KR102771741B1 - Method for recovering lithium from lithium containing metal salt solution - Google Patents

Abstract

The present invention relates to a method for recovering lithium ions contained in a metal salt aqueous solution containing at least lithium as a lithium salt, the method comprising: a first step of mixing an organic solvent extractant into a lithium-containing metal salt aqueous solution, so that lithium contained in the lithium-containing metal salt aqueous solution moves to the organic solvent extractant; a second step of allowing the mixture of the first step to stand, so as to separate layers of the metal salt aqueous solution and the organic solvent extractant, so as to recover the organic solvent extractant; a third step of mixing distilled water with the organic solvent extractant separated and recovered in the second step, and bubbling the mixture with carbon dioxide to generate carbonate ions and hydrogen ions in the distilled water, so that lithium contained in the organic solvent extractant ions exchange with hydrogen contained in the distilled water; a fourth step of allowing the mixture of the third step to stand, so as to separate layers of the distilled water and the organic solvent extractant, so as to recover distilled water; and a fifth step of allowing lithium ions and carbonate ions contained in the distilled water to react to generate lithium carbonate.

Description

{METHOD FOR RECOVERING LITHIUM FROM LITHIUM CONTAINING METAL SALT SOLUTION}

The present invention relates to a method for recovering lithium from a lithium-containing metal salt aqueous solution.

Lithium secondary batteries are generally composed of a cathode containing a cathode active material, a cathode containing a cathode active material, a separator, and an electrolyte, and are secondary batteries that are charged and discharged by intercalation-decalation of lithium ions. Lithium secondary batteries have the advantages of high energy density, large electromotive force, and high capacity, and are therefore applied in various fields.

The cathode active material of a lithium secondary battery includes lithium and transition metals such as nickel, cobalt, and manganese. Recently, in order to increase the capacity of lithium secondary batteries, there is a trend to increase the nickel content in lithium transition metal oxides. However, as the nickel content in the lithium transition metal oxide increases, there is a problem in that a large amount of lithium byproducts such as LiOH and Li ₂ CO ₃ are generated on the surface due to the tendency of the nickel to be maintained as ^{Ni 2+ .} In this way, when a lithium transition metal oxide having a high content of lithium byproducts on its surface is used, it may react with the electrolyte injected into the lithium secondary battery, thereby causing a swelling phenomenon in the lithium secondary battery, and a secondary battery including the same cannot sufficiently exhibit battery performance.

In order to solve these problems, the content of lithium byproducts existing on the surface of lithium transition metal oxides was reduced by performing a washing process after the synthesis of lithium transition metal oxides. However, wastewater containing positive electrode active material solids is generated due to the washing process. At this time, the wastewater contains lithium of several hundred ppm to several thousand ppm in addition to impurities such as positive electrode active material solids and sulfate ( _SO42 ⁺ ), so if high-purity lithium compounds can be recovered and recycled, price competitiveness can be secured, thereby increasing process efficiency. Therefore, studies on methods of crystallizing lithium from waste liquid or spent batteries and recovering it in the form of a lithium salt have been attempted recently.

In the past, _a method of recovering lithium ions in the form of a lithium salt by adding sodium carbonate such as _Na2CO3 and performing a lithium carbonation process _{from an aqueous solution containing lithium has been studied. However, in this case, since Na remains in the aqueous solution, a sodium salt such as Na2SO4 is} generated and exists as an impurity, and therefore a process for removing this is absolutely necessary.

In addition, a method of extracting lithium using a solvent extractant has also been studied. However, conventionally, lithium was extracted using an acidic solution such as a sulfuric acid solution, and in this case, lithium ions exist in the sulfuric acid solution, so an additional purification process was absolutely necessary to obtain lithium ions in the form of a lithium salt.

Therefore, a method is required that can easily recover lithium ions in the form of a lithium salt without a separate impurity removal process or additional purification process due to the generation of impurities.

Republic of Korea registered patent no. 1682217

The present invention is intended to solve the above problems and to provide a method for recovering lithium ions in the form of a lithium salt from a lithium-containing metal salt aqueous solution.

