Method for dissolving lithium compound, method for manufacturing lithium carbonate, and method for recovering lithium from lithium ion secondary cell scrap

Abstract

A method for dissolving a lithium compound according to the present invention includes bringing a lithium compound into contact with water or an acidic solution, and feeding, separately from the lithium compound, a carbonate ion to the water or the acidic solution to produce carbonic acid, and allowing the carbonic acid to react with the lithium compound to produce lithium hydrogen carbonate.

Claims

1. A method for recovering lithium from lithium ion secondary cell scrap, the method comprising: a calcination step of calcining the lithium ion secondary cell scrap; and a lithium dissolving step of bringing cell powder obtained after the calcination step into contact with water or an acidic solution and feeding, separately from the cell powder, a carbonate ion to the water or the acidic solution to dissolve lithium in the cell powder, wherein the cell powder contains cobalt and aluminum, wherein a pH of a lithium dissolved solution obtained in the lithium dissolving step is from 7 to 10, and wherein the cell powder comprises at least one selected from the group consisting of lithium hydroxide, lithium oxide and lithium carbonate.

2. The method for recovering lithium from lithium ion secondary cell scrap according to claim 1, wherein in the lithium dissolving step, the carbonate ion is fed so as to maintain a saturated state of carbonic acid in the water or the acidic solution.

3. The method for recovering lithium from lithium ion secondary cell scrap according to claim 1, wherein the feeding of the carbonate ion in the lithium dissolving step is carried out by blowing a carbon dioxide gas into the water or the acidic solution.

4. The method for recovering lithium from lithium ion secondary battery scrap according to claim 1, further comprising a lithium precipitating step of separating lithium from the lithium dissolved solution obtained in the lithium dissolving step, and precipitating a lithium ion in the lithium dissolved solution as lithium carbonate.

5. The method for recovering lithium from lithium ion secondary battery scrap according to claim 4, wherein in the lithium precipitating step, the lithium dissolved solution is heated to separate carbonic acid as a carbon dioxide gas from the lithium dissolved solution.

6. The method for recovering lithium from lithium ion secondary battery scrap according to claim 5, wherein in the lithium precipitating step, the lithium dissolved solution is heated at a temperature of from 50° C. to 90° C.

7. The method for recovering lithium from lithium ion secondary battery scrap according to claim 1, wherein in the lithium dissolving step, the water or the acidic solution has a temperature of from 5° C. to 25° C.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a flowchart showing a method for dissolving a lithium compound according to an embodiment of the present invention.

(2) FIG. 2 is a flowchart showing a method for recovering lithium from lithium ion secondary cell scrap according to an embodiment of the present invention.

(3) FIG. 3 is a graph showing a lithium concentration in a solution at each predetermined temperature in Example 1.

(4) FIG. 4 is a graph showing a result of XRD for residues in Example 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) Hereinafter, embodiments of the present invention will be described in detail.

(6) <Method of Dissolving Lithium Compound>

(7) A method for dissolving a lithium compound according to an embodiment according to the present invention includes bringing a lithium compound into contact with water or an acidic solution, and feeding, separately from the lithium compound, a carbonate ion to the water or the acidic solution to generate carbonic acid, and allowing the lithium compound to react with the carbonic acid to produce lithium hydrogen carbonate.

(8) (Lithium Compound)

(9) In the present invention, various solid lithium compounds can be used. For example, typical examples of the lithium compound include lithium carbonate or other lithium compounds obtained when recovering valuable metals from lithium ion secondary cell scrap.

(10) When the valuable metals from the lithium ion secondary cell scrap, the lithium ion secondary cell scrap is calcined to remove a harmful electrolyte, crushing and sieving are then carried out in this order, and cell powder obtained under a sieve of the sieving is then added to a leaching solution to leach it, and lithium, nickel, cobalt, manganese, iron, copper, aluminum, and the like that may be contained in the solution are dissolved in the solution. Subsequently, among the respective metal elements dissolved in the leached solution, valuable metals such as cobalt, manganese and nickel are recovered. More particularly, the leached solution is subjected to solvent extraction or neutralization at a plurality of stages depending on the metals to be separated, and further, each solution obtained at each stage is subjected to stripping, electrolysis, carbonation or other treatments. As a result, a lithium-containing solution containing a lithium ion is obtained. The lithium-containing solution thus obtained is subjected to carbonation by adding a carbonate salt, blowing a carbon dioxide gas, or the like, to obtain crude lithium carbonate which is lithium carbonate having a relatively low lithium quality. A lithium compound including the crude lithium carbonate can be used.

