Solvent extraction equipment and solvent extraction method

Abstract

To provide a solvent extraction system that can effectively reduce the magnesium concentration in an aqueous nickel sulfate solution. [Solution] Solvent extraction equipment AA comprises multiple solvent extraction tanks 10A to 10E that replace magnesium in the nickel sulfate aqueous solution with nickel in the organic solvent by bringing a nickel sulfate aqueous solution containing magnesium into countercurrent contact with an organic solvent containing an acidic extractant supported with nickel, and a first heating device 31 provided in a circulation channel that guides a portion of the exchanged liquid discharged from the aqueous phase outlet of the first solvent extraction tank 10A, located at the top of the organic solvent flow, to the aqueous phase inlet of the first solvent extraction tank. By increasing the temperature of the nickel sulfate aqueous solution in the first solvent extraction tank 10A, the magnesium distribution rate to the final exchanged liquid can be reduced.

Description

Technical Field

[0001] The present invention relates to a solvent extraction facility and a solvent extraction method. More specifically, the present invention relates to a solvent extraction facility and a solvent extraction method for removing magnesium from a crude nickel sulfate aqueous solution.

Background Art

[0002] A solvent extraction method is known as a method for removing impurities from a crude nickel sulfate aqueous solution. Specifically, a crude nickel sulfate aqueous solution containing impurities is brought into contact with an organic solvent containing an acidic extractant carrying nickel, so that the impurities in the crude nickel sulfate aqueous solution are substituted with the nickel in the organic solvent, and a high-purity nickel sulfate aqueous solution is obtained.

[0003] Examples of impurities contained in the crude nickel sulfate aqueous solution include magnesium. Compared with other impurities such as cobalt, calcium and iron, magnesium is less likely to be extracted by the acidic extractant, and its extraction characteristics are close to those of nickel. Therefore, it is difficult to completely remove magnesium from the crude nickel sulfate aqueous solution.

[0004] Patent Document 1 discloses that the higher the extraction temperature in solvent extraction, the higher the purity nickel sulfate aqueous solution with a lower magnesium concentration can be obtained. It is also disclosed that the extraction temperature is adjusted in the range of 48 to 60°C in order to obtain a high-purity nickel sulfate aqueous solution with a low magnesium concentration. However, details of temperature adjustment, in particular, how to control the extraction temperature in a multi-stage countercurrent solvent extraction facility to effectively reduce the magnesium concentration in the high-purity nickel sulfate aqueous solution is not disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0006] In view of the above circumstances, the present invention aims to provide a solvent extraction apparatus and a solvent extraction method that can effectively reduce the magnesium concentration in an aqueous nickel sulfate solution. [Means for solving the problem]

[0007] The solvent extraction apparatus of the first embodiment comprises a plurality of solvent extraction tanks that replace magnesium in the nickel sulfate aqueous solution with nickel in the organic solvent by bringing a nickel sulfate aqueous solution containing magnesium into countercurrent contact with an organic solvent containing a nickel-supported acidic extractant, and one or more heating devices for heating the nickel sulfate aqueous solution, wherein the plurality of solvent extraction tanks include a first solvent extraction tank located at the uppermost stage of the organic solvent flow and a final solvent extraction tank located at the lowermost stage, and the one or more heating devices include a first heating device provided in a circulation channel that guides a portion of the replacement final liquid, which is the nickel sulfate aqueous solution discharged from the aqueous phase outlet of the first solvent extraction tank, to the aqueous phase inlet of the first solvent extraction tank. The solvent extraction apparatus of the second embodiment is characterized in that, in the first embodiment, the circulation flow rate of the final exchange solution is 1.2 to 1.3 times the flow rate of the initial exchange solution, which is the nickel sulfate aqueous solution supplied to the final solvent extraction tank. The solvent extraction apparatus of the third embodiment comprises a plurality of solvent extraction tanks that replace magnesium in the nickel sulfate aqueous solution with nickel in the organic solvent by bringing a nickel sulfate aqueous solution and an acidic extractant supported with nickel into countercurrent contact, and one or more heating devices for heating the nickel sulfate aqueous solution, wherein the plurality of solvent extraction tanks include a first solvent extraction tank located at the top of the organic solvent flow, a second solvent extraction tank located next to the first solvent extraction tank, and a final solvent extraction tank located at the bottom, and the one or more heating devices include a first heating device provided in a flow path that guides all or part of the nickel sulfate aqueous solution discharged from the aqueous phase outlet of the second solvent extraction tank to the aqueous phase inlet of the first solvent extraction tank. The solvent extraction apparatus of the fourth embodiment is characterized in that, in any of the first to third embodiments, the one or more heating devices include a second heating device that heats all or part of the replacement initial solution, which is the nickel sulfate aqueous solution supplied to the final solvent extraction tank. The solvent extraction method of the fifth embodiment includes an exchange stage in which a nickel sulfate aqueous solution containing magnesium is brought into countercurrent contact with an organic solvent containing a nickel-supported acidic extractant using a plurality of solvent extraction tanks to replace the magnesium in the nickel sulfate aqueous solution with the nickel in the organic solvent, and a portion of the exchanged liquid, which is the nickel sulfate aqueous solution discharged from the aqueous phase outlet of the first solvent extraction tank located at the uppermost stage of the flow of the organic solvent among the plurality of solvent extraction tanks, is circulated to the aqueous phase inlet of the first solvent extraction tank, and the circulating exchanged liquid is heated. The solvent extraction method of the sixth embodiment is characterized in that, in the fifth embodiment, the circulation flow rate of the final exchange solution is 1.2 to 1.3 times the flow rate of the initial exchange solution, which is the nickel sulfate aqueous solution supplied to the final solvent extraction tank located at the lowest stage of the organic solvent flow among the multiple stages of solvent extraction tanks. The seventh embodiment of the solvent extraction method includes an exchange stage in which a nickel sulfate aqueous solution containing magnesium is brought into countercurrent contact with an organic solvent containing a nickel-supported acidic extractant in a plurality of solvent extraction tanks to replace the magnesium in the nickel sulfate aqueous solution with the nickel in the organic solvent, and is characterized in that all or part of the nickel sulfate aqueous solution supplied to the first solvent extraction tank from a second solvent extraction tank located next to a first solvent extraction tank located at the top of the flow of the organic solvent among the plurality of solvent extraction tanks is heated. The solvent extraction method of the eighth embodiment is characterized in that, in any of the fifth to seventh embodiments, all or part of the replacement initial solution, which is the nickel sulfate aqueous solution supplied to the final solvent extraction tank located at the lowest stage of the organic solvent flow among the multiple stages of solvent extraction tanks, is heated. The solvent extraction method of the ninth embodiment includes an exchange stage in which a nickel sulfate aqueous solution containing magnesium is brought into countercurrent contact with an organic solvent containing a nickel-supported acidic extractant using a plurality of solvent extraction tanks to replace the magnesium in the nickel sulfate aqueous solution with the nickel in the organic solvent, and is characterized in that the temperature of the nickel sulfate aqueous solution supplied to the first solvent extraction tank located at the top of the flow of the organic solvent among the plurality of solvent extraction tanks is higher than the average temperature of the nickel sulfate aqueous solution supplied to each of the plurality of solvent extraction tanks. [Effects of the Invention]

