JP5160215B2 - Method for treating sodium hydroxide waste solution of aluminum material - Google Patents

Description

  The present invention relates to a method for treating a sodium hydroxide treatment waste liquid of an aluminum material produced by etching an aluminum material with a sodium hydroxide solution and a method for producing a product derived from a sodium hydroxide treatment waste liquid of an aluminum material. More specifically, the present invention is suitable for treatment of an etching waste liquid generated in a surface treatment process of an aluminum material, in which an aluminum material is etched with a sodium hydroxide solution and then an anodized film is formed on the aluminum material in a sulfuric acid solution.

Aluminum materials such as building materials such as aluminum sashes and other aluminum industrial materials, for example, are etched with a sodium hydroxide solution as a pretreatment, and then electrolytically oxidized in a sulfuric acid solution to increase durability, and an anode is formed on the surface. An oxide film is formed. In the etching with the sodium hydroxide solution, the surface of the aluminum material is dissolved in the sodium hydroxide solution to produce sodium aluminate, and the concentration of sodium aluminate in the etching solution gradually increases. Since the etching ability of the etching solution decreases as the sodium aluminate concentration increases, it is necessary to replace the etching solution with a new etching solution when the sodium aluminate concentration increases to some extent.
As an example of a method for regenerating an etching waste liquid as a sodium hydroxide solution capable of etching aluminum, as shown in Patent Documents 1 and 2 below, (1) in an etching waste liquid in which sodium aluminate is supersaturated Etching waste liquid by hydrolyzing sodium aluminate, (2) precipitating aluminum hydroxide, (3) separating the precipitated aluminum hydroxide by filtration, and (4) adjusting the concentration by adding sodium hydroxide to the filtrate. The method of reproducing | regenerating is known.
JP-A-48-38890 Japanese Patent Laid-Open No. 05-279020

However, in order to hydrolyze sodium aluminate in the etching waste liquid to aluminum hydroxide, aluminum hydroxide seeds are introduced into the etching waste liquid as a core, and the liquid temperature is maintained at 40 to 60 ° C. in the crystallization reaction layer. However, stirring must be continued for a long period of 40 to 70 hours. For this reason, in order to process a large amount of etching waste liquid, there was a problem that the scale of the facility inevitably increased and the running cost increased.
Therefore, a main problem of the present invention is to provide a method for treating a sodium hydroxide treatment waste liquid of aluminum material that can separate and recover aluminum hydroxide from an etching waste liquid in a short time and at a low cost.

The present invention that has solved the above problems is as follows.
<Invention of Claim 1>
An aluminum characterized in that polyaluminum chloride is produced from a sodium hydroxide treatment waste solution of an aluminum material produced by treating the aluminum material with a solution containing sodium hydroxide as a main component by a method including the following steps: Of treatment of waste aluminum hydroxide treatment liquid.
(1) Carbon dioxide gas is blown into the sodium hydroxide treatment waste liquid in a state where the liquid temperature is 50 ° C. to 80 ° C.,
The precipitated aluminum hydroxide is recovered by filtration, and the sodium carbonate in the filtrate is recovered as it is in solution or as a solid by drying,
(2) adding all or part of the aluminum hydroxide to hydrochloric acid to form a slurry and reacting under pressure and heating conditions to obtain a reaction slurry;
(3) A step of adding a part of the sodium carbonate to the reaction slurry for reaction, and obtaining a filtrate by filtration; and (4) adding sodium sulfate to the filtrate for reaction, and filtering to form polyaluminum chloride as a filtrate. Obtaining.

<Invention of Claim 2>
An aluminum material characterized in that a sulfuric acid band is produced from a sodium hydroxide treatment waste liquid of an aluminum material produced by treating the aluminum material with a solution containing sodium hydroxide as a main component by a method including the following steps: Of treatment of aluminum hydroxide waste liquid.
(1) Carbon dioxide gas is blown into the sodium hydroxide treatment waste liquid in a state where the liquid temperature is 50 ° C. to 80 ° C.,
The precipitated aluminum hydroxide is recovered by filtration, and the sodium carbonate in the filtrate is recovered as it is in solution or as a solid by drying,
(2) adding sulfuric acid to all or a part of the aluminum hydroxide and obtaining a reaction slurry by stirring with air;
(3) A step of adjusting the concentration by adding water to the reaction slurry and then obtaining a sulfate band as a filtrate by filtration.