The present invention provides a method for recovering lithium ions contained in a metal salt aqueous solution containing at least lithium as a lithium salt, the method comprising: a first step of mixing an organic solvent extractant into a lithium-containing metal salt aqueous solution, so that lithium contained in the lithium-containing metal salt aqueous solution moves to the organic solvent extractant; a second step of allowing the mixture of the first step to stand, so as to separate layers of the metal salt aqueous solution and the organic solvent extractant, so as to recover the organic solvent extractant; a third step of mixing distilled water with the organic solvent extractant separated and recovered in the second step, and bubbling the mixture with carbon dioxide to generate carbonate ions and hydrogen ions in the distilled water, and allowing lithium contained in the organic solvent extractant to ion-exchange with hydrogen contained in the distilled water; a fourth step of allowing the mixture of the third step to stand, so as to separate layers of the distilled water and the organic solvent extractant, so as to recover the distilled water; and a fifth step of allowing lithium ions contained in the distilled water and carbonate ions to react to generate lithium carbonate.

According to the present invention, since no separate chemical is used to recover lithium ions in the form of a lithium salt from a lithium-containing metal salt aqueous solution, no waste is generated, and the problem of reduced process stability and the problem of performing an additional purification process, which were problems when using a strong acid aqueous solution, can be overcome, so that the process can be carried out efficiently.

Figure 1 is a flow chart showing a lithium salt recovery method of the present invention.

Hereinafter, the present invention will be described in more detail.

The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as having meanings and concepts that conform to the technical idea of the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner.

The terminology used in this specification is for the purpose of describing exemplary embodiments only and is not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

As used herein, the terms “comprise,” “include,” or “have,” etc., are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

According to the present invention, a method for recovering lithium ions contained in a metal salt aqueous solution containing at least lithium as a lithium salt comprises: a first step of mixing an organic solvent extractant into a lithium-containing metal salt aqueous solution, as shown in the flow chart of FIG. 1, so that lithium contained in the lithium-containing metal salt aqueous solution moves to the organic solvent extractant; a second step of allowing the mixture of the first step to stand, thereby separating layers of the metal salt aqueous solution and the organic solvent extractant, thereby recovering the organic solvent extractant; a third step of mixing distilled water with the organic solvent extractant separated and recovered in the second step, and bubbling the mixture with carbon dioxide to generate carbonate ions and hydrogen ions in the distilled water, and performing ion exchange between lithium contained in the organic solvent extractant and hydrogen contained in the distilled water; a fourth step of allowing the mixture of the third step to stand, thereby separating layers of the distilled water and the organic solvent extractant, thereby recovering the distilled water; and a fifth step of allowing lithium ions contained in the distilled water and carbonate ions to react to generate lithium carbonate.

Below, each step of the present invention is described in more detail.

First, prepare an aqueous metal salt solution containing at least lithium.

The above metal salt aqueous solution may contain lithium (Li) and sulfur (S), and may be, for example, a solution obtained by stirring a lithium transition metal oxide in a washing solution and then filtering it for the purpose of reducing waste liquid discarded during the manufacturing process for producing a cathode active material, for example, lithium byproducts present on the surface after producing a lithium transition metal oxide.

For example, the metal salt aqueous solution may contain lithium along with impurities such as sulfate (SO ₄ ²⁺ ).

The lithium contained in the above metal salt solution may be a mixture of Li ₂ CO ₃ and LiOH, and may contain several hundred ppm to several thousand ppm of lithium based on lithium.

Next, an organic solvent extractant is mixed into the metal salt aqueous solution prepared above, and lithium ions contained in the lithium-containing metal salt aqueous solution are transferred to the organic solvent extractant (step 1).

The solvent extraction method using the solvent extractant according to the present invention has three stages of extraction, washing, and stripping. First, the extraction process is a process of moving the target component from the aqueous solution to the solvent extractant in the organic phase, the washing process is a process of moving the impurities extracted together with the target component moved to the solvent extractant in the organic phase to the aqueous phase and removing them, and the stripping process is a process of desorbing the target component from the washed organic phase to the aqueous phase.

This solvent extraction method is one of the useful methods for separating and purifying metal ions from aqueous solutions or leachates. In the case of the metal ions, if they exist in a hydrated form in an aqueous solution, they do not easily move to a low-polarity organic solvent layer. Therefore, in order for the hydrated metal ions to move to the organic phase, the metal ions must form a charge-free complex, and the metal ions must be able to remove water molecules from the hydrated complex.

That is, the solvent extractant plays a role in causing metal ions to form a charge-free complex and removing water molecules from it, and the extraction efficiency at this time may be affected by the type of solvent extractant, equilibrium pH, concentration of metal ions in the aqueous solution, ratio of solvent extractant to aqueous solution, and composition and concentration of the stripping solution.

