How to recycle aluminum hydroxide from black lump

Abstract

A method for recycling aluminum hydroxide from aluminum-containing black mass, the method comprising, in a predetermined order, a first leaching step of leaching the black mass in an aqueous acid solution, thereby producing a first leach solution and a first leach residue; a first separation step of separating the first leach residue from the first leach solution; a pH adjustment step of adding a first aqueous base solution to the first leach solution, thereby adjusting the pH of the first leach solution to obtain a first pH-adjusted leach solution; and an Al / Fe precipitation step of precipitating an Al / Fe precipitate from the first pH-adjusted leach solution, wherein the Al / Fe precipitate is aluminum hydroxide-iron hydroxide. a second separation step, separating an Al / Fe precipitate from the first pH-adjusted leach solution; a second leaching step, leaching the Al / Fe precipitate with a second aqueous base solution, thereby producing a second leach solution and a second leach residue; a third separation step, separating the second leach residue from the second leach solution; an Al precipitation step, precipitating an Al precipitate from the second leach solution, wherein the Al precipitate comprises aluminum hydroxide and no carbon dioxide or carbonate is added to the second leach solution as a precipitation aid; and a fourth separation step, separating the Al precipitate from the second leach solution.

Description

[Technical Field]

[0001] The project that led to this application has received funding from the Bundesministerium fuer Wirtschaft und Klimaschutz (DE;FKZ:16BZF101A).

[0002] The present invention relates to a method for recycling aluminum hydroxide from battery materials, in particular lithium battery materials. Furthermore, the present invention relates to aluminum hydroxide obtainable by such a method. [Background technology]

[0003] Electrical energy storage is a topic of growing interest. Efficient storage of electrical energy allows for the generation of electrical energy at advantageous times and its use when and where needed. Secondary electrochemical cells are well suited for this purpose because they are rechargeable. Lithium-ion secondary batteries, therefore, have attracted particular attention for energy storage because they offer high energy density due to the small atomic weight and large ionization energy of lithium. They are widely used in many portable electronic devices, such as mobile phones, laptop computers, and mini cameras, as well as in electric vehicles.

[0004] Batteries, especially lithium-ion batteries, have an finite lifespan. Therefore, the number of used batteries is expected to increase. Used batteries contain important transition metals such as cobalt, nickel, lithium, and aluminum, and therefore could be a valuable source of raw materials for new generation batteries. Therefore, research is underway with the goal of recycling transition metals, and possibly even aluminum, from used lithium-ion batteries.

[0005] Furthermore, recent global market trends have significantly increased the prices of critical raw materials for battery production. Furthermore, on March 17, 2022, EU environment ministers unanimously adopted a Council Opinion on an EU battery regulation. Such a regulation is expected to ensure a certain recycling rate for batteries and for the metals used in batteries. Furthermore, such a regulation is likely to ensure that at least a certain amount of components used in battery production within the EU are produced within the EU. Because there are no significant resource deposits of the required components within the EU, recycling is the only way to produce such components within the EU. Therefore, a sustainable, efficient, and, at best, integrated process for recycling battery components, particularly lithium batteries, is needed.

[0006] Cathodes used in lithium batteries typically contain significant amounts of aluminum as a support foil for the cathode active material. Some cathode active materials contain aluminum, namely, nickel-cobalt aluminum oxide (NCA) materials. Therefore, there is a need to provide such a process for recovering metallic aluminum from battery materials.

[0007] Lithium ion batteries or lithium ion battery components that do not meet specifications and requirements, so-called off-spec materials and manufacturing waste, can also be a source of raw materials.

[0008] There are two main processes for material recovery: one is to smelt the corresponding battery scrap, followed by hydrometallurgical processing of the metal alloy or matte obtained from the smelting process. In such processes, aluminum ends up in the slag, from which it can be difficult to extract and recover, depending on the slag system and process.

[0009] Another major process is the direct hydrometallurgical treatment of battery scrap materials. The principle is disclosed in WO 2017 / 091562 and J. Power Sources, 2014, 262, 255ff. Such hydrometallurgical processes involve providing transition metals, either separately as aqueous solutions or in precipitated form, e.g., hydroxides, or already with the desired stoichiometry to create new cathode active materials, as proposed in DE-A-19842658 or Demidov et al., Ru. J. of Applied Chemistry 78, 356 (2005). In the latter case, the composition of the metal salt solution can be adjusted to the desired stoichiometry by adding individual metal components.

[0010] Generally, hydrometallurgical processes for the reduction and precipitation of transition metals such as nickel and cobalt from solution are known. A.R. Burkin, Powder Metallurgy 12, 243 (1969), describes the kinetic preference for nickel precipitation. Such processes also involve the addition of specific nucleating agents (GB-A-740797).

