JP7741532B2 - Cobalt recovery method - Google Patents

Description

The present invention relates to a method for recovering cobalt.

In Japan, cobalt is used in mobile phones, laptops, electric vehicles, special steel, etc. Cobalt is most commonly used as a cathode material in lithium-ion batteries. Demand is particularly driven by its use in automotive lithium-ion batteries, with cobalt compounds such as cobalt oxide and cobalt sulfate being the main forms used. Electric cobalt (cobalt bullion) is primarily used in special steel (super alloys, superalloys), but cobalt oxide is also used in some applications. Cobalt is also used in permanent magnets such as alnico magnets (Al-Ni-Co) and samarium-cobalt magnets, which are used in home appliances and audio equipment.

However, cobalt is a rare metal and has a higher market price than other metals. Furthermore, because production areas are unevenly distributed, supply is unstable, and currently most demand is met by imports.

Therefore, there is a need to recover and recycle the rare valuable materials cobalt and nickel from used lithium-ion batteries, special steel, etc. A method for recovering high-purity cobalt compounds from lithium-ion battery waste has been proposed (see Patent Document 1).

Japanese Patent Application Publication No. 11-6020

However, conventional recovery methods have had the problem that the cobalt purity in the cobalt precipitate is not high.

The cobalt recovery method of the present invention is a method for recovering cobalt from recycled raw materials containing cobalt, and includes a leaching step of dissolving the recycled raw materials in an acid solution and leaching the cobalt into the acid solution; an impurity precipitation step of precipitating impurities in the leachate produced by the leaching by adding an aqueous sodium hydroxide solution to the leachate; an impurity removal step of removing the precipitated impurities; and a cobalt precipitation step of precipitating the cobalt by adding an aqueous sodium hypochlorite solution to the leachate from which the impurities have been removed.

According to the present invention, it is possible to recover cobalt precipitate with high cobalt purity.

1 is a flowchart illustrating an example of a cobalt recovery method according to the present embodiment. The composition of the sludge measured by a fluorescent X-ray analyzer is shown. The composition of the sludge measured by ICP atomic emission spectrometry is shown. 1 is a graph showing the relationship between the solid-liquid ratio (sludge/hydrochloric acid) for each concentration at a hydrochloric acid concentration of 1.8 mol/L and the amount of cobalt leached per 1 g of sludge. 1 is a graph showing the relationship between the solid-liquid ratio (sludge/hydrochloric acid) for each concentration at a hydrochloric acid concentration of 6.0 mol/L and the amount of cobalt leached per 1 g of sludge. 1 is a graph showing the relationship between the solid-liquid ratio (sludge/hydrochloric acid) for each concentration at a hydrochloric acid concentration of 12 mol/L and the amount of cobalt leached per 1 g of sludge. 1 is a graph showing the relationship between the concentration of hydrochloric acid (1.8 mol/L, 6.0 mol/L, and 12 mol/L) and the leaching rates of cobalt, iron, and copper for each concentration (amount leached by hydrochloric acid/amount leached by aqua regia). 1 is a table showing the composition of the leachate used in the precipitation treatment of this embodiment. 1 is a graph showing the precipitation rate of each metal by adding an aqueous sodium hydroxide solution. 1 is a graph showing the weight of cobalt in the precipitate versus the pH change caused by the addition of an aqueous sodium hypochlorite solution. 1 is a graph showing the weight percentages of cobalt, iron, copper, and nickel in the leachate before impurity removal and in the leachate of the cobalt precipitate. 1 shows the composition of the cobalt precipitate measured by an X-ray fluorescence analyzer.

The cobalt recovery method of the present invention will be explained using the drawings. Figure 1 is a flowchart showing an example of the cobalt recovery method of this embodiment.

As shown in Figure 1, the cobalt recovery method recovers cobalt from recycled raw materials containing cobalt, and includes a leaching process (step 50) in which the recycled raw materials are dissolved in an acid solution and the cobalt is leached into the acid solution; an impurity precipitation process (step 51) in which impurities in the leachate produced by the leaching are precipitated by adding an aqueous sodium hydroxide solution to the leachate; an impurity removal process (step 52) in which the precipitated impurities are removed; and a cobalt precipitation process (step 53) in which an aqueous sodium hypochlorite solution is added to the leachate from which the impurities have been removed to precipitate the cobalt. The impurities include at least one of iron and copper.

