Process for producing lithium hydroxide monohydrate

Abstract

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 to selectively precipitate lithium hydroxide monohydrate, (c) separating the lithium hydroxide monohydrate precipitate from the first mother liquor solution, (d) adding a second aqueous lithium chloride-containing solution to the separated first mother liquor solution, thereby obtaining a lithium chloride-enriched first mother liquor solution, and (e) removing, preferably evaporating, water from the lithium chloride-enriched first mother liquor solution to selectively precipitate sodium chloride.

Description

[0001] PROCESS FOR PRODUCING LITHIUM HYDROXIDE MONOHYDRATE

[0002] Technical field

[0003] The present invention is directed to a process for producing lithium hydroxide monohydrate from lithium chloride, and in particular, to producing battery grade lithium hydroxide monohydrate.

[0004] Background

[0005] Commercial production of lithium hydroxide monohydrate from lithium chloride typically involves electrolysis of lithium chloride or the conversion of lithium chloride into lithium carbonate by reaction with sodium carbonate. These processes are expensive and inefficient. For example, the production of lithium hydroxide monohydrate from the electrolysis of lithium chloride uses very high quantities of electricity (it is very inefficient compared to chlor-alkali electrolysis), while the production of lithium carbonate requires expensive reagents and yields a relatively impure lithium hydroxide monohydrate product.

[0006] Accordingly, there is a need for cheaper and more efficient processes for preparing lithium hydroxide monohydrate from lithium chloride.

[0007] To this end, several publications have been issued concerning the production of lithium hydroxide monohydrate by reacting lithium chloride with a source of hydroxide.

[0008] WO 2022 / 147632 A1 , for example, describes the production of lithium hydroxide monohydrate directly from lithium chloride with sodium hydroxide. The process includes adding a first sodium hydroxide-containing solution to a lithium chloride-containing brine at a temperature of from 80 °C to 120 °C to form a mixture comprising lithium hydroxide and sodium chloride. This mixture is cooled to a temperature of from 20 °C to 60 °C (typically 35 °C), and lithium hydroxide monohydrate is said to be selectively separated by a fractional cooling crystallisation step at a NaOH concentration of from 0.1 to 10.5 wt.%. The mother liquor is then mixed with a second sodium hydroxide-containing solution before undergoing fractional evaporative crystallisation at a temperature of from 80 °C to 120 °C (typically 100 °C) to selectively separate sodium chloride ready for disposal.

[0009] In a similar approach, WO 2023 / 012512 A1 discloses reacting a lithium chloride solution with a potassium hydroxide solution to form a reciprocal salt system comprising potassium hydroxide, lithium chloride, potassium chloride, lithium hydroxide, and water, and precipitating the potassium chloride and the lithium hydroxide from the reciprocal salt system to form lithium hydroxide crystals and potassium chloride crystals. In Example 1 , the reciprocal salt system is cooled to selectively precipitate the potassium chloride (where temperatures down to -10 °C are exemplified) and is heated (up to temperatures of 96 °C), and water is evaporated, to selectively precipitate the lithium hydroxide.

[0010] The production methods described in WO 2022 / 147632 A1 and WO 2023 / 012512 A1 , however, are not optimized regarding process efficiency and lithium hydroxide monohydrate purity. WO 2022 / 147632 A1 , for example, requires periodic purging of the mother liquor in order to reduce impurity build up and it disposes of the sodium chloride. In addition, the highest purity lithium hydroxide monohydrate obtained, after washing, is 95.5 %. Likewise, WO 2023 / 012512 A1 describes large temperature swings between heating and cooling to sufficiently precipitate potassium chloride and lithium hydroxide, suggesting large energy needs. Working at the low temperature of -10 °C is also very costly.

[0011] Accordingly, there is a need for a process wherein these issues are addressed.

[0012] Summary of the Disclosure

[0013] The present disclosure is directed to 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 lithium hydroxide monohydrate precipitate and a first mother liquor solution, c) separating the lithium hydroxide monohydrate precipitate from the first mother liquor solution, d) adding a second aqueous lithium chloride-containing solution to the separated first mother liquor solution, thereby obtaining a lithium chloride-enriched first mother liquor solution, and e) removing, preferably evaporating, water from the lithium chloride-enriched first mother liquor solution to selectively precipitate sodium chloride, thereby obtaining sodium chloride precipitate and a second mother liquor solution. Advantageously, by adding sodium hydroxide to the process before lithium hydroxide monohydrate precipitation and by adding lithium chloride to the process before sodium chloride precipitation, it has been found that the process of the invention can selectively precipitate lithium hydroxide monohydrate and sodium chloride at different points in the process, with high purity. Temperature change is also used to further optimise the selectivity of precipitation. This finding is surprising in view of WO 2022 / 147632 A1 , which states that having an excess of sodium hydroxide influences the solubilities of lithium hydroxide monohydrate and sodium chloride, such that they can be selectively precipitated.

