Metal recovery method

Abstract

A method for recovering a metal from a metal-containing solution containing nickel ions, lithium ions, and anions of an inorganic acid, comprising: mixing the metal-containing solution with a solvent while adjusting an equilibrium pH using a pH adjuster containing lithium ions, transferring nickel ions in the metal-containing solution to the solvent, and performing extraction including separating the solvent containing nickel ions from an extraction residue liquid; and in the nickel extraction step, performing the extraction with the total of the lithium ion concentration of the metal-containing solution and the lithium ion concentration of the pH adjuster being not more than the lithium ion concentration in a saturated solution of a lithium salt formed by the anions of the inorganic acid and lithium ions contained in the metal-containing solution.

Description

Technical Field

[0001] This specification describes a method for recovering metals from a metal-containing solution.

Background Art

[0002] When recovering metals from ores or waste such as electric and electronic devices or lithium-ion batteries, a solvent extraction method can be used for a metal-containing solution obtained by leaching the metals in the ore or waste with an acidic leaching solution or the like (see, for example, Patent Documents 1 and 2).

[0003] In the above solvent extraction method, the metal-containing solution is brought into contact with a solvent, and among a plurality of types of metal ions in the metal-containing solution, a predetermined metal ion is extracted from the metal-containing solution into the solvent. Thereby, the metal ion can be separated from other metal ions in the metal-containing solution. Incidentally, thereafter, the solvent may be brought into contact with a stripping solution to strip the metal ions in the solvent into the stripping solution.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when nickel ions are extracted into a solvent from a metal-containing solution containing nickel ions and lithium ions using the solvent extraction method, precipitates may occur. In that case, the smooth progress of the nickel ion extraction operation is hindered by the precipitates, and in some cases, the operation is inevitably interrupted.

[0006] This specification provides a metal recovery method capable of effectively suppressing the generation of precipitates during the extraction of nickel ions.

Means for Solving the Problems

[0007] The metal recovery method disclosed in this specification is a method for recovering metal from a metal-containing solution containing nickel ions, lithium ions, and anions of inorganic acids. While adjusting the equilibrium pH using a pH adjuster containing lithium ions, the metal-containing solution is mixed with a solvent, nickel ions in the metal-containing solution are transferred to the solvent, and it has a nickel extraction step including extraction for separating the solvent containing nickel ions from the post-extraction liquid. In the nickel extraction step, the total of the lithium ion concentration of the metal-containing solution and the lithium ion concentration of the pH adjuster is made not more than the lithium ion concentration in a saturated solution of a lithium salt formed by the anions of the inorganic acids and lithium ions contained in the metal-containing solution, and the extraction is performed.

Advantages of the Invention

[0008] According to the above metal recovery method, the generation of precipitates during the extraction of nickel ions can be effectively suppressed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0010] The embodiments of the metal recovery method described above will be described in detail below. The metal recovery method of one embodiment is a method for recovering metal from a metal-containing solution containing nickel ions, lithium ions, and anions of inorganic acids, and includes a nickel extraction step using a solvent extraction method.

[0011] The nickel extraction step includes extraction for transferring nickel ions from the metal-containing solution to the solvent. More specifically, in the extraction of the nickel extraction step, for example, a mixer settler or the like is used, and nickel ions in the metal-containing solution are transferred to the solvent in the mixer, and then, in the settler, the solvent containing nickel ions and the post-extraction liquid are separated by specific gravity separation or the like.

[0012] In such extraction, it has newly been found that when the lithium ion concentration in the metal-containing solution is relatively high, precipitates containing lithium are generated in the mixer settler. When precipitates are generated, the extraction operation cannot be smoothly carried out, and in some cases, it is necessary to interrupt the operation to remove them. As a result of intensive studies by the inventors, it is considered that when a pH adjuster containing lithium ions comes into contact with the metal-containing solution, the lithium ion concentration locally increases significantly there, which causes the generation of the above-mentioned precipitates. In such a relatively minute contact area, when the total of the lithium ion concentration of the pH adjuster and the lithium ion concentration of the metal-containing solution exceeds the lithium ion concentration in a saturated solution of a lithium salt of the anion of the inorganic acid and lithium ions in the metal-containing solution (hereinafter, also referred to as "lithium ion concentration of the saturated lithium salt solution"), lithium salt precipitates. Since it is under mixing and stirring of the metal-containing solution and the solvent, immediately after precipitation, the surface is covered with the solvent and cannot be redissolved, which is presumed to become the precipitate. Based on such findings, in this embodiment, after adjusting the lithium ion concentration of each liquid so that the total of the lithium ion concentration of the metal-containing solution and the lithium ion concentration of the pH adjuster is equal to or lower than the lithium ion concentration of the saturated lithium salt solution, extraction is performed. Thereby, it is possible to suppress the local increase in the lithium ion concentration beyond the solubility when the pH adjuster comes into contact with the metal-containing solution, and effectively suppress the generation of precipitates during nickel ion extraction. Preferably, although it depends on the lithium ion concentration of the pH adjuster and the like, if the lithium ion concentration of the metal-containing solution is adjusted to be relatively low in advance so that the lithium ion concentration of the post-extraction liquid separated from the solvent in the settler is less than 15 g / L, the generation of precipitates can be suppressed more effectively. In this embodiment, in the extraction of the nickel extraction step, it is preferable to adjust the lithium ion concentration of the metal-containing solution so that the lithium ion concentration of the post-extraction liquid separated from the solvent is less than 15 g / L. Thereby, the generation of precipitates can be further suppressed. As a result, stable operation of the metal recovery method becomes possible.

