WO2024262505A1 - Method for producing leachate from hydroxide containing nickel and cobalt - Google Patents

Abstract

[Problem] To provide a method for producing a leachate that contains nickel ions and cobalt ions using a starting material that includes nickel and cobalt that is less expensive than a nickel metal powder. [Solution] According to the present invention, a slurry obtained by mixing hydroxide particles that contain nickel and cobalt and ammonia water that contains ammonium carbonate or ammonium bicarbonate and has preferably been prepared such that the ammonium carbonate or ammonium bicarbonate concentration is 0.50–4.1 mol/L is subjected to a leaching treatment under prescribed temperature conditions to produce a leachate that contains nickel ions and cobalt ions that have been leached from the hydroxide particles.

Description

Method for producing leachate from hydroxide containing nickel and cobalt

The present invention relates to a method for producing a leachate containing nickel ions and cobalt ions from a hydroxide containing nickel and cobalt.

Lithium-ion secondary batteries, which charge and discharge by the movement of lithium ions between the positive and negative electrodes, have a high energy density and do not deteriorate easily even when repeatedly charged and discharged, so in recent years demand has been increasing for them as power sources for electric vehicles and smart grid storage batteries, as well as for electronic devices such as mobile phones and laptops. Lithium-ion secondary batteries have a structure in which an electrolyte is filled between the positive and negative electrodes that face each other with a separator in between, and lithium nickel oxide is used as the active material for the positive electrode, which is the main component. Lithium nickel oxide can be manufactured by mixing lithium hydroxide with nickel hydroxide as a precursor and firing the mixture.

The above-mentioned nickel hydroxide as a precursor can be produced by a neutralization reaction caused by adding an aqueous sodium hydroxide solution to an aqueous nickel sulfate solution as a raw material. In this neutralization reaction of the nickel sulfate raw material, sodium sulfate (mirabilite) produced as a by-product in an equimolar amount with nickel hydroxide as shown in the following formula 1 can be problematic. That is, since total wastewater volume regulations are set for sodium sulfate in some regions, there have been cases where it has been necessary to install costly treatment facilities to meet the wastewater standards, or to limit the production volume of nickel hydroxide in order to suppress the discharge of sodium sulfate.
[Formula 1]
NiSO ₄ +2NaOH→Ni(OH) ₂ +Na ₂ SO ₄

Therefore, a method for producing nickel hydroxide that does not produce sodium sulfate as a by-product has been proposed. For example, Patent Document 1 proposes a technology in which oxygen is introduced into an aqueous ammonia solution containing powder of metallic nickel to leach the metallic nickel into the aqueous ammonia solution, and then seed crystals are added as necessary to the aqueous ammonia solution containing nickel and hydroxyl ions, and the aqueous ammonia solution is evaporated under atmospheric pressure or reduced pressure to precipitate and recover nickel hydroxide.

Japanese Patent Application Publication No. 10-324524

By using the technology of Patent Document 1, nickel hydroxide can be produced without producing sodium sulfate as a by-product, but this technology uses metallic nickel as the precursor raw material, and therefore is not economically advantageous. In other words, metallic nickel is generally produced by leaching nickel from intermediate raw materials such as matte, sulfide, or hydroxide obtained by processing nickel ore using acid or chlorine, and then separating the impurities leached together with the nickel through a refining process before electrolytic winning, so that the metallic nickel finally obtained is in the form of a plate or lump. Therefore, a process is required to process metallic nickel into powder so that it can be efficiently leached with an aqueous ammonia solution.

In addition, as in the case of ternary positive electrode active materials such as lithium nickel cobalt manganate (NCM) and lithium nickel cobalt aluminate (NCA) in which part of the nickel is replaced with an element such as cobalt, cobalt may be added to the precursor during the manufacturing stage of the lithium nickel oxide. In this case, it is not a problem if the nickel used as the raw material for the precursor contains cobalt, and it is preferable that it contains a certain amount of cobalt. However, although many of the intermediate raw materials used in the manufacture of metallic nickel contain cobalt, a process is carried out to separate and remove cobalt from nickel by a refining process such as a solvent extraction process prior to electrowinning, which results in unnecessary separation costs. As such, the method of manufacturing nickel hydroxide using metallic nickel as a raw material requires many processes that increase costs, so there is a demand for an alternative method of manufacturing nickel hydroxide using unrefined intermediate raw materials containing a wide variety of impurities obtained, for example, by processing nickel oxide ore or scrap.

