KR101009026B1 - Method for recovering acid from mixed waste acid occupied in preparing process of liquid crystal display - Google Patents

Abstract

The present invention relates to a method for recovering acid from the mixed waste acid generated in the liquid crystal display device manufacturing process, wherein the recovery method comprises a first vacuum evaporation process of the mixed waste acid generated in the liquid crystal display device and an evaporating solution comprising nitric acid and acetic acid; , And separated into a residual liquid containing phosphoric acid and a metal component, the evaporated liquid by secondary vacuum evaporation to separate acetic acid and nitric acid, and the residual liquid by diffusion dialysis to separate the phosphoric acid, 3 to the phosphoric acid And a secondary vacuum evaporation process.

By the method of recovering acid from the mixed waste acid 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.

Liquid crystal display, mixed waste acid, acid recovery, vacuum evaporation, diffusion dialysis

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 an ion chromatographic analysis showing the content of nitric acid, acetic acid and phosphoric acid in the evaporated liquid obtained in the first vacuum evaporation treatment for mixed waste acid in Example,

Figure 3 is an ion chromatography analysis showing the content of nitric acid, acetic acid and phosphoric acid in the residual liquid obtained during the first vacuum evaporation treatment for mixed waste acid in the Example,

Figure 4 is a graph showing the evaporation pattern of nitric acid and acetic acid with temperature during the second vacuum evaporation process 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 that can easily separate and purify 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, general landfilling is not possible, and there is a problem of incineration separately. 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. Or when nitric acid and acetic acid remain or when the concentration of phosphoric acid is high, it is difficult to use the ion exchange resin method. 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 provides a first vacuum evaporation process of the mixed waste acid generated in the liquid crystal display device to separate the evaporation liquid containing nitric acid and acetic acid, and the residual liquid containing phosphoric acid and metal components, Performing a second vacuum evaporation to separate acetic acid and nitric acid, and separating the residual liquid by diffusion dialysis to separate phosphoric acid, and concentrating the separated phosphoric acid by tertiary vacuum evaporation to a high concentration. Provided is a method for recovering acid from mixed waste acid generated in a manufacturing process.

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

The use of recycled mixed acid generated in the manufacturing process of LCD depends on the level of purification of the waste acid, and the added value thus obtained also varies. 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 performing vacuum evaporation on the mixed waste acid, followed by vacuum evaporation or diffusion dialysis. 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. Hereinafter, a method of recovering acid from the mixed waste acid of the present invention will be described with reference to the process diagram of FIG. 1. In the acid recovery method according to an embodiment of the present invention, the mixed waste acid 1 generated in the liquid crystal display device is first vacuum evaporated. Treatment (10) to separate the evaporating solution (12) comprising nitric acid and acetic acid and the residual solution (14) containing phosphoric acid and metal components, and the evaporating solution (12) is subjected to a second vacuum evaporation treatment (20). Separating the acetic acid (22) and nitric acid (24), each of the residual solution (14) by diffusion dialysis (30) to remove the metal component with the waste solution (32) and separating the phosphoric acid (34); And concentrating the phosphoric acid at a high concentration by tertiary vacuum evaporation 40 with respect to the separated phosphoric acid 34 to obtain a high concentration of phosphoric acid 42.

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 a first step to recover each of these components separately, the mixed waste acid is subjected to a first vacuum evaporation process. At this time, prior to the first vacuum evaporation process, a microfilter or the like may be further selectively filtered to remove insoluble solid impurities contained in the mixed waste acid.

Primary vacuum evaporation 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.

The first vacuum evaporation step uses a difference in boiling points of the acids present in the mixed waste acid, and the mixed waste acid is separated into an evaporate containing nitric acid and acetic acid and a residual liquid containing phosphoric acid and a metal component. .

 The first vacuum evaporation treatment step may be carried out using a conventional vacuum evaporation treatment apparatus. In order to increase the removal efficiency of acetic acid and nitric acid from the mixed waste acid, the first vacuum evaporation treatment is preferably performed at -650 to -760 mmHg vacuum degree, and more preferably at -680 to -730 mmHg vacuum degree. . If the vacuum degree is less than -650 mmHg, since the evaporation temperature must be increased to 140 ° C. or more, the energy cost and the investment cost of the manufacturing equipment are excessively increased, which is not preferable. In addition, when the degree of vacuum exceeds -760 mmHg, it is not preferable because a large-capacity vacuum pump cannot be continuously operated above -760 mmHg in a commercialization facility.

