Method and system for recovering graphite from black mass

Abstract

The present invention relates to a method for recovering graphite from black mass, characterized in that it comprises the following steps, in the following order: - providing black mass containing graphite; - adding water to the black mass to form a suspension of black mass in water; - introducing ozone as an oxidizing agent into the suspension and stirring said suspension of black mass with water; - flotation of the suspension and skimming off the graphite. The present invention also relates to a corresponding system.

Description

[Technical Field]

[0001] The present invention relates to a method for recovering graphite from black mass and a corresponding installation. [Background technology]

[0002] Global battery production is experiencing a very high growth rate. The demand for resources necessary for production, i.e., raw materials such as lithium and graphite, as well as metals such as nickel, cobalt, and manganese, is correspondingly increasing. While the necessary raw materials are primarily obtained from primary sources, the proportion of secondary sources from recycling will likely increase in the future. Such secondary sources are processed into so-called black mass, which is a mixture of lithium-ion battery scrap and / or scrap from the battery manufacturing process, processed into a fine powder. Thus, black mass typically contains a mixture of active anode and / or cathode materials from batteries. Furthermore, black mass may contain conductors such as plastics and / or copper and / or aluminum. However, while plastics, copper, and aluminum are separated as much as possible in the recycling process by mechanical processes, the remaining fraction is either processed into black mass or crushed. Furthermore, organic binders and electrolytes may also be present. The typical black color of black mass can be attributed to carbon, particularly graphite or carbon black, which is often used as the active anode material in lithium-ion batteries.

[0003] The proportion of graphite in black mass is often only about 15-20% by weight, and for advantageous starting materials, the proportion can be 20-40% by weight. Therefore, graphite reuse is often not considered. Instead, graphite from black mass is typically combusted. The increasing demand for graphite and undesirable COx emissions during combustion are increasingly encouraging the recycling of graphite from black mass. However, the requirements for the purity of graphite for use in battery cells are very high, which also places very high demands on the recycling process. The problem here is that traditional methods for obtaining and purifying graphite from natural sources, such as flotation, exhibit very low efficiency in the case of black mass, thus hindering their application. Summary of the Invention [Problem to be solved by the invention]

[0004] It is therefore an object of the present invention to provide a cost-effective method for recovering graphite from black mass that allows for efficient recovery with high purity. [Means for solving the problem]

[0005] The present invention solves this problem using the features of the independent claims.

[0006] A method for recovering graphite from black mass is proposed, comprising the following steps in the following order: step (a): providing a black mass containing graphite; - step (b): adding water to the black mass to form a suspension of black mass in water; Step (c): Ozone is introduced into the suspension as an oxidizing agent, and simultaneously, the suspension is heated for a period of preferably 11,000 s -1 agitating the suspension of black mass with water at a shear rate exceeding Step (f): Flotation of the suspension and skimming off of the graphite.

[0007] Surprisingly, it has been found that the steps of the proposed method achieve a pretreatment of the black mass that allows the separation of graphite from the black mass by flotation, achieving a purity similar to that achieved by separation from the primary graphite source.

[0008] The proposed method can achieve graphite concentrations of over 90% from black mass with yields of over 70%. For example, a carbon content of 91.5% can be achieved with a yield of 73%. In this way, graphite from black mass can be recovered very selectively, thereby allowing for more economical use of the graphite and avoiding combustion. Furthermore, the recovery of additional components from black mass can be improved by selective removal of carbon, especially graphite. Thus, the proposed method allows for very economical recovery of graphite from black mass.

[0009] Black mass in the sense of the present invention refers to materials from discarded batteries, e.g., lithium-ion batteries, and / or discarded parts thereof, and / or discarded materials from the battery manufacturing process, such as anode material. Black mass has a graphite content typically used in battery anodes. The graphite content in black mass is preferably greater than 10% by weight, more preferably greater than 15% by weight, e.g., 30% by weight. Ideally, black mass contains as high a graphite content as possible. However, in practice, the graphite content in black mass is usually less than 50% by weight. The starting materials described above are mechanically processed into a powdered material (referred to as black mass) with a high surface-to-mass ratio. The black mass is preferably in powder form. Preferably, less than 5% by weight of the black mass contains particles larger than 50 μm. Furthermore, due to its graphite content, black mass is visually dark.

