Lithium recovery method and metal recovery method

Abstract

This method for recovering lithium from a metal-containing solution that contains lithium ions and nickel ions includes: a nickel extraction step for performing extraction that involves extracting and separating nickel ions in the metal-containing solution into a solvent; a lithium concentration step for concentrating the lithium-containing solution obtained after the extraction of the nickel extraction step, and obtaining a lithium concentrate having a lithium ion concentration higher than that of the metal-containing solution at the time of extraction during the nickel extraction step; and a lithium recovery step for recovering lithium from the lithium concentrate.

Description

Lithium recovery method and metal recovery method

[0001] This specification describes a lithium recovery method and a metal recovery method.

[0002] In recent years, from the perspective of effective resource utilization, recovery of valuable metals from waste batteries such as waste lithium-ion batteries discarded due to product life, manufacturing defects, or other reasons has been widely considered.

[0003] To recover metals from lithium-ion battery waste, for example, battery powder obtained through heat treatment or other processes is brought into contact with an acidic leachate such as sulfuric acid to leach the metals in the battery powder into the acidic leachate, thereby obtaining a metal-containing solution in which nickel, cobalt, manganese, aluminum, iron, etc. are dissolved.

[0004] Next, the metals are separated from the metal-containing solution. Specifically, as described in Patent Documents 1 to 3, for example, aluminum ions, iron ions, and manganese ions are sequentially or simultaneously separated from the metal ions in the metal-containing solution by neutralization or solvent extraction. Thereafter, cobalt ions and nickel ions are separated and concentrated by solvent extraction and extracted.

[0005] The post-extraction solution after nickel extraction becomes a lithium-containing solution containing mainly lithium ions. This lithium-containing solution may be subjected to treatments such as carbonation, hydroxide by electrodialysis, or the like, to recover the lithium contained therein in the form of a predetermined solution or solid compound (see, for example, Patent Documents 4 to 6).

[0006] JP 2010-180439 A U.S. Patent Application Publication No. 2011 / 0135547 JP 2014-162982 A JP 2019-011518 A JP 2009-270188 A JP 2011-31232 A

[0007] However, when nickel ions are extracted from a metal-containing solution containing nickel ions and lithium ions into a solvent, unintended precipitates may be formed. The formation of precipitates can hinder the smooth progress of the nickel ion extraction operation, and in some cases, the operation may need to be interrupted. The formation of such precipitates is thought to be due to the high lithium ion concentration in the metal-containing solution during extraction. Therefore, from the viewpoint of suppressing the formation of precipitates, it is desirable to lower the lithium ion concentration of the metal-containing solution to a certain extent when extracting nickel ions.

[0008] However, in this case, the lithium-containing solution obtained after extracting nickel ions from the metal-containing solution also has a low lithium ion concentration. If an attempt is made to recover lithium from a lithium-containing solution with a low lithium ion concentration, the time and effort required for lithium recovery increases, which reduces the lithium recovery efficiency and raises concerns about increased costs.

[0009] This specification provides a lithium recovery method and a metal recovery method that can suppress the generation of precipitates during nickel ion extraction while increasing the efficiency of subsequent lithium recovery.

[0010] The lithium recovery method described in this specification is a method for recovering lithium from a metal-containing solution containing lithium ions and nickel ions, and includes a nickel extraction step including extraction of nickel ions in the metal-containing solution into a solvent to separate them, a lithium concentration step of concentrating the lithium-containing solution obtained after the extraction in the nickel extraction step to obtain a lithium concentrated solution having a higher lithium ion concentration than the metal-containing solution at the time of the extraction in the nickel extraction step, and a lithium recovery step of recovering lithium from the lithium concentrated solution.

[0011] The metal recovery method described in this specification is a method of leaching metals in battery powder of lithium ion battery waste and separating and recovering the metals from the metal-containing solution obtained thereby, and includes the lithium recovery method described above.

[0012] According to the above-described lithium recovery method, it is possible to suppress the generation of precipitates during the extraction of nickel ions, while increasing the efficiency of subsequent lithium recovery.

[0013] 1 is a flow chart showing an example of a metal recovery method including a lithium recovery method according to one embodiment. FIG. 2 is a flow chart showing an example of a pretreatment step for obtaining the battery powder of FIG. 1 from lithium-ion battery waste. FIG. 3 is a cross-sectional view schematically showing an example of a bipolar membrane electrodialysis device that can be used when hydroxide oxidation by electrodialysis is performed in the lithium recovery step included in the metal recovery method of FIG. 1. FIG. 4 is a graph showing the change over time in the lithium ion concentration of each solution during nickel ion extraction in Test Example 1 of the Examples. FIG. 5 is a graph showing the change over time in the lithium ion concentration and sodium ion concentration of a metal-containing solution in Test Example 2 of the Examples. FIG. 6 is a graph showing the relationship between the lithium ion concentration and current efficiency of a lithium-containing solution obtained in the electrodialysis test of Test Example 4.

[0014] The lithium recovery method according to one embodiment is a method for recovering lithium from a metal-containing solution containing lithium ions and nickel ions, and includes, in this order, a nickel extraction step, a lithium concentration step, and a lithium recovery step.

[0015] The nickel extraction step includes extracting and separating nickel ions in the metal-containing solution into a solvent. The subsequent lithium concentration step concentrates the lithium-containing solution obtained after the extraction in the nickel extraction step. In this lithium concentration step, the lithium-containing solution is concentrated to obtain a lithium-concentrated solution having a higher lithium ion concentration than the metal-containing solution obtained at the time of extraction in the nickel extraction step.

