All-in-one nickel smelting method for recovering nickel hydroxide from nickel-containing raw materials

Abstract

The present invention provides a nickel smelting method comprising: (A-i) 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 the roasted ore produced by the roasting step; (D) a neutralization step of neutralizing the second leach solution produced by the second leaching step; (E) a purification step of removing impurities contained in the neutralized solution produced by the neutralization step; and (F) a precipitation step of performing a precipitation method to recover nickel from the purified solution produced by the purification step, wherein nickel hydroxide is recovered by the precipitation step.

Description

Technical Field

[0001] The present invention relates to a nickel smelting method and a method for producing an aqueous nickel solution using the same. More specifically, the present invention relates to a method for smelting nickel from raw materials and recovering high-purity nickel in the form of nickel hydroxide.

Background Art

[0002] Nickel can be recovered using various raw materials such as nickel metal, nickel matte, nickel concentrate, and nickel-containing process by-products. Nickel sulfate, which is one of the various recovery forms of nickel, is usually known to preferably have a nickel sulfate content of 99% or more and other impurity contents of several hundred ppm or less.

[0003] To produce such nickel sulfate, conventionally, leaching was carried out at normal pressure using an inorganic acid, followed by neutralization using sodium hydroxide or sodium carbonate, impurity removal, etc. to produce a high-purity aqueous nickel sulfate solution, which was then crystallized to produce nickel sulfate hexahydrate.

[0004] However, in the conventional method, raw material substances with good solubility in specific inorganic acids are limited. To remove the substances (e.g., Na) introduced as neutralizing agents, a method of removing Na through water washing after sludge filtration was used. However, such a method has the demerits of an increase in the amount of wastewater and a long process time, leading to problems of a decrease in production volume and an increase in wastewater treatment costs.

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide an all-in-one process that can fluidly respond even when applying various nickel-containing raw materials in a hybrid process that combines dry smelting and wet smelting technologies to recover high-purity nickel from nickel-containing composite raw materials, and can obtain nickel in a desired form by appropriately applying subsequent processes.

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

[0007] The present invention aims to provide an economical and environmentally friendly nickel smelting process that can be applied to composite raw materials even in a single step by combining a recycling wet smelting method, which enables selective separation of lithium and conversion of composite compounds into single compounds through a dry smelting pretreatment method, as well as recovery of inorganic acids from harmful gases, and minimizes the inflow of Na impurities. [Means for solving the problem]

[0008] One aspect of the present invention is (A-i) a reduction heat treatment step of heat-treating a first raw material containing nickel and lithium; (B) a first leaching step of leaching the heat-treated product produced by the reduction heat treatment step; (A-ii) a roasting step of heat-treating a second raw material containing nickel and sulfur; (C) a second leaching step of leaching the first leaching residue produced by the first leaching step and the roasted ore produced by the roasting step; (D) a neutralization step of neutralizing the second leaching solution produced by the second leaching step; (E) a purification step of removing impurities contained in the neutralized solution produced by the neutralization step; and

[0009] (F) The process includes a precipitation step in which a precipitation method is used to recover nickel from the purified liquid produced by the purification step,

[0010] This invention relates to a nickel smelting method in which nickel hydroxide is recovered by the aforementioned precipitation step.

[0011] One embodiment of the present invention provides a nickel smelting method in which the first and second raw materials independently comprise at least one selected from the group consisting of oxides, hydroxides, sulfides, and sulfur oxides, and the oxides, hydroxides, sulfides, and sulfur oxides independently comprise concentrate (Ore), matte, black mass (BM), black powder (BP), mixed hydroxide precipitate (MHP), mixed carbonate precipitate (MCP), mixed sulfide precipitate (MSP), or mixtures thereof.

[0012] One embodiment of the present invention provides a nickel smelting method in which the first raw material comprises nickel in the form of nickel oxide or a nickel metal composite oxide.

[0013] One embodiment of the present invention provides a nickel smelting method in which the second raw material contains nickel in the form of nickel sulfide.

[0014] One embodiment of the present invention provides a nickel smelting method in which the reduction heat treatment step is carried out at a temperature of 650 to 950°C by introducing a first raw material into a heat treatment apparatus and injecting nitrogen gas.

[0015] One embodiment of the present invention provides a nickel smelting method in which the first leaching step is carried out using a first leaching agent comprising an inorganic acid, water, or a mixture thereof.

[0016] One embodiment of the present invention provides a nickel smelting method in which the first leaching solution obtained by the first leaching step contains lithium, and the first leaching residue contains nickel.

[0017] One embodiment of the present invention provides a nickel smelting method in which the roasting step is performed at a temperature of 650 to 950°C by introducing a second raw material into a heat treatment device and injecting oxygen gas.

[0018] One embodiment of the present invention provides a nickel smelting method in which, 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.

[0019] One embodiment of the present invention provides a nickel smelting method in which the second leaching step is carried out using a second leaching agent comprising an inorganic acid, water, or a mixture thereof.

[0020] One embodiment of the present invention provides a nickel smelting method in which the second leaching step is carried out at a temperature of 150 to 250°C and a pressure of 800 to 4,300 kPa.

[0021] One embodiment of the present invention provides a nickel smelting method in which the second leaching step is carried out in an atmosphere with an acidity of 100 to 200 g / L.

[0022] One embodiment of the present invention provides a nickel smelting method in which the neutralization step is carried out using a neutralizing agent containing MHP, MCP, nickel hydroxide (Ni(OH)2), nickel carbonate (NiCO3), sodium hydroxide (NaOH), sodium carbonate (Na2CO3), calcium hydroxide (Ca(OH)2), magnesium hydroxide (Mg(OH)2), calcium oxide (CaO), magnesium oxide (MgO), or a mixture thereof.

[0023] One embodiment of the present invention provides a nickel smelting method in which the neutralization step is carried out at 80°C under conditions of pH 2 to 4.5.

[0024] One embodiment of the present invention can provide a nickel smelting method, wherein the purification process includes: (E-i) a first purification process for removing impurities contained in the post-neutralization solution generated by the neutralization process; (E-ii) a second purification process for removing impurities contained in the first post-purification solution generated by the first purification process; and (E-iii) a third purification process for removing impurities contained in the second post-purification solution generated by the second purification process.