<Invention of Claim 3>
An aluminum characterized in that polyaluminum chloride is produced from a sodium hydroxide treatment waste solution of an aluminum material produced by treating the aluminum material with a solution containing sodium hydroxide as a main component by a method including the following steps: Of treatment of waste aluminum hydroxide treatment liquid.
(1) Carbon dioxide gas is blown into the sodium hydroxide treatment waste liquid at a temperature of 30 ° C. to 40 ° C., so that free sodium hydroxide is converted to sodium carbonate, precipitated, separated by filtration,
On the other hand, carbon dioxide is blown into the filtrate at a temperature of 50 ° C. to 80 ° C., and the precipitated aluminum hydroxide is recovered by filtration, and the sodium carbonate in the filtrate is recovered as it is or as a solid by drying. Process,
(2) adding all or part of the aluminum hydroxide to hydrochloric acid to form a slurry and reacting under pressure and heating conditions to obtain a reaction slurry;
(3) adding a part of the sodium carbonate to the reaction slurry to cause reaction, and obtaining a filtrate by filtration; and
(4) A step of adding sodium sulfate to the filtrate to cause reaction, and obtaining polyaluminum chloride as a filtrate by filtration.

<Invention of Claim 4>
An aluminum material characterized in that a sulfuric acid band is produced from a sodium hydroxide treatment waste liquid of an aluminum material produced by treating the aluminum material with a solution containing sodium hydroxide as a main component by a method including the following steps: Of treatment of aluminum hydroxide waste liquid.
(1) Carbon dioxide gas is blown into the sodium hydroxide treatment waste liquid at a temperature of 30 ° C. to 40 ° C., so that free sodium hydroxide is converted to sodium carbonate, precipitated, separated by filtration,
On the other hand, carbon dioxide is blown into the filtrate at a temperature of 50 ° C. to 80 ° C., and the precipitated aluminum hydroxide is recovered by filtration, and the sodium carbonate in the filtrate is recovered as it is or as a solid by drying. Process,
(2) adding sulfuric acid to all or a part of the aluminum hydroxide and obtaining a reaction slurry by stirring with air;
(3) A step of adjusting the concentration by adding water to the reaction slurry and then obtaining a sulfate band as a filtrate by filtration.

<Invention of Claim 5>
The carbon dioxide gas is a treatment method of a sodium hydroxide treatment waste liquid of an aluminum material according to any one of claims 1 to 4, wherein carbon dioxide gas generated from a combustion exhaust gas from a boiler, a fermentation exhaust gas, or a limestone roasting furnace is used.

(Function and effect)
As a result of investigating to solve the above-mentioned problems, the present inventors think that aluminum hydroxide can be obtained by blowing carbon dioxide into sodium aluminate in the sodium hydroxide treatment waste liquid of aluminum material. When this was carried out, it was found that it can be recovered simply and in a short time by changing to aluminum hydroxide and sodium carbonate.
The reaction formula for obtaining aluminum hydroxide by blowing carbon dioxide into sodium aluminate in the present invention is considered as follows.
NaAlO ₂ + 2H ₂ O = Na [Al (OH) ₄ ] = Al (OH) ₃ + NaOH (1)
2Na [Al (OH) ₄ ] + CO ₂ = 2Al (OH) ₃ + Na ₂ CO ₃ + H ₂ O (2)
The formula (1) shows the hydrolysis reaction of sodium aluminate, and the formula (2) shows the reaction of sodium aluminate and carbon dioxide. According to this formula, it can be seen that the aluminum content is aluminum hydroxide and the sodium content is sodium carbonate.
_{2NaOH + CO 2 = Na 2 CO} 3 + H 2 O ... (3)
In addition, a large amount of sodium hydroxide remains in the etching waste liquid, but this sodium hydroxide also becomes sodium carbonate and water when it reacts with carbon dioxide from the formula (3). From these, caused by etching the aluminum with sodium hydroxide, it is effective blowing of carbon dioxide gas into the process of etching waste liquid containing a large amount of sodium aluminate. Furthermore, the obtained aluminum hydroxide is insoluble in water, and the solubility of sodium carbonate in water varies with temperature . Therefore, if this property is utilized, both can be easily separated.

