Method for preparing lithium hydroxide from lithium-containing raw materials

Abstract

The present invention relates to a method for preparing lithium hydroxide, which comprises the following steps: a step of roasting a lithium-containing raw material with sulfuric acid; a step of leaching the roasted lithium-containing raw material to obtain a leaching step of obtaining a lithium sulfate solution; a first purification step of purifying the leached solution to a pH value of 7.1 to 9.5; a second purification step of purifying the first purified solution to a pH value of 9 to 11; and a step of performing a second purification step of the purified solution through bipolar electrodialysis to obtain a lithium hydroxide aqueous solution.

Description

Technical Field

[0001] One embodiment of the present invention can provide a method for preparing lithium hydroxide from a lithium-containing raw material. Specifically, one embodiment of the present invention can provide a method for preparing lithium hydroxide from a lithium-containing raw material using an electrodialysis method. Background Art

[0002] The conventional technology for preparing lithium hydroxide can be divided into a lithium leaching process and a process for obtaining lithium hydroxide.

[0003] The process of leaching lithium from ore begins with calcination, which transforms the ore into a crystalline structure that is easier to extract. Acid roasting then converts the lithium in the ore into a more readily extractable form. Leaching then produces an acidic solution containing lithium.

[0004] The acid roasting process primarily uses sulfuric acid (H2SO4). Although hydrochloric acid (HCl) is also used in some processes, sulfuric acid is now used in almost all commercial processes due to environmental concerns. The resulting lithium-containing acidic solution is an aqueous solution of lithium sulfate (Li2SO4), a well-known technique used in most processes for extracting lithium from ore.

[0005] Through the lithium sulfate extraction process, the lithium sulfate aqueous solution obtained contains various impurities (Mg, Ca, Fe, Ni, Mn, Si, Al, etc.) caused by the ore. In order to be put into the back-end process, it is purified to obtain the purified lithium sulfate aqueous solution, which is converted into lithium hydroxide through alkali treatment or the like.

[0006] Other known processes for obtaining lithium hydroxide from lithium sulfate include electrolysis or electrodialysis. These processes involve directly feeding a lithium sulfate solution into an electrolysis or electrodialysis unit to produce a lithium hydroxide solution, or adding phosphoric acid (H₃PO₄) to obtain lithium phosphate (Li₃PO₄), which is then converted to lithium sulfate and then fed into an electrolysis or electrodialysis unit to produce a lithium hydroxide aqueous solution.

[0007] These conventional technologies have the following problems: low yield of high-purity lithium hydroxide monohydrate (LiOH·H2O), which can be used as a battery material; management and loss of electrolysis electrodes during the process; and stability and environmental impact of the dialysis membrane caused by the use of phosphoric acid. Summary of the Invention

[0008] Technical issues

[0009] The present invention aims to provide a method for efficiently extracting lithium from lithium-containing raw materials. This method utilizes a method that reduces the amount of Na-based secondary raw materials used to minimize the amount of sodium hydroxide-containing wastewater generated during the production process, thereby providing an economically and environmentally friendly lithium hydroxide production process.

[0010] Technical Solution

[0011] A method for preparing lithium hydroxide according to one embodiment of the present invention comprises the following steps: a step of roasting a lithium-containing raw material with sulfuric acid; a step of leaching the roasted lithium-containing raw material to obtain a leaching step of lithium sulfate-containing solution; a first purification step of purifying the leached solution at a pH of 7.1 to 9.5; a second purification step of purifying the first purified solution at a pH of 9 to 11; and a step of obtaining a lithium hydroxide aqueous solution by bipolar electrodialysis of the second purified solution.

[0012] The lithium-containing raw material may be a lithium-containing ore.

[0013] Before acid roasting the lithium-containing raw material, the method may further include a step of calcining at 950 to 1100°C.

[0014] The step of acid roasting the lithium-containing raw material may use concentrated sulfuric acid with a concentration of 95% or more.

[0015] In the step of acid roasting the lithium-containing raw material: sulfuric acid equivalent is added at a weight ratio of 200 to 300% relative to the weight of lithium; the roasting temperature is 180 to 300° C.; and the roasting time is 40 to 120 minutes.

[0016] The leaching step of leaching the roasted lithium-containing raw material to obtain a lithium sulfate-containing solution may use water or dilute sulfuric acid.

[0017] The water is pure water. The dilute sulfuric acid is recycled dilute sulfuric acid produced in the second step of bipolar electrodialysis to purify the solution to obtain lithium hydroxide aqueous solution.

[0018] The first purification step of purifying the leachate solution at a pH of 7.1 to 9.5 may use a non-Na-based alkali metal supply source to adjust the pH.

[0019] The non-Na alkali metal supply source may be calcium hydroxide (Ca(OH)2).

[0020] The leaching step and the first purification step may be performed in a single reactor.

[0021] The second purification step of purifying the first purified solution at a pH of 9 to 11 may use an alkali metal carbonate supply to adjust the pH.

[0022] After the second purification step, the method may further include a purification step using an ion exchange resin to remove remaining trace impurities.

[0023] In the step of performing the second bipolar electrodialysis to purify the solution to obtain the lithium hydroxide aqueous solution, the method further comprises the step of supplying the generated dilute sulfuric acid to the leaching step reactor.

[0024] After the step of performing the second bipolar electrodialysis to purify the solution to obtain a lithium hydroxide aqueous solution, the method further includes the step of crystallizing the obtained lithium hydroxide aqueous solution.

[0025] The crystallization step may include: obtaining lithium hydroxide monohydrate by primary crystallization; re-dissolving the obtained lithium hydroxide monohydrate; and obtaining final lithium hydroxide monohydrate by secondary crystallization of the re-dissolved solution.

[0026] Effects of the Invention

[0027] According to one embodiment of the present invention, impurities can be effectively removed to obtain high-purity lithium hydroxide.

[0028] According to another embodiment of the present invention, the amount of sodium hydroxide produced during the preparation process can be reduced by not using a Na-based by-raw material. Therefore, an environmentally friendly and non-critical method for preparing lithium hydroxide can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flow chart of the lithium hydroxide preparation process according to one embodiment of the present invention.

[0030] Figure 2 1 is a flow chart of a lithium hydroxide preparation process according to another embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram showing the change in pH over time when sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)2) are used to adjust the pH in the first purification step.

[0032] Figure 4 This is a schematic diagram of the behavior of Ca, Mg, and Mn impurities as pH changes.

[0033] Figure 5 This is a schematic diagram of the behavior of Al and Si impurities as pH changes. DETAILED DESCRIPTION

[0034] The terms "first," "second," and "third" are used to describe various parts, components, areas, layers, and / or segments, but are not limited thereto. These terms are used solely to distinguish one part, component, area, layer, or segment from another. Thus, a first part, component, area, layer, and / or segment described below could also be described as a second part, component, area, layer, and / or segment without departing from the scope of the present invention.

[0035] The technical terms used herein are intended to describe specific embodiments only and are not intended to limit the present invention. Unless otherwise apparent, the singular as used herein encompasses the plural. The terms "comprise" and "include" as used in this specification specifically refer to a particular feature, field, integer, step, action, element, and / or component, and do not exclude the presence or addition of another feature, field, integer, step, action, element, and / or component.

[0036] When a part is described as being "on" another part, it can be directly on the other part or there can be other parts therebetween. When a part is described as being directly on another part, there can be no other parts therebetween.

[0037] In addition, unless otherwise specified, % means weight %, and 1 ppm means 0.0001 weight %.

[0038] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms defined in dictionaries should be interpreted as having meanings consistent with those in the relevant technical literature and disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0039] Hereinafter, the embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various ways and is not limited to the embodiments described herein.

[0040] Each step is described below in detail.

[0041] The present invention aims to provide a method for preparing lithium hydroxide by utilizing lithium-containing ore, specifically spodumene concentrate.

[0042] First, calcination of the lithium-containing ore raw material changes the crystalline state of the ore, transforming the initial α-phase spodumene into β-phase spodumene that is easier to roast and leach.

[0043] At this time, the calcination temperature may be in the range of 950 to 1100° C. Calcination at a temperature lower than the above temperature results in under-calcination, while calcination at a higher temperature results in reduced lithium leaching efficiency due to over-calcination.

[0044] The calcined ore is then subjected to acid roasting. Concentrated sulfuric acid (or anhydrous sulfuric acid) exceeding 95% is used for the acid roasting process. The weight ratio of sulfuric acid equivalent to the weight of lithium contained in the ore is 200-300%, and the roasting temperature is 180-300°C for 40 to 120 minutes.

[0045] The roasted ore is then leached. The solvent used can be pure water or dilute sulfuric acid, which is free of impurities. The pure water is fresh water treated by methods such as RO. To reduce process costs and recycle byproducts, the dilute sulfuric acid (6-10% H2SO4) produced in bipolar electrodialysis can be recycled.

