Manufacturing method of nickel sulfate aqueous solution

Abstract

To provide a manufacturing method of a nickel sulfate aqueous solution that can reduce nickel loss.SOLUTION: A manufacturing method of a nickel sulfate aqueous solution comprises a sulfidation step of making a crude nickel sulfate aqueous solution comprising zinc react with a sulfurizing agent by batch processing to generate a sulfide precipitate comprising zinc and obtain a sulfidation slurry, and a first solid-liquid separation step of removing the sulfide precipitate from the sulfidation slurry by solid-liquid separation to obtain a sulfidation final liquid. In the sulfidation step, the batch processing is terminated when the oxidation-reduction potential of the crude nickel sulfate aqueous solution decreases to a target value. The target value is a value predetermined within a range of 0 to 60 mV of oxidation-reduction potential (silver / silver chloride electrode standard). The sulfidation reaction is terminated when the oxidation-reduction potential of the crude nickel sulfate aqueous solution decreases to the target value, and thus precipitation of nickel is suppressed, and nickel loss can be reduced.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an aqueous nickel sulfate solution. More specifically, the present invention relates to a method for producing an aqueous nickel sulfate solution by removing zinc from an aqueous crude nickel sulfate solution. [Background technology]

[0002] The following method is known as a method for producing a high-purity nickel sulfate aqueous solution (for example, Patent Document 1). First, a crude nickel sulfate raw material is dissolved to obtain a crude nickel sulfate aqueous solution (dissolution step). Next, the crude nickel sulfate aqueous solution is reacted with a sulfiding agent in a pressurized reaction tank to remove zinc as a sulfide precipitate (sulfidation step). Next, iron contained in the crude nickel sulfate aqueous solution is removed as a neutralized precipitate by a neutralization reaction to obtain a neutralization end solution (neutralization step). Finally, nickel in the neutralization end solution is extracted and stripped by solvent extraction to obtain a high-purity nickel sulfate aqueous solution (solvent extraction step). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-56178 Summary of the Invention [Problem to be solved by the invention]

[0004] During the sulfurization process, nickel may precipitate along with the zinc contained in the crude nickel sulfate aqueous solution. In particular, if the sulfurization reaction is accelerated to increase the zinc removal rate, nickel sulfides are also more likely to be produced. When nickel precipitates, it is discharged from the system as sulfide precipitate, resulting in nickel loss.

[0005] In view of the above circumstances, an object of the present invention is to provide a method for producing an aqueous nickel sulfate solution that can reduce nickel loss. [Means for solving the problem]

[0006] A first aspect of the method for producing an aqueous nickel sulfate solution includes a sulfurization step in which a crude aqueous nickel sulfate solution containing zinc is brought into contact with hydrogen sulfide gas in a pressurized reaction tank by batch processing to produce a sulfide slurry, and a first solid-liquid separation step in which the sulfide precipitate is removed from the sulfide slurry by solid-liquid separation to obtain a final sulfide solution, wherein in the sulfurization step, the hydrogen sulfide gas is supplied so that the pressure in the pressurized reaction tank is constant, and the batch processing is terminated when the oxidation-reduction potential of the crude aqueous nickel sulfate solution decreases to a target value, and the target value is a predetermined value within a range of 0 to 60 mV of oxidation-reduction potential (based on a silver / silver chloride electrode). The method for producing an aqueous nickel sulfate solution of a second aspect is the method for producing an aqueous nickel sulfate solution of the first aspect, characterized in that the pH of the aqueous crude nickel sulfate solution in the sulfurizing step is adjusted to 1 to 5. The method for producing a nickel sulfate aqueous solution of the third aspect is the method of the first or second aspect, characterized in that it comprises: a neutralization step of blowing air into the final sulfurization solution containing residual zinc and adding an alkali thereto to produce a neutralized precipitate containing zinc by an oxidation neutralization reaction, thereby obtaining a neutralized slurry; and a second solid-liquid separation step of removing the neutralized precipitate from the neutralized slurry by solid-liquid separation to obtain a neutralized final solution. [Effects of the Invention]

