JP2012001750A - METHOD FOR PRODUCING Co-CONTAINING SOLUTION - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a Co-containing solution effectively separating and removing Ni from a CoNi material solution high in an Ni amount, and further selectively recovering Co.SOLUTION: In this method for producing a Co-containing solution, a reducing agent and CoS are added in a solution containing Ni and Co (called "a CoNi material solution") to adjust oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the CoNi material solution to -550 to -400 mV to precipitate and remove the Ni element in the solution as a sulfide, and the Co-containing solution containing the Co element in an ionized state is obtained.

Description

  The present invention relates to a method for producing a Co-containing solution containing a large amount of Co by reducing Ni from a solution containing Co and Ni (referred to as “CoNi raw material solution”). Such a manufacturing method can be used, for example, for a purpose of manufacturing a Co-containing solution or Co (metal) from a positive electrode material of a lithium ion battery.

  Lithium-ion batteries have a low weight per unit of electricity and yet high energy density, so they are rapidly becoming popular as power sources for portable electronic devices such as video cameras, laptop computers, and mobile phones, as well as electric vehicles and hybrid vehicles. I am doing. For this reason, recovery of valuable metals from used lithium ion batteries (referred to as “waste lithium ion batteries”) is regarded as important from the viewpoint of effective use of resources. Especially, since expensive Co is used for the positive electrode of the lithium secondary battery, the recovery of Co is particularly attracting attention.

Conventionally, LiCoO ₂ having a layer structure having a high voltage of 4 V has been used as a positive electrode active material of a lithium secondary battery. Recently, a part of expensive Co is made of a transition metal such as Ni or Mn. Substituted lithium composite oxides have been used as positive electrode active materials. Therefore, in order to recover Co from this kind of waste lithium ion battery, how to remove metals other than Co, especially Co and Ni are similar in chemical properties, so how to remove Ni and Co The only issue was whether it could be selectively recovered.

  As such a technique, for example, in Patent Document 1 (Japanese Patent Publication No. 6-96455), cobalt powder is added to an aqueous cobalt sulfate solution containing impurities, and sodium hydrosulfide, sodium sulfide, or hydrogen sulfide is added excessively thereto. By adding a small amount of sodium hypochlorite or hydrogen peroxide to the filtrate from which the generated precipitate has been separated, the impurities, such as nickel, iron and copper, are removed to a very low concentration. A method for obtaining pure cobalt sulfate is disclosed.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2006-8463) discloses a compound that dissolves cobalt metal containing nickel and iron as impurities in an aqueous sulfuric acid solution, and generates iron powder and sulfide ions in the resulting solution. Then, nickel sulfide is precipitated to remove nickel, and then an oxidizing agent for oxidizing divalent iron is added to the obtained solution and the pH of the solution is adjusted to 3 to 5. A method of obtaining an aqueous cobalt sulfate solution by precipitating iron hydroxide to remove iron is disclosed.

Japanese Examined Patent Publication No. 6-96455 JP 2006-8463 A

  As described above, recently, the ratio of Ni to Co is increasing in the positive electrode active material of lithium secondary batteries. The Co recovery method that has been proposed in the past was based on the premise that the Ni ratio was not so high, so Co could be recovered sufficiently while the Ni ratio was low. However, when the ratio of Ni increases, Ni cannot be sufficiently removed, and there is a problem that the recovery rate of Co cannot be increased.

  Accordingly, the present invention provides a method for producing a new Co-containing solution that can effectively separate and remove Ni from a CoNi raw material solution having a relatively high amount of Ni, and that can further selectively recover Co. Is intended to provide.

  In the present invention, a reducing agent and CoS are added to a solution containing Ni and Co (referred to as “CoNi raw material solution”), and the redox potential (reference electrode: silver-saturated silver chloride electrode) of the CoNi raw material solution is −550 mV. A method for producing a Co-containing solution, characterized by obtaining a Co-containing solution containing Co element in an ionized state while precipitating and removing Ni element in the solution as a sulfide by adjusting to ~ -400 mV, is proposed. .

