Production of calcium-reduced lithium carbonate

Abstract

The invention relates to a method for producing calcium-reduced lithium carbonate.

Description

[0001] Production of calcium-reduced lithium carbonate

[0002] The invention relates to a process for producing calcium-reduced lithium carbonate.

[0003] Lithium carbonate is an important material for the production of high-purity lithium, which is known to be used in lithium-ion batteries as an energy storage medium. The use of high-purity lithium is necessary for the production of lithium-ion batteries, as impurities reduce the capacity and lifespan of the batteries.

[0004] To produce high-purity lithium carbonate, chelate resins with iminodiacetic acid groups or aminoalkylenephosphonic acid groups are often used to remove alkaline earth ions from concentrated lithium-containing brine solutions. After adsorption of the alkaline earth ions onto the chelate resins, they are eluted with hydrochloric acid or other mineral acids, and the chelate resin is converted into the acid form (H form). To enable reuse of the chelate resin, it is converted into the Na or Li form using a strong base, e.g., sodium hydroxide or lithium hydroxide, and regenerated in the process to ensure a sufficiently high local pH value for the ion exchange groups.

[0005] Corresponding processes in which chelate resins loaded with calcium and / or magnesium are first treated with acids and, after elution of the calcium and / or magnesium ions, are treated with lithium- or sodium-containing basic solutions and thereby regenerated, are known from CN 107055577 A and WO 2013036983 A1.

[0006] DE 19809420 A1 discloses a process for producing purified lithium carbonate. This process involves converting a lithium carbonate solution to lithium bicarbonate using carbon dioxide. This bicarbonate is then brought into contact with a regenerated styrene / dimethylbenzene polymer functionalized with aminoalkylenephosphonic acid groups or iminodiacetic acid groups. The flow is heated, and the resulting pure lithium carbonate is converted into lithium fluoride by a further reaction with hydrofluoric acid.

[0007] The prior art processes require complex plant systems to regenerate the chelating resins used, generate additional waste streams due to the use of the regeneration solutions, and are therefore ecologically and economically disadvantaged. The objective was therefore to provide a process for producing lithium carbonate that overcomes the disadvantages of the prior art.

[0008] It has now surprisingly been found that calcium-reduced lithium carbonate can be prepared from calcium-containing aqueous lithium hydrogen carbonate solutions at a pH of 6.5 to 9.0 in the presence of a polystyrene copolymer which is functionalized with aminoalkylenephosphonic acid groups or with iminodiacetic acid groups and is present in the acid form.

[0009] The invention therefore relates to a process for the preparation of calcium-reduced lithium carbonate, in which in a process step a.) a calcium-containing aqueous lithium hydrogen carbonate solution is reacted with at least one chelate resin containing functional groups of the structural element (I) wherein stands for the polystyrene copolymer backbone and R 1 and R 2 independently represent -CH2COOH or -CH2PO(OH)2 or hydrogen, where R 1 and R 2 not both can be hydrogen at the same time, at a pH value of 6.5 to 9.0, and in a process step b.) the calcium-reduced aqueous lithium hydrogen carbonate solution from process step a.) is converted thermally, by decomposition or with a carbonate to calcium-reduced lithium carbonate.

[0010] The calcium-containing aqueous lithium bicarbonate solution preferably contains at least 0.1 wt.% lithium bicarbonate based on the total weight of the solution. The calcium-containing aqueous lithium bicarbonate solution particularly preferably contains 0.5 wt.% to 5 wt.% lithium bicarbonate based on the total weight of the solution.

[0011] The calcium-containing aqueous lithium bicarbonate solution preferably contains at least 1* 10 -4 % by weight of calcium ions based on the total weight of the solution. The calcium-containing aqueous lithium bicarbonate solution particularly preferably contains 1* 10 -4 Wt.% to 0.5 wt.% calcium ions based on the total weight of the solution. The calcium-containing aqueous lithium bicarbonate solution most preferably contains 1*10 -3 Wt% to 0.1 wt% calcium ions based on the total weight of the solution.

[0012] In one embodiment of the invention, the calcium-containing aqueous lithium bicarbonate solution preferably contains additional metal ions, other than calcium ions, in an amount < 20 ppb based on the total weight of the solution.

