JP7115123B2 - Lithium purification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a lithium purification method for purifying lithium from lithium-containing manufacturing process wastewater of positive electrode materials for lithium secondary batteries.

Lithium is widely used in industry as an additive for pottery and glass, glass flux for continuous steel casting, grease, pharmaceuticals, and batteries. In particular, lithium secondary batteries have high energy density and high voltage, so recently their use as batteries for electronic devices such as laptop computers and on-board batteries for electric and hybrid vehicles is expanding, and demand is rapidly increasing. ing.

Recently, for the purpose of effective utilization of resources, the recovery of lithium from wastewater discharged from the manufacturing process of positive electrode materials for lithium secondary batteries (hereinafter also referred to as "manufacturing process wastewater") has been promoted.

As a method for recovering lithium from waste water from manufacturing processes, Patent Document 1 proposes a solvent extraction method, and Patent Document 2 proposes a method using electrodialysis using an ion exchange membrane.

In addition, as a method for purifying lithium recovered as lithium carbonate, a method of reacting crude lithium carbonate with carbon dioxide to produce a lithium hydrogencarbonate aqueous solution, filtering this, followed by heat treatment to precipitate lithium carbonate is disclosed in the patent literature. 3 is proposed.

JP-A-2006-57142 JP 2012-234732 A JP-A-62-252315

However, the solvent extraction method of Patent Literature 1 has problems that safety measures are required, the process is long, and the cost is high. In addition, the method of using electrodialysis using an ion-exchange membrane in Patent Document 2 is disadvantageous in terms of cost and operation.

On the other hand, there is a recovery method using an ion exchange resin as an inexpensive and simple method.

However, since sulfuric acid and aqueous sodium sulfate solution are used as eluents in this recovery method, these impurities form a sparingly soluble double sulfate when recovering lithium as lithium carbonate, resulting in sulfur and sodium in lithium carbonate. There was a problem of quality improvement.

On the other hand, in the lithium purification method of Patent Document 3, the grades of sulfur and sodium in lithium carbonate are reduced. However, when calcium is contained in the raw material, lithium carbonate, a chelating agent must be used in order to lower the grade of calcium, which causes the problem of increased lithium recovery costs.

The present invention has been made in view of the above circumstances, and an object of the present invention is to purify lithium by recovering high-purity lithium carbonate from the manufacturing process wastewater of positive electrode materials for lithium secondary batteries containing lithium ions. do.

The inventors used an ion-exchange resin to adsorb lithium from the manufacturing process wastewater of a positive electrode material for a lithium secondary battery containing lithium ions, and extracted lithium from the ion-exchange resin using an aqueous solution containing sulfuric acid or sulfate. It was found that lithium is recovered as lithium carbonate from the eluted post-elution solution.

When a carbonic acid source such as sodium carbonate is added to the post-elution solution to obtain lithium carbonate, impurities form a sparingly soluble double sulfate. The present invention has been completed by discovering that lithium hydrogen carbonate can be converted to high lithium hydrogen carbonate and that lithium hydrogen carbonate releases carbon dioxide by heating and converts to lithium carbonate with low solubility.

One aspect of the present invention for achieving the above object is a lithium purification method for purifying lithium from manufacturing process wastewater containing lithium of a positive electrode material for lithium secondary batteries, wherein the manufacturing process wastewater is treated with an ion exchange resin. an ion-exchange step of bringing into contact; an elution step of bringing an eluent into contact with the ion-exchange resin after the ion-exchange step; a crystallization step of adding a carbonate source to the post-elution solution after the elution step; The method is characterized by comprising a hydrogencarbonation step of introducing carbon dioxide into the subsequent lithium carbonate, and a recrystallization step of heating the lithium hydrogencarbonate after the hydrogencarbonation step.

In this way, impurities generated in the crystallization step can be removed in the hydrogencarbonation step, so that high-purity lithium carbonate can be obtained from the lithium-containing manufacturing process wastewater of the positive electrode material for lithium secondary batteries. can purify lithium.

Further, in one aspect of the present invention, the functional group of the ion exchange resin is Na type, and the eluent may be an aqueous solution containing sodium sulfate.

