Method for purifying wastewater

Abstract

A wastewater purification method according to the present disclosure comprises a step of selectively removing manganese (Mn) from wastewater from a valuable metal recovery process.

Description

Wastewater purification method

[0001] The present disclosure relates to a method for purifying wastewater, and more particularly, to a method for purifying wastewater from a valuable metal recovery process.

[0002] The recent expansion of the battery electric vehicle (BEV) market has led to an increase in demand for secondary batteries. Scrap batteries or cathode materials generated during the secondary battery manufacturing process or discarded after use contain valuable metals such as nickel and cobalt. Recently, active development is underway in technologies to recover and recycle these valuable metals within secondary batteries.

[0003] Valuable metals such as nickel and cobalt can be recovered by dissolving secondary battery raw materials in acid and then using solvent extraction. Solvent extraction utilizes the principle that metal ions are extracted from an aqueous solution using an organic solvent. Typically, when recovering valuable metals like nickel and cobalt using solvent extraction, wastewater containing manganese, magnesium, and sodium is generated. Because this wastewater contains large amounts of manganese and magnesium, unpurified discharge can cause environmental problems. Therefore, a purification process is necessary to remove manganese and magnesium from the wastewater. However, the process of purifying the wastewater has been problematic in that it generates a large amount of waste.

[0004] The present disclosure aims to provide a wastewater purification method capable of reducing the amount of waste generated when purifying wastewater from a valuable metal recovery process.

[0005] A method for purifying wastewater according to one aspect of the present disclosure comprises a step of selectively removing manganese (Mn) from wastewater resulting from a valuable metal recovery process.

[0006] According to one aspect of the present disclosure, in the step of selectively removing manganese, manganese can be precipitated as manganese oxide from the wastewater.

[0007] According to one aspect of the present disclosure, the manganese oxide may be at least one selected from the group consisting of Mn3O4, Mn2O3, and MnO2.

[0008] A method for purifying wastewater according to one aspect of the present disclosure may further include a step of separating manganese oxide from the wastewater.

[0009] According to one aspect of the present disclosure, the step of selectively removing manganese may include the step of adjusting the pH of the wastewater, and the step of adjusting the oxidation reduction potential (ORP) of the wastewater.

[0010] According to one aspect of the present disclosure, the step of adjusting the pH of the wastewater may be adjusting the pH of the wastewater to 7 or higher.

[0011] According to one aspect of the present disclosure, the step of adjusting the pH of the wastewater may include the step of adding sodium hydroxide (NaOH) to the wastewater.

[0012] According to one aspect of the present disclosure, the step of controlling the redox potential of the wastewater may be controlling the redox potential of the wastewater to -200 mV to 900 mV.

[0013] According to one aspect of the present disclosure, the step of controlling the redox potential of the wastewater may include the step of adding oxygen to the wastewater.

[0014] According to one aspect of the present disclosure, the step of adding oxygen to the wastewater can be performed for 4 hours or more.

[0015] According to one aspect of the present disclosure, the step of selectively removing manganese can be performed at a temperature of 40°C to 90°C.

[0016] According to one aspect of the present disclosure, the valuable metal recovery process may be a process for recovering nickel and cobalt from waste battery materials or waste cathode materials.

[0017] According to one aspect of the present disclosure, wastewater from a metal recovery process may include manganese, magnesium and sulfate.

[0018] According to one aspect of the present disclosure, the wastewater from the metal recovery process may further comprise at least one selected from the group consisting of metals and non-ferrous metals.

[0019] According to one aspect of the present disclosure, the metal and non-ferrous metal may be capable of precipitating in the form of hydroxides when the pH of the wastewater is 7 to 9.

[0020] According to one aspect of the present disclosure, the metal and non-ferrous metal may include at least one selected from the group consisting of zinc, iron, nickel, cobalt, manganese and magnesium.

[0021] A wastewater purification method according to one aspect of the present disclosure may further include a deneutralization step of selectively removing manganese from the wastewater and then adjusting the pH of the wastewater to 6 to 8.