[0013] The calcium-containing aqueous lithium bicarbonate solution preferably contains metal ions other than calcium ions in a weight amount of 1*10 -7 Wt.% to 1 wt.% based on the total weight of the solution. Particularly preferably, the calcium-containing aqueous lithium bicarbonate solution contains metal ions other than calcium ions in a weight amount of 1*10 -5 Wt.% to 0.1 wt.% based on the total weight of the solution. Metal ions other than calcium ions are preferably Mg, Al, Fe, K, and Na. Additional anions that may also be present in the calcium-containing aqueous lithium bicarbonate solution are preferably Cl', SO4. 2 ; NO3 2PO 3 ',H2PO -,HPO 2 ' and CO3 2- .

[0014] In a further embodiment of the invention, the calcium-containing aqueous lithium bicarbonate solution preferably contains 0.1 wt.% to 5 wt.% lithium bicarbonate, 1*10 -3 wt.% to 0.1 wt.% calcium and between 1*10 -7 Wt.% to 1 wt.% of other metal ions other than calcium ions, based on the weight of the solution used.

[0015] In a further embodiment of the invention, the calcium-containing aqueous lithium bicarbonate solution preferably contains at least 0.1 wt.% lithium bicarbonate and at least 1*10 -3 Wt% calcium ions, based on the total weight of the solution.

[0016] In a further embodiment of the invention, the calcium-containing aqueous lithium bicarbonate solution preferably contains at least 0.1 wt.% lithium bicarbonate and at least 1*10 -3wt% calcium ions and < 20 ppb other metal ions other than calcium ions, based on the total weight of the solution.

[0017] The calcium-containing aqueous lithium bicarbonate solution preferably contains >75 wt.% water based on the weight of the solution used. Even more preferably, this embodiment contains at least 80 wt.% water based on the weight of the solution used.

[0018] In a further embodiment of the invention, the calcium-containing aqueous lithium bicarbonate solution preferably contains 0.1 wt.% to 5 wt.% lithium bicarbonate and 1*10 -3 wt% to 0.01 wt% calcium and 1*10 -6 Wt.% to 0.1 wt.% of other metal ions other than calcium ions, based on the weight of the solution used.

[0019] The pH of the calcium-containing aqueous lithium bicarbonate solution when brought into contact with the chelate resin containing functional groups of the structural element (I) is preferably 6.5 to 8.5, very particularly preferably 6.5 to 7.5.

[0020] As polystyrene copolymers in the chelate resin containing functional groups of the structural element (I), for example and preferably copolymers of styrene, vinyltoluene, ethylstyrene, a-methylstyrene, chlorostyrene, or chloromethylstyrene and mixtures of these monomers with polyvinylaromatic compounds (crosslinkers), such as preferably divinylbenzene, divinyltoluene, trivinylbenzene, divinylnaphthalene or trivinylnaphthalene, are used.

[0021] A styrene / divinylbenzene cross-linked copolymer is particularly preferably used as the polystyrene copolymer backbone.

[0022] The polymer of the chelate resin is preferably spherical and is therefore also called bead polymer.

[0023] In the polystyrene copolymer backbone, the -CH2-NR 1 R 2 -group is preferably bonded to a phenyl radical. The chelate resins used according to the invention containing functional groups of structural element (I) preferably have a macroporous structure.

[0024] In general and preferably, the pores of the macroporous bead polymers of the chelate resins used according to the invention containing functional groups of the structural element (I) have a diameter of 20 nm to 100 nm.

[0025] The chelate resins used according to the invention containing functional groups of the structural element (I) preferably have a monodisperse distribution.

[0026] In the present application, substances are referred to as monodisperse if at least 90% by volume or mass of the particles have a diameter that lies within the interval with a width of + / - 10% of the most common diameter around the most common diameter. For example, for a substance with a most common diameter of 0.5 mm, at least 90% by volume or mass lies in a size interval between 0.45 mm and 0.55 mm; for a substance with a most common diameter of 0.7 mm, at least 90% by volume or mass lies in a size interval between 0.77 mm and 0.63 mm.

[0027] The average degree of substitution of the amine groups of the chelate resin containing functional groups of the structural element (I), where R 1 and R 2 independently of each other = -CH2COOH or H, but R 1 and R 2 cannot simultaneously represent hydrogen is preferably 1.4 to 2.0.