[0011] WO 2022 / 042228 A1 describes a process for recycling aluminum carbonate from pyrolyzed black lumps derived from lithium batteries. In this process, the black lumps are leached with sulfuric acid, iron powder is added to precipitate copper, and the pH is gradually increased to precipitate first goethite, α-FeO(OH) [1310-14-1], followed by an iron-aluminum precipitate. The iron-aluminum precipitate is separated, leached in aqueous sodium hydroxide at 90°C for 3 hours, filtered, and the filtrate containing metaaluminate and alkali is recovered. The filtrate is treated with carbon dioxide at 30°C until the pH reaches 10. Aluminum hydroxide is precipitated, and the filtrate is filtered. However, the process of WO 2022 / 042228 A1 has the disadvantage of producing a certain amount of carbonate, which is mixed into the precipitate. For example, as disclosed in D. Marinos et al., Crystals, 2021, 11, 836, such carbonates may include the presence of dawsonite ([NaAl(OH)2CO3]), which is generally undesirable. It has also been described that aluminum hydroxide precipitated by carbon dioxide has an inferior morphology with many fine particles and a wide particle size distribution compared to the "sand-like" material obtained from the Bayer process, making it unsuitable for the electrolytic melt process for producing metallic aluminum (Hydrometallurgy 98, 52).

[0012] US 3,120,996 recognizes the problem of sodium carbonate impurity in the Bayer process. As a solution, US 3,120,996 discusses the addition of slaked lime to precipitate calcium carbonate and produce sodium hydroxide. However, this solution has the disadvantage of adding an additional step and therefore increasing complexity. Furthermore, it also increases the consumption of slaked lime. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] WO 2017 / 091562 [Patent Document 2] DE-A-19842658 [Patent Document 3] GB-A-740797 [Patent Document 4] WO 2022 / 042228 A1 [Patent Document 5] US 3,120,996 [Non-patent literature]

[0014] [Non-Patent Document 1] J.Power Sources,2014,262,255ff. [Non-patent document 2] Demidov et al., Ru.J.of Applied chemistry 78,356(2005) [Non-patent document 3] AR Burkin, Powder Metallurgy 12,243(1969) [Non-patent document 4] Marinos et al.,Crystals,2021,11,836 [Non-patent document 5] Hydrometallurgy 98,52 Summary of the Invention [Problem to be solved by the invention]

[0015] Therefore, there is a need for a method for efficiently recovering aluminum hydroxide from raw materials derived from lithium batteries, for producing "sand-like" aluminum hydroxide that does not produce carbonate, and is suitable for melt electrolysis to produce metallic aluminum.

[0016] It is therefore an object of the present invention to provide an efficient method for recycling aluminum hydroxide from battery materials, which produces aluminum hydroxide that is suitable for melt electrolysis to produce metallic aluminum, without forming carbonates in the precipitate containing aluminum hydroxide. [Means for solving the problem]

[0017] It has now surprisingly been found that the above object can be achieved by a method for recycling aluminum hydroxide from aluminum-containing black mass, which method comprises, in the given order, the following steps: leaching the black mass in an aqueous acid solution in a first leaching step, thereby producing a first leach solution and a first leach residue; separating the first leach residue from the first leach solution in a first separation step; a pH adjusting step of adding a first aqueous base solution to the first leach solution, thereby adjusting the pH of the first leach solution to obtain a first pH-adjusted leach solution; precipitating an Al / Fe precipitate from the first pH-adjusted leach solution in an Al / Fe precipitation step, the Al / Fe precipitate comprising an aluminum hydroxide-iron hydroxide mixture and / or aluminum hydroxide; separating the Al / Fe precipitate from the first pH adjusted leach solution in a second separation step; leaching the Al / Fe precipitate with a second aqueous base solution in a second leach step, thereby producing a second leach solution and a second leach residue; separating the second leach residue from the second leach solution in a third separation step; an Al precipitation step, precipitating an Al precipitate from the second leach solution, wherein the Al precipitate comprises aluminum hydroxide, and no carbon dioxide or carbonate is added to the second leach solution as a precipitation aid; a fourth separation step of separating the Al precipitate from the second leach solution; Includes.

[0018] Since the Al precipitation step is similar to the Al precipitation step carried out in the Bayer process, the Al / Fe precipitate obtained in the battery recycling process can be introduced into an aluminum hydroxide production plant operated according to the Bayer process. Therefore, preferably, the Al / Fe precipitate from the Al / Fe precipitation step is suitable for introduction into an aluminum hydroxide production plant operated according to the Bayer process. Preferably, the method of the present invention includes a step of introducing at least a portion of the Al / Fe precipitate from the Al / Fe precipitation step into an aluminum hydroxide production plant operated according to the Bayer process.

[0019] It has further been found that the object of the present invention can be achieved by providing aluminum hydroxide which can be obtained by the process as described above.

[0020] One advantage of the present invention is that it avoids the formation of carbonates throughout the process. Such carbonates are particularly problematic in the Al precipitation step to precipitate aluminum hydroxide. Another advantage of the present invention is that iron and aluminum are separated in a step after the initial leaching. Therefore, it is possible to recover iron as well as aluminum.

[0021] Materials obtained from the hydrometallurgical processing of battery materials may contain lithium, which may be introduced into the second leach solution and into the Al precipitate. The problem of lithium impurities in aluminum hydroxide production plants operating according to the Bayer process is known in the art, and separation concepts have been described (e.g., Ullmann's Encyclopedia of Industrial Chemistry - 2000 - Hudson - Aluminum Oxide 2012, p. 629; Han et al., Metals 2021, 11, 1148). [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram of the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] definition Before describing exemplary embodiments of the present invention in detail, definitions important for understanding the present invention are provided.

