JP5459656B2 - Method and apparatus for producing lithium salt - Google Patents

Description

  The present invention relates to a method for measuring a lithium ion concentration of a solution in which lithium is dissolved, and a method and an apparatus for producing a lithium salt using the method.

In general, most of the wastewater in which lithium is dissolved in a lithium battery manufacturing factory (or processing factory) is disposed of in the ocean or the like. Several thousand mg / L of lithium is dissolved in this waste water. On the other hand, as a raw material for producing a lithium salt, brine having a lithium ion concentration of about several tens to 1000 mg / L is often used. In other words, wastewater generated at lithium battery factories and the like is normally disposed of despite the fact that lithium is dissolved at a higher concentration than brine.

  Regarding the technique for producing a lithium salt from brine, for example, there are those described in Patent Documents 1 to 3. Further, for example, Patent Documents 4 and 5 describe a technique for recovering lithium as lithium carbonate from a used lithium battery.

JP 2004-142986 A JP 2004-25113 A JP 2003-245542 A JP 2005-26089 A JP 2006-57142 A

  The lithium recovery methods described in Patent Documents 4 and 5 are all techniques for recovering lithium from a used lithium battery. However, when lithium is separated and recovered from a used lithium battery, the lithium-dissolved solution generated in the process of separation and recovery contains a large amount of various impurities other than lithium. It is not easy to recover only a lithium salt from a solution containing not only lithium but also various impurities.

  On the other hand, when brine is used as a raw material for producing a lithium salt, as described above, since the lithium ion concentration of brine is as low as several tens to 1000 mg / L, it takes time to concentrate. There is also a concern that brine is a natural water and contains a lot of impurities.

  By the way, in producing a lithium salt from a solution in which lithium is dissolved, it is necessary to measure (understand) the lithium ion concentration of the solution. Patent Document 1 discloses a method for detecting lithium ions in an effluent from an adsorbent using an optical detector (Optical detector) as a method for measuring a lithium ion concentration in a solution. Patent Document 3 describes a method for measuring a lithium ion concentration using adsorption column chromatography.

  When the lithium ion concentration in a solution is measured by the method described in Patent Documents 1 and 3, a sampling operation is required for the solution, and time is also required for analyzing the sampling solution. When producing a lithium salt, if the method for measuring the lithium ion concentration as described in Patent Documents 1 and 3 is used, an analysis (measurement) work offline is required separately from the production of the lithium salt. It ’s time consuming and time consuming. As a method for solving this problem, there is an online measurement of lithium ion concentration. Measuring lithium ion concentration online means incorporating a measurement instrument in the production line and measuring the lithium ion concentration of the solution sequentially (continuously) with the measurement instrument during the production of the lithium salt.

  Devices that can measure lithium ion concentration online already exist. However, the device is not a general-purpose device and is very expensive. Thus, no technology has been established that can easily measure the lithium ion concentration online.

  The present invention has been made in view of the above circumstances, and its object is to find a solution suitable for lithium salt production having a relatively high lithium ion concentration and a relatively low impurity content, and from the solution. It is an object of the present invention to provide a method capable of easily measuring a lithium ion concentration online in producing a lithium salt, and a method for producing a lithium salt using the method.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have focused on active material production wastewater in which lithium generated in the production process of a lithium ion secondary battery is dissolved, for example, as a solution having a relatively small impurity content. . Moreover, it discovered that there was a correlation between lithium ion concentration and electrical conductivity. Based on these findings, the present invention has been completed.

  That is, the present invention is a method for measuring a lithium ion concentration by measuring the electrical conductivity of an active material production wastewater in which lithium is dissolved, and calculating the lithium ion concentration in the active material production wastewater from the electrical conductivity.

  The electrical conductivity of the solution can be easily measured with a commercially available electrical conductivity meter. In addition, the electric conductivity meter can be easily incorporated in the lithium salt production line, and the electric conductivity of the solution flowing through the production line can be measured by the electric conductivity meter. That is, by using the electrical conductivity having a correlation with the lithium ion concentration for the measurement of the lithium ion concentration, the lithium ion concentration can be easily measured on-line in producing the lithium salt.

  On the other hand, the active material production waste water in which lithium is dissolved has a higher lithium ion concentration than brine. Moreover, the active material production wastewater has a lower impurity content than a solution produced in the process of separating and recovering lithium from a used lithium battery. That is, by using the active material production wastewater as a lithium salt raw material, the amount of treatment during concentration is less than when using brine as a raw material (concentration does not take time). In addition, it is possible to recover lithium having a high purity as a lithium salt as compared with a case where a raw material is a solution generated in the process of separating and recovering lithium from a used lithium battery.