  In fact, the inventors of the present invention trially set the liquid temperature of the etching waste liquid to 15 ° C. and blown carbon dioxide gas with stirring. As a result, the liquid temperature gradually increased due to reaction heat. When carbon dioxide was continuously blown, white crystals started to form. When the liquid temperature of the etching waste liquid reached 42 ° C., the liquid temperature did not rise any further. Therefore, it was judged that the reaction was completed, and blowing of carbon dioxide gas was stopped, and solid-liquid separation was performed using a vacuum filter.

  The present inventors consider that the solid obtained by solid-liquid separation is a mixture of aluminum hydroxide and sodium carbonate, and separate the sodium carbonate content by washing with hot water at 60 ° C. to obtain high-purity hydroxide. When trying to obtain aluminum, the whole amount was dissolved. From this fact, the present inventors have found that the generated crystals are sodium carbonate, and free sodium hydroxide in the etching waste liquid is produced by reacting with carbon dioxide, and sodium in sodium aluminate is free water. While sodium oxide was present, it was difficult to react with carbon dioxide, so it was assumed that the reaction between sodium aluminate and carbon dioxide did not occur at 42 ° C. when the rise in the liquid temperature in this experiment stopped.

  Therefore, when carbon dioxide gas was blown in while adjusting the temperature with a water bath so that the temperature of the filtrate obtained by solid-liquid separation with a vacuum filter was kept at 60 ° C., the formation of crystals started again, so carbon dioxide gas was sufficient. And then separated by filtration. When the obtained solid was washed with hot water at 60 ° C., it was confirmed that high-purity aluminum hydroxide was produced. The present inventors have made further investigations and experiments based on this experiment, and have completed the present invention.

According to the present invention, aluminum hydroxide can be separated and recovered from the etching waste liquid in a shorter time than conventional, as shown in the experimental results in the following examples. In addition, since the processing time is short, even if the processing equipment for the etching waste liquid is small, it is possible to perform processing equivalent to or higher than conventional processing, and as a result, running costs can be kept low.
In addition, carbon dioxide gas used in practicing the present invention may be carbon dioxide gas generated from boiler combustion exhaust gas, fermentation exhaust gas, limestone roasting furnace, etc. There are no costs and costs can be reduced.

  Furthermore, by dividing the blowing of carbon dioxide gas into two stages, sodium carbonate can be recovered individually by the first stage, and sodium carbonate can be recovered by the solution at the second stage. Therefore, when it is desired to recover the sodium carbonate solution, the invention according to claim 4 is suitable.

  As described above, according to the present invention, it is possible to provide a method for treating a sodium hydroxide treatment waste liquid of an aluminum material that can separate and recover aluminum hydroxide from an etching waste liquid in a short time and at a low cost.

As described above, the present invention is a pretreatment of a building material such as an aluminum sash, an etching treatment with a sodium hydroxide solution, followed by electrolytic oxidation in a sulfuric acid solution to form an anodized film on the surface, as well as a lithographic printing plate. Various waste liquids such as an etching waste liquid for roughening an aluminum plate as a support can be targeted.
The recovered aluminum hydroxide can be used for the production of polyaluminum chloride or sulfuric acid band.

<Experimental example>
Below, the experiment which concerns on this invention and its result are shown. FIG. 1 shows an experimental apparatus for an experiment according to the present invention. The glass tall beaker 2 that can store the etching waste liquid is immersed in water filled in a water bath tank. The water bath 1 includes a heater so that the water filled in the water tank can be maintained at a constant temperature.

