Impurity removal method and metal recovery method

Abstract

Provided is a method for removing impurities including aluminum from a metal-containing solution which is obtained from lithium battery waste and which contains aluminum ions, iron ions, cobalt ions, and / or nickel ions, said method comprising a dealumination step for removing aluminum by raising the pH of the metal-containing solution under the presence of phosphate ions and precipitating aluminum, wherein the iron ions in the metal-containing solution provided for the dealumination step include divalent iron ions.

Description

Method for removing impurities and method for recovering metals

[0001] This specification describes a method for removing impurities and a method for recovering metals.

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

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

[0005] In this regard, Patent Document 4 describes "a method for removing aluminum and iron in the recycling of rechargeable batteries, the method comprising: a) preparing a leachate from black mass; b) adding phosphoric acid (H3PO4) to the leachate from step a); c) adjusting the pH to form iron phosphate (FePO4) and aluminum phosphate (AlPO4); d) precipitating and removing the formed FePO4 and AlPO4; and e) forming a filtrate for recovering cathode metals." Patent Document 4 also states that "the first precipitation at a low pH has the advantage of minimizing co-precipitation of lithium and NMC metals. When a second precipitation step is performed, fewer solids are present, which is advantageous because it counteracts the tendency for co-precipitation at higher pH."

[0006] JP 2010-180439 A U.S. Patent Application Publication No. 2011 / 0135547 JP 2014-162982 A JP 2022-528969 A

[0007] In order to precipitate and remove aluminum from a metal-containing solution by neutralization, it is believed to be advantageous to carry out the neutralization in the presence of phosphate ions in the metal-containing solution, for example by adding a phosphate ion source.

[0008] In this case, it was newly discovered that when iron ions are contained in the metal-containing solution together with aluminum ions, depending on the conditions, a larger amount of phosphate ions than that required for the precipitation of aluminum may be required. Because phosphate ion sources are relatively expensive, the use of a large amount of phosphate ion source increases the cost of treating lithium-ion battery waste.

[0009] This specification discloses a method for removing impurities and a method for recovering metals that can reduce the amount of phosphate ion source used and contribute to reducing processing costs.

[0010] One impurity removal method disclosed in this specification is a method for removing impurities containing aluminum from a metal-containing solution obtained from lithium-ion battery waste and containing aluminum ions, iron ions, and cobalt and / or nickel ions, and includes a dealumination step of increasing the pH of the metal-containing solution in the presence of phosphate ions to precipitate and remove aluminum, and the iron ions in the metal-containing solution subjected to the dealumination step include divalent iron ions.

[0011] Another impurity removal method disclosed in this specification is a method for removing impurities containing aluminum from a metal-containing solution obtained from lithium-ion battery waste and containing aluminum ions, iron ions, and cobalt and / or nickel ions, which includes a dealumination step of increasing the pH of the metal-containing solution in the presence of phosphate ions to precipitate and remove aluminum, and the redox potential (based on silver / silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is started.

[0012] The metal recovery method disclosed in this specification is for recovering metals including cobalt and / or nickel from a metal-containing solution from which impurities have been removed by the above-mentioned impurity removal method.

[0013] According to the above-described method for removing impurities, the amount of phosphate ion source used can be reduced, which contributes to reducing the processing cost.

[0014] FIG. 1 is a flow chart showing an example of a metal recovery method including an impurity removal method according to an embodiment of the present invention. FIG. 2 is a flow chart showing an example of a pretreatment step for obtaining battery powder from lithium ion battery waste. FIG. 3 is a flow chart showing details of an acid leaching step included in the metal recovery method of FIG. 1. FIG. 4 is a graph showing changes in iron ion concentration with respect to changes in pH during dealumination in Test Example 1. FIG. 5 is a graph showing changes in aluminum ion concentration with respect to changes in pH during dealumination in Test Example 1. FIG. 6 is a graph showing changes in phosphorus concentration with respect to changes in pH during dealumination in Test Example 1. FIG. 7 is a graph showing changes in oxidation-reduction potential (based on silver / silver chloride potential) with respect to changes in pH during dealumination in Test Example 1. FIG. 8 is a graph showing changes in iron ion concentration with respect to changes in pH during dealumination in Test Example 2. FIG. 9 is a graph showing changes in aluminum ion concentration with respect to changes in pH during dealumination in Test Example 2. FIG. 10 is a graph showing changes in phosphorus concentration with respect to changes in pH during dealumination in Test Example 2.

[0015] The present invention will be described in detail below with reference to an embodiment thereof. The impurity removal method of one embodiment is directed to a metal-containing solution obtained from lithium-ion battery waste, the metal-containing solution containing aluminum ions, iron ions, and cobalt ions and / or nickel ions.

[0016] This impurity removal method includes a dealumination step in which the pH of the metal-containing solution is increased in the presence of phosphate ions to precipitate and remove aluminum, among other impurities, from the metal-containing solution. Here, the iron ions in the metal-containing solution subjected to the dealumination step include divalent iron ions, and / or the oxidation-reduction potential (based on a silver / silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is initiated.

[0017] It has been discovered that when the metal-containing solution used in the dealumination step contains trivalent iron ions, a large amount of phosphate ions in the metal-containing solution are consumed in the reaction with the trivalent iron ions, resulting in the need for a larger amount of phosphate ion source than the amount required for the reaction with the aluminum ions. This is particularly evident when the iron ions are oxidized from divalent to trivalent when an oxidizing agent is added in the dealumination step. Based on this discovery, the metal-containing solution used in the aluminum step is assumed to contain divalent iron ions. Additionally or alternatively, the oxidation-reduction potential (based on silver / silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is initiated. If the oxidation-reduction potential (based on silver / silver chloride potential) of the metal-containing solution is less than 500 mV, it is believed that at least a portion, typically almost the majority, of the iron ions in the metal-containing solution have been converted to divalent iron ions. This allows more phosphate ions to be used in the reaction with the aluminum ions, thereby reducing the amount of phosphate ion source used. As a result, the cost of chemicals for the phosphate ion source is reduced, thereby reducing the cost of treating lithium-ion battery waste.

[0018] The impurity removal method of this embodiment may be carried out, for example, in a metal recovery method having the steps shown in Figure 1. In Figure 1, battery powder from lithium-ion battery waste is subjected to an acid leaching step, a dealumination step, a de-ironization step, a manganese extraction step, a cobalt extraction step, a nickel extraction step, a hydroxide step, and a crystallization step in this order. The battery powder can be obtained by subjecting lithium-ion battery waste to a pretreatment step, as shown in Figure 2. Here, the description will be made according to Figures 1 and 2, but Figures 1 and 2 are merely examples and the present invention is not limited to such specific flows.

[0019] (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.