  As described above, the active material production wastewater in which lithium is dissolved has a low impurity content. Therefore, the measurement error is reduced in the measurement of the lithium ion concentration using electric conductivity because the active material production wastewater having a small impurity content is a measurement target.

  The present invention also provides a concentration step of concentrating the active material production wastewater in which lithium is dissolved, a precipitation step of precipitating a lithium salt by adding a precipitant to the concentrated active material production wastewater, and the precipitated lithium salt. A solid-liquid separation step for solid-liquid separation and recovery, and a method for producing a lithium salt, measuring the electrical conductivity of the active material production wastewater, based on the lithium ion concentration calculated from the electrical conductivity, It is a method for producing a lithium salt, which controls at least one of the concentration step and the precipitation step.

  As described above, the lithium ion concentration can be measured online by using the electrical conductivity for the measurement of the lithium ion concentration in the production of the lithium salt from the active material production waste water in which lithium is dissolved. Moreover, the electrical conductivity of a solution can be easily measured with a commercially available electrical conductivity meter. That is, according to this configuration, offline analysis (measurement) work can be eliminated and the cost of the concentration measuring instrument can be suppressed, and lithium salt can be manufactured easily and inexpensively as compared with the conventional case. be able to. Moreover, since it can analyze on-line, operation control can be quickly performed with respect to the change of drainage property.

  Moreover, in this invention, it is preferable to control the addition amount of the said precipitation agent in the said precipitation process based on the lithium ion concentration computed from the electrical conductivity of the said active material manufacture waste_water | drain concentrated by the said concentration process.

  The lithium ion concentration of the active material production waste water before concentration may be obtained from the electrical conductivity, and the addition amount of the precipitation agent may be controlled from the lithium ion concentration. However, in the concentration step, a part of lithium in the active material production wastewater sometimes goes out of the system. In this case, the amount of the precipitant added becomes large. On the other hand, according to the above configuration of the present invention, it is not necessary to consider the amount of lithium that goes out of the system in the concentration step, that is, the addition amount of the precipitation agent can be made more accurate.

  Further, in the present invention, in the concentration step, based on the lithium ion concentration calculated from the electrical conductivity of the active material production wastewater concentrated in the concentration step, the active material production wastewater is adjusted so that the lithium ion concentration is constant. It is preferred to control the concentration.

  According to this structure, the lithium ion concentration of the concentrated active material production wastewater is stabilized. Thereby, precipitation of lithium salt is stabilized.

  According to the second aspect of the present invention, the concentration means for concentrating the active material production wastewater in which lithium is dissolved, and the precipitation for adding a precipitant to the concentrated active material production wastewater to precipitate the lithium salt Means, solid-liquid separation means for separating and recovering the deposited lithium salt by solid-liquid separation, and measuring the electrical conductivity of the active material production wastewater, and based on the lithium ion concentration calculated from the electrical conductivity, the concentration And a control means for controlling at least one of the precipitation means and a lithium salt production apparatus.

  The active material production waste water in which lithium is dissolved has a higher lithium ion concentration than brine. Moreover, the active material production wastewater has a lower impurity content than a solution produced in the process of separating and recovering lithium from a used lithium battery. That is, the active material production waste water in which lithium is dissolved is suitable as a raw material for producing a lithium salt. In addition, when lithium salt is produced from the active material production wastewater, the lithium ion concentration can be measured on-line and easily by measuring the lithium ion concentration using electrical conductivity.

It is a block diagram which shows one Embodiment of the manufacturing apparatus of the lithium salt which concerns on this invention. It is a graph which shows the correlation of lithium ion concentration and electrical conductivity.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a lithium salt production apparatus according to the present invention. In the following description, the configuration of the lithium salt manufacturing apparatus 100 and the method for measuring the lithium ion concentration shown in FIG. 1 will be described, and then the lithium salt manufacturing method (operation of the manufacturing apparatus 100) will be described.

  In addition, the measuring method of the lithium ion concentration according to the present invention is not a measuring method that can be used only for the purpose of producing a lithium salt. Naturally, it can be used simply by measuring the lithium ion concentration in the active material production waste water in which lithium is dissolved.

(Configuration of manufacturing equipment)
The lithium salt production apparatus 100 according to the present embodiment includes a reverse osmosis membrane device 1, a reaction tank 2, and a solid-liquid separation means 3 in order from the upstream side of the treatment process. These devices are connected to each other through paths 13 and 14. The manufacturing apparatus 100 also includes paths 12 and 15 to 17 and a control device 4 (control means). The paths 12 to 17 are made of piping, for example.

