Method for precipitating impurities

Abstract

According to an example aspect, there is provided a method for precipitating impurities from a black mass leachate, comprising steps of: 1a) providing a black mass leachate comprising at least one of nickel, cobalt and lithium, and impurities; 1b) mixing an aluminum sulfate solution with the black mass leachate to produce a first aluminum sulfate mixture; 1c) adding a lithium hydroxide solution to the first aluminum sulfate mixture, to produce a first aluminum hydroxide mixture; 1d) filtrating the first aluminum hydroxide mixture, to produce a first filter cake comprising impurities and a first process solution; 2a) mixing an aluminum sulfate solution with the first process solution, to produce a second aluminum sulfate mixture; 2b) adding a lithium hydroxide solution to the second aluminum sulfate mixture, to produce a second aluminum hydroxide mixture; 2c) filtrating the second aluminum hydroxide mixture, to produce a precipitate slurry comprising residual impurities and a sulfate solution.

Description

METHOD FOR PRECIPITATING IMPURITIESFIELD

[0001] The present invention relates to a method for precipitating impurities from a black mass leachate, particularly to a two-stage precipitation process for fluoride control in a black mass recycling.BACKGROUND AND OBJECTS

[0002] As both customer demand and technology readiness for electric appliances and vehicles increase, lithium-ion batteries (LIBs) are becoming more important to fill the role for mobile energy storage. While invented in 1985, recent developments to increase energy density and production costs have seen a large increase in demand for LIBs. The current most common LIB types for electric mobility are based on nickel, cobalt and manganese (NCM) or nickel, cobalt and aluminum (NCA) as cathode materials and graphite as anode material. Even though effective, the current price for virgin materials makes these technologies quite expensive to deploy while also causing significant greenhouse gas (GHG) emissions during mining and processing to battery grade chemicals. Therefore, in recent years, there has been a significant uptick in efforts to mitigate the prices and emissions caused by LIB production by recycling end-of-life batteries.

[0003] Routes for recycling are several, including pyro- and hydrometallurgical routes for metal recovery and separation. In hydrometallurgical routes, a mixture of electrode materials commonly referred to as black mass is often leached using a combination of an inorganic acid, e.g., sulfuric acid, and a reducing agent to dissolve the soluble elements after which the insoluble materials, e.g., graphite, can be separated by filtration. Metals are then separated from each other and / or purified using pH adjustments, or with liquid-liquid extraction technologies. Typically, impurities are removed prior to the separation of metals to achieve set targets or improved product quality. Fluoride is one of the key impurities present in black mass that requires strict control to not end up in final products.

[0004] In a one-stage precipitation, it is published fluoride levels below 50 ppm are close-to impossible to achieve, especially in pH areas in which valuable metals, e.g., nickel and cobalt, remain in solution. The precipitation may also lead to remarkable metal losses.In some applications, aluminium, fluoride and phosphate can be removed from the solution in the presence of added aluminium oxide. However, the fluoride precipitation may require employing a wide range of added chemicals in up to three stages.

[0005] An object of the present invention is to mitigate at least some of the above- mentioned problems. An object of the present invention is thus to develop an efficient and cost-effective method for removing impurities from a black mass.SUMMARY

[0006] According to a first aspect of the present disclosure, there is provided a method for precipitating impurities from a black mass leachate, comprising steps of: la) providing a black mass leachate comprising at least one of nickel, cobalt and lithium, and impurities; lb) mixing an aluminum sulfate solution with the black mass leachate to produce a first aluminum sulfate mixture; lc) adding a lithium hydroxide solution to the first aluminum sulfate mixture, to produce a first aluminum hydroxide mixture having pH of 4.3-4.7; ld) filtrating the first aluminum hydroxide mixture, to produce a first filter cake comprising impurities and a first process solution;2a) mixing an aluminum sulfate solution with the first process solution, to produce a second aluminum sulfate mixture;2b) adding a lithium hydroxide solution to the second aluminum sulfate mixture, to produce a second aluminum hydroxide mixture having pH of 4.5-4.9;2c) filtrating the second aluminum hydroxide mixture, to produce a precipitate slurry comprising residual impurities and a sulfate solution comprising at least one of the nickel, cobalt and lithium.