[0020] Lithium-ion battery waste has an aluminum-containing casing as an exterior that encases the battery. This casing can be made of aluminum alone, aluminum and iron, or aluminum laminate. Lithium-ion battery waste may also contain a cathode active material, such as 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 metals. The cathode active material may also be coated and fixed to an aluminum foil (cathode substrate) with an organic binder, such as polyvinylidene fluoride (PVDF). Lithium-ion battery waste may also contain copper, iron, etc. Furthermore, the casing of lithium-ion battery waste typically contains an electrolyte solution, such as lithium hexafluorophosphate, dissolved in an organic solvent. Examples of organic solvents that may be used include ethylene carbonate and diethyl carbonate.

[0021] (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.

[0022] In the roasting process, the lithium-ion battery waste is heated. For example, roasting can convert metals such as lithium and cobalt contained in the lithium-ion battery waste into a form that is easily soluble in the acid leaching solution during the acid leaching process. During roasting, the lithium-ion battery waste is preferably heated at a temperature ranging from 450°C to 1000°C, preferably from 600°C to 800°C, for 0.5 to 6 hours. Roasting can be performed either in air or in an inert atmosphere such as nitrogen. Alternatively, roasting can be performed in both air and inert atmospheres, either sequentially or in reverse. The roasting furnace may be either a batch or continuous furnace. For example, a stationary furnace is used for the batch process, and a rotary kiln is used for the continuous process. Various other furnaces can also be used.

[0023] During roasting, at least a portion of the electrolyte is removed from the lithium-ion battery waste, for example, by evaporation of the electrolyte solution. In many cases, when lithium-ion battery waste is heated during roasting, the components of the internal electrolyte evaporate sequentially, starting with those with low boiling points. Furthermore, when the lithium-ion battery waste reaches a higher temperature, resins such as organic binders decompose or vaporize. Even if a portion of the electrolyte solution and organic binder is removed in this way, certain components, such as fluorine, contained in the electrolyte solution and organic binder may remain and be included in the battery powder obtained after the pretreatment process. When roasting is performed, the electrolyte is removed and rendered harmless, and the organic binder is decomposed, facilitating the separation of the aluminum foil and the positive electrode active material during the crushing and sieving processes described below. Although the composition of the positive electrode active material changes upon roasting, the term "positive electrode active material" will be used here even if the material has undergone roasting.

[0024] After roasting, the lithium-ion battery waste can be crushed to remove the positive electrode active material and other materials from the casings. In the crushing, the casings of the lithium-ion battery waste are destroyed and the positive electrode active material is selectively separated from the aluminum foil on which the positive electrode active material is applied.

[0025] For crushing, various known devices or equipment can be used, but it is particularly preferable to use an impact crusher that can crush lithium-ion battery waste by applying impact while cutting the waste. Examples of this impact crusher include a sample mill, hammer mill, pin mill, wing mill, tornado mill, and hammer crusher. A screen can be installed at the outlet of the crusher, and the lithium-ion battery waste is discharged from the crusher through the screen once it has been crushed to a size that can pass through the screen.

[0026] After crushing the lithium-ion battery waste, it is sieved using a sieve with appropriate openings, whereby aluminum and copper remain on the sieve and battery powder from which aluminum and copper have been removed to some extent is obtained below the sieve.

[0027] If the battery powder obtained in the pretreatment step contains nickel, the nickel content is, for example, 1% by mass to 30% by mass, typically 5% by mass to 20% by mass. If the battery powder contains cobalt, the cobalt content in the battery powder is, for example, 1% by mass to 30% by mass, typically 5% by mass to 20% by mass. The battery powder may also contain, for example, 2% by mass to 8% by mass of lithium, 1% by mass to 30% by mass of manganese, 1% by mass to 10% by mass of aluminum, 1% by mass to 5% by mass of iron, and 1% by mass to 10% by mass of copper.

[0028] 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 to leach the lithium in the battery powder into the water. In this case, the battery powder as the water leaching residue is subjected to the acid leaching step. When the water leaching is performed, at least a portion of the electrolyte solution and other electrolytes in the lithium-ion battery waste is removed by, for example, flowing into the water.

[0029] However, water leaching requires special equipment, and performing both water leaching and acid leaching in the acid leaching step increases the processing time. Furthermore, it may be necessary to control roasting conditions, etc., to effectively leach lithium with water. Even with such control, the leaching rate of lithium with water may not be significantly increased. Therefore, the battery powder obtained as described above may 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 during wet processing after the acid leaching step.

[0030] In addition to the roasting and water leaching described above, in order to remove the electrolyte from the lithium ion battery waste in the pretreatment step, the lithium ion battery waste may be washed with a washing liquid such as water at any time during the pretreatment step.

[0031] (Acid Leaching Step) In the acid leaching step, metals in the battery powder, including at least aluminum, iron, cobalt, and / or nickel, are leached with an acidic leaching solution containing sulfuric acid, nitric acid, hydrochloric acid, or other inorganic or mineral acids. This results in a post-leaching solution (metal-containing solution) containing at least aluminum ions, iron ions, and cobalt ions and / or nickel ions. Here, the solution containing the metal ions resulting from the dissolution of the metals in the acid leaching step and sent to the next step, the dealumination step, is referred to as the metal-containing solution. The solution undergoing steps subsequent to the dealumination step may also be referred to as the metal-containing solution.

[0032] 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. During leaching, for example, the acidic leachate may be stirred at 100 rpm to 400 rpm using a stirrer as needed, and the temperature of the solution may be set to 50°C to 80°C, or further 65°C to 70°C.

[0033] In the acid leaching step, the acid leachate may contain phosphate ions. When the acid leachate contains phosphate ions, aluminum precipitates by forming a compound such as aluminum orthophosphate (AlPO), which can be removed. The phosphate ions not consumed in the acid leaching step can be used to precipitate and remove aluminum during neutralization in the next step, the dealumination step.

[0034] The phosphate ion source may be contained in the battery powder, but if this is not sufficient, a phosphate ion source can be added to the acidic leachate separately from the battery powder. The phosphate ion source may be added to the acidic leachate together with the battery powder, or may be added to the acidic leachate before or after contacting the battery powder with the acidic leachate. The phosphate ion source may be added after the start of leaching. For example, when the battery powder is mixed with water such as distilled water to form a slurry and then an acid such as sulfuric acid is added to the slurry to form the acidic leachate, the phosphate ion source may be added to the slurry before the acid is added, or may be added to the slurry together with the acid. If the phosphate ion source is contained in the lithium-ion battery waste and the battery powder obtained by performing a pretreatment process thereon, the acidic leachate will contain phosphate ions upon contact between the battery powder and the acidic leachate.

