阅读说明：本技术 精制锂化合物的制备方法和锂过渡金属复合氧化物的制备方法 (Method for producing purified lithium compound and method for producing lithium transition metal composite oxide ) 是由 高桑正宽 于 2019-07-08 设计创作，主要内容包括：本发明提供精制锂化合物的制备效率优异、能够应用于广泛种类的锂化合物、且能够降低得到精制锂化合物时的能量消耗的精制锂化合物的制备方法和使用利用该制备方法得到的精制锂化合物的锂过渡金属复合氧化物的制备方法。精制锂化合物的制备方法包含：粉碎工序,用于破碎含有磁性物质的粗制锂化合物聚集体；和磁选处理工序,使用磁选机对粉碎后的粗制锂化合物实施干式磁选,从所述粉碎后的粗制锂化合物去除所述磁性物质。(The invention provides a method for producing a purified lithium compound, which has excellent production efficiency of the purified lithium compound, can be applied to a wide variety of lithium compounds, and can reduce energy consumption in obtaining the purified lithium compound, and a method for producing a lithium transition metal composite oxide using the purified lithium compound obtained by the production method. The preparation method of the refined lithium compound comprises the following steps: a pulverization step for crushing crude lithium compound aggregates containing a magnetic substance; and a magnetic separation step of performing dry magnetic separation on the pulverized crude lithium compound by using a magnetic separator to remove the magnetic substance from the pulverized crude lithium compound.)

1. A method for producing a refined lithium compound, comprising:

a pulverization step for pulverizing aggregates of a crude lithium compound containing a magnetic substance; and

and a magnetic separation step of performing dry magnetic separation on the pulverized crude lithium compound by using a magnetic separator to remove the magnetic substance from the pulverized crude lithium compound.

2. The method for producing a purified lithium compound according to claim 1, wherein,

the pulverization is carried out by using a sieve having a mesh opening of 40 to 700 μm.

3. The production method of a refined lithium compound according to claim 1 or 2, wherein,

the magnetic separator is an electromagnetic separator.

4. The production method of a refined lithium compound according to any one of claims 1 to 3, wherein the magnetic separation is performed a plurality of times.

5. The method of producing a purified lithium compound according to any one of claims 1 to 4, wherein the magnetic separation is performed 5 times or more.

6. The method of producing a purified lithium compound according to any one of claims 1 to 5, wherein the magnetic flux density of the magnetic separation unit provided in the magnetic separator is 3000 Gauss or more.

7. The production method of a refined lithium compound according to any one of claims 1 to 6, wherein the lithium compound contains lithium carbonate.

8. The production method of a refined lithium compound according to any one of claims 1 to 7, wherein the lithium compound is used for production of a lithium transition metal composite oxide.

9. A method for preparing a lithium transition metal composite oxide, comprising:

a pulverization step for pulverizing aggregates of a crude lithium compound containing a magnetic substance;

a magnetic separation step of subjecting the pulverized crude lithium compound to dry magnetic separation using a magnetic separator to remove the magnetic substance from the pulverized crude lithium compound and purify the lithium compound; and

and a firing step of mixing the purified lithium compound with a transition metal composite hydroxide or a transition metal composite oxide and then firing the mixture.

Technical Field

The present invention relates to a method for producing a purified lithium compound having excellent purification process efficiency and a method for producing a lithium transition metal composite oxide using the purified lithium compound.

Background

In recent years, lithium secondary batteries have been used in a wide range of fields such as portable devices and vehicles using or sharing electricity as a power source. The lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode. A positive electrode of a lithium secondary battery can be prepared by preparing a positive electrode mixture containing a lithium transition metal composite oxide as a positive electrode active material, a conductive material, and a binder, and supporting the positive electrode mixture on a positive electrode current collector.

As a positive electrode active material used for a positive electrode of a lithium secondary battery, a lithium transition metal composite oxide is used. The lithium transition metal composite oxide is prepared, for example, by mixing a transition metal composite hydroxide such as a hydroxide containing nickel, cobalt, and/or manganese as a precursor or a transition metal composite oxide such as an oxide containing nickel, cobalt, and/or manganese with a lithium compound (lithium salt) and then firing the mixture.

