TWI428279B - Recovery of lithium from aqueous solutions - Google Patents

Description

Recovery of lithium from aqueous solution

Part of the invention relates to the recovery of lithium from a lithium-containing solution which is, for example, a feed stream used in the manufacture of lithium ion batteries and a feed stream obtained by extracting lithium from an ore-based material.

The present application claims the benefit of U.S. Provisional Application Serial No. 61/199, 495, filed on Jan. 17, 2008, which is hereby incorporated by reference.

Lithium-containing batteries have become the preferred battery in many existing and emerging applications due to their higher energy density to weight ratio and relatively long life compared to other types of batteries. Lithium-ion batteries are used in a variety of applications, such as mobile phones, laptops, medical devices, and implants (such as cardiac pacemakers).

Lithium-ion batteries are also an extremely useful energy source in the development of new types of vehicles, such as hybrid and electric vehicles. They are environmentally friendly and "green" because they reduce emissions and reduce dependence on hydrocarbon fuels. This is clearly a big advantage because the use of such batteries eliminates or reduces the need for hydrocarbon fuels and the resulting greenhouse gas emissions, as well as other related environmental damage due to fossil fuel combustion in internal combustion engines. In addition, the choice of lithium ion batteries for vehicle use is largely due to the higher energy density to weight ratio, thereby making the battery weight lighter than other batteries, which is an important factor in vehicle manufacturing.

Lithium-ion batteries usually consist of three main parts: 1) carbon anode, 2) The separator, and 3) lithium-containing cathode material. Preferred lithium-containing cathode materials include lithium and metal oxide materials such as lithium cobalt oxide, lithium nickel cobalt oxide, lithium manganese oxide, and lithium iron phosphate, but other lithium compounds may also be used.

Lithium iron phosphate is a particularly preferred compound for use as a lithium-containing cathode material because it provides an improved safety profile, acceptable operating characteristics, and lower toxicity compared to other cathode materials mentioned. This is especially true for relatively large battery sizes, such as those used in electric vehicles. The improvement in safety features is due to the fact that lithium iron phosphate (also known as LIP) can be easily overheated as other lithium ion batteries. This is especially important for larger batteries. At the same time, the battery operating characteristics of the LIP battery are equivalent to other compounds currently in use. Other lithium compounds reduce the tendency to overheat, but at the expense of operating characteristics. Lithium iron phosphate sulfate is similar to LIP and is also used in batteries.

Lithium iron phosphate can be prepared by a wet chemical method using an aqueous solution containing lithium ions derived from a lithium source such as lithium carbonate, lithium hydroxide monohydrate or lithium nitrate. A typical reaction scheme is described by Yang et al., Journal of Power Sources 146 (2005) 539-543, as follows: 3LiNO ₃ +3Fe(NO ₃ ) ₂ ̇ n H ₂ O+3(NH ₄ ) ₂ HPO ₄ → Fe ₃ (PO ₄ ) ₂ ̇ n H ₂ O+Li ₃ PO ₄ +6NH ₃ +9HNO ₃ (I)

Fe ₃ (PO ₄ ) ₂ ̇ n H ₂ O+Li ₃ PO ₄ → 3LiFePO ₄ + n H ₂ O (II)

Lithium iron phosphate can be prepared by a wet chemical method using an aqueous solution containing lithium ions derived from a lithium source such as lithium carbonate, lithium hydroxide monohydrate or lithium nitrate. Lithium iron phosphate sulfate is prepared in a similar manner, but a sulfate raw material is required for the preparation. For example, the preparation of an aqueous solution of lithium iron phosphate is described in U.S. Patent No. 5,910,382 to the name of U.S. Pat. In general, due to the low efficiency of the process, the wet chemical process for preparing lithium iron phosphate produces an aqueous solution stream containing a large amount of lithium ions and other impurities. The composition of a typical liquid stream produced by the wet chemical method for the preparation of lithium iron phosphate is as follows:

Since lithium is one of the major and valuable components of lithium iron phosphate materials, it will be necessary to recover any excess lithium to produce lithium iron phosphate in wet chemical processes. This is especially true when used in the manufacture of lithium iron phosphate products to provide a relatively large excess of lithium. A method of recovering and purifying lithium from lithium battery waste is known from the published PCT application WO 98/59385, but there is a need in the art for improvements and alternative methods of recovering lithium.

