Method for separating magnesium

Abstract

To provide a method for separating cobalt, magnesium and nickel, in one extraction step from a liquid containing cobalt, magnesium and nickel by an organic solvent.SOLUTION: A method for separating magnesium from a liquid containing cobalt, magnesium and nickel includes: a cobalt extraction step of adding an acidic organic phosphorus compound to a liquid containing cobalt, magnesium and nickel, and extracting the cobalt; and a magnesium extraction step of extracting the magnesium from an extraction residual liquid obtained in the cobalt extraction step. The liquid containing the magnesium and the nickel is preferably obtained through a dissolution step of dissolving active substance powder obtained by pre-treating a waste lithium ion battery in a mineral acid, and obtaining an acid dissolution liquid, a neutralization step of neutralizing the acid dissolution liquid with alkali, a manganese extraction step of extracting manganese from the acid dissolution liquid obtained in the neutralization step by using a first organic solvent as an extract, and a cobalt extraction step of extracting cobalt from the residual liquid of the manganese extraction step by using a second organic solvent as an extract.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for separating magnesium from a liquid containing cobalt, magnesium and nickel. [Background technology]

[0002] In recent years, with the widespread use of lithium ion batteries, methods have been considered for recovering valuable metals such as cobalt, nickel, manganese, and lithium from discarded lithium ion batteries and reusing them as materials for the lithium ion batteries.

[0003] Conventionally, when recovering the valuable metals from the waste lithium-ion batteries, the waste lithium-ion batteries are subjected to a heat treatment (roasting), and then crushed, classified, etc. to obtain a powder containing the valuable metals. From the powder, cobalt, nickel, manganese, and lithium are separated and refined by a wet process (see, for example, Patent Document 1).

[0004] In the present invention, the waste lithium ion batteries refer to used lithium ion batteries that have run out of life as battery products, lithium ion batteries that have been discarded as defective products in the manufacturing process, and the remaining positive and negative electrode materials used in the manufacturing process. The powder containing the positive and negative electrodes obtained from the waste lithium ion batteries is called the active material powder. Furthermore, the impurities refer to metals contained in the active material powder that do not require recovery. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7303947 Summary of the Invention [Problem to be solved by the invention]

[0006] In the manufacture of lithium-ion batteries, attempts have been made to add an appropriate amount of magnesium to improve battery performance. When valuable metals are separated and refined from waste lithium-ion batteries containing magnesium as an impurity by a wet process, there is a method of removing magnesium by neutralization, but due to the nature of neutralization separation, precise separation is difficult. As a result, magnesium is contained in both cobalt and nickel, and cobalt and nickel containing magnesium are of a quality that cannot be reused in the manufacture of lithium-ion batteries, so a method of separating magnesium from a solution containing cobalt, magnesium, and nickel is desired. The method for producing a cobalt solution described in Patent Document 1 includes a cobalt extraction step in which a cobalt-containing solution containing nickel ions and magnesium ions is obtained by at least subjecting battery powder from lithium-ion battery waste to a leaching treatment, and a magnesium separation step in which cobalt ions and some of the magnesium ions are extracted from the cobalt solution obtained in the cobalt extraction step using a solvent containing a carboxylic acid extractant to separate the magnesium ions, and then the cobalt ions are stripped from the solvent to obtain a cobalt solution as a stripped liquid.

[0007] However, in order to separate cobalt ions and magnesium ions in the magnesium separation step, two or more kinds of extractants and a pH adjuster in an amount twice the amount of cobalt are practically used, at least one cobalt back-extraction step is performed, and two or more cobalt extraction steps are required, and further, there is the inconvenience that the pH adjuster is not recovered. As a result, the amounts of the extractants, pH adjusters, and other chemicals used in the method for producing a cobalt solution are large.

[0008] The problem to be solved by the present invention is to provide a method capable of separating cobalt, magnesium, and nickel from a liquid containing cobalt, magnesium, and nickel in a single extraction step using an organic solvent, while reducing the amount of chemicals used. [Means for solving the problem]

[0009] The present inventors have conducted extensive research in light of the above problems and have found that cobalt, magnesium and nickel can be separated by extracting cobalt from a liquid containing cobalt, magnesium and nickel using an acidic organophosphorus compound as an extractant and then extracting magnesium. The present invention has been completed based on these findings.