Here, the positive electrode active material may contain magnetic powder such as iron powder or metal powder such as stainless steel powder derived from the raw material. When the magnetic powder is mixed into the positive electrode active material, a micro short circuit may occur between the electrodes even if the amount of the magnetic powder mixed is very small. When a micro short circuit occurs between the electrodes, the capacity of the lithium secondary battery may decrease, which may affect the charge and discharge characteristics of the lithium secondary battery. Therefore, the standards for the magnetic elements (Fe and the like) in the positive electrode active material have become strict year by year. In particular, the magnetic element is derived from a lithium compound added to the precursor of the lithium transition metal composite oxide and is mixed into the positive electrode active material.

Therefore, in the production of a lithium transition metal composite oxide, it is required to remove the magnetic substance contained in the lithium compound in advance and to sufficiently reduce the content of the magnetic substance. The content of the magnetic substance contained in the lithium compound is preferably smaller, and for example, the content of the magnetic substance is preferably reduced to less than 1.0ppm (on a mass basis). The method for removing the magnetic substance contained in the lithium compound includes, for example, removing impure Li by the following steps₂CO₃The method for removing the magnetic substance comprises the following steps: making impure Li in the 1 st aqueous solution₂CO₃With CO₂Reacting to prepare a solution containing LiHCO₃Containing Li derived from impurities₂CO₃A 2 nd aqueous solution of an insoluble compound and a dissolved compound of the impurity of (1); separation of unreacted CO from aqueous solution 2₂And an insoluble compound; separating the dissolved impurities from the 2 nd aqueous solution using an ion-exchange resin or other ion-selective medium; and reacting Li₂CO₃And (2) a step of precipitating from the aqueous solution (patent document 1).

The method of patent document 1 is a method of obtaining a purified lithium compound by a wet process, and in order to reliably remove a magnetic substance, a crude lithium compound, which is a lithium compound before purification containing a magnetic substance such as a metal component, is made into an aqueous solution. Therefore, in the method of patent document 1, after removing the magnetic substance in the state of the aqueous solution, when precipitating and collecting the lithium compound, it is necessary to perform heating and concentration of the aqueous solution.

However, in patent document 1, which is a wet purification method, although the magnetic material can be reliably removed, the purification process is complicated and the loss of the lithium compound occurs, and therefore, there is room for improvement in the production efficiency of the purified lithium compound. In addition, when patent document 1, which is a wet purification method, is applied to lithium hydroxide, there is a possibility that a part thereof is carbonated, and depending on the kind of the lithium compound, there is a lithium compound which is originally unsuitable for wet purification. Further, in patent document 1, there is a problem that a large amount of energy is consumed in recovering a lithium compound purified from an aqueous solution of the lithium compound.

Documents of the prior art

Patent document

Patent document 1: japanese Kohyo publication No. 2001-525313

Disclosure of Invention

Problems to be solved by the invention

In view of the above circumstances, an object of the present invention is to provide a method for producing a purified lithium compound, which is excellent in efficiency of producing a purified lithium compound, can be applied to a wide variety of lithium compounds, and can reduce energy consumption in obtaining a purified lithium compound, and a method for producing a lithium transition metal composite oxide using a purified lithium compound obtained by the production method.

Means for solving the problems

The gist of the configuration of the present invention for solving the above problems is as follows.

[1] A method for producing a refined lithium compound, comprising:

a pulverization step for pulverizing a crude lithium compound aggregate containing a magnetic substance; and

and a magnetic separation step of performing dry magnetic separation on the pulverized crude lithium compound by using a magnetic separator to remove the magnetic substance from the pulverized crude lithium compound.

[2] The method for producing a purified lithium compound according to [1], wherein the pulverization is performed using a sieve having a mesh of 40 μm to 700 μm.

[3] The production method of a refined lithium compound according to [1] or [2], wherein the magnetic separator is an electromagnetic separator.

[4] The production method of a refined lithium compound according to any one of [1] to [3], wherein the magnetic separation is performed a plurality of times.

[5] The method for producing a purified lithium compound according to any one of [1] to [4], wherein the magnetic separation is performed 5 times or more.

[6] The method for producing a purified lithium compound according to any one of [1] to [5], wherein the magnetic flux density of the magnetic separation unit of the magnetic separator is 3000 Gauss or more.

