KR102710458B1 - Method for recovering lithium element from lithium containing waste solution - Google Patents

Abstract

The present invention relates to a method for recovering a lithium component in an alkaline waste solution containing lithium, nickel, and a metal and sulfate generated during a process for manufacturing a cathode active material, the method comprising: a first step of filtering the alkaline waste solution to filter out solid metals contained in the alkaline waste solution; a second step of adding carbon dioxide to the waste solution from which the solid metals have been filtered to convert lithium hydroxide in the waste solution into lithium carbonate; a third step of adding barium carbonate to the waste solution in which lithium carbonate has been produced to convert sulfate contained in the alkaline waste solution into barium sulfate; a fourth step of filtering the barium sulfate to remove sulfate from the waste solution; and a fifth step of concentrating the waste solution to recover lithium carbonate.

Description

{METHOD FOR RECOVERING LITHIUM ELEMENT FROM LITHIUM CONTAINING WASTE SOLUTION}

The present invention relates to a method for recovering lithium components from lithium-containing waste liquid.

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, but nickel or waste water is generated due to the washing process. At this time, the waste water contains impurities such as nickel or sulfate (SO ₄ ) as well as hundreds of ppm to thousands of ppm of lithium, so if high-purity lithium compounds can be recovered and recycled, price competitiveness can be secured, thereby increasing process efficiency. Therefore, studies on methods for recovering metal components from waste liquids or spent batteries have been attempted recently.

Previously, research was mainly focused on recovering lithium from a solution obtained by leaching spent batteries with acid, and there was minimal research on a process for recovering lithium compounds from waste liquid generated during the cathode material manufacturing process.

In addition, since impurities contained in lithium-containing solutions are mainly metal components, they are removed by precipitating them as metal hydroxides using a strong alkaline reagent, or by using a solvent extraction method using an organic solvent and an extractant to remove metal components from spent batteries. However, in this case, there is a disadvantage in that a separate component is mixed in, and an additional purification process or acid treatment is required to remove the extracted metal.

Therefore, a method for easily recovering lithium without an additional purification process is required.

Republic of Korea Patent No. 1682217 (Announcement date: 2016.12.05)

The present invention is intended to solve the above problems and to provide a method for recovering lithium components at a high content from lithium-containing waste liquid.

The present invention provides a method for recovering a lithium component in an alkaline waste solution containing lithium, nickel, and a metal and sulfate generated during a process for manufacturing a cathode active material, the method comprising: a first step of filtering the alkaline waste solution to filter out solid metals contained in the alkaline waste solution; a second step of adding carbon dioxide to the waste solution from which the solid metals have been filtered to convert lithium hydroxide in the waste solution into lithium carbonate; a third step of adding barium carbonate to the waste solution in which lithium carbonate has been produced to convert sulfate contained in the alkaline waste solution into barium sulfate; a fourth step of filtering the barium sulfate to remove sulfate from the waste solution; and a fifth step of concentrating the waste solution to recover lithium carbonate.

According to the present invention, lithium ions and sulfate contained in waste liquid generated during the manufacture of a cathode active material can be easily removed, and since an additional purification process is not required, the process can be carried out efficiently, and furthermore, since metal components in the waste liquid are removed in advance, the cost of waste disposal can also be reduced.

Figure 1 is a drawing showing an XRD pattern of a filter cake obtained by filtering waste liquid after performing step 4 of the recovery method of Example 1.
Figure 2 is a drawing showing an XRD pattern of a lithium component recovered according to the recovery method of Example 1.

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.

The method for recovering lithium components in an alkaline waste solution containing lithium, nickel, and metals and sulfates generated during a process for manufacturing a cathode active material according to the present invention comprises: a first step of filtering the alkaline waste solution to filter out solid metals of residual cathode active material contained in the alkaline waste solution; a second step of adding carbon dioxide to the waste solution from which the solid metals have been filtered to convert lithium hydroxide in the waste solution into lithium carbonate; a third step of adding barium carbonate to the waste solution in which lithium carbonate has been produced to convert sulfate contained in the alkaline waste solution into barium sulfate; a fourth step of filtering the barium sulfate to remove sulfate from the waste solution; and a fifth step of concentrating the waste solution to recover lithium carbonate.

