Process for recovering acid and alkali from metal extraction sewage

Abstract

According to a specific embodiment of the invention, the process for recovering the acid and the alkali from the metal extraction sewage is provided, and the process comprises the following steps: pretreating the metal extraction sewage; and performing electrodialysis on the pretreated metal extraction sewage. By providing the above process, it is possible to recover and reuse a part of the components present in the metal extraction wastewater derived from the battery manufacturing and treatment process, thereby having economic and environmental benefits.

Description

Technical Field

[0001] The present invention relates to a process for recovering acid and alkali from metal extraction wastewater. Background Art

[0002] In recent years, as environmental problems caused by excessive use of fossil fuels have become global issues, the demand for transportation vehicles that use environmentally friendly alternative fuels instead of fossil fuels is increasing. Among the transportation vehicles that use these alternative fuels, electric vehicles that use electricity are currently the fastest-growing.

[0003] An electric vehicle includes a battery as a means for supplying power to the vehicle, and the maximum capacity of the battery decreases with use, and thus has a short life span of several years to a maximum of about 10 years.

[0004] As described above, with the rapid spread of electric vehicles, the amount of wastewater generated in the manufacturing process of batteries used therein is increasing worldwide, and the amount of wastewater generated in waste batteries of electric vehicles that have reached the end of their life is also increasing.

[0005] [Prior art literature]

[0006] [Patent Document]

[0007] (Patent Document 1) KR 10-2361906 B1. Summary of the invention

[0008] 1. Technical issues to be resolved

[0009] The object of the present invention is to provide a process for recovering acid and alkali from metal extraction wastewater.

[0010] (II) Technical solution

[0011] The process for recovering acid and alkali from metal extraction wastewater according to the first aspect of the present invention may include the following steps: pre-treating the metal extraction wastewater; and subjecting the pre-treated metal extraction wastewater to electrodialysis.

[0012] According to one embodiment of the present invention, the metal extraction wastewater may contain sodium and sulfur.

[0013] According to a specific embodiment of the present invention, the sum of the sodium content and the sulfur content contained in the metal extraction wastewater may be 1-25% by weight.

[0014] According to a specific embodiment of the present invention, the pH of the metal extraction wastewater may be 1 to 8.

[0015] According to a specific embodiment of the present invention, the step of pre-treating the metal extraction wastewater may include coagulation precipitation, adsorption, ion exchange, oxidation or a combination thereof.

[0016] According to a specific embodiment of the present invention, the step of subjecting the pretreated metal extraction wastewater to electrodialysis can be performed by using a bipolar membrane, a cationic membrane, an anionic membrane or a combination thereof.

[0017] According to a specific embodiment of the present invention, the step of subjecting the pretreated metal extraction wastewater to electrodialysis can be carried out at a temperature of 15-55°C.

[0018] According to a specific embodiment of the present invention, the process may further include the step of subjecting the metal extraction wastewater to an electrochemical-advanced oxidation process.

[0019] According to a specific embodiment of the present invention, the process may further include a step of microfiltration of the pretreated metal extraction wastewater.

[0020] The features and advantages of the present invention will become more apparent from the following detailed description based on the accompanying drawings.

[0021] The terms or words used in this specification and claims should not be interpreted as the conventional meaning or the dictionary meaning, but should be interpreted as the meaning and concept consistent with the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term in order to explain his own invention in the best way.

[0022] (III) Beneficial effects

[0023] According to the first aspect of the present invention, economic and environmental benefits can be achieved by recovering and reusing acid and alkali in metal extraction wastewater generated in a metal recovery process of waste batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a process flow chart according to each specific implementation scheme.

[0025] Figure 2 is a schematic diagram of an electrodialysis reaction using a bipolar membrane according to one specific embodiment.

[0026] Figure 3 is a schematic diagram of an electrodialysis reaction using a cation membrane and an anion membrane according to one specific embodiment. DETAILED DESCRIPTION

[0027] The objects, advantages and features of the present invention will be more clearly understood from the accompanying drawings and the following detailed description and preferred embodiments, but the present invention is not necessarily limited thereto. In addition, when describing the present invention, if it is determined that the specific description of the known technology related to the present invention may unnecessarily make the subject matter of the present invention unclear, the detailed description thereof will be omitted.

