Process for recycling aluminum hydroxide from black material

Abstract

A process for recycling aluminum hydroxide from a black material comprising aluminum, the process comprising, in a given order, the steps of: in a first leaching step, leaching the black material in an acidic aqueous solution, thereby producing a first leach solution and a first leach residue; in a first separation step, the first leach residue is separated from the first leach solution; in a pH adjustment step, adding a first aqueous alkaline solution to the first leach solution, thereby pH-adjusting the first leach solution, producing a first pH-adjusted leach solution; in an Al / Fe precipitation step, precipitating an Al / Fe precipitate from the first pH-adjusted leach solution wherein the Al / Fe precipitate comprises a mixed aluminum-iron hydroxide and / or aluminum hydroxide; in a second separation step, the Al / Fe precipitate is separated from the first pH-adjusted leach solution; in a second leaching step, the Al / Fe precipitate is leached in a second alkaline aqueous solution, thereby producing a second leach solution and a second leach residue; in a third separation step, the second leach residue is separated from the second leach solution; in an Al precipitation step, an Al precipitate is precipitated from the second leach solution, the Al precipitate comprising aluminum hydroxide, and wherein carbon dioxide or carbonate is not added to the second leach solution as a precipitation aid; in a fourth separation step, the Al precipitate is separated from the second leach solution.

Description

[0001] The project leading to this application has received funding from the Federal Ministry for Economic Affairs and Climate Action (Bundesministerium für Wirtschaft und Klimaschutz) (Germany; FKZ: 16BZF101A); the applicants are responsible for all disclosures in this article. Technical Field

[0002] The present invention relates to a method for recycling aluminum hydroxide from battery materials, in particular lithium battery materials. In addition, the present invention relates to aluminum hydroxide obtainable by this method. Background Art

[0003] Storing electrical energy is a subject of increasing interest. Efficient storage of electrical energy will allow it to be generated when it is advantageous and used when and where it is needed. Secondary electrochemical cells are well suited for this purpose due to their rechargeability. Lithium-ion batteries are therefore of particular interest for energy storage, since they offer high energy density due to the small atomic weight and large ionization energy of lithium, and they have been widely used as power sources for many portable electronic devices such as cellular phones, laptop computers, miniature cameras, etc., and also as power sources for electric vehicles.

[0004] The life of batteries, especially lithium-ion batteries, is not infinite. Therefore, it is expected that more and more waste batteries will appear. Since waste batteries contain important transition metals, such as but not limited to cobalt, nickel, lithium, and additionally aluminum, they may become a valuable source of raw materials for new generation batteries. For this reason, more and more research work has been carried out in order to recycle transition metals and optionally even aluminum from used lithium-ion batteries.

[0005] Furthermore, recent developments on the world market have significantly increased the prices of important raw materials for battery production. Furthermore, on March 17, 2022, the EU Environment Ministers unanimously adopted the Security Council position on the EU battery regulation. It is foreseeable that this regulation will provide for certain recycling rates for batteries and also for certain recycling rates for metals used in batteries. Furthermore, such a regulation will most likely make it so that at least a certain amount of the components used in the EU production of such batteries will also be components produced in the EU. Since the required components do not have large resource reserves in the EU, recycling will be the only way to produce such components within the EU. Therefore, a sustainable, efficient and preferably well-integrated method for recycling components of batteries, in particular lithium batteries, is needed.

[0006] The cathode used in lithium batteries usually contains a large amount of aluminum as a carrier foil for the cathode active material. Some cathode active materials also contain aluminum, namely nickel cobalt aluminum oxide materials (NCA). Therefore, it is necessary to provide a method as described above that facilitates the recovery of metallic aluminum from battery materials.

[0007] Lithium-ion batteries or parts of lithium-ion batteries that do not meet specifications and requirements (so-called substandard materials and production waste) can also be a source of raw materials.

[0008] Two main methods have been used for raw material recovery. One main method is based on smelting of the corresponding battery scrap and subsequent hydrometallurgical processing of the metal alloys or impure metals obtained from the smelting process. In such processes, the aluminum ends up in the slag, from which it can be difficult to extract and recover the aluminum, depending on the slag system and the method.

[0009] Another major method is direct hydrometallurgical processing of battery waste materials. The principle has been disclosed in WO 2017 / 091562 and J. Power Sources [Power Source Magazine], 2014, 262, 255 and below. Such hydrometallurgical methods will provide such transition metals as aqueous solutions or in precipitated form, for example, alone as hydroxides (DE-A-19842658), or already in the desired stoichiometry for the manufacture of new cathode active materials, as proposed by Demidov et al., Ru. J. of Applied chemistry [Russian Journal 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 a single metal component.

[0010] Hydrometallurgical methods for precipitating transition metals like nickel and cobalt from solution by reduction are generally known; AR Burkin, Powder Metallurgy 12, 243 (1969) describes a kinetic preference for nickel precipitation. Such methods also include the addition of certain nucleating agents (GB-A-740797).

