Process and plant for the recovery of graphite from black mass

Description

[0001] The invention relates to a process for recovering graphite from black mass.

[0002] Global battery production is experiencing very high growth rates. The demand for the resources required for production, namely raw materials such as lithium, graphite, and metals such as nickel, cobalt, and manganese, will increase accordingly. The required raw materials are mainly obtained from primary sources, but the proportion of secondary sources from recycling will increase in the future. Such secondary sources are processed into a so-called black mass, which is a mixture of lithium-ion battery scrap and / or scrap from battery production processes, which is processed into a fine powder. The black mass typically contains a mixture of active anode and / or cathode materials from batteries. It may also contain plastics and / or electrical conductors such as copper and / or aluminum. Organic binders and electrolytes may also be present.The typical black color of the black mass can be attributed to carbon, especially graphite or carbon black, which is often used in active anode materials of ion batteries.

[0003] The graphite content in the black mass is often only around 15 to 20 percent by weight, but with advantageous starting materials the proportion can be 20 to 40 percent by weight, so that recycling of the graphite is often not considered. Instead, the graphite from the black mass is usually incinerated. The growing demand for graphite and the undesirable COx emissions during combustion are increasingly favoring the recycling of graphite from black mass. However, the purity requirements for graphite for use in battery cells are very high, which also places very high demands on recycling processes. The problem here is that conventional processing techniques for extracting and purifying graphite from natural sources, such as flotation, are very inefficient with black mass and therefore prevent its use.

[0004] US 2023 / 0038978 A1 discloses a process for recycling lithium iron phosphate batteries. An oxidizing agent is added to a recycling stream to produce a lye solution. A residue of the lye solution containing lithium is separated by filtering. The lithium is then precipitated.

[0005] Furthermore, US 2022 / 0320619 A1 discloses a process for recycling lithium batteries, wherein concentrated sulfuric acid is used at a temperature of at least 100°C, and wherein at least one metallic component is obtained by wet chemical extraction.

[0006] EP 3 535 803 A1 discloses a process for recovering materials from Li-ion batteries. The process involves processing the batteries into a crushed feed stream and then, through a series of separation, isolation, and / or leaching steps, enables the recovery of a copper, cobalt, nickel, manganese, and / or graphite product, as well as a lithium product.

[0007] It is therefore the object of the invention to provide a cost-effective process for the recovery of graphite from black mass, which enables efficient recovery with high purity.

[0008] The invention solves this problem with the features of the independent claims.

[0009] A process for the recovery of graphite from black mass is proposed, which comprises the following steps in the following order: Step (a): Providing a black mass containing graphite; Step (b): Adding water to the black mass and preparing a suspension of the black mass in water; Step (c): Dosing ozone as an oxidizing agent into the suspension and simultaneously stirring the suspension of black mass with water, preferably at a shear rate greater than 11000s -1< ; Step (f): Flotation of the suspension and skimming off graphite.

[0010] Surprisingly, the proposed process steps have been shown to achieve a pretreatment of the black mass, enabling the separation of graphite from the black mass by flotation. Purities similar to those achieved from primary graphite sources can be achieved.

[0011] With the proposed process, graphite concentrations of more than 90% can be achieved with a yield of more than 70% from the black mass. For example, a carbon content of 91.5% can be achieved with a yield of 73%. In this way, the graphite from the black mass can be recovered very selectively, allowing the graphite to be put to further economic use and avoiding combustion. Furthermore, the recovery of other components from the black mass can be improved through the selective removal of carbon, especially graphite. The proposed process thus enables a very economical recovery of graphite from black mass.

[0012] Black mass, as defined in the present invention, is material from discarded batteries, e.g., lithium-ion batteries, and / or discarded parts thereof, and / or discarded materials from battery production processes, such as anode materials. The black mass contains a proportion of graphite, which is typically used in the anode of a battery. The above-mentioned starting materials are mechanically processed into a powdery material, which is then referred to as black mass and has a high surface-to-mass ratio.

[0013] Black mass therefore contains, within the meaning of this application, at least graphite and thus the element carbon (C) and, as a rule, several or all of the following elements: lithium (Li), cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), aluminum (Al), phosphorus (P), fluorine (F).

