Method for continuously treating high concentration salt wastewater of secondary battery using hydrothermal energy and crystallization method

Abstract

The present invention relates to a method for treating high-concentration salt waste water discharged from a process of producing a positive electrode active material precursor of a secondary battery. The method comprises: a first step of introducing and storing high-concentration salt waste water; a second step of discharging, to the outside of a hydrothermal reaction pipe, high-temperature steam generated while heating the high-concentration salt wastewater stored in the first step by introducing the high-concentration salt wastewater into the hydrothermal reaction pipe; a third step of introducing the high-concentration salt waste water heated in the second step into a carbon dioxide reaction tank and supplying carbon dioxide (CO2) to react with the high concentration salt waste water; a fourth step of producing sodium sulfate crystals by introducing the high-concentration salt wastewater that has reacted with carbon dioxide in the third step into a crystal precipitation tank and cooling same; and a fifth step of filtering and separating the sodium sulfate crystals generated in the fourth step.

Description

Continuous treatment method for high-concentration salt wastewater from secondary batteries using thermal energy and crystallization method

[0001] The proper treatment of high-concentration salt wastewater discharged from processes such as the production of precursors for cathode active materials, which are key materials for secondary batteries, is very important not only for the development of the secondary battery industry but also for the preservation of the ecosystem's water quality environment, and thus, attention is focused on this issue.

[0002] The present invention relates to a technology for providing a treatment method for continuously treating high-concentration salt wastewater discharged from the secondary battery industry, which reduces high-concentration sulfate ions, salinity, etc. based on hydrothermal energy and crystallization, and at the same time constructs a zero-discharge system in which the treated water (filtrate) is reused and recycled as process water, recycled water, desalinated water, etc.

[0003] Looking at the conventional treatment methods for high-concentration salt wastewater in the secondary battery industry, there is a method of connecting it to a sewage treatment plant and a method of first purifying it using electrolysis and then discharging it into the sea. However, these conventional methods are not fundamental solutions, so recently, a method of treating high-concentration salt wastewater by building an evaporative concentration (Mechanical Vapor Recompressor, MVR) system has been attempted. However, the high cost of building and maintaining the treatment facility for this evaporative concentration method is a big burden, and a solution is urgently needed.

[0004] To date, there have been no cases of application of technologies related to the construction of a zero-discharge system through the utilization of hydrothermal energy to induce a supersaturated state that can optimize the crystal growth of sodium sulfate, crystallization technology to precipitate a large amount of high-purity sodium sulfate crystals, and reuse and recycling of treated water (the remaining liquid after precipitation of sodium sulfate crystals).

[0005] Accordingly, there is an increasing need for an invention of a new concept of zero-discharge system that solves the high cost disadvantage of conventional treatment methods for high-concentration salt wastewater in the secondary battery industry, while reducing high-concentration sulfate ions and salinity, and reusing and recycling the treated water as process water, recycled water, desalinated water, etc.

[0006] [Prior Art Literature]

[0007] Registered Patent No. 10-1997528

[0008] Registered Patent No. 10-1137251

[0009] The purpose of the present invention, which was created in accordance with the needs as indicated in the background art, is as follows.

[0010] First, the purpose of the present invention is to provide a new method for continuous treatment of high-concentration salt wastewater from secondary batteries using thermal energy and crystallization.

[0011] Second, another purpose of the present invention is to implement a zero-discharge system at low cost that reduces high concentrations of sulfate ions and salinity contained in salt wastewater, while at the same time reusing and recycling the treated water as process water, recycled water, desalinated water, etc.

[0012] Third, another purpose of the present invention is to provide a new concept of salt wastewater treatment method capable of producing electricity by using steam generated during the process of supplying thermal energy.

[0013] The present invention, which was created to achieve the above-mentioned object, relates to a method for treating high-concentration salt wastewater discharged from a process for producing a precursor of a cathode active material for a secondary battery, and is characterized by including: a first step of introducing and storing high-concentration salt wastewater; a second step of introducing the high-concentration salt wastewater stored in the first step into a hydrothermal reaction tube and heating it, and discharging the generated high-temperature vapor to the outside of the hydrothermal reaction tube; a third step of introducing the heated high-concentration salt wastewater in the second step into a carbon dioxide reaction tank and then supplying carbon dioxide (CO2) to react with the high-concentration salt wastewater; a fourth step of introducing the high-concentration salt wastewater reacted with carbon dioxide in the fourth step into a crystallization tank and then cooling it to produce sodium sulfate crystals; and a fifth step of filtering and separating the sodium sulfate crystals produced in the fourth step.

