Zero-liquid-discharge recycling method of boe waste solution including multi-step recovery process

Abstract

The present invention relates to a method for recycling BOE waste liquid, comprising: (a) mixing BOE waste liquid and a lithium-containing solution; (b) adjusting the pH of the mixture to obtain lithium fluoride (LiF) and a first filtrate; and (c) circulating the first filtrate, wherein the step of circulating the first filtrate comprises: (c-1) adding a calcium compound to the first filtrate to obtain calcium fluoride (CaF2) and a second filtrate; (c-2) adding metallic aluminum to the second filtrate to recover residual Li ions in the form of Al-LDH; and (c-3) adding a carbonate compound to the Al-LDH to obtain lithium carbonate (Li2CO3) and a final filtrate. A recycling method for BOE waste liquid according to one embodiment of the present invention can realize a waste-free ESG recycling process by recovering useful resources such as lithium fluoride, fluorite, and lithium carbonate in stages, and simultaneously utilizing the filtrate after the process as a resource.

Description

Technology Field

[0001] The present invention relates to a method for recycling ESG-type BOE waste liquid including a complex recovery process. Specifically, the method is designed to recover useful resources such as lithium fluoride (LiF), fluorite (CaF2), and lithium carbonate (Li2CO3) in stages, while simultaneously enabling the recycling of the filtrate, which is a process byproduct, for the manufacture of inorganic coagulants, thereby enabling the realization of a waste-free process. Background Technology

[0002] With the rapid growth of the secondary battery industry, the demand for high-value lithium compounds is increasing sharply. Consequently, the stable securing of lithium resources and the development of recycling technologies have emerged as critical challenges. In particular, lithium compounds such as lithium carbonate and lithium fluoride are utilized as core materials in various industrial fields, including electrolytes, ceramics, and metal fluxes; however, securing high-purity products currently relies mostly on high-cost refining processes or supply chains based on new ore sources. Meanwhile, the semiconductor and display industries are also generating large quantities of Buffered Oxide Etchant (BOE) waste liquid. Containing high concentrations of fluorine, this liquid carries both environmental risks and significant resource value.

[0003] Conventional lithium fluoride (LiF) manufacturing technology typically utilizes high-purity lithium carbonate (Li2CO3) as a precursor and reacts it with expensive hydrofluoric acid (HF) or ammonium fluoride (NH4F). However, this process requires securing high-purity raw materials and faces various limitations from an industrial and environmental perspective due to the generation of hazardous gases, the burden of post-treatment, and reduced process stability. Furthermore, hydrofluoric acid-based processes impose significant constraints regarding worker safety and process control costs. Moreover, no integrated recycling technology has been proposed to date that utilizes BOE waste liquid and lithium-containing waste resources generated in the semiconductor and display industries, as well as the secondary battery industry, to recover high-value lithium compounds while simultaneously converting process filtrate into resources. Additionally, there are currently no examples of such technologies implemented as ESG-based zero-emission circular processes. Prior art literature

[0004] Republic of Korea Registered Patent Publication No. 10-2320475 The problem to be solved

[0005] The present invention aims to provide a method for recycling BOE waste liquid that overcomes the limitations of conventional high-purity lithium carbonate-based lithium fluoride manufacturing processes, such as high-cost structures, generation of hazardous substances, and underutilization of waste resources. By utilizing BOE waste liquid generated in the semiconductor and display industries and lithium-containing waste resources generated in the secondary battery industry as primary raw materials, the invention enables the stepwise recovery of various useful substances, such as lithium fluoride, fluorite, and lithium carbonate, and realizes a waste-free recycling system capable of recycling even the post-processing filtrate into inorganic coagulants or industrial diluents.

[0006] However, the problems that this invention seeks to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by a person skilled in the art from the description below. means of solving the problem

[0007] To achieve the above objectives, the present invention provides a method for recycling BOE waste liquid, comprising: (a) mixing BOE waste liquid and a lithium-containing solution; (b) adjusting the pH of the mixture to obtain lithium fluoride (LiF) and a first filtrate; and (c) circulating the first filtrate, wherein the step of circulating the first filtrate comprises: (c-1) adding a calcium compound to the first filtrate to obtain calcium fluoride (CaF2) and a second filtrate; (c-2) adding metallic aluminum to the second filtrate to recover residual Li ions in the form of Al-LDH; and (c-3) adding a carbonate compound to the Al-LDH to obtain lithium carbonate (Li2CO3) and a final filtrate.