[0013] The metal recovery method of the above-described embodiment can be used in a wet treatment process for recovering metals from battery powder of lithium-ion battery waste as shown in FIG. 1, for example. This process includes an acid leaching step of leaching metals in the battery powder to obtain a metal-containing solution, a neutralization step, a manganese extraction step, a cobalt extraction step, and a nickel extraction step performed on the metal-containing solution, a lithium hydroxide solution production step of producing a lithium hydroxide solution from the post-extraction liquid of the nickel extraction step, and a crystallization step of obtaining lithium hydroxide from the lithium hydroxide solution obtained in the lithium hydroxide solution production step. The battery powder may be obtained by performing pretreatment steps such as roasting, crushing, and sieving on the lithium-ion battery waste as exemplified in FIG. 2. Although the description will be made according to FIGS. 1 and 2 here, FIGS. 1 and 2 are merely illustrative and are not limited to such a specific flow.

[0014] (Lithium-ion battery waste) The lithium-ion battery waste targeted is a lithium-ion secondary battery that can be used in mobile phones and various other electronic devices, etc., and is discarded due to the life of the battery product, manufacturing defects, or other reasons. Recovering valuable metals from such lithium-ion battery waste is preferable from the viewpoint of effective utilization of resources. Lithium-ion battery waste refers to lithium-ion batteries that are targets for recycling, regardless of whether the lithium-ion batteries are traded at a valuable price or are traded free of charge or as industrial waste.

[0015] Lithium-ion battery waste has a housing containing aluminum as an outer package that wraps around it. Examples of such a housing include those made of only aluminum, those containing aluminum and iron, aluminum laminates, etc. Further, the lithium-ion battery waste contains, within the above housing, a positive electrode active material composed of a single metal oxide containing lithium and one selected from the group consisting of nickel, cobalt, and manganese, or a composite metal oxide containing two or more of them, etc. The positive electrode active material may include, for example, an aluminum foil (positive electrode substrate) coated and fixed with polyvinylidene fluoride (PVDF) or other organic binders. Additionally, lithium-ion battery waste may contain copper, iron, etc. Further, inside the housing of the lithium-ion battery waste, there is usually an electrolytic solution in which an electrolyte such as lithium hexafluorophosphate is dissolved in an organic solvent. Examples of the organic solvent that may be used include ethylene carbonate, diethyl carbonate, etc.

[0016] (Pretreatment process) In many cases, a pretreatment process is performed on lithium-ion battery waste. The pretreatment process may include at least one of roasting, crushing, and sieving. Lithium-ion battery waste becomes battery powder through the pretreatment process. The roasting, crushing, and sieving in the pretreatment process may each be performed as necessary and may be performed in any order. Battery powder means powder obtained by subjecting lithium-ion battery waste to some pretreatment so that the positive electrode material components are separated and concentrated. Battery powder may be obtained as a powdery material with the positive electrode material components concentrated by performing crushing and sieving on the lithium-ion battery waste with or without heat treatment.

[0017] In roasting, the above lithium-ion battery waste is heated. When roasting is performed, for example, metals such as lithium and cobalt contained in the lithium-ion battery waste can change into a form that is easily melted. During roasting, it is preferable to heat the lithium-ion battery waste while holding it in a temperature range of, for example, 450°C to 1000°C, preferably 600°C to 800°C, for 0.5 hours to 4 hours. In roasting, either heating in an air atmosphere or heating in an inert atmosphere such as nitrogen can be performed, and both heating in an air atmosphere and heating in an inert atmosphere can also be performed in this order or in the reverse order. The roasting furnace may be a batch type or a continuous type. For example, in the batch type, there is a stationary furnace, and in the continuous type, there is a rotary kiln furnace, etc., and various other furnaces can also be used.

[0018] During roasting, at least a part of the electrolyte is removed from the lithium-ion battery waste due to evaporation of the electrolyte or the like. In many cases, when the lithium-ion battery waste is heated during roasting, the low-boiling components in the internal electrolyte components evaporate sequentially. When roasting is performed, the electrolyte is removed and rendered harmless, and the organic binder is decomposed, which promotes the separation of the aluminum foil and the positive electrode active material during the subsequent crushing and sieving. Note that although the composition of the positive electrode active material changes due to roasting, here it will be referred to as the positive electrode active material even after roasting.

[0019] After roasting, crushing can be performed to take out the positive electrode active material and the like from the casing of the lithium-ion battery waste. In crushing, the casing of the lithium-ion battery waste is destroyed, and the positive electrode active material is selectively separated from the aluminum foil coated with the positive electrode active material.

[0020] For crushing, various known apparatuses or devices can be used. In particular, it is preferable to use an impact crusher that can apply an impact while cutting lithium-ion battery waste to crush it. Examples of such impact crushers include a sample mill, a hammer mill, a pin mill, a wing mill, a tornado mill, a hammer crusher, and the like. A screen can be installed at the outlet of the crusher, and thereby, the lithium-ion battery waste is discharged through the screen from the crusher after being crushed to a size that can pass through the screen.

[0021] After crushing the lithium-ion battery waste, screening is performed using a sieve with an appropriate mesh size. Thereby, aluminum and copper remain on the sieve, and battery powder with aluminum and copper removed to some extent can be obtained below the sieve.

[0022] The battery powder obtained in the pretreatment step contains nickel, cobalt, lithium, manganese, etc. For example, the nickel content of the battery powder is 1 mass% to 30 mass%, the cobalt content is 1 mass% to 30 mass%, the lithium content is 2 mass% to 8 mass%, and the manganese content is 1 mass% to 30 mass%, but it is not limited thereto. The battery powder may further contain 1 mass% to 10 mass% of aluminum, 1 mass% to 5 mass% of iron, and 1 mass% to 10 mass% of copper.