[0014] Depending on the starting material of the black mass, the proportions of graphite or other metals to be recovered in a recycling process can vary greatly. Different battery chemistries, known as NMC, NCA, LFP, for example, can lead to different proportions or the absence of valuable metals, e.g. Co, Ni or Mn. Different components with other elements in different compositions are possible. However, the black mass within the meaning of the invention always contains the element C in the form of graphite if black mass is provided in step (a). Frequently, the black mass also comprises Li, which can, for example, be chemically bound in the active cathode material and / or be metallic Li, particularly in / around the active anode material, which has a high graphite content.

[0015] With regard to step (b), it is further proposed that the black mass be suspended in water with a mass in the range of 10 g to 300 g, preferably in the range of 10 g to 250 g, more preferably in the range of 100 g to 200 g, per 1 l of water. For example, 200 g of black mass are suspended in 1 l of water.

[0016] In step (c) of the proposed process, ozone is dosed into the suspension as an oxidizing agent while the suspension is stirred. Preferably, ozone is dissolved in the water of the suspension. Thus, the black mass, or at least parts of the black mass, are oxidized with ozone. Ozone (O3) is known to be a strong oxidizing agent. However, the use of ozone as an oxidizing agent is associated with some disadvantages, as ozone is unstable towards dioxygen and decomposes rapidly. The half-life of ozone decreases further when dissolved in water, and it decreases even further with increasing temperature, which leads to very low process efficiency and may even prevent the ozone from reacting as intended when dissolved in water at high temperatures. The solubility of ozone in water is very low.

[0017] It has been shown that by stirring a black mass suspension in water, mass transfer can be increased to such an extent that the ozone can react with the black mass particles, especially with the surface of the black mass particles, in the suspension before the ozone decomposes. The effective use of ozone begins at high stirring speeds and becomes even more effective at further increased stirring speeds, allowing very high oxidation potentials (>850 mV) to be generated.

[0018] Therefore, it is proposed that the suspension be stirred vigorously or at high stirring speeds while ozone is dosed into the suspension as an oxidizing agent. Preferably, an oxidation / reduction potential (ORP) of >850 mV is generated in step (c) by dosing ozone into the suspension while the suspension is stirred. The ORP can be further increased to >1200 mV by very vigorous stirring during step (c). Ozone, as a strong oxidizing agent with a redox potential of >850 mV, oxidizes Co and Mn, for example, and does not require these to already be in the Co(III) and Mn(IV) state for recovery, so that black masses with different mineralogy and pretreatment can be successfully processed.

[0019] It is further proposed that a turbulent flow is generated in the suspension by stirring the suspension during step (c).

[0020] Preferably, the intensive stirring or stirring at high stirring speeds is above a 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 beginning of step (c).

[0021] According to a further development, it is proposed that in step (c) the suspension is stirred at a shear rate of greater than 11000s -1< , preferably greater than 25000s -1< , more preferably greater than 27000s -1< , more preferably greater than 29000s -1< , for example 30000s -1< .

[0022] A high shear rate, particularly above 11000s -1< , for example 12000s -1< , preferably above 29000s -1< , increases mass transfer sufficiently to allow ozone to react with the black mass before it decomposes. At a shear rate above 11000s -1< , for example 12000s -1< , a sufficiently high ORP can be achieved to leach the water and black mass suspension with ozone, although even higher shear rates can lead to an even higher ORP. At a shear rate greater than 25000s -1<, for example, an ORP of >850 mV can be achieved, while even higher shear rates can lead to an even higher ORP, e.g. >1200 mV.

[0023] For example, a shear rate in a fluid between two parallel plates can be determined by the relative velocity of the two plates divided by the separation between the plates.

[0024] This pretreatment enables graphite to be separated from the black mass by flotation, preferably by froth flotation. This is based on the varying hydrophobicity of the substances in the black mass, with different tendencies to cling 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 black mass through the proposed pretreatment, which frees the graphite particles in the black mass, as can also be seen, for example, in a Mineral Liberation Analysis (MLA).In the black mass, the graphite is largely present in composite particles due to its processing into an anode material, its use in a battery and its processing into a black mass, which, unlike graphite from natural sources, are not accessible to flotation.