[0035] The phosphate ion source to be added to the acidic leachate is a phosphate ion (PO4 3- ), various substances can be used, and specific examples include phosphoric acid (H3PO4), calcium phosphate (Ca3(PO4)2, etc.), calcium hydrogen phosphate (CaHPO4), trisodium phosphate (Na3PO4), disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), and lithium phosphate (Li3PO4).

[0036] The amount of phosphoric acid to be added to the acid leaching solution can be appropriately determined taking into consideration the aluminum content of the battery powder and other conditions. Specifically, the battery powder to be input into the acid leaching step may be subjected to a component analysis in advance to determine the aluminum content of the battery powder, and the amount of phosphoric acid may be determined based on this. For example, the molar ratio of phosphorus in the phosphoric acid to aluminum (P / Al molar ratio) is preferably 0.5 or more, and more preferably 1.0 or more but less than 1.5.

[0037] The acid leaching process may include multiple leaching stages, as described below, or may include only one leaching stage. Alternatively, as shown in FIG. 3, multiple leaching stages may be repeated multiple times. Each of the multiple leaching stages includes a first leaching stage in which the metals in the battery powder are leached with an acid leaching solution, the leaching is terminated before copper is eluted, and the leaching residue is separated to obtain a post-leaching solution. A second leaching stage in which the leaching residue from the first leaching stage is leached with an acid leaching solution, the leaching is terminated after copper is eluted, and a post-leaching solution is obtained. The post-leaching solution obtained in the first leaching stage is used as a metal-containing solution to be sent to the dealumination process described below. Meanwhile, the post-leaching solution obtained in the final leaching stage (the second leaching stage if there are two leaching stages) is used by incorporating it into the acid leaching solution for the next first leaching stage.

[0038] By repeating multiple leaching steps in this manner, it is possible to increase the leaching rate of the metals to be leached (such as cobalt and / or nickel) in the battery powder, while leaving much of the copper, the leaching of which should be suppressed, unleached and separating it as a leaching residue. More detailed information is provided below. Here, as an example, a battery powder containing cobalt, nickel, and copper will be described. However, the battery powder may contain neither cobalt nor nickel, or may further contain other metals.

[0039] As an example of repeating multiple leaching steps, in the first leaching step, leaching is terminated before copper dissolves (e.g., while the copper ion concentration in the acidic leaching solution is 0.01 g / L or less), and the leaching residue is extracted by solid-liquid separation. This results in a leaching solution that has a lower copper ion concentration than the leaching solution obtained in the second leaching step described below and contains cobalt ions and nickel ions. This leaching solution is sent to a subsequent process as a metal-containing solution. Meanwhile, the leaching residue contains copper as well as the remaining undissolved cobalt and nickel. A second leaching step is performed to further leach cobalt and nickel from this leaching residue.

[0040] In the first second leaching step, the leaching residue obtained in the first leaching step is contacted with an acidic leaching solution to leach cobalt and nickel from the leaching residue. In the second leaching step, leaching is continued even after copper has been dissolved (e.g., after the copper ion concentration in the acidic leaching solution becomes higher than 0.01 g / L). This allows almost all of the cobalt and nickel in the leaching residue to be leached. After copper has been dissolved and cobalt and nickel have been sufficiently leached, leaching is terminated and the leaching residue is extracted by solid-liquid separation. The leaching residue contains reduced cobalt and nickel and contains copper. The post-leaching solution after the leaching residue is extracted contains cobalt ions, nickel ions, and copper ions. In the second leaching step, new battery powder may be added to leach not only the metals in the leaching residue from the first leaching step, but also the metals in the new battery powder. In the second leaching stage, leaching is continued even after the copper has been dissolved, so that the cobalt and nickel in the new battery powder can also be sufficiently leached.

[0041] Next, in the second first leaching step, the post-leaching solution obtained in the first second leaching step is used as the acidic leaching solution. If necessary, new acidic leaching solution may be added. In the second first leaching step, copper ions in the post-leaching solution are reduced by a substitution reaction with a metal less noble than copper contained in new battery powder, resulting in copper precipitation and in the leaching residue. Furthermore, the second first leaching step, while intended to dissolve cobalt and nickel from the new battery powder, ends before copper dissolution. Therefore, the leaching residue contains copper derived from the new battery powder as well as undissolved cobalt and nickel. This leaching residue is separated by solid-liquid separation and then subjected to leaching in the second second leaching step. The post-leaching solution from which the leaching residue is removed contains not only the cobalt and nickel ions dissolved from the new battery powder but also the cobalt and nickel ions carried over from the first leaching step, and is sent to a downstream process.

[0042] The second second leaching stage is carried out in the same manner as the first second leaching stage, and therefore a detailed description thereof will be omitted. Solid-liquid separation in the second leaching stage does not need to be carried out every time. If solid-liquid separation is not carried out in the second leaching stage, the post-leaching solution containing the leaching residue will be sent to the next first leaching stage, and copper will accumulate in the leaching residue. If solid-liquid separation is carried out in at least one of multiple second leaching stages, the copper-containing leaching residue can be separated and removed in that second leaching stage. Preferably, solid-liquid separation is carried out in each second leaching stage, and the copper-containing leaching residue is removed each time.

[0043] Here, "before copper leaching" in the first leaching stage refers to a state in which the copper ion concentration in the acidic leaching solution is lower than that of the post-leaching solution obtained in the second leaching stage of that cycle. For example, a state in which the copper ion concentration in the acidic leaching solution is 0.01 g / L or less may be considered "before copper leaching." However, this copper ion concentration does not include the copper ion concentration in the post-leaching solution obtained in the previous second leaching stage and used as the acidic leaching solution in the current first leaching stage. When the post-leaching solution obtained in the previous second leaching stage is used as the acidic leaching solution in the first leaching stage, the period in which the relatively high copper ion concentration before leaching tends to decrease due to copper precipitation through a substitution reaction can be considered "before copper leaching" after the copper ion concentration once drops to 0.01 g / L or less and then remains at 0.01 g / L or less. In this case, leaching may be terminated while the copper ion concentration remains at 0.01 g / L or less (before the copper ion concentration exceeds 0.01 g / L).

[0044] Furthermore, "after copper leaching" in the second leaching stage refers to a state in which the copper ion concentration in the acidic leaching solution is higher than that of the post-leaching solution obtained in the first leaching stage of that cycle. Therefore, in each cycle, the copper ion concentration in the post-leaching solution obtained in the second leaching stage will be higher than that of the post-leaching solution obtained in the first leaching stage. For example, the state may be considered "after copper leaching" when the copper ion concentration in the acidic leaching solution is higher than 0.01 g / L. In the second leaching stage, leaching may be terminated, for example, after the copper ion concentration in the acidic leaching solution becomes higher than 0.01 g / L.