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

First, prepare the waste liquid generated during the positive electrode active material manufacturing process.

The above waste solution refers to a filtered solution in which a lithium transition metal oxide is stirred in a washing solution for the purpose of reducing lithium byproducts, etc. present on the surface after producing the lithium transition metal oxide.

For example, the metal in the waste liquid may include at least one of nickel, cobalt, or manganese, and preferably contains lithium together with impurities such as nickel or sulfate (SO ₄ ).

The lithium contained in the above waste liquid 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.

The above-mentioned waste solution is a basic solution having a pH of 7 to 14, preferably a pH of 10 to 13. For example, the above-mentioned waste solution may be basic due to the addition of an aqueous solution of NaOH and/or NH ₄ OH during a co-precipitation reaction for producing a positive electrode active material precursor.

Next, the basic waste solution prepared above was filtered to filter out the solid metal content contained in the basic waste solution (step 1).

In the case of the above step 1, the purpose is to remove impurities, for example, metal oxides, contained in the waste liquid in a solid form. For example, the metal in the solid form may be a composite oxide including at least one of nickel, cobalt, or manganese.

The filtration of the above step 1 may be performed by vacuum filtration using a filter paper, and the filter paper may preferably have pores of 1 to 5 μm, preferably 1 to 3 μm. For example, the pores may be smaller than the average particle size (D ₅₀ ) of the metal oxide in the solid content contained in the waste liquid. By using a filter paper having pores in the above-described range, the metal oxide in the waste liquid may be filtered through the filter paper, and other components may pass through the filter paper.

Next, carbon dioxide was added to the waste liquid from which the metal oxide had been filtered, thereby converting lithium hydroxide in the waste liquid into lithium carbonate (step 2).

Lithium contained in the above waste liquid exists as lithium hydroxide or lithium carbonate, and carbon dioxide is injected into the waste liquid to convert lithium hydroxide contained in the waste liquid into lithium carbonate.

For example, by adding carbon dioxide to the waste liquid, lithium hydroxide contained in the waste liquid may be converted into lithium carbonate by a reaction as in the following reaction scheme 1.

[Reaction Formula 1]

2LiOH + CO ₂ → Li ₂ CO ₃ + H ₂ O

Next, barium carbonate was added to the waste liquid in which lithium carbonate was produced.

The purpose of adding barium carbonate to the waste liquid is to remove sulfate contained in the basic waste liquid. For example, in the case of waste water generated during the manufacture of a cathode active material, a process of adding sulfate of a transition metal oxide during the co-precipitation reaction for the manufacture of a cathode active material is involved, so that a large amount of sulfate remains in the waste liquid. If the process of removing the sulfate is not performed and sulfate remains in the waste liquid, the sulfate acts as an impurity, which has the disadvantage of lowering the purity of the lithium carbonate salt finally obtained.

According to the present invention, barium carbonate was added to the waste liquid in which lithium carbonate was produced, and the sulfate contained in the basic waste liquid was converted into barium sulfate as shown in the following reaction scheme 2 (step 3).

[Reaction Formula 2]

BaCO ₃ + SO ₄ ^2- → BaSO ₄ (↓) + CO ₃ ^2-

For example, if barium carbonate is not added to the waste liquid in which lithium carbonate is generated, but is added immediately after metal filtration and then _CO2 is supplied (i.e., the order of steps 2 and 3 is reversed), since carbonization of the waste liquid does not occur overall, unreacted barium carbonate may remain in the waste liquid in the form of barium hydroxide [Ba(OH) ₂ ] when barium carbonate and sulfate react. If barium hydroxide remains in the waste liquid as described above, the problem of a decrease in the sulfate removal effect may occur.