[0014] By optimising the difference in solubilities of sodium chloride and lithium hydroxide monohydrate, the process of the invention is also able to achieve high (substantially full) conversion of lithium chloride into lithium hydroxide monohydrate. This enhances both the efficiency and water balance of the process.

[0015] Thus, as demonstrated in the below worked examples, the presently disclosed process has the following key advantages over WO 2022 / 147632 A1 :

[0016] • Increased amount of lithium hydroxide monohydrate formed on total mass;

[0017] • Lower energy costs due to less water needing to be removed (e.g., evaporated) to produce the same amount of lithium hydroxide monohydrate;

[0018] • Similar production capacity possible with smaller flows and thus smaller vessels, meaning reduced operational costs and lower capital investment; and

[0019] • Higher purity lithium hydroxide monohydrate obtained after washing.

[0020] Figures

[0021] Figure 1 is a flow diagram of preferred embodiments of the present disclosure.

[0022] Detailed description

[0023] The various aspects of the present invention will be elucidated further below.

[0024] As indicated above, in a first aspect, the present invention provides 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 lithium hydroxide monohydrate precipitate and a first mother liquor solution, c) separating the lithium hydroxide monohydrate precipitate from the first mother liquor solution, d) adding a second aqueous lithium chloride-containing solution to the separated first mother liquor solution, thereby obtaining a lithium chloride-enriched first mother liquor solution, and e) removing, preferably evaporating, water from the lithium chloride-enriched first mother liquor solution to selectively precipitate sodium chloride, thereby obtaining sodium chloride precipitate and a second mother liquor solution.

[0025] The expression “high purity”, as used herein, refers to levels above 98 %, for example, above 99 %.

[0026] In a), sodium hydroxide is added to lithium chloride to form lithium hydroxide and sodium chloride. The addition is preferably performed at a temperature in the range of from 10 °C to 100 °C, preferably 20 °C to 95 °C, and most preferably from 25 °C to 90 °C. Preferably, the first aqueous lithium chloride-containing solution is at, or above, this temperature range before the aqueous sodium hydroxide-containing solution is added. The molar ratio of sodium hydroxide added as aqueous solution to lithium chloride in the lithium chloride-containing solution is preferably in the range of from 0.1 :1 to 1 .5:1 , and more preferably from 0.3:1 to 0.9:1 .

[0027] The aqueous sodium hydroxide-containing solution typically has a sodium hydroxide concentration of from 10 to 50 wt.%, preferably from 15 to 40 wt.% and more preferably from 20 to 35 wt.%, based on the total weight of the aqueous sodium hydroxide-containing solution. In a preferred embodiment, at least a part and preferably all, or substantially all, of the aqueous sodium hydroxide-containing solution is obtained from electrolysing the sodium chloride precipitate of e).

[0028] The first aqueous lithium chloride-containing solution typically has a lithium concentration of from 1 .0 to 9.0 wt.%, preferably from 2.0 to 8.0 wt.%, more preferably from 2.5 to 7.5 wt.%, based on the total weight of the first aqueous lithium chloride-containing solution. In a preferred embodiment, at least a part and preferably all, or substantially all, of the first aqueous lithium chloride-containing solution is provided by the separated second mother liquor solution (see discussion of f) below). When the first aqueous lithium chloride-containing solution is provided by the separated second mother liquor solution, the first aqueous lithium chloride-containing solution preferably has a lithium concentration of from 2.5 to 6.0 wt.%, preferably from 2.5 to 4.0 wt.%, and more preferably from 2.8 to 3.4 wt.%, based on the total weight of the first aqueous lithium chloride-containing solution.

[0029] The mixture obtained in a) preferably has a molar ratio of lithium ions (Li+) to hydroxyl ions (OH ) of from 0.7:1 to 2.0:1 , preferably of from 0.9:1 to 1.7:1 , preferably of from 0.95:1 to 1 .5:1 , and more preferably of from 1 or 1 .05:1 to 1 .4:1 .