The present invention was made in consideration of the above circumstances, and aims to provide a method for producing a leachate containing nickel ions and cobalt ions using raw materials containing nickel and cobalt, which are cheaper than metallic nickel.

In order to achieve the above object, the method for producing a leachate according to the present invention is characterized in that a slurry is obtained by mixing hydroxide particles containing nickel and cobalt with ammonia water containing ammonium carbonate or ammonium hydrogen carbonate, and the slurry is subjected to a leaching treatment under a specified temperature condition to obtain a leachate containing nickel ions and cobalt ions leached from the hydroxide particles.

According to the present invention, it is possible to produce a leachate containing nickel ions and cobalt ions using raw materials containing nickel and cobalt, which are cheaper than metallic nickel, without producing sodium sulfate as a by-product.

FIG. 1 is a block flow diagram of a method for producing nickel hydroxide containing cobalt, which preferably includes the method for producing a leachate of the present invention. 1 is a graph plotting the leaching rates of nickel and cobalt achieved by the leaching solution manufacturing method of the embodiment of the present invention, with the horizontal axis representing the ammonium carbonate concentration and the vertical axis representing the leaching rate.

Below, an embodiment of the method for producing a leachate containing nickel ions and cobalt ions according to the present invention will be described. The method for producing a leachate according to this embodiment of the present invention is included in the method for producing nickel hydroxide containing cobalt as a precursor by subjecting a raw material nickel-cobalt mixed hydroxide to a series of treatments, as shown in Figure 1. This raw material nickel-cobalt mixed hydroxide contains impurities such as calcium, magnesium, zinc, sulfur, silicon, manganese, iron, and aluminum. Nickel-cobalt mixed hydroxide containing such various impurities is sometimes called a mixed hydroxide precipitate (MHP).

That is, the method for producing nickel hydroxide containing cobalt in FIG. 1 includes a water washing step in which nickel-cobalt mixed hydroxide particles (MHP) are washed preferably with water at room temperature to mainly remove calcium and magnesium, an alkali washing and reduction step in which the nickel-cobalt mixed hydroxide particles washed in the water washing step are washed and reduced with an alkali washing solution consisting of an aqueous caustic soda solution at room temperature and preferably with a concentration of about 8 mol/L that contains a reducing agent such as sodium sulfite, to mainly remove zinc, sulfur, and silicon, and a process for producing nickel hydroxide containing the alkali washed and reduced nickel. The process includes a leaching process in which nickel-cobalt mixed hydroxide particles are leached with an ammonia-containing aqueous solution containing ammonium carbonate or ammonium hydrogen carbonate, a thermal decomposition precipitation process in which the leaching solution obtained by the leaching process is heated to thermally decompose the ammonium carbonate or ammonium hydrogen carbonate into ammonia and carbonic acid, and nickel hydroxide and cobalt hydroxide are precipitated as precursors, and an alkaline washing process in which the precipitated nickel hydroxide and cobalt hydroxide are washed with an alkaline washing solution, preferably an aqueous caustic soda solution at room temperature with a concentration of about 4 mol/L, to mainly remove the carbon content. Each of these steps will be described below.

(1) Water washing step The water washing step is a step of removing mainly calcium and magnesium as impurities contained in the raw material nickel-cobalt mixed hydroxide using washing water preferably at a liquid temperature of 10 to 90°C, more preferably at room temperature. In this water washing step, although there is no limitation, it is preferable to adopt a method in which the nickel-cobalt mixed hydroxide is introduced into washing water previously charged in a container equipped with a stirrer, and washed for 0.50 to 1.0 hours while stirring with the stirrer. After washing, the slurry containing the nickel-cobalt mixed hydroxide particles is introduced into a solid-liquid separation device such as a centrifuge or a filter for solid-liquid separation, whereby the washed wet nickel-cobalt mixed hydroxide can be recovered.