[7] The production method of a refined lithium compound according to any one of [1] to [6], wherein the lithium compound contains lithium carbonate.

[8] The production method of a purified lithium compound according to any one of [1] to [7], wherein the lithium compound is used for producing a lithium transition metal composite oxide.

[9] A method for preparing a lithium transition metal composite oxide, comprising:

a pulverization step for pulverizing a crude lithium compound aggregate containing a magnetic substance;

a magnetic separation step of subjecting the pulverized crude lithium compound to dry magnetic separation using a magnetic separator to remove the magnetic substance from the pulverized crude lithium compound and further refine the lithium compound; and

and a firing step of mixing the purified lithium compound with the transition metal composite hydroxide or the transition metal composite oxide and then firing the mixture.

In the embodiment [1], the aggregation degree of the crude lithium compound can be reduced by pulverizing the crude lithium compound containing the magnetic substance, thereby imparting a highly dispersed state to the crude lithium compound. In the embodiment [1], since the crude lithium compound subjected to the pulverization treatment is subjected to the dry magnetic separation using the magnetic separator, a step of separately adding water to the crude lithium compound to be purified may not be included. In addition, the magnetic substance as an impurity can be removed from the crude lithium compound, whereby the crude lithium compound can be purified.

The electromagnetic separator as the magnetic separator according to the aspect [3] is provided with a screen magnetized by an electromagnet provided in the electromagnetic separator and functioning as a magnetic separation section. By passing the crude lithium compound through the magnetized screen, the magnetic substance contained in the crude lithium compound can be removed by the magnetic force of the screen.

In the embodiment [4], the lithium compound to be purified is fed to the magnetic separator a plurality of times, and magnetic separation is performed a plurality of times.

Effects of the invention

According to the embodiment of the present invention, the crude lithium compound containing the magnetic substance is pulverized and then subjected to dry magnetic separation using a magnetic separator, thereby providing excellent production efficiency of the purified lithium compound. That is, since the aggregation degree of the crude lithium compound containing the magnetic substance is reduced by pulverizing the crude lithium compound, when the pulverized crude lithium compound is introduced into the magnetic separation section of the magnetic separator, which is formed, for example, in a lattice or slit structure, the clogging of the magnetic separation section by the lithium compound is prevented. As a result, the magnetic separation processing capacity of the magnetic separator is improved, and the production efficiency of the refined lithium compound is improved. In addition, the crude lithium compound containing the magnetic substance is subjected to a sieve treatment to reduce the degree of aggregation of the crude lithium compound, whereby the magnetic substance entering the inside of the aggregated crude lithium compound is positioned in the vicinity of the surface of the crude lithium compound. When the magnetic substance is located near the surface of the crude lithium compound, the magnetic substance is easily magnetically adsorbed to the magnetic separation section of the magnetic separator, thereby improving the production efficiency of the purified lithium compound.

Further, according to the embodiment of the present invention, since the dry purification is performed by purifying the crude lithium compound containing the magnetic substance directly in a powder state without making it into an aqueous solution, even if the present invention is applied to, for example, crude lithium hydroxide, it is possible to prevent a part thereof from being carbonated, and therefore, the present invention can be applied to a wide variety of lithium compounds. Further, according to the embodiment of the present invention, since dry purification is performed, a purified lithium compound in powder form can be obtained without heating or drying. Therefore, energy consumption in obtaining a purified lithium compound in powder form can be reduced, and as a result, environmental load can be prevented. In addition, since the purified lithium compound in powder form can be obtained without heating or drying, the time required for producing the purified lithium compound can be shortened.

According to the embodiment of the present invention, by performing the pulverization using the sieve having the mesh openings of 40 μm to 700 μm, the aggregation of the crude lithium compound can be reliably reduced, and the pulverization treatment can be smoothly performed.

According to the embodiment of the present invention, the magnetic separator is an electromagnetic separator, and thus even in dry magnetic separation, the magnetic material can be reliably removed from the crude lithium compound.

According to the embodiment of the present invention, by performing magnetic separation a plurality of times, it is possible to reliably remove the magnetic substance from the crude lithium compound without increasing the size of the magnetic separator.