[0028] Hereinafter, a specific embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0029] Figure 1 is a process flow diagram according to a specific embodiment.

[0030] The process of recovering acid and alkali from metal extraction wastewater may include the following steps: pre-treating the metal extraction wastewater; and subjecting the pre-treated metal extraction wastewater to electrodialysis. The metal extraction wastewater refers to wastewater from a process of recovering reusable metal parts from waste batteries after the battery has reached the end of its life, and the metal extraction wastewater may be derived from a process of recovering valuable metals from waste lithium batteries containing, for example, nickel, cobalt, manganese, or a combination thereof.

[0031] According to a specific embodiment of the present invention, the metal extraction wastewater may contain sodium and sulfur. The metal extraction wastewater may include, for example, wastewater derived from a process for recovering reusable metal parts from waste batteries using sodium and sulfur as chemical components. Therefore, the metal extraction wastewater may contain an extractant, a diluent, metal ions, and sodium sulfate.

[0032] According to a specific embodiment of the present invention, the recycling process of waste batteries from metal extraction wastewater, for example, the NCM (Li (Ni, Co, Mn) O2) waste battery recycling process includes a process of discharging the waste batteries and physically screening the constituent elements of the waste batteries into positive electrode materials such as Cu and Al, positive / negative electrode powders and plastics, and reducing the black powder (positive electrode active material component) recovered in this process at high temperature using hydrogen or carbon, Na2CO3, etc. and then washing with water, thereby first recovering the lithium contained therein. The remaining residues contain nickel, cobalt and manganese, which can be introduced into wet extraction processes for respectively recovering these residues. The extractants used in these wet extraction processes are phosphoric acid-based extractants or organic acid-based extractants, and a large amount of salts may be generated during the extraction process, especially metal extraction wastewater containing sulfide salts.

[0033] As described above, in the recycling process of waste batteries, when the waste batteries contain harmful components or are discharged without separate treatment due to strong acidity and high salt content, metal extraction wastewater that may cause water pollution will be discharged, and the metal extraction wastewater contains a large amount of sodium and sulfur as described above, so it can become the feed of the process of the present invention. The LCO (LiCoO2), NCA (Li (Ni, Co, Al) O2), LMO (LiMn2O4) batteries are also subjected to a waste battery recycling process similar to that of the NCM batteries, thereby generating metal extraction wastewater containing sodium and sulfur, so the metal extraction wastewater generated in these waste battery recycling processes can also become the feed of the process of the present invention.

[0034] In a specific embodiment, the sum of the sodium content and the sulfur content contained in the metal extraction wastewater may be 1-25% by weight. When the sum of the sodium content and the sulfur content of the metal extraction wastewater is less than 1% by weight, the subsequent electrodialysis efficiency may be reduced due to the low conductivity of the wastewater. When the sum of the sodium content and the sulfur content exceeds 25% by weight, sodium sulfate crystallization occurs, thereby causing the membrane used for electrodialysis to be blocked.

[0035] In a specific embodiment, the pH of the metal extraction wastewater can be 1 to 8. The metal recovery process of the waste battery corresponds to the process of extracting specific metal components by changing the pH. For example, when the waste battery is an NCM waste battery, Mn is first recovered at a low pH, then the pH is increased to recover Co, and finally Ni is recovered, and the recovery of Ni is carried out by using a phosphoric acid-based extractant or an organic acid-based extractant. When a phosphoric acid-based extractant is used as a Ni extractant, the pH of the metal extraction wastewater after recovering Ni can be about 4 to 8. When an organic acid-based extractant is used as an extractant, the solubility of the organic acid in the water system is high, so a step of recovering the organic acid dissolved in the water system by reducing the pH of the water system is further performed. The pH of the metal extraction wastewater obtained after these additional organic acid recovery steps can be about 1 to 4.

