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 neutralization 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. In the neutralization step, the pH of the crude nickel sulfate solution is set to 4.6-4.9. Thus, a deposit containing chromium can be easily produced, resulting in a nickel sulfate solution with a low chromium content.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 nickel sulfate solution that can sufficiently remove chromium in the neutralization step for removing iron contained in the aqueous crude nickel sulfate solution. [Means for solving the problem]

[0008] The method for producing an aqueous nickel sulfate solution of the first invention includes 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, and is characterized in that the pH of the aqueous crude nickel sulfate solution is adjusted to 4.6 to 4.9 in the neutralization step. The method for producing an aqueous nickel sulfate solution of a second invention is characterized in that, in the neutralization step, the aqueous crude nickel sulfate solution is sequentially flowed through a plurality of reaction tanks connected in series, the pH of the aqueous crude nickel sulfate solution is increased stepwise from the reaction tank at the first stage to the reaction tank at the last stage, and the pH of the aqueous crude nickel sulfate solution in the reaction tank at the last stage is set to 4.6 to 4.9. The method for producing an aqueous nickel sulfate solution according to a third aspect of the present invention is characterized in that, in the first or second aspect of the present 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 pH of the aqueous solution of crude nickel sulfate in the neutralization reaction is adjusted to 4.6 to 4.9, so that a precipitate containing chromium is easily produced, and an aqueous solution of nickel sulfate with a low chromium concentration can be obtained. [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 neutralization reaction pH in a downstream reaction tank and the chromium concentration in the final neutralization solution. [Figure 6] 1 is a graph showing the relationship between the neutralization reaction pH in a downstream reaction tank and the iron concentration in the final neutralization solution. [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 only needs to include at least the neutralization 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 crude nickel sulfate aqueous solution is preferably set to 4.6 to 4.9. If the neutralization reaction pH is set to 4.6 to 4.9, a precipitate containing chromium is easily generated, so that a nickel sulfate aqueous solution with a low chromium concentration can be obtained. In addition, since the pH is not too high, the amount of nickel precipitation is small, and nickel loss can be suppressed.

[0022] When the neutralization step is carried out using multiple reaction tanks 10A, 10B, the neutralization reaction pH is increased stepwise from the first reaction tank 10A to the last reaction tank 10B. Since the level of impurity concentration in the final neutralization solution mainly depends on the pH of the last reaction tank 10B, it is preferable to set the pH of the aqueous crude nickel sulfate solution in the last reaction tank 10B to 4.6 to 4.9. In the reaction tanks 10A before the last reaction tank 10B, the pH is set lower than this.

[0023] When the neutralization step is carried out in a single-stage reaction tank, the pH of the reaction tank may be adjusted to 4.6 to 4.9.

[0024] Below, we will consider the principle by which the above pH adjustment results in an aqueous nickel sulfate solution with a low chromium concentration.

[0025] When an alkali is added to an aqueous solution of crude nickel sulfate containing iron and chromium as impurities, a neutralization reaction produces ferric hydroxide and chromium hydroxide. The solubility of chromium hydroxide is lower as the pH increases. As can be seen from equation (1) showing the equilibrium reaction of chromium hydroxide, Cr 3+ The concentration is OH - Depends on the concentration, i.e. pH and Cr3+ There is a certain relationship between the pH and the concentration. Therefore, it is possible to create a theoretical solubility curve with the pH on the horizontal axis and the chromium concentration on the vertical axis. Cr 3+ + 3OH - ⇔ Cr(OH)3 (1)

[0026] The theoretical solubility curve of chromium hydroxide is also shown in Figure 3. According to this theoretical solubility curve, the pH must be 5.5 or higher to keep the chromium concentration at 1 mg / L or less. Therefore, from the viewpoint of generating chromium hydroxide and removing chromium, it is preferable to set the neutralization reaction pH to 5.5 or higher.

[0027] However, when the present inventors carefully analyzed the relationship between the neutralization reaction pH and the chromium concentration in the final neutralization solution, it was confirmed that there exists a pH region in which the chromium concentration in the final neutralization solution becomes low in the region on the left side of the theoretical solubility curve (low pH region).

[0028] That is, as shown in Figure 3, when the neutralization reaction pH and the chromium concentration of the final neutralization solution were measured in an actual machine, it was confirmed that the chromium concentration of the final neutralization solution was lower than the theoretical solubility of chromium hydroxide.

[0029] In addition, a beaker test was used to investigate the relationship between the neutralization reaction pH and the chromium concentration of the final neutralization solution, and it was confirmed that the pH range in which the chromium concentration of the final neutralization solution is low is approximately in the range of 4.5 to 5.0.

