Preparation method of lithium hydroxide monohydrate

Abstract

A process for producing lithium hydroxide monohydrate from lithium chloride, the process comprising: (a) adding an aqueous solution comprising sodium hydroxide to a first aqueous solution comprising lithium chloride, thereby obtaining a mixture comprising lithium hydroxide, sodium chloride and water; (b) cooling the mixture to selectively precipitate lithium hydroxide monohydrate; (c) separating the lithium hydroxide monohydrate precipitate from the first mother liquor; (d) adding a second aqueous solution containing lithium chloride into the separated first mother solution to obtain a first mother solution enriched with lithium chloride; and (e) removing (preferably evaporating) moisture from the lithium chloride enriched first mother liquor to selectively precipitate sodium chloride.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process for the preparation of lithium hydroxide monohydrate from lithium chloride, in particular to the preparation of battery grade lithium hydroxide monohydrate. BACKGROUND

[0002] Commercial production of lithium hydroxide monohydrate from lithium chloride typically involves electrolysis of lithium chloride or conversion of lithium chloride to lithium carbonate by reaction with sodium carbonate. These processes are costly and inefficient. For example, production of lithium hydroxide monohydrate by electrolysis of lithium chloride is extremely energy intensive (very low efficiency compared to chlor-alkali electrolysis), while production of lithium carbonate requires expensive reagents and the resulting lithium hydroxide monohydrate product is relatively low purity.

[0003] Accordingly, there is a need for a more economical and efficient process for the preparation of lithium hydroxide monohydrate from lithium chloride.

[0004] To this end, a number of publications have been published on the production of lithium hydroxide monohydrate by reaction of lithium chloride with a hydroxide source.

[0005] For example, WO 2022 / 147632 Al describes the production of lithium hydroxide monohydrate directly from lithium chloride with sodium hydroxide. The process involves adding a first solution containing sodium hydroxide to a brine containing lithium chloride at a temperature of 80 °C to 120 °C to form a mixture comprising lithium hydroxide and sodium chloride. The mixture is cooled to a temperature of 20 °C to 60 °C (typically 35 °C) and it is claimed that lithium hydroxide monohydrate can be selectively isolated by performing a fractional cooling crystallisation step at a sodium hydroxide concentration of 0.1 to 10.5 wt.%. The mother liquor is then mixed with a second solution containing sodium hydroxide and a fractional evaporation crystallisation is performed at a temperature of 80 °C to 120 °C (typically 100 °C) to selectively isolate sodium chloride for disposal.

[0006] Similarly, WO 2023 / 012512 Al discloses reacting a lithium chloride solution with a potassium hydroxide solution to form a reciprocating salt system comprising potassium hydroxide, lithium chloride, potassium chloride, lithium hydroxide and water, and precipitating potassium chloride and lithium hydroxide from the reciprocating salt system to form lithium hydroxide crystals and potassium chloride crystals. In Example 1, the reciprocating salt system is cooled to selectively precipitate potassium chloride (example temperatures as low as -10 °C) and heated (up to 96 °C) and evaporated to selectively precipitate lithium hydroxide.

[0007] However, the production process described in WO 2022 / 147632 A1 and WO 2023 / 012512 A1 is not optimized in terms of process efficiency and purity of the lithium hydroxide monohydrate. For example, WO 2022 / 147632 A1 requires regular discharge of the mother liquor to reduce the accumulation of impurities and it disposes sodium chloride. Moreover, the highest purity of lithium hydroxide monohydrate obtained after washing is 95.5%. Likewise, WO 2023 / 012512 A1 describes that there is a large temperature fluctuation between heating and cooling to precipitate potassium chloride and lithium hydroxide sufficiently, which means that a large amount of energy is required. The operating cost at low temperature of -10°C is also very high.

[0008] Therefore, there is a need for a process method that can solve these problems. SUMMARY

[0009] The present disclosure relates to a method for producing lithium hydroxide monohydrate from lithium chloride, the method comprising: a) adding an aqueous solution containing sodium hydroxide to a first aqueous solution containing lithium chloride, thereby obtaining a mixture comprising lithium hydroxide, sodium chloride and water, b) cooling the mixture obtained in a) to selectively precipitate lithium hydroxide monohydrate, thereby obtaining a lithium hydroxide monohydrate precipitate and a first mother liquor, c) separating the lithium hydroxide monohydrate precipitate from the first mother liquor, d) adding a second aqueous solution containing lithium chloride to the separated first mother liquor, thereby obtaining a first mother liquor enriched in lithium chloride, and e) removing (preferably evaporating) water from the first mother liquor enriched in lithium chloride to selectively precipitate sodium chloride, thereby obtaining a sodium chloride precipitate and a second mother liquor.