[0036] According to a specific embodiment of the present invention, the process of recovering acid and alkali from the metal extraction wastewater may include a step of pre-treating the metal extraction wastewater. The pre-treatment step is equivalent to a step of purifying the metal extraction wastewater to a state suitable for introducing electrodialysis.

[0037] In a specific embodiment, the step of pre-treating the metal extraction wastewater may include coagulation precipitation, adsorption, ion exchange, oxidation or a combination thereof. Coagulation precipitation is a process in which the extractant, total phosphorus (TP), salt, heavy metal, and non-degradable organic matter present in the wastewater are coarsened by adding a chemical coagulant or by electrocoagulation so that they can be precipitated, thereby separating them from the treatment liquid. More specifically, the coagulation step is a step of adding a chemical coagulant or dissolving metal ions from an electrode to form hydroxides of the metal ions, and coagulating the pollutants through the coagulation reaction of these hydroxides with the pollutants present in the water system. Among them, the coagulant refers to the substance coagulated by the total phosphorus, salt, heavy metal, and non-degradable organic matter present in the water system through electrocoagulation, and the treatment liquid refers to the liquid component after the coagulant is separated from the metal extraction wastewater.

[0038] The precipitation step after the coagulation is a step of separating and removing the coagulation of harmful substances from the treatment liquid of the metal extraction wastewater according to the density difference between the treatment liquid of the metal extraction wastewater and the coagulation of harmful substances. In a specific embodiment, the precipitation step can be carried out by a known device for separating coagulation from the treatment liquid, for example, the precipitation step can be carried out by a known device such as a sedimentation tank and a skimmer. After the precipitation step, the coagulation separated from the treatment liquid can be discarded or introduced into an additional treatment step, and the treatment liquid can be introduced into the additional process step described later.

[0039] The adsorption step is a step of removing the diluent present in the metal extraction wastewater by adsorbing it with an adsorbent. The adsorption step is not limited as long as the treated liquid and the diluent of the metal extraction wastewater can be separated. As an example, it can be performed by filtering through a filter containing an adsorbent. The type of adsorbent is not limited as long as it can adsorb the diluent. As an example, activated carbon can be used.

[0040] The ion exchange step corresponds to a step of separating the polyvalent metal ions remaining in the treatment solution. In the ion exchange step, the polyvalent metal ions in the treatment solution are precipitated and separated in the form of salts by adding an ion exchange solution.

[0041] The oxidation step may be performed using chemical substances. For example, the oxidation step may include a step of using Fenton oxidation or ozone oxidation by injecting ozone, wherein the Fenton oxidation generates hydroxyl radicals (OH radicals) by a catalytic reaction of metal extraction wastewater and hydrogen peroxide. In addition, any process that oxidizes and removes harmful substances by oxidation reaction may be used without limitation.

[0042] The process for recovering acid and alkali from the metal extraction wastewater comprises the step of subjecting the pretreated metal extraction wastewater to electrodialysis. The electrodialysis step is to decompose the water component of the pretreated metal extraction wastewater into H by applying a power supply between two electrodes. + and OH - After that, it is combined with ionic components or salts, such as Na2SO4, present in the pretreated metal extraction wastewater and recovered in the form of acid and alkali. The device used in the electrodialysis step can be used without limitation as long as it can recover acid and alkali from the pretreated metal extraction wastewater.

[0043] In a specific embodiment, the step of electrodialyzing the pretreated metal extraction wastewater can be performed using a bipolar membrane, a cationic membrane, an anionic membrane or a combination thereof. The cationic membrane is a membrane composed of a polymer layer that can only penetrate cations, the anionic membrane is a membrane composed of a polymer layer that can only penetrate anions, and the bipolar membrane is a membrane composed of a polymer layer that can penetrate cations and a polymer layer that can penetrate anions. Preferably, the electrodialysis step can be performed using a bipolar membrane.

