Method for treating by-product sodium sulfate waste liquid

Abstract

The present invention relates to a method for treating a by-product sodium sulfate waste liquid generated in the secondary battery industry. More specifically, for the treatment of by-product sodium sulfate generated during the recovery of valuable metals, solid-phase sodium sulfate can be electrolyzed to produce sulfuric acid and sodium hydroxide in an environmentally friendly manner, of which sulfuric acid is converted into solid calcium sulfate or calcium carbonate through a separate treatment means.

Description

Method for treating byproduct gallwort wastewater

[0001] The present invention relates to a method for treating waste liquid from byproduct sodium sulfate generated in the secondary battery industry. More specifically, for the treatment of byproduct sodium sulfate generated during the recovery of valuable metals, sulfuric acid and sodium hydroxide can be produced in an environmentally friendly manner by electrolyzing solid sodium sulfate (sodium sulfate), and the sulfuric acid is converted into a solid form of calcium sulfate or calcium carbonate through a separate treatment means.

[0002] Wet processes for metal recovery generally involve the steps of leaching, precipitation, neutralization, and separation. Sulfuric acid is the most commonly used leaching solvent. After leaching metal components with sulfuric acid, a precipitation method is employed to remove impurities from the solution or to recover the target component; in this case, a large amount of alkali (NaOH) is used. Additionally, sodium hydroxide is used as a neutralizing agent when neutralizing the solution to facilitate wastewater treatment or separation processes. For these reasons, high concentrations of sodium sulfate (Na2SO4) wastewater are generated in the intermediate or post-process wastewater of wet processes.

[0003] Recently, in addition to existing wet smelting plants, a large amount of sodium sulfate waste is being generated in the process of recovering valuable metals such as Mn, Co, Ni, and Li from lithium batteries. In other words, the manufacturing process of lithium secondary batteries additionally involves a process of recovering valuable metals such as nickel, cobalt, and manganese as shown in Reaction Equation 1 below, and sodium sulfate waste is generated during this process.

[0004] (Ni, Co, Mn)2SO4 + 2NaOH → Na2SO4 + 2(Ni, Co, Mn)OH … … <Reaction Equation 1>

[0005] To recover 1 ton of nickel, manganese, and cobalt, approximately 13 tons of sodium sulfate waste liquid with a concentration of 20–30% is generated, and theoretically, 1.93 tons of sodium sulfate is generated in the process of manufacturing 1 ton of lithium carbonate. In addition, a large amount of sodium sulfate waste liquid is generated in the battery precursor manufacturing process because sodium hydroxide is used to obtain nickel, cobalt, and manganese hydroxides, and in particular, 12.3 tons of sodium sulfate is generated when manufacturing lithium hydroxide, a high-nickel battery precursor, using 1 ton of lithium.

[0006] In China, zero-discharge facilities are being constructed to recover Glauber's salt from wastewater and reuse it domestically; however, in Korea, reusing Glauber's salt containing trace heavy metals recovered from wastewater in food, paper, and dyeing processes is difficult due to domestic sentiment. Even if only pure Glauber's salt were recovered, the amount discharged would exceed 30 to 50 times the amount consumed domestically. Even if it were disposed of as waste salt, it is virtually impossible to construct a landfill capable of accommodating nearly 1 million tons of waste salt annually, and the secondary problem of leachate caused by its easily dissolving nature remains an unavoidable challenge.

[0007] Furthermore, battery waste liquid containing edible weeds has recently become a major issue as its discharge into natural ecosystems inhibits material transport across cell membranes, thereby hindering the spawning and growth of fish and other organisms; therefore, treatment measures for this are urgently needed.

[0008] As a method to treat such sodium sulfate wastewater, it is possible to process it using the conventional evaporation-distillation method or recover 96% pure Na2SO4 through an evaporation-crystallization process. However, processing using these methods requires high energy costs during the evaporation concentration process, and there are significant difficulties in recycling the recovered crystalline Na2SO4.

[0009] For Na2SO4 to be recycled for use as detergents or dyes, it must meet strict quality standards; however, the aforementioned recycled products are difficult to use because meeting these standards is challenging due to the influence of impurities. Furthermore, since the Na2SO4 generated during the process can cause further environmental pollution, appropriate disposal measures are required.

[0010] Electro-membrane technologies such as electrodialysis (ED) and bipolar membrane electrodialysis (BMED) are attracting attention as a way to properly treat and recycle such Na2SO4 waste liquid, but this is also not satisfactory.

