KR20070068206A - Method for recovering acid from mixed waste acid occupied in preparing process of liquid crystal display - Google Patents

Abstract

An acid recovery method capable of easily separating and purifying nitric acid, acetic acid and phosphoric acid from a mixed waste acid generated in a liquid crystal display fabricating process is provided. A method for recovering an acid from a mixed waste acid(1) generated in a liquid crystal display fabricating process comprises the steps of: performing solvent extraction(10) of a mixed waste acid generated from liquid crystal display devices to separate an organic phase(12) containing nitric acid and acetic acid and a water phase(14) containing phosphoric acid and metal components from the mixed waste acid; removing the organic phase from the mixed waste acid, and subjecting the organic phase to first vacuum evaporation(20) to separate acetic acid(22) and nitric acid(24) from the organic phase; subjecting the water phase to diffusion dialysis(30) to separate phosphoric acid(34) from the water phase; and subjecting the separated phosphoric acid to second vacuum evaporation(40) to concentrate phosphoric acid into a high concentration phosphoric acid(42).

Description

METHODS FOR RECOVERING ACID FROM MIXED WASTE ACID OCCUPIED IN PREPARING PROCESS OF LIQUID CRYSTAL DISPLAY}

1 is a process diagram schematically showing a method for recovering acid from mixed waste acid according to an embodiment of the present invention,

2 is a process diagram schematically showing a solvent extraction step in an acid recovery method according to an embodiment of the present invention,

3 is a graph showing the evaporation pattern of nitric acid and acetic acid with temperature during the first vacuum evaporation treatment for stripping solution in the embodiment.

[Technical Field]

The present invention relates to a method for recovering acid from mixed waste acid generated in a liquid crystal display (LCD) manufacturing process, and more particularly, to nitric acid, acetic acid and The present invention relates to an acid recovery method for easily separating and purifying phosphoric acid.

[Private Technology]

Recently, as the production amount of liquid crystal display (LCD) is rapidly increased, the amount of mixed waste acid generated during manufacturing of the LCD is also rapidly increasing. However, recycling techniques for these mixed waste acids are not yet established.

The mixed waste acid is usually mixed with other etching waste liquids in LCD and semiconductor manufacturing processes, and is incinerated, thus, an excessive energy cost is required for the mixed waste acid treatment. In addition, the neutralization precipitation method is also used as a treatment method of the mixed waste acid. In the neutralization precipitation method, since the mixed waste acid is a high concentration of acid, an alkaline neutralizing agent is excessively consumed during neutralization, and a large amount of sludge is generated after the treatment. In addition, since the sludge generated at this time contains heavy metals, there is a problem that general landfilling is not possible and must be separately incinerated. The treatment method of mixed waste acid as described above has a problem in that resources cannot be recycled because the treatment cost is high and expensive organic metals and acids are discarded.

On the other hand, as a technique for recycling mixed waste acid, Korean Patent No. 461849 describes a method for purifying a high concentration of phosphoric acid from an etching process waste liquid through a vacuum concentration and extraction process, and also in Korean Patent Application No. 2004-0008608 A method for regenerating phosphate containing waste etchant through distillation, cation exchange resins and electrochemical activation processes is described. However, in the above method, since nitric acid and acetic acid which are first removed by distillation under reduced pressure are mixed, nitric acid and acetic acid cannot be separated and recycled separately, and the concentration of metal components in the residual liquid remaining after distillation under reduced pressure is high. It is difficult to use the ion exchange resin method when the nitric acid and acetic acid remain or the concentration of phosphoric acid is high. Because the acid concentration is high, even the strong acid resin having a high degree of crosslinking is very difficult to adsorb the resin of the metal component. In addition, when the metal concentration is high, the amount of resin used increases the processing cost. In many cases, the metal component in the waste liquid forms a complex, and the complex is often present in the solution as an anion. Therefore, the cation exchange resin alone cannot completely separate and remove metal components.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an acid recovery method capable of easily separating and purifying nitric acid, acetic acid and phosphoric acid from mixed waste acid generated in the manufacturing process of a liquid crystal display device.

