Method for solvent extraction of aqueous nickel sulfate solution

Abstract

To provide a solvent extraction method of a nickel sulfate aqueous solution for efficiently obtaining a high-purity nickel sulfate aqueous solution by efficiently removing sodium contained in a nickel-containing organic solvent with a small amount of washing water when purifying a crude nickel sulfate aqueous solution by a solvent extraction method.SOLUTION: In the washing step in the washing solvent extraction vessel group, a part of the discharged outlet side aqueous phase is repeatedly circulated to the inlet side of the same mixer-settler-type solvent extraction vessel as a circulating liquid in the mixer-settler-type solvent extraction vessel, and when the flow rate of the nickel-containing organic solvent supplied from the extraction step is QO, the flow rate of the washing liquid is QW, and the flow rate of the circulating liquid is QR, the following formulas (1) and (2) are satisfied: 0.6 ≤ QO / (QW + QR) ≤ 1.8 (1) 4.0 ≤ QO / QW (2) SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for solvent extraction of an aqueous nickel sulfate solution, and more particularly to a method for solvent extraction of an aqueous nickel sulfate solution, which, when purifying a crude aqueous nickel sulfate solution by solvent extraction, removes impurities such as sodium and ammonium contained in an organic solvent and efficiently obtains a high-purity aqueous nickel sulfate solution. [Background technology]

[0002] Nickel sulfate is widely used in industrial applications such as general electrolytic plating and electroless plating, and in recent years has also seen increasing demand as a nickel raw material for secondary battery cathode materials. However, when used for these applications, it is necessary to minimize the content of impurities such as sodium and ammonium contained in nickel sulfate.

[0003] Conventionally, the purification of crude nickel sulfate aqueous solution has been performed using solvent extraction. However, when an acidic extractant is used as the extractant, a neutralizing agent is required to extract impurities or nickel from the raw solution. Caustic soda is generally used as the neutralizing agent due to its ease of handling. However, the use of caustic soda raises the possibility of sodium contamination not only in the aqueous phase but also in the resulting organic phase. Because sodium is technically difficult to separate from nickel sulfate, it distributes into the nickel sulfate aqueous solution. Furthermore, for example, when concentrating and crystallizing a purified high-purity nickel sulfate aqueous solution, it is extremely difficult to avoid the contamination of sodium as an impurity in the resulting nickel sulfate crystals.

[0004] When using solvent extraction to extract and remove impurities such as cobalt and calcium from crude nickel sulfate aqueous solution using an acidic extractant, alkyl sulfonic acids and alkyl sulfonate esters are often used as acidic extractants. Under pH conditions that allow nickel to partition into the aqueous phase, the sodium in caustic soda, used as a pH adjuster and neutralizer, naturally remains in the aqueous phase and is therefore incorporated into the crystals during crystallization of the purified nickel sulfate aqueous solution. While the pH adjuster and neutralizer are broadly the same, the terms "pH adjuster" and "neutralizer" are used to distinguish between agents used to adjust the pH and agents used to neutralize the hydrogen ions released during extraction. Furthermore, when nickel is extracted from a crude nickel sulfate aqueous solution into an acidic extractant using solvent extraction, the high pH conditions result in a large amount of sodium being co-extracted with nickel. Even when stripped with a mineral acid such as sulfuric acid, most of the sodium transfers to the aqueous phase after stripping, resulting in sodium being mixed into the crystals during nickel sulfate crystallization. Furthermore, even in the aqueous phase where some of the sodium remains, the aqueous phase may form tiny droplets called entrainment and remain in the organic phase, so the sodium in the entrainment will be distributed into the aqueous phase after the stripping. In other words, in the solvent extraction method using an acidic extractant, nickel and sodium behave chemically similarly, so it is not possible to clearly separate sodium as an impurity from nickel.

[0005] For example, Patent Documents 1 and 2 disclose a solvent extraction method comprising an extraction organic washing step in which sodium and ammonium extracted into the organic extractant are washed and removed in an organic solvent extraction tank, and an extraction step in which the wash water from which some of the nickel has been extracted is sent to an extraction tank together with a crude nickel sulfate solution, and nickel is extracted from the crude nickel sulfate by a countercurrent extraction reaction with fresh organic extractant in the extraction tank.

[0006] For example, in the case of the conventional methods disclosed in Patent Documents 1 and 2, the efficiency of removing sodium from the extracted organic phase is not necessarily high, and it is necessary to supply more wash water than necessary to more intensively wash the extracted organic phase, which leads to an increase in the repeated amount of high-purity nickel sulfate aqueous solution as a nickel source in the wash water, and an increase in the amount of caustic soda used for neutralization due to an increase in the amount of nickel supplied to the extraction step, resulting in a decrease in the nickel sulfate yield and an increase in the cost of refining nickel sulfate.

