Wastewater purification method

Abstract

The wastewater purification method relating to this disclosure includes a step of selectively removing manganese (Mn) from wastewater discharged from a valuable metal recovery process.

Description

[Technical Field]

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

[0002] In recent years, demand for secondary batteries has been increasing along with the growth of the battery electric vehicle (BEV) market. Scrap from waste batteries or waste cathode materials generated during the manufacturing process of secondary batteries or discarded after use contains valuable metals such as nickel and cobalt. Recently, active technological development has been conducted to recover and recycle valuable metals from secondary batteries.

[0003] Valuable metals such as nickel and cobalt can be recovered by solvent extraction after dissolving raw materials for secondary battery materials in an acid. Solvent extraction utilizes the principle that metal ions are extracted from an aqueous phase using an organic solvent. Generally, when valuable metals such as nickel and cobalt are recovered using solvent extraction, wastewater containing manganese, magnesium, sodium and the like is generated. Since such wastewater contains a large amount of manganese and magnesium, discharging the wastewater without purification may lead to problems such as environmental pollution. For this reason, a purification step for removing manganese, magnesium and the like from the wastewater is required. However, there has been a problem that a large amount of waste is generated in the process of purifying the wastewater. [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] An object of the present disclosure is to provide a wastewater purification method capable of reducing the amount of waste generated when purifying wastewater discharged from a valuable metal recovery process. [Means for Solving the Problem]

[0005] A wastewater purification method relating to one aspect of this disclosure includes a step of selectively removing manganese (Mn) from wastewater generated from a valuable metal recovery process.

[0006] According to one aspect of this disclosure, in the step of selectively removing manganese, manganese may precipitate from the wastewater as manganese oxide.

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

[0008] A wastewater purification method relating to one aspect of this disclosure may further include a step of separating manganese oxides from the wastewater.

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

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

[0011] According to one aspect of this 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 this disclosure, the step of adjusting the oxidation-reduction potential of wastewater may be to adjust the oxidation-reduction potential of wastewater to -200mV to 900mV.

[0013] According to one aspect of this disclosure, the step of adjusting the oxidation-reduction potential of wastewater may include the step of adding oxygen to the wastewater.

[0014] According to one aspect of this disclosure, the step of adding oxygen to the wastewater may be carried out for four hours or more.

[0015] According to one aspect of this disclosure, the step of selectively removing manganese may be carried out at a temperature of 40°C to 90°C.

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

[0017] According to one aspect of this disclosure, wastewater from a valuable metal recovery process may contain manganese, magnesium, and sulfates.

[0018] According to one aspect of this disclosure, wastewater from a valuable metal recovery process may further contain one or more metals selected from the group consisting of metals and non-ferrous metals.

[0019] According to one aspect of this disclosure, metals and non-ferrous metals may be precipitated in the form of hydroxides when the pH of the wastewater is between 7 and 9.

[0020] According to one aspect of this disclosure, the metals and nonferrous metals may include one or more selected from the group consisting of zinc, iron, nickel, cobalt, manganese, and magnesium.

[0021] A wastewater purification method relating to one aspect of this disclosure may further include a reverse neutralization step in which manganese is selectively removed from the wastewater, and the pH of the wastewater is adjusted to 6-8. [Effects of the Invention]

[0022] The wastewater purification method described herein includes a step of selectively removing manganese from wastewater discharged from a valuable metal recovery process. Compared to conventional methods that treat manganese and magnesium in a single purification step, this method reduces the amount of neutralizing agent used and significantly reduces the amount of waste generated. Furthermore, the wastewater from which manganese has been selectively removed by this disclosure meets discharge standards in terms of the concentrations of wastewater components (e.g., manganese, magnesium, sodium), allowing for direct discharge. Thus, the amount of waste that may be further generated during the wastewater purification process can be reduced. [Brief explanation of the drawing]

[0023] [Figure 1] Figure 1 is a process diagram of a wastewater purification method according to an embodiment of the present disclosure. [Figure 2] Figure 2 is a Pourbaix Diagram of manganese. Mode for Carrying Out the Invention

[0024] Hereinafter, specific details for carrying out the present disclosure will be described in detail with reference to the accompanying drawings. However, in the following description, if there is a risk that the gist of the present disclosure will rather be obscured, detailed descriptions of well-known functions and configurations shall be omitted.

