METHOD FOR RECOVERING HIGH-EFFICIENCY LITHIUM FROM LOW-CONCENTRATION LITHIUM WASTE LIQUID AND LITHIUM CARBONATE PRODUCED THEREBY
20260116755 ยท 2026-04-30
Assignee
Inventors
Cpc classification
C01B25/301
CHEMISTRY; METALLURGY
International classification
Abstract
The present invention provides a method for recovering high-efficiency lithium from a low-concentration lithium waste liquid, and lithium carbonate produced thereby, the method comprising the steps of: adsorbing lithium-containing metal ions from a lithium waste liquid onto an electrode in an electric adsorption system, and desorbing the metal ions adsorbed on the electrode with a desorption solution (S10); preparing an insoluble lithium compound by adding an aluminum source to the desorption solution (S20); preparing a leachate by acid leaching or roasting/water leaching of the insoluble lithium compound (S30); and producing at least one of lithium phosphate, liquid sulfate, and lithium carbonate from the leachate.
Claims
1. A method for recovering high-efficiency lithium from a low-concentration lithium waste liquid, comprising: a step (S10) of adsorbing lithium-containing metal ions from a lithium waste liquid onto an electrode in an electric adsorption system, and desorbing the metal ions adsorbed on the electrode with a desorption solution, wherein the lithium waste liquid has a lithium content of 100 ppm or less; a step (S20) of preparing an insoluble lithium compound by adding an aluminum source to the desorption solution; a step (S30) of preparing a leachate by acid leaching or roasting/water leaching of the insoluble lithium compound; a step of heat-treating the roasted insoluble lithium compound; and a step (S40) of producing at least one selected from the group consisting of lithium phosphate, lithium sulfate, and lithium carbonate from the leachate, wherein, in step (S10), lithium ion concentration in the desorption solution ranges from 500 to 1000 ppm, wherein, in step (S20), the insoluble lithium compound is LiAl-LDH(LiAl.sub.2(OH).sub.7.Math.2H.sub.2O), wherein, in step (S30), a 1.5 M sulfuric acid solution is used in the acid leaching, and wherein the heat-treating step is performed at a temperature of 700 C.
2. (canceled)
3. The method of claim 1, wherein, in step S10, the adsorption and the desorption are performed in an alternating manner, once or 2 to 20 times repeatedly under a potential of 1 V to 2 V, and wherein a residual solution remaining on the electrode is removed between the adsorption and the desorption and after the desorption.
4. The method of claim 1, wherein the aluminum source includes at least one selected from the group consisting of aluminum, sodium aluminate, aluminum hydroxide, alumina, aluminum chloride, and aluminum sulfate.
5. The method of claim 1, wherein, in step S20, the aluminum source is added to the desorption solution and reacted such that a molar ratio of Al to Li ranges from 1 to 4, to precipitate the insoluble lithium compound.
6. The method of claim 1, wherein, when the leachate is prepared by the acid leaching of the insoluble lithium compound, the insoluble lithium compound and a sulfuric acid solution are mixed and reacted such that a solid-to-liquid ratio (g/L) of the insoluble lithium compound to the sulfuric acid solution ranges from 50 to 500, and a molar concentration of the sulfuric acid solution ranges from 0.5 M to 5 M.
7. The method of claim 1, wherein, when the leachate is prepared by the roasting/water leaching of the insoluble lithium compound, the roasting performed prior to the water leaching is sulfuric acid roasting or salt roasting.
8. The method of claim 7, wherein, when the sulfuric acid roasting is performed, the insoluble lithium compound and a sulfuric acid solution are mixed such that a solid-to-liquid ratio (g/L) of the insoluble lithium compound to the sulfuric acid solution ranges from 100 to 2000, and reacted at a temperature of 200 C. to 400 C. for 30 minutes to 2 hours to produce a sulfuric acid roasting conversion product, and a molar concentration of the sulfuric acid solution ranges from 1 M to 5 M.
9. The method of claim 8, wherein the sulfuric acid roasting conversion product is heat-treated at a temperature of 600 C. to 1000 C. for 1 hour to 5 hours prior to the water leaching.
10. The method of claim 7, wherein, when the salt roasting is performed, at least one reactant selected from the group consisting of chlorides (Me-Cl) and sulfates (Me-SO.sub.4) is mixed with the insoluble lithium compound, wherein, when a chloride is used as the reactant, a molar ratio of Li to Cl is adjusted to range from 0.5 to 1.5, wherein, when a sulfate is used as the reactant, a molar ratio of Li to SO.sub.4 is adjusted to range from 1.6 to 2.5, and wherein the reactant mixed with the insoluble lithium compound is reacted at a temperature of 500 C. to 900 C. for 3 hours to 5 hours.
11. The method of claim 1, wherein the water leaching is performed once or 2 to 10 times repeatedly.
12. The method of claim 1, wherein step S40 includes: a step (S41) of producing lithium phosphate from the leachate; a step (S42) of producing a lithium sulfate solution from the lithium phosphate; and a step (S43) of producing lithium carbonate from the lithium sulfate solution.
13. The method of claim 12, wherein, in step S41, a phosphate source and a sodium source are added to the leachate such that a molar ratio of Li to PO.sub.4 ranges from 2 to 4 and a molar ratio of Na to PO.sub.4 ranges from 2 to 4, and the leachate mixed with the phosphate source and the sodium source is reacted for 4 hours to 30 hours.
14. The method of claim 12, wherein, in step S42, the lithium phosphate is mixed with a sulfate (Me-SO.sub.4) solution dissolved in distilled water and reacted such that a molar ratio of Li to SO.sub.4 ranges from 1 to 3 and a solid-to-liquid ratio (g/L) of the lithium phosphate to the sulfate solution ranges from 80 to 320, to produce the lithium sulfate solution.
15. The method of claim 14, wherein the sulfate includes at least one selected from the group consisting of MgSO.sub.4, (NH.sub.4).sub.2SO.sub.4, and Al.sub.2(SO.sub.4).sub.3.
16. The method of claim 14, wherein step S43 includes: a step of removing impurities by adding an alkaline agent to the lithium sulfate solution; and a step of producing the lithium carbonate by adding a carbonate source to the lithium sulfate solution from which the impurities have been removed.
17. The method of claim 16, wherein, in the step of removing impurities by adding an alkaline agent to the lithium sulfate solution, calcium hydroxide is added to the lithium sulfate solution to precipitate and remove aluminum, and sodium hydroxide is added to adjust the pH to 11 or higher to remove calcium ions.
18. The method of claim 16, wherein, in the step of producing the lithium carbonate by adding a carbonate source to the lithium sulfate solution from which the impurities have been removed, the carbonate source is added such that a molar ratio of Li to CO.sub.3 ranges from 1.5 to 2.5, and the lithium carbonate is precipitated by stirring the mixture at a temperature of 40 C. to 90 C. for 1 hour to 24 hours.
19. The method of claim 16, wherein the carbonate source includes at least one selected from the group consisting of sodium carbonate (Na.sub.2CO.sub.3), sodium bicarbonate (NaHCO.sub.3), potassium carbonate (K.sub.2CO.sub.3), potassium bicarbonate (KHCO.sub.3), calcium carbonate (CaCO.sub.3), magnesium carbonate (MgCO.sub.3), and barium carbonate (BaCO.sub.3).
20. Lithium carbonate produced by the method of claim 1.
Description
DESCRIPTION OF DRAWINGS
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BEST MODE
[0062] In order to solve the aforementioned problems, the purpose of the present disclosure is to provide a high-efficiency lithium ion recovery method that enhances efficiency through electric adsorption when recovering lithium components from low-concentration lithium waste liquids with low lithium content, and that, through a series of processes to increase the concentration of lithium ions and produce lithium carbonate, optimizes process conditions to suppress the incorporation of impurities, reduce the use of precipitants, and significantly decrease the amount of alkaline agents required for pH adjustment.
MODE FOR INVENTION
[0063] Before describing the present disclosure in detail, the terms or words used in this specification should not be construed as being unconditionally limited to their ordinary or dictionary meanings, and in order for the inventor of the present disclosure to describe his/her disclosure in the best way, concepts of various terms may be appropriately defined and used, and furthermore, the terms or words should be construed as means and concepts which are consistent with a technical idea of the present disclosure.