In this embodiment, experiments were conducted using sludge produced by burning and processing waste materials containing lithium-ion batteries, neodymium magnets, and other materials. The sludge contains rare metals such as cobalt, neodymium, and nickel, as well as impurities such as iron and copper. Therefore, in order to recover the cobalt contained in the sludge, the iron, copper, and other metals are removed as impurities, and the cobalt is recovered as a high-purity cobalt precipitate.

First, the leaching process (step 50) of this embodiment will be described. The recycled raw material, sludge, was measured using an energy dispersive X-ray fluorescence analyzer (SHIMADZU EDX-7000). Figure 2 shows the composition of the sludge measured using the X-ray fluorescence analyzer. As shown in Figure 2, the weight percentages of the main components of the sludge were 31.2 wt% cobalt, 25.7 wt% iron, 22.7 wt% neodymium, 3.85 wt% copper, 1.16 wt% nickel, 9.68 wt% chlorine, and approximately 5.71 wt% others.

In addition, the recycled sludge was leached in aqua regia, and the amount of leached main metals was measured using ICP atomic emission spectroscopy (ICP-AES). 1 g of sludge was leached in 20 mL of aqua regia (15 mL of concentrated sulfuric acid + 5 mL of concentrated nitric acid), and the amount of leached metals (cobalt, iron, and copper) was measured using ICP-AES (SHIMADZU ICPS-9000). Figure 3 shows the composition of the sludge measured using ICP atomic emission spectroscopy. As shown in Figure 3, the weights of the main components of the sludge per 1 g of sludge were 161.3 mg of cobalt, 127.2 mg of iron, and 23.6 mg of copper.

In this embodiment, it was assumed that the metals in the sludge were completely leached by aqua regia, and leaching experiments using hydrochloric acid were conducted using the amount leached by aqua regia as the standard.

Figures 4 to 6 are graphs showing the relationship between the amount of cobalt leached per gram of sludge and the solid-liquid ratio (sludge/hydrochloric acid) of 1/20 g/mL, 1/40 g/mL, 1/60 g/mL, 1/80 g/mL, and 1/100 g/mL for hydrochloric acid (manufactured by Wako) concentrations of 1.8 mol/L, 6.0 mol/L, and 12 mol/L.

Figure 4 is a graph showing the relationship between the solid-liquid ratio (sludge/hydrochloric acid) and the amount of cobalt leached per gram of sludge at each concentration when the hydrochloric acid concentration is 1.8 mol/L. Figure 5 is a graph showing the relationship between the solid-liquid ratio (sludge/hydrochloric acid) and the amount of cobalt leached per gram of sludge at each concentration when the hydrochloric acid concentration is 6.0 mol/L. Figure 6 is a graph showing the relationship between the solid-liquid ratio (sludge/hydrochloric acid) and the amount of cobalt leached per gram of sludge at each concentration when the hydrochloric acid concentration is 12 mol/L.

As shown in Figures 4 to 6, the weight of cobalt leached by hydrochloric acid was almost constant and was hardly affected by the solid-liquid ratio. These results revealed that the optimal solid-liquid ratio (sludge/hydrochloric acid) for leaching cobalt was 1/20 g/mL (20 mL of hydrochloric acid per 1.0 g of sludge). In subsequent experiments, sludge, the recycled raw material, was dissolved under these conditions.

Figure 7 is a graph showing the relationship between the concentration of hydrochloric acid (manufactured by Wako) (1.8 mol/L, 6.0 mol/L, and 12 mol/L) and the leaching rate (amount leached by hydrochloric acid/amount leached by aqua regia) of cobalt, iron, and copper for each concentration. As described above, in this embodiment, it was assumed that the metals in the sludge were completely leached by aqua regia, and leaching experiments using hydrochloric acid were conducted using the amount leached by aqua regia as the standard, as shown in equation (1).

Leaching rate [%] = (WD/WA) x 100 (1)

Here, WD is the leaching amount (weight [mg]) of each metal dissolved in 20 mL of hydrochloric acid, and WA is the leaching amount (weight [mg]) of each metal dissolved in 20 mL of aqua regia.