[0014] The technical effects of the present invention are as follows.

[0015] First, a new continuous treatment method for high-concentration salt wastewater from secondary batteries using thermal energy and crystallization is provided, enabling efficient and simple treatment of high-concentration salt wastewater discharged from the production process of positive electrode active material precursors for secondary batteries.

[0016] Second, the present invention reduces high concentrations of sulfate ions and salinity contained in salt wastewater, and at the same time, the treated water can be reused and recycled as process water, recycled water, desalinated water, etc.

[0017] In other words, if sodium sulfate crystals are separated and obtained from high-concentration salt wastewater through hydrothermal reaction and crystallization, the components and state of the remaining treated water (filtrate) can be utilized as process water or recycled water, and if this is recycled instead of being immediately discharged into rivers or the sea, positive effects can be expected in terms of environmental protection and water resource management.

[0018] Third, electricity can be produced using the steam generated during the thermal energy supply process.

[0019] In other words, instead of immediately discharging the steam generated from the high-concentration salt wastewater heated inside the water heat reactor to the outside air, the high-temperature steam is supplied to a steam turbine generator to produce electricity, and this electricity can be used as the power source required for the salt wastewater treatment process, thereby saving energy and drastically reducing operating costs according to the present invention.

[0020] Figure 1 is a block diagram illustrating a process for treating high-concentration salt wastewater according to the present invention.

[0021] Figure 2 shows sodium sulfate crystals obtained using the thermal energy and crystallization method.

[0022] Figure 3 shows high-purity sodium sulfate powder obtained by drying sodium sulfate crystals.

[0023] Below, the specific implementation process of the present invention is described in more detail.

[0024] A method for treating high-concentration salt wastewater discharged from a process for producing a precursor of a cathode active material for a secondary battery is provided, and as illustrated in FIG. 1, the method includes a process of introducing high-concentration salt wastewater, a process of introducing high-concentration salt wastewater into a hydrothermal reaction tube and performing a hydrothermal reaction (heating), a process of operating a steam turbine generator using steam generated during the hydrothermal reaction and thereby producing electricity, a process of producing a supersaturated sodium sulfate solution by supplying carbon dioxide to the high-concentration salt wastewater heated by the hydrothermal reaction, a process of growing and then obtaining sodium sulfate crystals, and a process of reusing or recycling the remaining filtrate (treated water) after obtaining the sodium sulfate crystals rather than discharging it directly into a river or the sea.

[0025] Let's look at this process in more detail by dividing it into stages.

[0026] (1) Stage 1

[0027] As a process of introducing and storing high-concentration salt wastewater, the high-concentration salt wastewater is temporarily stored in a storage tank before performing the treatment process according to the present invention.

[0028] (2) Stage 2

[0029] This is the process of introducing the high-concentration salt wastewater stored in the first stage into the water-thermal reaction tube and heating it, and then discharging the generated high-temperature steam outside the water-thermal reaction tube.

[0030] High-concentration salt wastewater is continuously supplied into a hydrothermal reaction tube maintaining a temperature range of 250 to 300°C, and a hydrothermal reaction is performed inside the hydrothermal reaction tube for 30 to 60 minutes. If necessary, heat is applied while circulating the high-concentration salt wastewater inside the hydrothermal reaction tube using a circulation pump.

[0031] Through this heating process, high-temperature steam is inevitably generated, and when this high-temperature steam reaches a preset pressure, it is discharged to the outside through a discharge pipe connected to the water heat reactor.

[0032] (2-1) Stage 2-1

[0033] This is the process of generating electricity by operating a steam turbine generator using the high-temperature steam discharged to the outside in the second stage.

[0034] In other words, rather than simply discharging high-temperature steam into the air, electricity is generated by supplying it to a steam turbine generator to rotate the turbine, and the generated electricity can be used as the power required for the treatment process of the present invention.

[0035] The operation of the steam turbine generator is already a commercially available technology, so a separate explanation is omitted.

[0036] (3) Stage 3

[0037] In the second stage, the heated high-concentration salt wastewater is introduced into a carbon dioxide reaction tank, and carbon dioxide (CO2) is supplied to react with the high-concentration salt wastewater.

[0038] In this third step, a supersaturated sodium sulfate (Na2SO4) solution is created through the following reaction in a carbon dioxide reactor that supplies carbon dioxide to the heated, high-concentration salt wastewater.