[0064] That is, the terms used in this specification are only used to describe preferred embodiments of the present disclosure, and are not used for the purpose of specifically limiting the contents of the present disclosure, and it should be noted that the terms are defined by considering various possibilities of the present disclosure.
[0065] Further, in this specification, it should be understood that, unless the context clearly indicates otherwise, the expression in the singular may include a plurality of expressions, and similarly, even if it is expressed in plural, it should be understood that the meaning of the singular may be included.
[0066] In the case where it is stated throughout this specification that a component includes another component, it does not exclude any other component, but may further include any other component unless otherwise indicated.
[0067] Further, hereinafter, in describing the present disclosure, a detailed description of a configuration determined that may unnecessarily obscure the subject matter of the present disclosure, for example, a detailed description of a known technology including the prior art may be omitted.
[0068] Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to related drawings.
[0069] According to the present disclosure, as shown in the process flow chart of
[0070] In an exemplary embodiment of the present disclosure, the lithium waste liquid may have a lithium content of 100 ppm or less, 70 ppm or less, or 10 to 50 ppm. Such low-concentration lithium waste liquid with a low lithium content has been treated as wastewater due to low economic feasibility, as previously developed non-evaporative lithium extraction technologies, such as adsorption, precipitation, and solvent extraction, require excessive amounts of precipitants, large quantities of alkaline agents for pH adjustment, and result in low recovery efficiency.
[0071] In response to this, the present disclosure aims to provide a high-efficiency and environmentally friendly lithium recovery technology capable of suppressing the excessive use of precipitants and significantly reducing the amount of alkaline agents required for pH adjustment during the conversion process when recovering lithium ions from low-concentration lithium waste liquids.
[0072] In an exemplary embodiment of the present disclosure, step S10 may be a step of adsorbing lithium ions using an electric adsorption system in order to efficiently separate low-concentration metal ions in the lithium waste liquid.
[0073] In step S10, the electric adsorption system may be configured with 2 to 500 sets, or 100 to 300 sets, of unit cells including carbon-based electrodes.
[0074] Each unit module (based on two sets) may have a lithium recovery capacity of 1 mg to 10 mg, or 2 mg to 5 mg.
[0075] The carbon-based electrodes may be made in various shapes and sizes using carbon materials conventionally used in anode fabrication, and the material, shape, and size are not particularly limited.
[0076] The unit module may have a structure of a negative electrode/cation exchange membrane (CEM)/spacer/anion exchange membrane (AEM)/positive electrode.
[0077] In step S10, the adsorption and desorption may be alternately performed once or 2 to 20 times under a potential of 0.5 V to 2 V, or 1 V to 1.5 V.
[0078] The adsorption and desorption may each be performed for 1 to 10 minutes, or 3 to 7 minutes.
[0079] During the adsorption and desorption, the lithium waste liquid and desorption solution may be supplied to the electric adsorption system using a metering pump (peristaltic pump). The desorption solution may be, for example, distilled water or the lithium waste liquid used in the electric adsorption step.
[0080] Residual solution remaining on the electrode between the adsorption and desorption and after the desorption may be removed. For example, after the adsorption process is completed, the residual solution inside may be removed by air blowing for 30 seconds to 2 minutes while maintaining the electric potential. Then, after performing the desorption process, the remaining desorption solution may be recovered by air blowing for 30 seconds to 2 minutes to enhance the recovery rate.
[0081] As such, by removing the residual solution from the electrode between the adsorption and desorption and after the desorption, lithium recovery efficiency can be improved and the number of adsorption/desorption cycles can be reduced.
[0082] In an exemplary embodiment of the present disclosure, step S20 may be a step of producing an insoluble lithium compound by adding an aluminum source to the desorption solution containing lithium-containing metal ions obtained through electric adsorption in step S10.
[0083] The lithium content in the desorption solution obtained through the electric adsorption may range from 500 ppm to 2000 ppm.
[0084] The aluminum source may include at least one selected from the group consisting of aluminum, sodium aluminate, aluminum hydroxide, alumina, aluminum chloride, and aluminum sulfate. In a specific example, the aluminum source may be sodium aluminate.
[0085] When sodium aluminate is mixed and reacted with the desorption solution, LiAl LDH((LiAl.sub.2(OH).sub.7.Math.2H.sub.2O) may be formed as the insoluble lithium compound.
[0086] In step S20, the aluminum source may be added to the desorption solution and reacted such that the molar ratio of Al to Li is 1 to 4, 1.5 to 3.5, or 2 to 3, to precipitate the insoluble lithium compound.
[0087] In an exemplary embodiment of the present disclosure, step S30 may be a step of preparing a leachate enriched with lithium ions by subjecting the insoluble lithium compound prepared in step S20 to acid leaching or roasting/water leaching.
[0088] In an exemplary embodiment of the present disclosure, when the leachate is prepared by acid leaching of the insoluble lithium compound, the leaching may be performed using a sulfuric acid solution having a molar concentration of 0.5 M to 5 M, 1.5 M to 4 M, or 2.5 M to 3.5 M.
[0089] In this case, the solid-to-liquid ratio (g/L) of the insoluble lithium compound to the sulfuric acid solution may be 50 to 500, 50 to 300, or 50 to 150.
[0090] In addition, the reaction temperature may be 40 C. to 90 C. or 60 C. to 80 C., and the reaction may be carried out for 1 to 12 hours or 2 to 6 hours.
[0091] When the leaching reaction is conducted using a sulfuric acid solution, a co-precipitation process using an alkaline agent may be performed to remove impurities.
[0092] Specifically, since aluminum impurities are excessively present in the leachate during sulfuric acid leaching, they must be removed in advance, as they lower purification efficiency in the subsequent lithium recovery process.
[0093] The alkaline agent may include at least one selected from the group consisting of sodium hydroxide, calcium hydroxide, and potassium hydroxide.
[0094] In a specific example, the alkaline agent may be calcium hydroxide, which may be more effective in removing aluminum from the leachate compared to sodium hydroxide.
[0095] In another exemplary embodiment of the present disclosure, when the leachate is prepared by roasting/water leaching of the insoluble lithium compound, the roasting performed prior to the water leaching may be sulfuric acid roasting or salt roasting.
[0096] First, in sulfuric acid roasting, the insoluble lithium compound and sulfuric acid solution may be mixed such that the solid-to-liquid ratio (g/L) of the insoluble lithium compound to the sulfuric acid solution is 100 to 2000, 500 to 1500, or 800 to 1200.
[0097] The sulfuric acid solution may have a molar concentration of 1 M to 5 M, 2 M to 5 M, or 2 M to 3 M.
[0098] The sulfuric acid roasting process may be performed at a temperature of 200 C. to 400 C. or 250 C. to 350 C. for 30 minutes to 2 hours or 50 minutes to 1 hour and 10 minutes to produce a sulfuric acid roasting conversion product.
[0099] The sulfuric acid roasting conversion product may then be heat-treated at 600 C. to 1000 C., 650 C. to 900 C., or 650 C. to 750 C. for 1 to 5 hours or 2 to 4 hours prior to water leaching.
[0100] By performing secondary heat treatment after sulfuric acid roasting, the incorporation of impurities, particularly aluminum, in the subsequent water leaching step can be prevented.
[0101] Next, in salt roasting, one or more reactants selected from chlorides (Me-Cl) and sulfates (Me-SO.sub.4) may be mixed and reacted with the insoluble lithium compound to form a salt-roasting conversion product.
[0102] The chloride may include at least one selected from the group consisting of CaCl.sub.2, AiCl.sub.3, and MgCl.sub.2. In a specific example, the chloride may be MgCl.sub.2.
[0103] In this case, high lithium ion concentrations can be achieved during subsequent water leaching while suppressing the incorporation of aluminum ions.
[0104] When a chloride is used as the reactant, the molar ratio of Li to Cl may be adjusted to 0.5 to 1.5 or 0.8 to 1.2, and the salt roasting reaction may be performed at a temperature of 500 C. to 900 C., 500 C. to 750 C., or 650 C. to 750 C. for 3 to 5 hours.