In order to achieve the above object, the present invention is solvent extraction of the mixed waste acid generated in the liquid crystal display device to separate the organic phase containing nitric acid and acetic acid and the aqueous phase containing phosphoric acid and metal components, and the organic phase after the stripping treatment Manufacturing a liquid crystal display device comprising the step of vacuum evaporation to separate acetic acid and nitric acid, and the aqueous phase to diffuse dialysis to separate phosphoric acid, and the separated phosphoric acid to secondary vacuum evaporation to concentrate the phosphoric acid at a high concentration. It provides a method for recovering acid from mixed waste acid generated in the process.

Hereinafter, the present invention will be described in more detail.

The recycling of mixed waste acids from the manufacturing process of LCDs depends on the degree of purification of the waste acids, and the added value that results. For example, ferric acid can be used if the content of acetic acid, nitric acid, and metals in phosphoric acid is less than about 3%, but in the case of phosphoric acid solutions used in LCD manufacturing processes, the total amount of impurity components in the phosphoric acid solution can be used. The content should be 1 ppm or less.

Therefore, in order to increase the added value in recycling the mixed waste acid, a recycling technology capable of purifying impurities such as nitric acid, acetic acid, aluminum, molybdenum, etc. to 1 ppm or less is required. Accordingly, various techniques such as vacuum evaporation, solvent extraction, diffusion or electrodialysis, and ion exchange resins have been used as techniques for recycling mixed waste acid.

In the case of vacuum evaporation, however, organic components such as nitric acid and acetic acid contained in the waste acid can be separated and removed by using a boiling point difference, but metal components, such as aluminum and molybdenum, cannot be removed. In addition, in the case of solvent extraction, organic materials capable of extracting some metal components have been developed but cannot be completely removed. In the case of diffusion dialysis and electrodialysis, the removal rate varies depending on the type of metal component and acid solution, but it is usually not possible to remove several ppm levels. In addition, in the case of the ion exchange resin method, if the metal ion concentration is too high, the exchange cycle and the cleaning cycle are too short, which is not economical. In addition, even if the acid concentration is too high or the pH is too low, it is difficult to apply, and the adsorption rate tends to drop rapidly, and thus cannot be used.

In contrast, the present invention can easily separate and purify nitric acid, acetic acid and phosphoric acid from the mixed waste acid by vacuum evaporation or diffusion dialysis treatment of the mixed waste acid after solvent extraction. In addition, the separated and purified phosphoric acid can be recycled to a high purity fertilizer crude acid, various pickling solutions and the like.

1 is a process diagram schematically showing a method for recovering acid from mixed waste acid according to an embodiment of the present invention. Referring to the acid recovery method of the present invention with reference to the process diagram of Figure 1, the method for recovering acid from the mixed waste acid according to an embodiment of the present invention is solvent extraction (10) of the mixed waste acid (1) generated in the liquid crystal display device ) And separating the organic phase 12 including nitric acid and acetic acid into an aqueous phase 14 including phosphoric acid and a metal component, and then removing the organic phase 12 by first vacuum evaporation 20 to treat acetic acid ( 22) and nitric acid 24 are separated, and the aqueous phase 14 is diffused dialysis 30 to remove metal components as the waste liquid 32 and to separate the high purity phosphoric acid 34 and the high purity phosphoric acid. The second vacuum evaporation treatment 40 may be further performed to obtain the high concentration of phosphoric acid 42 by concentrating the phosphoric acid to a high concentration.

The LCD mixed waste acid used in the present invention is a waste etching solution generated in the process of forming the metal circuit of the multilayer circuit board during the LCD manufacturing process. The waste etching solution contains phosphoric acid, nitric acid, acetic acid, aluminum, molybdenum and the like.

As the first step to recover each of these components separately, the mixed waste acid is solvent extracted. At this time, in order to remove the insoluble solid impurities contained in the mixed waste acid prior to the solvent extraction treatment, a microfilter or the like may be further selectively performed.

The solvent extraction process is performed with respect to the mixed waste acid which arose in the manufacturing process of a liquid crystal display device, or the filtrate obtained by the said filtration process.