[0007] According to the present invention, the sulfurization reaction is terminated when the oxidation-reduction potential (based on a silver / silver chloride electrode) of the aqueous crude nickel sulfate solution falls to a target value set within a range of 0 to 60 mV, thereby suppressing nickel precipitation and reducing nickel loss. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an overall process diagram showing a method for producing a nickel sulfate aqueous solution according to one embodiment. [Figure 2] FIG. 2 is a detailed process diagram of a solvent extraction step in one embodiment. [Figure 3] 1 is a graph showing the relationship between the zinc concentration in the final sulfurization solution and the nickel loss rate. [Figure 4]1 is a graph showing the relationship between the oxidation-reduction potential of a crude nickel sulfate aqueous solution in a sulfurization step and the zinc concentration in the final sulfurization solution. DETAILED DESCRIPTION OF THE INVENTION

[0009] Next, an embodiment of the present invention will be described with reference to the drawings. 1, a method for producing a nickel sulfate aqueous solution according to one embodiment of the present invention includes a dissolving step S1, a sulfurizing step S2, a first solid-liquid separation step S3, a neutralizing step S4, a second solid-liquid separation step S5, and a solvent extraction step S6. However, it is sufficient that at least the sulfurizing step S2 and the first solid-liquid separation step S3 are performed, and the other steps S1, S4, S5, and S6 may be performed as needed. Furthermore, other steps may be added.

[0010] As the crude nickel sulfate raw material, for example, crude nickel sulfate crystals obtained as a by-product of copper smelting are used. The crude nickel sulfate raw material contains zinc as an impurity. The crude nickel sulfate raw material may contain impurities such as iron and cadmium in addition to zinc.

[0011] In the dissolution step S1, a crude nickel sulfate raw material is dissolved in water to obtain a crude nickel sulfate aqueous solution. For example, a predetermined amount of crude nickel sulfate raw material is charged into a dissolution tank containing water, and the crude nickel sulfate raw material is dissolved while heating. As the water for dissolving the crude nickel sulfate raw material, industrial water, a low-concentration nickel sulfate aqueous solution generated in the system, or the like, can be used. In addition, an alkali such as calcium carbonate or sodium hydroxide is added to the dissolution tank to neutralize the sulfuric acid contained in the crude nickel sulfate raw material, thereby adjusting the pH of the crude nickel sulfate aqueous solution. The crude nickel sulfate aqueous solution obtained in the dissolution step S1 contains zinc as an impurity. In addition to zinc, the crude nickel sulfate aqueous solution may also contain impurities such as iron and cadmium.

[0012] In the sulfurization step S2, the crude nickel sulfate aqueous solution is contacted with hydrogen sulfide gas in a pressurized reaction vessel to produce a sulfide precipitate containing zinc, cadmium, and other elements, thereby obtaining a sulfide slurry. The sulfurization step S2 is performed by batch processing. For example, a predetermined amount of crude nickel sulfate aqueous solution is stored in a pressurized reaction vessel, and hydrogen sulfide gas is supplied to cause a sulfurization reaction of impurities such as zinc. The supply rate of hydrogen sulfide gas is controlled so that the pressure of the gas phase in the pressurized reaction vessel is constant at a preset pressure. This control ensures that the gas phase in the pressurized reaction vessel always maintains a constant hydrogen sulfide gas concentration, thereby maintaining high reaction efficiency. The pressure in the pressurized reaction vessel is preferably 0.01 to 0.1 MPa (gauge pressure). The pH of the crude nickel sulfate aqueous solution in the sulfurization step S2 is preferably 1 to 5. The crude nickel sulfate aqueous solution is supplied to the pressurized reaction vessel at the start of the batch process and discharged at the end of the batch process. Since hydrogen sulfide gas is consumed in the sulfurization reaction during the batch process, it is continuously supplied to compensate for this consumption.

[0013] In the first solid-liquid separation step S3, the sulfide precipitate is removed from the sulfide slurry by solid-liquid separation to obtain a sulfide end solution (aqueous nickel sulfate solution containing impurities). The sulfide precipitate is discharged outside the system.