Thus, when a reducing agent and CoS are added to the CoNi raw material solution to adjust the oxidation-reduction potential to -550 mV to -400 mV, a reaction represented by the following formula (1) occurs, and the Co element is ionized to enter the solution. On the other hand, Ni element can be precipitated and removed as a sulfide, so that a Co-containing solution that selectively takes in Co in an ionized state can be recovered.
Formula (1) .. 2 CoS + 3Ni ²⁺ + Fe → 2Co ²⁺ + Ni ₃ S ₂ ↓ + Fe ²⁺

  The Co-containing solution thus obtained is further precipitated, for example, by adding a reducing agent and a sulfurizing agent to adjust the oxidation-reduction potential of the solution to -550 mV to -400 mV. A solution in which the remaining Co element is dissolved (referred to as “Co high-purity solution”) can be obtained.

  Such a Co-containing solution manufacturing method and a Co high-purity solution manufacturing method can efficiently separate and remove Ni and effectively recover Co even in a CoNi raw material solution having a high Ni ratio. Therefore, for example, it can be suitably used for a method of recovering Co from a positive electrode material of a waste lithium ion battery, particularly a recent positive electrode material in which the ratio of Ni is increasing. Specifically, since the positive electrode material of the waste lithium ion battery includes Mn, Co, and Al in addition to Co and Ni, the recovered positive electrode material or positive electrode active material is dissolved in sulfuric acid or the like. Then, after removing contained substances other than Co and Ni by a known method, Ni can be more effectively removed by using the Co-containing solution manufacturing method and the Co high-purity solution manufacturing method of the present invention. Co can be recovered even more selectively.

It is the figure which showed the manufacturing process of 1st Embodiment mentioned later. It is the figure which showed the manufacturing process of 2nd Embodiment mentioned later. It is the figure which showed the manufacturing process of 3rd Embodiment mentioned later. 4 is a graph showing the relationship between ORP and the concentrations of Ni and Fe in the liquid and the relationship between ORP and Co recovery rate as a result of Test 1.

  Embodiments of the present invention will be described in detail below, but the scope of the present invention is not limited to the embodiments described below.

<First Embodiment>
In this embodiment, as shown in FIG. 1, a reducing agent and CoS are added to a solution containing Ni and Co (referred to as “CoNi raw material solution”), and the redox potential of the CoNi raw material solution (reference electrode: silver − (Saturated silver chloride electrode) is adjusted to -550 mV to -400 mV to precipitate and remove Ni elements in the solution as sulfides, while obtaining a Co-containing solution containing Co elements in an ionized state. It is a form.

Thus, when a reducing agent (for example, iron powder) and CoS are added to the CoNi raw material solution to adjust the oxidation-reduction potential to -550 mV to -400 mV, a reaction represented by the following formula (1) occurs, and Ni in the solution The element can be precipitated and removed as a sulfide, and the Co element of CoS can be ionized and dissolved in the solution, so that Co can be recovered in the Co-containing solution as the Co element in an ionized state.
At this time, for example, when iron powder is added as a reducing agent, Ni precipitates as a sulfide as shown in formula (1).
Formula (1) .. 2 CoS + 3Ni ²⁺ + Fe → 2Co ²⁺ + Ni ₃ S ₂ ↓ + Fe ²⁺

The CoNi raw material solution only needs to contain at least Ni and Co. Components other than Ni and Co may be included, but if other metal elements are included, there is a possibility that Ni may be removed, so that it is preferably removed by a known method.
For the CoNi raw material solution, for example, a composition containing Ni and Co (including an alloy) is preferably dissolved in sulfuric acid or the like, and if necessary, metal components other than Ni and Co are excluded by a known method. However, even if Fe is contained, there is little trouble, and since it can be eliminated in a later process, Fe may be contained in the CoNi raw material solution.
At this time, in addition to sulfuric acid, a known acid such as hydrochloric acid or nitric acid may be used for dissolution.
In addition, when a compound containing Ni and Co such as lithium cobaltate is acid-dissolved, it is preferable to add a reducing agent such as H ₂ O ₂ or iron powder.