2 is a process diagram schematically showing a solvent extraction step in the phosphoric acid recovery method according to an embodiment of the present invention. As shown in FIG. 2, the nitric acid and acetic acid contained in the mixed waste acid 1 are separated into the organic phase 12 using an extractant, and the metal component and phosphoric acid contained in the mixed waste acid are extracted toward the aqueous phase 14. Can be separated. Thereafter, the method may further include removing the organic phase 15 using a stripping agent to obtain stripping solution 16 prior to separation of nitric acid and acetic acid from the separated organic phase 12 through a first vacuum evaporation process. .

 At this time, the extractant may be selected from the group consisting of alkyl phosphate, haloalkyl phosphate, aryl phosphate and mixtures thereof, more preferably the extractant is trioctyl phosphate, trichloroethyl phosphate, n-butyldi ( m-crezyl) phosphate, n-butyldi (3,5-dimethylphenyl) phosphate, 2-ethylbutyldi (m-crezyl) phosphate and mixtures thereof may be used.

In addition, the extractant is dissolved in an organic solvent to form an organic phase, wherein the extractant may be included in 20 to 70% by weight, more preferably 40 to 60% by weight relative to the total weight of the organic phase. If the content of the extractant is less than 20% by weight, the separation rate of the extract is very slow. If the content of the extractant exceeds 70% by weight, the concentration of the extractant must be continuously maintained in the multi-step extraction, washing, and stripping process. It is not preferable because it is difficult to control.

In addition, as the organic solvent, petroleum hydrocarbon compounds such as kerosene may be used.

Water was used as the aqueous phase when the solvent was extracted for the mixed waste acid.

The water phase (A) and the organic phase (O) is preferably used in a mixed ratio (A / O) of 1/1 to 1/5, more preferably in a mixed ratio of 1/2 to 1/4 It is preferred to be used. If the ratio is less than 1/1, the separation and extraction rate of acetic acid and nitric acid is low, which is not preferable. If the ratio is more than 1/4, the extraction ratio of nitric acid and acetic acid is almost constant.

The mixed waste acid by the solvent extraction is an organic phase comprising nitric acid and draft; And an aqueous phase containing phosphoric acid and a metal component.

Subsequently, only the organic phase in the solvent extraction process is separated and then stripped and subjected to primary vacuum evaporation to separate nitric acid and acetic acid contained in the organic phase, respectively.

In the solvent extraction process, nitric acid and acetic acid are separated and included in the organic phase by an extracting agent, and nitric acid and acetic acid included in the organic phase are separated from the extracting agent using a stripping agent.

The stripping agent used in the stripping treatment may be one or more selected from the group consisting of distilled water, hydrochloric acid aqueous solution and sulfuric acid aqueous solution. The stripping agent itself becomes an aqueous phase.

The aqueous phase (A) containing the stripping agent is preferably added so that the phase ratio (A / O) is 1/2 to 1/7 with respect to the organic phase (O) separated in the solvent extraction step, and more preferably 1 It is good to add so that it is / 4 to 1/6. If the ratio of the aqueous phase and the organic phase is less than 1/2, the amount of wastewater generated is excessive and undesirable, and if it exceeds 1/7, the stripping rate is low, which is not preferable.

The stripping treatment separates the mixture of nitric acid and acetic acid from the organic phase into the aqueous phase. A stripping solution comprising a mixture of separated nitric acid and acetic acid is subjected to primary vacuum evaporation to separate into individual materials.

At this time, the first vacuum evaporation treatment is preferably performed at a vacuum degree of -650 mmHg or less, more preferably -600 to -650 mmHg vacuum degree. When the degree of vacuum is less than -650 mmHg, nitric acid hardly evaporates, but only acetic acid evaporates. However, when the degree of vacuum exceeds -650 mmHg, acetic acid also evaporates, which is not preferable because the separation of nitric acid and acetic acid is difficult.

Moreover, it is preferable to perform the said primary vacuum evaporation process in the temperature range of 70 degrees C or less, More preferably, it is good to carry out in the temperature range of 60-70 degreeC. If the treatment temperature exceeds 70 ° C, nitric acid is evaporated with acetic acid, which is not preferable.

Nitrogen and acetic acid can be separated from each other by the first vacuum evaporation treatment as described above.

Separately, phosphoric acid is separated by diffusion dialysis treatment on the extract, that is, the aqueous phase, extracted by the solvent extraction treatment.