[0025] The proposed process steps are generally carried out in alphabetical order within the scope of this application, unless the order is described otherwise, whereby individual process steps may be omitted according to the alphabetical order or may represent advantageous further developments.

[0026] In possible embodiments, the prepared black mass contains lithium in step (a). If Li is present in the black mass, step (c) allows lithium to be dissolved while the other components of the black mass remain as solids or are reprecipitated. Accordingly, the suspension of water and black mass can be leached with ozone, particularly in a neutral leaching process, whereby very high selectivity for Li can be achieved.

[0027] Preferably, in a step (d), the suspension from step (c) is filtered and the filtrate is separated, wherein the filtrate contains LiOH dissolved in water, and the Li-depleted residue contains black mass with graphite.

[0028] By filtering in step (d), a complete hydrometallurgical removal of Li can thus be carried out at the beginning of the recovery process, whereby the removal of Li can be carried out in parallel with the pretreatment of the black mass.

[0029] The proposed process exhibits very high selectivity for Li with very low levels of components other than LiOH dissolved in water. The leaching is extremely selective for Ni, Co, and Mn, down to below detectability, which are typically present in spent lithium-ion battery material and thus in the black mass. The high selectivity for Li can also be achieved for a wide range of black mass mineralogies and pretreatments. Furthermore, the proposed process also enables high extraction rates of Li >90%. Therefore, the process is very efficient and is preferably carried out as a batch process. Recirculation is possible and highly advantageous due to the high selectivity, as described below. In particular, contamination of the recovered lithium with alkali elements, especially Na and / or K, can be avoided.

[0030] The lithium is extracted from the lithium-depleted black mass residue in the form of solids and / or sludge at an early stage of the recovery process. Extraction at the beginning of the process allows the residue, which contains valuable elements such as Ni, Co, and Mn in addition to graphite, to be processed independently using other processing options. Furthermore, lithium losses to other products and intermediates due to low washing efficiency or co-precipitation are reduced.

[0031] In a preferred embodiment, in a step (e) with the residue from step (d) with the addition of water and / or recycled filtrate from step (d) whose Li content has been reduced, a suspension of black mass in water containing graphite is again prepared.

[0032] This is preferably followed by step (f) with flotation, whereby in possible embodiments step (h) with acid leaching can be carried out in between, which will be described below.

[0033] The suspension is floated in a flotation cell, for example, 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 the flotation concentrate and can be skimmed off accordingly.

[0034] According to a further development, it is proposed that the suspension after step (b) and before step (c), and / or after step (c) and before step (f) in an acid leaching step (h), wherein at least one acid, preferably sulfuric acid (H 2 SO 4 ), and / or recirculated acid is added and the pH is reduced below pH 3.

[0035] Before step (c), after step (c) and before step (f), the suspension contains graphite suspended in water with the black mass. After step (f), the graphite and / or carbon is removed from the suspension except for possible residues.

[0036] It is particularly advantageous to carry out the acid leaching step (h) after step (d) or (e). It is also particularly advantageous if at least one acid is added to the residue from the filtration of step (d) in the acid leaching step (h), i.e., after step (c) and before the flotation according to step (f). Preferably, 200 to 400 g of solids per liter are present in the acid leaching step (h).

[0037] In a possible embodiment, the acid leaching step (h) can be carried out before step (c), which may be advantageous for black mass without lithium, for example from the recycling of Na-ion batteries, since possible process steps for separating lithium before the acid leaching do not offer any advantage in such a situation.

[0038] The acid leaching step (h) is preferably initiated at a pH of 2 or less. Furthermore, in advantageous embodiments, the acid leaching step (h) is terminated at a pH in the range of 3 to 5.

[0039] By acid leaching in step (h), metals such as Ni, Co and Mn can be dissolved, whereas Cu and / or Al are present as solids.