[0010] Advantageously, it has been found that by adding sodium hydroxide to the process prior to the precipitation of lithium hydroxide monohydrate, and adding lithium chloride to the process prior to the precipitation of sodium chloride, the method of the present invention can selectively precipitate high purity lithium hydroxide monohydrate and sodium chloride at different nodes of the process. Temperature changes are also used to further optimize the selectivity of the precipitation. This finding is surprising in view of WO 2022 / 147632 A1 stating that an excess of sodium hydroxide would affect the solubility of lithium hydroxide monohydrate and sodium chloride, thereby enabling them to be selectively precipitated.

[0011] By optimizing the difference in solubility of sodium chloride and lithium hydroxide monohydrate, the method of the present invention also enables a high (substantially complete) conversion of lithium chloride to lithium hydroxide monohydrate. This improves the efficiency and water balance of the process.

[0012] Therefore, as shown in the following working examples, the method of this disclosure has the following key advantages compared to WO 2022 / 147632 A1: • Based on total mass calculations, the amount of lithium hydroxide monohydrate generated increases; • Reduced energy costs are achieved because less water needs to be removed (e.g., through evaporation) to produce the same quantity of lithium hydroxide monohydrate. • Similar production capacity can be achieved with smaller flow rates, thus requiring smaller equipment, which means lower operating costs and less capital investment; • The lithium hydroxide monohydrate obtained after washing has higher purity. Attached Figure Description

[0013] Figure 1 This is a flowchart of the preferred implementation scheme disclosed herein. Detailed Implementation

[0014] Various aspects of the present invention will be further explained below.

[0015] As described above, in a first aspect, the present invention provides a method for producing lithium hydroxide monohydrate from lithium chloride, the method comprising: a) An aqueous solution containing sodium hydroxide is added to a first aqueous solution containing lithium chloride to obtain a mixture containing lithium hydroxide, sodium chloride, and water. b) Cool the mixture obtained in a) to selectively precipitate lithium hydroxide monohydrate, thereby obtaining lithium hydroxide monohydrate precipitate and a first mother liquor. c) Separate the lithium hydroxide monohydrate precipitate from the first mother liquor. d) Add the second lithium chloride-containing aqueous solution to the separated first mother liquor to obtain a first mother liquor enriched with lithium chloride, and e) Remove (preferably evaporate) water from the first mother liquor enriched with lithium chloride to selectively precipitate sodium chloride, thereby obtaining a sodium chloride precipitate and a second mother liquor.

[0016] The term "high purity" as used in this article refers to a level higher than 98%, such as higher than 99%.

[0017] In step a), sodium hydroxide is added to lithium chloride to form lithium hydroxide and sodium chloride. The addition is preferably carried out at a temperature range of 10°C to 100°C, more preferably 20°C to 95°C, and most preferably 25°C to 90°C. Preferably, the first aqueous solution containing lithium chloride is at or above this temperature range before the addition of the aqueous solution containing sodium hydroxide. The molar ratio of sodium hydroxide added in aqueous form to lithium chloride in the lithium chloride solution is preferably in the range of 0.1:1 to 1.5:1, more preferably from 0.3:1 to 0.9:1.

[0018] Based on the total weight of the sodium hydroxide-containing aqueous solution, the sodium hydroxide-containing aqueous solution typically has a sodium hydroxide concentration of 10 to 50 wt.%, preferably 15 to 40 wt.%, more preferably 20 to 35 wt.%. In a preferred embodiment, at least a portion, preferably all or substantially all, of the sodium hydroxide-containing aqueous solution is obtained by electrolyzing the sodium chloride precipitate in e).

[0019] Based on the total weight of the first lithium chloride-containing aqueous solution, the first lithium chloride-containing aqueous solution typically has a lithium concentration of 1.0 to 9.0 wt.%, preferably 2.0 to 8.0 wt.%, more preferably 2.5 to 7.5 wt.%. In a preferred embodiment, at least a portion, preferably all or substantially all, of the first lithium chloride-containing aqueous solution is provided by a separated second mother liquor (see discussion in f below). When the first lithium chloride-containing aqueous solution is provided by a separated second mother liquor, based on the total weight of the first lithium chloride-containing aqueous solution, the solution preferably has a lithium concentration of 2.5 to 6.0 wt.%, preferably 2.5 to 4.0 wt.%, more preferably 2.8 to 3.4 wt.%.

[0020] The mixture obtained in (a) preferably has a lithium-ion (Li) ratio of 0.7:1 to 2.0:1, more preferably 0.9:1 to 1.7:1, more preferably 0.95:1 to 1.5:1, and even more preferably 1 or 1.05:1 to 1.4:1. + ) and hydroxide ions (OH) - The molar ratio of ).

