Method for regenerating a cation exchange resin

Abstract

The invention relates to methods for regenerating cation exchange resins used, in particular, in lithium carbonate production processes. The proposed method for regenerating a cation exchange resin is characterized in that regeneration is performed by feeding into a column containing a cation exchange resin a mother liquor obtained at a lithium carbonate precipitation stage of a lithium carbonate production process. The technical result consists in preserving the mechanical strength of a cation exchange resin after multiple regeneration cycles, increasing the level of desorption and end-to-end recovery of lithium in lithium carbonate production processes, reducing the use of additional reagents and minimizing the formation of calcium and magnesium precipitates.

Description

[0001] METHOD FOR REGENERATION OF CATION EXCHANGE RESIN

[0002] Field of technology

[0003] The invention relates to methods for regenerating cation exchange resins used, in particular, in processes for producing lithium carbonate.

[0004] Currently, processes for producing lithium carbonate from lithium-containing solutions require the removal of calcium and magnesium impurities that may be present in the feed solutions. Typically, calcium and magnesium are precipitated using various methods for this purpose. Calcium and magnesium impurities can also be removed using cation exchange resins. However, this requires regeneration of these resins, which also requires additional processes and costs.

[0005] The proposed invention is aimed at solving this problem and can be successfully applied in lithium carbonate production technologies.

[0006] Prior art

[0007] Currently, various methods exist for extracting lithium from lithium-containing solutions. For example, a method for the sorption extraction of lithium from lithium-containing solutions is described in patent RU 2516538C1. In this method, KU-2-8 cation exchange resin, saturated with calcium and magnesium, is treated with a secondary lithium concentrate, which converts the cation exchange resin into lithium. The resulting solution contains LiCl, MgCl2, and CaCl2, which is then mixed with the mother liquor from lithium carbonate precipitation and a soda solution, resulting in the formation of sparingly soluble compounds such as CaCO3 and Mg(OH)2 or Mg4(OH)2(CO3)3*3H2O.

[0008] The disadvantage of this method is:

[0009] - formation of sediments containing calcium and magnesium, which can cause hydrodynamic resistance in the sorption column and depressurization.

[0010] The article "One-Step Solvometallurgical Process for Purification of Lithium Chloride to Battery Grade" (Avdibegovic, D., Nguyen, V.T., & Binnemans, K., Journal of Sustainable Metallurgy, 2022, 8:893-899) mentions another method based on the use of ion-exchange resins. After calcium and magnesium are sorbed on these resins, they can be regenerated by rinsing with a solution containing excess sodium ions. This restores the resins' ability to perform a new cycle of calcium and magnesium sorption. The disadvantages of this method include:

[0011] - the need to introduce additional reagents into the process;

[0012] - an increase in sodium ions in the processed material and, as a consequence, an increase in their concentration in the finished product.

[0013] A method is known for regenerating the strongly acidic cationite KU-2-8 in sodium form with sodium chloride solutions in water desalination processes. This study examined the effect of regenerating solution concentration on the efficiency of hardness ion removal from the KU-2-8 cation exchange resin. It was found that an 8% sodium chloride solution is required for complete regeneration in the sodium form.

[0014] The article also notes that hydrogen ions, which have a greater affinity for the cation exchange resin than sodium ions, replace them in the cation exchange resin matrix. The optimal pH during Na-cation exchange should be no less than 6.5 and no more than 10.0. According to the article's authors, excessively high pH (over 10) negatively impacts the cation exchange resin's structure, so maintaining an optimal pH is essential to prevent resin degradation.

[0015] The disadvantages of this method are:

[0016] - the need to introduce additional reagents into the process;

[0017] - an increase in sodium ions in the processed material and, as a consequence, an increase in their concentration in the finished product.