[0022] The wastewater purification method according to the present disclosure includes a step of selectively removing manganese from wastewater generated from a valuable metal recovery process. Therefore, compared to conventional methods of processing manganese and magnesium through a single purification process, the amount of neutralizing agent used is reduced, thereby significantly reducing the amount of waste generated. Furthermore, since the wastewater from which manganese has been selectively removed according to the present disclosure satisfies discharge standards for the concentrations of wastewater components (e.g., manganese, magnesium, and sodium), it can be directly discharged. Therefore, the amount of waste that may be additionally generated during the wastewater purification process can be reduced.

[0023] Figure 1 is a process diagram of a wastewater purification method according to one embodiment of the present disclosure.

[0024] Figure 2 is a drawing showing a Pourbaix diagram of manganese.

[0025] Hereinafter, specific details for implementing the present disclosure will be described in detail with reference to the attached drawings. However, in the following description, specific descriptions of widely known functions or configurations will be omitted if they may unnecessarily obscure the gist of the present disclosure.

[0026] In the attached drawings, identical or corresponding components are assigned the same reference numerals. Furthermore, in the description of the embodiments below, duplicate descriptions of identical or corresponding components may be omitted. However, even if a description of a component is omitted, it is not intended that such component is not included in any embodiment.

[0027] The terms used in this disclosure will be briefly described, followed by a detailed description of the disclosed embodiments. The terms used in this specification have been selected from widely used, current terms, taking into account the functions of the present disclosure. However, these terms may vary depending on the intentions of engineers working in the relevant fields, precedents, the emergence of new technologies, etc. Furthermore, in certain cases, terms may be arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the relevant description of the invention. Therefore, the terms used in this disclosure should not be defined simply as names of terms, but rather based on their meanings and the overall content of the present disclosure.

[0028] In this disclosure, singular expressions include plural expressions unless the context clearly specifies that they are singular. Furthermore, plural expressions include singular expressions unless the context clearly specifies that they are plural.

[0029] In this disclosure, when it is said that a part includes a certain component, this does not mean that other components are excluded, but rather that other components may be included, unless specifically stated otherwise.

[0030] In this disclosure, the description of “A and / or B” means A, or B, or A and B.

[0031] The advantages and features of the disclosed embodiments, and methods for achieving them, will become clearer with reference to the embodiments described below, along with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms. These embodiments are provided solely to ensure the completeness of the disclosure and to fully inform those skilled in the art of the scope of the invention.

[0032] Typically, the process of recovering valuable metals such as nickel and cobalt from spent battery materials or waste cathode materials generates wastewater containing manganese and magnesium in the form of sulfates. Conventionally, to purify this wastewater, a neutralizing agent was added to increase the pH of the wastewater to 10 to 11, thereby precipitating and removing the manganese and magnesium from the wastewater. After purification, the wastewater satisfies discharge standards because both manganese and magnesium are precipitated out, but a large amount of neutralizing agent was required to remove the large amount of manganese and magnesium contained in the wastewater. For this reason, inexpensive calcium hydroxide (Ca(OH)2) was conventionally used as the neutralizing agent. When calcium hydroxide is used as the neutralizing agent, manganese and magnesium contained in the wastewater are precipitated out as hydroxides, and sulfates contained in the wastewater are precipitated out as calcium sulfate (CaSO4), as shown in Reaction Schemes 1 and 2.

[0033] [Reaction Formula 1]

[0034] MnSO4+ Ca(OH)2→ Mn(OH)2+ CaSO4

[0035] [Reaction Formula 2]

[0036] MgSO4+ Ca(OH)2→ Mg(OH)2+ CaSO4

[0037] However, according to these conventional methods, a large amount of sediment waste such as manganese hydroxide, magnesium hydroxide, and calcium sulfate is generated, which increases landfill costs and the corresponding process costs, and the problem of environmental pollution may arise during the process of landfilling a large amount of waste.