[0105] The sulfate may include at least one selected from the group consisting of Al.sub.2(SO.sub.4).sub.3.Math.xH.sub.2O(x:1418), MgSO.sub.4, and (NH.sub.4).sub.2SO.sub.4. In a specific example, the sulfate may be (NH.sub.4).sub.2SO.sub.4.
[0106] In this case, high lithium ion concentrations can be achieved during subsequent water leaching while suppressing the incorporation of aluminum ions.
[0107] When a sulfate is used as the reactant, the molar ratio of Li to SO.sub.4 may be adjusted to 1.6 to 2.5 or 1.8 to 2.2, and the salt roasting reaction may be carried out at a temperature of 500 C. to 900 C., 500 C. to 800 C., or 650 C. to 750 C. for 3 to 5 hours.
[0108] After sulfuric acid roasting or salt roasting, the water leaching may be performed at a solid-to-liquid ratio (g/L) of 50 to 200 or 80 to 130 for 1 to 30 hours or for 4 to 12 hours.
[0109] The water leaching may be performed once, or 2 to 10 times, or 3 to 5 times repeatedly.
[0110] The lithium ion content in the resulting leachate may be 2000 ppm or higher.
[0111] In an exemplary embodiment of the present disclosure, step S40 may be a step of producing at least one selected from lithium phosphate, lithium sulfate, and lithium carbonate from the leachate.
[0112] In particular, step S40 may include: a step (S41) of producing lithium phosphate from the leachate; a step (S42) of producing a lithium sulfate solution from the lithium phosphate; and a step (S43) of producing lithium carbonate from the lithium sulfate solution.
[0113] In particular, the present disclosure provides lithium phosphate (Li.sub.3PO.sub.4) as an intermediate to convert the leachate with high lithium content and reduced impurity ions into a high-concentration lithium solution required for lithium carbonate production.
[0114] The lithium content of the insoluble lithium compound, LiAl LDH, is 3.21% per gram, while that of lithium phosphate is approximately 17.98%, making lithium phosphate more suitable for producing high-concentration lithium solutions.
[0115] Meanwhile, although LiAl LDH has a lower lithium content and specific gravity and is not suitable for high-concentration lithium solution production, it has a much lower solubility than lithium phosphate, making it appropriate for efficiently separating lithium ions from solutions with lithium concentrations below 1000 ppm.
[0116] This compound is then converted via a sulfation reaction into a solution with lithium ion concentration of 2000 ppm or more and used as a raw material for lithium phosphate production.
[0117] In an exemplary embodiment of the present disclosure, step S41 may be carried out by adding a phosphate source and a sodium source to the lithium-containing leachate such that such that a molar ratio of Li to PO.sub.4 ranges from 2 to 4 and a molar ratio of Na to PO.sub.4 ranges from 2 to 4, and reacting for 1 to 30 hours.
[0118] In a specific example, step S41 may be carried out by adding a phosphate source and a sodium source to the lithium-containing leachate such that such that a molar ratio of Li to PO.sub.4 ranges from 2.5 to 3.5 and a molar ratio of Na to PO.sub.4 ranges from 2.5 to 3.5, and reacting for 22 to 24 hours.
[0119] The phosphate source may include phosphoric acid (H.sub.3PO.sub.4) or phosphate salts. The phosphate salts may include one or more selected from the group consisting of potassium phosphate, sodium phosphate, aluminum phosphate, zinc phosphate, ammonium polyphosphate, and sodium hexametaphosphate. In a specific example, the phosphate source may be phosphoric acid (H.sub.3PO.sub.4).
[0120] The sodium source may include one or more selected from the group consisting of sodium hydroxide, sodium phosphate, and sodium hexametaphosphate. In a specific example, the sodium source may be sodium hydroxide.
[0121] In step S42, the lithium phosphate is mixed with a sulfate (Me-SO.sub.4) solution dissolved in distilled water and reacted such that a molar ratio of Li to SO.sub.4 ranges from 1 to 3 or 1.5 to 2.5 and a solid-to-liquid ratio (g/L) of the lithium phosphate to the sulfate solution ranges from 80 to 320, 80 to 200 or 90 to 110, to convert the mixture to the lithium sulfate solution.
[0122] This reaction of the lithium phosphate and the sulfate may be performed at 40 C. to 95 C. or 75 C. to 85 C. for 5 to 10 hours or 7 to 9 hours.
[0123] The sulfate compound may include one or more selected from the group consisting of MgSO.sub.4, (NH.sub.4).sub.2SO.sub.4, and Al.sub.2(SO.sub.4).sub.3. In a specific example, the sulfate compound may be Al.sub.2(SO.sub.4).sub.3.
[0124] By producing a lithium sulfate solution from lithium phosphate through a substitution reaction using a sulfate compound in this manner, a lithium sulfate solution with a high lithium ion concentration can be obtained.
[0125] In order to prevent the evaporation of distilled water during the reaction of lithium phosphate and the sulfate compound, a reflux reactor may be used.
[0126] In this step S42, Al.sub.2(SO.sub.4).sub.3 may be dissolved in distilled water to adjust the Li/Al molar ratio to 0.317 to 0.367, 0.321 to 0.350, or 0.325 to 0.350, which allows production of a lithium sulfate solution with a high lithium ion concentration.
[0127] As a specific example, the highest lithium concentration may be achieved when the lithium phosphate/sulfate solution solid-to-liquid ratio (g/L) is 100 or 200 and the Al/Li ratio is 0.325 to 0.350, or when the solid-to-liquid ratio is 280 to 320 and the Al/Li ratio is 0.355 to 0.367.
[0128] The lithium ion concentration in the lithium sulfate solution produced as above may be 10,000 ppm or higher.
[0129] Step S43 may include: a step of removing impurities by adding an alkaline agent to the lithium sulfate solution; and a step of producing the lithium carbonate by adding a carbonate source to the lithium sulfate solution from which the impurities have been removed.
[0130] The alkaline agent may include one or more selected from the group consisting of sodium hydroxide, calcium hydroxide, and potassium hydroxide.
[0131] In one example, the step of removing impurities may be performed by adding calcium hydroxide to precipitate and remove aluminum, and then adding sodium hydroxide to adjust the pH to 11 or higher to remove calcium ions.
[0132] This allows additional impurity removal before lithium carbonate production, increasing the purity of the lithium carbonate.
[0133] The step of recovering lithium carbonate from the impurity-removed lithium sulfate solution may be performed by adding a carbonate source such that the Li/CO.sub.3 molar ratio is 1.5 to 2.5, and stirring at 40 C. to 90 C. for 1 to 24 hours to precipitate lithium carbonate.
[0134] This can result in a high conversion yield from lithium sulfate to lithium carbonate.
[0135] The carbonate source may include one or more selected from the group consisting of sodium carbonate (Na.sub.2CO.sub.3), sodium bicarbonate (NaHCO.sub.3), potassium carbonate (K.sub.2CO.sub.3), potassium bicarbonate (KHCO.sub.3), calcium carbonate (CaCO.sub.3), magnesium carbonate (MgCO.sub.3), and barium carbonate (BaCO.sub.3). In a specific example, the carbonate source may be sodium carbonate.
[0136] In an exemplary embodiment of the present disclosure, each step may be performed under stirring conditions. The stirring speed may be controlled to 100 rpm to 500 rpm, 200 rpm to 400 rpm, or 250 rpm to 350 rpm.
[0137] In addition, the present disclosure may provide at least one selected from the group consisting of lithium phosphate, lithium sulfate, and lithium carbonate, each of which is produced through the above-described method for recovering lithium from a low-concentration lithium waste liquid.
[0138] As described above, the method for recovering lithium from a low-concentration lithium waste liquid according to the present disclosure has been described and illustrated in the drawings. However, the descriptions and illustrations provided herein include only the essential components necessary for understanding the present disclosure. In addition to the processes and apparatuses described and illustrated, other processes and apparatuses not explicitly described or illustrated may be appropriately applied and utilized to implement the method and magnesium oxide produced by the method according to the present disclosure.
[0139] Hereinafter, exemplary embodiments will be described in detail to specifically explain the present disclosure. However, the exemplary embodiments according to the present disclosure may be modified in various forms, and the scope of the present disclosure should not be construed as being limited to the embodiments described below. The exemplary embodiments of the present disclosure are provided to more fully explain the present disclosure to those of ordinary skill in the art.