[0040] According to a further development, it is proposed that a reducing agent, preferably sulfur dioxide (SO 2 ), be added to the acid leaching step (h). This improves the effectiveness of the acid leaching in step (h).

[0041] It is further proposed that a calcium source, preferably calcium hydroxide (Ca(OH) 2 ) and / or calcium oxide (CaO) and / or calcium carbonate (CaCO 3 ), be added to the suspension from step (h). This can, for example, precipitate F.

[0042] Preferably, in a step (i) suspension from the acid leaching step (h) is filtered.

[0043] This allows graphite and, for example, Cu, Al and F to be separated from the residue, while, for example, Ni, Co and / or Mn from the acid leaching step (h) remain in solution.

[0044] The residue containing the graphite can then be brought back into a suspension with water, for example with 5 to 10% solids content, and fed to the flotation step (f).

[0045] According to an advantageous embodiment, it is proposed that step (c) is carried out for at least 3 hours, preferably at least 3.5 hours, for example 4 hours.

[0046] The concentration of Li dissolved in the water of the suspension increases over time up to the maximum extraction rate, which can be achieved, for example, within 4 hours. Furthermore, the oxidation of Co and Mn also depends on the reaction time, with a longer reaction time allowing complete recovery from the solution, e.g., after 3 hours for Mn and after 4 hours for Co. The Co and Mo oxides are thus precipitated after they have been dissolved in the solution. Therefore, carrying out step (c) for the above-mentioned duration enables a very high selectivity of the extraction process. This appropriate duration leads to good pretreatment of the black mass, so that good separation of graphite can be achieved by flotation.

[0047] In a preferred embodiment, in step (c) ozone is dosed into the suspension at a rate of at least 0.1 gram (O 3 ) / hour / gram (black mass), for example 1 gram (O 3 ) / hour / gram (black mass), and / or at a maximum rate of 2 grams (O 3 ) / hour / gram (black mass).

[0048] Accordingly, the mass flow of ozone per hour also depends on the mass of the black mass provided in the suspension. To provide ozone at the same rate of, for example, 1.5 grams (O 3 ) / hour / gram (black mass), the mass flow of ozone must be doubled if the black mass provided is doubled.

[0049] There is a lower limit for the dosage of ozone into the suspension to achieve a sufficient effect of pretreatment of the black mass, while an upper limit is mainly for economic reasons, since the proposed stirring sufficiently increases the effectiveness of the supplied ozone.

[0050] 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.

[0051] A temperature of 70°C or higher enables high lithium extraction rates of more than 90%, which can be increased to more than 95% at 90°C. Therefore, the suspension is preferably heated. Furthermore, this allows for good pretreatment of the graphite for flotation.

[0052] In a further development, it is proposed that an acid, preferably sulfuric acid (H 2 SO 4 ), is added to the suspension in step (b) and / or step (c) and the pH of the suspension is lowered to a pH in the range of 3 to 4.5, preferably 3 to 4. Step (c) is preferably terminated at a pH of 9.

[0053] A pH value below 4.5 increases the Li extraction rate even further compared to a process embodiment without lowering the pH, resulting in Li extraction rates above 90%, with Li extraction rates even above 95% possible. At the same time, improved pretreatment for liberating the graphite in the black mass is achieved. A pH value below 3 leads to an excessive loss of Li selectivity.

[0054] While Co and Mn can be completely recovered with the reaction time suggested above, e.g., 4 hours, lowering the pH to the range of 3.5 to 4.5 has the side effect that Ni extraction increases along with Li extraction at longer times. Thus, the Li extraction rate is increased to a very high value, but Ni is also dissolved.

[0055] The acid is preferably sulfuric acid (H 2 SO 4 ), which can have a further beneficial effect on the metal recovery process, e.g., for the crystallization of Ni sulfate. However, depending on the desired end products of the metal recovery process, other acids may also be suitable.

[0056] In an alternative embodiment, it is proposed that in step (c) the suspension of the black mass in water has a pH in the range of 6 to 8, preferably in the range of 7 to 8, e.g. a pH of 8.

