Method for producing cobalt sulfate salt

Abstract

In a method for producing a cobalt sulfate salt, a feed solution is prepared that includes cobalt sulfate and an aqueous sulfuric acid solution. The feed solution is evaporated and crystallized to produce a first solution. The first solution is filtered with a first purge to produce a first cobalt sulfate salt. The aqueous solution including the first cobalt sulfate salt is cooled and crystallized to produce a second solution. The second solution is filtered with a second purge to produce a second cobalt sulfate salt.

Description

Technical Field

[0001] The present invention relates to a method for producing cobalt sulfate salt, and more particularly to a method for producing cobalt sulfate salt including a purification step.

Background Art

[0002] In recent years, secondary batteries have been widely applied and developed as power sources for portable electronic communication devices such as camcorders, mobile phones, and notebook computers, and vehicles such as hybrid automobiles and electric automobiles. As the secondary battery, a lithium secondary battery has been actively developed and applied because of its high operating voltage and energy density per unit weight, and its advantages in charging speed and weight reduction.

[0003] As the active material for the positive electrode of the lithium secondary battery, a lithium metal oxide can be used. The lithium metal oxide can contain cobalt and can also contain transition metals such as nickel and manganese together.

[0004] Since the above-mentioned high-cost valuable metals are used in the active material for the positive electrode, more than 20% of the manufacturing cost is spent on the manufacture of the positive electrode material. Also, recently, due to the increasing interest in environmental protection, research on recycling methods for the active material for the positive electrode has been advanced.

[0005] For example, the waste positive electrode active material can be leached with a strong acid to recover cobalt in the form of cobalt sulfate, and the recovered cobalt sulfate can be utilized to manufacture the positive electrode active material again.

[0006] However, the recovered cobalt sulfate may contain other transition metals such as manganese as impurities. Therefore, it is necessary to design a process for obtaining a high-purity cobalt compound without excessively reducing the yield of cobalt.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The object of the present invention is to provide a method for producing cobalt sulfate salt that offers improved purity and yield. [Means for solving the problem]

[0008] In a method for producing cobalt sulfate according to an exemplary embodiment, a feeding solution containing cobalt sulfate and an aqueous sulfuric acid solution is prepared. The feeding solution is evaporated and crystallized to produce a first solution. The first solution is filtered together with a first purge to produce a first cobalt sulfate salt. The aqueous solution containing the first cobalt sulfate salt is cooled and crystallized to produce a second solution. The second solution is filtered together with a second purge to produce a second cobalt sulfate salt.

[0009] In some embodiments, the evaporation crystallization temperature may be 60 to 80°C.

[0010] In some embodiments, the cooling crystallization temperature may be 10 to 20°C.

[0011] In some embodiments, the proportion of the solution removed by the first purge from the weight of the first solution may be 5% by weight or less.

[0012] In some embodiments, the proportion of the solution removed by the first purge from the weight of the first solution may be 1 to 5% by weight.

[0013] In some embodiments, the percentage of the solution removed by the second purging relative to the weight of the second solution may be 5 to 20% by weight.

[0014] In some embodiments, the proportion of the solution removed by the second purging from the weight of the second solution may be 5 to 10% by weight.

[0015] In some embodiments, the proportion of the solution removed by the second purge from the weight of the second solution may be greater than or equal to the proportion of the solution removed by the first purge from the weight of the first solution.

[0016] In some embodiments, the feed solution may further contain manganese impurities.

[0017] In some embodiments, the amount of manganese impurities removed by the cooling crystallization may be greater than the amount of manganese impurities removed by the evaporation crystallization.

[0018] In some embodiments, the first cobalt sulfate salt may include cobalt sulfate monohydrate (CoSO4·H2O), and the second cobalt sulfate salt may include cobalt sulfate heptahydrate (CoSO4·7H2O).

[0019] In some embodiments, the step of filtering the first solution together with the first purge, or the step of filtering the second solution together with the second purge, may include recycling the liquid phase separated by filtration into the feed solution. [Effects of the Invention]

[0020] According to the exemplary embodiment described above, a cobalt sulfate salt can be obtained in high purity by sequentially performing evaporation crystallization and cooling crystallization on a feed solution containing cobalt sulfate.

[0021] According to an exemplary embodiment, the concentration of sulfuric acid in the solution can be reduced by performing a first purge between the evaporation crystallization and the cooling crystallization, thereby promoting the crystallization of cobalt sulfate salt. Furthermore, by performing a second purge after the cooling crystallization to reduce the amount of liquid phase, the amount of manganese remaining in the feed solution can be reduced.

