KR101009025B1 - Method for recovering high purity phosphoric 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 high-purity phosphoric acid from mixed waste acid generated in a liquid crystal display manufacturing process, wherein the recovery method is a method of recovering nitric acid and acetic acid in mixed waste acid by first vacuum evaporating the mixed waste acid generated in the liquid crystal display. To remove the metal components by diffusion dialysis treatment of the residual liquid remaining after the first vacuum evaporation, and to remove the remaining metal components by ion exchange resin treatment on the dialysis liquid obtained after the diffusion dialysis, and to carry out the ion exchange. And a second vacuum evaporation process after the resin treatment step.

By using the high purity phosphoric acid recovery method according to the present invention, it is possible to recover high purity phosphoric acid in which the impurity content is reduced to several ppm level from the mixed waste acid generated in the liquid crystal display manufacturing process. Accordingly, the recovered phosphoric acid may be recycled into an etching solution, high purity phosphoric acid, various pickling solutions, and the like in manufacturing a liquid crystal display.

Liquid crystal display device, mixed waste acid, recovery method, vacuum evaporation, diffusion dialysis, ion exchange resin.

Description

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

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

Figure 2 is an ion chromatography 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 acid waste in the embodiment,

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 acid waste in the embodiment.

[Technical Field]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering high purity phosphoric acid from mixed waste acid generated in a liquid crystal display device manufacturing process. More particularly, the present invention relates to a liquid crystal display device by recovering high purity phosphoric acid having a high content of impurities reduced to several ppm. The present invention relates to a method for recovering high purity phosphoric acid that can be recycled into an etching solution, high purity phosphoric acid, various pickling solutions, and the like during manufacture.

[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, nitric acid and acetic acid first removed by distillation under reduced pressure are mixed, and nitric acid and acetic acid cannot be separated and recycled, respectively, 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.

The present invention is to solve the above problems, the present invention is to provide a phosphoric acid recovery method that can recover high-purity phosphoric acid by reducing the content of impurities to several ppm level from the mixed waste acid generated in the manufacturing process of the liquid crystal display device For the purpose of

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 to remove nitric acid and acetic acid in the mixed waste acid, and the residual liquid remaining after the first vacuum evaporation is subjected to diffusion dialysis treatment First removing the components, treating the dialysate obtained after the diffusion dialysis, ion-exchange resin treatment to remove residual metal components, and performing secondary vacuum evaporation on the remaining filtrate after the ion-exchange resin treatment. Provided is a method for recovering high purity phosphoric acid from mixed waste acid generated in an apparatus 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, removal rates vary depending on the metal component and the type of acid solution, but are usually not removed to 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 the present invention, by treating the mixed waste acid in the order of first vacuum evaporation, diffusion dialysis, ion exchange resin and second vacuum evaporation, the high purity phosphoric acid which reduced the content of impurities from the mixed waste acid to several ppm level at high concentration It can be recovered. The phosphoric acid thus obtained may be recycled into an etching solution, high purity phosphoric acid, various pickling solutions, and the like in the manufacture of a liquid crystal display device.

1 is a process diagram schematically showing a method for recovering high purity phosphoric acid from mixed waste acid according to an embodiment of the present invention. Hereinafter, the high purity phosphoric acid recovery method of the present invention will be described with reference to the process diagram of FIG. 1. In the method of recovering high purity phosphoric acid from the mixed waste acid according to an embodiment of the present invention, the mixed waste acid 1 generated in the liquid crystal display device may be first-order Vacuum evaporation (10) to remove nitric acid and acetic acid in the mixed waste acid as the evaporation solution (12), and the residual liquid (14) remaining after the vacuum evaporation is subjected to diffusion dialysis (20) to remove the metal components (22). ) To remove the remaining metal component by the ion exchange resin treatment (30) of the dialysis solution (24) obtained after the diffusion dialysis, and the high purity phosphoric acid (32) obtained after the ion exchange resin treatment. ) To obtain a high purity and high concentration of phosphoric acid (42) by performing a process (40) of the secondary vacuum evaporation process.

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. This waste acid contains phosphoric acid, nitric acid, acetic acid, aluminum, molybdenum and the like.

Each of these components is separated and subjected to a first vacuum evaporation treatment as the first step to recover high purity phosphoric acid. At this time, prior to the first vacuum evaporation process, to remove insoluble solid impurities contained in the mixed waste acid, a filtration process using a microfilter or the like may be selectively performed.

The first vacuum evaporation step uses a difference in boiling points of acids present in the mixed waste acid, and nitric acid and acetic acid contained in the mixed waste acid are evaporated and removed by the method, and only phosphoric acid and metal components remain.