As shown in Test 2 to be described later, in the CoNi raw material solution, the higher the initial Ni concentration, the higher the Co recovery rate from CoS, but conversely the Ni separation rate tends to decrease. The molar ratio (Ni / Co) of Ni in the CoNi raw material solution to Co in CoS is preferably 0.2 to 0.8 (mol / mol), particularly 0.3 (mol / mol) or more or 0. 0.7 (mol / mol) or less, more preferably 0.4 (mol / mol) or more or 0.6 (mol / mol) or less.
The initial temperature of the CoNi raw material solution, that is, the liquid temperature when the reducing agent is added, is preferably 30 to 50 ° C. in order to make the dissolution rate of the iron powder appropriate.

  The initial pH of the CoNi raw material solution, that is, the initial pH of the solution to which the reducing agent is added is preferably adjusted to 3.0 to 6.0. If pH is 3.0 or more, it can prevent that the produced | generated sulfide volatilizes as hydrogen sulfide. Moreover, if it is pH 6.0 or less, the production | generation of a hydroxide can be suppressed and a sulfide can be produced preferentially. From this point of view, the pH of the solution when adding the reducing agent is more preferably 4 or more, or 5 or less, particularly 4.5 or less.

In this embodiment, it is important to adjust the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the CoNi raw material solution to −400 mV or less from the viewpoint of the effect of precipitating and removing Ni element in the solution as sulfides. It is. That is, the Ni concentration can be effectively reduced only when the oxidation-reduction potential of the solution is adjusted to −400 mV or less. On the other hand, even if it lowers from -550 mV, the removal rate of Ni cannot be raised any more, but a reducing agent melt | dissolves in a solution in large quantities, and the load of a post process will increase.
Therefore, the redox potential (reference electrode: silver-saturated silver chloride electrode) of the CoNi raw material solution adjusted by adding a reducing agent is preferably adjusted to -550 mV to -400 mV, and in particular, adjusted to -550 mV to -450 mV. In particular, it is more preferable to adjust to −550 mV to −500 mV.

Examples of the reducing agent include iron (Fe), cobalt (Co), zinc (Zn), aluminum (Al) and other base metal powders such as Ni and hydrazine. From the viewpoint of adjusting the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) to -550 mV to -400 mV, it is particularly preferable to use iron powder.
What is necessary is just to adjust the addition amount of a reducing agent so that the oxidation-reduction potential of a CoNi raw material solution can be adjusted to a predetermined range.

As the sulfiding agent that makes Ni element in the solution sulfide, for example, a sulfiding agent such as NaHS, Na ₂ S, H ₂ S, K ₂ S can be used. It is particularly preferable to use CoS from the viewpoints of reduction efficiency and the need for an extra separation step.

<Second Embodiment>
In the present embodiment, as shown in FIG. 2, a reducing agent and CoS are added to a CoNi raw material solution containing Ni and Co, and the redox potential (reference electrode: silver-saturated silver chloride electrode) of the CoNi raw material solution is- Adjusting to 550 mV to -400 mV to precipitate and remove Ni element in the solution as a sulfide, while reducing Ni to obtain a Co-containing solution containing Co element in an ionized state;
A reducing agent and a sulfurizing agent are added to the Co-containing solution obtained in the Ni reduction step to adjust the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the Co-containing solution to -550 mV to -400 mV, The Ni element in the solution is precipitated as Ni sulfide, and a part of the Co element in the solution is precipitated as CoS and then separated into solid and liquid, and the Ni sulfide and the CoS-containing composition containing the CoS are separated. And a CoS preparation step of separating and recovering a solution in which the remaining Co element is dissolved (referred to as “Co high-purity solution”) obtained by dissolving the remaining Co element.

