Method for producing nickel sulfate aqueous solution

Abstract

To provide a method for producing a nickel sulfate solution that can sufficiently remove chromium in a step for removing iron contained in a crude nickel sulfate solution.SOLUTION: A method for producing a nickel sulfate solution includes: a neutralization step for adding an alkali to a crude nickel sulfate solution containing iron and chromium as impurities, to produce a deposit containing impurities by a neutralization reaction, resulting in neutralized slurry; and a filtration step for subjecting the neutralized slurry to solid-liquid separation with a batch cake filter to produce a neutralized final liquid with the deposit removed therefrom. In the filtration step, a total filtrate volume for each unit filtration area per batch to the cake filter is set to 0.4 m3 / m2 or more. Thus, a nickel sulfate solution with a low chromium content can be produced.SELECTED DRAWING: Figure 5

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 having a low chromium concentration. [Background technology]

[0002] The following method is known as a method for producing an aqueous nickel sulfate solution (for example, Patent Document 1). First, a metal sulfide is pressure leached to obtain an aqueous crude nickel sulfate solution. Next, iron contained in the aqueous crude nickel sulfate solution is removed as hydroxide by a neutralization reaction to obtain an end neutralization solution (neutralization step). Next, impurities contained in the end neutralization solution are removed by solvent extraction to obtain an aqueous nickel sulfate solution (solvent extraction step). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-225217 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the neutralization process, some of the impurities other than iron, such as chromium, are removed along with the iron contained in the crude nickel sulfate solution. However, since chromium hydroxide has a larger solubility product than iron hydroxide, it is difficult to sufficiently remove chromium through the neutralization reaction. Increasing the pH in the neutralization reaction makes it easier to remove chromium as hydroxide, but the amount of nickel precipitation increases, leading to nickel loss.

[0005] Chromium that was not completely removed by the neutralization reaction is extracted into the organic solvent together with other impurities in the solvent extraction process. The impurities extracted into the organic solvent are stripped using sulfuric acid. However, since chromium is difficult to strip, as shown in Figure 7, chromium gradually accumulates in the organic solvent over the operating time of the nickel sulfate production process.

[0006] If chromium accumulates in the organic solvent, the extraction ability of the organic solvent decreases and the chromium concentration in the aqueous nickel sulfate solution increases, so it is preferable to remove most of the chromium in a step prior to the solvent extraction step.

[0007] In view of the above circumstances, an object of the present invention is to provide a method for producing an aqueous solution of nickel sulfate capable of sufficiently removing chromium in a step of removing iron contained in the aqueous solution of crude nickel sulfate. [Means for solving the problem]

[0008] The method for producing an aqueous nickel sulfate solution according to the first aspect of the present invention comprises a neutralization step of adding an alkali to an aqueous crude nickel sulfate solution containing iron and chromium as impurities to produce a precipitate containing the impurities by a neutralization reaction to obtain a neutralized slurry, and a filtration step of subjecting the neutralized slurry to solid-liquid separation using a batch-type cake filter to obtain a final neutralized liquid from which the precipitate has been removed, and in the filtration step, the total amount of filtrate per unit filtration area per batch fed to the cake filter is 0.4 m 3 / m 2 More than The iron concentration in the liquid phase of the neutralized slurry at the time of supply to the filtration step is more than 0 mg / L and not more than 5 mg / L, and the chromium concentration is 1 to 2 mg / L. It is characterized by: The method for producing an aqueous nickel sulfate solution according to a second aspect of the present invention is characterized in that in the neutralization step, the pH of the aqueous crude nickel sulfate solution is adjusted to 4.6 to 4.9 in the first aspect of the present invention. The third invention relates to a method for producing an aqueous nickel sulfate solution, and is characterized in that, in the first or second invention, the aqueous crude nickel sulfate solution has an iron concentration of 50 to 300 mg / L and a chromium concentration of 10 to 30 mg / L at the time of supplying the aqueous crude nickel sulfate solution to the neutralization step. 。 Effect of the Invention