According to the embodiment of the present invention, since the magnetic flux density of the magnetic separation unit provided in the magnetic separator is 3000 gauss or more, the magnetic material can be reliably removed from the crude lithium compound even in the dry magnetic separation.

According to an embodiment of the present invention, the purified lithium compound obtained by the above method is mixed with the transition metal composite hydroxide or the transition metal composite oxide and then fired, whereby the lithium transition metal composite oxide can be obtained while preventing the magnetic substance from being mixed. By using the lithium transition metal composite oxide obtained while preventing the magnetic substance from being mixed in as the positive electrode of the lithium secondary battery, the capacity of the lithium secondary battery can be prevented from being reduced.

Drawings

FIG. 1 is a flow chart of a production method of a purified lithium compound.

Fig. 2 is an explanatory diagram showing an outline of a magnetic separation process for removing a magnetic substance from a crude lithium compound.

Detailed Description

Next, a method for producing a purified lithium compound according to the present invention will be described in detail with reference to the drawings. Fig. 1 is a flowchart of a method for producing a purified lithium compound. Fig. 2 is an explanatory diagram showing an outline of a magnetic separation process for removing a magnetic substance from a crude lithium compound.

As shown in fig. 1, the method for producing a purified lithium compound of the present invention includes: a pulverization step for pulverizing a crude lithium compound aggregate containing a magnetic substance; and a magnetic separation step of performing dry magnetic separation on the pulverized crude lithium compound by using a magnetic separator to remove the magnetic substance from the pulverized crude lithium compound. Examples of the magnetic substance contained in the crude lithium compound include metal powders such as iron powder and stainless steel powder. The magnetic substance contained in the lithium compound is an impurity.

The content of the magnetic substance in the crude lithium compound to be purified is, for example, 1.0ppm (mass basis, the same applies hereinafter) or more and 7.0ppm or less. In addition, in the case of producing a purified lithium compound, the higher the removal rate of the magnetic substance contained in the crude lithium compound is, the more preferable it is, for example, 80 mass% or more. When the content of the magnetic substance in the crude lithium compound is 1.0ppm to 7.0ppm, the content of the magnetic substance in the purified lithium compound is reduced to, for example, less than 1.0 ppm.

(grinding step)

First, the crude lithium compound containing the magnetic substance is pulverized to loosen the crude lithium compound aggregate, thereby improving the dispersibility. As the pulverization step, for example, as shown in fig. 1, a sieve treatment of passing a crude lithium compound containing a magnetic substance through a sieve can be exemplified. The average particle size of the aggregated crude lithium compound before passing through the sieve is, for example, on the order of 1mm to 5 mm. The lithium compound and the magnetic substance are both powder, and the lithium compound has the property of easy aggregation. The crude lithium compound of the powder is subjected to a sieve treatment, thereby reducing the degree of aggregation of the crude lithium compound and imparting a high dispersion state and fluidity to the crude lithium compound. In addition, the degree of aggregation of the crude lithium compound is reduced by the sieve treatment, whereby the magnetic substance that has entered into the interior of the aggregated crude lithium compound is located near the surface of the crude lithium compound.

For the sieving treatment, for example, the crude lithium compound in a powder form is placed on a sieve having a desired mesh, and the sieve is appropriately vibrated as necessary to pass the crude lithium compound through the sieve, whereby the crude lithium compound can be subjected to the sieving treatment. In the case of subjecting the crude lithium compound to the sieving treatment, it is preferable to pass the crude lithium compound through the sieve in a dry state without adding a liquid such as water, from the viewpoint of smoothing the sieving treatment step and preventing aggregation of the crude lithium compound.

The mesh of the sieve is not particularly limited, but from the viewpoint of reliably reducing the aggregation of the crude lithium compound by the action of the sieve, the mesh is preferably 700 μm or less, more preferably 400 μm or less, and particularly preferably 350 μm or less. In addition, the mesh openings of the sieve are preferably 40 μm or more, more preferably 75 μm or more, and particularly preferably 150 μm or more, in order to smoothly pass the crude lithium compound through the sieve to improve the efficiency of the sieve treatment step and reduce the aggregation of the crude lithium compound. The upper limit value and the lower limit value may be arbitrarily combined. The crude lithium compound is passed through a sieve to break up the crude lithium compound aggregates, whereby the average particle size of the crude lithium compound is, for example, about 5 μm to 700 μm.