[0046] The aqueous solution obtained from the leaching process described above is a solution composed primarily of lithium sulfate (Li2SO4). This solution contains various impurities (such as Al, Si, Ca, Mg, Fe, Ni, Na, and K) derived from the ore raw materials, and therefore undergoes purification steps described below.

[0047] To purify the lithium sulfate solution, a two-step chemical purification process can be performed. The first purification step utilizes a non-Na alkali metal source. The pH of the first purification step can be between 7.1 and 9.5. In other words, the first purification step is performed within a pH range exceeding the 5-7 range, where Al and Si impurities are precipitated and purified.

[0048] Furthermore, in the first purification step of the present invention, calcium hydroxide (Ca(OH)2) can be used as a non-Na alkali metal supply source. This is relatively stable in pH fluctuation compared to the process using NaOH as the alkali metal supply source. This is because when NaOH is used, due to the rapid reaction, the pH rises sharply at the initial stage of addition and then falls again, resulting in the disadvantage of being difficult to adjust the pH during the process (pH 4 to 9 fluctuations). In contrast, when a non-Na alkali metal source is used, that is, when calcium hydroxide is used, the pH rises to above 8 immediately after addition, and even after two hours after addition, the pH of the solution can be maintained above 7.1. That is, the pH range of the first purification process in the developed process will not be lower than 7.1, and this is especially true because the reaction time of the initial process is less than 1 hour.

[0049] At this time, due to the low solubility of calcium hydroxide, in order to smoothly supply it, it can be supplied in the form of slurry. The solid-liquid ratio of calcium hydroxide slurry is 5:1 by weight ratio of 'water: calcium hydroxide', and the addition variation of ±20% is allowed for the 5:1 condition. That is, the solid-liquid ratio can be 4:1 to 6:1. - The molar ratio of OH is 0.13 mol, and the addition variation of ±20% is allowed. - The molar ratio may be from 0.104 to 0.156.

[0050] (See Figure 3 ).

[0051] [Table 1]

[0052]

[0053] Generally, for pure Al materials, the maximum theoretical precipitation pH range is between 5 and 7. However, the lithium sulfate aqueous solution obtained by leaching contains a variety of impurity ions, which may cause common ion effects and interactions with suspended oxide particles.

[0054] Thus, the pH range for precipitation of Al in a lithium sulfate aqueous solution can be slightly beyond the theoretical precipitation pH range of pH 7.1 to 9.5. The first purification step disclosed in the present invention is characterized by the use of this pH range. Specifically, the pH in the first purification step is 7.2 to 9.5; more specifically, it can be 7.6 to 9.5; more specifically, it can be 7.9 to 9.5; more specifically, it can be 7.1 to 7.9; more specifically, it can be 7.2 to 7.9; and more specifically, it can be 7.6 to 7.9.

[0055] Furthermore, the leaching and first purification steps are described as two separate processes. However, in practice, the leaching and first purification steps can be performed in a single reactor. Specifically, the roasted ore is placed in a reactor, filled with leach water, and then reacted with a non-Na alkali metal source slurry, allowing the leaching and first purification steps to proceed simultaneously. As previously mentioned, the leach water can be purified water or dilute sulfuric acid.

[0056] Then, a second purification step is performed. The second purification step may be a step of removing trace impurity elements not removed in the first purification step and residual metal (e.g., Ca) components caused by the non-Na alkali metal supply source (e.g., calcium hydroxide) added. In the second purification step, an alkali metal carbonate may be used to adjust the pH to a range of 9 to 11 to remove trace impurities remaining in the form of carbonates. The alkali metal carbonate may specifically be Na2CO3.

[0057] If trace amounts of Ca and Mg remain in the lithium sulfate aqueous solution after the second purification step, a further purification step may be performed using an ion exchange resin. The further purification step is initiated when the concentrations of Ca and Mg in the lithium sulfate aqueous solution after the second purification step each exceed 10 ppm. If these concentrations do not reach these levels, the further purification step is not required.

[0058] In order to convert the purified lithium sulfate aqueous solution obtained through the first and second purification steps (further purification steps may be performed as needed) into lithium hydroxide (LiOH), a bipolar electrodialysis step may be performed. The bipolar electrodialysis step is a step of converting the lithium sulfate aqueous solution introduced into a bipolar electrodialysis machine into a lithium hydroxide aqueous solution and a sulfuric acid solution.

