KR20100048603A - Method of collecting phosphoric acid from waste solution - Google Patents

Abstract

PURPOSE: A method for collecting phosphoric acid from waste liquid is provided to effectively reduce environmental contamination while improving economical effect by recycling resources after collecting phosphoric acid of high concentration. CONSTITUTION: A method for collecting phosphoric acid from waste liquid includes the following steps: concentration the waste liquid after removing nitric acid and acetic acid from the waste liquid including phosphoric acid, nitric acid, acetic acid and molybdenum; depositing molybdenum sulfide crystals by sucking hydrogen sulfide into the waste liquid; filtering and removing the deposited molybdenum sulfide crystals; and removing remaining hydrogen sulfide by oxidizing the water liquid.

Description

Method of collecting phosphoric acid from waste solution

The present invention relates to a method for recovering phosphoric acid from a waste solution comprising phosphoric acid, nitric acid, acetic acid and molybdenum.

 In the semiconductor device, the process of forming the metal wiring on the substrate is typically a metal film forming process by sputtering; Forming a photoresist pattern by photoresist coating, exposure and development; And a step by an etching process, and a cleaning process before and after an individual unit process, and the like. This etching process refers to a process of leaving a metal film in a selective region using a photoresist mask, and typically, dry etching using a plasma or the like or wet etching using an etching solution is used.

 In such a semiconductor device, in the case of a molybdenum-based metal film containing molybdenum which is generally used as a wiring material for a thin film transistor liquid crystal display (TFT-LCD), it is usually etched with an etching solution mainly containing phosphoric acid, nitric acid, and acetic acid, In the waste etching solution generated here, a large amount of phosphoric acid, nitric acid, acetic acid and molybdenum are present.

Although the waste etching solution differs depending on the reaction conditions and reaction conditions of the etching process, on average, it contains 50 to 70 wt% of phosphoric acid, 2 to 10 wt% of acetic acid, 1 to 10 wt% of nitric acid, and residual amount of water and metal. In particular, since such a large amount of molybdenum metal ions is contained in the waste etching solution as described above, the treatment is difficult and no treatment method has been developed.

Most of the waste etching liquids as described above are entrusted to a treatment company and disposed of by neutralization treatment. In the neutralization treatment, since phosphate ions (PO ₄ ^3- ) form poorly soluble salts with calcium, acetate ions are removed by inducing neutralization precipitation using calcium carbonate or calcium hydroxide, and not removed by neutralization. CH ₃ COO ^-) and nitrate ions (NO ₃ ^-) it is separated by treatment with activated sludge.

However, the neutralization treatment as described above has a disadvantage in that the treatment cost is high due to the generation of a large amount of precipitate and the use of activated sludge. In particular, there is no problem in the waste of resources because there is no process for regenerating components such as expensive phosphoric acid.

In addition to the neutralization treatment as described above, as the method for recovering the acid in the waste etching solution, a membrane separation method, an ion exchange method, a solvent extraction method, or the like may be used. Among them, membrane separation method has advantages of high acid recovery rate and high purity of recovered acid, but it requires a lot of equipment cost such as membrane material and equipment, and complicated operation, and ion exchange method is anion exchange resin or calcium zeolite. Although acid is recovered by using these ion exchange resins in general, the exchange capacity is small, there is a problem that can be applied only to the full concentration of acid. And solvent extraction method is a closed system (Closed System), it is possible to continuously process, the equipment cost is low and the purity of the extract is good, but the extract is included in the phosphate solution, there is a disadvantage that a lot of the waste solution is extracted.

On the other hand, in order to obtain a high purity phosphoric acid can be used a recrystallization method, this method is possible to purify high purity phosphoric acid, but the efficiency is less than 50% and equipped with facilities, there is a disadvantage in difficult crystal growth.

The present invention has been made to solve the above problems of the prior art, and an object thereof is to provide a method for efficiently recovering high concentration of phosphoric acid from a waste solution containing phosphoric acid, nitric acid, acetic acid and molybdenum.

The present invention,

a) distilling under reduced pressure the waste solution containing phosphoric acid, nitric acid, acetic acid and molybdenum at a temperature of 40-200 ° C. to separate and remove nitric acid and acetic acid, and concentrating the waste solution;

b) inhaling hydrogen sulfide into the waste solution obtained in step a) to precipitate molybdenum into molybdenum sulfide crystals;

c) filtering and removing the molybdenum sulfide crystals precipitated in step b); And

d) recovering phosphoric acid from a waste solution comprising phosphoric acid, nitric acid, acetic acid and molybdenum comprising the step of oxidizing the waste solution obtained in step c) to remove residual hydrogen sulfide.

According to the phosphoric acid recovery method of the present invention, it is possible to efficiently recover phosphoric acid from a waste solution containing phosphoric acid, nitric acid, acetic acid and molybdenum at high concentration without additional equipment. Therefore, according to the phosphoric acid recovery method of the present invention, it is possible to obtain not only an economic effect by efficient recycling of resources, but also an effect of reducing environmental pollution.