[0010] Thus, for the purposes of this application, black mass comprises at least graphite, and thus the element carbon (C), and typically some or all of the elements lithium (Li), cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), aluminum (Al), phosphorus (P), fluorine (F).

[0011] Depending on the starting material of the black mass, the percentage of graphite or other metals recovered in the recycling process may vary greatly. Different battery chemistries, such as those known as NMC, NCA, and LFP, may result in different percentages or even the absence of valuable metals such as Co, Ni, or Mn. Therefore, different compositions with different compositions of other elements are possible. However, for purposes of the present invention, black mass always contains the element C in the form of graphite, as provided in step (a). Black mass often also contains Li, which may be, for example, chemically bound in the active cathode material and / or metallic Li in / around the active anode material, particularly those with a high graphite content.

[0012] In a preferred embodiment, the black mass has a proportion of Al of preferably at most 10% by weight, a proportion of Ca of preferably at most 0.7% by weight, a proportion of Co of preferably at most 20% by weight, a proportion of Cu of preferably at most 15% by weight, a proportion of Li of preferably at most 4.8% by weight, a proportion of F of preferably at most 4.4% by weight, a proportion of Fe of preferably at most 4.2% by weight, a proportion of P of preferably at most 2.2% by weight, a proportion of Mn of preferably at most 7.6% by weight, and a proportion of Ni of preferably at most 26% by weight. At the same time, the maximum total proportion of the elements Al, Ca, Co, Cu, Li, F, Fe, P, Mn, and Ni in the black mass, together with the proportion of C, which is always present in the form of graphite, is also limited to not exceed 100% by weight. Possible differences from 100% by weight of the sum of the elements Al, Ca, Co, Cu, Li, F, Fe, P, Mn, Ni, and C can be made up by residues of other elements.

[0013] For step (b), it is further proposed to suspend the black mass in water at a mass ranging from 10 g to 300 g, preferably from 10 g to 250 g, more preferably from 100 g to 200 g per liter of water, e.g., 200 g of black mass are suspended in 1 liter of water.

[0014] In step (c) of the proposed method, ozone is introduced into the suspension as an oxidizing agent while the suspension is being stirred. Preferably, the ozone is dissolved in the water of the suspension. Thus, the black mass, or at least a portion of the black mass, is oxidized with ozone. Ozone (O3) is known as a strong oxidizing agent. However, since ozone is less stable than carbon dioxide and decomposes quickly, using ozone as an oxidizing agent has several disadvantages. The half-life of ozone decreases when dissolved in water and further decreases as the temperature increases, resulting in very low efficiency of the process and even in the event that ozone does not react as intended when dissolved in water at high temperatures. The solubility of ozone in water is very low.

[0015] It has been shown that stirring a suspension of black mass in water can increase mass transfer, allowing ozone to react with the black mass particles, particularly their surfaces, before decomposing. Effective use of ozone begins at high stirring rates, and becomes even more effective with further increases in stirring rate, which can generate very high oxidation potentials (>850 mV).

[0016] Therefore, it is proposed to intensively or at a high stirring speed agitate the suspension while dosing ozone as an oxidizing agent into the suspension. Preferably, in step (c), an oxidation / reduction potential (ORP) of >850 mV (greater than 850 mV) is generated by dosing ozone into the suspension while the suspension is being stirred. The ORP can be further increased to >1200 mV (greater than 1200 mV) by very vigorous stirring during step (c). Ozone, as a strong oxidizing agent with a redox potential of >850 mV (greater than 850 mV), can successfully process black masses with different mineralogy and pretreatment, for example, since it oxidizes Co and Mn and does not depend on them already being present in the Co(III) and Mn(IV) state for recovery.

[0017] It is further proposed that turbulence is generated in the suspension by stirring the suspension during step (c).

[0018] Vigorous stirring or stirring at high stirring speed preferably exceeds a certain threshold above which the proportion of ozone that can react with the black mass is greater than the proportion of ozone that decomposes prematurely at the start of step (c).

[0019] According to a further development, in step (c), the suspension is heated in the suspension for 11,000 s -1 Larger, especially the 25000s -1 Larger, especially the 27000s -1 Larger, preferably 29000s -1 , for example 30000s -1 It is suggested that the mixture be stirred at a higher shear rate.