[0059] The concentration of lithium hydroxide produced in the bipolar electrodialysis step is typically 2-3 mol, and the concentration of the resulting sulfuric acid can be adjusted to 5-10%. Furthermore, a portion of the desalted water produced can be recycled to produce lithium carbonate. The lithium carbonate is obtained by diluting the purge solution from the crystallizer. Furthermore, the dilute sulfuric acid produced can be recycled as leach water in the leaching process.

[0060] The bipolar electrodialysis machine used in the present invention is configured in order: an anode chamber with an anode; a first bipolar membrane, an anion selective dialysis membrane; a cation selective dialysis membrane; a second bipolar membrane; a cathode chamber with a cathode. The bipolar electrodialysis machine is used to treat SO4 that moves through the anion selective dialysis membrane. 2- The lithium ions react with hydrogen generated by hydrolysis in the anode-side bipolar membrane to produce sulfuric acid, and the lithium ions that migrate toward the cathode through the positive ion selective dialysis membrane react with hydroxide anions generated in the bipolar membrane to produce LiOH.

[0061] In the present invention, the purified lithium sulfate aqueous solution obtained through the first and second purification steps (further purification steps may be performed as needed) is placed in a bipolar electrodialysis machine. When a voltage in the range of 1.8 to 2.2 V is applied to the bipolar electrodialysis machine, the cations and anions in the lithium sulfate aqueous solution react by the electrophoretic effect as described above to generate LiOH.

[0062] In the step of converting LiOH using the bipolar electrodialysis machine, the bipolar electrodialysis machine may utilize a bipolar electrodialysis stack device consisting of a first bipolar membrane, an anion-selective dialysis membrane, a cation-selective dialysis membrane, and a second bipolar membrane. Furthermore, the voltage applied to each stack may be in the range of 1.8 to 2.2 V. Furthermore, the applied current density may be 30 mA / cm 2 Up to 90mA / cm 2 If the current density is lower than 30mA / cm 2 When the lithium is moved slowly, the production speed is reduced; if it exceeds 90mA / cm 2 When the bipolar electrodialysis membrane is damaged due to heat generation.

[0063] The lithium hydroxide preparation method of the present invention may further include a crystallization step for solidifying and purifying the lithium hydroxide aqueous solution obtained in the bipolar electrodialysis step. The crystallization step may include: a first crystallization step for obtaining lithium hydroxide monohydrate; a redissolving step for the obtained lithium hydroxide monohydrate; and a second crystallization step for obtaining the final lithium hydroxide monohydrate.

[0064] During the crystallization step, the method for removing monovalent ion impurities, Na and K ions, from the lithium-containing ore is as follows: In the first crystallization step, the amount of purge solution in the crystallizer can be 17 to 18% of the introduced lithium concentration. To recover the lithium in the purge solution, the lithium in the purge solution can be fixed as lithium carbonate. Because the purge solution produced in the crystallizer is a saturated lithium hydroxide solution, desalted water produced in bipolar electrodialysis can be used to dilute it to a concentration of less than 30 g / L (<30 g / L) based on the lithium concentration. Because the diluted purge solution is alkaline, lithium carbonate can be produced using carbon dioxide (CO2). The resulting lithium carbonate is then washed to obtain purified lithium carbonate, and the monovalent ion impurities, Na and K ions, from the ore are discharged through the wash water.

[0065] The dilute sulfuric acid (6-10%) produced in the bipolar electrodialysis step of one embodiment of the present invention is the sulfate SO4 contained in the purified water. 2- ) status.

[0066] In the process, the recycling method is as follows:

[0067] First, the dilute sulfuric acid produced in the bipolar electrodialysis step is supplied to the reactor for the leaching and first purification steps. The sulfates other than water are fed to the non-Na alkali metal supply source (e.g., calcium hydroxide) in the leaching / first purification step reactor and converted into dihydrate gypsum (CaSO4·2H2O). This is processed and discharged together with the generated ore residue (see Figure 1 ).

[0068] Furthermore, when dilute sulfuric acid is concentrated and used in the process, it can be concentrated to 93% to 97%. The concentrated sulfuric acid can replace the sulfuric acid used in the roasting process. The entire amount of water obtained at this time can be used as leaching water used in the process (refer to Figure 2 ).

[0069] In order to facilitate implementation by those skilled in the art, embodiments of the present invention are described below. However, the present invention can be implemented in various forms and is not limited to the following embodiments.

[0070] Example

[0071] Lithium hydroxide is prepared using spodumene concentrate containing lithium ore, and the preparation method is carried out in the same manner as described above.