The present invention,

a) distilling under reduced pressure the waste solution containing phosphoric acid, nitric acid, acetic acid and molybdenum at a temperature of 40-200 ° C. to separate and remove nitric acid and acetic acid, and concentrating the waste solution;

b) inhaling hydrogen sulfide into the waste solution obtained in step a) to precipitate molybdenum into molybdenum sulfide crystals;

c) filtering and removing the molybdenum sulfide crystals precipitated in step b); And

d) a method of recovering phosphoric acid from a waste solution comprising phosphoric acid, nitric acid, acetic acid and molybdenum comprising the step of oxidizing the waste solution obtained in step c) to remove residual hydrogen sulfide.

In the recovery method of the phosphoric acid, the steps b) to d) may be repeatedly performed until the desired purity of the phosphoric acid is obtained. By this repetition, a phosphoric acid solution having a molybdenum concentration of 1 ppm or less can be obtained.

Oxidation of the waste solution of step d) may be performed using ozone or hydrogen peroxide, air or ozone may be inhaled into the waste solution, and hydrogen peroxide may be used as a method of dissolving it in the waste solution.

In the crystal precipitation process of molybdenum sulfide in step b), the hydrogen sulfide is preferably inhaled at 1 to 10 equivalents to 1 equivalent of molybdenum.

Steps b) to d) may be performed at 20 to 40 ° C., and filtration of step c) may be performed using a 0.05 to 1 μm filter. In particular, filtration can be performed more effectively when using filters stacked in multiple layers.

In step a), the concentration of phosphoric acid in the waste solution is preferably concentrated to 80% by weight or more.

By the above-mentioned method of recovering phosphoric acid, a high concentration of phosphoric acid solution of 80% by weight or more containing molybdenum of 1 ppm or less can be recovered.

In addition, the phosphate solution recovered above can be used as a raw material of the etching solution of the metal film, the etching solution containing such a regenerated phosphoric acid solution is almost no difference from the use of commercially available phosphate solution in terms of effect.

In particular, the use of the regenerated phosphoric acid solution in the etching solution of the film containing molybdenum exhibits the same performance as in the case of using a commercially available product.

Therefore, the regenerated phosphoric acid solution prepared by the recovery method of the present invention is used as a raw material of the etching solution used in the formation of the source electrode and the drain electrode of the thin film transistor (TFT) of the flat panel display which mainly use a film containing molybdenum as the electrode material. The quality is comparable.

Hereinafter, the present invention will be described in more detail using examples. However, the following examples are provided to illustrate the present invention, and the present invention is not limited to the following examples and may be variously modified and changed.

Example 1.

Waste etching solution was dissolved by dissolving 250 ppm molybdenum powder to the weight of the etching solution in 1 kg of an etching solution composed of 700 g of phosphoric acid solution (85%), 71 g of nitric acid solution (70%), 100 g of acetic acid solution (100%), and 129 g of water used for TFT-LCD. A waste solution similar to the one was prepared. Distillation under reduced pressure at 100 to 150 ° C separated and removed nitric acid and acetic acid to obtain 83% by weight of highly concentrated phosphoric acid in which 350 ppm molybdenum was dissolved relative to the residual solution weight.

Hydrogen sulfide was injected into the high concentration phosphoric acid solution obtained above to 10 times the equivalent of molybdenum and reacted with molybdenum ions dissolved in the phosphoric acid solution to form molybdenum sulfide crystals. The molybdenum sulfide crystal formed was filtered and removed using a 0.05-0.4 μm filter, followed by oxidizing a high concentration of phosphoric acid solution using ozone (0 ₃ ). The process of injecting hydrogen sulfide, the process of filtering out molybdenum sulfide crystals by filtration, and the process of oxidizing with ozone were repeated three times to obtain results as shown in Table 1 below.

Example 2.

Waste etching solution was dissolved by dissolving 300 ppm molybdenum powder in 1 kg of etching solution consisting of 700 g of phosphoric acid solution (85%), 71 g of nitric acid solution (70%), 100 g of acetic acid solution (100%) and 129 g of water used for TFT-LCD. A waste solution similar to the one was prepared. Distillation under reduced pressure at 100 to 150 ° C separated and removed nitric acid and acetic acid to obtain 83% by weight of high concentration of phosphoric acid in which 410 ppm molybdenum was dissolved relative to the residual solution weight.

Hydrogen sulfide was injected into the high concentration phosphoric acid solution obtained above to 10 times the equivalent of molybdenum and reacted with molybdenum ions dissolved in the phosphoric acid solution to form molybdenum sulfide crystals. The molybdenum sulfide crystal formed was filtered and removed using a 0.05-0.4 μm filter, followed by oxidizing a high concentration of phosphoric acid solution using ozone (0 ₃ ). The process of injecting hydrogen sulfide, the process of filtering out molybdenum sulfide crystals by filtration, and the process of oxidizing with ozone were repeated three times to obtain results as shown in Table 1 below.