[0011] Therefore, there is a need for a method to convert the byproduct Glauber's salt into sodium hydroxide and sulfuric acid, which have relatively high added value, and there is a demand for the development of a process that can carry out this conversion in a simple and environmentally friendly manner.

[0012] [Prior Art Literature]

[0013] [Patent Literature]

[0014] (Patent Document 1) Korean Registered Patent No. 10-0693943 (Registration Date: March 6, 2007)

[0015] (Patent Document 2) Korean Published Patent No. 10-2000-0060533 (Publication Date: Oct. 16, 2000)

[0016] (Patent Document 3) Korean Registered Patent No. 10-2686164 (Registration Date: July 15, 2024)

[0017] (Patent Document 4) Korean Published Patent No. 10-2024-0132580 (Publication Date: September 4, 2024)

[0018] (Patent Document 5) Japanese Published Patent No. Hei 5-214572 (Published on Aug. 24, 1993)

[0019] [Non-patent literature]

[0020] (Non-patent literature 1) Jo Yeon-cheol et al., “Electro-membrane application for regeneration of NaOH and H2SO4 from Na2SO4 waste liquid generated in metal recovery process”, Resources Recycling, Vol. 31, No. 5, 2022, 3-19.

[0021] (Non-patent Literature 2) Jo Yeon-cheol et al., “Study on the Treatment and Recovery of Sodium Sulfate Generated During the Recovery of Valuable Metals (Ni, Co, Mn, Li) from Waste Lithium Batteries (LIBs)”, Korean Journal of Metals and Materials, Vol. 62, No. 4 (2024) pp.275-283.

[0022] The present invention was devised to solve the above problems and aims to provide a simple and eco-friendly process that utilizes solid sodium sulfate to produce sulfuric acid and sodium hydroxide from byproduct sodium sulfate waste liquid.

[0023] To solve the above problem, the present invention provides a method for treating byproduct sodium sulfate waste liquid generated in the secondary battery industry, comprising: (a) a step of crystallizing sodium sulfate in the byproduct sodium sulfate waste liquid; (b) a step of dissolving the crystallized solid sodium sulfate in water in an anode tank (100) to produce an aqueous sodium sulfate solution; (c) an electrolysis step of receiving the aqueous sodium sulfate solution and separately producing a mixed aqueous solution containing sulfuric acid (Na2SO4 + H2SO4) and sodium hydroxide through an electrolysis reaction; and (d) a step of separately discharging the mixed aqueous solution containing sulfuric acid and sodium hydroxide produced through the electrolysis reaction.

[0024] The aqueous sodium sulfate solution prepared in step (b) above undergoes a separate purification process step prior to step (c).

[0025] The above purification process step (b-1) includes removing impurities in sodium sulfate through an ion exchange reaction.

[0026] The electrolytic cell (200) of the above (c) electrolysis step has a structure including an anode, a cathode, and a diaphragm separating them, and the sodium sulfate aqueous solution is supplied to the anode section and discharged in the state of an aqueous solution mixed with sulfuric acid, and sodium hydroxide is generated at the cathode section.

[0027] The electrolytic cell (210) of the above (c) electrolysis step is structured to have an anode and a cathode and two diaphragms between them, and the sodium sulfate aqueous solution is supplied to an intermediate chamber between the diaphragms, and is configured to generate sulfuric acid (H2SO4) in the anode chamber and sodium hydroxide (NaOH) in the cathode chamber and discharge them, respectively, through separate outlets of the electrolytic cell, and the sodium sulfate aqueous solution supplied to the intermediate chamber is discharged as a mixed aqueous solution containing some sulfuric acid.

[0028] The mixed aqueous solution (Na2SO4 + H2SO4) discharged from the anode or intermediate chamber is separated by removing sulfuric acid through a separate sulfuric acid treatment means (300) at the downstream end, and the sodium sulfate aqueous solution remaining after sulfuric acid treatment is supplied back to the step of preparing the sodium sulfate aqueous solution in step (b).

[0029] The above sulfuric acid treatment means (300) may select one or more of the methods of treatment by ion exchange reaction or treatment by adding a chemical.

[0030] The above ion exchange reaction is characterized by converting sulfuric acid into sodium sulfate through the exchange of hydrogen ions and sodium ions.