[0028] In a further embodiment of the invention, the average degree of substitution of the amine groups of the chelate resin containing functional groups of the structural element (I), where R 1 and R 2 independently of each other = -CH2COOH or H, but R 1 and R 2 cannot simultaneously represent hydrogen, preferably 1.4 to 1.9.

[0029] The average degree of substitution indicates the statistical ratio between unsubstituted, monosubstituted, and disubstituted amino groups. The average degree of substitution can therefore range between 0 and 2. With a degree of substitution of 0, no substitution would have occurred, and the amine groups of structural element (I) would be present as primary amino groups. With a degree of substitution of 2, all amino groups in the resin would be disubstituted. With a degree of substitution of 1, statistically speaking, all amino groups in the resin would be monosubstituted.

[0030] In a further embodiment of the invention, a macroporous, monodisperse chelate resin containing functional groups of the structural element (I) is used in process step a.). In this case, R 1 and R 2independently of one another = - CH2PO(OH)2, or hydrogen, where both cannot simultaneously represent hydrogen. The bead polymer of the chelate resin containing functional groups of structural element (I) preferably has a diameter of 250 to 700 pm, particularly preferably 250 to 450 pm, in process step a.).

[0031] In a further embodiment of the invention, a macroporous, monodisperse chelate resin containing functional groups of the structural element (I) is used in process step b.). In this case, R 1 and R 2 independently of each other = - CH2COOH or H, but R 1 and R 2 do not simultaneously represent hydrogen. The bead polymer of the chelate resin containing functional groups of structural element (I) in process step a.) preferably has a diameter of 250 to 700 pm, particularly preferably 250 to 450 pm.

[0032] The determination of the total hydrogen capacity of the macroporous, monodisperse chelate resin containing functional groups of the structural element (I) is carried out according to DIN 54403 (Testing of ion exchangers - Determination of the total capacity of cation exchangers).

[0033] Preferably, macroporous, monodisperse chelate resins containing functional groups of the structural element (I) have a total hydrogen capacity of 2.0 mol / L to 3.5 mol / L.

[0034] Particularly preferred in process step a.) is a chelate resin containing functional groups of the structural element (I) in which R 1 and R 2 independently of each other = - CH2COOH or H, but R 1 and R 2 cannot simultaneously represent hydrogen.

[0035] The chelate resins containing functional groups of the structural element (I) in which R 1 and R 2 independently of each other = -CH2COOH or H, but R1 and R 2 do not simultaneously represent hydrogen, are commercially available, for example from LANXESS Deutschland GmbH under the trade name Lewati® MonoPlus TP 207, Lewati® MDS TP 208, Lewatit® MonoPlus TP 208 or Lewatit® TP 207.

[0036] The chelate resins containing functional groups of the structural element (I) in which R 1 and R 2 independently of one another = -CH2PO(OH)2, or hydrogen, where both cannot simultaneously represent hydrogen, are commercially available, for example from LANXESS Deutschland GmbH under the trade name Lewati® MonoPlus TP 260 or Lewati® MDS TP 260.

[0037] The chelate resin containing functional groups of structural element (I) is used in the process according to the invention in the H form. This means that the functional groups of structural element (I) are present in the H form, i.e., as -CH2COOH or -CH2PO(OH)2.

[0038] If the resin is in a different charge state, it is preferably converted to the H form by reaction with an inorganic acid. In this case, it is preferably reacted with three times the bed volume of the chelate resins containing functional groups of structural element (I). This is preferably done with hydrochloric acid. A dilute inorganic acid in a concentration range of 5 to 10 wt.% is preferably used for the charge conversion. The resin is then preferably washed with water until the pH is between 6.0 and 8.0, particularly preferably 7.0.

[0039] In a further embodiment of the invention, the calcium-containing aqueous lithium bicarbonate solution used in process step a.) is prepared from a calcium-containing aqueous lithium carbonate solution by introducing carbon dioxide. The reaction is preferably carried out with carbon dioxide, with a pH of 6.0 to 8.0 preferably being established. The carbon dioxide is preferably reacted with the aqueous lithium carbonate solution at a pressure of 0.05 to 0.5 bar.