Since sodium is more selective than lithium, the elution step can be performed regardless of the concentration of the aqueous solution containing sodium sulfate. In addition, since a waste liquid containing a large amount of sodium sulfate is generated in the manufacturing process of positive electrode materials for lithium secondary batteries, the utilization of this waste liquid is advantageous in terms of cost.

Further, in one aspect of the present invention, the functional group of the ion exchange resin may be H-type, and the eluent may be sulfuric acid.

Since the H-type ion exchange resin has a higher selectivity for lithium than for hydrogen, the ion exchange process can be carried out regardless of the concentration of sulfuric acid.

Further, in one aspect of the present invention, the lithium concentration in the waste water from the manufacturing process may be 0.3 g/L or more.

By increasing the lithium concentration, the ion exchange step can be performed even with an ion exchange resin having Na-type functional groups.

In one aspect of the present invention, the carbonate source may be sodium carbonate.

In this way, since water-soluble sodium sulfate is generated in the crystallization step, it can be separated from lithium carbonate having low solubility, and the grade of impurities in lithium carbonate can be lowered.

Moreover, in one aspect of the present invention, the manufacturing process waste water may contain calcium.

In the refining method according to one aspect of the present invention, calcium, which is an impurity, can be removed to obtain highly purified lithium carbonate.

In one aspect of the present invention, the calcium concentration in the purified lithium carbonate after the recrystallization step may be less than 5 ppm.

In the purification method according to one aspect of the present invention, highly purified lithium carbonate can be obtained.

Moreover, in one aspect of the present invention, the introduction of the carbon dioxide in the hydrogen carbonate step may be performed at normal pressure.

Since there is no need to pressurize and introduce carbon dioxide, there is no need for equipment required for pressurization, which is advantageous in terms of cost.

According to the present invention, it is possible to purify lithium by obtaining high-purity lithium carbonate from lithium-containing manufacturing process wastewater of positive electrode materials for lithium secondary batteries.

FIG. 2 is a flow diagram showing an outline of a manufacturing process of a positive electrode material for lithium secondary batteries. 1 is a flowchart for explaining a method for purifying lithium according to an embodiment of the present invention; FIG.

Specific embodiments of the present invention (hereinafter referred to as "present embodiments") will be described in detail below. It should be noted that the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the purpose of the present invention.

[1. Overview of manufacturing process of positive electrode material for lithium secondary battery]
First, the outline of the manufacturing process of the positive electrode material for lithium secondary batteries will be described with reference to the drawings. FIG. 1 is a flow diagram showing an outline of the manufacturing process of a positive electrode material for lithium secondary batteries. As shown in FIG. 1, the manufacturing process of the positive electrode material for lithium secondary batteries comprises a crystallization step S101, a separation step S102, a baking step S103, and a water washing step S104. Specifically, in the crystallization step S101, an aqueous sodium hydroxide solution is added to a mixed aqueous solution of metal sulfates made of raw materials such as nickel, cobalt, and aluminum to coprecipitate these metal hydroxides to form a metal. This is a step of obtaining a slurry containing hydroxide. Further, the separation step S102 is a step of separating the metal composite hydroxide from the obtained slurry containing the metal hydroxide by solid-liquid separation or the like. Further, the firing step S103 is a step of mixing the obtained metal composite hydroxide and lithium hydroxide and firing the mixture at a predetermined temperature to obtain a lithium metal composite oxide. The water washing step S104 is a step of washing the obtained lithium metal composite oxide with water.

In the water washing step S104 in the manufacturing process of the positive electrode material for lithium secondary batteries, manufacturing process waste water containing a high concentration of lithium ions and a small amount of calcium ions is discharged. The concentration of wastewater from the manufacturing process is, for example, 1 to 5 g/L for lithium ions and 1 to 10 mg/L for calcium ions. Lithium is an alkali metal and, like sodium and potassium, has no water pollution regulations. In the wastewater treatment process of factories, usually only metals regulated by the Water Pollution Law and ordinances are treated and removed, so lithium in wastewater from the manufacturing process is not removed in the wastewater treatment process and is discharged into public waters. Lithium is a metal contained in seawater, and there is no environmental problem even if it is discharged into public water areas. However, lithium is a valuable metal, and from the viewpoint of resource saving, it is not preferable to discharge such manufacturing process wastewater into public water areas. In the recycling of resources, it is required to collect and effectively utilize lithium discharged in the manufacturing process without discarding it.

