Extraction Method Of Lithium Fluoride Using Low-purity Lithium Carbonate

Abstract

The method for extracting lithium fluoride from low-purity lithium carbonate according to the present invention comprises: a) a process for preparing an aqueous solution in which lithium carbonate is dissolved; b) a filtering process for separating impurities from the aqueous solution prepared in the preparation process; c) a reaction process for obtaining an aqueous suspension of solid lithium fluoride by reacting the filtered aqueous solution with hydrogen fluoride; d) a solid-liquid separation process for separating solid lithium fluoride from the aqueous suspension; e) a process for washing the separated lithium fluoride; and e) a process for drying the washed lithium fluoride.

Description

Technology Field

[0001] The present invention relates to a method for extracting lithium fluoride for extracting rare earth metals from waste rare earth magnets from low-purity lithium carbonate. Background Technology

[0002] The production of rare-earth permanent magnets using rare-earth metals has expanded globally for use in electronic and information devices due to the proliferation of computers, and recently, demand continues to increase, centered on the environmental, automotive, and bio-industries.

[0003] In particular, among rare earth permanent magnets, neodymium (Nd) and dysprosium (Dy) are essential for hard disk drives, wind power generation, hybrid cars, and the defense industry.

[0004] In the case of Korea, while the demand for Nd-Fe-B magnets among rare-earth permanent magnets is expected to continue expanding, the country relies on imports for most of its materials and raw materials. Furthermore, not only is the supply of rare earth elements unstable, but the reserves of natural resources themselves are also insufficient.

[0005] In this regard, strategies are being sought to secure a stable supply of rare earth metals, which can leave natural resources for the potential needs of other countries and future generations, in terms of equal opportunity across nations and generations regarding global resources.

[0006] Accordingly, research related to resource recovery regarding recycling technologies for rare-earth permanent magnets is underway, and in particular, due to the supply and importance of rare-earth resources, various process developments for Nd-Fe-B permanent magnets are being carried out.

[0007] Recently, a method for recovering rare earth metals has been developed that uses a dry method capable of recovering high-purity rare earths, which is simple in process, and can selectively separate rare earth elements contained in rare earth alloys using a ternary molten salt.

[0008] In recently developed dry methods, lithium fluoride is essential for the extraction of rare earth metals. Prior art literature

[0009] Korean Patent Publication No. 10-2493146 (Registered on Jan. 25, 2023) The problem to be solved

[0010] The present invention provides a method for extracting lithium fluoride from low-purity lithium carbonate, which is necessary for the dry extraction of rare earth metals. means of solving the problem

[0011] The method for extracting lithium fluoride from low-purity lithium carbonate according to the present invention comprises: a) a preparation process for an aqueous solution in which lithium carbonate is dissolved; b) a filtering process for separating impurities from the aqueous solution prepared in the preparation process; c) a reaction process for obtaining an aqueous suspension of solid lithium fluoride by reacting the filtered aqueous solution with hydrogen fluoride; d) a solid-liquid separation process for separating solid lithium fluoride from the aqueous suspension; e) a washing process for washing the separated lithium fluoride; and e) a drying process for drying the washed lithium fluoride.

[0012] The lithium carbonate dissolved in the above a) preparation process is in the range of 7.2 to 15.4 g / L.

[0013] Based on 100 parts by weight of the aqueous solution prepared in the above preparation process a), a complexing agent may be included in an amount of 0.001 to 1 weight%, preferably 0.005 to 0.2 weight%.

[0014] The above lithium carbonate has a purity of 95 to 99.5 weight% based on the anhydrous state before dissolution and contains sodium, chlorine, carbon, silicon, sulfur, iron, magnesium, and aluminum as impurities.

[0015] The aqueous solution prepared in the above a) preparation process has a pH of 9.0 to 14.0.

[0016] The above reaction process c) can be performed by spraying an aqueous lithium carbonate solution into a gas stream containing gaseous hydrogen fluoride, or by introducing liquid hydrogen fluoride into an aqueous lithium carbonate solution and stirring.

[0017] The aqueous suspension in the reaction process c) above has a pH of 5.0 to 7.2.

[0018] After separating the solid lithium fluoride from the reaction process c) above, the aqueous suspension is circulated back to the aqueous solution of the preparation process a) for reuse. Effects of the invention

[0019] The present invention enables the extraction of lithium fluoride from low-purity lithium carbonate without undergoing a high-purity process, thereby shortening the manufacturing process and reducing the extraction process time.