[0021] In b), the mixture obtained in a) is cooled to a temperature of 5 to 50°C, preferably 10 to 45°C, more preferably 20 to 45°C, thereby selectively precipitating lithium hydroxide monohydrate. Cooling can be achieved by any cooling method known in the art, such as using a coolant (e.g., water) in the double walls of a jacketed reactor or passing the reactor contents through a heat exchanger.

[0022] The addition in a) and the precipitation in b) can be carried out sequentially or simultaneously. Similarly, the addition in a) and the precipitation in b) can be carried out in a single device (e.g., a crystallization reactor) or in separate devices (e.g., a reactor and a crystallizer). Preferably, an aqueous solution containing sodium hydroxide and a first aqueous solution containing lithium chloride are added to a reactor controlled at a specific temperature, and then the reactor contents are maintained at that temperature for a specific mixing time, and the precipitated solids are separated.

[0023] The lithium hydroxide monohydrate precipitate obtained in b) can be separated from the first mother liquor in c) using typical solid-liquid separation techniques (e.g., filtration, sedimentation, and / or centrifugation). Preferably, the separated lithium hydroxide monohydrate precipitate, after washing, has a purity of at least 96%, preferably at least 97%, more preferably at least 98%, and most preferably at least 99%. The washing step may include washing the precipitate with a saturated aqueous lithium hydroxide solution on any solid / liquid separation device (e.g., a filter or centrifuge). Alternatively, any other liquid with a higher solubility for sodium chloride than lithium hydroxide monohydrate can be used.

[0024] Following the washing step, a subsequent recrystallization step known in the art can be employed. In this step, lithium hydroxide is redissolved in water and recrystallized, for example, by evaporating the water and then cooling. This can potentially further improve the purity of the final lithium hydroxide.

[0025] In step d), a second aqueous solution containing lithium chloride is added to the separated first mother liquor. The second aqueous solution containing lithium chloride can be obtained from naturally occurring brine, such as geothermal brine, or from mineral-bearing rocks (such as spodumene).

[0026] Based on the total weight of the second lithium chloride-containing aqueous solution, the solution typically has a lithium chloride concentration of 10 to 55 wt.%, preferably 20 to 50 wt.%, and more preferably 30 to 45 wt.%.

[0027] Preferably, lithium chloride and sodium hydroxide are added to the process in equimolar amounts via a second aqueous solution containing lithium chloride and an aqueous solution containing sodium hydroxide, respectively. This is particularly advantageous when the process is continuous (or cyclic), as described below.

[0028] Preferably, the lithium ions (Li) obtained in the first mother liquor enriched with lithium chloride obtained in d) + ) and hydroxide ions (OH) - The molar ratio of the components is 0.9:1 to 3.5:1, more preferably 0.95:1 to 2.5:1, and most preferably 1.0:1 to 2.0:1.

[0029] In step e), water is removed (preferably evaporated) from the first mother liquor enriched with lithium chloride to selectively precipitate sodium chloride. When removing water by evaporation, evaporation can be induced by heating the first mother liquor and / or the first mother liquor enriched with lithium chloride to a temperature of 50 to 120°C, preferably 60 to 95°C, more preferably 75 to 90°C. If desired, evaporation can be carried out under vacuum to lower the evaporation temperature. The vacuum pressure is controlled by the cooling water temperature, preferably between 40 and 500 mbar.

[0030] The addition in d) and the removal (e.g., evaporation) in e) can be performed sequentially or simultaneously. Similarly, the addition in d) and the removal (e.g., evaporation) in e) can be performed in a single device (e.g., a crystallization reactor) or in separate devices (e.g., a reactor and a crystallizer). Preferably, evaporation and crystallization are performed using a multi-effect evaporator (MEE) or a mechanical vapor recompression (MVR) crystallizer.

[0031] Preferably, the method of the present invention further includes: f) Separate the sodium chloride precipitate from the second mother liquor to obtain a first aqueous solution containing lithium chloride.

[0032] In f), the sodium chloride precipitate obtained in e) can be separated from the second mother liquor in particulate or solution form. This is typically accomplished using solid-liquid separation techniques (e.g., filtration, sedimentation, and / or centrifugation). Preferably, the filtered solid is fed to the electrolytic cell as a sodium-rich slurry. Preferably, the separated sodium chloride precipitate, after washing, has a purity of at least 80%, more preferably at least 90%, and most preferably at least 95%. The washing step may include washing with a saturated aqueous sodium chloride solution.