[0022] According to an exemplary embodiment, by adjusting the purge amount of each of the first purge and the second purge, both the yield and purity of the recovered cobalt sulfate salt can be improved.

Brief Description of Drawings

[0023] [Figure 1] FIG. 1 is a schematic flowchart for explaining a method for producing cobalt sulfate salt according to an exemplary embodiment. Modes for Carrying Out the Invention

[0024] Embodiments of the present invention provide a method for producing cobalt sulfate salt with high purity and high yield from a positive electrode active material of a lithium secondary battery, for example.

[0025] However, the embodiments of the present invention are not limited to the recovery process from a lithium secondary battery, and can be applied to various manufacturing and product processes involving a purification process of cobalt sulfate salt.

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, these embodiments are merely exemplary and do not limit the present invention.

[0027] FIG. 1 is a schematic flowchart for explaining a method for producing cobalt sulfate salt according to an exemplary embodiment.

[0028] Referring to FIG. 1, a feed solution containing cobalt can be prepared (for example, step S10).

[0029] The feed solution can contain cobalt sulfate (CoSO4). In some embodiments, cobalt sulfate can be obtained from a waste lithium secondary battery or a used positive electrode active material of a lithium secondary battery.

[0030] For example, the positive electrode can be separated from the waste lithium secondary battery and recovered. The waste positive electrode comprises a positive electrode current collector (e.g., aluminum (Al)) and a positive electrode active material layer, and the positive electrode active material layer may include, for example, a nickel-cobalt-manganese (NCM) type lithium transition metal oxide (e.g., Li(NCM)O2).

[0031] After separating the positive electrode active material layer from the waste positive electrode and collecting the active material mixture, the mixture can be treated with sulfuric acid along with a reducing agent such as hydrogen peroxide (H2O2) to form an active material solution.

[0032] In some embodiments, further steps such as alkali-based precipitation, filtration, centrifugation, and washing may be performed to reduce the current collector, conductive material, and / or binder components remaining in the active material mixture.

[0033] By adding a transition metal extractant to the active material solution, nickel sulfate (NiSO4), cobalt sulfate (CoSO4), and manganese sulfate (MnSO4) can be produced and collected from Ni, Co, and Mn, respectively. For example, the transition metal extractant may include phosphate-based compounds.

[0034] In some embodiments, the extraction of the transition metals can be carried out by gradually increasing the pH. For example, Mn, Co, and Ni can be extracted sequentially while increasing the pH.

[0035] For example, manganese sulfate (MnSO4), cobalt sulfate (CoSO4), and nickel sulfate (NiSO4) can be sequentially extracted while gradually increasing the pH of the active material solution.

[0036] A feed solution containing the cobalt sulfate collected as described above can be prepared. The feed solution contains cobalt sulfate contained in the sulfuric acid aqueous solution and may contain unextracted manganese sulfate as an impurity. As described later, a crystallization step can be performed to obtain high-purity cobalt sulfate.

[0037] For example, in step S20, evaporation crystallization can be performed on the feed solution.

[0038] The evaporation crystallization process may include a reduced-pressure evaporation step. For example, the evaporation crystallization can be carried out in a temperature range of approximately 60 to 80°C. As shown in Figure 1, the evaporation crystallization process can partially remove water (H2O) and prepare a first solution in which the concentration of cobalt sulfate has increased.

[0039] Subsequently, for example, in steps S30 and S40, the first cobalt sulfate salt can be obtained by performing a first filtration step on the first solution.

[0040] The first filtration step may include, for example, a solid-liquid phase separation (solid-liquid separation) step by a filter press or a centrifugal dehydration step. The first filtration step removes and separates the liquid phase at least partially, allowing the solid phase of the first cobalt sulfate salt to be extracted.

[0041] In some embodiments, the liquid phase portion separated by the first filtration step can be recycled back into the feed solution (e.g., first recycling (C1)). This allows for the recirculation of cobalt that could not be recovered by evaporation and crystallization, thereby improving the cobalt recovery rate.

[0042] In some embodiments, the first cobalt sulfate salt may include cobalt sulfate monohydrate (CoSO4·H2O).

[0043] According to exemplary embodiments, a first purging can be performed on the first solution. In some embodiments, as shown in Figure 1, the first purging can be performed while the first filtration step is being carried out.