(2) Alkaline Washing Reduction Step The alkaline washing reduction step is a step for removing impurities that are difficult to remove in the previous water washing step, mainly zinc, sulfur, and silicon, by washing with an alkaline washing solution such as a caustic soda solution with a concentration of 1.0 to 8.0 mol/L. The washing wastewater discharged after this washing contains impurities such as zinc, sulfur, and silicon, and is then repeatedly used as an alkaline washing solution after removing these impurities by a precipitation method or the like. Here, the precipitation method refers to a method for extracting solutes dissolved in a solution as precipitate particles, and for example, the above-mentioned precipitate particles can be obtained by changing the above-mentioned solution from an unsaturated state to a supersaturated state and promoting the generation and growth of crystal nuclei. In addition, manganese, iron, and aluminum that are not leached in the above-mentioned leaching step remain as leaching residue, and are separated and removed from the leaching solution by solid-liquid separation means such as filtration. Furthermore, the ammonia and carbonic acid generated by the thermal decomposition in the thermal decomposition precipitation means are recovered and reused as ammonia water containing ammonium carbonate or ammonium hydrogen carbonate in the preceding leaching step, and the carbon content in the washing wastewater discharged after washing in the alkaline washing step can be precipitated as sodium carbonate by using the precipitation method in the same manner as above, since the solubility of the carbon content decreases when the temperature of the washing wastewater drops. After removing the sodium carbonate in this way, the washing wastewater is repeatedly used as an alkaline washing liquid.

(3) Leaching process The leaching process is a process in which the nickel-cobalt mixed hydroxide washed in the previous alkaline washing and reduction process is leached with an ammonia-containing aqueous solution. Specifically, water is first charged into a container equipped with a stirrer, and ammonia water (NH ₄ OH) is added thereto, and ammonium carbonate ((NH ₄ ) ₂ CO ₃ ) or ammonium hydrogen carbonate (NH ₃ HCO ₃ ) is further added to prepare an ammonia-containing aqueous solution. Next, nickel-cobalt mixed hydroxide particles are charged into the container containing the prepared ammonia-containing aqueous solution, and the mixture is stirred and mixed with the stirrer to prepare a slurry having a uniform concentration. In this state, the temperature of the slurry is preferably maintained under a temperature condition of 20°C or more and 60°C or less to perform the leaching process. This allows nickel ions and cobalt ions to be leached from the nickel-cobalt mixed hydroxide particles. If the slurry temperature is below 20°C, the reaction rate is too slow, resulting in a decrease in production efficiency, whereas if it exceeds 60°C, ammonium carbonate is easily thermally decomposed, making it difficult to leach it satisfactorily. If the slurry temperature is below 0°C, water freezes, making it difficult to leach it satisfactorily.

In the above-mentioned leaching treatment, when preparing an ammonia-containing aqueous solution by adding ammonium carbonate, the ammonium carbonate concentration in the above-mentioned ammonia-containing aqueous solution is preferably prepared within the range of 0.50 mol/L to 4.1 mol/L, more preferably within the range of 1.5 mol/L to 3.5 mol/L, and most preferably within the range of 2.0 mol/L to 3.0 mol/L. If the ammonium carbonate concentration is less than 1.5 mol/L, the leaching rate may decrease, and especially if it is less than 0.50 mol/L, the effect of the present invention may not be exhibited well. On the other hand, even if the ammonium carbonate concentration is increased beyond about 3.5 mol/L, the leaching rate does not change much, but the cost required for neutralization increases, which is not preferable, and if it exceeds 4.1 mol/L, the ammonium carbonate becomes supersaturated and precipitates, which may have an adverse effect on the leaching treatment. The ammonium carbonate concentration can be measured by absorptiometry, ion chromatography, etc. If the ammonium carbonate concentration falls outside the above range, it can be adjusted by adjusting the amount of ammonium carbonate added.

Alternatively, in the above-mentioned leaching treatment, when the ammonia-containing aqueous solution is prepared by adding ammonium bicarbonate instead of ammonium carbonate, similarly to the above, the ammonium bicarbonate concentration in the ammonia-containing aqueous solution is preferably adjusted to within the range of 0.50 mol/L to 4.1 mol/L, more preferably within the range of 1.5 mol/L to 3.5 mol/L, and most preferably within the range of 2.0 mol/L to 3.0 mol/L.

In addition, during the above leaching treatment, it is preferable to adjust the free ammonia concentration in the slurry to within the range of 0.10 to 1.3 mol/L. If the free ammonia concentration is within this range, nickel and cobalt can be leached stably in the form of ammine complexes. Even if the free ammonia concentration exceeds 1.3 mol/L, it has almost no effect on the stable leaching in the form of the above amine complexes, and it is not preferable because it increases costs and increases the load on wastewater treatment. Note that free ammonia refers to molecular ammonia (NH ₃ ), and its concentration can be measured by absorptiometry after separating it by distillation and converting it to NH ₄ ⁺ . If the free ammonia concentration is outside the above range, it can be adjusted by adding an amount of ammonia water.