[0045] In the first and second leaching stages, the oxidation-reduction potential (based on silver / silver chloride potential) of the acidic leaching solution may be well below 0 mV before leaching and may gradually increase as leaching progresses. Hereinafter, "oxidation-reduction potential (based on silver / silver chloride potential)" will be simply referred to as "oxidation-reduction potential." This oxidation-reduction potential may also be referred to as ORP.

[0046] In the first leaching stage, leaching is preferably terminated before the redox potential of the acidic leaching solution becomes equal to or higher than 0 mV, more preferably before it becomes higher than −300 mV. This is because if the redox potential becomes high, the copper ion concentration may increase to a certain extent, and copper ions may be contained in the leaching solution.

[0047] On the other hand, in the second leaching stage, it is preferable to terminate leaching after the redox potential of the acidic leachate reaches 0 mV or higher. This allows most of the cobalt and nickel to be leached, thereby suppressing loss of cobalt and nickel. However, in the second leaching stage, it is preferable to terminate leaching before the redox potential of the acidic leachate reaches 60 mV or higher in order to prevent excessive copper leaching.

[0048] Furthermore, in the first and second leaching stages, the rate of increase in the redox potential of the acidic leachate tends to accelerate once metal leaching has progressed to a certain extent. In the first leaching stage, in order to suppress copper leaching, it is preferable to terminate the leaching before the hourly increase in the redox potential of the acidic leachate reaches 233 mV or more. On the other hand, in the second leaching stage, from the viewpoint of leaching as much cobalt and nickel as possible, it is preferable to terminate the leaching after the hourly increase in the redox potential of the acidic leachate reaches 233 mV or more. Here, the hourly increase in redox potential refers to the value obtained by subtracting the redox potential value one hour prior to a given time from the redox potential value at that time.

[0049] In the first leaching stage or the second leaching stage, leaching can be considered to be completed, for example, when the stirring by the stirrer that was performed during leaching is stopped and the next operation, such as solid-liquid separation or the addition of new battery powder, is started. Solid-liquid separation for removing the leaching residue from the post-leaching solution can be performed using known devices and methods such as a filter press or a thickener.

[0050] The multiple leaching stages may include not only a first leaching stage and a second leaching stage, but also three or more leaching stages. For example, the first leaching stage and / or the second leaching stage may be divided into multiple stages. In this case, each of the multiple first leaching stages may be terminated while the copper ion concentration in the acidic leachate is lower than the copper ion concentration in the post-leaching solution obtained in the second leaching stage. For example, each of the multiple first leaching stages may be terminated while the copper ion concentration in the acidic leachate is 0.01 g / L or less. Furthermore, each of the multiple second leaching stages may be terminated after the copper ion concentration in the acidic leachate is higher than the copper ion concentration in the post-leaching solution obtained in the first leaching stage. For example, each of the multiple second leaching stages may be terminated after the copper ion concentration in the acidic leachate is higher than the copper ion concentration in the post-leaching solution obtained in the first leaching stage.

[0051] When the first leaching stage and the second leaching stage are repeated multiple times as described above, it is desirable to minimize the loss of cobalt and nickel if cobalt or nickel transfers to the leaching residue of the second leaching stage. Specifically, when the battery powder contains cobalt, it is preferable that, when the sum or total of the cobalt content of the battery powder subjected to the first leaching stage in a given leaching run and the cobalt ion content of the acidic leaching solution used in the first leaching stage in that run is taken as 100%, the sum of the cobalt ion content of the post-leaching solution obtained in the first leaching stage and the post-leaching solution obtained in the second leaching stage in each run is 95% or more, on a mass basis. Furthermore, when the battery powder contains nickel, the sum of the nickel ion content in the post-leaching solution obtained in the first leaching step and the nickel ion content in the post-leaching solution obtained in the second leaching step is preferably 95% or more in each leaching step, where the sum or total of the nickel content of the battery powder subjected to the first leaching step in a given cycle and the nickel ion content of the acid leaching solution used in the first leaching step in that cycle is 100% by mass. Here, in the first leaching step, the cobalt ion content and nickel ion content of the acid leaching solution used in the first leaching step are both zero. In the second and subsequent leaching steps, the cobalt ion content and nickel ion content of the acid leaching solution used in the first leaching step refer to the cobalt ion content and nickel ion content of the post-leaching solution obtained in the previous second leaching step and used as the acid leaching solution in the first leaching step.

[0052] When a phosphate ion source is added in an acid leaching process including multiple leaching stages, the timing of the addition is not particularly limited as long as it is before the end of the leaching stage (or after the end of leaching but before solid-liquid separation, if solid-liquid separation is performed), but it is preferable to add it in the first leaching stage. In this case, the first leaching stage is likely to reduce the aluminum ion concentration of the post-leaching solution sent to the dealumination step as a metal-containing solution, and it is also possible to increase the phosphate ion concentration in the acid leaching solution. If a phosphate ion source is added to the acid leaching solution in the second leaching stage to precipitate aluminum, the phosphate ions will be consumed in the second leaching stage. In this case, if the post-leaching solution obtained in the second leaching stage is used as the acid leaching solution for the next first leaching stage, there is a risk that the amount of phosphate ions obtained will be insufficient to precipitate aluminum in the new battery powder. Note that even if a phosphate ion source is added in the first leaching stage, aluminum may precipitate in the second leaching stage. If the phosphorus content of the battery powder is insufficient during each leaching stage, a necessary amount of phosphoric acid may be added separately.

[0053] The metal-containing 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, 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-containing solution may contain at least one of nickel ions and cobalt ions, but may not contain the other.

[0054] (Dealuminization Step) The dealumination step is carried out to remove aluminum ions from the metal-containing solution obtained in the acid leaching step. Specifically, the pH of the metal-containing solution is increased to precipitate at least a portion of the aluminum ions. Thereafter, solid-liquid separation such as filtration is carried out using known devices and methods such as a filter press or a thickener to remove neutralization residue and obtain a dealumination solution.

[0055] In the dealumination step, the pH of the metal-containing solution is increased in the presence of phosphate ions. This facilitates precipitation of aluminum ions in the metal-containing solution by the phosphate ions, enabling effective removal of aluminum. At this time, the iron ions in the metal-containing solution subjected to the dealumination step should contain divalent iron ions. This reduces the consumption of phosphate ions due to reaction with trivalent iron ions, allowing aluminum to be precipitated with a smaller amount of phosphate ions.

[0056] For example, if the metal-containing solution already contains the required amount of phosphate ions due to the presence of phosphorus in the battery powder or the addition of a phosphate ion source in the acid leaching step, it may not be necessary to further add a phosphate ion source to the metal-containing solution. Alternatively, if the metal-containing solution does not contain phosphate ions or if the phosphate ions in the metal-containing solution are insufficient, a phosphate ion source may be added to the metal-containing solution before, during, and / or after the pH of the metal-containing solution is increased to a predetermined value.