[0033] The separated second mother liquor can provide at least a portion, preferably all or substantially all, of the first lithium chloride-containing aqueous solution for a). Therefore, including f) makes the method of the present invention a closed loop, thereby eliminating the need for discharging or disposing of certain product streams.

[0034] Preferably, the method of the present invention further includes: g) Electrolyze sodium chloride precipitate to obtain an aqueous solution containing sodium hydroxide.

[0035] Electrolysis in g) provides the advantage of recycling sodium chloride precipitate back into the process as an aqueous solution containing sodium hydroxide. This eliminates the need for sodium chloride disposal. Including the electrolysis loop also reduces the amount of water that needs to be removed (e.g., by evaporation) in e), thereby improving the process's water balance. The chlorine and hydrogen produced during electrolysis can then react to form hydrochloric acid.

[0036] Electrolysis in g) also means that a higher concentration of lithium is permissible in the sodium chloride precipitate. This is because all the precipitate is recycled back into the process via an aqueous solution containing sodium hydroxide. In other words, there is no loss of co-precipitated lithium, for example, through the disposal of the sodium chloride precipitate. This also allows for process control, reducing the required separation energy compared to situations where high-purity sodium chloride is needed (e.g., when it is used as a product or for disposal). Therefore, the total concentration of lithium hydroxide and lithium chloride in the sodium chloride slurry electrolyzed in g) can be 0 to 20 wt.%, preferably 0 to 15 wt.%, more preferably 0 to 10 wt.%, and most preferably 0 to 6 wt.%, based on the total weight of the sodium chloride precipitate.

[0037] The electrolysis in g) is preferably performed using an optimized membrane-based chlor-alkali electrolysis process. Chlor-alkali electrolysis is well-known in the art, and its description can be found, for example, in *Chlor-Alkali Technology Handbook* by TF O'Brien et al., DOI https: / / doi.org / 10.1007 / b113786, eBook ISBN 978-0-306-48624-1, published December 31, 2008. This process involves feeding a sodium chloride solution into an electrolytic cell, where the sodium chloride is converted into sodium hydroxide, chlorine gas, and hydrogen gas. An advantage of using this standard chlor-alkali process is that it has a higher current efficiency than the electrolysis of lithium-containing solutions, making it a more efficient process step.

[0038] Therefore, as described above and as Figure 1 As shown, the method for producing lithium hydroxide monohydrate from lithium chloride according to the present invention may include: a) An aqueous solution containing sodium hydroxide is added to a first aqueous solution containing lithium chloride to obtain a mixture containing lithium hydroxide, sodium chloride, and water. b) Cool the mixture obtained in a) to selectively precipitate lithium hydroxide monohydrate, thereby obtaining lithium hydroxide monohydrate precipitate and a first mother liquor. c) Separate the lithium hydroxide monohydrate precipitate from the first mother liquor. d) Add the second lithium chloride-containing aqueous solution to the separated first mother liquor to obtain a first mother liquor enriched with lithium chloride. e) Remove (preferably evaporate) water from the first mother liquor enriched with lithium chloride to selectively precipitate sodium chloride, thereby obtaining a sodium chloride precipitate and a second mother liquor. f) Separate the sodium chloride precipitate from the second mother liquor to obtain a first aqueous solution containing lithium chloride, and g) Electrolyze sodium chloride precipitate to obtain an aqueous solution containing sodium hydroxide.

[0039] A preferred embodiment of the method of the present invention is as follows: Figure 1 The diagram illustrates this schematically. Wherein: LiCl(aq) 1 It is the first aqueous solution containing lithium chloride, LiCl(aq). 2The first lithium chloride-containing aqueous solution is a second lithium chloride-containing aqueous solution. H₂O(g) is evaporated water, NaCl(s) is sodium chloride precipitate, LHM is lithium hydroxide monohydrate precipitate, and NaOH(aq) is an aqueous solution containing sodium hydroxide. A and B are crystallization reactors, and C is a chlor-alkali electrolytic cell. In this process, the sodium hydroxide-containing aqueous solution is added to the first lithium chloride-containing aqueous solution via step 2, and the mixture is fed into crystallization reactor A via step 1. Here, the mixture is cooled to selectively precipitate lithium hydroxide monohydrate, and the precipitate is separated via step 3. The separated first mother liquor leaves crystallization reactor A via step 4. The second lithium chloride-containing aqueous solution is added to the separated first mother liquor via step 5, and the lithium chloride-enriched first mother liquor is fed into crystallization reactor B. In crystallization reactor B, the lithium chloride-enriched first mother liquor is heated, and water is evaporated via step 6 to selectively precipitate sodium chloride. The sodium chloride precipitate is separated from crystallization reactor B via step 7.