(Concentration means)
The reverse osmosis membrane device 1 (RO membrane device) corresponds to the concentration means of the present invention. The reverse osmosis membrane device 1 is a device that allows water to pass therethrough and does not pass impurities (such as ions and salts) other than water such as ions. The reverse osmosis membrane device 1 includes a main body 1a having a reverse osmosis membrane (RO membrane), a high-pressure pump 1b, and the like. The high-pressure pump 1b is a pump that is attached to the path 12 and supplies active material production wastewater to the main body 1a. The membrane material of the reverse osmosis membrane (RO membrane) constituting the main body 1a is polyamide, cellulose acetate or the like.

  A flow meter 6, an electric conductivity meter 7, and a pressure gauge 8 are attached to the path 12 between the high-pressure pump 1 b and the reverse osmosis membrane device 1 in order from the upstream side. The high pressure pump 1 b, the flow meter 6, the electrical conductivity meter 7, and the pressure gauge 8 are electrically connected to the control device 4. As the electrical conductivity meter 7, a commercially available electrical conductivity meter may be used. In the present embodiment, the flow meter 6 and the electrical conductivity meter 7 are measuring instruments for grasping the flow rate of the active material production wastewater flowing through the path 12 and the lithium ion concentration thereof. The flow meter 6 and the electric conductivity meter 7 can also be used for operation control of the reverse osmosis membrane device 1 and the reaction tank 2 (feeder 5).

  Here, the active material production wastewater refers to wastewater generated in the process of producing the active material. For example, in order to manufacture a positive electrode of a lithium ion secondary battery, a lithium transition metal oxide such as lithium cobalt oxide is manufactured. The lithium transition metal oxide such as lithium cobalt oxide is an active material.

In the active material production wastewater such as a lithium ion secondary battery, several thousand mg / L of lithium is dissolved. On the other hand, this active material production wastewater contains less impurities than a solution produced in the process of separating and recovering lithium from a used lithium battery. Impurities here refer to dissolved substances (ions, salts, etc.) and solids of various elements and compounds other than lithium, especially when measuring electrical conductivity in wastewater using an electric conductivity meter. Substances other than lithium ions that affect the electrical conductivity, such as cobalt and nickel. A lithium salt with high purity can be produced by producing a lithium salt from an active material production wastewater having a low impurity content. In addition, since the active material production wastewater has a higher lithium ion concentration than the brine, for example, when producing the same amount of lithium, using the active material production wastewater as a raw material, compared with using brine. Therefore, the processing amount for concentration is small. That is, the active material production waste water in which lithium is dissolved is suitable as a raw material for producing a lithium salt.
In addition, as wastewater to which the present invention can be suitably applied, it can be applied to wastewater with a low content of impurities in wastewater. I can do it.

  Examples of the concentration means other than the reverse osmosis membrane device 1 include an evaporation concentration device. An evaporative concentration device refers to a concentration device that utilizes the difference in boiling points. Water is evaporated by an evaporating and concentrating device, and the component is concentrated by leaving a component having a boiling point higher than that of water. Examples of the evaporation concentration apparatus include a thin film evaporation apparatus, a natural circulation external heating pipe type apparatus, a natural circulation calandria type apparatus, and a forced circulation type apparatus.

(Precipitation means)
The reaction tank 2 corresponds to the precipitation means of the present invention. The reaction tank 2 includes a stirrer 2a, a liquid level meter 2b, and a feeder 5 as accessories. The feeder 5 is for feeding a precipitation agent such as sodium hydrogen carbonate into the reaction vessel 2. The stirrer 2a is for mixing and stirring the concentrated active material production wastewater charged into the reaction tank 2 and the precipitating agent to promote precipitation of lithium salt. The liquid level meter 2b is for monitoring the liquid level in the reaction tank 2, and is used for grasping the amount of liquid in the reaction tank 2 and preventing the stirrer 2a from being idle. Although the electrode type liquid level gauge 2b is illustrated, a differential pressure type liquid level gauge or the like may be used. The precipitation means is not limited to an apparatus such as the reaction tank 2 shown in FIG.