According to the present invention, the introduction of the barium carbonate into the waste liquid may be by introducing 0.02 to 0.13 parts by weight, preferably 0.05 to 0.10 parts by weight, of a barium carbonate aqueous solution, wherein barium carbonate is mixed with distilled water in a weight ratio of 3:1 to 7:1, based on the total weight of the waste liquid. For example, when the amount of the barium carbonate aqueous solution introduced into the waste liquid satisfies the above-described range, not only can sulfate be removed, but also metal ions present in small amounts in the solution can be effectively removed. On the other hand, when the amount of the barium carbonate aqueous solution introduced is less than the above-described range, the removal of impurities (metal ions) may be insufficient, and when it exceeds the above-described range, the process cost increases, and barium ions may remain in the solution and act as impurities.

By adding barium carbonate to the waste liquid, nickel in the waste liquid can be converted into nickel carbonate as shown in the following reaction formula 3.

[Reaction Formula 3]

BaCO ₃ + Ni ^{2 +} → NiCO ₃ (↓) + Ba ^{2 +}

By adding barium carbonate to the waste liquid, cobalt in the waste liquid can be converted into cobalt carbonate as shown in the following reaction formula 4.

[Reaction Formula 4]

BaCO ₃ + Co ^{2 +} → CoCO ₃ (↓) + Ba ^{2 +}

By adding barium carbonate to the waste liquid, metal ions present in the waste liquid, particularly metal ions such as nickel and cobalt that were not filtered out in step 1, may react with the barium carbonate and precipitate in the waste liquid, and can be easily removed through a subsequent filtration process.

In addition, when adding a barium carbonate aqueous solution to the waste liquid, carbon dioxide may be additionally added as needed, and added in the form of a barium bicarbonate solution.

For example, by supplying carbon dioxide at a rate of 20 mL/min for more than 1 hour to a barium carbonate slurry containing barium carbonate mixed in distilled water, the barium carbonate aqueous solution can be prepared into a barium bicarbonate solution.

As described above, when adding a barium carbonate aqueous solution to the waste liquid and adding _CO2 at the same time, barium bicarbonate can be formed as shown in the following reaction formula 5. Since the barium bicarbonate has a high solubility compared to the barium carbonate, the conversion rate of the sulfate present in the waste liquid into barium sulfate can be further accelerated by adding the barium bicarbonate.

[Reaction Formula 5]

(1) CO ₂ + H ₂ O → HCO ₃ ^- + H ⁺

(2) BaCO ₃ + HCO ₃ ^- + H ⁺ → Ba(HCO ₃ ) ₂

Next, the barium sulfate was filtered to remove sulfate from the waste liquid (step 4).

It may be possible to remove not only sulfate precipitated in the waste liquid by the reaction with the above barium carbonate, but also nickel carbonate and cobalt carbonate, and the filtration in step 4 may be performed by reduced pressure filtration using a filter paper, and the filter paper may preferably have pores of 1 to 5 μm, preferably 1 to 3 μm. For example, the pores may be smaller than the average size of barium sulfate contained in the waste liquid. By using a filter paper having pores in the above-described range, barium sulfate in the waste liquid may be filtered through the filter paper, and other components may pass through the filter paper.

According to the present invention, the method may further include mixing and calcining the filtered sulfate and carbon source.

For example, the filtered sulfate, preferably barium sulfate, can be mixed with a carbon source (for example, the carbon source is at least one of coke, anthracite coal or lignite), calcined at 900° C. to 1,100° C., preferably 950° C. to 1,050° C., and then exposed to a carbon dioxide atmosphere, thereby reducing the sulfate to barium carbonate, and the barium carbonate thus obtained can be reused in step 3.

For example, the reaction of the above barium sulfate and carbon source can be performed as shown in the following reaction scheme 6.

[Reaction Formula 6]

(1) BaSO ₄ + 2C → BaS + 2CO ₂

(2) BaS + CO ₂ + H ₂ O → H ₂ S + BaCO ₃

Finally, the waste liquid was concentrated to recover lithium carbonate (step 5).