[0031] The above-mentioned drug is characterized by being a drug that dissolves in water to generate hydroxide ions capable of neutralizing hydrogen ions in sulfuric acid, and simultaneously reacts with sulfate ions to form a crystalline phase in an aqueous solution.

[0032] The above-mentioned drug is characterized as being one of Ca(OH)2, CaO, or CaCO3.

[0033] The total concentration of the remaining drug component dissolved in the above aqueous solution is 0.02M or less.

[0034] The above residual drug components are characterized by adding means to remove them by applying one or more of CO2 or ion exchange resins.

[0035] The above step (a) is characterized by being crystallized by a low-temperature crystallization method.

[0036] The above step (a) is characterized by being crystallized by a high-temperature evaporative drying method.

[0037] The sodium hydroxide generated in step (d) above is circulated to an electrolytic decomposition tank with a separate cathode tank, characterized by separating and discharging a portion of the sodium hydroxide generated at the desired concentration and supplying additional water corresponding to the amount consumed.

[0038] As described above, by using an electrolysis device instead of an electrodialysis device, the present invention can simplify the process and recover or process byproduct sodium sulfate in an environmentally friendly manner.

[0039] In addition, since the present invention allows sulfuric acid to be converted into a solid form of calcium sulfate or calcium carbonate through a sulfuric acid treatment means, waste acid can be reduced and energy consumption due to the concentration process can be reduced.

[0040] Figure 1 is a graph showing the solubility characteristics of Na2SO4 according to temperature.

[0041] FIG. 2 is a process schematic diagram of a method for treating byproduct sodium sulfate waste liquid according to an embodiment of the present invention.

[0042] FIG. 3 is a process schematic diagram of a method for treating byproduct sodium sulfate waste liquid according to another embodiment of the present invention.

[0043] FIG. 4 is a process schematic diagram of a method for treating byproduct sodium sulfate waste liquid according to another embodiment of the present invention.

[0044] Figure 5 is a graph showing the results of an experiment confirming the removal of sulfuric acid from a mixed solution of aqueous sulfuric acid and sodium hydroxide. (a) Temperature 25℃ (b) Temperature 50℃

[0045] FIG. 6 is a schematic diagram of the process when a diaphragm-type three-compartment electrolytic cell is used in a method for treating byproduct sodium sulfate waste liquid according to one embodiment of the present invention.

[0046] The present invention will be described in detail below with reference to FIGS. 1 to 6.

[0047] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. Furthermore, since the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the invention and do not represent all of the technical spirit of the invention, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0048] In the manufacturing of lithium batteries for the secondary battery industry, processes such as producing lithium hydroxide from lithium sulfate (Li2SO4 + 2NaOH → Na2SO4 + 2LiOH) or recovering valuable metals such as nickel, cobalt, and manganese are involved, and the waste generated from these processes is sodium sulfate. Since it is produced as a byproduct, it is called 'byproduct sodium sulfate'.

[0049] Sodium sulfate (Na2SO4) is commonly referred to as "mangcho." Its anhydrous form (or anhydrous salt) is a colorless crystal with the chemical formula Na2SO4. It dissolves in 100g of water at 0°C (about 5g) and 100°C (about 42g), but it does not dissolve in alcohol. Sodium sulfate containing water exists in decahydrate (Na2SO4·10H2O) and heptahydrate (Na2SO4·7H2O). The term "mangcho" originates from a term in traditional Korean medicine and is a crystal obtained by processing and purifying Mirabilite, a mineral belonging to the Mangcho group of sulfate minerals.

[0050] Figure 1 shows the solubility characteristics of Na2SO4 according to temperature; Na2SO4 exhibits maximum solubility at 32°C and subsequently tends to gradually decrease as the temperature increases (see https: / / commons.wikimedia.org / wiki / File:Na2SO4_Solubility.png). That is, at temperatures below 32°C, Na2SO4 forms a hydrated solid surrounded by 10 H2O molecules (Na2SO4·10H2O). When the solution is heated, water dissolves, and Na + and SO4 2- It separates into ions.

[0051] The present invention is characterized by crystallizing the byproduct waste liquid of sodium sulfate generated during the recovery of valuable metals from lithium batteries to produce a solid state, and then reprocessing it through an electrolysis reaction to produce sulfuric acid and sodium hydroxide in an environmentally friendly manner, wherein the sulfuric acid is converted into a byproduct in the form of calcium sulfate or calcium carbonate through a separate treatment means.