PREPARATION EXAMPLES
[0140] A lithium waste solution generated from a domestic industrial company (Company K) was collected, and suspended solids were removed through filtration.
[0141] The separated lithium waste solution had a pH of approximately 7. The main cationic components contained in the lithium waste solution were lithium (Li, 70 ppm), sodium (Na, 43 ppm), and calcium (Ca, 39 ppm), and the main anionic component was chloride (Cl, 2320 ppm).
Preparation Example 1: Adsorption Reaction Using Adsorbents
[0142] To recover low-concentration lithium ions contained in the lithium waste solution, adsorbents LiMn.sub.2O.sub.4 and Li.sub.1.33Mn.sub.1.67O.sub.4 were used, respectively.
[0143] Prior to the adsorption experiment, lithium ions in the adsorbent structure were exchanged with hydrogen ions by performing a leaching reaction for 48 hours under the condition of 2 g of adsorbent per 1 L of 0.5 M HCl (leaching efficiency: >98%).
[0144] Based on 1 L of lithium waste solution, 3 g of adsorbent was used, and the adsorption reaction was conducted for 5 days. The filtrate was sampled and filtered at different reaction times, and the concentrations of components were analyzed using ICP (PerkinElmer 7300 DV). The results are shown in Tables 1 and 2 below.
[0145] In addition,
[0146] From the experimental results, the time to reach adsorption equilibrium was observed to be within 12 hours, and the lithium ion adsorption capacity was observed to be approximately 1.61.9 mg-Li/g-adsorbent.
TABLE-US-00001 TABLE 1 Reaction Li Recovery time Li Na Ca uptake efficiency (min) (ppm) (ppm) (ppm) (mg/g) (%) LiMn.sub.2O.sub.4 3 g + 68.9 43.45 38.85 0 Lithium Waste 10 68.65 42.3 38.55 0.08 0.36 Solution 1 L 30 68.15 42.45 38.2 0.25 1.09 (Room Tempera- 60 67.45 42.2 38.05 0.48 2.10 ture, 300 RPM) 120 66.05 42.4 38.15 0.95 4.14 240 65.15 42.35 38.3 1.25 5.44 360 64.85 42.35 37.95 1.35 5.88 480 64.05 42.35 38 1.62 7.04 720 63.9 42.3 37.6 1.67 7.26 1440 63.85 42.25 37.55 1.68 7.33 2880 63.8 42.25 35.35 1.70 7.40 4320 63.9 42.15 35.3 1.67 7.26 5760 63.95 42.1 35.05 1.65 7.18 7200 63.85 42.05 34 1.68 7.33
TABLE-US-00002 TABLE 2 Reaction Li Recovery time Li Na Ca uptake efficiency (min) (ppm) (ppm) (ppm) (mg/g) (%) Li.sub.1.33Mn.sub.1.67O.sub.4 3 g + 68.9 43.45 38.85 0 0 Lithium Waste 10 68.55 43.95 38.9 0.12 0.51 Solution 1 L 30 67.95 44.3 37.3 0.32 1.38 (Room Tempera- 60 66.7 43.2 36.55 0.73 3.19 ture, 300 RPM) 120 65.15 42.4 36.5 1.25 5.44 240 63.15 42.05 36.5 1.92 8.35 360 63.45 42.3 36.5 1.82 7.91 480 63.1 42.35 36.45 1.93 8.42 720 63.25 42.1 36 1.88 8.20 1440 63.1 42.15 35.6 1.93 8.42 2880 63.15 42.25 35.35 1.92 8.35 4320 63.25 42.35 34.8 1.88 8.20 5760 63.2 42.35 34.85 1.90 8.27 7200 63.05 42.25 34.8 1.95 8.49
[0147] The Li uptake was calculated using Equation 1 below, and the lithium ion recovery efficiency was calculated using Equation 2 below.
Preparation Example 2: Adsorption Reaction Based on Lithium Content/Adsorbent Ratio
[0152] In Preparation Example 1 above, the lithium adsorption performance was observed to be significantly lower than typical values for lithium adsorbents. Therefore, the adsorption experiment was conducted by adjusting the lithium content-to-adsorbent ratio in the lithium waste solution.
[0153] Using 150 mL of lithium waste solution as a basis, 0.05 to 1 g of adsorbent was used, and the adsorption reaction was carried out for 3 days at room temperature under stirring at 300 RPM. After the reaction, the filtrate was sampled and filtered, and the concentrations of the components were analyzed, as shown in Table 3.
[0154] In addition, changes in (a) residual lithium ion concentration and (b) lithium ion uptake and solution pH according to the amount of adsorbent added can be seen in
[0155] From the experimental results, lithium ion uptake was observed to be approximately 0.61.8 mg-Li/g-adsorbent, and the lithium ion recovery efficiency was confirmed to be low, at approximately 0.2910%.
[0156] After the reaction, the initial solution pH of about 7 decreased to around 4 as the amount of adsorbent used increased. This is attributed to the ion exchange reaction between the H.sup.+ ions in the adsorbent structure and Li.sup.+ ions in the solution, resulting in an increase of H.sup.+ ions in the solution and, consequently, a decrease in pH. It was also confirmed that lower adsorption capacity was observed in the lower pH range during the adsorption reaction.
TABLE-US-00003 TABLE 3 Absorbent Li Li Ion Weight Li Na Ca uptake Recovery Reactants (g) (ppm) (ppm) (ppm) (mg/g) pH Rate (%) Li.sub.1.33Mn.sub.1.67O.sub.4 + Initial 69.55 42.55 38.65 7.03 Lithium Waste 0.05 69.35 41.2 37.75 0.60 4.83 0.29 Solution 150 mL 0.1 68.8 41.5 38.7 1.13 4.61 1.08 0.2 67.45 42.05 38.4 1.58 4.38 3.02 0.5 63.5 41.5 38.3 1.82 4.18 8.70 1 62.6 41.65 38.4 1.04 4.03 9.99 LiMn.sub.2O.sub.4 + 0.05 69.35 41.95 38.25 0.60 5.03 0.29 Lithium Waste 0.1 68.85 41.75 38.6 1.05 4.89 1.01 Solution 150 mL 0.2 67.8 41.5 38.35 1.31 4.67 2.52 0.5 63.95 41.5 38.05 1.68 4.48 8.05 1 63.65 41.75 38.1 0.89 4.3 8.48
Preparation Example 3: Adsorption Reaction Depending on the pH of Lithium Waste Solution
[0157] Based on 50 mL of lithium waste solution, NaOH was added to adjust the pH of the solution in the range of 7 to 13. Then, 0.15 g of the adsorbent was used to perform an adsorption reaction at room temperature under stirring at 300 RPM for 1 day. After the reaction, the filtrate was sampled/filtered and the concentrations of the components were analyzed. The results are shown in Table 4 below.
[0158] In addition,
[0159] According to the experimental results, the lithium ion adsorption capacity increased as the pH value of the lithium waste solution increased. At a pH of approximately 13, the lithium ion adsorption capacity was about 13 mg-Li/g-adsorbent for LiMn.sub.2O.sub.4 and about 19.7 mg-Li/g-adsorbent for Li.sub.1.33Mn.sub.1.67O.sub.4. The lithium ion recovery efficiency was approximately 59.6% for LiMn.sub.2O.sub.4 and about 85.7% for Li.sub.1.33Mn.sub.1.67O.sub.4.
[0160] In addition, it was confirmed that increasing the pH of the solution during the adsorption reaction led to an increase in lithium ion recovery efficiency. In the case of Ca ions, it was found that when the pH of the solution was increased above 12, the Ca ions were precipitated as Ca(OH).sub.2, allowing for separation before the adsorption reaction.
[0161] Furthermore, in the application of the adsorption reaction to low-concentration lithium waste solution, it was observed that the efficiency of the LiH ion exchange reaction decreased due to the drop in pH during the adsorption process. This confirms that pH adjustment is essential during the adsorption reaction. It is presumed that the decrease in solution pH during the adsorption process is induced by anions such as Cl, SO.sub.4, and CO.sub.3, which are the major anionic constituents of the lithium waste solution.