[0023] (Acid Leaching Step) In the acid leaching step, the battery powder is leached with an acidic leaching solution of a mineral acid such as sulfuric acid, hydrochloric acid, or nitric acid. Thereby, a solution containing metal ions and anions of inorganic acids formed by dissolving the metals in the battery powder and undissolved leaching residue are obtained. Here, in each step from the end of the leaching in the acid leaching step to the nickel extraction step described later, the solution in which the metals in the battery powder are dissolved is also referred to as a metal-containing solution.

[0024] In the acid leaching process, the pH of the acidic leachate or the post-leachate may be less than 3.5. Also, the oxidation-reduction potential (ORP value, silver / silver chloride electrode reference) may be 100 mV or less. After the leaching is completed, solid-liquid separation may be performed to separate the leaching residue from the metal-containing solution, or the metal-containing solution containing the leaching residue may be directly fed to the next neutralization process without performing solid-liquid separation. Here, as a diluent for adjusting the pH of the acidic leachate in the acid leaching process, the post-extraction solution (such as an aqueous lithium sulfate solution) of the nickel extraction process described later can be used. By doing so, lithium ions can circulate within a series of processes in the wet treatment, and the lithium ions in the solution can be concentrated within the process.

[0025] The metal-containing solution obtained in the acid leaching process may have, for example, a nickel ion concentration of 10 g / L to 50 g / L, a cobalt ion concentration of 5 g / L to 50 g / L, a lithium ion concentration of 2 g / L to 10 g / L, a manganese ion concentration of 0 g / L to 50 g / L, an aluminum ion concentration of 1.0 g / L to 20 g / L, an iron ion concentration of 0.1 g / L to 5.0 g / L, and a copper ion concentration of 0.005 g / L to 0.2 g / L.

[0026] (Neutralization Process) When the metal-containing solution obtained in the acid leaching process contains aluminum ions and / or iron ions, first, a neutralization process can be carried out to increase the pH of the metal-containing solution and separate the neutralization residue to obtain a post-neutralization solution. The neutralization process may include an aluminum removal stage and an iron removal stage. However, when the metal-containing solution does not contain aluminum ions and / or iron ions, the aluminum removal stage and / or the iron removal stage may be omitted.

[0027] In the aluminum removal stage, by increasing the pH of the metal-containing solution, at least a part of the aluminum ions is precipitated and removed by solid-liquid separation. At this time, for example, when the liquid temperature is 50 °C to 90 °C and the pH is increased to the range of 4.0 to 5.0 by a pH adjuster, aluminum ions can be effectively separated while suppressing the precipitation of nickel ions and / or cobalt ions.

[0028] In the iron removal stage, an oxidizing agent is added, and a pH adjuster is further added to raise the pH within the range of 4.0 to 5.0. Thereby, ferrous ions are oxidized from divalent to trivalent, and precipitate as solids such as oxides or iron hydroxide (Fe(OH)3), which can be removed by solid-liquid separation. The oxidation-reduction potential (ORP value, silver / silver chloride electrode reference) during oxidation is preferably 300 mV to 900 mV. The oxidizing agent is not particularly limited as long as it can oxidize iron, but it is preferably manganese dioxide, a positive electrode active material, and / or a manganese-containing leaching residue obtained by leaching the positive electrode active material. The manganese-containing leaching residue obtained by leaching the positive electrode active material with an acid may contain manganese dioxide. When using the above positive electrode active material or the like as the oxidizing agent, a precipitation reaction occurs in which manganese dissolved in the liquid becomes manganese dioxide, and thus the precipitated manganese can be removed together with iron.

[0029] Examples of the pH adjuster used in the neutralization such as the above-described de-aluminum stage and iron removal stage include lithium hydroxide, sodium hydroxide, sodium carbonate, ammonia, etc. Using lithium hydroxide is preferable because it can prevent contamination of sodium or the like in the lithium hydroxide recovered in the subsequent hydroxide process. When using the lithium hydroxide solution obtained in the hydroxide process or the crystallization process, lithium ions circulate within the wet treatment.

[0030] (Manganese extraction process) After the metal-containing solution has undergone the above neutralization process as necessary, manganese ions can be extracted and removed by a solvent extraction method. Here, if aluminum ions remain in the metal-containing solution, not only manganese ions but also aluminum ions are extracted and removed.

[0031] For the extraction of manganese ions, it is preferable to use an extractant containing a phosphate ester-based extractant. Specific examples of the phosphate ester-based extractant include di-2-ethylhexyl phosphoric acid (abbreviation: D2EHPA, for example, trade name: DP8R). Further, the extractant may be a mixture of a phosphate ester-based extractant and an oxime-based extractant. In this case, the oxime-based extractant is preferably an aldoxime or one mainly composed of an aldoxime. Specifically, for example, 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicylaldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), 5-nonylsalicylaldoxime (trade name: ACORGAM5640), etc. are available.

[0032] The extractant may be diluted with a hydrocarbon-based organic solvent such as an aromatic-based, paraffin-based, or naphthene-based one so that the concentration becomes 10% to 30% by volume and used as a solvent.

[0033] During extraction, the equilibrium pH is preferably set to 2.3 to 3.5, more preferably 2.5 to 3.0. For the pH adjuster used at this time, it is preferable to use a lithium hydroxide solution. For example, the lithium hydroxide solution obtained in the subsequent lithium hydroxide process or crystallization process can be used.

[0034] As an example, extraction is more specifically carried out by bringing a solution (aqueous phase) into contact with a solvent (organic phase) and typically stirring and mixing them with a mixer for, for example, 5 to 60 minutes to react metal ions with the extractant. The temperature during extraction is from normal temperature (about 15 to 25°C) to 60°C or lower, and it is preferably carried out at 35 to 45°C for reasons such as extraction rate, phase separation property, and evaporation of the organic solvent. Then, the mixed organic phase and aqueous phase are separated by a separator based on the specific gravity difference. Extraction in processes other than the manganese extraction process can also be carried out in substantially the same manner.