(11) In addition, the cell powder may contain at least one of lithium carbonate, lithium hydroxide, and lithium oxide. Since lithium is dissolved from such cell powder, lithium compounds in such cell powder can be used.

(12) The use of the lithium compounds as described above lead to recycling of metals contained in the lithium ion secondary cell scrap used in mobile phones or various other electronic devices and discarded due to the life of the cell products, manufacturing defect, or other reasons, which is preferable in terms of effective utilization of resources.

(13) (Dissolution of Lithium Compound)

(14) To dissolve the lithium compound as described above, the lithium compound is brought into contact with water or an acidic solution, and a carbonate ion is fed to the water or the acidic solution, separately from the lithium compound, to generate carbonic acid, and the lithium compound is allowed to react with the carbonic acid to produce lithium hydrogen carbonate.

(15) For example, when the lithium compound contains at least one selected from the group consisting of lithium hydroxide, lithium oxide and lithium carbonate, the lithium compound is added to water or an acidic solution together with the feeding of the carbonate ion by blowing a carbon dioxide gas or adding a carbonate salt, whereby, for lithium carbonate, the carbonic acid would be firstly generated by the reaction: H.sub.2O+CO.sub.2.fwdarw.H.sub.2CO.sub.3, and lithium hydrogen carbonate would be then generated under the assumed reaction formula: Li.sub.2CO.sub.3+H.sub.2CO.sub.3.fwdarw.2LiHoCO.sub.3. This can facilitate dissolution of lithium carbonate in water or the acidic solution. Also, for lithium hydroxide and lithium oxide, it is presumed that lithium hydrogen carbonate is produced by the reaction: 2LiOH.fwdarw.Li.sub.2O+H.sub.2O and Li.sub.2O+H.sub.2CO.sub.3+CO.sub.2.fwdarw.2LiHCO.sub.3, Li.sub.2O+CO.sub.2.fwdarw.Li.sub.2CO.sub.3 and Li.sub.2CO.sub.3+H.sub.2CO.sub.3.fwdarw.2LiHCO.sub.3. Therefore, these lithium hydroxide and lithium oxide can also be easily dissolved.

(16) Accordingly, to dissolve the lithium compound, it is important to feed the carbonate ion to water or the acidic solution in at least one period of time selected from before, during and after the addition of the lithium compound to the water or the acidic solution. Examples of the method for feeding the carbonate ion include blowing of a carbon dioxide gas into the water or the acidic solution, and adding of the carbonate salt or carbonated water (carbonate-containing solution). Among them, the blowing of the carbon dioxide gas is preferable because it can suppress contamination of impurities and suppress an increase in an amount of the solution, so that the concentration of lithium cannot be diluted. Specific examples of the carbonate salt when the carbonate salt is added include sodium carbonate and the like. In this case, an amount of the carbonate salt added can be, for example, from 1.0 to 2.0 fold molar equivalent, and preferably from 1.0 to 1.2 fold molar equivalent.

(17) From the viewpoint of effectively producing lithium hydrogen carbonate by the above reaction formula, it is preferable to feed the carbonate ion so as to maintain a saturated state of carbonic acid in the water or the acidic solution. This can facilitate generation of lithium hydrogen carbonate, so that an increased amount of lithium compound can be effectively dissolved.

(18) The water or acidic solution used herein can be tap water, industrial water, distilled water, purified water, ion-exchanged water, pure water, ultrapure water, or the like, or mixtures of them with sulfuric acid.