[0057] The form of the phosphate ion source added to the metal-containing solution is not particularly limited, and examples include phosphoric acid (H3PO4), calcium phosphate (Ca3(PO4)2, etc.), calcium hydrogen phosphate (CaHPO4), trisodium phosphate (Na3PO4), disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), lithium phosphate (Li3PO4), etc. When the metal-containing solution contains phosphate ions, the neutralization residue generated in the dealumination step may contain compounds such as aluminum orthophosphate (AlPO4).

[0058] In the metal-containing solution, aluminum ions and phosphate ions are reacted with each other to form a compound of the formula: Al 3+ +PO4 3-→It is believed that the reaction occurs with AlPO4, and therefore, when starting the dealumination step, the content of phosphate ions in the metal-containing solution is preferably 0.1 to 1.5 molar equivalents of the amount required to react with the aluminum ions in the metal-containing solution. 0.5 to 1.5 molar equivalents is more preferable. If the amount of phosphate ions is too small, aluminum may not be sufficiently precipitated, while if it is too large, a large amount of phosphate ion source may be required, resulting in a certain increase in chemical costs.

[0059] In the dealumination step, the pH of the metal-containing solution can be increased, for example, to within a range of 3.0 to 4.0 by adding a pH adjuster. Since the metal-containing solution contains phosphate ions, aluminum can be effectively precipitated even at such a relatively low pH, thereby suppressing the coprecipitation of cobalt and nickel that would occur at a higher pH. In other words, if the metal-containing solution does not contain phosphate ions, the pH of the metal-containing solution must be increased to a relatively high value to precipitate aluminum, which would also precipitate cobalt and nickel, resulting in their loss. To further suppress the coprecipitation of cobalt and nickel, the pH of the metal-containing solution may be increased to a range of 3.0 or more and 3.5 or less (or less than 3.5). On the other hand, to more effectively precipitate aluminum, the pH of the metal-containing solution may be increased to a range of 3.5 or more (or more than 3.5) and 4.0 or less.

[0060] In the dealumination step, it is preferable not to add an oxidizing agent in order to suppress oxidation of iron ions and convert as many iron ions as possible to divalent iron ions. The oxidizing agent can act to oxidize iron from divalent to trivalent iron, and examples of the oxidizing agent include hydrogen peroxide, manganese dioxide, a positive electrode active material for lithium ion batteries, and a manganese-containing leaching residue obtained by leaching a positive electrode active material.

[0061] Furthermore, in the dealumination step, it is preferable to set the oxidation-reduction potential (based on silver / silver chloride potential) of the metal-containing solution to less than 500 mV at the start of the dealumination step. It is presumed that if the oxidation-reduction potential (based on silver / silver chloride potential) at the start is low to a certain extent, the metal-containing solution will contain a large amount of iron ions in a divalent state. The temperature of the metal-containing solution in the dealumination step can be set to 50°C to 90°C.

[0062] When the dealumination step is completed, the phosphorus concentration of the metal-containing solution is preferably in the range of 0.4 g / L to 1.0 g / L. After the phosphate ions have been sufficiently consumed in the dealumination step and the phosphorus concentration has been reduced, the iron removal step described below can be carried out.

[0063] (Iron removal step) After the dealumination step, a iron removal step can be carried out. In the iron removal step, an oxidizing agent is added to the metal-containing solution as the dealumination liquid, thereby precipitating iron in the metal-containing solution. The precipitated iron can be removed as a neutralization residue by solid-liquid separation.

[0064] To precipitate iron, the oxidation-reduction potential (based on the silver / silver chloride potential) during oxidation is preferably 300 mV to 900 mV. After the addition of the oxidizing agent, an acid such as sulfuric acid, hydrochloric acid, or nitric acid can be added to lower the pH to, for example, less than 3. Thereafter, if necessary, an alkaline pH adjuster can be added to raise the pH to, for example, within a range of 3.0 to 4.0, thereby precipitating iron. The addition of the oxidizing agent oxidizes the iron ions in the solution from divalent to trivalent. Since trivalent iron ions are more likely to precipitate as solids such as oxides or hydroxides, typically iron hydroxide (Fe(OH)), at lower pHs than divalent iron ions, it may not be necessary to raise the pH.

[0065] The oxidizing agent used in the iron removal step is not particularly limited as long as it can oxidize iron, but 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 or the like may contain manganese dioxide. When the above-mentioned positive electrode active material or the like is used as the oxidizing agent, a precipitation reaction occurs in which manganese dissolved in the liquid becomes manganese dioxide, and the precipitated manganese can be removed together with the iron. Alternatively, the oxidizing agent may be supplied by adding hydrogen peroxide or blowing in a gas such as ozone or oxygen-containing air.

[0066] Specific examples of alkaline pH adjusters used in the dealumination step and iron removal step include lithium hydroxide, sodium hydroxide, sodium carbonate, ammonia, etc. Among these, the lithium hydroxide solution obtained in the hydroxide step described below can be used, and in this case, lithium ions circulate within the series of steps in the wet treatment.

[0067] (Manganese Extraction Step) The metal-containing solution obtained after the iron removal step as a post-iron removal solution can be subjected to solvent extraction to extract and remove manganese ions, and in some cases, residual aluminum ions as well. In this case, the residual manganese ions and aluminum ions are extracted to obtain a post-manganese extraction solution from which they have been removed.

[0068] In the manganese extraction step, it is preferable to use an extractant containing a phosphate ester extractant. Examples of phosphate ester extractants include di-2-ethylhexyl phosphoric acid (abbreviated as D2EHPA or product name: DP-8R). The extractant may also be a mixture of a phosphate ester extractant and an oxime extractant. In this case, the oxime extractant is preferably an aldoxime or one containing aldoxime as the main component. Specific examples include 2-hydroxy-5-nonylacetophenone oxime (product name: LIX84), 5-dodecylsalicyaldoxime (product name: LIX860), a mixture of LIX84 and LIX860 (product name: LIX984), and 5-nonylsalicylaldoxime (product name: ACORGAM5640).

[0069] During extraction, the equilibrium pH is preferably adjusted to 2.3 to 3.5, more preferably 2.5 to 3.0. The alkaline or other pH adjuster used here is preferably the lithium hydroxide solution obtained in the hydroxide step described below, although separately prepared sodium hydroxide or the like may also be used. When the lithium hydroxide solution obtained in the hydroxide step is used as the pH adjuster, it is possible to prevent the sodium from remaining in the lithium-containing solution after the nickel extraction step described below, as well as to prevent the sodium from being mixed as an impurity into the lithium hydroxide solution produced from the lithium-containing solution, as occurs when sodium hydroxide is used as the pH adjuster.