[0009] According to the present invention, the chromium contained in the liquid phase of the neutralized slurry is adsorbed by the iron hydroxide contained in the cake, thereby reducing the chromium concentration in the filtrate, thereby obtaining an aqueous nickel sulfate solution with a low chromium concentration. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an overall process diagram of a nickel sulfate manufacturing process. [Diagram 2] FIG. 2 is an explanatory diagram of an apparatus for carrying out the neutralization and filtration steps. [Diagram 3] 1 is a graph showing the relationship between the neutralization reaction pH and the chromium concentration in the final neutralization solution. [Figure 4] Graph showing pH dependence of Fe(OH)3 surface species concentration. Source: David A. Dzombak and Francois MM Morel: Surface Complexation Modeling, (Wiley-Interscience, New York, 1990) [Diagram 5] 1 is a graph showing the relationship between the total filtrate volume per unit filtration area and the chromium concentrations of the filtrate and the final neutralization solution. [Figure 6] 1 is a graph showing the relationship between the total filtrate volume per unit filtration area and the chromium concentration and pH of the filtrate. [Figure 7] 1 is a graph showing the change in chromium concentration in an organic solvent. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Next, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a method for producing an aqueous nickel sulfate solution according to one embodiment of the present invention includes a pressure leaching step, a neutralization step, a filtration step, and a solvent extraction step.

[0012] In the pressure leaching process, metal sulfides such as nickel-cobalt mixed sulfide are pressure leached to obtain a crude nickel sulfate aqueous solution. The crude nickel sulfate aqueous solution contains impurities such as iron. In the neutralization process, an alkali is added to the crude nickel sulfate aqueous solution, and a neutralization reaction occurs to produce a precipitate containing impurities, resulting in a neutralized slurry. In the filtration process, the neutralized slurry is subjected to solid-liquid separation to obtain a neutralized end solution from which the neutralized precipitate has been removed. In the solvent extraction process, impurities contained in the neutralized end solution are removed by solvent extraction to obtain a nickel sulfate aqueous solution. In the solvent extraction process, a crude cobalt chloride aqueous solution can also be obtained from the cobalt contained in the neutralized end solution.

[0013] In the solvent extraction process, impurities contained in the neutralization end solution are extracted into an organic solvent. The impurities extracted into the organic solvent are back-extracted with sulfuric acid. However, chromium is difficult to back-extract. Therefore, it is possible to add hydrochloric acid to the organic solvent to back-extract chromium and then wash it with sulfuric acid.

[0014] The method for producing a nickel sulfate aqueous solution according to the present embodiment may include at least the neutralization step and the filtration step, and other steps may be omitted or added.

[0015] As shown in FIG. 2, the neutralization step is generally performed using multiple reaction tanks 10A and 10B. Specifically, multiple reaction tanks 10A and 10B are connected in series, and the aqueous solution of crude nickel sulfate is allowed to flow in sequence from the reaction tank 10A at the front to the reaction tank 10B at the rear. An alkali is added to each reaction tank 10A, 10B to adjust the pH (neutralization reaction pH) of the aqueous solution of crude nickel sulfate. In this case, it is preferable to increase the pH of the aqueous solution of crude nickel sulfate stepwise from the reaction tank 10A at the front to the reaction tank 10B at the rear. That is, the pH of the reaction tank 10B is made higher than the pH of the reaction tank 10A immediately preceding it.

[0016] The number of stages of the reaction vessels 10A and 10B is not particularly limited. The number of stages of the reaction vessels may be one.

[0017] Neutralized slurry is discharged from the final stage reaction tank 10B. The neutralized slurry is a slurry containing a precipitate (neutralized precipitate) generated by the neutralization reaction. The neutralized slurry is separated into solid and liquid by a filter 20 to obtain a neutralized precipitate and a filtrate.