[0007] Thus, when nickel is extracted using an acidic extractant by solvent extraction, the nickel-containing organic solvent after extraction must be vigorously washed with wash water to separate and remove sodium from the organic phase into the wash water phase. However, conventional washing methods require a large amount of wash water, which increases the amount of nickel lost in the wash water after washing, and require post-treatment of the wash water after washing, such as wastewater treatment, making them extremely economically disadvantageous. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 10-310436 [Patent Document 2] Japanese Patent Application Publication No. 10-310434 Summary of the Invention [Problem to be solved by the invention]

[0009] Patent Documents 1 and 2 disclose the appropriate pH range for the extraction step and the nickel concentration of the wash water. They also disclose the phase ratio of the organic phase to the aqueous phase in the extraction step, but do not disclose the optimal flow rate ratio of the organic solvent to the aqueous phase in the organic solvent extraction tank or the optimal flow rate ratio of the organic solvent to the wash water in the extraction organic wash step.

[0010] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for solvent extraction of an aqueous nickel sulfate solution, which, when purifying an aqueous crude nickel sulfate solution by solvent extraction, efficiently removes sodium contained in a nickel-containing organic solvent with a small amount of wash water, thereby efficiently obtaining an aqueous high-purity nickel sulfate solution. [Means for solving the problem]

[0011] The inventors focused on the operating conditions of the solvent extraction tank and found that it is possible to improve the efficiency of sodium removal by specifying the flow rate ratio of the organic phase to the aqueous phase and the flow rate ratio of the organic phase to the wash water that enable the most efficient separation and removal of sodium from the nickel-containing organic solvent.

[0012] That is, one aspect of the present invention is a method for solvent extraction of an aqueous nickel sulfate solution, in which nickel is extracted with an acidic extractant from an aqueous crude nickel sulfate solution containing impurities mainly composed of sodium and ammonium, and the impurities are washed away in a plurality of mixer-settler-type solvent extraction tanks configured in a multistage countercurrent series. The plurality of mixer-settler-type solvent extraction tanks are composed of a group of extraction solvent extraction tanks on the front stage side and a group of washing solvent extraction tanks on the rear stage side, and the method includes an extraction step in which an organic solvent containing an acidic extractant is supplied from the front stage side of the extraction solvent extraction tank group, and a crude nickel sulfate aqueous solution is supplied from the rear stage side of the extraction solvent extraction tank group, thereby causing an extraction reaction between the organic solvent and the crude nickel sulfate aqueous solution in a countercurrent manner, and nickel in the crude nickel sulfate aqueous solution is extracted into the organic solvent; and a step in which the nickel-containing organic solvent obtained in the extraction step is supplied from the front stage side of the washing solvent extraction tank group, and the washing solvent extraction tank group is and a washing step in which a washing liquid is supplied from the rear end of the tank group to wash and remove sodium and ammonium in the nickel-containing organic solvent in a countercurrent manner, and the washed liquid discharged from the front end of the washing step is supplied from the rear end of the extraction step. In this solvent extraction step, the pH of the liquid phase during the extraction reaction is set to 6.0 to 7.0, and in the washing step, the nickel concentration of the washing liquid is set to 10 g / L or more, the pH of the liquid phase during washing and removal is set to 6.0 to 6.8, and the nickel concentration in the nickel-containing organic solvent is set to 95 g / L or more based on the volume of the acidic extractant contained in the nickel-containing organic solvent. In the washing step, in a mixer-settler type solvent extraction tank, a part of the aqueous phase discharged from the outlet side is repeatedly used as a circulating liquid to the inlet side of the same mixer-settler type solvent extraction tank, and the flow rate of the nickel-containing organic solvent supplied from the extraction step is set to Q O , the flow rate of the cleaning solution is Q W , the flow rate of the circulating fluid is Q R Then, the following equation (1) 0.6≦Q O / (Q W +Q R )≦1.8 (1) And the following formula (2) 4.0≦Q O / Q W ···(2) The present invention is characterized in that:

[0013] In one embodiment of the present invention, a compound represented by the following formula (3) 1.3≦Q O / (Q W +Q R )≦1.5 (3) may be set to satisfy the following. [Effects of the Invention]

