Method for separating li ions and na ions

Abstract

The invention relates to a method for separating Li ions and Na ions from sulfate-containing solutions, and to a device for carrying out the method.

Description

[0001] Process for the separation of Li and Na ions

[0002] The present invention relates to a method for separating Li and Na ions from sulfate-containing solutions and to a device for carrying out the method.

[0003] Electric vehicles powered by electricity from low-emission sources are considered to have the greatest climate protection potential of all land-based transport technologies over their entire life cycle. Accordingly, electromobility is considered a central component of a sustainable and climate-friendly transport system based on renewable energies. The focus of electric drive systems is on lithium-ion / polymer batteries as a promising storage system, although these batteries have a limited lifespan. Therefore, the desired extent of electrification can only be achieved in conjunction with a sustainable recycling concept. In particular, the planned ban on the sale of new vehicles with combustion engines makes the holistic recovery of valuable metals contained in used batteries, such as cobalt, nickel, and manganese, as well as lithium, which is only obtainable through lengthy processes, essential.

[0004] The state of the art describes a number of processes that deal with the recovery of valuable metals from spent lithium-ion / polymer batteries.

[0005] US 2017 / 0077564 relates to a method for recycling lithium-ion batteries, comprising: (i) identifying a molar ratio for cathode materials for a new battery; (ii) forming a leach solution by combining crushed battery material from a lithium battery recycling stream with an acidic leaching agent and hydrogen peroxide (H2O2) to separate cathode materials from undissolved materials; (iii) filtering the undissolved materials from the formed leach solution such that the dissolved salts of the cathode materials remain in the leach solution; (iv) determining a composition of the leach solution by identifying a molar ratio of the salts of the cathode material dissolved therein;(v) adding Ni, Co, Mn, or Al salts in sulfate (xSO4) based on the determined composition to adjust the molar ratio of the dissolved cathode material salts in the leach solution to correspond to the identified molar ratio for the recycled battery, including the addition of a solution of aluminum sulfates and a chelating agent; and (iv) increasing the pH of the leaching solution to at least 10 to precipitate and filter metal ions of the cathode materials to form a precursor pCAM for the actual cathode active material CAM, in which the Ni, Co, Mn, and Al salts remaining in the solution are present as combined hydroxide (OH)2 or carbonate (CO3) with a molar ratio as desired for the new CAM. The precursor is then intensively mixed with LiOH*H2O or U2CO3 and converted into the cathode active material at temperatures >800°C.

[0006] US 2013 / 0302226 discloses a method for recycling batteries in which a solution of aggregated battery materials from spent cells is produced, impurities are precipitated from the produced solution, a predetermined ratio of desired materials is set in the solution, and the desired material is precipitated and further processed into cathode material for new batteries.

[0007] However, the processes described in the prior art have the disadvantage that, due to the process design, the lithium to be recovered is present as U2SO4 in a solution together with Na2SO4, so that it can only be recovered as sparingly soluble U2CO3 towards the end of the process chain. Due to the solubility ratios of U2CO3 and Na2CO3, as well as Na2SO4 and U2SO4, the detailed separation of Na and Li ions is very complex and makes actual quantitative recovery of the lithium practically impossible from an economic perspective.

[0008] In order to achieve sustainable and complete reprocessing of spent lithium-ion / polymer batteries, there is still a need for a process that enables improved recovery of lithium from sodium-containing sulfate solutions. The object of the present invention is therefore to meet this need.

[0009] In the context of the present invention, it was surprisingly found that the poor separability of Li and Na ions from sulfate-containing solutions can be circumvented by converting them into the corresponding hydroxides.

[0010] Therefore, a first object of the present invention is a process for the separation of Na and Li ions, in which an aqueous solution A comprising Na2SO4 and U2SO4 is subjected to electrolysis to obtain a solution B and the resulting solution B is treated with a carbonate source to form U2CO3.

[0011] The skilled person is aware that the compounds Na2SC, U2SO4, Na2CO3, U2CO3, and all other salts exist in solution in the form of their ions. Therefore, unless otherwise stated, they are used as synonyms for the corresponding ions, and their explicit mention is omitted.

[0012] It was surprisingly found that the greater solubility differences between U2CO3 and Na2CO3 compared to the solubilities of Na2SO4 and U2SO4 can be advantageously utilized to achieve a more effective separation. While the solubilities of Na2SO4 and U2SO4 differ only by a factor of 2, U2CO3 is significantly less soluble than Na2CO3, allowing a more effective separation of the two metals. Therefore, an embodiment in which U2CO3 is separated to obtain a Na2CO3-containing filtrate is preferred.