[0038] A wastewater purification method according to the present disclosure is characterized by including a step of selectively removing manganese from wastewater generated from an organometallic recovery process. Compared to conventional methods that process manganese and magnesium through a single purification process, the wastewater purification method according to the present disclosure significantly reduces the amount of waste generated by reducing the amount of neutralizing agent used. Furthermore, wastewater from which manganese has been selectively removed according to the present disclosure satisfies discharge standards and can therefore be directly discharged, thereby reducing the amount of waste that may be additionally generated during the wastewater purification process.

[0039] According to the present disclosure, in the step of selectively removing manganese, manganese can be precipitated from wastewater as manganese oxide. The wastewater purification method of the present disclosure, which removes manganese by precipitation in the form of manganese oxide, can significantly reduce the amount of waste generated compared to the conventional method of removing manganese by precipitation in the form of manganese hydroxide. The manganese oxide may be at least one selected from the group consisting of Mn3O4, Mn2O3, and MnO2. For example, since Mn(OH)2 corresponding to manganese hydroxide contains 62 wt% of manganese, 1.6 tons of Mn(OH)2 must be precipitated from wastewater to remove 1 ton of manganese. On the other hand, since Mn3O4, Mn2O3, and MnO2, which correspond to manganese oxides, contain 72 wt%, 70 wt%, and 63 wt% of manganese, respectively, in order to remove 1 ton of manganese, 1.39 tons, 1.44 tons, and 1.58 tons of Mn3O4, Mn2O3, and MnO2, respectively, need to be precipitated from wastewater. Therefore, the wastewater purification method of the present disclosure, which removes manganese in the form of oxides, can significantly reduce the amount of precipitated waste compared to the conventional method, which removes it in the form of manganese hydroxide.

[0040] The wastewater purification method according to the present disclosure may further include a step of separating manganese oxide from the wastewater. The separated manganese oxide may be used in a subsequent process for producing manganese sulfate or the like.

[0041] The step of selectively removing manganese according to the present disclosure may include a step of adjusting the pH of the wastewater and a step of adjusting the oxidation reduction potential (ORP) of the wastewater. Specifically, the wastewater purification method according to the present disclosure can selectively remove manganese from the wastewater by simultaneously adjusting the pH and oxidation reduction potential of the wastewater. In this case, manganese can be removed by precipitation in the form of manganese oxide. The step of adjusting the pH of the wastewater and the step of adjusting the oxidation reduction potential of the wastewater may be performed simultaneously or separately.

[0042] The step of adjusting the pH of the wastewater may be adjusting the pH of the wastewater to 7 or higher, specifically 7 to 10, and more specifically 7 to 8.5. When the pH of the wastewater satisfies the above numerical range, manganese is in the form of a precipitable compound, and the precipitation of magnesium from the wastewater can be prevented, making it easy to selectively remove manganese from the wastewater.

[0043] According to one embodiment of the present disclosure, the step of adjusting the pH of the wastewater may include a step of adding sodium hydroxide (NaOH) to the wastewater. The wastewater purification method according to the present disclosure can reduce the amount of basic auxiliary material added to the wastewater because it selectively removes manganese among various components contained in the wastewater. Therefore, in the wastewater purification method of the present disclosure, sodium hydroxide, which is relatively more expensive than calcium hydroxide, can be used as the basic auxiliary material. When sodium hydroxide is added to the wastewater as a basic auxiliary material, sulfate contained in the wastewater exists dissolved in the wastewater in the form of sodium sulfate (Na2SO4). Therefore, the wastewater purification method of the present disclosure can reduce the amount of precipitated waste generated compared to a conventional method that uses calcium hydroxide to precipitate and remove sulfate in the form of calcium sulfate (CaSO4). According to the wastewater purification method of the present disclosure, calcium sulfate does not precipitate from the wastewater in the step of selectively removing manganese.

[0044] The step of controlling the redox potential of the wastewater may be controlling the redox potential of the wastewater to -200 mV to 900 mV, specifically -200 mV to 500 mV, and more specifically -200 mV to 200 mV. When measuring the redox potential of the wastewater, a silver / silver chloride electrode may be used as a reference electrode, but is not limited thereto, and various electrodes suitable for measuring the redox potential may be used. When the redox potential of the wastewater satisfies the above numerical range, manganese can be precipitated and removed in the form of an oxide rather than a hydroxide, and as a result, the amount of precipitated waste can be reduced.

