Manufacturing method of nickel sulfate salt

Abstract

To provide an efficient manufacturing method of nickel sulfate salt.SOLUTION: In a manufacturing method of nickel sulfate salt, a feed solution comprising a nickel salt and an aqueous sulfuric acid solution is prepared. The feed solution is crystallized to generate a mixture containing nickel sulfate solid. The mixture is subjected to solid-liquid separation to collect the nickel sulfate salt. The filtrate generated from the solid-liquid separation is recycled together with purge.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing nickel sulfate salts, and more particularly to a method for producing nickel sulfate salts that includes a purification step. [Background technology]

[0002] In recent years, secondary batteries have been widely developed and applied as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop computers, as well as for vehicles such as hybrid cars and electric cars. As secondary batteries, lithium secondary batteries have been actively developed and applied because of their high operating voltage and energy density per unit weight, as well as their advantages in terms of charging speed and light weight.

[0003] For example, a lithium secondary battery includes a positive electrode active material, and the positive electrode active material may include lithium cobalt oxide (LiCoO2); lithium nickel oxide (LiNiO2); lithium manganese oxide (LiMnO2, LiMn2O4, etc.), lithium iron phosphate compound (LiFePO4); NCM-based lithium metal oxide containing nickel, cobalt, and manganese; NCA-based lithium metal oxide containing nickel, cobalt, and aluminum; etc.

[0004] Since the cathode active material contains such expensive and valuable metals, the production of the cathode material is costly. Furthermore, with the recent increase in interest in environmental protection, research into methods for recycling the cathode active material has been progressing. To recycle the cathode active material, it is necessary to recover the metals from the cathode with high efficiency and high purity.

[0005] However, the recovered nickel sulfate salt may contain other metals such as lithium and sodium as impurities, and therefore there is a need to design a process that can produce high-purity nickel sulfate without reducing the yield of nickel sulfate. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to provide an efficient method for producing nickel sulfate salts. [Means for solving the problem]

[0007] In the method for producing nickel sulfate salt of the present disclosure, a feed solution containing a nickel salt and an aqueous sulfuric acid solution is prepared. The feed solution is crystallized to produce a mixed solution containing nickel sulfate solids. The mixed solution is subjected to solid-liquid separation to collect nickel sulfate salt. The filtrate produced from the solid-liquid separation is recycled together with a purge.

[0008] According to an exemplary embodiment, recycling the filtrate may include circulating the filtrate back into the feed solution.

[0009] According to an exemplary embodiment, the purging may include purging 1% to 20% by weight of the total weight of the filtrate.

[0010] According to an exemplary embodiment, the purging may include purging 5% to 10% by weight of the total weight of the filtrate.

[0011] According to an exemplary embodiment, the recycling can include circulating 90% or more of the total nickel contained in the filtrate back into the feed solution.

[0012] According to an exemplary embodiment, the step of producing the mixed liquid can include evaporating and concentrating the feed solution to produce a first solution, and cooling and crystallizing the first solution to produce a second solution as the mixed liquid.

[0013] According to an exemplary embodiment, preparing the feed solution may include recovering a positive electrode active material from a lithium secondary battery and extracting the nickel salt from the positive electrode active material.

[0014] According to an exemplary embodiment, the positive electrode active material may include manganese or cobalt.

[0015] According to an exemplary embodiment, the feed solution may contain 3% to 10% nickel by weight based on the total weight.

[0016] According to an exemplary embodiment, the feed solution may further include a lithium impurity or a sodium impurity.

[0017] According to an exemplary embodiment, the lithium impurity content may be less than or equal to 0.4 wt. % based on the total weight of the feed solution.

[0018] According to an exemplary embodiment, the sodium impurity content may be less than or equal to 0.5% by weight based on the total weight of the feed solution.

[0019] According to an exemplary embodiment, the nickel sulfate salt may contain 500 ppm or less of the lithium impurity or the sodium impurity.