(19) In the case of an acidic solution to which an acid is added, an amount of the acid added is preferably adjusted such that a pH of the lithium hydrogen carbonate solution obtained by dissolving the lithium compound is from 7 to 10. If the pH of the lithium hydrogen carbonate solution is less than 7, metals such as cobalt that may be contained in the cell powder and the like may be dissolved together with the lithium compound, and if the pH is more than 10, aluminum that may be contained may be dissolved out. It should be noted that the acid may be added before, during and/or after dissolving the lithium.

(20) A method of bringing the lithium compound into contact with the water or the acidic solution includes various methods such as spraying, immersing, and dipping. From the viewpoint of reaction efficiency, a method of immersing the lithium compound in water and stirring it is preferred.

(21) A solution temperature at the time of bringing the lithium compound into contact with the water or the acidic solution is preferably 5° C. to 25° C. The solution temperature of the water or acidic solution at the time of contact of a relatively low temperature of that level can lead to more effective generation of lithium hydrogen carbonate having higher solubility as the temperature is lower, in the solution. It is preferable to dissolve the lithium compound such that a lithium concentration in the water or the acidic solution is as close as possible to the solubility of lithium hydrogen carbonate at the predetermined solution temperature.

(22) Here, a pulp concentration can be from 50 g/L to 500 g/L. The pulp concentration means a ratio of dry weight (g) of the lithium compound to an amount (L) of the water or acidic solution to be contacted with the lithium compound.

(23) Due to dissolution of the lithium compound, a dissolution rate of lithium in the water or the acidic solution is preferably from 30% to 70%, or more preferably from 45% to 75%. The lithium hydrogen carbonate solution preferably has a lithium concentration of from 7.0 g/L to 10.0 g/L, and more preferably 8.0 g/L to 9.0 g/L. The lithium hydrogen carbonate solution may contain from 0 mg/L to 1000 mg/L of sodium and from 0 mg/L to 500 mg/L of aluminum.

(24) When the cell powder containing the lithium compound is brought into contact with the water or the acidic solution, residues of the cell powder, which remain without being dissolved in the water or the acidic solution, are removed by solid-liquid separation, and the residues are then subjected to acid leaching, solvent extraction, electrolytic extraction, and other treatments to recover various metals contained therein. Herein, detailed descriptions of the residues are omitted.

(25) (Production of Lithium Carbonate)

(26) After dissolution of the lithium compound as described above, a lithium precipitating step can be carried out by separating carbonic acid from the resulting lithium hydrogen carbonate solution and precipitating a lithium ion in the lithium hydrogen carbonate solution as lithium carbonate.

(27) Here, the lithium hydrogen carbonate solution can be preferably heated at a temperature of from 50° C. to 90° C. to concentrate it, and carbonic acid can be separated as a carbon dioxide gas from the lithium hydrogen carbonate solution. Based on the novel finding that the solubility of lithium hydrogen carbonate is decreased with an increase in the temperature, in the lithium precipitating step, lithium that has been sufficiently dissolved in the lithium hydrogen carbonate solution due to the generation of lithium hydrogen carbonate can be effectively precipitated as lithium carbonate by heating.

(28) If the heating temperature of the lithium hydrogen carbonate solution is lower than 50° C., there is a concern that carbonic acid may not be effectively separated. Therefore, the heating temperature is preferably 50° C. or higher. On the other hand, if the heating temperature is higher than 90° C., a problem may be caused due to boiling. Therefore, the upper limit may be 90° C. From this viewpoint, the heating temperature of the lithium hydrogen carbonate solution is more preferably from 70° C. to 80° C.

(29) Alternatively, it is also possible to add methanol, ethanol, or the like to the lithium hydrogen carbonate solution and carry out separation of carbonic acid using such a non-aqueous solvent. Among them, methanol and ethanol are preferably used as non-aqueous solvents because they are inexpensive. Here, specific examples of the addition method include mixing the non-aqueous solvent with the lithium hydrogen carbonate solution with stirring.