Methods for recovering lithium from manufacturing process wastewater include a solvent extraction method (for example, Patent Document 1), a method using electrodialysis using an ion exchange membrane (for example, Patent Document 2), and a recovery method using an ion exchange resin. .

However, when using the solvent extraction method, it is necessary to treat organic matter in the wastewater, safety measures are required because it is a facility that handles dangerous substances under the Fire Service Law, and multi-stage extraction is required. Therefore, the problem is that the process is long and the cost is high. Further, the method using electrodialysis using an ion exchange membrane requires a large-scale electrodialysis apparatus for wastewater treatment, which is disadvantageous in terms of cost and operation.

Compared to these recovery methods, the recovery method using an ion-exchange resin is considered to be a cheap and simple method.

However, since lithium has low selectivity for ion exchange resins, there is a problem that impurity elements with higher selectivity than lithium, such as calcium, are concentrated.

In addition, when lithium carbonate recycled as a raw material for positive electrode materials for lithium secondary batteries is crystallized, there is a problem that many impurities derived from the acid used in the eluent and salts contained remain in the lithium carbonate.

Mineral acids, which are easy to use industrially, are used as the eluent, but the disadvantage is that, for example, aqueous solutions containing hydrochloric acid and chlorides are highly corrosive to stainless steel, which is a material often used industrially. However, aqueous solutions containing nitric acid or nitrates have the disadvantage of reacting with the ion-exchange resin, which is an organic matter, and causing deterioration. In addition, since nitrate nitrogen is subject to strict wastewater regulations, it has the disadvantage of requiring high costs for wastewater treatment. For this reason, an aqueous solution containing sulfuric acid or a sulfate is easy to use as an eluent, but when lithium carbonate is recovered by crystallization, the grade of sulfur derived from sulfuric acid increases. Further, when an aqueous solution of sodium sulfate is used as an eluent, there is a problem that the grade of sodium as well as sulfur is increased.

In response to this problem, in Patent Document 3, as a method for purifying lithium carbonate, an aqueous solution containing lithium hydrogen carbonate obtained by reacting crude lithium carbonate and carbon dioxide is microfiltered, and then the lithium hydrogen carbonate is contained. The aqueous solution is heat-treated to deposit lithium carbonate and reduce the grades of sulfur and sodium. However, when calcium is contained in the raw material, lithium carbonate, a chelating agent must be used in order to lower the grade of calcium, which causes the problem of increased lithium recovery costs.

Under these circumstances, a method for obtaining lithium carbonate with a low impurity grade has been desired in order to use lithium carbonate recycled from manufacturing process waste water containing lithium ions as a raw material for manufacturing positive electrode materials for lithium secondary batteries.

In view of such circumstances, as a result of extensive studies, the inventors have found that lithium can be recovered from manufacturing process wastewater by utilizing ion exchange by adsorption and elution to ion exchange resins.

Then, by blowing carbon dioxide into the lithium carbonate crystallized from the post-elution liquid and dissolving it as lithium hydrogen carbonate, the poorly soluble impurities remaining in the post-elution liquid are separated, and then the solution is heated to improve the quality of the impurities. The present inventors have found that purified lithium carbonate with a low volatility can be precipitated, and have completed the present invention.

Hereinafter, a method for purifying lithium according to an embodiment of the present invention will be described in detail.

[2. Refining method of lithium]
A method for purifying lithium according to an embodiment of the present invention is for purifying lithium from waste water from the manufacturing process of positive electrode materials for lithium secondary batteries, and comprises an ion exchange step, an elution step, a crystallization step, and a hydrogen carbonate step. , and a recrystallization step. An overview of the method for purifying lithium and each step will be described below.

[2-1. Overview of Lithium Refining Method]
First, an overview of the method for refining lithium will be described with reference to the drawings. FIG. 2 is a flow chart for explaining the method for purifying lithium according to one embodiment of the present invention. As shown in FIG. 2, the method for purifying lithium according to one embodiment of the present invention includes an ion exchange step S1, an elution step S2, a crystallization step S3, a hydrogencarbonation step S4, and a recrystallization step S5. be.