[0040] Furthermore, optional recycling steps in the process are indicated by dashed lines 8, 9, and 10. Line 8 refers to the return of at least a portion (preferably all or substantially all) of the second mother liquor obtained in crystallization reactor B to provide a first lithium chloride-containing aqueous solution, LiCl(aq). 1 Line 9 involves recycling at least a portion (preferably all or substantially all) of the sodium chloride precipitate obtained from crystallization reactor B to chlor-alkali electrolyzer C; Line 10 involves returning at least a portion of the electrolyzed sodium chloride precipitate to provide an aqueous solution of sodium hydroxide, NaOH(aq). Thus, via lines 3 and 12, this recycling process produces only lithium hydroxide monohydrate, chlorine, and hydrogen as products.

[0041] The method of the present invention can be performed continuously or in batches.

[0042] Lithium hydroxide monohydrate produced by the method of this invention can be directly used in lithium-ion batteries. It can also be converted into lithium carbonate by methods known in the art (e.g., reaction with carbon dioxide).

[0043] It should be noted that the various elements of the present invention, including but not limited to the preferred ranges of various parameters, can be combined unless they are mutually exclusive.

[0044] The present invention will be illustrated by the following embodiments, but is not limited thereto. Example

[0045] In the following experiments: - For simulation Figure 1 The circulating process shown estimated the concentrations of LiCl, LiOH, NaOH, and NaCl in the first and second mother liquors and prepared solutions accordingly as the starting mixture for each experiment.

[0046] - Chloride analysis (and recalculation as % NaCl) was performed using a Metrohm Titrino plus instrument by 0.1 M AgNO3 silver titration.

[0047] Sodium analysis was performed using inductively coupled plasma (ICP) spectroscopy.

[0048] - Drying was performed at 105-110°C using an infrared moisture analyzer (Sartorius MA35).

[0049] - The obtained lithium hydroxide monohydrate sample was washed three times in batches on a glass filter with a saturated lithium hydroxide solution prepared with deionized water.

[0050] The XRD procedure is as follows: The sample was placed in a standard sample holder, and the diffraction pattern was recorded using a Bruker AXS D8 reflection diffractometer equipped with a Cu-Kα radiation source. The generator was set to 40 kV, 40 mA. The sample was irradiated using a 2.5° Soler slit and a 15 mm fixed sample. An anti-scattering scalpel was used. Measurement range: 2θ = 5 – 70.0°, using a Lynxeye_XE_T (1D mode) detector, measurement time 0.25 seconds / step. Example 1 (Comparative): Efficiency of the method described in WO 2022 / 147632 A1

[0051] WO 2022 / 147632 A1 describes adding a lithium chloride solution to a returned mother liquor (ML-2), followed by cooling the mixture to 35°C to precipitate lithium hydroxide monohydrate (LHM). The filtrate (mother liquor 1, ML-1) is then mixed with a sodium hydroxide (NaOH) solution, and the water is evaporated at 100°C, resulting in sodium chloride (NaCl) precipitation. The filtrate is returned as ML-2 and mixed again with the lithium chloride.

[0052] WO 2022 / 147632 A1 does not describe the amount of LHM precipitated, nor the amount of water that must be evaporated to produce NaCl. Therefore, to determine the efficiency of this method, the process mass balance equation was defined using the reported composition, and the required parameters were calculated until the calculated composition matched the measured composition, thus determining these parameters.

[0053] The precipitation amounts of LHM and NaCl were calculated according to the following rules: 1) Lithium added in the form of lithium chloride is converted to LHM through the following reaction: LiCl + NaOH → LiOH + NaCl LiOH + H2O → LHM 2) The composition and mass flow rate after a complete cycle must match the starting point to ensure a closed, steady-state process.

[0054] 3) The molar amount of LiCl added must equal the molar amount of NaOH added; otherwise, LiCl or NaOH will begin to accumulate. [Note: This assumption can be relaxed if there are large emissions.] Based on these rules, a set of equations describing the process quality balance was defined, including some variables calculated from the results and some variables retained as "fitting" parameters. These fitting parameters were adjusted using a computational global optimization procedure until the composition of each stream perfectly matched the reported composition. Only one unique solution was found to describe the experimental data. The calculated compositions of ML-1 and ML-2 were matched with the measured compositions of sample-4 (given according to WO 2022 / 147632 A1 and expected to be the most stable since these are the most recent in time), yielding the results shown in Table 1.

[0055] Table 1: Comparison of Measured and Calculated Compositions of ML-1 and ML-2

[0056] Based on the calculated LHM precipitation and evaporation water volume, the efficiency of the method in WO 2022 / 147632 A1 was determined as follows: 1. The amount of LHM precipitate is approximately 1.75 wt.% of the total mass entering the LHM crystallizer.