[0014] In the sulfurization step S2, nickel may precipitate along with the zinc contained in the crude nickel sulfate aqueous solution. When nickel precipitates, it is discharged from the system as a sulfide precipitate, resulting in nickel loss. To reduce nickel loss, it is necessary to suppress nickel precipitation in the sulfurization step S2.

[0015] Therefore, in the sulfurization step S2, the batch process is terminated when the oxidation-reduction potential of the crude nickel sulfate aqueous solution is relatively high. Specifically, under control of supplying hydrogen sulfide gas so as to maintain a constant pressure in the pressurized reaction vessel, as impurities such as zinc dissolved in the crude nickel sulfate aqueous solution decrease with the progress of the sulfurization reaction, the amount of hydrogen sulfide gas dissolved in the crude nickel sulfate aqueous solution increases. As a result, the oxidation-reduction potential of the crude nickel sulfate aqueous solution decreases as the sulfurization reaction progresses. The batch process is terminated when the oxidation-reduction potential of the crude nickel sulfate aqueous solution decreases to a target value. Here, the target value is set to a predetermined value within the range of 0 to 60 mV of oxidation-reduction potential (based on a silver / silver chloride electrode; the same applies hereinafter). Terminating the sulfurization reaction when the oxidation-reduction potential of the crude nickel sulfate aqueous solution decreases to the target value in this way suppresses nickel precipitation and reduces nickel loss. From the perspective of suppressing nickel precipitation, the target value is preferably set within the range of 20 to 60 mV, and more preferably within the range of 30 to 60 mV.

[0016] If the sulfurization reaction is terminated when the oxidation-reduction potential of the crude nickel sulfate aqueous solution is relatively high, the zinc removal rate decreases. Therefore, zinc remains in the sulfurization-finished solution. If the remaining zinc is removed in a subsequent step, a nickel sulfate aqueous solution with higher purity can be obtained. Although not particularly limited, it is preferable to remove 40 to 80% of the total zinc contained in the crude nickel sulfate raw material in the sulfurization step S2 and the remainder in the neutralization step S4.

[0017] In the neutralization step S4, air is blown into the sulfurization end solution and an alkali is added to produce a neutralized precipitate of zinc, iron, etc. by an oxidation-neutralization reaction, thereby obtaining a neutralized slurry. Calcium hydroxide, for example, is used as the alkali.

[0018] In the second solid-liquid separation step S5, the neutralized precipitate is removed from the neutralized slurry by solid-liquid separation to obtain a neutralized end solution (aqueous nickel sulfate solution containing impurities).

[0019] Nickel contained in the sulfurization end solution may also precipitate in the neutralization step S4. Therefore, discharging the neutralized precipitate outside the system results in nickel loss. Therefore, the neutralized precipitate may be repulped with sulfuric acid to dissolve the nickel hydroxide contained in the neutralized precipitate, and the filtrate obtained after filtration may be repeated, for example, in the dissolution step S1. This reduces nickel loss even if nickel precipitates in the neutralization step S4.

[0020] In the solvent extraction step S6, nickel contained in the final neutralization solution is extracted into an organic solvent, and then nickel is selectively stripped from the organic solvent to obtain a high-purity aqueous nickel sulfate solution. The solvent extraction step S6 consists of multiple substeps, for example, as shown in Figure 2. A countercurrent multistage solvent extraction apparatus, particularly a mixer-settler, is preferably used for these steps. Note that the solid arrows in Figure 2 indicate the flow of the aqueous phase, and the dashed arrows indicate the flow of the organic phase.

[0021] The end-of-neutralization solution obtained in the neutralization step S4 is supplied to extraction stage S61. In extraction stage S61, nickel contained in the end-of-neutralization solution is extracted into an organic phase, and the nickel is supported on the acidic extractant. Impurities contained in the end-of-neutralization solution, such as zinc, are also extracted into the organic phase.

[0022] In solvent extraction using an acidic extractant, hydrogen ions are involved in the extraction reaction, so the extraction rate changes 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. By lowering the pH in the organic phase flow from the extraction stage S61 to the scrubbing stage S62, exchange stage S63, nickel recovery stage S64, cobalt recovery stage S65, and stripping stage S66, each metal can be separated and recovered at each stage.