(magnetic separation treatment Process)

As shown in fig. 1, a magnetic separator is used to perform dry magnetic separation on a powdery crude lithium compound that has been pulverized (for example, by sieving) to break up aggregates, and further to remove magnetic substances from the sieved crude lithium compound. By removing the magnetic substance from the crude lithium compound, the crude lithium compound can be purified.

As shown in fig. 2, in the magnetic separation treatment, for example, the coarse lithium compound 12 in a powder form after the sieve treatment is introduced into the introduction port 11 provided above the magnetic separator 1, and while the coarse lithium compound 12 falls from above to below from the magnetic separation unit 13 provided inside the magnetic separator 1, the magnetic material contained in the coarse lithium compound 12 is magnetically adsorbed to the magnetic separation unit 13 by the magnetic force of the magnetic separation unit 13, whereby the magnetic separation can be performed. On the other hand, the lithium compound is not a magnetic substance and is not magnetically adsorbed by the magnetic separator 1, and the lithium compound 14 in powder form is discharged from the discharge port 15 provided below the magnetic separator 1. Therefore, by the magnetic separation treatment, the lithium compound and the magnetic substance can be separated. In the present invention, since the dry magnetic separation is performed using the magnetic separator 1, a step of separately adding water to the crude lithium compound 12 to be purified may not be included.

Since the crude lithium compound 12 to be subjected to the magnetic separation is in a state in which the aggregate is broken by the sieve treatment, when the crude lithium compound 12 is introduced into the magnetic separation section 13 of the magnetic separator 1, which is formed in a lattice or slit structure, for example, clogging of the magnetic separation section 13 due to the lithium compound is prevented. Therefore, the amount of the lithium compound to be charged into the magnetic separator 1 can be increased, the magnetic separation processing capacity of the magnetic separator 1 can be improved, and the production efficiency of the purified lithium compound can be improved. In addition, since the magnetic substance that has entered the inside of the aggregated crude lithium compound 12 is located near the surface of the crude lithium compound 12 by preliminarily pulverizing the crude lithium compound 12, the magnetic substance is likely to directly contact the magnetic separation section 13 of the magnetic separator 1. Therefore, the magnetic substance is easily magnetically adsorbed to the magnetic separation section 13, and as a result, the production efficiency of the purified lithium compound is improved.

Further, since the crude lithium compound 12 containing the magnetic substance is not prepared as an aqueous solution but purified in a powder (solid) state, chemical changes of the crude lithium compound 12 can be prevented, and the method can be applied to a wide variety of lithium compounds. Since the crude lithium compound 12 containing the magnetic substance is purified in a powder state, a purified lithium compound in a powder state can be obtained without a heating or drying step. Therefore, energy consumption in obtaining a purified lithium compound in the form of powder can be reduced, and further, the load on the environment can be prevented. In addition, since the purified lithium compound in powder form can be obtained without heating or drying, the time required for producing the purified lithium compound can be shortened, and the process for producing the purified lithium compound can be simplified.

The magnetic separator 1 may be, for example, an electromagnetic separator. By using an electromagnetic separator as the magnetic separator 1, even in dry magnetic separation, the magnetic substance can be reliably removed from the crude lithium compound 12. The electromagnetic separator includes a grid-like mesh which is magnetized by an electromagnet provided in the electromagnetic separator, thereby functioning as a magnetic separation section 13. Further, as shown in FIG. 2, the magnetic separation section 13 may be formed by providing a plurality of screens in the vertical direction. In this case, the number of meshes can be selected depending on the degree of purification of the lithium compound passing through the mesh and the content of the magnetic substance.

The number of times of the magnetic separation treatment in the magnetic separator 1 is not particularly limited, but as shown in fig. 1, it is preferable to perform the magnetic separation treatment a plurality of times. That is, it is preferable to feed the lithium compound 14 discharged from the discharge port 15 of the magnetic separator 1 into the feed port 11 of the magnetic separator 1 again and perform the magnetic separation again. By performing the magnetic separation treatment a plurality of times, the magnetic substance can be removed more reliably without increasing the size of the magnetic separator 1, and the degree of purification of the lithium compound can be further improved. When the magnetic separation treatment is performed a plurality of times, the number of times is preferably 5 or more, for example. In the case of performing the magnetic separation treatment after the 2 nd and 2 nd times, it is not necessary to perform the pulverization again.