[0025] One embodiment of the present invention can provide a nickel smelting method, wherein the first purification process uses a precipitation method to remove impurities including copper, iron, aluminum, silicon, zinc, cobalt, magnesium, or combinations thereof.

[0026] One embodiment of the present invention can provide a nickel smelting method, wherein the first purification process is performed by: (i) a sulfide precipitation process in which a sulfide precipitating agent is added to the post-neutralization solution at a content of 1.0 to 2.5 equivalents of the copper content in the post-neutralization solution; (ii) a hydroxide precipitation process in which a hydroxide precipitating agent is added to the post-neutralization solution at a content of 0.8 to 1.5 equivalents of the impurity content in the neutralized solution; or a combination of (i) and (ii).

[0027] One embodiment of the present invention can provide a nickel smelting method, wherein the second purification process uses a solvent extraction method to remove impurities including zinc, magnesium, manganese, or combinations thereof.

[0028] One embodiment of the present invention can provide a nickel smelting method, wherein the second purification process includes: (i) a loading process in which a first solvent extraction agent is added to the first post-purification solution to extract impurities including zinc, magnesium, or combinations thereof into the organic phase; and (ii) a stripping process in which an inorganic acid is added to the organic phase to extract impurities including zinc, manganese, or combinations thereof contained in the organic phase into the aqueous phase.

[0029] One embodiment of the present invention can provide a nickel smelting method, wherein the third purification process uses a solvent extraction method to remove impurities containing cobalt.

[0030] One embodiment of the present invention provides a nickel smelting method in which the third purification step includes (i) a loading step of adding a second solvent extractant to the second purified liquid to extract cobalt-containing impurities into the organic phase, and (ii) a stripping step of adding an inorganic acid to the organic phase to extract cobalt-containing impurities contained in the organic phase into the aqueous phase.

[0031] One embodiment of the present invention provides a nickel smelting method in which the precipitation step is carried out using a precipitant containing sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2), magnesium hydroxide (Mg(OH)2), calcium oxide (CaO), magnesium oxide (MgO), or a mixture thereof.

[0032] One embodiment of the present invention provides a nickel smelting method in which the precipitation step is carried out at 85°C and under conditions of pH 6.5 to 10.0. [Effects of the Invention]

[0033] According to the present invention, selective leaching and recovery of lithium is possible through heat treatment of raw materials containing lithium with a strong chemical bond structure by utilizing a reduction heat treatment process.

[0034] According to the present invention, by utilizing the roasting process, nickel-containing raw materials with diverse chemical bonding configurations can be transformed into a single phase, ensuring uniformity in subsequent processes and improving the overall usability of the process to enable flexible responses to the rapidly changing nickel raw material market. [Brief explanation of the drawing]

[0035] [Figure 1] Figure 1 is a diagram showing the entire process for smelting nickel and producing nickel hydroxide according to one embodiment of the present invention. [Modes for carrying out the invention]

[0036] The embodiments of the present invention are provided as examples for the purpose of illustrating the technical idea of ​​the present invention. The scope of rights according to the present invention is not limited to the embodiments presented below or the specific descriptions relating thereto.

[0037] In this specification, unless otherwise specified, "%" is understood to mean measurements based on weight (wt).

[0038] The present invention will be described below with reference to the drawings.

[0039] Figure 1 is a diagram showing the entire process for smelting nickel and producing nickel hydroxide according to one embodiment of the present invention.

[0040] Referring to Figure 1, a method may be provided for smelting nickel to high purity through a series of steps, and for producing nickel hydroxide using such nickel. Such a method can improve versatility for various raw materials and products, operational stability and purity, and reduce manufacturing costs. Each step will be described in detail below with reference to the respective drawings.

[0041] raw material

[0042] The first and second raw materials, which are the starting materials of the present invention, are composite raw materials mainly containing nickel and may independently include at least one selected from the group consisting of oxides, hydroxides, sulfides, and sulfur oxides. For example, the oxides, hydroxides, sulfides, and sulfur oxides may independently include concentrate (Ore), matte, black mass (BM), black powder (BP), mixed hydroxide precipitate (MHP), mixed carbonate precipitate (MCP), mixed sulfide precipitate (MSP), or mixtures thereof.

[0043] For example, the first raw material may include black mass (BM), black powder (BP), mixed hydroxide precipitate (MHP), mixed carbonate precipitate (MCP), or mixtures thereof. For example, in addition to nickel (Ni) and lithium (Li), the first raw material may contain iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), magnesium (Mg), sodium (Na), silicon (Si), or combinations thereof as impurities. For example, the composition of the first raw material may be as shown in Table 1 below. For example, the first raw material may contain nickel in the form of nickel oxide (NiO) or nickel metal composite oxides mixed with other metals.

[0044] (Unit: wt%) [Table 1]

[0045] For example, the second raw material may include concentrate, matte, mixed sulfide precipitate (MSP), or mixtures thereof. For example, in addition to nickel (Ni) and sulfur (S), the second raw material may contain impurities such as iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), magnesium (Mg), sodium (Na), silicon (Si), or combinations thereof. For example, the composition of the second raw material may be as shown in Table 2 below. For example, the second raw material may contain nickel in the form of nickel sulfide (NiS).

[0046] (Unit: wt%) [Table 2]

[0047] Reduction heat treatment process (S10)

[0048] A reduction heat treatment step (S10) may be performed as a pretreatment step for the first raw material.

[0049] In the reducing heat treatment step (S10), the first raw material containing nickel and lithium in a composite oxide form that can bond with various metals may be subjected to a heat treatment in a reducing atmosphere to induce a phase change to oxides and / or carbonites, thereby converting the lithium-containing compound into a substance with high solubility in water or inorganic acids.

[0050] Thus, by changing the compound form of the lithium-containing first raw material through a reducing heat treatment step (S10) before performing the first leaching step (S20) for leaching / extracting lithium, as described later, the leaching efficiency in the first leaching step (S20) for leaching / extracting lithium can be increased.