[0025] In the accompanying drawings, identical or corresponding components are denoted by the same reference signs. In addition, in the following description of the embodiments, repeated descriptions of identical or corresponding components may be omitted. However, even if descriptions of components are omitted, this is not intended to mean that such components are not included in the embodiment.

[0026] Terms used in the present disclosure will be briefly explained, and the disclosed embodiments will be specifically described. For the terms used in the present specification, after considering their functions in the present disclosure, general terms that are widely used at present are selected as far as possible; however, this may be changed depending on the intention of engineers engaged in the relevant field, judicial precedents, or the emergence of new technologies. In addition, in certain cases, some terms are arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the description part of the corresponding invention. Therefore, the terms used in the present disclosure should be defined based not on the mere names of the terms, but on the meanings of the terms and the entire content of the present disclosure.

[0027] In the present disclosure, singular expressions also include plural expressions unless the context clearly specifies that it is singular. In addition, plural expressions also include singular expressions unless the context clearly specifies that it is plural.

[0028] In this disclosure, when a part is said to include one component, this means that, unless otherwise specified, it may include other components rather than excluding them.

[0029] In this disclosure, the phrase "A and / or B" means A, or B, or A and B.

[0030] The advantages and features of the disclosed embodiments, as well as the methods for achieving them, will become clear from the embodiments described below, together with the accompanying drawings. However, this disclosure is not limited to the embodiments disclosed below and may be embodied in various other forms, and these embodiments are provided merely to complete the disclosure and to fully inform a person of the ordinary skill of the scope of the invention.

[0031] Generally, in the process of recovering valuable metals such as nickel and cobalt from waste battery materials or waste cathode materials, wastewater containing manganese and magnesium in the form of sulfates is generated. Conventionally, to purify such wastewater, a neutralizing agent was added to increase the pH of the wastewater to 10-11, thereby precipitating and removing manganese and magnesium from the wastewater. Although the purified wastewater meets discharge standards with all manganese and magnesium precipitated out, a large amount of neutralizing agent was required to remove the large amount of manganese and magnesium contained in the wastewater. For this reason, conventionally, low-cost calcium hydroxide (Ca(OH)2) was used as a neutralizing agent. When calcium hydroxide is used as a neutralizing agent, as shown in reaction equations 1 and 2, the manganese and magnesium contained in the wastewater are precipitated and removed in the form of hydroxides, and the sulfates contained in the wastewater are precipitated and removed in the form of calcium sulfate (CaSO4).

[0032] [Reaction Equation 1] MnSO4 + Ca(OH)2 → Mn(OH)2 + CaSO4

[0033] [Reaction Equation 2] MgSO4 + Ca(OH)2 → Mg(OH)2 + CaSO4

[0034] However, such conventional methods generate large amounts of precipitated waste, such as manganese hydroxide, magnesium hydroxide, and calcium sulfate, which increases landfill and related process costs, and can also lead to environmental pollution problems during the landfilling process.

[0035] The wastewater purification method according to this disclosure is characterized by including a step of selectively removing manganese from wastewater discharged from a valuable metal recovery process. Compared to conventional methods that treat manganese and magnesium in a single purification step, the wastewater purification method according to this disclosure reduces the amount of neutralizing agent used, thereby significantly reducing the amount of waste generated. Furthermore, since the wastewater from which manganese has been selectively removed by this disclosure meets discharge standards, it can be discharged directly, thus reducing the amount of waste that may be further generated during the wastewater purification process.

[0036] According to this disclosure, manganese can precipitate from wastewater as manganese oxide during the selective removal stage. The wastewater purification method of this disclosure, which precipitates and removes manganese in the form of manganese oxide, can significantly reduce the amount of waste generated compared to conventional methods that precipitate and remove manganese in the form of manganese hydroxide. The manganese oxide may be one or more selected from the group consisting of Mn3O4, Mn2O3, and MnO2. For example, Mn(OH)2, which corresponds to manganese hydroxide, contains 62% by weight of manganese, so 1.6 tons of Mn(OH)2 must be precipitated from the wastewater to remove 1 ton of manganese. In contrast, Mn3O4, Mn2O3, and MnO2, which correspond to manganese oxide, contain 72% by weight, 70% by weight, and 63% by weight of manganese, respectively, so to remove 1 ton of manganese, it is only necessary to precipitate 1.39 tons, 1.44 tons, and 1.58 tons of Mn3O4, Mn2O3, and MnO2, respectively, from the wastewater. Therefore, the wastewater purification method of this disclosure, which removes manganese in the form of manganese oxide, can significantly reduce the amount of precipitated waste compared to conventional methods that remove manganese in the form of manganese hydroxide.