[0011] WO 2022 / 042228 A1 describes a method for recycling aluminum carbonate from black matter derived from the pyrolysis of lithium batteries. In this method, the black matter is leached in sulfuric acid, iron powder is added to precipitate copper, the pH is increased in a stepwise manner, and goethite α-FeO(OH)[1310-14-1] is first precipitated, and an iron-aluminum precipitate is obtained thereafter. The iron-aluminum precipitate is separated and leached in a sodium hydroxide solution at 90°C for 3h, filtered, and the filtrate containing aluminate and alkali is collected. The filtrate is treated with carbon dioxide at 30°C until the pH reaches 10. Aluminum hydroxide is precipitated and the filtrate is filtered out. However, the method of WO2022 / 042228 A1 has the disadvantage of forming a certain amount of carbonate, which is introduced into the precipitate. 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 unfavorable. It has also been described that aluminum hydroxide precipitated from carbon dioxide has a poorer morphology than the "sand-like" aluminum hydroxide obtained by the Bayer process, with a large number of fine particles and a wide particle size distribution, which makes this material less suitable for the molten electrolytic process for producing metallic aluminum (Hydrometallurgy 98, 52).

[0012] US 3,120,996 recognises the problem of sodium carbonate impurities in the Bayer process. As a solution, US 3,120,996 discusses the addition of slaked lime resulting in the formation of calcium carbonate and sodium hydroxide as precipitates. However, this solution has the disadvantage of adding a separate process step and thus increasing complexity. Furthermore, the slaked lime consumption of the process is increased. Summary of the invention

[0013] Therefore, there is a need for a process that allows for the efficient recovery of aluminum hydroxide from lithium battery derived materials, which process does not produce carbonates and produces "sand-like" aluminum hydroxide that is most suitable for molten electrolysis to produce metallic aluminum.

[0014] It is therefore an object of the present invention to provide an efficient process for recycling aluminium hydroxide from battery material which in particular does not lead to the formation of carbonates in the precipitate comprising the aluminium hydroxide and which produces aluminium hydroxide which is most suitable for molten electrolysis for the production of metallic aluminium.

[0015] It has now been found, surprisingly, that the above objects can be achieved by a process for recycling aluminium hydroxide from aluminium-containing ferrous materials, which process comprises the following steps in the given order:

[0016] In a first leaching step, leaching the black matter in an acidic aqueous solution, thereby producing a first leaching solution and a first leaching residue;

[0017] In a first separation step, a first leaching residue is separated from a first leaching solution;

[0018] In a pH adjustment step, a first alkaline aqueous solution is added to the first leach solution, thereby pH adjusting the first leach solution to produce a first pH adjusted leach solution;

[0019] in an Al / Fe precipitation step, precipitating an Al / Fe precipitate from the first pH adjusted leaching solution, wherein the Al / Fe precipitate comprises mixed aluminum-iron hydroxides and / or aluminum hydroxide;

[0020] In a second separation step, the Al / Fe precipitate is separated from the first pH adjusted leaching solution;

[0021] in a second leaching step, leaching the Al / Fe precipitate in a second alkaline aqueous solution, thereby producing a second leaching solution and a second leaching residue;

[0022] In a third separation step, the second leach residue is separated from the second leach solution;

[0023] in an Al precipitation step, precipitating an Al precipitate from the second leaching solution, wherein the Al precipitate comprises aluminum hydroxide, and wherein no carbon dioxide or carbonate is added to the second leaching solution as a precipitation aid;

[0024] In the fourth separation step, the Al precipitate is separated from the second leaching solution.

[0025] Since the Al precipitation step is similar to the Al precipitation step carried out in the Bayer process, the Al / Fe precipitate obtained during the recycling process of the battery can be introduced into an aluminum hydroxide production plant operated according to the Bayer process. Therefore, preferably, the Al / Fe precipitate of the Al / Fe precipitation step is preferably suitable for being introduced into an aluminum hydroxide production plant operated according to the Bayer process. Preferably, the method of the present invention includes 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.

[0026] It has further been found that the objects of the present invention can be achieved by providing an aluminium hydroxide obtainable by the process as described above.

[0027] One advantageous effect of the present invention is that the formation of carbonates is avoided during the entire process route. Such carbonates are particularly problematic in the Al precipitation step for precipitating aluminum hydroxide. Another advantageous effect of the present invention is the separation of iron and aluminum in a step after the first leaching. Thus, not only aluminum but also iron can be recovered.

[0028] Since the material obtained from the hydrometallurgical processing of the battery material may contain lithium, lithium may also enter the second leaching solution and also 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 (see, for example, Ullmann's Encyclopedia of Industrial Chemistry - 2000 - Hudson - Aluminum Oxide [aluminum oxide] 2012, page 629, Han et al., Metals [metal] 2021, 11, 1148). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic illustration of the method of the invention is shown.

[0030] definition

[0031] Before describing exemplary embodiments of the present invention in detail, definitions important for understanding the present invention are given.

[0032] The term "black mass" as used herein refers to the solid residue obtained by disassembling and pulverizing the battery. The black mass is obtained as a fine fraction of the classification stage and contains the active materials of the cathode and anode of the battery as well as some impurity particles. This black mass can be processed directly in a hydrometallurgical process or after the pyrolysis treatment. After the pyrolysis step, a lithium extraction step can subsequently be carried out, producing a lithium salt solution and a lithium-poor residue, which is also denoted as black mass hereinafter.