[0007] Significant benefits are gained with aid of the present method. The method enables efficient use of chemicals and ensures high product quality cost-effectively. The method enables producing the sulfate solution comprising less than 50 ppm of fluoride. The method is flexible towards impurity levels and hence a wider range of black masses can be refined in the process. In this method, impurities are precipitated in two stages, i.e., a first stage comprising the steps la)— 1 d) and a second stage comprising the steps 2a)-2c), instead of one stage. Net loss of valuable metals will remarkably decrease, which enables lower impurity levels in the final products. In the method, pH is adjusted with the lithium hydroxidesolution to the value that leaves the dissolved metals untouched in the solution and removes part of the impurities in the first stage. pH is adjusted with the lithium hydroxide solution in the following stages until the pH is adjusted to the value in which desired level of the impurities in the solution is achieved in the last stage. The method does not require use of aluminium oxide and a separate fluoride removal step. In the method, aluminum in the form of added aluminum sulfate is used to precipitate fluoride. Aluminum is employed because it is already present in the black mass, and is one of the few elements capable of precipitating fluoride in the pH area employed. In the method, the aluminum sulfate solution is fed into the second stage of precipitation to precipitate residual impurities, especially fluoride.

[0008] One or more embodiments may comprise one or more features from the following itemized list:- the method further comprises a step 3 a), wherein at least part of the precipitate slurry is circulated to the step la) and mixed with the black mass leachate- further comprising a step 3b) after the step 3a) instead of the steps lb) to 2c)- in the step 3b), a lithium hydroxide solution is added to the mixture of the black mass leachate and the precipitate slurry, to produce a third aluminum hydroxide mixture having pH of 4.3-4.7- further comprising a step 3c) after the step 3b) instead of the steps lb) to 2c)- in the step 3c), the third aluminum hydroxide mixture is filtrated, to produce a second filter cake comprising impurities and a second process solution- the impurities and the residual impurities are selected from a group of aluminum, fluoride and phosphorus- the mixing is conducted at a temperature of 75-85 °C, preferably 80 °C, in the step lb) and / or the step 2a)- in the step 1c), the lithium hydroxide solution is added to the first aluminum sulfate mixture at a pumping rate of 3.8-4.2 ml / min per liter of the first aluminum sulfate mixture until pH 2.8-3.2 is reached, and after that at a pumping rate of 1.8-2.2 ml / min per liter of the first aluminum sulfate mixture until pH 4.3-4.7 is reached- in the step 1c), lithium hydroxide solution is added every 25-35 minutes to the first aluminum hydroxide mixture to maintain the pH at 4.3-4.7- the first aluminum hydroxide mixture is mixed for at least 1.5 hours in the step 1c)- in the step 2b), the lithium hydroxide solution is added to the second aluminum sulfate mixture at a pumping rate of 1.8-2.2 ml / min per liter of the second aluminum sulfate mixture- in the step 2b), the lithium hydroxide solution is added every 25-35 minutes to the second aluminum hydroxide mixture to maintain the pH at 4.5-4.9- the second aluminum hydroxide mixture is mixed for at least 1.5 hours in the step 2b)- in the step 3b), the lithium hydroxide solution is added to the mixture of the black mass leachate and the precipitate slurry at a pumping rate of 3.8-4.2 ml / min per liter of the black mass leachate until pH 2.8-3.2 is reached, and after that at a pumping rate of 1.8-2.2 ml / min per liter of the black mass leachate until pH 4.3-4.7 is reached- the third aluminum hydroxide mixture is mixed for at least 1.5 hours in the step 3b)- in the step Id), the first process solution comprises less than 100 ppm, such as less than 90 ppm, of fluoride- in the step 2c), the sulfate solution comprises less than 50 ppm, such as less than 10 ppm, of fluoride- the lithium hydroxide solution is produced by dissolving solid lithium hydroxide monohydrate in water

[0009] According to a second aspect of the present disclosure, there is provided use of the method to produce a lithium sulfate solution suitable for electrodialysis.