[2-2. Ion exchange process]
The ion-exchange step S1 is a step in which the manufacturing process wastewater containing lithium ions is brought into contact with an ion-exchange resin for ion-exchange treatment, and the ion-exchange resin adsorbs the lithium ions. The ion exchange resin is not particularly limited as long as it is a cation exchange resin, and for example, those having a sulfonic acid group or those having a carboxylic acid group can be used. The form of the functional group may be either Na-type or H-type. In the case of Na-type, an aqueous solution containing sodium sulfate is used for elution of lithium in the elution step S2, and in the case of H-type, the elution step S2 Sulfuric acid will be used to elute lithium.

Adsorption of lithium is carried out by bringing the ion exchange resin into contact with waste water from the production process of positive electrode materials for lithium secondary batteries. The contact method may be batch mixing or a column method, and is not particularly limited. However, when the scale is large, the column method is more convenient. The ion exchange method is often used in wastewater treatment, etc., but when the concentration of the metal to be removed is high, after rough separation of the metal by sedimentation separation, etc., precise separation is performed to reduce the concentration of the remaining metal to below the regulation value. It is generally used as a law. In this way, when trying to adsorb a metal present at a low concentration, if the functional group is Na type, the metal with higher selectivity than sodium preferentially adsorbs, so lithium with lower selectivity than sodium adsorbs. hard to do. However, when a liquid having a high lithium concentration is passed through, lithium, which has a lower selectivity than sodium, is adsorbed.

This is the same principle as the exchange reaction by passing a solution containing a high-concentration acid or sodium salt during elution or regeneration. It is desirable that the concentration of lithium in the wastewater from the production process to be passed is 0.3 g/L or more, preferably 0.5 g/L or more. In the case of the H-type, since lithium has higher selectivity than hydrogen, the concentration of lithium is not particularly important.

In addition, as described above, there is also the problem that calcium, which has a higher selectivity than lithium, is concentrated. However, after connecting the ion exchange resins in series to concentrate calcium in the ion exchange resin in the former stage and adsorbing lithium to the ion exchange resin in the latter stage, lithium is eluted only from the ion exchange resin in the latter stage. The grade of calcium in the lithium carbonate obtained in the crystallization step can be lowered.

[2-3. Elution process]
The elution step S2 is a step of contacting an eluent with the cation exchange resin used in the ion exchange step S1 to elute lithium ions adsorbed on the cation exchange resin and separate lithium. In order to elute lithium, high-concentration sulfuric acid can be used for H-type lithium, and high-concentration sodium sulfate aqueous solution can be used for Na-type lithium. A saline solution, hydrochloric acid, or the like can also be used, but when lithium is eluted using these aqueous solutions and recovered as lithium carbonate, chlorine remains at a high concentration. The collected lithium carbonate will be used again in the manufacturing process of the positive electrode material for secondary batteries. water is undesirable. Therefore, an aqueous sulfuric acid solution or an aqueous sodium sulfate solution is desirable. _{Furthermore , nickel , cobalt _ _ _} Sulfate is used as a raw material for manganese and manganese, and a waste liquid containing a large amount of sodium sulfate is generated during waste water treatment of manufacturing waste liquid, which can be utilized. In the case of the Na-type, since sodium has a higher selectivity than lithium, the concentration during elution is not particularly important. In the case of the H-type, hydrogen has a lower selectivity than lithium, so a high concentration of sulfuric acid is preferable. It is desirable to use the minimum necessary concentration because the risk of Elution is possible at a concentration of approximately 6.4% by weight or more.

[2-4. Crystallization process]
The crystallization step S3 is a step of adding a carbonate source to convert lithium sulfate in the post-elution solution into lithium carbonate to precipitate. Sodium carbonate is preferred as the carbonate source. In this way, since water-soluble sodium sulfate is generated in the crystallization step, it can be separated from lithium carbonate having low solubility, and the grade of impurities in lithium carbonate can be lowered. Also, the solubility of lithium carbonate is 13.3 g/L at 20°C, 8.5 g/L at 80°C, and 7.2 g/L at 100°C. For this reason, the higher the temperature during precipitation, the better. Generally, however, if the temperature is 80° C. or higher, there are disadvantages such as difficulty in operation from the viewpoint of heat resistance of the reaction vessel and peripheral equipment, and an increase in cost. Furthermore, at 90°C or higher, the boiling points are close to each other. From the slurry containing lithium carbonate obtained in the crystallization step S3, the crystallization mother liquor and lithium carbonate are subjected to solid-liquid separation using a filtering device such as a filter press. Lithium carbonate recovered by solid-liquid separation may be dried if necessary.