[0008] According to the present invention, by increasing the temperature of the nickel sulfate aqueous solution in the first solvent extraction tank, the magnesium distribution rate to the final exchanged solution can be reduced. As a result, the magnesium concentration of the nickel sulfate aqueous solution can be effectively reduced. [Brief explanation of the drawing]

[0009] [Figure 1] This is an overall process diagram for the manufacturing of nickel sulfate aqueous solution. [Figure 2] This is a detailed process diagram of the solvent extraction process. [Figure 3] This is an explanatory diagram of the solvent extraction equipment according to the first embodiment. [Figure 4] This is an explanatory diagram of the solvent extraction equipment according to the second embodiment. [Figure 5] This is an explanatory diagram of a solvent extraction apparatus according to a reference embodiment. [Figure 6] This graph shows the aqueous phase temperature distribution in Example 1 and Comparative Example 1. [Figure 7] This graph shows the relationship between the average aqueous phase temperature and the magnesium distribution rate to the final exchanged liquid in Example 1 and Comparative Example 1. [Figure 8] This graph shows the relationship between the average aqueous phase temperature and the magnesium distribution rate to the replacement fluid when the circulation flow rate of the replacement fluid is changed in Example 1. [Figure 9]This is a graph showing the relationship between the average aqueous phase temperature and the magnesium partition ratio to the exchange final solution when the circulation flow rate of the exchange final solution is changed in Reference Example 1. [Mode for Carrying Out the Invention]

[0010] Next, embodiments of the present invention will be described based on the drawings. The solvent extraction equipment and solvent extraction method according to one embodiment of the present invention can be applied, for example, to one step of the nickel sulfate aqueous solution production process described below.

[0011] (Nickel Sulfate Aqueous Solution Production Process) As shown in Figure 1, in the nickel sulfate aqueous solution production process, nickel-cobalt mixed sulfide (MS: Mixed Sulfide) is used as the nickel raw material. Nickel oxide ores such as low-grade laterite ore and limonite ore are subjected to high pressure acid leaching (HPAL), impurities such as iron are removed from the leachate, and then hydrogen sulfide gas is blown into the leachate to cause a sulfidation reaction, whereby the nickel-cobalt mixed sulfide is obtained.

[0012] The composition of the nickel-cobalt mixed sulfide is 50 to 60 wt% of nickel, 4 to 6 wt% of cobalt, and 30 to 34 wt% of sulfur (all based on dry mass). The nickel-cobalt mixed sulfide contains impurities such as magnesium, iron, copper, and zinc. The nickel-cobalt mixed sulfide contains a relatively large amount of magnesium, with a content ratio of 80 to 150 ppm.

[0013] In the pressure leaching step, the slurry containing the nickel-cobalt mixed sulfide is subjected to pressure leaching in an autoclave. The leaching conditions are, for example, a pressure (gauge pressure) of 1.8 to 2.0 MPaG and a temperature of 140 to 180°C. Through pressure leaching, nickel, cobalt, and other impurities contained in the nickel-cobalt mixed sulfide are leached, and a pressure leachate is obtained.

[0014] In the iron removal step, impurities, mainly iron, contained in the pressurized leachate are removed as neutralized precipitates through an oxidation-neutralization reaction. Air can be used as the oxidizing agent. As the neutralizing agent, slaked lime, sodium hydroxide, calcium carbonate and the like are used. Since slaked lime is easily available and inexpensive, it is generally used as the neutralizing agent, but slaked lime contains magnesium as an impurity. The neutralized precipitate is removed by solid-liquid separation to obtain a crude nickel sulfate aqueous solution.

[0015] The nickel-cobalt mixed sulfide contains a relatively large amount of magnesium. In addition, the slaked lime added in the iron removal step contains magnesium. Furthermore, the industrial water used in each step contains a certain amount of magnesium. Therefore, the crude nickel sulfate aqueous solution contains magnesium. The crude nickel sulfate aqueous solution also contains other impurities such as cobalt.

[0016] In the solvent extraction step, impurities such as magnesium are removed from the crude nickel sulfate aqueous solution by solvent extraction to obtain a high-purity nickel sulfate aqueous solution. The obtained high-purity nickel sulfate aqueous solution is then subjected to a treatment according to its intended use. For example, the high-purity nickel sulfate aqueous solution is concentrated and crystallized using a crystallizer to form nickel sulfate crystals. In addition, the high-purity nickel sulfate aqueous solution is used as a raw material for producing positive electrode materials of secondary batteries while remaining in an aqueous solution state.