[0020] According to an exemplary embodiment, the nickel sulfate salt can include nickel sulfate hexahydrate (NiSO4·6H2O). [Effects of the Invention]

[0021] According to the method for producing nickel sulfate salt according to the embodiment of the present disclosure, a feed solution containing a nickel salt and an aqueous sulfuric acid solution can be crystallized to produce a mixed solution containing nickel sulfate solids. The mixed solution can be subjected to solid-liquid separation, and the filtrate produced from the solid-liquid separation can be recycled together with purging. By purging and recycling the filtrate, nickel sulfate salt can be continuously and repeatedly produced. Furthermore, the yield can be improved without reducing the purity of the nickel sulfate salt. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic process flow diagram illustrating a method for producing nickel sulfate salts according to an exemplary embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating a system for producing nickel sulfate salt according to an exemplary embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Embodiments of the present disclosure provide a method for producing nickel sulfate salts.

[0024] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, these embodiments are merely illustrative of the present disclosure and are not intended to limit the present disclosure.

[0025] FIG. 1 is a schematic process flow diagram illustrating a method for producing nickel sulfate salts according to an exemplary embodiment.

[0026] Referring to FIG. 1, a feed solution containing a nickel salt and an aqueous sulfuric acid solution can be prepared (eg, step S10).

[0027] The feed solution can include nickel sulfate (NiSO4) as a nickel salt. In some embodiments, the nickel sulfate (NiSO4) can be present in a dissolved state.

[0028] In some embodiments, the feed solution can be prepared by recovering a positive electrode active material from a lithium secondary battery and extracting the nickel salt from the positive electrode active material.

[0029] For example, the positive electrode active material can be recovered from the positive electrode of a lithium secondary battery, and the nickel salt can be extracted from the positive electrode active material.

[0030] For example, the positive electrode includes a positive electrode current collector (e.g., aluminum (Al)) and a positive electrode active material layer, and the positive electrode active material layer can include a conductive material and a binder in addition to the above-mentioned positive electrode active material.

[0031] The positive electrode may be, for example, a positive electrode obtained from a used, waste lithium secondary battery, or a positive electrode that has been damaged or defective during the manufacturing process.

[0032] For example, the positive electrode active material can include lithium and a transition metal. The transition metal can include nickel. In some embodiments, the transition metal can include manganese or cobalt.

[0033] In some embodiments, the positive electrode active material may include an NCM-based lithium metal composite oxide containing nickel, cobalt, and manganese. However, embodiments of the present disclosure are applicable not only to positive electrode materials containing the NCM-based lithium metal composite oxide, but also to lithium metal composite oxide positive electrode materials containing nickel. For example, the positive electrode active material may include an NCA-based lithium metal composite oxide containing nickel, cobalt, and aluminum.

[0034] For example, the positive electrode active material layer can be separated from the positive electrode to collect the positive electrode active material mixture.

[0035] In some embodiments, an additional step such as alkali precipitation, filtration, centrifugation, or washing may be performed to reduce the amount of the current collector, conductive material, and / or binder components remaining in the positive electrode active material mixture.

[0036] For example, the positive electrode active material mixture may be treated with sulfuric acid together with a reducing agent to form a positive electrode active material solution.

[0037] For example, transition metals contained in the positive electrode active material solution can be extracted.

[0038] For example, the reducing agent may include at least one of hydrogen peroxide (H2O2), SO2, Na2S, NaHS, Na2S2O5, NaHSO3, Na2S2O3, KHSO3, K2SO3, FeSO4, H2S, glucose, sucrose, and ascorbic acid. The use of such a reducing agent facilitates extraction of transition metals contained in the positive electrode active material mixture.

[0039] For example, when the reducing agent is hydrogen peroxide, the extraction can be carried out according to the reaction represented by the following reaction formula 1.

[0040] [Reaction Scheme 1] 2Li(NCM)O2+H2O2+3H2SO4→Li2SO4+2(NCM)SO4+4H2O+O2

[0041] For example, the amount of the reducing agent used may be 0.5 mol or less per mol of the positive electrode active material mixture, but this is merely an example and is not intended to be limiting.