As shown in Figure 7, at a hydrochloric acid concentration of 1.8 mol/L, the leaching rates of all metals were insufficient. Furthermore, at a hydrochloric acid concentration of 6.0 mol/L, the leaching rates of iron and copper were over 95%, and the leaching rate of cobalt was approximately 80%. At a hydrochloric acid concentration of 12 mol/L, the leaching rates of all metals were over 95%. The leaching rate of cobalt increased in the following order of hydrochloric acid concentrations: 1.8 mol/L, 6.0 mol/L, and 12 mol/L, demonstrating that the leaching rate increased as the hydrochloric acid concentration increased.

However, because a hydrochloric acid concentration of 12 mol/L is high and poses risks in subsequent reactions and processing, as well as increases the amount of reagents used in subsequent reactions, it is preferable to reduce the hydrochloric acid concentration while still achieving a sufficient cobalt leaching rate in order to efficiently recover a high-concentration cobalt precipitate. Therefore, when sludge was dissolved using hydrochloric acid with a concentration of 6.0 mol/L to 8.0 mol/L (preferably 6.0 mol/L) and a solid-liquid ratio (sludge/hydrochloric acid) of 1/18 g/mL to 1/22 g/mL (preferably 1/20 g/mL) at a temperature of 45°C to 55°C (preferably 45°C to 50°C) for 10 to 14 hours (preferably 12 hours), no solid residue remained after filtration, and the sludge was completely dissolved.

The acid solution in which sludge dissolves most easily is hydrochloric acid, which is one of the safest acid solutions and is easy to handle, making it suitable for industrial use. In this embodiment, sludge was dissolved in hydrochloric acid, and the optimal leaching conditions for the metals contained in the sludge were verified under various conditions.

Next, the precipitation process (steps 51 to 54) will be described. Figure 8 is a table showing the composition of the leachate used in the precipitation process of this embodiment. The sludge was dissolved using hydrochloric acid with a concentration of 6.0 mol/L, with a solid-liquid ratio (sludge/hydrochloric acid) of 1/20 g/mL, by stirring at a temperature of 50°C for 12 hours.

As shown in Figure 8, the weight percentages of the main components of the leachate obtained by dissolving the recycled sludge raw material in hydrochloric acid were 51.7% cobalt, 39.6% iron, and 6.8% copper.

The second most common metal in sludge after cobalt is iron. One way to efficiently remove iron is to precipitate iron hydroxide through hydroxide precipitation. Copper can also be removed through this hydroxide precipitation. Experimental results on the dependence of the hydrogen ion exponent (pH) on the hydrolysis reaction of metal ions show that as the hydrogen ion exponent increases, the precipitates are precipitated in the following order: trivalent iron, copper, divalent iron, and cobalt. Adjusting the hydrogen ion exponent makes it possible to selectively precipitate iron and copper.

In this embodiment, in the impurity removal process (step 51), a 2.5 mol/L aqueous sodium hydroxide solution (manufactured by Wako) was added to the leachate to change the hydrogen ion concentration.

Then, in the impurity recovery process (step 52), the deposited precipitate was separated using a centrifuge. To measure the composition of the precipitate, the precipitate was dissolved in 20 mL of 12 mol/L hydrochloric acid, and the weights of cobalt, iron, copper, and nickel were measured using ICP-AES. The weights of cobalt, iron, copper, and nickel in the leachate after precipitate separation were also measured using ICP-AES.

Figure 9 is a graph showing the precipitation rate of each metal due to the addition of sodium hydroxide solution. Figure 9 shows the effect of hydrogen ion exponent (pH) on the precipitation rate of cobalt, iron, copper, and nickel due to the addition of sodium hydroxide. The precipitation rate of each metal is calculated using equation (2).

Sedimentation rate [%] = [WP / (WP + WS)] x 100 (2)

Here, WP is the weight [mg] of the precipitate of each metal, and WS is the weight [mg] of each metal in the supernatant (leachate) after separating the precipitate.

As shown in Figure 9, the precipitation selectivity increased with increasing pH of the leachate, in the order of iron, copper, and cobalt. Iron precipitated almost completely when the pH of the leachate was 3 or higher, and copper precipitated almost completely when the pH of the leachate was 5 or higher.

Furthermore, when the pH of the leachate was 5.42, iron and copper completely precipitated. The cobalt precipitation rate at this time was 21.2%, which was the lowest under the conditions of the leachate in which iron and copper had completely precipitated.

