Method for producing nickel sulfate aqueous solution from nickel-containing raw material

Abstract

The present invention provides a method for producing an aqueous nickel sulfate solution, comprising: (Ai) a reduction heat treatment step of heat-treating a first feedstock containing nickel and lithium; (B) a first leaching step of leaching a heat-treated product produced by the reduction heat treatment step; (A-ii) a roasting step of heat-treating a second feedstock containing nickel and sulfur; (C) a second leaching step of leaching the first leach residue produced by the first leaching step and roasted ore produced by the roasting step; (D) a neutralization step of neutralizing the second leachate produced by the second leaching step; and (E) a solvent extraction step of purifying nickel from the neutralized liquor produced by the neutralization step.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an aqueous nickel sulfate solution from a nickel-containing raw material, and more particularly to a method for producing an aqueous high-purity nickel sulfate solution from a nickel-containing raw material that can be used for various applications (particularly as a precursor raw material that is a raw material for a positive electrode active material of a lithium secondary battery). [Background technology]

[0002] Nickel can be recovered using various raw materials such as nickel metal, nickel matte, nickel concentrate, and nickel-containing process by-products. It is known that an aqueous solution of nickel sulfate, which is one of the various forms of nickel recovery, preferably has a nickel content of 110 g / L or more and a content of other impurities of several hundred mg / L or less.

[0003] In order to prepare such an aqueous nickel sulfate solution, a high-purity aqueous nickel sulfate solution has been prepared by leaching the solution at atmospheric pressure using an inorganic acid, neutralizing the solution using sodium hydroxide or sodium carbonate, and removing impurities.

[0004] However, in conventional methods, raw materials that are highly soluble in a specific inorganic acid are limited, and in order to remove substances (e.g., Na) added as neutralizing agents, a method of removing Na by washing with water after sludge filtration is used. However, this method has the disadvantage of increasing the amount of wastewater and lengthening the process time, which can lead to increased wastewater treatment costs and reduced production. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide an all-in-one process that can flexibly respond to the nickel-containing raw material by a hybrid process that combines pyrometallurgy and hydrometallurgy techniques to produce a high-purity nickel sulfate aqueous solution from a nickel-containing composite raw material.

[0006] The present invention aims to provide an economical and environmentally friendly process that allows for the recycling of process by-products.

[0007] The present invention aims to provide an environmentally friendly process that enables selective separation of lithium, conversion of complex compounds to single compounds, and recovery of inorganic acids from harmful gases through pyrometallurgical pretreatment.

[0008] The present invention aims to provide an economical and environmentally friendly process that can reduce additional wastewater treatment costs by using hydrometallurgy including a solvent extraction process that can reduce the amount of auxiliary materials used by recycling the process liquid and thereby minimizing the inflow of impurities from the precipitant or auxiliary materials. [Means for solving the problem]

[0009] One aspect of the present invention relates to a method for producing an aqueous nickel sulfate solution, comprising: (Ai) a reduction heat treatment step of heat-treating a first feedstock containing nickel and lithium; (B) a first leaching step of leaching a heat-treated product produced by the reduction heat treatment step; (A-ii) a roasting step of heat-treating a second feedstock containing nickel and sulfur; (C) a second leaching step of leaching a first leach residue produced by the first leaching step and roasted ore produced by the roasting step; (D) a neutralization step of neutralizing a second leach solution produced by the second leaching step; and (E) a solvent extraction step of purifying nickel from the neutralized solution produced by the neutralization step.

[0010] In one embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, wherein the first source material and the second source material each independently include at least one selected from the group consisting of an oxide, a hydroxide, a sulfide, and a sulfate, and the oxide, hydroxide, sulfide, and sulfate each independently include ore, matte, black mass (BM), black powder (BP), mixed hydroxide precipitate (MHP), mixed carbonate precipitate (MCP), mixed sulfide precipitate (MSP), or a mixture thereof.

[0011] An embodiment of the present invention may provide a method for producing a nickel sulfate aqueous solution, wherein the first source material contains nickel in the form of nickel oxide or nickel metal composite oxide.

[0012] An embodiment of the present invention may provide a method for producing a nickel sulfate aqueous solution, wherein the second source material contains nickel in the form of nickel sulfide.

[0013] In one embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, wherein the reduction heat treatment step is carried out at a temperature of 650 to 950°C by feeding the first raw material into a heat treatment device and injecting nitrogen gas.

[0014] One embodiment of the present invention provides a method for producing an aqueous nickel sulfate solution, wherein the first leaching step is carried out using a first leaching agent including an inorganic acid, water, or a mixture thereof.

[0015] One embodiment of the present invention provides a method for producing an aqueous nickel sulfate solution, wherein the first leaching solution obtained in the first leaching step contains lithium and the first leaching residue contains nickel.

[0016] In one embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, wherein the roasting step is carried out at a temperature of 650 to 950°C by feeding the second raw material into a heat treatment device and injecting oxygen gas.

[0017] In one embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, wherein in the second leaching step, the first leaching residue is leached in an atmospheric pressure reactor, and the roasted ore is leached in a high-temperature, high-pressure reactor.

[0018] One embodiment of the present invention provides a method for producing a nickel sulfate aqueous solution, wherein the second leaching step is carried out using a second leaching agent including an inorganic acid or a mixture of an inorganic acid and water.

[0019] One embodiment of the present invention provides a method for producing an aqueous nickel sulfate solution, wherein the second leaching step is carried out at a temperature of 150 to 250° C. and a pressure of 800 to 4300 kPa.

[0020] One embodiment of the present invention provides a method for producing an aqueous nickel sulfate solution, wherein the second leaching step is carried out in an atmosphere having an acidity of 100 to 200 g / L.

[0021] One embodiment of the present invention can provide a method for producing a nickel sulfate aqueous solution, wherein the neutralization step is performed using a neutralizing agent including MHP, MCP, nickel hydroxide (Ni(OH)), nickel carbonate (NiCO), sodium hydroxide (NaOH), sodium carbonate (NaCO), calcium hydroxide (Ca(OH)), magnesium hydroxide (Mg(OH)), calcium oxide (CaO), magnesium oxide (MgO), or a mixture thereof.

[0022] One embodiment of the present invention can provide a method for producing an aqueous nickel sulfate solution, wherein the neutralization step is carried out under conditions of 80° C. and pH 2 to 4.5.

[0023] According to an embodiment of the present invention, there is provided a method for producing an aqueous nickel sulfate solution, wherein the neutralization step is carried out for 2 hours or more, and the residual acidity of the neutralized solution produced by the neutralization step is 10 g / L or less.

[0024] One embodiment of the present invention can provide a method for producing an aqueous nickel sulfate solution, wherein the solvent extraction step includes: (Ei) a first solvent extraction step of purifying nickel from a post-neutralization solution produced in the neutralization step; and (E-ii) a second solvent extraction step of purifying nickel from the first post-extraction solution produced in the first solvent extraction step.