 A large amount of metal can be efficiently removed by the diffusion dialysis method. In the present invention, the phosphoric acid can be separated with high purity by removing the metal component contained in the aqueous phase as an extract using the selective permeability of the anion exchange membrane which passes only the phosphoric acid solution and does not pass the metal salt. As the diffusion dialysis membrane, a commercially available anion exchange membrane for acid recovery may be used.

In the diffusion dialysis treatment, a conventional diffusion dialysis apparatus may be used, and in the present invention, a diffusion dialysis apparatus in which a large number of ion exchange membranes are alternately interposed with a gasket in order to flow water and water sequentially is used. Accordingly, the gasket for supplying the water and the water in the diffusion dialysis apparatus is preferable because the plastic nets are woven like a net so that the solution can be uniformly mixed and the turbulence can be minimized to minimize membrane contamination.

In the diffusion dialysis apparatus, the water phase is supplied upward from the bottom of the diffusion dialysis apparatus, and water is supplied from the upper side downwards. The water phase fed into the diffusion dialysis apparatus is separated into metal ions and phosphoric acid by the selective permeability of the dialysis membrane. The separated phosphoric acid is then diluted in contact with the countercurrent water, and the dialysate containing the diluted phosphoric acid is discharged to the bottom of the diffusion dialysis apparatus. On the other hand, the metal component and some of the phosphoric acid that failed to pass through the dialysis membrane come out upwards.

 By such diffusion dialysis treatment, 98% or more of metal components of aluminum and molybdenum contained in the water phase obtained after the solvent extraction treatment can be removed.

The aqueous solution of phosphoric acid obtained after the diffusion dialysis treatment may be subjected to ion exchange resin treatment to further remove metal components remaining in the aqueous solution of phosphoric acid.

The ion exchange resin treatment can be used both cation exchange resin and anion exchange resin together. In the case of aluminum, it exists as a cation in the mixed waste acid, but in the case of molybdenum, it exists in the form of an anion complex, and molybdenum contained in the mixed waste acid cannot be removed only by cation exchange resin treatment. Therefore, it is preferable to pass through two types of resin towers, a cation exchange resin and an anion exchange resin.

In addition, a styrene-based strong acid cation exchange resin may be used as the cation exchange resin when the cation exchange resin is treated. As the anion exchange resin, a styrene strong acid anion exchange resin having excellent chemical stability and organic contamination resistance may be used. desirable. In addition, the strong acid resin in this invention means resin which has strong resistance to an acid and has more ion exchange ability in a strong acid solution.

The phosphoric acid solution obtained after the diffusion dialysis treatment was first treated with a cation exchange resin to remove aluminum in the phosphoric acid aqueous solution, and then treated with an anion exchange resin to remove molybdenum, thereby reducing the concentration of the metal component to 1 ppm or less. Can be obtained. At this time, the order of treatment of the anion exchange resin and the cation exchange resin is not particularly limited.

Phosphoric acid aqueous solution obtained by the ion exchange resin treatment after the diffusion dialysis or diffusion dialysis is high purity, but since the concentration of phosphoric acid is low, further secondary vacuum evaporation treatment can be performed to obtain a high concentration of phosphoric acid.

 At this time, the secondary vacuum evaporation treatment is preferably carried out at -650 to -760 mmHg vacuum degree, more preferably -680 to -730 mmHg vacuum degree. If the degree of vacuum is less than -650 mmHg, the evaporation temperature must be increased to 140 ° C or higher. Therefore, the energy cost and the investment cost of the manufacturing equipment are excessively increased. It is not preferable because it is difficult to continuously operate above 760 mmHg.

In addition, it is preferable to perform the said secondary vacuum evaporation process in the temperature range of 100-160 degreeC, More preferably, it is good to carry out in the temperature range of 110-130 degreeC. It is not preferable because the evaporation itself does not occur below 100 ° C, and if it exceeds 160 ° C, the energy cost is excessive, and when the waste steam is used, it is difficult to use the waste steam because the waste steam usually does not exceed 140 ° C. Not desirable

Most preferably, the vacuum degree is -650 mmHg at a temperature of 140 ° C or higher, the vacuum degree is -700mmHg at a temperature of 120 ° C or higher, and in the case of a vacuum degree of -730mmHg, the temperature is set at 110 ° C or higher.