TABLE-US-00004 TABLE 4 Absorbent Li Li Ion Weight Li Na Ca uptake Recovery (g) (ppm) (ppm) (ppm) (mg/g) pH Rate (%) LiMn.sub.2O.sub.4 + Initial 69.15 54.9 35.58 Lithium Waste 0.15 67.71 53.31 34.62 0.48 7.03 2.08 Solution 50 mL 65.91 57.24 34.29 1.08 8.11 4.69 64.8 71.94 32.7 1.45 10.08 6.29 60.27 90.39 29.25 2.96 11.16 12.84 28.41 258.72 6.02 13.58 12.06 58.92 27.9 N.D. 13.75 13.03 59.65 Li.sub.1.33Mn.sub.1.67O.sub.4 + 66.45 53.25 1.23*30 0.9 7.03 3.90 Lithium Waste 67.41 57.51 36.27 0.58 8.11 2.52 Solution 50 mL 63.33 68.7 33.51 1.94 10.08 8.42 57.99 89.1 32.64 3.72 11.16 16.14 18.51 237.99 13.11 16.88 12.06 73.23 9.87 N.D. 19.76 13.03 85.73
Preparation Example 4: Precipitation Reaction Depending on the Amount of Sodium Aluminate Added
[0162] To recover low-concentration lithium ions contained in lithium waste solution, sodium aluminate was used as a precipitant capable of converting lithium into a low-solubility LiAl LDH (Layered Double Hydroxide, (LiAl.sub.2(OH).sub.7.Math.2H.sub.2O)).
[0163] Based on 50 mL of waste solution, sodium aluminate powder was added while adjusting the Al/Li molar ratio in the range of 2 to 7. The precipitation reaction was carried out at room temperature for 24 hours under stirring at 300 RPM. After the reaction, the filtrate was sampled and filtered, and the concentrations of the components were analyzed.
[0164] The results are shown in Table 5 below. In addition,
[0165] After the reaction, the concentrations of lithium and calcium ions in the filtrate decreased as the amount of sodium aluminate increased, while the concentrations of sodium and aluminum ions, which are components of the precipitant, increased.
[0166] According to the experimental results, the lithium ion recovery efficiency was approximately 4% when the Al/Li molar ratio was 2, and the lithium ion recovery efficiency increased to approximately 91% when the molar ratio was raised to 7. The pH of the solution, which was initially around 7, increased to approximately 12.3 as the Al/Li molar ratio increased up to 7.
[0167] The results of the precipitation reaction using sodium aluminate at various stoichiometric ratios targeting low-concentration lithium ions in lithium waste solution confirmed that the lithium ion recovery efficiency was initially low, and that an excess amount of precipitant was required to significantly improve the recovery efficiency.
TABLE-US-00005 TABLE 5 NaAlO.sub.2 Al/Li Li Dosage molar Li Na Ca Al Recovery Solution Condition (g) ratio (ppm) (ppm) (ppm) (ppm) Rate (%) pH Lithium Waste Initial 69.25 43.25 38.65 Solution 50 mL + 0.133 2 66.15 639 22.37 437.85 4.5 11.77 NaAlO.sub.2 0.199 3 53.4 900.5 21.7 570.5 22.9 11.96 0.266 4 44.55 1195.5 18.8 736.5 35.7 12.1 0.332 5 10.63 1460.5 15.25 741 84.6 12.25 0.398 6 10.08 1763.5 12.15 1019.5 85.4 12.35 0.465 7 6.33 2006.5 10.9 1243 90.9 12.42
Preparation Example 5: Precipitation Reaction According to Lithium Ion Concentration
[0168] In Preparation Example 4, it was confirmed that the lithium ion recovery rate was low when a precipitation reaction using sodium aluminate was applied to a lithium waste solution containing low-concentration lithium ions.
[0169] Therefore, in order to analyze the recovery rate according to lithium ion concentration, model solutions (Li.sup.+ conc: 10-1000 ppm) were prepared using LiCl and LiOH, and applied to the precipitation reaction.
[0170] Based on 50 mL of LiCl solution, sodium aluminate powder was added at an Al/Li molar ratio of 2. The precipitation reaction was carried out at room temperature for 24 hours while stirring the mixture at 300 RPM. After the reaction, the filtrate was sampled and filtered, and the concentrations of the components were analyzed. The results are shown in Tables 6 and 7 below.
[0171] In addition, referring to
[0172] According to the experimental results, as the initial lithium ion concentration increased, the amount of residual lithium ions after the reaction also increased. The highest residual lithium ion concentration was observed at an initial concentration of 250 ppm. However, when the initial concentration increased beyond 250 ppm, the residual lithium ion concentration began to decrease.
[0173] It was also confirmed that the final pH of the solution increased as the initial concentration increased. This is presumed to be due to the increase in OH.sup. ions in the same volume of solution resulting from the increased amount of added precipitant component at a fixed Al/Li molar ratio.
TABLE-US-00006 TABLE 6 Al/Li LiCl sol. NaAlO.sub.2 Li molar Li conc. Dosage Li Na Al Recovery Condition ratio (ppm) (g) (ppm) (ppm) (ppm) Rate (%) pH LiCl solution 2 10 0.019 10.08 80.83 60.4 7.3 11.23 50 mL + 30 0.057 26.84 242.19 178.83 13.5 11.68 NaAlO.sub.2 50 0.095 40.2 395.5 242.55 20.4 12.03 70 0.133 50.55 491.85 344.95 27.5 12.24 100 0.19 70.15 785 394.05 30.3 12.48 250 0.474 116.9 1937.1 311.2 53.2 12.73 500 0.948 112.6 3585 253.6 78.1 12.91 1000 1.897 10.45 7340 66.8 98.9 13.14
TABLE-US-00007 TABLE 7 Al/Li LiOHl sol. NaAlO.sub.2 Li molar Li conc. Dosage Li Na Al Recovery Condition ratio (ppm) (g) (ppm) (ppm) (ppm) Rate (%) pH LiOH solution 2 10 0.019 11.08 68.28 71.43 4.21 11.98 50 mL + 30 0.057 30.13 277.78 254.80 4.40 12.21 NaAlO.sub.2 50 0.095 36.48 406.31 241.62 26.55 12.65 70 0.133 39.46 513.07 247.25 43.60 12.93 100 0.19 42.20 881.05 293.22 57.84 13.21 250 0.474 55.38 2186.07 265.68 77.75 13.36 500 0.948 76.65 4151.81 324.93 84.87 13.49 1000 1.897 10.74 8745.10 500.13 99.00 13.53
EXEMPLARY EMBODIMENTS
Exemplary Embodiment 1: Electro-Adsorption of Metal Ions in Lithium Waste Liquid
[0174] When the adsorption method using LiMnO material and the precipitation method using sodium aluminate were applied to lithium waste liquid, a low lithium ion recovery rate was observed. This is attributed to the characteristics of the waste liquid, which has a low lithium ion concentration and a chloride-based composition, resulting in low efficiency when non-evaporative lithium extraction technologies are applied.
[0175] To address this, the present disclosure considered electro-adsorption technology for the efficient separation of low-concentration metal ions. An adsorption system including 10 cm10 cm carbon electrodes was utilized to adsorb and separate metal ions.
[0176] For evaluating the adsorption performance through electro-adsorption, lithium waste liquid (Li.sup.+ concentration: 50 ppm) was prepared using LiCl. Adsorption/desorption experiments were conducted for 5 minutes each at an applied voltage of 1.4 V using a unit cell configured as (-electrode/CEM/spacer/AEM/+electrode). The recovery capacity was observed to be approximately 2 mg-Li per unit cell.
[0177] Based on 1 L of lithium waste liquid, an adsorption system consisting of three sets of unit cells was used. During repeated adsorption/desorption cycles, the conductivity of the lithium waste liquid and the recovered desorption solution was measured, as shown in
[0178] During adsorption and desorption, the operation potential applied to the system was maintained at 1.4 V, and 50 mL of desorption solution was used to recover the adsorbed ions.
[0179] A peristaltic pump was used to supply the solution to the system at a flow rate of 100 mL/min for 5 minutes each during adsorption and desorption.
[0180] Referring to Table 8, it was observed that the concentration of metal ions in the desorption solution increased with the number of adsorption/desorption cycles. In addition, depending on whether air blowing was applied inside the electrodes to remove residual solvent, a difference of approximately 100 ppm in the lithium ion concentration of the recovered lithium waste liquid was confirmed.