[0020] High shear rates, especially 11000s -1 Exceeding, for example, 12000s -1 , especially the 29000s -1 High shear rates above 11,000 s increase mass transfer sufficiently so that ozone can react with the black mass before decomposing. -1 Shear rates exceeding 12000 s -1At 25,000 s, a high enough ORP can be achieved to leach a suspension of water and black mass with ozone, and higher shear rates can result in even higher ORPs. -1 At shear rates above 850 mV an ORP of >850 mV can be achieved, while higher shear rates can result in higher ORPs, eg, >1200 mV.

[0021] For example, the shear rate of a fluid between two parallel plates can be determined by dividing the relative velocity of the two plates by the distance between the plates.

[0022] This pretreatment allows the graphite to be separated from the black mass by flotation, preferably by froth flotation. This is based on the different hydrophobicity of the substances in the black mass, which differ in their tendency to adhere to air bubbles and form a froth layer. The hydrophobic graphite can be separated from the black mass, while the remaining hydrophilic substances remain in the residue. However, this is only possible with high efficiency from the black mass by the proposed pretreatment, which liberates the graphite particles in the black mass, as reflected, for example, in mineral liberation analysis (MLA). For processing into anode material, use in batteries, and processing into black mass, the graphite in the black mass is mostly present in composite particles that cannot be flotated, in contrast to graphite from natural sources.

[0023] The proposed method steps are generally performed in alphabetical order within the present application unless that order is otherwise stated, although individual method steps following alphabetical order may be omitted or may represent advantageous further developments.

[0024] In step (a), in a possible embodiment, the black mass provided contains lithium. If Li is present in the black mass, step (c) dissolves the lithium, while the other components of the black mass remain as solids or are reprecipitated. Thus, a suspension of water and black mass can be leached with ozone, particularly in neutral leaching, and very high selectivity for Li can be achieved.

[0025] Preferably, in step (d), the suspension from step (c) is filtered and a filtrate is separated, the filtrate containing LiOH dissolved in water and the Li-depleted residue containing a black mass containing graphite.

[0026] By filtration in step (d), complete hydrometallurgical removal of Li can therefore be performed at the start of the recovery process, where Li removal can be performed in parallel with the pre-treatment of the black mass.

[0027] The proposed method has very high selectivity for Li with very low proportions of components other than LiOH dissolved in the water. Leaching is highly selective for Ni, Co, and Mn (typically present in spent lithium-ion battery materials and therefore in black mass) below detectability. High selectivity for Li can be achieved over a wide range of mineralogy and pretreatment of black mass. Furthermore, the proposed method also allows high extraction rates of Li >90%. Therefore, the method is highly efficient, preferably carried out as a batch process, and is recyclable, which is highly advantageous due to its high selectivity, as described further below. In particular, contamination of the recovered lithium with alkali elements, especially Na and / or K, can be avoided.

[0028] Li is removed from the Li-depleted residue of black mass early in the recovery process in the form of solids and / or sludge. By extracting it at the beginning of the process, the residue, which contains valuable elements such as Ni, Co, and Mn in addition to graphite, can be processed independently of other processing options. Furthermore, lithium loss to other products and intermediates is reduced by low washing efficiency or co-precipitation.

[0029] In a preferred embodiment, a suspension of black mass in water containing graphite is regenerated in step (e) using the residue from step (d) by addition of water and / or recycled filtrate with reduced Li content from step (d).

[0030] This is followed by step (f), which preferably involves flotation, during which, in a possible embodiment, step (h), which involves acidic leaching, as described below, can be carried out.

[0031] The suspension is floated in a flotation cell, e.g., a conventional mechanical flotation cell, according to step (f). Flotation is preferably carried out according to the froth method. The graphite is separated from the flotation residue in a flotation concentrate and can be skimmed off accordingly.

[0032] According to a further development, the suspension is after step (b) and before step (c), and / or After step (c) and before step (f), it is proposed to add at least one acid, preferably sulfuric acid (H2SO4), and / or a recirculated acid, leached in an acid leaching step (h), to reduce the pH to below pH 3.

[0033] Before step (c), and after step (c), and before step (f), the suspension comprises graphite, which is present in suspension together with the black mass in water. After step (f), the graphite and / or carbon are removed from the suspension, excluding possible residues.

[0034] It is particularly advantageous to carry out an acidic leaching step (h) after step (d) or (e). It is even more particularly advantageous if at least one acid is added in acidic leaching step (h) to the residue from the filtration in step (d), i.e. after carrying out step (c) and before the flotation according to step (f). Preferably, in acidic leaching step (h), 200 to 400 g of solids are present per liter.