[0035] At the time of extraction, it is desirable to perform extraction by countercurrent multi-stage extraction in which the flow directions of the aqueous phase and the solvent used for each extraction are opposite. By doing so, it is possible to suppress the extraction of cobalt ions, nickel ions, and lithium ions and increase the extraction rate of manganese ions. When performing countercurrent multi-stage extraction, for example, it is effective to set the equilibrium pH at the time of the first-stage extraction to a value within the above range and lower the equilibrium pH at the time of extraction as the stages progress.

[0036] The cobalt ion concentration in the metal-containing solution after the manganese extraction step is, for example, 0 g / L to 50 g / L, typically 1 g / L to 15 g / L, the nickel ion concentration is, for example, 0 g / L to 50 g / L, typically 1 g / L to 20 g / L, and the lithium ion concentration is, for example, 1 g / L to 30 g / L, typically 5 g / L to 20 g / L.

[0037] (Cobalt Extraction Step and Crystallization Step) After extracting manganese ions, cobalt ions can be extracted and separated from the metal-containing solution by a solvent extraction method.

[0038] For the extraction of cobalt ions, it is preferable to use a solvent containing a phosphoric acid-based extractant, particularly a phosphonate ester-based extractant. In particular, 2-ethylhexyl 2-ethylhexylphosphonate (trade name: PC-88A, Ionquest 801) is suitable from the viewpoint of the separation efficiency between nickel and cobalt. The extractant can be diluted with a hydrocarbon-based organic solvent so that the concentration is 10% by volume to 30% by volume and used as a solvent.

[0039] When extracting cobalt ions, the equilibrium pH at the time of extraction is preferably 5.0 to 6.0, more preferably 5.0 to 5.5. If the pH is less than 5.0, there is a possibility that cobalt ions cannot be sufficiently extracted into the solvent. As the pH adjuster in this case, it is preferable to use a lithium hydroxide solution, and for example, the lithium hydroxide solution obtained in the subsequent lithium hydroxide step or crystallization step can be used.

[0040] Even when extracting cobalt ions, it is desirable to perform extraction by countercurrent multi-stage extraction in which the flow directions of the aqueous phase and the solvent used for each extraction are opposite. By doing so, it is possible to increase the extraction rate of cobalt ions while suppressing the extraction of nickel ions and lithium ions.

[0041] During the above extraction, not only cobalt ions but also nickel ions and lithium ions may be slightly extracted into the solvent. In this case, if necessary, the solvent containing cobalt ions may be scrubbed one or more times using a scrubbing solution to remove nickel ions and lithium ions that may be contained in the solvent. The scrubbing solution can be, for example, a sulfuric acid acidic solution with a pH of 3.5 to 5.5. The scrubbed solution may contain nickel ions and lithium ions. Therefore, it is desirable to mix part or all of the scrubbed solution with the metal-containing solution after the manganese extraction step and use it as the pre-extraction solution to perform the cobalt extraction step. Thereby, nickel ions and lithium ions can be circulated or retained in the wet treatment without loss. However, if the solvent containing cobalt ions does not contain nickel ions and lithium ions, scrubbing may not be necessary.

[0042] Thereafter, back extraction is performed on the solvent containing cobalt ions. The back extraction solution used for back extraction may be any of inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, but sulfuric acid is desirable when obtaining sulfate in the subsequent crystallization step. Here, it is carried out under pH conditions such that as much cobalt ions as possible transfer from the solvent to the back extraction solution. Specifically, the pH is preferably in the range of 2.0 to 4.0, and more preferably in the range of 2.5 to 3.5.

[0043] For the post-back extraction liquid, a crystallization process can be performed. In the crystallization process, the post-back extraction liquid is heated to, for example, 40°C to 120°C and concentrated. As a result, cobalt ions crystallize, and cobalt salts such as cobalt sulfate are obtained. The cobalt salt thus obtained has a nickel content of preferably 5 mass ppm or less, and since nickel is sufficiently removed, it can be effectively used as a raw material for manufacturing lithium-ion secondary batteries and other batteries. Here, the post-crystallization liquid may contain cobalt ions and lithium ions that did not crystallize. Therefore, the post-crystallization liquid is preferably mixed with the post-back extraction liquid before the crystallization process and subjected to the crystallization process again, used to adjust the cobalt ion concentration of the scrubbing liquid used in the solvent for extracting cobalt ions, or mixed with the metal-containing solution after the manganese extraction process and subjected to the cobalt extraction process. In this way, cobalt ions and lithium ions can be circulated or retained within the wet treatment and concentrated without loss.

[0044] (Nickel Extraction Process and Crystallization Process) The metal-containing solution after extracting cobalt ions in the cobalt extraction process mainly contains nickel ions and lithium ions. To recover nickel ions from this metal-containing solution, nickel ions can be extracted from the metal-containing solution into a solvent by solvent extraction.

[0045] For extraction, a mixer settler may be used. In this case, first, the pH is adjusted, for example, by including a pH adjuster in the solvent, and then the metal-containing solution (aqueous phase) and the solvent (organic phase) are mixed in the mixer to form a mixed solution, and the mixed solution is stirred. At this time, nickel ions in the metal-containing solution migrate to the solvent. Then, the mixed solution is allowed to stand in the settler, and the aqueous phase and the organic phase are separated based on their specific gravity difference. As a result, an extraction liquid from which the solvent has been separated is obtained.

[0046] Here, when the aluminum content of the metal-containing solution for performing the above neutralization step is high, or when the amount of the component to be extracted in each extraction step is large, the amount of the pH adjuster required to adjust the pH increases. When a lithium hydroxide solution is used as the pH adjuster, the metal-containing solution to be subjected to the above extraction may have a lithium ion concentration that is somewhat high. Further, as described above, when the post-extraction solution (such as an aqueous lithium sulfate solution) of the nickel extraction step is used as the diluent for adjusting the pH of the acidic leachate in the acid leaching step, the lithium ion concentration of the metal-containing solution to be subjected to the above extraction may be somewhat high.