[0025] One embodiment of the present invention can provide a method for producing an aqueous nickel sulfate solution, wherein the first solvent extraction step is carried out by: (i) a first loading step of adding a first organic extractant to the aqueous nickel sulfate solution to load nickel in the organic phase; (ii) a first extraction step of adding an organic extractant after the first loading step to the post-neutralization solution to strip-extract nickel in the aqueous phase; (iii) a first scrubbing step of adding an inorganic extractant to the organic extractant after the first extraction to recover cobalt as an aqueous phase; or (iv) a first stripping step of adding an inorganic extractant to the organic extractant after the first scrubbing step to recover copper as an aqueous phase, or a combination thereof.

[0026] An embodiment of the present invention provides a method for producing an aqueous nickel sulfate solution, wherein the volume ratio of the first organic extractant to the aqueous nickel sulfate solution in the first loading step is 3.5 to 6.5.

[0027] According to one embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, in which the first post-loading solution produced in the first loading step is precipitated, and the precipitated nickel-containing by-product is used as a neutralizing agent in the neutralization step.

[0028] In one embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, wherein in the first extraction step, the volume ratio of the organic extractant after the first loading to the neutralized solution is 1.5 to 4.5.

[0029] In one embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, wherein the volume ratio of the organic extractant to the inorganic extractant in the first scrubbing step and the volume ratio of the organic extractant to the inorganic extractant in the first stripping step are each 9.5 to 12.5.

[0030] One embodiment of the present invention provides a method for producing a nickel sulfate aqueous solution, wherein the first scrubbing step is carried out under a condition of pH 2 to 3.

[0031] One embodiment of the present invention provides a method for producing a nickel sulfate aqueous solution, wherein the first stripping step is carried out under a condition of pH 0.5 to 1.5.

[0032] According to one embodiment of the present invention, there is provided a method for producing an aqueous nickel sulfate solution, in which the organic extractant after the first stripping is reused as the first organic extractant.

[0033] According to an embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, further comprising a first precipitation step of adding a first precipitating agent to the first post-scrubbing solution produced by the first scrubbing step to recover cobalt.

[0034] According to an embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, further comprising a second precipitation step of adding a second precipitant to the first post-stripping solution produced by the first stripping step to recover copper.

[0035] One embodiment of the present invention can provide a method for producing an aqueous nickel sulfate solution, wherein the second solvent extraction step is carried out by: (i) a second loading step of adding a second organic extractant to the aqueous nickel sulfate solution to load nickel in the organic phase; (ii) a second extraction step of adding a second post-loading organic extractant to the first post-extraction solution to strip-extract nickel in the aqueous phase; or (iii) a second stripping step of adding an inorganic extractant to the second post-extraction organic extractant to recover impurities as the aqueous phase, or a combination thereof.

[0036] In one embodiment of the present invention, there is provided a method for producing an aqueous nickel sulfate solution, wherein the volume ratio of the second organic extractant to the aqueous nickel sulfate solution in the second loading step is 4.5 to 8.5.

[0037] According to one embodiment of the present invention, there is provided a method for producing a nickel sulfate aqueous solution, in which the second loading solution produced in the second loading process is precipitated, and the precipitated nickel-containing by-product is used as a neutralizing agent in the neutralization process.

[0038] One embodiment of the present invention provides a method for producing a nickel sulfate aqueous solution, wherein the volume ratio of the second post-loading organic extractant to the first post-extraction solution in the second extraction step is 0.3 to 1.5.

[0039] An embodiment of the present invention provides a method for producing an aqueous nickel sulfate solution, wherein the volume ratio of the organic extractant to the inorganic extractant in the second stripping step is 3.5 to 7.5.

[0040] One embodiment of the present invention provides a method for producing an aqueous nickel sulfate solution, wherein the second stripping step is carried out under a condition of pH 0.25 to 1.5.

[0041] According to one embodiment of the present invention, there is provided a method for producing an aqueous nickel sulfate solution, in which the organic extractant after the second stripping is reused as a second organic extractant. [Effects of the Invention]

[0042] According to the present invention, a high-purity aqueous nickel sulfate solution can be produced from various nickel-containing raw materials.

[0043] According to the present invention, selective leaching and recovery of lithium is possible by heat treating raw materials containing lithium in a strongly chemically bonded form using a reduction heat treatment process.

[0044] According to the present invention, nickel-containing raw materials having various chemical bond forms are converted into a single phase through a roasting process, thereby ensuring the uniformity of subsequent processes and improving the usability of the entire process through a process that can flexibly respond to the rapidly changing nickel raw material market.

[0045] According to the present invention, by-products of the process are utilized as a neutralizing agent in the neutralization process, which can prevent the inflow of impurities from commonly used neutralizing agents or precipitants and can also improve the concentration of the target metal, nickel.

[0046] According to the present invention, nickel sulfate can be suitably used as a precursor raw material among the raw materials for the positive electrode active material of a lithium secondary battery. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 1 is a diagram illustrating an overall process for producing a nickel sulfate aqueous solution according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a first solvent extraction step among steps for producing an aqueous nickel sulfate solution according to one embodiment of the present invention. [Figure 3] FIG. 2 is a diagram showing a second solvent extraction step among the steps for producing an aqueous nickel sulfate solution according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0048] The following examples of the present invention are provided to illustrate the technical concept of the present invention, and the scope of the present invention is not limited to the following examples or the specific descriptions of these examples.

[0049] In this specification, "%" is understood to be measured by weight (wt) unless otherwise specified.

[0050] The present invention will now be described with reference to the drawings.

[0051] Fig. 1 is a diagram showing the overall process for producing a nickel sulfate aqueous solution according to one embodiment of the present invention, while Fig. 2 and Fig. 3 are diagrams showing a first solvent extraction step and a second solvent extraction step, respectively, of the process for producing a nickel sulfate aqueous solution according to one embodiment of the present invention.

[0052] 1 to 3, a method for smelting nickel to high purity through a series of steps and producing a nickel aqueous solution using such nickel can be provided. This method can improve versatility for various raw materials and products, operational stability, and purity, and reduce production costs. Each step will be described in detail below with reference to the figures.

[0053] raw material

[0054] The first and second raw materials, which are starting materials of the present invention, are raw materials mainly containing nickel and may each independently include at least one selected from the group consisting of oxide, hydroxide, sulfide, and sulfate. For example, the oxide, hydroxide, sulfide, and sulfate may each independently include ore, matte, black mass (BM), black powder (BP), mixed hydroxide precipitate (MHP), mixed carbonate precipitate (MCP), mixed sulfide precipitate (MSP), or a mixture thereof.

[0055] For example, the first raw material may include black mass (BM), black powder (BP), mixed hydroxide precipitate (MHP), mixed carbonate precipitate (MCP), or a mixture thereof. For example, the first raw material may include impurities such as iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), magnesium (Mg), sodium (Na), silicon (Si), or a combination thereof, in addition to nickel (Ni) and lithium (Li). For example, the composition of the first raw material may be as shown in Table 1 below. For example, the first raw material may include nickel in the form of nickel oxide (NiO) or a nickel-metal composite oxide mixed with other metals.