[0018] Disclosure of the essence of the invention

[0019] As is known, acid solutions are used to regenerate most cation exchange resins (hereinafter referred to as resin or cation exchanger) https: / / 7universum.com / nj / nature / archi ve / item / 12057 ). In lithium carbonate production processes, this complicates the subsequent processing of acidic lithium-containing solutions, since they require initial neutralization, and only then can lithium be extracted. Furthermore, the cation exchange resin contracts in an acidic environment and expands in an alkaline one (this process is also known as "osmotic shock"). This negatively impacts the service life of the cation exchange resin. The objective of the claimed invention is to create a method for regenerating the cation exchange resin with alkaline solutions, allowing for the simultaneous desorption of calcium and magnesium and the regeneration of the cation exchange resin, converting it to the required working form.

[0020] The authors also faced the challenge of recycling the mother liquor after the lithium carbonate precipitation stage, with the possibility of returning residual lithium from the mother liquor to the process. This product is formed by the interaction of sodium carbonate with lithium-containing concentrate.

[0021] The technical result from the implementation of the claimed invention includes:

[0022] - use of recycling processes for the regeneration of cation exchange resins without the introduction of additional reagents;

[0023] - elimination of contamination of finished products with foreign elements due to the introduction of additional reagents;

[0024] - no need to introduce acids into the regeneration process;

[0025] - combination of the processes of desorption of calcium and magnesium and regeneration of the cation exchanger with its conversion into the required working form;

[0026] - reduction of overall water consumption due to reuse of liquids from other stages of the process;

[0027] - maintaining the mechanical strength of the cation exchanger after repeated regeneration cycles;

[0028] - no need to neutralize by-products (mother solution from lithium carbonate precipitation);

[0029] - increasing the through extraction of lithium in lithium carbonate production processes;

[0030] - minimization of calcium and magnesium precipitation during the regeneration process, up to the complete elimination of this effect;

[0031] - increasing the degree of desorption.

[0032] In addition, the use of the claimed method allows:

[0033] - carry out regeneration of cation exchanger at pH greater than 10;

[0034] - reduce water consumption by at least 142 ml when regenerating 20 ml of cationite saturated with calcium and magnesium ions;

[0035] - maintain the structure of the cation exchanger during regeneration at a pH greater than 10; - maintain the mechanical strength of the cation exchanger at about 99% after 15 regeneration cycles;

[0036] - increase the through extraction of lithium in lithium carbonate production processes to 92%;

[0037] - increase the degree of desorption up to 90%.

[0038] To solve the above problem and achieve the technical result, a method for regenerating a cation exchange resin is proposed, in which regeneration is carried out by feeding the mother liquor obtained at the lithium carbonate precipitation stage of the lithium carbonate production process into a column with a cation exchange resin.

[0039] The above conditions are sufficient to achieve the technical result, and the preferred embodiments described below allow for more complete utilization of the advantages of the claimed invention and improved results in cation exchanger regeneration, increased desorption, reduced consumption of water and other reagents, and preservation of the cation exchanger's mechanical strength. Preferably, the mother liquor has a pH in the range of 7.0 to 14.0, preferably 10.0 to 13.0, and most preferably 11.5 to 12.5.

[0040] Preferably, the mother liquor is supplied in a volume of 1-10 KO, preferably 3-7 KO, most preferably 4-6 KO,

[0041] Preferably, the mother liquor is fed at a rate of 0.5-5.0 KO / h, preferably 0.8-3.0 KO / h, most preferably 1.0-2.0 KO / h.

[0042] Preferably, the regeneration process of the cation exchange resin is carried out at a temperature of 30-85 °C, more preferably 46-85 °C, most preferably 75-85 °C.

[0043] Preferably, the pH of the mother liquor is adjusted by adding alkali to it before feeding it to the cation exchange resin column.

[0044] Preferably, sodium hydroxide is used as the alkali, preferably sodium hydroxide in the form of an aqueous solution with a concentration of 40%;

[0045] Preferably, the mother liquor is fed in an upward flow.

[0046] Preferably, one of the following is used as the cation exchange resin: strongly acidic cation exchangers with sulfonic or phosphonic functional groups, or weakly acidic cation exchangers with carboxyl functional groups or chelating resins, aminophosphonic or iminodiacetate resins, ion exchange resin, styrene-divinylbenzene copolymers. Preferably, after feeding the mother liquor, lithium-containing concentrate is fed to the column with the cation exchange resin.