(30) (Purification of Lithium Carbonate)

(31) If a lithium quality of lithium carbonate thus obtained is lower than a target quality, the lithium carbonate can be optionally purified to obtain lithium carbonate having higher quality. As used herein, the target lithium quality of lithium carbonate can be, for example, 16% or more, preferably 17% or more. However, this lithium purification step is not necessarily required.

(32) More particularly, the purification of lithium carbonate is carried out by subjecting lithium carbonate obtained by separation of carbonic acid from the lithium hydrogen carbonate solution to repulp washing, and blowing a carbon dioxide gas into the solution to dissolve carbonic acid in the solution, and then separating calcium, magnesium, and the like from the lithium hydrogen carbonate solution by solid-liquid separation. Subsequently, deacidification and concentration are carried out and the purified lithium carbonate is separated from a filtrate by solid-liquid separation. When the impurity quality in the purified lithium carbonate is higher, it can be further washed.

(33) <Method of Recovering Lithium from Lithium Ion Secondary Cell Scrap>

(34) The method for recovering lithium from lithium ion secondary cell scrap according to an embodiment of the present invention includes at least a calcination step of calcining the lithium ion secondary cell scrap, and a lithium dissolving step of bringing cell powder obtained after the calcination step into contact with water or an acidic solution and feeding, separately from the cell powder, a carbonate ion to the water or the acidic solution to dissolve lithium in the cell powder.

(35) (Lithium Ion Secondary Cell Scrap)

(36) Lithium ion secondary cell scrap targeted by this invention is lithium ion secondary cells that can be used in mobile phones and other various electronic devices and have been discarded due to expired cell product life, production defects or other reasons. It is preferable to recover lithium from such lithium ion secondary cell scrap in terms of effective utilization of resources.

(37) Here, this invention is directed to lithium ion secondary cell scrap containing at least lithium. In an embodiment of this invention, the lithium ion secondary cell scrap generally contains from 0.1% to 10% by mass of lithium.

(38) In general, the lithium ion secondary cell scrap has a housing containing aluminum as an exterior that wraps around the lithium ion secondary cell scrap. Examples of the housing include those made only of aluminum and those containing aluminum, iron, aluminum laminate, and the like.

(39) The lithium ion secondary cell scrap may also contain, in the above housing, positive electrode active materials composed of one or more single metal oxides or two or more composite metal oxides or the like, of lithium, nickel, cobalt and manganese, and aluminum foils (positive electrode substrate) to which the positive electrode active materials are applied and fixed by, for example, polyvinylidene fluoride (PVDF) or other organic binder. In addition, the lithium ion secondary cell scrap may contain copper, iron, or the like.

(40) Further, the lithium ion secondary cell scrap generally contains electrolytic solutions in the housing. For example, ethylene carbonate, diethyl carbonate or the like may be used as the electrolytic solution.

(41) (Calcination Step)

(42) In the calcination step, the lithium ion secondary cell scrap is heated. The calcination step is generally carried out for the purposes of increasing a temperature of the lithium ion secondary cell scrap by heating, removing the internal electrolytic solutions to renders them harmless, and also decomposing the binder that binds the aluminum foils to the positive electrode active materials to facilitate separation of the aluminum foils from the positive electrode active materials during crushing and sieving and increase a recovery rate of the positive electrode active materials recovered under the sieve, and further changing a metal such as lithium and cobalt contained in the lithium ion secondary cell scrap to a form of the metal which can be easily dissolved.

(43) Through the calcination step, lithium in the lithium ion secondary cell scrap will be in the form of lithium oxide, lithium carbonate, lithium hydroxide or the like, and lithium in this form is easily dissolved in the water or the acidic solution. On the other hand, metals such as cobalt are difficult to be dissolved in the water.

(44) By utilizing such a difference of solubility in the water or the acidic solution of the metals contained in the lithium ion secondary cell scrap after the calcination step to carried out a lithium dissolving step as described below, only lithium in the lithium ion secondary cell scrap can be selectively removed to recover lithium at an early stage in processing of the lithium ion secondary cell scrap. As a result, it is possible to prevent substances contained in various reagents that can be used in the processing of lithium ion secondary cell scrap from being mixed into lithium carbonate obtained in the lithium dissolving step, whereby high-quality lithium carbonate is produced.