[0035] In one possible embodiment, the acid leaching step (h) can be carried out before step (c), which can be advantageous, for example, in the case of lithium-free black mass, for example from Na-ion battery recycling, since possible process steps for separating lithium before the acid leaching do not offer any advantage in such situations.

[0036] The acidic leaching step (h) is preferably started at a pH below 2. Furthermore, in an advantageous embodiment, the acidic leaching step (h) is finished at a pH in the range of 3-5.

[0037] The acid leaching in step (h) can dissolve metals such as Ni, Co and Mn, while Cu and / or Al are present as solids.

[0038] According to a further development, it is proposed to add a reducing agent, preferably sulfur dioxide (SO2), to the acid leaching step (h), which improves the effectiveness of the acid leaching in step (h).

[0039] It is further proposed to add a calcium source, preferably calcium hydroxide (Ca(OH)2) and / or calcium oxide (CaO) and / or calcium carbonate (CaCO3), to the suspension from step (h), so that, for example, F can be precipitated.

[0040] Preferably, in step (i), the suspension from the acidic leaching step (h) is filtered.

[0041] As a result, in the residue graphite and e.g. Cu, Al and F can be separated, while e.g. Ni, Co and / or Mn from the acid leaching step (h) remain dissolved.

[0042] The graphite-containing residue can then be returned to a suspension containing water, for example with a solids content of 5-10%, and subjected to a flotation step (f).

[0043] According to an advantageous embodiment, it is proposed to carry out step (c) for at least 3 hours (3h), preferably for at least 3.5 hours (3.5h), for example for 4 hours (4h).

[0044] The concentration of Li dissolved in the water of the suspension increases with time until the maximum extraction rate, which can be achieved within, for example, 4 hours. Furthermore, the oxidation of Co and Mn also depends on the reaction time, with longer reaction times allowing for complete recovery from the solution, for example, 3 hours for Mn and 4 hours for Co. Thus, Co and Mo oxides precipitate after being dissolved in the solution. Therefore, carrying out step (c) for the above-mentioned time allows for very high selectivity of the extraction process. The corresponding time results in good pretreatment of the black mass so that good separation of graphite by flotation can be achieved.

[0045] In a preferred embodiment, in step (c), ozone is dosed into the suspension at a rate of at least 0.1 gram (O3) / hour / gram (black mass), for example 1 gram (O3) / hour / gram (black mass), and / or at a maximum rate of 2 grams (O3) / hour / gram (black mass).

[0046] Therefore, the mass flow rate of ozone per hour also depends on the mass of black mass provided in the suspension. For example, to provide ozone at a constant rate of 1.5 grams O3 / hour / gram black mass, if the amount of black mass provided is doubled, the mass flow rate of ozone must be doubled.

[0047] To achieve a sufficient effect of the pretreatment of black mass, there is a lower limit to the dosage of ozone into the suspension, while the upper limit is mainly for economic reasons, since the proposed stirring increases in a sufficient way the effectiveness of the added ozone.

[0048] According to a further development, it is proposed that in step (c) the temperature of the suspension is above 69°C, preferably above 80°C.

[0049] At temperatures above 70°C, high Li extraction rates of over 90% are obtained, rising to over 95% at 90°C. Therefore, the suspension is preferably heated. Furthermore, this can achieve good pretreatment of the graphite for flotation.

[0050] In a further development, it is proposed to add an acid, preferably sulfuric acid (H2SO4), to the suspension of step (b) and / or step (c) in order to lower the pH of the suspension to a pH in the range of 3 to 4.5, preferably 3 to 4. Step (c) is preferably completed at a pH of 9.

[0051] A pH below 4.5 further increases the Li extraction rate compared to embodiments of the process without lowering the pH, resulting in Li extraction rates of over 90%, with even Li extraction rates of over 95% being possible. At the same time, improved pretreatment for liberating graphite in the black mass is achieved. A pH below 3 results in excessive loss of Li selectivity.

[0052] Although Co and Mn can be completely recovered within the reaction time suggested above, e.g., 4 hours, lowering the pH to the range of 3.5-4.5 has the side effect of increasing Ni extraction along with Li extraction for longer durations. Thus, the extraction rate of Li increases to very high values, but Ni also dissolves.