[0051] For example, the reduction heat treatment process (S10) can be carried out using heat treatment equipment such as an electric furnace (e.g., a box furnace) or a rotary furnace.

[0052] According to one embodiment of the present invention, the reduction heat treatment step (S10) can be carried out at a temperature of 650 to 950°C by introducing a first raw material into a heat treatment apparatus and injecting nitrogen gas. For example, a fixed amount of the first raw material can be charged into the heat treatment apparatus, and nitrogen gas (N2gas) can be injected sufficiently to maintain a reducing atmosphere, and the reduction heat treatment can be carried out at 650 to 950°C. In this process, not only lithium but also other metals can react together, and a phase change can occur through the reaction shown in [Reaction Equation 1] below. In addition, further reactions can occur through the reaction equations shown in [Reaction Equation 2] and [Reaction Equation 3] below.

[0053] [Reaction Equation 1]

[0054] 9LiLi 1 / 3 Co 1 / 3 Mn 1 / 3 O2+0.25C→3NiO+3MnO2+Co3O4+4.5Li2O+0.25CO2(g)

[0055] [Reaction Equation 2]

[0056] 4MnO2 + C → 2Mn2O3 + CO2(g)

[0057] [Reaction Equation 3]

[0058] Li2O + CO2(g) → Li2CO3

[0059] 1st leaching process (S20)

[0060] In the first leaching step (S20), nickel and lithium-containing raw materials that have undergone phase change by the reducing heat treatment step (S10) can be leached out.

[0061] The first leaching step (S20) may be performed after the reducing 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, rod mill, bead mill, attrition mill, etc. The first leaching step can selectively leach heat-treated lithium using a first leaching agent (e.g., an inorganic acid, water, or a mixture thereof).

[0062] In one embodiment, the inorganic acid may be at least one selected from the group consisting of sulfuric acid (H2SO4), hydrochloric acid (HCl), and nitric acid (HNO3), or an inorganic acid diluted with water may be used, or sulfuric acid produced by collecting sulfur dioxide gas generated in the subsequent roasting step (S30) may be used.

[0063] 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) through the following [reaction formula 4] to produce the first leached solution. The first leached solution may contain lithium.

[0064] [Reaction Equation 4] Li2CO3 + 2H2O → 2LiOH + H2O + CO2

[0065] In one embodiment, metals other than lithium may remain in the residue. For example, metals such as nickel (Ni), cobalt (Co), and manganese (Mn) may remain in the residue and be included in the first leaching residue.

[0066] The lithium concentration of the first leaching solution obtained in the first leaching step may be approximately 0.1 to 8.5 g / L. This can be used as a raw material for the cathode material of lithium-ion batteries, and can be produced into lithium hydroxide (LiOH·H2O), lithium carbonate (Li2CO3), lithium phosphate (Li3PO4), etc., through generally known precipitation and crystallization processes.

[0067] In the case of MHP and MCP generated during the lithium-ion battery recycling process, they may contain Li in addition to Ni, Co, and Mn, and can be used as the first raw material for the first leaching process.

[0068] Roasting process (S30)

[0069] A roasting process (S30) may be performed as a pretreatment process for the second raw material.

[0070] In the roasting process (S30), inorganic acids can be produced through the phase change of nickel-containing raw materials bound to various compounds, as well as through the recycling of sulfur dioxide (SO2gas) generated during the heat treatment process.

[0071] Before the roasting process (S30), the nickel-containing second raw material may be in the form of a sulfide, which can be converted to an oxide by the roasting process (S30). If the nickel-containing second raw material is leached in the sulfide state, the generation of hydrogen sulfide gas (H2S gas) will cause a reprecipitation reaction of the metal, resulting in a lower leaching rate. Therefore, by converting the form of the nickel-containing second raw material compound through the roasting process (S30) before the second leaching process (S40), the leaching efficiency in the second leaching process (S40) can be increased. Here, the roasting process (S30) can be carried out using heat treatment equipment such as an electric furnace (box furnace) or a tubular furnace (rotary kiln).

[0072] According to one embodiment of the present invention, the roasting process (S30) involves charging a certain amount of nickel-containing raw material into an electric furnace, sufficiently injecting oxygen (O2) for conversion to nickel oxide, and proceeding with roasting at 650-950°C. In this process, not only nickel but also other impurities react together, and a phase change may occur through the reaction equation shown in [Reaction Equation 5] below. Furthermore, the sulfur dioxide gas generated in the roasting process (S30) can be produced as sulfuric acid (H2SO4) by mixing it with water through a separate collection facility and used in the subsequent leaching process.

[0073] [Reaction Equation 5] 2NiS + 3O2 → 2NiO + 2SO2

[0074] 2nd leaching process (S40)

[0075] In the second leaching step (S40), the first leaching residue remaining in the residue after the first leaching step (S20) can be leached together with the roasting residue (roasted 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 roasting 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), a second leaching agent (for example, an inorganic acid, water, or a mixture thereof) may be used for leaching. 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 (H2SO4), hydrochloric acid (HCl), and nitric acid (HNO3), or an inorganic acid diluted with water may be used, or sulfuric acid produced by collecting sulfur dioxide gas generated in the roasting process (S30) may be used.

[0076] In one embodiment, sulfuric acid may be used as a second leaching agent. In this case, nickel may be leached from the first leaching residue and the roasting residue containing nickel in the form of nickel sulfate (NiSO4) through the reaction formula 6 below to produce a second leaching solution.

[0077] [Reaction Equation 6] NiO + H2SO4 → NiSO4 + H2O

[0078] The second leaching step (S40) can be carried out at a temperature of approximately 150-250°C and a pressure of 800-4,300 kPa. As the reaction temperature rises, a constant pressure level is maintained by the saturated water vapor pressure, and additional pressure can be applied for a complete reaction.

[0079] For example, the second leaching step (S40) can be carried out in an atmosphere with an acidity of 100 to 200 g / L. After performing the second leaching step (S40) in an acidic atmosphere with a low pH to secure a sufficient amount of the second leached solution, the subsequent neutralization step (S50) can be carried out.