[0010] According to an embodiment, the lithium sulfate solution comprises less than 50 ppm of fluoride.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIGURE 1 illustrates a first and a second stage of a method in accordance with at least some embodiments of the present invention; and

[0012] FIGURE 2 illustrates a first stage of a method using a precipitate slurry from a second stage in accordance with at least some embodiments of the present invention.DETAILED DESCRIPTIONDefinitions

[0013] In the present context, the term “black mass” refers to a mixture of cathode and / or anode active materials, which are separated from battery components. The black mass can be either from spent or fresh / unused Li-ion batteries processed using any number of mechanical routes and / or from off-specification cathode active material (CAM).

[0014] By “removing”, it is meant in this description that at least 90 wt-% of the desired elements or compounds, are removed, preferably at least 95 wt-%, more preferably at least 98 wt-%are removed.Embodiments

[0015] The present embodiments relate to higher-grade products produced from a black mass by a hydrometallurgical process. Especially, the present embodiments relate to a two-stage precipitation process for fluoride control in a black mass recycling.

[0016] According to an aspect, there is provided a method for precipitating impurities from a black mass leachate, comprising steps of: la) providing a black mass leachate comprising at least one of nickel, cobalt and lithium, and impurities; lb) mixing an aluminum sulfate solution with the black mass leachate to produce a first aluminum sulfate mixture; lc) adding a lithium hydroxide solution to the first aluminum sulfate mixture, to produce a first aluminum hydroxide mixture having pH of 4.3-4.7; ld) filtrating the first aluminum hydroxide mixture, to produce a first filter cake comprising impurities and a first process solution;2a) mixing an aluminum sulfate solution with the first process solution, to produce a second aluminum sulfate mixture;2b) adding a lithium hydroxide solution to the second aluminum sulfate mixture, to produce a second aluminum hydroxide mixture having pH of 4.5-4.9;2c) filtrating the second aluminum hydroxide mixture, to produce a precipitate slurry comprising residual impurities and a sulfate solution comprising at least one of the nickel, cobalt and lithium.

[0017] The method provides considerable advantages. The method enables efficient use of chemicals and ensures high product quality cost-effectively. The method enables producing the sulfate solution comprising less than 50 ppm of fluoride. The method is flexible towards impurity levels and hence a wider range of black masses can be refined in the process. In this method, impurities are precipitated in two stages, i.e., a first stage comprising the steps la)-ld) and a second stage comprising the steps 2a)-2c), instead of one stage. Net loss of valuable metals will remarkably decrease, which enables lower impurity levels in the final products. In the method, pH is adjusted with the lithium hydroxide solution to the value that leaves the dissolved metals untouched in the solution and removes part of the impurities in the first stage. pH is adjusted with the lithium hydroxide solution in the following stages until the pH is adjusted to the value in which desired level of the impurities in the solution is achieved in the last stage. The method does not require use of aluminium oxide and a separate fluoride removal step. In the method, aluminum in the form of added aluminum sulfate is used to precipitate fluoride. Aluminum is employed because it is already present in the black mass, and is one of the few elements capable of precipitating fluoride in the pH area employed. In the method, the aluminum sulfate solution is fed into the second stage of precipitation to precipitate residual impurities, especially fluoride.

[0018] The black mass leachate used in the step la) can be copper and manganese separated solution, i.e., copper and manganese can be removed from the black mass leachate before the black mass leachate is used in the step la).

[0019] In the step la), the nickel can be in a form of nickel sulfate, the cobalt can be in a form of cobalt sulfate and the lithium can be in a form of lithium sulfate.

[0020] The black mass leachate used in the step la) can be produced and copper can be separated from the black mass leachate by the processes disclosed in European Patent Application EP4245869A1. Therefore, the black mass leachate used in the step la) can be produced by leaching black mass using sulfuric acid and optionally a reducing agent, to produce a process solution comprising at least one of copper, manganese, nickel, cobalt and lithium, and impurities, which process solution can be separated from graphite by filtration. Copper can be separated from the process solution, for example, by an ion exchange process and manganese can be separated from the process solution, for example, by precipitating with persulfate, to produce the black mass leachate.

[0021] The step la) can further comprise heating the black mass leachate to a temperature of 79-81 °C, and optionally mixing with a mixing speed of 200-300 rpm.