Thus, when a reducing agent (for example, iron powder) and a sulfiding agent (for example, NaHS) are added to the Co-containing solution obtained in the Ni reduction step to adjust the oxidation-reduction potential to -550 mV to -400 mV, the following equation is obtained: (2) (3) A reaction occurs, and a part of Co element in the solution is precipitated as CoS, and Ni element in the solution is precipitated as Ni sulfide (for example, N ₃ S ₂ ). Obtainable.
Formula (2) ·· 3Ni ²⁺ + 2NaHS + Fe → Ni ₃ S ₂ ↓ + 2Na ⁺ + 2H ⁺ + Fe ²⁺
Formula (3) ·· Co ²⁺ + NaHS → CoS ↓ + Na ⁺ + H ⁺

  Moreover, in this embodiment, if the CoS-containing composition recovered in the CoS production process is added as CoS in the Ni reduction process of the next batch and subsequent batches, the Co recovery rate can be further increased. Therefore, Co can be continuously recovered by repeating the Ni reduction step and the CoS preparation step in this way.

In the present embodiment, the Ni reduction process may be performed in the same manner as in the first embodiment.
It is preferable to remove the precipitate generated in the Ni reduction step before the CoS preparation step.

On the other hand, in the CoS preparation step, the initial pH of the Co-containing solution, that is, the pH when the reducing agent is added is the same as the initial pH of the CoNi raw material solution in the first embodiment.
Further, the initial temperature of the Co-containing solution in the CoS production process, that is, the liquid temperature when the reducing agent is added is the same as the initial temperature of the CoNi raw material solution in the first embodiment.

In the CoS production process, it is important to adjust the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the Co-containing solution to −400 mV or less from the viewpoint of removing Ni to a low concentration. That is, Ni can be removed to a low concentration only when the oxidation-reduction potential of the solution is adjusted to −400 mV or less. On the other hand, even if it lowers from -550 mV, the removal rate of Ni cannot be raised any more, but a reducing agent melt | dissolves in a solution in large quantities, and the load of a post process will increase.
From this point of view, the redox potential of the Co-containing solution to be adjusted by adding a reducing agent (reference electrode: silver-saturated silver chloride electrode) is preferably adjusted to -550 mV to -400 mV, and in particular, -550 mV to -450 mV. It is more preferable to adjust to −550 mV, and it is more preferable to adjust to −550 mV to −500 mV among them.

Examples of the reducing agent used in the CoS manufacturing process include iron (Fe), cobalt (Co), zinc (Zn), aluminum (Al), and other base metal powders such as Ni and hydrazine. However, from the viewpoint of adjusting the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the Co-containing solution to -550 mV to -400 mV, iron powder is particularly preferable.
What is necessary is just to adjust the addition amount of a reducing agent so that the oxidation-reduction potential of Co containing solution can be adjusted to a predetermined range.

In the CoS production process, for example, NaHS, Na ₂ S, H ₂ S, K ₂ S, or the like can be used as a sulfiding agent that uses Ni element in the solution as a sulfide. From the viewpoint, NaHS is particularly preferable. However, it is not limited to NaHS.
From the viewpoint that Ni can be sufficiently removed, it is preferable to add 1 to 10 times the molar amount of sulfide (S conversion) with respect to the initial Ni content in the solution at the start of the reaction. In particular, it is preferable to add 2 to 10-fold molar amount, especially 5-fold molar amount or more of sulfide (S conversion).

On the other hand, the CoS-containing composition recovered in the CoS production process is added as CoS in the Ni reduction process of the next batch and thereafter, that is, the Ni reduction process and the CoS production are performed so as to be input to the Ni reduction process of the subsequent batch. If the process is repeated, Ni can be replaced with Co in CoS to precipitate and remove as Ni sulfide (for example, Ni ₃ S ₂ ), and Co can be recovered from the CoS into the solution. Co recovery rate can be further increased. Therefore, even a raw material having a high Ni ratio is excellent in that Ni can be separated and removed to increase the Co recovery rate.
At this time, since the CoS-containing composition recovered in the CoS manufacturing process contains Ni sulfide (for example, N ₃ S ₂ ) and CoS, it contains Ni sulfide (for example, N ₃ S ₂ ) and CoS. A composition (referred to as “CoS-containing composition”) may be added as CoS in the Ni reduction step, or Ni sulfide (eg, N ₃ S ₂ ) may be reduced and added as CoS.
Regarding the CoS-containing composition to be input to the Ni reduction step, the higher the CoS ratio, the more the Ni reduction amount is preferable, so the Co: Ni molar ratio in the CoS-containing composition is preferably 50:50 to 100: 0. In particular, 70:30 to 100: 0, more preferably 90:10 to 100: 0 is even more preferable.