[0047] Preferably, the lithium-containing concentrate contains at least 1 mol of lithium per liter of concentrate, preferably at least 1.5 mol of lithium per liter of concentrate.

[0048] Preferably, the volume of lithium-containing concentrate supplied is 5-25 KO, preferably 10-20, most preferably 13-16 KO.

[0049] Preferably, maintaining the pH of the supplied lithium-containing concentrate at 4-7;

[0050] Preferably, the feed rate of lithium-containing concentrate is 2-5 KO / h.

[0051] Preferably, the lithium-containing concentrate is collected from any stage of the lithium carbonate production process, preferably from the stage with the highest lithium concentration in the solution.

[0052] Preferably, the lithium-containing concentrate is withdrawn from any stage of the lithium carbonate production process, preferably after the stage of thermal concentration of the lithium-containing solution.

[0053] Preferably, the mother liquor after contact with the cation exchange resin is fed to the lithium sorption extraction stage of the lithium carbonate production process.

[0054] Preferably, the lithium-containing concentrate, after contact with the cation exchange resin, is fed to the thermal concentration stage of the lithium carbonate production process.

[0055] The sorption method for purifying lithium-containing solutions from metal ion impurities, particularly Ca and Mg, involves the use of cation exchange resins with various functional groups, such as strongly acidic cation exchangers with sulfonic or phosphonic functional groups, weakly acidic cation exchangers with carboxyl functional groups, or chelating resins. Examples of chelating resins that can be used include aminophosphonic or iminodiacetate resins.

[0056] The most preferred conditions for implementing the method are indicated below.

[0057] As is known, a higher pH can remove more sodium ions from a cation exchange resin during regeneration, which can improve the efficiency of the ion exchange process and extend the service life of the cation exchange resin. Therefore, a higher pH during regeneration can promote more efficient removal of sodium ions from the resin, making the process more productive.

[0058] However, according to the aforementioned prototype method, a pH above 10 negatively impacts the structure and stability of the cation exchange resin. High pH (over 10) can also lead to the rupture of polymer bonds in the cation exchange resin matrix due to repeated osmotic compression and expansion, resulting in a reduction in mechanical strength.

[0059] In addition to the above-mentioned disadvantages, as is known, the interaction of an alkaline environment with calcium and magnesium ions should lead to the precipitation of these elements (Effective Removal of Calcium and Magnesium Ions from Water, Zhuqing Wang, Zhongmin Feng, Leilei Yang and Min Wang, https: / / cyberieninka.rU / articie / n / pojucheisie-

[0060] Mg 2+ + 2OH~ -> Mg(0H)2f

[0061] The precipitation will lead to an increase in hydrodynamic resistance in the sorption column, with a subsequent risk of its depressurization.

[0062] For the reasons stated above, regenerating the cation exchanger with an alkaline solution in lithium carbonate production processes is not an obvious solution.

[0063] The authors also faced the challenge of disposing of the mother liquor after the lithium carbonate precipitation stage. This product is formed by the interaction of sodium carbonate with lithium-containing concentrate. During lithium carbonate precipitation, a concomitant reaction of sodium carbonate hydrolysis occurs:

[0064] Na2CO2+ 2H2O = 2NaOH + H2O + CO2

[0065] The result is an alkaline solution. Typically, the pH of the resulting solution (mother liquor) is 10-12, but other parameters are possible depending on the composition of the feedstock. Also, the possible presence of unprecipitated carbonate ions in the mother liquor should, in theory, promote the formation of insoluble precipitates of calcium and magnesium carbonates:

[0066] Ca 2+ (aq) + CO3 2 '(aq) -> CaCO3(s)

[0067] Mg 2+ (aq) + CO3 2 '(aq) -> MgCO3(s)

[0068] Thus, the claimed method for regenerating cation exchange resin has an inventive step, since it represents a non-standard solution for specialists in this field and opens up new possibilities in the field of purifying solutions from calcium and magnesium ions.