[0080] In one embodiment, not only nickel but also other impurities may leach out. For example, impurities such as iron (Fe), cobalt (Co), copper (Cu), and zinc (Zn) may leach out together with nickel and be included in the second leaching solution.

[0081] The nickel concentration of the second leaching solution obtained in the second leaching step (S40) may be approximately 45-105 g / L, and the residual acidity may be 10-80 g / L.

[0082] Neutralization process (S50)

[0083] In the neutralization step (S50), the second leaching solution produced by the second leaching step (S40) can be neutralized. The neutralization step (S50) may be performed after the second leaching step (S40).

[0084] When a second leachate is formed in a high-pH atmosphere, a small amount of the second leachate may be produced.

[0085] In one embodiment, the second leaching step (S40) can be performed in an acidic atmosphere with a low pH to secure a sufficient amount of the second leached solution, after which the neutralization step (S50) can be carried out.

[0086] In the neutralization step (S50), a neutralizing agent may be added to raise the pH of the second leaching solution produced in the second leaching step (S40). The addition of the neutralizing agent may also be for the purpose of subsequent purification steps.

[0087] In one example, the neutralizing agent may be at least one selected from the group consisting of nickel-containing by-products (MHP, MCP), nickel hydroxide (Ni(OH)2), nickel carbonate (NiCO3), sodium hydroxide (NaOH), sodium carbonate (Na2CO3), calcium hydroxide (Ca(OH)2), magnesium hydroxide (Mg(OH)2), calcium oxide (CaO), and magnesium oxide (MgO).

[0088] The reason for using MHP and MCP as neutralizing agents, even though they are used as raw materials, is that hydroxides and carbon dioxide generally have high solubility in acid without roasting, eliminating the need for high-temperature, high-pressure leaching conditions which are costly to process. Furthermore, it has the effect of preparing the purification process (S60), which is carried out in a high pH range by consuming the acid (H2SO4) remaining after the second leaching process (S40).

[0089] 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 water-containing cake-like nickel-containing by-product. When using a nickel-containing by-product, the amount of neutralizing agent added separately can be reduced, thus saving costs. In addition, the inflow of other impurities can be prevented, and the concentration of nickel in the solution after neutralization can be increased.

[0090] In one embodiment, the neutralization step (S50) may be carried out at 80°C with a pH of approximately 2 to 4.5. During this process, some impurities, including iron (Fe) and aluminum (Al), may precipitate and be removed.

[0091] Purification process (S60)

[0092] In the purification step (S60), impurities contained in the neutralized solution produced in the neutralization step (S50) are removed, and the neutralized solution can be purified. The purification step (S60) may be performed after the neutralization step (S50).

[0093] In one embodiment, the purification step (S60) may include a first purification step (S61) for removing impurities contained in the neutralized liquid produced by the neutralization step (S50); a second purification step (S62) for removing impurities contained in the first purified liquid produced by the first purification step (S61); and a third purification step (S63) for removing impurities contained in the second purified liquid produced by the second purification step (S62).

[0094] 1st purification step (S61)

[0095] In the first purification step (S61), the neutralized solution produced in the neutralization step (S50) can be purified. The neutralized solution may be the neutralized leachate. The first purification step (S61) is a step to remove impurities from the neutralized solution after the neutralization step (S50).

[0096] The first purification step (S61) may be a step to remove impurities using a precipitation method. In the first purification step (S61), at least one selected from the group consisting of sodium sulfide (Na2S), sodium hydrosulfide (NaSH), ammonium hydrogen sulfide (NH4HS), and hydrogen sulfide (H2S) can be used as a precipitant to remove impurities using a sulfide precipitation method. Through this, a precipitate mainly composed of copper sulfide (CuS) and containing impurities such as zinc, lead, and cadmium can be recovered. This can then be produced as copper metal through purification steps such as solvent extraction and substitution.

[0097] Furthermore, in the first purification step (S61), at least one selected from the group consisting of sodium hydroxide (NaOH), sodium carbonate (Na2CO3), calcium hydroxide (Ca(OH)2), magnesium hydroxide (Mg(OH)2), calcium oxide (CaO), and magnesium oxide (MgO) can be used to remove impurities using the hydroxide precipitation method. Through this, impurities such as aluminum (Al), iron (Fe), chromium (Cr), and silicon (Si) can be precipitated and removed. When sodium hydrosulfide is used as the precipitating agent, the reaction equation is as shown in [Reaction Equation 7] below, and when sodium hydroxide is used as the precipitating agent, the reaction equation is as shown in [Reaction Equation 8] below.

[0098] [Reaction Equation 7] 2CuSO4 + 2NaSH → Na2SO4 + H2SO4 + 2CuS↓

[0099] [Reaction Equation 8] MSO4 + 2NaOH → Na2SO4 + M(OH)2↓ (M = Al, Fe, Cr, Si)

[0100] In the first purification step (S61), during the sulfide precipitation method, the precipitant can be added in an equivalent ratio of approximately 1.0 to 2.5 relative to the copper contained in the neutralized solution. If the sulfide precipitant is added in an equivalent ratio of less than 1.0 relative to copper, the copper precipitation rate may be 83% or less, and a complete reaction may not occur. If the sulfide precipitant is added in an equivalent ratio greater than 2.5 relative to copper, excess impurities originating from the precipitant will flow in, negatively impacting the process, and the recovery rate will decrease due to the coprecipitation of nickel. The pH range in which this reaction takes place may be 0.8 to 2.5 at 70°C.

[0101] In the purification process using the hydroxide precipitation method, the precipitating agent can be added in an equivalent ratio of approximately 0.8 to 1.5 relative to the impurities in the neutralized solution. If the hydroxide precipitating agent is added in an equivalent ratio of less than 0.8 relative to the impurities, the impurity removal rate may be 85% or less, and a complete reaction may not occur. If the hydroxide precipitating agent is added in an equivalent ratio greater than 1.5 relative to the heavy metals, excess impurities originating from the precipitating agent will flow in, negatively impacting the process, and the recovery rate will decrease due to the coprecipitation of nickel. The pH range in which this reaction takes place may be 2.5 to 4.5 at 60°C.