The present invention utilizes bipolar electrodialysis for this and other purposes, and bipolar electrodialysis is also known as a salt splitting technique for recovering lithium from a feed stream. The recovered lithium is in the form of a lithium hydroxide solution which can be recycled to the feed stream used to produce lithium iron phosphate using wet chemical methods. A sulfuric acid solution is also produced in the process which can be recovered and used in other processes or sold as a commodity. In a preferred embodiment, any phosphate ions in the feed stream are reduced or better removed prior to bipolar electrodialysis of the feed stream, as it has been found that phosphate tends to contaminate the membrane, thereby reducing lithium hydroxide. Yield or completely prevent its formation. Alternatively, in the reduction of sulfuric acid containing lithium ore, the resulting purified lithium sulfate stream can also be treated in this manner. The advantage is that a flow of sulfuric acid is also produced, which, if concentrated, can be used to offset the cost of purchasing the desired sulfuric acid.

Bipolar membrane electrodialysis utilizes separate chambers and membranes to produce the acid and base of the individual salt solutions introduced. According to this method, the ion exchange membrane separates the ionic species in the solution via an electric field. The bipolar membrane will hydrolyze into positively charged hydrogen ions (H ⁺ , in the form of H ₃ O ⁺ (hydrated hydrogen ions) in aqueous solution) and negatively charged hydroxide anions (OH ^- )

Bipolar membranes are typically formed from an anion exchange layer and a cation exchange layer that are bonded together. Provide a water diffusion layer or interface, water from an external aqueous salt solution Spread in it.

Further provided are anion and cation selectively permeable membranes to direct salt ion separation, such as lithium ions and sulfate ions, if desired. Therefore, a three-membrane system is commonly used in bipolar membrane electrodialysis.

Membranes from commercially available sources, such as Astom's ACM, CMB, AAV and BP1 membranes or FumaTech's FKB membranes, may be resistant to unwanted ions (H ⁺ or OH ^- ), low resistivity and the resulting acid and base The resistance to the potentially corrosive nature of the solution is used in combination. These membranes are positioned between the electrodes, that is, between the anode and the cathode, and direct current (DC) is applied between the electrodes.

Preferred cell manufacturers include Eurodia, with EUR20 and EUR40 being preferred.

A preferred configuration for recovering lithium in the form of lithium hydroxide from a liquid stream containing lithium sulfate using a bipolar membrane technique is shown in FIG. As shown in Fig. 1, "A" is an anion permeable membrane; "C" is a cationic permeable membrane. "B" is a bipolar membrane. The anionic membrane allows the passage of negatively charged sulfate ions, but prevents the passage of positively charged lithium ions. Conversely, the cation membrane allows positively charged lithium ions to pass through, but prevents the passage of sulfate anions. The pre-charged acid and alkali reservoir is shown in the middle of the figure, and the resulting H ⁺ or OH ^- ions are combined with the precipitated negatively charged sulfate ions and positively charged lithium ions. Thus, a lithium hydroxide solution is produced which can be fed into the process stream for the preparation of lithium iron phosphate. A sulfuric acid solution was obtained on the cathode side.

Preferably, the lithium sulphate solution of the type previously described is pretreated by the addition of a suitable base, preferably an alkali metal hydroxide, to a relatively high pH, typically to a pH of from 10 to 11. Lithium hydroxide, hydrogen hydroxide Sodium and potassium hydroxide are especially preferred. Adjusting the pH to this range removes impurities, such as precipitates, especially phosphates that may interfere with the electrochemical reactions in the electrodialysis unit. It is especially preferred to remove the phosphate from at least the feed, as it has been found that this impurity particularly causes the membrane to become contaminated, thereby disrupting the process. These precipitates were filtered from the solution before being fed into the bipolar electrodialysis cell. The solution can then be adjusted to a lower pH, such as pH 1-4, and preferably 2-3, as desired, preferably by adjustment from the acid obtained in the process, followed by feeding the solution into the electrodialysis cell. As described above, in this process, lithium ions pass through the cation membrane to produce a lithium hydroxide stream; and the sulfate passes through the anion membrane to produce a sulfuric acid stream. (see picture 1)

The resulting LiOH and sulfuric acid streams are relatively weak streams for the molar content of the individual components. For example, the test shows the following average range: LiOH: 1.6-1.85MH ₂ SO ₄ : 0.57-1.1M

Another aspect of the invention pertains to the purity of the lithium hydroxide product, as the purified lithium hydroxide product is highly desirable.

It has been found that a reduction in the sulfuric acid product concentration of about 50% causes the sulfate concentration in the hydroxide solution to decrease by a corresponding amount (from 430 ppm to 200 ppm). In addition, as the acid concentration decreases, the current efficiency relative to the acid generation increases by about 10%.

A block diagram of the above process is shown in FIG.