[0016] In this way, in the nickel extraction step, extraction is performed on a metal-containing solution having a lower lithium ion concentration than the lithium concentrate obtained in the subsequent lithium concentration step, thereby suppressing the generation of precipitates due to the high lithium ion concentration of the metal-containing solution. On the other hand, in the lithium recovery step following the lithium concentration step, lithium is recovered from the lithium concentrate obtained in the lithium concentration step and having a higher lithium ion concentration than the metal-containing solution. This reduces the time and effort required for lithium recovery and improves the lithium recovery efficiency. Furthermore, in the case of lithium recovery by carbonation, the lithium recovery rate can be increased, and in the case of lithium recovery by hydroxide oxidation using electrodialysis, the current efficiency of electrodialysis can be improved.

[0017] The lithium recovery method of this embodiment may be implemented by incorporating it into a metal recovery method having the steps shown in FIG. 1 , for example. In FIG. 1 , battery powder from lithium-ion battery waste is subjected to an acid leaching step, a neutralization step, a manganese and / or aluminum extraction step, a cobalt extraction step, a nickel extraction step, a lithium concentration step, and a lithium recovery step, in this order. As shown in FIG. 2 , the battery powder can be obtained by subjecting lithium-ion battery waste to a pretreatment step. Here, the description will be given with reference to FIGS. 1 and 2 , but FIGS. 1 and 2 are merely examples and the present invention is not limited to such specific flows.

[0018] (Lithium-ion battery waste) The target lithium-ion battery waste is lithium-ion secondary batteries that can be used in mobile phones and various other electronic devices, etc., that have been discarded due to the end of the battery product's life, manufacturing defects, or other reasons. Recovering valuable metals from such lithium-ion battery waste is preferable from the perspective of effective resource utilization.

[0019] Lithium-ion battery waste may have an aluminum casing containing a cathode active material made of a single metal oxide containing lithium and one or more selected from the group consisting of nickel, cobalt, and manganese, or a composite metal oxide containing two or more selected from the group consisting of lithium and nickel, cobalt, and manganese, or an aluminum foil (cathode substrate) to which the cathode active material is coated and fixed with, for example, polyvinylidene fluoride (PVDF) or other organic binders. Lithium-ion battery waste may also contain copper, iron, etc. Furthermore, the casing may contain an electrolyte solution prepared by dissolving an electrolyte such as lithium hexafluorophosphate in an organic solvent such as ethylene carbonate or diethyl carbonate.

[0020] (Pretreatment Process) A pretreatment process is often performed on lithium-ion battery waste. The pretreatment process may include at least one of roasting, crushing, and sieving. Lithium-ion battery waste is converted into battery powder through the pretreatment process. The roasting, crushing, and sieving processes of the pretreatment process may be performed individually as needed, or may be performed in any order. Battery powder refers to powder obtained by separating and concentrating positive electrode material components from lithium-ion battery waste through some kind of pretreatment. Battery powder may also be obtained as a powder by concentrating positive electrode material components by crushing and sieving lithium-ion battery waste with or without heat treatment.

[0021] In the roasting process, the lithium-ion battery waste is heated. The roasting process decomposes and removes the electrolyte and organic binder, and metals such as lithium and cobalt contained in the lithium-ion battery waste may be converted into forms that are easily soluble in the acid leaching solution during the acid leaching process. Although the composition of the positive electrode active material changes during roasting, the roasted material is still referred to as the positive electrode active material. During roasting, the lithium-ion battery waste is preferably heated and maintained at a temperature ranging from 600°C to 800°C for 0.5 to 6 hours. The roasting process can be carried out in air or an inert atmosphere such as nitrogen. The roasting process can be carried out in this order or the reverse order. For example, a batch-type stationary furnace, a continuous rotary kiln furnace, or other various furnaces can be used as the roasting furnace.

[0022] After roasting, crushing can be performed. In crushing, the housing of the lithium-ion battery waste is broken and the positive electrode active material is selectively separated from the aluminum foil on which the positive electrode active material is applied. Various known devices or equipment can be used for crushing, but it is particularly preferable to use an impact crusher that can crush the lithium-ion battery waste by applying impact while cutting it. Examples of such impact crushers include a sample mill, hammer mill, pin mill, wing mill, tornado mill, and hammer crusher.

[0023] After shredding the lithium-ion battery waste, it is sieved using a sieve with appropriate mesh size. This leaves aluminum and copper on the sieve, while leaving battery powder with some of the aluminum and copper removed. When the battery powder contains nickel, the nickel content is, for example, 1% to 30% by mass, typically 5% to 20% by mass. When cobalt is contained, the cobalt content in the battery powder is, for example, 1% to 30% by mass, typically 5% to 20% by mass. The battery powder may also contain, for example, 2% to 8% by mass of lithium, 1% to 30% by mass of manganese, 1% to 10% by mass of aluminum, 1% to 5% by mass of iron, and 1% to 10% by mass of copper.

[0024] In order to extract substantially only lithium from the battery powder, the battery powder may be brought into contact with water before the acid leaching step described below, and the lithium in the battery powder may be leached into water. In this case, the battery powder as a water leaching residue is subjected to the acid leaching step. However, the battery powder may also be subjected to the acid leaching step without water leaching. If water leaching is not performed, it becomes easier to maintain a high lithium ion concentration in the solution in the wet treatment after the acid leaching step.