[0010] The present invention relates to a method for separating magnesium from a liquid containing cobalt, magnesium, and nickel, comprising a cobalt extraction step of adding an acidic organophosphorus compound to the liquid containing cobalt, magnesium, and nickel to extract cobalt, and a magnesium extraction step of extracting magnesium from the extraction residue obtained in the cobalt extraction step.

[0011] The method for separating magnesium preferably includes a dissolving step of dissolving an active material powder obtained by pretreating a waste lithium ion battery in a mineral acid to obtain an acid solution, a neutralizing step of neutralizing the acid solution with an alkali, a manganese extraction step of extracting manganese from the acid solution obtained in the neutralizing step using a first organic solvent as an extracting solution, a cobalt extraction step of extracting cobalt from the extraction residue obtained in the manganese extraction step using a second organic solvent as an extracting solution, a magnesium extraction step of making the residue of the cobalt extraction step into a liquid containing magnesium and nickel, and a further step of extracting nickel from the residue of the magnesium extraction step using a third organic solvent as an extracting solution. and obtaining a first lithium salt aqueous solution as a residual liquid; and a membrane electrolysis step of subjecting the first lithium salt aqueous solution to membrane electrolysis using an ion exchange membrane to obtain a lithium hydroxide aqueous solution, an acid, and a second lithium salt aqueous solution that is more dilute than the first lithium salt aqueous solution, wherein the lithium hydroxide aqueous solution obtained in the membrane electrolysis step is reused in at least one selected from the group consisting of the neutralization step, the manganese extraction step, the cobalt extraction step, the magnesium extraction step, and the nickel extraction step, and the acid obtained in the membrane electrolysis step is reused as the mineral acid used in the dissolution step.

[0012] The acidic organophosphorus compound preferably includes at least one selected from the group consisting of bis(2,4,4-trimethylpentyl)phosphinic acid, phosphoric acid diester, and 2-ethylhexylphosphonic acid mono 2-ethylhexyl ester. Preferably, the manganese extraction step is carried out in the pH range of 1.5 to 3.0, the cobalt extraction step in the pH range of 3.0 to 4.5, the magnesium extraction step in the pH range of 4.5 to 5.5, and the nickel extraction step in the pH range of 5.0 to 6.5. The mineral acid preferably includes at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, and more preferably includes hydrochloric acid. The alkali used in the neutralization step preferably comprises lithium hydroxide. The electricity used in the membrane electrolysis step preferably includes electricity obtained from renewable energy, and more preferably includes electricity obtained from at least one selected from the group consisting of solar power generation, wind power generation, geothermal power generation, hydroelectric power generation, and biomass power generation. Effect of the Invention

[0013] The method for separating magnesium from a liquid containing cobalt, magnesium and nickel according to the present invention provides a method for continuously separating cobalt, magnesium and nickel from a liquid containing magnesium and nickel by a single extraction step using an organic solvent, respectively, and the amount of chemicals used in the extraction step is small. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of one embodiment of the method for separating magnesium of the present invention. [Diagram 2] FIG. 2 is an explanatory cross-sectional view showing the structure of an ion exchange membrane electrolytic cell used in the method for separating magnesium of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention will now be described in further detail. In addition, unless otherwise specified, "~" in a numerical range means from above to below, and both ends of the range are included. In addition, when a numerical range is indicated, the upper limit and the lower limit can be appropriately combined, and the numerical range obtained by combining them is also disclosed. In addition, in the description of the drawings, the same elements are denoted by the same reference numerals, and duplicated description will be omitted. Also, the dimensional ratios of the drawings are exaggerated for the convenience of explanation, and may differ from the actual ratios.

[0016] The method of the present invention for separating magnesium from a liquid containing cobalt, magnesium, and nickel (hereinafter, may be referred to as a Mg separation method) includes a magnesium extraction step of adding an acidic organophosphorus compound to the liquid containing cobalt, magnesium, and nickel to extract magnesium.

[0017] The liquid containing cobalt, magnesium and nickel is obtained, for example, by carrying out a dissolution step, a neutralization step and a manganese extraction step, which will be described later.