[0102] After the first purification step (S61), the content of copper, iron, aluminum, and silicon in the first purified solution may be reduced to 5 mg / L or less, and the content of zinc, cobalt, and magnesium in the first purified solution may be reduced to 20 mg / L or less.

[0103] 2nd purification step (S62)

[0104] In the second purification step (S62), the first purified liquid produced in the first purification step (S61) may be further purified. The second purification step (S62) may be performed after the first purification step (S61). The second purification step (S62) may be a step in which impurities are removed using a solvent extraction method.

[0105] In the second purification step (S62), organic extractants may be used to remove impurities such as zinc (Zn), magnesium (Mg), and manganese (Mn).

[0106] In one embodiment, the second purification step (S62) may include a loading step and a stripping step. 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.

[0107] The loading step may be a step of extracting impurities, including zinc, magnesium, or combinations thereof, contained in the first purified liquid into the organic phase. The loading step may be a step of extracting zinc, magnesium, and manganese contained in the first purified liquid after the first purification step (S61) into the organic phase using an organic extractant.

[0108] The amount of the organic phase relative to water added in the loading process can be approximately 1 to 3 by volume. If the amount of the organic phase relative to water added in the loading process is less than 1 by volume, the binding between the target metal and the organic extractant will not be complete, and the extraction rate will be 90% or less. If the volume ratio of the organic phase added in the loading process exceeds 3, the process cost will increase due to the excessive use of the organic extractant. To adjust the pH range of the loading process to 2.0 to 4.0, at least one selected from the group consisting of sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) may be used. The reaction temperature at this time can be 30 to 40°C.

[0109] Once the extraction of zinc, magnesium, and manganese into the organic phase is complete through mixing of the aqueous and organic phases, phase separation is possible due to the difference in specific gravity between the organic and aqueous phases. A second purified solution can be produced through phase separation. This second purified solution is a nickel-containing aqueous solution from which zinc and magnesium have been removed, and the nickel content may be 50-100 g / L.

[0110] An organic phase containing zinc and magnesium may undergo a stripping process. In the stripping process, an inorganic acid can be added to the organic phase after the loading process to remove impurities contained in the organic phase. The stripping process may involve back-extracting the zinc, magnesium, and manganese contained in the organic phase into the aqueous phase.

[0111] The amount of organic phase relative to water added in the stripping process can be approximately 5 to 10 by volume. If the amount of organic phase added in the stripping process is less than 5 by volume, complete extraction of impurities is possible, but the amount of water used may increase. If the volume ratio of organic phase added in the stripping process exceeds 10, the back-extraction efficiency of impurities may decrease. The pH range of the stripping process can be approximately 0.5 to 1.5. Sulfuric acid (H2SO4) may be used to adjust the pH range of the stripping process to approximately 0.5 to 1.5. The reaction temperature at this time can be 30 to 40°C.

[0112] Third purification step (S63)

[0113] In the third purification step (S63), the second purified solution produced in the second purification step (S62) may be further purified. The third purification step (S63) may be performed after the second purification step (S62). The third purification step (S63) may be a step to remove impurities using solvent extraction. An organic extractant may be used in the third purification step (S63) to remove impurities including cobalt. In one example, the third purification step (S63) may include a loading step and a stripping step. 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.

[0114] The loading process may be a process of extracting cobalt-containing impurities from the second purified liquid into the organic phase. The loading process may be a process of extracting cobalt contained in the second purified liquid after the second purification process (S62) into the organic phase using an organic extractant.

[0115] The amount of the organic phase relative to water added in the loading process can be approximately 1 to 3 by volume. If the amount of the organic phase relative to water added in the loading process is less than 1 by volume, the binding between the target metal and the organic extractant may not be complete, and the extraction rate may be 90% or less. If the volume ratio of the organic phase added in the loading process exceeds 3, the process cost may increase due to excessive use of the organic extractant. To adjust the pH range of the loading process to 4 to 5, at least one selected from the group consisting of sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) may be used. The reaction temperature at this time may be 30 to 40°C.

[0116] Once the extraction of cobalt into the organic phase is complete through mixing of the aqueous and organic phases, phase separation is possible due to the difference in specific gravity between the organic and aqueous phases. A third purified solution can be produced through phase separation. This third purified solution is a nickel-containing aqueous solution from which cobalt has been removed, and its nickel content may range from 65 to 125 g / L.

[0117] The organic phase containing cobalt may undergo a stripping process.

[0118] In the stripping process, after the loading process, an inorganic acid can be added to the organic phase to remove the cobalt contained in the organic phase. The stripping process may be a process of back-extracting the cobalt contained in the organic phase into the aqueous phase.

[0119] The amount of organic phase relative to water added to the stripping process can be approximately 3 to 10 by volume. If the amount of organic phase added to the stripping process is less than 3 by volume, complete extraction of impurities is possible, but the amount of water used may increase. If the amount of organic phase added to the stripping process is greater than 10 by volume, the back-extraction efficiency of cobalt may decrease. The pH range of the stripping process can be approximately 0.5 to 1.5. Sulfuric acid (H2SO4) may be used to adjust the pH range of the stripping process to approximately 0.5 to 1.5. The reaction temperature at this time can be 30 to 40°C.

[0120] Once the extraction of cobalt into the organic phase is complete through mixing of the aqueous and organic phases, phase separation is possible due to the difference in specific gravity between the organic and aqueous phases. Through phase separation, a process solution containing cobalt can be produced, which can then be further purified through precipitation and crystallization to produce high-purity cobalt sulfate.

[0121] Sedimentation process (S70)

[0122] In the precipitation step (S70), the purified liquid produced by the purification step (S60) (for example, the third purified liquid produced by the third purification step (S63)) may precipitate. The precipitation step (S70) may be performed after the third purification step (S63).

[0123] The precipitation step (S70) may be a step in which nickel is precipitated using a precipitation method and impurities are removed. In the precipitation step (S70), at least one selected from the group consisting of sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2), magnesium hydroxide (Mg(OH)2), calcium oxide (CaO), and magnesium oxide (MgO) can be used as a precipitating agent for precipitation of nickel.