[0057] The extraction of Li in step (c) can, in an advantageous embodiment, be carried out in a neutral leaching without any pH adjustment, wherein the effect of ozone is disregarded, which simplifies the process and is therefore cost-effective. If ozone is dosed into the suspension as an oxidizing agent and the suspension is stirred, preferably with a shear rate >11000s -1<, the suspension preferably has a pH in the range of 6 to 8, in particular in the range of 7 to 8, which enables extraction rates of approximately over 70% for Li. In addition, the proposed pH range, in particular a pH of 7 to 8, has the advantageous effect that Co, Mn and in particular Ni are precipitated or extracted from the solution.is not dissolved, resulting in a very high selectivity of Li extraction as LiOH in water from black mass, while still achieving good extraction rates for Li and at the same time achieving good liberation of the graphite in the black mass.

[0058] Accordingly, the Li-containing filtrate from step (d) may also have a pH in the range of 6 to 8, in particular 7 to 8, which enables cost-effective further processing of the filtrate.

[0059] 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 and the pH of the suspension before step (d) or the pH of the filtrate from step (d) is raised to a pH above 6, for example 9, preferably to a pH above 9, more preferably to a pH above 10.

[0060] In particular, a pH value above 9, for example 10, preferably a pH value above 10, enables the complete precipitation of Ni(II) as hydroxide from the Li-containing liquor. This is particularly advantageous when the pH of the suspension has been lowered with an acid to below or equal to 6, or in particular to below or equal to 4.5, in order to maximize the Li extraction rate. In this way, the side effect of dissolved Ni can be reversed, leading to a very high extraction rate of Li dissolved in water of over 90%, e.g., 95%, while at the same time achieving a very high selectivity or purity of the dissolved Li.

[0061] Raising the pH of the suspension or filtrate with a base is preferably carried out at a temperature of 25°C to 70°C.

[0062] Preferably, the pH value is adjusted to pH > 9, e.g. pH = 10, more preferably to pH > 10 before filtration of the suspension.

[0063] Accordingly, the filtrate contains Li, dissolved in water as LiOH, with very high purity. The 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.

[0064] In addition, 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 is achieved in the filtrate.

[0065] Adjusting the pH with Na-containing bases, especially sodium hydroxide, leaves F and P in solution, allowing for the separation of F from the residue and further processing of the residue. This can advantageously prevent the accumulation of HF in other downstream processes, e.g., in black acid. The amount of Na required to adjust the pH to the values ​​described above is well below the solubility limit and does not lead to Na contamination of the Li product.

[0066] As a result, the filtrate produced by the proposed process, which contains high-purity LiOH dissolved in water, and the Li-depleted residue or the residue with a greatly reduced Li content, can be independently processed to the desired final product form of the metals recovered from the black mass. This allows for the high selectivity and extraction rate for Li of the proposed process.

[0067] In particularly advantageous embodiments, the flotation according to step (f) is carried out after a filtering, for example according to step (d) and / or step (i), on a suspension prepared with the residue of this filtering, which suspension preferably has 5 to 10% solids in water.

[0068] The flotation according to step (f) is preferably carried out with a supply of air, which is further preferably supplied at a rate of 0.8 to 5 l / min per l of floated suspension.

[0069] In a preferred embodiment, in step (f) during flotation, the pH value is in a range of 9 to 10.

[0070] Preferably, 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 during the flotation in step (f).

[0071] In a particularly advantageous embodiment, the skimmed flotation concentrate is suspended in water with graphite from step (f), and a purification flotation of the suspension and skimming of graphite are carried out.

[0072] With the proposed repeated flotation in the purification flotation process after appropriate pretreatment of the black mass, which demonstrates a high degree of liberation of graphite in the powdered black mass, a graphite concentration of more than 96% can be achieved in the repeated flotation concentration with a recovery rate of more than 90%. Overall, the entire process for recovering graphite from black mass can achieve a recovery rate of more than 65% and a purity of over 96%, which is a very good result for the recovery of graphite from black mass. Therefore, the graphite recovered in this way can be reused as a high-quality product.

[0073] It is further proposed that the flotation residue from the flotation in step (f) be fed to a residual flotation unit. This allows additional liberated graphite to be recovered and the overall recovery rate to be further increased.