[0030] In b), the mixture obtained in a) is cooled to a temperature of from 5 to 50 °C, preferably from 10 to 45 °C, more preferably from 20 to 45 °C to selectively precipitate lithium hydroxide monohydrate. Cooling may be achieved by any cooling method known in the art, such as with a cooling liquid (e.g., water) in the double wall of a jacketed reactor or by passing the reactor content through a heat exchanger.

[0031] The adding in a) and precipitating in b) may be performed sequentially or simultaneously. Likewise, the adding in a) and precipitating in b) may be performed in a single device, for example, a crystallisation reactor, or in separate devices, for example, a reactor and a crystal lise r. Preferably, the aqueous sodium hydroxide-containing solution and the first aqueous lithium chloride-containing solution are added into a reactor that is controlled at a specified temperature, after which the reactor content is kept at that temperature for a specific mixing time and the precipitated solids are separated.

[0032] The lithium hydroxide monohydrate precipitate obtained in b) may be separated from the first mother liquor solution in c) by typical solid-liquid separation technologies such as filtration, sedimentation and / or centrifugation. Preferably, the separated lithium hydroxide monohydrate precipitate has a purity, after washing, of at least 96 %, preferably at least 97 %, more preferably at least 98 %, and most preferably at least 99 %. Washing steps may comprise washing the precipitate with water saturated with lithium hydroxide on any solid / liquid separation equipment, such as filter or centrifuges. Alternatively, any other liquid that has a higher solubility for sodium chloride than lithium hydroxide monohydrate can be used.

[0033] After the washing step(s), a subsequent re-crystallization step can be employed, as is known in the art. In this step, the lithium hydroxide is re-dissolved in water and can be crystallized again by, for instance, water evaporation, followed by cooling. This can potentially increase the purity of the final lithium hydroxide even further.

[0034] In d), a second aqueous lithium chloride-containing solution is added to the separated first mother liquor solution. The second aqueous lithium chloride-containing solution may be obtained from naturally occurring brine, such as, a geothermal brine, or from mineral containing rock, such as spodumene.

[0035] The second aqueous lithium chloride-containing solution typically has a lithium chloride concentration of from 10 to 55 wt.%, preferably from 20 to 50 wt.% and more preferably from 30 to 45 wt.%, based on the total weight of the second aqueous lithium chloride-containing solution.

[0036] It is preferred that equimolar quantities of lithium chloride and sodium hydroxide are added to the process by the second aqueous lithium chloride-containing solution and the aqueous sodium hydroxide-containing solution, respectively. This is especially advantageous when the process is continuous (or circular), as discussed below.

[0037] Preferably, the lithium chloride-enriched first mother liquor solution obtained in d) has a molar ratio of lithium ions (Li+) to hydroxyl ions (OH ) of from 0.9:1 to 3.5:1 , more preferably of from 0.95:1 to 2.5:1 , and most preferably of from 1 .0:1 to 2.0:1 .

[0038] In e), water is removed, preferably evaporated, from the lithium chloride-enriched first mother liquor solution to selectively precipitate sodium chloride. When water is removed by evaporation, the evaporation can be caused by heating the first mother liquor solution and / or the lithium chloride-enriched first mother liquor solution to a temperature of from 50 to 120 °C, preferably 60 to 95 °C, more preferably 75 to 90 °C. If required, evaporation can be done under vacuum to lower the evaporation temperature. Vacuum pressure is controlled by the cooling water temperature and is preferably between 40 to 500 mbar.

[0039] The adding in d) and removing (e.g., evaporating) in e) may be performed sequentially or simultaneously. Likewise, the adding in d) and removing (e.g., evaporating) in e) may be performed in a single device, for example, a crystallisation reactor, or in separate devices, for example, a reactor and a crystal liser. Preferably, a multi-effect evaporator (MEE) or a mechanical vapor recompression (MVR) crystalliser is used for the evaporation and crystallisation.

[0040] Preferably, the process of the present invention further includes: f) separating the sodium chloride precipitate from the second mother liquor solution to obtain the first aqueous lithium chloride-containing solution.

[0041] In f), the sodium chloride precipitate obtained in e) may be separated from the second mother liquor solution in particulate form or in solution. This is typically done using solid-liquid separation technologies such as filtration, sedimentation and / or centrifugation. Preferably, the solids filtered off are sent to the electrolyser as a sodium rich slurry. Preferably, the separated sodium chloride precipitate has a purity, after washing, of at least 80 %, more preferably at least 90 % and most preferably at least 95 %. Washing steps may comprise washing with water being saturated with sodium chloride.