[0039] (1) 2H20 + 2CO2→ 2H + + 2HCO3 -

[0040] (2) 2NaOH + 2HCO3 - → 2NaHCO3

[0041] (3) 2NaHCO3+ H2SO4→ Na2SO4+ 2CO2+ 2H20

[0042] That is, when carbon dioxide (CO2) is supplied after the hydrothermal reaction, the water (H2O) and carbon dioxide (CO2) in the salt wastewater react primarily to form H + and HCO3 - is generated, and NaOH and HCO3 contained in the salt wastewater - A secondary reaction occurs to produce NaHCO3, and H2SO4 and NaHCO3 contained in the salt wastewater react to produce Na2SO4, CO2, and H2O. Through this process, a supersaturated sodium sulfate (Na2SO4) solution is produced.

[0043] The pH of the salt wastewater solution concentrated and activated using a hydrothermal reaction process is in the range of 9 to 10, and CO2 is supplied into the carbon dioxide reactor to control the pH of the solution inside the carbon dioxide reactor to the range of 7 to 7.5.

[0044] The reason why the pH of the solution inside the carbon dioxide reactor is controlled to be in the range of 7 to 7.5 is because it is the optimal pH for sodium sulfate crystal growth, and the amount of carbon dioxide supplied is appropriately controlled so that the pH inside the carbon dioxide reactor is maintained at 7 to 7.5 during the generation process of the supersaturated sodium sulfate solution.

[0045] (4) Step 4

[0046] In the fourth step, the high-concentration salt wastewater reacted with carbon dioxide is introduced into a crystallization tank and then cooled to produce sodium sulfate crystals.

[0047] That is, sodium sulfate (Na2SO4) that has gone through the third stage After the supersaturated solution is introduced into a crystallization tank maintained at a temperature range of 1 to 5°C, a process of precipitating sodium sulfate crystals is carried out inside the crystallization tank for 12 to 24 hours.

[0048] (5) Step 5

[0049] This is a process of filtering and separating the sodium sulfate crystals generated in the fourth step. The sodium sulfate (Na2SO4) crystals and the remaining filtrate are separated using a 60 to 100 mesh net. The separated sodium sulfate crystals can be seen in Figure 2.

[0050] (5-1) Step 5-1

[0051] This is a process of obtaining high-purity sodium sulfate powder by drying the sodium sulfate crystals obtained in the fifth step at a temperature range of 150 to 200°C for 30 to 60 minutes.

[0052] By drying the sodium sulfate crystals in this way, high-purity sodium sulfate powder can be obtained as shown in Fig. 3.

[0053] (5-2) Step 5-2

[0054] Step 5 involves filtering and separating sodium sulfate crystals, then reusing or recycling the remaining filtrate as process water, recycled water, or desalinated water. In other words, rather than discharging the treated water (filtrate) directly into rivers or the ocean, it is reused as process water, recycled water, or desalinated water for facility operation.

[0055] (5-3) Step 5-3

[0056] This is a process of further purifying the filtrate by adding functional materials such as catalysts, ceramics, and activators, or by using electrolysis, etc., in the process of reusing and recycling the filtrate in step 5-2.

[0057] Below, specific examples of the processing method of the present invention will be examined.

[0058] (1) Example 1

[0059] In this example, the treatment results of high-concentration salt wastewater from secondary batteries, which is being processed in conjunction with a sewage treatment plant, are presented. A continuous treatment method for high-concentration salt wastewater from secondary batteries using hydrothermal energy and crystallization was performed according to the process diagram shown in Figure 1. The concentration of sulfate ions in the introduced salt wastewater was analyzed using ion chromatography, and the results were 68,802.0 mg / L and the salinity was 6.20%. This salt wastewater was introduced into a hydrothermal reaction tube maintained at 250°C and circulated using a circulation pump for 30 minutes to cause a hydrothermal reaction. The solution, which was concentrated and activated using the hydrothermal energy obtained here, was transferred to a separate carbon dioxide reaction tank, and carbon dioxide was supplied for 10 minutes to produce a supersaturated sodium sulfate solution. And the supersaturated sodium sulfate solution was transferred to a crystallization tank maintained at a temperature range of 1 to 5℃ and crystallized for 12 hours. The photograph of the sodium sulfate crystals obtained using this crystallization method is shown in Figure 2. And the sodium sulfate crystals were dried at 150℃ for 30 minutes to obtain high-purity sodium sulfate powder as shown in Figure 3. Meanwhile, the sulfate ion concentration of the filtrate from which the sodium sulfate crystals were separated was 3,950.8 mg / L, the salinity was 0.67%, and the sulfate ion removal rate was 94.2% and the salinity removal rate was 89.2%. And the treated water was reused and recycled as process water, recycled water, desalinated water, etc. and was not discharged. Table 1 shows the results of a water quality test requested from Korea E&C Co., Ltd. and the analysis results for the raw water (inflowed salt wastewater) and treated water.