By the acid recovery method of the present invention as described above, nitric acid, acetic acid and phosphoric acid can be easily separated and purified from the mixed waste acid generated in the liquid crystal display device manufacturing process. In addition, the purified phosphoric acid can be recycled to high purity fertilizer crude acid, various pickling solutions and the like.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

Example  1. Mix From waste acid  Acid recovery method.

1) LCD mix Waste acid  Ready

The mixed waste acid having the composition shown in Table 1 was used to recover high purity phosphoric acid from the mixed waste acid discharged from the LCD manufacturing process.

Analysis item density(%) Metal ion (mg / kg) Acetic acid nitric acid Phosphoric Acid Al Mo LCD mixed waste acid 6.8 6.7 62.2 211.5 206

2) LCD mix Waste acid  Solvent extraction treatment

In order to separate acetic acid and nitric acid which exist in mixed waste acid, the solvent extraction process was performed as follows.

The mixed waste acid having the composition shown in Table 1 above was mixed and added so that the phase ratio (A / O) of the aqueous phase (A) and the organic phase (O) became 1/4. By the solvent extraction treatment, nitric acid and acetic acid in the mixed waste acid diffuse and move into the organic phase, and phosphoric acid and metal components are extracted and remain in the aqueous phase. When the two phases were left to be completely separated and equilibrated, a separatory funnel was used to separate the aqueous phase and the organic phase. The amount of extraction was determined by measuring the acid concentration of the aqueous phase and the acid concentration of the organic phase.

In the stripping process, an aqueous phase containing a stripping agent is added to the organic phase so that the phase ratio (A / O) of the aqueous phase (A) and the organic phase (O) is 1/2, and acetic acid and nitric acid are recovered in two stages. It was. At this time, distilled water was used as the stripping agent. By the stripping process, acetic acid and nitric acid were separated into an aqueous phase (a stripping solution). The theoretical extraction and stripping stages are optimal after constructing the McCabe-Thiele diagram, which is a combination of the extraction isothermal curve and the stripping isothermal curve with the operating line (A / O ratio). The theoretical number of stages required for extraction and removal of was determined.

In order to confirm complete separation of nitric acid and acetic acid from the mixed waste acid by the solvent extraction, the acid concentration in the solvent extract (aqueous phase) and stripping solution was measured using an ion chromatography (Ion Chromatography: ICS-2500, DIONEX) analyzer. Measured. In addition, metal components such as Al and Mo in the residual liquid were analyzed by using plasma spectrometry (ICP-AES). The measurement results are shown in Table 2 below.

Analysis item Acid concentration (%) Metal ion (mg / kg) Acetic acid nitric acid Phosphoric Acid Al Mo Stripping solution 2.7 3.9 - - - Extract (water phase) - - 61.7 212.0 206.5

As shown in Table 2 above, acetic acid and nitric acid were separated from the mixed waste acid by almost 99.9% or more into the organic phase by solvent extraction. At this time, the extracted phosphoric acid and metal components were maintained at about the same level as the concentration in the initial mixed waste acid, but was different from the initial concentration because distilled water was used as a stripping agent for nitric acid and acetic acid.

2) From stripping liquid  Separation of nitric acid and acetic acid

In order to separate acetic acid and nitric acid present in the stripping solution obtained by the stripping treatment after the solvent extraction, a first vacuum evaporation treatment was performed using a vacuum evaporation apparatus in the following manner.

The vacuum evaporation apparatus is composed of a Pyrex reactor, a vacuum pump, a cooling tube, an acid recovery tank, and a heating mantle. The Pyrex reactor is an improved round bottom flask and has a capacity of 2L. A normal reflux cooling tube was used as the cooling tube, and it was connected with tap water to perform the role of a cooler. The acid recovery tank used a 300 ml Erlenmeyer flask. The heating mantle used to raise the temperature inside the reactor used a digital heating magnetic stirrer (MSH-10, WiseStir) capable of temperature control up to 400 ° C ± 2 ° C.

First, the stripping solution was placed in a Pyrex reactor and the pressure inside the reactor was kept constant at -730 mmHg using a vacuum pump, and then vacuum evaporated by raising the temperature from 60 to 120 ° C. using a digital heating magnetic stirrer (MSH-10, WiseStir). . The concentrations of acetic acid and nitric acid contained in the evaporate were measured, respectively. The results are shown in FIG.