(4) Pyrolysis precipitation step The pyrolysis precipitation step is a step in which the leachate produced in the previous leaching step is heated by preferably maintaining the temperature at 60°C to 100°C for 0.50 to 2.0 hours, thereby pyrolyzing the ammine complexes of nickel and cobalt, precipitating the nickel and cobalt as hydroxides, and recovering them as precipitates. In this pyrolysis precipitation step, it is preferable to stir while blowing in an oxidizing agent such as air, which promotes the oxidation of cobalt, making it possible to recover both nickel and cobalt as hydroxides at a high recovery rate. That is, the ammine complex of cobalt is usually converted to divalent cobalt by pyrolysis, but by oxidizing it to trivalent cobalt, recovery as hydroxides is promoted. It is preferable to recover the ammonia and carbonic acid generated by pyrolysis in this pyrolysis precipitation step and reuse them as ammonia water containing ammonium carbonate or ammonium hydrogen carbonate in the previous leaching step.

(5) Alkaline Washing Step The alkaline washing step is a step in which the nickel-cobalt mixed hydroxide recovered in the preceding thermal decomposition precipitation step is washed, preferably with the same alkaline washing solution as that used in the alkaline washing and reduction step described above. This removes zinc, sulfur, and silicon that could not be completely removed in the alkaline washing and reduction step, as well as carbon derived from the ammonium carbonate and ammonium bicarbonate added in the leaching step, and makes it possible to produce a high-purity precursor with extremely few impurities that can be suitably used as a positive electrode active material for lithium-ion secondary batteries.

As described above, the method for producing a leachate according to an embodiment of the present invention makes it possible to produce a leachate containing nickel and cobalt from the raw material nickel-cobalt mixed hydroxide particles without by-producing sodium sulfate, and also makes it possible to easily separate and remove impurities such as manganese, iron, and aluminum contained in the raw material, so that the leachate can be produced more inexpensively than when expensive metallic nickel is used as the raw material. The present invention will now be described in more detail with reference to examples, but the present invention is not limited in any way to the following examples.

Example 1
An aqueous solution containing 28.82 g of ammonium carbonate (( _NH4 ) _2CO3 ) was added to 185 mL of pure water and 15 mL of 25% ammonia water placed in a container to prepare an aqueous ammonia-containing solution with an ammonium carbonate concentration of 1.5 mol/L. 20 g of powdered nickel-cobalt mixed hydroxide ( _MHP ) having the composition shown in Table 1 below was mixed with the resulting aqueous ammonia-containing solution to prepare a slurry, which was stirred with a stirrer while maintaining the liquid temperature at 20°C for 2 hours to perform a leaching treatment.

After the above leaching treatment, solid-liquid separation was performed by filtration to obtain a leaching residue with a dry mass of 10.8 g and a leaching solution of 270 mL. The element concentrations of the leaching residue and the leaching solution were measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the leaching rate of each element was calculated by the following formula 2.
[Formula 2]
Leaching rate of element α=mass of element α in leaching solution/(mass of element α in leaching solution+mass of element α in leaching residue)×100

As a result, the nickel leaching rate was 71.2% and the cobalt leaching rate was 65.3%, and a leachate consisting of an aqueous ammonia solution containing a large amount of nickel ions and cobalt ions was produced.

Example 2
Leaching of MHP and subsequent solid _{- liquid separation} were carried out in the same manner as in Example 1, except that an ammonia-containing aqueous solution with an ammonium carbonate concentration of 3.0 mol/L was prepared by changing the amount of ammonium carbonate ((NH4)2CO3) added from 28.82 g to 57.65 g, resulting in a leaching residue with a dry mass of 6.30 g and a leachate of 310 mL. The element concentrations of the obtained leachate residue and leachate were measured in the same manner as in Example 1, and the leachate rate of nickel was 90.3% and the leachate rate of cobalt was 84.6%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions was produced.

Example 3
Leaching treatment of MHP and subsequent solid-liquid separation were carried out in the same manner as in Example 1, except that the amount of ammonium carbonate (( _NH4 ) _2CO3 ) added was changed from 28.82 g to 115.30 _g to prepare an ammonia-containing aqueous solution with an ammonium carbonate concentration of 4.1 mol/L. A leaching residue with a dry mass of 5.53 g and a leachate of 355 mL were obtained. The element concentrations of the obtained leachate residue and leachate were measured in the same manner as in Example 1, and the leachate rate of nickel was 94.4% and the leachate rate of cobalt was 88.9%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions was produced.