The magnetic flux density of the magnetic separation section 13 is not particularly limited, and the lower limit value thereof is preferably 3000 gauss in order to reliably remove the magnetic substance from the crude lithium compound 12 even in the dry magnetic separation, and more preferably 6000 gauss, even more preferably 8000 gauss, and particularly preferably 12000 gauss in order to further improve the degree of purification of the lithium compound. On the other hand, the higher the upper limit value of the magnetic flux density of the magnetic separation section 13 is, the higher the upper limit value is, for example, 30000 gauss.

Examples of the lithium compound to be purified include lithium carbonate and lithium hydroxide.

The purified lithium compound obtained by the production method of the present invention can be used, for example, as a raw material for a lithium transition metal composite oxide. The lithium transition metal composite oxide is used as a positive electrode active material for a lithium secondary battery.

Next, a method for producing a lithium transition metal composite oxide using the purified lithium compound obtained by the production method of the present invention will be described.

First, a transition metal composite hydroxide, which is a precursor of the lithium transition metal composite oxide, is prepared. The preparation method of the transition metal composite hydroxide comprises the following steps: first, a salt solution of a transition metal (for example, a salt solution of nickel (for example, a sulfate solution), a salt solution of cobalt (for example, a sulfate solution), a salt solution of manganese (for example, a sulfate solution), or the like), a complexing agent, and a pH adjuster are appropriately added by a coprecipitation method, and thereby they are reacted in a reaction tank to prepare transition metal composite hydroxide particles, and a slurry-like suspension containing the transition metal composite hydroxide particles is obtained. Examples of the solvent for the suspension include water.

The complexing agent is not particularly limited as long as it can form a complex with ions of a transition metal (e.g., nickel, cobalt, manganese, etc.) in an aqueous solution, and examples thereof include ammonium ion donors (ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracil diacetic acid, and glycine. In the precipitation, an alkali metal hydroxide (for example, sodium hydroxide or potassium hydroxide) may be added as necessary to adjust the pH of the aqueous solution.

When the pH adjuster and the complexing agent are appropriately and continuously supplied to the reaction tank in addition to the salt solution of the transition metal, the transition metal (for example, nickel, cobalt, manganese, or the like) undergoes a coprecipitation reaction to produce transition metal composite hydroxide particles. In the coprecipitation reaction, the temperature of the reaction tank is controlled, for example, within a range of 10 to 80 ℃, preferably 20 to 70 ℃, and the pH value in the reaction tank is controlled, for example, within a range of pH9 to 13, preferably pH11 to 13, based on the liquid temperature of 40 ℃, and the substances in the reaction tank are appropriately stirred. Examples of the reaction tank include a continuous type in which the formed transition metal composite hydroxide particles are overflowed to separate them, and a batch type in which the particles are not discharged outside the system until the reaction is completed.

The transition metal composite oxide particles obtained as described above are filtered from the suspension, washed with water, and subjected to a heat treatment, whereby powdery transition metal composite hydroxide particles that are precursors of the lithium transition metal composite oxide can be obtained. In addition, transition metal composite oxide particles obtained by further subjecting the transition metal composite hydroxide particles to a heat treatment may be used as a precursor of the lithium transition metal composite oxide, if necessary.

Next, the precursor of the lithium transition metal composite oxide obtained as described above and a purified lithium compound obtained by pulverizing the crude lithium compound and then performing a magnetic separation treatment are mixed to obtain a mixture. Next, the obtained mixture is fired, whereby a lithium transition metal composite oxide can be produced. Examples of the firing step include primary firing and secondary firing performed after the primary firing. In the mixing and/or firing step, a transition metal (e.g., Al, W, Zr, etc.) may be added as appropriate. The firing temperature of the primary firing is, for example, 700 to 1000 ℃, the firing time is, for example, 5 to 20 hours, and the temperature rising rate is, for example, 50 to 550 ℃/h. The primary firing environment is not particularly limited, and examples thereof include air, oxygen, and the like. The firing furnace used for the primary firing is not particularly limited, and examples thereof include a static box furnace, a Roller-Hearth (Roller-Hearth) type continuous furnace, and the like. The firing temperature of the secondary firing is, for example, 600 ℃ to 1000 ℃, the firing time is, for example, 1 to 20 hours, and the temperature rise rate is, for example, 50 to 550 ℃/h. The secondary firing environment is not particularly limited, and examples thereof include air, oxygen, and the like. The firing furnace used for the secondary firing is not particularly limited, and examples thereof include a static box furnace, a roll-hearth continuous furnace, and the like.