Example 3.

Waste etching solution was dissolved by dissolving 400 ppm molybdenum powder by weight of the etching solution in 1 kg of an etching solution consisting of 700 g of phosphoric acid solution (85%), 71 g of nitric acid solution (70%), 100 g of acetic acid solution (100%), and 129 g of water used for TFT-LCD. A waste solution similar to the one was prepared. Distillation under reduced pressure at 100 to 150 ° C separated and removed nitric acid and acetic acid to obtain 83% by weight of highly concentrated phosphoric acid in which 550 ppm molybdenum was dissolved relative to the residual solution weight.

Hydrogen sulfide was injected into the high concentration phosphoric acid solution obtained above to 10 times the equivalent of molybdenum and reacted with molybdenum ions dissolved in the phosphoric acid solution to form molybdenum sulfide crystals. The molybdenum sulfide crystal formed was filtered and removed using a 0.05-0.4 μm filter, followed by oxidizing a high concentration of phosphoric acid solution using ozone (0 ₃ ). The process of injecting hydrogen sulfide, the process of filtering out molybdenum sulfide crystals by filtration, and the process of oxidizing with ozone were repeated three times to obtain results as shown in Table 1 below.

No. Before treatment Treated solution Phosphate solution (85%) Nitric acid solution (70%) Acetic acid solution (100%) Mo (relative to gross weight of phosphoric acid, nitric acid and acetic acid) Concentration of phosphoric acid Mo Example 1 700 g 71 g 100 g 250 ppm 83% by weight Less than 1ppm Example 2 700 g 71 g 100 g 300 ppm 82% by weight Less than 1ppm Example 3 700 g 71 g 100 g 400 ppm 80 wt% Less than 1ppm

Test Example 1.

Based on the total weight of the composition, an etching solution 1 containing 60 to 70 wt% of the phosphoric acid solution recovered in Example 1, 2 to 10 wt% of nitric acid, 1 to 10 wt% of acetic acid, and a residual amount of water was prepared. In addition, except that the phosphoric acid solution of the components of the etching solution 1 was replaced with a commercial product, an etching solution 2 was prepared with the same components and contents.

A test piece was prepared by depositing a Mo single film on a glass substrate. The test pieces were etched by the spray method using the etching solutions 1 and 2 and photographed with a scanning electron microscope (SEM) (FIGS. 1 and 2).

As shown in FIGS. 1 and 2, an etching solution prepared by etching Mo single layer using etching solution 1 containing the phosphoric acid solution recovered by the method of the present invention (FIG. 1) and commercially available phosphoric acid. In the case where the Mo single film was etched with 2 (FIG. 2), the same result was shown that there is no division.

FIG. 1 is an SEM image showing a result of etching a Mo single layer using the etching solution 1 including the regenerated phosphoric acid solution recovered in Example 1 of the present invention.

FIG. 2 is an SEM image showing a result of etching a Mo single film using an etching solution 2 containing a commercial phosphoric acid solution.

Claims (6)

a) distilling under reduced pressure the waste solution containing phosphoric acid, nitric acid, acetic acid and molybdenum at a temperature of 40-200 ° C. to separate and remove nitric acid and acetic acid, and concentrating the waste solution; b) inhaling hydrogen sulfide into the waste solution obtained in step a) to precipitate molybdenum into molybdenum sulfide crystals; c) filtering and removing the molybdenum sulfide crystals precipitated in step b); And d) recovering phosphoric acid from a waste solution comprising phosphoric acid, nitric acid, acetic acid and molybdenum comprising oxidizing the waste solution obtained in step c) to remove residual hydrogen sulfide. The method of claim 1, wherein the steps b) to d) are repeated until the desired purity of the phosphoric acid is obtained. The method of claim 1, wherein the oxidation of the waste solution of step d) is carried out using air, ozone or hydrogen peroxide. The method for recovering phosphoric acid from a waste solution comprising phosphoric acid, nitric acid, acetic acid and molybdenum. The method of claim 1, wherein the steps b) to d) is carried out at 20 ~ 40 ℃ a method for recovering phosphoric acid in a waste solution containing phosphoric acid, nitric acid, acetic acid and molybdenum. The method of claim 1, wherein the filtration of step c) is carried out using a 0.05 ~ 1㎛ filter for recovering phosphoric acid from the waste solution containing phosphoric acid, nitric acid, acetic acid and molybdenum. The method for recovering phosphoric acid from a waste solution comprising phosphoric acid, nitric acid, acetic acid and molybdenum according to claim 1, wherein the concentration of the phosphoric acid in the waste solution is 80% or more in the step a).

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