[0023] The nickel-loaded organic phase obtained in the extraction stage S61 is sent to the washing stage S62. The extraction residue is discharged outside the system. In the washing stage S62, the nickel-loaded organic phase is washed with a washing solution containing nickel. In the exchange stage S63, the washed nickel-loaded organic phase (nickel-loaded acidic extractant) is brought into contact with a cobalt-containing nickel sulfate aqueous solution containing impurities such as cobalt, and the nickel in the nickel-loaded organic phase is replaced with the impurities in the cobalt-containing nickel sulfate aqueous solution. This produces a high-purity nickel sulfate aqueous solution.

[0024] In the nickel recovery stage S64, 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 from which the nickel has been stripped is sent to the cobalt recovery stage S65.

[0025] In the cobalt recovery stage S65, hydrochloric acid is added to the organic phase to adjust the pH to about 1.0, thereby stripping the cobalt supported in the organic phase to obtain a cobalt recovery solution, which is an aqueous solution of cobalt chloride.

[0026] In the stripping stage S66, sulfuric acid is added to the organic phase to remove impurities such as zinc remaining in the organic phase. The organic phase from which the impurities have been removed in the stripping stage S66 is repeatedly supplied to the extraction stage S61 and the exchange stage S63.

[0027] As described above, in this embodiment, the oxidation-reduction potential of the crude nickel sulfate aqueous solution in the sulfurization step S2 is higher than that of the conventional method, thereby suppressing nickel precipitation and reducing nickel loss. Furthermore, zinc that was not completely removed in the sulfurization step S2 is removed in the neutralization step S4 and the solvent extraction step S6. Therefore, a high-purity nickel sulfate aqueous solution is obtained. [Example]

[0028] Next, an example will be described. The sulfurization step and the first solid-liquid separation step were carried out in a nickel sulfate aqueous solution manufacturing plant. The sulfurization step was carried out by batch processing. Specifically, a predetermined amount of crude nickel sulfate aqueous solution was stored in a pressurized reaction vessel, and then hydrogen sulfide gas was supplied to the crude nickel sulfate aqueous solution to produce zinc sulfide precipitate by a sulfurization reaction.

[0029] The sulfurization process was performed in multiple batches, and the zinc concentration of the final sulfurization solution was measured for each batch. Zinc concentration was measured using atomic absorption spectrometry. Batch processing was performed two to three times per day, so the daily average zinc concentration was calculated from the measured values ​​for each batch. The insoluble nickel content of the sulfurized precipitate was also measured to determine the nickel loss rate. The nickel loss rate was measured using the following procedure. First, the total nickel content of the sulfurized precipitate sampled each day was measured using X-ray fluorescence analysis. Next, 1 g of the sulfurized precipitate was washed with 200 mL of hot water at 40°C for 1 hour to elute the water-soluble nickel. After washing, the nickel content of the sulfurized precipitate was measured using X-ray fluorescence analysis to determine the insoluble nickel content. The daily nickel loss amount was then calculated by multiplying the insoluble nickel content of the sulfurized precipitate by the weight of the sulfurized precipitate per day. Next, the daily nickel treatment amount was calculated based on the amount of crude nickel sulfate raw material treated. The nickel loss rate was calculated by dividing the amount of nickel lost per day by the amount of nickel treated per day. The relationship between the zinc concentration in the sulfurization end solution and the nickel loss rate obtained as a result is shown in Figure 3.

[0030] As can be seen from Figure 3, the lower the zinc concentration in the sulfurization end solution, the higher the nickel loss rate. This is thought to be because the more the sulfurization reaction of zinc is promoted, the more easily nickel precipitates. If the zinc concentration in the sulfurization end solution is set to 60% of the upper limit control value, the nickel loss rate can be reduced to approximately 0.2%. On the other hand, if the zinc concentration in the sulfurization end solution is set to 20% of the upper limit control value, the nickel loss rate will be approximately 0.3%. Therefore, if the zinc concentration in the sulfurization end solution is increased from 20% to 60% of the upper limit control value, the nickel loss rate can be reduced by approximately 0.1%.