TABLE-US-00008 TABLE 8 Sample Li Na Ca Condition Experimental Method name (ppm) (ppm) (ppm) Unit cell 3ea With solvent removal Initial lithium 69.05 42.05 38.65 Adsorption/ inside electrodes (O) waste liquid Desorption 13 cycles of Final lithium 14.22 9.35 1.75 Potential: 1.4 V adsorption/desorption waste liquid Flow rate: 100 mL/min Desorption 997 628 590.5 solution Without solvent removal Initial lithium 69.05 42.05 38.65 inside electrodes (X) waste liquid 16 cycles of Final lithium 23.7 13.17 2.71 adsorption/desorption waste liquid Desorption 889.5 557.5 470.5 solution
Exemplary Embodiment 2: Recovery of Metal Ions Using an Electric Adsorption System Comprising 200 Unit Cells
[0181] An electric adsorption system comprising 200 sets of unit cells was applied to a lithium waste liquid to analyze the ion recovery efficiency.
[0182] Specifically, adsorption and desorption experiments were carried out at a potential of 1.4 V for 5 minutes each. The lithium waste liquid and the desorption solution were supplied into the system at a flow rate of 2 L/min.
[0183] After adsorption, while maintaining the applied potential, air blowing was performed inside the electrode for approximately 1 minute to remove residual solvent and separate the ions. Subsequently, the desorption solution was introduced into the electrode to recover the adsorbed ions. After completion of desorption, air blowing was again performed for about 1 minute to collect the residual desorption solution and thereby improve the recovery efficiency.
[0184] The volumes of the lithium waste liquid and the desorption solution used for the electro-adsorption/desorption reaction were 8 L and 1 L, respectively.
[0185] Referring to Table 9 and
[0186] The pH of the recovered desorption solution containing the separated ions was approximately 12.1, and the pH of the lithium waste liquid after removal of the ions was approximately 6.3.
TABLE-US-00009 TABLE 9 # of Sample Li Condition cycles name (ppm) pH Unit cell 200ea Initial lithium waste liquid 67.4 6.9 Adsorption/ 1step Lithium waste 18.55 Desorption liquid Potential: 1.4 V Desorption 458 Flow rate: 2 L/min solution 2step Lithium waste 1.02 liquid Desorption 523 solution 3step Lithium waste 0.465 6.37 liquid Desorption 532.5 12.16 solution
Exemplary Embodiment 3: Lithium Ion Separation after Electric Adsorption
[0187] In order to separate lithium ions from the desorption solution in which lithium was concentrated by electric adsorption from lithium waste liquid, sodium aluminate was reacted to convert the lithium ions into LiAl LDH.
[0188] Based on the lithium ion content in the desorption solution, sodium aluminate powder was added at an Al/Li molar ratio of 2 to 4, and the mixture was subjected to a precipitation reaction at room temperature for one day.
[0189] As shown in Table 10, the experimental results demonstrated a lithium recovery rate of approximately 66% at an Al/Li molar ratio of 2, and approximately 99% of lithium recovery rate when the Al/Li molar ratio was increased to 4.
[0190] Compared to the precipitation reaction results using lithium waste liquid and sodium aluminate, the residual lithium ion concentration after the precipitation reaction from the desorption solution was found to be lower. This confirms that a higher Al/Li ratio and alkaline pH conditions lead to higher recovery efficiency.
[0191] Meanwhile, the calcium contained in the desorption solution was found to be precipitated and separated as Ca(OH).sub.2 when the solution pH was increased to 12 or higher using NaOH.
[0192] In this experiment, trace amounts of residual calcium were not separately removed as Ca(OH).sub.2 during the pretreatment process, since it could be easily separated in a subsequent process for preparing a high-concentration lithium solution.
TABLE-US-00010 TABLE 10 Condition Li (Al/Li Content (ppm) recovery Solution molar ratio) Li Na Ca Al rate (%) pH Initial 542 364.5 38.7 12.1 2 179.5 4825 3.195 350 66.8 13.1 2.5 58.2 6670 2.575 729.5 89.2 13.2 3 11.3 8250 2.75 1910.5 97.9 13.3 4 1.45 12030 1.67 5615 99.732 13.4
Exemplary Embodiment 4: Conversion of Lithium into a Lithium Solution after Separation (Sulfuric Acid Leaching)
[0193] After separating lithium ions in the form of LiAl LDH by reacting the desorption solution obtained through electric adsorption with sodium aluminate, the resulting LiAl LDH was converted into a concentrated lithium solution.
[0194] The conversion from LiAl LDH to lithium solution was conducted by leaching the LiAl LDH using sulfuric acid solutions at concentrations ranging from 0.5 M to 2 M under room temperature and 80 C. conditions.
[0195] The experimental results are shown in Table 11,
[0196] According to the experimental results, under a solid (g) to liquid (L) ratio of 100 for the LiAl LDH/sulfuric acid solution, a lithium recovery rate of over 90% was achieved when using sulfuric acid with a molarity of 2 M or higher at room temperature, and a lithium recovery rate of over 90% was achieved when using sulfuric acid with a molarity of 1.5 M or higher at 80 C.
TABLE-US-00011 TABLE 11 Li-Al LDH/Sulfuric Acid Leaching Experiment Reaction Stirring Reaction Sulfuric Li Al Leaching Temp. Speed Time Acid conc. Li conc. Leaching Al conc. leaching Condition ( C.) (RPM) (h) (M) (ppm) Rate (%) (ppm) Rate (%) LDH 20 g + Room 300 12 0.5 674.42 24.09 4848.16 19.47 H.sub.2SO.sub.4 200 mL Temperature 1 1831.01 65.39 13171.77 52.90 1.5 2428.51 86.73 17399.37 69.88 2 2590.02 92.50 18362.49 73.74 80 0.5 653.54 23.34 4808.53 19.31 1 1967.31 70.26 14251.81 57.24 1.5 2727.64 97.42 19397.97 77.90 2 2796.07 99.86 19267.12 77.38
Exemplary Embodiment 5: Conversion to Lithium Solution after Lithium Ion Separation (Sulfuric Acid Leaching)
[0197] For the conversion from LiAl LDH to a lithium solution, leaching was carried out at 80 C. for 12 hours under stirring at 300 RPM using 25 M sulfuric acid solution to obtain a high-concentration lithium solution.
[0198] The sulfuric acid leaching experiment was conducted under conditions in which the solid-to-liquid (S/L) ratio of LiAl LDH to sulfuric acid solution ranged from 100 to 500 (g/L). The results of the experiment are shown in Table 12 and
[0199] From the experimental results, the maximum lithium leaching rate was observed under the condition of a 3 M sulfuric acid solution with an S/L ratio of 100. When the S/L ratio was increased to 200 or higher, the leaching rate tended to decrease.
[0200] Although the lithium ion concentration in the leachate increased with the molarity of the sulfuric acid solution and the S/L ratio, the leaching efficiency decreased as the S/L ratio increased for each acid concentration. Notably, the maximum leaching efficiency for each acid molarity was observed at an S/L ratio of 100.
[0201] This is presumed to be due to a reverse reaction induced by the increased concentrations of lithium and aluminum ions in the leachate during the sulfuric acid leaching of LiAl LDH, thereby reducing the overall leaching efficiency.
TABLE-US-00012 TABLE 12 Li Al H.sub.2SO.sub.4 S/L Ratio Li conc. Al conc. Leaching Leaching conc. (M) (g/L) (ppm) (ppm) Rate (%) Rate (%) 2 100 2702.66 19144.22 96.52 76.88 200 4033.48 32511.59 72.03 65.28 300 3122.14 25206.37 37.17 33.74 400 2713.62 22489.99 24.23 22.58 3 100 2757.25 17804.39 98.47 71.50 200 4255.52 34031.03 75.99 68.34 300 4080.28 36497.58 48.57 48.86 400 3883.94 32152.25 34.68 32.28 4 100 2651.14 18015.84 94.68 72.35 200 4207.68 33647.17 75.14 67.56 300 5430.07 45248.34 64.64 60.57 400 4771.49 43802.99 42.60 43.98 5 100 2646.92 16388.78 94.53 65.82 200 4230.38 33942.10 75.54 68.16 300 5651.63 40742.82 67.28 54.54 400 6741.94 57869.11 60.20 58.10 500 4125.12 36648.27 29.47 29.44
Exemplary Embodiment 6: Separation of Lithium Ions from Lithium Leachate (Sulfuric Acid Leaching)
[0202] The lithium leachate obtained through sulfuric acid leaching of LiAl LDH contains an excessive amount of aluminum (Al), which is required to be removed during the lithium recovery process.