[0017] In this specification, the nickel sulfate aqueous solution containing impurities before solvent extraction is referred to as the crude nickel sulfate aqueous solution. The nickel sulfate aqueous solution with reduced impurity concentration through solvent extraction is referred to as the high-purity nickel sulfate aqueous solution. In addition, the term "nickel sulfate aqueous solution" is a concept that includes both the crude nickel sulfate aqueous solution and the high-purity nickel sulfate aqueous solution, regardless of the amount of impurities.

[0018] (Solvent Extraction Step) Next, the details of the solvent extraction step will be described based on Figure 2. In Figure 2, solid line arrows indicate the flow of the aqueous phase (water or aqueous solution), and broken line arrows indicate the flow of the organic phase (organic solvent).

[0019] Acidic extractants are used for solvent extraction. While not particularly limited, phosphate ester-based acidic extractants such as 2-ethylhexyl phosphonic acid mono-2-ethylhexyl and di-(2-ethylhexyl)phosphonic acid (commonly known as D2EHPA) are commonly used.

[0020] Generally, acidic extractants are used diluted with a diluent. The concentration of the acidic extractant in the organic solvent is adjusted to 10-40% by volume. Diluting the acidic extractant is done to adjust the viscosity of the organic solvent to an appropriate level, thereby improving oil-water separation, or phase separation. The diluent is not particularly limited as long as it has low solubility in water, low viscosity, and does not react with the acidic extractant, but saturated hydrocarbons are used as an example.

[0021] The solvent extraction process consists of an extraction stage, a washing stage, a replacement stage, a nickel recovery stage, a cobalt recovery stage, and a back-extraction stage. These will be explained in order below.

[0022] The extraction stage is supplied with the post-wash solution from the washing stage. The post-wash solution is an aqueous solution of nickel sulfate. In the extraction stage, nickel in the post-wash solution is extracted into an organic solvent, and the nickel is supported on an acidic extractant. The resulting organic solvent is called the nickel-retaining organic solvent. The post-wash solution contains impurities such as magnesium and calcium, which are extracted into the organic solvent at a lower pH than nickel. These impurities are also extracted into the organic solvent in the extraction stage. Therefore, the nickel-retaining organic solvent also contains these impurities.

[0023] In solvent extraction using acidic extractants, hydrogen ions are involved in the extraction reaction, so the extraction rate changes with pH. The extraction rate differs depending on the metal, with Fe > Zn > Cu > Mn > Co > Ca > Mg > Ni being extracted in that order. By sequentially lowering the pH along the flow of the organic solvent—from the extraction stage to the washing stage, exchange stage, nickel recovery stage, cobalt recovery stage, and back extraction stage—each metal can be separated and recovered at each stage.

[0024] The extraction reaction with an acidic extractant is represented by the following equation (1), where R represents the entire organic compound containing the functional group. As shown in equation (1), hydrogen ions are released along with the extraction of metal ions. 2R-H+Ni 2+ →R2-Ni+2H + ...(1)

[0025] When hydrogen ions are released, the pH decreases. To remove impurities, it is necessary to maintain the correct pH, so in the extraction stage, an alkali such as caustic soda is added to adjust the pH.

[0026] The nickel-retaining organic solvent obtained in the extraction stage is sent to the washing stage. In the washing stage, the nickel-retaining organic solvent is washed with a nickel-containing washing solution. The washing solution is a portion of the highly purified nickel sulfate aqueous solution purified in the exchange stage, diluted with water. When producing nickel sulfate crystals from a highly purified nickel sulfate aqueous solution using a crystallizer, the mother liquor discharged from the crystallization process, diluted with water, may be used as part or all of the washing solution. The washed solution is supplied to the extraction stage.

[0027] In the extraction stage, fine droplet particles may remain in the organic solvent. If caustic soda is added in the extraction stage, the droplet particles in the organic solvent will contain sodium. In other words, the nickel-retaining organic solvent will contain sodium. In the washing stage, the droplet particles in the organic solvent are replaced with a washing solution, thereby removing the sodium contained in the nickel-retaining organic solvent.

[0028] The exchange stage is supplied with the initial exchange solution. The initial exchange solution is a crude nickel sulfate aqueous solution obtained in the iron removal process. In the exchange stage, the nickel sulfate aqueous solution containing impurities is brought into contact with a nickel-retaining organic solvent to replace the impurities in the nickel sulfate aqueous solution with nickel in the organic solvent, thereby obtaining a high-purity nickel sulfate aqueous solution. The high-purity nickel sulfate aqueous solution discharged from the exchange stage is called the final exchange solution.

[0029] The composition of the initial exchange solution (crude nickel sulfate aqueous solution) supplied to the exchange stage is, for example, 110-140 g / L nickel concentration, 8-12 g / L cobalt concentration, 19-31 mg / L magnesium concentration, 0.3-0.6 g / L calcium concentration, and approximately 0.02 g / L iron concentration.

[0030] The composition of the final exchange solution (high-purity nickel sulfate aqueous solution) discharged from the exchange stage is, for example, 118-152 g / L nickel concentration, 1-60 mg / L cobalt concentration, 1-20 mg / L magnesium concentration, 1-15 mg / L calcium concentration, and 1-5 mg / L iron concentration.

[0031] Typically, the amount of nickel in nickel-supported organic solvents is adjusted to an excess amount such that a certain amount of nickel remains in the organic solvent after the substitution reaction. Therefore, nickel is supported in the organic solvent after the exchange.

[0032] In the nickel recovery stage, sulfuric acid is added to the replaced organic solvent to adjust the pH to approximately 3.5. This back-extracts most of the nickel supported in the organic solvent, yielding a nickel recovery solution. The nickel recovery solution is an aqueous solution of nickel sulfate containing impurities such as cobalt and magnesium.