[0013] A variety of compounds can be used as carbonate sources in the process according to the invention. The carbonate source is preferably selected from the group consisting of Na2CO3, CO2, NaHCl, (NH4)2CO3, (NH4)HCO3, and mixtures thereof. The use of CO2 as a carbonate source has proven particularly advantageous and therefore preferred. This can be obtained, for example, from exhaust gases from other processes and thus be used sustainably, thereby reducing CO2 emissions.

[0014] The process according to the invention involves subjecting a solution of the sulfate salts of Na and Li to electrolysis, with the assumption that this converts the sulfate salts into the corresponding hydroxides, which can be separated more advantageously. In this regard, membrane electrolysis is preferred, particularly electrodialysis, and especially electrodialysis with bipolar membranes. Multi-chamber electrolysis with a cation exchange membrane and an anion exchange membrane is particularly preferred.

[0015] In the process according to the invention, the lithium is recovered as U2CO3, which can be removed from the solution as a solid in a further step. Preferably, the U2CO3 is separated using at least one method selected from the group consisting of sedimentation, filtration, and centrifugation. The separation may include a short washing process, whereby the washing liquors can be recycled into the overall process at suitable points.

[0016] The process according to the invention allows for the effective separation of Na and Li. If the purity of the U2CO3 obtained is deemed insufficient, the U2CO3 can be subjected to further purification steps. In a preferred embodiment, the obtained U2CO3 is converted into soluble UHCO3 in a further step by treatment with CO2. By heating the UHCO3-containing solution, highly pure U2CO3 can be obtained from this solution. Therefore, an embodiment in which the UHCO3-containing solution is heated to form U2CO3 is preferred. This purification step offers the advantage that the mother liquor obtained during the separation of the U2CO3 and the CO2 obtained during the formation of U2CO3 and expelled from the reaction mixture can be returned to the process, thus creating a sustainable cycle.

[0017] The starting solution A of the process according to the invention can be obtained by a number of processes such as those used in recycling processes. The sulfate-containing aqueous solution A is preferably obtained by treating a solution X, wherein the solution X comprises U2SO4 and at least one compound MSC, where M is a transition metal, preferably selected from the group consisting of Ni, Co, Mn, Al and mixtures thereof. This treatment can be carried out, for example, using NaOH and optionally further addition of H2SO4. It is assumed that by treating the solution X with NaOH, the metal M is converted into its hydroxide with the formation of Na2SO4 as a by-product.Alternatively, the metal can first be transferred into the organic phase via reactive extraction in the presence of an organic extractant and then extracted from the organic phase as MSO4 back into the aqueous phase using sulfuric acid and thus returned to the further value creation cycle.

[0018] Solution X is preferably obtained in the process according to the invention by treating a suspension Y comprising at least one compound UMO2 with H2SO4 and a reducing agent, where M is a transition metal, preferably one selected from the group consisting of Ni, Co, Mn, Al, and mixtures thereof. The reducing agent is preferably selected from the group consisting of H2O2 and SO2. The process according to the invention is particularly aimed at the recovery of Li from lithium-ion / polymer batteries. Therefore, an embodiment is preferred in which the suspension comprising UMO2 is obtained from used lithium-ion batteries and / or production waste during their manufacture.In this way, the process according to the invention provides a comprehensive recycling cycle that allows efficient recovery of the lithium used in lithium-ion / polymer batteries and thus makes a valuable contribution to the success of the desired electromobility concept.

[0019] As part of the comprehensive recycling approach, the transition metal hydroxide obtained during the treatment of solution X can also be further processed, for example for further use as cathode active material in new batteries. In a preferred embodiment of the process according to the invention, the treatment of solution X is therefore carried out in such a way that a transition metal mixed hydroxide NixCo y Mn z(OH)2 is obtained by adjusting the transition metal stoichiometry and precipitation with NaOH. The adjustment of the stoichiometry can be achieved, for example, by targeted separation or targeted addition of one or more of the components of the transition metal mixed hydroxide. In this way, the desired ratio of Ni:Co:Mn in the subsequent cathode material can be adjusted in the transition metal mixed hydroxide. In the context of the current shift to nickel-enriched cathode active materials, adjusting the stoichiometry by targeted separation of one or more of the components of the transition metal mixed hydroxide is preferred. In a preferred embodiment, the ratio Ni:Co:Mn in the transition metal mixed hydroxide is 1:1:1, alternatively preferably 8:1:1.