[0069] Without being bound by a particular theory, the present inventors hypothesized that this effect may be due, in particular, to the fact that the carbonate ion content of the mother liquor is not critical for its subsequent use in cation exchanger regeneration. The authors propose that during lithium carbonate precipitation, a significant portion of the carbonate ions precipitates along with the lithium carbonate. Predominantly, hydrogen carbonates remain in solution. Calcium and magnesium hydrogen carbonates are more soluble than their carbonates. When the cation exchanger is regenerated with an alkaline mother liquor, calcium and magnesium ions are replaced by alkali metal ions, and calcium and magnesium ions remain in solution as hydroxides.

[0070] Hmm 2+ + 20H~ = Mg(OH)2

[0071] In this way, the precipitation of calcium and magnesium is minimized during the regeneration process, even to the point of completely eliminating this effect.

[0072] The feed rate of the mother liquor into the cation exchange resin column is preferably 0.5-5 KO / h, more preferably 0.8-3 KO / h, and most preferably 1-2 KO / h. This affects the total volume of mother liquor required for calcium and magnesium desorption. The lower the feed rate, the less solution is needed for desorption, since the exchange reaction has time to proceed more completely at a lower rate. If the rate is high, some of the ions are not replaced.

[0073] Selecting the optimal temperature can also influence the process. Preferably, cation exchange resin regeneration is carried out at a temperature of 30-85°C, more preferably at 50-85°C, and most preferably at 75-85°C. Using a higher temperature increases the rate of chemical reactions and, consequently, the rate of desorption.

[0074] According to the claimed invention, a calcium- and magnesium-saturated cation exchange resin is treated with a mother liquor obtained during the lithium carbonate precipitation stage of the lithium carbonate production process. The mother liquor contains a residual lithium content of 1 g / l. As a result of this treatment, 80% of the cation exchange resin is converted to the sodium form, while the remaining 20% ​​is converted to the lithium form.

[0075] In a preferred embodiment, the sodium-form cation exchange resin is then converted to the lithium form by treatment with a lithium-containing concentrate containing lithium at a concentration of at least 1 mol / liter, preferably at least 1.5 mol / liter. At higher lithium concentrations, the conversion of the entire cation exchange resin to the lithium form occurs more rapidly.

[0076] The conversion of the cationite into lithium form allows the cationite to fully restore its exchange capacity, thus combining the processes of sorption and desorption during the regeneration process.

[0077] Lithium-containing concentrate can be collected from any stage of the lithium carbonate production process, but it is preferable to take it from the thermal concentration stage, since it is at this stage that the lithium content in the concentrate is highest.

[0078] In a preferred embodiment, the mother liquor used for regeneration is sent to the lithium sorption stage after contact with the resin. In a preferred embodiment, the lithium-containing concentrate, after contact with the resin, is returned to the thermal concentration stage. The schematic is shown in Fig. 1.

[0079] Brief description of the drawings

[0080] The drawings are presented for a better understanding of the invention, however, it will be obvious to a person skilled in the art that the disclosed invention is not limited to the embodiment shown in them.

[0081] Fig. 1 shows a diagram of the process for producing lithium carbonate.

[0082] Fig. 2 shows a graph of the cumulative desorption curves of calcium and magnesium. Implementation of the invention. The best embodiment of the invention

[0083] The process of obtaining lithium carbonate contains the following stages (see Fig. 1):

[0084] 1. Sorption (sorption extraction) of lithium to obtain a raffinate (a solution purified from the extracted (recoverable) component) and a lithium eluate (a solution containing the extracted component - lithium),

[0085] 2. Sorption of Ca, Mg (purification of lithium eluate from Ca, Mg) with removal of lithium-containing solution to the concentration stage.

[0086] 3. Concentration (thermal) of lithium-containing (lithium) solution to obtain lithium-containing concentrate.

[0087] 4. Precipitation of lithium carbonate from lithium-containing concentrate to obtain mother liquor and lithium carbonate.

[0088] The mother liquor obtained in stage 4 of lithium carbonate precipitation is fed into a column with a cation exchange resin (sorbent) for its regeneration after it has been used for the sorption of Ca, Mg (purification from Ca, Mg).