3 is a graph showing the evaporation pattern of nitric acid and acetic acid with temperature in the process of the first vacuum evaporation.

As shown in FIG. 3, it can be seen that the evaporation concentrations of nitric acid and acetic acid are significantly different near the initial boiling point. That is, it can be seen that nitric acid and acetic acid can be separated by adjusting the evaporation temperature to 67 ° C. or lower at a vacuum degree of -730 mmHg or by lowering the vacuum degree and adjusting the temperature appropriately.

In order to know the first vacuum evaporation treatment conditions for separating the nitric acid and acetic acid contained in the stripping solution, as shown in Table 3 below by maintaining for 1 hour in the evaporation conditions near the initial flow point (-730mmHg, 67 ℃) acetic acid and nitric acid The separation of was observed. The results are shown in Table 3.

Solution condition mountain(%) Metal ion (mg / kg) Acetic acid nitric acid Phosphoric Acid Al Mo One Vacuum degree -700mmHg, temperature 70 ℃ 2.4 2.8 - - - 2 Vacuum degree -700mmHg, temperature 65 ℃ 2.3 1.7 - 3 Vacuum degree -700mmHg, temperature 60 ℃ 1.8 0.5 - 4 Vacuum degree -650mmHg, temperature 70 ℃ 1.5 0.1 - - - 5 Vacuum degree -650mmHg, temperature 65 ℃ 1.5 - - 6 Vacuum degree -650mmHg, temperature 60 ℃ 1.2 - - 7 Vacuum degree -600mmHg, temperature 70 ℃ 1.2 - - - - 8 Vacuum degree -600mmHg, temperature 65 ℃ 1.1 - - 9 Vacuum degree -600mmHg, temperature 60 ℃ 0.9 - -

As shown in Table 3 above, nitric acid was hardly evaporated but only acetic acid was evaporated under vacuum evaporation conditions at a vacuum degree of −650 mmHg or lower and a temperature of 70 ° C. or lower. From this it can be seen that the nitric acid and acetic acid contained in the stripping liquid can be separated when the vacuum evaporation process in the vacuum degree and temperature range. In addition, the lower the vacuum and temperature, the lower the concentration of evaporated acetic acid is because the evaporation of water is slightly stronger than acetic acid.

3) Phosphoric Acid Separation from Extract

In order to remove the metal components present in the extraction liquid (aqueous phase) obtained after the solvent extraction step of 2) and to separate phosphoric acid, diffusion dialysis treatment was performed as follows.

Diffusion dialysis apparatus (T-Ob Selemion dialyzer) in the opposite direction with the dialysis membrane (DSV, ASAHI GLASS Co.), which is an anion exchange membrane, while controlling the flow rates of the extract liquid and water obtained after the solvent extraction treatment to 0.97L / Hr · m ² , ASAHI GLASS Co.). It carried out by the continuous process which continues to carry out until a recovery is reached to steady state. The pump used in the diffusion dialysis apparatus is a Masterflex pump (Cole Parmer company) which is a peristaltic pump having a maximum rotational speed of 600 rpm. In addition, the flow rate can be adjusted to 0.006 ~ 380mL / min depending on the tube size. Flow control was able to achieve the desired flow rate by controlling the rotational speed of the Masterflex pump and controlling the tube size. In addition, the area of the used dialysis membrane was 0.327 m ² / unit, and the flow rate calculation was calculated by dividing the amount of the waste acid solution and the acid recovered in both measuring cylinders by the time after passing through the dialyzer.

The acid concentration in the filtrate was measured and analyzed using an ion chromatography (ICS-2500, DIONEX) analyzer for the filtrate recovered in the diffusion dialysis apparatus, and then the recovery rate was determined. In addition, metal components such as Al and Mo in the filtrate were analyzed using plasma spectroscopy (ICP-AES). The measurement results are shown in Table 4 below.