[0203] To separate impurities such as aluminum, a co-precipitation method using calcium hydroxide (Ca(OH).sub.2) was applied. This is because, when using pH adjustment via sodium hydroxide (NaOH), both lithium and aluminum ions in the leachate are subjected to reverse reaction into LiAl LDH as the pH increases.
[0204] Specifically, a leachate was prepared by leaching LiAl LDH (g) at a solid-to-liquid (g/L) ratio of 100 in 1.5 M sulfuric acid (L) at 80 C. for 8 hours. To this leachate, Ca(OH).sub.2 was added, and the mixture was stirred at 300 RPM at room temperature for 24 hours. The effect of Ca(OH).sub.2 addition on the concentrations of lithium and aluminum in the filtrate was analyzed. The titration reaction was performed using 50 mL of leachate while increasing the solid-to-liquid (g/L) ratio of Ca(OH).sub.2 to leachate. The experimental results are shown in Table 13,
[0205] From the experimental results, it was confirmed that as the Ca(OH).sub.2-to-leachate (g/L) ratio increased, the concentration of aluminum ions decreased. However, it was also observed that the loss of lithium ions occurred in parallel. When aluminum ions were completely removed, the remaining lithium in the filtrate exhibited a loss rate of approximately 32%.
TABLE-US-00013 TABLE 13 Leachate Ca(OH).sub.2 Li Al Ca Leaching Volume Weight conc. conc. conc. Condition (mL) (g) (ppm) (ppm) (ppm) LiAl LDH(g)/ 50 2548.12 19240.88 1.5M H.sub.2SO.sub.4 1.391 1644.43 13274.07 442.37 (L):100, 1.669 1473.73 11551.43 425.99 80 C., 8 hours 1.947 1642.72 2789.15 376.92 2.2248 1712.67 0.00 404.41 2.503 541.53 0.00 409.46 2.781 207.02 6.36 478.67
Exemplary Embodiment 7: Conversion to Lithium Solution after Lithium Ion Separation (Sulfuric Acid Roasting/Water Leaching)
[0206] In the process of producing a high-concentration lithium solution from LiAl LDH, the recovery efficiency of lithium during sulfuric acid leaching is low, and the lithium ion concentration in the recovered solution is also low. Consequently, the conversion rate during the subsequent lithium carbonate precipitation process is limited. Furthermore, the recovered solution contains an excessive amount of aluminum, leading to lithium loss and excessive sludge formation in the downstream purification process.
[0207] To increase the lithium ion concentration during the conversion of LiAl LDH to a lithium solution and to suppress the incorporation of aluminum into the solution, roasting with sulfuric acid followed by water leaching was performed using sulfuric acid solutions of 1-5 M. The results are shown in Table 14 and
[0208] Based on the experimental results, after sulfuric acid roasting at 300 C. for 1 hour under a solid-to-liquid (LiAl LDH/sulfuric acid) ratio of 1000 (g/L), and subsequent water leaching at a solid-to-liquid (converted material/water) ratio of 100 (g/L), it was confirmed that aluminum incorporation could be suppressed at sulfuric acid concentrations of 2 M or lower, while at concentrations of 4 M or higher, aluminum incorporation occurred but the lithium recovery rate exceeded 90%.
TABLE-US-00014 TABLE 14 Water Leaching Experiment after Sulfuric Acid Roasting according to Sulfuric Acid Molar Concentration Sulfuric Acid Water Leaching Experiment of Sulfuric Acid Roasting Conversion Product Roasting Experiment Stirring Water Li Li Al Roasting Sulfuric Acid Reaction Speed Leaching Concentra- Recovery Concentra- Conditions Molarity (M) Time (h) (RPM) Conditions tion (ppm) Rate (%) tion (ppm) 300 C. 1 h, 1 24 h 300 Converted 586.54 17.05 10.19 LiAl LDH(g)/Sulfuric 2 Material(g)/ 2602.68 82.34 0.000 Acid(L) Ratio: 1000 3 Water(L) 2527.14 84.44 455.33 4 Ratio: 100 2527.46 91.44 910.33 5 2445.56 95.81 1020.65
Exemplary Embodiment 8: Lithium Leaching from Sulfuric Acid Roasting Conversion Product of LiAl LDH
[0209] As shown in Exemplary Embodiment 7, selective separation of lithium ions was observed when using a 2M sulfuric acid solution under a solid-to-liquid ratio of 1000, based on the analysis of lithium and aluminum contents in the leachate recovered after water leaching of the sulfuric acid roasting conversion product of LiAl LDH.
[0210] However, when the concentration of the sulfuric acid solution increased to 3M or higher, the aluminum content was found to increase due to the incorporation of aluminum sulfate formed during the water leaching process after the reaction.
[0211] Although the selective separation of lithium ions was possible by adjusting the sulfuric acid concentration during the sulfuric acid roasting of LiAl LDH, a limitation of low recovery yield was observed. To address this, aluminum sulfate formed under high sulfuric acid concentration was converted into aluminum oxide to suppress its incorporation during water leaching.
[0212] LiAl LDH and sulfuric acid solution were mixed at a solid-to-liquid ratio of 1000 (g/L) and subjected to sulfuric acid roasting at 300 C. for 1 hour using 3M sulfuric acid. The resulting roasting conversion product was then heat-treated at various temperatures. The XRD analysis results before (a) and after (b) water leaching of the heat-treated product are shown in
[0213] The results confirmed that the peak of aluminum sulfate disappeared at temperatures of approximately 600 C. or higher.
[0214] After sulfuric acid roasting of LiAl LDH at 300 C. for 1 hour using 3M sulfuric acid solution at a solid-to-liquid ratio of 1000 (g/L), the roasted product was heat-treated at different temperatures, and water leaching was conducted at a solid-to-liquid (converted material/water) ratio of 100 (g/L). The concentrations of lithium and aluminum in the leachate were then analyzed. The results are shown in Table 15 and
[0215] The results showed that heat treatment at 500 C. or higher led to a decrease in aluminum content in the leachate.
[0216] Furthermore, when the product roasted at 300 C. was heat-treated at 700 C. or higher and then subjected to water leaching, lithium was identified as the main component of the leachate. In contrast, aluminum was not detected due to its conversion into insoluble aluminum oxide.
[0217] It was also observed that sulfuric acid roasting at 700 C. resulted in reduced reactivity due to sulfuric acid loss, considering that the boiling point of sulfuric acid is 337 C. Therefore, it is deemed appropriate to perform sulfuric acid roasting of the LiAl LDH and sulfuric acid mixture at 300 C. followed by heat treatment at 700 C. or higher.
TABLE-US-00015 TABLE 15 Results of water leaching after 3M sulfuric acid roasting, secondary heat treatment Sulfuric acid roasting/ Heat treatment conditions Secondary Water leaching process LiAl LDH Heat Treatment Water Li Sulfuric Acid Sample Temperature Reaction Stirring Leaching Recovery Roasting Condition Weight ( C.) Time Speed Condition Li Al Rate (%) 3M H.sub.2SO.sub.4 4 g 500 24 h 300 3 g/ 2545.437 430.225 75.749 300 C.-1 h 600 RPM 30 mL 3020.308 221.612 89.726 30 g/30 mL 700 3154.179 0.000 93.578 800 2938.821 0.000 84.209 900 2354.868 0.000 67.337
Exemplary Embodiment 9: Preparation of High-Concentration Lithium Solution from Sulfuric Acid Roasting Conversion Product of LiAl LDH
[0218] A high-concentration lithium solution was prepared by repeatedly applying water leaching to the sulfuric acid roasting conversion product under the conditions of a solid-to-liquid (conversion product/water) ratio of 100 (g/L). The conversion product was obtained by sulfuric acid roasting using a 3M sulfuric acid solution under the conditions of a solid-to-liquid ratio (LiAl LDH (g)/sulfuric acid solution (L)) of 1000.