More specifically, referring to Figure 2, the lithium sulfate-containing feed stream is purified by adjusting the pH to from about 10 to about 11 to precipitate any solid impurities from the feed stream, thereby removing any solid impurities. It is preferably a feed stream from the production of lithium battery components. The resulting purified lithium sulfate feed stream is then doubled Extremely dialysis, preferably prior to dialysis, the pH is adjusted to about 2-3.5 with sulfuric acid, using a suitable bipolar membrane to separate lithium from the liquid stream, which will be recovered as lithium hydroxide. In a preferred embodiment, prior to the bipolar electrodialysis of the lithium sulfate feed stream, prior to the purification step or possibly during the purification step, for example, by adjusting the pH to remove phosphate or by using appropriate ions The membrane is exchanged to remove phosphate from the solution, thereby removing any phosphate. Alternatively, the lithium sulphate stream from the sulphate ore extraction process has been suitably purified according to the practices known in the art, which can be subjected to bipolar dialysis. Preferably, the pH is adjusted to about 2-3.5 with sulphuric acid prior to dialysis. Suitable bipolar membranes separate lithium from the liquid stream, which will be recovered as lithium hydroxide.

It is believed that current efficiency is low, especially when it involves a cationic membrane, which results in a higher local pH of the adjacent membrane, thereby forming a precipitate in the central feed chamber. This can also be observed outside the cell by intentionally raising the pH of the feed to 10 and allowing the formation of a precipitate. Table 1 shows the composition of the solids collected from the 10 L batch of the lithium sulfate feed solution that had been adjusted to pH 10 and allowed to stand overnight and filtered. A total of 3.02 g of solid was recovered. A portion of the solid (0.3035 g) was redissolved in 100 mL of 1 M HCl for analysis by ICP. As can be seen from Table 1 below, the main impurities in the precipitate appear to be Fe, Cu, P, Si, Zn and Mn3.

The lithium hydroxide solution and the sulfuric acid solution were obtained by bipolar dialysis of the lithium sulfate feed stream with a suitable bipolar membrane, as shown in the right side and the left side of Fig. 2, respectively.

The lithium hydroxide solution can be recovered, or preferably it can be directly introduced into the process of preparing LiFePO ₄ or other lithium-containing salts or products. Of course, lithium hydroxide can be recovered and used, for example, as a base suitable for chemical reactions or to adjust the pH of the initial feed stream to remove impurities such as phosphate.

The recovered lithium hydroxide solution may be concentrated before use, or may be subjected to other purification steps as necessary.

Turning now to the left side of Figure 2, the sulfuric acid solution is recovered and sold, or used as an acid suitable for chemical and industrial processes. Alternatively, it can be concentrated and used to offset the associated costs of purchasing the sulfuric acid required to extract lithium from the lithium-containing ore.

Figure 3 shows an alternative embodiment of the invention in which lithium hydroxide and sulfur The acid stream is recovered and used in the manufacture of lithium iron phosphate, which essentially allows the process to proceed continuously. Since iron is added in the form of ferric sulfate in the process, it is feasible to form the ferric sulfate using the recovered sulfuric acid stream. This will depend on the purity requirements of the ferric sulphate and the level of concentration required. However, according to this method, an alternative source of iron for ferric sulfate and a solution of sulfuric acid derived from a sulfate source can be utilized.

More specifically, in Figure 3, the lithium sulfate feed stream was purified prior to electrodialysis by adjusting the pH to 10-11, followed by downregulating the pH to 2-3.5, as described above.

As in Figure 2, the purified stream was subjected to bipolar electrodialysis using a suitable membrane to form an aqueous solution of aqueous sulfuric acid and a feed stream of aqueous lithium hydroxide solution. In this embodiment, the focus is on recovering the sulfuric acid and lithium hydroxide feed streams and returning them for use in the production of lithium products, particularly lithium iron phosphate. Focusing now on the left side of Figure 3, the aqueous sulfuric acid stream is converted to ferric sulfate by the addition of an iron source to the sulfuric acid solution. The iron source can be of any suitable source, including metallic iron as seen in naturally occurring iron ore. Since the ferric sulfate solution already contains sulfate ions, ferric sulfate is a preferred iron salt. Iron is added to obtain an iron phosphate solution, and then the iron phosphate solution is finally mixed with a lithium hydroxide solution recovered from the bipolar electrodialysis process and a phosphate raw material to obtain lithium iron phosphate.

As shown on the right side of Figure 3, the lithium hydroxide solution is preferably adjusted to the desired lithium hydroxide content by introducing lithium hydroxide from another source or by concentrating the recovered stream.

Another preferred embodiment is shown in FIG. In this alternative, a lithium source other than lithium hydroxide, such as lithium carbonate, is used in the process. In this embodiment, the sulfuric acid stream is reacted with lithium carbonate of a predetermined purity to produce an additional lithium sulfate solution, which is then added to the original recycle solution and subsequently fed to the bipolar electrodialysis cell. This process is shown on the left side of the flow chart in Figure 4. Therefore, different lithium sources can be used to obtain a lithium solution in which lithium hydroxide can be extracted. The pH adjustment step of the LiSO ₄ feed stream is as described above.