[0074] For this purpose, it is further proposed that the flotation concentrate with graphite from the residual flotation and / or the flotation residue from the purification flotation is recycled to step (f).

[0075] Furthermore, a system for carrying out a method according to one of claims 1 to 19 is proposed.

[0076] In the following, the invention is explained using preferred embodiments with reference to the drawings. Fig. 1 shows the distribution of black mass graphite particles across particle sizes and their availability for flotation in the prior art; Fig. 2 shows the distribution of black mass graphite particles across particle sizes and their availability for flotation after step (c); Fig. 3 shows the distribution of black mass graphite particles across particle sizes and their availability for flotation after steps (c) and (h); and Fig. 4 shows the distribution of black mass graphite particles across particle sizes and their availability for flotation after purification flotation.

[0077] The black mass is provided in step (a) as a graphite-containing feedstock. 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 feedstock or scrap materials.

[0078] Using an example of the composition of black mass, the effect of the proposed process for recovering graphite from black mass will be illustrated. Table 1 shows a possible composition of black mass containing graphite. The black mass was ground into a powdery mass, resulting in a high surface area-to-mass ratio. Table 1 shows the weight fractions of black mass for the listed elements. Table 1: element C Al Ca Co Cu Fe % by weight 31,1 4,4 0,30 16,0 5,6 0,72 element Li Mn Ni P F % by weight 4,4 6,9 9,6 0,70 2,7

[0079] The carbon content is correspondingly high at 31.1%, so that in principle a large proportion of graphite should be available for recovery.

[0080] First, a direct flotation of the present black mass according to the state of the art without the application of the proposed method will be presented. Figure 1shows the distribution of graphite particles from black mass across particle sizes and their availability for flotation by Mineral Liberation Analysis (MLA). Liberated graphite particles are symbolized by white bars and bound graphite particles by the black bar. MLA is used to quantitatively measure the extent to which the individual minerals, constituents, and elements of a fine solid or powder, here black mass, are assembled into whole particles. If individual minerals, constituents, and elements occur predominantly as individual particles, they are considered liberated or outsourced and can be recovered by physical separation methods (e.g., gravity / magnetic / flotation). If this is not the case, the minerals, constituents, and elements are present in composite particles with others and are considered bound.

[0081] As shown in the illustration of the Figure 1 recognizable, is only in particle size classes 5µ m to 15 µ m and 15 µ m to 30 µ m a measurable portion of the carbon is liberated. Therefore, only about 15% of the carbon is liberated in total, meaning that the majority of approximately 85% of the carbon, and thus of the graphite in the black mass, is bound in a composite particle. Accordingly, the efficiency of recovery by conventional flotation according to the state of the art is correspondingly low, as shown in Table 2. Table 2: element C Cu Al Li-Ni-Co-Mn Recovery rate in flotation concentrate / % 64,7 21,4 27,8 22,7 Flotation concentrate / wt.% 45,6 6,9 5,6 23,4

[0082] In a conventional flotation process, therefore, a significant proportion of the active cathode materials and lithium are entrained into the floated graphite, so that efficient separation and recovery of the graphite from black mass cannot be achieved using a conventional process.

[0083] In an advantageous embodiment, the exemplary black mass with a graphite content according to Table 1 is provided as a powder according to step (a) and first brought into a suspension with water with a concentration of 100 to 200 g solids per l water according to step (b).

[0084] In the following step (c), the suspension is mixed and stirred at a very high shear rate, in this advantageous embodiment, at a shear rate of 34,000 s -1 <. At the same time, ozone is added at a rate of, for example, 0.05 to 0.4 g of ozone per g of black mass per hour for several hours. The temperature of the suspension is maintained at more than 80°C during stirring and the simultaneous addition of ozone. Furthermore, the pH is adjusted and maintained between 3 and 4. This step is continued for several hours.

[0085] In this advantageous embodiment, the pH value is additionally increased significantly at the end of this step, for example to a pH value of 9, in order to selectively leach Li from the black mass.