[0031] Next, in the sulfurization step, the crude nickel sulfate aqueous solution in the pressurized reaction tank was sampled at predetermined time intervals from the start of the reaction to measure the zinc concentration. In addition, the oxidation-reduction potential of the crude nickel sulfate aqueous solution in the pressurized reaction tank was measured at the time of sampling. Similar measurements were performed for three batches. The results are shown in the graph in Figure 4.

[0032] As the sulfurization reaction progresses, the redox potential of the crude nickel sulfate aqueous solution decreases. As can be seen from Figure 4, the lower the redox potential of the crude nickel sulfate aqueous solution, the lower the zinc concentration in the final sulfurization solution. If the sulfurization reaction is carried out until the redox potential of the crude nickel sulfate aqueous solution reaches 60 mV, the zinc concentration in the final sulfurization solution can be kept below the upper limit control value.

[0033] Therefore, to keep the zinc concentration in the sulfurization end solution below the upper limit, the sulfurization reaction can be carried out until the oxidation-reduction potential of the crude nickel sulfate aqueous solution reaches 60 mV. On the other hand, to prevent nickel precipitation, a higher oxidation-reduction potential of the crude nickel sulfate aqueous solution at the end of the batch is preferable. By carrying out the sulfurization reaction until the oxidation-reduction potential of the crude nickel sulfate aqueous solution reaches 0 mV, the zinc concentration in the sulfurization end solution will be approximately 20% of the upper limit, and the nickel loss rate can be reduced to approximately 0.3%. By carrying out the sulfurization reaction until the oxidation-reduction potential of the crude nickel sulfate aqueous solution reaches 30 mV, the zinc concentration in the sulfurization end solution will be approximately 60% of the upper limit, and the nickel loss rate can be reduced to approximately 0.2%. Therefore, changing the oxidation-reduction potential of the crude nickel sulfate aqueous solution at the end of the batch from 0 mV to 30 mV can reduce the nickel loss rate by approximately 0.1%. A 0.1% reduction in the nickel loss rate in the sulfurization process can reduce the total nickel loss in the nickel sulfate aqueous solution manufacturing plant by 4%.

[0034] Furthermore, if the oxidation-reduction potential of the crude nickel sulfate aqueous solution at the end of the batch is changed from 0 mV to 30 mV, the time required for batch treatment will be shortened, which will have the additional effect of reducing the amount of hydrogen sulfide gas used by 15%.

Claims

1. a sulfurization step in which a zinc-containing crude nickel sulfate aqueous solution is brought into contact with hydrogen sulfide gas in a pressurized reaction tank by batch processing to generate a zinc-containing sulfide precipitate and obtain a sulfide slurry; a first solid-liquid separation step of removing the sulfide precipitate from the sulfide slurry by solid-liquid separation to obtain a final sulfide solution; In the sulfurization step, the hydrogen sulfide gas is supplied so that the pressure in the pressurized reaction tank is kept constant, and the batch treatment is terminated when the oxidation-reduction potential of the crude nickel sulfate aqueous solution is reduced to a target value; The target value is a predetermined value within the range of 0 to 60 mV of oxidation-reduction potential (based on a silver / silver chloride electrode).

1. A method for producing a nickel sulfate aqueous solution comprising the steps of:

2. The pH of the aqueous solution of crude nickel sulfate in the sulfurization step is adjusted to 1 to 5.

2. The method for producing an aqueous nickel sulfate solution according to claim 1.

3. a neutralization step in which air is blown into the sulfurization end solution containing residual zinc, and an alkali is added thereto, thereby generating a neutralized precipitate containing zinc through an oxidation-neutralization reaction, thereby obtaining a neutralized slurry; a second solid-liquid separation step of removing the neutralized precipitate from the neutralized slurry by solid-liquid separation to obtain a neutralization end liquid.

3. The method for producing an aqueous nickel sulfate solution according to claim 1 or 2.

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