Note that according to a wet chemical process such as described herein, it is shown that iron sulphate is added to all or a portion of the sulphuric acid stream to obtain an iron sulphate solution for use with the recovered lithium hydroxide solution to produce lithium iron phosphate.

Example 1

The EUR-2C electrodialysis cell purchased from Euroduce was modified to include Astom bipolar membrane (BP1) and FuMaTech anion and cationic membranes (FAB and FKB, respectively). A feed solution pretreated to adjust the pH to 10 was introduced into the cell to precipitate phosphate and other impurities, which were then filtered to remove the precipitate. The pH was then adjusted to pH 3.5 and then fed into the cell.

It can be seen from Table 2 that the cation membrane produces up to 2.16 M LiOH at a current efficiency of about 75%. At a current efficiency of 40%, the anion exchange membrane produced a 0.6 MH ₂ SO ₄ product solution. The average current density was close to 62 mA/cm ² throughout the operation while the cell was operated at a constant voltage of 25 V (this voltage was applied between all seven sets of membranes and the electrode wash chamber). Under this short-term work, no solids were observed in the pool, indicating that the pH was adjusted to 10 by pretreatment before introducing the feed solution into the tank, and the results were improved compared to the unadjusted feed solution. .

Since we have to use a product stream to maintain the pH in the central chamber, The overall efficiency of this cell appears to be determined by the lowest current efficiency of any particular membrane. Therefore, in Example 1, it is necessary to add some of the product LiOH back to the central chamber to neutralize the protons relocated from the acid chamber. Therefore, the total current efficiency of the cell should be 40%, eliminating the advantages of the FKB film.

Example 2-5

Examples 2 through 5 were all operated using Astom membranes (ACM, CMB and BPI). Examples 2 and 3 are short-term experiments using a lithium sulfate feed solution pretreated to pH 10 as previously described. Both examples obtained acid and alkali current efficiencies close to 60% and maintained good current densities in the short term, indicating that the pretreatment was improved compared to previous operations. Example 4 is an overnight experiment that operates using the same conditions and shows a significant decrease in current density, which may be due to contamination of the membrane with phosphate or other deposits.

Figure 5 shows the current densities of all three operations. After 1250 minutes, pause the pool and turn off the pump to load. When the system was restarted, the current density recovered significantly, indicating that the current drop was due to a small amount of precipitate which was subsequently washed away from the cell.

Since pretreatment to pH 10 may cause some contaminants to remain in the feed stream, Example 5 used a solution that was pretreated to pH 11 and maintained for 3 days, followed by filtration. As shown in Fig. 6, the current density was maintained for more than 24 hours, and the result was remarkably improved. The final drop in current is believed to be due to the gradual depletion of lithium sulfate in the feed, which is operated in a single large batch.

Figure 6 also shows that the concentration of acid and base is maintained fairly constant by constant addition of water. Therefore, it is necessary and sometimes necessary to add a product acid or base to control the pH in the central feed chamber. To help control this room, choose a higher acid The concentration, thereby reducing the acid current efficiency, allows the pH in the central chamber to be controlled to 3.5 only by the addition of LiOH. The average current density of the hydroxide formed is about 60%.

Figure 6 shows that the sulfate concentrations in all three chambers vary with time. The central chamber was operated in a single batch and at the end of the experiment, the concentration reached approximately 0.2M. The sulfate in LiOH is about 400 mg/L, which accounts for about 0.85% of the current. Lowering the sulfuric acid concentration further reduces the sulfate content in LiOH.

Example 6-10

In Examples 6-10, the Eurodia EUR-2C electrodialysis cell was used to demonstrate the feasibility of three-chamber salt cracking of lithium sulfate. The cell is equipped with seven sets of cation, anion and bipolar membranes, configured as shown in Figure 1. The effective area of each film was 0.02 m ² .

It is believed that due to the reversion of hydroxide ions, lithium phosphate formed in the high pH region adjacent to the cation membrane is the main cause of membrane fouling. The phosphate solution and other impurities were removed by pretreatment of the feed solution by raising the pH to 11 to adjust the pH to only 10, so that most of the salts precipitated and improved results were obtained.

Example 9 is a representative example and is described in detail below. The 1 M lithium sulfate starting solution was pretreated to remove insoluble phosphate by raising the pH to 11 with 4M LiOH in a ratio of about 1 L LiOH to 60 L 1 M Li ₂ SO ₄ . The treated lithium sulfate was thoroughly mixed, and the precipitate was allowed to settle overnight, followed by filtration through a glass fiber filter paper (1 μm pore size). The pH of the filtered Li ₂ SO ₄ was adjusted to pH 2 by adding about 12 mL of 4 M sulfuric acid per liter of Li ₂ SO ₄ .