[0033] As used in this specification and the appended claims, unless the context clearly stipulates otherwise, the singular form "a / an" also includes the corresponding plural. In the context of the present invention, the terms "about" and "approximately" represent that those skilled in the art will understand that the precision interval of the technical effect of the feature discussed is still guaranteed. The term typically indicates a deviation from the indicated numerical value of ±10%, preferably ±8%, more preferably ±5%, and even more preferably ±2%. It should be understood that the terms "comprising" and "including / encompassing" are not restrictive. For the purposes of the present invention, the term "consisting of..." is considered to be a preferred embodiment of the term "consisting of...". If a group is defined as including at least a certain number of embodiments below, this means that a group preferably consisting of only these embodiments is also covered. In addition, the terms "first", "second", "third" or "(a)", "(b)", "(c)", "(d)" and the like in this specification and claims are used to distinguish similar elements and are not necessarily used to describe sequential or chronological order. It should be understood that the terms used in this way are interchangeable where appropriate, and the embodiments of the present invention described herein can operate in other sequences except as described or illustrated herein. In the case where the terms "first", "second", "third" or "(a)", "(b)", "(c)", "(d)", "i", "ii" etc. relate to a step of a method or purpose or a determination, there is no time or time interval coherence between these steps, i.e., these steps can be performed simultaneously or there can be a time interval of seconds, minutes, hours, days, weeks, months or even years between such steps, unless otherwise indicated in the present application as described above or below. It should be understood that the present invention is not limited to the particular methods, schemes, reagents, etc. described herein, because these can vary. It should also be understood that the terms used herein are only for the purpose of describing a particular embodiment, and are not intended to limit the scope of the present invention, which will be limited only by the appended claims. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art.

[0034] As used herein, the term "does not comprise", "does not contain" or "does not contain" in this context means that the composition of the present invention does not contain a specific compound or group of compounds (which may be combined under collective terms), meaning that the composition does not contain said compound or group of compounds in an amount exceeding 0.8% by weight based on the total weight of the composition. Furthermore, it is preferred that the composition according to the present invention does not contain said compound or group of compounds in an amount exceeding 0.5% by weight, preferably the composition does not contain said compound or group of compounds at all.

[0035] When referring to weight percentages of compositions and ingredients contained therein, it is to be understood that the total amount of ingredients according to the present invention does not exceed 100% (± 1% due to rounding). DETAILED DESCRIPTION

[0036] In the method of the present invention, aluminum hydroxide is recycled from a black substance containing aluminum and / or aluminum compounds. The metallic aluminum may originate from the electrode current collector foil or the housing, and the aluminum compound that may be present in the black substance is in the form of aluminum oxide, lithium nickel cobalt aluminum oxide (NCA), aluminum phosphate, lithium aluminate and / or aluminosilicate. 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 aluminosilicate. However, it is preferred that the black substance originates from a battery material, preferably a lithium battery material. In a lithium-ion battery, typically, the cathode foil is made of aluminum, and the cathode active material may contain aluminum. Therefore, such a lithium battery material typically contains a large amount of aluminum.

[0037] Typically, in the recycling process of batteries, especially lithium-ion based batteries, a pyrolysis step is involved. This pyrolysis step is usually a thermal pretreatment step, in which pre-sorted batteries or battery components are heated so that their constituent organics are decomposed. Although the present invention is suitable for any black substance, in the method according to the present invention, the black substance is preferably a pyrolyzed material, most preferably a pyrolyzed lithium battery material.

[0038] After pretreatment by pyrolysis, the method of the present invention can be roughly described by three process steps: a) a first leaching step, in which the black material is first leached out in an acidic environment and subsequently partially precipitated again, b) a second leaching step, in which the precipitate is leached in an alkaline environment, thereby separating the resulting aluminate solution from the filter residue, and c) a precipitation step (indicated herein as 'Al precipitation step'), in which neither carbon dioxide nor any carbonates are added, and which results in the formation of aluminum hydroxide.

[0039] In some methods, after pyrolysis, lithium is first extracted from the black mass, and the lithium-poor residue is then treated in the manner of the invention described above, starting from step a). Lithium pre-extraction can be carried out by treatment with water or alkaline earth metal oxides or hydroxides in polar solvents. There are also methods known in the art in which pyrolysis is carried out in the presence of acidic salts such as sodium bisulfate. In the latter case, lithium is subsequently extracted in the form of the corresponding neutral salt, for example lithium sulfate.

[0040] In the process according to the invention preferably no carbonates are formed, i.e. no carbon dioxide or any carbonates are added to any spent solution during the process between the first leaching step and the recovery of the Al precipitate in the fourth separation step. In the Al precipitation step no carbon dioxide or carbonates are added.