[0047] In this case, when a pH adjuster containing lithium ions such as a lithium hydroxide solution is used to adjust the equilibrium pH during nickel ion extraction, the lithium ion concentration locally increases at the location where the above metal-containing solution comes into contact with the pH adjuster, and thus, due to exceeding the lithium ion concentration of the saturated lithium salt solution, precipitates are generated. In particular, the lithium hydroxide solution of the post-crystallization solution obtained in the crystallization step described later often has a higher lithium ion concentration as it is closer to the saturated concentration. Therefore, when this is used as a pH adjuster for nickel ion extraction, precipitates are likely to be generated.

[0048] In contrast, in this embodiment, the lithium ion concentration of the metal-containing solution and / or the lithium ion concentration of the pH adjuster are adjusted in advance so that the sum of the lithium ion concentration of the metal-containing solution and the lithium ion concentration of the pH adjuster is equal to or less than the lithium ion concentration of the saturated lithium salt solution. Thereby, even if the lithium ion concentration locally increases, the generation of lithium salts can be suppressed.

[0049] As used herein, the saturated lithium salt solution refers to the lithium ion concentration of a saturated solution of a lithium salt formed by lithium ions and anions of the main inorganic acids contained in the metal-containing solution (such as sulfate ions, nitrate ions, or chloride ions, etc.). If the metal-containing solution contains the most sulfate ions among the anions of the inorganic acids contained therein, the above lithium salt is lithium sulfate. Also, in many cases, solubility depends on temperature, so the above solubility is the solubility at the temperature during extraction.

[0050] During the above extraction, precipitates are generated in the mixer settler, which may cause blockage of pipes due to these precipitates, etc., making it impossible to smoothly perform the extraction operation. These precipitates may contain lithium, specifically, for example, a mixture of Li2SO4(H2O) and the oil of the solvent.

[0051] In the extraction of the nickel extraction process, when not considering the lithium ion concentration of the pH adjuster or when the lithium ion concentration of the lithium hydroxide solution as the pH adjuster is a predetermined value, it may be preferable to adjust the lithium ion concentration of the metal-containing solution so that the lithium ion concentration of the post-extraction liquid separated from the solvent is less than 15 g / L. As an example, the above predetermined value may be 28 g / L. Thereby, the generation of precipitates is suppressed, and in some cases, the generation of precipitates may almost disappear. However, as described above, even when the lithium ion concentration of the post-extraction liquid separated from the solvent exceeds 15 g / L, if the total lithium ion concentration of the metal-containing solution and the pH adjuster is below the solubility of the lithium salt, it is possible to suppress the generation of precipitates. In addition, if the lithium ion concentration of the solution separated from the solvent in the settler after extraction is below the lithium ion concentration of the saturated lithium salt solution, there is a high possibility that no precipitates will be generated there.

[0052] From the perspective of preparing a sufficient amount of lithium hydroxide solution in the hydroxylation step, it is desirable to increase the lithium ion concentration in the metal-containing solution to a certain extent. On the other hand, when the lithium ion concentration in the metal-containing solution is high, there is a risk of precipitation during extraction as described above. Therefore, the lithium ion concentration in the post-extraction liquid separated from the solvent is preferably 10 g / L to 14 g / L.

[0053] The lithium ion concentration in the aqueous phase (metal-containing solution, post-extraction liquid) before and after extraction may vary depending on, for example, the amount of pH adjuster in the solvent before mixing with the metal-containing solution. Therefore, here, for the post-extraction liquid separated from the solvent after the addition of the pH adjuster, the lithium ion concentration that can suppress the generation of precipitates is defined as described above. Furthermore, the lithium ion concentration in the metal-containing solution before extraction is preferably 9 g / L to 13 g / L. Thereby, the generation of precipitates can be more effectively suppressed.

[0054] The solvent used in the nickel extraction step preferably contains a carboxylic acid-based extractant. Examples of the carboxylic acid-based extractant include neodecanoic acid, naphthenic acid, etc. Among them, neodecanoic acid (such as Versatic Acid 10 (VA-10) manufactured by Shell Chemical Co., Ltd.) is preferred due to its nickel ion extraction ability. The extractant may be diluted with a hydrocarbon-based organic solvent such as aromatic, paraffinic, or naphthenic solvents to a concentration of 10% to 30% by volume and used as the solvent. It should be noted that the above-mentioned precipitates are considered to occur even when an extractant other than the carboxylic acid-based extractant is used.

[0055] The equilibrium pH during extraction is preferably 6.0 to 8.0, more preferably 6.8 to 7.2. As the pH adjuster used for adjusting the pH at this time, it is preferable to use a lithium hydroxide solution. For example, the lithium hydroxide solution obtained in the hydroxylation step described later can be used.

[0056] It is desirable to perform extraction in a countercurrent flow where the flow directions of the metal-containing solution and the solvent are opposite in a plurality of stages. By doing so, the extraction of lithium ions into the solvent can be suppressed, and the extraction rate of nickel ions can be increased. In the case of performing countercurrent multi-stage extraction, for example, it is effective to set the equilibrium pH at the time of the first-stage extraction to a value within the above range and lower the equilibrium pH at the time of extraction for each successive stage. When performing countercurrent multi-stage extraction, in any extraction of each stage, it is preferable that the lithium ion concentration of the post-extraction liquid separated from the solvent is less than 15 g / L, and the lithium ion concentration of the metal-containing solution before extraction is preferably 9 g / L to 13 g / L.