[2-5. Hydrocarbonation step]
In the hydrogencarbonation step S4, the lithium carbonate obtained in the crystallization step S3 is mixed with water to form a slurry, and carbon dioxide is blown into the slurry to convert it into highly soluble lithium hydrogencarbonate.

In the crystallization step S3, in addition to lithium carbonate, a poorly soluble sulfuric acid double salt that becomes an impurity such as (Na Li) _SO4 is produced, so the lithium carbonate obtained in this step has a sodium and sulfur concentration of several. Hundreds to thousands of ppm. In addition, calcium in the eluent forms sparingly soluble calcium carbonate in the crystallization step S3, increasing the calcium concentration.

In order to remove these poorly soluble impurities generated in the crystallization step S3, in the hydrogencarbonation step S4, only lithium carbonate is converted into easily soluble lithium hydrogencarbonate by the following reaction (Formula 1) and dissolved. .
Li ₂ CO ₃ + CO ₂ + H ₂ O → 2LiHCO ₃ (Formula 1)

In the hydrogencarbonation step S4, impurities remain in the form of solid matter as insoluble residues. Therefore, by subjecting the aqueous solution after hydrogencarbonation to solid-liquid separation, a high-purity lithium hydrogencarbonate aqueous solution can be obtained. At high temperatures, lithium bicarbonate decomposes into carbon dioxide and lithium carbonate. The temperature is desirably 50° C. or less. Further, the blowing of carbon dioxide can be carried out under pressure, but can also be carried out under normal pressure. From the viewpoint of equipment cost, it is preferable to carry out at normal pressure. In addition, when carbon dioxide is blown under pressure, the reaction between the calcium carbonate formed in the crystallization step S3 and carbon dioxide proceeds, and there is a possibility that the formed calcium hydrogen carbonate remains in the aqueous solution together with lithium hydrogen carbonate. be. Therefore, it is preferable to blow carbon dioxide under normal pressure.

[2-6. Recrystallization step]
The recrystallization step S5 is a step of heating the lithium hydrogencarbonate aqueous solution obtained in the hydrogencarbonation step S4 to convert it into lithium carbonate with low solubility by the following reaction (Formula 2). The lithium carbonate recovered in the crystallization step S3 is converted into purified lithium carbonate from which impurities are removed in the recrystallization step S5. As described above, lithium hydrogen carbonate decomposes into lithium carbonate and carbon dioxide when the temperature is high. The produced carbon dioxide is released from the lithium hydrogen carbonate aqueous solution. Here, the higher the temperature, the lower the solubility of lithium carbonate, so the higher the heating temperature, the better. In general, the temperature range of 60 to 80°C can be said to be an appropriate temperature range because the boiling point becomes close to that of 90°C or higher. Then, the heated lithium hydrogencarbonate aqueous solution is filtered, and the purified lithium carbonate and the residual liquid are subjected to solid-liquid separation. Purified lithium carbonate recovered by solid-liquid separation may be dried if necessary.
2LiHCO ₃ →Li ₂ CO ₃ + CO ₂ + H ₂ O (Formula 2)

Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.

<Example>
(3-1. Ion exchange step/elution step)
Four resin columns filled with 1 L of strongly acidic cation exchange resin (manufactured by Sumika Chemtech Co., Ltd.: Duolite CF20LF) were prepared.

(3-1-1. Ion exchange step)
Four columns were connected in series, and 100 L of waste water from the manufacturing process of positive electrode materials for lithium secondary batteries containing 2100 mg/L of lithium and 2 mg/L of calcium and having a pH of 12 was passed through the column.

(3-1-2. Elution step)
After the ion exchange, the columns connected in series were arranged in parallel, and 10 L of pure water was flowed through each column to wash the resin in the columns. Thereafter, 6 L of a 150 g/L sodium sulfate aqueous solution was passed through each column in parallel to elute lithium. Of the post-elution liquids, only the liquid with a high lithium concentration was collected separately, and 4 L of the liquid with a lithium concentration of about 10 g/L was collected.