[0018] The acidic organic phosphorus compound is not limited to a specific phosphorus compound. The acidic organic phosphorus compound preferably includes at least one selected from the group consisting of bis(2,4,4-trimethylpentyl)phosphinic acid, phosphoric acid diester, and 2-ethylhexylphosphonic acid mono 2-ethylhexyl ester, more preferably includes bis(2,4,4-trimethylpentyl)phosphinic acid, and even more preferably is bis(2,4,4-trimethylpentyl)phosphinic acid.

[0019] One embodiment of the Mg separation method of the present invention will be described in more detail with reference to the accompanying drawings. As shown in FIG. 1, one embodiment of the Mg separation method of the present invention may start with active material powder 1.

[0020] The active material powder 1 will be described. When the waste lithium ion battery is a used lithium ion battery whose life as a battery product has expired, or a lithium ion battery that has been discarded as a defective product in the manufacturing process, a discharge treatment is first performed. Various methods with high safety, such as resistance discharge, can be adopted for the discharge treatment. After discharging all remaining charges by discharging, and then forming an opening in the housing of the waste lithium ion battery, for example, heat treatment (roasting) at a temperature in the range of 100 to 800 ° C. or without heat treatment, the battery is crushed with a crusher such as a hammer mill or a jaw crusher, and the housing, current collector, etc. constituting the waste lithium ion battery are removed by sieving (classification), thereby obtaining the active material powder. Alternatively, the waste lithium ion battery after the discharge treatment may be crushed with the crusher, the housing, current collector, etc. are removed by sieving, and then the active material powder 1 may be obtained by heat treatment at a temperature in the range.

[0021] When the waste lithium ion batteries are residual positive electrode materials or the like used in commercialization in a manufacturing process, the active material powder may be obtained by pulverizing the waste lithium ion batteries in the pulverizer after heat treatment at a temperature in the above range or without heat treatment without performing the discharge treatment and the formation of openings, and removing the current collectors and the like by sieving.Furthermore, the waste lithium ion batteries may be pulverized in the pulverizer, removing the current collectors and the like by sieving, and then heat treatment at a temperature in the above range or without heat treatment to obtain the active material powder.

[0022] The magnesium separation method of the present invention may include a dissolving step (STEP 1 in FIG. 1) of dissolving the active material powder 1 in a mineral acid to obtain an acid solution. The active material powder 1 may contain valuable metals such as iron, aluminum, manganese, cobalt, magnesium, nickel, etc., in addition to lithium. The mineral acid preferably contains at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid, more preferably contains hydrochloric acid, and even more preferably is hydrochloric acid.

[0023] The magnesium separation method of the present invention may include a neutralization step (STEP 2 in FIG. 1) of neutralizing the acid solution with an alkali. The alkali may be added in at least one form selected from the group consisting of an aqueous solution and a solid form. The alkali preferably includes at least one selected from the group consisting of an alkali metal hydroxide and ammonia. The alkali metal constituting the alkali metal hydroxide preferably includes at least one selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and francium, more preferably includes lithium, sodium, and potassium, further preferably lithium, sodium, or potassium, and particularly preferably lithium.

[0024] The magnesium separation method of the present invention may include a manganese extraction step (STEP 3 in FIG. 1) in which manganese is extracted from the acid solution obtained in the neutralization step using a first organic solvent as an extraction solution. The residual solution in the manganese extraction step can be the liquid containing cobalt, magnesium, and nickel.

[0025] The magnesium separation method of the present invention may include a cobalt extraction step (STEP 4 in FIG. 1) of extracting cobalt from the residual liquid of the manganese extraction step using a second organic solvent as an extracting solution, and a nickel extraction step (STEP 6 in FIG. 1) of extracting nickel from the residual liquid of the magnesium extraction step (STEP 5 in FIG. 1) using a third organic solvent as an extracting solution, and obtaining a first lithium salt aqueous solution as the residual liquid.

[0026] When the alkali is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide, the first lithium salt aqueous solution and at least one salt of sodium and potassium are each separated from the aqueous alkali mixed salt solution obtained in the nickel extraction step by the method disclosed in Japanese Patent No. 7084669. The lithium salt contained in the first lithium salt aqueous solution becomes lithium chloride when hydrochloric acid is used in the dissolving step.