[0022] The black mass leachate can comprise at least one of nickel, cobalt and lithium, depending on the black mass. For example, the black mass leachate can comprise:- lithium,- cobalt,- nickel,- nickel and cobalt,- cobalt and lithium,- nickel and lithium,- lithium and at least one of nickel and cobalt, or- nickel, cobalt and lithium.

[0023] The black mass leachate can comprise lithium, at least one of nickel and cobalt, and impurities.

[0024] The impurities and the residual impurities can be selected from a group of aluminum, fluoride and phosphorus.

[0025] The aluminum can be in in a form of aluminum sulfate, the fluoride can be in a form of hydrogen fluoride or fluorophosphate compound, and / or the phosphorus can be in a form of fluorophosphate compound.

[0026] The step lb) can further comprise providing the aluminum sulfate solution. The aluminum sulfate solution can be produced by mixing aluminum sulfate with water, preferably reserve osmosis (RO) water. The aluminum sulfate solution can be heated to a temperature of 79-81 °C to ensure homogeneity and high solubility before mixing the aluminum sulfate solution with the black mass leachate. Alternatively, the aluminum sulfate can be produced by dissolving aluminum hydroxide and / or oxide in sulfuric acid.

[0027] A molar ratio of aluminum to fluoride can be, for example, 2-3 in the step lb).

[0028] The mixing of the aluminum sulfate solution with the black mass leachate can be conducted at a temperature of 75-85 °C, preferably 80 °C, in the step lb).

[0029] In the step 1c), the lithium hydroxide solution can be added to the first aluminum sulfate mixture at a pumping rate of 3.8-4.2 ml / min per liter of the first aluminumsulfate mixture until pH 2.8-3.2 is reached, and after that at a pumping rate of 1.8-2.2 ml / min per liter of the first aluminum sulfate mixture until pH 4.3-4.7 is reached. Thus, the pH can be adjusted until the first aluminum sulfate mixture starts buffering. The lithium hydroxide solution is preferable added slowly to avoid formation of amorphous aluminum hydroxide.

[0030] In the step 1c), lithium hydroxide solution can be added every 25-35 minutes to the first aluminum hydroxide mixture to maintain the pH at 4.3-4.7.

[0031] The first aluminum hydroxide mixture can be mixed for at least 1.5 hours in the step 1c).

[0032] In the step Id), the first process solution can comprise less than 100 ppm, such as less than 90 ppm, of fluoride.

[0033] The step Id) can further comprise separating the first filter cake and the first process solution. The separation can be conducted by thickening, which is an economical method for separating solids.

[0034] The filter cake separated in the step Id) can be removed from the process, and hence serve as an outlet for precipitated impurities. The first solution process solution comprising the valuable metals, i.e., lithium, nickel and / or cobalt, can be guided to the second stage, wherein the valuable metals can be recovered.

[0035] The step 2a) can further comprise providing the aluminum sulfate solution. The aluminum sulfate solution can be produced by mixing aluminum sulfate with water, preferably reserve osmosis (RO) water. The aluminum sulfate solution can be heated to a temperature of 79-81 °C to ensure homogeneity before mixing the aluminum sulfate solution with the first process solution.

[0036] A molar ratio of aluminum to fluoride can be, for example, 70-75 in the step 2a).

[0037] The mixing of the aluminum sulfate solution with the first process solution can be conducted at a temperature of 75-85 °C, preferably 80 °C, in the step 2a).

[0038] In the step 2b), the lithium hydroxide solution can be added to the second aluminum sulfate mixture at a pumping rate of 1.8-2.2 ml / min per liter of the second aluminum sulfate mixture.

[0039] In the step 2b), the lithium hydroxide solution can be added every 25-35 minutes to the second aluminum hydroxide mixture to maintain the pH at 4.5-4.9.

[0040] The second aluminum hydroxide mixture can be mixed for at least 1.5 hours in the step 2b).

[0041] In the step 2c), the hydroxide solution can comprise less than 50 ppm, such as less than 10 ppm, of fluoride.

[0042] The step 2c) can further comprise separating the precipitate slurry and the sulfate solution. The separation can be conducted by thickening, which is an economical method for separating solids. Alternatively, a flocculant can be used to hasten the flocculation of the precipitate.