[0124] When sodium hydroxide is used as a precipitating agent, the reaction equation is as follows [Reaction Equation 9].

[0125] [Reaction Equation 9] NiSO4 + 2NaOH + xH2O → Ni(OH)2 + Na2SO4 + xH2O (x≧0)

[0126] The precipitation process (S70) can be carried out at 75-85°C and a pH of 6.5-10.0. If the pH is below 6.5, the nickel recovery rate may be less than 80%. If the pH exceeds 10.0, excess impurities originating from the precipitating agent will flow in, negatively impacting the process and leading to reduced economic efficiency due to excessive use of the precipitating agent.

[0127] In the precipitation step (S70), some impurities, including sodium (Na) and potassium (K), may be removed. In one example, after the precipitation reaction, the nickel-containing precipitate is recovered through solid-liquid separation, and at least some of these impurities may be removed by washing with diluting acid and water.

[0128] The nickel-containing precipitate residue produced by the present invention can be used as a nickel compound in powder form after drying, and through further processing, can be appropriately used as a precursor nickel raw material among the raw materials for the positive electrode active material of lithium secondary batteries.

[0129] Experimental example

[0130] [Raw materials]

[0131] A first raw material was prepared by mixing A to C, each containing the elements listed in Table 3 below, in predetermined proportions.

[0132] (Unit: wt%) [Table 3]

[0133] *In addition to the metal ions mentioned above, the sum of ions including sulfur (S), oxygen (O), and hydrogen (H) results in a weight ratio of 100.

[0134] A second raw material containing the elements listed in Table 4 below was prepared.

[0135] (Unit: wt%) [Table 4]

[0136] In addition to the metal ions mentioned above, the sum of ions including oxygen (O) and hydrogen (H) results in a weight ratio of 100.

[0137] [Reducing heat treatment process]

[0138] A first raw material containing nickel, lithium, etc., was subjected to a reduction heat treatment. Specifically, 2.0 kg of the raw material was charged into a tubular furnace, and while maintaining a reducing atmosphere with N2 gas, it was subjected to a reduction heat treatment at 850°C for 3 hours to obtain the residue after the reduction heat treatment, which was converted from lithium oxide (Li2O) to lithium carbonate (Li2CO3).

[0139] [First leaching process]

[0140] Lithium was recovered through water leaching of the residue after reductive heat treatment. Specifically, 100g of raw material was loaded into a ball mill, ground with 2.5L of water (H2O) for 2 hours, and then water leached. Solid-liquid separation using vacuum filtration was then performed to obtain a first leaching residue containing the elements listed in Table 5 and a first post-leaching liquid containing the elements listed in Table 6.

[0141] (Unit: wt%) [Table 5]

[0142] In addition to the metal ions mentioned above, the sum of ions including oxygen (O) and hydrogen (H) results in a weight ratio of 100.

[0143] (Unit: g / L) [Table 6]

[0144] [Roasting process]

[0145] A roasting process was carried out on the second raw material containing nickel, sulfur, etc. Specifically, 2 kg of the raw material was charged into a tubular furnace, and after sufficient oxygen (O2) was injected, it was roasted at 850°C for 3 hours to obtain the roasted residue (roasted ore) which was converted from nickel sulfide (NiS) to nickel oxide (NiO).

[0146] [Second leaching process]

[0147] The raw materials, which consisted of a mixture of the residue after the reduction heat treatment and the residue after roasting in a weight ratio of 2:8, were subjected to high-temperature, high-pressure leaching.

[0148] In an autoclave, 450g of the raw material mixture was mixed with 3L of water, and the mixture was maintained at 240°C and 3,500kPa for 3 hours at an initial acidity of 120g / L. As a result, a second leaching solution was obtained with a nickel leaching rate of 95% and a nickel concentration of 60g / L.

[0149] [Neutralization process]

[0150] A neutralization process was carried out using nickel-containing by-products from the second leaching solution.

[0151] By maintaining the pH of 2 L of the second leaching solution at 2.5 for 3 hours at 80°C after adding a nickel-containing by-product, a neutralized solution with a nickel concentration of 82 g / L was obtained.

[0152] [First purification step]

[0153] A first purification step was performed using a precipitation method to remove impurities contained in the neutralized solution.

[0154] After neutralization, sodium hydrogen sulfide (NaSH) in an equivalent ratio of 1.3 equivalents (eq) of copper (Cu) was added to the solution, and the pH was maintained at 2.5 at 70°C for 2 hours. As a result, 99.8% of the copper was removed. Furthermore, to remove aluminum, iron, and silicon contained in the solution, nickel-containing by-products and sodium hydroxide (NaOH) were used, and the pH was maintained at 4.5 for 2 hours. As a result, a first purified solution was obtained in which more than 99.5% of the aforementioned impurities were removed.

[0155] [Second purification process]

[0156] A second purification step was performed using solvent extraction to remove impurities contained in the first purified solution.

[0157] To load impurities containing zinc and magnesium with an extractant, 500 mL of the first purified solution was mixed with 1,000 mL of a 25% diluted Di-2-Ethylhexyl Phosphoric Acid extractant, and the mixture was stirred at 40°C for 10 minutes at a pH of 3.5. 99% of zinc and 43% of magnesium were extracted through phase separation due to gravity difference. Complete extraction of impurities was then possible using a mixer-settler via a countercurrent exchange method.

[0158] [Third purification step]

[0159] A third purification step was performed using solvent extraction to remove cobalt contained in the second purified solution.

[0160] 500 mL of the second purified solution containing cobalt was mixed with 1,000 mL of Bis (2,4,4-TRIMETHYLPENTYL) Phosphinic Acid extractant diluted to 25%, and stirred at pH 5.0 at 40°C for 10 minutes. Approximately 55% of the cobalt was extracted by phase separation due to the difference in specific gravity, and complete extraction of impurities was possible using a mixer settler via countercurrent exchange.

[0161] Through this process, the cobalt was purified to 3 mg / L or less, and a third purified solution containing the elements listed in Table 7 below was obtained.

[0162] (Unit: mg / L) [Table 7]

[0163] [Precipitation process]

[0164] A precipitation step was performed using the precipitation method to recover nickel contained in the third purified liquid in the form of a precipitate.