[0014] According to the present invention, when a crude nickel sulfate aqueous solution is purified by a solvent extraction method, sodium contained in a nickel-containing organic solvent can be efficiently removed with a small amount of wash water, and a high-purity nickel sulfate aqueous solution can be efficiently obtained. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a flow chart showing a process for producing an aqueous nickel sulfate solution. [Figure 2] FIG. 2 is a flow chart showing the process of the solvent extraction step in the method for producing an aqueous nickel sulfate solution. [Figure 3] FIG. 3 is a schematic diagram showing the process flow in a method for solvent extraction of an aqueous nickel sulfate solution according to one embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing a mixer-settler type solvent extraction tank in a method for solvent extraction of an aqueous nickel sulfate solution according to one embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram showing the flow of the aqueous phase and the organic phase in the washing step of the method for solvent extraction of an aqueous nickel sulfate solution according to one embodiment of the present invention. [Figure 6] FIG. 6 is a graph showing the relationship between the organic phase / aqueous phase flow rate ratio and sodium washing efficiency in four washing solvent extraction tanks in the washing step of the method for solvent extraction of an aqueous nickel sulfate solution according to one embodiment of the present invention. [Figure 7] FIG. 7 is a graph showing the relationship between the organic phase / aqueous phase flow rate ratio and sodium washing efficiency in the same washing solvent extraction tank in the washing step of the method for solvent extraction of an aqueous nickel sulfate solution according to one embodiment of the present invention. [Figure 8] FIG. 8 is a graph showing the relationship between the organic phase / washing liquid flow rate ratio in the washing solvent extraction tank and the sodium washing efficiency in Example 4 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will be described in the following order with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention as defined in the claims, and not all of the configurations described in the embodiments are necessarily essential as means for solving the problems of the present invention. 1.Method for producing nickel sulfate aqueous solution 2. Solvent extraction method for nickel sulfate aqueous solution

[0017] <1. Method for producing nickel sulfate aqueous solution> First, prior to a more specific description of the method for solvent extraction of a nickel sulfate aqueous solution, a brief description will be given of a method for producing a nickel sulfate aqueous solution to which a method for solvent extraction of a nickel sulfate aqueous solution according to one embodiment of the present invention is applied. Figure 1 is a flow chart showing a process related to the method for producing a nickel sulfate aqueous solution.

[0018] As shown in Figure 1, the method for producing an aqueous nickel sulfate solution uses, as raw materials, nickel matte produced by pyrometallurgy, deleaded precipitate produced in an electrolytic nickel production process, and crude nickel sulfate generated in copper smelters, etc. Of these, the nickel matte is preferably crushed to a predetermined size and then leached under high-temperature and high-pressure conditions in a pressure leaching process to produce a crude aqueous nickel sulfate solution.

[0019] The deleaded precipitate is dissolved in sulfuric acid in the sulfuric acid dissolution process, and then reduced and dissolved with a reducing agent such as SO2 gas in the reduction dissolution process to produce a crude nickel-cobalt sulfate mixed aqueous solution. The deleaded precipitate is produced in the deleading process of the so-called MCLE method (Matte Chlorine Leach Electrowinning). The MCLE method is a process in which nickel matte and nickel-cobalt mixed sulfide (MS) are repulped with electrolytic wastewater, and then treated in the cementation and chlorine leaching processes to produce electrolytic nickel. The deleaded precipitate is recovered in the deleading process that follows the cementation process.

[0020] The crude nickel sulfate aqueous solution and the mixed aqueous solution of crude nickel sulfate and cobalt sulfate, respectively, produced from the nickel matte and deleaded precipitate, are subjected to iron removal (Fe removal) in the iron removal process to produce an exchange-system Fe removal end solution consisting of a crude nickel sulfate aqueous solution containing at least cobalt.

[0021] On the other hand, after the crude nickel sulfate is dissolved in the dissolution step, Zn and Cd are removed in the Zn and Cd removal step, and iron is removed in the iron removal (Fe removal) step to produce an extract-based Fe-free final solution consisting of an aqueous solution of crude nickel sulfate. This extract-based Fe-free final solution corresponds to the "aqueous solution of crude nickel sulfate" of the present invention.

[0022] In the solvent extraction step, nickel contained in the extraction-system Fe-removal final solution (crude nickel sulfate aqueous solution) obtained in the Fe-removal step is extracted by solvent extraction, and nickel is further released from the organic solvent into which the nickel has been extracted by substitution with cobalt ions or the like, thereby obtaining a high-purity nickel sulfate aqueous solution. The high-purity nickel sulfate aqueous solution obtained through the solvent extraction step has impurities containing iron and zinc removed, as well as impurities such as sodium and ammonium. The solvent extraction method for a nickel sulfate aqueous solution according to the present invention is mainly concerned with this solvent extraction step.