[0053] The acid is preferably sulfuric acid (H2SO4), which can have further beneficial effects on the process for recovering metals, for example, the process for crystallizing Ni-sulfate, however, other acids may also be suitable depending on the desired end product of the process for recovering metals.

[0054] In an alternative embodiment, it is proposed that in step (c) the suspension of black mass in water has a pH in the range of 6-8, preferably in the range of 7-8, for example 8.

[0055] In an advantageous embodiment, the extraction of Li in step (c) can be carried out by neutral leaching without pH adjustment, in which case the effect of ozone is ignored (or not taken into account), which simplifies the process and is therefore cost-effective. Ozone is introduced into the suspension as an oxidizing agent, and the suspension is heated for a period of time during which the ozone is added, preferably for 11,000 s -1When stirred at shear rates above 1000 K, the suspension preferably has a pH in the range of 6-8, especially in the range of 7-8, which allows for extraction rates of greater than about 70% for Li. In addition, the proposed pH range, especially a pH of 7-8, has the advantageous effect that Co, Mn, and especially Ni precipitate out of solution or do not dissolve, resulting in very high selectivity for extraction of Li as LiOH in water from the black mass, while still achieving good extraction rates for Li and simultaneously achieving good liberation of graphite in the black mass.

[0056] Thus, the Li-containing filtrate from step (d) may also have a pH in the range of 6 to 8, especially 7 to 8, which allows for cost-effective further processing of the filtrate.

[0057] It is further proposed that after step (c) a base, preferably sodium hydroxide (NaOH) and / or calcium hydroxide (Ca(OH)2) and / or calcium oxide (CaO), is added to raise the pH of the suspension before step (d) or the pH of the filtrate of step (d) to a pH above 6, such as 9, preferably above 9, more preferably above 10.

[0058] In particular, a pH above 9, for example 10, preferably above 10, allows for the complete precipitation of Ni(II) as hydroxide from the Li-containing leachate. This is particularly advantageous when the pH of the suspension is lowered with acid to below 6, or especially below 4.5, in order to maximize the rate of Li extraction. In this way, the side effect of dissolved Ni can be reversed, resulting in very high extraction rates of Li dissolved in water, for example above 90%, for example 95%, and at the same time very high selectivity or purity of the dissolved Li.

[0059] Raising the pH of the suspension or filtrate with a base is preferably carried out at a temperature of 25°C to 70°C.

[0060] The pH is preferably adjusted to pH>9, for example pH=10, more preferably pH>10, before filtering the suspension.

[0061] The filtrate therefore contains very pure Li dissolved in water as LiOH. Graphite and other elements that may be present in the black mass, such as Ni, Co, Mn, Cu, Al, and Fe, remain in the residue.

[0062] Furthermore, pH adjustment with Ca-containing bases, especially calcium hydroxide and / or calcium oxide, removes F and / or P from the solution, so that a lower content of F and P in the filtrate is achieved.

[0063] Adjusting the pH with a Na-containing base, especially sodium hydroxide, leaves F and P in solution, which allows for separation of F from the residue and further processing of the residue, which may advantageously prevent other downstream processes, such as enrichment of HF in black acid. The amount of Na required to adjust the pH to the above values ​​is significantly below the solubility limit and does not result in Na contamination of the Li product.

[0064] As a result, the filtrate produced by the proposed method, which contains high-purity LiOH dissolved in water, and the Li-depleted or highly depleted residue can be processed independently of each other to the desired form of final product for metals recovered from black mass. The high selectivity and extraction rate for Li of the proposed method can be utilized.

[0065] In a particularly advantageous embodiment, the flotation according to step (f) is carried out, for example after the filtration according to step (d) and / or step (i), on a suspension (preferably having a solids content of 5-10% in water) prepared with the residue of this filtration.

[0066] The flotation according to step (f) is preferably carried out with the supply of air, more preferably at a rate of 0.8 to 5 liters per minute (l / min) per liter of suspension to be flotated.

[0067] In a preferred embodiment, in step (f), the pH value during flotation is in the range of 9-10.

[0068] Preferably, during the flotation in step (f), 800 to 5400 g of kerosene per ton of black mass and / or 100 to 1000 g of MIBC (4-methyl-2-pentanol) per ton of black mass are added as additives.