[0040] In process step a.), the chelate resin containing functional groups of the structural element (I) can be brought into contact with the calcium-containing aqueous lithium bicarbonate solution in a batch or column process. The batch process is preferably carried out in such a way that the calcium-containing aqueous lithium bicarbonate solution is first introduced. The chelate resin containing functional groups of the structural element (I) is then added, preferably with stirring. The mixture is preferably kept in contact for 0.5 to 10 hours, preferably with stirring. The chelate resin containing functional groups of the structural element (I) is then separated off by methods known to those skilled in the art, such as preferably by filtration. The process is preferably carried out in a column process. The calcium-containing aqueous lithium bicarbonate solution can be applied in the downstream or upstream flow.The application is preferably carried out upflow, i.e. against the direction of gravity. The pumping rate at which the calcium-containing aqueous lithium bicarbonate solution is applied to the column is preferably 5 to 15 bed volumes per hour. Preferably, while the calcium-containing aqueous lithium bicarbonate solution is brought into contact with the chelating resin containing functional groups of the structural element (I), carbon dioxide is continuously introduced into the calcium-containing aqueous lithium bicarbonate solution. The calcium-reduced aqueous lithium bicarbonate solution from process step a.) preferably has a calcium content of < 100 ppb, more preferably a calcium content of < 20 ppb, most preferably a calcium content of < 10 ppb, based on the amount by weight of the calcium-reduced aqueous lithium bicarbonate solution.

[0041] In process step b.), the calcium-reduced lithium carbonate is precipitated from the aqueous calcium-reduced lithium bicarbonate solution from process step a.), preferably at a pH of 10.0 to 12.0. The pH is preferably adjusted by adding an aqueous alkali metal hydroxide solution, preferably by adding sodium hydroxide. Alkali metal carbonates, in particular potassium carbonate or sodium carbonate, can preferably be added as carbonates in process step b.). Sodium carbonate is preferably added as the carbonate source in process step b.). Process step b.) is preferably carried out at a temperature of 80°C to 95°C. Process step b.) is preferably carried out at atmospheric pressure.

[0042] However, it is also possible to produce the calcium-reduced lithium carbonate from the aqueous calcium-reduced lithium bicarbonate solution from process step a.) by thermal decomposition. For this purpose, the aqueous calcium-reduced lithium bicarbonate solution from process step a.) is preferably refluxed. The lithium carbonate precipitated as a solid is then dried, preferably at 280 °C to 320 °C. This process produces lithium carbonate from the lithium bicarbonate.

[0043] In a further embodiment of the invention, a process for producing a lithium salt is included, in which in a process step a1.) a calcium-containing aqueous lithium carbonate solution is reacted with carbon dioxide to produce a calcium-containing aqueous lithium bicarbonate solution and in a process step b1.) the calcium-containing aqueous lithium bicarbonate solution from process step a1.) is reacted with at least one chelate resin containing functional groups of the structural element (I) wherein stands for the polystyrene copolymer backbone and R 1 and R 2 independently represent -CH2COOH or -CH2PO(OH)2 or hydrogen, where R 1 and R 2not both can be hydrogen at the same time at a pH value of 6.5 to 9.0, and in a process step c1.) the aqueous calcium-reduced lithium hydrogen carbonate solution from process step a.) is converted thermally, by decomposition or with a carbonate to lithium carbonate and optionally in a process step d1.) this calcium-reduced lithium carbonate is converted into corresponding lithium salts by reaction with other inorganic or organic acids.

[0044] These lithium salts are preferably selected from the group consisting of lithium chloride, lithium fluoride, lithium sulfate, lithium nitrate, and lithium bromide. Hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, or hydrobromic acid are then preferably used as inorganic acids.

[0045] Preferably, inorganic acids are used in process step d1.).

[0046] The chelate resin containing functional groups of the structural element (I) is also used in the H-form in process step b1.) in the process according to the invention.

[0047] The process according to the invention for the adsorption of calcium also applies to the adsorption of magnesium to the same extent.