(45) From such a viewpoint, in the calcination step, the lithium ion secondary cell scrap is preferably heated by maintaining it in a temperature range of from 550° C. to 650° C. for 1 hour to 4 hours. If the heating temperature is too low or the heating time is too short, the change of lithium to a form that is easily dissolved in the water or the acidic solution would be insufficient, and there is a concern that a large amount of lithium cannot be dissolved in the lithium dissolution step. On the other hand, if the heating temperature is too high or the heating time is too long, aluminum deteriorates to become powdered during crushing, and there is a risk that a large number of aluminum will be mixed in the sieved product. In addition, the above temperature is measurable by measuring a surface temperature of the housing of the lithium ion secondary cell scrap.

(46) The calcination step can be carried out by using various heating equipment such as a rotary kiln furnace or other various furnaces, and a furnace for heating in an air atmosphere, as long as the temperature of the lithium ion secondary cell scrap can be controlled as described above.

(47) (Crushing Step)

(48) In this embodiment, after heating the lithium ion secondary cell scrap in the calcination step, a crushing step is carried out by removing positive electrode materials and negative electrode materials from the housing.

(49) In other embodiments, the lithium ion secondary cell scrap after the calcination step can be subjected to a lithium dissolving step as described below. In this case, residues that remain without being dissolved in the lithium dissolving step can be subjected to the crushing step and a subsequent sieving step.

(50) The crushing step is carried out to selectively separate the positive electrode active materials from the aluminum foils to which the positive electrode active materials are applied, while destroying the housing of the lithium ion secondary cell scrap. Various known apparatuses or devices can be used herein. In particular, it is preferable to use an impact-type crusher that can crush lithium ion secondary cell scrap by applying an impact while cutting. Examples of the impact-type crusher include a sample mill, a hammer mill, a pin mill, a wing mill, a tornado mill, and a hammer crusher. It should be noted that a screen can be installed at an exit of the crusher, whereby the lithium ion secondary cell scrap is discharged from the crusher through the screen when crushed to a size that can pass through the screen.

(51) (Sieving Step)

(52) In this embodiment, after crushing the lithium ion secondary cell scrap in the crushing step, the lithium ion secondary cell scrap is sieved using a sieve having an appropriate opening, for example, for the purpose of removing aluminum powder. Thus, for example, aluminum or copper remains on the sieve, and powdered lithium ion secondary cell scrap from which aluminum or copper has been removed to some extent can be obtained under the sieve.

(53) However, in other embodiments, after the crushing step, the lithium dissolving step as described later can be carried out by dissolving lithium in the lithium ion secondary cell scrap, and in this case, residues remaining without being dissolved in the lithium dissolution step can be subjected to the sieving step.

(54) (Lithium Dissolving Step)

(55) After the calcination step, after the crushing step or after the sieving step, the resulting cell powder is brought into contact with the water or the acidic solution in the lithium dissolving step and a carbonate ion is fed to the water or the acidic solution to dissolve lithium contained in the cell powder in the water. This can provide a lithium dissolved solution containing lithium ions.

(56) In view of handling, the lithium dissolving step is preferably carried out after all of the calcination step, the crushing step, and the sieving step. For example, when the lithium dissolving step is carried out before the crushing step or before the sieving step, it is necessary to dry residues after lithium dissolution.