The organic solvent extractant above may be any organic solvent extractant generally used in the relevant technical field as a solvent extractant without particular limitation, preferably one containing a hydrogen ion at a terminal group, and more preferably one selected from the group consisting of vinyl phosphonic acid, acrylic acid, dialkyl phosphonic acid, di-2-ethylhexyl phosphate (D-2-EHPA), and 2-ethylhexylhydrogen 2-ethylhexyl phosphate (PC88A), or a polymer thereof. For example, CYANEX 272 from Cytec Co., Ltd. or ALBRITECT TH1 from Solvay Co., Ltd. may be used, but is not limited thereto.

When the metal salt aqueous solution and the organic solvent extractant are mixed as in the present invention, the metal ions in the metal salt aqueous solution form a charge-free complex by the organic solvent extractant, and the metal ions are ion-exchanged with the organic solvent extractant, so that the lithium ions contained in the metal salt aqueous solution move to the organic solvent extractant.

The organic solvent extractant added above may be added in an amount of 20 to 400 mol%, preferably 30 to 200 mol%, and more preferably 40 to 160 mol%, based on 100 mol% of lithium contained in the lithium-containing metal salt aqueous solution. When the solvent extractant is added in the above-described range, the extraction efficiency for extracting lithium ions from the lithium-containing metal salt aqueous solution can be further improved.

The viscosity of the solvent extractant of the above organic phase is 70 Pa·s to 100 Pa·s, preferably 80 Pa·s to 90 Pa·s, more preferably 88 Pa·s to 90 Pa·s at 25°C. Since the viscosity is high, before adding it to the metal salt aqueous solution of the first step described above, the solvent extractant may be diluted by optionally mixing the solvent extractant and a viscosity regulator as needed and then used. When diluting the solvent extractant by mixing a viscosity regulator, the viscosity of the solvent extractant may be diluted to 30% to 50%, preferably about 40% of the viscosity described above and then used.

For example, the viscosity modifier may include kerosene.

Next, the mixture of the first step is purified to separate the layers of the metal salt aqueous solution and the organic solvent extractant, thereby recovering the organic solvent extractant (second step).

Since the above metal salt aqueous solution is in the water phase and the solvent extractant is in the organic phase, a clear layer separation occurs when the metal salt aqueous solution and the solvent extractant are mixed and then allowed to settle.

After the layers of the metal salt aqueous solution and the solvent extractant are separated, any method that can easily separate the organic phase and the aqueous phase can be used to separate the metal salt aqueous solution and the solvent extractant without particular limitation. For example, a multi-stage mixer settler or a separating funnel may be used to separate the metal salt aqueous solution in the aqueous phase and the solvent extractant in the organic phase. Preferably, for process efficiency, a separating funnel may be used to allow the solution to settle for a certain period of time, and then the aqueous phase and the organic phase may be separated.

Next, distilled water is mixed with the organic solvent extractant separated and recovered in the second step and bubbled with carbon dioxide to generate carbonate ions and hydrogen ions in the distilled water, and lithium contained in the organic solvent extractant performs ion exchange with hydrogen contained in the distilled water (third step).

For example, by mixing distilled water with an organic solvent extractant and bubbling carbon dioxide, the production of carbonic acid (H ₂ CO ₃ ) is induced as in the following reaction scheme 1, and this is used to produce bicarbonate ions (HCO ₃ ^- ) and protons (H ⁺ ).

(1) H ₂ O + CO ₂ ↔ H ₂ CO ₃ ↔ H ⁺ + HCO ₃ ^-

Lithium ions may move to the water phase (distilled water) by ion exchange between hydrogen ions (H ⁺ ) generated by the bubbling of the carbon dioxide and lithium ions (Li ⁺ ) included in the organic solvent extractant. Since the polarity of the distilled water is higher than that of the organic solvent extractant, lithium ions included in the solvent extractant with low polarity may easily undergo ion exchange with hydrogen ions by mixing with the distilled water.

For example, instead of adding the distilled water and bubbling the carbon dioxide, if a strong acid aqueous solution (e.g., sulfuric acid aqueous solution) is added and stirred as in the past, the hydrogen ions in the sulfuric acid aqueous solution and the lithium ions in the organic solvent extractant are exchanged, layer separation occurs, and lithium ions (Li ⁺ ) and sulfate ions (SO ₄ ^2- ) coexist, and in order to recover lithium as lithium carbonate, there is a disadvantage that a separate carbonate must be added to perform additional purification.

In the present invention, since distilled water is added instead of a strong acid solution and carbon dioxide is bubbled, a strong acid solution is not used, and a separate carbonate addition process due to the use of a strong acid solution is not required, so the process stability is excellent and it can be effective in terms of process efficiency.