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, the temperature is 140 ° C or more, the vacuum degree is -700mmHg, the temperature is 120 ° C or more, and in the case of the vacuum degree -730mmHg, the temperature is preferably set to 110 ° C or more.

By the vacuum evaporation process, nitric acid and acetic acid contained in the mixed waste acid can be completely removed.

In the 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 further performing a vacuum evaporation treatment on the evaporating liquid containing nitric acid and acetic acid.

Subsequently, a diffusion dialysis treatment is performed on the residual liquid remaining after the vacuum evaporation treatment of the mixed waste liquid to first remove the metal component contained in the residual liquid.

A large amount of metal can be efficiently removed by the diffusion dialysis method. In the present invention, a high-purity phosphoric acid aqueous solution can be obtained 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 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 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.

Next, the dialysis solution obtained after the diffusion dialysis treatment is subjected to ion exchange resin treatment to remove secondary metal components in the dialysis solution to obtain high purity 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 dialysate, but in the case of molybdenum, it exists in the form of an anion complex, so the molybdenum contained in the dialysate 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. Preferably, since the concentration of phosphoric acid contained in the dialysate obtained after the diffusion dialysis treatment is high, a highly acidic cation having a high crosslinking degree It is better to use an exchange resin. Accordingly, the styrene-based strongly acidic cation exchange resin may more preferably have a crosslinking degree of 10% or more, and even more preferably 10-16%. If the crosslinking degree of styrene type strong acid cation exchange resin is higher than 10%, the water content in resin, ion exchange capacity is increased, and oxidation resistance is increased. On the other hand, it is difficult to regenerate after adsorption and easily contaminated by organic matter. . However, in the present invention, since a high concentration of acid solution is treated, when the crosslinking degree is lower than 10%, the resin is oxidized to reduce durability, and the ion exchange capacity is low, which is difficult to treat, which is not preferable. In the present invention, the strong acid resin means a resin that has a strong resistance to acid and retains more ion exchange capacity in a strong acid solution.

As the cation exchange resin, commercially available cation exchange resins can be used.

Moreover, it is preferable to use the styrene type strong acidic anion exchange resin which is excellent in chemical stability and organic pollution resistance as said anion exchange resin. The anion exchange resin is also preferably a styrene-based strong acid anion exchange resin having a crosslinking degree of 10% or more.

The flow velocity S.V. (space velocity) of the dialysate during the ion exchange resin treatment means a value obtained by dividing the waste liquid through-hour by the resin volume and depends on the type of resin. In this invention, it is preferable to use the thing whose S.V. is 2-6. Within the above range, aluminum and molybdenum may be treated at 1 ppm or less, but if it is less than 2 outside the above range, the processing speed may be too slow, resulting in excessive investment of equipment required for a certain amount of waste liquid treatment. And molybdenum are not preferred because they cannot be treated below 1 ppm.

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

Since the aqueous phosphoric acid solution obtained by the ion exchange resin treatment is high purity, but the concentration of phosphoric acid is low, a high concentration of phosphoric acid can be obtained by performing a second vacuum evaporation treatment.

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

By the high-purity recovery method as described above, it is possible to recover high-purity phosphoric acid in which the impurity content is reduced to several ppm levels from the mixed waste acid at a high concentration. The phosphoric acid thus obtained may be recycled into an etching solution, high purity phosphoric acid, various pickling solutions, and the like in the manufacture of a liquid crystal display device.

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  Recovery of high purity phosphoric acid.

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 Acid concentration in residual solution (%) 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 81.0 125 0 0 80.7 -730 100 0.86 0 79.0 110 0 0 82.4 150 0 0 84.1

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.

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 removed by the vacuum evaporation process. It was confirmed that it was completely separated from phosphoric acid. The results are shown in FIGS. 2 and 3.

2 is an IC analysis result showing the contents of nitric acid, acetic acid and phosphoric acid in the evaporated vacuum evaporation, Figure 3 is an IC analysis result showing the contents of nitric acid, acetic acid and phosphoric acid in the residual liquid.

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) obtained after the first vacuum evaporation In residue  For diffuse dialysis treatment

The diffusion dialysis treatment was carried out in the following manner to separate and remove the metal components present in the residual liquid obtained after the first vacuum evaporation treatment of 2).

The first of the remaining liquid and the water flow rate obtained from the vacuum evaporation step 0.97L / Hr · m ^2, while adjusting to an anion exchange membrane dialysis membrane (DSV, ASAHI GLASS Co.) for diffusion dialysis equipment in opposite directions by a boundary (T- 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 was calculated by dividing the amount of the dialysate and the acid recovered in both measuring cylinders after passing through the dialyzer.