[0042] The second mother liquor solution, once separated, can provide at least a part and preferably all, or substantially all, of the first aqueous lithium chloride-containing solution for a). As such, the inclusion of f) allows the process of the present invention to be a closed loop, thus eliminating the need to purge or dispose of certain product streams.

[0043] Preferably, the process of the present invention further includes: g) electrolysing the sodium chloride precipitate to obtain the aqueous sodium hydroxide-containing solution.

[0044] The electrolysing in g) provides the advantage of recycling the sodium chloride precipitate to the process as the aqueous sodium hydroxide-containing solution. This eliminates the need to dispose of sodium chloride. The inclusion of an electrolysis loop also reduces the amount of water that needs to be removed (e.g., evaporated) in e), hence improving the water balance of the process. The chlorine and hydrogen produced in the electrolysis process may subsequently be reacted to form hydrochloric acid.

[0045] The electrolysing in g) also means that a higher concentration of lithium in the sodium chloride precipitate is acceptable. This is because all precipitate is recycled to the process in the aqueous sodium hydroxide-containing solution. That is, no co-precipitated lithium is lost, e.g., through disposal of the sodium chloride precipitate. This also gives the possibility to control the process such that a reduced amount of separation energy is required as compared to when the sodium chloride needs to be of high purity, for instance, when it is disposed of or sold as a product. The sodium chloride slurry electrolysed in g) may therefore have a total concentration of lithium hydroxide and lithium chloride of from 0 to 20 wt.%, preferably from 0 to 15 wt.%, more preferably from 0 to 10 wt.% and most preferably from 0 to 6 wt.%, based on the total weight of the sodium chloride precipitate.

[0046] The electrolysing in g) is preferably performed using an optimised membrane-based chlor-alkali electrolysis. Chlor-alkali electrolysis is well known in the art and a description can be found, for instance, in T. F O'Brien et al, The Handbook of Chlor-Alkali Technology, DOI https: / / doi.org / 10.1007 / b1 13786, eBook ISBN978-0-306-48624-1 , Published: 31 December 2008. The process comprises of feeding a solution of sodium chloride into an electrolyser, where the sodium chloride is converted to sodium hydroxide, chlorine and hydrogen. The advantage of being able to use such standard chlor-alkali process is that the current efficiency of such process is higher than for electrolysis of a lithium containing solution, making this a more efficient process step.

[0047] Thus, as described above and shown in Figure 1 , the process for producing lithium hydroxide monohydrate from lithium chloride of the present invention may include: 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 lithium hydroxide monohydrate precipitate and a first mother liquor solution, c) separating the lithium hydroxide monohydrate precipitate from the first mother liquor solution, d) adding a second aqueous lithium chloride-containing solution to the separated first mother liquor solution, thereby obtaining a lithium chloride-enriched first mother liquor solution, e) removing, preferably evaporating, water from the lithium chloride-enriched first mother liquor solution to selectively precipitate sodium chloride, thereby obtaining sodium chloride precipitate and a second mother liquor solution, f) separating the sodium chloride precipitate from the second mother liquor solution to obtain the first aqueous lithium chloride-containing solution, and g) electrolysing the sodium chloride precipitate to obtain the aqueous sodium hydroxide-containing solution.

[0048] A preferred embodiment of the present process is illustrated schematically in Figure 1 . Here: LiCI(aq)1is a first aqueous lithium chloride-containing solution, LiCI(aq)2is a second aqueous lithium chloride-containing solution, H2O(g) is evaporated water, NaCI(s) is sodium chloride precipitate, LHM is lithium hydroxide monohydrate precipitate, NaOH(aq) is an aqueous sodium hydroxide-containing solution, A and B are a crystallisation reactor and C is a chlor-alkali electrolyser. In the process, an aqueous sodium hydroxide-containing solution is added to a first aqueous lithium chloride-containing solution, via 2, and the mixture is fed, via 1 , into crystallisation reactor A. Here, the mixture is cooled to selectively precipitate lithium hydroxide monohydrate, which is separated, via 3. The separated first mother liquor solution leaves crystallisation reactor A, via 4. A second aqueous lithium chloride-containing solution is added to the separated first mother liquor solution, via 5, and the lithium chloride-enriched first mother liquor solution is fed into crystallisation reactor B. In crystallisation reactor B, the lithium chloride-enriched first mother liquor solution is heated, and water is evaporated, via 6, to selectively precipitate sodium chloride. The sodium chloride precipitate is separated from crystallisation reactor B, via 7.