[0027] The first to third organic solvents each preferably contain at least one organic phosphorus compound selected from the group consisting of phosphoric acid esters, phosphonic acid esters, phosphinic acid, and phosphine oxides, more preferably the organic phosphorus compounds, and even more preferably bis(2,4,4-trimethylpentyl)phosphinic acid. The organic phosphorus compounds are commercially available, and examples thereof include D2EHPA (di(2-ethylhexyl)phosphate) as an acidic phosphoric acid ester, PC-88A manufactured by Daihachi Chemical Industry Co., Ltd. as a phosphonic acid ester, CYANEX272 manufactured by Solvay as a bis(2,4,4-trimethylpentyl)phosphinic acid, TBP (tributyl phosphate) as a neutral phosphoric acid ester, and tri-n-octylphosphine (TOPO) as a phosphine oxide.

[0028] The acidic organic phosphorus compound and the first to third organic solvents may each be diluted with a hydrocarbon such as kerosene or decane.

[0029] Preferably, the manganese extraction step is carried out in the pH range of 1.5 to 3.0, the cobalt extraction step in the pH range of 3.0 to 4.5, the magnesium extraction step in the pH range of 4.5 to 5.5, and the nickel extraction step in the pH range of 5.0 to 6.5.

[0030] Although not shown in FIG. 1, after each of the manganese extraction step, the cobalt extraction step, the magnesium extraction step, and the nickel extraction step, scrubbing of each extract solution may be performed, and each aqueous solution after the scrubbing may be returned to each step. Unnecessary valuable metals are extracted in each extract solution. Scrubbing can remove these unnecessary valuable metals, making it possible to improve the quality of the recovered metals. Furthermore, since the valuable metals are returned to each step together with each aqueous solution after the scrubbing, they can be recovered later, making it possible to increase the recovery rate of the valuable metals. The extract from each of the above steps may be back-extracted with, for example, sulfuric acid to recover each valuable metal as sulfates 2A to 2D.

[0031] When bis(2,4,4-trimethylpentyl)phosphinic acid is used as the acidic organic phosphorus compound and the first to third organic solvents, the manganese extraction step, the cobalt extraction step, the magnesium extraction step, and the nickel extraction step can be carried out without a back-extraction step, and valuable metals (manganese, cobalt, nickel, and lithium) can be recovered from waste lithium-ion batteries at a high recovery rate and at low cost using small-sized equipment.

[0032] The magnesium separation method of the present invention may next include a membrane electrolysis step of subjecting the first lithium salt aqueous solution to membrane electrolysis using an ion exchange membrane in STEP 7. The membrane electrolysis step in STEP 7 can be performed using, for example, an electrolytic cell 11 shown in FIG.

[0033] The electrolytic cell 11 is equipped with an anode plate 12 on one of its inner surfaces and a cathode plate 13 on the inner surface opposite the anode plate 12, the anode plate 12 being connected to an anode 14 of a power supply, and the cathode plate 13 being connected to a cathode 15 of the power supply. The electrolytic cell 11 is also partitioned by an ion exchange membrane 16 into an anode chamber 17 equipped with the anode plate 12 and a cathode chamber 18 equipped with the cathode plate 13.

[0034] In the electrolytic cell 11, when the first lithium salt aqueous solution, for example, lithium chloride, is supplied to the anode chamber 17 and membrane electrolysis is performed, chloride ions are converted into chlorine gas (Cl) on the anode plate 12. 2 ), while the lithium ions migrate through the ion exchange membrane 16 to the cathode chamber 18.

[0035] In the cathode chamber 18, water (H 2 O) is converted to hydroxide ion (OH - ) and hydrogen ions (H + ) and hydrogen ions are ionized into hydrogen gas (H 2 ), while the hydroxide ions combine with lithium to produce a lithium hydroxide aqueous solution 3.

[0036] The electricity used in the membrane electrolysis step preferably includes electricity obtained from renewable energy, and more preferably includes electricity obtained from at least one selected from the group consisting of solar power generation, wind power generation, geothermal power generation, hydroelectric power generation, and biomass power generation.

[0037] The hydrogen gas (H 2 ) and chlorine gas (Cl 2 ) to obtain hydrochloric acid as mineral acid 4, which can be used to dissolve active material powder 1 in STEP 1.