<Third Embodiment>
In this embodiment, the manufacturing method of the present invention is used in a method for recovering Co from a positive electrode material of a waste lithium ion battery.

  In addition to Co and Ni, the positive electrode active material of the lithium ion battery contains a large amount of Mn, and impurities due to the positive electrode current collector and the negative electrode material, such as Al and Cu, may be contained as impurities. There is sex. Therefore, in order to use the manufacturing method of the present invention to recover Co from the positive electrode material of a lithium ion battery, the positive electrode material is separated from the waste lithium ion battery, and the separated positive electrode material is known as necessary. After the treatment, the positive electrode material, preferably a composition mainly composed of the positive electrode active material, for example, a composition containing Ni, Mn and Co (referred to as “CoMnNi-containing composition”) is used with sulfuric acid or the like. Next, a metal element other than Co and Ni is removed to prepare a CoNi raw material solution, which is then processed in the same manner as in the first embodiment or the second embodiment.

More specifically, as shown in FIG. 3, first, a positive electrode material, preferably a composition mainly composed of a positive electrode active material, may be dissolved in sulfuric acid to obtain a raw material solution.
At this time, in addition to sulfuric acid, a known acid such as hydrochloric acid or nitric acid may be used for dissolution.

Next, Mn in the solution may be separated and removed.
As a method for separating Mn, for example, at pH 1 to ₄ and about 40 to 80 ° C., an oxidizing agent such as KMnO ₄ or sodium hypochlorite is added to the raw material solution, and precipitated as manganese dioxide (MnO ₂ ) or the like. The solid may be removed by the solid-liquid separation method.
For example, Co, Ni, Al, Cu and the like are dissolved as ions in the solution in which Mn is separated and removed.

Next, Cu in the solution may be separated and removed.
As a Cu separation method, for example, a reducing agent such as Fe powder may be added to the raw material solution to precipitate as Cu metal, and the precipitate may be removed by a known solid-liquid separation method.
In this case, as the reducing agent, a metal that is baser than Cu, such as Co powder or Al foil, can also be used.
For example, Co, Ni, Al, Fe, and the like are dissolved as ions in the solution in which Cu is separated and removed.

Next, Al and Fe in the solution may be separated and removed.
As a method for separating Al, an alkali is added to the solution and the pH is adjusted to 3 to 5, whereby Al precipitation treatment 1 for precipitating Al in the solution as Al (OH) ₃ is performed, and a known solid-liquid separation is performed. If the precipitate is removed by the method, a CoNi raw material solution preferable as the raw material of the first embodiment or the second embodiment can be obtained.
In this case, for example, sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) ₂ ), cobalt hydroxide (Co (OH) ₂ ), or the like can be used as the alkali.

Further, H ₂ O ₂ was added as an oxidizing agent to the obtained solution to oxidize Fe, and then, for example, an alkali was added to adjust the pH to 5 to 6, and Fe and Al in the solution were respectively changed to Fe ( OH) ₃ , Al precipitation treatment 2 for precipitation as Al (OH) ₃ is performed, and if the precipitate is removed by a known solid-liquid separation method, as the raw material of the first embodiment or the second embodiment, An even more preferable CoNi raw material solution can be obtained.
In this case, any oxidizing agent may be used as long as it can oxidize divalent iron in the solution to trivalent, and examples thereof include sodium hypochlorite in addition to hydrogen peroxide.
Examples of the alkali for adjusting the pH include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) ₂ ), cobalt hydroxide (Co (OH) ₂ ) and the like. Can do.
In addition, since Co and Ni are slightly contained in the precipitate obtained in the Al precipitation treatment 2, it is possible to further increase the Co recovery rate by returning to the treatment liquid of the Al precipitation treatment 1 again and repeating the treatment. it can.