[0024] The term "black mass" as used herein refers to the solid residue obtained by dismantling and crushing a battery. Black mass is obtained as a fine fraction in the classification stage and contains the active materials of the battery's cathode and anode as well as some impurity particles. This black mass can be directly processed by hydrometallurgical processes or processed after a pyrolysis treatment. After the pyrolysis step, a lithium extraction step is performed to obtain a lithium salt solution and a lithium-depleted residue (hereinafter also referred to as black mass).

[0025] As used in this specification and the appended claims, the singular forms "a" and "an" also include their respective plural forms, unless the context clearly dictates otherwise. In the context of the present invention, the terms "about" and "approximately" indicate an interval of accuracy that a person skilled in the art would understand to still ensure the technical effect of the feature in question. This term typically indicates a deviation from the indicated numerical value of ±10%, preferably ±8%, more preferably ±5%, and even more preferably ±2%. The terms "comprise" and "include" should be understood as non-limiting. For purposes of the present invention, the term "consisting of" is considered a preferred embodiment of the term "comprise." Hereinafter, when a group is defined as including at least a certain number of embodiments, this also preferably includes a group consisting only of these embodiments. Furthermore, the terms "first," "second," "third," "(a)," "(b)," "(c)," "(d)," etc. in this specification and claims are used to distinguish between similar elements and not necessarily to describe a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments of the invention described herein can operate in sequences other than those described or illustrated herein. When terms such as "first," "second," "third," or "(a)," "(b)," "(c)," "(d)," "i," "ii," etc., refer to steps in a method or method of use or assay, there is no consistency in time or time interval between the steps; i.e., the steps may be performed simultaneously, or there may be a time interval of seconds, minutes, hours, days, weeks, months, or years between such steps, unless otherwise indicated in this application, as described above or below herein. It is to be understood that the present invention is not limited to the particular methodology, protocols, reagents, etc., described herein, as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention, which is limited solely by the appended claims.Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

[0026] As used herein, the terms "free," "free of," or "free" mean that the composition of the present invention does not contain a particular compound or group of compounds, which may be combined under a generic name, and that the composition does not contain more than 0.8% by weight of said compound or group of compounds, based on the total weight of the composition. Furthermore, it is preferred that the composition according to the present invention does not contain more than 0.5% by weight of said compound or group of compounds, and preferably the composition is completely free of said compound or group of compounds.

[0027] When referring to weight percentages of compositions and the components contained therein, it is understood that in accordance with the present invention, the total amount of components does not exceed 100% (±1% due to rounding).

[0028] Detailed Description of the Invention In the method of the present invention, aluminum hydroxide is recycled from black mass containing aluminum and / or aluminum compounds. Metallic aluminum may originate from the electrode current collector foil or casing. Aluminum compounds may be present in the black mass in the form of aluminum oxide, lithium nickel cobalt aluminum oxide (NCA), aluminum phosphate, lithium aluminate, and / or alumosilicate. Therefore, in general, the method of the present invention can be used to recycle aluminum from any material containing aluminum oxide, lithium nickel cobalt aluminum oxide (NCA), aluminum phosphate, lithium aluminate, and / or alumosilicate. However, it is preferred that the black mass originate from battery materials, preferably lithium battery materials. In lithium-ion batteries, cathode foils are typically made from aluminum, and the cathode active material may contain aluminum. Therefore, such lithium battery materials typically contain a significant amount of aluminum.

[0029] Recycling processes for batteries, particularly lithium-ion based batteries, typically involve a pyrolysis step. Such pyrolysis steps are typically thermal pretreatment steps in which pre-sorted batteries or battery components are heated to decompose their constituent organic matter. While the present invention works with any black mass, in the methods according to the present invention, the black mass is preferably pyrolyzed material, most preferably pyrolyzed lithium battery material.

[0030] After pyrolysis pretreatment, the method of the present invention can be broadly described by three process steps: a) a first leaching step, in which the black mass is first leached in an acidic environment and then partially re-precipitated; b) a second leaching step, in which the precipitate is leached in a basic environment and the resulting aluminate solution is separated from the filtration residue; and c) a precipitation step (herein referred to as the "Al precipitation step"), in which neither carbon dioxide nor carbonate is added, resulting in the formation of aluminum hydroxide.

[0031] In some processes, after pyrolysis, lithium is first extracted from the black mass, and then the lithium-depleted residue is treated with the method of the invention described above, starting with step a). Pre-extraction of lithium can be carried out by treatment with water or alkaline earth oxides or hydroxides in a polar solvent. Processes in which pyrolysis is carried out in the presence of acid salts such as sodium bisulfate are also known in the art. In the latter case, lithium is subsequently extracted in the form of the corresponding neutral salt, such as lithium sulfate.

[0032] In the method according to the invention, preferably no carbonates are formed, i.e. no carbon dioxide or any carbonates are added to any of the solutions used in the process between the first maceration step and the recovery of the Al precipitate in the fourth separation step. No carbon dioxide or carbonates are added in the Al precipitation step.