[0038] The lithium hydroxide aqueous solution 3 obtained by the membrane electrolysis is crystallized in STEP 7 to produce lithium hydroxide monohydrate (LiOH·H 2 In STEP 8, lithium carbonate (Li 2 CO 3 The carbonation can also be carried out by converting the lithium hydroxide aqueous solution 3 into carbon dioxide (CO 2 ) can be reacted.

[0039] When the lithium hydroxide aqueous solution 3 is used in at least one selected from the group consisting of the manganese extraction step, the cobalt extraction step, the magnesium extraction step, and the nickel extraction step, the lithium hydroxide aqueous solution 3 is added to the extraction solvent in each of the extraction steps. As a result, the added lithium is not discharged outside the system, and is recycled. The extraction solvent used in at least one selected from the group consisting of the manganese extraction step, the cobalt extraction step, the magnesium extraction step, and the nickel extraction step is a cation exchange extractant, so that the liquid tends to become acidic when used continuously, and the extraction rate decreases, but the decrease in the extraction rate can be suppressed by adding the lithium hydroxide aqueous solution 3. Here, it is necessary to add lithium hydroxide in an amount necessary to extract the valuable metal to be extracted once. In other words, in the extraction step, the total amount of lithium hydroxide used is determined depending on the amount of each valuable metal contained in the active material powder obtained by pretreating the waste lithium ion battery. In the present invention, since cobalt, magnesium, and nickel can be separated in each extraction step, only the minimum amount of lithium hydroxide required needs to be added. This allows the amount of drug used to be reduced.

[0040] In the membrane electrolysis step, the first lithium salt aqueous solution is subjected to membrane electrolysis, resulting in the production of a second lithium salt aqueous solution that is more dilute than the first lithium salt aqueous solution. Therefore, in the magnesium separation method of the present invention, the second lithium salt aqueous solution may be concentrated in a concentration step in STEP 10 and added to the first lithium salt aqueous solution. The concentration step in STEP 10 may be performed using, for example, a reverse osmosis membrane (RO membrane).

[0041] In the magnesium separation method of the present invention, cobalt, magnesium, and nickel can be separated from a liquid containing cobalt, magnesium, and nickel in a single extraction step using an organic solvent. The amount of chemicals used in the extraction step is small. In addition, in the magnesium separation method of the present invention, since there is no unnecessary alkaline source other than lithium, the lithium hydroxide obtained by membrane electrolysis can be returned to the process as it is, making it possible to recycle resources. EXAMPLES

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

[0043] In the examples and comparative examples, the content of valuable metals in each solution was measured by inductively coupled plasma optical emission spectrometry (ICP-OES) using an OPTIMA8300 manufactured by PerkinElmer.

[0044] [Example 1] 10 kg of positive electrode powder obtained from waste lithium ion batteries was dissolved in hydrochloric acid adjusted to a hydrochloric acid concentration of 9 to 10 mol / L to obtain 50 L of an acid solution (dissolution step). The contents of each valuable metal in the acid solution are shown in Table 1.

[0045] Next, 50 L of D2EHPA (manufactured by Nacalai Tesque, Inc., kerosene content 70% by mass) diluted with kerosene was added to the 50 L of the solution, and the pH was adjusted to a range of 2 to 3 to extract manganese, and an aqueous cobalt salt solution was obtained as the extraction residue (manganese extraction step). The contents of each valuable metal in the aqueous cobalt salt solution are shown in Table 1.

[0046] Next, 50 L of bis(2,4,4-trimethylpentyl)phosphinic acid (Solvay CYANEX272, decane content 70% by mass) diluted with decane was added to the 50 L of the dissolution solution, and the pH was adjusted to a range of 3 to 4.5 to extract cobalt, and a liquid containing magnesium and nickel was obtained as the extraction residue (cobalt extraction step). The contents of each valuable metal in the liquid containing magnesium and nickel are shown in Table 1.