[0165] To 1 L of the third-stage purified solution containing 42 g / L of nickel, the pH was maintained at 8.0 for 2 hours at 85°C using sodium hydroxide (NaOH). Solid-liquid separation was then performed using vacuum filtration, and after washing with 1 L of distilled water (DIW), a precipitate containing the elements listed in Table 8 below was obtained.

[0166] (Unit: wt%) [Table 8]

[0167] Although embodiments of the present invention have been described above with reference to the attached drawings, persons with ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing its technical idea or essential features.

[0168] Therefore, the embodiments described above should be understood to be illustrative and not limiting in all respects. The scope of the present invention is indicated by the claims rather than by the above detailed description, and all modifications or modified forms derived from the meaning and scope of the claims and the concept of equivalents thereof should be interpreted as being included within the scope of the present invention. Furthermore, it should be confirmed that the present invention described above encompasses the following aspects. [1] (A-i) A reduction heat treatment step in which a first raw material containing nickel and lithium is heat-treated; (B) A first leaching step in which the heat treatment product generated by the reduction heat treatment step is leached out; (A-ii) A roasting process in which the second raw material containing nickel and sulfur is heat-treated; (C) A second leaching step in which the first leaching residue produced by the first leaching step and the roasted ore produced by the roasting step are leached out; (D) A neutralization step to neutralize the second leaching solution produced by the second leaching step; (E) A purification step to remove impurities contained in the neutralized liquid produced by the neutralization step; and (F) The process includes a precipitation step in which a precipitation method is used to recover nickel from the purified liquid produced by the purification step, A nickel smelting method in which nickel hydroxide is recovered by the aforementioned precipitation step. [2] The first and second raw materials each independently include at least one selected from the group consisting of oxides, hydroxides, sulfides, and sulfur oxides. The nickel smelting method according to item 1, wherein the oxides, hydroxides, sulfides, and sulfur oxides independently comprise concentrate (Ore), matte, black mass (BM), black powder (BP), mixed hydroxide precipitate (MHP), mixed carbonate precipitate (MCP), mixed sulfide precipitate (MSP), or mixtures thereof. [3] The nickel smelting method according to claim 1, wherein the first raw material comprises nickel in the form of nickel oxide or a nickel metal composite oxide. [4] The nickel smelting method according to item 1 or 2, wherein the second raw material comprises nickel in the form of nickel sulfide. [5] The nickel smelting method according to any one of items 1 to 4, wherein the reduction heat treatment step is performed at a temperature of 650 to 950°C by introducing a first raw material into a heat treatment apparatus and injecting nitrogen gas. [6] The nickel smelting method according to any one of claims 1 to 5, wherein the first leaching step is carried out using a first leaching agent comprising an inorganic acid, water, or a mixture thereof. [7] A nickel smelting method according to any one of claims 1 to 6, wherein the first leaching liquid obtained by the first leaching step contains lithium, and the first leaching residue contains nickel. [8] The nickel smelting method according to any one of items 1 to 7, wherein the roasting step is performed at a temperature of 650 to 950°C by introducing a second raw material into a heat treatment device and injecting oxygen gas. [9] Nickel smelting method according to any one of items 1 to 8, 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 nickel smelting method according to any one of claims 1 to 9, wherein the second leaching step is carried out using a second leaching agent comprising an inorganic acid, water, or a mixture thereof.

[11] The nickel smelting method according to any one of items 1 to 10, wherein the second leaching step is carried out at a temperature of 150 to 250°C and a pressure of 800 to 4,300 kPa.

[12] The nickel smelting method according to any one of items 1 to 11, wherein the second leaching step is carried out in an atmosphere with an acidity of 100 to 200 g / L.

[13] The neutralization step involves MHP, MCP, nickel hydroxide (Ni(OH) 2 ), nickel carbonate (NiCO2) 3 ), sodium hydroxide (NaOH), sodium carbonate (Na 2 CO 3 ), calcium hydroxide (Ca(OH) 2 ), magnesium hydroxide (Mg(OH) 2 A nickel smelting method according to any one of claims 1 to 12, carried out using a neutralizing agent comprising calcium oxide (CaO), magnesium oxide (MgO), or a mixture thereof.

[14] The nickel smelting method according to any one of items 1 to 13, wherein the neutralization step is carried out at 80°C under conditions of pH 2 to 4.5.

[15] The aforementioned purification process is (E-i) A first purification step to remove impurities contained in the neutralized liquid produced by the neutralization step; (E-ii) A second purification step to remove impurities contained in the first purified liquid produced by the first purification step; and (E-iii) A nickel smelting method according to any one of claims 1 to 14, comprising a third purification step of removing impurities contained in the second purified liquid produced by the second purification step.

[16] The nickel smelting method according to item 15, wherein the first refining step uses a precipitation method to remove impurities including copper, iron, aluminum, silicon, zinc, cobalt, magnesium, or combinations thereof.

[17] The nickel smelting method according to claim 15 or 16, wherein the first refining step is carried out by (i) a sulfide precipitation step in which a sulfide precipitant is added to the neutralized liquid at a content of 1.0 to 2.5 equivalents of the copper content in the neutralized liquid, (ii) a hydroxide precipitation step in which a hydroxide precipitant is added to the neutralized liquid at a content of 0.8 to 1.5 equivalents of the impurity content in the neutralized liquid, or a combination of (i) and (ii).

[18] The nickel smelting method according to any one of claims 15 to 17, wherein the second purification step is to remove impurities including zinc, magnesium, manganese, or a combination thereof using a solvent extraction method.

[19] The nickel smelting method according to any one of claims 15 to 18, wherein the second purification step comprises (i) a loading step of adding a first solvent extractant to the first purified liquid to extract impurities containing zinc, magnesium, manganese, or a combination thereof into an organic phase, and (ii) a stripping step of adding an inorganic acid to the organic phase to extract impurities containing zinc, magnesium, manganese, or a combination thereof contained in the organic phase into an aqueous phase.

[20] The nickel smelting method according to any one of items 15 to 19, wherein the third purification step is to remove impurities containing cobalt using a solvent extraction method.