[0033] Nevertheless, since the method necessarily involves more steps than these, the method of the present invention comprises the following steps: leaching the black mass in an aqueous acid solution in a first leaching step, thereby producing a first leach solution and a first leach residue; separating the first leach residue from the first leach solution in a first separation step; a pH adjusting step of adding a first aqueous base solution to the first leach solution, thereby adjusting the pH of the first leach solution to obtain a first pH-adjusted leach solution; precipitating an Al / Fe precipitate from the first pH-adjusted leach solution in an Al / Fe precipitation step, the Al / Fe precipitate comprising an aluminum hydroxide-iron hydroxide mixture and / or aluminum hydroxide; separating the Al / Fe precipitate from the first pH adjusted leach solution in a second separation step; leaching the Al / Fe precipitate with a second aqueous base solution in a second leach step, thereby producing a second leach solution and a second leach residue; separating the second leach residue from the second leach solution in a third separation step; an Al precipitation step, precipitating an Al precipitate from the second leach solution, wherein the Al precipitate comprises aluminum hydroxide, and no carbon dioxide or carbonate is added to the second leach solution as a precipitation aid; and separating the Al precipitate from the second leach solution in a fourth separation step.

[0034] The first leaching step of the method of the present invention is used to dissolve most of the elements, including aluminum and iron. Therefore, the black mass is treated with an acid, where in the first leaching step, the acid of the aqueous acid solution is preferably selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, citric acid, oxalic acid, and mixtures thereof. Most preferably, the acid of the aqueous acid solution is sulfuric acid, as this is a highly available strong acid that reliably dissolves most of the elements in the black mass. Furthermore, sulfuric acid produces sulfates that are environmentally friendly.

[0035] To achieve a good leaching yield, the acid concentration of the aqueous acid solution in the first leaching step of the method according to the invention is preferably 0.05M to 5M or 0.1N to 10N. However, to achieve an optimal leaching yield, not only the acid concentration but also the absolute molar ratio between the acid and the elements of the black mass is crucial. Therefore, preferably, in the method of the invention, the mass ratio of the black mass to the aqueous acid solution is in the range of 10% to 35% by mass, preferably 12% to 30% by mass, and most preferably 14% to 25% by mass.

[0036] To achieve optimal intermixing, the first leaching step in the process of the present invention includes stirring the aqueous acid solution. Preferably, the first leaching step, particularly the stirring of the aqueous acid solution, is carried out at a temperature in the range of 80°C to 100°C. Also preferably, the stirring of the aqueous acid solution in the first leaching step is carried out for a time in the range of 30 minutes to 600 minutes.

[0037] It should be understood that the conditions used in the first leaching step, particularly the pH environment and redox potential, can control which elements dissolve from the black mass and which do not. Typically, the carbon content of the black mass is not dissolved by the aqueous acid solution. Furthermore, the pH environment and redox potential are typically changed gradually to allow for separate dissolution of the several metal fractions of the black mass.

[0038] Thus, with respect to copper, reaction conditions can be selected to be sufficiently reducing to ensure that copper does not dissolve in the aqueous acid solution. Typically, this is achieved by excluding oxidizing agents such as air or oxygen in the first leaching step. Conversely, oxidizing conditions can be used so that copper exists in its more soluble oxidation state +2. Preferably, such oxidizing conditions are achieved by the addition of an oxidizing agent selected from the group consisting of oxygen, air, hydrogen peroxide, nitrous oxide, lithium metal oxide, high-valent metal oxides such as permanganate ferrate, and mixtures thereof. When lithium metal oxide or high-valent metal oxides are used, excess amounts of these compounds can be reduced by the addition of a suitable reducing agent and, optionally, by adjusting the pH of the reaction mixture. Preferably, such reducing conditions are achieved by the addition of reducing agents such as hydrogen peroxide, sulfur dioxide, sodium metabisulfite, and / or hydrogen.

[0039] However, if copper is dissolved in the aqueous acid solution, it must be selectively separated from the aluminum and iron so that it does not precipitate in the subsequent Al / Fe precipitation step. Thus, in one embodiment of the present invention, conditions can be selected such that copper does not dissolve in the aqueous acid solution. In such an embodiment, the first leaching step is carried out under the exclusion of air, oxygen, or oxidizing agents such as hydrogen peroxide, and the copper remains in the leached black mass, which can be separated from the aqueous acid solution and then subjected to another leaching step.

[0040] However, if copper separation is also required in the same process, the method of the present invention preferably further comprises a copper separation step in which copper is separated from the aqueous acid solution, which can be carried out as precipitation of copper sulfide followed by separation, for example, by filtration, solvent extraction, or precipitation using inorganic metal powders (e.g., iron, nickel, cobalt, manganese, although iron is not preferred as it adds additional unwanted iron to the leachate) followed by separation, for example, by filtration.

[0041] After the first leaching step, the leaching residue, which mainly contains carbon and optionally copper, must be separated from the leaching solution containing the majority of the elements to be recycled. Preferably, the first separation step is carried out as a separation step by one or more of the group consisting of a filtration step, a centrifugation step, a sedimentation step, and a decantation step, and most preferably, the first separation step is carried out as a filtration step. The leaching residue can be further processed to recover the carbon and optionally the copper, depending on the selection in terms of copper solvation.