[0042] In some embodiments, a transition metal extractant can be added to the positive electrode active material solution, for example, to generate and collect nickel sulfate (NiSO), cobalt sulfate (CoSO), and manganese sulfate (MnSO) from the Ni, Co, and Mn contained in the positive electrode active material solution.

[0043] For example, the transition metal extractant may include at least one of a phosphoric acid extractant, a phosphate extractant, a phosphine oxide extractant, and a carboxylic acid extractant.

[0044] For example, the extractant can include at least one of di-2-ethylhexyl phosphoric acid (D2EHPA), bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272), 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (PC88A), tributyl phosphate, trioctyl phosphine oxide, and alkyl monocarboxylic acid.

[0045] In some embodiments, the extractant may be diluted with an organic solvent diluent, such as at least one of kerosene, hexane, benzene, and toluene.

[0046] In some embodiments, the transition metals can be extracted by increasing the pH stepwise. For example, if the positive electrode active material solution contains Ni, Co, and Mn, Mn, Co, and Ni can be extracted sequentially by increasing the pH of the positive electrode active material solution.

[0047] For example, manganese sulfate, cobalt sulfate, and nickel sulfate can be extracted in sequence while gradually increasing the pH of the positive electrode active material solution.

[0048] In some embodiments, transition metals can be extracted from the cathode active material solution to produce a feed solution.

[0049] For example, manganese sulfate and cobalt sulfate can be extracted sequentially while gradually increasing the pH of the positive electrode active material solution, and a feed solution can be prepared from the remaining positive electrode active material solution. However, the method for preparing the feed solution is not limited to the above-mentioned method.

[0050] For example, the feed solution may contain nickel sulfate contained in an aqueous sulfuric acid solution, and may contain unextracted remaining manganese sulfate or cobalt sulfate as impurities.

[0051] For example, the feed solution may further contain lithium or sodium contained in the positive electrode active material as an impurity.

[0052] According to an exemplary embodiment, the feed solution can contain 3 wt% to 10 wt% nickel based on the total weight. In one embodiment, the feed solution can contain 4 wt% to 10 wt%, 4 wt% to 9 wt%, or 5 wt% to 8 wt% nickel based on the total weight. This range can improve the purity and yield of nickel sulfate salts by purging and recycling, as described below.

[0053] According to exemplary embodiments, the feed solution may contain 0.5 wt% or less of lithium impurities based on total weight. In one embodiment, the feed solution may contain 0.4 wt% or less, 0.35 wt% or less, 0.3 wt% or less, or 0.2 wt% or less of lithium impurities based on total weight.

[0054] According to exemplary embodiments, the feed solution may contain 0.6% or less by weight sodium impurities based on total weight. In one embodiment, the feed solution may contain 0.5% or less, 0.4% or less, 0.35% or less, 0.3% or less, or 0.2% or less by weight sodium impurities based on total weight.

[0055] The lower limits of the lithium content and the sodium content are not particularly limited, but may be, for example, 0.001% by weight or more, or 0.002% by weight or more, based on the total weight of the feed solution.

[0056] When nickel sulfate salt is produced using a feed solution containing nickel, lithium, or sodium within the above ranges, the formation of nickel sulfate complexes can be suppressed regardless of the proportion of filtrate to be purged, and nickel sulfate salt with a purity of 99% or more can be produced.

[0057] The lithium and sodium contents contained in the feed solution can be controlled, and the contents can be determined in consideration of the crystallization temperature described below. Also, the crystallization temperature described below can be determined by checking the lithium and sodium contents contained in the feed solution.

[0058] For example, if the crystallization temperature of the feed solution is high, the lithium and sodium contents contained in the feed solution may decrease.

[0059] In one embodiment, when the temperature of evaporation and concentration in the crystallization of the feed solution described below is 60°C or less, the lithium content in the feed solution may be 0.4% by weight or less, and the sodium content may be 0.6% by weight or less, or 0.4% by weight or less.

[0060] In one embodiment, when the cooling crystallization temperature in the crystallization of the feed solution described below is 20°C or less, the lithium content in the feed solution may be 0.4% by weight or less, and the sodium content may be 0.6% by weight or less, or 0.4% by weight or less.