Example 4
Leaching of MHP and subsequent solid-liquid separation were carried out in the same manner as in Example 1, except that the liquid temperature during the leaching treatment was changed to 50° C. instead of 20° C., and a leaching residue with a dry mass of 6.07 g and a leachate of 203 mL were obtained. The element concentrations of the obtained leachate residue and leachate were measured in the same manner as in Example 1, and the leaching rate of nickel was 73.9%, and the leaching rate of cobalt was 73.6%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

Example 5
Leaching of MHP and subsequent solid-liquid separation were carried out in the same manner as in Example 2, except that the liquid temperature during the leaching treatment was changed to 50° C. instead of 20° C., and a leaching residue with a dry mass of 3.57 g and a leachate of 235 mL were obtained. The element concentrations of the obtained leachate residue and leachate were measured in the same manner as in Example 1, and the leaching rate of nickel was 92.5%, and the leaching rate of cobalt was 87.3%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

Example 6
Leaching of MHP and subsequent solid-liquid separation were carried out in the same manner as in Example 3, except that the liquid temperature during the leaching treatment was changed to 50° C. instead of 20° C., and a leaching residue with a dry mass of 5.05 g and a leachate of 415 mL were obtained. The element concentrations of the obtained leachate residue and leachate were measured in the same manner as in Example 1, and the leaching rate of nickel was 95.2%, and the leaching rate of cobalt was 89.2%, indicating that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions could be produced.

(Example 7)
In Example 1, ammonium carbonate was used in the leaching treatment, but this was replaced with ammonium hydrogen carbonate, and the same procedure was followed as in Example 1. As a result, it was confirmed that a leachate consisting of an aqueous ammonia solution containing large amounts of nickel ions and cobalt ions, almost equivalent to that in Example 1, was obtained.

(Comparative Example 1)
A slurry was prepared by mixing 20 g of powdered nickel-cobalt mixed hydroxide (MHP) having the composition shown in Table 1 with 25% ammonia water charged in a container, and the slurry was stirred with a stirrer while controlling the liquid temperature at 20° C. for 2 hours to carry out a leaching treatment. Thereafter, solid-liquid separation was carried out in the same manner as in Example 1 to obtain 150 mL of a leachate. The element concentrations of this leachate were measured in the same manner as in Example 1 to determine the leaching rate of each element.

As a result, the leaching rate of nickel was 14.6%, and the leaching rate of cobalt was 0.2%, which was insufficient for nickel ions to be leached and almost no cobalt ions were leached compared to Examples 1 to 3, in which the leaching treatment was carried out at the same temperature. In this Comparative Example 1, the leaching rate of each element was calculated by the following formula 3.
[Formula 3]
Leaching rate of element α=mass of element α in leaching solution/mass of element α in MHP×100

(Comparative Example 2)
The leaching of MHP and the subsequent solid-liquid separation and concentration measurement were carried out in the same manner as in Comparative Example 1, except that the liquid temperature during the leaching treatment was changed from 20°C to 50°C. The nickel leaching rate was 17.5%, and the cobalt leaching rate was 0.3%, which means that the leaching of nickel ions was insufficient and almost no cobalt ions were leached compared to Examples 4 to 6, in which the leaching treatment was carried out at the same temperature. The leaching rates were calculated in the same manner as in Comparative Example 1. The measurement results of Examples 1 to 6 and Comparative Examples 1 and 2 are shown in Table 2 below.

Claims (3)

A method for producing a leachate from a hydroxide containing nickel and cobalt, comprising: mixing hydroxide particles containing nickel and cobalt with ammonia water containing ammonium carbonate or ammonium hydrogen carbonate to obtain a slurry; and subjecting the slurry to a leaching treatment under a specified temperature condition to obtain a leachate containing nickel ions and cobalt ions leached from the hydroxide particles. The method for producing a leachate from a hydroxide containing nickel and cobalt according to claim 1, characterized in that the ammonium carbonate or ammonium bicarbonate concentration in the ammonia water containing the ammonium carbonate or ammonium bicarbonate is adjusted to be within the range of 0.50 mol/L to 4.1 mol/L. The method for producing a leachate from a hydroxide containing nickel and cobalt according to claim 1 or 2, characterized in that a precursor obtained by subjecting the leachate containing nickel ions and cobalt ions to a thermal decomposition and precipitation treatment is used as a raw material for a positive electrode active material of a lithium ion battery.

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