Next, the mixture of the third step is purified to separate the layers of the metal salt aqueous solution and the organic solvent extractant, thereby recovering the metal salt aqueous solution (fourth step).

As in the second step, since the distilled water is the water phase and the solvent extractant is the organic phase, a clear layer separation occurs when the distilled water and the solvent extractant are mixed and allowed to stand.

For example, after the layers of distilled water and solvent extractant are separated, the distilled water and solvent extractant may be separated by separating the aqueous phase and the organic phase using a separatory funnel.

Finally, lithium ions and carbonate ions contained in the distilled water react to produce lithium carbonate, as shown in the following reaction formula (2) (step 5).

(2) Li ⁺ + HCO ₃ ^- ↔ LiHCO ₃

In addition, according to the present invention, after the fourth step, the method may further include concentrating the distilled water under reduced pressure.

For example, concentrating the distilled water may be done by removing moisture by concentrating the distilled water in which the lithium bicarbonate is produced through reduced pressure evaporation, thereby converting the lithium bicarbonate into lithium carbonate.

Preferably, when the reaction is carried out under the conditions of 200 mbar at a reactor jacket temperature of 40°C to 95°C during the above-decreased concentration, the desorption of carbon dioxide from the lithium bicarbonate may proceed as in the following reaction formula (3), thereby obtaining lithium carbonate.

(3) 2LiHCO ₃ -> Li ₂ CO ₃ (s) + CO ₂ + H ₂ O

For example, when the reaction is carried out under the above-described reduced pressure concentration conditions, the vapor can be recovered as condensate and discarded above the boiling point of the aqueous solution, so the problem of lithium carbonate obtained later reacting further with carbon dioxide to bicarbonate into lithium bicarbonate can be solved.

Hereinafter, the present invention will be described in detail by way of examples in order to specifically explain the present invention. However, the examples according to the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided in order to more completely explain the present invention to a person having average knowledge in the art.

Example

Example 1

A mixed solution of 57.6 g of a solvent extractant (AlbritectTH1, Solvay) and 86.4 g of kerosene (Kerosene) was added to 500 g of a lithium-containing aqueous solution containing 6,485 ppm of Li and 7,800 ppm of S, and stirred at 25°C for 2 hours (Stage 1).

Afterwards, the above-mentioned mixture was allowed to settle for 2 hours, and the layers of the lithium-containing aqueous solution and the solvent extractant were confirmed to be separated, and then each was separated and recovered (step 2).

After adding 500 g of distilled water to the solvent extractant recovered above, _CO2 with a purity of 99.9% was bubbled at a flow rate of 20 cc/min for 10 minutes (step 3).

Afterwards, it was left to settle for 12 hours, and it was confirmed that the layers of the solvent extractant and distilled water were separated, and then each was separated and recovered (Step 4).

Next, 479 g of the recovered distilled water was concentrated under reduced pressure at 80°C and 150 mbar, filtered under reduced pressure using a 2.5 μm filter paper, and vacuum-dried in an oven at 50°C to recover lithium carbonate (Step 5).

Example 2

Lithium carbonate was recovered in the same manner as in Example 1, except that a mixture of 115.2 g of a solvent extractant and 172.8 g of kerosene was used as the mixed solution added to the lithium-containing aqueous solution in the first step.

Example 3

61.6 g of a solvent extractant (AlbritectTH1, Solvay) was added to 250 g of a lithium-containing aqueous solution containing 3,545 ppm of Li and 2,650 ppm of S, and stirred at 25°C for 2 hours (step 1).

Afterwards, the above-mentioned mixture was allowed to settle for 2 hours, and the layers of the lithium-containing aqueous solution and the solvent extractant were confirmed to be separated, and then each was separated and recovered (step 2).

After adding 500 g of distilled water to the solvent extractant recovered above, _CO2 with a purity of 99.9% was bubbled at a flow rate of 20 cc/min for 10 minutes (step 3).

Afterwards, it was left to settle for 12 hours, and it was confirmed that the layers of the solvent extractant and distilled water were separated, and then each was separated and recovered (Step 4).

Next, 479 g of the recovered distilled water was concentrated under reduced pressure at 80°C and 150 mbar, filtered using a 2.5 μm filter paper, and vacuum-dried in an oven at 50°C to recover lithium carbonate (Step 5).

Example 4

Lithium carbonate was recovered in the same manner as in Example 3, except that 82.1 g of solvent extractant was added in the first step.

Example 5

Lithium carbonate was recovered in the same manner as in Example 3, except that 102.7 g of solvent extractant was added in the first step.