The pretreated Li ₂ SO ₄ feed had a starting volume of 8 L and was preheated to about 60 ° C and subsequently transferred to a 20 L glass feed reservoir. The initial LiOH base was 3 liters of heel from Example 8, which was analyzed to give a LiOH of 1.8 M at the beginning of the experiment. The initial acid from Example 8 is also the dross 2L H ₂ SO _4, and H ₂ SO ₄ to give analysis was 0.93M. The electrode wash was 2 liters of 50 mM sulfuric acid. The solution was pumped into the Eurodia pool (EUR-2C-BP7) at approximately 0.5 L/well (total flow rate 3-4 L/min), maintaining equal back pressure (3-4 psi) on each chamber to prevent either membrane The pressure is too large and causes internal leakage. The flow rate and pressure of each chamber were monitored, as well as feed temperature, feed pH, current, voltage, charge passed, and feed volume.

Electrodialysis was carried out at a constant voltage of 25 volts. The Li ₂ SO ₄ feed temperature was controlled at 35 °C. The pump (TE-MDK-MT3, Kynar March Pump) and the ED pool provide enough heat to maintain the temperature. A 20 liter feed tank is jacketed so that when the temperature exceeds 35 ° C, the cooling water can be pumped into the jacket via a solenoid valve and temperature controller (OMEGA CN76000).

The cell membrane provides sufficient heat transfer to cool other chambers. To allow this experiment to run continuously for 20 hours, the Li ₂ SO ₄ feed pretreated to pH 2 was pumped and the continuous rate of ₁ M Li ₂ SO ₄ feed was 10 mL/min. The protons that migrate through the ACM membrane are more than the hydroxides that migrate back through the FKB cation membrane, so the pH of the central compartment usually decreases. The pH of the central chamber was controlled by the addition of 4M LiOH using a high sodium pH electrode and a JENCO pH/ORP controller set at pH 2. An electronic data record of the feed pH per minute during the 20 hour experiment showed a pH ranging from 1.9 to 2.1, so a total of 3.67 L of 4 M LiOH was added to the feed to neutralize the hydroxide reversion. After 20 hours of operation, the feed volume increased from 8 L to 15.3 L due to the addition of 11.8 L Li ₂ SO ₄ and 3.7 L LiOH and the transport of 6.8 L of water to the acid and 0.7 L of water to the base.

LiOH base is circulated through the cell from a 1 gallon closed polypropylene tank. The 3 liter volume was maintained by draining from the top using a tube fixed to the LiOH surface, and the LiOH product was collected in a 15 gallon overflow container using a peristaltic pump. The LiOH concentration was maintained at a concentration of 1.85 M LiOH by adding water to the LiOH tank at a constant rate of 17 mL/min.

Sulfuric acid is circulated through the acid chamber of the cell from a 2 L glass reservoir. The overflow port near the top of the reservoir maintains a constant volume of 2.2 LH ₂ SO ₄ and the overflowed acid product flows into the 15 gallon tank. The H ₂ SO ₄ concentration was kept constant at 1.9 M by adding water at a constant rate of 16 mL/min.

An electrode wash (50 mM H ₂ SO ₄ ) is circulated through the anolyte and catholyte end chambers and recombined at the top of the 2 liter polypropylene can at the cell outlet, where the O ₂ and H ₂ gases generated at the electrodes flow to the fume hood rear.

Several samples were taken during the experiment to ensure that the rate of water addition to the acid and base was sufficient to maintain a constant concentration during the experiment. At the end of the 19.9 hour experiment, the power was turned off, the can was emptied, and the final product and the final volume of Li ₂ SO ₄ and electrode wash were measured. A total of 30.1 L of 1.86 M LiOH (including 3 L of slag) and 21.1 L of 1.92 MH ₂ SO ₄ (including 2 L of slag) were obtained. The final feed was 15.3 liters of 0.28 M Li ₂ SO ₄ and the final electrode wash contained 1.5 L of 67 mM H ₂ SO ₄ . 0.5 L of water in the electrode wash was passed through the cation membrane to the acid. The total amount of water added to the acid and alkali was 18.6 liters and 20.4 liters, respectively. The total charge passed was 975,660 coulombs (70.78 moles), of which 33.8 moles H relocated, 20.2 moles of OH ^- rebound, and 14.97 moles of LiOH were added to the feed. The average current density of this experiment was 67.8 mA/cm ² . Based on the analysis of the sulfate enriched in the acid, the H ₂ SO ₄ current efficiency was 52.5%; based on the analysis of Li ⁺ in the LiOH product, the LiOH current efficiency was 72.4%.