[0018] As the filter 20, a cake filter such as a filter press or a leaf filter can be suitably used. A cake filter captures solid particles contained in the liquid to be filtered with a filter medium to form a cake layer, and filters the liquid by passing it through the cake layer. Most cake filters are operated in a batch mode. That is, when a predetermined amount of cake is formed by passing the liquid through, the filtering operation is terminated and the cake is discharged.

[0019] The filtrate discharged from the filter 20 is stored in the filtrate tank 30. The liquid stored in the filtrate tank 30 is called the end neutralization liquid.

[0020] The aqueous solution of crude nickel sulfate supplied to the neutralization step contains at least iron and chromium as impurities. For example, the aqueous solution of crude nickel sulfate has an iron concentration of 50 to 300 mg / L and a chromium concentration of 10 to 30 mg / L at the time of supply to the neutralization step.

[0021] In the neutralization step, the pH of the aqueous solution of crude nickel sulfate is preferably adjusted to 4.6 to 4.9. When the neutralization step is performed using a plurality of reaction tanks 10A, 10B, it is preferable to increase the neutralization reaction pH stepwise from the first reaction tank 10A to the last reaction tank 10B, and to adjust the pH of the aqueous solution of crude nickel sulfate in the last reaction tank 10B to 4.6 to 4.9. When the neutralization step is performed in a single reaction tank, the pH of the reaction tank may be adjusted to 4.6 to 4.9.

[0022] The neutralization reaction produces precipitates of impurities contained in the crude nickel sulfate aqueous solution. This reduces the impurity concentration in the liquid phase. For example, at the time of supplying the neutralized slurry to the filtration process, the iron concentration in the liquid phase of the neutralized slurry is 0 to 5 mg / L, and the chromium concentration is 1 to 2 mg / L.

[0023] If the neutralized slurry is subjected to solid-liquid separation using a batch-type cake filter, a neutralized final liquid with a lower chromium concentration can be obtained. The chromium contained in the liquid phase of the neutralized slurry is adsorbed onto the surface of the iron hydroxide contained in the cake, thereby lowering the chromium concentration in the filtrate. This results in an aqueous nickel sulfate solution with a low chromium concentration.

[0024] In a batch-type cake filter, the more the total amount of liquid passing through a batch, the thicker the cake layer will be. The thicker the cake layer, the more the contact between chromium and iron hydroxide will be promoted, and the lower the chromium concentration of the filtrate will be. Therefore, the more the total amount of liquid passing through a batch is increased, the lower the chromium concentration of the final neutralization liquid will be.

[0025] Specifically, the total amount of filtrate per unit filtration area per batch into the cake filter is 0.4 m 3 / m 2 Here, the total amount of filtrate per unit filtration area is the total amount of filtrate supplied to the cake filter [m 3 ] is the filtering area of ​​the cake filter [m 2 If the iron concentration of the crude nickel sulfate aqueous solution is 50 mg / L, the total filtrate volume per unit filtration area per batch is 0.4 m 3 / m 2 is the iron loading per unit filtration area per batch of 20g / m 2 is equivalent to.

[0026] If the total amount of liquid passing through the cake filter is too large, the filtration resistance increases and the liquid flow rate decreases, resulting in a decrease in the throughput. Therefore, although it varies somewhat depending on the slurry concentration of the neutralized slurry, it is recommended to set the total amount of filtrate per unit filtration area per batch to 1 m 3 / m 2 It is preferable to do the following:

[0027] The principle by which a nickel sulfate aqueous solution with a low chromium concentration can be obtained by cake filtration will be discussed below.

[0028] The inventors conducted a beaker test to confirm that Fe was dissolved in a crude nickel sulfate solution. 2+ion or Fe 3+ The neutralization reaction was carried out by adding Fe ions. The results are shown in Figure 3. As can be seen from Figure 3, 3+ The chromium concentration in the final neutralization solution is significantly reduced when ions are added. 3+ The ion is Fe 3+ The present inventors have investigated the principle of chromium removal by dividing the coprecipitation reaction into two types of reactions, a substitution reaction and an adsorption reaction.