[0045] According to one embodiment of the present disclosure, the step of controlling the redox potential of wastewater may include a step of adding oxygen to the wastewater. Introducing oxygen to the wastewater may increase the redox potential of the wastewater. The step of adding oxygen to the wastewater may be performed for 4 hours or more, specifically, 4 to 10 hours. When the reaction time of the step of adding oxygen to the wastewater satisfies the above numerical range, the redox potential of the wastewater sufficiently increases, thereby increasing the likelihood of manganese oxide, rather than manganese hydroxide, being precipitated.

[0046] Figure 1 is a process diagram of a wastewater purification method according to one embodiment of the present disclosure. According to one embodiment of the present disclosure, the wastewater purification method may include a step of selectively removing manganese by adding sodium hydroxide (NaOH) and oxygen (O2) to wastewater from a valuable metal recovery process, a step of de-neutralizing the wastewater by adding sulfuric acid (H2SO4) to the wastewater, and a step of discharging the de-neutralized wastewater. At this time, the wastewater from the valuable metal recovery process may contain manganese and magnesium. In the step of selectively removing manganese, manganese may be precipitated from the wastewater in the form of manganese oxide as shown in the following reaction formulas 3 to 5.

[0047] [Reaction Formula 3]

[0048] 6 MnSO4+ 12 NaOH + O2→ 2 Mn3O4+ 6 Na2SO4+ 6 H2O

[0049] [Reaction Formula 4]

[0050] 4 MnSO4+ 8 NaOH + O2→ 2 Mn2O3+ 4 Na2SO4+ 4 H2O

[0051] [Reaction Formula 5]

[0052] 2 MnSO4+ 4 NaOH + O2→ 2 MnO2+ 2 Na2SO4+ 2 H2O

[0053] Meanwhile, Fig. 2 is a drawing showing the Pourbaix diagram of manganese. The Pourbaix diagram shows the potential (E H ) and pH as a function of the thermodynamically most stable species or phase of an element. As shown in Fig. 2, manganese in solution has the most thermodynamically stable species and phase under specific potential and pH conditions, for example, manganese ion (Mn 2+ ), solid manganese metal (Mn(s)), solid manganese hydroxide (Mn(OH)2(s)), solid manganese oxide (Mn3O4(s), Mn2O3(s), MnO2(s), MnO4(s)).

[0054] The wastewater purification method of the present disclosure can selectively remove manganese from wastewater by controlling the pH and redox potential of wastewater so that manganese exists in the form of manganese oxide and removing the precipitated manganese oxide. For example, as illustrated in Fig. 2, when the pH of wastewater is controlled to 8 and the redox potential is controlled to 200 mV, Mn3O4 is precipitated in a solid state from wastewater and manganese can be selectively removed from wastewater by removing the precipitated Mn3O4.

[0055] The step of selectively removing manganese can be performed at a temperature of 40°C to 90°C, specifically 50°C to 90°C, and more specifically 60°C to 80°C. When the temperature in the step of selectively removing manganese satisfies the above numerical range, all of the manganese components contained in the wastewater can be removed, and all of the other impurity components except for magnesium and sodium components can be removed.

[0056] According to one embodiment of the present disclosure, the valuable metal recovery process may be a process for recovering nickel and cobalt from spent battery materials or spent cathode materials. For example, the valuable metal recovery process may be a process for leaching a sulfate solution from spent battery materials and recovering the valuable metal from the sulfate solution using a conventional method, such as solvent extraction.

[0057] Spent battery materials can be recovered through a pretreatment process. This pretreatment process may include a discharge process, a disassembly process, a crushing / pulverizing process, a drying process, and a calcination process. Spent battery materials may include, but are not limited to, scrap waste batteries, black mass (black mass) recycled from waste batteries, waste cathode materials generated during the cathode material manufacturing process, or a combination thereof.