[0061] In one embodiment, in the crystallization of the feed solution described below, when the evaporation and concentration temperature exceeds 60°C, the lithium content in the feed solution may be 0.2 wt% or less or 0.15 wt% or less, and the sodium content may be less than 0.3 wt%, 0.25 wt% or less, 0.2 wt% or less, 0.15 wt% or less, or 0.10 wt% or less.

[0062] In one embodiment, in the crystallization of the feed solution described below, when the cooling crystallization temperature exceeds 20°C, the lithium content in the feed solution may be 0.2 wt% or less or 0.15 wt% or less, and the sodium content may be less than 0.3 wt%, 0.25 wt% or less, 0.2 wt% or less, 0.15 wt% or less, or 0.10 wt% or less.

[0063] By controlling the lithium or sodium content according to the temperature of evaporation and concentration, or by adjusting the temperature of evaporation and concentration according to the lithium or sodium content, it is possible to suppress the formation of nickel sulfate complexes regardless of the proportion of filtrate to be purged, and to produce nickel sulfate salt with a purity of 99% or more.

[0064] The feed solution can be crystallized (eg, step S20).

[0065] For example, crystallization can be achieved by changing the temperature of the feed solution. The temperature change can include both heating and cooling. For example, the temperature change of the feed solution can include heating the feed solution followed by cooling it.

[0066] According to an exemplary embodiment, the feed solution can be evaporated to produce a first solution.

[0067] For example, the evaporation can include a reduced pressure evaporation process. For example, the evaporation can evaporate water contained in the feed solution.

[0068] In some embodiments, the evaporation of the feed solution can be carried out at a temperature between 40°C and 80°C.

[0069] Within this temperature range, the concentration of nickel sulfate salt contained in the feed solution can be increased, thereby increasing the amount of nickel sulfate salt produced after cooling and crystallization, which will be described later.

[0070] According to an exemplary embodiment, the first solution can be cooled and crystallized to produce a second solution.

[0071] In some embodiments, the cooling crystallization of the first solution can be carried out at a temperature of 0°C to 40°C.

[0072] In this temperature range, nickel sulfate solids may be formed due to supersaturation of the nickel sulfate salt contained in the first solution.

[0073] The temperature for the evaporation concentration or cooling crystallization can be determined taking into consideration the content of impurities (lithium, sodium, etc.) contained in the feed solution.

[0074] According to an exemplary embodiment, the second solution can include nickel sulfate solids.

[0075] The second solution can be subjected to solid-liquid phase separation (solid-liquid separation) to collect nickel sulfate salt (for example, step S30).

[0076] For example, the solid nickel sulfate salt and the liquid filtrate can be separated from the mixture.

[0077] According to an exemplary embodiment, the nickel sulfate salt can include nickel sulfate hexahydrate (NiSO4·6H2O).

[0078] The nickel sulfate salt can be collected through a filtration process.

[0079] The filtration step can be, for example, a solid-liquid separation step using a filter press or a centrifugal dehydration step, in which the liquid phase of the mixed solution is at least partially removed and separated, and the solid phase nickel sulfate salt can be extracted.

[0080] The filtrate can include liquid separated from the nickel sulfate salt.

[0081] In some embodiments, the filtering step can be accompanied by purging of the mixture.

[0082] The filtrate produced by solid-liquid separation can be purged (for example, purge (P1)). The filtrate can be recycled to the feed solution (for example, recycle (C1)).

[0083] For example, the filtrate may contain nickel, which may include residual nickel that was not solidified in the previous step.

[0084] For example, the filtrate can be fractionated and purged, with the remaining remainder recycled. For example, the filtrate can include a purged fraction and a retentate fraction. For example, the compositions of the purged fraction and the retentate fraction can be substantially identical.

[0085] According to an exemplary embodiment, recycling the filtrate can include circulating the retentate fraction back into the feed solution.