[0037] The wastewater purification method relating to this disclosure may further include a step of separating manganese oxide from the wastewater. The separated manganese oxide can be used in subsequent processes for producing manganese sulfate or the like.

[0038] The step of selectively removing manganese according to this disclosure may include the step of adjusting the pH of the wastewater and the step of adjusting the oxidation-reduction potential (ORP) of the wastewater. Specifically, the wastewater purification method according to this disclosure can selectively remove manganese from wastewater by adjusting both the pH and the oxidation-reduction potential of the wastewater. In this case, manganese may be precipitated and removed 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.

[0039] The step of adjusting the pH of the wastewater may involve adjusting the pH of the wastewater to 7 or higher, specifically 7 to 10, or more specifically 7 to 8.5. When the pH of the wastewater satisfies the aforementioned numerical range, manganese becomes a precipitateable compound, preventing magnesium from precipitating from the wastewater, thus facilitating the selective removal of manganese from the wastewater.

[0040] According to one embodiment of the present disclosure, the step of adjusting the pH of wastewater may include the step of adding sodium hydroxide (NaOH) to the wastewater. The wastewater purification method according to the present disclosure selectively removes manganese from among several components contained in the wastewater, thus reducing the amount of basic auxiliary raw materials added to the wastewater. Therefore, in the wastewater purification method of the present disclosure, sodium hydroxide, which is more expensive than calcium hydroxide, may be used as the basic auxiliary raw material. When sodium hydroxide is added to wastewater as a basic auxiliary raw material, sulfates contained in the wastewater exist 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 conventional methods that use calcium hydroxide to precipitate and remove sulfates 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.

[0041] The step of adjusting the oxidation-reduction potential of wastewater may involve adjusting the oxidation-reduction potential of the wastewater to -200mV to 900mV, specifically -200mV to 500mV, and more specifically -200mV to 200mV. A silver / silver chloride electrode can be used as a reference electrode when measuring the oxidation-reduction potential of wastewater, but is not limited to this, and various electrodes suitable for measuring oxidation-reduction potential can be used. When the oxidation-reduction potential of 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.

[0042] According to one embodiment of the present disclosure, the step of adjusting the oxidation-reduction potential of wastewater may include the step of adding oxygen to the wastewater. Adding oxygen to wastewater can increase the oxidation-reduction potential of the wastewater. The step of adding oxygen to the wastewater may be carried out 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 oxidation-reduction potential of the wastewater increases sufficiently, and it becomes more likely that manganese oxide rather than manganese hydroxide will precipitate.

[0043] 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 the steps of selectively removing manganese by adding sodium hydroxide (NaOH) and oxygen (O2) to wastewater from a valuable metal recovery process, back-neutralizing the wastewater by adding sulfuric acid (H2SO4) to the wastewater, and discharging the back-neutralized wastewater. In this case, the wastewater from the valuable metal recovery process may contain manganese and magnesium. In the step of selectively removing manganese, manganese can precipitate from the wastewater in the form of manganese oxide as shown in the following reaction equations 3 to 5.

[0044] [Reaction Equation 3] 6MnSO4 + 12NaOH + O2 → 2Mn3O4 + 6Na2SO4 + 6H2O

[0045] [Reaction Equation 4] 4MnSO4 + 8NaOH + O2 → 2Mn2O3 + 4Na2SO4 + 4H2O

[0046] [Reaction Equation 5] 2MnSO4 + 4NaOH + O2 → 2MnO2 + 2Na2SO4 + 2H2O

[0047] On the other hand, Figure 2 is the Pourbaix diagram of manganese. The Pourbaix diagram is a graph that shows the thermodynamically most stable species or phase of an element as a function of potential (EH) and pH. As shown in Figure 2, manganese in solution has thermodynamically most stable species and phases under specific potential and pH conditions, for example, manganese ions (Mn 2+ Manganese can exist in the following states: solid manganese metal (Mn(s)), solid manganese hydroxide (Mn(OH)2(s)), and solid manganese oxides (Mn3O4(s), Mn2O3(s), MnO2(s), MnO4(s)).