[0041] However, the method necessarily includes more than these steps, so that the method of the present invention includes the following steps:

[0042] In a first leaching step, leaching the black matter in an acidic aqueous solution, thereby producing a first leaching solution and a first leaching residue;

[0043] In a first separation step, a first leaching residue is separated from a first leaching solution;

[0044] In a pH adjustment step, a first alkaline aqueous solution is added to the first leach solution, thereby pH adjusting the first leach solution to produce a first pH adjusted leach solution;

[0045] in an Al / Fe precipitation step, precipitating an Al / Fe precipitate from the first pH adjusted leaching solution, wherein the Al / Fe precipitate comprises mixed aluminum-iron hydroxides and / or aluminum hydroxide;

[0046] In a second separation step, the Al / Fe precipitate is separated from the first pH adjusted leaching solution;

[0047] in a second leaching step, leaching the Al / Fe precipitate in a second alkaline aqueous solution, thereby producing a second leaching solution and a second leaching residue;

[0048] In a third separation step, the second leach residue is separated from the second leach solution;

[0049] in an Al precipitation step, precipitating an Al precipitate from the second leaching solution, wherein the Al precipitate comprises aluminum hydroxide, and wherein no carbon dioxide or carbonate is added to the second leaching solution as a precipitation aid;

[0050] In the fourth separation step, the Al precipitate is separated from the second leaching solution.

[0051] 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, wherein in the first leaching step, the acid of the acidic aqueous solution is preferably selected from the list consisting of sulfuric acid, hydrochloric acid, nitric acid, citric acid, oxalic acid, and mixtures thereof. Most preferably, the acid of the acidic aqueous solution is sulfuric acid, because sulfuric acid is a highly available strong acid, ensuring that most of the elements in the black mass are dissolved. In addition, it produces sulfates that are harmless to the environment.

[0052] In order to achieve a good leaching yield, in the method according to the present invention, in the first leaching step, the concentration of the acid in the acidic aqueous solution is preferably 0.05 M to 5 M or 0.1 N to 10 N. However, not only the concentration of the acid is decisive for achieving the best leaching yield, but also the absolute molar ratio between the acid and the elements of the black matter. Therefore, preferably, in the method of the present invention, the mass ratio of the black matter to the acidic aqueous solution is in the range of 10 wt% to 35 wt%, preferably 12 wt% to 30 wt%, and most preferably 14 wt% to 25 wt%.

[0053] In order to achieve optimal mutual mixing, in the method of the present invention, the first leaching step includes a step of stirring the acidic aqueous solution. Preferably, the first leaching step and in particular the step of stirring the acidic aqueous solution is carried out at a temperature in the range of 80° C. to 100° C. Likewise, it is also preferred that the first leaching step and in particular the step of stirring the acidic aqueous solution is carried out for a time in the range of 30 minutes to 600 minutes.

[0054] It will be appreciated that, depending on the conditions used in the first leaching step, in particular taking into account the pH environment and the redox potential, which can be adjusted, which elements will be dissolved from the black mass and which will not. Typically, carbon fractions such as those contained in the black mass are not dissolved by the acidic aqueous solution. Furthermore, typically, the pH environment and the redox potential are gradually varied to allow for the separate dissolution of several metal fractions of the black mass.

[0055] Therefore, considering copper, reaction conditions can be selected to achieve sufficient reduction to ensure that copper is not dissolved in the acidic aqueous solution. Typically, this is achieved by excluding oxidants such as air or oxygen in the first leaching step. In contrast, oxidizing conditions can be used to ensure that copper is present in the +2 oxidation state so that it is more easily solvated. Preferably, such oxidizing conditions are achieved by adding an oxidant selected from the list consisting of: oxygen, air, hydrogen peroxide, nitrous oxide, lithium metal oxide, high-valent metal oxides such as permanganate, ferrate, and mixtures thereof. In the case of using lithium metal oxide or high-valent metal oxide, any excess of these compounds can be reduced by adding a suitable reducing agent and optionally adjusting the pH of the reaction mixture. Preferably, such reducing conditions are achieved by adding a reducing agent like hydrogen peroxide, sulfur dioxide, sodium metabisulfite and / or hydrogen.

[0056] However, in the case where copper dissolves in the acidic aqueous solution, it is necessary to selectively separate the copper from the aluminum and iron to ensure that it does not precipitate in the subsequent Al / Fe precipitation step. Therefore, in one embodiment of the present invention, conditions can be selected so that the copper does not dissolve in the acidic aqueous solution. In this embodiment, the first leaching step is carried out in the absence of an oxidizing agent such as air, oxygen or hydrogen peroxide, and the copper is retained in the leached black mass, which can be subjected to any other leaching process after separation from the acidic aqueous solution.

[0057] However, in case it is necessary to also provide copper separation in the same process, the process of the invention preferably comprises an additional copper separation step, in which copper is separated from the acidic aqueous solution. This copper separation step can be carried out by precipitation of copper sulfide and subsequent separation, such as filtration, solvent extraction or precipitation using non-precious metal powders (e.g. iron, nickel, cobalt, manganese, where iron is not preferred as it adds additional unwanted iron to the leaching solution) and subsequent separation, such as filtration.

[0058] After the first leaching step, the leaching residue, which mainly contains carbon and optionally copper, has to be separated from the leaching solution, which contains most of the elements to be recycled. Preferably, the first separation step is carried out as a separation step according to one or more of the list consisting of a filtration step, a centrifugation step, a sedimentation step and a decantation step, most preferably, the first separation step is carried out as a filtration step. Depending on the choice made with regard to the solvation of copper, the leaching residue can be further processed to recover carbon and optionally copper.