[0023] The solvent extraction step will be described in more detail. Figure 2 is a process diagram showing the solvent extraction step in the method for producing an aqueous nickel sulfate solution. The solvent extraction step includes, for example, an extraction step S1, a washing step S2, an exchange step S3, a nickel recovery step S4, a cobalt recovery step S5, and a stripping step S6. A mixer-settler, which is a countercurrent multistage extraction device, is used in these steps.

[0024] The extraction step S1 is supplied with the final solution (crude nickel sulfate aqueous solution) from the extraction system of the Fe removal step, which precedes the solvent extraction step. In extraction step S1, nickel from the crude nickel sulfate aqueous solution is extracted into an organic phase, and the nickel is supported on an acidic extractant. The acidic extractant is not particularly limited, but a phosphate ester-based acidic extractant such as di-(2-ethylhexyl)phosphonic acid (commonly known as D2EHPA) is used. Mono-2-ethylhexyl 2-ethylhexylphosphonate is particularly preferred. In solvent extraction using an acidic extractant, hydrogen ions are involved in the extraction reaction, so the extraction rate varies depending on the pH. The extraction rate varies depending on the metal, with the order of ease of extraction being Fe > Zn > Cu > Mn > Co > Ca > Mg > Ni.

[0025] By lowering the pH in order along the flow of the organic phase from extraction step S1 to washing step S2, exchange step S3, nickel recovery step S4, cobalt recovery step S5, and stripping step S6, each metal can be separated and recovered in each step. In the solvent extraction step, nickel and cobalt are mainly separated.

[0026] The nickel-containing organic solvent obtained in the extraction step S1 is sent to the washing step S2. The extraction residue discharged from the extraction step S1 is sent outside the system. In the washing step S2, the nickel-containing organic solvent is washed with a washing solution containing nickel. In the exchange step S3, the washed nickel-containing organic solvent (nickel-supported acidic extractant) is brought into contact with a cobalt-containing nickel sulfate aqueous solution containing impurities such as cobalt (exchange system Fe-removal end solution), and the nickel in the nickel-containing organic solvent is replaced with the impurities in the cobalt-containing nickel sulfate aqueous solution. This allows a high-purity nickel sulfate aqueous solution to be obtained.

[0027] In the nickel recovery step S4, sulfuric acid is added to the post-exchange organic phase to adjust the pH to about 4.0. This strips the nickel remaining in the post-exchange organic phase, yielding a nickel recovery solution. The post-nickel recovery organic phase after nickel stripping is sent to the cobalt recovery step S5. In the cobalt recovery step S5, hydrochloric acid is added to the organic phase to adjust the pH to about 1.0. This strips the cobalt supported on the organic phase, yielding a cobalt recovery solution. The cobalt recovery solution is an aqueous cobalt chloride solution.

[0028] In the stripping step S6, sulfuric acid is added to the organic phase to remove impurities remaining in the organic phase. The organic phase from which the impurities have been removed in the stripping step is repeatedly supplied to the extraction step S1 and the exchange step S3.

[0029] Each step in the solvent extraction process has been described above, but the method for solvent extraction of an aqueous nickel sulfate solution according to the present invention relates to the extraction step S1 and the washing step S2 in the solvent extraction process.

[0030] <2. Solvent extraction method for nickel sulfate aqueous solution> The method for solvent extraction of an aqueous nickel sulfate solution according to the present invention will now be described. FIG. 3 is a schematic diagram showing the process flow in the method for solvent extraction of an aqueous nickel sulfate solution according to one embodiment of the present invention. In the present invention, nickel is extracted from an aqueous crude nickel sulfate solution containing impurities mainly composed of sodium and ammonium using an acidic extractant in a plurality of mixer-settler-type solvent extraction tanks configured in a multistage countercurrent series, and the impurities are also washed away. Note that the plurality of mixer-settler-type solvent extraction tanks configured in a multistage countercurrent series refers to an apparatus configuration in which a plurality of mixer-settler-type solvent extraction tanks are connected in series, as shown in FIG. 3, and an organic phase (organic solvent) and an aqueous phase (washing solution, etc.) flow in opposite directions.