[0043] The step 2c) can further comprise separating the valuable metals, i.e., lithium, nickel and / or cobalt, from the sulfate solution. The valuable metals can be separated by the processes disclosed in European Patent Application EP4245869A1. Therefore, lithium can be separated from the sulfate solution using, for example, chromatographic separation. Nickel and / or cobalt can be separated from the sulfate solution, for example, by ion exchange.

[0044] The method can further comprise a step 3a), wherein at least part of the precipitate slurry is circulated to the step la) and mixed with the black mass leachate. This enables fortifying the aluminum content in the step la), allowing the fluoride precipitation to ~50 ppm during the first stage. In addition, the valuable metals can be recovered due to the internal circulation loop. The valuable metals will precipitate as hydroxides and are hence relatively easy to leach.

[0045] The method can further comprise a step 3b) after the step 3a) instead of the steps lb) to 2c). In the step 3b) a lithium hydroxide solution can be added to the mixture of the black mass leachate and the precipitate slurry, to produce a third aluminum hydroxide mixture having pH of 4.3-4.7.

[0046] In the step 3b), the lithium hydroxide solution can be added to the mixture of the black mass leachate and the precipitate slurry at a pumping rate of 3.8-4.2 ml / min per liter of the black mass leachate until pH 2.8-3.2 is reached, and after that at a pumping rate of 1.8-2.2 ml / min / / liter of the black mass leachate until pH 4.3-4.7 is reached.

[0047] The third aluminum hydroxide mixture can be mixed for at least 1.5 hours in the step 3b).

[0048] The method can further comprise a step 3c) after the step 3b) instead of the steps lb) to 2c). In the step 3c) the third aluminum hydroxide mixture can be filtrated, to produce a second filter cake comprising impurities and a second process solution.

[0049] The lithium hydroxide solution used in the method can be produced by dissolving solid lithium hydroxide monohydrate in water.

[0050] According to an aspect, there is provided use of the method to produce a lithium sulfate solution suitable for electrodialysis. In this case, the black mass leachate can comprise at least lithium and impurities, and optionally nickel and / or cobalt.

[0051] The lithium sulfate solution can comprise less than 50 ppm of fluoride. Therefore, the sulfate solution is suitable for electrolysis.DETAILED DESCRIPTION OF THE DRAWINGS

[0052] FIGURE 1 illustrates a first and a second stage of a method in accordance with at least some embodiments of the present invention. In the first stage, a black mass leachate 1 comprising at least one of nickel, cobalt and lithium, and impurities is provided. An aluminum sulfate solution 2 is mixed with the black mass leachate 1 to produce a first aluminum sulfate mixture 3. A lithium hydroxide solution 4 is added to the first aluminum sulfate mixture 3, to produce a first aluminum hydroxide mixture 5. The first aluminum hydroxide mixture 5 is filtrated 6, to produce a first filter cake 7 comprising impurities and a first process solution 8. In the second stage, an aluminum sulfate solution 9 is mixed with the first process solution 8, to produce a second aluminum sulfate mixture 10. A lithium hydroxide solution 11 is added to the second aluminum sulfate mixture 10, to produce a second aluminum hydroxide mixture 12. The second aluminum hydroxide mixture 12 is filtrated 13, to produce a precipitate slurry 14 comprising residual impurities and a sulfate solution 15 comprising at least one of the nickel, cobalt and lithium.

[0053] FIGURE 2 illustrates a first stage of a method using a precipitate slurry from a second stage in accordance with at least some embodiments of the present invention. First, at least part of the precipitate slurry 14 is mixed with the black mass leachate 1. A lithium hydroxide solution 16 is added to the black mass leachate 1, to produce a third aluminumhydroxide mixture 17. The third aluminum hydroxide mixture 17 is filtrated 18, to produce a second filter cake 19 comprising the impurities and a second process solution 20.EXAMPLE1st Stage

[0054] To begin the cycling two-step precipitation process, 40 grams of aluminum sulfate (A12(SO4)3.18H2O) is mixed with 46 ml of RO-water and heated up to 80±l °C to ensure homogeneity. One liter of Cu and Mn separated solution is measured into a three-liter reactor and heated to 80±l °C, with a 200-300 rpm mixing speed. The aluminum sulfate solution is added into the reactor, and pH is raised to 3.0 with a 128 g / L lithium hydroxide monohydrate (LiOH.H2O) solution added at a 4 ml / min pump rate. After pH 3.0 the pump rate is decreased to 2 ml / min until target pH 4.5 is reached.