[0086] For example, the retentate fraction of the filtrate, excluding the purge fraction, can be included in the feed solution. The recycling can reduce the amount of wastewater treatment, thereby enabling the production of nickel sulfate salts in an environmentally friendly manner.

[0087] According to exemplary embodiments, 1% to 40% by weight of the filtrate may be purged, and in some embodiments, 1% to 30%, 1% to 25%, 1% to 20%, 3% to 20%, or 5% to 15% by weight of the filtrate may be purged.

[0088] For example, the content of the purge fraction may correspond to the ranges described above.

[0089] In some embodiments, 5% to 10% by weight of the filtrate may be purged, based on the total weight of the filtrate.

[0090] The recovery rate of nickel may vary depending on whether or not the filtrate is purged and the weight percentage of the purged solution. Also, the purity of the nickel sulfate salt repeatedly produced may vary depending on the weight percentage of the filtrate purged.

[0091] For example, if the filtrate is not purged, the impurities contained in the filtrate may be contained in large amounts in the feed solution, which may reduce the purity of the nickel sulfate salt.

[0092] For example, if the filtrate is purged beyond the above range, nickel may be unnecessarily removed, which may result in a lower nickel recovery rate.

[0093] For example, if the filtrate is purged below the above range, impurities (e.g., lithium, sodium, etc.) may accumulate in the continuously repeated nickel sulfate salt production process, which may make it impossible to recycle the filtrate.

[0094] In some embodiments, the recycle can recycle 90% or more of the nickel contained in the filtrate back into the feed solution.

[0095] For example, 90% or more of the total weight of nickel contained in the filtrate can be contained in the feed solution, thereby improving the production efficiency of nickel sulfate salt.

[0096] According to an exemplary embodiment, nickel recovery from the filtrate purging and filtrate recycling may be 90% or greater.

[0097] The recovery rate of nickel can be calculated by the following formula 1.

[0098] Equation 1: Nickel recovery rate (%) = (weight of nickel contained in nickel sulfate salt produced at steady state / weight of nickel in feed solution) x 100

[0099] Here, the term "steady state" may refer to a state in which the purity, weight, etc. of the nickel sulfate salt repeatedly produced, including the recycling process according to the above-described embodiment, are maintained constant.

[0100] For example, a first nickel sulfate salt and a first filtrate can be obtained from a first feed solution through the aforementioned steps (S10 to S40). A second feed solution distinct from the first feed solution can be prepared, and the first filtrate can be recycled using the second feed solution. A second nickel sulfate salt and a second filtrate can be obtained from a solution containing the second feed solution and the first filtrate through the aforementioned steps. The above procedure can be repeated so that the purity, weight, etc. of the nickel sulfate salt produced remain constant. A state in which the purity, weight, etc. of the nickel sulfate salt repeatedly produced remains constant is considered to be a steady state, and the recovery rate can be calculated by measuring the weight of nickel contained in the nickel sulfate salt produced in the steady state.

[0101] For example, the steady state criterion may refer to a case where the purity of the produced nickel sulfate salt is maintained constant for three or more times, i.e., the steady state may refer to a case where the purity of the produced nickel sulfate salt is maintained within ±0.1% for three or more times.

[0102] In some embodiments, the nickel recovery may be 93% or more, 95% or more, 97% or more, or 98% or more by weight.

[0103] According to an exemplary embodiment, the method may further include washing the nickel sulfate salt.

[0104] For example, the nickel sulfate salt may be washed to remove solution residue, impurities, etc. For example, the nickel sulfate salt may contain lithium or sodium as an impurity, and the impurities may be reduced by washing.

[0105] In some embodiments, the washing step can include washing the nickel sulfate salt with a saturated nickel solution.

[0106] For example, the amount of the saturated nickel solution used may vary depending on the amount of the separated nickel sulfate salt, and for example, a saturated nickel solution equivalent in weight to 1 to 10 times the weight of the separated nickel sulfate salt can be used.

[0107] In some embodiments, the nickel sulfate salt may have a lithium impurity content of 500 ppm or less. In some embodiments, the nickel sulfate salt may have a sodium impurity content of 500 ppm or less.