  The tall beaker 2 includes a thermometer 9 capable of measuring the temperature of the etching waste liquid stored in the tall beaker 2, and a propeller attached to the lower end in FIG. 1 with the etching waste liquid stored in the tall beaker 2. And a gas blowing tube 4 capable of injecting a mixed gas of carbon dioxide and nitrogen gas from the lower end in FIG. 1 are inserted. The amounts of carbon dioxide gas and nitrogen gas fed into the gas blowing pipe 4 are adjusted by the flow rate adjusting valves 6 and 8, respectively. The flow rate is adjusted with reference to the flow rates shown in the carbon dioxide flow meter 7 and the nitrogen flow meter 5 provided in the respective gas flow paths.

The composition of the etching waste solution (hereinafter referred to as the stock solution) used in this experiment is as follows.
Na ₂ O: 17.3 wt%
Al ₂ O ₃ : 12.2 wt%
NaOH: 12.7 wt%
H ₂ O and others: 57.8 wt%
The liquid specific gravity is 1.345.
In the experiment, 1 liter of undiluted solution was placed in a tall beaker 2, the reaction solution temperature was kept constant in the water bath 1, and the carbon dioxide gas was refined to improve the reaction. The carbon dioxide gas was supplied while changing.

  The amount of carbon dioxide supplied is 259.1 grams when the theoretical value that reacts with sodium carbonate is calculated from the analytical value of the stock solution and the above reaction formulas (2) and (3), but 10 wt% extra in consideration of the reaction rate Was supplied with 285 grams. Solid-liquid separation was performed by vacuum filtration using a filter bottle.

  The yield of aluminum hydroxide was calculated based on aluminum. Immediately after supplying the specified amount of carbon dioxide, vacuum filtration was performed, and the liquid was washed with 500 ml of hot water having a liquid temperature of 60 ° C., and the obtained solid content was calculated by moisture and composition analysis.

  The yield of sodium carbonate was calculated based on sodium. The above filtrate and washing solution were combined and calculated by composition analysis of the solid content obtained by evaporation to dryness. However, in an experiment in which the blowing of carbon dioxide gas is divided into two stages, the solid matter obtained by filtration and drying of the solid matter obtained by the first stage reaction and the sodium carbonate fraction obtained by the second stage reaction are obtained. The yield was calculated from the total amount.

<About Experiment 1>
In this experiment, carbon dioxide gas was supplied in two stages. In this experiment, the stock solution was put into a tall beaker 2, carbon dioxide gas was supplied while stirring with a stirrer 3, kept at 40 ° C. in the water bath 1 in the first stage reaction, and allowed to react for 2 hours. The amount of carbon dioxide supplied at this time was determined by calculating the theoretical amount necessary for sodium hydroxide in the stock solution to react with sodium carbonate (103.3 grams). The precipitated crystals were separated by filtration, and the filtrate after completion of the first stage reaction was placed in a tall beaker 2 and carbon dioxide gas was further supplied. The water bath 1 was maintained at 60 ° C. and the second stage reaction was carried out for 2 hours. The amount of carbon dioxide supplied at this time was determined by calculating the theoretical amount necessary for Na ₂ O in the stock solution to react with sodium carbonate (181.7 grams).

<About Experiment 2 to Experiment 5>
Experiment 2 to Experiment 5 were performed in one stage without supplying carbon dioxide gas in two stages. In these experiments, the stock solution is put in a container and carbon dioxide gas is supplied while stirring with the stirrer 3, and the liquid temperature is kept at 50 ° C., 60 ° C., 70 ° C. and 80 ° C. in the water bath 1 and the reaction is performed for 4 hours. It was. The amount of carbon dioxide supplied at this time was determined by calculating the theoretical amount necessary for NaOH and Na ₂ O in the stock solution to react with sodium carbonate.