[0056] [Table 1]

[0057] For example, the second raw material may include concentrate, matte, mixed sulfide precipitate (MSP), or a mixture thereof. For example, the second raw material may include impurities such as iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), magnesium (Mg), sodium (Na), silicon (Si), or a combination thereof, in addition to nickel (Ni) and sulfur (S). For example, the composition of the second raw material may be as shown in Table 2 below. For example, the second raw material may include nickel in the form of nickel sulfide (NiS).

[0058] [Table 2]

[0059] Reduction heat treatment step (S10)

[0060] A reduction heat treatment step (S10) may be performed as a pretreatment step of the first raw material.

[0061] In the reduction heat treatment step (S10), a first raw material containing nickel and lithium in the form of a composite oxide capable of bonding with various metals may be subjected to a heat treatment in a reducing atmosphere to cause a phase change to an oxide and / or carbonate, thereby converting the lithium-containing compound into a substance that is highly soluble in water or an inorganic acid.

[0062] In this way, by converting the form of the compound of the lithium-containing first raw material by the reduction heat treatment step (S10) before carrying out the first leaching step (S20) described below in which lithium is leached / extracted, it is possible to increase the leaching efficiency in the first leaching step (S20) in which lithium is leached / extracted.

[0063] For example, the reduction heat treatment step (S10) may be carried out using heat treatment equipment such as an electric furnace (for example, a box furnace), a rotary kiln, or the like.

[0064] According to one embodiment of the present invention, the reduction heat treatment step (S10) may be performed at a temperature of 650 to 950°C by introducing the first raw material into a heat treatment device and injecting nitrogen gas. For example, a certain amount of the first raw material may be introduced into the heat treatment device, and reduction heat treatment may be performed at 650 to 950°C while injecting sufficient nitrogen gas (N2 gas) to maintain a reducing atmosphere. During this process, other metals may also react with lithium, causing a phase change according to the following [Reaction Scheme 1]. Further reactions may occur according to the following [Reaction Scheme 2] and [Reaction Scheme 3].

[0065] [Reaction Scheme 1] 9LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2+0.25C→3NiO+3MnO2+Co3O4+4.5Li2O+0.25CO2(g)

[0066] [Reaction Scheme 2] 4MnO2+C→2Mn2O3+CO2(g)

[0067] [Reaction Scheme 3] Li2O+CO2(g) → Li2CO3

[0068] 1st leaching process (S20)

[0069] In the first leaching step (S20), the nickel and lithium-containing raw material that has undergone a phase change by the reduction heat treatment step (S10) may be leached.

[0070] The first leaching step (S20) may be performed after the reduction heat treatment step (S10). For example, the first leaching step (S20) may be performed in a wet mill. The wet mill may be a ball mill, a rod mill, a bead mill, an attrition mill, or the like. In the first leaching step, the heat-treated lithium can be selectively leached using a first leaching agent (e.g., an inorganic acid, water, or a mixture thereof).

[0071] In one embodiment, the inorganic acid may be at least one selected from the group consisting of sulfuric acid (HSO), hydrochloric acid (HCl), and nitric acid (HNO), and may be an inorganic acid diluted with water. Alternatively, sulfuric acid produced by capturing sulfur dioxide gas generated in the subsequent roasting step (S30) may be used.

[0072] In one embodiment, water may be used as the first leaching agent. In this case, lithium may be leached from the lithium-containing raw material in the form of lithium hydroxide (LiOH) according to the following [Reaction Scheme 4], producing a first leaching solution. The first leaching solution may contain lithium.

[0073] [Reaction Scheme 4] Li2CO3+2H2O→2LiOH+H2O+CO2

[0074] In one embodiment, metals other than lithium may remain in the residue, for example, metals such as nickel (Ni), cobalt (Co), manganese (Mn), etc. may remain in the residue and be included in the first leach residue.

[0075] The lithium concentration of the first leaching solution obtained in the first leaching step may be about 0.1 to 8.5 g / L. To use this as a raw material for lithium-ion battery cathode materials, it may be prepared as lithium hydroxide (LiOH·H2O), lithium carbonate (Li2CO3), lithium phosphate (Li3PO4), etc. by commonly known precipitation and crystallization methods.

[0076] The MHP and MCP generated in the recycling process of lithium-ion batteries may contain Li in addition to Ni, Co, and Mn, and can be used as the first raw material for the first leaching step.

[0077] Roasting process (S30)

[0078] As a pretreatment process of the second raw material, a roasting process (S30) may be performed.

[0079] In the roasting step (S30), a phase change of the nickel-containing raw material combined with various compounds may occur, and inorganic acid may be produced by recycling sulfur dioxide gas (SO2 gas) generated during the heat treatment process.

[0080] Before the roasting step (S30), the nickel-containing second raw material may be in the form of a sulfide, which may be converted to an oxide through the roasting step (S30). If the nickel-containing second raw material is leached in the sulfide state, the leaching rate may be reduced due to the reprecipitation of the metal caused by the generation of hydrogen sulfide gas (HS gas). Therefore, by converting the compound form of the nickel-containing second raw material through the roasting step (S30) before the second leaching step (S40), the leaching efficiency of the second leaching step (S40) can be improved. In this case, the roasting step (S30) may be performed using heat treatment equipment such as a box furnace or a rotary kiln.

[0081] According to one embodiment of the present invention, the roasting step (S30) may involve charging a certain amount of nickel-containing raw material into an electric furnace, injecting sufficient oxygen (O2) to convert it into nickel oxide, and roasting at 650 to 950°C. During this process, not only nickel but also other impurities may react, causing a phase change according to the reaction shown in [Reaction Scheme 5] below. In addition, sulfur dioxide gas generated in the roasting step (S30) may be passed through a separate collection facility and mixed with water to produce sulfuric acid (H2SO4), which may be used in subsequent leaching.

[0082] [Reaction Scheme 5] 2NiS+3O2→2NiO+2SO2

[0083] 2nd leaching process (S40)

[0084] In the second leaching step (S40), the first leaching residue remaining in the residue from the first leaching step (S20) may be leached together with the roasted residue (roaster ore) that has undergone a phase change in the roasting step (S30). The second leaching step (S40) may be performed after the roasting step (S30) and the first leaching step. In the second leaching step, the roasted residue may be leached in a high-temperature, high-pressure reactor, and the first leaching residue may be leached in an atmospheric pressure reactor. In the second leaching step (S40), leaching may be performed using a second leaching agent (e.g., an inorganic acid or a mixture of an inorganic acid and water). In one embodiment, the second leaching step (S40) may be performed using an inorganic acid. For example, the inorganic acid may be at least one selected from the group consisting of sulfuric acid (HSO), hydrochloric acid (HCl), and nitric acid (HNO), or an inorganic acid diluted with water may be used. Alternatively, sulfuric acid produced by capturing sulfur dioxide gas generated in the previous roasting step (S30) may be used.