(3-2. Crystallization step)
Of the liquid collected in the elution step, 2 L of the post-elution liquid was placed in a 3 L plastic beaker and heated to 80° C., 400 g of sodium carbonate was added, and the mixture was stirred and mixed for about 1 hour. The resulting slurry was suction-filtered using 5C filter paper (5 type C specified in JIS P 3801), washed with pure water, and then vacuum-dried. After vacuum drying, 253 g of lithium carbonate was recovered.

(3-3. Hydrocarbonation step)
150 g of the lithium carbonate recovered in the crystallization step and 3 L of pure water were placed in a 3 L plastic beaker and mixed with stirring to form a slurry. While stirring and mixing this slurry at 25° C., carbon dioxide was blown in at normal pressure to convert and dissolve lithium carbonate into lithium hydrogen carbonate. The obtained lithium hydrogencarbonate aqueous solution was subjected to suction filtration with a 5C filter paper to remove a trace amount of insoluble residue by filtration, thereby obtaining a clear liquid.

(3-4. Recrystallization step)
The clarified liquid obtained in the hydrogencarbonation step was placed in a 3 L plastic beaker, heated to 80° C., and stirred and mixed for about 1 hour to convert lithium hydrogencarbonate into lithium carbonate and precipitate. The resulting slurry was suction-filtered using 5C filter paper, washed with pure water, and vacuum-dried. Table 1 shows analytical values for obtaining 66 g of purified lithium carbonate after vacuum drying.

<Comparative example>
The procedure from the ion exchange step to the crystallization step was carried out in the same manner as in Example 1. No post-hydrocarbonation steps were performed.

Table 1 shows analytical values of lithium carbonate in Examples and Comparative Examples.

From the results in Table 1, it was found that the present invention can reduce impurities derived from the eluent. In particular, it was found that the impurity concentrations of sodium and sulfur were reduced, and the impurity concentration of calcium was reduced to less than 5 ppm.

Although the embodiments and examples of the present invention have been described in detail as described above, it should be understood by those skilled in the art that many modifications are possible without substantially departing from the novel matters and effects of the present invention. , will be easily understood. Accordingly, all such modifications are intended to be included within the scope of the present invention.

For example, a term described at least once in the specification or drawings together with a different, broader or synonymous term can be replaced with the different term anywhere in the specification or drawings. Also, the configuration and operation of the method for refining lithium are not limited to those described in the embodiments and examples of the present invention, and various modifications are possible.

S1 ion exchange step, S2 elution step, S3 crystallization step, S4 hydrogen carbonate step, S5 recrystallization step, S101 crystallization step, S102 separation step, S103 firing step, S104 water washing step

Claims (8)

A lithium purification method for purifying lithium from lithium-containing manufacturing process wastewater of a positive electrode material for a lithium secondary battery, comprising:
An ion exchange step of contacting the manufacturing process waste water with an ion exchange resin;
an elution step of contacting an eluent with the ion exchange resin after the ion exchange step;
a crystallization step of adding a carbonate source to the post-elution solution after the elution step;
a hydrogencarbonation step of introducing carbon dioxide into the lithium carbonate after the crystallization step;
and a recrystallization step of heating the lithium hydrogencarbonate after the hydrogencarbonation step. 2. The method for purifying lithium according to claim 1, wherein the functional group of said ion exchange resin is Na type, and said eluent is an aqueous solution containing sodium sulfate. 2. The method for purifying lithium according to claim 1, wherein the ion exchange resin has an H-type functional group, and the eluent is sulfuric acid. 3. The method for purifying lithium according to claim 2, wherein the concentration of lithium in the waste water from the manufacturing process is 0.3 g/L or more. 5. The method for purifying lithium according to claim 1, wherein the carbonate source is sodium carbonate. 6. The method for purifying lithium according to any one of claims 1 to 5, wherein the manufacturing process waste water contains calcium. 7. The method for purifying lithium according to any one of claims 1 to 6, wherein the purified lithium carbonate after the recrystallization step has a calcium concentration of less than 5 ppm. 8. The method for purifying lithium according to any one of claims 1 to 7, wherein said introduction of said carbon dioxide in said hydrogencarbonation step is performed at normal pressure.

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