The dialysis solution recovered in the diffusion dialysis apparatus was measured using an ion chromatography (ICS-2500, DIONEX) analyzer to measure and analyze the acid concentration in the dialysis solution, and then a recovery rate was obtained. In addition, metal components such as Al and Mo in the dialysate 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 Dialysate - - 65.4 3.11 4.46

As shown in Table 4, as a result of the diffusion dialysis treatment for the residue after the vacuum evaporation treatment, aluminum concentration 289.73mg / kg was lowered to 3.11mg / kg, molybdenum 282.19mg / kg to 4.46mg / kg. By such diffusion dialysis treatment, a dialysis liquid obtained by removing about 98% of the metal components in the residual liquid was obtained.

4) Spread After dialysis  Ion exchange resin treatment on the obtained dialysate

In order to remove the metal component remaining in the dialysate obtained after the diffusion dialysis step of 3), ion exchange resin treatment was carried out as follows.

The dialysate obtained after the diffusion dialysis treatment was treated with a styrene strong acid cation exchange resin (SK1B, manufactured by Mitsubishi), and then passed through a tower containing a strong acid anion exchange resin (A103, manufactured by PuroliteE) to treat an ion exchange resin. At this time, the flow rate of the dialysate was such that the S.V was 2.5.

About the filtrate obtained after the ion exchange resin treatment, the acid concentration in the filtrate was measured and analyzed using an ion chromatography (ICS-2500, DIONEX) analyzer, 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 density(%) Metal ion (mg / kg) Acetic acid nitric acid Phosphoric Acid Al Mo Filtrate obtained after treatment with ion exchange resin - - 68.8 0.11 0.22

As shown in Table 5 above, as a result of performing ion exchange resin treatment on the dialysis solution from which the metal component was first removed by diffusion dialysis treatment, both aluminum and molybdenum were removed to 0.23 ppm or less. From this, it was confirmed that the metal component was completely removed to 1 ppm or less by the ion exchange resin treatment.

5) Secondary vacuum evaporation of remaining filtrate after ion exchange resin treatment

As a result of the ion exchange resin treatment, the metal component was completely removed, but the concentration of phosphoric acid in the filtrate was lowered from 85.4% to about 65.4%. Accordingly, in order to obtain a high concentration of phosphoric acid, a secondary vacuum evaporation process was performed as follows.

After passing through the ion exchange resin step, the filtrate containing 68.8% purified phosphoric acid was placed in 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 was maintained at a temperature of 120 ° C., and the pressure inside the reactor was kept constant at 730 mmHg 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 by plasma spectrometry (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 the second vacuum evaporation - - 85.1 0.15 0.23

As shown in Table 6, the concentration of phosphoric acid was concentrated to 85.1% through a second vacuum evaporation process.

By using the high purity phosphoric acid recovery method according to the present invention, it is possible to recover high purity phosphoric acid in which the impurity content is reduced to several ppm level from the mixed waste acid generated in the liquid crystal display manufacturing process. Thus, the recovered phosphoric acid can be recycled into an etching solution, high purity phosphoric acid, various pickling solutions, and the like in the preparation of the display device.

Claims (9)

Firstly vacuum evaporating the mixed waste acid generated in the liquid crystal display to remove nitric acid and acetic acid in the mixed waste acid; Firstly removing the metal component by diffusion dialysis treatment of the residual liquid remaining after the first vacuum evaporation treatment; Treating the dialysate obtained after the diffusion dialysis with ion exchange resin to remove residual metal components in a second manner; And And performing a second vacuum evaporation process after the ion exchange resin treatment step. A method for recovering high purity phosphoric acid from mixed waste acid generated in a liquid crystal display manufacturing process. The method of claim 1, Wherein said first vacuum evaporation treatment is carried out at a vacuum degree of -650 to -760 mmHg. The method of claim 1, The first vacuum evaporation process is a method for recovering high purity phosphoric acid from the mixed waste acid is carried out at 100 to 160 ℃. The method of claim 1, Wherein said ion exchange resin treatment is performed by treating a cation exchange resin treatment and an anion exchange resin to recover high purity phosphoric acid from mixed waste acid. The method of claim 4, wherein Wherein said cation exchange resin is a styrenic strongly acidic cation exchange resin, and the anion exchange resin is a styrenic strongly acidic anion exchange resin. The method of claim 5, Wherein said styrenic strongly acidic cation exchange resin has a crosslinking degree of at least 10%. The method of claim 5, Wherein said styrenic strongly acidic anion exchange resin has a crosslinking degree of at least 10%. The method of claim 1, Wherein said second 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 performed at 100 to 160 ° C. to recover high purity phosphoric acid.

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