[21] The nickel smelting method according to any one of claims 15 to 20, wherein the third purification step includes (i) a loading step of adding a second solvent extractant to the second purified liquid to extract cobalt-containing impurities into an organic phase, and (ii) a stripping step of adding an inorganic acid to the organic phase to extract cobalt-containing impurities contained in the organic phase into an aqueous phase.

[22] The aforementioned precipitation step involves sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH) 2 ), magnesium hydroxide (Mg(OH) 2 A nickel smelting method according to any one of claims 15 to 21, carried out using a precipitant comprising calcium oxide (CaO), magnesium oxide (MgO), or a mixture thereof.

[23] The nickel smelting method according to any one of items 1 to 22, wherein the precipitation step is carried out at 85°C under conditions of pH 6.5 to 10.0.

Claims

1. (A-i) A reduction heat treatment step in which a first raw material containing nickel and lithium is heat-treated; (B) A first leaching step in which the heat treatment product generated by the reduction heat treatment step is leached out; (A-ii) A roasting process in which a second raw material containing nickel and sulfur is heat-treated; (C) A second leaching step in which the first leaching residue produced by the first leaching step and the roasted ore produced by the roasting step are leached out; (D) A neutralization step to neutralize the second leached liquid produced by the second leaching step; (E) A purification step to remove impurities contained in the neutralized liquid produced by the neutralization step; and (F) A precipitation step is performed to recover nickel from the purified liquid produced by the purification step, Nickel hydroxide is recovered by the aforementioned precipitation process. The aforementioned purification process is (E-i) A first purification step to remove impurities contained in the neutralized liquid produced by the neutralization step; (E-ii) A second purification step to remove impurities contained in the first purified liquid produced by the first purification step; and (E-iii) A third purification step is included in which impurities contained in the second purified liquid produced by the second purification step are removed. The second purification step is a nickel smelting method, wherein impurities containing zinc, magnesium, manganese, or combinations thereof are removed using a solvent extraction method.

2. The first and second raw materials each independently include at least one selected from the group consisting of oxides, hydroxides, sulfides, and sulfur oxides. The nickel smelting method according to claim 1, wherein the oxides, hydroxides, sulfides, and sulfur oxides independently comprise concentrate (Ore), matte, black mass (BM), black powder (BP), mixed hydroxide precipitate (MHP), mixed carbonate precipitate (MCP), mixed sulfide precipitate (MSP), or mixtures thereof.

3. The nickel smelting method according to claim 1, wherein the first raw material comprises nickel in the form of nickel oxide or a nickel metal composite oxide.

4. The nickel smelting method according to claim 1, wherein the second raw material contains nickel in the form of nickel sulfide.

5. The nickel smelting method according to claim 1, wherein the reduction heat treatment step is performed at a temperature of 650 to 950°C by introducing a first raw material into a heat treatment apparatus and injecting nitrogen gas.

6. The nickel smelting method according to claim 1, wherein the first leaching step is carried out using a first leaching agent comprising an inorganic acid, water, or a mixture thereof.

7. The nickel smelting method according to claim 1, wherein the first leaching solution obtained by the first leaching step contains lithium, and the first leaching residue contains nickel.

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

9. The nickel smelting method 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 nickel smelting method according to claim 1, wherein the second leaching step is carried out using a second leaching agent comprising an inorganic acid, water, or a mixture thereof.

11. The nickel smelting method according to claim 1, wherein the second leaching step is carried out at a temperature of 150 to 250°C and a pressure of 800 to 4,300 kPa.

12. The nickel smelting method according to claim 1, wherein the second leaching step is carried out in an atmosphere with an acidity of 100 to 200 g / L.

13. The neutralization step involves MHP, MCP, and nickel hydroxide (Ni(OH) ２ ), nickel carbonate (NiCO2) ３ ), sodium hydroxide (NaOH), sodium carbonate (Na ２ CO ３ ), calcium hydroxide (Ca(OH) ２ ), magnesium hydroxide (Mg(OH) ２ The nickel smelting method 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.

14. The nickel smelting method according to claim 1, wherein the neutralization step is carried out at 80°C under conditions of pH 2 to 4.

5.

15. The nickel smelting method according to claim 1, wherein the first refining step uses a precipitation method to remove impurities including copper, iron, aluminum, silicon, zinc, cobalt, magnesium, or combinations thereof.

16. The nickel smelting method according to claim 1, wherein the first refining step is performed by (i) a sulfide precipitation step in which a sulfide precipitant is added to the neutralized liquid in an amount equal to 1.0 to 2.5 equivalents of the copper content in the neutralized liquid, (ii) a hydroxide precipitation step in which a hydroxide precipitant is added to the neutralized liquid in an amount equal to 0.8 to 1.5 equivalents of the impurity content in the neutralized liquid, or a combination of (i) and (ii).

17. The nickel smelting method according to claim 1, wherein the second purification step includes (i) a loading step of adding a first solvent extractant to the first purified liquid to extract impurities containing zinc, magnesium, manganese, or a combination thereof into an organic phase, and (ii) a stripping step of adding an inorganic acid to the organic phase to extract impurities containing zinc, magnesium, manganese, or a combination thereof contained in the organic phase into an aqueous phase.

18. The nickel smelting method according to claim 1, wherein the third purification step removes impurities containing cobalt using a solvent extraction method.

19. The nickel smelting method according to claim 1, wherein the third purification step includes (i) a loading step of adding a second solvent extractant to the second purified liquid to extract cobalt-containing impurities into the organic phase, and (ii) a stripping step of adding an inorganic acid to the organic phase to extract cobalt-containing impurities contained in the organic phase into the aqueous phase.

20. The aforementioned precipitation step involves sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH) ２ ), magnesium hydroxide (Mg(OH) ２ The nickel smelting method according to claim 1, wherein the method is carried out using a precipitant containing calcium oxide (CaO), magnesium oxide (MgO), or a mixture thereof.

21. The nickel smelting method according to claim 1, wherein the precipitation step is carried out at 85°C and under conditions of pH 6.5 to 10.0.

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