[0089] As a result, the cation exchange resin (sorbent) is in the sodium form, then to convert it into the lithium form it is treated with lithium-containing (lithium) concentrate from stage 3 of thermal concentration.

[0090] After contact with the cation exchange resin, the lithium-containing concentrate is fed (returned) to the thermal concentration stage.

[0091] The mother liquor after contact with the cation exchange resin is fed to stage 1 of the lithium sorption extraction.

[0092] Below is an example of the sorption of Ca and Mg on the cation exchanger KU 2-8 from a lithium-containing solution:

[0093] KU 2-8 cation exchange resin is a high-molecular-weight polymer compound with a three-dimensional gel and macroporous structure, containing acidic functional groups capable of cation exchange reactions. The ionic form is H+, the functional group is a sulfonic acid group, the matrix is ​​styrene-divinylbenzene, and the structure is gel (GOST 20298-74).

[0094] A model solution simulating primary lithium concentrate was used to remove calcium and magnesium ions. 9.5 liters of lithium solution were passed upward through a column filled with 80 ml of KU 2-8 cation exchange resin in the Na form at a flow rate of 120 ml / hour (1.5 column volumes per hour). The concentrations of the main elements in the lithium eluate are presented in Table 1.

[0095] Table 1 - Content of elements in lithium-containing solution (lithium eluate)

[0096] During the sorption process, calcium and magnesium ions absorbed by the cation exchanger replace sodium ions in the cation exchanger's functional groups and displace them into the raffinate. Table 2 shows the content of the main elements in the raffinate.

[0097] Table 2 - Content of main elements in the raffinate

[0098] Calcium recovery was 97.7%, magnesium recovery 99.4%. The saturated cation exchange resin was washed with water in a downward flow at a rate of 480 ml / hour (6 column volumes per hour) for 50 minutes. The saturated and washed cation exchange resin from this example was used for regeneration using various methods.

[0099] The following examples illustrate, but are not intended to limit, the feasibility of implementing the invention. It will be apparent to those skilled in the art that other embodiments are possible without changing the essence of the invention.

[0100] Example 1 (preferred option)

[0101] Selection of cation exchange resin: KU-2-8, which is saturated with calcium and magnesium ions, is used as a cation exchange resin.

[0102] Regeneration of cation exchange resin:

[0103] The mother liquor, after lithium carbonate precipitation, is fed upward into a column with a cation exchange resin saturated with calcium and magnesium ions at a rate of 1 KO / h, with a pH of 12. To achieve optimal pH, 40% sodium hydroxide (alkali) can be added to the mother liquor. The cation exchange resin expands in an alkaline environment, so an upward flow is preferable, as it prevents the column from becoming clogged with swollen cation exchange resin. The mother liquor is fed at a rate of 5 KO / h, resulting in 80% of the cation exchange resin being converted to lithium.

[0104] Column volume (VO) is the volume of liquid equal to the volume of sorbent involved in the technological stage / operation.

[0105] The solution passed through the cation exchanger is returned to the lithium sorption extraction stage. This design allows lithium from the wastewater to be recycled back into the process, increasing the throughput of lithium recovery.

[0106] After contacting the resin with the mother liquor, the cation exchange resin is treated with lithium-containing concentrate taken from the thermal concentration stage of lithium solutions. The concentrate contains 5 mol / liter of lithium, and the pH is 5.5. The concentrate is fed at a rate of 5 KO / h. The volume of the concentrate is 15 KO. After passing the lithium concentrate through the cation exchange resin, it is returned to the thermal concentration stage.

[0107] The process of regeneration of cation exchange resin is carried out at a temperature of 80°C. Under these parameters, the degree of desorption reaches 95%.

[0108] This approach achieves a number of technical results, including regeneration at a pH greater than 10, increased cation exchange resin capacity, extended cation exchange resin service life, preservation of the cation exchange resin structure during regeneration, maintenance of mechanical strength after multiple regeneration cycles, and the elimination of calcium and magnesium precipitation during the regeneration process. It also leads to reduced water consumption due to the reuse of liquids from other process stages.