  Then, the CoNi raw material solution thus obtained may be treated in the same manner as in the first embodiment or the second embodiment.

The Co high-purity solution obtained as in the first to third embodiments is a known method after removing metal elements other than Co such as iron (Fe) in the solution by a known method as necessary. Can be recovered as Co (metal).
For example, an oxidizing agent such as hydrogen peroxide (H ₂ O ₂ ) is added to a Co high-purity solution containing Fe, and the pH of the solution to which the oxidizing agent is added is adjusted to 3 to 5 by adding an alkali. Thus, the iron in the solution can be precipitated and removed as iron hydroxide (Fe (OH) ₃ ).
In this case, any oxidizing agent may be used as long as it can oxidize divalent iron in the solution to trivalent, and examples thereof include sodium hypochlorite in addition to hydrogen peroxide.
Examples of the alkali for adjusting the pH include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) ₂ ), cobalt hydroxide (Co (OH) ₂ ) and the like. Can do.
Thereafter, for example, sodium hydroxide or the like is added to a Co high-purity solution, and Co element in the solution is precipitated as Co (OH) ₂ , dissolved using sulfuric acid, and then electrocollected to obtain Co (metal). It can be recovered.

  In addition to the processes described in the first to third embodiments, other known processes and processes can be arbitrarily added. For example, when a component other than those described above is included in the raw material, a known process or treatment may be added to remove the component, but it is not limited thereto. .

<Explanation of words>
In the present invention, when described as “X to Y” (X and Y are arbitrary numbers), unless otherwise specified, “X is preferably greater than X” or “preferably Y”. It also includes the meaning of “smaller”.
Further, when described as “X or more” (X is an arbitrary number), it means “preferably larger than X” unless otherwise specified, and described as “Y or less” (Y is an arbitrary number). In the case, unless otherwise specified, the meaning of “preferably smaller than Y” is also included.

  Examples of the present invention and comparative examples will be described below. However, the present invention is not limited to the contents described below.

<Test 1>
A CoNi raw material solution having a high Co concentration relative to Ni is prepared, and the redox potential (ORP, reference electrode: silver-saturated silver chloride electrode) is adjusted to a predetermined value, and NaHS as a sulfiding agent is added, The relationship between ORP and Ni concentration, Fe concentration, and Co recovery rate was examined.

(First step: CoS production step)
To 200 mL of CoNi raw material solution (pH 4.0 to 4.5, 40 ° C.) containing Co at a rate of 34 g / L and Ni at a rate of 3.7 g / L, a solution obtained by dissolving 2.65 g of NaHS in 40 mL of water is added. Then, 1 g of iron powder was added and stirred for 30 minutes, followed by filtration through a membrane filter having a pore size of 5 μm to recover a CoS composition as a precipitate.

(Second step: Ni reduction step)
CoNi raw material solution (pH 4.0 to 4.5, 40 ° C.) containing Co at a rate of 21 g / L and Ni at a rate of 21 g / L is obtained in the first step with 0.5 g to 2.5 g of iron powder. The total amount of the CoS composition was added and the ORP was appropriately changed, stirred for 30 minutes, and then filtered through a membrane filter having a pore size of 5 μm. The Ni concentration in the filtrate, the Fe concentration in the filtrate, and the Co concentration Was measured to confirm the Co recovery rate (%) from the CoS composition.

(Discussion)
As shown in FIG. 4, it was confirmed that when iron powder was added and ORP was lowered, Ni was separated from the liquid and the iron powder was dissolved. From this, it is thought that reaction like Formula (4) has arisen.
Formula (4) 3Ni ⁺² + 2CoS + Fe → Ni ₃ S ₂ + 2Co ²⁺ + Fe ²⁺

As a result of many tests, it was found that in the Ni reduction step, it is preferable to set the ORP to −400 mV or less, particularly −450 mV or less, in order to halve the initial Ni concentration (21 g / L).
In the Ni reduction step, it has been found that it is most efficient to reduce the Ni concentration to 4 to 6 g / L. In order to obtain such a Ni concentration, the ORP should be set to −500 mV or less. I also found it preferable.