[0033] After nickel is back-extracted and nickel is recovered, the organic solvent is sent to the cobalt recovery stage. In the cobalt recovery stage, hydrochloric acid is added to the organic solvent to adjust the pH to approximately 1.0. This back-extracts the cobalt supported in the organic solvent, yielding a cobalt recovery solution. The cobalt recovery solution is an aqueous solution of cobalt chloride. Some of the impurities contained in the organic solvent, such as magnesium, calcium, copper, and zinc, are also back-extracted into the cobalt recovery solution.

[0034] After cobalt is back-extracted and recovered, the organic solvent is sent to the back-extraction stage. In the back-extraction stage, the organic solvent is brought into contact with an aqueous solution of an acid such as sulfuric acid or hydrochloric acid to back-extract impurities contained in the organic solvent. The organic solvent from which impurities have been removed in the back-extraction stage is repeatedly supplied to the extraction stage and the exchange stage.

[0035] [First Embodiment] (Solvent extraction equipment) The solvent extraction apparatus according to the first embodiment of the present invention can be applied, for example, to the exchange stage in the solvent extraction process described above. However, the solvent extraction apparatus of this embodiment may be used in a process in which an aqueous nickel sulfate solution containing at least magnesium as an impurity is brought into contact with an organic solvent containing an acidic extractant supporting nickel to replace the magnesium in the aqueous nickel sulfate solution with the nickel in the organic solvent, and is not limited to the exchange stage described above. Furthermore, the aqueous nickel sulfate solution may contain other impurities such as cobalt in addition to magnesium, and these other impurities may replace the nickel in the organic solvent together with the magnesium.

[0036] As shown in Figure 3, the solvent extraction equipment AA of this embodiment has multiple stages of solvent extraction tanks 10A to 10E connected in series. For example, a mixer-settler type solvent extraction apparatus can be used as each of the solvent extraction tanks 10A to 10E. In the illustrated example, the solvent extraction equipment AA has five solvent extraction tanks 10A to 10E, but the number of solvent extraction tanks 10A to 10E is not limited to this.

[0037] In multiple solvent extraction tanks 10A to 10E, an aqueous nickel sulfate solution (aqueous phase) and an organic solvent containing an acidic extractant (organic phase) are passed in a countercurrent. In each of the solvent extraction tanks 10A to 10E, the aqueous nickel sulfate solution containing magnesium comes into contact with the organic solvent containing the nickel-supported acidic extractant, and the magnesium in the aqueous nickel sulfate solution is replaced by the nickel in the organic solvent. In other words, a countercurrent multi-stage extraction is performed in the solvent extraction tanks 10A to 10E.

[0038] Of the multiple solvent extraction tanks 10A to 10E, the solvent extraction tank located at the top of the organic solvent flow is called the first solvent extraction tank 10A. Following the organic solvent flow, the tank immediately following the first solvent extraction tank 10A is called the second solvent extraction tank 10B, the tank immediately following the second solvent extraction tank 10B is called the third solvent extraction tank 10C, and the tank immediately following the third solvent extraction tank 10C is called the fourth solvent extraction tank 10D. The solvent extraction tank located at the bottom of the organic solvent flow is called the final solvent extraction tank 10E. In the case of the nickel sulfate aqueous solution flow, the tanks are arranged in the order of final solvent extraction tank 10E, fourth solvent extraction tank 10D, third solvent extraction tank 10C, second solvent extraction tank 10B, and first solvent extraction tank 10A, from upstream to downstream.

[0039] The nickel sulfate aqueous solution supplied to the aqueous phase inlet of the final solvent extraction tank 10E is called the initial exchange solution. The nickel sulfate aqueous solution discharged from the aqueous phase outlet of the first solvent extraction tank 10A is called the final exchange solution. The initial exchange solution is a crude nickel sulfate aqueous solution, and the final exchange solution is a high-purity nickel sulfate aqueous solution.

[0040] Solvent extraction equipment AA has a heating device for heating an aqueous nickel sulfate solution. Specifically, solvent extraction equipment AA has a discharge channel 21 connected to the aqueous phase outlet of the first solvent extraction tank 10A. The discharge channel 21 branches off into a circulation channel 22 midway. The circulation channel 22 connects the discharge channel 21 to the aqueous phase inlet of the first solvent extraction tank 10A. A portion of the exchanged liquid discharged from the aqueous phase outlet of the first solvent extraction tank 10A is guided to the aqueous phase inlet of the first solvent extraction tank 10A via the circulation channel 22, and the remainder is discharged to the outside via the discharge channel 21. The first solvent extraction tank 10A is supplied with the aqueous phase as the aqueous phase of the aqueous nickel sulfate solution discharged from the second solvent extraction tank 10B and the exchanged liquid circulated by the circulation channel 22.

[0041] A first heating device 31 is provided in the circulation channel 22. The first heating device 31 can be any device capable of heating the exchangeable waste liquid flowing through the circulation channel 22; for example, a heat exchanger can be used. The exchangeable waste liquid heated by the first heating device 31 is supplied to the first solvent extraction tank 10A. Therefore, a portion of the nickel sulfate aqueous solution supplied to the first solvent extraction tank 10A is heated by the first heating device 31.

[0042] Since a high-temperature nickel sulfate aqueous solution is supplied to the first solvent extraction tank 10A, the temperature of the organic solvent in contact with the nickel sulfate aqueous solution in the first solvent extraction tank 10A also increases. That is, the temperatures of both the aqueous phase and the organic phase in the first solvent extraction tank 10A increase. Furthermore, the organic solvent whose temperature has risen in the first solvent extraction tank 10A is supplied to the subsequent solvent extraction tanks 10B to 10E. As a result, the temperatures of the aqueous phase and the organic phase in the solvent extraction tanks 10B to 10E also rise. By using the first heating device 31, the temperature distribution of the aqueous phase is highest in the first solvent extraction tank 10A and gradually decreases in the subsequent stages.