In addition, it is preferable to perform the said primary 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 first vacuum evaporation process, nitric acid and acetic acid contained in the mixed waste acid can be completely removed.

In the first vacuum evaporation process, nitric acid and acetic acid are mixed with each other and evaporated. Accordingly, nitric acid and acetic acid may be separated by performing a second vacuum evaporation process on the evaporating liquid containing nitric acid and acetic acid.

At this time, the secondary vacuum evaporation treatment is preferably performed at a vacuum degree of -650 mmHg or less, and 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 secondary 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, respectively, by the secondary vacuum evaporation process as described above.

Separately, diffusion dialysis treatment is performed on the residual liquid remaining after the first vacuum evaporation to remove metal components contained in the residual liquid and to separate phosphoric acid.

A large amount of metal can be efficiently removed by the diffusion dialysis method. In the present invention, it is possible to obtain phosphoric acid in the form of an aqueous solution by removing the metal components contained in the residual liquid by using the selective permeability of the anion exchange membrane that passes only the acid solution but does not pass the metal salt.

In the diffusion dialysis treatment, a conventional diffusion dialysis apparatus may be used. In the present invention, in order to allow the residual liquid obtained after the vacuum evaporation treatment and water to flow in turn, diffusion dialysis diaphragm having a plurality of ion exchange membranes interposed therebetween with a gasket interposed therebetween. The device was used. Accordingly, the gasket for supplying the residual liquid and the water in the diffusion dialysis apparatus is preferable because the plastic nets are woven like a net so that the solution is uniformly mixed and turbulent flow can be minimized to minimize membrane fouling.

In the diffusion dialysis apparatus, the residual liquid is supplied upwards from the bottom of the diffusion dialysis apparatus, and water is supplied downwards from the top. The residual liquid fed into the diffusion dialysis apparatus is separated from metal ions and phosphoric acid by 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 the diffusion dialysis treatment, 98% or more of the metal components of aluminum and molybdenum contained in the residual liquid obtained after the evaporation 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 the concentration of phosphoric acid is low, so that the phosphoric acid aqueous solution can be concentrated by performing a tertiary vacuum evaporation process to obtain a high concentration of phosphoric acid.

The vacuum evaporation step may be performed in the same manner as the first vacuum evaporation step described above. By the vacuum evaporation treatment, high purity phosphoric acid can be obtained at a high concentration of 85% or more.

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 a 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  Primary vacuum evaporation treatment

In order to separate acetic acid and nitric acid present in the mixed waste acid, the first vacuum evaporation process 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, prior to the vacuum evaporation step, the mixed waste acid having the composition shown in Table 1 was filtered through a microfilter to remove insoluble solid impurities in the mixed waste acid. The mixed waste acid from which solid impurities have been removed is placed in a Pyrex reactor and maintained at a temperature of 120 ° C. using a digital heating magnetic stirrer (MSH-10, WiseStir), and a constant pressure inside the reactor is maintained at -730 mmHg using a vacuum pump. I was. At this time, the inside of the reactor was decompressed to a condition lower than atmospheric pressure so that a mixture of low boiling point nitric acid and acetic acid was evaporated first. The mixtures of evaporated nitric acid and acetic acid were liquefied, separated and removed through a condenser in which cooling water was circulated.

 After completion of the evaporation process, phosphoric acid in the distillate (high concentration phosphoric acid) from which acetic acid and nitric acid are separated and removed is contained at a concentration of 95% or more. Pure water was added to adjust the concentration of phosphoric acid to 85%, the product standard for fertilizer crude phosphoric acid.

 In order to confirm the complete separation of nitric acid and acetic acid in the mixed waste acid, the acid concentration in the evaporated liquid and the residual liquid recovered after vacuum evaporation was measured using an ion chromatography (Ion Chromatography: ICS-2500, DIONEX) analyzer. 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 Evaporate 17.3 18.5 - - - Residue - - 85.4 289.73 282.19

As shown in Table 2, the concentration of nitric acid and acetic acid in the evaporated liquid evaporated by vacuum evaporation was about three times the concentrations of nitric acid and acetic acid in the raw mixed waste acid in Table 1, and the mixing of phosphoric acid and metal components Was found to be absent at all.