The above-mentioned concentrating of the waste liquid may be performed by removing moisture by concentrating the waste liquid from which impurities have been removed through reduced pressure evaporation, for example, by using a rotary evaporator to maintain the temperature of the reactor (bath) at 85°C and remove moisture of 50% or more relative to the initial weight at a pressure of 200 mbar or less, thereby making the concentration of the lithium carbonate higher than the solubility of lithium carbonate (80°C, 0.85 wt%), thereby forming lithium carbonate crystals.

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

After mixing and calcining Ni _{0 . 8} Co _{0 . 1} Mn _{0 .} 1 (OH) ₂ and lithium salt, the waste liquid generated during the washing process was obtained.

After washing, the waste liquid was filtered under reduced pressure at 200 mbar using a 2.5 μm filter to remove the solids contained in the waste liquid (step 1). At this time, the pH of the waste liquid was pH 12.5.

Next, _CO2 was supplied to the waste liquid from which the solids had been removed using a carbon dioxide bomb and a flow meter for 90 minutes (step 2).

Next, 36 g of a slurry containing BaCO ₃ and distilled water in a ratio of 1:5 was added to 800 g of the waste liquid supplied with CO ₂ , and stirred at 40°C for 90 minutes (step 3).

After stirring, the solution was filtered under reduced pressure at 200 mbar using a 2.5 μm filter paper to remove BaSO ₄ precipitated by the reaction of BaCO ₃ and SO ₄ ^2- in the waste solution (step 4).

100 g of the filtrate from which impurities had been removed was subjected to reduced pressure evaporation and concentration at 85°C and 200 mbar to remove 72 g of moisture, and then filtered and dried to recover lithium carbonate (Step 5).

Example 2

Lithium carbonate was recovered in the same manner as in Example 1, except that CO ₂ was supplied simultaneously at a rate of 20 mL/min for more than 1 hour when the BaCO ₃ slurry was injected in the third step.

Comparative example 1

Lithium carbonate was recovered in the same manner as in Example 1, except that step 3 was not performed.

Comparative example 2

Lithium carbonate was recovered in the same manner as in Example 1, except that Ca(OH) ₂ slurry was used instead of BaCO ₃ slurry in Step 3.

Comparative example 3

After step 1, barium carbonate slurry was added to the waste liquid from which the solid content had been removed, and then _CO2 was supplied to the slurry into which the barium carbonate slurry had been added, and the barium treatment solution was recovered by performing up to step 4 of Example 1.

Experimental example 1

When recovering lithium components in waste liquid by the same steps as in Example 1 above, the components of the solution recovered at each step are shown in Table 1, Figure 1, and Figure 2 below.

Unit:ppm Ni Mn Na Al Ca Cr Cu Fe S Step 2 4 <2 146 <2 <2 <2 <2 <2 1340 Step 3 <2 <2 175 <2 <2 <2 <2 <2 685

As shown in Table 1 above, the metal ion components in the wastewater that had gone through step 2 could be confirmed by filtering the wastewater to remove the solid metal and supplying _CO2 . Next, by adding barium carbonate to the wastewater that had gone through step 2, it was confirmed that the contents of Ni, Mn, and S were further reduced (step 3).

Referring to FIGS. 1 and 2, the XRD analysis results of the waste liquid that performed step 4 confirmed that it contained BaSO ₄ and BaCO ₃ phases, as shown in FIG. 1. Through this, it was confirmed that sulfate was easily removed by performing step 4.

Additionally, the XRD analysis results of the waste liquid that performed step 5 confirmed the lithium carbonate (Li ₂ CO ₃ ) phase, as shown in Fig. 2.

Experimental example 2

In Examples 1 to 2 and Comparative Examples 1 to 3, after the solid content was filtered under reduced pressure, _CO2 was supplied for 90 minutes, and the filtered solution, that is, the solution filtered after performing only step 4 of Examples 1 to 2 and Comparative Examples 1 to 3, was measured for the content of metal elements using an inductively coupled plasma optical emission spectrometer (ICP-OES), and the results are shown in Table 2 below.

unit:
ppm Ni Mn Na Al Ca Cr Cu Fe S Example 1 <2 <2 175 <2 <2 <2 <2 <2 685 Example 2 <2 <2 176 <2 <2 <2 <2 <2 703 Comparative Example 1 4 <2 146 <2 <2 <2 <2 <2 1340 Comparative Example 2 <2 <2 154 <2 <2 <2 <2 <2 1214 Comparative Example 3 <2 <2 179 <2 <2 <2 <2 <2 1316

As shown in Table 2 above, in the case of the solution filtered in step 4 of Examples 1 to 2, it was confirmed that metal ions were hardly detected, and when barium carbonate or barium bicarbonate was added to the wastewater to convert sulfate into barium sulfate and then filtered, it was confirmed that the content of S in the wastewater was reduced.