[0025] (Acid Leaching Process) In the acid leaching process, the metals in the battery powder are brought into contact with an acidic leaching solution containing a mineral or inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid to leach the metals. This dissolves the metals in the battery powder, resulting in a leached solution containing the metals as metal ions. Here, the solution containing the metals in the battery powder as metal ions is referred to as a metal-containing solution. The metal-containing solution includes the leached solution obtained in the acid leaching process and sent to the subsequent neutralization process, as well as solutions in the middle of the neutralization process or various metal extraction processes.

[0026] The pH of the acidic leachate during leaching is preferably -0.5 to 3.0, and the pH of the post-leaching solution after leaching may be 0.5 to 2.0. The pH of the solution can be measured using a multi-purpose water quality meter MX-43X and a composite electrode GST-5841C manufactured by DKK-TOA Corporation. During leaching, for example, the acidic leachate may be stirred at 100 to 400 rpm using a stirrer as needed, and the temperature of the solution may be set to 50 to 80°C, or even 65 to 70°C.

[0027] The post-leaching solution obtained in the acid leaching step may have, for example, a cobalt ion concentration of 10 g / L to 50 g / L, a nickel ion concentration of 10 g / L to 50 g / L, a manganese ion concentration of 0 g / L to 50 g / L, a lithium ion concentration of 1.0 g / L to 30.0 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. The metal ion concentrations in the solution can be confirmed by analysis using an ICP optical emission spectrometer (e.g., SPS3300 manufactured by SII NanoTechnology Inc.).

[0028] (Neutralization Step) In the neutralization step, the pH of the metal-containing solution (the post-leaching solution) is increased, and the neutralization residue is separated to obtain a post-neutralization solution. The neutralization step may include, for example, a dealumination step in which the pH is increased to that of the metal-containing solution to precipitate and remove at least a portion of the aluminum ions, followed by a de-ironization step in which an oxidizing agent is added to oxidize the iron ions, and if necessary, the pH is further increased to precipitate and remove the iron ions. However, if the metal-containing solution does not substantially contain iron ions, the de-ironization step may be omitted.

[0029] In each of the dealumination and deironization stages, the pH may be set within a range of 3.0 to 4.5. In the deironization stage, the oxidation-reduction potential (based on silver / silver chloride potential, ORP) during oxidation may be set to 300 mV to 900 mV. The oxidation-reduction potential of the solution can be measured using a multi-water quality meter MX-43X and a composite electrode PST-5721C manufactured by DKK-TOA Corporation, for example. After aluminum has been precipitated in the dealumination stage, and after iron has been precipitated in the deironization stage, the neutralization residue as the precipitate can be removed by solid-liquid separation such as filtration using known devices and methods such as a filter press or a thickener.

[0030] In the dealumination and iron removal steps, alkaline pH adjusters such as lithium hydroxide, sodium hydroxide, sodium carbonate, and ammonia can be used. The lithium hydroxide solution can be obtained by electrodialysis in the lithium recovery step described below. In this case, lithium ions circulate within the series of steps in the wet treatment. The oxidizing agent used in the iron removal step is not particularly limited as long as it can oxidize iron, but manganese dioxide, a positive electrode active material, and / or a manganese-containing leaching residue obtained by leaching the positive electrode active material are preferred.

[0031] (Manganese and / or Aluminum Extraction Step) The metal-containing solution as the post-neutralization solution can be subjected to solvent extraction to extract and separate manganese ions and / or the remaining aluminum ions that were not completely removed in the neutralization step. In this case, the remaining manganese ions and aluminum ions are extracted, thereby obtaining a post-manganese-extraction solution from which they have been removed.

[0032] In the manganese and / or aluminum extraction step, a phosphate ester extractant (such as di-2-ethylhexyl phosphoric acid (abbreviation: D2EHPA or trade name: DP-8R)) or a mixture of a phosphate ester extractant and an aldoxime or an oxime extractant containing aldoxime as the main component (such as 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicyldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), or 5-nonylsalicylaldoxime (trade name: ACORGAM5640)) can be used. During extraction, the equilibrium pH is preferably 2.3 to 3.5, more preferably 2.5 to 3.0. The alkaline pH adjuster used here is preferably a lithium hydroxide solution obtained by electrodialysis in the lithium recovery step described below, but separately prepared sodium hydroxide or the like may also be used.

[0033] During extraction, it is desirable to perform extraction by countercurrent multistage extraction, in which the aqueous phase and solvent used in each extraction flow in opposite directions. This can suppress the extraction of other metal ions such as cobalt ions, nickel ions, and lithium ions, and increase the extraction rate of manganese ions. When using countercurrent multistage extraction, it is effective to set the equilibrium pH during the first extraction stage within the above-mentioned range and increase the equilibrium pH during each subsequent extraction stage. Countercurrent multistage extraction is also suitable for the cobalt extraction step and nickel extraction step described below.

[0034] (Cobalt Extraction Step) In the cobalt extraction step, cobalt ions are separated by solvent extraction from the metal-containing solution as the post-manganese extraction solution obtained after the manganese extraction step. During this step, magnesium ions that may be contained in the metal-containing solution are also extracted, and there is a possibility that these can be removed.

[0035] In cobalt extraction, it is preferable to use a solvent containing a phosphonate ester extractant such as 2-ethylhexyl 2-ethylhexylphosphonate (trade names: PC-88A, Ionquest 801). During extraction, the equilibrium pH can be adjusted to preferably 5.0 to 6.0, more preferably 5.0 to 5.5. In this case, it is preferable to use a lithium hydroxide solution obtained by electrodialysis in the lithium recovery step described below as the pH adjuster, but separately prepared sodium hydroxide or the like may also be used.