[0059] The next step in the process of the present invention is to selectively precipitate aluminum and iron from the solution of the elements to be recovered from the ferrous material. This is performed by adjusting the pH of the leaching solution. The pH value of the leaching solution is generally low, for example in the range between 0 and 2. Therefore, in order to ensure the selective precipitation of aluminum and iron, in the pH adjustment step of the process of the present invention, a first alkaline aqueous solution is added to the leaching solution. For optimal precipitation conditions, the first pH-adjusted leaching solution preferably has a pH value equal to or higher than 3.5, and more preferably equal to or higher than 4. Likewise, the first pH-adjusted leaching solution preferably has a pH value equal to or lower than 7, and more preferably equal to or higher than 5, and most preferably equal to or higher than 4. In order to achieve ideal conditions, most preferably, in the pH adjustment step of the process according to the present invention, the first pH-adjusted leaching solution has a pH value in the range of 4.3 to 4.7. Preferably, in the pH adjustment step, the concentration of the alkali in the second alkaline aqueous solution is 3N to 25N.

[0060] Preferably, in the pH adjustment step of the process of the present invention, the base of the first alkaline aqueous solution is selected from a list consisting of metal oxides, hydroxides or carbonates. Preferred metals among these compounds are alkali metals and alkaline earth metals, nickel, cobalt and manganese and mixtures thereof, preferably selected from a list consisting of sodium hydroxide, lithium hydroxide, potassium hydroxide or sodium carbonate. Ammonium hydroxide is also a suitable base and can be used alone or in combination with the metal bases. In order to prevent any risk of introducing carbonates at a later Al precipitation stage, it is most preferred that the base of the first alkaline aqueous solution is an alkali metal hydroxide, most preferably sodium hydroxide.

[0061] In order to ensure complete precipitation of iron in the Al / Fe precipitation, it is preferred to oxidize all of the iron species in the solution to ferric iron species before or during pH adjustment. This oxidation can be achieved by introducing, for example, oxygen or air or hydrogen peroxide or nitrous oxide. This oxidation ensures that most of the Fe present in the solution is 2+ The ions are oxidized to Fe 3+ ions, further improving the separation efficiency of aluminum and iron separation and is particularly useful when the first leaching step has been carried out under reducing conditions.

[0062] By adjusting the pH value in the pH adjustment step, conditions are prepared to allow selective precipitation of aluminum and iron. Typically, the Al / Fe precipitate will precipitate after a period of time. However, preferably, the Al / Fe precipitation step includes a step of stirring the first pH-adjusted leaching solution. This ensures better homogenization of conditions such as pH and temperature. Preferably, the Al / Fe precipitation of the process of the present invention is carried out at a temperature in the range of 10°C to 90°C, more preferably 18°C ​​to 90°C, even more preferably 20°C to 80°C, and most preferably, the Al / Fe precipitation step and in particular the step of stirring the first pH-adjusted leaching solution is carried out at room temperature. Preferably, the Al / Fe precipitation step and in particular the step of stirring the first pH-adjusted leaching solution is carried out for a time in the range of 1h to 15h, more preferably 2h to 11h, and most preferably 7h to 9h.

[0063] In order to increase the precipitation yield and speed, the Al / Fe precipitation step is preferably carried out in the presence of aluminum hydroxide seeds. Furthermore, in order to increase the separation efficiency, the Al / Fe precipitation step of precipitating mixed aluminum / iron hydroxide and / or aluminum hydroxide is preferably carried out in more than one stage, i.e. by collecting the pH-adjusted leaching solution after the second separation step and subjecting it to a second Al / Fe precipitation step. In this second Al / Fe precipitation step, it is particularly preferred to use aluminum hydroxide seeds.

[0064] It should be understood that, although the pH adjustment step and the Al / Fe precipitation step are in principle connected in series, they can also show a certain overlap. Therefore, in general, the Al / Fe precipitation step can be initiated by the pH adjustment step. However, other parameters can also affect the precipitation, such as the addition of seed crystals and changes in concentration. However, the pH adjustment can be carried out step by step, thereby inducing Al / Fe precipitation in each step. However, this observation does not touch on the serial nature of pH adjustment followed by Al / Fe precipitation.

[0065] After the Al / Fe precipitation step is completed, the Al / Fe precipitate containing mixed aluminum-iron hydroxides and / or aluminum hydroxide (i.e., if only aluminum and no iron is present in the black mass) must be separated from the pH-adjusted leaching solution in a second separation step. In parallel with the first separation step, the second separation step is also preferably performed as a separation step according to one or more of the list consisting of a filtration step, a sedimentation step, a centrifugation step, and a decantation step, most preferably, the second separation step is performed as a filtration step.