(57) Here, since the cell powder obtained through the calcination step generally contains at least one selected from the group consisting of lithium hydroxide, lithium oxide and lithium carbonate, the lithium compound is added to water or an acidic solution together with the feeding of a carbonate ion by blowing a carbon dioxide gas or adding a carbonate salt, whereby, for lithium carbonate, the carbonic acid would be firstly generated by the reaction: H.sub.2O+CO.sub.2.fwdarw.H.sub.2CO.sub.3, and lithium hydrogen carbonate would be then generated under the assumed reaction formula: Li.sub.2CO.sub.3+H.sub.2CO.sub.3.fwdarw.2LiHoCO.sub.3. This facilitates dissolution of lithium carbonate in the water or the acidic solution. Also, for lithium hydroxide and lithium oxide, it is presumed that lithium hydrogen carbonate is produced by the reaction: 2LiOH.fwdarw.Li.sub.2O+H.sub.2O and Li.sub.2O+H.sub.2CO.sub.3+CO.sub.2.fwdarw.2LiHCO.sub.3, Li.sub.2O+CO.sub.2.fwdarw.Li.sub.2CO.sub.3 and Li.sub.2CO.sub.3+H.sub.2CO.sub.3.fwdarw.2LiHCO.sub.3. Therefore, these lithium compounds can also be easily dissolved.

(58) Accordingly, in the lithium dissolving step, it is important to feed the carbonate ion to the water or the acidic solution in at least one period of time selected from before, during and after the addition of the lithium compound to the water or the acidic solution. Examples of the method for feeding the carbonate ion include blowing of a carbon dioxide gas into the water or the acidic solution, and adding of the carbonate salt or carbonated water (carbonate-containing solution). Among them, the blowing of the carbon dioxide gas is preferable because it can suppress the contamination of impurities and suppress an increase in an amount of the solution, so that the concentration of lithium cannot be diluted. Specific examples of the carbonate salt when the carbonate salt is added include sodium carbonate and the like. In this case, an amount of the carbonate added can be, for example, from 1.0 to 2.0 fold molar equivalent, and preferably from 1.0 to 1.2 fold molar equivalent.

(59) From the viewpoint of effectively producing lithium hydrogen carbonate by the above reaction formula, it is preferable to feed the carbonate ion so as to maintain a saturated state of carbonic acid in the water or the acidic solution. This can facilitate generation of lithium hydrogen carbonate, so that an increased amount of lithium compound can be effectively dissolved.

(60) The water or acidic solution used herein can be tap water, industrial water, distilled water, purified water, ion-exchanged water, pure water, ultrapure water, or the like, or mixtures of them with sulfuric acid.

(61) In the case of an acidic solution to which an acid is added, an amount of the acid added is preferably adjusted such that a pH of the lithium dissolved solution finally obtained in the lithium dissolving step is from 7 to 10. If the pH of the lithium dissolved solution is less than 7, metals such as cobalt may be dissolved out, and if the pH is more than 10, aluminum may be dissolved out. It should be noted that the acid may be added before, during and/or after dissolving the lithium.

(62) A method of bringing the cell powder into contact with the water or the acidic solution includes various methods such as spraying, immersing, and dipping. From the viewpoint of reaction efficiency, it is preferable that the cell powder is immersed in water with stirring.

(63) A solution temperature at the time of bringing the cell powder into contact with the water or the acidic solution is preferably 5° C. to 25° C. The solution temperature of the water or acidic solution at the time of contact of a relatively low temperature of that level can lead to more effective generation of lithium hydrogen carbonate having higher solubility as the temperature is lower, in the solution. It is preferable to leach lithium in the cell powder such that a lithium concentration in the water or the acidic solution is as close as possible to the solubility of lithium hydrogen carbonate at the predetermined solution temperature.

(64) Here, a pulp concentration can be 50 g/L to 500 g/L. The pulp concentration means a ratio of dry weight (g) of the cell powder to an amount (L) of the water or the acidic solution to be contacted with the cell powder.

(65) In the lithium dissolving step, a dissolution rate of lithium in the water or the acidic solution is preferably from 30% to 70%, or more preferably from 45% to 55%.

(66) The lithium dissolved solution preferably has a lithium concentration of from 7.0 g/L to 10.0 g/L, and more preferably 8.0 g/L to 9.0 g/L. The lithium dissolved solution may contain from 0 mg/L to 1000 mg/L of sodium and from 0 mg/L to 500 mg/L of aluminum.

(67) Residues of the cell powder, which remain without being dissolved in the water or the acidic solution, are removed by solid-liquid separation, and they can be then subjected to acid leaching, solvent extraction, electrolytic extraction or other treatments using known methods to recover various metals contained therein. Here, detailed descriptions of the residues are omitted.