[0029] The substitution reaction here refers to the formation of ferric hydroxide by Fe 3+ Ion and Cr 3+ This refers to a reaction in which ions are exchanged. In general, poorly soluble metal hydroxides have a structure of metal oxide hydrate. For example, 2Fe(OH)3 can be regarded as Fe2O3·3H2O, and 2Cr(OH)3 as Cr2O3·3H2O. Comparing Fe2O3 and Cr2O3, the crystal structures of Fe2O3 and Cr2O3 are isomorphic (corundum type). As shown in Table 1, the difference in lattice constant between Fe2O3 and Cr2O3 is 1-2%. It is known that substitution reactions can occur when the difference in lattice constant is 10% or less, so Cr 3+ The ion is Fe 3+ It is believed that they are removed by a substitution reaction with ions.

[0030] [Table 1]

[0031] It is known that the surface of ferric hydroxide (Fe(OH)3) in an aqueous solution becomes electrically charged by the adsorption and desorption of hydrogen ions. The reaction formulas are as shown in formulas (1) and (2). ≡FeOH 0 + H + ⇔ ≡FeOH2 + (1) ≡FeOH 0 ⇔ ≡FeO - + H + (2)

[0032] The reactions in formulas (1) and (2) occur on the surface of Fe(OH)3. The symbol ≡ in the formula indicates a solid-liquid interface. The surface hydroxyl groups of Fe(OH)3 (≡FeOH 0 ) is positively charged by adsorbing hydrogen ions in the pH range lower than its isoelectric point, but is negatively charged in the pH range higher than its isoelectric point. The isoelectric point of Fe(OH)3 is around pH 8.0. Since the pH of the neutralization reaction is around 5.0, the surface of Fe(OH)3 is positively charged.

[0033] Positively charged surface hydroxyl groups (≡FeOH2 + ) and Cr 3+ The adsorption reaction with ions occurs as shown in formula (3). 3+ The ions are thought to be removed by an adsorption reaction onto the Fe(OH)3 surface. ≡FeOH2 + + Cr 3+ + H2O ⇔ ≡FeOCrOH + + 3H + (3)

[0034] Figure 4 shows the pH dependence of the Fe(OH)3 surface species concentration. As the pH decreases, the reaction of formula (1) proceeds in the direction of hydrogen ion adsorption, while the Cr 3+ ≡FeOH2, which is an adsorption site for ions + On the other hand, the lower the pH, the more the reaction of equation (3) 3+ Therefore, it is believed that the Cr removal ability is determined by the reactions of formula (1) and formula (3). EXAMPLES

[0035] Next, an embodiment will be described. An alkali was added to the aqueous solution of crude nickel sulfate, and a precipitate containing impurities was generated by a neutralization reaction. Here, the aqueous solution of crude nickel sulfate was passed through two reactors connected in series, one after the other, to cause the neutralization reaction.

[0036] The crude nickel sulfate aqueous solution at the time of supply to the upstream reaction tank has a nickel concentration of 130 to 150 g / L, a cobalt concentration of 11 to 14 g / L, an iron concentration of 50 to 300 mg / L, a chromium concentration of 10 to 30 mg / L, an SS concentration of 0 to 10 g / L, and a pH of 1.1 to 1.4.

[0037] The flow rate of the crude nickel sulfate aqueous solution to the reaction tank is 80 to 170 L / min. The neutralization reaction pH of the first reaction tank is 3.70 to 4.05, and the neutralization reaction pH of the second reaction tank is 4.6 to 4.9. The reaction temperature (temperature of the crude nickel sulfate aqueous solution in the reaction tank) is 50 to 60°C.

[0038] The neutralized slurry discharged from the latter stage reaction tank was separated into solid and liquid using a filter, and the filtrate was stored in a filtrate tank. A fully automatic compression filter press was used as the filter. The filtration area was 78.8 m 2 The filtration volume was 1089 L, the chamber thickness was 30 mm, the number of chambers was 54, and the maximum filtration pressure was 0.4 MPa. The maximum liquid passing time through the filter was 400 minutes.