[0008] In one embodiment of the present invention, in step (a), the equivalent ratio (Li:F) of Li and F contained in the lithium-containing solution and the BOE waste liquid, respectively, may be about 1:0.6 to about 1:1.1.

[0009] In one embodiment of the present invention, in step (b), the pH may be adjusted to about 6 to about 7, and it may be most preferable to adjust it to about 6.5.

[0010] In one embodiment of the present invention, in step (c-1), the calcium compound may comprise one or more selected from calcium hydroxide (Ca(OH)2), calcium chloride (CaCl2), calcium nitrate (Ca(NO3)2), or calcium carbonate (CaCO3), but is not limited thereto.

[0011] In one embodiment of the present invention, step (c-3) may involve dissolving the Al-LDH in an acid and then adding a carbonate compound; or dissolving it in an alkaline aqueous solution and adjusting the pH, and then adding a carbonate compound to obtain lithium carbonate (Li2CO3) and a final filtrate.

[0012] In one embodiment of the present invention, the final filtrate may be used as water for manufacturing an inorganic coagulant for water treatment. Effects of the invention

[0013] The recycling method for BOE waste liquid according to the embodiments of the present invention can provide a composite recovery process capable of recovering high-value inorganic resources such as lithium fluoride (LiF), fluorite (CaF2), aluminum-layered double hydroxide (Al-LDH), and lithium carbonate (Li2CO3) in stages by simultaneously utilizing high-concentration fluorine-based waste liquid generated in semiconductor and display processes and lithium-containing waste resources from the secondary battery industry. A multi-stage structure in which residual fluorine is stabilized as fluorite after controlling the reaction between lithium and fluorine, and lithium carbonate is selectively precipitated and separated from aluminum-based intermediates, exhibits excellent recovery efficiency and reaction selectivity, making it suitable for the production of high-purity lithium materials.

[0014] The recycling method for BOE waste liquid according to the embodiments of the present invention can be expanded into a Zero-Liquid-Discharge (ZLD) type resource circulation system that minimizes waste discharge by securing a water quality sufficient to recycle the filtrate generated in the pre-process stage for the manufacture of inorganic coagulants or water for water treatment. Through this, it can provide effects such as reduced process costs, inter-industry resource linkage, and stabilization of lithium supply, along with the realization of environmental sustainability (ESG). Brief explanation of the drawing

[0015] FIG. 1 is a flowchart of BOE waste liquid recycling to which a composite recovery process according to one embodiment of the present invention is applied. Specific details for implementing the invention

[0016] Hereinafter, embodiments are described in detail with reference to the attached drawings. However, various modifications may be made to the embodiments, and thus the scope of the patent application is not limited or restricted by these embodiments. It should be understood that all modifications, equivalents, and substitutions to the embodiments are included within the scope of the rights.

[0017] Specific structural or functional descriptions of the embodiments are disclosed for illustrative purposes only and may be modified and implemented in various forms. Accordingly, the embodiments are not limited to the specific disclosed forms, and the scope of this specification includes modifications, equivalents, or substitutions that fall within the technical concept.

[0018] Terms such as first or second may be used to describe various components, but these terms should be interpreted solely for the purpose of distinguishing one component from another. For example, the first component may be named the second component, and similarly, the second component may also be named the first component.

[0019] When it is stated that a component is "connected" to another component, it should be understood that it may be directly connected to or joined to that other component, or that there may be other components in between.

[0020] The terms used in the embodiments are for illustrative purposes only and should not be interpreted as intended to be limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0021] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the embodiments pertain. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0022] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described in detail below. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided 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, and the present invention is defined only by the scope of the claims.

[0023] In the embodiments of the present invention, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in the embodiments of the present invention.

[0024] Furthermore, in describing the present invention, if it is determined that a detailed description of related prior art could unnecessarily obscure the essence of the present invention, such detailed description is omitted. Where terms such as "includes," "has," or "is made up" are used in this specification, other parts may be added unless "only" is used. Where a component is expressed in the singular, it includes cases where it is included in the plural unless specifically stated otherwise.

[0025] In interpreting the components, they are interpreted to include a margin of error even in the absence of a separate explicit statement.

[0026] The features of each of the various embodiments of the present invention may be combined or combined with one another, either partially or wholly, and as will be fully understood by those skilled in the art, various technical interlocking and operation are possible, and each embodiment may be implemented independently of one another or together in an interlocking relationship.

[0028] Embodiments of the present invention have been described in detail below, but the present invention may not be limited thereto.