[0043] The solvent extraction equipment AA may have only one heating device for heating the nickel sulfate aqueous solution, or it may have multiple heating devices. In the illustrated example, the solvent extraction equipment AA has a first heating device 31 and a second heating device 32 for heating the exchange starter solution. Specifically, the solvent extraction equipment AA has a supply channel 23 connected to the aqueous phase inlet of the final solvent extraction tank 10E. The exchange starter solution is supplied to the aqueous phase inlet of the final solvent extraction tank 10E via the supply channel 23. The second heating device 32 is provided in the supply channel 23. The second heating device 32 can be any device capable of heating the exchange starter solution flowing through the supply channel 23, for example, a heat exchanger can be used. The exchange starter solution heated by the second heating device 32 is supplied to the final solvent extraction tank 10E.

[0044] The entire or partial supply of the replacement starter solution to the final solvent extraction tank 10E may be heated. If a second heating device 32 is provided in the supply channel 23, the entire replacement starter solution can be heated. If a bypass channel is provided in the supply channel 23, a portion of the replacement starter solution will be guided to the final solvent extraction tank 10E via the bypass channel. By providing a second heating device 32 in the bypass channel, a portion of the replacement starter solution can be heated.

[0045] By supplying a high-temperature nickel sulfate aqueous solution to the final solvent extraction tank 10E, the temperatures of the nickel sulfate aqueous solution and organic solvent in the final solvent extraction tank 10E can be increased. Furthermore, the high-temperature nickel sulfate aqueous solution is also supplied to the other solvent extraction tanks 10A to 10D. This allows for an overall increase in the aqueous phase temperature across the multiple solvent extraction tanks 10A to 10E. Since the second heating device 32 heats the initial exchange solution, it can more effectively increase the overall aqueous phase temperature across the multiple solvent extraction tanks 10A to 10E compared to the first heating device 31, which heats the final exchange solution.

[0046] (Solvent extraction method) Next, we will explain the solvent extraction method using solvent extraction equipment AA. The solvent extraction method of this embodiment includes an exchange stage. In the exchange stage, multiple solvent extraction tanks 10A to 10E are used to bring a nickel sulfate aqueous solution containing magnesium into countercurrent contact with an organic solvent containing an acidic extractant supporting nickel, thereby replacing the magnesium in the nickel sulfate aqueous solution with the nickel in the organic solvent.

[0047] Here, a portion of the nickel sulfate aqueous solution supplied to the first solvent extraction tank 10A is heated. Specifically, a portion of the replacement liquid discharged from the aqueous phase outlet of the first solvent extraction tank 10A is circulated to the aqueous phase inlet of the first solvent extraction tank 10A, and the circulating replacement liquid is heated. The first heating device 31 is used to heat the replacement liquid. By supplying the heated replacement liquid to the first solvent extraction tank 10A, the aqueous phase temperature in the first solvent extraction tank 10A can be increased. In addition, the aqueous phase temperatures in the subsequent solvent extraction tanks 10B to 10E also rise.

[0048] Alternatively, the exchange starter solution supplied to the final solvent extraction tank 10E may be heated. The second heating device 32 is used to heat the exchange starter solution. By supplying the heated exchange starter solution to the final solvent extraction tank 10E, the aqueous phase temperature of the multiple solvent extraction tanks 10A to 10E can be raised overall.

[0049] As described above, by controlling the temperature of the nickel sulfate aqueous solution, a high-purity nickel sulfate aqueous solution with a low magnesium concentration can be obtained. The reason for this is presumed to be as follows: During the process in which the nickel sulfate aqueous solution flows from the final solvent extraction tank 10E to the first solvent extraction tank 10A, a substitution reaction between magnesium in the nickel sulfate aqueous solution and nickel in the organic solvent proceeds. Since the first solvent extraction tank 10A is located at the downstream end of the aqueous phase, the magnesium concentration of the nickel sulfate aqueous solution in the first solvent extraction tank 10A is relatively low. Since the substitution reaction between magnesium and nickel proceeds according to equilibrium theory, the lower the magnesium concentration of the nickel sulfate aqueous solution, the less likely the substitution reaction is to proceed. By raising the temperature of the nickel sulfate aqueous solution in the first solvent extraction tank 10A, which extracts magnesium from the nickel sulfate aqueous solution with a low magnesium concentration, the magnesium distribution rate to the final exchange solution can be reduced. As a result, the magnesium concentration of the high-purity nickel sulfate aqueous solution can be effectively reduced.

[0050] Based on the above, it is preferable that the distribution of aqueous phase temperatures in the multi-stage solvent extraction tanks 10A to 10E gradually increases from upstream to downstream of the aqueous phase (from downstream to upstream of the organic phase). For example, it is preferable to make the temperature of the nickel sulfate aqueous solution supplied to the first solvent extraction tank 10A higher than the average temperature of the nickel sulfate aqueous solutions supplied to each of the multi-stage solvent extraction tanks 10A to 10E. In this way, the aqueous phase temperature can be increased in the first solvent extraction tank 10A, where the magnesium concentration of the nickel sulfate aqueous solution is low, and the magnesium distribution rate to the exchanged final solution can be reduced.