[0085] In one embodiment, sulfuric acid may be used as the second leaching agent. In this case, nickel may be leached from the nickel-containing primary leach residue and roasted residue in the form of nickel sulfate (NiSO4) according to the following [Reaction Scheme 6], producing a second leach solution.

[0086] [Reaction Scheme 6] NiO+H2SO4→NiSO4+H2O

[0087] The second leaching step (S40) may be carried out at a temperature of about 150-250°C and a pressure of 800-4300 kPa. The pressure is maintained at a constant level by the saturated water vapor pressure due to the increase in reaction temperature, and further pressure may be applied to ensure complete reaction.

[0088] For example, the second leaching step (S40) may be carried out in an atmosphere with an acidity of 100 to 200 g / L. After the second leaching step (S40) is carried out in an acidic atmosphere with a low pH to obtain a sufficient amount of second leaching solution, the subsequent neutralization step (S50) can be carried out.

[0089] In one embodiment, other impurities may be leached along with the nickel. For example, impurities such as iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), etc. may be leached along with the nickel and included in the second leach solution.

[0090] The second leaching solution obtained in the second leaching step (S40) may have a nickel concentration of about 45 to 105 g / L and a residual acidity of 10 to 80 g / L.

[0091] Neutralization process (S50)

[0092] In the neutralization step (S50), the second post-leaching solution produced in the second leaching step (S40) may be neutralized. The neutralization step (S50) may be performed after the second leaching step (S40).

[0093] When the second leaching solution is produced in an atmosphere with a high pH, ​​the amount of second leaching solution produced may be small.

[0094] In one embodiment, the second leaching step (S40) is carried out in an acidic atmosphere with a low pH to obtain a sufficient amount of second leaching solution, after which the neutralization step (S50) can be carried out.

[0095] In the neutralization step (S50), a neutralizing agent may be added to raise the pH of the second post-leaching solution produced in the second leaching step (S40), and the addition of the neutralizing agent may be for the subsequent solvent extraction step.

[0096] In one embodiment, the neutralizing agent may be at least one selected from the group consisting of nickel-containing by-products (MHP, MCP), nickel hydroxide (Ni(OH)), nickel carbonate (NiCO), sodium hydroxide (NaOH), sodium carbonate (NaCO), calcium hydroxide (Ca(OH)), magnesium hydroxide (Mg(OH)), calcium oxide (CaO), and magnesium oxide (MgO).

[0097] The reason why MHP and MCP are used as raw materials but also as neutralizing agents is that hydroxides and carbonates generally have high solubility in acids even without roasting, so there is no need to process them under high-temperature, high-pressure leaching conditions, which are costly to process. In addition, the acid (H2SO4) remaining after the second leaching step (S40) is consumed, which has the effect of preparing in advance for the refining step (S60), which is carried out in a high pH range.

[0098] In one embodiment, the nickel-containing by-product may be used as a neutralizing agent in the neutralization step (S50) in the form of a wet cake. When the nickel-containing by-product is used for neutralization, the amount of neutralizing agent added separately can be reduced by utilizing the by-product generated in the process, thereby saving costs. In addition, the inflow of other impurities can be prevented, and the nickel concentration in the neutralized solution can be increased.

[0099] In one embodiment, the neutralization step (S50) may be carried out at 80° C. and a pH of about 2 to 4.5. During this process, some impurities, including iron (Fe), aluminum (Al), etc., may be precipitated and removed.

[0100] In one embodiment, the neutralization step (S50) is carried out for 2 hours or more, and the residual acidity of the neutralized solution produced by the neutralization step may be 10 g / L or less. For example, the neutralization step (S50) may be carried out for 10 hours or less.

[0101] Solvent extraction step (S60)

[0102] In the solvent extraction step (S60), nickel may be purified from the neutralized solution produced in the neutralization step (S50). The solvent extraction step (S60) may be performed after the neutralization step (S50).

[0103] In one embodiment, the solvent extraction step (S60) may include a first solvent extraction step (S70) of purifying nickel from the post-neutralization solution produced in the neutralization step (S50), and a second solvent extraction step of purifying nickel from the first post-extraction solution produced in the first solvent extraction step.

[0104] First solvent extraction step (S70)

[0105] In the first solvent extraction step (S70), nickel may be purified from the neutralized solution produced in the neutralization step (S50). The neutralized solution may be a neutralized leaching solution. The first solvent extraction step (S70) is a step for purifying nickel by removing impurities from the neutralized solution after the neutralization step (S50), and an organic extractant (first organic extractant) may be used.

[0106] The first solvent extraction step (S70) may include a first loading step (S71), a first extraction step (S72), a first scrubbing step (S73), and a first stripping step (S74). The organic extractant may be at least one selected from the group consisting of di-2-ethylhexyl phosphoric acid, mono-2-ethylhexyl (2-ethylhexyl) phosphonate, and bis(2,4,4-trimethylpentyl)phosphinic acid.

[0107] First loading step (S71)

[0108] The first loading step (S71) may be a step of increasing the nickel concentration in the organic phase. The first loading step (S71) may be a step of using an aqueous nickel sulfate (NiSO4) solution and a first organic extractant to load nickel contained in the aqueous nickel sulfate solution into the first organic extractant and transfer it to the organic phase.

[0109] The volume ratio of the first organic extractant (organic phase) to the aqueous nickel sulfate solution (aqueous phase) in the first loading step (S71) may be 3.5 to 6.5. If the volume ratio of the organic phase to the aqueous phase in the first loading step (S71) is less than 3.5, the binding between the target metal (nickel) and the organic extractant may be incomplete, resulting in a low extraction rate (e.g., 85% or less). If the volume ratio of the organic phase to the aqueous phase in the first loading step (S71) is more than 6.5, excessive use of the first organic extractant may increase process costs.

[0110] The first loading step (S71) may be carried out in a pH range of 4.5 to 6.0, and at least one selected from the group consisting of sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) may be used to adjust the pH to such a range.

[0111] When the extraction of nickel into the organic phase is completed by mixing the aqueous phase and the organic phase, phase separation can occur due to the difference in specific gravity between the organic phase and the aqueous phase. This phase separation can produce a first post-loading solution (aqueous phase). The first post-loading solution is a nickel-containing aqueous solution from which most of the nickel has been extracted, and the nickel content may be 0.1 to 4.5 g / L.

[0112] After precipitating the first post-loading solution, the precipitated nickel-containing by-products can be used as a neutralizing agent in the neutralization step (S50). For example, nickel-containing by-products such as nickel hydroxide (Ni(OH)2) and nickel carbonate (NiCO3) can be precipitated using precipitating agents such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3).

[0113] 1st extraction step (S72)

[0114] In the first extraction step (S72), the neutralized solution is mixed with a first post-loading organic extractant containing nickel to remove impurities from the neutralized solution and simultaneously increase the concentration of nickel in the neutralized solution. The first extraction step (S72) may be performed after the first loading step (S71). The first post-loading organic extractant may be used to purify impurities in the first extraction step (S72).