[0030] The present invention provides a method for recycling BOE waste liquid, comprising: (a) mixing BOE waste liquid and a lithium-containing solution; (b) adjusting the pH of the mixture to obtain lithium fluoride (LiF) and a first filtrate; and (c) circulating the first filtrate, wherein the step of circulating the first filtrate comprises: (c-1) adding a calcium compound to the first filtrate to obtain calcium fluoride (CaF2) and a second filtrate; (c-2) adding metallic aluminum to the second filtrate to recover residual Li ions in the form of Al-LDH; and (c-3) adding a carbonate compound to the Al-LDH to obtain lithium carbonate (Li2CO3) and a final filtrate.

[0031] In one embodiment of the present invention, in step (a), the BOE waste liquid may have a pH of about 3 to 5.5. The pH range may be a condition for maintaining a stable state of fluoride ions (F) participating in the lithium fluoride formation reaction, while simultaneously ensuring reactivity with the lithium-containing solution used during the process. In an acidic region with a pH of less than 3, fluoride ions may be converted into the form of HF, which may reduce reactivity, and in an environment with a pH greater than 5.5, the likelihood of unnecessary hydroxide or complex salt precipitation forming increases, which may impede the efficiency of the lithium fluoride precipitation reaction.

[0032] In one embodiment of the present invention, in step (a), F of the BOE waste liquid -The concentration may be approximately 4 wt% to approximately 30 wt%. The above concentration range may be a concentration condition that ensures a sufficient reactant concentration for F ions to react with lithium ions (Li) to form lithium fluoride (LiF), while simultaneously considering the physicochemical safety of the process and the controllability of the reaction. If the F concentration is less than approximately 4 wt%, the precipitation efficiency of lithium fluoride decreases, which may result in a sharp decrease in yield or incomplete reaction. On the other hand, if it exceeds approximately 30 wt%, process stability may be compromised due to increased viscosity or solid aggregation, and the load on subsequent separation and purification processes may increase.

[0033] In one embodiment of the present invention, in step (a), the lithium-containing solution may be washing water generated in the cathode material manufacturing process, process water generated during the production of lithium hydroxide from raw ore (spodumene) or salt lake brine, a lithium-containing solution leached from a waste crucible generated in the cathode material calcination process, a lithium ion solution recovered during the hydrometallurgical leaching step in the lithium-ion battery recycling process, a lithium aqueous solution pre-leached from the black mass of a waste battery, a diluted aqueous solution of a lithium salt reagent (LiOH, Li2CO3, etc.), a lithium ion-containing intermediate water obtained before the neutralization or filtration step in the wastewater treatment process, or a combination thereof.

[0034] In one embodiment of the present invention, in step (a), the equivalent ratio (Li:F) of Li and F contained in the lithium-containing solution and the BOE waste liquid, respectively, may be about 1:0.6 to about 1:1.1. If the Li:F equivalent ratio is less than about 1:0.6, there may be insufficient fluoride ions, which may cause incomplete LiF precipitation, and the remaining lithium ions may remain in the aqueous solution, thereby hindering the recovery rate. On the other hand, if it exceeds about 1:1.1, an excess amount of fluoride ions may be present, which may cause the formation of unnecessary interionic complexes or excessive aggregation within the reaction system, and the size or particle size distribution of the generated LiF crystals may become non-uniform. In addition, it may have an adverse effect on filtration and drying properties in subsequent processes.

[0035] In one embodiment of the present invention, the mixing of the lithium-containing solution and the BOE waste liquid performed in step (a) may be carried out in a temperature range of about 25°C to about 80°C, and specifically, it may be preferable to carry out the reaction at around 65°C in terms of reaction rate and crystallization uniformity. In addition, the reaction may be carried out for about 1 hour to about 6 hours, and most preferably for about 3 hours, which may be effective in improving the stability and yield of the lithium fluoride precipitation reaction.

[0036] In one embodiment of the present invention, the mixing of step (a) may be performed using a magnetic stirrer, a mechanical stirrer, or an ultrasonic mixer, and the stirring speed may be about 100 rpm to about 300 rpm, most preferably about 200 rpm. This may be a condition to prevent particle aggregation while maintaining a uniform reaction between lithium ions and fluoride ions in the mixture.

[0038] In one embodiment of the present invention, in step (b), the pH may be adjusted to about 6 to about 7, and may be most preferably adjusted to about 6.5. The pH 6.5 condition may be a point where both chemical stability and consistency of particle formation can be ensured under the crystallization conditions of lithium fluoride. If the pH is lowered to less than 6, fluoride ions (F - ) is converted into the HF form, which may reduce reactivity and precipitation efficiency; conversely, if the pH exceeds 7, lithium ions (Li + ) may be converted into lithium hydroxide (LiOH) or lithium-based complex salts, which may reduce the selectivity of the precipitation reaction or generate unnecessary byproducts.

