WO2024262506A1 - Method for producing leach solution from hydroxide including nickel and cobalt - Google Patents

Abstract

[Problem] To provide a method for producing a leach solution that includes nickel ions and cobalt ions, using a raw material that includes nickel and cobalt and is less expensive than metallic nickel powder. [Solution] A leach solution including nickel ions and cobalt ions leached from hydroxide particles is obtained by subjecting a slurry to a leaching process under prescribed temperature conditions, said slurry having been obtained by mixing the hydroxide particles, which include nickel and cobalt, and aqueous ammonia that includes ammonium sulfate and has preferably been adjusted such that the ammonium sulfate concentration is within the range 0.5-4.1 mol/L.

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 sulfate, 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.

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).

In other words, 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 alkaline washing reduction step in which the nickel-cobalt mixed hydroxide particles washed in the water washing step are washed and reduced with an alkaline washing solution consisting of an aqueous caustic soda solution at room temperature and preferably with a concentration of about 8 mol/L, which contains a reducing agent such as sodium sulfite, to mainly remove zinc, sulfur, and silicon, and a process for reducing the nickel-cobalt mixed hydroxide particles washed in the water washing step. The process includes a leaching process in which the reduced nickel-cobalt mixed hydroxide particles are leached with an ammonia-containing aqueous solution containing ammonium sulfate, a thermal decomposition precipitation process in which the leaching solution obtained by the leaching process is heated to thermally decompose the ammonium sulfate into ammonia and sulfur trioxide and precipitate the precursors nickel hydroxide and cobalt hydroxide, 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 sulfur trioxide generated by the thermal decomposition in the thermal decomposition precipitation means are recovered and reused as the ammonia water containing ammonium sulfate in the previous leaching step, and the carbon content in the cleaning solution discharged after cleaning in the alkaline cleaning step is reduced in solubility as the temperature of the cleaning wastewater drops, so in this case too, it is possible to precipitate the carbon content as sodium carbonate by using the precipitation method in the same manner as above. After removing the sodium carbonate in this way, the cleaning wastewater is repeatedly used as the alkaline cleaning solution.

(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 ammonium sulfate aqueous solution. Specifically, water is first charged into a container equipped with a stirrer, and ammonia (NH ₃ ) water and ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) are added thereto to prepare an ammonium sulfate aqueous solution. Next, nickel-cobalt mixed hydroxide particles are charged into the container containing the prepared ammonium sulfate solution, and a slurry having a homogeneous concentration is prepared by stirring and mixing with the stirrer. In this state, the temperature of the slurry is preferably maintained under a temperature condition of 20°C or higher and 60°C or lower 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 lower than 20°C, the reaction rate is too slow and the production efficiency is reduced, and conversely, if it exceeds 60°C, ammonium sulfate is easily thermally decomposed, making it difficult to leach it well. If the slurry temperature is below 0° C., the water will freeze, making it difficult to prepare the ammonium sulfate solution.

In this leaching treatment, the ammonium sulfate concentration in the ammonium sulfate aqueous solution is preferably adjusted to a range of 0.50 mol/L to 4.1 mol/L, more preferably 1.5 mol/L to 3.5 mol/L, and most preferably 2.0 mol/L to 3.0 mol/L. If the ammonium sulfate 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 sulfate 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, ammonium sulfate becomes supersaturated and precipitates, which may have a negative effect on the leaching treatment. The ammonium sulfate concentration can be measured by absorptiometry, ion chromatography, etc. If the ammonium sulfate concentration is outside the above range, it can be adjusted by the amount of ammonium sulfate added.

In addition, during the above leaching treatment, it is preferable to adjust the free ammonia concentration in the slurry to within the range of 0.1 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 sulfur trioxide generated by pyrolysis in this pyrolysis precipitation step and reuse them as ammonia water containing ammonium sulfate 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 ammonium sulfate 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)
39.64 g of ammonium sulfate (( _NH4 ) _{2SO4 )} was added to 185 mL of pure water and 15 mL of 25% ammonia water placed in a container to prepare an ammonium sulfate aqueous solution with an ammonium sulfate 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 ammonium sulfate aqueous solution to prepare a slurry, which was stirred with a stirrer while maintaining the liquid temperature at 50°C for 2 hours to carry out 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 12.5 g and a leaching solution of 204 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 45.6% and the cobalt leaching rate was 15.4%, and a leachate consisting of an aqueous ammonia solution containing a large amount of nickel ions and cobalt ions was produced.

Comparative Example
200 mL of 25% ammonia water was placed in a container, and 20 g of powdered nickel-cobalt mixed hydroxide (MHP) having the composition shown in Table 1 was mixed to form a slurry, which was stirred with a stirrer and held for 2 hours while adjusting the liquid temperature to 50° C., to carry out a leaching treatment. Thereafter, solid-liquid separation was carried out in the same manner as in the examples, and 200 mL of leachate was obtained. The element concentrations of this leachate were measured in the same manner as in the examples, and the leaching rate of each element was determined.

As a result, the leaching rate of nickel was 14.6%, and that of cobalt was 0.2%, which means that about 1/3 of the nickel was leached compared to the example in which the leaching treatment was performed at the same temperature, but almost no cobalt was leached. In this comparative example, the leaching rate of each element was calculated using the following formula 3. The measurement results of the above example and comparative example are summarized in Table 2 below.
[Formula 3]
Leaching rate of element α=mass of element α in leaching solution/mass of element α in MHP×100

Claims (2)

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 sulfate to obtain a slurry; and subjecting the slurry to a leachate 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 sulfate concentration in the ammonia water containing ammonium sulfate is adjusted to be within the range of 0.50 to 4.1 mol/L.

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