[0058] The sulfate solution can be extracted from the spent battery material through a wet process. For example, the sulfate solution can be extracted from the spent battery material recovered through the aforementioned pretreatment process. The sulfate solution can be extracted not only from the spent battery material, but also from one or more selected from the group consisting of nickel ore, nickel MHP (Mixed Hydroxide Precipitate), and nickel oxide. The metal sulfate contained in the sulfate solution can be one or more sulfates selected from the group consisting of nickel, cobalt, manganese, lithium, copper, and aluminum.

[0059] According to the present disclosure, the wastewater from the valuable metal recovery process may be wastewater generated after recovering nickel and cobalt from a sulfate solution. The wastewater from the valuable metal recovery process may contain manganese, magnesium, and sulfate.

[0060] The wastewater from the valuable metal recovery process may further contain one or more selected from the group consisting of metals and non-ferrous metals. In this case, the metals and non-ferrous metals may be capable of precipitating in the form of hydroxides when the pH of the wastewater is 7 to 9. That is, the wastewater purification method according to the present disclosure is also applicable even when the wastewater further contains metals and non-ferrous metals capable of precipitating in the form of hydroxides when the pH of the wastewater is 7 to 9. The metals and non-ferrous metals may include one or more selected from the group consisting of zinc, iron, nickel, cobalt, manganese, and magnesium, but are not limited thereto.

[0061] The wastewater purification method according to the present disclosure may further include a deneutralization step of selectively removing manganese from the wastewater and then adjusting the pH of the wastewater to 6 to 8. The deneutralization step may refer to a step of adjusting the pH of the wastewater so that the wastewater from which manganese has been selectively removed has a pH suitable for discharge standards.

[0062] According to one embodiment of the present disclosure, the de-neutralization step may include adding an acid to the wastewater. Specifically, the type of acid that can be added may be one or more selected from the group consisting of H2SO4, HCl, and HNO3, but is not limited thereto.

[0063] Hereinafter, embodiments of the present disclosure will be described in detail so that those skilled in the art can easily implement the present disclosure. However, the present disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0064] Examples and Comparative Examples

[0065] Example 1

[0066] A 2 L sulfate solution (wastewater) was prepared in which the concentration of each metal ion had the values ​​shown in Table 1 below. Sodium hydroxide (NaOH) and oxygen were added to the wastewater and the solution was allowed to react for 4 hours at a temperature of 70°C to purify the wastewater.

[0067] Ingredients MnMgNaZnFeConcentration 3~5(g / L) 4~7(g / L) 5~15(g / L) 20~1000 (mg / L) 20~1000 (mg / L)

[0068] Example 2

[0069] Purification of wastewater was performed in the same manner as in Example 1, except that sodium hydroxide and oxygen were added to 2 L of wastewater and reacted for 8 hours at a temperature of 70°C.

[0070] Comparative Example 1

[0071] Purification of wastewater was performed in the same manner as in Example 1, except that no oxygen was added to the wastewater.

[0072] Experimental Example 1: The amount of manganese residue generated and the types of its compounds removed by precipitation from wastewater depending on the presence or absence of oxygen injection.

[0073] The amount of manganese residue generated and the type of its compound removed by precipitation from wastewater depending on whether oxygen was added were confirmed in Example 1 and Comparative Example 1, respectively, and are shown in Table 2 below.

[0074] Example 1 Comparative Example 1 Amount of residue generated (g) 17~18 20~21 Type of residue compound Mn3O4 Mn(OH)2

[0075] According to Table 2, in Example 1, where oxygen was added during wastewater purification, the residual compound was manganese oxide (Mn3O4), whereas in Comparative Example 1, where oxygen was not added during wastewater purification, the residual compound was manganese hydroxide (Mn(OH)2). In addition, in Example 1, where manganese was precipitated and removed in the form of manganese oxide, it was confirmed that the amount of residue generated (amount of precipitate) was less compared to Comparative Example 1, where manganese was precipitated and removed in the form of manganese hydroxide.