[0108] In some embodiments, the nickel sulfate salt may have a lithium impurity content of 500 ppm or less, 300 ppm or less, 200 ppm or less, 150 ppm or less, or 100 ppm or less.

[0109] In some embodiments, the nickel sulfate salt may have a sodium impurity content of 500 ppm or less, 300 ppm or less, 200 ppm or less, 150 ppm or less, or 100 ppm or less.

[0110] According to an exemplary embodiment, the saturated nickel solution may be a saturated nickel sulfate solution based on a temperature of 20° C. to 30° C. For example, the content of nickel contained in the saturated nickel sulfate solution may be 1% by weight to 20% by weight.

[0111] FIG. 2 is a schematic diagram illustrating a system for producing nickel sulfate salt according to an exemplary embodiment.

[0112] As shown in FIG. 2 , a supply unit 100 for supplying a nickel salt and an aqueous sulfuric acid solution can be connected to a reactor 110. A feed solution 200 containing a nickel salt and an aqueous sulfuric acid solution can be supplied to the reactor 110 via the supply unit 100. Alternatively, the nickel salt and the aqueous sulfuric acid solution supplied from the supply unit 100 can be mixed in the reactor 110 to produce the feed solution 200. The feed solution 200 can be crystallized in the reactor 110 to produce solid nickel sulfate. A nickel sulfate salt collection unit 250 for collecting the produced solid nickel sulfate can be connected to the reactor 110. A filtrate collection unit 115 can be connected to the reactor 110. The filtrate collection unit 115 can be connected to the bottom of the reactor 110. A filtrate 210 from which the nickel sulfate salt has been separated can be transferred from the reactor 110 to the filtrate collection unit 115. A purge flow path 220 for purging the filtrate 210 can be connected to the filtrate collection unit 115. The purge flow path 220 can include one or more pipes. A regeneration flow path 230 that supplies the filtrate 210 to the reactor 110 can be connected to the filtrate collection section 115 and the reactor 110. The regeneration flow path 230 can include one or more lines.

[0113] According to an exemplary embodiment, reactor 110 can include a temperature control section (not shown) that includes a temperature measurement device and a controller. The temperature control section can be connected to reactor 110 or can be at least partially internal to reactor 110. For example, at least one temperature measurement device can be located internal to the reactor to measure the temperature of feed solution 200 at at least one location, and the at least one temperature measurement device can be operatively coupled to a temperature controller of a temperature control section located external to reactor 110.

[0114] According to an exemplary embodiment, purge flow path 220 may be directly connected to reactor 110. When purge flow path 220 is directly connected to reactor 110, the purged filtrate may be purged without passing through filtrate collection unit 115.

[0115] Specific examples are presented below to aid in understanding the present disclosure, but these examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the examples are possible within the scope and technical spirit of the present disclosure, and it is natural that such changes and modifications also fall within the scope of the appended claims.

[0116] Examples and Comparative Examples Example 1 An aqueous sulfuric acid solution containing 6.6 wt % of nickel, 0.11 wt % of lithium, and 0.03 wt % of sodium based on the total weight of the solution, and containing 2 to 3 wt % of sulfuric acid, was used as the feed solution.

[0117] The feed solution was evaporated under reduced pressure while maintaining the temperature at 60°C to produce a first solution containing nickel sulfate salt. The first solution was then cooled to 0°C to produce a mixed solution (second solution) containing solid nickel sulfate salt. The mixed solution was filtered using a vacuum pump to produce nickel sulfate salt.

[0118] The nickel sulfate salt was washed with about three times the weight of a saturated nickel sulfate solution (containing about 11% by weight of nickel relative to the total weight of the solution) based on the total weight of the nickel sulfate salt to obtain nickel sulfate hexahydrate (NiSO4·6H2O).

[0119] Furthermore, the filtrate from the mixed solution was recycled to the feed solution while purging 5% by weight of the total weight of the filtrate, and the same process was repeated to produce nickel sulfate hexahydrate.