[0115] In the first extraction step (S72), the volume ratio of the organic extractant (organic phase) after the first loading to the neutralized solution (aqueous phase) may be 1.5 to 4.5. If the volume ratio of the organic phase to the aqueous phase in the first extraction step (S72) is less than 1.5, the extraction efficiency of impurities may decrease (e.g., less than 75%). If the volume ratio of the organic phase to the aqueous phase in the first extraction step (S72) is more than 4.5, the amount of nickel remaining in the organic phase may increase, which may reduce the process efficiency. The pH range of the first extraction step (S72) may be approximately 3.5 to 5.0.

[0116] When the aqueous phase and the organic phase are mixed to complete the stripping of nickel into the aqueous phase, phase separation is possible due to the difference in specific gravity between the organic phase and the aqueous phase. This phase separation can produce a first post-extraction solution (aqueous phase). The first post-extraction solution is an aqueous solution containing nickel as a main component, and the nickel content may be 75 to 110 g / L.

[0117] First scrubbing step (S73)

[0118] In the first scrubbing step (S73), the cobalt contained in the first post-extraction organic extractant can be recovered as an aqueous phase by mixing the first post-extraction organic extractant containing other impurities such as cobalt (Co), magnesium (Mg), or manganese (Mn) with an inorganic extractant. The first scrubbing step (S73) may be performed after the first extraction step (S72).

[0119] The inorganic extractant may be an inorganic acid, water or a mixture thereof.

[0120] The volume ratio of the first post-extraction organic extractant (organic phase) to the inorganic extractant (aqueous phase) in the first scrubbing step (S73) may be 9.5 to 12.5. If the volume ratio of the organic phase to the aqueous phase in the first scrubbing step (S73) exceeds 12.5, the cobalt recovery rate may decrease (e.g., less than 65%). If the volume ratio of the organic phase to the aqueous phase in the first scrubbing step (S73) is less than 9.5, the cobalt recovery rate may increase, but the process cost may increase due to the use of unnecessary inorganic extractant. The pH range of the first scrubbing step (S73) may be approximately 2.0 to 3.0.

[0121] When the aqueous phase and the organic phase are mixed to complete the stripping of impurities, including cobalt, into the aqueous phase, phase separation is possible due to the difference in specific gravity between the organic phase and the aqueous phase. This phase separation can produce a first post-scrubbing solution (aqueous phase). The first post-scrubbing solution is an aqueous solution containing cobalt as a major component, and the cobalt content may be 3.5 to 8.5 g / L.

[0122] First stripping step (S74)

[0123] In the first stripping step (S74), the copper-containing first post-extraction organic extractant is mixed with an inorganic extractant to recover the copper contained in the first post-extraction organic extractant as an aqueous phase, and the pure organic extractant can be recovered. The first stripping step (S74) may be performed after the first scrubbing step (S73).

[0124] The inorganic extractant may be an inorganic acid, water or a mixture thereof.

[0125] The volume ratio of the first post-extraction organic extractant (organic phase) to the inorganic extractant (aqueous phase) in the first stripping step (S74) may be 9.5 to 12.5. If the volume ratio of the organic phase to the aqueous phase in the first stripping step (S74) exceeds 12.5, the copper recovery rate may decrease (e.g., less than 90%). If the volume ratio of the organic phase to the aqueous phase in the first stripping step (S74) is less than 9.5, the copper recovery rate may increase, but the process cost may increase due to the use of unnecessary inorganic extractant. The pH range of the first stripping step (S74) may be approximately 0.5 to 1.5.

[0126] When the stripping of copper into the aqueous phase is completed by mixing the aqueous and organic phases, phase separation can occur due to the difference in specific gravity between the organic and aqueous phases. Phase separation can produce a first post-stripping solution (aqueous phase) and a first post-stripping organic extractant (organic phase). The first post-stripping solution is an aqueous solution containing copper as a major component, and the copper content may be 40 to 50 g / L. The first post-stripping organic extractant may be reused as the first organic extractant in the first loading step (S71) (see FIG. 2).

[0127] Second solvent extraction step (S80)

[0128] In the second solvent extraction step (S80), nickel may be purified from the first post-extraction solution produced in the first solvent extraction step (S70). The second solvent extraction step (S80) may be performed after the first solvent extraction step (S70). The second solvent extraction step (S80) is a step for purifying nickel by removing impurities from the first post-extraction solution, and an organic extractant (second organic extractant) may be used.

[0129] The second solvent extraction step (S80) may include a second loading step (S81), a second extraction step (S82), and a second stripping step (S84). As the organic extractant, at least one selected from the group consisting of di-2-ethylhexyl phosphoric acid, mono-2-ethylhexyl (2-ethylhexyl) phosphonate, and bis(2,4,4-trimethylpentyl)phosphinic acid can be used.

[0130] Second loading step (S81)

[0131] The second loading step (S81) may be a step of increasing the nickel concentration in the organic phase. The second loading step (S81) may be a step of using an aqueous nickel sulfate (NiSO4) solution and a second organic extractant to load nickel contained in the aqueous nickel sulfate solution into the second organic extractant and transfer it to the organic phase.

[0132] The volume ratio of the second organic extractant (organic phase) to the aqueous nickel sulfate solution (aqueous phase) in the second loading step (S81) may be 4.5 to 8.5. If the volume ratio of the organic phase to the aqueous phase in the second loading step (S81) is less than 4.5, the binding between the target metal (nickel) and the organic extractant may be incomplete, resulting in a low extraction rate (e.g., 90% or less). If the volume ratio of the organic phase to the aqueous phase in the second loading step (S81) is greater than 8.5, excessive use of the second organic extractant may increase process costs.

[0133] The second loading step (S81) may be carried out in a pH range of 5.5 to 6.5, and at least one selected from the group consisting of sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) may be used to adjust the pH to such a range.

[0134] When the extraction of nickel into the organic phase is completed by mixing the aqueous phase and the organic phase, phase separation can occur due to the difference in specific gravity between the organic phase and the aqueous phase. This phase separation can produce a second post-loading solution (aqueous phase). The second post-loading solution is a nickel-containing aqueous solution from which most of the nickel has been extracted, and the nickel content may be 0.1 to 9.5 g / L.

[0135] After precipitating the second post-loading solution, the precipitated nickel-containing by-products can be used as a neutralizing agent in the neutralization step (S50). For example, nickel-containing by-products such as nickel hydroxide (Ni(OH)2) and nickel carbonate (NiCO3) can be precipitated using precipitating agents such as sodium hydroxide (NaOH) and sodium carbonate (Na2CO3).

[0136] 2nd extraction step (S82)

[0137] In the second extraction step (S82), the first post-extraction solution from the first solvent extraction step (S70) is mixed with a second post-loading organic extractant containing nickel, thereby removing impurities contained in the first post-extraction solution and increasing the nickel concentration in the first post-extraction solution. The second extraction step (S82) may be performed after the second loading step (S81). The second post-loading organic extractant may be used to purify impurities in the second extraction step (S82).