[0042] The next step in the method of the present invention is to selectively precipitate aluminum and iron from the solution of elements to be recovered from the black mass. This is accomplished by adjusting the pH of the leach solution. The pH value of the leach solution is typically low, for example, in the range of 0 to 2. Therefore, to ensure selective precipitation of aluminum and iron, a first aqueous basic solution is added to the leach solution in the pH adjustment step of the method of the present invention. For optimal precipitation conditions, the first pH-adjusted leach solution preferably has a pH value of 3.5 or higher, more preferably 4 or higher. Similarly, the first pH-adjusted leach solution preferably has a pH value of 7 or lower, more preferably 5 or higher, and most preferably 4 or higher. To achieve ideal conditions, most preferably, the first pH-adjusted leach solution in the pH adjustment step of the method of the present invention has a pH value in the range of 4.3 to 4.7. Preferably, the concentration of base in the second aqueous basic solution in the pH adjustment step is 3N to 25N.

[0043] Preferably, in the pH adjustment step of the process of the present invention, the base of the first aqueous base solution is selected from the group consisting of metal oxides, hydroxides, or carbonates. Preferred metals in these compounds are alkali and alkaline earth metals, nickel, cobalt, manganese, and mixtures thereof, and are preferably selected from the group consisting of sodium hydroxide, lithium hydroxide, potassium hydroxide, or sodium carbonate. Ammonium hydroxide is also a suitable base and can be employed alone or in combination with the metal bases. To avoid the risk of introducing carbonates in the subsequent Al precipitation step, most preferably, the base of the first aqueous base solution is an alkali hydroxide, most preferably sodium hydroxide.

[0044] To ensure complete precipitation of iron in the Al / Fe precipitate, it is preferable to oxidize all iron species in the solution to ferric species before or during the pH adjustment. This oxidation can be achieved, for example, by introducing oxygen, air, hydrogen peroxide, or nitrous oxide. This oxidation is carried out by oxidizing the Fe present in the solution to ferric species. 2+ The majority of ions are Fe 3+ This ensures that the aluminum and iron are oxidized to ions, further improving the separation efficiency of aluminum and iron, especially when the first leaching step is carried out under reducing conditions.

[0045] By adjusting the pH in the pH adjustment step, conditions for selective precipitation of aluminum and iron are established. Typically, the Al / Fe precipitate precipitates after a period of time. However, preferably, the Al / Fe precipitation step includes a step of stirring the first pH-adjusted leach solution. This ensures uniformity of conditions such as pH and temperature. Preferably, the Al / Fe precipitation of the method of the present invention is carried out at a temperature ranging from 10°C to 90°C, more preferably from 18°C ​​to 90°C, and even more preferably from 20°C to 80°C. Most preferably, the Al / Fe precipitation step, particularly the step of stirring the first pH-adjusted leach solution, is carried out at room temperature. Preferably, the Al / Fe precipitation step, particularly the step of stirring the first pH-adjusted leach solution, is carried out for a period ranging from 1 hour to 15 hours, more preferably from 2 hours to 11 hours, and most preferably from 7 hours to 9 hours.

[0046] To increase the precipitation yield and precipitation rate, the Al / Fe precipitation step is preferably carried out in the presence of aluminum hydroxide seeds. Furthermore, to increase the separation efficiency, the Al / Fe precipitation step to precipitate mixed aluminum / iron hydroxide and / or aluminum hydroxide is preferably carried out in two or more stages, i.e., by recovering the pH-adjusted leach solution after a second separation step and carrying out a second Al / Fe precipitation step thereon. It is particularly preferred to use aluminum hydroxide seeds in this second Al / Fe precipitation step.

[0047] It should be understood that the pH adjustment step and the Al / Fe precipitation step are in principle connected sequentially, but may also show a certain overlap. Therefore, in general, the Al / Fe precipitation step can be triggered by the pH adjustment step. However, other parameters, such as the addition of seed crystals and changes in concentration, can also affect precipitation. Nevertheless, pH adjustment can be performed in stages, thereby triggering Al / Fe precipitation at each stage. However, such observations do not take into account the sequential nature of pH adjustment and subsequent Al / Fe precipitation.

[0048] After the Al / Fe precipitation step is completed, the Al / Fe precipitate, which contains mixed aluminum-iron hydroxide and / or aluminum hydroxide (i.e., if only aluminum, but no iron, is present in the black mass), must be separated from the pH-adjusted leach solution in a second separation step. Similar to the first separation step, the second separation step is also preferably carried out as one or more of the following separation steps: filtration, sedimentation, centrifugation, and decantation, and most preferably as a filtration step.

[0049] It should be understood that increasing the pH value also increases the coprecipitation of Ni and Co. Ideally, therefore, the pH conditions in the Al / Fe precipitation step are adjusted to minimize the precipitation of Ni or Co. However, if Ni and Co are likely to be present in the Al / Fe precipitate, it is possible to separate the aluminum from the precipitate in a second leaching step, thereby obtaining a Ni / Co-containing leaching residue containing primarily iron hydroxide. This residue can then be recycled to the first leaching step or recycled as a metal base after the first leaching step, before or during the pH adjustment step. Prior to this recycling, it is also possible to selectively separate the Ni / Co precipitate from the iron precipitate, for example, by selectively dissolving the Ni / Co hydroxide at a pH in the range of 3.5 to 7.