[0031] FIG. 4 is a schematic diagram showing a mixer-settler-type solvent extraction tank in a solvent extraction method for an aqueous nickel sulfate solution according to one embodiment of the present invention. As shown in FIG. 4, the mixer-settler-type solvent extraction tank comprises a mixer section and a settler section. The aqueous and organic phases are mixed and stirred in the mixer section to increase contact efficiency, and then separated from each other by allowing them to stand in the settler section. In one embodiment of the present invention, multiple such mixer-settler-type solvent extraction tanks are arranged in series. The aqueous and organic phases separated in each mixer-settler-type solvent extraction tank are sent to separate mixer-settler-type solvent extraction tanks located before and after the mixer section. There, the aqueous and organic phases are again mixed and stirred in the mixer section, and then allowed to stand in the settler section to separate the aqueous and organic phases. In one embodiment of the present invention, a portion of the separated aqueous phase is sent to the mixer section of the same mixer-settler-type solvent extraction tank, rather than being sent to another mixer-settler-type solvent extraction tank, and this process is repeated. Details will be described later.

[0032] In one embodiment of the present invention, the multiple mixer-settler-type solvent extraction tanks comprise a group of extraction solvent extraction tanks on the front side and a group of washing solvent extraction tanks on the rear side, as shown in Figure 3. More specifically, the process comprises an extraction step S1 in which an organic solvent containing an acidic extractant is supplied from the front side of the extraction solvent extraction tank group and a crude nickel sulfate aqueous solution is supplied from the rear side of the extraction solvent extraction tank group, thereby causing a countercurrent extraction reaction between the organic solvent and the crude nickel sulfate aqueous solution, and extracting nickel from the crude nickel sulfate aqueous solution into the organic solvent; and a washing step S2 in which the nickel-containing organic solvent obtained in the extraction step S1 is supplied from the front side of the washing solvent extraction tank group and a washing liquid is supplied from the rear side of the washing solvent extraction tank group, thereby washing and removing sodium and ammonium from the nickel-containing organic solvent in a countercurrent manner.

[0033] That is, in one embodiment of the present invention, as shown in Figure 3, mixer-settler type solvent extraction tanks are arranged in series for the extraction step S1 and the washing step S2. The solvent extraction tank used in the extraction step S1 is referred to as the "extraction solvent extraction tank," and the solvent extraction tank used in the washing step S2 is referred to as the "washing solvent extraction tank." The washing liquid (aqueous phase) is introduced into the washing solvent extraction tank at the rear stage and is sent toward the extraction solvent extraction tank at the front stage, while repeatedly undergoing mixing, stirring, and separation in each solvent extraction tank (solid arrows in Figure 3). Conversely, the organic solvent (organic phase) is introduced into the extraction solvent extraction tank at the front stage and is sent toward the washing solvent extraction tank at the rear stage (dashed arrows in Figure 3).

[0034] In one embodiment of the present invention, as shown in FIG. 3, the crude nickel sulfate aqueous solution is introduced into the final extraction solvent extraction tank and then transported toward the first extraction solvent extraction tank. During this extraction step S1, nickel ions in the crude nickel sulfate aqueous solution are extracted from the aqueous phase into the acidic extractant in the countercurrent organic solvent. As shown in FIG. 3, this nickel-containing organic solvent is introduced from the final extraction solvent extraction tank into the first washing solvent extraction tank for the next washing step S2. As the nickel-containing organic solvent is transported toward the final washing solvent extraction tank, it comes into countercurrent contact with the washing solution and is washed. Specifically, washing here refers to the replacement of tiny droplets (entrainment) contained in the nickel-containing organic solvent with the washing solution. That is, droplets derived from the extraction residue, which has a high concentration of impurities such as sodium, with wash water, which has a low concentration of impurities such as sodium. Furthermore, sodium and ammonium extracted into the acidic extractant in the nickel-containing organic solvent are replaced with nickel in the washing solution.

[0035] The number of stages (number of tanks) of the mixer-settler type solvent extraction tank used in the extraction step S1 and the washing step S2 in the present invention is not particularly limited. As an example, in the examples described below, a two-stage extraction solvent extraction tank and a four-stage washing solvent extraction tank are used.

[0036] In the present invention, in the extraction step S1, the pH of the liquid phase during the extraction reaction is set to 6.0 to 7.0, and in the washing step S2, the nickel concentration of the washing liquid is set to 10 g / L or more, and the pH of the liquid phase during washing removal is set to 6.0 to 6.8. Furthermore, the nickel concentration in the nickel-containing organic solvent is set to 95 g / L or more based on the volume of the acidic extractant contained in the nickel-containing organic solvent.

[0037] According to the above-mentioned Patent Documents 1 and 2 filed by the present applicant, it has been found that when nickel is extracted from an aqueous solution of crude nickel sulfate with an acidic extractant in the extraction step S1, the amounts of extracted impurities such as sodium and ammonium increase as the pH during extraction increases, but conversely, when the pH reaches 6.0 or higher, the extraction of these impurities is suppressed. Furthermore, it has been found that in the washing step S2, washing with a washing solution containing nickel replaces the sodium and ammonium extracted into the acidic extractant with nickel contained in the washing solution, and these impurities are removed from the acidic extractant, but in order for this substitution reaction to occur efficiently, it is necessary for the nickel concentration in the washing solution to be 10 g / L or more.