  An automatic valve 9, a flow meter 10 and an electric conductivity meter 11 are attached in order from the upstream side to a path 13 connecting the reverse osmosis membrane device 1 and the reaction tank 2. The automatic valve 9 is an accessory of the reverse osmosis membrane device 1 and is an electric or air operated valve. The automatic valve 9, the flow meter 10, the electrical conductivity meter 11, the liquid level meter 2 b, and the feeder 5 are electrically connected to the control device 4. As the electrical conductivity meter 11, a commercially available electrical conductivity meter may be used.

(Solid-liquid separation means)
The solid-liquid separation means 3 is for recovering lithium salt precipitated in the active material production waste water after concentration by solid-liquid separation. Examples of the solid-liquid separation means 3 include a centrifuge, a filter press, and a filtration device. Further, the solid-liquid separation means 3 may be configured by combining these devices (machines). For example, after the active material production waste water containing the precipitated lithium salt is passed through a centrifuge, the solid solution separation means 3 is constituted by the centrifuge and the filtration device by further passing the centrifugal supernatant water through the filtration device. May be.

(Measurement method of lithium ion concentration)
The present inventors have found through experiments that there is a correlation between the lithium ion concentration of the solution and the electrical conductivity. A plurality of solutions having different lithium ion concentrations were prepared, and the electric conductivity of each solution was measured with an electric conductivity meter. FIG. 2 is a graph showing the correlation between lithium ion concentration and electrical conductivity. As shown in FIG. 2, there is a linear relationship between lithium ion concentration and electrical conductivity.

  From this, the lithium ion concentration can be known by measuring the electrical conductivity of the active material production wastewater in which lithium is dissolved and calculating the lithium ion concentration in the active material production wastewater from the electrical conductivity.

  Here, the electrical conductivity of the solution can be easily measured with a commercially available electrical conductivity meter. In addition, the electric conductivity meter can be easily incorporated into the lithium salt production line (for example, in the path 13 or the path 12), and the electric conductivity of the solution flowing through the production line is measured by the electric conductivity meters 7 and 11, respectively. Continuous measurement is possible. That is, by using the electrical conductivity having a correlation with the lithium ion concentration for the measurement of the lithium ion concentration, the lithium ion concentration can be easily measured on-line in producing the lithium salt.

  As described above, the active material production wastewater in which lithium is dissolved has a low impurity content. Therefore, the measurement error is reduced in the measurement of the lithium ion concentration using electric conductivity because the active material production wastewater having a small impurity content is a measurement target.

(Control means)
In the lithium salt manufacturing apparatus 100 of the present embodiment, the lithium ion concentration is automatically obtained in the control apparatus 4. The control device 4 is a device for controlling the amount of precipitation agent added and the concentration (concentration) of the active material production waste water.

  An electric circuit for controlling the amount of added precipitant and the concentration (concentration) of active material production wastewater is configured in the control panel using various switches and relays (relays), etc., and a program for performing these controls A sequencer that has been entered may be placed in the control panel. A control panel in which an electric circuit composed of various switches / relays (relays) or the like is incorporated, or a control panel in which a sequencer to which a control program is input is provided is the control device 4 and corresponds to the control means of the present invention. To do. The control device 4 is installed beside the reverse osmosis membrane device 1, for example.

  Next, a method for manufacturing a lithium salt (operation of the manufacturing apparatus 100) will be described.

(Concentration process)
The active material production waste water in which lithium is dissolved is concentrated by the reverse osmosis membrane device 1. As shown in FIG. 1, the active material production waste water in which lithium is dissolved is supplied from the high pressure pump 1b to the main body 1a of the reverse osmosis membrane device 1 to concentrate the active material production waste water. The permeated water that has permeated through the reverse osmosis membrane (RO membrane) of the main body 1a is discharged as drainage. On the other hand, the active material production wastewater that has not permeated the reverse osmosis membrane (RO membrane), that is, the concentrated active material production wastewater, is charged into the reaction tank 2.

(Concentration control of active material manufacturing wastewater)
For example, a calculation formula (for example, a primary formula based on FIG. 2) for obtaining the lithium ion concentration from the electrical conductivity is input in advance to the sequencer in the control device 4. The control device 4 receives an electrical signal related to the electrical conductivity of the active material production waste water concentrated by the reverse osmosis membrane device 1 from the electrical conductivity meter 11. The control device 4 calculates the lithium ion concentration D1 (mg / L) from this electric signal based on the above calculation formula, and controls the concentration of the active material production waste water based on the calculated lithium ion concentration D1.

  Specifically, the control device 4 controls the concentration of the active material production waste water so that the lithium ion concentration D1 (mg / L) of the concentrated liquid (concentrated active material production waste water) becomes constant at a predetermined concentration. To do. Thereby, the lithium ion concentration of the concentrate is stabilized. As a result, precipitation of the lithium salt is stabilized.