[0039] The chromium concentration of the filtrate and the filtrate (neutralization end liquid) in the filtrate tank were measured by atomic absorption spectrometry at regular intervals from the start of one batch of solid-liquid separation. The filtrate tank stores the filtrate for one batch of solid-liquid separation. Therefore, the chromium concentration of the neutralization end liquid is the average chromium concentration of the filtrate discharged up to that point.

[0040] Figure 5 shows the relationship between the total filtrate volume per unit filtration area and the chromium concentration of the filtrate and the final neutralization liquid when the neutralization reaction pH in the downstream reaction tank is 4.9. As can be seen from Figure 5, the chromium concentration of the filtrate decreases as the total filtrate volume per unit filtration area increases. This means that the chromium concentration of the filtrate decreases with an increase in the total amount of liquid passing or with the passage of time.

[0041] The filtrate tank stores one batch of filtrate. Therefore, the more the total amount of liquid passing through the tank, the more the end neutralization solution in the filtrate tank is diluted with filtrate with a lower chromium concentration. As a result, the end neutralization solution with a lower chromium concentration is finally obtained. In other words, the more the total amount of filtrate per unit filtration area per batch is increased, the lower the chromium concentration of the end neutralization solution becomes.

[0042] From Figure 5, the total filtrate volume per unit filtration area is 0.4 m 3 / m 2 In this case, the chromium concentration of the filtrate will be 0 mg / L, and the chromium concentration of the final neutralization solution will be 1.0 mg / L. Therefore, from the viewpoint of reducing the chromium concentration of the final neutralization solution, the total filtrate volume per unit filtration area should be 0.4 m 3 / m 2 The total amount of filtrate per unit filtration area is preferably 0.4 m or more. 3 / m 2 If this is done, the chromium concentration in the final neutralized solution can be reduced to 1.0 mg / L or less.

[0043] Figure 6 shows the relationship between the total filtrate volume per unit filtration area and the chromium concentration and pH of the filtrate when the neutralization reaction pH in the downstream reaction tank is set to 4.7. It can be seen from Figure 6 that the greater the total filtrate volume per unit filtration area, the lower the pH of the filtrate. This suggests that the reaction shown in formula (3) proceeded when the neutralized slurry was separated into solid and liquid by the filter. That is, Cr was added to the ferric hydroxide contained in the filter cake. 3+ It is believed that the ions were adsorbed. The greater the total amount of liquid passed, the thicker the cake became, and the more ferric hydroxide and Cr ions in the cake were adsorbed. 3+ This promotes contact with ions. Therefore, it is believed that the chromium concentration in the filtrate decreases as the total amount of liquid passed increases. [Explanation of symbols]

[0044] 10A, 10B Reactor 20 filtration machine 30 Filtrate tank

Claims

1. a neutralization step of adding an alkali to an aqueous solution of crude nickel sulfate containing iron and chromium as impurities to generate a precipitate containing the impurities by a neutralization reaction, thereby obtaining a neutralized slurry; A filtration step of subjecting the neutralized slurry to solid-liquid separation using a batch-type cake filter to obtain a neutralized final liquid from which the precipitate has been removed, In the filtration step, the total amount of filtrate per unit filtration area per batch in the cake filter is 0.4 m ３ / m ２ More than that, The iron concentration in the liquid phase of the neutralized slurry at the time of supply to the filtration step is greater than 0 mg / L and less than 5 mg / L, and the chromium concentration is 1 to 2 mg / L.

2. The method for producing an aqueous nickel sulfate solution comprising the steps of:

2. In the neutralization step, the pH of the aqueous solution of crude nickel sulfate is adjusted to 4.6 to 4.

9.

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

3. The iron concentration of the aqueous solution of crude nickel sulfate at the time of supplying to the neutralization step is 50 to 300 mg / L, and the chromium concentration is 10 to 30 mg / L.

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

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