Examples

Next, examples of the method for producing a purified lithium compound of the present invention will be described, but the present invention is not limited to these examples as long as the method does not depart from the gist thereof.

Example 1

10kg of crude lithium carbonate containing 3.0ppm of a powdery magnetic substance was sieved through a sieve having a mesh opening of 300. mu.m. The sieve was a vibrating sieve machine ("zoteng vibrating sieve machine" manufactured by shinning industries co.). The content of the magnetic substance in the crude lithium carbonate was measured by wet recovery of the magnetic powder.

Next, the sieved crude lithium carbonate was supplied to a magnetic separator at a supply rate of 1.0 kg/min, and magnetic substances were removed from the crude lithium carbonate to perform magnetic separation. The lithium carbonate was magnetically separated 5 times to obtain purified lithium carbonate. The magnetic separator used was an electromagnetic separator ("electromagnetic separator CG-150HHH model" manufactured by Magnetics corporation, Japan).

The electromagnetic separator has the following specifications.

Magnetic flux density of the screen: 12000 Gauss

Screen mesh shape: a grid shape with 5mm meshes,

Number of meshes: 20 sheets of paper are stacked up and down

Example 2

Purified lithium carbonate was obtained in the same manner as in example 1, except that the sieved crude lithium carbonate was supplied to the magnetic separator at a supply rate of 2.0 kg/min.

Comparative example 1

Lithium carbonate was obtained in the same manner as in example 1, except that the crude lithium carbonate was not subjected to the sieve treatment and was supplied to the magnetic separator at a supply rate of 0.3 kg/min. The reason why the supply amount of 0.3 kg/min was used in comparative example 1 was: at a supply rate of 1.0 kg/min, clogging occurred in the magnetic separation path, and lithium carbonate could not be supplied to the magnetic separator, but the supply rate of 0.3 kg/min was the limit.

The conditions for producing the purified lithium carbonates of examples 1 and 2 and comparative example 1 and the results of the mass-based content (ppm) of the magnetic substance and the removal rate (mass%) of the magnetic substance with respect to the lithium carbonate obtained by the production methods of examples 1 and 2 and comparative example 1 are shown in table 1 below.

[ Table 1]

According to table 1 above, in the lithium carbonates of examples 1 and 2 obtained by performing the sieving process and the magnetic separation process, the magnetic material was reduced to 0.6ppm (removal rate of the magnetic material: 80.0 mass%) and 0.4ppm (removal rate of the magnetic material: 86.7 mass%) after 5 times of the magnetic separation. Therefore, in examples 1 and 2, the content of the magnetic substance was 0.6ppm or less, and purified lithium carbonate having high lithium purity was obtained. In examples 1 and 2, the lithium carbonate was supplied to the magnetic separator in an amount of 1.0 kg/min and 2.0 kg/min, respectively, and the magnetic separation rate was increased.

On the other hand, in the lithium carbonate of comparative example 1 obtained by performing the magnetic separation step without performing the sieving step, the magnetic substance after 5 times of the magnetic separation treatment reached 1.0ppm (removal rate of the magnetic substance was 66.7 mass%). Therefore, in comparative example 1, sufficiently purified lithium carbonate could not be obtained. In comparative example 1, as described above, the lithium carbonate was supplied to the magnetic separator in an amount of 0.3 kg/min, and the magnetic separation rate could not be increased.

Industrial applicability of the invention

The present invention can simply and efficiently produce a purified lithium compound having a sufficiently reduced content of a magnetic substance, and therefore has a high utility value in the field of producing a lithium raw material of a lithium transition metal composite oxide used as a positive electrode active material for a lithium secondary battery.

Description of the symbols

1, a magnetic separator; 12 a crude lithium compound.