<About Experiment 6>
In this experiment, the supply of carbon dioxide gas was performed in one stage without being divided into two stages. In this experiment, the stock solution is put into a tall beaker 2 and a pseudo boiler exhaust gas in which carbon dioxide gas concentration is adjusted to 10% by adding nitrogen gas to carbon dioxide while stirring with a stirrer 3 is supplied to the water bath 1. The liquid temperature was kept at 60 ° C. and the reaction was carried out for 10 hours. The amount of carbon dioxide supplied at this time was determined by calculating the theoretical amount necessary for NaOH and Na ₂ O in the stock solution to react with sodium carbonate.

  From the above results, paying attention to the yield of aluminum hydroxide, the higher the reaction temperature, the better the yield, but there is a concentration of the etching waste liquid due to evaporation of moisture, and the higher the temperature, the more the gas blowing tube 4 and the stirrer 3 Since the precipitation of hard crystals increases on the shaft, the inner wall of the tall beaker 2, etc., it is not desirable to raise the temperature of the etching waste liquid to 80 ° C. or higher. Further, in Experiment 2, the yield of aluminum hydroxide was as low as 62% at 50 ° C., but in the case of actual equipment, the reaction rate increases by increasing the liquid depth and improving gas dispersion. 50 ° C to 80 ° C, preferably 60 to 80 ° C is suitable.

  In addition, with regard to the recovery of sodium carbonate in Experiment 1, it can be recovered as a solid after the supply of the first stage carbon dioxide gas, and the sodium carbonate solution can be recovered as the aluminum hydroxide filtrate by the second stage carbon dioxide gas supply. When both a solid and a solution are required, it is better to divide the carbon dioxide supply into two stages. When there is a lot of powdery demand, as shown in Experiment 2 to Experiment 6, the carbon dioxide gas is supplied in one stage without dividing into two stages, and the filtrate and the washing liquid are combined and easily used by a vacuum dryer or a spray dryer. It was confirmed in this experiment that it can be recovered in powder form.

<Utilization of aluminum hydroxide and sodium carbonate>
Next, an example of the flow of the etching waste liquid treatment according to the present invention and the flow of the utilization method of aluminum hydroxide and sodium carbonate generated during the etching waste liquid treatment process according to the present invention will be described in detail with reference to FIG.
First, the processing flow of the etching waste liquid will be described in detail. The etching waste liquid is extracted from the etching waste liquid storage tank 21, and hot water is poured into the jacket so that the tank is heated to an etching waste liquid reaction tank 22 that can be heated. The temperature of the etching waste liquid stuck in the etching waste liquid reaction tank 22 is maintained at 60 ° C., and the etching waste liquid in the tank is stirred by a stirrer and carbon dioxide gas is blown. The reaction liquid supplied with a predetermined amount of carbon dioxide gas is applied to the aluminum hydroxide filter 23, the filtrate is transferred to the sodium carbonate storage tank 25, and after the filtration of the entire reaction liquid in the aluminum hydroxide filter 23 is finished, the aluminum hydroxide filter Washing the filter cake (cake) in the vessel 23 with hot water at 60 ° C. to wash away sodium carbonate deposited on the aluminum hydroxide, and then blowing the aluminum hydroxide washed with hot water into the water content to 15% or less Until the aluminum hydroxide hopper 24 is discharged. Since the cleaning liquid and the air blowing liquid contain about 5 wt% sodium carbonate, they are stored in the cleaning liquid storage tank 26 without being discarded as they are. The filtrate stored in the sodium carbonate storage tank 25 is dried with hot air in a spray dryer 27, stored in a powdered sodium carbonate hopper 28, and shipped as a product.