[0052] FIG. 2 is a process schematic diagram of a method for treating byproduct sodium sulfate waste liquid according to an embodiment of the present invention.

[0053] Specifically, the present invention relates to a method for treating byproduct sodium sulfate waste liquid generated in the secondary battery industry, comprising: (a) a step of crystallizing sodium sulfate (Na2SO4) in the byproduct sodium sulfate waste liquid; (b) a step of preparing an aqueous sodium sulfate solution by dissolving the crystallized solid sodium sulfate in water in an anode tank (100); (c) an electrolysis step of receiving the aqueous sodium sulfate solution and separately producing a mixed aqueous solution containing sulfuric acid (Na2SO4 + H2SO4) and sodium hydroxide through an electrolysis reaction; and (d) a step of separately discharging the mixed aqueous solution containing sulfuric acid and sodium hydroxide produced through the electrolysis reaction.

[0054] In particular, the technical features lie in the use of low-temperature crystallization or high-temperature evaporative drying methods to crystallize solid sodium sulfate, and the recovery of sulfuric acid by converting it into various solid sulfate forms using sulfuric acid treatment methods. Therefore, low-value byproduct sodium sulfate can be simply recycled in an environmentally friendly manner.

[0055] Generally, a large amount of sodium sulfate waste liquid is generated in wet processes for recovering valuable metals such as Mn, Co, Ni, and Li from lithium batteries. There are various crystallization methods to crystallize this into a solid, and in the present invention, low-temperature crystallization and high-temperature evaporative drying were used.

[0056] Low-temperature crystallization is the simplest method and involves slowly cooling a hot, saturated solution. As the solution cools, its ability to retain dissolved substances decreases, leading to the formation of crystals. This method is widely used in the chemical industry and is characterized by its ability to be effectively carried out in a crystallization reactor. Additionally, high-temperature evaporative drying is a crystallization method that induces a change in the solution's concentration by evaporating the solvent; this method is also simple and common.

[0057] The above crystallization method has the advantages of using only about 30 to 50 percent of the energy compared to traditional separation processes, having a simple process configuration, and low equipment, and in particular, can obtain high-purity products.

[0058] In addition, known electrochemical methods for producing sulfuric acid and sodium hydroxide mainly include electrodialysis and electrolysis.

[0059] Since electrodialysis is a physical ion separation process rather than a chemical treatment, it can be considered a method capable of efficiently decomposing Na2SO4 with lower energy consumption compared to electrolysis; however, electrodialysis efficiency may decrease in high-concentration Na2SO4 solutions, and the performance and durability of the ion exchange membrane can affect the long-term process. Additionally, it has disadvantages such as high initial equipment costs and the need for membrane fouling and maintenance.

[0060] Meanwhile, electrolysis is a chemical process that uses electrical energy to decompose compounds and obtain desired substances; this process can also be used in the lithium battery recycling industry and is particularly effective for recovering sulfuric acid and sodium hydroxide through the decomposition of Na2SO4.

[0061] Accordingly, the inventor has invented an electrolysis method comprising the following steps for treating byproduct sodium sulfate generated during the recovery of valuable metals from lithium batteries. With reference to FIGS. 2 to 4 and FIGS. 6, the configuration and operation of the electrolysis method according to the present invention will be explained step by step as follows.

[0062] (a) Step

[0063] In the present invention, sodium sulfate is crystallized in the waste liquid of byproduct sodium sulfate using the low-temperature crystallization or high-temperature evaporative drying method described above. This allows for the simple precipitation of solid sodium sulfate by utilizing the solubility characteristics of Na2SO4.

[0064] (b) Step and (b-1) Step

[0065] In the anode tank (100), the solid sodium sulfate is dissolved in water to produce a 30% aqueous solution of sodium sulfate (sodium sulfate). Since process efficiency increases with increasing concentration, it is necessary to increase the concentration of sodium sulfate to the saturation level as much as possible.

[0066] In addition, a separate purification process step (b-1) utilizing an ion exchange reaction can be added to remove impurities from the above aqueous solution of sodium sulfate. It is preferable to use an ion exchange resin for this purpose.

[0067] (c) Step

[0068] The above sodium sulfate aqueous solution is supplied, and a mixed aqueous solution containing sulfuric acid (Na2SO4 + H2SO4) and sodium hydroxide are separately prepared through an electrolysis reaction.