[0039] In one embodiment of the present invention, the pH adjustment in step (b) may be adjusted using sodium hydroxide (NaOH), potassium hydroxide (KOH), water ammonia (NH4OH), triethanolamine, or sodium carbonate (Na2CO3).

[0040] In one embodiment of the present invention, in step (b), a reaction mixture may be formed by adding about 25 to about 40 parts by weight of BOE waste liquid (F concentration about 18 wt%) and about 3 to about 7 parts by weight of sodium hydroxide (NaOH, 50 wt%) based on 1,000 parts by weight of a lithium-containing solution having a lithium ion concentration of about 420 ppm.

[0041] In one embodiment of the present invention, step (b) may be performed for about 1 hour to about 5 hours at a temperature range of about 25°C to about 80°C.

[0042] In one embodiment of the present invention, the lithium fluoride obtained in step (b) may include a washing step for removing residual impurities. The washing may be performed using RO (reverse osmosis) purified water or industrial pure water, and may be performed under conditions of a solid-liquid ratio of about 1:10 to about 1:30, most preferably about 1:20, using washing water with a weight of about 10 to about 30 times that of the solid phase.

[0043] In one embodiment of the present invention, the washed lithium fluoride can be dried for 4 to 12 hours at a temperature of about 60°C to about 120°C, and the lithium fluoride obtained after drying can be produced as a high-purity product with a purity of about 99.0% or higher. The drying can be performed using a circulating hot air dryer or a vacuum dryer capable of precise temperature control, and the drying conditions can be adjusted according to the moisture content and crystallinity maintenance state of the particles.

[0045] In one embodiment of the present invention, in step (c-1), the calcium compound may comprise one or more selected from calcium hydroxide (Ca(OH)2), calcium chloride (CaCl2), calcium nitrate (Ca(NO3)2), or calcium carbonate (CaCO3), but is not limited thereto. The calcium compound may be added dropwise or in portions at a temperature of about 25°C to 60°C, and the reaction may be maintained for about 30 minutes to 2 hours under stirring.

[0047] In one embodiment of the present invention, in step (c-2), the metallic aluminum may be added at a concentration of about 0.5% to about 2.0% by weight based on the total weight of the mixture, and most preferably at a concentration of about 1.0% by weight. Such concentration conditions can ensure reaction efficiency with lithium ions, while simultaneously ensuring the precipitation stability of Al-LDH and the efficiency of the subsequent filtration process.

[0048] In one embodiment of the present invention, step (c-2) may be performed for about 1 hour to about 3 hours at a temperature range of about 25°C to about 80°C, most preferably at a temperature of about 65°C for 2 hours. During the reaction, the pH may be maintained in the range of about 6.0 to about 9.0, and metallic aluminum may be added in divided portions or gradually depending on the reaction conditions. These conditions may be intended to optimize the reactivity between lithium ions and aluminum ions and to stably induce the precipitation of Al-LDH with a layered double hydroxide structure.

[0050] In one embodiment of the present invention, in step (c-3), Al-LDH may be dissolved by acid treatment, and the acid may include one or more selected from hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), acetic acid (CH3COOH), or formic acid (HCOOH), but is not limited thereto.

[0051] In one embodiment of the present invention, the carbonate compound may comprise one or more selected from sodium carbonate (Na2CO3), ammonium carbonate ((NH4)2CO3), potassium carbonate (K2CO3), sodium bicarbonate (NaHCO3), or ammonium bicarbonate (NH4HCO3), but is not limited thereto. The reaction of step (c-3) may be carried out at a temperature of about 30°C to about 70°C for about 10 minutes to about 1 hour after adding the carbonate compound.

[0052] In one embodiment of the present invention, step (c-3) may involve dissolving the Al-LDH in an acid and then adding a carbonate compound; or dissolving it in an alkaline aqueous solution, adjusting the pH, and then adding a carbonate compound to obtain lithium carbonate (Li2CO3) and a final filtrate. The alkaline aqueous solution may comprise one or more selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH4OH), triethanolamine, or potassium carbonate (K2CO3). Subsequently, an acidic substance may be added to adjust the pH to about 7.5 to about 8 to precipitate aluminum hydroxide (Al(OH)3), and the precipitate may be removed by filtration or centrifugation. Subsequently, by adding a carbonate compound to precipitate lithium ions as lithium carbonate, a high-purity lithium compound may be selectively recovered.