[0036] The solvent from which the cobalt ions have been extracted can be scrubbed as needed, and then stripped using a stripping solution containing sulfuric acid, hydrochloric acid, nitric acid, or the like, at a pH of, for example, 2.0 to 4.0. The stripped solution can then be heated and concentrated to crystallize the cobalt ions as a cobalt salt.

[0037] (Nickel Extraction Step) The metal-containing solution as the post-cobalt extraction solution after the cobalt ions have been extracted in the cobalt extraction step mainly contains nickel ions and lithium ions. In the nickel extraction step, nickel ions are extracted and separated from this metal-containing solution.

[0038] A mixer-settler may be used for extraction, not limited to the nickel extraction process. In this case, for example, a pH adjuster is first added to the solvent to adjust the equilibrium pH during extraction, and then the metal-containing solution (aqueous phase) and the solvent (organic phase) are mixed in a mixer to form a mixed solution, which is then stirred. At this time, the metal ions to be extracted in the metal-containing solution (nickel ions in the case of extraction in the nickel extraction process) are transferred to the solvent. The mixed solution is then left to stand in a settler, and the aqueous and organic phases are separated based on the difference in their specific gravities. This results in a post-extraction solution from which the solvent has been separated.

[0039] However, when the aluminum content of the metal-containing solution to be subjected to the neutralization step is high or when the amount of components to be extracted in each extraction step is large, a large amount of pH adjuster is required to adjust the pH. When a lithium hydroxide solution is used as a pH adjuster, the metal-containing solution to be subjected to the extraction may have a relatively high lithium ion concentration. Furthermore, as described above, when the post-extraction solution (lithium sulfate solution, etc.) from the nickel extraction step is used as a diluent to adjust the pH of the acid leaching solution in the acid leaching step, the lithium ion concentration of the metal-containing solution to be subjected to the extraction may have a relatively high lithium ion concentration.

[0040] Here, if the lithium ion concentration of the metal-containing solution used in the nickel extraction step is high, a lithium-containing precipitate may form in the mixer settler during nickel ion extraction. In this case, the precipitate may clog the piping, preventing the extraction operation from proceeding smoothly. This precipitate may contain lithium, specifically, a mixture of LiSO(HO) and the oil solvent. To suppress the formation of precipitates, it is preferable that the metal-containing solution used in the nickel extraction step has a low lithium ion concentration. Specifically, the lithium ion concentration of the metal-containing solution used during nickel ion extraction in the nickel extraction step is set lower than the lithium ion concentration of the lithium concentrated solution obtained in the lithium concentration step described below. This effectively suppresses the formation of precipitates during nickel ion extraction.

[0041] Metal-containing solutions often contain inorganic acid anions such as sulfate ions. When a saturated solution of a lithium salt consisting of inorganic acid anions and lithium ions contained in the metal-containing solution is called a saturated lithium salt solution, it is preferable that the lithium ion concentration of the metal-containing solution during nickel ion extraction is equal to or lower than the lithium ion concentration of the saturated lithium salt solution. The saturated lithium salt solution here refers to a saturated solution of a lithium salt formed from lithium ions and the main inorganic acid anions (sulfate ions, nitrate ions, chloride ions, etc.) contained in the metal-containing solution. If the metal-containing solution contains sulfate ions in the largest amount among the inorganic acid anions contained therein, the lithium salt is lithium sulfate.

[0042] In addition, a pH adjuster containing lithium ions may be used to adjust the equilibrium pH during nickel ion extraction. In this case, the lithium ion concentration of the metal-containing solution during nickel ion extraction refers to the lithium ion concentration of a mixture of the metal-containing solution and the pH adjuster before use (before mixing), and it is preferable that the lithium ion concentration of the mixture be equal to or lower than the lithium ion concentration of a saturated lithium salt solution. The lithium ion-containing pH adjuster is not particularly limited, but examples thereof include lithium hydroxide. Lithium hydroxide may be a solid, such as a powder, or a solution. The lithium hydroxide solution may be the lithium hydroxide solution obtained in the lithium recovery step described below.

[0043] However, when a pH adjuster such as a lithium hydroxide solution is used to adjust the equilibrium pH during nickel ion extraction, the lithium ion concentration increases locally at the contact point between the metal-containing solution and the pH adjuster. This lithium ion concentration exceeds the solubility limit, resulting in significant formation of a precipitate containing lithium salt. The reason for this precipitation is believed to be that, during the nickel extraction process, a mixture of the metal-containing solution (aqueous phase) and the solvent (organic phase) is stirred, so that the surface of the lithium salt is covered with the solvent immediately after precipitation. As a result, the lithium salt becomes less soluble in the aqueous phase, resulting in precipitation as a precipitate. Therefore, when a lithium ion-containing pH adjuster is used, the sum of the lithium ion concentration (g / L) of the metal-containing solution before use (before mixing) of the pH adjuster and the lithium ion concentration (g / L) of the pH adjuster may be set to be equal to or less than the lithium ion concentration (g / L) of the saturated lithium salt solution. In other words, when the lithium ion concentration (g / L) of the metal-containing solution before use (before mixing) of the pH adjuster is X, the lithium ion concentration (g / L) of the pH adjuster is Y, and the lithium ion concentration (g / L) of the saturated lithium salt solution is Z, the following relationship may be satisfied: X + Y ≦ Z. For example, if the main inorganic acid anion contained in the metal-containing solution is sulfate ion, and the lithium ion concentration of the metal-containing solution before use (before mixing) of the pH adjuster is 10 g / L, the lithium ion concentration of the pH adjuster is 20 g / L, and the lithium ion concentration of the saturated lithium sulfate salt solution at a temperature of 40°C is 42.5 g / L, substituting these values ​​into the above formula yields 10 + 20 = 30 ≦ 42.5, which satisfies the above relationship. By satisfying this relationship, local increases in lithium ion concentration and the resulting formation of precipitates during mixing with the pH adjuster can be effectively suppressed. In addition, since the solubility often depends on the temperature, the above solubility is the solubility at the temperature at which the extraction is carried out.