It has been shown that iron(II) hydroxide hardly precipitates when the leachate has a pH of 3. However, in this measurement, almost 100% of the iron precipitated when the leachate had a pH of 3. Therefore, it is believed that the iron in the leachate in this embodiment was trivalent. This is presumably because the divalent iron contained in the leachate was oxidized to trivalent iron when dissolved in hydrochloric acid at a specified temperature (45°C or higher and 55°C or lower, preferably 45°C or higher and 50°C or lower). Therefore, in this embodiment, by leaching the sludge with hydrochloric acid at a specified temperature in the leaching process, the iron in the leachate was almost always trivalent, and by raising the pH of the leachate to 3 or higher, the iron precipitated as iron(III) hydroxide.

Furthermore, in this embodiment, copper precipitated almost completely when the pH of the leachate was 5 or higher, demonstrating that copper can be removed by increasing the pH of the leachate to 5 or higher.

However, a small amount of cobalt precipitated along with the iron and copper precipitates. As can be seen from Figure 9, cobalt precipitation began when the pH of the leachate reached 3 or higher. In this case, since iron precipitated almost completely when the pH of the leachate reached 3, it is inferred that cobalt co-precipitated with iron(III) hydroxide. Furthermore, when the pH of the leachate reached 5, the cobalt precipitation rate increased. In this case, since copper precipitated almost completely when the pH of the leachate reached 5, it is inferred that cobalt co-precipitated with copper(II) hydroxide.

This is thought to be due to the fact that when iron (III) hydroxide and copper (II) hydroxide precipitate, they co-precipitate with the coexisting heavy metals. Therefore, the reason cobalt precipitated was because the cobalt remaining in the supernatant of the leachate was induced to co-precipitate by iron (III) hydroxide and copper (II) hydroxide.

As described above, when iron was removed from the leachate after sludge dissolution using sodium hydroxide, the iron in the leachate was almost completely recovered as iron(III) hydroxide due to the oxidizing action of hydrochloric acid at a specified temperature (45°C to 55°C, preferably 45°C to 50°C). When the pH of the leachate was 3 or higher, iron could be precipitated and recovered with high efficiency. Furthermore, when the pH of the leachate was 5 or higher, 0.13% copper remained, but copper could be precipitated and recovered with high efficiency.

On the other hand, cobalt precipitates when the pH of the leachate increases, so it is necessary to suppress cobalt precipitation while recovering iron and copper with high efficiency.

In this embodiment, the impurity precipitation process includes a step of precipitating the impurities (iron, copper, etc.) in the leachate by adding an aqueous sodium hydroxide solution so that the hydrogen ion exponent of the leachate becomes pH 5.0 or higher and pH 6.0 or lower (preferably pH 5.0 or higher and pH 5.5 or lower).

In this embodiment, we verified the optimal conditions for the impurity removal process (steps 51 and 52) using sodium hydroxide to remove impurities from the sludge leachate, which is the recycled raw material.

After iron and copper were removed from the sludge leachate, the main metals remaining in the leachate were cobalt and nickel. The nickel content in the sludge was low, at approximately 1%. Therefore, in this embodiment, the cobalt precipitation process (step 53) selectively precipitated cobalt, allowing for the recovery of a precipitate with a high cobalt purity.

To selectively recover cobalt, a method of obtaining a precipitate using sodium hypochlorite is used. In this embodiment, sodium hypochlorite is added as an oxidizing agent to recover the cobalt by precipitation (step 54).

The sludge was dissolved in 6.0 mol/L hydrochloric acid at a solid-liquid ratio (sludge/hydrochloric acid) of 1/20 g/mL by stirring at 50°C for 12 hours. The leachate obtained by filtration was added with a 2.5 mol/L aqueous sodium hydroxide solution to adjust the pH of the leachate to between 5 and 6, resulting in iron and copper precipitates. The precipitate was then removed by centrifugation, and sodium hypochlorite (manufactured by Wako) was added to the supernatant to precipitate a cobalt precipitate. The precipitate was recovered by centrifugation and dissolved in 20 mL of 12 mol/L hydrochloric acid. The cobalt, iron, copper, and nickel contents were measured using ICP-AES to determine the weight and recovery rate of each metal.

Figure 10 is a graph showing the weight of cobalt in the precipitate as a function of pH change due to the addition of an aqueous sodium hypochlorite solution. When the pH of the leachate after impurity removal was between 3.0 and 3.3, the amount of cobalt precipitated was relatively small, and the recovery rate was around 10%. The amount of cobalt precipitated was greatest when the pH of the leachate after impurity removal was 3.34, and thereafter the amount of cobalt precipitated decreased as the pH increased.