[0053] In one embodiment of the present invention, step (c-3) may encompass both acid dissolution and alkali dissolution methods for recovering lithium from Al-LDH, and each method may be selectively applied depending on site conditions, requirements for byproducts, and device configuration. The acid dissolution method is superior in terms of process simplicity and reaction rate and has the advantage of being suitable for batch processing as it can induce direct precipitation of lithium ions, while the alkali dissolution method is advantageous for recovering byproducts such as Al(OH)3 and for linking with selective impurity removal processes, making it suitable for continuous processes or production lines linked with subsequent purification processes.

[0055] In one embodiment of the present invention, the final filtrate may be used as water for manufacturing an inorganic coagulant for water treatment. The final filtrate has a pH stabilized in the range of about 6.0 to about 8.0, a turbidity of less than about 10 NTU, and a heavy metal content that can be controlled to a level satisfying water quality environmental standards. Here, the heavy metals are lead (Pb), cadmium (Cd), and chromium (Cr).6+ It may contain mercury (Hg), arsenic (As), etc. Since the final filtrate has low residual concentrations of organic matter, aluminum ions, lithium ions, etc., and solids have been completely removed, it can be used industrially without a separate purification process. In particular, the filtrate can be used as dilution water or process water in the manufacture of inorganic coagulants, and can also be applied to the manufacture of water treatment chemicals, as washing water for circulating water systems, or as recycled water in non-discharge processes.

[0057] A recycling method for BOE waste liquid according to one embodiment of the present invention can be performed under hydrothermal conditions of approximately 25°C to 80°C without organic solvents, chelating agents, or high-temperature and high-pressure devices, and since reaction conditions are consistently maintained in an aqueous environment based on hydroxides and carbonates, process control is easy and the risk of fire and explosion is low, resulting in excellent equipment safety. This structure provides process flexibility that allows each recovery step to be easily arranged in a serial or parallel manner, so it can be easily expanded and applied as a batch or continuous modular process depending on site conditions.

[0058] A recycling method for BOE waste liquid according to one embodiment of the present invention can effectively reduce the concentration of harmful ions by stably recovering lithium and fluorine components into solid compounds such as lithium fluoride and fluorite, respectively, and then separating residual lithium and aluminum ions into aluminum-based precipitates and lithium carbonate, respectively. Accordingly, the final filtrate is discharged with sludge formation suppressed, and stable subsequent filtrate treatment and recycling can be achieved without the need for separate coagulants or overloading of the dewatering device.

[0059] A recycling method for BOE waste liquid according to one embodiment of the present invention can provide a structure capable of integrated resource utilization of complex waste resources from across industries by simultaneously utilizing fluorine-based waste liquid generated in semiconductor and display processes and lithium-containing waste liquid derived from the secondary battery industry, thereby enabling the simultaneous realization of environmental and economic values ​​such as process cost reduction, waste reduction, and the establishment of an ESG-based resource circulation system.

[0060] A recycling method for BOE waste liquid according to one embodiment of the present invention can provide a composite processing structure capable of sequentially recovering lithium fluoride, fluorite, lithium carbonate, etc., within a single process. This reduces the number of processes, device configurations, and processing area compared to conventional individual recovery methods, thereby reducing facility construction and operating costs. Furthermore, by simultaneously recovering multiple high-value inorganic resources from a single waste resource stream, resource utilization can be maximized, and effects such as waste reduction, lower product unit costs, and securing eco-friendly certifications can be expected.

[0061] The recycling method for BOE waste liquid according to one embodiment of the present invention is based on the reaction control of inorganic ions such as lithium, fluorine, and aluminum, and can be applied to various waste water series, such as display cleaning water, lithium-based catalyst waste liquid, and CMP waste water. Accordingly, the present technology can be designed as an industry-specific customized module and can be flexibly integrated into distributed water treatment systems. This technological scalability can be utilized as a foundational technology capable of responding to various waste water characteristics and resource recovery requirements in the future.

[0064] Hereinafter, the structure of the present invention and the resulting effects will be explained in more detail through specific embodiments and comparative examples. However, these embodiments are intended to explain the present invention more specifically, and the scope of the present invention is not limited to these embodiments.

[0066] [Example]

[0067] Example 1. Preparation of lithium fluoride using BOE waste liquid

[0068] (1) Mixing of BOE waste liquid and lithium-containing solution

[0069] After preparing BOE wastewater derived from a semiconductor process with a fluoride ion (F) concentration of about 18 wt% and a pH of 3 to 5.5, suspended solids were removed using a 0.45 μm PTFE membrane filter. Meanwhile, a lithium-containing solution with a lithium ion concentration of 420 ppm was prepared by combining cleaning water generated in the cathode material manufacturing process, process water generated in the lithium hydroxide manufacturing process of spodumene, and a solution leached from a waste crucible generated in the cathode material manufacturing process.