[0038] 5 is a schematic diagram showing the flow of the aqueous phase and the organic phase in the washing step of the solvent extraction method for an aqueous nickel sulfate solution according to one embodiment of the present invention. In the washing step S2 of one embodiment of the present invention, a part of the aqueous phase discharged from the outlet of the mixer-settler type solvent extraction tank is repeatedly used as a circulating liquid at the inlet side of the same mixer-settler type solvent extraction tank, and the flow rate of the nickel-containing organic solvent supplied from the extraction step is increased to Q O , the flow rate of the cleaning solution is Q W , the flow rate of the circulating fluid is Q R Then, the following equation (1) 0.6≦Q O / (Q W +Q R )≦1.8 (1) And the following formula (2) 4.0≦Q O / Q W ···(2) Adjust so that:

[0039] That is, as an example, in a mixer-settler type solvent extraction tank in the washing step S2 as shown in FIG. 5, the flow rate Q of the washing liquid W Flow rate Q of nickel-containing organic solvent O 4.0≦Q O / Q W At the same time, a part of the aqueous phase at the outlet is repeatedly fed into the same mixer-settler type solvent extraction tank, and the flow rate of the circulating liquid is adjusted to Q R By adjusting O / (Q W +Q R ) for 0.6≦Q O / (Q W +Q R )≦1.8.

[0040] Q O / (Q W +Q R If the flow rate ratio calculated by Q exceeds 1.8, the aqueous phase volume relative to the organic phase volume in the mixer section of the washing solvent extraction tank will be insufficient, and impurities such as sodium contained in the organic phase will not be sufficiently removed. O / (Q W +Q R If the flow rate ratio calculated by (1) is less than 0.6, the residence time of the mixed phase consisting of the organic phase and the aqueous phase in the mixer section will be short, and impurities such as sodium contained in the organic phase will not be sufficiently removed. In addition, the residence time in the settler section will be short, which will result in insufficient oil-water separation and increased entrainment in the organic phase. In other words, this will cause an increase in impurities such as sodium in the organic phase.

[0041] Q O / Q W If the flow rate ratio calculated by is less than 4.0, the amount of post-wash liquid increases, shortening the residence time in the extraction process, resulting in insufficient oil-water separation and increased entrainment in the organic phase. In other words, this causes an increase in impurities such as sodium in the organic phase. Furthermore, the amount of residual liquid increases, resulting in an increased loss of nickel carried over as residual liquid. The residual liquid is treated, for example, in a wastewater treatment process, but this increases the treatment load and treatment costs of the wastewater treatment process.

[0042] The above Q O / (Q W +Q R ) 1.3≦Q O / (Q W +Q R )≦1.5 is more preferable. These numerical ranges have been found by the inventors as optimal numerical ranges as a result of trial and error in the examples described below.

[0043] The flow rate of the organic solvent is primarily determined by the extraction capacity of the organic solvent and the amount of metal to be extracted. For example, if the organic solvent contains 20% acidic extractant (80% diluent), 2 moles of the 20% acidic extractant (mono-2-ethylhexyl 2-ethylhexylphosphonate) can extract 1 mole of divalent metal ions. Once the organic solvent flow rate is determined, the entire process will be run at that flow rate. Therefore, the flow rate of the aqueous phase involved in washing and stripping will be determined accordingly. Meanwhile, the flow rate ratio of the organic phase to the aqueous phase (O / A) is an important control factor in solvent extraction reactions, as it influences reactivity, oil-water separation, and other factors. While the flow rate ratio between the organic phase and the input aqueous phase is determined by balance, the flow rate ratio of the organic phase to the aqueous phase in the mixer-settler must also be controlled separately. For this reason, in principle, the O / A is adjusted by repeatedly changing the aqueous phase in any mixer-settler. For example, in the washing process, the post-wash liquid is ultimately sent to wastewater treatment, so there is a desire to keep it as low as possible. Therefore, the new charge flow rate is reduced as much as possible, but on the other hand, considering washing efficiency, it is also desirable to wash with a relatively large amount of aqueous phase. However, if impurities are concentrated in the aqueous phase and the impurity concentration becomes high, the washing efficiency will decrease, and washing with a large amount of aqueous phase is also undesirable because it increases the amount of water droplets (entrainment) in the organic phase.