Analysis of the starting and final samples by using a Dionex DX600 equipped with a GP50 gradient pump, AS 17 analytical column, ASRS300 anion suppressor, CD25 conductivity detector, EG40 KOH eliminator and AS40 autosampler SO ₄ ^2- . 25 μL of the sample was injected onto a separation column in which a concentration gradient of 1 mM to 30 mM KOH was used, and a gradient of 5 mM/min was raised to dissolve the anion at 1.5 mL/min. The sulfate concentration is determined by using a peak area generated by conductivity detection relative to a four-point calibration curve, which is in the range of 2 to 200 mg/L SO ₄ ^2- . The sample was analyzed by a similar technique using a Dionex DX320 IC equipped with an IC25A isocratic pump, CS12a analytical column, CSRS300 cation suppressor, IC25 conductivity detector, ECG II MSA eliminator and AS40 autosampler. Li ⁺ . 25 μL of the sample was injected onto a separation column in which the anion was eluted at a concentration gradient of 20 mM to 30 mM methanesulfonic acid (MSA) at 1.0 mL/min. The lithium concentration is determined by using a peak area generated by conductivity detection with respect to a four-point calibration curve, which is in the range of 10 to 200 mg/L Li ⁺ . The acid concentration of H ₂ SO _{4 was} determined by titrating the pH to pH 7 with standard 1.0 N sodium hydroxide. The alkali concentration was determined by titration with a standard 0.50 N sulfuric acid to pH 7 using a microburrete.

Table 3 summarizes the results of electrodialysis experiments performed on Astom ACM membranes. Example 6 also used Astom CMB cation membrane and BP1 bipolar membrane, respectively. The lithium sulfate feed solution was pretreated to pH 11, filtered, and then adjusted to pH 3.5, and then passed to the cell. The results for current efficiency are comparable to those reported last month; however, the average current density is lower than the current operating current density, indicating some contamination. The pH gradient of the cationic membrane appeared to cause precipitation problems at pH 3.5, the pH of the feed compartment was lowered to pH 2, and a FuMaTech FKB cation membrane with less hydroxide reversion was used. The FI (13 and ACM film) pairing means that the pH in the central chamber is determined by the relocation of protons through the ACM, and the pH is controlled only by the addition of LiOH.

Examples 7 through 9 were repeated using the FKB/ACM/BP1 combination, and the three batches were totaled for 70 hours. As can be seen from Table 3, the reproducibility of these operations is excellent, and the LiOH current efficiency measured in three different ways is 71-75% (loss of Li ⁺ in the feed, Li ⁺ and hydroxide ions in the alkali chamber) Increase to measure). Similarly, the acid current efficiency measured by all three measurement methods is 50-52%. The data for these examples shows the consistency of the average current density. Figure 7 illustrates this situation where the initial current densities match each other very well. Due to the difference in batch size, there is a deviation at the end of each batch, so the final lithium sulfate concentration is different.

The high current efficiency of the FKB film appears to help avoid precipitation problems at the boundary layer on the feed side of the cation membrane. The total current efficiency of the process is determined by the worst performing film. That is, the inefficiency of the ACM film must be compensated by adding the LiOH in the alkali chamber back to the feed chamber, so the overall efficiency is due to the anion membrane. reduce. To increase the efficiency of the anion membrane, the acid concentration in the acid compartment of the product is reduced. Example 10 was operated using 0.61 M sulfuric acid which increased the acid current efficiency by about 10% to about 62%. (See Table 3)

Example 11-12

To further increase the acid current efficiency, in Examples 11 and 12, the cell was modified with an AAV replacement anion membrane from Astom. The AAV film is an acid blocking film originally available from Ashahi Chemical. Table 4 shows an overview of the data for conducting such experiments using a combination of FKB, AAV, and BP-1 bipolar membranes.

The current efficiency of the acid and base of these membranes is very similar to the combination of Examples 7-9. When a lower acid concentration is used, the acid current efficiency is increased by about 10%. The average current density of this film combination was slightly lower than when using an ACM film (about 10 mA/cm ² at the same acid concentration and when operating at a constant stack voltage of 25V). External AC impedance measurements confirmed that the AAV resistance was higher than ACM when measured in Li ₂ SO ₄ solution.

The purity of the lithium hydroxide product to be recycled to the process of preparing lithium iron phosphate is extremely important. Using this salt cracking technique, the main impurity in the LiOH stream is the sulfate ion, which is transported from the acid chamber through the bipolar membrane to the base. The amount of transport should be directly related to the acid concentration. It is clearly seen by comparing Example 9 with Example 10 (see Table 3), and Comparative Example 11 and Example 12 (see Table 4). Under various conditions, when the acid concentration was lowered from 1 M to 0.6 M, the sulfate contamination in 1.88 M LiOH was reduced by about half. Steady-state sulfate concentrations of 430ppm and 200, respectively Ppm.