[0066] It will be appreciated that at higher pH values, the co-precipitation of Ni and Co also increases. Therefore, ideally, the pH conditions in the Al / Fe precipitation step are adjusted to precipitate as little Ni or Co as possible. However, in the case of possible Ni and Co entrainment into 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 consisting mainly of iron hydroxide. This residue can then be recycled as a metal base to the first leaching step or to or during the pH adjustment step after the first leaching step. It is also possible to selectively separate the Ni / Co precipitate from the iron precipitate before such recycling, for example by selectively dissolving the Ni / Co hydroxide in the pH range between 3.5 and 7.

[0067] In order to selectively separate aluminum from iron and other residual metals (e.g. nickel and cobalt contained in the Al / Fe precipitate), the Al / Fe precipitate is treated with a second alkaline aqueous solution. Preferably, in this second leaching step of the process of the invention, the base of the second alkaline aqueous solution is an alkali metal hydroxide or a mixture of alkali metal hydroxides, preferably sodium hydroxide or potassium hydroxide. It is particularly important for the present invention to prevent any risk of introducing carbonates into the precipitate. Therefore, the base in the second alkaline aqueous solution preferably does not contain any carbonates.

[0068] Preferably, the second leaching step further comprises a step of stirring the first alkaline aqueous solution. In order to achieve optimal separation conditions, the second leaching step and in particular the step of stirring the first alkaline aqueous 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 and in particular the step of stirring the first alkaline aqueous solution is carried out for a time in the range of 30 minutes to 90 minutes, preferably 40 minutes to 80 minutes, and most preferably 50 minutes to 70 minutes.

[0069] After the second leaching step is completed, the second leaching solution contains a major part of the aluminum portion, while the second leaching residue contains a major part of the iron portion. In parallel with the first and second separation steps, the third separation step is also preferably performed as a separation step according to one or more of the list consisting of a filtration step, a sedimentation step, a centrifugation step, and a decantation step, most preferably, the third separation step is performed as a filtration step. Preferably, the filter residue, i.e., the second leaching residue, is washed, and the washed portion is recombined with the second leaching solution. The second leaching solution is used for a subsequent precipitation step, while the second leaching residue can be subjected to a new acidic leaching step to recover iron. Alternatively, the second leaching residue can be subjected to pyrometallurgical treatment to ultimately recover metallic iron.

[0070] To induce precipitation, the second leach solution is cooled. Therefore, preferably, the Al precipitation step and in particular the step of stirring the second leach solution is carried out at a temperature lower than the temperature of the second leach step, more preferably at room temperature. In addition, time is required to achieve a good separation efficiency. In order to ensure uniform conditions in the second leach solution, the Al precipitation step preferably includes a step of stirring the second leach solution. As indicated above, the time for precipitation is important. Therefore, preferably, the Al precipitation step and in particular the step of stirring the second leach solution is carried out for a time in the range of 1 h to 60 h, more preferably 2 h to 55 h, and most preferably 35 h to 48 h.

[0071] In order to improve the precipitation yield and speed, preferably, the method of the present invention further comprises a step of adding aluminum hydroxide seeds to the second leaching solution before the Al precipitation step. Preferably, the weight of the aluminum hydroxide seeds is in the range of 0.03 to 0.30, preferably 0.05 to 0.1, and most preferably 0.05 to 0.07 relative to the weight of the Al precipitate. For the present invention, it is mandatory not to add carbon dioxide or carbonate as a precipitation aid to the second leaching solution. Preferably, no precipitation aid other than aluminum hydroxide is added to the second leaching solution.

[0072] After the Al precipitation step has been completed, the Al precipitate containing aluminum hydroxide must be separated from the second leaching solution in a fourth separation step. In parallel with the first, second and third separation steps, the fourth separation step is also preferably performed as a separation step according to one or more of the list consisting of a filtration step, a sedimentation step, a centrifugation step, and a decantation step, most preferably, the fourth separation step is performed as a filtration step. Typically, the Al precipitate is washed with water. Finally, the Al precipitate is dried. The aluminum precipitation recovery rate of the second leaching step is preferably greater than 19%. In addition, 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 (optionally after a concentration step) to the second leaching stage.

[0073] Finally and preferably, the method of the invention comprises a refining step after the fourth separation step, wherein in this refining step, aluminum is separated from aluminum hydroxide contained in the Al precipitate, thereby producing metallic aluminum. Preferably, the refining step comprises a molten salt electrolysis step. Aluminum refining by molten salt electrolysis has been known in the prior art for decades.

[0074] Measurement method

[0075] a) Sample preparation for elemental analysis

[0076] The black substance sample was dried for analysis. The solution had been pre-diluted in a ratio of 1:10 and acidified with 2.5 ml of concentrated HNO3. The chemical laboratory is accredited according to DIN EN ISO 9001:2015. All subsequent work steps and applications are subject to the scope of accreditation.

[0077] b) Sample preparation solid

[0078] 50mg sample is weighed into the Teflon container on the analytical balance, mixed with 6ml concentrated HNO and 2ml concentrated HCl. After about 30 minutes of pre-reaction time, the container is sealed and placed in the high pressure microwave "TurboWave Pro" from MLS (MLS Microwave Laboratory System Co., Ltd. (Mikrowellen-Labor-Systeme GmbH), Leutkirchen, Germany). The sample is processed with the "charcoal" program for about 40 minutes, until they dissolve without leaving any residue. After being transferred to a 50ml volumetric flask, the sample is additionally diluted with a ratio of 1:10 and 1:100. At each dilution, 2.5ml concentrated HNO is added to the solution. Each solid sample is prepared in duplicate.