[0070] During extraction, it is desirable to perform extraction by countercurrent multistage extraction, in which the aqueous phase and the solvent used in each extraction flow in opposite directions. This suppresses the extraction of cobalt ions, nickel ions, and lithium ions, and increases the extraction rate of manganese ions. When using countercurrent multistage extraction, it is effective to set the equilibrium pH of the deironized solution at a value within the above-mentioned range during the first extraction stage and then increase the equilibrium pH during each subsequent extraction stage.

[0071] Since the solvent used to extract manganese ions may contain cobalt ions, nickel ions, and lithium ions, it can be subjected to stripping after scrubbing. For example, the scrubbing solution can be a sulfuric acid solution with a pH of 2.0 to 3.0, and the stripping solution can be a sulfuric acid solution with a pH of 0.0 to 1.0. It is desirable to use the post-scrubbing solution or the post-stripping solution for manganese extraction (for example, by mixing the post-scrubbing solution with a metal-containing solution and using the resulting mixture as a pre-extraction solution for extracting manganese ions, using the post-stripping solution for scrubbing the solvent used to extract manganese ions, or using the post-scavenging solution as a stripping solution for the solvent used to extract manganese ions). This allows the cobalt ions, nickel ions, and lithium ions to be circulated or retained within the process without loss. However, if the solvent used to extract manganese ions does not contain cobalt ions, nickel ions, or lithium ions, scrubbing or stripping may not be necessary.

[0072] (Cobalt Extraction Step) Next, the cobalt extraction step can be carried out. In the cobalt extraction step, cobalt ions are separated by solvent extraction from the manganese extraction solution obtained after the manganese extraction step.

[0073] In the cobalt extraction step, it is preferable to use a solvent containing a phosphonate ester extractant. Among these, 2-ethylhexyl 2-ethylhexyl phosphonate (trade names: PC-88A, Ionquest 801) is particularly suitable from the viewpoint of the separation efficiency of nickel and cobalt. 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.

[0074] When cobalt ions are extracted, the equilibrium pH during extraction can be preferably adjusted to 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 in the hydroxide oxidation step described below as a pH adjuster, but separately prepared sodium hydroxide or the like may also be used. If the pH is lower than 5.0, there is a risk that the cobalt ions may not be sufficiently extracted into the solvent. This allows the cobalt ions in the post-manganese extraction solution to be extracted into the solvent.

[0075] It is also desirable to perform the extraction of cobalt ions by countercurrent multistage extraction, in which the aqueous phase and the solvent flow in opposite directions in each extraction. This can increase the extraction rate of cobalt ions while suppressing the extraction of nickel ions and lithium ions.

[0076] During the extraction, not only cobalt ions but also small amounts of nickel ions and lithium ions, which become impurities in the cobalt extraction process, may be extracted into the solvent. In this case, if necessary, the solvent from which cobalt ions have been extracted may be subjected to one or more scrubbing steps using a scrubbing solution to remove impurities such as nickel ions that may be contained in the solvent. The scrubbing solution may be, for example, a sulfuric acid solution with a pH of 3.5 to 5.5. The post-scrubbing solution may contain nickel ions and lithium ions. Therefore, it is desirable to use a portion or all of the post-scrubbing solution for cobalt extraction (i.e., mix a portion or all of the post-scrubbing solution with a manganese extraction solution and use this as a pre-extraction solution for cobalt extraction). This allows nickel ions and lithium ions to be circulated or retained within the process without loss. However, if the solvent from which cobalt ions have been extracted does not contain nickel ions or lithium ions, scrubbing may not be necessary.

[0077] The solvent from which the cobalt ions have been extracted is then subjected to stripping. The stripping solution used for stripping may be any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, but sulfuric acid is preferred when obtaining sulfate by crystallization, as described below. Here, the stripping is carried out under pH conditions such that as much of the cobalt ions as possible are extracted from the organic phase (solvent) into the aqueous phase (stripping solution). Specifically, the pH is preferably in the range of 2.0 to 4.0, and even more preferably in the range of 2.5 to 3.5. The O / A ratio and the number of times can be determined as appropriate. The liquid temperature may be room temperature, but is preferably 10°C to 50°C.

[0078] The strip-extracted solution, such as a cobalt sulfate solution obtained by strip-extraction of cobalt ions, can be crystallized. In this process, the strip-extracted solution is concentrated by heating, for example, to 40°C to 120°C, thereby crystallizing the cobalt ions as a cobalt salt. The cobalt salt thus produced preferably has a nickel content of 5 mass ppm or less, and since nickel has been sufficiently removed, it can be effectively used as a raw material for the production of lithium-ion secondary batteries and other batteries. The crystallized solution may contain uncrystallized cobalt ions and lithium ions. Therefore, it is desirable to mix the crystallized solution with the strip-extracted solution before crystallization and use it again for crystallization, to adjust the cobalt ion concentration of the scrubbing solution used as a solvent after cobalt ion extraction, or to use it for cobalt extraction. By repeatedly using the crystallized solution within the process in this way, the cobalt ions and lithium ions can be circulated or retained within the process and concentrated without loss.

[0079] (Nickel Extraction Step) Thereafter, the cobalt-extracted solution after the cobalt ions have been extracted can be subjected to a nickel extraction step.

[0080] In the nickel extraction step, a carboxylic acid extractant is preferably used to separate nickel ions from the post-cobalt extraction solution. Examples of carboxylic acid extractants include neodecanoic acid and naphthenic acid, with neodecanoic acid being 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% to 30% by volume, and this may be used as the solvent.

[0081] When extracting nickel ions, the equilibrium pH is preferably set to 6.0 to 8.0, more preferably 6.8 to 7.2. The pH adjuster used to adjust the pH at this time may be sodium hydroxide or the like, but it is preferable to use a lithium hydroxide solution obtained in the hydroxide oxidation step described below. Similarly to the extraction of cobalt ions described above, the extraction of nickel ions is also preferably performed by countercurrent multistage extraction. This suppresses the extraction of lithium ions, thereby increasing the extraction rate of nickel ions.

[0082] The solvent from which nickel ions have been extracted may be subjected to one or more scrubbing steps using a scrubbing solution, as needed, to remove impurities such as lithium ions and sodium ions that may be present in the solvent. The scrubbing solution may be, for example, a sulfuric acid solution with a pH of 5.0 to 6.0. The post-scrubbing solution may contain lithium ions. Therefore, it is desirable to use a portion or all of the post-scrubbing solution for nickel extraction (i.e., to mix a portion or all of the post-scrubbing solution with a post-cobalt extraction solution and use this as a pre-extraction solution for nickel extraction). This allows lithium ions to be circulated or retained within the process and concentrated without loss. However, if the solvent from which nickel ions have been extracted does not contain lithium ions, scrubbing may not be necessary.