In addition, the experiment was conducted to find the optimal conditions for the separation of nitric acid and acetic acid in the mixed waste acid by varying the degree of vacuum and temperature in the vacuum evaporation step.

In the test conditions, the vacuum degree was fixed at -730, -700, and -650mmHg, respectively, and the temperature was raised to 140 ° C, and vacuum evaporation was performed for each temperature section. The residual liquid remaining after vacuum evaporation was sampled and analyzed, and the conditions and behavior of nitric acid and acetic acid separated from phosphoric acid were investigated. The results are shown in Table 3 below.

Exam conditions density(%) Vacuum degree (mmHg) Temperature (℃) Acetic acid nitric acid Phosphoric Acid -650 120 1.30 1.25 86.6 140 0 0 87.3 160 0 0 87.4 -700 100 1.16 1.18 79.6 110 0.69 0 81.0 120 0 0 85.1 -730 100 0.86 0 79.0 110 0 0 82.4 120 0 0 85.4

As shown in Table 3, it can be seen that the lower the degree of vacuum, it is preferable to perform the vacuum evaporation at a higher temperature. In the vacuum evaporation step, when the degree of vacuum was -650 mmHg, it was completely separated at a temperature of 140 ° C or higher, and when the degree of vacuum was -700mmHg, it was completely separated at a temperature of 120 ° C or higher. In the case of a vacuum degree of -730 mmHg, complete separation was possible even at a temperature of 110 ° C. or higher.

In addition, when the mixed waste acid was vacuum evaporated at the vacuum degree of -650 mmHg and the temperature of 140 ° C., the content of nitric acid, acetic acid and phosphoric acid in the evaporated liquid and the residual liquid was analyzed by anion, and the nitric acid and acetic acid in the mixed waste acid were subjected to the vacuum evaporation process. It was confirmed that it was completely separated from this phosphoric acid. The results are shown in FIGS. 2 and 3.

FIG. 2 is an IC analysis result showing the contents of nitric acid, acetic acid and phosphoric acid in the evaporated liquid obtained during the first vacuum evaporation treatment for mixed waste acid, and FIG. 3 shows the nitric acid, acetic acid and IC analysis results showing the content of phosphoric acid.

 In FIG. 2 and FIG. 3, the X axis represents a retention time and means a separation time according to the dissociation degree of the anion. This shows the kind of anion. In addition, the Y-axis shows conductivity and strength against anion content. By integrating the analysis curves of these two axes, the concentration of anions can be determined.

2 and 3, no peaks for phosphoric acid were found in the evaporated solution, and no peaks for nitric acid and acetic acid were found in the remaining solution. From this, it was confirmed that nitric acid and acetic acid present in the mixed waste acid were completely separated and removed by the vacuum evaporation process.

3) Separation of nitric acid and acetic acid from evaporates

After the first vacuum evaporation process, a second vacuum evaporation process was performed to separate acetic acid and nitric acid present in the evaporation solution.

The vacuum evaporation apparatus used in the second vacuum evaporation treatment was the same as that used in the first vacuum evaporation treatment.

First, the evaporated liquid 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.

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

As shown in FIG. 4, it can be seen that the evaporation concentrations of nitric acid and nitric 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 addition, in order to know the vacuum evaporation treatment conditions for separating the nitric acid and acetic acid contained in the stripping solution, as shown in Table 3 by maintaining for 1 hour at the evaporation conditions near the initial flow point (-730mmHg, 67 ℃) of acetic acid and nitric acid Separation was observed. The results are shown in Table 4.