[0049] Further, optional, recycling steps in the process are shown by dashed lines 8, 9, and 10. Here, line 8 is the return of at least a part, preferably all, or substantially all, of the second mother liquor solution obtained from crystallisation reactor B to provide the first aqueous lithium chloride- containing solution LiCI(aq)1, line 9 is the recycle of at least a part, preferably all, or substantially all, of the sodium chloride precipitate obtained from crystallisation reactor B to chlor-alkali electolyser C, and line 10 is the return of at least a part of the electrolysed sodium chloride precipitate, to provide the aqueous sodium hydroxide-containing solution NaOH(aq). As such, the circular process generates only lithium hydroxide monohydrate, chlorine and hydrogen as products, via 3 and 12.

[0050] The process of the invention can be performed continuously or batch-wise.

[0051] The lithium hydroxide monohydrate produced by the present process can be used in lithium-ion batteries as such. It can also be converted to lithium carbonate by means known in the art, such as reaction with carbon dioxide.

[0052] It is noted that various elements of the present invention, including but not limited to preferred ranges for the various parameters, can be combined unless they are mutually exclusive.

[0053] The invention will be elucidated by the following examples without being limited thereto or thereby.

[0054] Examples

[0055] In the following experiments: To mimic the circular process shown in Figure 1 , concentrations of recycled LiCI, LiOH, NaOH and NaCI in the first and second mother liquor were estimated, and corresponding solutions prepared as the starting mixtures for each experiment.

[0056] - Analysis of chloride (and recalculation to % NaCI) was performed by argentometric titration with 0.1 M AgNOs, using Metrohm Titrino plus equipment.

[0057] - Analysis of sodium was performed by Inductively Coupled Plasma (ICP) Spectroscopy. Drying was carried out at 105-110 °C in an infrared moisture analyser (Sartorius MA35). The obtained lithium hydroxide monohydrate sample was washed, batchwise, three times on a glass filter with a saturated solution of lithium hydroxide in demineralised water.

[0058] The XRD procedure was as follows:

[0059] Samples were placed in a standard sample holder and the diffraction pattern was recorded using a BrukerAXS D8 reflection-diffractometer with Cu-Ka radiation. Generator settings were 40 kV, 40 mA. Seller slits 2.5° and 15 mm fixed sample irradiation. An antiscatter knife was used. Measuring range: 29 = 5 - 70.0° with Lynxeye_XE_T (1 D mode) detector, measuring time 0.25 sec / step.

[0060] Example 1 (Comparative): Efficiency of process described in WO 2022 / 147632 A1

[0061] WO 2022 / 147632 A1 describes adding a lithium chloride solution to a returning mother liquor (ML-2) followed by cooling the mixture to 35 °C to effect lithium hydroxide monohydrate (LHM) precipitation. The filtrate (mother liquor 1 , ML-1 ) is subsequently mixed with a sodium hydroxide (NaOH) solution, after which water is evaporated at 100 °C, leading to precipitation of sodium chloride (NaCI). The filtrate is returned as ML-2 and mixed again with lithium chloride.

[0062] WO 2022 / 147632 A1 does not describe the amount of LHM that is precipitated nor the amount of water that must be evaporated to generate the NaCI. In order to determine the efficiency of this process therefore, these parameters were determined by defining mass balance equations for the process, using the compositions as reported, and subsequently computing the required parameters until the calculated compositions matched the measured compositions.

[0063] The amount of precipitation of LHM and NaCI were computed, based on the following rules:

[0064] 1 ) The lithium added as lithium chloride reacts to LHM via the reaction:

[0065] 2) The composition and mass flow after a full cycle needs to match the starting point to ensure a closed, steady state process. 3) The molar amount of LiCI added is equal to the molar amount of NaOH added as otherwise either LiCI or NaOH would start building up. [Note that this assumption can be loosened with a substantial purge.]

[0066] Based upon these rules, a set of equations was defined describing the mass balance of the process, including a number of variables that were computed from the results and a number of variables that remained as ‘fit’-parameters. These fit parameters were varied using a computational global optimization routine, until the compositions of the various streams exactly matched the reported compositions. It was found that only one unique solution described the experimental data. Matching the computed compositions of ML-1 and ML-2 with the measured compositions from sample-4 (as given in WO 2022 / 147632 A1 and anticipated to be most stable as these were most advanced in time), the results shown in Table 1 were obtained.

[0067] Table 1: Comparison of measured and calculated compositions of ML-1 and ML-2

[0068] Based on the computed amount of LHM precipitated and amount of water evaporated, the following efficiency was determined for the process of WO 2022 / 147632 A1 :

[0069] 1 ) LHM-precipitation is about 1 .75 wt.% on the total mass going into LHM crystallizer.

[0070] 2) About 152 g LHM was produced per kg of water evaporated.

[0071] Example 2: Production of lithium hydroxide monohydrate using the present process

[0072] This experiment was performed in a jacketed reactor (Radleys Reactor-Ready, 1 liter) that contains an internal filter, making it possible to filter at the reactor temperature.

[0073] To mimic the separated first mother liquor solution of the present process, a mixture containing lithium hydroxide, sodium chloride and water was prepared by dissolving 49.8 g LiOH and 144.9 g NaCI in 610.2 g H2O to give a clear solution. To this solution, 196.7 g of a 40 wt.% solution of LiCI in H2O was added at 80 °C to obtain a lithium chloride-enriched mixture. This represents streams 4 and 5 going into B, as shown in Figure 1 .

[0074] Upon mixing the two solutions, immediate precipitation of solid material was visually detected. After 3 hours of stirring at 80 °C and evaporating water by applying a vacuum of ca. 450 mbar, the mixture was filtered. In total, 45 g of wet solids was obtained and 815.8 g of clear filtrate solution, while 138 g of water had been removed from the mixture by evaporation. Determination of chloride by AgNOs titration (and taking into account the presence of chloride as LiCI in the attached liquor) showed that the unwashed, wet filter cake contained 90.0 % NaCI. After infrared drying, this was measured again via titration and determined to be 97.5 %.

[0075] Of the filtrate, 770.3 grams were added into the cleaned jacketed reactor and kept at 40 °C. To this, 251 .1 g of a 24% NaOH solution (made and kept at room temperature) was added while stirring. This represents streams 8, 1 and 2 going into A, as shown in Figure 1 .

[0076] The mixture was mixed at 40 °C for one hour after which the solution was filtered. 39 g of wet solids were obtained. Moisture content as determined by infra-red drying at 105 °C was found to be 48.5 % (including crystal water present in the LHM) and NaCI content was found to be 4.6 %, determined by AgNOs titration. From this, the mass of LHM in the solids was calculated as 32.04 g. A sample was subsequently washed 3 times with water saturated with LiOH and subsequently infra-red dried at 105 °C removing all water including crystal water. The NaCI content was measured and calculated to be 0.25 % relative to LHM, giving a LHM purity of 99.75%.

[0077] This shows that the present process has the following efficiency:

[0078] 1 ) LHM precipitation is about 3.1 wt.% on total mass at start of LHM crystallization (32 g LHM on 1022 g total mass).

[0079] 2) About 232 g LHM was produced per kg of water evaporated (32 g LHM per 138 g water evaporated).

[0080] Example 3A and 3B: Selective precipitation of sodium chloride and lithium hydroxide

[0081] Example 3A: Selective precipitation of sodium chloride

[0082] To mimic the separated first mother liquor solution of the present process, a mixture containing lithium hydroxide, sodium chloride and water was prepared by mixing 31 .0 g LiOH, 53.9 g NaCI and 303.1 g H2O in a beaker glass using a magnetic stirrer at 80 °C. To this mixture, an aqueous lithium chloride-containing solution (at room temperature), containing 56.15 g LiCI and 56.2 g H2O, was added rapidly (i.e., within 5 seconds), to obtain a lithium chloride-enriched mixture. This represents stream 4 and 5 going into B, as shown in Figure 1 .

[0083] After 1 hour of stirring at 80 °C, without forced evaporation of water, the lithium chloride-enriched mixture was passed through a Buchner funnel at 80 °C. This represents stream 7 in Figure 1 .

[0084] The obtained filter cake contained 0.9 g H2O, 6.8 g NaCI and 1 .3 g LHM as determined by X-ray diffraction analysis (XRD). From this, it was estimated that about 12.6 % of the original NaCI amount and about 2.4 % of the original LiOH amount precipitated, showing that predominantly sodium chloride was precipitated via this process.

[0085] Example 3B: Selective precipitation of lithium hydroxide

[0086] To 423.9 g of the filtrate of Example 3A, 83.8 g of a 28.0 % solution of NaOH (made and kept at room temperature) was added. This represents stream 8, 1 and 2 going into A, as shown in Figure 1 . The mixture was kept at 40 °C for 1 hour and then filtered over a glass filter.