[0044] The solvent used in the nickel extraction step preferably contains a carboxylic acid extractant. Examples of carboxylic acid extractants include neodecanoic acid and naphthenic acid. Of these, neodecanoic acid (such as Versatic Acid 10 (VA-10) manufactured by Shell Chemical Industries, Ltd.) is preferred due to its ability to extract nickel ions. The extractant may be diluted with a hydrocarbon organic solvent such as an aromatic, paraffinic, or naphthenic solvent to a concentration of 10% by volume to 30% by volume, and this may be used as the solvent.

[0045] The equilibrium pH during extraction is preferably 6.0 to 8.0, more preferably 6.8 to 7.2. A lithium hydroxide solution is preferably used as a pH adjuster for adjusting the pH, and for example, a lithium hydroxide solution obtained by electrodialysis in the lithium recovery step described below can be used. When countercurrent extraction is performed in multiple stages, it is desirable to adjust the lithium ion concentration of the metal-containing solution as described above in each extraction stage.

[0046] As described above, it is preferable to adjust the lithium ion concentration of the metal-containing solution or the pH adjuster so that the lithium ion concentration of the lithium-containing solution as the post-extraction solution separated from the solvent by extraction is less than 15 g / L, for example, 10 g / L to 14 g / L. If the lithium ion concentration of the lithium-containing solution is too low, the load in the lithium concentration step described below increases and the lithium recovery rate in the lithium recovery step may decrease.

[0047] After extraction, the solvent containing nickel ions may be scrubbed one or more times using a scrubbing solution to remove lithium ions that may be contained in the solvent. The solvent containing nickel ions is then stripped using a stripping solution such as sulfuric acid. Further, electrolysis and dissolution are performed as needed, followed by heating to crystallize the nickel ions as nickel salts such as nickel sulfate.

[0048] At least a portion of the lithium-containing solution after nickel ions have been extracted can be mixed with the acid leaching solution in the acid leaching step and used, thereby circulating the lithium ions contained in the lithium-containing solution through a series of steps in the wet treatment from the acid leaching step to the nickel extraction step.

[0049] (Lithium Concentration Step) By adjusting the lithium ion concentration of the metal-containing solution during extraction in the nickel extraction step, the lithium-containing solution obtained after nickel ions are extracted has a relatively low lithium ion concentration. If this solution is subjected to the lithium recovery step as is, it may result in a decrease in the lithium recovery rate and a decrease in the current efficiency when performing electrodialysis. To address this, in this embodiment, a lithium concentration step is performed to concentrate the lithium-containing solution prior to the lithium recovery step.

[0050] In the lithium concentration step, the concentration method is not particularly limited as long as it can produce a lithium concentrated solution having a higher lithium ion concentration than the metal-containing solution obtained during extraction in the nickel extraction step. Specific examples include filtration using a filtration membrane and heat concentration. Among these, filtration is preferred because, by selecting an appropriate filtration membrane, it can effectively remove at least a portion of impurity metal ions, such as manganese ions, cobalt ions, nickel ions, and magnesium ions, that may be contained in the lithium-containing solution in addition to lithium ions. However, even in the case of heat concentration, a solution purification treatment may be performed separately from the heat concentration to remove at least a portion of the impurity metal ions.

[0051] Examples of filtration membranes used in filtration include microfiltration (MF) membranes, ultrafiltration (UF) membranes, nanofiltration (NF) membranes, and reverse osmosis (RO) membranes. The lithium concentration process can increase the lithium ion concentration of the lithium-containing solution if it includes filtration using a water-permeable filtration membrane. In particular, it is preferable to use a nanofiltration membrane and a reverse osmosis membrane in combination. Generally, a reverse osmosis membrane is a filtration membrane that uses the reverse osmosis phenomenon to allow water to pass through while blocking other ions, particles, etc., and a nanofiltration membrane is understood to be a pressure-driven filtration membrane that has performance intermediate between a reverse osmosis membrane and an ultrafiltration membrane and inhibits the penetration of ions, particles, etc., of less than 2 nm. By using them in combination, it is possible to effectively concentrate lithium ions by permeation and remove at least a portion of the above-mentioned impurity metal ions.

[0052] In the lithium concentration step, it is preferable to obtain a lithium concentrated solution having a lithium ion concentration of 15 g / L or more by concentrating the lithium-containing solution as described above. More preferably, the lithium ion concentration of the lithium concentrated solution is 20.0 g / L to 30.0 g / L. This further facilitates improving the lithium recovery rate in the subsequent lithium recovery step and improving the current efficiency of electrodialysis. Furthermore, it is preferable that the lithium concentrated solution has a manganese ion concentration of 0.001 g / L or less, a cobalt ion concentration of 0.001 g / L or less, a nickel ion concentration of 0.001 g / L or less, and a magnesium ion concentration of 0.001 g / L or less.