[0044] See also Figure 2 , schematically shows the electrodialysis step using a bipolar membrane. Water is decomposed into H at the interface of the bipolar membrane's cation-permeable polymer layer and anion-permeable polymer layer. + and OH - After that, OH - Na2SO4 salt decomposition produces + The ions combine to form NaOH, a base, H + SO4 generated by decomposition of Na2SO4 salt 2- The ions combine to generate H2SO4 as an acid. The existing membrane process is characterized by selectivity of substances that can pass through the membrane, however, the bipolar membrane is characterized by the electrolysis of water occurring at the interface where the polymer layer that passes cations and the polymer layer that passes anions meet, rather than at the electrode surface. Therefore, the bipolar membrane has the following advantages: there is no need to set electrodes between each membrane, and electrodialysis can be performed by only setting electrodes at both ends of the membrane stack, and it can also operate at a lower voltage, so the device design cost and device operation cost can be reduced.

[0045] See also Figure 3, schematically showing the electrodialysis step using only a cationic membrane and an anionic membrane. Unlike the case of using a bipolar membrane, in the case of electrodialysis using only a cationic membrane and an anionic membrane, electrodes are not only arranged at both ends of the membrane stack, but also arranged inside the membrane stack, and a voltage for electrolyzing water needs to be applied. However, the concentration of acid and alkali generated by electrodialysis using only a cationic membrane and an anionic membrane is higher than the concentration of acid and alkali generated by electrodialysis using a bipolar membrane.

[0046] According to a specific embodiment of the present invention, the electrodialysis step can be carried out at a temperature of 15-55°C. Na2SO4 contained in metal extraction wastewater is usually crystallized after removing other harmful substances contained in the wastewater by coagulation, filtration, etc., so as to be reused as a chemical substance in other processes. This crystallization of Na2SO4 requires a large amount of water, and the water used therein requires high temperature, so it is not efficient in terms of energy consumption. However, in a specific embodiment of the present invention, as described above, by using, for example, a bipolar membrane to electrodialyze the Na2SO4 contained in the pretreated metal extraction wastewater to recover NaOH that can be used for saponification of the wet extractant and H2SO4 as the wet extractant, this electrodialysis can be carried out at a temperature lower than the above-mentioned crystallization temperature, i.e., 15-55°C, so it may be advantageous in terms of energy consumption compared to the existing Na2SO4 crystallization process. The electrodialysis step can preferably be carried out at a temperature of 20-50°C, and more preferably at a temperature of 30-40°C.

[0047] According to a specific embodiment of the present invention, the process for recovering acid and alkali from the metal extraction wastewater may further include the step of introducing the metal extraction wastewater into reverse osmosis treatment after the electrodialysis step. There is still a low concentration of salt in the metal extraction wastewater of electrodialysis, and the reverse osmosis treatment can separate pure water therefrom through a reverse osmosis membrane. The separated pure water is called regenerated water, and the regenerated water is recycled to the electrodialysis device. The metal extraction wastewater remaining after the pure water separation contains salt, which is called concentrated water. The concentrated water is transferred to the pretreatment step again and used as a feed for recovering acid and alkali.

[0048] According to a specific embodiment of the present invention, the process for recovering acid and alkali from the metal extraction wastewater may further include an electrochemical advanced oxidation step. The electrochemical advanced oxidation step may be performed before or after the pretreatment step. Electrochemical advanced oxidation is a process in which hydroxyl radicals (OH radicals) are generated on the electrode surface by electrolysis of water, and the high reactivity of hydroxyl radicals is utilized to oxidize and remove harmful substances present in the wastewater. The electrochemical advanced oxidation step may be used without restriction as long as it is a process in which harmful substances are oxidized and removed by an oxidation reaction utilizing electrical energy.

[0049] According to a specific embodiment of the present invention, the process for recovering acid and alkali from the metal extraction wastewater may further include an additional purification step of the pretreated metal extraction wastewater. The additional purification step corresponds to a step of removing fine harmful substances remaining in the pretreated metal extraction wastewater that have not been removed in the pretreatment step. The additional purification step is not particularly limited as long as the residual pollutants can be removed. According to a specific embodiment of the present invention, the additional purification step may preferably be microfiltration or ultrafiltration. The additional purification step may be performed before or after the pretreatment step, and may be performed once or multiple times.