[0020] In addition to the recovery of the materials used, particularly the valuable metals, a further aspect of a sustainable recycling strategy is the environmentally friendly use of resources. This means, among other things, that, wherever possible, chemicals required for the recycling process are also recovered or recycled. In the present process, this particularly applies to the sulfuric acid required to obtain solution X. Therefore, an embodiment of the process according to the invention is preferred in which the sulfuric acid produced during the electrolysis is at least partially used to produce solution X. The present invention further provides a device for carrying out the process according to the invention. The device comprises at least one electrolysis unit with at least one inlet for introducing solution A and at least one outlet for discharging solution B.

[0021] The present invention is explained in more detail with reference to the following examples and figures, which are in no way to be understood as a limitation of the inventive concept.

[0022] Figure 1 schematically shows the concept of the process according to the invention, according to which a solution A containing U2SO4 and Na2SC obtained during the recycling of lithium-ion / polymer batteries is subjected to electrolysis, whereby the sulfates are converted into the corresponding hydroxides and the Li is separated as U2CO3 by treatment with CO2 as a carbonate source, while Na2CO3 remains in solution.

[0023] Figure 2a schematically shows the preparation of solution A starting from a suspension Y obtained during the processing of lithium-ion / polymer batteries, which contains Li in the form of a lithium transition metal oxide UMO2. The lithium transition metal oxide is converted into U2SO4 and the corresponding transition metal sulfate MSO4 (solution X) by treatment with H2SO4 and a reducing agent, preferably H2O2 or SO2. By treating solution X with NaOH, the transition metal sulfate can be converted into the corresponding hydroxide M(OH)2 and separated, thereby obtaining a solution containing Na2SO4 and U2SO4, which serves as starting solution A for the process according to the invention.

[0024] According to the scheme shown in Figure 2b, solution X can be further treated with H2SO4 to obtain the transition metal in the form of its sulfate.

[0025] Figure 3 shows the schematic sequence of the process according to the invention, in which a solution A of U2SO4 and Na2SO4 is subjected to electrolysis to obtain solution B, from which U2CO3 can then be separated by treatment with a carbonate source. In this way, an effective separation of the two ions can be achieved.

Claims

Patent claims:

1. A process for the separation of Na and Li ions, characterized in that an aqueous solution A comprising Na2SC and U2SO4 is subjected to electrolysis to obtain a solution B and the resulting solution B is treated with a carbonate source to form U2CO3.

2. Process according to claim 1, characterized in that the carbonate source is selected from the group consisting of Na2CO3, CO2, NaHCl, (NF^CCh, (NH4)HCO3 and mixtures thereof.

3. Process according to at least one of the preceding claims, characterized in that the electrolysis is a multi-chamber membrane electrolysis with a cation exchange membrane and anion exchange membrane, in particular an electrodialysis, preferably an electrodialysis with bipolar membranes.

4. Process according to at least one of the preceding claims, characterized in that the U2CO3 formed is separated by means of at least one method selected from the group consisting of sedimentation, filtration and centrifugation.

5. Process according to at least one of the preceding claims, characterized in that the U2CO3 obtained is converted into soluble UHCO3 in a further step by treatment with CO2.

6. Process according to at least one of the preceding claims, characterized in that the aqueous solution A is obtained by treating a solution X, wherein the solution X comprises U2SO4 and at least one compound MSO4, wherein M is a transition metal, preferably selected from the group consisting of Ni, Co, Mn, Al and mixtures thereof.

7. Process according to claim 6, characterized in that solution X is obtained by treating a suspension Y comprising at least one compound UMO2 with H2SO4 and a reducing agent, where M is a transition metal, preferably one selected from the group consisting of Ni, Co, Mn, Al and mixtures thereof.

8. The method according to claim 7, characterized in that the compound comprising UMO2 is obtained from used lithium ion / polymer batteries and / or production waste during their manufacture.

9. Process according to at least one of claims 6 to 8, characterized in that in the treatment of the solution X a transition metal mixed hydroxide Ni x Mn y Coz(OH)2 is obtained by adjusting the transition metal stoichiometry and precipitation with sodium hydroxide solution.

10. The process according to claim 9, characterized in that the adjustment of the transition metal stoichiometry is carried out by selectively separating or adding one or more of the constituents of the transition metal mixed hydroxide.

11. Process according to at least one of claims 6 to 10, characterized in that the sulfuric acid produced during the electrolysis is used at least partly to prepare the solution X.

12. Apparatus for carrying out a process according to at least one of the preceding claims, comprising an electrolysis unit with at least one inlet for introducing the solution A and at least one outlet for discharging the solution B.

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