  For example, the control device 4 controls the opening degree of the automatic valve 9 based on the lithium ion concentration D1 (mg / L) of the concentrate. When the lithium ion concentration D1 is higher than a predetermined value, the opening degree of the automatic valve 9 is controlled to the large side, and when it is lower than the predetermined value, the opening degree is controlled to the small side. When the opening degree of the automatic valve 9 increases, the flow rate flowing through the path 13 increases, and the flow rate flowing through the path 13 increases without being concentrated by the reverse osmosis membrane, so the lithium ion concentration D1 decreases. On the other hand, when the opening degree of the automatic valve 9 decreases, the flow rate flowing through the path 13 decreases, the resistance increases, and the flow rate of permeate passing through the main body 1a of the reverse osmosis membrane device 1 increases, so the lithium ion concentration D1 increases. .

  Moreover, you may control the rotation speed of the high pressure pump 1b based on the lithium ion concentration D1 (mg / L) of a concentrate. When the lithium ion concentration D1 is higher than a predetermined value, the rotational speed of the high-pressure pump 1b is controlled to the lower side, and when lower than the predetermined value, the rotational speed is controlled to the higher side. When the rotation speed of the high-pressure pump 1b decreases, the filtration pressure decreases and the permeate decreases, so the lithium ion concentration D1 decreases. On the other hand, when the rotation speed of the high-pressure pump 1b increases, the filtration pressure increases and the permeate increases, so the lithium ion concentration D1 increases. The filtration pressure can be grasped with the pressure gauge 8. In order to control the rotation speed of the high-pressure pump 1b, for example, an inverter is used.

  Note that either the opening control of the automatic valve 9 or the rotation speed control of the high-pressure pump 1b may be performed by the control device 4, or these two controls may be combined.

  Next, Table 1 shows the solubility of various lithium salts and the lithium solubility (lithium ion concentration) converted from this solubility. All the solubilities are those at 25 ° C. and 1 atm (atmospheric pressure).

  Examples of the lithium salt that is the production target of the present invention include lithium carbonate, lithium bromide, lithium chloride, and lithium sulfate shown in Table 1. Here, the lithium salt to be manufactured is preferably lithium carbonate. As shown in Table 1, the solubility (25 ° C., 1 atm) of lithium carbonate is 1.29 g / 100 mL, which is lower than other lithium salts. That is, lithium is likely to precipitate as a salt. That is, it is easy to collect more lithium by producing lithium carbonate. In the following description, the lithium salt to be manufactured is described as lithium carbonate.

  As described above, it is preferable to control the concentration of the active material production waste water so that the lithium ion concentration D1 (mg / L) of the concentrated solution is constant at a predetermined concentration, but it is more preferably 5000 mg / L or more and 20000 mg / L. It is preferable to control the concentration so that a predetermined constant concentration within a range of L or less is obtained.

  From Table 1, the lithium solubility (lithium ion concentration) of lithium carbonate is 2440 mg / L (25 ° C., 1 atm). On the other hand, the lithium solubility of lithium sulfate having the second lowest solubility as lithium is 21900 mg / L (25 ° C., 1 atm). Furthermore, the lithium solubility of the lithium salts shown in Table 1 other than lithium carbonate and lithium sulfate is higher than the lithium solubility of lithium sulfate.

  Therefore, the precipitation of other salts such as lithium sulfate can be prevented by setting the lithium ion concentration D1 to 20000 mg / L or less. That is, precipitation of impurities such as lithium sulfate can be suppressed, and as a result, high-purity lithium carbonate can be produced. Further, by setting the lithium ion concentration D1 to 5000 mg / L or more, it is possible to ensure the precipitation of lithium carbonate, and it is possible to reduce the throughput in the subsequent precipitation step and solid-liquid separation step.

  The lithium ion concentration D1 (mg / L) does not necessarily need to be controlled to be constant at a predetermined concentration, and the lithium ion concentration D1 (mg / L) is in a range of 5000 mg / L to 20000 mg / L. ) May be controlled.