[0048] Accordingly, the invention also relates to a process for the preparation of magnesium-reduced lithium carbonate, in which in a process step a.) a magnesium-containing aqueous lithium hydrogen carbonate solution is reacted with at least one chelate resin containing functional groups of the structural element (I) wherein represents the polystyrene copolymer backbone and Ri and R2 independently represent -CH2COOH or -CH2PO(OH)2 or hydrogen, where Ri and R2 cannot both be hydrogen at the same time, at a pH of 6.5 to 9.0, and in a process step b.) the magnesium-reduced aqueous lithium hydrogen carbonate solution from process step a.) is converted thermally, by decomposition or with a carbonate to magnesium-reduced lithium carbonate.

[0049] The invention also includes the use of chelate resins containing functional groups of the structural element (I) wherein stands for the polystyrene copolymer backbone and R 1 and R 2 independently represent -CH2COOH or -CH2PO(OH)2 or hydrogen, where R 1 and R 2not both can be hydrogen at the same time for the removal of calcium ions from calcium-containing aqueous lithium hydrogen carbonate solutions at a pH value of 6.5 to 9.0.

[0050] Using the process according to the invention, lithium carbonate is preferably produced in a purity of at least 99.9970 wt.% based on the total weight of the lithium carbonate. Particularly preferably, using the process according to the invention, lithium carbonate is produced in a purity of at least 99.9995 wt.% based on the total weight of the lithium carbonate. Very particularly preferably, using the process according to the invention, lithium carbonate is produced in a purity of at least 99.99999 wt.% based on the total weight of the lithium carbonate.

[0051] By means of the process according to the invention, calcium-reduced lithium carbonate is produced with a calcium content of preferably < 100 ppb, particularly preferably with a calcium content of < 20 ppb, very particularly preferably with a calcium content of < 10 ppb, based on the amount by weight of the lithium carbonate.

[0052] The process according to the invention can be used to obtain high-purity lithium carbonate. Furthermore, the conditioning and regeneration of the chelate resin containing functional groups of the structural element (I) into the Na or Li form by reaction with sodium hydroxide and lithium hydroxide can be omitted, thus allowing the use of simpler plant systems and reducing waste streams, thus improving the process both ecologically and economically.

[0053] The following examples serve only to describe the invention and are not intended to limit it.

[0054] Methods

[0055] The ion concentration can be determined using methods known to those skilled in the art. The ion concentration in the method according to the invention is preferably determined using an inductively coupled plasma spectrometer (ICP).

[0056] The effluent from the ion exchange column was fractionated into 10 ml fractions and analyzed by ICP, and the ion concentration was determined.

[0057] A) Production of lithium hydrocarbon

[0058] In a flat-ground reactor, 48.1 g (0.65 mol) of l_i2CO3 (calcium content < 50 ppm) are suspended in 1 L of deionized water and treated with CO2 for 5 to 6 hours until lithium bicarbonate LiHCO3 forms and dissolves. The CO2 gas is introduced through a glass frit and stirred under slight pressure at 0.1–0.3 bar. This process is continued until the pH is approximately 7.5 and a clear solution is formed. Subsequently, 184 mg of CaCl2 × 2H2O are added and dissolved. The feed solution contains 8.8 g / L Li and 47.1 mg / L Ca (47.1 ppm).

[0059] B) Removal of Ca 2+ by means of an imi Chelate resin

[0060] The lithium bicarbonate solution containing 50 ppm Ca 2+ from Example 1 A) is then passed upstream over 10 ml of a macroporous, monodisperse, chelate resin containing functional groups of the structural element (I) where R 1 and R 2independently of each other = -CH2COOH or H, but R 1 and R 2 cannot simultaneously represent hydrogen and the polymer of this chelate resin is a cross-linked polystyrene-divinylbenzene copolymer (Lewatit® MDS TP 208), in the H form, at pH 6.9, pumped. The bead polymer of the chelate resin has a diameter of 380 pm. The average degree of substitution of the chelate resin used here containing functional groups of the structural element (I) is 1.6. The resin has a total hydrogen capacity of 2.8 mol / l. The experiment is carried out at RT and at a rate of 10 BV (bed volume) / h. Stirring is slow throughout the entire run and CO2 is introduced. Samples are taken at 10 BV, 20 BV, 40 BV, 60 BV, 80 BV and 100 BV. In addition, a feed sample is taken at the beginning.