[0057] In order to adjust the lithium ion concentration as described above, water or a post-desalting liquid or other diluent described later can be added to the metal-containing solution at any time before mixing with the solvent during extraction to dilute the metal-containing solution. The timing of dilution is not particularly limited as long as it is before mixing with the solvent at the time of extraction in the nickel extraction step after the metal-containing solution is obtained in the acid leaching step. However, if it is much earlier than the nickel extraction step, an increase in the volume of the metal-containing solution due to dilution may cause problems in transporting and handling the metal-containing solution between processes. Therefore, it is preferable to dilute the metal-containing solution immediately before mixing with the solvent at the time of extraction in the nickel extraction step.

[0058] In addition, when the aluminum content in the battery powder is high, it is necessary to add a large amount of lithium hydroxide solution as a pH adjuster in the neutralization step described above, and accordingly, the lithium ion concentration of the metal-containing solution tends to increase. From the viewpoint of reducing the load of adjusting the lithium ion concentration, it is desirable that the aluminum content in the battery powder is low, for example, 3 mass% or less.

[0059] When extracting nickel ions, a pH adjuster may be preliminarily included in the solvent before mixing with the metal-containing solution, and this solvent may be mixed with the metal-containing solution. In this case, when the solvent containing the pH adjuster comes into contact with the metal-containing solution, the above-described local increase in lithium ion concentration and the resulting generation of precipitates may become apparent. Therefore, particularly when the pH adjuster is included in the solvent in advance, a countermeasure of making the total of the lithium ion concentration of the metal-containing solution and the lithium ion concentration of the pH adjuster be equal to or less than the solubility of the lithium salt is effective.

[0060] Alternatively, the pH adjuster may be added by dropping it or the like when mixing the metal-containing solution and the solvent, or the metal-containing solution may be mixed with the pH adjuster before mixing with the solvent. Also in this case, it is preferable to make the total of the lithium ion concentration of the metal-containing solution and the lithium ion concentration of the pH adjuster be equal to or less than the lithium ion concentration of the saturated lithium salt solution.

[0061] By the way, for the solvent that has become a substance containing nickel ions by extraction, if necessary, scrubbing may be performed one or more times using a scrubbing solution to remove lithium ions that may be contained in the solvent. The scrubbing solution can be, for example, a sulfuric acid acidic solution having a pH of 5.0 to 6.0. Here, the scrubbed solution may contain lithium ions. Therefore, it is desirable to mix a part or all of the scrubbed solution with the metal-containing solution after the cobalt extraction step and perform the nickel extraction step using this as the pre-extraction solution. Thereby, it is possible to circulate or retain and concentrate within the wet treatment without losing lithium ions. However, when the solvent containing nickel ions does not contain lithium ions, scrubbing may not be performed.

[0062] Thereafter, back extraction is carried out using a back extraction liquid with respect to the solvent containing nickel ions. The back extraction liquid may be any of inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, but sulfuric acid is preferable when obtaining a sulfate in the subsequent crystallization step. The pH is preferably in the range of 1.0 to 3.0, and more preferably 1.5 to 2.5. Note that the O / A ratio and the number of times can be determined as appropriate, but the O / A ratio is 5 to 1, and more preferably 4 to 2.

[0063] When a post-back extraction liquid such as a nickel sulfate solution is obtained by back extraction, after electrolysis and dissolution are carried out as necessary, it is heated to 40°C to 120°C in the crystallization step, and nickel ions can be crystallized as nickel salts such as nickel sulfate. Thereby, a nickel salt is obtained. Here, the post-crystallization liquid may contain nickel ions and lithium ions that did not crystallize. Therefore, the post-crystallization liquid is preferably mixed with the post-back extraction liquid before the crystallization step and subjected to the crystallization step again, used to adjust the nickel ion concentration of the scrubbing liquid with respect to the solvent containing nickel ions, or mixed with the metal-containing solution after the cobalt extraction step and subjected to the nickel extraction step. In this way, nickel ions and lithium ions can be circulated or retained in the wet treatment without loss and concentrated.

[0064] The post-extraction liquid after nickel ions have migrated into the solvent mainly contains lithium ions and may be added to the acidic leaching solution in the acid leaching step. Thereby, the lithium ions contained in the post-extraction liquid can be circulated within a series of steps from the acid leaching step to the nickel extraction step. Preferably, after the lithium ions are circulated in this way and the lithium ion concentration of the post-extraction liquid has increased to a certain extent, the subsequent hydroxylation step can be carried out.

[0065] (Hydroxylation step) In the hydroxylation process, a lithium hydroxide solution is prepared from the post-extraction solution such as a lithium sulfate solution. Regarding the details of the hydroxylation process, as long as a lithium hydroxide solution can be prepared, there are no particular restrictions. For example, a carbonation and conversion method using calcium hydroxide after preparing lithium carbonate, a conversion method using barium hydroxide, a method by electrodialysis, etc. can be adopted.

[0066] In the case of the carbonation and conversion method, first, a lithium carbonate solution is obtained by adding a carbonate to the lithium-containing solution or blowing in carbon dioxide gas, etc. Then, in the so-called conversion method, calcium hydroxide is added to the lithium carbonate solution, and based on the reaction formula of Li2CO3 + Ca(OH)2 → 2LiOH + CaCO3, a lithium hydroxide solution can be produced. Calcium ions that may remain in the solution can be removed by a cation exchange resin, a chelate resin, or the like.

[0067] When using barium hydroxide, barium hydroxide is added to the lithium-containing solution, and based on the reaction of Li2SO4 + Ba(OH)2 → 2LiOH + BaSO4, a lithium hydroxide solution can be obtained. At this time, barium that can dissolve in the solution can be separated and removed using a cation exchange resin, a chelate resin, or the like.