(RO enrichment experiment results)
A lithium ion concentration: 3690 mg / L of solution was supplied to the reverse osmosis membrane device 1 to conduct a concentration experiment. The experimental results were such that the lithium ion concentrations of concentrated water and permeated water were 9490 mg / L and 57.6 mg / L, respectively. In addition, the high pressure pump which comprises the reverse osmosis membrane apparatus 1 used the pump of lift (pressure): 4MPa. Thus, by concentrating the active material production wastewater using the reverse osmosis membrane device 1, the active material production wastewater can be concentrated with little loss. That is, the recovery rate of lithium can be increased. The lithium contained in the permeated water (the amount of permeated water (L) × 57.6 mg / L) is a loss, but the loss is very small and less than 1%, so it has little effect on the recovery rate of lithium. do not do. Moreover, by using the reverse osmosis membrane device 1, the active material production waste water can be easily concentrated.

  An evaporation concentrator such as the above-described thin film evaporator is also suitable as the concentration means. By using the evaporating and concentrating device, the high-pressure operation required in the case of the reverse osmosis membrane device 1 becomes unnecessary. In addition, in the precipitation process described later, the active material production wastewater may be heated. However, according to the evaporative concentration apparatus, the temperature of the active material production wastewater rises at the stage of the concentration process, so that heating in the precipitation process is unnecessary. Become.

(Addition of acid)
As shown in FIG. 1, acid is added to the active material production wastewater to adjust the pH of the active material production wastewater to 7 or more and 10 or less, and then the pH is adjusted using the reverse osmosis membrane device 1. Is preferably concentrated. Examples of the acid to be added include hydrochloric acid and sulfuric acid. The acid to be added is not particularly limited, and other acids may be used.

  The pH of the active material production waste water in which lithium is dissolved is often 12 or more. By adding an acid to the active material production wastewater and setting the pH of the active material production wastewater to 7 or more and 10 or less, deterioration of the reverse osmosis membrane (RO membrane) can be prevented. Note that even if the pH of the active material production wastewater is lowered below 7, the effect of preventing the reverse osmosis membrane (RO membrane) from being deteriorated does not increase dramatically. Conversely, there is a demerit that the amount of acid (chemical) used is increased. Moreover, the salt concentration (salt concentration other than lithium) in active material manufacture waste_water | drain rises by addition of the acid to active material manufacture waste_water | drain. Here, salts other than lithium remain as impurities in the active material production wastewater concentrated by the reverse osmosis membrane device 1. That is, it is not preferable to lower the pH below 7. For this reason, the pH is preferably 7 or more, and more preferably 9 or more.

  Moreover, in the precipitation process mentioned later, carbonate or a carbon dioxide is added to the concentrated active material manufacture waste_water | drain as a depositing agent, and lithium carbonate is deposited. Here, when carbonate etc. are added to the active material manufacturing waste_water | drain of an acidic state, some carbonic acid will escape in the air. As a result, the amount of carbonate or carbon dioxide added increases. That is, it is preferable to deposit lithium carbonate in an alkaline state. Also from this viewpoint, it is not preferable to lower the pH below 7, and the pH of the active material production waste water is preferably 7 or more and 10 or less, and more preferably 9 or more.

(Precipitation process)
In the precipitation step, carbonate or carbon dioxide (carbon dioxide) is added as a precipitating agent to the active material production wastewater concentrated by the reverse osmosis membrane device 1 in the concentration step to precipitate lithium carbonate. For example, sodium hydrogen carbonate is added from the feeder 5 to the concentrated liquid (concentrated active material production waste water) supplied from the reverse osmosis membrane device 1 to the reaction tank 2 and stirred by the stirrer 2a. Thereby, lithium carbonate precipitates.

More specifically, the concentrated liquid is supplied to the reaction tank 2, and once the amount of liquid in the reaction tank 2 reaches a predetermined amount (for example, V (m ³ ), liquid level H (m)), the concentrated liquid is temporarily supplied. Stop. Then, the added sodium hydrogen carbonate and the concentrated liquid are sufficiently stirred to precipitate lithium carbonate. Thereafter, the stirred liquid (active material production wastewater) containing the precipitated lithium carbonate is removed from the reaction tank 2 and sent to the solid-liquid separation means 3 (this operation is called batch operation).

  In addition, when the reaction tank 2 is large, or when the reaction tank 2 is long (when the inflow position and the extraction position of the concentrate are far apart), lithium salt precipitation is not performed in batch operation but in continuous operation. You may go. The continuous operation refers to an operation of extracting the concentrate from the reaction tank 2 while supplying the concentrate to the reaction tank 2.

(Controlling the amount of precipitation agent added)
The calculation of the lithium ion concentration D1 (mg / L) by the control device 4 using the electrical conductivity of the concentrated liquid (concentrated active material production wastewater) is as described above. The control device 4 calculates the amount of precipitation agent added from this lithium ion concentration D1. Then, a command is issued to the feeder 5 so that the calculated addition amount is obtained. In this manner, the addition amount of the precipitant is controlled by the control device 4.