[0070] The above BOE waste liquid and the above lithium-containing solution were mixed so that the Li:F equivalent ratio was 1:0.9, and the mixture was placed in a 250 mL three-necked flask, maintained in a 65°C constant temperature water bath, and stirred with a magnetic stirrer (200 rpm).

[0071] (2) pH adjustment

[0072] After the mixing reaction was completed, a 50 wt% NaOH solution was added dropwise to adjust the pH of the mixture to 6.5, and the reaction was maintained at the same temperature (65℃) for 3 hours. At this time, the weight of the mixture was 1,000 g of the lithium-containing solution, 31 g of the BOE waste liquid, and 5 g of the 50 wt% sodium hydroxide (NaOH) solution.

[0073] (3) Obtaining lithium fluoride (LiF)

[0074] After the reaction was completed, the precipitate generated was filtered using a 0.8 μm glass fiber filter to obtain lithium fluoride (LiF) and the first filtrate, respectively. The obtained lithium fluoride was washed three times repeatedly with RO (reverse osmosis) purified water at a solid-to-liquid ratio of 1:20, and then dried at 80°C for 6 hours to obtain high-purity lithium fluoride with a purity of 99.6%.

[0075] (4) Circulation of the first filtrate

[0076] (4-1) Removal of residual F ions (CaF 2 purchase)

[0077] 3.5 g of calcium hydroxide (Ca(OH)2) and 2.8 g of calcium chloride (CaCl2) were added to the first filtrate and stirred for 1 hour at 200 rpm to remove residual F ions. Calcium fluoride (CaF2) formed through this reaction was obtained as a precipitate, and the supernatant was separated as the second filtrate.

[0078] (4-2) Removal of residual Li ions (conversion to Al-LDH)

[0079] Residual Li ions were removed by adding 1 wt% of fine-particle metallic aluminum powder to the above second filtrate (about 930 g) and reacting at 65°C for 2 hours to obtain aluminum-based double hydroxide (Al-LDH; Al-Layered Double Hydroxide) in the form of a precipitate.

[0080] (4-3) Lithium carbonate (Li 2 CO 3 ) obtain

[0081] The obtained Al-LDH was dissolved in 1 M hydrochloric acid (HCl) under conditions of pH 2 or lower, and a 1 M sodium carbonate (Na2CO3) solution was added dropwise to the solution to react. The reaction was carried out at 50°C for 30 minutes, from which lithium carbonate (Li2CO3) and the final filtrate were obtained, respectively. The obtained lithium carbonate was recovered by centrifugation and drying at 60°C.

[0082] (5) Use of the final filtrate

[0083] As the above final filtrate exhibited water quality characteristics satisfying pH 6.8, turbidity of less than 10 NTU, and heavy metal concentration standards, it was used as dilution water for the production of inorganic coagulants for water treatment.

[0084] Example 2. Change in Li:F equivalent ratio

[0085] In step (1) of Example 1 above, the Li:F equivalent ratio was adjusted to 1:0.7, except that the same method as Example 1 above was used.

[0086] Example 3. pH Adjustment

[0087] In step (2) of Example 1 above, after the mixing reaction was completed, a 50 wt% NaOH solution was added dropwise to adjust the pH of the mixture to 6.5, except that the same method as in Example 1 above was used.

[0088] Example 4. Recovery of lithium carbonate from alkali-dissolution-based Al-LDH

[0089] Al-LDH obtained by performing steps (4-2) of Example 1 above was placed in a 250 mL beaker with 100 mL of purified water and dispersed by stirring at 400 rpm for 5 minutes. Then, 5 M sodium hydroxide (NaOH) solution was added dropwise to adjust the pH to 12.5, and the Al-LDH was dissolved by stirring for an additional 30 minutes. Subsequently, 2 M hydrochloric acid (HCl) was added to lower the pH to 7.5. The resulting Al(OH)3 precipitate was removed by filtration, and a 1 M sodium carbonate (Na2CO3) aqueous solution was added to the supernatant and reacted at 60°C for 1 hour. The precipitate produced after the reaction was filtered and dried to obtain lithium carbonate (Li2CO3) and the final filtrate.

[0091] Comparative Example 1. Excess equivalent of F (Li:F = 1:1.2)

[0092] In step (1) of Example 1 above, the Li:F equivalent ratio was adjusted to 1:1.2, except that the same method as Example 1 above was used.