[0051] The higher the circulation flow rate of the final exchanged solution via the circulation channel 22, the more of the high-temperature nickel sulfate aqueous solution can be supplied to the first solvent extraction tank 10A. This allows for a higher aqueous phase temperature in the solvent extraction tanks 10A to 10E, which contributes to a decrease in the magnesium distribution rate to the final exchanged solution. On the other hand, if the circulation flow rate of the final exchanged solution is too high, the magnesium concentration in the nickel sulfate aqueous solution in the first solvent extraction tank 10A may become too low, potentially causing the magnesium distribution rate to the final exchanged solution to increase. Therefore, from the viewpoint of lowering the final magnesium distribution rate to the final exchanged solution, it is preferable to set the circulation flow rate of the final exchanged solution to an appropriate flow rate. Specifically, it is preferable that the circulation flow rate of the final exchanged solution be 1.2 to 1.3 times the flow rate of the initial exchanged solution.

[0052] [Second Embodiment] (Solvent extraction equipment) Next, a solvent extraction apparatus according to a second embodiment of the present invention will be described. As shown in Figure 4, the solvent extraction equipment BB of this embodiment is a modified version of the solvent extraction equipment AA of the first embodiment, with the arrangement of the first heating device 31 changed. The same reference numerals are used for components identical to those in the first embodiment, and their descriptions are omitted.

[0053] The solvent extraction apparatus BB has a connecting channel 24 that connects the aqueous phase outlet of the second solvent extraction tank 10B to the aqueous phase inlet of the first solvent extraction tank 10A. The nickel sulfate aqueous solution discharged from the aqueous phase outlet of the second solvent extraction tank 10B is supplied to the aqueous phase inlet of the first solvent extraction tank 10A via the connecting channel 24. The first heating device 31 is installed in this connecting channel 24. The nickel sulfate aqueous solution heated by the first heating device 31 is supplied to the first solvent extraction tank 10A.

[0054] The nickel sulfate aqueous solution supplied to the first solvent extraction tank 10A may be heated entirely or partially. By providing the first heating device 31 in the connecting channel 24, the entire nickel sulfate aqueous solution supplied to the first solvent extraction tank 10A can be heated. By providing a bypass channel in the connecting channel 24, a portion of the nickel sulfate aqueous solution discharged from the aqueous phase outlet of the second solvent extraction tank 10B can be guided to the aqueous phase inlet of the first solvent extraction tank 10A via the bypass channel. By providing the first heating device 31 in the bypass channel, a portion of the nickel sulfate aqueous solution supplied to the first solvent extraction tank 10A can be heated.

[0055] (Solvent extraction method) Next, we will explain the solvent extraction method using the solvent extraction equipment BB. In this embodiment as well, multiple solvent extraction tanks 10A to 10E are used to bring a nickel sulfate aqueous solution containing magnesium into countercurrent contact with an organic solvent containing an acidic extractant supporting nickel, thereby replacing the magnesium in the nickel sulfate aqueous solution with the nickel in the organic solvent.

[0056] Here, all or part of the nickel sulfate aqueous solution supplied from the second solvent extraction tank 10B to the first solvent extraction tank 10A is heated. The first heating device 31 is used to heat the nickel sulfate aqueous solution. By supplying the heated nickel sulfate aqueous solution to the first solvent extraction tank 10A, the aqueous phase temperature in the first solvent extraction tank 10A can be increased. In addition, the aqueous phase temperatures in the subsequent solvent extraction tanks 10B to 10E can also be increased.

[0057] In the first solvent extraction tank 10A, which extracts magnesium from a nickel sulfate aqueous solution with a reduced magnesium concentration, increasing the temperature of the nickel sulfate aqueous solution can lower the magnesium distribution rate to the final exchanged solution. As a result, the magnesium concentration in the high-purity nickel sulfate aqueous solution can be effectively reduced.

[0058] [Reference Embodiment] Next, a solvent extraction apparatus according to a reference embodiment will be described. As shown in Figure 5, the solvent extraction equipment CC of this embodiment is a modified version of the solvent extraction equipment AA of the first embodiment, with the arrangement of the first heating device 31 changed. The same reference numerals are used for components identical to those in the first embodiment, and their descriptions are omitted.

[0059] In the solvent extraction equipment CC, the circulation channel 22 connects the discharge channel 21 to the aqueous phase inlet of the second solvent extraction tank 10B. Therefore, a portion of the exchanged liquid is guided to the aqueous phase inlet of the second solvent extraction tank 10B via the circulation channel 22. In addition, a first heating device 31 is provided in the circulation channel 22. Therefore, a portion of the nickel sulfate aqueous solution supplied to the second solvent extraction tank 10B is heated by the first heating device 31.

[0060] A high-temperature nickel sulfate aqueous solution is supplied to the second solvent extraction tank 10B. This high-temperature nickel sulfate aqueous solution is also supplied to the first solvent extraction tank 10A. This allows the aqueous phase temperature in both the second solvent extraction tank 10B and the first solvent extraction tank 10A to be increased. Furthermore, the organic solvent, now at a high temperature in the second solvent extraction tank 10B, is supplied to the subsequent solvent extraction tanks 10C to 10E. This also increases the aqueous phase temperature in the solvent extraction tanks 10C to 10E.

[0061] Since the first and second solvent extraction tanks 10A and 10B are located downstream of the aqueous phase flow, the magnesium concentration in the nickel sulfate aqueous solution held inside is relatively low. By increasing the temperature of the nickel sulfate aqueous solution in the first and second solvent extraction tanks 10A and 10B, the magnesium distribution rate to the final exchanged solution can be reduced. As a result, the magnesium concentration in the high-purity nickel sulfate aqueous solution can be effectively reduced.