(Calculation of precipitation agent addition amount)
Since the chemical formula of lithium carbonate is Li ₂ CO ₃ , when an equal amount of CO ₃ is added to lithium dissolved in the active material production wastewater, the molar ratio of Li and CO ₃ is 2: 1. . That is, 1/2 mol of CO ₃ is added to 1 mol of Li. Below, the example of calculation of the addition amount at the time of using sodium hydrogencarbonate as a precipitation agent is shown.

(Concentrated lithium ion concentration control and batch operation)
Assuming that the capacity of the reaction tank 2, that is, the processing amount in one batch is V (m ³ ), the addition amount q (g / 1 batch) of sodium hydrogen carbonate (NaHCO ₃ ) is calculated by the following equation. In this case, since the lithium ion concentration D1 is constant, the addition amount q (g / 1 batch) is also constant.
q = V × D1 × 1/2 × 84/7
84: Molecular weight of sodium bicarbonate 7: Atomic weight of lithium

(In the case of batch operation without constant control of the lithium ion concentration of the concentrate)
When the lithium ion concentration at time t _i in one batch is D1 _i (mg / L), the addition amount q (g / 1 batch) of sodium hydrogen carbonate (NaHCO ₃ ) is calculated by the following equation. In this case, it is preferable that the signal acquisition interval from the electric conductivity meter 11 by the control device 4 is short.
q = V × ΣD1 _i × 1/2 × 84/7
84: Molecular weight of sodium bicarbonate 7: Atomic weight of lithium

(For continuous operation)
Assuming that the flow rate of the concentrate obtained from the electrical signal from the flow meter 10 is Q1 (m ³ / sec), the addition amount q (g / sec) of sodium hydrogen carbonate (NaHCO ₃ ) is calculated by the following equation. The controller 4 updates the values of the flow rate Q1 and the lithium ion concentration D1 at predetermined intervals. A shorter update interval is preferable.
q = Q1 × D1 × 1/2 × 84/7
84: Molecular weight of sodium bicarbonate 7: Atomic weight of lithium

  Examples of the carbonate (precipitating agent) include sodium carbonate, magnesium carbonate, potassium bicarbonate, potassium carbonate, and calcium carbonate in addition to sodium bicarbonate. Table 2 shows the carbonic acid content of these carbonates. In addition, as a precipitating agent other than carbonate or carbon dioxide, sulfate, nitrate, or the like may be used.

  As shown in Table 2, the carbonate content of sodium bicarbonate and magnesium carbonate is higher than the carbonate content of other carbonates. That is, sodium bicarbonate or magnesium carbonate is suitable for reducing the amount of carbonate used (the amount of chemical used). When comparing sodium bicarbonate and magnesium carbonate, sodium bicarbonate is generally less expensive than magnesium carbonate. Therefore, sodium bicarbonate is more suitable as a carbonate to be added than magnesium carbonate.

(Solid-liquid separation process)
In the solid-liquid separation step, the lithium carbonate precipitated in the precipitation step is recovered by solid-liquid separation. The stirring liquid (active material production waste water) sufficiently stirred in the reaction tank 2 is sent to the solid-liquid separation means 3. The lithium carbonate precipitated in the stirring liquid is captured and recovered by the solid-liquid separation means 3.

  By performing solid-liquid separation with a filtration device, stable solid-liquid separation becomes possible. In addition, by performing solid-liquid separation with a centrifuge, it is possible to perform solid-liquid separation at a lower cost than in the case of a filtration device. Further, by performing solid-liquid separation with a filter press, solid-liquid separation can be performed easily and at a lower cost than in the case of a filtration device, and stable solid-liquid separation is possible.

  Moreover, you may perform with a centrifuge before performing solid-liquid separation with a filtration apparatus. After performing solid-liquid separation with a centrifuge, the centrifugal supernatant water can be further solid-liquid separated with a filtration device to reduce the load on the filtration device. Compared to solid-liquid separation with a single filtration device. Thus, the maintenance cost of the filtration device can be reduced.

  As explained above, according to the method for producing a lithium salt of the present invention, offline analysis (measurement) work can be eliminated and the cost of the concentration measuring instrument can be reduced (commercial electric conductivity). Therefore, the lithium salt can be easily and inexpensively manufactured as compared with the conventional case. Further, by performing on-line measurement, it is possible to easily optimize the addition amount of the precipitation agent even if there is a large variation in the lithium ion concentration. In other words, the amount of precipitation agent added can be optimized without stopping production of the lithium salt.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. .