  Next, the flow until manufacturing PAC (polyaluminum chloride) from aluminum hydroxide separated from the etching waste liquid will be described in detail. Hydrochloric acid having a concentration of 35 wt% is poured into the slurry tank 29, and a predetermined amount of aluminum hydroxide is metered into the slurry tank 29 from the aluminum hydroxide hopper 24 and stirred to form a slurry. Then, the slurry of aluminum hydroxide is transferred to a PAC reaction kettle 30 that can heat the inside of the tank by feeding steam heated into the jacket, and heated from room temperature to 100 ° C. From there, the pressure in the reaction vessel 30 is further set to a gauge pressure of 0.39 megapascal, the temperature of the slurryed aluminum hydroxide is set to 150 ° C., and the reaction vessel 30 is sealed to cause a pressure reaction. When the reaction is completed, the supply of steam to the jacket of the PAC reaction kettle 30 is stopped, and the internal pressure of the PAC reaction kettle 30 is gradually lowered. Next, cooling water is supplied to the jacket of the PAC reaction kettle 30, and the temperature of the reaction solution in the PAC reaction kettle 30 is lowered to 65 ° C. When the temperature of the reaction liquid reaches 65 ° C., the reaction liquid is transferred to a sodium carbonate addition tank 31, a prescribed amount of sodium carbonate is extracted from the washing liquid storage tank 26 and added, and the reaction is carried out for 1 hour with stirring by a stirrer. It is put into a vessel 32 and separated into filtrate and filter cake. The filtrate separated by the first filter 32 is transferred to a sodium sulfate addition tank 33, a prescribed amount of sodium sulfate is added and stirred by a stirrer, and then passed through a second filter 34 to be separated into PAC and filter cake. Is stored in the PAC storage tank 35 and shipped as a product.

  Next, the flow from manufacturing aluminum sulfate separated from the etching waste liquid to producing a sulfuric acid band (aluminum sulfate) will be described in detail. A predetermined amount of aluminum hydroxide is metered into the reaction tank 36 from the aluminum hydroxide hopper 24, and sulfuric acid having a concentration of 98 wt% is supplied. The reaction slurry obtained by the reaction in the reaction tank 36 is stirred by circulating the reaction slurry with the circulation pump 37, and the reaction is promoted by blowing air and stirring with air, and is allowed to react for 1 hour as it is. Thereafter, the reaction slurry is transferred to the adjustment tank 38 and water is added so that the concentration of alumina (aluminum oxide) is 8 wt%. And after concentration adjustment, it applies to the 3rd filter 39, The filtrate obtained there is stored in the sulfuric acid band storage tank 40, and is shipped as a product.

  The present invention is applicable to the treatment of etching waste liquid generated by etching an aluminum material with a sodium hydroxide solution.

It is the schematic of the experimental apparatus used for this invention. It is a flow sheet of the example of the manufacturing method of the sodium hydroxide treatment waste liquid origin product of aluminum material.

  DESCRIPTION OF SYMBOLS 1 ... Water bath, 2 ... Tall beaker, 3 ... Stirrer, 4 ... Gas injection pipe, 5 ... Nitrogen flow meter, 6 ... Flow rate adjustment valve, 7 ... Carbon dioxide gas flow meter, 8 ... Flow rate adjustment valve, 9 ... Thermometer, DESCRIPTION OF SYMBOLS 21 ... Etching waste liquid storage tank, 22 ... Reaction tank, 23 ... Aluminum hydroxide filter, 24 ... Aluminum hydroxide hopper, 25 ... Sodium carbonate storage tank, 26 ... Cleaning liquid storage tank, 27 ... Spray dryer, 28 ... Sodium carbonate hopper , 29 ... Slurry tank, 30 ... PAC reaction tank, 31 ... Sodium carbonate addition tank, 32 ... First filter, 33 ... Sodium sulfate addition tank, 34 ... Second filter, 35 ... PAC storage tank, 36 ... Reaction tank 37 ... circulation pump, 38 ... regulating tank, 39 ... third filter, 40 ... sulfuric acid band storage tank.