Since sulfate ions and lithium ions are transported through the ion exchange membrane, water is also transferred due to ion hydration (electroosmosis) and osmosis. However, the delivery of water to the central outdoor is not sufficient to maintain a constant concentration. This is illustrated by considering the transfer of water in Example 8. When a lithium ion is transferred through the cation membrane, 7 water is also transferred. Similarly, an average of 1.8 waters are transferred together with sulfate ions, and a single lithium sulfate has a total of 15.8 waters. Since the lithium sulfate in the feed solution is only 1 mole, each lithium sulfate contains almost 55 moles of water, so that the lithium sulfate in the central chamber is continuously diluted. This continuous dilution can be controlled by removing water from the feed chamber and can be controlled by, for example, reverse osmosis.

All references cited herein are hereby incorporated by reference in their entirety for all purposes.

The temperature was 35 ° C, constant voltage = 25, and the feed pH was controlled at 3.5.

The temperature was 35 ° C, the constant voltage was 25, and the feed pH was controlled at 3.5/2.0.

The temperature was 35 ° C, the constant voltage was 25, and the feed pH was controlled at 3.5/2.0.

Figure 1 : Schematic diagram of a bipolar electrodialysis cell for recovering lithium in the form of lithium hydroxide from a liquid stream containing lithium sulfate.

Figure 2: Lithium hydroxide and lithium sulfate is recycled to the process for producing lithium iron phosphate of a simplified lithium sulfate bipolar electrodialysis recycle process block of FIG.

Figure 3 : Block diagram of a lithium sulfate bipolar electrodialysis recycle process for recycling lithium hydroxide and sulfuric acid to the manufacture of lithium iron phosphate.

Figure 4 : A block diagram of a lithium sulfate bipolar electrodialysis recycle process using recycled lithium hydroxide, sulfuric acid, and lithium hydroxide produced from another lithium source to produce lithium iron phosphate.

Figure 5 : A graph of current density as a function of time during the passage of a feed solution pretreated to pH 10 into an electrodialysis cell with an Astom membrane.

Figure 6 : A plot of current density and concentration of acid and base product over time during the passage of a feed solution pretreated to pH 11 into an electrodialysis cell.

Figure 7 : Graph of current density as a function of time during the operation of the Eurodia EUR-2c electrodialysis cell operated with a feed solution at a constant voltage.

Claims (35)