Solution condition mountain(%) Metal ion (mg / kg) Acetic acid nitric acid Phosphoric Acid Al Mo One Vacuum degree -730mmHg, temperature 120 ℃ 17.3 18.5 - - - 2 Vacuum degree -700mmHg, temperature 70 ℃ 16.5 5.4 - - - 3 Vacuum degree -700mmHg, temperature 65 ℃ 14.7 3.8 - 4 Vacuum degree -700mmHg, temperature 60 ℃ 13.4 1.3 - 5 Vacuum degree -650mmHg, temperature 70 ℃ 14.0 0.1 - - - 6 Vacuum degree -650mmHg, temperature 65 ℃ 12.7 - - 7 Vacuum degree -650mmHg, temperature 60 ℃ 10.1 - - 8 Vacuum degree -600mmHg, temperature 70 ℃ 13.2 - - - - 9 Vacuum degree -600mmHg, temperature 65 ℃ 11.6 - - 10 Vacuum degree -600mmHg, temperature 60 ℃ 10.3 - -

As shown in Table 4, 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.

4) obtained by the first vacuum evaporation process From residue  Phosphate Separation

The diffusion dialysis treatment was carried out in the following manner to remove metal components present in the residual liquid obtained by the first vacuum evaporation treatment and to separate phosphoric acid.

Diffusion dialysis apparatus (T) in the opposite direction to the dialysis membrane (DSV, ASAHI GLASS Co.), which is an anion exchange membrane, while adjusting the flow rates of the residual liquid and water obtained by the first vacuum evaporation treatment to 0.97 L / Hr · m ² . -Ob Selemion dialyzer, 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) and a peristaltic pump having a maximum rotation 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 5 below.

Analysis item
fair
density(%) Metal ion (mg / kg) Acetic acid nitric acid Phosphoric Acid Al Mo Filtrate after diffusion dialysis - - 63.4 2.63 3.62

As shown in Table 5, as a result of diffusion dialysis treatment of the residual liquid obtained after the first vacuum evaporation treatment, aluminum aluminum 289.7 mg / kg was lowered to 2.6 mg / kg, molybdenum 282.1 mg / kg to 3.6 mg / kg . By this diffusion dialysis treatment, about 98% of the metal components were removed from the residual liquid to obtain a high-purity phosphoric acid aqueous solution.

5) tertiary vacuum evaporation of phosphoric acid solution obtained after diffusion dialysis;

As a result of the diffusion dialysis treatment, the metal component was completely removed, but the concentration of phosphoric acid in the filtrate was lowered from 85.4% to 63.5%. Accordingly, in order to obtain a high concentration of phosphoric acid, a third 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, inside the reactor, the pressure is reduced to a condition lower than atmospheric pressure, and the vacuum concentration proceeds to a phosphoric acid concentration of 85%.

The acid concentration was measured using an ion chromatography (ICS-2500, DIONEX) analyzer and Al, Mo, etc. in the acid solution were analyzed using plasma spectroscopy (ICP-AES). The results are shown in Table 6 below.

Analysis item density(%) Metal ion (mg / kg) Acetic acid nitric acid Phosphoric Acid Al Mo Phosphoric acid aqueous solution obtained after vacuum evaporation - - 85.3 3.54 4.87

As shown in Table 6, the high-purity phosphoric acid could be concentrated to a high concentration of 85.3% through the vacuum evaporation treatment.

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 (7)

Firstly vacuum-evaporating the mixed waste acid generated in the liquid crystal display into an evaporating solution containing nitric acid and acetic acid and a residual solution containing phosphoric acid and a metal component; Separating the acetic acid and nitric acid by second vacuum evaporation of the evaporated solution; Diffusing dialysis of the residue to separate phosphoric acid; Tertiary vacuum evaporating the phosphoric acid; A method for recovering acid from mixed waste acid generated in the liquid crystal display manufacturing process. The method of claim 1, Wherein said first vacuum evaporation treatment step is carried out at a vacuum degree of -650 to -760 mmHg. The method of claim 1, Wherein said first vacuum evaporation treatment step is carried out at 100 to 160 ° C. The method of claim 1, Wherein said secondary vacuum evaporation process is conducted at a vacuum degree of -650 mmHg or less. The method of claim 1, Wherein said second vacuum evaporation process is carried out at a temperature of 70 ° C. or less. The method of claim 1, Wherein said third vacuum evaporation step is carried out at a vacuum degree of -650 to -760 mmHg. The method of claim 1, Wherein said third vacuum evaporation step is carried out at 100 to 160 ° C.

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