[0069] In the present invention, the electrolytic cell (200) of the electrolysis step has a structure including an anode, a cathode, and a diaphragm separating them, and an aqueous sodium sulfate solution is supplied to the anode section and discharged in the state of an aqueous solution mixed with sulfuric acid, and sodium hydroxide is produced at the cathode section.

[0070] The anode received in the anode portion comprises a substrate of titanium, zirconium, niobium, tantalum, or tungsten, or an alloy mainly composed of one or more of these metals, and an electrocatalytically active material, such as one or more platinum group metals, alloys of said metals, such as platinum, rhodium, iridium, ruthenium, osmium, and palladium, and / or oxides or a coating of oxides.

[0071] Additionally, the cathode accommodated in the cathode portion may comprise a metal substrate coated with at least one platinum group metal and / or at least one platinum group metal oxide to reduce hydrogen overpotential. Examples of the metal substrate may include ferrous metals such as iron, or preferably non-ferrous metals such as copper or molybdenum, or alloys of these metals. However, the metal substrate more preferably comprises nickel or a nickel alloy. The metal substrate of the cathode may be made of nickel or a nickel alloy, or may comprise a core of other metals, such as iron or steel, or copper, and an outer surface of nickel or a nickel alloy.

[0072] (d) Step

[0073] This is a step of separately discharging the mixed aqueous solution containing sulfuric acid and sodium hydroxide generated through the above electrolysis reaction.

[0074] In addition, the mixed sodium sulfate aqueous solution and sulfuric acid aqueous solution (0.5~10% concentration) discharged from the anode section are separated by passing through a separate sulfuric acid treatment means (300) at the downstream end to remove the sulfuric acid, and the sodium sulfate aqueous solution remaining after the sulfuric acid has been treated is recirculated to the anode tank that produces the sodium sulfate aqueous solution in step (b). This aqueous solution can play an auxiliary role in resaturating the sodium sulfate in the anode tank, thereby allowing the saturation concentration of the sodium sulfate aqueous solution to be easily controlled.

[0075] In addition, the sodium hydroxide generated in step (d) above can be circulated to an electrolytic cell with a separate cathode tank (not shown), so that a portion of the sodium hydroxide generated at the desired concentration is separated and discharged, and additional water corresponding to the amount consumed can be supplied.

[0076] Below, we will examine the sulfuric acid treatment methods in detail.

[0077] As illustrated in FIG. 2, the sulfuric acid treatment means (300) can be treated by an ion exchange reaction. The ion exchange reaction is characterized by converting sulfuric acid into sodium sulfate through the exchange of hydrogen ions and sodium ions.

[0078] Generally, ion exchange reactions can be classified into methods utilizing ion exchange resins and methods utilizing ion exchange membranes. In the method utilizing ion exchange resins, Na is attached to the functional groups (sulfonic acid groups) of the cation exchange resin. + H in a state where ions are attached + Ions are adsorbed, and Na + H in a reaction where ions are desorbed + It removes ions. Another method utilizing ion exchange membranes uses electrodialysis to selectively allow only one of the hydrogen or sodium ions to pass through, thereby H + Separate ions.

[0079] In addition, as illustrated in FIG. 3, the sulfuric acid treatment means (300) is characterized by treatment with a chemical, and the chemical may be selected to be one that dissolves in water to generate hydroxide ions capable of neutralizing hydrogen ions in sulfuric acid, and simultaneously reacts with sulfate ions to form a crystalline phase in an aqueous solution. It is preferable that the total concentration of the chemical component dissolved and remaining in the aqueous solution be 0.02M or less. According to the following reaction equation 2, most of the remaining chemical component contains CaSO4.

[0080] That is, Ca + Cations such as are added to precipitate it in the form of solid calcium sulfate (CaSO4), converting it into a byproduct. The above Ca + Examples of compounds with cations such as Ca(OH)2, CaO, and CaCO3.

[0081] For example, in the case of Ca(OH)2, the reaction equation is as follows.

[0082] H2SO4 + Ca(OH)2 → CaSO4(s) + 2H2O … … <Reaction Equation 2>

[0083] Afterward, carbon dioxide (CO2) can be injected to remove unreacted Ca and convert it into calcium carbonate (CaCO3) (see reaction equation 3 below). Alternatively, instead of injecting CO2, the remaining unreacted Ca can be removed by applying an ion exchange resin that utilizes an ion exchange reaction.