[0079] c) Sample preparation solution

[0080] Liquid samples were also diluted at ratios of 1:10 and 1:100 and acidified with concentrated nitric acid to give approximately 5% acid matrix.

[0081] d) Measurement of metal cations and phosphorus

[0082] The measured metal concentrations were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). An "ICP-OES 5900SVDS" type device from Agilent (Agilent Technologies Inc, Santa Clara, CA, USA) was purchased, especially for analyzing black material samples. For this purpose, an external calibration series was prepared based on DIN 38402-51 by certified single element standards obtained from LGC. In order to monitor the measurement process, synthetic control samples of known concentrations were also used to obtain references between sample measurements. In order to prevent physical interference, the samples and solutions of the calibration series were applied to the matrix (5% HNO3) of the rinse solution. The measurement results above the highest calibration standard were determined by the lowest possible dilution. The values ​​below the lowest calibration standard were indicated with the annotation "<detection limit". The wavelengths of the individual elements were manually selected by trained users for each element so that no chemical interference interfered with the measurement. Only in this way can correct measurements be guaranteed.

[0083] e) Measurement of carbon content

[0084] The solid sample is inductively burned in an oxygen stream in a device of the "CS2000" type from the company Eltra (ELTRA GmbH, Haan, Germany). The carbon contained in the exhaust gas stream is catalytically converted into CO2 at the platinum network and detected by a resistance measuring cell. A certified standard sample is used as a reference.

[0085] f) Measurement of fluoride content (solid / liquid)

[0086] The fluoride content of solids and solutions was determined using an ion-sensitive electrode (ISE) of the Titrando type (Metrohm AG, Heirsau, Switzerland). For this purpose, 2 ml of undiluted sample was made up to 20 ml, placed in a container and 25 ml of TISAB IV solution was added. The concentration of fluoride was determined using an external calibration via the voltage applied between the ISE and a silver reference electrode. Synthetic reference standards were used for monitoring.

[0087] Examples

[0088] In the following, three examples are described which illustrate the three steps of the process of the present invention leading to the final production of aluminum hydroxide (ie, before the refining step).

[0089] Example 1: Leaching

[0090] 14 kg of black material was leached in 70 liters of 6N / 3M H2SO4 at 80°C for 120 minutes. The leached solution was filtered, the filter cake was washed and dried at 80°C. The filtrate was further used for 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.

[0091] For the elements listed, up to the following leaching yields can be achieved: Li 93.50%, Al 83.42%, Fe 92.05%, Cu 0.00%, Ni 45.11%, Mn 94.10%, Co 56.58%, P 93.71% and F 90.10%. All carbon is retained in the filter cake. The composition of the input material and the filter residue as well as the leaching yields are given in Table 1. The mass of the filter residue produced is 9244.04 kg.

[0092] Table 1

[0093]

[0094] Example 2: Precipitation of aluminum-iron hydroxide

[0095] 70 liters of the leaching filtrate produced as in Example 1 were used to precipitate aluminum-iron hydroxide at room temperature. Continuously, 4 l / min of oxygen was injected into the solution for Fe 2+ ions. The pH was adjusted using 10 M NaOH solution until a final value of pH 4.5 was reached. At pH 4, 131.35 g of Al(OH)3 seeds were added to the solution. After the desired final pH value was reached, the solution was stirred for an additional nine hours. The filter residue and liquid samples were analyzed for Li, Al, Fe, Ni, Co, Mn, P, and F.

[0096] 65.01 wt% of the aluminum and 48.77 wt% of the iron in the solution can both be recovered as hydroxides by this method. The hydroxide product is contaminated with other battery-related elements, making it possible to achieve a purity of 77.64% relative to Al / Fe(OH)3. The most abundant impurities are nickel up to 3.69 wt% and phosphorus up to 2.62 wt%. The composition of the precipitate is given in Table 2. The mass of the precipitate produced is 2.148 kg.

[0097] Table 2

[0098]

[0099] Example 3: Precipitation of aluminum hydroxide

[0100] 200 g of the aluminum-iron hydroxide produced 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 produce a filtrate containing 17.9 g / l Al, which is equivalent to an Al leaching yield of 49%. The filtrate was then stirred at room temperature for 48 h for Al(OH)3 precipitation. 3 g of Al(OH)3 seeds were added to the solution. Liquid samples and precipitated products were analyzed for Li, Al, Fe, Ni, Co, Mn, P and F.

[0101] Fe, Ni, Mn and Co were below the ICP-OES detection limit of 0.5 mg / l in the leaching solution and therefore they remained in the filter cake. However, about 1.87 mg of Fe and Co were detected in the final product. The aluminum precipitated in the solution and the resulting filtrate contained 14.4 g / l Al, which is close to the solubility limit of about 15 g / l calculated under the given parameters. The aluminum precipitation recovery was calculated to be 19.6%. The final aluminum hydroxide product had a purity of 85.9%. Due to the initial input materials and process, the relevant remaining impurities were Li, P and F. Table 3 shows the final product and filtrate composition. The mass of the resulting precipitate was 9.33 g.