[0120] Examples 1-2 to 1-7 Nickel sulfate hexahydrate was obtained in the same manner as in Example 1, except that the proportion of the filtrate to be purged was changed to 10% by weight (Example 1-2), 20% by weight (Example 1-3), 30% by weight (Example 1-4), 40% by weight (Example 1-5), 60% by weight (Example 1-6), and 80% by weight (Example 1-7).

[0121] Examples 2-1 to 2-12 Nickel sulfate hexahydrate was obtained in the same manner as in Example 1, except that the lithium content and sodium content in the feed solution were adjusted as shown in Table 1 below.

[0122] [Table 1]

[0123] Example 3 Nickel sulfate hexahydrate was obtained in the same manner as in Example 1, except that the evaporation under reduced pressure was carried out at 80°C and the cooling temperature of the first solution was changed to 40°C.

[0124] Examples 3-2 to 3-9 Nickel sulfate hexahydrate was obtained in the same manner as in Example 3, except that the lithium content and sodium content in the feed solution were adjusted as shown in Table 2 below.

[0125] [Table 2]

[0126] Comparative Example Nickel sulfate hexahydrate was obtained in the same manner as in Example 1, except that the filtrate was not purged.

[0127] Experimental example Experimental example 1. Analysis of recycling rate The nickel recovery rate was calculated from the weight of nickel contained in the nickel sulfate obtained in the above-mentioned Examples and Comparative Examples. Specifically, the total weight of nickel contained in the feed solution and the total weight of nickel when a steady state was reached were calculated, and the recovery rate was calculated using the following formula 1. The steady state refers to a state in which the purity, weight, etc. of nickel sulfate repeatedly produced, including the recycling step, are maintained constant.

[0128] Equation 1: Recovery rate (%) = (weight of nickel contained in nickel sulfate salt produced under normal conditions / weight of nickel in the feed solution) x 100

[0129] The results of Examples 1 to 1-7 and Comparative Example are shown in Table 3 below, and the results of Examples 2-1 to 3-9 are shown in Table 4 below.

[0130] Experimental Example 2: Purity Analysis The lithium and sodium contents contained in the nickel sulfate hexahydrate obtained in some of the examples and comparative examples were analyzed by ICP analysis, and the purity of the nickel sulfate salt was calculated.

[0131] The results of Examples 1 to 1-7 are shown in Table 3 below.

[0132] The results of Examples 2-1 to 3-9 were evaluated according to the following criteria, and the results are shown in Table 4 below.

[0133] <Evaluation criteria for the formation of nickel sulfate hexahydrate> ○: Only nickel sulfate is produced regardless of the ratio of filtrate to be purged △: Nickel sulfate complex (Na2Ni(SO4)2(H2O)4, etc.) is generated depending on the proportion of filtrate to be purged. X: Nickel sulfate complexes (e.g., Na2Ni(SO4)2·(H2O)4) are formed regardless of the proportion of filtrate purged.

[0134] [Table 3]

[0135] [Table 4]

[0136] Referring to Table 3, in the cases of Example 1 and Examples 1-1 to 1-7 in which the filtrate was purged and recycled, the content of impurities contained in the nickel sulfate hexahydrate was reduced.

[0137] In Examples 1-5 to 1-7, in which 40 wt% or more of the total weight of the filtrate was purged, the recovery rate of nickel was less than 90%.In Examples 1 to 4, in which 30 wt% was purged, the recovery rate of nickel was less than 95%.

[0138] In the comparative example where the filtrate was not purged, the impurity content was significantly higher.

[0139] Referring to Table 4 above, depending on the lithium content, sodium content, evaporation temperature, or cooling temperature in the feed solution, nickel sulfate complexes such as Li2SO4·H2O, Na2SO4·NiSO4·4H2O, 3Na2SO4·Li2SO4·12H2O, and Na2SO4·10H2O may be formed, or the nickel recovery rate may decrease.

[0140] Regardless of the lithium and sodium concentrations in the feed solution, when the proportion of filtrate purged was 30 wt % or more, the nickel recovery rate corresponded to less than 95%.