Therefore, cobalt precipitated most effectively when the pH of the leachate after impurity removal was between 3.3 and 3.5 (preferably between 3.3 and 3.4).

Figure 11 is a graph showing the weight percentages of cobalt, iron, copper, and nickel in the leachate before impurity removal and in the cobalt precipitate leachate. Figure 11(a) is a graph showing the weight percentages of the composition of the leachate before impurity removal shown in Figure 8. Figure 11(b) is a graph showing the weight percentages of the composition of the cobalt precipitate leachate obtained by adding 5 mL of sodium hypochlorite to the leachate after impurity removal, setting the pH at 3.5, and leaching the cobalt precipitate with 20 mL of 12 mol/L hydrochloric acid, followed by ICP-AES leaching of the cobalt precipitate.

As shown in Figure 11, after the addition of sodium hypochlorite, the cobalt purity of the cobalt precipitate was 98.2%. Since the cobalt purity in the leachate before impurity removal was 51.7%, this embodiment was able to recover cobalt as a high-purity cobalt precipitate.

Furthermore, in this embodiment, no nickel precipitate was deposited. The reason for this is thought to be that, while the addition of sodium hypochlorite oxidized cobalt from divalent to trivalent, nickel remained divalent and was not oxidized to trivalent, so cobalt selectively precipitated, making it possible to selectively recover cobalt. As a result, cobalt was recovered as a high-purity cobalt precipitate containing almost no nickel. Therefore, although not shown in Figure 11, the cobalt purity in the leachate after impurity removal was 96.5%, and after the addition of sodium hypochlorite, the cobalt purity of the cobalt precipitate further increased to 98.2%.

Figure 12 shows the composition of the cobalt precipitate measured using an X-ray fluorescence analyzer. As shown in Figure 12, the weight percentages of the main components of the cobalt precipitate were 51.7% cobalt, 5.43% neodymium, 1.20% copper, 39.3% chlorine, and 2.37% others. Therefore, it can be said that the metal in the recovered material was almost entirely cobalt.

As described above, adding sodium hypochlorite to the leachate after impurities (iron, copper, etc.) have been removed results in the deposition of high-purity cobalt precipitates, making it possible to recover high-purity cobalt precipitates. Comparing the pH of the leachate after impurities have been removed and the amount of cobalt precipitate, the most cobalt precipitated was found at a pH of 3.3 or higher and 3.5 or lower (preferably 3.3 or higher and 3.4 or lower). This revealed that the optimal condition for adding sodium hypochlorite is to ensure that the pH of the leachate after impurities have been removed is 3.3 or higher and 3.5 or lower (preferably 3.3 or higher and 3.4 or lower).

In this embodiment, the cobalt precipitation process (step 53) includes a step of precipitating the cobalt in the leachate by adding a sodium hypochlorite aqueous solution so that the hydrogen ion exponent of the leachate from which the impurities have been removed is between pH 3.3 and pH 3.5.

The above describes embodiments of the present invention, but the present invention is not limited to these and can be modified and varied within the scope of the claims.

The present invention is useful as a cobalt recovery method that can recover cobalt precipitates with high cobalt purity.

50 Leaching treatment 51 Impurity precipitation treatment 52 Impurity removal treatment 53 Cobalt precipitation treatment 54 Cobalt precipitate recovery treatment

Claims (1)

A cobalt recovery method for recovering cobalt from a recycled raw material containing cobalt, comprising:
an impurity precipitation step of using an acid solution obtained by leaching the cobalt with hydrochloric acid having a concentration of 6.0 mol/L at a solid-liquid ratio of the recycled raw material to hydrochloric acid of 1/20 g/mL at a temperature of 50°C, and adding an aqueous sodium hydroxide solution to the acid solution so that the hydrogen ion exponent of the acid solution containing at least one of iron and copper as impurities and the cobalt is between pH 5.0 and pH 6.0;
an impurity removal step of removing the precipitated impurities;
a cobalt precipitation step of precipitating the cobalt by adding a sodium hypochlorite aqueous solution to the acid solution from which the impurities have been removed so that the pH of the acid solution becomes equal to or higher than 3.3 and equal to or lower than 3.5;
A cobalt recovery method comprising: