Method for producing lioh

Abstract

The invention relates to a method for producing LiOH, having the steps of: (1) providing a mixture A containing Li2CO3; (2) treating the mixture A provided in (1) with carbonic acid, thereby at least partly converting the Li2CO3 contained therein into LiHCO3 and obtaining a mixture B containing LiHCO3; and (3) reacting the mixture B obtained in (2) with M(OH)2, thereby at least partly reacting the LiHCO3 contained therein in order to form LiOH and obtaining a mixture C containing LiOH, wherein M represents an alkaline earth metal.

Description

Process for the production of LiOH  TECHNICAL FIELD The present invention relates to a method for obtaining lithium hydroxide from lithium-containing minerals.  INTRODUCTION WO 2019 / 220004 A1 relates to a process for obtaining lithium hydroxide from a lithium-containing mineral by mixing the mineral with water and an alkali metal carbonate, leaching the resulting mixture at elevated temperature, and subsequently subjecting it to a second leaching in an aqueous solution containing an alkaline earth metal hydroxide. WO 2018 / 234614 A1 relates to a process for producing lithium carbonate from lithium-containing minerals. The process comprises a leaching step, in which the lithium-containing mineral is leached in an aqueous solution containing alkali metal carbonate, a carbonation step, in which the leach slurry is reacted with an alkaline earth metal compound in the presence of CO2, and a solid-liquid separation step, in which the carbonated mixture is subjected to a solid-liquid separation. EP 2749535 A1 relates to a process for producing high-purity lithium carbonate. The process comprises reacting a first aqueous solution containing lithium carbonate and CO2 to form a second aqueous solution containing dissolved LiHCO3, which is further separated using a gas-liquid-solid separator to obtain a third aqueous solution. The third aqueous solution is contacted with an ion-selective medium to produce a fourth aqueous solution, from which high-purity lithium carbonate is precipitated. CN 101948124 B relates to a process for obtaining lithium carbonate from spodumene, in which, in a first step, alpha-spodumene is converted into beta-spodumene, which is further leached with an alkaline salt and water, whereby lithium carbonate is obtained. The lithium carbonate is further reacted with CO2 and converted into lithium bicarbonate, which is further treated thermally to obtain lithium carbonate. WO 2011 / 148040 A1 relates to a process for the thermal processing of alpha-spodumene to beta-spodumene. The process comprises treating concentrate or ore in a fluidized bed reactor at temperatures of 800 to 100 °C using an oxygen-containing gas. CN 103183366 A relates to a process for obtaining lithium salts from spodumene by soda leaching and subsequent acid conversion of the resulting lithium carbonates into soluble lithium salts. CN 113428882 A relates to a process for producing battery-grade lithium carbonate from spodumene. WO 2023 / 081961 A1 relates to a process for extracting metals from a metal-containing material, the process comprising a step in which the metal is dissolved in the process stream with carbon dioxide as a carbonate or bicarbonate. The metal is preferably lithium and the metal-containing material may be spodumene. Furthermore, the process preferably comprises a carbonation step in which an aqueous Li2CO3 solution is contacted with carbon dioxide in order to obtain a solution containing LiHCO3. The LiHCO3-containing solution is then subjected to a decarbonation step, whereby Li2CO3 is formed. Optionally, the Li2CO3 is preferably treated with Ca(OH)2 in order to obtain LiOH and CaCO3. CN 107265483 A relates to a process for producing LiOH monohydrate. In step S120 of the document, an aqueous Li2CO3 solution is contacted with carbon dioxide and converted into LiHCO3. The LiHCO3 obtained is then pyrolysed to Li2CO3 in step S140, and in step 200 the Li2CO3 is preferably contacted with an aqueous lime-containing solution in order to obtain a LiOH solution. Habashi Fathi, Handbook of Extractive Metallurgy, 1997, page 2045, and Wietelmann Ulrich et al., Ullmann's Encyclopedia of Industrial Chemistry, 2000, page 354, each describe a process for producing LiOH starting from Li2CO3. In this process, Li2CO3 is reacted with CO2 in water to provide LiHCO3, and the aqueous LiHCO3 solution is subsequently heated in order to obtain Li2CO3 and CO2. A further reaction of Li2CO3 with Ca(OH)2 to provide LiOH is also described. CN 111635999 A describes a process for extracting lithium from lithium-containing brines. In a first step, lithium ions are extracted from the lithium-containing brine by means of an extractant, and the upper extraction phase is separated off. Preferred extractants include, inter alia, alkyl phosphates, cyclohexanone and n-butanol. In a second step, water and CO2 are added to the upper extraction phase in order to obtain an aqueous LiHCO3 solution. Finally, Ca(OH)2 is added in order to obtain LiOH. WO 2024 / 089394 A2 describes a process for producing LiOH monohydrate or anhydrous LiOH from lithium mica. In step ix) of the document, a carbonate source is added to a lithium-containing solution in order to obtain a suspension containing Li2CO3, which is filtered in order to obtain a first waste solution and Li2CO3. In step x), the Li2CO3 is converted into LiOH in water by adding Ca(OH)2. This step x) preferably comprises dissolving Li2CO3 in water by introducing CO2 into this solution in order to produce LiHCO3, and subsequently adding Ca(OH)2 in order to obtain a suspension containing LiOH. This suspension is then filtered in order to recover a filter cake containing CaCO3 and a solution containing LiOH.  Although numerous processes for producing lithium hydroxide from spodumene already exist, there is still a need for further optimization of the process. In order to meet the growing demand for high-purity lithium hydroxide for battery production, the following points in particular have to be taken into account:Sustained production of lithium hydroxide of consistently high purity, which allows high-performance and long-lasting batteries to be manufacturedOptimization of the production processes with regard to the use of energy and raw materials  DETAILED DESCRIPTION It was therefore an object of the present invention to provide a new, more efficient and more environmentally friendly process for treating lithium-containing minerals for the sustained recovery of lithium hydroxide in high purity. It was found in this context that the introduction of carbon dioxide into a suspension containing lithium carbonate lowers the pH of the liquid phase from 10–11 to a value of about 7.5. A change in pH from basic to neutral therefore takes place without any substances foreign to the process having to be used. In the course of this, the more readily soluble lithium hydrogen carbonate is formed, which remains in the aqueous phase. Impurities that are soluble under basic conditions can be precipitated under these conditions and separated off together with the suspended analcime. Furthermore, it is not to be expected that heavy metals which can be dissolved in an acidic medium will be leached out of the solid under these conditions. Contamination of the lithium-containing solution by such compounds therefore does not occur. Furthermore, this reaction procedure allows the analcime to be separated off from the reaction mixture before the alkaline earth metal hydroxide is added. The solid analcime is therefore separated off under mild conditions before the reaction conditions change to strongly basic. Undesired side reactions which arise from a reaction of analcime with the alkaline earth metal hydroxide are thus avoided. As a result of the introduction of carbon dioxide, the resulting change in pH and the transfer of the lithium species into the aqueous phase, impurities can therefore be separated off more efficiently, or their formation is avoided from the outset. The invention described thus makes a significant contribution to improving the purity of the end product lithium hydroxide. In addition, the range of raw materials (i.e. lithium ores of different provenance) is broadened, since accompanying substances present in varying proportions by weight can be separated off more efficiently. Surprisingly, it was found that, by directly reacting lithium hydrogen carbonate with alkaline earth metal hydroxide, the additional step of thermally decomposing lithium hydrogen carbonate to lithium carbonate can be omitted. It was further found that, as a result of the omission of the thermal decomposition of lithium hydrogen carbonate to lithium carbonate, less carbon dioxide is generated in the production of lithium hydroxide by the process according to the invention. In particular, it is an object of the present invention to provide a process for obtaining lithium hydroxide in high yield and high purity. It was additionally found that the purification of the lithium hydroxide obtained can be improved by filtering undesired by-products such as analcime out of the process at an early stage, so that no filter cake is formed which contains both analcime and calcium carbonate. Moreover, it was unexpectedly found that, independently of one another, the pH of the starting mixture containing Li2CO3 and the temperature during the subsequent treatment of the mixture with carbonic acid permit a considerable additional optimization of the process according to the invention. The present invention relates to a process for producing LiOH, comprising(1) providing a mixture A containing Li2CO3;(2) treating the mixture A provided in (1) with carbonic acid, with at least partial conversion of the Li2CO3 contained therein into LiHCO3, to obtain a mixture B containing LiHCO3;(3) reacting the mixture B obtained in (2) with M(OH)2, with at least partial conversion of the LiHCO3 contained therein into LiOH, to obtain a mixture C containing LiOH, wherein M is an alkaline earth metal. It is preferred that the Li2CO3 content of the mixture A in (1) is in the range of from 0.1 to 16.0 wt.-%, preferably in the range of from 5 to 12 wt.-%, alternatively and particularly preferably in the range of from 1 to 5 wt.-%. It is further preferred that the Li2CO3 content of the mixture A in (1), based on the solids content of the mixture A, is in the range of from 0.1 to 16.0 wt.-%, particularly preferably in the range of from 5 to 12 % wt.-%.It is preferred that the Li content of the mixture A in (1), calculated as elemental lithium, is in the range of from 0.1 to 3.0 wt.-%, preferably in the range of from 0.80 to 2.25 wt.-%, alternatively and particularly preferably in the range of from 0.30 to 2.25 wt.-%. It is further preferred that the Li content of the mixture A in (1), calculated as elemental lithium and based on the solids content of the mixture A, is in the range of from 0.1 to 3.0 wt.-%, particularly preferably in the range of from 0.80 to 2.25 wt.-%.Alternatively, it is preferred that the mixture A further comprises water and that the water content of the mixture A in (1) is in the range of from 50 to 90 wt.-%, preferably in the range of from 60 to 70 wt.-%. It is further preferred that the Li2CO3 content of the mixture A in (1) is in the range of from 0.01 to 8.0 wt.-%, preferably in the range of from 1 to 5 wt.-%.It is preferred that providing the mixture A according to (1) comprises(1.a) providing a mixture M0 containing one or more lithium-containing minerals;(1.b) calcining the mixture M0 to obtain a mixture M1 containing one or more calcined lithium-containing minerals;(1.c) reacting the mixture M1 obtained in (b) with an alkali metal carbonate, with at least partial conversion of the one or more calcined lithium-containing minerals into Li2CO3, to obtain a mixture A containing Li2CO3. In the case where the process comprises steps (1.a) to (1.c), it is preferred that the mixture M0 contains one or more lithium-containing minerals in the range of from 50 to 100 wt.-%, preferably in the range of from 60 to 95 wt.-%. It is further preferred that the one or more lithium-containing minerals are selected from the group consisting of spodumene, petalite, lepidolite or mixtures thereof, wherein the one or more lithium-containing minerals are preferably spodumene, wherein the one or more lithium-containing minerals are particularly preferably alpha-spodumene.It is further preferred that during calcining in (1.b) the temperature is in the range of from 800 to 1500 °C, preferably in the range of from 950 to 1100 °C.It is further preferred that calcining in (1.b) is carried out for a period of time in the range of from 0.1 to 16 h, preferably in the range of from 0.5 to 5 h.It is further preferred that the one or more calcined lithium-containing minerals are selected from the group consisting of spodumene, petalite, lepidolite or mixtures thereof, wherein the one or more calcined lithium-containing minerals are preferably spodumene, wherein the one or more calcined lithium-containing minerals are particularly preferably beta-spodumene.It is further preferred that the alkali metal carbonate is selected from the group consisting of sodium carbonate, potassium carbonate or mixtures thereof, wherein the alkali metal carbonate is preferably sodium carbonate.It is further preferred that the weight ratio of calcined lithium-containing mineral to alkali metal carbonate in (1.c) is in the range of from 1:0.1 to 1:2, preferably in the range of from 1:0.1 to 1:0.4.It is further preferred that the molar ratio of lithium to sodium, calculated as elemental lithium and sodium, in (1.c) is in the range of from 1:0.4 to 1:8, preferably in the range of from 1:0.9 to 1:1.6.It is further preferred that during reacting in (1.c) the temperature is in the range of from 150 to 350 °C, preferably in the range of from 200 to 250 °C. It is further preferred that during reacting in (1.c) the pressure is in the range of from 10 to 200 bar (absolute), preferably in the range of from 14 to 50 bar (absolute), more preferably in the range of from 20 to 50 bar (absolute).It is further preferred that reacting in (1.c) is carried out for a period of time in the range of from 0.1 to 8 h, preferably in the range of from 0.5 to 1.5 h.It is further preferred that reacting in (1.c) comprises water, preferably aqueous alkali metal carbonate solution.It is further preferred that the process comprises(1.d) separating off at least a portion of the unreacted alkali metal carbonate from the mixture A obtained in (1.c) and obtaining a mixture M2 containing unreacted alkali metal carbonate;(1.e) providing the mixture M2 for reacting in (1.c) as a source of alkali metal carbonate. Alternatively, it is preferred that providing the mixture A according to (1) comprises(1.a') providing a mixture M0' containing one or more lithium-containing minerals;(1.b') reacting the mixture M0' with an alkali metal carbonate, with at least partial conversion of the one or more lithium-containing minerals into Li2CO3, to obtain a mixture A containing Li2CO3. In the case where the process comprises steps (1.a') and (1.b'), it is preferred that the mixture M0' contains the one or more lithium-containing minerals in the range of from 50 to 100 wt.-%, preferably in the range of from 60 to 95 wt.-%.It is further preferred that the Li content of the mixture M0' is in the range of from 0.03 to 4.00 wt.-%, preferably in the range of from 2.00 to 3.75 wt.-%.It is further preferred that the one or more lithium-containing minerals are selected from the group consisting of spodumene, petalite, lepidolite or mixtures thereof, wherein the one or more lithium-containing minerals are preferably spodumene, wherein the one or more lithium-containing minerals are particularly preferably alpha-spodumene.It is further preferred that the alkali metal carbonate is selected from the group consisting of sodium carbonate, potassium carbonate or mixtures thereof, wherein the alkali metal carbonate is preferably sodium carbonate.It is further preferred that in (1.b') the weight ratio of the one or more lithium-containing minerals to alkali metal carbonate is in the range of from 1:0.1 to 1:2, preferably in the range of from 1:0.2 to 1:0.4.It is further preferred that the molar ratio of lithium to sodium, calculated as elemental lithium and sodium, in (1.b') is in the range of from 1:0.4 to 1:8, preferably in the range of from 1:0.9 to 1:1.4.It is further preferred that reacting in (1.b') is carried out for a period of time in the range of from 0.1 to 10 h, preferably in the range of from 1 to 4 h.It is further preferred that reacting in (1.b') comprises water, preferably steam. In the case where reacting in (1.b') comprises water, it is preferred that during reacting in (1.b') the pressure is in the range of from 10 to 200 bar (absolute), preferably in the range of from 14 to 180 bar (absolute), more preferably in the range of from 14 to 50 bar (absolute), particularly preferably in the range of from 20 to 50 bar (absolute).In the case where the process comprises steps (1.a') and (1.b'), it is preferred that reacting in (1.b') comprises(1.b'.1) calcining the mixture M0' and an alkali metal carbonate, and obtaining a mixture M1';(1.b'.2) reacting the mixture M1' obtained in (1.b'.1) and obtaining a mixture A containing Li2CO3. In the case where the process comprises steps (1.b'.1) and (1.b'.2), it is preferred that during calcining in (1.b'.1) the temperature is in the range of from 900 to 1500 °C, preferably in the range of from 1000 to 1100 °C. It is further preferred that reacting in (1.b'.2) comprises water, preferably steam. In the case where reacting in (1.b'.2) comprises water, it is preferred that during reacting in (1.b'.2) the pressure is in the range of from 10 to 200 bar (absolute), preferably in the range of from 14 to 180 bar (absolute), more preferably in the range of from 14 to 50 bar (absolute), particularly preferably in the range of from 20 to 50 bar (absolute).In the case where the process comprises steps (1.a') and (1.b'), it is preferred that the process comprises(1.c') separating off unreacted alkali metal carbonate from the mixture A obtained in (1.b') and obtaining a mixture M2' containing unreacted alkali metal carbonate;(1.d') providing the mixture M2' for reacting in (1.b') as a source of alkali metal carbonate. It is preferred that during treating in (2) the temperature is in the range of from 0 to 150 °C, more preferably in the range of from 15 to 100 °C, more preferably in the range of from 20 to 80 °C, more preferably in the range of from 25 to 70 °C, more preferably in the range of from 30 to 60 °C, more preferably in the range of from 35 to 50 °C, particularly preferably in the range of from 40 to 45 °C.It is preferred that treating in (2) takes place in aqueous solution and that CO2 is introduced into the aqueous solution.In the case where treating in (2) takes place in aqueous solution and CO2 is introduced into the aqueous solution, it is preferred that, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 9 to 13, more preferably of from 10 to 12.5, more preferably of from 10.5 to 12, particularly preferably of from 11 to 11.5.It is further preferred that the pH of the aqueous solution is adjusted, prior to the introduction of CO2, by adding acid and / or base. In this case, it is preferred that the base contains one or more hydroxide salts, wherein the base preferably contains one or more alkali metal hydroxide salts, wherein the base preferably contains NaOH. In particular, it is preferred that the base consists of one or more hydroxide salts, wherein the base preferably consists of one or more alkali metal hydroxide salts, wherein the base is preferably NaOH.Independently thereof, in the case where the pH is adjusted by adding acid, it is preferred that the acid contains one or more Bronsted acids, wherein the acid preferably contains one or more mineral acids, wherein the acid preferably contains H2SO4 and / or HCl, wherein the acid preferably contains H2SO4. In particular, it is preferred that the acid consists of one or more Bronsted acids, wherein the acid preferably consists of one or more mineral acids, wherein the acid preferably consists of H2SO4 and / or HCl, wherein the acid preferably consists of H2SO4.It is further alternatively preferred that the pH of the aqueous solution is not adjusted, prior to the introduction of CO2, by adding acid and / or base, wherein the pH of the aqueous solution is not adjusted prior to the introduction of CO2.It is further preferred that, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 9 to 13 and that during treating in (2) the temperature is in the range of from 25 to 70 °C,wherein more preferably, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 10 to 12.5 and during treating in (2) the temperature is in the range of from 30 to 60 °C,wherein more preferably, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 10.5 to 12 and during treating in (2) the temperature is in the range of from 35 to 50 °C,wherein particularly preferably, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 11 to 11.5 and during treating in (2) the temperature is in the range of from 40 to 45 °C. It is further preferred that CO2 is introduced into the aqueous solution at a pressure of from 1 to 15 bar (absolute), more preferably of from 1 to 10 bar (absolute), more preferably of from 3 to 8 bar (absolute), particularly preferably of from 5 to 6 bar (absolute). According to the present invention, the pressure of the CO2 refers to the partial pressure at which CO2 is introduced into the aqueous solution, wherein the partial pressure corresponds to the total pressure of the gas stream when CO2 is introduced into the aqueous solution in pure form.It is preferred that treating in (2) comprises(2.1) treating the mixture A provided in (1) with carbonic acid, with at least partial conversion of the Li2CO3 contained therein into LiHCO3;(2.2) subjecting the mixture obtained in (2.1) to a solid-liquid separation step and obtaining a solid mixture M4 containing unreacted Li2CO3 and a liquid mixture B containing LiHCO3. In the case where the process comprises steps (2.1) and (2.2), it is preferred that treating in (2) further comprises(2.3) providing the mixture M4 for treating in (2) as a source of Li2CO3. It is preferred that treating in (2.3) comprises(2.3.1) washing the solid mixture M4 obtained in (2.2) with water and obtaining wash water containing Li2CO3;(2.3.2) providing at least a portion of the wash water containing Li2CO3 obtained in (2.3.1) for reacting in (3). Independently thereof, it is preferred that treating in (2.3) comprises(2.3.1) washing the solid mixture M4 obtained in (2.2) with water and obtaining wash water containing Li2CO3;(2.3.2) providing at least a portion of the wash water containing Li2CO3obtained in (2.3.1) for treating with carbonic acid in (2). It is preferred that reacting in (3) further comprises(3.1) thermally converting a portion of the mixture B obtained in (2) and obtaining a mixture B' containing Li2CO3;(3.2) reacting the mixture B' obtained in (3.1) with M(OH)2, with at least partial conversion of the Li2CO3contained therein into LiOH, to obtain a mixture C' containing LiOH, wherein M is an alkaline earth metal. It is preferred that reacting in (3.2) comprises(3.2.1) subjecting the mixture B' obtained in (3.1) to a solid-liquid separation step and obtaining a suspension containing solid Li2CO3 and a solution containing Li2CO3;(3.2.2) providing at least a portion of the solution containing Li2CO3 obtained in (3.2.1) for treating with carbonic acid in (2);(3.2.3) reacting the suspension containing solid Li2CO3 obtained in (3.2.1) with M(OH)2, with at least partial conversion of the Li2CO3 contained therein into LiOH, to obtain a mixture C' containing LiOH, wherein M is an alkaline earth metal. In the case where the process comprises step (3.2.1), it is preferred that the solids content of the suspension containing solid Li2CO3 obtained in (3.2.1) is in the range of from 1 to 10 wt.-%, more preferably in the range of from 3 to 9 wt.-%, particularly preferably in the range of from 4 to 8 wt.-%.In the case where the process comprises step (3.2.1), it is preferred that the solid-liquid separation step in (3.2.1) is carried out by cross-flow filtration of the mixture B' obtained in (3.1).In the case where the process comprises steps (3.1) and (3.2), it is preferred that during thermally converting in (3.1) the temperature is in the range of from 50 to 200 °C, preferably in the range of from 70 to 150 °C, particularly preferably in the range of from 70 to 110 °C. It is further preferred that during the thermal conversion in (3.1) the pressure is in the range of from 0.1 to 10 bar (absolute), preferably in the range of from 0.2 to 6 bar (absolute), particularly preferably in the range of from 0.3 to 1 bar (absolute).It is preferred that, independently of one another, the alkaline earth metal M in (3) and / or in (3.2) is selected from the group consisting of barium, calcium and magnesium, wherein the alkaline earth metal M is preferably calcium.It is preferred that, independently of one another, during the reacting in (3) and / or (3.2) the temperature is in the range of from 10 to 100 °C, more preferably in the range of from 15 to 80 °C, more preferably in the range of from 20 to 60 °C, more preferably in the range of from 20 to 50 °C, more preferably in the range of from 25 to 45 °C, more preferably in the range of from 30 to 45 °C, more preferably in the range of from 35 to 45 °C, particularly preferably in the range of from 38 to 42 °C.In particular, it was unexpectedly found that in (3.2) the temperature at which treating of the mixture B' with an alkaline earth metal hydroxide takes place has a considerable influence on the amount of impurities in the LiOH obtained in (3.2).It is preferred that, independently of one another, during reacting in (3) and / or (3.2) the pressure is in the range of from 0.5 to 1.5 bar (absolute), preferably in the range of from 0.8 to 1.2 bar (absolute).It is preferred that, independently of one another, the alkaline earth metal hydroxide M(OH)2 used in (3) and / or (3.2) is dissolved or suspended in water prior to reacting in (3) and / or (3.2).In the case where the alkaline earth metal hydroxide M(OH)2 used in (3) and / or (3.2) is dissolved or suspended in water prior to reacting, it is preferred that the proportion by weight of alkaline earth metal hydroxide M(OH)2 in the aqueous solution or the aqueous suspension is in the range of from 1 to 50 wt.-%, preferably in the range of from 10 to 30 wt.-%.It is preferred that the process further comprises(4) separating off MCO3 from the mixture C obtained in (3) and / or from the mixture C' obtained in (3.2) to obtain a mixture D containing LiOH. It is preferred that separating off in (4) comprises(4.1) subjecting the mixture C obtained in (3) and / or the mixture C' obtained in (3.2) to a solid-liquid separation step and obtaining a solid mixture M5 containing CaCO3 and a liquid mixture D containing LiOH;(4.2) washing the solid mixture M5 obtained in (4.1) with water and obtaining wash water containing LiOH,(4.3) providing at least a portion of the wash water containing LiOH obtained in (4.2) reacting in (3), wherein at least a portion of the wash water containing LiOH is preferably admixed with alkaline earth metal hydroxide M(OH)2 prior to being recycled into (3).The wash water containing LiOH obtained in (4.2) thus serves to prepare at least a portion of the aqueous suspension of the alkaline earth metal hydroxide M(OH)2 which is used for reacting in (3) and is recycled into (3) in this way. In the case where the process comprises steps (4.1) to (4.3), it is preferred that separating off in (4) further comprises an ion exchange, preferably a cationic ion exchange. The present invention is illustrated in more detail by the following embodiments and combinations of embodiments resulting from the dependencies and back-references indicated. In particular, it is pointed out that in each case where a range of embodiments is mentioned, for example in connection with a term such as "The process according to any one of embodiments 1 to 4", every embodiment within this range is intended to be explicitly disclosed to the person skilled in the art, i.e. the wording of this term is to be understood by the person skilled in the art as being synonymous with "The process according to any one of embodiments 1, 2, 3 and 4". Furthermore, it is expressly pointed out that the following series of embodiments is not the set of claims determining the scope of protection, but represents a suitably structured part of the description directed to general and preferred aspects of the present invention. 1. A process for producing LiOH, comprising(1) providing a mixture A containing Li2CO3;(2) treating the mixture A provided in (1) with carbonic acid, with at least partial conversion of the Li2CO3 contained therein into LiHCO3, to obtain a mixture B containing LiHCO3; (3) reacting the mixture B obtained in (2) with M(OH)2, with at least partial conversion of the LiHCO3 contained therein into LiOH, to obtain a mixture C containing LiOH, wherein M is an alkaline earth metal.2. The process of embodiment 1, wherein the Li2CO3 content of the mixture A in (1) is in the range of from 0.1 to 16.0 wt.-%, preferably in the range of from 5 to 12 wt.-%, alternatively and particularly preferably in the range of from 1 to 5 wt.-%.3. The process of embodiment 2, wherein the Li2CO3 content of the mixture A in (1), based on the solids content of the mixture A, is in the range of from 0.1 to 16.0 wt.-%, preferably in the range of from 5 to 12 wt.-%.4. The process according to any one of embodiments 1 to 3, wherein the Li content of the mixture A in (1), calculated as elemental lithium, is in the range of from 0.1 to 3.0 wt.-%, preferably in the range of from 0.80 to 2.25 wt.-%, alternatively and particularly preferably in the range of from 0.30 to 2.25 wt.-%.5. The process according to embodiment 4, wherein the Li content of the mixture A in (1), calculated as elemental lithium and based on the solids content of the mixture A, is in the range of from 0.1 to 3.0 wt.-%, particularly preferably in the range of from 0.80 to 2.25 wt.-%.6. The process according to embodiment 1, wherein the mixture A further comprises water, and the water content of the mixture A in (1) is in the range of from 50 to 90 wt.-%, preferably in the range of from 60 to 70 wt.-%. 7. The process according to embodiment 6, wherein the Li2CO3 content of the mixture A in (1) is in the range of from 0.01 to 8.0 wt.-%, preferably in the range of from 1 to 5 wt.-%.8. The process according to any one of embodiments 1 to 7, wherein providing the mixture A according to (1) comprises(1.a) providing a mixture M0 containing one or more lithium-containing minerals;(1.b) calcining the mixture M0 to obtain a mixture M1 containing one or more calcined lithium-containing minerals;(1.c) reacting the mixture M1 obtained in (b) with an alkali metal carbonate, with at least partial conversion of the one or more calcined lithium-containing minerals into Li2CO3, to obtain a mixture A containing Li2CO3.9. The process according to embodiment 8, wherein the mixture M0 contains one or more lithium-containing minerals in the range of from 50 to 100 wt.-%, preferably in the range of from 60 to 95 wt.-%.10. The process according to embodiment 8 or 9, wherein the one or more lithium-containing minerals are selected from the group consisting of spodumene, petalite, lepidolite or mixtures thereof, wherein the one or more lithium-containing minerals are preferably spodumene, wherein the one or more lithium-containing minerals are particularly preferably alpha-spodumene.11. The process according to any one of embodiments 8 to 10, wherein during calcining in (1.b) the temperature is in the range of from 800 to 1500 °C, preferably in the range of from 950 to 1100 °C.12. The process according to any one of embodiments 8 to 11, wherein calcining in (1.b) is carried out for a period of time in the range of from 0.1 to 16 h, preferably in the range of from 0.5 to 5 h.13. The process according to any one of embodiments 8 to 12, wherein the one or more calcined lithium-containing minerals are selected from the group consisting of spodumene, petalite, lepidolite or mixtures thereof, wherein the one or more calcined lithium-containing minerals are preferably spodumene, wherein the one or more calcined lithium-containing minerals are particularly preferably beta-spodumene.14. The process according to any one of embodiments 8 to 13, wherein the alkali metal carbonate is selected from the group consisting of sodium carbonate, potassium carbonate or mixtures thereof, wherein the alkali metal carbonate is preferably sodium carbonate.15. The process according to any one of embodiments 8 to 14, wherein the weight ratio of calcined lithium-containing mineral to alkali metal carbonate in (1.c) is in the range of from 1:0.1 to 1:2, preferably in the range of from 1:0.1 to 1:0.4.16. The process according to any one of embodiments 8 to 15, wherein the molar ratio of lithium to sodium, calculated as elemental lithium and sodium, in (1.c) is in the range of from 1:0.4 to 1:8, preferably in the range of from 1:0.9 to 1:1.6.17. The process according to any one of embodiments 8 to 16, wherein during reacting in (1.c) the temperature is in the range of from 150 to 350 °C, preferably in the range of from 200 to 250 °C.18. The process according to any one of embodiments 8 to 17, wherein during reacting in (1.c) the pressure is in the range of from 10 to 200 bar (absolute), preferably in the range of from 14 to 50 bar (absolute), more preferably in the range of from 20 to 50 bar (absolute).19. The process according to any one of embodiments 8 to 18, wherein reacting in (1.c) is carried out for a period of time in the range of from 0.1 to 8 h, preferably in the range of from 0.5 to 1.5 h.20. The process according to any one of embodiments 8 to 19, wherein reacting in (1.c) comprises water, preferably aqueous alkali metal carbonate solution.21. The process according to any one of embodiments 8 to 20, comprising(1.d) separating off at least a portion of the unreacted alkali metal carbonate from the mixture A obtained in (1.c) and obtaining a mixture M2 containing unreacted alkali metal carbonate;(1.e) providing the mixture M2 for reacting in (1.c) as a source of alkali metal carbonate.22. The process according to any one of embodiments 1 to 7, wherein providing the mixture A according to (1) comprises(1.a') providing a mixture M0' containing one or more lithium-containing minerals;(1.b') reacting the mixture M0' with an alkali metal carbonate, with at least partial conversion of the one or more lithium-containing minerals into Li2CO3, to obtain a mixture A containing Li2CO3.23. The process according to embodiment 22, wherein the mixture M0' contains the one or more lithium-containing minerals in the range of from 50 to 100 wt.-%, preferably in the range of from 60 to 95 wt.-%. 24. The process according to embodiment 22 or 23, wherein the Li content of the mixture M0' is in the range of from 0.03 to 4.00 wt.-%, preferably in the range of from 2.00 to 3.75 wt.-%.25. The process according to any one of embodiments 22 to 24, wherein the one or more lithium-containing minerals are selected from the group consisting of spodumene, petalite, lepidolite or mixtures thereof, wherein the one or more lithium-containing minerals are preferably spodumene, wherein the one or more lithium-containing minerals are particularly preferably alpha-spodumene.26. The process according to any one of embodiments 22 to 25, wherein the alkali metal carbonate is selected from the group consisting of sodium carbonate, potassium carbonate or mixtures thereof, wherein the alkali metal carbonate is preferably sodium carbonate.27. The process according to any one of embodiments 22 to 26, wherein in (1.b') the weight ratio of the one or more lithium-containing minerals to alkali metal carbonate is in the range of from 1:0.1 to 1:2, preferably in the range of from 1:0.2 to 1:0.4.28. The process according to any one of embodiments 22 to 27, wherein the molar ratio of lithium to sodium, calculated as elemental lithium and sodium, in (1.b') is in the range of from 1:0.4 to 1:8, preferably in the range of from 1:0.9 to 1:1.4.29. The process according to any one of embodiments 22 to 28, wherein reacting in (1.b') is carried out for a period of time in the range of from 0.1 to 10 h, preferably in the range of from 1 to 4 h.30. The process according to any one of embodiments 22 to 29, wherein reacting in (1.b') comprises water, preferably steam.31. The process according to embodiment 30, wherein during reacting in (1.b') the pressure is in the range of from 10 to 200 bar (absolute), preferably in the range of from 14 to 180 bar (absolute), more preferably in the range of from 14 to 50 bar (absolute), particularly preferably in the range of from 20 to 50 bar (absolute).32. The process according to any one of embodiments 22 to 29, wherein reacting in (1.b') comprises(1.b'.1) calcining the mixture M0' and an alkali metal carbonate, and obtaining a mixture M1';(1.b'.2) reacting the mixture M1' obtained in (1.b'.1) and obtaining a mixture A containing Li2CO3.33. The process according to embodiment 32, wherein during calcining in (1.b'.1) the temperature is in the range of from 900 to 1500 °C, preferably in the range of from 1000 to 1100 °C.34. The process according to embodiment 32 or 33, wherein reacting in (1.b'.2) comprises water, preferably steam.35. The process according to embodiment 34, wherein during reacting in (1.b'.2) the pressure is in the range of from 10 to 200 bar (absolute), preferably in the range of from 14 to 180 bar (absolute), more preferably in the range of from 14 to 50 bar (absolute), particularly preferably in the range of from 20 to 50 bar (absolute).36. The process according to any one of embodiments 22 to 35, comprising(1.c') separating off unreacted alkali metal carbonate from the mixture A obtained in (1.b') and obtaining a mixture M2' containing unreacted alkali metal carbonate;(1.d') providing the mixture M2' for reacting in (1.b') as a source of alkali metal carbonate.37. The process according to any one of embodiments 1 to 36, wherein during treating in (2) the temperature is in the range of from 0 to 150 °C, preferably in the range of from 15 to 100 °C, more preferably in the range of from 20 to 80 °C, more preferably in the range of from 25 to 70 °C, more preferably in the range of from 30 to 60 °C, more preferably in the range of from 35 to 50 °C, particularly preferably in the range of from 40 to 45 °C.38. The process according to any one of embodiments 1 to 37, wherein treating in (2) takes place in aqueous solution and CO2 is introduced into the aqueous solution.39. The process according to embodiment 38, wherein, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 9 to 13, preferably of from 10 to 12.5, more preferably of from 10.5 to 12, particularly preferably of from 11 to 11.5.40. The process according to embodiment 39, wherein the pH of the aqueous solution is adjusted, prior to the introduction of CO2, by adding acid and / or base.41. The process according to embodiment 40, wherein the base contains one or more hydroxide salts, wherein the base preferably contains one or more alkali metal hydroxide salts, wherein the base preferably contains NaOH.42. The process according to embodiment 41, wherein the base consists of one or more hydroxide salts, wherein the base preferably consists of one or more alkali metal hydroxide salts, wherein the base is preferably NaOH.43. The process according to any one of embodiments 40 to 42, wherein the acid contains one or more Bronsted acids, wherein the acid preferably contains one or more mineral acids, wherein the acid preferably contains H2SO4 and / or HCl, wherein the acid preferably contains H2SO4.44. The process according to embodiment 43, wherein the acid consists of one or more Bronsted acids, wherein the acid preferably consists of one or more mineral acids, wherein the acid preferably consists of H2SO4 and / or HCl, wherein the acid preferably consists of H2SO4.45. The process according to embodiment 39, wherein the pH of the aqueous solution is not adjusted, prior to the introduction of CO2, by adding acid and / or base, wherein the pH of the aqueous solution is not adjusted prior to the introduction of CO2.46. The process according to any one of embodiments 39 to 45, wherein, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 9 to 13 and during treating in (2) the temperature is in the range of from 25 to 70 °C,wherein preferably, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 10 to 12.5 and during treating in (2) the temperature is in the range of from 30 to 60 °C,wherein more preferably, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 10.5 to 12 and during treating in (2) the temperature is in the range of from 35 to 50 °C,wherein particularly preferably, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 11 to 11.5 and during treating in (2) the temperature is in the range of from 40 to 45 °C.47. The process according to any one of embodiments 1 to 46, wherein CO2is introduced into the aqueous solution at a pressure of from 1 to 15 bar (absolute), preferably from 1 to 10 bar (absolute), more preferably from 3 to 8 bar (absolute), particularly preferably from 5 to 6 bar (absolute).48. The process according to any one of embodiments 1 to 47, wherein treating in (2) comprises(2.1) treating the mixture A provided in (1) with carbonic acid, with at least partial conversion of the Li2CO3 contained therein into LiHCO3;(2.2) subjecting the mixture obtained in (2.1) to a solid-liquid separation step and obtaining a solid mixture M4 containing unreacted Li2CO3 and a liquid mixture B containing LiHCO3.49. The process according to embodiment 48, wherein treating in (2) further comprises(2.3) providing the mixture M4 for treating in (2) as a source of Li2CO3.50. The process according to embodiment 49, wherein treating in (2.3) comprises(2.3.1) washing the solid mixture M4 obtained in (2.2) with water and obtaining wash water containing Li2CO3;(2.3.2) providing at least a portion of the wash water containing Li2CO3obtained in (2.3.1) for reacting in (3). 51. The process according to embodiment 49 or 50, wherein treating in (2.3) comprises(2.3.1) washing the solid mixture M4 obtained in (2.2) with water and obtaining wash water containing Li2CO3;(2.3.2) providing at least a portion of the wash water containing Li2CO3obtained in (2.3.1) for treating with carbonic acid in (2).52. The process according to any one of embodiments 1 to 51, wherein reacting in (3) further comprises(3.1) thermally converting a portion of the mixture B obtained in (2) and obtaining a mixture B' containing Li2CO3;(3.2) reacting the mixture B' obtained in (3.1) with M(OH)2, with at least partial conversion of the Li2CO3contained therein into LiOH, to obtain a mixture C' containing LiOH, wherein M is an alkaline earth metal. 53. The process according to embodiment 52, wherein reacting in (3.2) comprises(3.2.1) subjecting the mixture B' obtained in (3.1) to a solid-liquid separation step and obtaining a suspension containing solid Li2CO3and a solution containing Li2CO3;(3.2.2) providing at least a portion of the solution containing Li2CO3 obtained in (3.2.1) for treating with carbonic acid in (2);(3.2.3) reacting the suspension containing solid Li2CO3obtained in (3.2.1) with M(OH)2, with at least partial conversion of the Li2CO3contained therein into LiOH, to obtain a mixture C' containing LiOH, wherein M is an alkaline earth metal. 54. The process according to embodiment 53, wherein the solids content of the suspension containing solid Li2CO3obtained in (3.2.1) is in the range of from 1 to 10 wt.-%, preferably in the range of from 3 to 9 wt.-%, particularly preferably in the range of from 4 to 8 wt.-%. 55. The process according to embodiment 53 or 54, wherein the solid-liquid separation step in (3.2.1) is carried out by cross-flow filtration of the mixture B' obtained in (3.1). 56. The process according to any one of embodiments 52 to 55, wherein during thermally converting in (3.1) the temperature is in the range of from 50 to 200 °C, preferably in the range of from 70 to 150 °C, particularly preferably in the range of from 70 to 110 °C. 57. The process according to any one of embodiments 52 to 56, wherein during the thermally converting in (3.1) the pressure is in the range of from 0.1 to 10 bar (absolute), preferably in the range of from 0.2 to 6 bar (absolute), particularly preferably in the range of from 0.3 to 1 bar (absolute).58. The process according to any one of embodiments 1 to 57, wherein, independently of one another, the alkaline earth metal M in (3) and / or in (3.2) is selected from the group consisting of barium, calcium and magnesium, wherein the alkaline earth metal M is preferably calcium.59. The process according to any one of embodiments 1 to 58, wherein, independently of one another, during reacting in (3) and / or (3.2) the temperature is in the range of from 10 to 100 °C, preferably in the range of from 15 to 80 °C, more preferably in the range of from 20 to 60 °C, more preferably in the range of from 20 to 50 °C, more preferably in the range of from 25 to 45 °C, more preferably in the range of from 30 to 45 °C, more preferably in the range of from 35 to 45 °C, particularly preferably in the range of from 38 to 42 °C.60. The process according to any one of embodiments 1 to 59, wherein, independently of one another, during reacting in (3) and / or (3.2) the pressure is in the range of from 0.5 to 1.5 bar (absolute), preferably in the range of from 0.8 to 1.2 bar (absolute).61. The process according to any one of embodiments 1 to 60, wherein, independently of one another, the alkaline earth metal hydroxide M(OH)2 used in (3) and / or (3.2) is dissolved or suspended in water prior to reacting in (3) and / or (3.2).62. The process according to embodiment 61, wherein the proportion by weight of alkaline earth metal hydroxide M(OH)2 in the aqueous solution or the aqueous suspension is in the range of from 1 to 50 wt.-%, preferably in the range of from 10 to 30 wt.-%. 63. The process according to any one of embodiments 1 to 62, the process further comprising(4) separating off MCO3 from the mixture C obtained in (3) and / or from the mixture C' obtained in (3.2) to obtain a mixture D containing LiOH.64. The process according to embodiment 63, wherein separating off in (4) comprises(4.1) subjecting the mixture C obtained in (3) and / or the mixture C' obtained in (3.2) to a solid-liquid separation step and obtaining a solid mixture M5 containing CaCO3 and a liquid mixture D containing LiOH;(4.2) washing the solid mixture M5 obtained in (4.1) with water and obtaining wash water containing LiOH,(4.3) providing at least a portion of the wash water containing LiOH obtained in (4.2) for reacting in (3), wherein at least a portion of the wash water containing LiOH is preferably admixed with alkaline earth metal hydroxide M(OH)2 prior to being recycled into (3). 65. The process according to embodiment 64, wherein separating off in (4) further comprises an ion exchange, preferably a cationic ion exchange. EXPERIMENTAL SECTION As described in the introductory part of the detailed description, it was surprisingly found that the two-stage treatment of Li2CO3 with carbonic acid and an alkaline earth metal hydroxide for producing LiOH consistently leads to a product of higher purity, which made it possible to develop an optimized production process. As further described in the introductory part of the detailed description, it was additionally unexpectedly found that, independently of one another, the pH of the starting mixture containing Li2CO3 and the temperature during the subsequent treatment of the mixture with carbonic acid permit a considerable additional optimization of the process according to the invention. These further effects of the process according to the invention are demonstrated by the following series of experiments. In this series, the reaction of lithium carbonate (Li2CO3) to lithium hydrogen carbonate (LiHCO3) was carried out using H2CO3, which was generated in situ by means of CO2. The CO2was metered in continuously during the reaction at a maximum pressure of about 5 bar. The series of experiments comprises various pH values which were adjusted prior to the addition of CO2. For the pH values of 4 and 10.5, 96 % sulfuric acid (H2SO4) was used. For the pH value of 13, 50 % sodium hydroxide solution (NaOH) was used. For the experiment at a pH value of 11, neither acid nor base had to be added. Example 1: Preparation of LiHCO3 at pH 11 and 40 °CIn a batch approach, filter cake containing Li2CO3, which had been obtained from a pressure leach of beta-spodumene, was resuspended in water with stirring and sparged with CO2at 40 °C. For this purpose, the filter cake (500.6 g; 33.2 % residual moisture; 19.9 mg / g Li2CO3; 35 g Li2CO3; 480 mmol Li2CO3) was initially charged and resuspended with 1204 mL of H2O. The suspension was heated to the target temperature of 40 °C with stirring. After 8 min, the target temperature of 40 °C was reached and the addition of 5.5 bar of CO2was started. After a reaction time of 10 min, the pressure was released, the suspension was removed and filtered through a Büchner funnel. The filter cake was washed with 500 g of DI water. Example 2: Preparation of LiHCO3 at pH 4 and 40 °CIn a batch approach, filter cake containing Li2CO3, which had been obtained from a pressure leach of beta-spodumene as in Example 1, was resuspended in water with stirring and sparged with CO2 at 40 °C. For this purpose, the filter cake (450.0 g; 36.0 % residual moisture; 17.1 mg / g Li2CO3; 26 g Li2CO3; 355 mmol Li2CO3) was initially charged and resuspended with 849 mL of H2O. The initial pH of the suspension was 11.1. By adding 17 g of 96 % H2SO4, the target pH of 4.0 was reached. The suspension was then heated to the target temperature of 40 °C with stirring. After 16 min, the target temperature of 40 °C was reached and the addition of 5.2 bar of CO2was started. After a reaction time of 10 min, the pressure was released, the suspension was removed and filtered through a Büchner funnel. The filter cake was washed with 450 g of DI water. Example 3: Preparation of LiHCO3 at pH 13 and 40 °CIn a batch approach, filter cake containing Li2CO3, which had been obtained from a pressure leach of beta-spodumene as in Example 1, was resuspended in water with stirring and sparged with CO2 at 40 °C. For this purpose, the filter cake (450.7 g; 36.0 % residual moisture; 17.1 mg / g Li2CO3; 26 g Li2CO3; 355 mmol Li2CO3) was initially charged and resuspended with 849 mL of H2O. The initial pH of the suspension was 11.1. By adding 27 g of 50 % NaOH, the target pH of 13.0 was reached. The suspension was then heated to the target temperature of 40 °C with stirring. After 15 min, the target temperature of 40 °C was reached and the addition of 5.5 bar of CO2 was started. After a reaction time of 10 min, the pressure was released, the suspension was removed and filtered through a Büchner funnel. The filter cake was washed with 450 g of DI water. Example 4: Preparation of LiHCO3 HCO3 at pH 11 and room temperatureIn a batch approach, filter cake containing Li2CO3, which had been obtained from a pressure leach of beta-spodumene as in Example 1, was resuspended in water with stirring and sparged with CO2 at room temperature. For this purpose, the filter cake (450.1 g; 36.0 % residual moisture; 17.1 mg / g Li2CO3; 26 g Li2CO3; 355 mmol Li2CO3) was initially charged and resuspended with 849 mL of H2O. At a temperature of 27 °C, 5.2 bar of CO2 were added. After a reaction time of 14 min, the pressure was released, the suspension was removed and filtered through a Büchner funnel. The filter cake was washed with 450 g of DI water. Example 5: Preparation of LiHCO3 at pH 10.5 and 100 °CIn a batch approach, filter cake containing Li2CO3, which had been obtained from a pressure leach of beta-spodumene as in Example 1, was resuspended in water with stirring and sparged with CO2 at 100 °C. For this purpose, the filter cake (450.1 g; 36.0 % residual moisture; 17.1 mg / g Li2CO3; 26 g Li2CO3; 355 mmol Li2CO3) was initially charged and resuspended with 849 mL of H2O. The initial pH of the suspension was 11.0. By adding 0.8 g of 96 % H2SO4, the target pH of 10.5 was reached. The suspension was then heated to the target temperature of 100 °C with stirring. After 21 min, the target temperature of 100 °C was reached and the addition of 5.3 bar of CO2 was started. After a reaction time of 10 min, the pressure was released, the suspension was removed and filtered through a Büchner funnel. The filter cake was washed with 450 g of DI water. Discussion of the results of the series of experiments for the preparation of LiHCO3 Table1: Yield of lithium determined by ICP-MS of Li in the filtrate and the wash filtrate.ExampleTemperature(°C)Initial pHYield of Li(n / n)1401195.6 %240487.5 %3401379.3 %4271182.9 %510010,580.3 % As can be seen from the results in Table 1, Example 1 at pH 11 and 40 °C showed the highest yield. The yield of Example 2 at pH 4 is also still relatively high. This is because the sulfuric acid partially destroys the analcime and thus extracts more lithium than the experiments in the basic range. However, a disadvantage here is that lithium sulfate is formed and thus a new anion enters the process which subsequently has to be separated off again. The yield in the experiment according to Example 5 at pH 10.5 and 100 °C is lower by comparison. With regard to the pH in the step of introducing CO2, it can thus be stated that, as a comparison of the results of Examples 1, 2 and 3 shows, which were carried out at the same temperature, the highest yield could be achieved at pH 11. Both a higher and a lower pH of the starting mixture gave lower yields. It was thus surprisingly found that a considerable optimization of the lithium yield can be achieved by adjusting the pH of the starting mixture. Furthermore, it was unexpectedly found that an optimization can also be achieved via the temperature at which the introduction of CO2 takes place. Thus, a comparison of the results for Examples 1, 4 and 5, which were carried out at pH 10.5 and 11 respectively, shows that Example 1 achieved the highest yield. In particular, the results of Example 4, which was carried out at a lower temperature, and of Example 5, which was carried out at a higher temperature, show that a likewise considerable optimization of the lithium yield can be achieved by adjusting the temperature at which the introduction of CO2 takes place. The exact composition of the filtrate was investigated by means of ICP-MS. The following table shows the elemental composition of the filtrate on the basis of the relevant elements. Table2: ICP measurement of the filtrates from the series of experiments for the preparation of LiHCO3.ExampleTemperature(°C)Initial pHLi(mg / L)Na(mg / L)Al(mg / L)Si(mg / L)Ca(mg / L)K(mg / L)1401145872430.7835119240442054900.4376874234013374270690.1211061704271139333700.2788330510010,539135820.11163272 As can be seen from the results in Table 2, the results for Example 1 show, in addition to the highest yields of Li already apparent from Table 1 (here in the filtrate), also – apart from Al – the lowest amounts of impurities from Na, Si, Ca and K. This optimization can again be clearly seen both with regard to the pH (by comparing the respective results for Examples 1 to 3) and with regard to the temperature (by comparing the respective results for Examples 1, 4 and 5). Although the results for Example 1 show the highest value for an impurity of Al, this impurity nevertheless constitutes by far the smallest amounts of impurities compared with the impurities of Na, Si, Ca and K in all examples. Moreover, a lower impurity of Si is preferable to a higher impurity of Al, since silicon is difficult to separate off. CITED LITERATURE WO 2019 / 220004 A1 WO 2018 / 234614 A1 EP 2749535 A1 CN 101948124 BWO 2011 / 148040 A1 CN 103183366 A CN 113428882 AWO 2023 / 081961 A1CN 107265483 AHabashi Fathi, Handbook of Extractive Metallurgy, 1997, Seite 2045Wietelmann Ulrich et al., Ullmann’s Encyclopedia of Industrial Chemistry, 2000, Seite 354CN 111635999 AWO 2024 / 089394 A2

Claims

1. A process for producing LiOH, comprising(1) providing a mixture A containing Li2CO3;(2) treating the mixture A provided in (1) with carbonic acid, with at least partial conversion of the Li2CO3 contained therein into LiHCO3, to obtain a mixture B containing LiHCO3; (3) reacting the mixture B obtained in (2) with M(OH)2, with at least partial conversion of the LiHCO3 contained therein into LiOH, to obtain a mixture C containing LiOH, wherein M is an alkaline earth metal.

2. The process according to claim 1, wherein the Li2CO3 content of the mixture A in (1), based on the solids content of the mixture A, is in the range of from 0.1 to 16.0 wt.-%.

3. The process according to claim 1 or 2, wherein providing the mixture A according to (1) comprises(1.a) providing a mixture M0 containing one or more lithium-containing minerals;(1.b) calcining the mixture M0 to obtain a mixture M1 containing one or more calcined lithium-containing minerals;(1.c) reacting the mixture M1 obtained in (b) with an alkali metal carbonate, with at least partial conversion of the one or more calcined lithium-containing minerals into Li2CO3, to obtain a mixture A containing Li2CO3;(1.d) separating off at least a portion of the unreacted alkali metal carbonate from the mixture A obtained in (1.c) and obtaining a mixture M2 containing unreacted alkali metal carbonate;(1.e) providing the mixture M2 for reacting (1.c) as a source of alkali metal carbonate.

4. The process according to claim 1 or 2, wherein providing the mixture A according to (1) comprises(1.a') providing a mixture M0' containing one or more lithium-containing minerals;(1.b') reacting the mixture M0' with an alkali metal carbonate, with at least partial conversion of the one or more lithium-containing minerals into Li2CO3, to obtain a mixture A containing Li2CO3;(1.c') separating off unreacted alkali metal carbonate from the mixture A obtained in (1.b') and obtaining a mixture M2' containing unreacted alkali metal carbonate;(1.d') providing the mixture M2' for reacting in (1.b') as a source of alkali metal carbonate.

5. The process according to any one of claims 1 to 4, wherein during treating in (2) the temperature is in the range of from 0 to 150 °C.v6. The process according to any one of claims 1 to 5, wherein treating in (2) takes place in aqueous solution and CO2 is introduced into the aqueous solution.

7. The process according to claim 6, wherein, prior to the introduction of CO2, the aqueous solution has a pH in the range of from 9 to 13.

8. The process according to claim 7, wherein during treating in (2) the temperature is in the range of from 25 to 70 °C.

9. The process according to any one of claims 6 to 8, wherein CO2 is introduced into the aqueous solution at a pressure of from 1 to 15 bar (absolute).

10. The process according to any one of claims 1 to 9, wherein treating in (2) comprises(2.1) treating the mixture A provided in (1) with carbonic acid, with at least partial conversion of the Li2CO3 contained therein into LiHCO3;(2.2) subjecting the mixture obtained in (2.1) to a solid-liquid separation step and obtaining a solid mixture M4 containing unreacted Li2CO3 and a liquid mixture B containing LiHCO3.

11. The process according to any one of claims 1 to 10, wherein reacting in (3) further comprises(3.1) thermally converting a portion of the mixture B obtained in (2) and obtaining a mixture B' containing Li2CO3;(3.2) reacting the mixture B' obtained in (3.1) with M(OH)2, with at least partial conversion of the Li2CO3 contained therein into LiOH, to obtain a mixture C' containing LiOH, wherein M is an alkaline earth metal. 12. The process according to any one of claims 1 to 11, wherein, independently of one another, the alkaline earth metal M in (3) and / or in (3.2) is selected from the group consisting of barium, calcium and magnesium.

13. The process according to any one of claims 1 to 12, wherein, independently of one another, during reacting in (3) and / or (3.2) the temperature is in the range of from 10 to 100 °C.

14. The process according to claim 13, wherein during reacting in (3.2) the temperature is in the range of from 10 to 50 °C.

15. The process according to any one of claims 1 to 14, wherein, independently of one another, during reacting in (3) and / or (3.2) the pressure is in the range of from 0.5 to 1.5 bar (absolute).

16. The process according to any one of claims 1 to 15, the process further comprising(4) separating off MCO3 from the mixture C obtained in (3) and / or from the mixture C' obtained in (3.2) to obtain a mixture D containing LiOH.

17. The process according to claim 16, wherein separating off in (4) comprises(4.1) subjecting the mixture C obtained in (3) and / or the mixture C' obtained in (3.2) to a solid-liquid separation step and obtaining a solid mixture M5 containing CaCO3 and a liquid mixture D containing LiOH;(4.2) washing the solid mixture M5 obtained in (4.1) with water and obtaining wash water containing LiOH,(4.3) providing at least a portion of the wash water containing LiOH obtained in (4.2) for reacting in (3), wherein at least a portion of the wash water containing LiOH is preferably admixed with alkaline earth metal hydroxide M(OH)2 prior to being recycled into (3).

18. The process according to claim 17, wherein separating off in (4) further comprises an ion exchange.