[0062] From the viewpoint of reducing the magnesium distribution rate to the final exchange solution, it is preferable to set the circulation flow rate of the exchange solution to an appropriate flow rate. When circulating the exchange solution to the second solvent extraction tank 10B, it is preferable that the circulation flow rate of the exchange solution be 0.3 to 0.5 times the flow rate of the initial exchange solution. [Examples]

[0063] Next, we will describe some examples. (Example 1) The solvent extraction process was operated using solvent extraction equipment AA configured as shown in Figure 3, specifically the exchange stage. The flow rate of the initial exchange solution was 95 L / min. The entire initial exchange solution was heated by the second heating device 32 and supplied to the final solvent extraction tank 10E. The temperature of the initial exchange solution after heating was 49°C. A portion of the final exchange solution discharged from the aqueous phase outlet of the first solvent extraction tank 10A was circulated to the aqueous phase inlet of the first solvent extraction tank 10A via the circulation channel 22. Here, the circulation flow rate of the final exchange solution was set to 120 L / min. This circulation flow rate of the final exchange solution is equivalent to 1.26 times the flow rate of the initial exchange solution. The circulating final exchange solution was also heated by the first heating device 31. The temperature of the final exchange solution after heating was 68°C.

[0064] (Comparative Example 1) In Example 1, the flow rate of the initial exchange solution was set to 95 L / min, and the entire solution was heated to 64°C before being supplied to the final solvent extraction tank 10E. The temperature of the initial exchange solution was higher than in Example 1. Furthermore, the final exchange solution was not circulated or heated.

[0065] In Example 1 and Comparative Example 1, the temperature of the nickel sulfate aqueous solution at the aqueous phase outlet of each solvent extraction tank 10A to 10E was measured. The results are shown in Figure 6. In Figure 6, solvent extraction tank numbers 1, 2, 3, 4, and 5 refer to the first solvent extraction tank 10A, the second solvent extraction tank 10B, the third solvent extraction tank 10C, the fourth solvent extraction tank 10D, and the final solvent extraction tank 10E, respectively.

[0066] As can be seen from Figure 6, in Comparative Example 1, the temperature distribution shows that the water phase temperature gradually decreases from upstream to downstream. In contrast, in Example 1, the temperature distribution shows that the water phase temperature gradually increases from upstream to downstream. This is because in Example 1, the heated exchange liquid was supplied to the first solvent extraction tank 10A.

[0067] Next, in Example 1 and Comparative Example 1, the average temperature of the aqueous phase and the magnesium distribution ratio to the final exchanged solution were determined. Here, the average temperature of the aqueous phase is obtained by dividing the sum of the temperature measurements of the nickel sulfate aqueous solution at the aqueous phase outlet of each solvent extraction tank 10A to 10E by the number of stages in the solvent extraction tanks 10A to 10E, i.e., 5. The magnesium distribution ratio to the final exchanged solution is calculated using the following formula. [Magnesium distribution ratio] = [Amount of magnesium in the final exchange solution] ÷ [Amount of magnesium in the initial exchange solution] × 100%

[0068] The results are shown in Figure 7. As can be seen from Figure 7, even with the same average aqueous phase temperature, Example 1 has a lower magnesium distribution rate to the exchanged final solution compared to Comparative Example 1. From this, it was confirmed that by supplying heated exchanged final solution to the first solvent extraction tank 10A, the aqueous phase temperature distribution can be effectively controlled, and the magnesium distribution rate to the exchanged final solution can be reduced.

[0069] Next, in Example 1, the average aqueous phase temperature was determined while increasing the circulation flow rate of the final replacement solution from 0 L / min, 60 L / min, and 120 L / min, and the magnesium distribution ratio to the final replacement solution was also determined. The results are shown in Figure 8. As can be seen from Figure 8, increasing the circulation flow rate of the final replacement solution to 120 L / min lowers the magnesium distribution ratio to the final replacement solution compared to when the final replacement solution is not circulated. The circulation flow rate of the final replacement solution at 120 L / min corresponds to 1.26 times the flow rate of the initial replacement solution. From this, it was confirmed that a circulation flow rate of the final replacement solution at 1.2 to 1.3 times the flow rate of the initial replacement solution is preferable.

[0070] (Reference example 1) The solvent extraction process was operated using the solvent extraction equipment CC configured as shown in Figure 5, specifically the exchange stage. The flow rate of the initial exchange solution was 90-110 L / min. The entire initial exchange solution was heated by the second heating device 32 and supplied to the final solvent extraction tank 10E. The temperature of the initial exchange solution after heating was 56°C. A portion of the final exchange solution discharged from the aqueous phase outlet of the first solvent extraction tank 10A was circulated through the circulation channel 22 to the aqueous phase inlet of the second solvent extraction tank 10B. The circulating final exchange solution was also heated by the first heating device 31. The temperature of the final exchange solution after heating was 68°C.

[0071] The average aqueous phase temperature and the magnesium distribution ratio to the final exchange solution were determined while increasing the circulation flow rate of the final exchange solution from 0 L / min, 30 L / min, 50 L / min, 60 L / min, and 120 L / min. The results are shown in Figure 9. As can be seen from Figure 9, setting the circulation flow rate of the final exchange solution to 30 L / min or 50 L / min allows for a lower magnesium distribution ratio to the final exchange solution compared to when the final exchange solution is not circulated. When the circulation flow rate of the final exchange solution is increased above 60 L / min, the magnesium distribution ratio to the final exchange solution begins to increase. Circulation flow rates of 30 L / min and 50 L / min of the final exchange solution correspond to 0.3 times and 0.5 times the flow rate of the initial exchange solution, respectively. From this, it was confirmed that when the final exchange solution is circulated to the second solvent extraction tank 10B, it is preferable that the circulation flow rate of the final exchange solution be 0.3 to 0.5 times the flow rate of the initial exchange solution.