[0061] Table 1 C) Extraction of lithium carbonate by precipitation

[0062] The pH of the aqueous lithium bicarbonate solution from flow-through B) (1 L) was adjusted to pH 10 using NaOH. Then, 0.3 L of 18 g of 400 g / L Na2CO3 was added at 90 °C, and the precipitated Li2CO3 was filtered off as a white solid. The mixture was filtered at 2 bar, yielding 32.5 g of Li2CO3 with a purity of 99.998% and a calcium content of <20 ppb. This corresponds to a yield of 88%.

Claims

Patent claims 1 . A process for the preparation of calcium-reduced lithium carbonate, characterized in that in a process step a.) a calcium-containing aqueous lithium hydrogen carbonate solution with at least one chelate resin containing functional groups of the structural element (I) wherein stands for the polystyrene copolymer backbone and R 1 and R 2 independently represent -CH2COOH or -CH2PO(OH)2 or hydrogen, where R 1 and R 2 not both can be hydrogen at the same time, at a pH value of 6.5 to 9.0, and in a process step b.) the aqueous calcium-reduced lithium hydrogen carbonate solution from process step a.) is converted thermally, by decomposition or with a carbonate to calcium-reduced lithium carbonate.

2. Method according to claim 1, characterized in that R 1 and R 2independently of each other = -CH2COOH or H, but R 1 and R 2 cannot simultaneously represent hydrogen.

3. Process according to claim 1 or 2, characterized in that the average degree of substitution is 1.4 to 2.

0.

4. Process according to one of claims 1 to 3, characterized in that the polystyrene copolymer backbone is a styrene / divinylbenzene crosslinked copolymer.

5. Process according to one of claims 1 to 4, characterized in that the bead polymer of the chelate resin containing functional groups of the structural element (I) has a diameter of 250 pm to 700 pm.

6. Process according to at least one of claims 1 to 5, characterized in that the pH value is 6.5 to 8.

5.

7. Process according to at least one of claims 1 to 6, characterized in that the calcium-containing aqueous lithium hydrogen carbonate solution in Process step a.) contains at least 0.1 wt.% lithium hydrogen carbonate based on the total weight of the solution.

8. Process according to at least one of claims 1 to 7, characterized in that the calcium-containing aqueous lithium bicarbonate solution in process step a.) contains 0.1 wt.% to 5 wt.% lithium bicarbonate based on the total weight of the solution.

9. Process according to at least one of claims 1 to 8, characterized in that the calcium-containing aqueous lithium bicarbonate solution used in process step a.) contains at least 1*10 -3 wt.% calcium ions based on the total weight of the solution.

10. Process according to at least one of claims 1 to 9, characterized in that the calcium-containing aqueous lithium bicarbonate solution used in process step a.) contains 1*10 -3Contains 0.1 wt.% to 0.1 wt.% calcium ions based on the total weight of the solution.

11. Process according to at least one of claims 1 to 10, characterized in that in process step a.) the calcium-containing aqueous lithium bicarbonate solution contains metal ions which are not calcium ions in a weight amount of < 20 ppb based on the total weight amount of the solution.

12. Process according to at least one of claims 1 to 10, characterized in that in process step a.) the calcium-containing aqueous lithium bicarbonate solution contains metal ions which are not calcium ions in a weight amount of 1*10 -7 wt.% to 0.1 wt.% based on the total weight of the solution.

13. Process according to at least one of claims 1 to 10, characterized in that the calcium-containing aqueous lithium bicarbonate solution used in process step a.) contains 0.1 wt.% to 5 wt.% lithium bicarbonate, 1*10 -3 wt.% to 0.01 wt.% calcium and between 1*10 -6 wt.% to 1 wt.% of other metal ions other than calcium ions, based on the weight of the solution used.

14. Process according to at least one of claims 1 to 13, characterized in that the pH value during the reaction of the aqueous calcium-reduced lithium bicarbonate solution from process step a.) in process step b.) with a carbonate is 10.0 to 12.

0.

15. Use of at least one chelating resin containing functional groups of the structural element (I) wherein stands for the polystyrene copolymer backbone and R 1 and R 2independently represent -CH2COOH or -CH2PO(OH)2 or hydrogen, where R 1 and R 2 not both can be hydrogen at the same time, at a pH of 6.5 to 9.0 for the removal of calcium ions from calcium-containing aqueous lithium bicarbonate solutions.

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