[0072] In an embodiment, calcium hydroxide (Ca(OH)2) is used in the first purification step to adjust the pH to 7.1 to 9.5.

[0073] In the comparative example, lithium hydroxide was prepared in the same manner as in the example, except that NaOH was used to adjust the pH in the first purification step.

[0074] The results of the actual process equipment test are summarized in Table 2.

[0075] The comparison results of impurity behavior between the embodiment and the comparative example are as follows: Figure 4 、 5 shown.

[0076] Because the Mg, Mn, and Si concentrations in the Examples operated at pH 7.1 to 8.4 were lower than in the Comparative Examples, it can be confirmed that purification was performed better in the Examples. Mg and Mn leaching was improved with increasing pH. Conversely, the residual Ca content remained unchanged because it is determined by the solubility of Ca, not the amount of Ca(OH)2 used.

[0077] Furthermore, in the examples, Si leaching increases due to coprecipitation as the leaching amount of divalent cations such as Mg and Mn increases. Al also shows a slight increase when the pH exceeds 8.

[0078] Therefore, it can be confirmed that when lithium hydroxide is prepared using the pH range of the first purification step of the embodiment, there are no problems in the preparation process management and the preparation of battery-grade lithium hydroxide monohydrate.

[0079] [Table 2]

[0080]

[0081] The present invention is not limited to the above-described embodiments and can be prepared in various different ways. Those skilled in the art will appreciate that the present invention can be implemented in other specific ways without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not restrictive.

Claims

1. A method for preparing lithium hydroxide, comprising the following steps: The step of roasting the lithium-containing raw material with sulfuric acid; Leaching the roasted lithium-containing raw material to obtain a lithium sulfate-containing solution; a first purification step of purifying the leachate solution at a pH of 7.1 to 7.6; a second purification step of purifying the first purified solution at a pH of 9 to 11; as well as The step of a second bipolar electrodialysis purification solution to obtain a lithium hydroxide aqueous solution, wherein: The first purification step of purifying the leachate solution at a pH of 7.1 to 7.6 uses calcium hydroxide to adjust the pH, wherein The step of roasting the lithium-containing raw material uses concentrated sulfuric acid with a concentration of more than 95%.

2. The method for preparing lithium hydroxide according to claim 1, wherein The lithium-containing raw material is lithium-containing ore.

3. The method for preparing lithium hydroxide according to claim 1, wherein Before acid roasting the lithium-containing raw material, the method further comprises: A calcination step at 950 to 1100°C.

4. The method for preparing lithium hydroxide according to claim 1, wherein In the step of roasting the lithium-containing raw material: The sulfuric acid equivalent is added in a weight ratio of 200 to 300% relative to the weight of lithium; the roasting temperature is 180 to 300° C.; and the roasting time is 40 to 120 minutes.

5. The method for preparing lithium hydroxide according to claim 1, wherein The leaching step of leaching the roasted lithium-containing raw material to obtain a lithium sulfate solution Use water or dilute sulfuric acid.

6. The method for preparing lithium hydroxide according to claim 5, wherein The water is pure water, The dilute sulfuric acid is the recycled dilute sulfuric acid produced in the step of performing the second bipolar electrodialysis to purify the solution to obtain the lithium hydroxide aqueous solution.

7. The method for preparing lithium hydroxide according to claim 1, wherein The leaching step and the first purification step are carried out in a single reactor.

8. The method for preparing lithium hydroxide according to claim 1, wherein The second purification step of purifying the first purified solution at a pH of 9 to 11 The pH was adjusted using an alkali metal carbonate supply.

9. The method for preparing lithium hydroxide according to claim 1, wherein After the second purification step, the method further comprises: In order to remove the remaining trace impurities, an ion exchange resin is used for further purification.

10. The method for preparing lithium hydroxide according to claim 1, wherein The step of the second bipolar electrodialysis purification solution to obtain a lithium hydroxide aqueous solution further comprises: The step of supplying the generated dilute sulfuric acid to the leaching step reactor.

11. The method for preparing lithium hydroxide according to claim 1, wherein After the step of the second bipolar electrodialysis purification solution to obtain a lithium hydroxide aqueous solution, the method further comprises: A step of crystallizing the obtained lithium hydroxide aqueous solution.

12. The method for preparing lithium hydroxide according to claim 11, wherein the crystallization step comprises: a step of obtaining lithium hydroxide monohydrate by primary crystallization; a step of redissolving the obtained lithium hydroxide monohydrate; A step of secondary crystallizing the redissolved solution to obtain the final lithium hydroxide monohydrate.

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