Claims (5)

An aluminum characterized in that polyaluminum chloride is produced from a sodium hydroxide treatment waste solution of an aluminum material produced by treating the aluminum material with a solution containing sodium hydroxide as a main component by a method including the following steps: Of treatment of waste aluminum hydroxide treatment liquid.
(1) Carbon dioxide gas is blown into the sodium hydroxide treatment waste liquid in a state where the liquid temperature is 50 ° C. to 80 ° C.,
The precipitated aluminum hydroxide is recovered by filtration, and the sodium carbonate in the filtrate is recovered as it is in solution or as a solid by drying,
(2) adding all or part of the aluminum hydroxide to hydrochloric acid to form a slurry and reacting under pressure and heating conditions to obtain a reaction slurry;
(3) A step of adding a part of the sodium carbonate to the reaction slurry for reaction, and obtaining a filtrate by filtration; and (4) adding sodium sulfate to the filtrate for reaction, and filtering to form polyaluminum chloride as a filtrate. Obtaining. An aluminum material characterized in that a sulfuric acid band is produced from a sodium hydroxide treatment waste liquid of an aluminum material produced by treating the aluminum material with a solution containing sodium hydroxide as a main component by a method including the following steps: Of treatment of aluminum hydroxide waste liquid.
(1) Carbon dioxide gas is blown into the sodium hydroxide treatment waste liquid in a state where the liquid temperature is 50 ° C. to 80 ° C.,
The precipitated aluminum hydroxide is recovered by filtration, and the sodium carbonate in the filtrate is recovered as it is in solution or as a solid by drying,
(2) adding sulfuric acid to all or a part of the aluminum hydroxide and obtaining a reaction slurry by stirring with air;
(3) A step of adjusting the concentration by adding water to the reaction slurry and then obtaining a sulfate band as a filtrate by filtration. An aluminum characterized in that polyaluminum chloride is produced from a sodium hydroxide treatment waste solution of an aluminum material produced by treating the aluminum material with a solution containing sodium hydroxide as a main component by a method including the following steps: Of treatment of waste aluminum hydroxide treatment liquid.
  (1) Carbon dioxide gas is blown into the sodium hydroxide treatment waste liquid at a temperature of 30 ° C. to 40 ° C., so that free sodium hydroxide is converted to sodium carbonate, precipitated, separated by filtration,
  On the other hand, carbon dioxide is blown into the filtrate at a temperature of 50 ° C. to 80 ° C., and the precipitated aluminum hydroxide is recovered by filtration, and the sodium carbonate in the filtrate is recovered as it is or as a solid by drying. Process,
  (2) adding all or part of the aluminum hydroxide to hydrochloric acid to form a slurry and reacting under pressure and heating conditions to obtain a reaction slurry;
  (3) adding a part of the sodium carbonate to the reaction slurry to cause reaction, and obtaining a filtrate by filtration; and
  (4) A step of adding sodium sulfate to the filtrate to cause reaction, and obtaining polyaluminum chloride as a filtrate by filtration. An aluminum material characterized in that a sulfuric acid band is produced from a sodium hydroxide treatment waste liquid of an aluminum material produced by treating the aluminum material with a solution containing sodium hydroxide as a main component by a method including the following steps: Of treatment of aluminum hydroxide waste liquid.
  (1) Carbon dioxide gas is blown into the sodium hydroxide treatment waste liquid at a temperature of 30 ° C. to 40 ° C., so that free sodium hydroxide is converted to sodium carbonate, precipitated, separated by filtration,
  On the other hand, carbon dioxide is blown into the filtrate at a temperature of 50 ° C. to 80 ° C., and the precipitated aluminum hydroxide is recovered by filtration, and the sodium carbonate in the filtrate is recovered as it is or as a solid by drying. Process,
  (2) adding sulfuric acid to all or a part of the aluminum hydroxide and obtaining a reaction slurry by stirring with air;
  (3) A step of adjusting the concentration by adding water to the reaction slurry and then obtaining a sulfate band as a filtrate by filtration.   The carbon dioxide gas is a treatment method of a sodium hydroxide treatment waste liquid of an aluminum material according to any one of claims 1 to 4, wherein carbon dioxide gas generated from a combustion exhaust gas from a boiler, a fermentation exhaust gas, or a limestone roasting furnace is used.

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