[0138] In the second extraction step (S82), the volume ratio of the second post-loading organic extractant (organic phase) to the first post-extraction solution (aqueous phase) may be 0.3 to 1.5. If the volume ratio of the organic phase to the aqueous phase in the second extraction step (S82) is less than 0.3, the extraction efficiency of impurities may decrease (e.g., less than 90%). If the volume ratio of the organic phase to the aqueous phase in the second extraction step (S82) is greater than 1.5, the amount of nickel remaining in the organic phase may increase, reducing process efficiency. The pH range for the second extraction step (S82) may be approximately 4.5 to 5.5.

[0139] When the aqueous phase and the organic phase are mixed to complete the stripping of nickel into the aqueous phase, phase separation is possible due to the difference in specific gravity between the organic phase and the aqueous phase. A second post-extraction solution (aqueous phase) can be produced by the phase separation. The second post-extraction solution is an aqueous solution containing nickel as a main component, and the nickel content may be 85 to 125 g / L. The second post-extraction solution may be used as a precursor raw material for a positive electrode active material raw material for a lithium secondary battery.

[0140] Second stripping step (S84)

[0141] In the second stripping step (S84), the impurities contained in the second post-extraction organic extractant are mixed with the inorganic extractant, and the impurities contained in the second post-extraction organic extractant are recovered as an aqueous phase, and the pure organic extractant is recovered. The second stripping step (S84) may be performed after the second extraction step (S82).

[0142] The inorganic extractant may be an inorganic acid, water or a mixture thereof.

[0143] The volume ratio of the second post-extraction organic extractant (organic phase) to the inorganic extractant (aqueous phase) in the second stripping step (S84) may be 3.5 to 7.5. If the volume ratio of the organic phase to the aqueous phase in the second stripping step (S84) exceeds 7.5, the impurity removal rate may decrease (e.g., less than 85%). If the volume ratio of the organic phase to the aqueous phase in the second stripping step (S84) is less than 3.5, the impurity removal rate may increase, but the process cost may increase due to the use of unnecessary inorganic extractant. The pH range of the second stripping step (S84) may be approximately 0.25 to 1.5.

[0144] After the back-extraction of impurities into the aqueous phase is completed by mixing the aqueous and organic phases, phase separation is possible due to the difference in specific gravity between the organic and aqueous phases. This phase separation can produce a second post-stripping organic extractant (organic phase). This second post-stripping organic extractant may be reused as the second organic extractant in the second loading step (S81) (see FIG. 3).

[0145] First precipitation step (S90)

[0146] In the first precipitation step (S90), the first post-scrubbing solution produced by the first scrubbing step (S73) in the first solvent extraction step (S70) may be purified. The first precipitation step (S90) may be performed after the first scrubbing step (S73). The first precipitation step (S90) is a step for removing magnesium from the first post-scrubbing solution and recovering cobalt.

[0147] In one embodiment, a first precipitating agent may be used to remove magnesium in the first precipitation step (S90). The first precipitating agent may be at least one selected from the group consisting of sodium fluoride (NaF), oxalic acid (C2H2O4), sodium oxalate (Na2C2O4), sodium hydroxide (NaOH), and sodium carbonate (Na2CO3). For example, when sodium fluoride is used as the first precipitating agent, the reaction formula is as shown in [Reaction Formula 7] below.

[0148] [Reaction Scheme 7] MgSO4+2NaF → MgF2↓+Na2SO4

[0149] In the first precipitation step (S90), the first precipitating agent may be added at an equivalent ratio of about 1.0 to 3.0 relative to the magnesium contained in the first post-scrubbing solution. If the first precipitating agent is added at an equivalent ratio of less than 1.0 relative to the magnesium, the magnesium precipitation rate may be less than 80%, and the reaction may not be complete. If the first precipitating agent is added at an equivalent ratio of more than 3.0 relative to the magnesium, excessive impurities caused by the first precipitating agent may flow in, negatively affecting the entire process. The pH range of the first precipitation step (S90) may be about 4.5 to 5.5.

[0150] After the precipitation reaction in the first precipitation step (S90) is completed, the solid phase and the liquid phase can be separated by a commonly used solid-liquid separation step. A first post-precipitation solution may be produced by the solid-liquid separation. The first post-precipitation solution is a cobalt-containing aqueous solution from which most impurities have been removed, and may have a cobalt content of 20 to 45 g / L. The first post-precipitation solution may be further purified and used as a precursor raw material for a positive electrode active material for a lithium secondary battery.

[0151] Second precipitation step (S100)

[0152] In the second precipitation step (S100), the first post-stripping solution produced by the first stripping step (S74) in the first solvent extraction step (S70) may be purified. The second precipitation step (S100) may be performed after the first stripping step (S74). The second precipitation step (S100) is a step for recovering copper from the first post-stripping solution.

[0153] In one embodiment, a second precipitating agent may be used to remove copper in the second precipitation step (S100). The second precipitating agent may be at least one selected from the group consisting of sodium sulfide (NaS), sodium hydrosulfide (NaSH), ammonium hydrogen sulfide (NHHS), hydrogen sulfide (HS), and sodium sulfide (NaS). For example, when sodium sulfide is used as the second precipitating agent, the reaction is as shown in Reaction Scheme 8 below.

[0154] [Reaction Scheme 8] 2CuSO4+2NaSH→Na2SO4+H2SO4+2CuS↓

[0155] In the second precipitation step (S100), the second precipitating agent may be added at an equivalent ratio of about 0.8 to 2.0 relative to the copper contained in the first post-stripping solution. If the second precipitating agent is added at an equivalent ratio of less than 0.8 relative to the copper, the copper recovery rate may be less than 80%, and the reaction may not be complete. If the second precipitating agent is added at an equivalent ratio of more than 2.0 relative to the copper, excessive impurities caused by the second precipitating agent may flow in, negatively affecting the entire process. The pH range of the second precipitation step (S100) may be about 2.0 to 3.0.

[0156] After the precipitation reaction in the second precipitation step (S100) is completed, the solid phase and the liquid phase can be separated by a commonly used solid-liquid separation process. A second post-precipitation residue can be produced by the solid-liquid separation. The second post-precipitation residue is a copper-containing precipitate, and the copper content may be 45 to 55 wt %. The first post-precipitation solution may be further refined and used as a precursor raw material for a cathode active material of a lithium secondary battery.

[0157] Experimental Example

[0158] [Raw materials]

[0159] A first raw material was prepared by mixing A to C, each containing the elements shown in Table 3 below, in a predetermined ratio.

[0160] [Table 3] *In addition to the metal ions, the sum of ions including sulfur (S), oxygen (O), and hydrogen (H) makes up a weight ratio of 100.

[0161] A second raw material containing the elements shown in Table 4 below was prepared.

[0162] [Table 4] *The weight ratio of 100 is the sum of the above metal ions, as well as ions containing oxygen (O) and hydrogen (H).