[0053] (Lithium recovery step) In the lithium recovery step, lithium is recovered in the form of a solution, a solid, etc. from the lithium concentrated solution obtained in the lithium concentration step. Typically, hydroxylation and / or carbonation can be carried out in the lithium recovery step.

[0054] In the hydroxylation, a lithium hydroxide solution may be prepared from the lithium concentrated solution such as a lithium sulfate solution. The details of the method are not particularly limited as long as the lithium hydroxide solution can be prepared, but for example, a carbonation and chemical conversion method in which calcium hydroxide is used after lithium carbonate is prepared, a chemical conversion method in which barium hydroxide is used, or a method using electrodialysis may be employed.

[0055] In the carbonation and chemical conversion methods, a lithium carbonate solution is first obtained by adding a carbonate or blowing carbon dioxide gas into a lithium-containing solution, and then calcium hydroxide is added to the lithium carbonate solution to produce a lithium hydroxide solution according to the reaction formula Li2CO3 + Ca(OH)2 → 2LiOH + CaCO3. In the chemical conversion method using barium hydroxide, barium hydroxide is added to a lithium-containing solution to produce a lithium hydroxide solution based on the reaction Li2SO4 + Ba(OH)2 → 2LiOH + BaSO4. Calcium ions and barium ions that may remain in the lithium hydroxide solution obtained by the chemical conversion method can be removed using a cation exchange resin, a chelating resin, or the like. Electrodialysis will be described in detail below.

[0056] In electrodialysis, a lithium hydroxide solution can be produced from a lithium concentrate solution by electrodialysis using, for example, a commercially available bipolar membrane electrodialysis device 1 (hereinafter simply referred to as "electrodialysis device 1") as shown in Figure 3. The illustrated electrodialysis device 1 includes an anode 2, a cathode 3, and a bipolar membrane 4, an anion exchange membrane 5, a cation exchange membrane 6, and a bipolar membrane 7 arranged in this order from the anode 2 side to the cathode 3 side between the anodes 2 and 3. The interior of the cell is partitioned into a deionization chamber R1 between the anion exchange membrane 5 and the cation exchange membrane 6, an acid chamber R2 between the bipolar membrane 4 and the anion exchange membrane 5, and an alkaline chamber R3 between the cation exchange membrane 6 and the bipolar membrane 7. Each of the bipolar membranes 4 and 7 is composed of a cation exchange layer and an anion exchange layer stacked one on top of the other.

[0057] To perform electrodialysis with this electrodialysis device 1, a lithium concentrate solution is supplied to the deionization compartment R1, and pure water is supplied to each of the acid compartment R2 and alkaline compartment R3. A predetermined voltage is then applied between the anode 2 and the cathode 3. Then, the lithium ions (Li + ) passes through the cation exchange membrane 6 and moves to the alkaline chamber R3. In the alkaline chamber R3, water (HO) is decomposed by the bipolar membrane 7 to form hydroxide ions (OH - ) is present, a lithium hydroxide solution is obtained as the post-dialysis solution.

[0058] On the other hand, the anions of inorganic acid in the lithium concentrate in the deionization compartment R1 pass through the anion exchange membrane 5 and move to the acid compartment R2. In the acid compartment R2, the anions and hydrogen ions (H + ) produces an acid solution such as a sulfuric acid solution. As a result, the post-dialysis solution (lithium hydroxide solution) obtained in the alkaline chamber R3 contains almost no inorganic acid anions. In the illustrated example, the inorganic acid anions are sulfate ions (SO 2- ), but depending on the type of acid used in the acid leaching process, nitrate ions (NO3 - ) or chloride ions (Cl - ) may be.

[0059] In the deionization chamber R1, lithium salts are separated from the lithium concentrated solution as described above, and a deionized solution remains. The concentration of inorganic acid anions tends to be higher in the acid solution than in the post-dialysis solution (lithium hydroxide solution), and also tends to be higher in the deionized solution than in the post-dialysis solution (lithium hydroxide solution).

[0060] The lithium hydroxide solution obtained by hydroxylation can be effectively used as a pH adjuster in the neutralization step and the extraction step of various metals. After hydroxylation, if necessary, the lithium ion concentration of the lithium hydroxide solution may be increased by heating and concentration or the like, and then the resulting solution may be used as a pH adjuster. Furthermore, after hydroxylation, solid lithium hydroxide may be precipitated from the lithium hydroxide solution by a crystallization procedure such as heating and concentration or vacuum distillation.

[0061] As mentioned above, the lithium concentrated solution subjected to electrodialysis has an increased lithium ion concentration. Therefore, the current efficiency during electrodialysis can be improved. This is based on the results that the higher the lithium ion concentration of the solution subjected to electrodialysis, as will be explained in detail in the Examples section, and shows that the current efficiency during electrodialysis improves as the lithium ion concentration of the solution subjected to electrodialysis increases. This is thought to be because, when the lithium ion concentration of the solution subjected to electrodialysis is high, the difference in lithium ion concentration between the solution and the lithium hydroxide solution obtained by electrodialysis increases, thereby improving the current efficiency.

[0062] When carbonation is carried out in the lithium recovery step, the carbonation may be carried out by adjusting the pH to 10 to 13, adding a carbonate such as sodium carbonate or ammonium carbonate to the lithium concentrated solution, or by blowing carbon dioxide gas into the lithium concentrated solution, thereby recovering lithium ions in the lithium concentrated solution as solid lithium carbonate. Since the solubility of lithium carbonate is about 2 g / L in terms of lithium ion concentration, the higher the lithium ion concentration in the lithium concentrated solution before carbonation, the higher the recovery rate of lithium.