[0069] In a particularly advantageous embodiment, the skimmed flotation concentrate with graphite from step (f) is suspended in water and subjected to purification flotation of the suspension and skimming off of the graphite.

[0070] In the proposed repeated flotation in the purification flotation after corresponding pretreatment of black mass, which shows a high degree of liberation of graphite in the powdered black mass, a graphite concentration of more than 96% of the concentration in the repeated flotation can be achieved with a recovery rate of more than 90%. Overall, a recovery rate of more than 65% and a purity of more than 96% can be achieved throughout the entire process for recovering graphite from black mass, which is a very good result for recovering graphite from black mass. Therefore, the graphite recovered in this way can be reused as a high-quality product.

[0071] It is further proposed that the flotation residue from the flotation from step (f) be subjected to residual flotation, so that more free graphite can be recovered, further increasing the overall recovery rate.

[0072] Furthermore, for this purpose it is proposed to return the graphite-containing flotation concentrate from the residual flotation and / or the flotation residue from the refinery flotation to step (f).

[0073] Furthermore, an installation for carrying out the method according to any one of claims 1 to 19 is proposed. [Brief explanation of the drawings]

[0074] A preferred embodiment will now be described with reference to the drawings. [Figure 1] FIG. 1 shows the distribution of black mass graphite particles across particle sizes and their applicability for flotation in the prior art. [Figure 2] FIG. 2 shows the distribution of black mass graphite particles across particle sizes and their availability for flotation after step (c). [Figure 3] FIG. 3 shows the distribution of black mass graphite particles across particle sizes and their availability for flotation after steps (c) and (h). [Figure 4] FIG. 4 shows the distribution of black mass graphite particles across particle sizes and their availability for flotation after refinement flotation.

[0075] In step (a), black mass is provided as a graphite-containing starting material. The black mass is made from Li-ion battery scrap that has been processed into a powder. The mineralogy of the black mass can vary depending on the starting or scrap material.

[0076] The effectiveness of the proposed method for recovering graphite from black mass is illustrated using an example composition of black mass. Table 1 shows the possible compositions of graphite-containing black mass. The black mass was ground into a powdery mass, resulting in a high surface-to-mass ratio. Table 1 also shows the weight percentage of the listed elements in the black mass. Table 1: TIFF2026507278000002.tif62169

[0077] The carbon content is as high as 31.1% so that, in principle, most of the graphite is available for recovery.

[0078] First, direct flotation of black mass according to the prior art, without applying the proposed method, is presented. Figure 1 shows the distribution of black mass graphite particles across particle sizes and their potential for flotation by mineral liberation analysis (MLA). Free graphite particles are represented by white bars, while black bars represent connected graphite particles. MLA is used to quantitatively measure the degree to which individual minerals, constituents, and elements of fine solids or powders, here black mass, are aggregated into whole particles. When individual minerals, constituents, and elements exist primarily as individual particles, they are considered free or liberated and can be obtained by physical separation processes (e.g., gravity, magnetic, or flotation processes). Otherwise, minerals, constituents, and elements exist in composite particles with others and are considered bound.

[0079] As can be seen from the diagram in Figure 1, measurable proportions of carbon are liberated only in the particle size classes 5 μm-15 μm and 15 μm-30 μm. Overall, therefore, only about 15% of the carbon is liberated, i.e., the majority of about 85% of the carbon, and therefore the majority of the graphite in the black mass, is bound in the composite particles. Therefore, the recovery efficiency by conventional flotation according to the prior art is correspondingly low, as shown in Table 2. Table 2: TIFF2026507278000003.tif59169

[0080] Therefore, in conventional flotation processes, a significant proportion of the active cathode material and lithium is carried in the flotated graphite, and as a result, efficient separation and recovery of graphite from the black mass cannot be achieved by conventional methods.

[0081] In an advantageous exemplary embodiment, an exemplary black mass having a graphite content according to Table 1 is provided as a powder according to step (a) and is first made into a suspension with water according to step (b) having a concentration of 100-200 g solids per liter of water.

[0082] In the next step (c), the suspension is subjected to a very high shear rate, in this advantageous exemplary embodiment 34000 s -1 The mixture is mixed and stirred at a shear rate of 0.05-0.4 g of ozone per gram of black mass per hour for several hours. During the simultaneous stirring and ozone addition, the temperature of the suspension is maintained above 80°C. The pH is then adjusted and maintained in the range of 3-4. This process is maintained for several hours.