[0068] In electrodialysis, in a bipolar membrane electrodialysis device, a lithium-containing solution is placed in the desalination chamber between the anion exchange membrane and the cation exchange membrane, and pure water is placed in each of the acid chamber between the bipolar membrane and the anion exchange membrane and the alkali chamber between the cation exchange membrane and the bipolar membrane, and a voltage is applied between the electrodes. Then, lithium ions in the metal-containing solution in the desalination chamber move to the alkali chamber, and in the alkali chamber, pure water is decomposed into hydroxide ions by the bipolar membrane, and a lithium hydroxide solution is obtained. In addition, anions of inorganic acids such as sulfate ions in the metal-containing solution in the desalination chamber pass through the anion exchange membrane and move to the acid chamber.

[0069] In electrodialysis, as a result of separating most of the lithium salt from the metal-containing solution in the desalination chamber, a post-desalination solution containing almost no lithium salt is obtained. However, the post-desalination solution may contain trace amounts of lithium ions. From the perspective of reducing lithium loss, when electrodialysis is employed in the hydroxylation step, dilution of the metal-containing solution for suppressing the generation of precipitates during extraction in the aforementioned nickel extraction step is preferably carried out by adding the post-desalination solution as a diluent to the metal-containing solution. Thereby, the lithium ion concentration of the metal-containing solution can be adjusted.

[0070] At least a part of the lithium hydroxide solution obtained as described above can be effectively used as an alkaline pH adjuster in the metal recovery method (in the process of FIG. 1, at least one step selected from the group consisting of a neutralization step, a manganese extraction step, a cobalt extraction step, and a nickel extraction step).

[0071] (Crystallization step) A part of the lithium hydroxide solution obtained in the hydroxylation step can be subjected to the crystallization step. For example, when the lithium hydroxide solution is returned to the wet treatment as a pH adjuster as described above, the lithium ion concentration in the solution may gradually increase due to lithium in the battery powder newly introduced into the wet treatment. The crystallization step may be carried out according to the lithium ion concentration, and lithium may be recovered as lithium hydroxide.

[0072] In the crystallization step, in order to precipitate lithium hydroxide, crystallization operations such as heating concentration or vacuum distillation can be performed. In the case of heating concentration, the higher the temperature during crystallization, the faster the treatment progresses, which is preferable. However, after crystallization, the temperature of the crystallized product is preferably set to less than 60°C at which crystal water does not desorb. This is because anhydrous lithium hydroxide from which crystal water has desorbed has deliquescence and is difficult to handle. Thereafter, the above lithium hydroxide can be subjected to a pulverization treatment or the like to adjust it to the required physical properties.

[0073] As described above, the lithium hydroxide solution obtained in the hydroxylation step substantially does not contain anions of inorganic acids such as sulfate ions. Therefore, the lithium hydroxide produced in the crystallization step has high purity and excellent quality. The lithium hydroxide solution obtained by separating the lithium hydroxide produced in the crystallization step by solid-liquid separation may be used as a pH adjuster in the neutralization step, manganese extraction step, cobalt extraction step, and / or nickel extraction step.

Example

[0074] Next, the above-described metal recovery method was experimentally carried out to confirm its effect, and the description is as follows. However, the description here is for the purpose of mere illustration and is not intended to be limited thereto.

[0075] (Test Example 1) As shown in Figure 1, the lithium hydroxide solution prepared in the hydroxylation step was used as a pH adjuster in each of the neutralization step, manganese extraction step, cobalt extraction step, and nickel extraction step, and the process was carried out continuously. The pH adjuster was a lithium hydroxide solution, and its lithium ion concentration was 28 g / L.

[0076] In the extraction of the nickel extraction step, using a mixer settler, a solvent containing VA-10, a carboxylic acid-based extractant, was used for the metal-containing solution to transfer nickel ions from the metal-containing solution to the solvent. The nickel ion concentration of the metal-containing solution before extraction was 8 to 12 g / L, and the nickel ion concentration of the solution after extraction was 0.001 to 0.01 g / L. The solvent was a mixture of VA-10 and a hydrocarbon-based organic solvent, containing VA-10 at a concentration of 25% by volume. The equilibrium pH during extraction was set to 6.8 to 7.2, typically about 7.0, using the above pH adjuster.

[0077] Then, the lithium ion concentration of each of the metal-containing solution (pre-extraction solution) before the above extraction and the post-extraction solution (MS solution) in the mixer settler was measured, and the amount of the precipitate generated in the mixer settler was visually confirmed. The results are shown in Table 1. Also, the change over time in the lithium ion concentration of each solution is shown in Figure 3. Here, three-stage extraction was performed in a countercurrent flow in which the flow directions of the metal-containing solution and the solvent were opposite. Figure 3 shows the change in the lithium ion concentration in the post-extraction solution in the mixer settler during extraction at each stage.

[0078]

Table 1

[0079] In period A, the metal-containing solution was not diluted before extraction, whereas in periods B and C, the metal-containing solution was diluted with water before extraction. As a result, the lithium ion concentration of each solution decreased according to the degree of dilution in periods B and C, as shown in Table 1 and Figure 3.

[0080] The anion of the inorganic acid contained in the pre-extraction solution is sulfate ion, and the lithium ion concentration in the saturated solution of lithium sulfate as a lithium salt (lithium ion concentration of the saturated lithium salt solution) is 42.5 g / L at the extraction temperature (40 °C). This lithium ion concentration of the saturated lithium salt solution can be obtained from the lithium sulfate (Li2SO4) concentration of 337 g / L in the saturated lithium sulfate solution at 40 °C by the formula: 337×6.94×2 / 109.945≒42.5. Since the lithium ion concentration of the pH adjuster is 28 g / L, the total concentration of the lithium ion concentration of the pre-extraction solution and the lithium ion concentration of the pH adjuster was 46 g / L to 48 g / L in period A, which was higher than the lithium ion concentration (42.5 g / L) of the saturated lithium salt solution. In period B, the total concentration was 40 g / L to 41 g / L, which was lower than the lithium ion concentration (42.5 g / L) of the saturated lithium salt solution. In period C, the total concentration was 43 g / L to 44 g / L, which was higher than the lithium ion concentration (42.5 g / L) of the saturated lithium salt solution.