[0141] In Examples 2-1 to 2-12, in which the lithium concentration and sodium concentration in the feed solution were adjusted without changing the evaporation temperature and cooling temperature, when the sodium concentration in the feed solution exceeded 0.4 wt %, a nickel sulfate complex was sometimes produced.

[0142] In Examples 2-9 to 2-12, in which the lithium concentration in the feed solution exceeded 0.4 wt %, even when the proportion of the solution to be purged was equivalent to 10 wt %, the recovery rate of nickel was equivalent to less than 95%.

[0143] In Examples 2-3, 2-4, 2-7, 2-11, and 2-12, in which the sodium concentration in the feed solution exceeded 0.4% by weight, when the proportion of purged filtrate was 20% by weight, the nickel recovery rate was sometimes less than 95%.

[0144] In Examples 3-2 to 3-9, in which the evaporation temperature and cooling temperature were changed to adjust the lithium concentration and sodium concentration in the feed solution, when the lithium concentration in the feed solution exceeded 0.2 wt % or the sodium concentration exceeded 0.4 wt %, a nickel sulfate complex was sometimes produced.

[0145] In Examples 3-6 to 3-9, in which the lithium concentration in the feed solution exceeded 0.2 wt %, even when the proportion of purged filtrate was equivalent to 20 wt %, the recovery rate of nickel was equivalent to less than 95%.

[0146] In Examples 3-4, 3-5, 3-8, and 3-9, in which the sodium concentration in the feed solution was 0.3% by weight or more, the nickel recovery rate was less than 95% even when the proportion of purged filtrate was 10% by weight. [Explanation of symbols]

[0147] 100: Supply department 110: Reactor 200: Feed solution 210: Filtrate 220: Purge flow path 230: Regenerated flow path 250: Nickel sulfate collection section

Claims

1. providing a feed solution comprising a nickel salt and an aqueous sulfuric acid solution; crystallizing the feed solution to produce a mixed liquor containing nickel sulfate solids; subjecting the mixed liquid to solid-liquid separation to collect nickel sulfate salt; and recycling the filtrate produced from the solid-liquid separation together with a purge.

2. The method for producing nickel sulfate salt according to claim 1 , wherein the step of recycling the filtrate comprises circulating the filtrate to the feed solution.

3. 3. The method for producing nickel sulfate salt according to claim 2, wherein the purging comprises purging 1% by weight to 20% by weight of the total weight of the filtrate.

4. 3. The method for producing nickel sulfate salt according to claim 2, wherein the purging comprises purging 5% by weight to 10% by weight of the total weight of the filtrate.

5. 3. The method for producing nickel sulfate salt according to claim 2, wherein the recycling comprises circulating 90% or more of the total nickel contained in the filtrate to the feed solution.

6. The step of generating the mixture includes: evaporating the feed solution to form a first solution; and a step of cooling and crystallizing the first solution to produce a second solution as the mixed solution.

7. The step of preparing the feed solution comprises: recovering a positive electrode active material from the lithium secondary battery; and extracting the nickel salt from the positive electrode active material.

8. The method for producing nickel sulfate according to claim 7 , wherein the positive electrode active material contains manganese or cobalt.

9. 9. The method for producing nickel sulfate salt according to claim 8, wherein the feed solution contains 3% to 10% by weight of nickel based on the total weight of the feed solution.

10. The method for producing nickel sulfate salt according to claim 1 , wherein the feed solution further contains lithium impurities or sodium impurities.

11. 11. The method for producing nickel sulfate salt according to claim 10, wherein the content of the lithium impurity is 0.4 wt % or less based on the total weight of the feed solution.

12. 11. The method for producing nickel sulfate salt according to claim 10, wherein the content of the sodium impurity is 0.5% by weight or less based on the total weight of the feed solution.

13. The method for producing nickel sulfate salt according to claim 10, wherein the nickel sulfate salt contains the lithium impurity or the sodium impurity in an amount of 500 ppm or less.

14. The nickel sulfate salt is nickel sulfate hexahydrate (NiSO ４ ・6H ２ 10. The method for producing nickel sulfate salt according to claim 1, further comprising:

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