Moreover, as FIG. 4 showed, when the addition amount of iron powder was increased, it turned out that ORP approaches -550mV and melt | dissolution Fe density | concentration increases. However, since ORP does not decrease even if iron powder is added excessively, it is wasteful of iron powder to make ORP lower than -550 mV. Moreover, since iron powder melt | dissolves in large quantities and the load of a post process increases, it is not appropriate. Furthermore, reaction like Formula (5) can be considered and Co may be lost as CoS again.
Formula (5) Ni ₃ S ₂ + 2Co ⁺² + 2Fe → 3Ni + 2CoS + 2Fe 2 ⁺

Furthermore, the Co recovery rate from the CoS composition when ORP = −540 mV is 59%, and it is considered that Co is recovered from the CoS added according to the formula (4) into the liquid from the behavior of Ni and Fe. .
The element ratio of the residue obtained by filtration was S: Ni: Co = 2: 2.8: 0.4, and a compound close to the composition of Ni ₃ S ₂ was formed. When the ORP is approximately −400 mV or more, the Ni separation rate tends to be low, and it is considered that the formula (4) does not proceed sufficiently and the Co recovery rate is low.
From the above points, it can be considered that it is desirable to adjust the ORP in the range of −400 mV to −550 mV in both the first step and the second step.

<Test 2>
To CoNi raw material solution (raw material) containing Ni and Co, iron powder and NaHS (sodium hydrosulfide) are added in different amounts to produce a CoS precipitate (CoS high content composition), and high CoS content The amount of Ni and the amount of Co in the composition were measured.

  CoNi raw material solution (Co concentration: 40 g / L (68 mmol), Ni concentration: 1.0 g / L (1.7 mmol)) at 100 ° C. and an initial pH of 5 was added to 0.21 g of Fe powder and NaHS 3.4-6. .8 mmoL was added, reacted for 30 minutes, filtered, separated into a filtrate and a CoS-rich composition, and the amount of Ni and Co in the CoS-rich composition were calculated.

The amount of Ni and the amount of Co in the CoS-rich composition were calculated as follows.
At this time, it was assumed that Ni in the high CoS-containing composition was Ni ₃ S ₂ .
-Ni amount in CoS high content composition = Ni amount in CoNi raw material solution-Ni amount in filtrate-Ni amount in CoS high content composition = NaHS addition amount-Ni amount in CoS high content composition x 2/3

<Test 3>
Iron powder, CoS and Ni ₃ S ₂ are added to a CoNi raw material solution containing Ni and Co, and the amount of Ni is changed, and Ni is removed to obtain a high concentration Ni filtrate and a high concentration Co composition. The Ni separation rate and the Co recovery rate were obtained.

CoNi raw material solution (Co concentration: 40 g / L (68 mmol), Ni concentration: 4 to 8 g / L (6.8 to 13.6 mmol)) with a liquid temperature of 40 ° C. and an initial pH of 5 was added to 100 mL, Fe powder 0.84 g, CoS 2 .4~5.8mmoL, Ni ₃ S ₂ 0.5mmoL were reacted 30 minutes added, was filtered, and the high concentration Ni filtrate, to obtain a high concentration Co composition, the respective amount of Ni and Co content It was measured.

Ni separation rate and Co recovery rate were calculated as follows.
-Separated Ni amount = Ni amount in CoNi raw material solution-Ni amount in highly concentrated Ni filtrate-Ni separation rate = Separated Ni amount / Ni amount in CoNi raw material solution x 100
Co recovery rate = 100-Co amount in Ni residue / Co amount in high-concentration Co composition × 100

When the moL ratio between the CoS addition amount (1.8 to 5.4 mmoL) and the initial Ni amount (4 to 8 g / L) is examined, if the CoS / initial Ni amount is too small, the Ni separation rate becomes insufficient. / It was found that the Co recovery rate deteriorates when the initial Ni content is too large.
From this viewpoint, the amount of CoS / initial Ni is preferably 0.2 to 0.8 mol / mol, particularly 0.3 to 0.7 mol / mol, and more preferably 0.4 to 0.6 mol / mol. Can be considered.