(68) (Lithium Precipitating Step)

(69) After the lithium dissolving step as described above, a lithium precipitating step can be carried out by separating carbonic acid from the resulting lithium dissolved solution and precipitating a lithium ion in the lithium dissolved solution as lithium carbonate.

(70) Here, the lithium dissolved solution can be preferably heated at a temperature of from 50° C. to 90° C. to concentrate it, and carbonic acid can be separated as a carbon dioxide gas from the lithium dissolved solution. Based on the novel finding that the solubility of lithium hydrogen carbonate is decreased with an increase in the temperature, in the lithium precipitating step, lithium that has been sufficiently dissolved in the lithium dissolved solution due to the generation of lithium hydrogen carbonate can be effectively precipitated as lithium carbonate by heating.

(71) If the heating temperature of the lithium dissolved solution is lower than 50° C., there is a concern that carbonic acid may not be effectively separated. Therefore, the heating temperature is preferably 50° C. or higher. On the other hand, if the heating temperature is more than 90° C., a problem may be caused due to boiling. Therefore, the upper limit may be 90° C. From this viewpoint, the heating temperature of the lithium dissolved solution is more preferably from 70° C. to 80° C.

(72) Alternatively, it is also possible to add methanol, ethanol, or the like to the lithium dissolved solution and carry out separation of carbonic acid using such a non-aqueous solvent. Among them, methanol and ethanol are preferably used as non-aqueous solvents because they are inexpensive. Here, specific examples of the addition method include mixing the non-aqueous solvent with the lithium dissolved solution with stirring.

(73) (Purification of Lithium Carbonate)

(74) If a lithium quality of lithium carbonate thus obtained is lower than a target quality, the lithium carbonate can be optionally purified to obtain lithium carbonate having higher quality. As used herein, the target lithium quality of lithium carbonate can be, for example, 16% or more, preferably 17% or more. However, this lithium purification step is not necessarily required.

(75) More particularly, the purification of lithium carbonate is carried out by subjecting lithium carbonate obtained by separation of carbonic acid from the lithium dissolved solution to repulp washing, and blowing a carbon dioxide gas into the solution to dissolve carbonic acid in the solution, and then separating calcium, magnesium, and the like from the lithium hydrogen carbonate solution by solid-liquid separation. Subsequently, deacidification and concentration are carried out and the purified lithium carbonate is separated from a filtrate by solid-liquid separation. When the impurity quality in the purified lithium carbonate is higher, it can be further washed.

EXAMPLES

(76) Next, the present invention was experimentally carried out and the effects thereof were confirmed, as described below. However, the descriptions herein are merely for illustrative and are not intended to be limited.

Example 1: Method for Dissolving Lithium Compound

Test Example 1

(77) Reagent grade lithium carbonate having a dry mass of 30 g was added to 300 mL of pure water to form a slurry. The slurry was heated at each of temperatures of 20° C., 30° C., 40° C., 50° C., 60° C., 70° C., and 80° C. Once each temperature was reached, a large excess of carbon dioxide gas was blown for the assumed reaction formula: Li.sub.2CO.sub.3+H.sub.2CO.sub.3.fwdarw.2LiHoCO.sub.3. After blowing the carbon dioxide gas, the slurry was subjected to solid-liquid separation, and an amount of a filtrate and a lithium concentration in the solution were measured. Results are shown in Table 1 and FIG. 2. Further, the same test was conducted with the exception that no carbon dioxide gas was blown, and a lithium concentration was measured. Results are also plotted in FIG. 2 as “Li Carbonate”. Here, the lithium concentration was measured by performing quantitative analysis for the filtrate by means of high frequency inductively coupled plasma atomic emission spectroscopy (ICP-AES).