[0087] The wet, unwashed filter cake weighed 43.41 g and contained 27 g of LHM. After washing with a saturated LiOH solution, the moist solids contained 84.4 % w / w LHM and 15.4 % H2O. In the final LHM produced, 0.89 g / kg Na was detected by ICP analysis, which corresponds to 0.23 wt.% NaCI. It is estimated that about 28 % of the total amount of LiOH in the mixture precipitated as LHM. This shows that the procedure used can produce significant amounts of a high purity LHM.

[0088] As 27 g LHM were produced from in total 507.7 g of mass going into the crystallization step, the process has an (unwashed) LHM efficiency of about 5.3 % (= 27 / 507.7).

[0089] Example 4: Production of lithium hydroxide monohydrate using the present process with recycling

[0090] This experiment was performed in the jacketed reactor of Example 2. a): To mimic the separated second mother liquor solution of the present process, a first aqueous lithium chloride-containing solution was prepared by dissolving 68 g LiOH, 135 g NaCI, and 75 g LiCI in 720 g H2O and heating to 85 °C. To this solution, 203 g of a 27 wt.% NaOH solution (prepared by diluting a 50 wt.% NaOH stock solution with water) was added to obtain a mixture comprising lithium hydroxide, sodium chloride and water. This represents streams 1 and 2 going into A, as shown in Figure 1 . b): The mixture obtained in a) was then cooled to 35 °C and mixed for 1 hour. c): The solution obtained in b) was filtered. 70.5 g of wet solids were obtained. Moisture content as determined by infra-red drying at 105 °C was found to be 49.7 % (including crystal water present in the LHM) and NaCI content was found to be 4.7 %, determined by AgNOs titration. From this, the mass of LHM in the solids was calculated as 56.4 g. A sample was subsequently washed 3 times with water saturated with LiOH and subsequently infra-red dried at 105 °C removing all water including crystal water. The NaCI content was measured and calculated to be 0.2 % relative to LHM, giving a LHM purity of 99.8 %. d): Of the filtrate obtained in c), 1093 g was added into the cleaned jacketed reactor and heated to 85 °C. To this, 140 g of a 40% solution of LiCI in H2O (at a temperature of from 40 to 55 °C) was added to obtain a lithium chloride-enriched mixture. This represents streams 4 and 5 going into B, as shown in Figure 1 . e): The lithium chloride-enriched mixture obtained in d) was stirred for 2 hours at 85 °C under an applied vacuum of ca. 600 mbar to evaporate water, and then for 1 hour at 85 °C under atmospheric pressure, before filtration. In total, 94 g of wet solids was obtained and 914 g of clear filtrate solution, while 221 g of water had been removed from the mixture by evaporation. Determination of chloride by AgNOs titration (and taking into account the presence of chloride as LiCI in the attached liquor) showed that the unwashed, wet filter cake contained 76.7 % NaCI.

[0091] This shows that, after one cycle (i.e., a) to e)), the present process has the following efficiency:

[0092] 1 ) LHM precipitation is about 4.7 wt.% on total mass at start of LHM crystallization (56.4 g LHM on 1201 g total mass).

[0093] 2) About 257 g LHM was produced per kg of water evaporated (56.4 g LHM per 221 g water evaporated).

[0094] To exemplify the optional recycling steps of the present process, 870 g of the filtrate obtained in e) was added into the cleaned jacketed reactor at 85 °C. To this solution, 177 g of a 27 wt.% NaOH solution was added to obtain a mixture comprising lithium hydroxide monohydrate, sodium chloride and water. This represents streams 8, 1 and 2 going into A, as shown in Figure 1 . The mixture was then cooled to 35 °C and mixed for 1 hour, after which the solution was filtered. 59.7 g of wet solids were obtained. Moisture content as determined by infra-red drying at 105 °C was found to be 45.4% (including crystal water present in the LHM) and NaCI content was found to be 7.8 %, determined by AgNOs titration. From this, the mass of LHM in the solids was calculated as 48.9 g. A sample was subsequently washed 3 times with water saturated with LiOH and subsequently infra-red dried at 105 °C removing all water including crystal water. The NaCI content was measured and calculated to be 0.1 % relative to LHM, giving a LHM purity of 99.9 %.

[0095] Of this filtrate, 932 g was added into the cleaned jacketed reactor and heated to 85 °C. To this, 119 g of a 40% solution of LiCI in H2O (at a temperature of from 40 to 55 °C) was added to obtain a lithium chloride-enriched mixture. This represents streams 4 and 5 going into B, as shown in Figure 1.