On the other hand, in the case of the solution filtered in step 4 of Comparative Examples 1 to 3, it was confirmed that the content of S in the waste liquid was higher than in Examples 1 to 2. In particular, in the case of Comparative Example 2, instead of barium carbonate according to the present invention, calcium salt was added to attempt to remove sulfate in the form of calcium sulfate, but since it is not easy to form calcium sulfate precipitate in the case of a basic solution, it was confirmed that the content of S in the waste liquid was higher than in the present invention. In addition, in the case of Comparative Example 3, it was confirmed that the content of S in the waste liquid was higher than in Examples 1 to 2 due to the unreacted portion of barium carbonate and sulfate.

Experimental example 3

The content of each element was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES) for lithium salts recovered from waste liquid obtained after performing steps 1 to 2 and 5 of Comparative Examples 1 to 3, and the results are shown in Table 3 below.

unit:
ppm Ni Mn Na Al Ca Cr Cu Fe S Example 1 <2 <2 390 <2 26 <2 <2 <2 1190 Example 2 <2 <2 381 <2 26 <2 <2 <2 1216 Comparative Example 1 145 <2 820 14 60 3 <2 <2 6900 Comparative Example 2 22 <2 1123 38 158 <2 <2 <2 4185

As shown in Table 3 above, in the case of lithium salts recovered by the same method as Examples 1 and 2, it was confirmed that the content of impurities was significantly lower than in the lithium salts recovered by the same method as Comparative Examples 1 and 2.

Claims (8)

A method for recovering lithium components from alkaline waste liquid containing lithium, nickel, and metals and sulfates generated during a cathode active material manufacturing process,
A first step of filtering the above-mentioned basic waste liquid to filter out the solid metal contained in the basic waste liquid;
A second step of converting lithium hydroxide in the waste liquid into lithium carbonate by adding carbon dioxide to the waste liquid from which the solid metal has been filtered;
A third step of converting sulfate contained in the basic waste solution into barium sulfate by adding barium carbonate to the waste solution in which lithium carbonate is generated;
A fourth step of filtering the barium sulfate to remove sulfate from the waste liquid; and
A method for recovering lithium components in waste liquid, comprising a fifth step of concentrating the waste liquid to recover lithium carbonate.
In the first paragraph,
A method for recovering lithium components in waste liquid, wherein the barium carbonate aqueous solution is added to the waste liquid in an amount of 0.02 to 0.13 parts by weight based on the total weight of the waste liquid.
In the first paragraph,
A method for recovering lithium components in waste liquid, wherein nickel in the waste liquid is converted into nickel carbonate by adding barium carbonate to the waste liquid.
In the first paragraph,
A method for recovering lithium components in waste liquid, wherein cobalt in the waste liquid is converted into cobalt carbonate by adding barium carbonate to the waste liquid.
In the first paragraph,
A method for recovering lithium components in waste liquid, wherein adding barium carbonate to the waste liquid is done by adding carbon dioxide to a slurry containing distilled water and barium carbonate, and adding it in the form of a barium bicarbonate solution.
In paragraph 5,
A method for recovering lithium components in waste liquid, wherein the distilled water and barium carbonate are mixed in a weight ratio of 3:1 to 7:1.
In the first paragraph,
A method for recovering lithium components in waste liquid, wherein the metal in the waste liquid includes at least one of nickel, cobalt, and manganese.
In the first paragraph,
A method for recovering lithium components in waste liquid, wherein the waste liquid is a basic solution having a pH of 7 to 14.