[0044] As described above, in the present invention, in a solvent extraction method for an aqueous nickel sulfate solution in which various factors intertwine, by adjusting the optimal flow rate ratio (O / A) of the organic phase to the aqueous phase and the flow rate ratio of the organic phase to the washing solution, sodium contained in the nickel-containing organic solvent can be efficiently removed with a small amount of washing water, and a high-purity aqueous nickel sulfate solution can be efficiently obtained.

[0045] By applying the solvent extraction method for an aqueous nickel sulfate solution according to the present invention, it is possible to separate and remove sodium from a nickel-containing organic solvent more efficiently than in conventional methods, thereby enabling a further reduction in the sodium concentration in a high-purity aqueous nickel sulfate solution. Furthermore, because an aqueous solution containing at least 10 g / L of nickel is required as wash water, it was previously necessary to prepare the wash water by adding a high-purity aqueous nickel sulfate solution to water. However, by improving the sodium removal efficiency, the amount of wash water required can be reduced, thereby reducing the amount of nickel lost in the wash water after washing and improving production efficiency compared to conventional methods. Furthermore, because nickel used repeatedly as wash water consumes a chemical equivalent amount of caustic soda as a neutralizing agent when extracted in the extraction process, reducing the amount of wash water also allows for a reduction in chemical costs. [Example]

[0046] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples in any way.

[0047] Example 1 The relationship between the organic phase / aqueous phase flow rate ratio in the four washing solvent extraction tanks and the sodium removal efficiency was investigated. Figure 6 is a graph showing the relationship between the organic phase / aqueous phase flow rate ratio in the four washing solvent extraction tanks and the sodium removal efficiency in the washing step of the method for solvent extraction of an aqueous nickel sulfate solution according to one embodiment of the present invention. From the results shown in Figure 6, it can be seen that the organic phase / aqueous phase flow rate ratio (Q O / (Q W +Q R )) exceeds 1.8, the sodium (Na) cleaning efficiency decreases.

[0048] The sodium washing efficiency was calculated by ((input organic phase Na concentration - output organic phase Na concentration) / input organic phase Na concentration) × 100%.

[0049] Example 2 The relationship between the organic phase / aqueous phase flow rate ratio and sodium removal efficiency was investigated for the same washing solvent extraction tank when the organic phase / aqueous phase flow rate ratio was changed. Figure 7 is a graph showing the relationship between the organic phase / aqueous phase flow rate ratio and sodium removal efficiency for the same washing solvent extraction tank in the washing step of the method for solvent extraction of an aqueous nickel sulfate solution according to one embodiment of the present invention. From the results shown in Figure 7, it can be seen that the organic phase / aqueous phase flow rate ratio (Q O / (Q W +Q R It can be seen that the sodium washing efficiency is maximized when the ratio (%) approaches 1.3. In FIG. 7, the washing efficiency exceeds 100% because the amount of sodium in the nickel-containing organic solvent obtained in the extraction step fluctuates during continuous operation, and therefore the amount of sodium supplied to the washing step also fluctuates. Note that, in Example 2 only, the sodium washing efficiency was calculated by (amount of sodium in the aqueous phase output / (amount of sodium in the organic phase input+amount of sodium in the aqueous phase input)) × 100%.

[0050] Example 3 Applying this invention, the organic phase / aqueous phase flow rate ratio (Q O / (Q W +Q R )) was set to 1.3 to 1.5, and a solvent extraction method for an aqueous nickel sulfate solution was carried out.

[0051] (Comparative Example 1) The organic phase / aqueous phase flow rate ratio (Q O / (Q W +Q R )) was set to 0.7 to 2.4, and the organic phase / washing water flow rate ratio (Q O / Q W The solvent extraction method for the nickel sulfate aqueous solution was carried out with the organic phase / aqueous phase flow rate ratio (Q) set to 3.8. O / (Q W +Q R )) was sometimes below 1.8, which is the range specified in the present invention, but this was due to the organic phase / aqueous phase flow rate ratio (Q O / (Q W +Q R )) itself was not managed and operations were conducted on a haphazard basis.

[0052] Table 1 shows the sodium washing efficiency when the solvent extraction method for an aqueous nickel sulfate solution was carried out in Example 3 and Comparative Example 1. In Comparative Example 1, which is a conventional method, the sodium washing efficiency was 90%, but in Example 3 according to one aspect of the present invention, the sodium washing efficiency was 98%, and a high sodium washing efficiency was achieved. [Table 1]

[0053] Example 4 By applying this invention, the organic phase / aqueous phase flow rate ratio (Q O / (Q W +Q R )) was set to 1.3 to 1.5, and the organic phase / washing water flow rate ratio (Q O / Q W ) was adjusted in the range of 4.0 to 4.6, and a solvent extraction method for an aqueous nickel sulfate solution was carried out.