Claims (8)

  A reducing agent and CoS are added to a solution containing Ni and Co (referred to as “CoNi raw material solution”) to reduce the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the CoNi raw material solution to −550 mV to −400 mV. A method for producing a Co-containing solution, characterized in that a Co-containing solution containing Co element in an ionized state is obtained while Ni element in the solution is precipitated and removed as a sulfide.   The method for producing a Co-containing solution according to claim 1, wherein iron powder is used as the reducing agent.   The method for producing a Co-containing solution according to claim 1 or 2, wherein 0.2 to 0.8-fold molar amount of CoS is added to Ni in the solution at the start of the reaction.   A reducing agent and a sulfurizing agent are added to the Co-containing solution obtained by the production method according to any one of claims 1 to 3, and the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the Co-containing solution is- The solution was adjusted to 550 mV to -400 mV, Ni element in the solution was precipitated as Ni sulfide, and a part of Co element in the solution was precipitated as CoS, and the remaining Co element was dissolved (“Co high purity A method for producing a Co high-purity solution.   5. The method for producing a Co-containing solution according to claim 4, wherein a 1 to 10-fold molar amount of a sulfurizing agent (in terms of S) is added to Ni in the solution. A reducing agent and CoS are added to a CoNi raw material solution containing Ni and Co, and the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the CoNi raw material solution is adjusted to -550 mV to -400 mV. Ni reduction step of obtaining a Co-containing solution containing Co element in an ionized state while precipitating and removing Ni element as sulfide,
A reducing agent and a sulfurizing agent are added to the Co-containing solution obtained in the Ni reduction step to adjust the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the Co-containing solution to -550 mV to -400 mV, The Ni element in the solution is precipitated as Ni sulfide, and a part of the Co element in the solution is precipitated as CoS and then separated into solid and liquid, and the Ni sulfide and the CoS-containing composition containing the CoS are separated. And a CoS preparation step of separating and recovering a Co high-purity solution in which the remaining Co element is dissolved,
A Co high purity solution characterized by repeating the Ni reduction step and the CoS preparation step so that the CoS-containing composition recovered in the CoS preparation step is added as CoS in the Ni reduction step of the next batch and subsequent batches. Production method.   The method for producing a Co high-purity solution according to any one of claims 1 to 6, wherein the CoNi raw material solution is obtained by dissolving a positive electrode material of a waste lithium ion battery. A dissolution step of dissolving a composition containing Ni, Mn and Co (referred to as “CoMnNi-containing composition”) in an acid to prepare a CoMnNi raw material solution;
An Mn removal step of adding an oxidizing agent to the CoMnNi raw material solution, and precipitating and removing Mn element in the solution as a Mn oxide to obtain a CoNi raw material solution containing Ni and Co;
A reducing agent and CoS are added to the CoNi raw material solution obtained in the Mn removing step to adjust the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the CoNi raw material solution to -550 mV to -400 mV to obtain a solution. Ni reduction step of obtaining a Co-containing solution containing Co element in an ionized state while precipitating and removing Ni element therein as a sulfide,
A reducing agent and a sulfurizing agent are added to the Co-containing solution obtained in the Ni reduction step to adjust the oxidation-reduction potential (reference electrode: silver-saturated silver chloride electrode) of the Co-containing solution to -550 mV to -400 mV, The Ni element in the solution is precipitated as Ni sulfide, and a part of the Co element in the solution is precipitated as CoS and then separated into solid and liquid, and the Ni sulfide and the CoS-containing composition containing the CoS are separated. And a CoS preparation step of separating and recovering a Co high-purity solution in which the remaining Co element is dissolved,
A Co high purity solution characterized by repeating the Ni reduction step and the CoS preparation step so that the CoS-containing composition recovered in the CoS preparation step is added as CoS in the Ni reduction step of the next batch and subsequent batches. Production method.

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