[0055] After the target pH is reached, a 30-minute reaction time is given at the previously mentioned temperature and mixing speed. The pH decreases during the reaction time, so it is raised back to the target pH between every 30-minute reaction time cycle. Total reaction time should be 1.5 hours at a minimum. The mixture is filtered. The filter cake is dried overnight at a 108 °C temperature before ICP analysis. The results of the first stage with added aluminum sulfate are presented in Table 1. The reaction yield-% is calculated as Equation 1 shows:Yield - % = 100 (Eq. 1)Table 1. The first stage results with added aluminum sulphate in aluminum removal.

[0056] The results show that 99.3 % aluminum was precipitated. From the impurities, 89.5 % phosphorous and 68.1 % silicon precipitated reducing the concentration of the impurities from 2500 ppm to 90 ppm. Cobalt had a reaction yield of 96.6 %, lithium 95.7 % and nickel 94.7 %.2nd Stage

[0057] The second step begins by mixing 70 ml of RO-water and 59 g A12(SO4)3.18H2O and heating the mixture to 80±l °C to ensure homogeneity. The filtrate from the first step is poured into a three-liter reactor and the aluminum sulfate solution is added into it. Temperature is kept at 80±l °C and mixing speed at 200-300 rpm. The pH of the solution is increased to 4.7 with a 128 g / L LiOH.H2O solution at a 2 ml / min pumping rate. After the target pH has been reached, a 30-minute reaction time is given at the previously mentioned temperature and mixing speed. The pH decreases during the reaction time, so it is raised back to the target pH between every 30-minute reaction time cycle. Total reaction time should be 1.5 hours at a minimum. After a total reaction time, the filtrate is separated from the precipitate, and the precipitate is recycled back into the first step pH increase as a slurry with a new base solution. A flocculant is used to hasten the flocculation of the precipitate. 1 ml of 0,1 % anionic flocculant is used per each liter of initial starting solution. The results are presented in Table 2.Table 2. The received solution from second stage precipitation.

[0058] The results shows that fluoride was precipitated to below 10 ppm. Phosphorous was precipitated below the ICP-OES limit which is 1.4 mg / L. The final solution contains 6.2 mg / L aluminum due to excess dosing.1st stage with 2nd stage slurry

[0059] The first step is repeated, measuring one liter of Cu and Mn separated leachate solution into a three-liter reactor, and the second step precipitate slurry is added to the reactor. The pH is increased to 3 with a 128 g / L Li0H.H20 solution at a pumping speed of 4 ml / min. After pH 3, the pH is continued to raise at a 2 ml / min pumping rate until the target pH of 4.5 and is maintained for the minimum reaction time of 1.5 hours. The results are presented in Table 3. The reaction yield-% is calculated as the Equation 1 shows.Table 3. The results of the first stage precipitation with addition of the second stage slurry.

[0060] The aluminum is removed as well than with added aluminum sulfate. Cobalt loss-% is 3.3 % and lithium loss-% 4.6 % are similar as with added aluminum sulfate. Nickel has higher loss-% of 8.5 % compared to 5.3 %. The phosphorus and silicon have removed similar levels as with using aluminum sulfate.

[0061] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0062] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention.

[0063] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e., a singular form, throughout this document does not exclude a plurality.

Claims

CLAIMS:

1. A method for precipitating impurities from a black mass leachate, comprising steps of: la) providing a black mass leachate (1) comprising at least one of nickel, cobalt and lithium, and impurities; lb) mixing an aluminum sulfate solution (2) with the black mass leachate (1) to produce a first aluminum sulfate mixture (3); lc) adding a lithium hydroxide solution (4) to the first aluminum sulfate mixture (3), to produce a first aluminum hydroxide mixture (5) having pH of 4.3-4.7; ld) filtrating (6) the first aluminum hydroxide mixture (5), to produce a first filter cake (7) comprising impurities and a first process solution (8);2a) mixing an aluminum sulfate solution (9) with the first process solution (8), to produce a second aluminum sulfate mixture (10);2b) adding a lithium hydroxide solution (11) to the second aluminum sulfate mixture (10), to produce a second aluminum hydroxide mixture (12) having pH of 4.5-4.9;2c) filtrating (13) the second aluminum hydroxide mixture (12), to produce a precipitate slurry (14) comprising residual impurities and a sulfate solution (15) comprising at least one of the nickel, cobalt and lithium.