[0054] (Comparative Example 2) The solvent extraction method for nickel sulfate aqueous solution was carried out using the conventional method without adjusting the organic phase / aqueous phase flow rate ratio. The organic phase / aqueous phase flow rate ratio (Q O / (Q W +Q R )) is 1.4 to 6.7, and the organic phase / washing water flow rate ratio (Q O / Q W The organic phase / aqueous phase flow rate ratio (Q O / (Q W +Q R )) was sometimes below 1.8, which is the range specified in the present invention, but this was due to the organic phase / aqueous phase flow rate ratio (Q O / (Q W +Q R )) itself was not managed and operations were conducted on a haphazard basis.

[0055] Fig. 8 is a graph showing the relationship between the organic phase / washing water flow rate ratio and sodium washing efficiency in the washing solvent extraction tank in Example 4 and Comparative Example 2. As shown in Fig. 8, in the case of Comparative Example 2 before the application of the present invention, the sodium washing efficiency was 92.9%, but by applying the present invention, the sodium washing efficiency improved, demonstrating high sodium washing efficiency. In Example 4, the organic phase / washing water flow rate ratio was larger than in Comparative Example 2, and despite the reduced amount of washing water, the sodium washing efficiency improved. In other words, sodium was able to be removed efficiently with a small amount of washing water.

[0056] Although one embodiment of the present invention and each example have been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present invention. Therefore, all such modifications are intended to be included within the scope of the present invention.

[0057] For example, a term that is described at least once in the specification or drawings together with a different term having a broader or equivalent meaning can be replaced with that different term anywhere in the specification or drawings. Furthermore, the configuration of the method for solvent extraction of an aqueous nickel sulfate solution is not limited to the one embodiment of the present invention and the examples described above, and various modifications are possible.

Claims

1. A method for solvent extraction of an aqueous nickel sulfate solution, in which nickel is extracted from an aqueous crude nickel sulfate solution containing impurities mainly composed of sodium and ammonium using an acidic extractant and the impurities are washed away in a plurality of mixer-settler type solvent extraction tanks configured in a multistage countercurrent series, The plurality of mixer-settler type solvent extraction tanks comprise a group of solvent extraction tanks for extraction at the front stage and a group of solvent extraction tanks for washing at the rear stage, an extraction step in which an organic solvent containing the acidic extractant is supplied from the front-most stage of the group of extracting solvent extraction tanks, and the crude nickel sulfate aqueous solution is supplied from the rear-most stage of the group of extracting solvent extraction tanks, thereby causing an extraction reaction between the organic solvent and the crude nickel sulfate aqueous solution in a countercurrent manner, thereby extracting nickel in the crude nickel sulfate aqueous solution into the organic solvent; a washing step in which the nickel-containing organic solvent obtained in the extraction step is supplied from the front-most stage of the group of washing solvent extraction tanks, and a washing liquid is supplied from the rear-most stage of the group of washing solvent extraction tanks, thereby washing and removing sodium and ammonium in the nickel-containing organic solvent in a countercurrent manner; and In the solvent extraction step, the post-washing liquid discharged from the front stage of the washing step is supplied to the rear stage of the extraction step, In the extraction step, the pH of the liquid phase during the extraction reaction is set to 6.0 to 7.0, and in the washing step, the nickel concentration of the washing solution is set to 10 g / L or more, and the pH of the liquid phase during the washing and removal is set to 6.0 to 6.8, The nickel concentration in the nickel-containing organic solvent is 95 g / L or more based on the volume of the acidic extractant contained in the nickel-containing organic solvent; In the washing step, a part of the aqueous phase discharged from the outlet side of the mixer-settler type solvent extraction tank is repeatedly used as a circulating liquid at the inlet side of the same mixer-settler type solvent extraction tank, and the flow rate of the nickel-containing organic solvent supplied from the extraction step is set to Q O , the flow rate of the cleaning liquid is Q Ｗ , the flow rate of the circulating fluid is Q Ｒ Then, the following equation (1) 0.6≦Q O / (Q Ｗ +Q Ｒ )≦1.8 ・・・(1) And the following formula (2) 4.0≦Q O / Q Ｗ ・・・(2) A method for solvent extraction of an aqueous nickel sulfate solution, comprising:

2. The following formula (3) 1.3≦Q O / (Q Ｗ +Q Ｒ )≦1.5 ・・・(3) 2. The method for solvent extraction of an aqueous nickel sulfate solution according to claim 1, wherein the above formula (1) is satisfied.

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