[0044] The first purging allows for the removal of a predetermined fraction of the first solution that is introduced into the first filtration step. This reduces the concentration of sulfuric acid in the first filtration step, improving the solid-liquid separation efficiency in the first filtration step. Consequently, the collection efficiency and yield of the first cobalt sulfate salt can be improved.

[0045] In Figure 1, steps S20 and S30 are shown separated into evaporation crystallization and first filtration, respectively, but it is also possible to include both steps S20 and S30 as evaporation crystallization.

[0046] The collected first cobalt sulfate salt can be further subjected to cooling crystallization, for example, in step S50. For example, distilled water can be added to the first cobalt sulfate salt to form an aqueous solution. The temperature of the distilled water may be about 60-80°C from the viewpoint of dissolution efficiency. The aqueous solution can then be cooled to a temperature of about 10-20°C to produce a second solution.

[0047] Subsequently, for example, in steps S50 and S60, a second filtration step is performed on the cooled second solution to obtain the second cobalt sulfate salt.

[0048] The second filtration step may include, for example, a solid-liquid phase separation (solid-liquid separation) step by a filter press or a centrifugal dehydration step. The second filtration step removes or separates at least partially the liquid phase of the second solution, allowing the solid phase of the second cobalt sulfate salt to be extracted.

[0049] In some embodiments, the second cobalt sulfate salt may include cobalt sulfate heptahydrate (CoSO4·7H2O).

[0050] In some embodiments, the liquid phase portion separated by the second filtration step can be recycled back into the feed solution (e.g., second recycling (C2)). This allows for the recirculation of cobalt that could not be recovered by the cooling crystallization process, thereby improving the cobalt recovery rate.

[0051] According to exemplary embodiments, a second purging can be performed on the second solution. In some embodiments, as shown in Figure 1, the second purging can be performed while the second filtration step is being carried out.

[0052] The second purging can remove a predetermined fraction of the second solution that is introduced into the second filtration step. cooling This reduces the amount of manganese that remains after crystallization. Thus, the second filtration improves the manganese removal efficiency and manganese separation efficiency. This improves the purity of the second cobalt sulfate salt collected in step S70.

[0053] In Figure 1, steps S50 and S60 are shown separated into cooling crystallization and second filtration, respectively, but it is also possible to include both steps S50 and S60 as a single cooling crystallization step.

[0054] In some embodiments, the purge rate in the second purge may be greater than or equal to the purge rate in the first purge.

[0055] In one embodiment, the proportion of the solution removed in the first purge (first purge rate) may be about 5% by weight or less, preferably about 1 to 5% by weight, of the weight of the first solution. Within the range of the first purge rate, the separation efficiency of the first cobalt sulfate salt increases, and the overall yield does not decrease excessively.

[0056] In one embodiment, the proportion of the solution removed in the second purge (second purge rate) may be about 5 to 20% by weight, preferably about 5 to 15% by weight, and more preferably about 5 to 10% by weight, of the weight of the second solution. Within the range of the second purge rate, manganese impurities can be sufficiently removed while preventing an excessive decrease in the overall yield of the cobalt sulfate salt.

[0057] As described above, in one embodiment, the second purging rate can be adjusted to be equal to or greater than the first purging rate. This makes it possible to improve the overall crystallization efficiency of the sulfate in the evaporation crystallization while improving the removal efficiency of manganese impurities in the cooling crystallization.

[0058] For example, the liquid phase can be separated from the feed solution by evaporation crystallization, and the efficiency of solid salt production can be improved by the first purging. The first solution formed after evaporation crystallization contains a relatively large amount of manganese impurities, and these manganese impurities can be removed by cooling crystallization.

[0059] Therefore, the amount of manganese removed by the cooling crystallization may be greater than the amount of manganese removed by the evaporation crystallization. By combining the cooling crystallization with the second purging, the efficiency of manganese impurity removal is further improved, and a high-purity cobalt sulfate salt can be obtained.

[0060] The following are specific examples to aid in understanding the present invention, but these examples are merely illustrative and do not limit the scope of the appended claims. It will be obvious to those skilled in the art that various changes and modifications can be made to these examples within the scope of the present invention and the technical concept, and it is also obvious that these variations and modifications fall within the scope of the appended claims.

[0061] Example 1 3 kg of CoSO4 containing 800 ppm MnSO4 and 5-6% H2SO4 was used as the feed solution.

