphorus recovery step before introducing the crystalline aluminum hydroxide into the first recovery step and / or the second recovery step. And, in this phosphorus recovery step, calcium hydroxide is added to the sludge solution to precipitate crystalline calcium phosphate, and then dehydrated to recover the phosphorus component in the sludge solution as crystalline calcium phosphate. Or the processing method of the aluminum hydroxide containing solution of 3.   In the first recovery step of crystalline aluminum hydroxide, the aluminum-containing separation liquid recovered by settling and separating the slurry solution is used when the clarified liquid and / or crystalline aluminum hydroxide obtained by the settling and separation of the slurry solution is dehydrated. It is the obtained filtrate, The processing method of the aluminum hydroxide containing solution in any one of Claims 2-4.   A part of the aluminum-containing separation liquid recovered in the first recovery process of crystalline aluminum hydroxide is returned to the sludge dissolution process, and the alkaline solution or a part thereof is prepared by dissolving the aluminum hydroxide sludge to prepare the sludge solution. The processing method of the aluminum hydroxide containing solution in any one of Claims 2-5 used.   The method for treating an aluminum hydroxide-containing solution according to any one of claims 2 to 6, wherein in the second recovery step of crystalline aluminum hydroxide, the pH value of the acidic sludge solution is pH 4.2 ± 0.2.   In the second recovery step of crystalline aluminum hydroxide, the crystalline aluminum hydroxide added as a seed in the acidic sludge solution is the crystalline aluminum hydroxide obtained in the second recovery step of crystalline aluminum hydroxide. The processing method of the aluminum hydroxide containing solution in any one of Claims 2-7.   The method for treating an aluminum hydroxide-containing solution according to any one of claims 2 to 8, wherein a part of the aluminum-containing separation liquid recovered in the first recovery step of crystalline aluminum hydroxide is extracted to adjust the amount of liquid in the system. .   Any one of Claims 2-9 which collect | recover arbitrarily the mixture of a dibsite or a dibsite and pseudo boehmite in a 1st collection | recovery process of crystalline aluminum hydroxide, and / or a mixture of pseudo boehmite or a dibsite and pseudo boehmite in a 2nd collection process. A method for treating an aluminum hydroxide-containing solution according to claim 1.   The aluminum hydroxide-containing solution is an aluminum hydroxide waste solution containing aluminum hydroxide generated in the surface treatment process of the aluminum material. This aluminum hydroxide waste solution is introduced into the second recovery step of crystalline aluminum hydroxide, and the crystal 2. The method for treating an aluminum hydroxide-containing solution according to claim 1, wherein, in the second recovery step of the basic aluminum hydroxide, an alkali is added to the prepared acidic solution to neutralize to pH 4.5 ± 0.2.   The aluminum hydroxide-containing solution is an aluminum hydroxide waste solution containing aluminum hydroxide generated in the surface treatment process of the aluminum material. This aluminum hydroxide waste solution is introduced into the second recovery step of crystalline aluminum hydroxide, and the crystal The processing method of the aluminum hydroxide containing solution of Claim 1 which neutralizes to pH 7 +/- 0.5 by adding an alkali in an acidic solution at the 2nd collection | recovery process of the property aluminum hydroxide.

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