[0057] 2. Approximately 152 grams of LHM are produced for every kilogram of water evaporated. Example 2: Production of lithium hydroxide monohydrate using the method of the present invention

[0058] This experiment was conducted in a jacketed reactor (Radleys Reactor-Ready, 1 liter) equipped with an internal filter that allows filtration at reactor temperature.

[0059] To simulate the first mother liquor separated in the method of this invention, a mixture containing lithium hydroxide, sodium chloride, and water was prepared by dissolving 49.8 g of LiOH and 144.9 g of NaCl in 610.2 g of H2O, resulting in a clear solution. At 80°C, 196.7 g of a 40 wt.% LiCl / H2O solution was added to this solution to obtain a mixture enriched with lithium chloride. This corresponds to streams 4 and 5 entering B, as... Figure 1 As shown.

[0060] Upon mixing the two solutions, a solid substance was observed to precipitate immediately. After stirring at 80°C for 3 hours and applying a vacuum of approximately 450 mbar to evaporate the water, the mixture was filtered. A total of 45 g of wet solid and 815.8 g of clear filtrate were obtained, with 138 g of water removed from the mixture by evaporation. Chloride determination by AgNO3 titration (considering chloride present as LiCl in the adsorbate) showed that the unwashed wet filter cake contained 90.0% NaCl. After infrared drying, a second titration yielded 97.5%.

[0061] Add 770.3 g of filtrate to a clean jacketed reactor and maintain at 40°C. While stirring, add 251.1 g of 24% NaOH solution (prepared and maintained at room temperature). This corresponds to streams 8, 1, and 2 entering A, as follows: Figure 1 As shown.

[0062] The mixture was mixed at 40°C for one hour and then filtered. 39 g of wet solid was obtained. The moisture content (including water of crystallization in LHM) was determined to be 48.5% by infrared drying at 105°C, and the NaCl content was determined to be 4.6% by AgNO3 titration. Therefore, the mass of LHM in the solid was calculated to be 32.04 g. Subsequently, the sample was washed three times with a saturated LiOH aqueous solution and then infrared dried at 105°C to remove all moisture (including water of crystallization). The NaCl content was measured and calculated to be 0.25% relative to LHM, indicating an LHM purity of 99.75%.

[0063] This indicates that the method of the present invention has the following efficiency: 1. The amount of LHM precipitate was approximately 3.1 wt.% of the total mass at the start of LHM crystallization (total mass 1022 g, yielding 32 g of LHM).

[0064] 2. Evaporation of 1 kg of water produces approximately 232 g of LHM (evaporation of 138 g of water yields 32 g of LHM). Examples 3A and 3B: Selective precipitation of sodium chloride and lithium hydroxide

[0065] Example 3A: Selective precipitation of sodium chloride

[0066] To simulate the first mother liquor separated in the method of this invention, 31.0 g LiOH, 53.9 g NaCl, and 303.1 g H2O were mixed in a glass beaker at 80°C using a magnetic stirrer to obtain a mixture containing lithium hydroxide, sodium chloride, and water. An aqueous solution containing 56.15 g LiCl and 56.2 g H2O (at room temperature) was then rapidly (i.e., within 5 seconds) added to this mixture to obtain a mixture enriched with lithium chloride. This corresponds to streams 4 and 5 entering B, as... Figure 1 As shown.

[0067] After stirring at 80°C for 1 hour (without forced evaporation of moisture), the lithium chloride-enriched mixture was filtered through a Buchner funnel at 80°C. This corresponds to Figure 1 Logistics 7.

[0068] X-ray diffraction (XRD) analysis determined that the obtained filter cake contained 0.9 g H₂O, 6.8 g NaCl, and 1.3 g LHM. Based on this, it was estimated that approximately 12.6% of the original NaCl and approximately 2.4% of the original LiOH precipitated, indicating that sodium chloride was the primary precipitate produced during this process.

[0069] Example 3B: Selective precipitation of lithium hydroxide

[0070] To 423.9 g of the filtrate from Example 3A, add 83.8 g of 28.0% NaOH solution (prepared and maintained at room temperature). This corresponds to streams 8, 1, and 2 entering A, as follows: Figure 1 As shown. Keep the mixture at 40°C for 1 hour, then filter it through a glass filter.

[0071] The unwashed wet filter cake weighed 43.41 g and contained 27 g of LHM. After washing with a saturated LiOH solution, the wet solid contained 84.4 wt.% LHM and 15.4 wt.% H2O. ICP analysis detected 0.89 g / kg Na in the final LHM produced, which is equivalent to 0.23 wt.% NaCl. It is estimated that approximately 28% of the total LiOH in the mixture precipitated as LHM. This indicates that the method used can produce large quantities of high-purity LHM.