[0093] Comparative Example 2. Insufficient equivalent of F (Li:F = 1:0.5)

[0094] In step (1) of Example 1 above, the Li:F equivalent ratio was adjusted to 1:0.5, except that the same method as Example 1 above was used.

[0095] Comparative Example 3. pH Upward Adjustment

[0096] In step (2) of Example 1 above, after the mixing reaction was completed, a 50 wt% NaOH solution was added dropwise to adjust the pH of the mixture to 8, except that the same method as in Example 1 above was used.

[0097] Comparative Example 4. pH Down-adjustment

[0098] In step (2) of Example 1 above, after the mixing reaction was completed, a 50 wt% NaOH solution was added dropwise to adjust the pH of the mixture to 5, except that the same method as in Example 1 above was used.

[0099] Comparative Example 5. Calcium hydroxide (Ca(OH)₂) 2 ) Not added

[0100] In step (4-1) of Example 1 above, the procedure was carried out in the same manner as Example 1, except that 6.3 g of calcium chloride was added instead of calcium hydroxide.

[0102] Experimental Example 1. Lithium Fluoride (LiF) Yield

[0103] The lithium fluoride yields and yield rates of Examples 1 to 3 and Comparative Examples 1 to 4 are as shown in Table 1 below (Example 4 and Comparative Example 5 were excluded from this experiment as they have compositions that do not directly affect the lithium fluoride yield rate):

[0104] LiF yield (g) LiF yield (%) Example 1 6.12 93.4 Example 2 5.31 81.2 Example 3 5.61 85.7 Comparative Example 1 3.0 45.3 Comparative Example 2 2.48 37.5 Comparative Example 3 2.66 40.2 Comparative Example 4 2.23 33.8

[0105] Examples 1 to 3 showed excellent yields of 6.12 g, 5.31 g, and 5.61 g, respectively, and in particular, Example 1 showed a yield of about 93%.

[0106] On the other hand, in Comparative Examples 1 to 4, the yield of lithium fluoride was low at 33.8% to 45.3%, and the yield was also significantly reduced to 2.23 g to 3.00 g.

[0107] Experimental Example 2. Residual fluoride removal rate in the first filtrate (CaF 2 formation efficiency)

[0108] The results regarding the residual fluoride removal rates of Examples 1 to 3 and Comparative Examples 1 to 5 are as shown in Table 2 below (Example 4 was excluded from this experiment as it is a composition that does not directly affect the residual fluoride removal rate in the first filtrate):

[0109] Fluoride concentration (ppm) of the first filtrate Fluoride concentration (ppm) of the second filtrate Fluoride removal rate (%) CaF2 yield (%) CaF2 yield (g) Example 1 980 86 91.2 91.2 4.96 Example 2 960 122 87.3 87.3 4.74 Example 3 970 110 88.6 88.6 4.81 Comparative Example 1 1005 490 51.2 51.2 2.78 Comparative Example 2 990 556 43.8 43.8 2.38 Comparative Example 3 1010 632 37.4 37.4 2.03 Comparative Example 4 995 680 31.6 31.6 1.72 Comparative Example 5 1002 951 5.1 5.1 0.28

[0110] In Examples 1 to 3, the CaF2 yields were found to be 91.2%, 87.3%, and 88.6%, respectively, and the corresponding yields were confirmed to be 4.96 g, 4.74 g, and 4.81 g, respectively.

[0111] On the other hand, Comparative Examples 1 to 4 showed very low values ​​for both the yield and yield of CaF2. In particular, Comparative Example 5 was not added, so there was insufficient supply of OH, and it is possible that the reaction did not proceed sufficiently with only CaCl2, and accordingly, it is judged that the formation of CaF2 precipitates was inhibited.

[0112] Experimental Example 3. Al-LDH Precipitation Amount and Lithium Recovery Rate

[0113] The results regarding the precipitation amount of Al-LDH and the lithium recovery rate for Example 1 are as shown in Table 3 below (Examples 2 to 4 and Comparative Examples 1 to 5 were excluded from this experiment as they are compositions that do not directly affect the precipitation amount of Al-LDH and the lithium recovery rate):

[0114] Al-LDH precipitate amount (g) Li content (%) in precipitate Total amount of recovered Li (mg) Unrecovered Li concentration (ppm) Example 1 3.71 1.65 61.2 28

[0115] Example 1 showed excellent results with an Al-LDH precipitation amount of 3.71 g, a lithium recovery amount of 61.2 mg, and an unrecovered lithium concentration of 28 ppm in the filtrate. It is believed that the Al-LDH precipitation reaction conditions (65°C, 2 hours) contributed to effectively fixing residual lithium ions in a solid state. In particular, the result of recovering a total of 61.2 mg of lithium from an initial lithium ion concentration of 420 ppm in the mixture demonstrates superior recovery performance compared to simple coagulation or ion exchange resin-based methods, suggesting that the efficient recovery and resource utilization of valuable metals in wastewater can be practically realized.