[0050] In order to selectively separate aluminum from iron and other residual metals, such as nickel and cobalt, contained in the Al / Fe precipitate, the Al / Fe precipitate is treated with a second aqueous basic solution. Preferably, in this second leaching step of the process of the present invention, the base of the second aqueous basic solution is an alkali hydroxide or a mixture of alkali hydroxides, preferably sodium hydroxide or potassium hydroxide. Of particular importance to the present invention is to avoid the risk of introducing carbonates into the precipitate. Therefore, the base of the second aqueous basic solution is preferably carbonate-free.

[0051] Preferably, the second leaching step also includes the step of stirring the first aqueous base solution. To achieve optimal separation conditions, the second leaching step, particularly the step of stirring the first aqueous base solution, is preferably carried out at a temperature in the range of 150°C to 230°C, more preferably 160°C to 190°C, and most preferably 170°C to 180°C. Preferably, the second leaching step, particularly the step of stirring the first aqueous base solution, is carried out for a time in the range of 30 to 90 minutes, preferably 40 to 80 minutes, and most preferably 50 to 70 minutes.

[0052] After the second leach step is completed, the second leach solution contains most of the aluminum fraction, while the second leach residue contains most of the iron fraction. Like the first and second separation steps, the third separation step is preferably carried out as a separation step using one or more of the following processes: filtration, sedimentation, centrifugation, and decantation. Most preferably, the third separation step is carried out as a filtration step. Preferably, the filtration residue, i.e., the second leach residue, is washed, and the washed fraction is recombined with the second leach solution. The second leach solution is used in a subsequent precipitation step, and the second leach residue can be subjected to a new acid leach step to recover iron. Alternatively, the second leach residue can be subjected to pyrometallurgical processing to ultimately recover metallic iron.

[0053] To induce precipitation, the second leaching solution is cooled. Therefore, the Al precipitation step, particularly the step of stirring the second leaching solution, is preferably carried out at a temperature lower than that of the second leaching step, more preferably at room temperature. Furthermore, time is required to achieve good separation efficiency. To ensure a homogeneous state of the second leaching solution, the Al precipitation step preferably includes a step of stirring the second leaching solution. As noted above, time is important for precipitation. Therefore, the Al precipitation step, particularly the step of stirring the second leaching solution, is preferably carried out for a time period ranging from 1 hour to 60 hours, more preferably from 2 hours to 55 hours, and most preferably from 35 hours to 48 hours.

[0054] To increase the precipitation yield and precipitation rate, the method of the present invention preferably further comprises the step of adding aluminum hydroxide seed crystals to the second leach solution before the Al precipitation step. Preferably, the ratio of the mass of the aluminum hydroxide seed crystals to the mass of the Al precipitate is in the range of 0.03 to 0.30, preferably 0.05 to 0.1, and most preferably 0.05 to 0.07. In the present invention, it is essential that no carbon dioxide or carbonate is added to the second leach solution as a precipitation aid. Preferably, no precipitation aid other than aluminum hydroxide is added to the second leach solution.

[0055] After the Al precipitation step is completed, the Al precipitate containing aluminum hydroxide must be separated from the second leaching solution in a fourth separation step. Like the first, second, and third separation steps, the fourth separation step is preferably carried out as a separation step by one or more of the following steps: filtration, sedimentation, centrifugation, and decantation; most preferably, the fourth separation step is carried out as a filtration step. The Al precipitate is usually washed with water. Finally, the Al precipitate is dried. The aluminum precipitate recovery rate of the second leaching step is preferably greater than 19%. Furthermore, the purity of the Al precipitate, i.e., aluminum hydroxide, is preferably greater than 85%. The liquid solution may still contain aluminum and can be recycled to the second leaching step (optionally after a concentration step).

[0056] Finally, the method of the present invention preferably includes a purification step after the fourth separation step, in which aluminum is separated from aluminum hydroxide contained in the Al precipitate, thereby producing metallic aluminum. Preferably, the purification step includes a molten salt electrolysis step. Aluminum purification by molten salt electrolysis has been known in the prior art for several decades.

[0057] Measurement method a) Sample preparation for elemental analysis A sample of the black mass was dried for analysis. The solution was previously diluted 1:10 and acidified with 2.5 ml of HNO3. The chemical laboratory is certified according to DIN EN ISO 9001:2015. All subsequent work steps and applications comply with the scope of certification.

[0058] b) Preparation of sample solids 50 mg of sample was weighed into a Teflon container using an analytical balance and mixed with 6 ml of concentrated HNO3 and 2 ml of concentrated HCl. After a pre-reaction time of approximately 30 minutes, the container was sealed and placed in a high-pressure microwave "TurboWave Pro" from MLS (MLS Mikrowellen-Labor-Systeme GmbH, Leutkirchen, Germany). The sample was treated for approximately 40 minutes on the "Charcoal" program until dissolved without residue. After transferring to a 50 ml volumetric flask, the sample was further diluted in a ratio of 1:10 and 1:100. 2.5 ml of concentrated HNO3 was added to each dilution. Each solid sample was prepared in duplicate.