[0050] Hereinafter, preferred embodiments are presented to help understand the present invention. However, the following embodiments are provided only to make it easier to understand the present invention, and the present invention is not limited thereto.

[0051] Example

[0052] Example 1: Electrodialysis Pretreatment for Metal Extraction Wastewater

[0053] The metal extraction wastewater from the waste battery recycling process having the properties shown in Table 1 below was introduced into pretreatment such as coagulation precipitation, oxidation, adsorption and ion exchange to remove impurities. The removal degree of total organic carbon (TOC), total phosphorus (TP) and metal in the metal extraction wastewater pretreated according to the combination of each pretreatment step is shown in Table 2.

[0054] [Table 1]

[0055]

[0056] [Table 2]

[0057]

[0058] As shown in Table 2, it was confirmed that the TOC, TP and metal ion contents of the metal extraction wastewater pretreated by coagulation / precipitation, Fenton oxidation / precipitation, ozone oxidation / precipitation, activated carbon adsorption and ion exchange were reduced.

[0059] When multivalent metal ions undergo electrodialysis, they form metal hydroxides on the membrane, which may cause membrane fouling. Pre-treating metal extraction wastewater with reduced metal ion content can reduce such fouling.

[0060] In addition, the metal extractant remaining in the metal extraction wastewater is a hydrophobic oil. In the subsequent electrodialysis step, a hydrophobic film is formed on the membrane surface, which may hinder the movement of ions. The reduced TOC and TP in Table 2 indicate that the content of the metal extractant present in the metal extraction wastewater is reduced.

[0061] As described above, the pretreatment of metal extraction wastewater has the advantages of preventing degradation of membrane performance and allowing the electrodialysis device to be operated for a long time by removing components that adversely affect the performance and life of the membrane in the subsequent electrodialysis step.

[0062] The present invention is described in detail above through specific embodiments. The specific embodiments are used to specifically illustrate the present invention, and the present invention is not limited thereto. It is natural that those skilled in the art can modify or improve it within the scope of the technical concept of the present invention.

[0063] Simple modifications or changes of the present invention all fall within the scope of the present invention, and the specific protection scope of the present invention will become more specific through the claims.

Claims

1. A process for recovering acid and alkali from metal extraction wastewater, comprising the following steps: Pre-treat metal extraction wastewater; as well as The pretreated metal extraction wastewater is subjected to electrodialysis.

2. The process for recovering acid and alkali from metal extraction wastewater according to claim 1, wherein: The metal extraction wastewater contains sodium and sulfur.

3. The process for recovering acid and alkali from metal extraction wastewater according to claim 1, wherein: The metal extraction wastewater contains a sodium content and a sulfur content which is 1-25% by weight in total.

4. The process for recovering acid and alkali from metal extraction wastewater according to claim 1, wherein: The pH of the metal extraction wastewater is 1 to 8.

5. The process for recovering acid and alkali from metal extraction wastewater according to claim 1, wherein: The steps of pre-treating the metal extraction wastewater include coagulation precipitation, adsorption, ion exchange, oxidation or a combination thereof.

6. The process for recovering acid and alkali from metal extraction wastewater according to claim 1, wherein: The step of subjecting the pretreated metal extraction wastewater to electrodialysis is performed by using a bipolar membrane, a cationic membrane, an anionic membrane or a combination thereof.

7. The process for recovering acid and alkali from metal extraction wastewater according to claim 1, wherein: The step of subjecting the pretreated metal extraction wastewater to electrodialysis is carried out at a temperature of 15-55°C.

8. The process for recovering acid and alkali from metal extraction wastewater according to claim 1, wherein: The process further comprises the step of subjecting the metal extraction wastewater to electrochemical advanced oxidation.

9. The process for recovering acid and alkali from metal extraction wastewater according to claim 1, wherein: The process further comprises the step of subjecting the pretreated metal extraction wastewater to microfiltration.

Images