2. The method of claim 1, further comprising a step 3a), wherein at least part of the precipitate slurry (14) is circulated to the step la) and mixed with the black mass leachate (1).

3. The method of claim 2, further comprising a step 3b) after the step 3a) instead of the steps lb) to 2c), wherein a lithium hydroxide solution (16) is added to the mixture of the black mass leachate and the precipitate slurry, to produce a third aluminum hydroxide mixture (17) having pH of 4.3 4.7.

4. The method of claim 3, further comprising a step 3c) after the step 3b) instead of the steps lb) to 2c), wherein the third aluminum hydroxide mixture (17) is filtrated (18), to produce a second filter cake (19) comprising impurities and a second process solution5. The method of any one of the preceding claims, wherein the impurities and the residual impurities are selected from a group of aluminum, fluoride and phosphorus.

6. The method of any one of the preceding claims, wherein the mixing is conducted at a temperature of 75-85 °C, preferably 80 °C, in the step lb) and / or the step 2a).

7. The method of any one of the preceding claims, wherein in the step 1c), the lithium hydroxide solution (4) is added to the first aluminum sulfate mixture (3) at a pumping rate of 3.8-4.2 ml / min per liter of the first aluminum sulfate mixture (3) until pH 2.8- 3.2 is reached, and after that at a pumping rate of 1.8-2.2 ml / min per liter of the first aluminum sulfate mixture (3) until pH 4.3-4.7 is reached.

8. The method of any one of the preceding claims, wherein in the step 1c), lithium hydroxide solution (4) is added every 25-35 minutes to the first aluminum hydroxide (5) mixture to maintain the pH at 4.3-4.7.

9. The method of any one of the preceding claims, wherein the first aluminum hydroxide mixture (5) is mixed for at least 1.5 hours in the step 1c).

10. The method of any one of the preceding claims, wherein in the step 2b), the lithium hydroxide solution (11) is added to the second aluminum sulfate mixture (10) at a pumping rate of 1.8-2.2 ml / min per liter of the second aluminum sulfate mixture (10).

11. The method of any one of the preceding claims, wherein in the step 2b), the lithium hydroxide solution (11) is added every 25-35 minutes to the second aluminum hydroxide mixture (12) to maintain the pH at 4.5-4.9.

12. The method of any one of the preceding claims, wherein the second aluminum hydroxide mixture (12) is mixed for at least 1.5 hours in the step 2b).

13. The method of any one of the claims 3-12, wherein in the step 3b), the lithium hydroxide solution (16) is added to the mixture of the black mass leachate and the precipitate slurry at a pumping rate of 3.8-4.2 ml / min per liter of the black mass leachate until pH 2.8-3.2 is reached, and after that at a pumping rate of 1.8-2.2 ml / min per liter of the black mass leachate until pH 4.3-4.7 is reached.

14. The method of any one of the claims 3-13, wherein the third aluminum hydroxide mixture (17) is mixed for at least 1.5 hours in the step 3b).

15. The method of any one of the preceding claims, wherein in the step Id), the first process solution (8) comprises less than 100 ppm, such as less than 90 ppm, of fluoride.

16. The method of any one of the preceding claims, wherein in the step 2c), the sulfate solution (15) comprises less than 50 ppm, such as less than 10 ppm, of fluoride.

17. The method of any one of the preceding claims, wherein the lithium hydroxide solution (4) is produced by dissolving solid lithium hydroxide monohydrate in water.

18. Use of the method of any one of the claims 1-17 to produce a lithium sulfate solution suitable for electrodialysis.

19. The use of claim 18, wherein the lithium sulfate solution comprises less than 50 ppm of fluoride.

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