Comparative example 1

61.6 g of a solvent extractant (AlbritectTH1, Solvay) was added to 250 g of a lithium-containing aqueous solution containing 3,545 ppm of Li and 2,650 ppm of S, and stirred at 25°C for 2 hours.

Afterwards, the above-mentioned mixture was allowed to settle for 2 hours, and it was confirmed that the layers of the lithium-containing aqueous solution and the solvent extractant were separated, and then each was separated and recovered.

The solvent extractant containing the Li recovered above was mixed with 500 g of a 0.5 M sulfuric acid aqueous solution, hand-shaken for 2 minutes, and then allowed to settle, and phase separation was performed using a separatory funnel.

Next, 479 g of the recovered distilled water was concentrated under reduced pressure at 80°C and 150 mbar, filtered using a 2.5 μm filter paper, and vacuum dried in an oven at 50°C to recover lithium carbonate.

Experimental example 1

When the lithium component is recovered by the same method as in Examples 1 to 5 and Comparative Example 1, the components of the solution recovered in the second step are shown in Table 1 below.

Unit: ppm Li S Example 1 5090 7810 Example 2 4440 7690 Example 3 1545 2600 Example 4 1480 2620 Example 5 1420 2640 Comparative Example 1 1612 2610

It was confirmed that Li included in the solution recovered in the second step of Examples 1 and 2 was recovered in an amount of about 68 to 78% of the Li content initially included in the metal salt aqueous solution, and it was confirmed that Li included in the solution recovered in the second step of Examples 3 to 5 was recovered in an amount of about 40 to 43% of the Li content initially included in the metal salt aqueous solution.

Experimental example 2

When the lithium component is recovered by the same method as in Examples 3 to 5 and Comparative Example 1, the content of lithium ions included in the solution recovered in the fourth step and the weight of the lithium salt recovered by drying the same under reduced pressure are shown in Table 2 below.

Step 4 Step 5 Unit: ppm Li (ppm) Li salt (g) Example 3 610 0.79 Example 4 660 0.80 Example 5 685 0.81 Comparative Example 1 590 0.78

As shown in Table 2 above, it was confirmed that the content of lithium salt recovered by the methods of Examples 3 to 5 was greater than the content of lithium salt recovered by the method of Comparative Example 1.

Claims (8)

A method for recovering lithium ions contained in a metal salt aqueous solution containing at least lithium as a lithium salt,
A first step of mixing an organic solvent extractant into a lithium-containing metal salt aqueous solution to move lithium contained in the lithium-containing metal salt aqueous solution to the organic solvent extractant;
A second step of separating the metal salt aqueous solution and the organic solvent extractant layer by purifying the mixture of the first step and recovering the organic solvent extractant layer;
A third step of mixing distilled water with the organic solvent extractant separated and recovered in the second step and bubbling it with carbon dioxide to generate carbonate ions and hydrogen ions in the distilled water, and performing ion exchange between lithium contained in the organic solvent extractant and hydrogen contained in the distilled water;
A fourth step of separating the mixture of the third step by distilling the distilled water and the organic solvent extractant layer to recover the distilled water; and
A lithium salt recovery method comprising a fifth step in which lithium ions and carbonate ions contained in the distilled water react to produce lithium carbonate.
In the first paragraph,
A lithium salt recovery method, wherein the organic solvent extractant introduced in the first step is introduced in an amount of 20 mol% to 400 mol% with respect to 100 mol% of lithium included in the lithium-containing metal salt aqueous solution.
In the first paragraph,
A method for recovering a lithium salt, wherein the organic solvent extractant contains a hydrogen ion at a terminal group.
In the first paragraph,
A method for recovering a lithium salt, wherein the organic solvent extractant comprises a compound selected from the group consisting of vinyl phosphonic acid, acrylic acid, dialkyl phosphonic acid, di-2-ethylhexyl phosphate (D-2-EHPA), and 2-ethylhexylhydrogen 2-ethylhexyl phosphate (PC88A), or a polymer thereof.
In the first paragraph,
A lithium salt recovery method further comprising using the organic solvent extractant of the first step in a mixture with a viscosity modifier.
In the first paragraph,
A method for recovering a lithium salt, wherein the viscosity of the solvent extractant is 70 Pa·s to 100 Pa·s.
In the first paragraph,
A lithium salt recovery method further comprising, after the fourth step, concentrating the distilled water under reduced pressure.
In Article 7,
A method for recovering a lithium salt further comprising filtering after concentrating the distilled water under reduced pressure.