[0096] The lithium chloride-enriched mixture was stirred for 2 hours at 85 °C under an applied vacuum of ca. 600 mbar to evaporate water, and then for 1 hour at 85 °C under atmospheric pressure, before filtration. In total, 69 g of wet solids was obtained and 801 g of clear filtrate solution, while 176 g of water had been removed from the mixture by evaporation. Determination of chloride by AgNOs titration (and taking into account the presence of chloride as LiCI in the attached liquor) showed that the unwashed, wet filter cake contained 78.7 % NaCI.

[0097] Thus, the second cycle of the present process can be seen to have the following efficiency:

[0098] 1 ) LHM precipitation is about 4.7 wt.% on total mass at start of LHM crystallization (48.9 g LHM on 1047 g total mass).

[0099] 2) About 277 g LHM was produced per kg of water evaporated (48.9 g LHM per 176 g water evaporated).

[0100] Whilst the invention has been described with reference to an exemplary embodiment, it will be appreciated that various modifications are possible within the scope of the invention.

[0101] In this specification, unless expressly otherwise indicated, the word ‘or’ is used in the sense of an operator that returns a true value when either or both of the stated conditions is met, as opposed to the operator ‘exclusive or’ which requires that only one of the conditions is met. The word ‘comprising’ is used in the sense of ‘including’ rather than to mean ‘consisting of’. All prior teachings acknowledged above are hereby incorporated by reference. No acknowledgement of any prior published document herein should be taken to be an admission or representation that the teaching thereof was common general knowledge in Europe or elsewhere at the date hereof.

Claims

CLAIMS1 . 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 lithium hydroxide monohydrate precipitate and a first mother liquor solution, c) separating the lithium hydroxide monohydrate precipitate from the first mother liquor solution, d) adding a second aqueous lithium chloride-containing solution to the separated first mother liquor solution, thereby obtaining a lithium chloride-enriched first mother liquor solution, and e) removing, preferably evaporating, water from the lithium chloride-enriched first mother liquor solution to selectively precipitate sodium chloride, thereby obtaining sodium chloride precipitate and a second mother liquor solution.

2. A process as claimed in claim 1 , wherein the mixture obtained in a) has a molar ratio of lithium ions (Li+) to hydroxyl ions (OH ) of from 0.7:1 to 2.0:1 , preferably from 0.9:1 to 1 .7:1 , preferably from 0.95:1 to 1 .5:1 , and more preferably of from 1 or 1 .05:1 to 1 .4:1 .

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

4. A process as claimed in any preceding claim, wherein the lithium chloride-enriched first mother liquor solution has a molar ratio of lithium ions (Li+) to hydroxyl ions (OH ) of from 0.9:1 to 3.5:1 , preferably from 0.95:1 to 2.5:1 , more preferably from 1 .0:1 to 2.0:1 .

5. A process as claimed in any preceding claim, wherein the first mother liquor solution and / or the lithium chloride-enriched first mother liquor solution is heated to a temperature of from 50 to 120 °C, preferably 60 to 95 °C, more preferably 75 to 90 °C to effect removal by evaporation in e).

6. A process as claimed in any preceding claim, wherein the aqueous sodium hydroxide- containing solution has a sodium hydroxide concentration of from 10 to 50 wt.%, preferably from 15 to 40 wt.% and more preferably from 20 to 35 wt.%, based on the total weight of the aqueous sodium hydroxide-containing solution.

7. A process as claimed in any preceding claim, wherein the second aqueous lithium chloride-containing solution has a lithium chloride concentration of from 10 to 55 wt.%, preferably from 20 to 50 wt.% and more preferably from 30 to 45 wt.%, based on the total weight of the second aqueous lithium chloride-containing solution.

8. A process as claimed in any preceding claim, wherein equimolar quantities of lithium chloride and sodium hydroxide are added to the process by the second aqueous lithium chloride-containing solution and the aqueous sodium hydroxide-containing solution, respectively.

9. A process as claimed in any preceding claim, further comprising: f) separating the sodium chloride precipitate from the second mother liquor solution to obtain the first aqueous lithium chloride-containing solution.

10. A process as claimed in claim 9, further comprising: g) electrolysing the sodium chloride precipitate to obtain the aqueous sodium hydroxide-containing solution.1 1. A process as claimed in claim 10, wherein the sodium chloride precipitate has a total concentration of lithium chloride and lithium hydroxide of from 0 to 15 wt.%, preferably from 0 to 10 wt.%, more preferably from 0 to 6 wt.%, based on the total weight of the sodium chloride precipitate.

12. A process as claimed in claim 10 or claim 1 1 , wherein the electrolysing is performed using a membrane-based chlor-alkali electrolysis.

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