[0020] In addition, since rare earth elements, which are high-value materials, can be recovered from waste resources, hazardous substances such as industrial waste can be treated, resulting in an eco-friendly effect. Brief explanation of the drawing

[0021] FIG. 1 is a process flowchart for extracting lithium fluoride from low-purity lithium carbonate according to the present invention. Specific details for implementing the invention

[0022] Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. For reference, the size, line thickness, etc., of the components illustrated in the drawings referenced for describing the present invention may be depicted somewhat exaggerated for ease of understanding.

[0023] Furthermore, the terms used in the description of the present invention are defined considering their functions within the invention and may vary depending on the user's or operator's intent, convention, etc. Accordingly, it is appropriate to define these terms based on the entire content of this specification.

[0024] Furthermore, in this application, terms such as 'comprising' and 'having' refer to the existence of specific numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0025] In addition, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms, and the embodiments provided are merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention.

[0026] Therefore, the present invention is susceptible to various modifications and may take various forms, and embodiments (aspects or examples) are to be described in detail in the specification. However, this is not intended to limit the present invention to specific disclosed forms, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the technical scope of the present invention, and singular expressions used in this specification include plural expressions unless the context clearly indicates otherwise.

[0027] However, in describing the present invention, specific descriptions of well-known or known functions or configurations are omitted in order to clarify the gist of the invention.

[0028] The method for extracting lithium fluoride from low-purity lithium carbonate according to the present invention comprises: a) a process for preparing an aqueous solution in which lithium carbonate is dissolved; b) a filtering process for separating impurities from the aqueous solution prepared in the preparation process; c) a reaction process for obtaining an aqueous suspension of solid lithium fluoride by reacting the filtered aqueous solution with hydrogen fluoride; d) a solid-liquid separation process for separating solid lithium fluoride from the aqueous suspension; e) a washing process for washing the separated lithium fluoride; and e) a drying process for drying the washed lithium fluoride.

[0029] a) In the preparation process of the aqueous solution in which lithium carbonate is dissolved according to the present invention, the aqueous solution may be distilled water, or a mixture of distilled water and an organic solvent may be used.

[0030] It is desirable for the aqueous solution to have a specific electrical resistivity of 5 MΩ·cm or more at 25℃.

[0031] The organic solvent mixed in the above aqueous solution is a monohydric or polyhydric alcohol such as methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol, propane-1,3-diol, or glycerol, or a ketone such as acetone or ethylmethyl ketone.

[0032] The organic solvent mixed with distilled water is 0.0 to 20 parts by weight based on 100 parts by weight of the aqueous solution, and the remainder is distilled water.

[0033] Lithium carbonate dissolved in the aqueous solution is in the range of 7.2 to 15.4 g / L.

[0034] The aqueous solution prepared in the above a) preparation process has a pH of 9.0 to 14.0.

[0035] The above lithium carbonate has a purity of 95 to 99.5 weight% based on the anhydrous state before dissolution and contains sodium, chlorine, carbon, silicon, sulfur, iron, magnesium, aluminum, etc. as impurities.

[0036] The above a) preparation process may include 0.005 to 0.2 weight percent of a complexing agent based on 100 weight parts of the aqueous solution prepared.

[0037] The above complexing agent is an alkali metal or ammonium salt that is ionically bonded with sodium, chlorine, carbon, silicon, sulfur, iron, magnesium, aluminum, etc., which are included as impurities in lithium carbonate.

[0038] After the above a) preparation process, the aqueous solution prepared in the above preparation process is filtered to separate impurities.

[0039] At this time, foreign substances are filtered by a filter having a mesh size of 1㎛ or less. Preferably, a filter having a mesh size in the range of 0.3㎛ to 1㎛ is used, taking into account the filtration speed.

[0040] After the filtering process b) above, the reaction process c) is carried out by adding a small amount of liquid hydrogen fluoride to the aqueous solution in which lithium carbonate is dissolved and stirring.

[0041] In the above reaction process, lithium carbonate dissolved in an aqueous solution reacts with the added hydrogen fluoride to precipitate and form an aqueous suspension containing solid lithium fluoride.

[0042] The reacted aqueous suspension has a pH of 4.0 to 7.5. Preferably, reaching a pH of 5.0 to 7.2 is effective for the reaction. At this time, carbon dioxide and hydrogen are generated, and the aqueous suspension is stirred to facilitate the release of the generated gases.

[0043] The reaction temperature should be in the range of 16 to 24°C.