[0062] The feed solution was evaporated under reduced pressure at 70°C and a pressure of 200-500 mbar for 8 hours to produce the first solution. The first solution was filtered using a vacuum pump while maintaining a first purging rate of 5% by weight to obtain cobalt sulfate monohydrate (CoSO4·H2O) as the first cobalt sulfate salt.

[0063] 0.6 kg of distilled water (70°C) was added to the obtained first cobalt sulfate salt, and the mixture was cooled to 15°C for 2 hours to produce a second solution. The second solution was filtered using a vacuum pump while maintaining a second purging rate of 5% by weight to obtain cobalt sulfate heptahydrate (CoSO4·7H2O) as the second cobalt sulfate salt.

[0064] Example 2 ~4 1st purge rate, Cobalt sulfate heptahydrate (CoSO4·7H2O) was obtained in the same manner as in Example 1, except that the second purging rate was adjusted as shown in Table 1.

[0065] Comparative Example 1 Cobalt sulfate heptahydrate (CoSO4·7H2O) was obtained in the same manner as in Example 1, except that a second purge was not performed during the cooling crystallization.

[0066] Comparative Example 2 Cobalt sulfate heptahydrate (CoSO4·7H2O) was obtained in the same manner as in Example 1, except that the first purging was not performed during evaporation crystallization.

[0067] For the products obtained in the aforementioned examples and comparative examples, the amount of recovered cobalt (recovery rate (%)), manganese content, and purity of the cobalt sulfate salt were measured compared to the feed solution. Purity was calculated as the weight of cobalt sulfate heptahydrate relative to the total weight of the obtained product. The weight of cobalt sulfate heptahydrate was determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) analysis.

[0068] The evaluation results are summarized in Table 1 below.

[0069] [Table 1]

[0070] As shown in Table 1, according to the example, by combining the first and second purges, the amount of manganese impurities was reduced, and a cobalt recovery rate of 85% or more was achieved.

[0071] In Comparative Example 1 or Comparative Example 2, where the first or second purge was omitted, the amount of residual manganese increased, or the amount of sulfuric acid was not sufficiently removed and the mixture became concentrated, resulting in a decrease in the purity of the cobalt salt.

Claims

1. The steps include preparing a feed solution containing cobalt sulfate and an aqueous sulfuric acid solution, The process involves evaporating and crystallizing the feed solution to produce a first solution containing a solid phase of the first cobalt sulfate salt, The steps include purging the first solution, filtering the purged first solution to produce a first cobalt sulfate salt, The steps include: cooling and crystallizing the aqueous solution containing the first cobalt sulfate salt to produce a second solution containing a solid-phase second cobalt sulfate salt; The process includes the steps of purging the second solution a second time, and filtering the second purged second solution to produce a second cobalt sulfate salt, A method for producing cobalt sulfate salt, wherein the proportion of the solution removed by the first purging is 1% to 5% by weight of the first solution, and the proportion of the solution removed by the second purging is 5% to 20% by weight of the second solution.

2. The method for producing a cobalt sulfate salt according to claim 1, wherein the evaporation crystallization temperature is 60°C to 80°C.

3. The method for producing a cobalt sulfate salt according to claim 1, wherein the temperature of the cooling crystallization is 10°C to 20°C.

4. The method for producing a cobalt sulfate salt according to claim 1, wherein the proportion of the solution removed by the second purging in the weight of the second solution is 5 to 10% by weight.

5. The method for producing a cobalt sulfate salt according to claim 1, wherein the proportion of the solution removed by weight of the second solution by the second purging is equal to or greater than the proportion of the solution removed by weight of the first solution by the first purging.

6. The method for producing a cobalt sulfate salt according to claim 1, wherein the feed solution further contains manganese impurities.

7. The method for producing a cobalt sulfate salt according to claim 6, wherein the amount of manganese impurities removed by the cooling crystallization is greater than the amount of manganese impurities removed by the evaporation crystallization.

8. The first cobalt sulfate salt is cobalt sulfate monohydrate (CoSO4). ４ ・H ２ The second cobalt sulfate salt contains (O), and the second cobalt sulfate salt is cobalt sulfate heptahydrate (CoSO4). ４ 7H ２ A method for producing a cobalt sulfate salt according to claim 1, comprising O).

9. The method for producing a cobalt sulfate salt according to claim 1, further comprising recycling the liquid phase separated by filtration of the first purged first solution or by filtration of the second purged second solution into the feed solution.

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