[0102] Table 3

[0103]

Claims

1. A method for recycling aluminum hydroxide from a ferrous material containing aluminum, the method comprising the following steps in the given order: In a first leaching step, the black material is leached in an acidic aqueous solution, thereby producing a first leaching solution and a first leaching residue; In a first separation step, the first leach residue is separated from the first leach solution; In a pH adjustment step, a first alkaline aqueous solution is added to the first leach solution, thereby pH adjusting the first leach solution to produce a first pH adjusted leach solution; in an Al / Fe precipitation step, precipitating an Al / Fe precipitate from the first pH adjusted leaching solution, wherein the Al / Fe precipitate comprises mixed aluminum-iron hydroxides and / or aluminum hydroxide; in a second separation step, separating the Al / Fe precipitate from the first pH adjusted leaching solution; in a second leaching step, leaching the Al / Fe precipitate in a second alkaline aqueous solution, thereby producing a second leaching solution and a second leaching residue; in a third separation step, separating the second leaching residue from the second leaching solution; in an Al precipitation step, precipitating an Al precipitate from the second leaching solution, wherein the Al precipitate comprises aluminum hydroxide, and wherein no carbon dioxide or carbonate is added to the second leaching solution as a precipitation aid; In a fourth separation step, the Al precipitate is separated from the second leaching solution.

2. The method according to claim 1, wherein: The black substance is a pyrolyzed battery material, preferably a pyrolyzed lithium battery material.

3. The method according to any one of claims 1 or 2, wherein: In the first leaching step, the acid of the acidic aqueous solution is selected from the list consisting of sulfuric acid, hydrochloric acid, nitric acid, citric acid, oxalic acid, and mixtures thereof, preferably sulfuric acid.

4. A method according to any one of the preceding claims, wherein: In the pH adjustment step, the first pH adjusted leaching solution has a pH value in the range of 3.5 to 5, preferably 4.

5.

5. A method according to any one of the preceding claims, wherein: In the pH adjustment step, the base of the first alkaline aqueous solution is selected from the list consisting of ammonium hydroxide, alkali metal hydroxides, alkali metal carbonates, alkaline earth metal hydroxides, and mixtures thereof, preferably sodium hydroxide or sodium carbonate, most preferably sodium hydroxide.

6. A method according to any one of the preceding claims, wherein: In the Al / Fe precipitation step comprising the step of stirring the first pH adjusted leaching solution, the step of stirring the first pH adjusted leaching solution is carried out at a temperature in the range of 18°C ​​to 90°C, preferably 20°C to 80°C, most preferably at room temperature.

7. The method according to claim 6, wherein: In the Al / Fe precipitation step, the step of stirring the first pH adjusted leaching solution is performed for a time ranging from 1 h to 15 h, preferably from 2 h to 11 h, most preferably from 7 h to 9 h.

8. The method according to claim 1, wherein: The second leaching step is carried out at a temperature ranging from 150°C to 230°C, preferably from 160°C to 190°C, and most preferably from 170°C to 180°C.

9. A method according to any one of the preceding claims, wherein: The pH adjustment step and / or the Al / Fe precipitation step is performed in the presence of an oxidizing agent, preferably in the presence of an oxidizing agent selected from the list consisting of oxygen, air, hydrogen peroxide, or mixtures thereof.

10. The method according to claim 9, wherein: In the pH adjustment step and / or the Al / Fe precipitation step, the oxidant comprises oxygen and is injected into the first leaching solution.

11. A method according to any one of the preceding claims, wherein: The Al precipitation step is carried out at a temperature lower than the temperature of the second leaching solution in the second leaching step, preferably at room temperature.

12. A method according to any one of the preceding claims, wherein: The Al precipitation step is carried out for a time ranging from 1 h to 60 h, preferably from 2 h to 55 h, most preferably from 35 h to 48 h.

13. A method according to any one of the preceding claims, wherein: The method further comprises the step of adding aluminum hydroxide seeds to the second leaching solution before the Al precipitation step and / or before the Al / Fe precipitation step.

14. The method according to claim 13, wherein: The ratio of the weight of the aluminum hydroxide seeds to the weight of the Al precipitate ranges from 0.03 to 0.30, preferably from 0.05 to 0.1, and most preferably from 0.05 to 0.

07.

15. A method according to any one of the preceding claims, wherein: The Al / Fe precipitate of the Al / Fe precipitation step is suitable for introduction into an aluminium hydroxide production plant operated according to the Bayer process, and wherein preferably the method of the present invention further comprises the step of introducing at least a portion of the Al / Fe precipitate of the Al / Fe precipitation step into an aluminium hydroxide production plant operated according to the Bayer process.

16. A method according to any one of the preceding claims 2 to 15, wherein: The black substance is a lithium-poor residue, from which lithium is extracted after pyrolysis of the battery material.

17. The method according to any one of the preceding claims, further comprising the step of reintroducing the second leaching residue into the first leaching step or the pH adjustment step.

18. Aluminium hydroxide obtainable by the method according to any one of the preceding claims 1 to 17.

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