  In the above-described embodiment, the example in which the addition amount of the precipitating agent is controlled based on the lithium ion concentration calculated from the electrical conductivity of the active material production wastewater (concentrated liquid) concentrated in the concentration step has been described. The lithium ion concentration D0 (mg / L) of the substance production waste water may be obtained from the signal from the electric conductivity meter 7, and the addition amount of the precipitation agent may be controlled by the controller 4 from the lithium ion concentration D0.

  Further, the lithium ion concentration D0 (mg / L) of the active material production waste water before concentration is obtained from the signal from the electric conductivity meter 7, and the lithium ion concentration D1 of the active material production waste water after concentration from the lithium ion concentration D0. May be controlled.

  In the present invention, the lithium ion concentration may be obtained from the electrical conductivity measured using the correlation equation shown in FIG. 2, and if necessary, the concentration of wastewater to be treated is changed in advance. The off-line analysis measures the electrical conductivity and lithium ion concentration at each concentration, and obtains a correlation between the electrical conductivity and lithium ion concentration in the wastewater. Using this correlation, the electrical conductivity in the wastewater The lithium ion concentration may be obtained from the measured value. Since the wastewater is originally low in impurity content, the lithium ion concentration can be obtained by the correlation equation shown in FIG. 2, but by obtaining the correlation equation for each drainage and using the correlation equation, the individual can be more accurately obtained. The lithium ion concentration in the waste water can be obtained.

  In addition, regarding the concentration control, a bypass path may be connected between the latter stage of the electric conductivity meter 7 and the former stage of the flow meter 10 in the path 13, and an automatic valve may be provided here. For example, based on the lithium ion concentration D1 (mg / L) of the concentrate, the control device 4 controls the opening degree of the automatic valve provided in the bypass path. When the lithium ion concentration D1 is higher than a predetermined value, the opening degree of the automatic valve is controlled to the large side, and when it is lower than the predetermined value, the opening degree is controlled to the small side. When the opening degree of the automatic valve increases, the flow rate flowing through the bypass path increases, and the flow rate bypassed without being concentrated increases, so the lithium ion concentration D1 decreases. On the other hand, when the opening degree of the automatic valve decreases, the flow rate flowing through the bypass path decreases and the flow rate passing through the main body 1a of the reverse osmosis membrane device 1 increases, so the lithium ion concentration D1 increases. By controlling in this way, it is also possible to control the lithium ion concentration and flow rate in the concentrate flowing through the path 13 to be substantially constant. Further, an automatic valve 9 may also be installed, and the bypass path may be connected between the automatic valve 9 and the flow meter 10.

  In the above-described embodiment, an example is shown in which both the amount control of the precipitating agent and the concentration control of the active material production wastewater are performed by the control device 4. Only one of these may be performed by the control device 4.

1: Reverse osmosis membrane device 1a: Main body 1b of reverse osmosis membrane device: High pressure pump 2: Reaction tank 3: Solid-liquid separation means 4: Control device 6, 10: Flow meter 7, 11: Conductivity meter 100: Lithium salt Manufacturing equipment

Claims (3)

A concentration step of concentrating the active material production wastewater in which lithium is dissolved;
A precipitation step of adding a precipitating agent to the concentrated active material production wastewater to precipitate a lithium salt;
A solid-liquid separation step of recovering the precipitated lithium salt by solid-liquid separation; and
A method for producing a lithium salt comprising:
The method for producing a lithium salt, wherein, in the precipitation step, the amount of the precipitation agent is controlled based on a lithium ion concentration calculated from the electrical conductivity of the active material production waste water concentrated in the concentration step . In the concentration step, based on the lithium ion concentration calculated from the electrical conductivity of the active material production wastewater concentrated in the concentration step, control the concentration of the active material production wastewater so that the lithium ion concentration is constant, The method for producing a lithium salt according to claim 1 . A concentration means for concentrating the active material production wastewater in which lithium is dissolved;
A precipitation means for adding a precipitant to the concentrated active material production wastewater to precipitate a lithium salt;
Solid-liquid separation means for solid-liquid separation and recovery of the deposited lithium salt;
Control means for measuring the electrical conductivity of the active material production wastewater concentrated by the concentration means, and controlling the amount of the precipitation agent based on the lithium ion concentration calculated from the electrical conductivity;
An apparatus for producing a lithium salt.

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