[0083] The solvent from which nickel ions have been extracted is then back-extracted using a back-extraction solution such as sulfuric acid, hydrochloric acid, or nitric acid. If crystallization is to be performed afterwards, sulfuric acid is preferred. The pH is preferably in the range of 1.0 to 3.0, more preferably 1.5 to 2.5. The O / A ratio and number of times can be determined as appropriate, but the O / A ratio is preferably 5 to 1, more preferably 4 to 2.

[0084] When a stripping solution such as a nickel sulfate solution is obtained by stripping, it can be electrolyzed and dissolved as needed, and then heated to 40°C to 120°C to crystallize the nickel ions as nickel salts such as nickel sulfate. This process yields nickel salts. The crystallized solution may contain uncrystallized nickel ions and lithium ions. Therefore, it is desirable to mix the crystallized solution with the stripping solution before crystallization and use it for further crystallization, to adjust the nickel ion concentration in the scrubbing solution used as the solvent after nickel ion extraction, or to use it for nickel extraction. By repeatedly using the crystallized solution within the process in this way, nickel ions and lithium ions can be circulated or retained within the process and concentrated without loss.

[0085] As described above, at least a portion of the lithium-containing solution from which nickel ions have been extracted can be mixed with the acid leaching solution in the acid leaching step and used. This allows the lithium ions contained in the lithium-containing solution to be circulated through a series of steps including the acid leaching step, the dealumination step, the iron removal step, and various extraction steps. Preferably, after the lithium ion concentration in the lithium-containing solution has increased to a certain extent by circulating the lithium ions in this way, the hydroxide step described below is carried out.

[0086] (Hydroxylation Step) The lithium-containing solution obtained after the nickel extraction step contains substantially only lithium ions as a result of the separation of manganese ions, cobalt ions, and nickel ions in the aforementioned extractions. In the hydroxide step, a lithium hydroxide solution is prepared from the lithium-containing solution (lithium sulfate solution, etc.) by various methods described below.

[0087] For example, a lithium carbonate solution is first obtained by adding a carbonate or blowing carbon dioxide gas into a lithium sulfate solution. Then, as a so-called chemical conversion method, 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. Calcium ions that may remain in the solution can be removed using a cation exchange resin, a chelating resin, or the like.

[0088] Alternatively, a lithium hydroxide solution can be obtained by adding barium hydroxide to a lithium sulfate solution and carrying out the reaction LiSO + Ba(OH) → 2LiOH + BaSO. Note that barium that may dissolve in the solution at this time can be separated and removed using a cation exchange resin, a chelating resin, or the like.

[0089] Alternatively, when a so-called electrolysis method is employed, a lithium sulfate solution is supplied to the anode side and electrolysis is performed in an electrolytic cell provided with a cation exchange membrane that separates the anode side from the cathode side, whereby a lithium hydroxide solution can be produced on the cathode side.

[0090] The lithium hydroxide solution thus obtained can be effectively used as a pH adjuster (neutralizer) in the dealumination step and iron removal step, as well as an alkaline pH adjuster in each of the manganese extraction step, cobalt extraction step, and nickel extraction step.

[0091] In the electrolysis method among the above-mentioned techniques, electrodialysis may be performed by supplying a lithium sulfate solution to a deionization compartment between an anion exchange membrane and a cation exchange membrane in a bipolar membrane electrodialysis apparatus. In this case, a lithium hydroxide solution may be obtained in the alkaline compartment between the cation exchange membrane and the bipolar membrane, while an acidic solution such as a sulfuric acid solution may be obtained in the acid compartment between the bipolar membrane and the anion exchange membrane. Such an acidic solution may be included in the post-separation liquid as described above and mixed with the acidic leaching solution in the acid leaching step.

[0092] The lithium-containing solution may contain trace amounts of cations, such as nickel ions and magnesium ions, that were not completely separated during the nickel extraction process. Nickel ions and magnesium ions are cations, just like lithium ions, and behave similarly to lithium ions during electrodialysis, making them difficult to separate from lithium ions. Furthermore, electrodialysis of a lithium-containing solution containing nickel ions and magnesium ions can result in the generation of nickel and magnesium hydroxides in the resulting lithium hydroxide solution, potentially leading to process problems that could prevent the electrodialysis from continuing. Therefore, in such cases, it is desirable to perform washing to remove cations, such as nickel ions and magnesium ions, from the lithium-containing solution prior to electrodialysis. For example, an ion exchange resin or a chelating resin can be used for this washing.

[0093] (Crystallization Step) After the hydroxide step, a crystallization step may be performed to precipitate lithium hydroxide from the lithium hydroxide solution. For example, when a series of steps including the acid leaching step to the nickel extraction step are repeated, the lithium ion concentration in a solution such as a lithium sulfate solution may gradually increase as new lithium ion battery waste is added to the series of steps. After the lithium ion concentration in the solution has increased to a certain level, the crystallization step may be performed.

[0094] In the crystallization step, a crystallization procedure such as heat concentration or vacuum distillation can be performed to precipitate lithium hydroxide. In the case of heat concentration, a higher temperature during crystallization is preferable because the process proceeds more quickly. However, after crystallization, the crystallized product is preferably dried at a temperature of less than 60°C, at which water of crystallization does not detach. This is because, if water of crystallization detaches, anhydrous lithium hydroxide becomes deliquescent and becomes difficult to handle. The lithium hydroxide obtained in the crystallization step can be subjected to a pulverization process or the like to adjust the desired physical properties.

[0095] Next, tests were conducted to confirm the effectiveness of the above-described impurity removal method, which will be described below. However, this description is for illustrative purposes only and is not intended to be limiting.

[0096] Test Example 1 Metals in battery powder obtained by pretreatment such as roasting in an air atmosphere on lithium-ion battery waste were leached by acid leaching including multiple leaching stages as shown in Figure 3. In this acid leaching, the pH in the first leaching stage was set to 2.5, and the pH in the second leaching stage was set to 1.5, and calcium phosphate (Ca3(PO4)2) was added in the first leaching stage so that the P / Al molar ratio was 0.75. As a result, a metal-containing solution with the metal concentrations, pH, and oxidation-reduction potential (based on silver / silver chloride potential, ORP) shown in Table 1 was obtained as the leaching filtrate from the first leaching stage. The metal concentration was measured using an ICP optical emission spectrometer SPS3300 manufactured by SII NanoTechnology Inc., the pH was measured using a multi-purpose water quality meter MX-43X and a composite electrode GST-5841C manufactured by DKK-TOA Corporation, and the redox potential was measured using a multi-purpose water quality meter MX-43X and a composite electrode PST-5721C manufactured by DKK-TOA Corporation. Similar analysis or measurement devices were used in Test Example 2 described below.