[0072] Since 27 g of LHM was generated from a total of 507.7 g of material entering the crystallization step, the (unwashed) LHM efficiency of this method is approximately 5.3% (= 27 / 507.7). Example 4: Using the method of the present invention and comprising the cyclic production of lithium hydroxide monohydrate.

[0073] This experiment was conducted in the jacketed reactor of Example 2.

[0074] a): To simulate the second mother liquor separated in the method of the present invention, a first lithium chloride-containing aqueous solution was prepared by dissolving 68 g LiOH, 135 g NaCl, and 75 g LiCl in 720 g H2O and heating to 85°C. 203 g of a 27 wt.% NaOH solution (prepared by diluting a 50 wt.% NaOH stock solution with water) was added to this solution to obtain a mixture containing lithium hydroxide, sodium chloride, and water. This corresponds to streams 1 and 2 entering A, as follows: Figure 1 As shown.

[0075] b): Cool the mixture obtained in a) to 35°C and mix for 1 hour.

[0076] c): Filter the solution obtained in b). 70.5 g of wet solid was obtained. The moisture content (including water of crystallization in LHM) was determined to be 49.7% by infrared drying at 105°C, and the NaCl content was determined to be 4.7% by titration with AgNO3. Therefore, the mass of LHM in the solid was calculated to be 56.4 g. Subsequently, the sample was washed three times with saturated LiOH aqueous solution and then infrared dried at 105°C to remove all moisture (including water of crystallization). The NaCl content was measured and calculated to be 0.2% relative to LHM, indicating a purity of 99.8% for LHM.

[0077] d): Add 1093 g of the filtrate obtained in c) to a clean jacketed reactor and heat to 85°C. Add 140 g of a 40% LiCl / H₂O solution (temperature 40-55°C) to obtain a mixture enriched with lithium chloride. This corresponds to streams 4 and 5 entering B, as... Figure 1 As shown.

[0078] e): The lithium chloride-enriched mixture obtained in d) was stirred at 85°C for 2 hours, a vacuum of approximately 600 mbar was applied to evaporate the water, and then stirred again at 85°C under normal pressure for 1 hour, followed by filtration. A total of 94 g of wet solids and 914 g of clear filtrate were obtained, while 221 g of water was removed from the mixture by evaporation. Chloride determination by AgNO3 titration (considering chlorides present in the adsorbate as LiCl) showed that the unwashed wet filter cake contained 76.7% NaCl.

[0079] This indicates that after one cycle (i.e., a) to e), the method of the present invention has the following efficiency: 1. The amount of LHM precipitate was approximately 4.7 wt.% of the total mass at the start of LHM crystallization (total mass 1201 g, yielding 56.4 g of LHM).

[0080] 2. Evaporation of 1 kg of water produces approximately 257 g of LHM (evaporation of 221 g of water yields 56.4 g of LHM).

[0081] To illustrate an optional cyclic step of the method of the present invention, 870 g of the filtrate obtained in e) is added to a clean jacketed reactor at 85°C. 177 g of a 27 wt.% NaOH solution is added to this solution to obtain a mixture comprising lithium hydroxide monohydrate, sodium chloride, and water. This corresponds to streams 8, 1, and 2 entering A, as follows. Figure 1 As shown.

[0082] The mixture was then cooled to 35°C and mixed for 1 hour, followed by filtration of the solution. 59.7 g of wet solid was obtained. The moisture content (including water of crystallization in LHM) was determined to be 45.4% by infrared drying at 105°C, and the NaCl content was determined to be 7.8% by titration with AgNO3. The calculated mass of LHM in the solid was 48.9 g. Subsequently, the sample was washed three times with a saturated LiOH aqueous solution and then infrared dried at 105°C to remove all moisture (including water of crystallization). The NaCl content was measured and calculated to be 0.1% relative to LHM, indicating a purity of 99.9% for LHM.

[0083] Add 932 g of this filtrate to a clean jacketed reactor and heat to 85°C. Add 119 g of a 40% LiCl / H₂O solution (temperature 40-55°C) to obtain a mixture enriched with lithium chloride. This corresponds to streams 4 and 5 entering B, as... Figure 1 As shown.

[0084] The lithium chloride-enriched mixture was stirred at 85°C for 2 hours, then a vacuum of approximately 600 mbar was applied to evaporate the water. The mixture was then stirred again at 85°C under normal pressure for 1 hour, followed by filtration. A total of 69 g of wet solids and 801 g of clear filtrate were obtained, with 176 g of water removed from the mixture by evaporation. Chloride determination by AgNO3 titration (considering chlorides present as LiCl in the adsorbate) showed that the unwashed wet filter cake contained 78.7% NaCl.