[0063] When the purity of the lithium carbonate is low, it can be purified as necessary. In the purification, the crude lithium carbonate is subjected to repulp washing, and carbon dioxide gas is blown into the crude lithium carbonate to dissolve carbon dioxide in the liquid, and then impurities are separated from the lithium hydrogen carbonate solution by solid-liquid separation. Thereafter, the solution is deoxidized and concentrated, and then separated into purified lithium carbonate and a filtrate by solid-liquid separation. Thereafter, further washing can be performed.

[0064] Next, tests related to the lithium recovery method and metal recovery method described above were conducted and are described below. However, this description is merely for illustrative purposes and is not intended to be limiting. In the following tests, metal ion concentrations were measured using an ICP optical emission spectrometer SPS3300 manufactured by SII NanoTechnology Inc., and pH was measured using a multi-purpose water quality meter MX-43X and a composite electrode GST-5841C manufactured by DKK-TOA Corporation.

[0065] (Test Example 1) A lithium hydroxide solution prepared by hydroxide oxidation in the lithium recovery process was used as a pH adjuster in each of the neutralization process, manganese and / or aluminum extraction process, cobalt extraction process, and nickel extraction process, and a metal recovery method including these processes was continuously carried out. The lithium ion concentration of the lithium hydroxide solution used as a pH adjuster was 28 g / L.

[0066] In the nickel extraction step, nickel ions were transferred from the metal-containing solution to the solvent in a mixer settler using a solvent containing VA-10, a carboxylic acid extractant. The nickel ion concentration in the metal-containing solution before extraction was 8 to 12 g / L, and the nickel ion concentration in the post-extraction solution was 0.001 to 0.01 g / L. The solvent was a mixture of VA-10 and a hydrocarbon organic solvent, containing VA-10 at a concentration of 25% by volume. The equilibrium pH during extraction was adjusted to 6.8 to 7.2, typically about 7.0, using the pH adjuster described above.

[0067] The lithium ion concentrations of the metal-containing solution (pre-extraction solution) before the extraction and the post-extraction solution (MS solution) in the mixer-settler were measured, and the amount of precipitate generated in the mixer-settler was visually confirmed. The results are shown in Table 1. The change in lithium ion concentration of each solution over time is shown in Figure 4. Here, a three-stage extraction was performed using a countercurrent system in which the metal-containing solution and the solvent flowed in opposite directions. Figure 4 shows the change in lithium ion concentration in the post-extraction solution in the mixer-settler during each stage of extraction.

[0068]

[0069] 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 in Periods B and C according to the degree of dilution, as shown in Table 1 and FIG. 4.

[0070] The anion of the inorganic acid contained in the pre-extraction solution is sulfate ion, and the lithium ion concentration in a saturated solution of lithium sulfate (lithium salt) (lithium ion concentration of the saturated lithium salt solution) is 42.5 g / L at the temperature during extraction (40°C). The lithium ion concentration of this saturated lithium salt solution can be calculated from the lithium sulfate (LiSO) concentration of 337 g / L in the saturated lithium sulfate solution at 40°C by the following equation: 337 x 6.94 x 2 / 109.945 ≒ 42.5. Since the lithium ion concentration of the pH adjuster is 28 g / L, the sum of the lithium ion concentration of the pre-extraction solution and the lithium ion concentration of the pH adjuster was 46 to 48 during Period A, which was higher than the lithium ion concentration of the saturated lithium salt solution (42.5 g / L). During Period B, the sum was 40 to 41, which was lower than the lithium ion concentration of the saturated lithium salt solution (42.5 g / L). In period C, the total was 43 to 44, which was higher than the lithium ion concentration (42.5 g / L) of the saturated lithium salt solution.

[0071] As a result, as shown in Table 1 and Fig. 4, a certain amount of precipitates were generated in periods A and C. In contrast, almost no precipitates were generated in period B.

[0072] The precipitates formed in the mixer settler were analyzed by X-ray diffraction (XRD), and it was confirmed that the precipitates contained Li2SO4(H2O). Furthermore, because the precipitates were insoluble in water or acid, and based on their properties, it was estimated that the precipitates were a mixture of Li2SO4(H2O) and oil.

[0073] (Test Example 2) The metal recovery method of Test Example 1 was continuously carried out in the same manner as in Test Example 1, except that the lithium hydroxide solution prepared by hydroxide oxidation was not used, and separately prepared sodium hydroxide was used as a pH adjuster in each of the neutralization step, manganese and / or aluminum extraction step, cobalt extraction step, and nickel extraction step. At this time, the lithium ion concentration and sodium ion concentration of the metal-containing solution subjected to the nickel extraction step were measured, and the changes in each concentration over time were confirmed. The results are shown in Figure 5.

[0074] 5, it can be seen that when sodium hydroxide is used as a pH adjuster, the lithium ion concentration of the metal-containing solution remains sufficiently low. Furthermore, no precipitates were generated in the mixer-settler used for the nickel extraction process. This suggests that the generation of precipitates becomes evident when lithium hydroxide solution is used as a pH adjuster and lithium is circulated in the wet process, as in Test Example 1. Therefore, the metal recovery method described above is considered to be particularly effective in such cases.

[0075] Test Example 3 Extraction in the nickel extraction step was carried out substantially in the same manner as in Test Example 1.