[0084] Ca + + H2O + CO2 → CaCO3(s) + H2… … <Reaction Equation 3>

[0085] FIG. 4 is a process schematic diagram for a method of treating byproduct sodium sulfate waste liquid according to another embodiment of the present invention, wherein the residual chemical component (which is H remaining in the solution) in the process of FIG. 3 + , Ca 2+ , OH - , SO4 - The present invention relates to a treatment method comprising means for removing unreacted Ca by injecting CO2 into a chemical (meaning a drug containing CaSO4, etc., generated after reaction with the etc.) and applying an ion exchange resin together.

[0086] Through these steps, sulfuric acid is treated and completely removed. The experimental results regarding removal are shown in Figure 5.

[0087] Experimental Example: Sulfuric acid removal test from a mixed solution using Ca(OH)2

[0088] To remove sulfuric acid from a mixed solution of aqueous sulfuric acid and sodium hydroxide produced through an electrolysis reaction, calcium hydroxide (Ca(OH)2) was selected as the chemical and injected at various molar concentrations of 0.487 M, 0.500 M, 0.513 M, and 0.550 M.

[0089] 500 mL of this mixed solution contains 1.97 M Na2SO4 and 0.5 M H2SO4. When the chemical reaction was observed over time by adding the chemicals and stirring at a speed of 540 rpm, at a temperature of 25℃, when 1.10 times (0.550 M) of the chemicals compared to the theoretical amount was added, the pH value changed rapidly (7.5 minutes) from acidic (pH 4) to basic (pH 10) (see Fig. 5, (a)), and this curve indicates that the sulfuric acid was completely removed.

[0090] A similar pattern was observed at 50°C, and although there were slight differences in the amount of chemical added and the reaction time, it was confirmed that sulfuric acid was completely removed. Although sulfuric acid could be removed even when the chemical was added at a lower molar concentration (0.500M, 0.513M) compared to 25°C, the removal time took 17 minutes and 41 minutes (see Fig. 5, (b)).

[0091] In addition, as shown in FIG. 6, for efficient electrolysis of byproduct magma according to the present invention, a diaphragm-type three-compartment electrolytic decomposition cell (210) may be used instead of the electrolytic cell (200) of the (c) electrolysis step.

[0092] This structure is configured such that an anode and a cathode are installed inside the main body of the electrolytic cell (210), and two diaphragms are installed between the anode and the cathode. The main body of the electrolytic cell is divided into three compartments: an anode room, an intermediate room, and a cathode room. In this electrolytic cell, an aqueous sodium sulfate solution is supplied to the intermediate room between the diaphragms, and sulfuric acid (H2SO4) is produced at the anode and sodium hydroxide (NaOH) is produced at the cathode, and each is discharged through a separate outlet of the electrolytic cell. The aqueous sodium sulfate solution supplied to the intermediate room is discharged as a mixed aqueous solution containing some sulfuric acid.

[0093] The above intermediate chamber is configured by installing two cation exchange membranes in close proximity and configuring the two cation exchange membranes in the form of microchannels, thereby minimizing the difference in inter-electrode distance compared to conventional electrolytic cells and preventing an increase in power consumption. If necessary, a pH control device, such as a separate chemical injection device, can be additionally included in the piping to control the pH of the intermediate chamber.

[0094] In addition, the mixed aqueous solution (Na2SO4 + H2SO4) containing sulfuric acid discharged from the above intermediate room can also have the sulfuric acid removed by passing through a separate sulfuric acid treatment means (300) at the downstream end.

[0095] Therefore, the electrolysis process of Na2SO4 as described in the present invention is highly useful in that it can process the remaining Na2SO4 solution after purifying metals recovered from batteries and convert it into a recyclable form. In particular, since the sulfuric acid separated by decomposing Na2SO4 using only physical electrical energy without the addition of chemicals can be treated as a byproduct and high-purity NaOH can also be produced, it is considered environmentally friendly and suitable for the utilization of circular resources.

[0096] The electrolysis process, which includes the steps described above, is a chemical process that utilizes electrical energy and can be used in various industries such as metal refining, hydrogen production, and water treatment, in addition to lithium battery recycling.