[0083] In this advantageous exemplary embodiment, the pH is further increased significantly at the end of this step, for example to pH 9, in order to selectively leach Li from the black mass.

[0084] The suspension from step (c) is then filtered in step (d), the residue comprising a Li-depleted black mass residue with graphite, while the filtrate comprises LiOH dissolved in water.

[0085] Figure 2 shows a further mineral liberation analysis (MLA) of the graphite-bearing black mass residue after step (c) has been carried out. Looking at the white bars, the proportion of free graphite can be significantly increased compared to the starting material (see Figure 1), so that a total of 42.8% of the graphite is free and only 57.2% of the graphite is bound.

[0086] The residue with the pretreated black mass containing graphite is then returned to suspension with a solids content of 5-10% by weight in water according to step (e).

[0087] The suspension is then floated in a flotation cell, for example a conventional mechanical flotation cell, according to step (f). In this case, the pH is advantageously adjusted and maintained in the range of 9 to 10. Furthermore, 800 to 5,400 g of kerosene per ton of the solids in suspension, here black mass in suspension, and 100 to 1,000 g of MIBC (4-methyl-2-pentanol) per ton of the solids in suspension are added for flotation. Air for flotation is supplied, for example, at a flow rate of 0.8 to 5 liters per minute (l / min) per liter of cell volume or suspension.

[0088] Table 3 shows the graphite concentrate obtained after flotation with the proposed pretreatment, where a significantly increased selectivity for graphite can be achieved: a proportion of graphite in the flotation concentrate of more than 80 wt. % can be achieved, and the recovery of graphite in the flotation skimmed concentrate is more than 65%. Table 3: TIFF2026507278000004.tif59169

[0089] In an alternative exemplary embodiment, after agitation and parallel ozone feeding according to the procedure described above and subsequent filtration according to step (d), the residue from the filtration is first subjected to an acidic leaching step (h) before flotation.

[0090] The Li-depleted residue of the graphite-containing black mass is put back into suspension in water, the suspension being advantageously adjusted to 100-200 g solids / l.

[0091] The suspension is then leached at a pH of 1-2, which can be achieved, for example, by adding sulfuric acid. The temperature is adjusted to above 60°C, for example 70°C, by heating the vessel. Simultaneously, sulfur dioxide (SO2) is added with stirring. This process is continued for several hours, for example 2, 3, or 4 hours, and the process is completed at a pH in the range of 3-5.

[0092] Figure 3 shows that in MLA, the proposed process can be used to liberate even more carbon across the entire particle size range, for example, so that 54% of the carbon can be made available for physical separation.

[0093] The suspension is then filtered, and the solid residue is returned to a suspension containing 5-10% by weight of solids in water. In this exemplary embodiment, the suspension is now floated in a flotation cell, for example, a conventional mechanical flotation cell, according to step (f). In this case, the pH is advantageously adjusted and maintained in the range of 9-10. Furthermore, 800-5400 g of kerosene per ton of solids in suspension, here black mass in suspension, and 100-1000 g of MIBC (4-methyl-2-pentanol) per ton of solids in suspension are added for flotation. Air for flotation is supplied, for example, at a flow rate of 0.8-5 l / min (l / min) per liter of cell volume or suspension.

[0094] Table 4 shows the graphite concentrate obtained after flotation, which was subjected to an additional acid leaching step before flotation to further increase the selectivity of graphite. In this way, a concentration of more than 90 wt. % of graphite in the flotation concentrate can be achieved, with 73% of the graphite recovered. Table 4: TIFF2026507278000005.tif58169

[0095] The graphite concentration obtained in the two aforementioned exemplary embodiments by skimming off after flotation can be further increased in a further advantageous exemplary embodiment, for which purpose one of the aforementioned flotation processes is repeated on the skimmed concentrate from the flotation according to step (f).

[0096] For example, a further flotation process may be carried out using the concentrate from the flotation that has been subjected to an acid leaching step during the process, e.g., using the same parameters as the refinement flotation (see Table 4). The results of this repeated flotation are shown in Table 5. Table 5: TIFF2026507278000006.tif44169

[0097] The concentration of recovered graphite reached over 96 wt%, where the graphite was of sufficient purity for reuse. Furthermore, Figure 4 shows the MLA of the concentrate from repeated flotation, with a free graphite fraction of 97.4%. This reflects the importance of free graphite throughout the steps of the proposed method.