A method of recovering lithium in the form of lithium hydroxide comprising feeding an aqueous solution containing lithium sulfate into a bipolar electrodialysis cell, wherein the cell forms a lithium hydroxide solution. The method of claim 1, comprising the steps of: (a) feeding a lithium sulfate-containing liquid stream into the apparatus containing the bipolar electrodialysis cell; (b) electrodialyzing the lithium sulfate-containing solution to separate the positively charged one. Lithium ions and negatively charged ions; (c) lithium recovered in the form of a lithium hydroxide solution obtained from the electrodialysis separation step. The method of claim 1 wherein the lithium hydroxide is fed to a process stream in which the lithium hydroxide is required. The method of claim 1, wherein the lithium hydroxide is fed into a lithium hydroxide-requiring process in which the lithium hydroxide is required, so that the lithium hydroxide-requiring process is continuously performed. The method of claim 1, wherein the feed stream is used to prepare lithium iron phosphate. The method of claim 1, wherein the liquid stream comprises lithium ions from a lithium source selected from the group consisting of lithium carbonate, lithium hydroxide monohydrate, and lithium nitrate. The method of claim 1, wherein the liquid stream is obtained by extracting lithium from a lithium-containing ore or a material based on a lithium-containing ore. The method of claim 2, further comprising recycling the lithium hydroxide recovered from the electrodialysis separation to the process required for the lithium hydroxide In the feed stream. The method of claim 2, further comprising reducing or removing phosphate ions in the feed stream prior to bipolar electrodialysis. A bipolar electrodialysis unit for separating ionic species in a lithium sulfate-containing liquid stream by using a bipolar electrodialysis cell, wherein the bipolar electrodialysis cell comprises: (a) an anion permeable membrane that allows negatively charged ions Pass, but prevent positively charged lithium ions from passing through; (b) a cation permeable membrane that allows positively charged lithium ions to pass, but prevents negatively charged ions from passing through; (c) is located in an anion permeable membrane and cation permeable a bipolar membrane between the membranes forming a separate chamber with the anion permeable membrane and the cationic permeable membrane, respectively; (d) an anode and a cathode, wherein the anion permeable membrane, the cationic permeable membrane, and the bipolar a membrane is located between the anode and the cathode; and (e) a direct current applied across the electrodes. The bipolar membrane of claim 10, wherein the bipolar membrane is formed from an anion exchange layer and a cation exchange layer, and the layers are bonded together. The bipolar membrane of claim 11 further comprising a water diffusion layer or interface to allow diffusion of water from the external aqueous salt solution. The film of claim 10 is from a commercially available source. The membrane of claim 13 is from a commercially available source selected from the group consisting of ACM, CMB, AAV, BP or FumaTech FKB of Astom. The membrane of claim 10 is resistant to unwanted ion migration, low The resistivity and the resistance to the potential corrosion properties of the resulting acid to the base solution are used in combination. The method of claim 1, wherein the feed stream contains lithium ions in the form of lithium sulfate, the method comprising the steps of: (a) feeding a lithium sulfate stream into a device containing a bipolar electrodialysis cell; (b) The lithium sulfate liquid stream is subjected to electrodialysis to separate positively charged lithium ions and negatively charged sulfate ions; (c) generating a lithium hydroxide solution on the anode side and generating a sulfuric acid solution on the cathode side; and (d) recovering from The bipolar electrodialysis gives lithium in the form of a lithium hydroxide solution. The method of claim 16, wherein the lithium sulfate-containing liquid stream is a feed stream from the production of lithium battery components. The method of claim 16, further comprising the steps of: (a) adjusting the pH of the lithium sulfate stream to 10 to 11 by adding an alkali metal hydroxide to remove impurities; and (b) removing impurities therefrom. Precipitating in the lithium sulfate stream; (c) filtering impurities from the lithium sulfate stream; and (d) adjusting the pH of the resulting stream to pH 1 to 4, and then feeding the stream to the bipolar In the dialysis unit. The method of claim 18, wherein the alkali metal hydroxide is selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide. The method of claim 18, wherein the impurity is a phosphate. The method of claim 18, wherein the pH of the lithium sulfate stream in step (d) is It is adjusted to 2 to 3.5. The method of claim 18, wherein the pH of the lithium sulfate stream of step (d) is adjusted to 2 to 3. The method of claim 16, further comprising removing phosphate from the lithium sulfate stream by using an ion exchange membrane, and subsequently feeding the stream into the bipolar electrodialysis unit. The method of claim 16, wherein the lithium hydroxide solution is introduced into the process of preparing LiFePO ₄ or other lithium-containing salt or product. The method of claim 16, wherein the recovered lithium hydroxide is used as a base in a chemical reaction. The method of claim 16, wherein the lithium hydroxide solution is used to adjust the pH of the lithium sulfate-containing feed stream. The method of claim 16, further comprising concentrating the lithium hydroxide solution. The method of claim 16, which further comprises purifying the lithium hydroxide solution. The method of claim 16, further comprising the steps of: (a) recovering the sulfuric acid solution produced by the bipolar electrodialysis; (b) adding an iron source to the recovered sulfuric acid solution; (c) causing the sulfuric acid The solution is converted into iron sulfate; (d) the sulfate ion, the recovered lithium hydroxide solution and the phosphate raw material are mixed to prepare lithium iron phosphate, wherein the lithium phosphate is produced in a continuous process. The method of claim 29, wherein the source of iron is naturally occurring iron ore Metal iron seen. The method of claim 29, wherein the recovered lithium hydroxide solution is adjusted to a desired lithium hydroxide concentration by introducing lithium hydroxide from another source. The method of claim 29, wherein the recovered lithium hydroxide solution is adjusted to a desired lithium hydroxide concentration by concentrating the recovered lithium hydroxide solution. The method of claim 29, further comprising the steps of: (a) adjusting the pH of the lithium sulfate stream to 10 to 11 by adding an alkali metal hydroxide to remove impurities; and (b) removing impurities therefrom. Precipitating in the lithium sulfate stream; (c) filtering impurities from the lithium sulfate stream; and (d) adjusting the pH of the resulting stream to pH 2 to 3.5, and then feeding the stream to the bipolar In the dialysis unit. The method of claim 16, further comprising: (a) recovering the lithium hydroxide liquid stream obtained by the bipolar electrodialysis and the sulfuric acid liquid stream; (b) reacting the sulfuric acid liquid stream with lithium carbonate to produce additional a lithium sulfate solution; (c) adding the additional lithium sulfate solution to the original feed stream containing lithium sulfate; and (d) continuously feeding the lithium sulfate liquid stream to the bipolar electrodialysis unit. The method of claim 34, further comprising the steps of: (a) adjusting the pH of the lithium sulfate stream to 10 to 11 by adding an alkali metal hydroxide to remove impurities; (b) precipitating impurities from the lithium sulfate stream; (c) filtering impurities from the lithium sulfate stream; and (d) adjusting the pH of the resulting stream to pH 2 to 3.5, followed by the liquid The flow is fed into the bipolar electrodialysis unit.