[0059] c) Preparation of sample solution Liquid samples were also diluted in ratios of 1:10 and 1:100 and acidified with concentrated nitric acid to give approximately a 5% acid matrix.

[0060] d) Measurement of metal cations and phosphorus The concentrations of the target metals were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). We used an Agilent ICP-OES 5900 SVDS instrument (Agilent Technologies Inc., Santa Clara, CA, USA), specifically purchased for the analysis of black block samples. For purposes according to DIN 38402-51, an external calibration series was prepared from certified single-element standards obtained from LGC. To monitor the measurement process, synthetic control samples of known concentrations were also used to provide a reference between sample measurements. To prevent physical interference, the sample and calibration series solutions were matched to the matrix of the rinse solution (5% HNO3). Measurement results exceeding the highest calibration standard were determined from the lowest possible dilution. Values ​​below the lowest calibration standard are indicated with a "<detection limit" note. The wavelengths for individual elements were manually selected for each element by a trained user to ensure that chemical interferences did not interfere with the measurement. Only in this way could accurate measurements be guaranteed.

[0061] e) Carbon content measurement The solid samples were subjected to induction combustion in a stream of oxygen in an apparatus of the type "CS 2000" from Eltra GmbH (Eltra GmbH, Haan, Germany). Carbon contained in the exhaust gas stream was catalytically converted to CO2 on a platinum network and detected by a resistive measuring cell. Certified reference samples were used as standards.

[0062] f) Determination of fluoride content, solid / liquid The fluoride content was determined in solids and solutions using an ion-sensitive electrode (ISE) of the Titrando type (Metrohm AG, Heirsau, Switzerland). For this purpose, 2 ml of the stock sample was made up into a 20 ml container and 25 ml of TISAB IV solution was added. The fluoride concentration was determined by applying a voltage between the ISE and a silver reference electrode using external calibration. A synthetic reference standard was used for monitoring. [Example]

[0063] The following three examples illustrate three steps of the process of the invention that ultimately result in aluminum hydroxide (i.e., before the purification step).

[0064] Example 1: Leaching 14 kg of black mass was leached in 70 liters of 6N / 3M H2SO4 at 80°C for 120 minutes. The leachate was filtered and the filter cake was washed and dried at 80°C. The filtrate served for further precipitation of aluminum-iron hydroxides. The filter residue and liquid samples were analyzed for Li, Al, Fe, Cu, Ni, Co, Mn, P, F, and C.

[0065] The following leaching yields could be achieved for the listed elements: Li 93.50%, Al 83.42%, Fe 92.05%, Cu 0.00%, Ni 45.11%, Mn 94.10%, Co 56.58%, P 93.71%, F 90.10%. All of the carbon remained in the filter cake. The composition of the input materials and filter residue, as well as the leaching yield, are shown in Table 1. The mass of the filter residue produced was 9244.04 kg.

[0066] [Table 1]

[0067] Example 2: Precipitation of Aluminum-Iron Hydroxide 70 L of the leach filtrate prepared in Example 1 was used to precipitate aluminum-iron hydroxide at room temperature. 2+ Oxygen was continuously injected into the solution at 4 L / min for oxidation of the ions. The pH was adjusted using 10 M NaOH solution until a final pH value of 4.5 was reached. At a pH of 4, 131.35 g of Al(OH)3 seed crystals were added to the solution. After the desired final pH value was reached, the solution was stirred for an additional 9 h. The filter residue and liquid samples were analyzed for Li, Al, Fe, Ni, Co, Mn, P, and F.

[0068] This method allowed the recovery of 65.01 wt% aluminum and 48.77 wt% iron in solution as hydroxides. Because of contamination of the hydroxide product with other battery-relevant elements, a purity of 77.64% for Al / Fe(OH)3 could be achieved. The largest impurities were ∼3.69 wt% nickel and ∼2.62 wt% phosphorus. The composition of the precipitate is shown in Table 2. The mass of the resulting precipitate was 2.148 kg.

[0069] [Table 2]

[0070] Example 3: Precipitation of Aluminum Hydroxide 200 g of the aluminum-iron hydroxide prepared in Example 2 was leached in 1 liter of 3N / 3M NaOH solution in an autoclave at 175°C for 60 minutes. The solution was filtered to obtain a filtrate containing 17.9 g / l of Al, corresponding to an Al leaching yield of 49%. The filtrate was then stirred at room temperature for 48 hours for precipitation of Al(OH). 3 g of Al(OH) seed crystals were added to the solution. The liquid sample and the precipitated product were analyzed for Li, Al, Fe, Ni, Co, Mn, P, and F.

[0071] Fe, Ni, Mn, and Co remained in the filter cake because their ICP-OES detection limit in the leachate was less than 0.5 mg / L. Nevertheless, approximately 1.87 mg of Fe and Co were detected in the final product. Aluminum precipitated from the solution, and the resulting filtrate contained 14.4 g / L of Al, which is close to the calculated solubility limit of approximately 15 g / L for the given parameters. This resulted in a calculated aluminum precipitation recovery of 19.6%. The purity of the final aluminum hydroxide product was 85.9%. Table 3 shows the compositions of the final product and filtrate. The mass of the precipitate formed was 9.33 g.