[0086] The suspension from step (c) is then filtered in a step (d) and the residue contains the Li-depleted residue black mass with graphite, while the filtrate contains LiOH dissolved in water.

[0087] Figure 2 shows a further Mineral Liberation Analysis (MLA) of the residue of black mass with graphite after step (c) was carried out. The proportion of liberated graphite, see white bars, could be compared to the starting material, see Figure 1 can be significantly increased, so that a total of 42.8% of the graphite is released and only 57.2% of the graphite is bound.

[0088] The residue containing the pretreated black mass with graphite is then brought back into a suspension with 5 to 10 wt.% solids in water, according to step (e).

[0089] The suspension is then floated in a flotation cell, for example, a conventional mechanical flotation cell, according to step (f). The pH is advantageously adjusted and maintained between 9 and 10. For the flotation, 800 to 5400 g of kerosene per ton of solids, in this case the black mass in the suspension, and 100 to 1000 g of MIBC (4-methyl-2-pentanol) per ton of solids in the suspension are also added. Air is supplied to the flotation process, for example, at a flow rate of 0.8 to 5 l / min per liter of cell volume or suspension.

[0090] Table 3 shows the resulting graphite concentrate after flotation with the proposed pretreatment, where a significantly increased selectivity for graphite can be achieved. A graphite content of over 80 wt.% can be achieved in the flotation concentrate, with the graphite recovery rate in the skimmed flotation concentrate exceeding 65%. Table 3: Element / wt.% C Cu Al Li-Ni-Co-Mn Recovery rate in flotation concentrate / % 66,2 24,5 20,2 3,73 Flotation concentrate / wt.% 83,5 3,0 0, 9 6,1

[0091] In an alternative embodiment, after stirring and the parallel addition of ozone according to the procedure described above and subsequent filtration according to step (d), the residue of the filtration before flotation is first fed to an acidic leaching step (h).

[0092] The Li-depleted residue of the black mass with graphite is then brought back into a suspension in water, whereby the suspension is advantageously adjusted to 100 to 200 g solid / l.

[0093] The suspension is then leached at a pH of 1 to 2, which can be achieved, for example, by adding sulfuric acid. The temperature is adjusted to more than 60°C, for example, 70°C, by heating the vessel. At the same time, sulfur dioxide (SO 2 ) is added while stirring. This process is continued for several hours, for example, 2, 3, or 4, terminating at a pH in the range of 3 to 5.

[0094] Figure 3 shows in a MLA that the proposed process can release even more carbon across all particle size ranges, so that, for example, 54% of the carbon can be made accessible to physical separation.

[0095] The suspension is then filtered and the solid residue is returned to a suspension containing 5 to 10 wt.% solids in water. In this embodiment, the suspension is then floated in a flotation cell, for example a conventional mechanical flotation cell, in accordance with step (f). The pH is advantageously set and maintained in a range between 9 and 10. For the flotation, 800 to 5400 g of kerosene per t of solids, here black mass in the suspension, and 100 to 1000 g of MIBC (4-methyl-2-pentanol) per t of solids in the suspension are also added. Air is supplied to the flotation, for example, at a flow rate of 0.8 to 5 l / min per liter of cell volume or suspension.

[0096] Table 4 shows the resulting graphite concentrate after flotation, which was subjected to an additional acid leaching step prior to flotation, allowing for further increased graphite selectivity. A graphite concentration of over 90 wt.% can be achieved in the flotation concentrate, with 73% of the graphite being recovered. Table 4: Element / wt.% C Cu Al Li-Ni-Co-Mn Recovery rate in flotation concentrate / % 73 10,2 9, 1 7,4 Flotation concentrate / wt.% 91,5 0,77 1 0,32

[0097] The graphite concentrations obtained in the two previously described embodiments can be further increased by skimming after flotation in another advantageous embodiment. For this purpose, one of the previously described flotation processes is repeatedly performed on the skimmed concentrate from the flotation according to step (f).