[0098] In a further possible exemplary embodiment, the flotation residue from step (f) according to one of the two exemplary embodiments described, i.e. with or without an acid leaching step, and / or the flotation residue from the repeated flotation, which may also be referred to as refinement flotation, may be subjected to a residue flotation, the concentrate of which may be returned to step (f). Furthermore, in an advantageous exemplary embodiment, the flotation residue of the refinement flotation may be returned directly to step (f).

Claims

1. 1. A method for recovering graphite from black mass, characterized in that it comprises the following steps in the following order: step (a): providing a black mass comprising graphite; - step (b): adding water to the black mass to form a suspension of the black mass in water; - step (c): introducing ozone as an oxidizing agent into said suspension while stirring said suspension of black mass with water; - step (f): flotation of said suspension and skimming off the graphite.

2. 2. The method according to claim 1, characterized in that in step (f), when flotation is carried out, the pH value is in the range of 9 to 10.

3. 3. The method according to claim 1 or 2, characterized in that in step (f), when flotation is carried out, 800 to 5400 g of kerosene per ton of black mass and / or 100 to 1000 g of MIBC (4-methyl-2-pentanol) per ton of black mass are added as additives.

4. 4. The method according to claim 1, wherein in step (d), the suspension from step (c) is filtered and a filtrate is separated, the filtrate containing LiOH dissolved in water and the Li-depleted residue containing black mass including graphite.

5. The suspension after step (b) and before step (c), and / or After step (c) and before step (f), it is leached in an acidic leaching step (h), in which at least one acid, preferably sulfuric acid (H ２ SO ４ 5. The method according to claim 1, wherein a recycled acid is added to reduce the pH to below pH 3.

6. - in the acidic leaching step (h), a reducing agent, preferably sulfur dioxide (SO ２ 6. The method according to claim 5, characterized in that:

7. - adding to said suspension from step (h) a calcium source, preferably calcium hydroxide (Ca(OH) ２ ) and / or calcium oxide (CaO) and / or calcium carbonate (CaCO ３ 7. The method according to claim 5 or 6, characterized in that:

8. 8. The method according to any one of claims 1 to 7, characterized in that in step (i) the suspension from step (h) is filtered.

9. - in step (c), the suspension is heated for 11,000 s in the suspension －１ 9. The method according to claim 1, wherein the mixture is stirred at a shear rate of more than 100 rpm.

10. - in step (c), the suspension is heated for 25,000 s in the suspension －１ 10. The method according to claim 1, wherein the mixture is stirred at a shear rate of more than 100 rpm.

11. A method according to any one of claims 1 to 10, characterized in that step (c) is carried out for at least 3 hours.

12. In step (c), ozone is added in an amount of at least 0.1 grams (O ３ ) / hour / gram (black mass), and / or 2 grams (O ３ 12. The method according to claim 1, wherein the sieving agent is added to the suspension at a maximum rate of 1000 kJ / hour / gram (black mass).

13. 13. The method according to any one of claims 1 to 12, characterized in that in step (c), the temperature of the suspension is above 69°C.

14. 14. A method according to any one of claims 1 to 13, characterized in that in step (c), the suspension of the black mass in water comprises a pH value ranging from 6 to 8.

15. 14. The method according to any one of claims 1 to 13, characterized in that it comprises the step of adding an acid to the suspension in step (b) and / or step (c) to reduce the pH value of the suspension to a pH value in the range of from 3 to 4.5, preferably from 3 to 4.

16. - adding a caustic agent after step (c); 16. The method according to claim 15, characterized in that it comprises a step of increasing the pH value of the suspension before step (d) or of increasing the pH value of the filtrate from step (d) to a pH value higher than 6.

17. 17. A method according to any one of claims 1 to 16, characterized in that it comprises suspending the skimmed flotation concentrate with graphite from step (f) in water and carrying out a refinement flotation of the suspension and skimming off of the graphite.

18. 18. The method according to any one of claims 1 to 17, characterized in that the flotation residue from the flotation in step (f) is fed to a residue flotation.

19. - A method according to claim 17 or claim 18 when dependent on claim 17, characterized in that the flotation concentrate with graphite from the residual flotation and / or the flotation residue from the refinery flotation are recycled to step (f).

20. Equipment for carrying out the method according to any one of claims 1 to 19.

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