[0076] Experimental Example 2: Changes in manganese and magnesium concentrations in wastewater according to reaction time with oxygen input

[0077] In the wastewater purification process according to Example 2, the change in the concentration of manganese and magnesium in the wastewater according to the reaction time according to the oxygen input was confirmed and is shown in Table 3 below.

[0078] Reaction time (hr) 0 1 2 4 6 8 Concentration (g / L) Mn 4.7 6 4.1 0 3.5 20.8 9 0.0 20.0 0.0 39 Mg 5.2 5.2 0 5.1 9 5.1 7 5.1 6 5.1 6

[0079] According to Table 3, in Example 2, where purification was performed by adding sodium hydroxide and oxygen to wastewater, the concentration of manganese was significantly reduced over the reaction time. This confirms that manganese is selectively removed from wastewater through the wastewater purification method according to one embodiment of the present disclosure.

[0080] While the present disclosure has been described in connection with certain embodiments herein, it should be understood that various modifications and variations may be made without departing from the spirit and scope of the present disclosure, as would be understood by those skilled in the art. Furthermore, such modifications and variations are intended to fall within the scope of the claims appended to this specification.

[0081] Anyone having ordinary skill in the art to which the present disclosure pertains can make various substitutions, modifications, and changes within the scope that does not depart from the technical spirit of the present disclosure, and therefore the present disclosure is not limited to the above-described embodiments and the attached drawings.

Claims

1. A method for purifying wastewater, comprising a step of selectively removing manganese (Mn) from wastewater from a metal recovery process.

2. In paragraph 1, In the step of selectively removing the above manganese, A method for purifying wastewater, wherein the manganese is precipitated as manganese oxide from the wastewater.

3. In paragraph 2, A method for purifying wastewater, wherein the manganese oxide is at least one selected from the group consisting of Mn3O4, Mn2O3, and MnO2.

4. In paragraph 2, A wastewater purification method further comprising a step of separating the manganese oxide from the wastewater.

5. In paragraph 1, The step of selectively removing the above manganese is: A step of adjusting the pH of the wastewater; and A wastewater purification method comprising a step of controlling the oxidation reduction potential (ORP) of the wastewater.

6. In paragraph 5, A wastewater purification method, wherein the step of adjusting the pH of the wastewater is to adjust the pH of the wastewater to 7 or higher.

7. In paragraph 5, The step of adjusting the pH of the above wastewater is: A wastewater purification method comprising a step of adding sodium hydroxide (NaOH) to the wastewater.

8. In paragraph 5, A method for purifying wastewater, wherein the step of controlling the oxidation-reduction potential of the wastewater is to control the oxidation-reduction potential of the wastewater to -200 mV to 900 mV.

9. In paragraph 5, A method for purifying wastewater, wherein the step of controlling the oxidation-reduction potential of the wastewater includes a step of adding oxygen to the wastewater.

10. In paragraph 9, A method for purifying wastewater, wherein the step of adding oxygen to the wastewater is performed for 4 hours or more.

11. In paragraph 1, A method for purifying wastewater, wherein the step of selectively removing manganese is performed at a temperature of 40°C to 90°C.

12. In paragraph 1, The above-mentioned valuable metal recovery process is a wastewater purification method that recovers nickel and cobalt from waste battery materials or waste cathode materials.

13. In paragraph 1, A method for purifying wastewater from the above metal recovery process, wherein the wastewater contains manganese, magnesium and sulfate.

14. In paragraph 13, A wastewater purification method, wherein the wastewater from the above metal recovery process further comprises at least one selected from the group consisting of metals and non-ferrous metals.

15. In paragraph 14, A method for purifying wastewater, wherein the above metal and non-ferrous metal can be precipitated in the form of a hydroxide when the pH of the wastewater is 7 to 9.

16. In paragraph 14, A method for purifying wastewater, wherein the above metal and non-ferrous metal include at least one selected from the group consisting of zinc, iron, nickel, cobalt, manganese, and magnesium.

17. In paragraph 1, A wastewater purification method further comprising a deneutralization step of selectively removing manganese from the wastewater and then adjusting the pH of the wastewater to 6 to 8.

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