[0085] Therefore, the second cycle of the method of the present invention can be seen to have the following efficiency: 1. The amount of LHM precipitate was approximately 4.7 wt.% of the total mass at the start of LHM crystallization (total mass 1047 g, yielding 48.9 g of LHM).

[0086] 2. Evaporation of 1 kg of water produces approximately 277 g of LHM (evaporation of 176 g of water yields 48.9 g of LHM).

[0087] Although the invention has been described with reference to exemplary embodiments, it should be understood that various modifications may be made within the scope of the invention.

[0088] In this specification, unless otherwise expressly stated, the word “or” refers to the operator that returns a truth value when one or both of the stated conditions are met, and not the operator “exclusive OR” that only one of the conditions is met. The word “includes” means “includes”, not “consisting of”. All prior teachings acknowledged above are incorporated herein by reference. Any acknowledgment of any prior publication herein should not be construed as an acknowledgment or statement that its teachings were common general knowledge in Europe or elsewhere as of the date of this application.

Claims

1. A process for producing lithium hydroxide monohydrate from lithium chloride, the process comprising: a) adding an aqueous sodium hydroxide-containing solution to a first aqueous lithium chloride-containing solution, thereby obtaining a mixture comprising lithium hydroxide, sodium chloride and water, b) cooling the mixture obtained in a) to selectively precipitate lithium hydroxide monohydrate, thereby obtaining a lithium hydroxide monohydrate precipitate and a first mother liquor, c) separating the lithium hydroxide monohydrate precipitate from the first mother liquor, d) adding a second aqueous lithium chloride-containing solution to the separated first mother liquor, thereby obtaining a first lithium chloride-enriched mother liquor, and e) removing (preferably evaporating) water from the first lithium chloride-enriched mother liquor to selectively precipitate sodium chloride, thereby obtaining a sodium chloride precipitate and a second mother liquor.

2. The method according to claim 1, wherein the mixture obtained in a) has a molar ratio of lithium ions (Li + ) to hydroxide ions (OH - ) of 0.7:1 to 2.0:1, preferably 0.9:1 to 1.7:1, preferably 0.95:1 to 1.5:1, more preferably 1 or 1.05:1 to 1.4:

1.

3. The process according to claim 1 or 2, wherein in b) the mixture obtained in a) is cooled to a temperature of 5 to 50 °C, preferably 10 to 45 °C, more preferably 20 to 45 °C.

4. The process according to any one of the preceding claims, wherein the first mother liquor enriched in lithium chloride has a molar ratio of lithium ions (Li + ) to hydroxide ions (OH - ) of 0.9:1 to 3.5:1, preferably of 0.95:1 to 2.5:1, more preferably of 1.0:1 to 2.0:

1.

5. The process according to any one of the preceding claims, wherein the first mother liquor and / or the first lithium chloride-enriched mother liquor is heated to a temperature of 50 to 120 °C, preferably 60 to 95 °C, more preferably 75 to 90 °C to effect removal of water by evaporation in e).

6. The method according to any of the preceding claims, wherein, The aqueous sodium hydroxide-containing solution has a sodium hydroxide concentration of 10 to 50 wt.%, preferably 15 to 40 wt.%, more preferably 20 to 35 wt.%, based on the total weight of the aqueous sodium hydroxide-containing solution.

7. The method according to any of the preceding claims, wherein, The second aqueous lithium chloride-containing solution has a lithium chloride concentration of 10 to 55 wt.%, preferably 20 to 50 wt.%, more preferably 30 to 45 wt.%, based on the total weight of the second aqueous lithium chloride-containing solution.

8. The method according to any of the preceding claims, wherein, Equal molar amounts of lithium chloride and sodium hydroxide are added to the process via the second aqueous lithium chloride-containing solution and the aqueous sodium hydroxide-containing solution, respectively.

9. The process according to any one of the preceding claims, further comprising: f) separating the sodium chloride precipitate from the second mother liquor to obtain the first aqueous lithium chloride-containing solution.

10. The process according to claim 9, further comprising: g) electrolyzing the sodium chloride precipitate to obtain the aqueous sodium hydroxide-containing solution.

11. The method of claim 10, wherein, The sodium chloride precipitate has a total concentration of lithium chloride and lithium hydroxide of 0 to 15 wt.%, preferably 0 to 10 wt.%, more preferably 0 to 6 wt.%, based on the total weight of the sodium chloride precipitate.

12. The process according to claim 10 or 11, wherein the electrolysis is performed using membrane chlor-alkali electrolysis.

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