[0030] Furthermore, Fe was added to the crude nickel sulfate solution. 2+ ion or Fe 3+ When ions were added to cause a neutralization reaction, Fe 3+ It was found that the chromium concentration in the final neutralization solution was significantly reduced when ions were 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.

[0031] 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.

[0032] [Table 1]

[0033] 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 (2) and (3). ≡FeOH 0 + H + ⇔ ≡FeOH2 + (2) ≡FeOH 0 ⇔ ≡FeO - + H + (3)

[0034] The reactions in formulas (2) and (3) 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.

[0035] Positively charged surface hydroxyl groups (≡FeOH2 + ) and Cr 3+ The adsorption reaction with ions occurs as shown in formula (4). 3+ The ions are thought to be removed by an adsorption reaction onto the Fe(OH)3 surface. ≡FeOH2 + + Cr 3+ + H2O ⇔ ≡FeOCrOH + + 3H + (4)

[0036] Figure 4 shows the pH dependence of the Fe(OH)3 surface species concentration. As the pH decreases, the reaction of formula (2) proceeds in the direction of hydrogen ion adsorption, while the Cr 3+ Ion adsorption site ≡FeOH2 + On the other hand, the lower the pH, the more the reaction of equation (4) 3+ Therefore, it is believed that the Cr removal ability is determined by the reactions of formula (2) and formula (4). EXAMPLES

[0037] 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.

[0038] 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.

[0039] 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 4.50 to 5.15. The reaction temperature (temperature of the crude nickel sulfate aqueous solution in the reaction tank) is 50 to 60°C.

[0040] The neutralized slurry discharged from the latter stage reaction tank was separated into solid and liquid using a filter press, and the filtrate was stored in the filtrate tank. The filtrate for one batch of solid-liquid separation was stored in the filtrate tank. Each time one batch of solid-liquid separation was completed, the chromium and iron concentrations of the filtrate (final neutralization liquid) in the filtrate tank were measured by atomic absorption spectrometry.

[0041] Figure 5 shows the relationship between the neutralization pH in the downstream reaction vessel and the chromium concentration in the final neutralization solution. As can be seen from Figure 5, the chromium concentration in the final neutralization solution depends on the neutralization pH in the downstream reaction vessel. Specifically, at least in the range of pH 4.50 to 5.15, the lower the pH, the lower the chromium concentration in the final neutralization solution. This is because the lower the pH, the higher the chromium concentration in the final neutralization solution. 3+ Ion adsorption site ≡FeOH2 + The proportion of Cr increases 3+ This is thought to be because the ions are adsorbed onto the ferric hydroxide.

[0042] 5, from the viewpoint of reducing the chromium concentration in the final neutralization solution, the neutralization reaction pH is preferably 4.9 or less, and more preferably 4.8 or less. If the neutralization reaction pH is 4.9 or less, the chromium concentration in the final neutralization solution can be 1.0 mg / L or less, and if the neutralization reaction pH is 4.8 or less, the chromium concentration in the final neutralization solution can be 0.5 mg / L or less.

[0043] Figure 6 shows the relationship between the neutralization reaction pH in the downstream reaction tank and the iron concentration in the neutralization end solution. As can be seen from Figure 6, the higher the neutralization reaction pH, the lower the iron concentration in the neutralization end solution. From the viewpoint of reducing the iron concentration in the neutralization end solution, the neutralization reaction pH is preferably 4.6 or higher, and more preferably 4.7 or higher. If the neutralization reaction pH is 4.6 or higher, the iron concentration in the neutralization end solution can be reduced to 0.5 mg / L or lower, and if the neutralization reaction pH is 4.7 or higher, the iron concentration in the neutralization end solution can be reduced to 0.3 mg / L or lower.

[0044] From the above, it was confirmed that if the neutralization reaction pH is set to 4.6 to 4.9, the iron concentration in the final neutralization solution can be kept to 0.5 mg / L or less, while the chromium concentration can be kept to 1.0 mg / L or less. [Explanation of symbols]

[0045] 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, In the neutralization step, the aqueous solution of crude nickel sulfate is sequentially flowed through a plurality of reaction tanks connected in series, and the pH of the aqueous solution of crude nickel sulfate is increased stepwise from the first reaction tank to the last reaction tank, and the pH of the aqueous solution of crude nickel sulfate in the last reaction tank is set to 4.6 to 4.

9.

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

2. 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.

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

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