[0081] As a result, as shown in Table 1 and Figure 3, a relatively large amount of precipitates occurred during Periods A and C. In contrast, almost no precipitates occurred during Period B.

[0082] When the precipitates generated in the mixer settler were analyzed by X-ray diffraction (XRD), it was confirmed that the precipitates contained Li2SO4(H2O). Also, from the fact that the precipitates did not dissolve in water or acid and from the properties of the precipitates, it was estimated that the precipitates were a mixture of Li2SO4(H2O) and oil.

[0083] (Test Example 2) In the process shown in Figure 1, the process was continuously carried out in the same manner, except that sodium hydroxide prepared separately was used as the pH adjuster in each of the neutralization step, manganese extraction step, cobalt extraction step, and nickel extraction step without using the lithium hydroxide solution prepared in the hydroxylation step. At this time, the lithium ion concentration and sodium ion concentration of the metal-containing solution to be subjected to the nickel extraction step were measured, and the change over time of each concentration was confirmed. The results are shown in Figure 4.

[0084] From Figure 4, it can be seen that when sodium hydroxide is used as the pH adjuster, the lithium ion concentration of the metal-containing solution remains sufficiently low continuously. Also, no precipitates occurred in the mixer settler used for the extraction in the nickel extraction step. From this, it can be said that the generation of precipitates becomes apparent when the lithium hydroxide solution is used as the pH adjuster as in Test Example 1 and lithium is circulated in the wet treatment. Therefore, in such a case, the above-described metal recovery method is considered to be particularly effective.

[0085] (Test Example 3) The extraction in the nickel extraction step was carried out in substantially the same manner as in Test Example 1.

[0086] Here, the lithium hydroxide solution obtained in the hydroxylation step was used as a pH adjuster. The lithium ion concentration of this pH adjuster was 12 g / L, and the lithium ion concentration of the solution before extraction was set to 17 g / L or less. The total of the lithium ion concentration of the pH adjuster and the lithium ion concentration of the metal-containing solution was 29 g / L or less. Under these conditions, extraction was performed with the equilibrium pH set to 6.8 to 7.0, and no precipitate was generated. The lithium ion concentration of the solution after extraction separated from the solvent was 18 g / L or less.

[0087] From the above, it was found that according to the metal recovery method described above, the generation of precipitates during the extraction of nickel ions can be effectively suppressed.

Claims

1. A method for recovering a metal from a metal-containing solution containing nickel ions, lithium ions, and anions of an inorganic acid, comprising: while adjusting the equilibrium pH using a pH adjuster containing lithium ions, mixing the metal-containing solution with a solvent to transfer nickel ions in the metal-containing solution to the solvent, and performing extraction including separating the solvent containing nickel ions from the extraction residue liquid, having a nickel extraction step; in the nickel extraction step, performing the extraction with the total of the lithium ion concentration in the metal-containing solution and the lithium ion concentration in the pH adjuster being not more than the lithium ion concentration in a saturated solution of a lithium salt formed by the anions of the inorganic acid and lithium ions contained in the metal-containing solution. A metal recovery method.

2. Adjusting the lithium ion concentration in the metal-containing solution, and in the extraction in the nickel extraction step, making the lithium ion concentration in the extraction residue liquid separated from the solvent less than 15 g / L. The metal recovery method according to claim 1.

3. In the nickel extraction step, making the lithium ion concentration in the extraction residue liquid separated from the solvent 10 g / L to 14 g / L. The metal recovery method according to claim 2.

4. In the nickel extraction step, making the lithium ion concentration in the metal-containing solution before performing the extraction 9 g / L to 13 g / L. The metal recovery method according to claim 1 or 2.

5. Performing the extraction in the nickel extraction step in a countercurrent manner in which the flow directions of the metal-containing solution and the solvent are opposite, in a plurality of stages, and in the extraction at each stage, making the lithium ion concentration in the extraction residue liquid separated from the solvent less than 15 g / L. The metal recovery method according to claim 1 or 2.

6. In the nickel extraction step, using the solvent containing a carboxylic acid-based extractant and making the equilibrium pH of the extraction 6.0 to 8.

0. The metal recovery method according to claim 1 or 2.

7. The lithium salt is lithium sulfate, and the metal-containing solution contains sulfate ions as the anions of the inorganic acid. The metal recovery method according to claim 1 or 2.

8. Including a hydroxylation step of preparing a lithium hydroxide solution from the extraction residue liquid obtained in the nickel extraction step, and using at least a part of the lithium hydroxide solution as a pH adjuster used in the metal recovery method. The metal recovery method according to claim 1 or 2.

9. In the lithium hydroxide production step, a lithium hydroxide solution is produced by electrodialysis, and a lithium salt is separated from the post-extraction solution to obtain a desalted solution. The metal recovery method according to claim 8, wherein the desalted solution is added to the metal-containing solution to dilute the metal-containing solution and adjust the lithium ion concentration of the metal-containing solution.

10. The metal recovery method according to claim 1 or 2, wherein in the nickel extraction step, the pH adjuster is included in the solvent before mixing the metal-containing solution and the solvent.

11. The metal recovery method according to claim 1 or 2, wherein in the nickel extraction step, the pH adjuster is added during mixing of the metal-containing solution and the solvent, and / or the metal-containing solution is mixed with the pH adjuster before mixing with the solvent.

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