[0163] [Reduction heat treatment process]

[0164] A reduction heat treatment was carried out on the first raw material containing nickel, lithium, etc. Specifically, 2.0 kg of the raw material was charged into a tubular furnace, and then reduction heat treatment was carried out at 850°C for 3 hours while maintaining a reducing atmosphere using nitrogen (N2) gas, and a post-reduction heat treatment residue was obtained in which the form of lithium oxide (Li2O) was converted to the form of lithium carbonate (Li2CO3).

[0165] [First leaching process]

[0166] Lithium recovery was carried out using water leaching of the residue after reduction heat treatment. Specifically, 100 g of raw material was charged into a ball mill, and then crushed and leached with 2.5 L of water (HO) for 2 hours. After that, solid-liquid separation was carried out using vacuum filtration to obtain a first leaching residue containing the elements listed in Table 5 below and a first leaching solution containing the elements listed in Table 6 below.

[0167] [Table 5] *The weight ratio of 100 is the sum of the above metal ions, as well as ions containing oxygen (O) and hydrogen (H).

[0168] [Table 6]

[0169] [Roasting process]

[0170] A roasting process was carried out on the second raw material containing nickel, sulfur, etc. Specifically, 2 kg of raw material was charged into a tubular furnace and roasted at 850°C for 3 hours while injecting sufficient oxygen (O2), obtaining a roasting residue (roasted ore) that had been converted from nickel sulfide (NiS) to nickel oxide (NiO).

[0171] [Second leaching process]

[0172] The residue after the reduction heat treatment and the residue after the roasting were mixed in a weight ratio of 2:8, and the mixture was subjected to high-temperature and high-pressure leaching.

[0173] 450g of the mixed raw material was mixed with 3L of water in an autoclave, and the mixture was kept at 240°C and 3500kPa for 3 hours with an initial acidity of 120g / L. As a result, a second leaching solution with a nickel concentration of 60g / L was obtained, with a nickel leaching rate of 95%.

[0174] [Neutralization process]

[0175] A neutralization step was carried out using nickel-containing by-products from the second leaching solution.

[0176] 2 L of the second leaching solution was maintained at pH 2.5 by adding nickel-containing by-products at 80°C for 3 hours, resulting in a neutralized solution with a nickel concentration of 82 g / L.

[0177] [First solvent extraction process]

[0178] The first solvent extraction step was carried out to purify the nickel contained in the neutralized solution.

[0179] The first loading process is a process of extracting nickel contained in the nickel sulfate aqueous solution with di-2-ethylhexyl phosphate extractant to produce a nickel-containing organic extractant. 500 mL of nickel sulfate aqueous solution containing nickel at a concentration of 100 g / L was mixed with 2,000 mL of organic extractant and stirred at pH 5.0 for 10 minutes, and 95% of the nickel was extracted by phase separation due to the difference in specific gravity.

[0180] Next, the first extraction step was carried out to extract impurities contained in the neutralized solution with the organic phase and simultaneously back-extract nickel contained in the first-loading organic extractant with the aqueous phase. 500 mL of the neutralized solution was mixed with 1,500 mL of the first-loading organic extractant and stirred for 10 minutes at pH 4.0. Phase separation due to differences in specific gravity resulted in a first-extraction solution containing 105 g / L of nickel.

[0181] Next, the first scrubbing step was carried out to extract the cobalt contained in the first post-extraction organic extractant into the aqueous phase. 1,000 mL of the first post-extraction organic extractant was mixed with 100 mL of distilled water and stirred at pH 2.5 for 10 minutes. 95% of the cobalt was back-extracted by phase separation due to the difference in specific gravity.

[0182] Next, the first stripping step was carried out to extract the copper contained in the organic extractant after the first scrubbing into the aqueous phase. 1,000 mL of the organic extractant after the first scrubbing was mixed with 100 mL of distilled water and stirred at pH 1.0 for 10 minutes. 95% of the copper was back-extracted by phase separation due to the difference in specific gravity.

[0183] [Second solvent extraction process]

[0184] In order to further purify the nickel contained in the first post-extraction solution in the first solvent extraction, a second solvent extraction step was carried out.

[0185] The second loading process is a process in which nickel contained in the nickel sulfate aqueous solution is extracted into bis(2,4,4-trimethylpentyl)phosphinic acid extractant to produce a nickel-containing organic extractant. 1,000 mL of nickel sulfate aqueous solution containing 110 g / L of nickel was mixed with 5,500 mL of organic extractant and stirred at pH 6.5 for 10 minutes, and 95% of the nickel was extracted by phase separation due to the difference in specific gravity.

[0186] Next, the impurities contained in the first post-extraction solution were extracted with the organic phase, and at the same time, nickel contained in the second post-loading organic extractant was back-extracted with the aqueous phase in a second extraction step. 1,000 mL of the neutralized solution was mixed with 500 mL of the first post-loading organic extractant and stirred at pH 5.0 for 10 minutes. Phase separation due to differences in specific gravity resulted in a second post-extraction solution with a nickel concentration of 115 g / L.

[0187] Next, a second stripping step was carried out to extract impurities contained in the second post-extraction organic extractant into the aqueous phase. 500 mL of the second post-extraction organic extractant was mixed with 50 mL of distilled water and stirred at pH 1.0 for 10 minutes. 95% of the impurities were back-extracted by phase separation due to the difference in specific gravity.

[0188] [First precipitation step]

[0189] The first precipitation step was carried out to remove magnesium contained in the first scrubbing liquid in the first solvent extraction.

[0190] 1 L of the first scrubbing liquid was maintained at pH 5.5 for 2 hours by adding sodium fluoride and sodium carbonate, resulting in the removal of magnesium and the securing of a first precipitation liquid with a cobalt concentration of 27 g / L.

[0191] [Second precipitation step]

[0192] A second precipitation step was carried out to recover copper contained in the first post-stripping solution in the first solvent extraction.

[0193] 1 L of the liquid after the first stripping was maintained at pH 2.5 with sodium hydrosulfide for 2 hours, subjected to solid-liquid separation using vacuum filtration, and washed with 1 L of distilled water (DIW) to obtain a second precipitate residue containing 51% copper.

[0194] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, it will be understood by those skilled in the art that the present invention may be embodied in other specific forms without changing the technical spirit or essential characteristics thereof.

[0195] Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not limiting. The scope of the present invention is defined by the claims rather than the above detailed description, and any modifications or alterations derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention.

Claims

1. (A-i) a reduction heat treatment step of heat-treating a first raw material containing nickel and lithium; (B) a first leaching step in which the heat-treated product produced by the reduction heat treatment step is leached; (A-ii) a roasting step of heat-treating a second raw material containing nickel and sulfur; (C) a second leaching step in which the first leaching residue produced in the first leaching step and the roasted ore produced in the roasting step are leached; (D) a neutralization step of neutralizing the second post-leaching solution produced by the second leaching step; and (E) A method for producing an aqueous nickel sulfate solution, comprising a solvent extraction step of purifying nickel from the neutralized solution produced in the neutralization step.