[0060] Sulfate ion removal rate Salinity removal rate Raw water (inflowed salt wastewater) 68,802.0 mg / L 94.2 % 6.20 % 89.2 % Treated water 3,950.8 mg / L 0.67 %

[0061] (2) Example 2

[0062] In this example, the same high-concentration salt wastewater from a secondary battery as in Example 1 was introduced, and the sulfate ion concentration was analyzed to be 60,096.0 mg / L and the salinity was 5.10%. The procedure is the same as in Example 1 except that the salt wastewater was crystallized in a crystallization tank for 24 hours. In this example, the sulfate ion concentration of the filtrate from which sodium sulfate crystals were separated was 1,455.6 mg / L, the salinity was 0.30%, the sulfate ion removal rate was 97.6%, and the salinity removal rate was 94.1%. In addition, the treated water was reused and recycled as process water, recycled water, desalinated water, etc., and there was no discharge. Table 2 shows the results of analyzing the sulfate ion concentration of the raw water (inflowed salt wastewater) and the treated water, which were tested by Korea E&C Co., Ltd.

[0063] Sulfate ion removal rate Salinity removal rate Raw water (inflowed salt wastewater) 60,096.0 mg / L 97.6 % 5.10 % 94.1 % Treated water 1,455.6 mg / L 0.30 %

[0064] (3) Example 3

[0065] In this example, the concentration of sulfate ions in high-concentration salt wastewater from secondary batteries, which was initially purified by electrolysis and then discharged into the sea, was analyzed to be 33,429.5 mg / L and the salinity was 3.60%. This salt wastewater was introduced into a hydrothermal reaction tube maintained at 300°C and circulated using a circulation pump to cause a hydrothermal reaction for 60 minutes. The solution, which was concentrated and activated using the hydrothermal energy obtained here, was transferred to a separate carbon dioxide reaction tank and carbon dioxide was supplied for 10 minutes to produce a supersaturated sodium sulfate solution. The supersaturated sodium sulfate solution was then transferred to a crystallization tank maintained at a temperature range of 1 to 5°C and crystallized for 12 hours. The sodium sulfate crystals and high-purity sodium sulfate powder obtained using this crystallization method were the same as in Example 1. Meanwhile, the sulfate ion concentration of the filtrate from which the sodium sulfate crystals were separated was 3,555.3 mg / L, the salinity was 0.50%, and the sulfate ion removal rate was 89.3% and the salinity removal rate was 86.1%. In addition, the treated water was reused and recycled as process water, recycled water, desalinated water, etc., and was discharged without discharge. Table 3 shows the test results according to the Korea Environment Corporation's Water Quality Pollution Process Test Standards (National Institute of Environmental Research Notice No. 2022-12), and shows the results of analyzing the sulfate ion concentration of the effluent (inflowed salt wastewater) and the treated water.

[0066] Sulfate ion removal rate Salinity removal rate Effluent (inflowed salt wastewater) 33,429.5 mg / L 89.3 % 3.60 % 86.1 % Treated water 3,555.3 mg / L 0.50 %

[0067] (4) Example 4

[0068] In this example, the same high-concentration salt wastewater from a secondary battery as in Example 3 was introduced, and the sulfate ion concentration was analyzed to be 33,429.5 mg / L and the salinity was 3.60%. The procedure is the same as in Example 3 except that the salt wastewater is crystallized for 24 hours in a crystallization tank. In this example, the sulfate ion concentration of the filtrate from which sodium sulfate crystals were separated was 889.5 mg / L and the salinity was 0.16%. The sulfate ion removal rate was 97.3% and the salinity removal rate was 95.6%. In addition, the treated water was reused and recycled as process water, recycled water, desalinated water, etc., and there was no discharge. Table 4 shows the test results according to the water quality pollution process test standards of the Korea Environment Corporation (National Institute of Environmental Research Notice No. 2022-12), and shows the analysis results for the effluent (inflowed salt wastewater) and the treated water.