[0048] The wastewater purification method of this disclosure allows for the selective removal of manganese from wastewater by adjusting the pH and oxidation-reduction potential of the wastewater so that manganese exists in the form of manganese oxide, and then removing the precipitated manganese oxide. For example, as shown in Figure 2, when the pH of the wastewater is adjusted to 8 and the oxidation-reduction potential is adjusted to 200 mV, Mn3O4 precipitates from the wastewater in a solid state, and manganese can be selectively removed from the wastewater by removing the precipitated Mn3O4.

[0049] The step of selectively removing manganese may be carried out at a temperature of 40°C to 90°C, specifically 50°C to 90°C, or more specifically 60°C to 80°C. When the temperature in the step of selectively removing manganese satisfies the above numerical range, all manganese components contained in the wastewater can be removed, and all impurity components other than magnesium and sodium components can be removed.

[0050] According to one embodiment of the present disclosure, the valuable metal recovery step may be a step of recovering nickel and cobalt from waste battery material or waste cathode material. For example, the valuable metal recovery step may be a step of leaching a sulfate solution from waste battery material and recovering the valuable metal from the sulfate solution by a conventional method such as solvent extraction.

[0051] Waste battery materials may be recovered after undergoing a pre-treatment process for waste batteries. In this case, the pre-treatment process may include a discharge process, a dismantling process, a crushing / crushing process, a drying process, and a firing process. Waste battery materials include, but are not limited to, waste battery scrap, black mass processed from waste batteries into raw materials through a recycling process, waste cathode material generated during the manufacturing process of cathode material, or a combination thereof.

[0052] The sulfate solution may be extracted from the waste battery material via a wet process. For example, the sulfate solution may leach from the waste battery material recovered through the pretreatment process described above. In addition to the waste battery material, the sulfate solution may leach from one or more materials selected from the group consisting of nickel ore, nickel MHP (Mixed Hydroxide Precipitate), and nickel oxide. The metal sulfate contained in the sulfate solution may be one or more sulfates selected from the group consisting of nickel, cobalt, manganese, lithium, copper, and aluminum.

[0053] According to this disclosure, the wastewater from the valuable metal recovery process may be the wastewater generated after recovering nickel and cobalt from a sulfate solution. The wastewater from the valuable metal recovery process may contain manganese, magnesium, and sulfates.

[0054] The wastewater from the valuable metal recovery process may further contain one or more metals and non-ferrous metals selected from the group consisting of metals and non-ferrous metals. In this case, the metals and non-ferrous metals may be those that can precipitate in the form of hydroxides when the pH of the wastewater is 7 to 9. That is, the wastewater purification method according to this disclosure is also applicable when the wastewater further contains metals and non-ferrous metals that can precipitate in the form of hydroxides when the pH of the wastewater is 7 to 9. The metals and non-ferrous metals may include, but are not limited to, one or more metals selected from the group consisting of zinc, iron, nickel, cobalt, manganese, and magnesium.

[0055] The wastewater purification method according to this disclosure may further include a reverse neutralization step in which manganese is selectively removed from the wastewater, and the pH of the wastewater is adjusted to 6-8. The reverse neutralization step can mean a step in which the pH of the wastewater is adjusted so that the wastewater from which manganese has been selectively removed has a pH that meets the discharge standards.

[0056] According to one embodiment of the present disclosure, the reverse neutralization step may include the step of 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.

[0057] The embodiments of this disclosure will be described in detail below so that they can be easily implemented by a person with ordinary skill in the art to which this disclosure pertains. However, this disclosure may be embodied in various other forms and is not limited to the embodiments described herein.

[0058] Examples and Comparative Examples

[0059] Example 1

[0060] Two liters of sulfate solution (wastewater) with concentrations of each metal ion as shown in Table 1 below were prepared. Sodium hydroxide (NaOH) and oxygen were added to the wastewater, and the mixture was reacted at a temperature of 70°C for four hours to purify the wastewater.

[0061] [Table 1]

[0062] Example 2

[0063] The wastewater was purified using the same method as in Example 1, except that sodium hydroxide and oxygen were added to 2 L of wastewater and the reaction was carried out at a temperature of 70°C for 8 hours.

[0064] Comparative Example 1

[0065] Except for not adding oxygen to the wastewater, the wastewater was purified using the same method as in Example 1.