(78) TABLE-US-00001 TABLE 1 Temperature Solubility of Li Hydrogen Carbonate (° C.) (g/100 g-H2O) 20 9.1 30 8.3 40 7.4 50 7.7 60 6.9 70 6.2 80 5.9

(79) A filtrate having a lithium concentration of 7.0 g/L obtained at 40° C. was heated at 60° C. for 2 hours with stirring to separate carbonic acid. Solid-liquid separation was then carried out, and an amount of the solution was measured. As a result, there was substantially no decrease in the amount of the solution due to volatilization, and the reduced amount of the solution was of only water adhering to the generated precipitate. A concentration of lithium in the filtrate after the separation of carbonic acid was 5.0 g/L, and an amount of lithium decreased from the solution before and after the separation of carbonic acid was 0.65 g. The precipitate was dried and then identified by X-ray diffraction (XRD), revealing that it was lithium carbonate, and the amount of lithium was 0.48 g.

Test Example 2

(80) When dissolving 30 g of lithium carbonate in pure water as in Test Example 1, a plurality of tests where the temperature of pure water was changed were conducted for each of cases where a carbon dioxide gas was fed and the carbon dioxide gas was not fed. Table 2 shows the results. The dissolution rate as shown in Table 2 means a dissolution rate of lithium in pure water, and it was calculated from the residue weight after leaching.

(81) TABLE-US-00002 TABLE 2 Temperature Dissolution Rate (%) (° C.) CO2 Present CO2 Absent 20 47.9 13.0 30 43.7 13.0 40 38.6 12.0 50 38.5 11.0 60 33.0 10.0 70 27.9 9.0 80 24.9 8.0

(82) As can be seen from the results shown in Table 2, it is found that the feeding of the carbon dioxide gas significantly increases the dissolution rate of lithium, and this tendency is particularly remarkable when the solution temperature is lower.

(83) As described above, according to the present invention, it was found that lithium carbonate can be effectively dissolved and lithium carbonate having relatively high quality can be obtained. It was also found that the recovery rate of lithium can be further improved by decreasing the temperature as low as possible within the range where coagulation does not occur during the dissolution of carbonic acid, and by increasing the temperature as high as possible during the separation of carbonic acid.

Example 2: Method for Recovering Lithium from Lithium Ion Secondary Cell Scrap

Test Example 1

(84) Cell powder having a lithium quality of 4.1% by mass, obtained by calcining the lithium ion secondary cell scrap, was repulped with pure water such that a pulp concentration was 500 g/L. To the lithium in the cell powder was brown a carbon dioxide gas at one fold molar equivalent in the assumed reaction formula: Li.sub.2CO.sub.3+H.sub.2CO.sub.3.fwdarw.2LiHoCO.sub.3.

(85) A filtrate having a lithium concentration of 6.2 g/L was then obtained by solid-liquid separation. The filtrate was concentrated by heating at a two-fold volume ratio, and then subjected to solid-liquid separation. The lithium concentration on the solution side was 3.3 g/L. After drying the residue side, qualitative analysis was carried out by X-ray diffraction (XRD). The results are shown in FIG. 2. As shown in FIG. 2, it is found that most of substances contained in the residues are lithium carbonate.

Test Example 2

(86) When dissolving 30 g of lithium carbonate obtained in Test Example 1 in pure water, a plurality of tests where the temperature of pure water was changed were conducted for each of cases where a carbon dioxide gas was fed and the carbon dioxide gas was not fed. Table 3 shows the results. The dissolution rate as shown in Table 3 means a dissolution rate of lithium in pure water, and it was calculated from the residue weight after leaching.

(87) TABLE-US-00003 TABLE 3 Temperature Dissolution Rate (%) (° C.) CO2 Present CO2 Absent 20 47.9 13.0 30 43.7 13.0 40 38.6 12.0 50 38.5 11.0 60 33.0 10.0 70 27.9 9.0 80 24.9 8.0

(88) As can be seen from the results shown in Table 3, it is found that the feeding of the carbon dioxide gas significantly increases the dissolution rate of lithium, and this tendency is particularly remarkable when the solution temperature is lower.

(89) In view of the foregoing, it was found that according to the present invention, lithium can be effectively leached from the lithium ion secondary cell scrap and recovered by a relatively simple process.