[0069] Sulfate ion removal rate Salinity removal rate Effluent (inflowed salt wastewater) 33,429.5 mg / L 97.3 % 3.60 % 95.6 % Treated water 889.5 mg / L 0.16 %

[0070] (5) Example 5

[0071] As a result of conducting an ecotoxicity test after treating the secondary battery high-concentration salt wastewater as in the above examples (Examples 1 to 4) using the treatment method of the present invention, as shown in Table 5, when the average concentration of sulfate ions was 6,500 mg / L or less and the salinity was 1.0% or less, the ecotoxicity value (TU) was 2 or less, and when the average concentration of sulfate ions was 3,000 mg / L or less and the salinity was 0.4% or less, the ecotoxicity value (TU) was 1 or less. This ecotoxicity value (TU) is a test result according to the Korea Environment Corporation's Water Quality Pollution Process Testing Standard (ES04704.1b).

[0072] Sulfate ion salinity Ecotoxicity value Average 6,500 mg / L or less 1.0% or less TU 2 or less Average 3,000 mg / L or less 0.4% or less TU 1 or less

[0073] As described above, the contents of the present invention have been described according to the processing process and embodiments of the present invention, but the protection scope of the present invention is not necessarily strictly limited to the described contents, and it is made clear that various design changes, additions or deletions of known technologies, simple numerical limitations, etc., within the scope that does not change the technical gist of the present invention, also fall within the protection scope of the present invention.

Claims

1. A method for treating high-concentration salt wastewater discharged from the production process of a precursor of a cathode active material for a secondary battery. Step 1: Introducing and storing high-concentration salt wastewater; The second stage is to introduce the high-concentration salt wastewater stored in the first stage into the water heat reactor and heat it, and discharge the high-temperature steam generated therefrom outside the water heat reactor; The third stage is to introduce the heated high-concentration salt wastewater in the second stage into a carbon dioxide reaction tank and then supply carbon dioxide (CO2) to react with the high-concentration salt wastewater; Step 4: In step 4, the high-concentration salt wastewater reacted with carbon dioxide is introduced into a crystallization tank and then cooled to produce sodium sulfate crystals; and, Step 5: filtering and separating the sodium sulfate crystals produced in Step 4; Including, Step 2 is, High-concentration salt wastewater is continuously supplied into a hydrothermal reaction tube maintaining a temperature range of 250 to 300 ℃, and a hydrothermal reaction is performed inside the hydrothermal reaction tube for 30 to 60 minutes. It further includes a second stage, which generates electricity by operating a steam turbine generator using the high-temperature steam discharged to the outside; Step 3 is, In the process of generating a supersaturated sodium sulfate (Na2SO4) solution, the amount of carbon dioxide supplied is controlled so that the pH inside the carbon dioxide reactor is maintained at 7 to 7.

5. By supplying carbon dioxide to the heated high concentration salt wastewater <h2 style=";text-align:left;direction:ltr">(1) 2H2O + 2CO2 → 2H<h2 style=";text-align:left;direction:ltr"> + <h2 style=";text-align:left;direction:ltr"> + 2HCO3<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr">(2) 2NaOH + 2HCO3<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> → 2NaHCO3 (3) 2NaHCO3+ H2SO4→ Na2SO4+ 2CO2+ 2H20 Through the reaction process, a supersaturated solution of sodium sulfate (Na2SO4) is created, Step 4 is, Sodium sulfate (Na2SO4) A continuous treatment method for high-concentration salt wastewater from a secondary battery using thermal energy and a crystallization method, characterized in that a supersaturated solution is introduced into a crystallization tank maintained at a temperature range of 1 to 5°C and then a process of precipitating sodium sulfate crystals for 12 to 24 hours is performed inside the crystallization tank.

2. In paragraph 1, Step 5-1 of obtaining high-purity sodium sulfate powder by drying the sodium sulfate crystals obtained in Step 5 at a temperature range of 150 to 200°C for 30 to 60 minutes; A continuous treatment method for high-concentration salt wastewater from a secondary battery using a crystallization method and a series energy, characterized in that it further includes.

3. In paragraph 2, Step 5-2: After filtering and separating the sodium sulfate crystals in Step 5, the remaining liquid is reused or recycled as process water, recycled water, or desalinated water; A continuous treatment method for high-concentration salt wastewater from a secondary battery using a crystallization method and a series energy, characterized in that it further includes.

4. In paragraph 3, Step 5-3: In the process of reusing or recycling the residue from Step 5-2, a catalyst, ceramic, or activator is added to the residue, or the residue is further purified by electrolysis; A continuous treatment method for high-concentration salt wastewater from a secondary battery using a crystallization method and a series energy, characterized in that it further includes.

5. In any one of paragraphs 1 to 4, Step 5 is, A continuous treatment method for high-concentration salt wastewater from a secondary battery using thermal energy and a crystallization method, characterized by separating sodium sulfate (Na2SO4) crystals and the remaining filtrate using a 60 to 100 mesh screen.

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