2. the first raw material and the second raw material each independently contain at least one selected from the group consisting of oxides, hydroxides, sulfides, and sulfates; 2. The method for producing a nickel sulfate aqueous solution according to claim 1, wherein the oxides, hydroxides, sulfides, and sulfates each independently include concentrate (ore), matte, black mass (BM), black powder (BP), mixed hydroxide precipitate (MHP), mixed carbonate precipitate (MCP), mixed sulfide precipitate (MSP), or a mixture thereof.

3. 2. The method for producing a nickel sulfate aqueous solution according to claim 1, wherein the first source material contains nickel in the form of nickel oxide or nickel metal composite oxide.

4. 2. The method for producing an aqueous nickel sulfate solution according to claim 1, wherein the second source material contains nickel in the form of nickel sulfide.

5. 2. The method for producing a nickel sulfate aqueous solution according to claim 1, wherein the reduction heat treatment step is carried out at a temperature of 650 to 950°C by introducing the first raw material into a heat treatment device and injecting nitrogen gas.

6. 2. The method for producing an aqueous nickel sulfate solution according to claim 1, wherein the first leaching step is carried out using a first leaching agent containing an inorganic acid, water, or a mixture thereof.

7. 2. The method for producing a nickel sulfate aqueous solution according to claim 1, wherein the first leaching solution obtained in the first leaching step contains lithium, and the first leaching residue contains nickel.

8. 2. The method for producing a nickel sulfate aqueous solution according to claim 1, wherein the roasting step is performed at a temperature of 650 to 950°C by introducing the second raw material into a heat treatment device and injecting oxygen gas.

9. 2. The method for producing a nickel sulfate aqueous solution according to claim 1, wherein in the second leaching step, the first leaching residue is leached in an atmospheric pressure reactor, and the roasted ore is leached in a high-temperature, high-pressure reactor.

10. The neutralization step is carried out by mixing MHP, MCP, nickel hydroxide (Ni(OH) ２ ), nickel carbonate (NiCO ３ ), sodium hydroxide (NaOH), sodium carbonate (Na ２ CO ３ ), calcium hydroxide (Ca(OH) ２ ), magnesium hydroxide (Mg(OH) ２ 2. The method for producing a nickel sulfate aqueous solution according to claim 1, wherein the method is carried out using a neutralizing agent comprising calcium oxide (CaO), magnesium oxide (MgO), or a mixture thereof.

11. 2. The method for producing a nickel sulfate aqueous solution according to claim 1, wherein the neutralization step is carried out under conditions of 80°C and pH 2 to 4.

5.

12. 2. The method for producing an aqueous nickel sulfate solution according to claim 1, wherein the neutralization step is carried out for 2 hours or more, and the residual acidity of the neutralized solution produced by the neutralization step is 10 g / L or less.

13. The solvent extraction step comprises: (E-i) a first solvent extraction step of purifying nickel from the neutralized solution produced by the neutralization step; and (E-ii) a second solvent extraction step of purifying nickel from the first post-extraction solution produced in the first solvent extraction step.

14. 14. The method for producing an aqueous nickel sulfate solution according to claim 13, wherein the first solvent extraction step is carried out by: (i) a first loading step of adding a first organic extractant to the aqueous nickel sulfate solution to load nickel in the form of an organic phase; (ii) a first extraction step of adding a post-first loading organic extractant to the post-neutralization solution to strip-extract nickel in the form of an aqueous phase; (iii) a first scrubbing step of adding an inorganic extractant to the post-first extraction organic extractant to recover cobalt as an aqueous phase; or (iv) a first stripping step of adding an inorganic extractant to the post-first scrubbing organic extractant to recover copper as an aqueous phase, or a combination thereof.

15. 15. The method for producing a nickel sulfate aqueous solution according to claim 14, wherein in the first loading step, a volume ratio of the first organic extractant to the nickel sulfate aqueous solution is 3.5 to 6.

5.

16. 15. The method for producing a nickel sulfate aqueous solution according to claim 14, wherein the first post-loading solution produced in the first loading step is precipitated, and the precipitated nickel-containing by-product is used as a neutralizing agent in the neutralization step.

17. 15. The method for producing a nickel sulfate aqueous solution according to claim 14, wherein in the first extraction step, a volume ratio of the first post-loading organic extractant to the post-neutralization solution is 1.5 to 4.

5.

18. 15. The method for producing a nickel sulfate aqueous solution according to claim 14, wherein a volume ratio of the organic extractant to the inorganic extractant in the first scrubbing step and a volume ratio of the organic extractant to the inorganic extractant in the first stripping step are each 9.5 to 12.

5.

19. The method for producing a nickel sulfate aqueous solution according to claim 14, wherein the first scrubbing step is carried out under a condition of pH 2 to 3.

20. The method for producing a nickel sulfate aqueous solution according to claim 14, wherein the first stripping step is carried out under a condition of pH 0.5 to 1.

5.

21. The method for producing an aqueous nickel sulfate solution according to claim 14, wherein the first stripped organic extractant is reused as the first organic extractant.

22. 15. The method for producing a nickel sulfate aqueous solution according to claim 14, further comprising a first precipitation step of adding a first precipitating agent to the first post-scrubbing solution produced in the first scrubbing step to recover cobalt.

23. 15. The method for producing a nickel sulfate aqueous solution according to claim 14, further comprising a second precipitation step of adding a second precipitant to the first post-stripping solution produced in the first stripping step to recover copper.

24. 14. The method for producing an aqueous nickel sulfate solution according to claim 13, wherein the second solvent extraction step is carried out by: (i) a second loading step of adding a second organic extractant to the aqueous nickel sulfate solution to load nickel in the form of an organic phase; (ii) a second extraction step of adding a second post-loading organic extractant to the first post-extraction solution to strip-extract nickel in the form of an aqueous phase; or (iii) a second stripping step of adding an inorganic extractant to the second post-extraction organic extractant to recover impurities as an aqueous phase, or a combination thereof.

25. 25. The method for producing an aqueous nickel sulfate solution according to claim 24, wherein in the second loading step, a volume ratio of the second organic extractant to the aqueous nickel sulfate solution is 4.5 to 8.

5.

26. 25. The method for producing a nickel sulfate aqueous solution according to claim 24, wherein the second post-loading solution produced in the second loading step is precipitated, and the precipitated nickel-containing by-product is used as a neutralizing agent in the neutralization step.

27. 25. The method for producing a nickel sulfate aqueous solution according to claim 24, wherein in the second extraction step, a volume ratio of the second post-loading organic extractant to the first post-extraction solution is 0.3 to 1.

5.

28. 25. The method for producing a nickel sulfate aqueous solution according to claim 24, wherein a volume ratio of the organic extractant to the inorganic extractant in the second stripping step is 3.5 to 7.

5.

29. The method for producing a nickel sulfate aqueous solution according to claim 24, wherein the second stripping step is carried out under a condition of pH 0.25 to 1.

5.

30. 25. The method for producing an aqueous nickel sulfate solution according to claim 24, wherein the second stripped organic extractant is reused as a second organic extractant.

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