[0044] c) Gaseous hydrogen fluoride may also be introduced in the reaction process.

[0045] While supplying gaseous hydrogen fluoride, the reaction is carried out by spraying an aqueous solution of dissolved lithium carbonate into the gaseous hydrogen fluoride gas.

[0046] At this time, in addition to gaseous hydrogen fluoride gas, an inert gas may be used as a carrier gas. The inert gas may be air, nitrogen, or argon gas. Preferably, it is nitrogen gas. The inert gas is 1 to 20 volume percent of the total gas, and the remainder is hydrogen fluoride gas.

[0047] c) After the reaction process, the aqueous suspension containing solid lithium fluoride is d) separated into solid and liquid phases.

[0048] In the extraction method of the present invention, after solid-liquid separation a) to d), the aqueous suspension is used repeatedly multiple times. The recovery rate of dissolved lithium carbonate is increased by repetition.

[0049] The solid lithium fluoride obtained by solid-liquid separation has a water content of 5 to 30 weight percent.

[0050] Afterward, the lithium fluoride separated into a solid phase is washed multiple times with water or an organic solvent mixed with water.

[0051] Preferably, it is washed with water having an electrical resistivity of 15 MΩ·cm or higher at 25℃.

[0052] After the washing process, the lithium fluoride is dried. The drying temperature is 200–500℃.

[0054] Example 1

[0055] 5.625 kg of low-grade lithium carbonate was dissolved in 500 L of distilled water while stirring for 1 hour. The resulting aqueous solution exhibited a strong basicity of 14 pH.

[0056] Afterwards, organic matter was removed using a filter with a mesh size of 0.35㎛.

[0057] Afterwards, hydrogen fluoride was added to react with lithium fluoride. At this time, the amount of hydrogen fluoride added was adjusted to achieve a pH of 5 to 7.2.

[0058] Afterwards, lithium fluoride was manufactured by separating the solid and liquid, washing, and drying.

[0059] Analysis of the extracted lithium fluoride showed a purity of 99.79%.

Claims

Claim 1 a) a process for preparing an aqueous solution in which lithium carbonate is dissolved; b) a filtering process for separating impurities from the aqueous solution prepared in the above preparation process; c) a reaction process for obtaining an aqueous suspension of solid lithium fluoride by reacting the filtered aqueous solution with hydrogen fluoride; d) a solid-liquid separation process for separating solid lithium fluoride from the aqueous suspension; e) a washing process for washing the separated lithium fluoride; and e) a drying process for drying the washed lithium fluoride. In the above a) process for preparing an aqueous solution in which lithium carbonate is dissolved, the aqueous solution has a specific electrical resistivity of 5 MΩ·cm or more at 25°C and lithium carbonate having a purity of 95–99.5 wt% is dissolved in the aqueous solution in a range of 7.2–15.4 g / L. The aqueous solution is prepared by mixing distilled water and an organic solvent, wherein the organic solvent mixed with the distilled water is in an amount of 0.0 to 20 parts by weight based on 100 parts by weight of the aqueous solution, and the aqueous solution contains Based on 100 parts by weight, 0.005 to 0.2 weight percent of a complexing agent is included, and the remainder is distilled water; the complexing agent is an alkali metal or ammonium salt that is ionically bonded with sodium, chlorine, carbon, silicon, sulfur, iron, magnesium, aluminum, etc., contained as impurities in lithium carbonate; the aqueous solution prepared in the preparation process has a pH of 9.0 to 14.0; in c) a reaction process to obtain an aqueous suspension of solid lithium fluoride by reacting the filtered aqueous solution with hydrogen fluoride, the reaction is carried out by spraying the aqueous solution in which lithium carbonate is dissolved onto gaseous hydrogen fluoride gas; in addition to gaseous hydrogen fluoride gas, an inert gas is used as a carrier gas, the inert gas is 1 to 20 volume percent of the total gas, and the remainder is hydrogen fluoride gas; the reacted aqueous suspension has a pH of 5.0 to 7.2; the aqueous suspension is stirred to discharge carbon dioxide and hydrogen generated during the reaction, and the reaction temperature is 16 to 24°C A method for extracting lithium fluoride from lithium carbonate, characterized in that the solid lithium fluoride obtained by solid-liquid separation has a water content of 5 to 30 weight% in a solid-liquid separation process in which the temperature range is d) the solid lithium fluoride is separated from an aqueous suspension. Claim 2 delete Claim 3 delete

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