[0098] For example, a further flotation process can be carried out using the flotation concentrate, which has undergone an acid leaching step during the process (see Table 4), as a purification flotation with, for example, the same parameters. The result of this repeated flotation is shown in Table 5. Table 5: Element / wt.% C Cu Al Li-Ni-Co-Mn Source material 91 68 64 62 Flotation concentrate 96,4 0,2 0,8 0,26

[0099] The concentration of the recovered graphite reaches over 96% by weight, which means that the graphite has sufficient purity for reuse. Furthermore, Figure 4 an MLA for the concentrate from repeated flotation, with the liberated graphite content at 97.4%. This reflects the importance of the liberated graphite through the proposed process steps.

[0100] In another possible embodiment, the flotation residues from step (f) can be fed to a residual flotation according to one of the two embodiments described above, i.e., with or without an acid leaching step, and / or from a repeated flotation, which can also be referred to as purification flotation, whose concentrate can be recycled to step (f). Furthermore, in an advantageous embodiment, the flotation residue from the purification flotation can be recycled directly to step (f).

Claims

1. Process for the recovery of graphite from black mass, characterized by the following steps in the following order: - step (a): providing a black mass containing graphite; - step (b): adding water to the black mass and creating a suspension of the black mass in water; - step (c): dosing ozone as an oxidizing agent to the suspension and simultaneously stirring the suspension of black mass with water; - step (f): flotation of the suspension and skimming off graphite.

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

4. Process according to any one of the preceding claims, characterized in that - in a step (d) the suspension from step (c) is filtered and the filtrate is separated, wherein the filtrate contains LiOH dissolved in water and the residue depleted in Li contains black mass with graphite, wherein in a step (e) the residue from step (d) with the addition of water and / or recycled filtrate from step (d), the Li content of which has been reduced, is again processed to form a suspension of black mass in water, which contains graphite.

5. Process according to any one of the preceding claims, characterized in that the suspension - after step (b) and before step (c), and / or - with reference to claim 4 after step (e) and before step (f) is leached in an acidic leaching step (h), wherein at least one acid, preferably sulfuric acid (H2SO4), and / or recirculated acid is added and the pH value is reduced to below pH 3.

6. Process according to claim 5, characterized by - adding a reducing agent, preferably sulfur dioxide (SO2), to the acidic leaching step (h).

7. Process according to claim 5 or 6, characterized by - adding 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).

8. Process according to any one of the preceding claims, characterized in that in a step (i) the suspension from step (h) is filtered.

9. Process according to any one of the preceding claims, characterized in that - in step (c) the suspension is stirred with a shear rate of greater than 11,000 s-1 in the suspension.

10. Process according to any one of the preceding claims, characterized in that - in step (c) the suspension is stirred at a shear rate of greater than 25,000 s-1 in the suspension.

11. Process according to any one of the preceding claims, characterized in that - step (c) is carried out for at least 3 hours.

12. Process according to any one of the preceding claims, characterized in that - in step (c), ozone is dosed into the suspension at a rate of at least 0.1 gram (O3) / hour / gram (black mass) and / or at a maximum rate of 2 grams (O3) / hour / gram (black mass) .

13. Process according to any one of the preceding claims, characterized in that - in step (c), the temperature of the suspension is above 69°C.

14. Process according to any one of the preceding claims, characterized in that - in step (c), the suspension of the black mass in water comprises a pH value in the range from 6 to 8.

15. Process according to any one of claims 1 to 13, characterized by the step of: - adding an acid to the suspension in step (b) and / or step (c) and lowering the pH value of the suspension to a pH value in the range of 3 to 4.5, preferably 3 to 4.

16. Process according to claim 15, characterized by the step of - adding a caustic after step (c); and - raising the pH value of the suspension before step (d) or raising the pH value of the filtrate from step (d) to a pH value higher than 6.

17. Process according to any preceding claim, characterized in that - the skimmed flotation concentrate with graphite from step (f) is suspended in water and a purification flotation of the suspension and a skimming of graphite is carried out.

18. Process according to any one of the preceding claims, characterized in that - the flotation residue from the flotation in step (f) is fed to a residual flotation.

19. Process according to claim 17 or 18 with reference to claim 17, characterized in that - the flotation concentrate with graphite from the residual flotation and / or the flotation residue from the purification flotation is recycled to step (f).