[0097] Although exemplary embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

1. A method for treating byproduct sodium sulfate waste liquid generated in the secondary battery industry, (a) A step of crystallizing sodium sulfate in byproduct sodium sulfate waste liquid; (b) a step of preparing an aqueous sodium sulfate solution by dissolving the crystallized solid sodium sulfate in water in the anode tank (100); (c) an electrolysis step of supplying the above sodium sulfate aqueous solution and separating and producing a mixed aqueous solution containing sulfuric acid (Na2SO4 + H2SO4) and sodium hydroxide, respectively, through an electrolysis reaction; and (d) a step of separately discharging a mixed aqueous solution containing sulfuric acid and sodium hydroxide generated through the above electrolysis reaction; comprising a method for treating byproduct sodium hydroxide waste liquid 2. In Claim 1, (b-1) A method for treating byproduct sodium sulfate waste liquid comprising the sodium sulfate aqueous solution prepared in step (b) above undergoing a separate purification process step prior to step (c) above.

3. In Claim 2, The above (b-1) purification process step is a method for treating byproduct sodium sulfate waste liquid, which removes impurities in sodium sulfate through an ion exchange reaction.

4. In Claim 1, The electrolytic cell (200) of the above (c) electrolysis step has a structure including an anode and a cathode and a diaphragm separating them, and a sodium sulfate aqueous solution is supplied to the anode section and discharged in the state of an aqueous solution mixed with sulfuric acid, and sodium hydroxide is generated at the cathode section, a method for treating byproduct sodium sulfate waste liquid.

5. In Claim 1, The electrolytic cell (210) of the above (c) electrolysis step is structured to have an anode and a cathode and two diaphragms between them, and the sodium sulfate aqueous solution is supplied to an intermediate chamber between the diaphragms, and is configured to generate sulfuric acid (H2SO4) in the anode chamber and sodium hydroxide (NaOH) in the cathode chamber and discharge them respectively through separate outlets of the electrolytic cell, and the sodium sulfate aqueous solution supplied to the intermediate chamber is discharged as a mixed aqueous solution containing some sulfuric acid, comprising a method for treating byproduct sodium sulfate waste liquid.

6. In claim 4 or claim 5, A method for treating byproduct sodium sulfate waste liquid, wherein the mixed aqueous solution (Na2SO4 + H2SO4) discharged from the anode or intermediate chamber is separated by removing sulfuric acid through a separate sulfuric acid treatment means (300) at the downstream end, and the sodium sulfate aqueous solution remaining after sulfuric acid treatment is supplied back to the step of manufacturing the sodium sulfate aqueous solution in step (b).

7. In Claim 6, The above sulfuric acid treatment means (300) is a method for treating byproduct sodium sulfate waste liquid, selecting one or more of the methods of treating by ion exchange reaction or treating by adding chemicals.

8. In Claim 7, A method for treating byproduct sodium sulfate waste liquid, characterized in that the above ion exchange reaction converts sulfuric acid into sodium sulfate through the exchange of hydrogen ions and sodium ions.

9. In Claim 7, A method for treating byproduct sodium sulfate waste liquid, characterized in that the above-mentioned chemical dissolves in water to generate hydroxide ions capable of neutralizing hydrogen ions in sulfuric acid, and simultaneously reacts with sulfate ions to form a crystalline phase in an aqueous solution.

10. In Claim 9, A method for treating byproduct sodium sulfate waste liquid, characterized in that the above chemical is one of Ca(OH)2, CaO, or CaCO3.

11. In Claim 9, A method for treating byproduct sodium sulfate waste liquid, characterized in that the total concentration of the chemical component remaining dissolved in the above aqueous solution is 0.02M or less.

12. In Clause 11, A method for treating byproduct sodium sulfate waste liquid, characterized by adding means to remove the above-mentioned residual chemical components by applying one or more of CO2 or ion exchange resins.

13. In Claim 1, A method for treating byproduct sorghum waste liquid, characterized in that the above step (a) is crystallized by a low-temperature crystallization method.

14. In Claim 1, A method for treating byproduct sorghum waste liquid, characterized in that the above step (a) is crystallized by a high-temperature evaporative drying method.

15. In Claim 1, A method for treating byproduct sodium hydroxide waste liquid, characterized in that the sodium hydroxide generated in step (d) above is circulated to an electrolytic decomposition cell with a separate cathode tank, a portion of the sodium hydroxide generated at a desired concentration is separated and discharged, and additional water corresponding to the amount consumed is supplied.

Images