[0097]

[0098] Thereafter, 600 mL of the metal-containing solution was neutralized with a 4N LiOH aqueous solution to precipitate aluminum for dealumination. In Comparative Example 1, 1 mL of 30% hydrogen peroxide (HO) water was added as an oxidizing agent, while in Example 1, no hydrogen peroxide (HO) was added. As a result, graphs showing the changes in iron ion concentration, aluminum ion concentration, phosphorus concentration, and oxidation-reduction potential (based on silver / silver chloride potential, ORP) with changes in pH were obtained, as shown in Figures 4 to 7.

[0099] 4 to 6 show that Example 1, in which hydrogen peroxide was not added, had a higher iron ion concentration, a generally lower aluminum ion concentration, and a higher phosphorus concentration than Comparative Example 1, in which hydrogen peroxide was added. This is thought to be because, in Example 1, no hydrogen peroxide was added, so that iron ions were not oxidized from divalent to trivalent, making it difficult for iron to precipitate, and also because consumption of phosphate ions due to reaction with iron was suppressed, allowing more phosphate ions to react with aluminum ions and resulting in the precipitation of aluminum.

[0100] 7, in Example 1, in which hydrogen peroxide was not added, the oxidation-reduction potential (based on the silver / silver chloride potential) was lower in the initial and middle stages, including the start of dealumination, but was higher at the end than in Comparative Example 1, in which hydrogen peroxide was added. This is presumably because, in Example 1, the oxidation-reduction potential (based on the silver / silver chloride potential) was low in the initial and middle stages due to the presence of divalent iron ions, which are reducing substances, in the solution, but as the concentration of divalent iron ions decreased, the oxidation-reduction potential (based on the silver / silver chloride potential) shifted to a side with higher oxidizing power.

[0101] (Test Example 2) A lithium-ion battery waste different from that used in Test Example 1 was subjected to substantially the same pretreatment as in Test Example 1 to obtain a battery powder. This battery powder was subjected to acid leaching under substantially the same conditions except that calcium phosphate was not added. As a result, a metal-containing solution having the metal concentrations, pH, and oxidation-reduction potential (based on silver / silver chloride potential, ORP) shown in Table 2 was obtained as the leaching filtrate from the first leaching stage.

[0102]

[0103] The metal-containing solution was then treated in a manner substantially similar to that of Test Example 1, except that the pH was increased to 3.0, phosphoric acid (H3PO4) was added in accordance with the aluminum ion concentration at that time, and the pH was further increased to 3.5, and phosphoric acid (H3PO4) was added in accordance with the aluminum ion concentration at that time. In Comparative Example 2, 1 mL of 30% aqueous hydrogen peroxide (H2O2) was added as an oxidizing agent, while in Example 2, no hydrogen peroxide (H2O2) was added. The total amount of 85% phosphoric acid (H3PO4) added was 5.717 mL in Comparative Example 2 and 5.600 mL in Example 2. As a result, graphs showing the changes in iron ion concentration, aluminum ion concentration, and phosphorus concentration with changes in pH were obtained, as shown in Figures 8 to 10.

[0104] 8, it can be seen that the iron ion concentration was higher in Example 2, in which hydrogen peroxide was not added, than in Comparative Example 2, in which hydrogen peroxide was added. This is thought to be because, in Example 2, no hydrogen peroxide was added, so the iron ions were not oxidized from divalent to trivalent, making it difficult for the iron to precipitate.

[0105] 9 and 10 show that, near pH 3, where phosphoric acid was added, Example 2 (no H2O2 added) had a lower aluminum ion concentration and a higher phosphorus concentration than Comparative Example 2 (with H2O2 added). This suggests that, similar to Example 1, the absence of hydrogen peroxide in Example 2 prevented iron ions from being oxidized from divalent to trivalent, making iron less likely to precipitate. Furthermore, the consumption of phosphate ions due to reaction with iron was suppressed, allowing more phosphate ions to react with aluminum ions. Furthermore, because more phosphoric acid was added near pH 3.5 and the total amount added was greater in Comparative Example 2 than in Example 2, it is presumed that the final Al and P concentrations in Example 2 and Comparative Example 2 were similar.

[0106] From the above, it was suggested that the above-mentioned impurity removal method may be able to reduce the amount of phosphate ion source used, thereby contributing to a reduction in processing costs.

Claims

1. A method for removing impurities, including aluminum, from a metal-containing solution obtained from lithium-ion battery waste and containing aluminum ions, iron ions, and cobalt and / or nickel ions, the method comprising a dealumination step of increasing the pH of the metal-containing solution in the presence of phosphate ions to precipitate and remove aluminum, wherein the iron ions in the metal-containing solution subjected to the dealumination step include divalent iron ions.

2. A method for removing impurities, including aluminum, from a metal-containing solution obtained from lithium-ion battery waste and containing aluminum ions, iron ions, cobalt ions, and / or nickel ions, comprising a dealumination step of increasing the pH of the metal-containing solution in the presence of phosphate ions to precipitate and remove aluminum, and the oxidation-reduction potential (based on silver / silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is initiated.

3. The method for removing impurities according to claim 1 or 2, wherein the pH of the metal-containing solution is increased to 3.0 to 4.0 in the dealumination step.

4. The method for removing impurities according to claim 1 or 2, wherein when the dealumination step is initiated, the content of phosphate ions in the metal-containing solution is 0.1 to 1.5 times the molar equivalent of the amount required for reaction with aluminum ions in the metal-containing solution.

5. The method for removing impurities according to claim 1, wherein the oxidation-reduction potential (based on silver / silver chloride potential) of the metal-containing solution is set to less than 500 mV when the dealumination step is initiated.

6. The method for removing impurities according to claim 1 or 2, wherein no oxidizing agent is added in the dealumination step.

7. The method for removing impurities according to claim 1 or 2, wherein the phosphorus concentration of the metal-containing solution upon completion of the dealumination step is in the range of 0.4 g / L to 1.0 g / L.

8. The method for removing impurities according to claim 1 or 2, further comprising a de-ironizing step of adding an oxidizing agent to the metal-containing solution after the dealumination step, thereby precipitating and removing iron from the metal-containing solution.

9. The method for removing impurities according to claim 8, wherein the pH of the metal-containing solution is increased in the iron removal step.

10. The method for removing impurities according to claim 8, wherein the pH of the metal-containing solution is set within the range of 3.0 to 4.0 in the iron removal step.

11. The method for removing impurities according to claim 1 or 2, further comprising, prior to the dealumination step, an acid leaching step in which battery powder from lithium ion battery waste containing aluminum, iron, cobalt and / or nickel is leached in an acidic leaching solution to obtain the metal-containing solution.

12. A metal recovery method for recovering metals containing cobalt and / or nickel from a metal-containing solution from which impurities have been removed by the impurity removal method according to claim 1 or 2.

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