[0109] Prototype example

[0110] A 20 ml sample of KU 2-8 cation exchange resin, saturated with a model lithium-containing concentrate, was loaded into a column and washed with a 3M sodium chloride solution at a flow rate of 30 ml / h (1.5 column volumes per hour) in an ascending flow for 5 hours. The elution (regeneration) curves for this example are presented in Table 3.

[0111] Table 3

[0112]

[0113] The water consumption in the prototype method was 142 ml.

[0114] A series of experiments using the proposed method were also conducted. The results are presented in the tables below.

[0115] Table 4 demonstrates desorption with a mother liquor containing 1.5 g / L of lithium. The first column shows the cumulative volume. Based on the results of this experiment, a graph of the cumulative desorption curves for calcium and magnesium was constructed (Fig. 2). As the graph shows, the optimal mother liquor volume for cation exchanger regeneration is 4-6 KO.

[0116] Table 4

[0117]

[0118]

[0119] All the presented embodiments of the invention according to the claimed method did not require additional water consumption due to the reuse of liquids from other stages of the process.

Claims

Invention formula 1. A method for regenerating a cation exchange resin, characterized in that the regeneration is carried out by feeding into a column with a cation exchange resin a mother liquor obtained in the lithium carbonate precipitation stage of the lithium carbonate production process.

2. The method according to claim 1, characterized in that the mother liquor has a pH in the range from 7.0 to 14.0, preferably from 10.0 to 13.0, most preferably 11.5-12.

5.

3. The method according to item 1, characterized in that the mother liquor is supplied in a volume of 1-10 KO, preferably 3-7 KO, most preferably 4-6 KO.

4. The method according to item 1, characterized in that the mother liquor is fed at a rate of 0.5-5.0 KO / h, preferably 0.8-3.0 KO / h, more preferably 1.0-2.0 KO / h.

5. The method according to claim 1, characterized in that the process of regeneration of the cation exchange resin is carried out at a temperature of 30-85 °C, preferably at a temperature of 46-85 °C, most preferably at a temperature of 75-85 °C.

6. The method according to item 1, characterized in that before feeding the mother liquor into the column with the cation exchange resin, the pH of the mother liquor is adjusted by adding alkali to it.

7. The method according to item 6, characterized in that sodium hydroxide is used as the alkali, preferably sodium hydroxide in the form of an aqueous solution with a concentration of 40%.

8. The method according to item 1, characterized in that the mother liquor is fed in an ascending flow.

9. The method according to claim 1, characterized in that one of the following is used as the cation exchange resin: strongly acidic cationites with sulfonic or phosphonic functional groups, or weakly acidic cationites with carboxyl functional groups or chelate resins, aminophosphonic or iminodiacetate resins, ion exchange resin, copolymers of styrene and divinylbenzene.

10. The method according to item 1, characterized in that after feeding the mother liquor into the column with the cation exchange resin, lithium-containing concentrate is fed.

11. The method according to claim 10, characterized in that the lithium-containing concentrate contains at least 1 mol of lithium per liter of concentrate, preferably at least 1.5 mol of lithium per liter of concentrate.

12. The method according to claim 10, characterized in that the volume of lithium-containing concentrate supplied is 5-25 KO, preferably 10-20, most preferably 13-16 KO.

13. The method according to claim 10, characterized in that the pH of the supplied lithium-containing concentrate is 4-7.

14. The method according to item 10, characterized in that the rate of supply of lithium-containing concentrate is 2-5 KO / h.

15. The method according to claim 10, characterized in that the lithium-containing concentrate is taken from any stage of the process of obtaining lithium carbonate, preferably from the stage with the highest concentration of lithium in the solution.

16. The method according to claim 10, characterized in that the lithium-containing concentrate is taken from any stage of the process of obtaining lithium carbonate, preferably after the stage of thermal concentration of the lithium-containing solution.

17. The method according to claim 1, characterized in that the mother liquor, after contact with the cation exchange resin, is fed to the stage of sorption extraction of lithium in the process of obtaining lithium carbonate.

18. The method according to item 16, characterized in that the lithium-containing concentrate, after contact with the cation exchange resin, is fed to the thermal concentration stage of the process for obtaining lithium carbonate.

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