[0066] Experimental Example 1: Amount of manganese residue and types of compounds precipitated and removed from wastewater with or without oxygen input

[0067] The amount of manganese residue and the types of compounds precipitated and removed from wastewater with or without oxygen input were confirmed from Example 1 and Comparative Example 1, respectively, and are shown in Table 2 below.

[0068] [Table 2]

[0069] 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). Furthermore, in Example 1, where manganese was precipitated and removed in the form of manganese oxide, the amount of residue generated (amount of precipitate) was smaller compared to Comparative Example 1, where manganese was precipitated and removed in the form of manganese hydroxide.

[0070] Experimental Example 2: Changes in manganese and magnesium concentrations in wastewater at different reaction times with oxygen input.

[0071] In the wastewater purification process according to Example 2, the changes in manganese and magnesium concentrations in the wastewater were confirmed for different reaction times with oxygen input, and are shown in Table 3 below.

[0072] [Table 3]

[0073] According to Table 3, in Example 2, where wastewater was purified by adding sodium hydroxide and oxygen, it was confirmed that the manganese concentration decreased significantly with increasing reaction time. This confirms that manganese can be selectively removed from wastewater by the wastewater purification method according to one embodiment of the present disclosure.

[0074] While this disclosure has been described in relation to some embodiments, it is clear that various modifications and alterations are possible, provided they do not deviate from the spirit and scope of this disclosure as understood by a person of ordinary skill in the art to which this disclosure pertains. Furthermore, such modifications and alterations should be considered to fall within the scope of the claims appended to this specification.

[0075] A person with ordinary skill in the art to which this disclosure pertains can make various substitutions, modifications, and alterations without departing from the technical spirit of this disclosure, and this disclosure is not limited by the embodiments described above and the accompanying drawings.

Claims

1. A wastewater purification method comprising the step of selectively removing manganese (Mn) from wastewater generated from a valuable metal recovery process.

2. The wastewater purification method according to claim 1, wherein, in the step of selectively removing the manganese, the manganese precipitates from the wastewater as manganese oxide.

3. The aforementioned manganese oxide is Mn ３ O ４ Mn ２ O ３ MnO ２ The wastewater purification method according to claim 2, wherein one or more are selected from the group consisting of the following.

4. The wastewater purification method according to claim 2, further comprising the step of separating the manganese oxide from the wastewater.

5. The wastewater purification method according to claim 1, wherein the step of selectively removing manganese includes the step of adjusting the pH of the wastewater and the step of adjusting the oxidation-reduction potential (ORP) of the wastewater.

6. The wastewater purification method according to claim 5, wherein the step of adjusting the pH of the wastewater is to adjust the pH of the wastewater to 7 or higher.

7. The wastewater purification method according to claim 5, wherein the step of adjusting the pH of the wastewater includes the step of adding sodium hydroxide (NaOH) to the wastewater.

8. The wastewater purification method according to claim 5, wherein the step of adjusting the oxidation-reduction potential of the wastewater is to adjust the oxidation-reduction potential of the wastewater to -200 mV to 900 mV.

9. The wastewater purification method according to claim 5, wherein the step of adjusting the oxidation-reduction potential of the wastewater includes the step of adding oxygen to the wastewater.

10. The wastewater purification method according to claim 9, wherein the step of adding oxygen to the wastewater is performed for four hours or more.

11. The wastewater purification method according to claim 1, wherein the step of selectively removing manganese is performed at a temperature of 40°C to 90°C.

12. The wastewater purification method according to claim 1, wherein the step of recovering valuable metals is a step of recovering nickel and cobalt from waste battery material or waste cathode material.

13. The wastewater purification method according to claim 1, wherein the wastewater discharged from the valuable metal recovery process contains manganese, magnesium, and sulfate.

14. The wastewater purification method according to claim 13, wherein the wastewater obtained from the valuable metal recovery process further contains one or more metals selected from the group consisting of metals and non-ferrous metals.

15. The wastewater purification method according to claim 14, wherein the metal and non-ferrous metal can precipitate in the form of hydroxides when the pH of the wastewater is 7 to 9.

16. The wastewater purification method according to claim 14, wherein the aforementioned metal and non-ferrous metal include one or more selected from the group consisting of zinc, iron, nickel, cobalt, manganese, and magnesium.

17. The wastewater purification method according to claim 1, further comprising a reverse neutralization step of selectively removing manganese from the wastewater and then adjusting the pH of the wastewater to 6 to 8.

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