[0072] [Table 3]

Claims

1. 1. A method for recycling aluminum hydroxide from aluminum-containing black mass, comprising the steps of: leaching the black mass in an aqueous acid solution in a first leaching step, thereby producing a first leach solution and a first leach residue; separating the first leach residue from the first leach solution in a first separation step; adding a first aqueous base solution to the first leach solution in a pH adjustment step, thereby adjusting the pH of the first leach solution to obtain a first pH-adjusted leach solution; precipitating an Al / Fe precipitate from the first pH-adjusted leach solution in an Al / Fe precipitation step, wherein the Al / Fe precipitate comprises an aluminum hydroxide-iron hydroxide mixture and / or aluminum hydroxide; separating the Al / Fe precipitate from the first pH adjusted leach solution in a second separation step; leaching the Al / Fe precipitate with a second aqueous base solution in a second leach step, thereby producing a second leach solution and a second leach residue; separating the second leach residue from the second leach solution in a third separation step; an Al precipitation step, precipitating an Al precipitate from the second leach solution, wherein the Al precipitate comprises aluminum hydroxide and no carbon dioxide or carbonate is added to the second leach solution as a precipitation aid; a fourth separation step of separating the Al precipitate from the second leach solution. A method comprising:

2. 2. The method of claim 1, wherein the black mass is pyrolyzed material, preferably pyrolyzed lithium battery material.

3. 3. The method according to claim 1 or 2, wherein in the first leaching step, the acid of the aqueous acid solution is selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, citric acid, oxalic acid, and mixtures thereof, preferably sulfuric acid.

4. 3. The method according to claim 1 or 2, wherein in the pH adjusting step, the first pH adjusted leach solution has a pH value in the range of from 3.5 to 5, preferably up to 4.

5.

5. 3. The method of claim 1 or 2, wherein in the pH adjusting step, the base of the first aqueous base solution is selected from the group consisting of ammonium hydroxide, alkali hydroxide, alkali carbonate, alkaline earth hydroxide, and mixtures thereof, preferably sodium hydroxide or sodium carbonate, and most preferably sodium hydroxide.

6. 3. The method of claim 1 or 2, wherein the Al / Fe precipitation step comprises agitating the first pH-adjusted leach solution, and wherein the agitation of the first pH-adjusted leach solution is carried out at a temperature in the range of 18 to 90°C, preferably at a temperature in the range of 20 to 80°C, and most preferably at room temperature.

7. 7. The method of claim 6, wherein in the Al / Fe precipitation step, the step of stirring the first pH adjusted leach solution is carried out for a time in the range of from 1 hour to 15 hours, preferably from 2 hours to 11 hours, and most preferably from 7 hours to 9 hours.

8. 2. The process of claim 1, wherein the second leaching step is carried out at a temperature in the range of from 150°C to 230°C, preferably from 160°C to 190°C, most preferably from 170°C to 180°C.

9. 3. The method according to claim 1 or 2, wherein the pH adjustment step and / or the Al / Fe precipitation step is carried out in the presence of an oxidizing agent, preferably in the presence of an oxidizing agent selected from the group consisting of oxygen, air, hydrogen peroxide or mixtures thereof.

10. 10. The method of claim 9, wherein the oxidizing agent comprises oxygen and is injected into the first leach solution in the pH adjustment step and / or the Al / Fe precipitation step.

11. 3. The method of claim 1 or 2, wherein the Al precipitation step is carried out at a temperature below the temperature of the second leach solution in the second leach step, preferably at room temperature.

12. 3. The method according to claim 1 or 2, wherein the Al precipitation step is carried out for a time in the range of from 1 hour to 60 hours, preferably from 2 hours to 55 hours, most preferably from 35 hours to 48 hours.

13. 3. The method of claim 1 or 2, further comprising the step of adding aluminum hydroxide seeds to the second leach solution prior to the Al precipitation step and / or the Al / Fe precipitation step.

14. 14. The method of claim 13, wherein the ratio of the mass of the aluminum hydroxide seed crystals to the mass of the Al precipitate is in the range of 0.03 to 0.30, preferably 0.05 to 0.1, most preferably 0.05 to 0.

07.

15. 3. The method according to claim 1 or 2, wherein the Al / Fe precipitate of the Al / Fe precipitation step is suitable for being introduced into an aluminum hydroxide production plant operated according to the Bayer process, and preferably the method according to the invention further comprises the step of introducing at least a portion of the Al / Fe precipitate of the Al / Fe precipitation step into an aluminum hydroxide production plant operated according to the Bayer process.

16. 3. The method of claim 2, wherein the black mass is a lithium-depleted residue, wherein lithium is extracted after thermal decomposition of the battery material.

17. 3. The method of claim 1 or 2, further comprising the step of reintroducing the second leaching residue into the first leaching step or the pH adjustment step.

18. 3. Aluminium hydroxide obtainable by the method according to claim 1 or 2.

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