Analysis item density(%) Metal ion (mg / kg) Acetic acid nitric acid Phosphoric Acid Al Mo Filtrate after diffusion dialysis - - 51.5 3.27 2.65

As shown in Table 4 above, as a result of diffusion dialysis treatment for the extract (water phase) obtained after the solvent extraction treatment, aluminum 212.0 mg / kg was lowered to 3.27 mg / kg, molybdenum 206.5 mg / kg to 2.65 mg / kg. By this diffusion dialysis treatment, about 98% of the metal components were removed from the extract solution to obtain a high-purity aqueous solution of phosphoric acid.

4) Secondary vacuum evaporation of phosphoric acid aqueous solution obtained after diffusion dialysis treatment

Although the metal component was completely removed as a result of the diffusion dialysis treatment, the concentration of phosphoric acid in the filtrate was lowered from 61.7% to 51.5%. Accordingly, in order to obtain a high concentration of phosphoric acid, a secondary vacuum evaporation process was performed as follows.

Phosphoric acid solution containing 51.5% purified phosphoric acid concentration after passing the ion exchange resin step into a 2L Pyrex reactor using a digital heating magnetic stirrer (MSH-10, WiseStir) capable of temperature control up to 400 ° C ± 2 ° C The temperature in the reactor was kept at a temperature of 120 ° C., and the pressure inside the reactor was kept constant at −730 mm Hg using a vacuum pump. At this time, the inside of the reactor was pressurized under a condition lower than atmospheric pressure, and vacuum concentration was performed at a phosphoric acid concentration of 85%.

The acid concentration was measured using an ion chromatography (ICS-2500, DIONEX) analyzer, and Al, Mo, and the like in the acid solution were analyzed using plasma spectroscopy (ICP-AES). The results are shown in Table 5 below.

Analysis item density(%) Metal ion (mg / kg) Acetic acid nitric acid Phosphoric Acid Al Mo Phosphoric acid aqueous solution obtained after the second vacuum evaporation - - 85.3 4.54 3.67

As shown in Table 5, the second vacuum evaporation process was able to concentrate the high purity phosphoric acid to a high concentration of 85.3%.

By the acid recovery method method according to the present invention, nitric acid, acetic acid and phosphoric acid can be easily separated and purified from the mixed waste acid generated in the liquid crystal display device manufacturing process. In addition, the purified phosphoric acid can be recycled to a high purity fertilizer crude acid, various pickling solutions and the like.

Claims (10)

Solvent extraction of the mixed waste acid generated in the liquid crystal display device to separate the organic phase including nitric acid and acetic acid into an aqueous phase including phosphoric acid and a metal component; Stripping the organic phase and first vacuum evaporating to separate acetic acid and nitric acid, respectively; Diffusing dialysis of the aqueous phase to separate phosphoric acid; And Concentrating the phosphoric acid to a high concentration by the second vacuum evaporation of the separated phosphoric acid A method for recovering acid from mixed waste acid generated in the liquid crystal display manufacturing process. The method of claim 1, The solvent extraction step is water (A) in the mixed waste acid; And recovering the acid from the mixed waste acid, wherein the organic phase (O) comprising the extractant is added by mixing the mixture in a ratio of 1/1 to 1/5 (A / O). The method of claim 2, Wherein said extractant is at least one selected from the group consisting of alkyl phosphates, haloalkyl phosphates, aryl phosphates and mixtures thereof. The method of claim 2, Wherein said extractant is used at a concentration of 20 to 70% by weight relative to the total weight of the organic phase. The method of claim 1, The stripping step for the organic phase is carried out by adding an aqueous phase such that the phase ratio of the aqueous phase (A) including the stripping agent and the organic phase (O) obtained in the solvent extraction step is 1/2 to 1/7. How to recover. The method of claim 5, The stripping agent is a method for recovering acid from the mixed waste acid is at least one selected from the group consisting of distilled water, aqueous hydrochloric acid and aqueous sulfuric acid solution. The method of claim 1, And wherein said first vacuum evaporation treatment is conducted at a vacuum degree of -650 mmHg or less. The method of claim 1, Wherein said first vacuum evaporation process is carried out at a temperature of 70 ° C. or less. The method of claim 1, Wherein said secondary vacuum evaporation process is carried out at a vacuum degree of -650 to -760 mmHg. The method of claim 1, Wherein said second vacuum evaporation process is carried out at 100 to 160 ° C.

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