[0072] Furthermore, when a portion of the final replacement liquid discharged from the aqueous phase outlet of the first solvent extraction tank 10A is recirculated to the aqueous phase inlet of the first solvent extraction tank 10A via the circulation channel 22, as shown in Figure 8, it has been confirmed that it is preferable for the circulation flow rate of the final replacement liquid to be 120 L / min, that is, for the circulation flow rate of the final replacement liquid to be 1.2 to 1.3 times the flow rate of the initial replacement liquid. On the other hand, when a portion of the final replacement liquid discharged from the aqueous phase outlet of the first solvent extraction tank 10A is recirculated to the aqueous phase inlet of the second solvent extraction tank 10B via the circulation channel 22, as shown in Figure 9, it has been confirmed that it is preferable for the circulation flow rate of the final replacement liquid to be 30 L / min or 50 L / min, that is, for the circulation flow rate of the final replacement liquid to be 0.3 to 0.5 times the flow rate of the initial replacement liquid. This difference is thought to occur because, when a portion of the exchanged wastewater discharged from the aqueous phase outlet of the first solvent extraction tank 10A is circulated through the circulation channel 22 to the aqueous phase inlet of the second solvent extraction tank 10B, the magnesium concentration in the nickel sulfate aqueous solution in the second solvent extraction tank 10B becomes too low. This makes it easier for the equilibrium to shift in a direction that makes it difficult for the substitution reaction between magnesium in the nickel sulfate aqueous solution and nickel in the organic solvent to proceed. [Explanation of symbols]

[0073] AA, BB, CC Solvent Extraction Equipment 10A~10E Solvent Extraction Tank 21 Discharge channel 22 Circulation channel 23 Supply channel 24 Connection Channels 31 1st heating device 32 Second heating device

Claims

1. A multi-stage solvent extraction vessel that replaces magnesium in the nickel sulfate aqueous solution with nickel in the organic solvent by countercurrent contact between an aqueous nickel sulfate solution containing magnesium and an organic solvent containing an acidic extractant supported with nickel, The system comprises one or more heating devices for heating the nickel sulfate aqueous solution, The aforementioned multi-stage solvent extraction tank includes a first solvent extraction tank located at the top of the organic solvent flow and a final solvent extraction tank located at the bottom. The one or more heating devices include a first heating device provided in a circulation channel that guides a portion of the replacement liquid, which is the nickel sulfate aqueous solution discharged from the aqueous phase outlet of the first solvent extraction tank, to the aqueous phase inlet of the first solvent extraction tank. A solvent extraction apparatus characterized by the following features.

2. The circulation flow rate of the final exchange solution is 1.2 to 1.3 times the flow rate of the initial exchange solution, which is the nickel sulfate aqueous solution supplied to the final solvent extraction tank. The solvent extraction apparatus according to claim 1, characterized in that it is as described above.

3. A multi-stage solvent extraction vessel that replaces magnesium in the nickel sulfate aqueous solution with nickel in the organic solvent by countercurrent contact between an aqueous nickel sulfate solution containing magnesium and an organic solvent containing an acidic extractant supported with nickel, The system comprises one or more heating devices for heating the nickel sulfate aqueous solution, The aforementioned multi-stage solvent extraction tank includes a first solvent extraction tank located at the top of the organic solvent flow, a second solvent extraction tank located next to the first solvent extraction tank, and a final solvent extraction tank located at the bottom. The one or more heating devices include a first heating device provided in a flow path that guides all or part of the nickel sulfate aqueous solution discharged from the aqueous phase outlet of the second solvent extraction tank to the aqueous phase inlet of the first solvent extraction tank. A solvent extraction apparatus characterized by the following features.

4. The one or more heating devices include a second heating device that heats all or part of the exchange starter solution, which is the nickel sulfate aqueous solution supplied to the final solvent extraction tank. The solvent extraction apparatus according to any one of the features 1 to 3.

5. The system includes a multi-stage solvent extraction tank, which provides an exchange stage in which an aqueous nickel sulfate solution containing magnesium is brought into countercurrent contact with an organic solvent containing a nickel-supported acidic extractant to replace the magnesium in the aqueous nickel sulfate solution with the nickel in the organic solvent. A portion of the exchangeable liquid, which is the nickel sulfate aqueous solution discharged from the aqueous phase outlet of the first solvent extraction tank located at the top of the flow of the organic solvent among the multiple stages of solvent extraction tanks, is circulated to the aqueous phase inlet of the first solvent extraction tank, and the circulating exchangeable liquid is heated. A solvent extraction method characterized by the following features.

6. The circulation flow rate of the final exchange solution is 1.2 to 1.3 times the flow rate of the initial exchange solution, which is the nickel sulfate aqueous solution supplied to the final solvent extraction tank located at the lowest stage of the organic solvent flow among the multiple stages of solvent extraction tanks. The solvent extraction method according to claim 5, characterized in that it is a feature of the present invention.

7. The system includes a multi-stage solvent extraction tank, which provides an exchange stage in which an aqueous nickel sulfate solution containing magnesium is brought into countercurrent contact with an organic solvent containing a nickel-supported acidic extractant to replace the magnesium in the aqueous nickel sulfate solution with the nickel in the organic solvent. The nickel sulfate aqueous solution supplied to the first solvent extractor from the second solvent extractor, which is located next to the first solvent extractor, which is located at the top of the flow of the organic solvent among the multiple stages of solvent extractors, is heated. A solvent extraction method characterized by the following features.

8. The nickel sulfate aqueous solution, which is the replacement starter solution supplied to the final solvent extraction tank located at the lowest stage of the organic solvent flow among the multiple stages of solvent extraction tanks, is heated in whole or in part. The solvent extraction method according to any one of claims 5 to 7.

9. The system includes a multi-stage solvent extraction tank, which provides an exchange stage in which an aqueous nickel sulfate solution containing magnesium is brought into countercurrent contact with an organic solvent containing a nickel-supported acidic extractant to replace the magnesium in the aqueous nickel sulfate solution with the nickel in the organic solvent. The temperature of the nickel sulfate aqueous solution supplied to the first solvent extractor, which is located at the top of the flow of the organic solvent among the multiple stages of solvent extractors, is set higher than the average temperature of the nickel sulfate aqueous solution supplied to each of the multiple stages of solvent extractors. A solvent extraction method characterized by the following features.

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