[0047] Next, 50 L of bis(2,4,4-trimethylpentyl)phosphinic acid (CYANEX272 manufactured by Solvay, decane content 70% by mass) diluted with decane was added to 50 L of the liquid containing magnesium and nickel, and the pH was adjusted to a range of 4.5 to 5.5 to extract magnesium, and a first aqueous nickel salt solution was obtained as an extraction residue (magnesium extraction step). The extract obtained in the magnesium extraction step was scrubbed with 1.5 mol / L hydrochloric acid, and the obtained second aqueous nickel salt solution was returned to the liquid containing magnesium and nickel to be subjected to the magnesium extraction step.

[0048] 50 L of the organic phase after the scrubbing was back-extracted with 5 L of sulfuric acid having a concentration of 16 mass % to obtain an aqueous magnesium salt solution. The contents of each valuable metal in the first aqueous nickel salt solution and the aqueous magnesium salt solution are shown in Table 1.

[0049] [Table 1] [Explanation of symbols]

[0050] 1 Active material powder, 2 Valuable metal sulfate, 3 Lithium hydroxide aqueous solution, 4 Mineral acid, 5 Lithium hydroxide monohydrate, 6 Lithium carbonate, 11 Electrolyzer, 12 Anode plate, 13 cathode plate, 14 anode, 15 cathode, 16 ion exchange membrane, 17 anode chamber, 18···Cathode chamber.

Claims

1. A method for separating magnesium from a liquid containing cobalt, magnesium and nickel, comprising the steps of: a cobalt extraction step in which an acidic organophosphorus compound is added to a liquid containing cobalt, magnesium and nickel to extract cobalt; A method for separating magnesium, comprising a magnesium extraction step of extracting magnesium from the extraction residue obtained in the cobalt extraction step.

2. 2. The method for separating magnesium according to claim 1, A dissolving step of dissolving the active material powder obtained by pretreating the waste lithium ion batteries in a mineral acid to obtain an acid solution; a neutralization step of neutralizing the acid solution with an alkali; a manganese extraction step of extracting manganese from the acid solution obtained in the neutralization step using a first organic solvent as an extraction solution; a cobalt extraction step of extracting cobalt from the extraction residue obtained in the manganese extraction step using a second organic solvent as an extraction solution; a magnesium extraction step of converting a residual liquid from the cobalt extraction step into a liquid containing magnesium and nickel; a nickel extraction step of extracting nickel from the residual liquid of the magnesium extraction step using a third organic solvent as an extraction liquid to obtain a first lithium salt aqueous solution as the residual liquid; and a membrane electrolysis step of subjecting the first lithium salt aqueous solution to membrane electrolysis using an ion exchange membrane to obtain a lithium hydroxide aqueous solution, an acid, and a second lithium salt aqueous solution that is more dilute than the first lithium salt aqueous solution, The lithium hydroxide aqueous solution obtained in the membrane electrolysis step is reused in at least one step selected from the group consisting of the neutralization step, the manganese extraction step, the cobalt extraction step, the magnesium extraction step, and the nickel extraction step; A method for separating magnesium, wherein the acid obtained in the membrane electrolysis step is reused as the mineral acid used in the dissolution step.

3. 2. The method for separating magnesium according to claim 1, wherein the acidic organophosphorus compound comprises at least one selected from the group consisting of bis(2,4,4-trimethylpentyl)phosphinic acid, phosphoric acid diester, and 2-ethylhexylphosphonic acid mono 2-ethylhexyl ester.

4. 3. The method for separating magnesium according to claim 2, wherein the manganese extraction step is carried out in the pH range of 1.5 to 3.0, the cobalt extraction step is carried out in the pH range of 3.0 to 4.5, the magnesium extraction step is carried out in the pH range of 4.5 to 5.5, and the nickel extraction step is carried out in the pH range of 5.0 to 6.

5.

5. 3. The method for separating magnesium according to claim 2, wherein the mineral acid comprises at least one selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid.

6. 6. The method of claim 5, wherein the mineral acid comprises hydrochloric acid.

7. 3. The method of claim 2, wherein the alkali used in the neutralization step comprises lithium hydroxide.

8. The method for separating magnesium according to any one of claims 1 to 7, wherein the electricity used in the membrane electrolysis step includes electricity obtained by renewable energy.

9. 9. The method for separating magnesium according to claim 8, wherein the electricity obtained by renewable energy includes electricity obtained by at least one selected from the group consisting of solar power generation, wind power generation, geothermal power generation, hydroelectric power generation, and biomass power generation.

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