[0116] Experimental Example 4. Lithium carbonate (Li 2 CO 3 ) yield

[0117] The yield and conversion efficiency of lithium carbonate (Li2CO3) for Examples 1 and 4 are as shown in Table 4 below (Examples 2, 3, and Comparative Examples 1 to 5 were excluded from this experiment as they have compositions that do not directly affect the yield of Li2CO3):

[0118] Li2CO3 yield (g) Conversion efficiency (%) Example 1 1.82 89.2 Example 4 1.78 87.6

[0119] The lithium carbonate obtained in Example 1 was confirmed to have a total amount of 1.82 g and a conversion efficiency of 89.2%, which suggests that the lithium captured in the form of Al-LDH was effectively converted through acid dissolution and carbonate reaction. In the case of Example 4, a similar yield and efficiency were observed as in Example 1.

[0120] Experimental Example 5. Evaluation of Water Quality and Usability of the Final Filtrate

[0121] To analyze the water quality characteristics of the final filtrate, the pH, turbidity, and heavy metal content of the final filtrate were evaluated for Examples 1 and 4, and the results are shown in Table 5 below (Examples 2, 3, and Comparative Examples 1 to 5 were excluded from this experiment as their compositions did not directly affect the water quality evaluation):

[0122] pH Turbidity (NTU) Heavy metal content (mg / L) Example 1 6.8 7.2 0.06 Example 4 7.1 7.5 0.07

[0123] The final filtrate obtained in Example 1 was measured to have a pH of 6.8, a turbidity of 7.2 NTU, and a heavy metal content of 0.06 mg / L, which exhibited excellent water quality characteristics satisfying both industrial water standards and the requirements for inorganic coagulant dilution water. The filtrate of Example 4 was evaluated to have a pH of 7.1, a turbidity of 7.5 NTU, and a heavy metal content of 0.07 mg / L, which was assessed to be generally not significantly different from Example 1 and was confirmed to be usable in practical water treatment applications. Consequently, both examples demonstrated water quality levels suitable for reuse as dilution water in the manufacture of inorganic coagulants without a separate purification process.

[0126] The various embodiments described above may be embodied in other specific forms without departing from the technical idea and essential features. Accordingly, the above detailed description should not be interpreted restrictively in all respects but should be considered exemplary. The scope of the various embodiments shall be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the various embodiments are included within the scope of the various embodiments. Furthermore, embodiments may be constructed by combining claims that do not have an explicit citation relationship in the patent claims, or they may be included as new claims through amendments made after filing.

Claims

Claim 1 A method for recycling BOE waste liquid comprising: (a) a step of mixing BOE waste liquid and a lithium-containing solution; (b) a step of adjusting the pH of the mixture to obtain lithium fluoride (LiF) and a first filtrate; and (c) a step of circulating the first filtrate, wherein the step of circulating the first filtrate comprises: (c-1) a step of adding a calcium compound to the first filtrate to obtain calcium fluoride (CaF2) and a second filtrate; (c-2) a step of adding metallic aluminum to the second filtrate to recover residual Li ions in the form of Al-LDH; and (c-3) a step of adding a carbonate compound to the Al-LDH to obtain lithium carbonate (Li2CO3) and a final filtrate, wherein in step (a), the BOE waste liquid has a pH of 3 to 5.5, and in step (a), the F of the BOE waste liquid - A method for recycling BOE waste liquid, wherein the concentration is 4 wt% to 30 wt%, in step (a), the equivalent ratio (Li:F) of Li and F contained in the lithium-containing solution and the BOE waste liquid, respectively, is 1:0.6 to 1:1.1, in step (b), the pH is adjusted to 6 to 7, and in step (c-2), the metallic aluminum is added at a concentration of 0.5 wt% to 2.0 wt% based on the total weight of the mixed liquid. Claim 2 delete Claim 3 A method for recycling BOE waste liquid according to claim 1, wherein step (c-3) is to dissolve the Al-LDH in an acid and then add a carbonate compound; or to dissolve it in an alkaline aqueous solution, adjust the pH, and then add a carbonate compound to obtain lithium carbonate (Li2CO3) and a final filtrate.

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