[0076] Here, a lithium hydroxide solution obtained by hydroxide oxidation 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 pre-extraction solution was 17 g / L or less. The sum of the lithium ion concentration of the pH adjuster and the lithium ion concentration of the metal-containing solution was 29 or less, which is equal to or less than the lithium ion concentration of a saturated lithium salt solution (42.5 g / L). Under these conditions, extraction was performed with an equilibrium pH of 6.8 to 7.0, and no precipitate was generated. The lithium ion concentration of the post-extraction solution after separation from the solvent was 18 g / L or less.

[0077] (Test Example 4) A test was conducted in which a plurality of lithium-containing solutions having different lithium ion concentrations ranging from 10 g / L to 20 g / L were subjected to electrodialysis to prepare lithium hydroxide solutions (post-dialysis solutions). The electrodialysis conditions were a constant voltage of 32 V and a liquid supply rate of 0.13 L / min / m. 2 It was decided.

[0078] A graph showing the relationship between the lithium ion concentration (feedstock solution concentration) and current efficiency obtained as a result of the test is shown in Figure 6. It can be seen from Figure 6 that the higher the lithium ion concentration of the lithium-containing solution used in electrodialysis, the more improved the current efficiency in electrodialysis. Therefore, concentrating the lithium-containing solution before electrodialysis to increase the lithium ion concentration is thought to contribute to improving the current efficiency in electrodialysis. Note that Figure 6 also shows the Li loss rate, which is the amount of lithium ions in the post-dialysis solution divided by the amount of lithium ions in the lithium-containing solution. The Li loss rate was similar regardless of the Li concentration of the lithium-containing solution.

[0079] From the above, it was suggested that the lithium recovery method described above may be able to suppress the generation of precipitates during the extraction of nickel ions, while subsequently enabling the effective recovery of lithium.

[0080] (Potential Contribution to SDGs) According to the above-described embodiment, it is possible to effectively recover lithium while suppressing the generation of precipitates during the extraction of nickel ions, which may improve the recovery rate of target metals such as lithium from lithium-ion battery waste and the current efficiency of electrodialysis. Therefore, this embodiment may contribute to Goal 9 "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation" and Goal 12 "Ensure sustainable consumption and production patterns" of the United Nations-led Sustainable Development Goals (SDGs) by promoting the reuse of waste and improving resource utilization efficiency.

[0081] 1 Bipolar membrane electrodialysis device 2 Anode 3 Cathode 4, 7 Bipolar membrane 5 Anion exchange membrane 6 Cation exchange membrane R1 Deionization chamber R2 Acid chamber R3 Alkaline chamber

Claims

1. A method for recovering lithium from a metal-containing solution containing lithium ions and nickel ions, comprising: a nickel extraction step including extraction in which nickel ions in the metal-containing solution are extracted and separated into a solvent; a lithium concentration step in which the lithium-containing solution obtained after the extraction in the nickel extraction step is concentrated to obtain a lithium concentrated solution having a higher lithium ion concentration than the metal-containing solution at the time of the extraction in the nickel extraction step; and a lithium recovery step in which lithium is recovered from the lithium concentrated solution.

2. The method for recovering lithium according to claim 1, wherein, when the metal-containing solution contains an anion of an inorganic acid, and a saturated solution of a lithium salt consisting of the anion of the inorganic acid and lithium ions contained in the metal-containing solution is made into a saturated lithium salt solution, the lithium ion concentration of the metal-containing solution during the nickel extraction step is set to be equal to or lower than the lithium ion concentration of the saturated lithium salt solution.

3. The method for recovering lithium according to claim 2, wherein in the extraction of the nickel extraction step, an equilibrium pH is adjusted using a pH adjuster containing lithium ions, and the sum of the lithium ion concentration (g / L) of the metal-containing solution before use of the pH adjuster and the lithium ion concentration (g / L) of the pH adjuster is equal to or less than the lithium ion concentration (g / L) of the saturated lithium salt solution.

4. The method for recovering lithium according to any one of claims 1 to 3, wherein the lithium ion concentration of the metal-containing solution separated from the solvent in the extraction of nickel in the nickel extraction step is adjusted to less than 15 g / L.

5. The method for recovering lithium according to claim 4, wherein the lithium ion concentration of the lithium-containing solution separated from the solvent in the nickel extraction step is adjusted to 10 g / L to 14 g / L.

6. The method for recovering lithium according to any one of claims 1 to 3, wherein the lithium ion concentration of the lithium concentrate obtained in the lithium concentration step is 15 g / L or more.

7. The method for recovering lithium according to any one of claims 1 to 3, wherein the lithium-containing solution contains impurity metal ions, and the lithium concentration step removes at least a portion of the impurity metal ions in the lithium-containing solution.

8. The method for recovering lithium according to any one of claims 1 to 3, wherein the lithium concentration step includes filtration using a water-permeable filtration membrane.

9. The method for recovering lithium according to claim 8, wherein the filtration uses a nanofiltration membrane and a reverse osmosis membrane.

10. The method for recovering lithium according to any one of claims 1 to 3, wherein the lithium recovery step includes hydroxylation to obtain a lithium hydroxide solution and / or carbonation to obtain a lithium carbonate solution from the lithium concentrated solution.

11. The method for recovering lithium according to claim 10, wherein the lithium recovery step includes the hydroxylation, and the hydroxylation is performed by electrodialysis using a bipolar membrane, and the lithium hydroxide solution is obtained as a post-dialysis solution.

12. A method for recovering metals by leaching metals from battery powder of lithium-ion battery waste and separating and recovering the metals from the metal-containing solution obtained thereby, the method comprising the lithium recovery method according to any one of claims 1 to 3.

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