[0219] In the preparation of the high-concentration lithium solution, the roasted conversion product was subjected to water leaching under a solid-to-liquid ratio (conversion product (g)/water (L)) of 100. The resulting solution (the leachate from the first water leaching cycle) was reused for subsequent leaching cycles, and the process was repeated up to the fifth cycle.
[0220] Referring to Table 16 and
[0221] Furthermore, in order to suppress the incorporation of aluminum ions during sulfuric acid roasting/water leaching, the conversion product was subjected to secondary heat treatment at 700 C. for 4 hours after sulfuric acid roasting. Repeated water leaching was then performed up to the fifth cycle under the solid-to-liquid (conversion product/water) ratio of 100.
[0222] As shown in Table 17 and
[0223] The experimental results indicate that aluminum incorporation decreased after sulfuric acid roasting and secondary heat treatment, and the suppression of reformation into LiAl LDH led to improved lithium ion recovery efficiency.
[0224] Moreover, performing secondary heat treatment at 700 C. or higher after sulfuric acid roasting increased the lithium content per unit weight, making it easier to produce high-concentration lithium solutions within the same number of water leaching cycles.
TABLE-US-00016 TABLE 16 Results of Repeated Water Leaching After 3M Sulfuric Acid Roasting Sulfuric Acid Roasting LiAl LDH Water Leaching Process Sulfuric Acid Water Leaching Li Roasting Reaction Stirring Condition Recovery Conditions Time Speed (Cycle, g/mL) Li Al Rate (%) 3M H.sub.2SO.sub.4, 24 h 300 1st 30/300 2521.97 456.54 84.26 300 C.-1 h, RPM 2nd 28/280 4678.81 1090.94 82.15 50 g/50 mL 3rd 25.8/258 6383.79 1438.58 79.09 4th 23.4/234 7644.56 2123.97 76.20 5th 21.2/212 8376.27 2839.08 73.27
TABLE-US-00017 TABLE 17 Results of Repeated Water Leaching After 3M Sulfuric Acid Roasting and Secondary Heat Treatment Sulfuric Acid Roasting/ Heat Treatment Condition Secondary LiAl LDH Heat Water Leaching Process Sulfuric Acid Treatment Water Leaching Li Roasting Sample Temperature Reaction Stirring Condition Recovery Condition Weight ( C./h) Time Speed (Cycle, g/mL) Li Al Rate (%) 3M H.sub.2SO.sub.4 50 g 700/4 24 h 300 1st 30/300 3159.45 3.25 93.77 300 C.-1 h RPM 2nd 28/280 6198.90 6.40 91.78 50 g/50 mL 3rd 26/260 9029.96 37.65 89.89 4th 23.8/238 11573.80 86.92 87.45 5th 21.8/218 13664.21 158.52 85.37
Exemplary Embodiment 10: Application of Salt Roasting to LiAl LDH
[0225] Salt roasting reactions were performed using chloride and sulfate compounds as reactants to obtain high-concentration lithium chloride and lithium sulfate solutions from LiAl LDH.
[0226] A comparison was made of the lithium ion concentrations recovered after performing salt roasting and water leaching of LiAl LDH(LiAl.sub.2(OH).sub.7.Math.2H.sub.2O) with Me-Cl and Me-SO.sub.4.
[0227] For the chloride-based salt roasting, CaCl.sub.2, AlCl.sub.3, and MgCl.sub.2 were used, while for the sulfate-based salt roasting, Al.sub.2(SO.sub.4).sub.3.Math.xH.sub.2O (x:1418), MgSO.sub.4, and (NH.sub.4).sub.2SO.sub.4 were employed. The molar ratio of Li/Cl was set to 1 for the chloride-based reactions, and the molar ratio of Li/SO.sub.4 was set to 2 for the sulfate-based reactions. Each mixture was subjected to salt roasting for 4 hours at varying temperatures.
[0228] As shown in Table 18, the sulfate-based salt roasting using Me-SO.sub.4 and subsequent water leaching yielded higher lithium ion concentrations compared to the chloride-based roasting process using Me-Cl and subsequent water leaching.
[0229] In addition, when using the sulfate compounds (Me-SO.sub.4), the application of (NH.sub.4).sub.2SO.sub.4 at 700 C. for 4 hours resulted in the highest lithium ion concentration in the leachate.
TABLE-US-00018 TABLE 18 LiAl LDH/Me-SO.sub.4 or Me-Cl Salt Roasting (by temperature) Salt Roasting Water Leaching (1 g/10 mL, 300 RPM, Room Temperature-24 h) LDH/(Me-Cl or Reaction Sample Li Al Ca Mg Na Me-SO.sub.4) Conditions Weight conc. conc. conc. conc. conc. Mixing Ratio ( C.-h) (g) (ppm) (ppm) (ppm) (ppm) (ppm) LDH + CaCl.sub.2 500-4 4.003 1044.88 20.47 2395.01 (Li/Ca = 2) 600-4 4.009 1185.54 21.41 2424.91 Ball milling 700-4 4.007 1486.19 22.58 2161.33 800-4 3.007 893.33 23.67 1534.69 900-4 3.002 187.81 101.11 126.72 LDH + AlCl.sub.3 500-4 4.008 1313.24 3.01 (Li/Al = 3) 600-4 4.009 1358.94 3.34 Ball milling 700-4 4.006 1451.78 6.47 800-4 4.001 599.60 3.73 900-4 4.003 85.34 2.95 LDH + MgCl.sub.2 500-4 4.008 1535.19 4.46 N.D. (Li/Mg = 2) 600-4 4.006 1636.82 6.10 N.D. Ball milling 700-4 4.007 1897.82 7.32 N.D. 800-4 3.005 821.64 4.83 N.D. 900-4 3.006 104.06 13.88 N.D. LDH + Al.sub.2(SO.sub.4).sub.3 500-4 4.007 1907.92 N.D. (Li/Al = 3) 600-4 4.008 2216.34 N.D. Ball milling 700-4 4.004 2614.98 N.D. 800-4 3.005 2036.15 N.D. 900-4 3.005 1791.46 N.D. LDH + MgSO.sub.4 500-4 4.005 861.81 2867.43 (Li/Mg = 2) 600-4 4.008 1602.64 1874.61 Ball milling 700-4 4.009 2226.30 936.94 800-4 3.006 2220.75 495.19 900-4 3.007 2199.30 101.30 LDH + Na.sub.2SO.sub.4 500-4 4.006 425.77 16.00 7288.26 (Li/Na = 1) 600-4 4.004 376.15 5.94 7929.00 Ball milling 700-4 4.009 365.28 35.65 8151.27 800-4 3.005 380.19 13.67 7683.75 900-4 3.005 542.81 91.47 7988.55 LDH + (NH.sub.4).sub.2SO.sub.4 500-4 4.003 1968.34 114.52 (Li/NH.sub.4 = 1) 600-4 4.003 2527.89 N.D. Ball milling 700-4 4.005 2928.02 N.D. 800-4 3.002 2304.35 N.D. 900-4 3.007 1997.41 N.D.
Exemplary Embodiment 11: Preparation of Lithium Phosphate
[0230] In the preparation of high-concentration lithium solution for lithium carbonate synthesis from LiAl LDH, the sulfuric acid leaching method requires a reaction with a high-concentration sulfuric acid solution under low solid-to-liquid (g/L) ratio conditions. However, this method has limitations due to the relatively low lithium ion concentration in the recovered solution and the high amount of co-leached aluminum, which leads to excessive sludge generation and lithium loss during subsequent purification steps.
[0231] In contrast, the sulfuric acid roasting and water leaching method enables the production of a high-concentration lithium solution with more than 1% lithium ion content, but it requires repeated leaching processes and a high solid-to-liquid (g/L) ratio for water leaching.
[0232] To address these issues, the present disclosure proposes a method for converting a lithium solution containing approximately 3000 ppm of lithium ions, obtained by leaching LiAl LDH with dilute sulfuric acid, into an insoluble lithium compound such as lithium phosphate, followed by the regeneration of a high-concentration lithium solution via a wet process.
[0233] Specifically, LiAl LDH was subjected to sulfuric acid roasting using 3M H.sub.2SO.sub.4 under the condition of a solid-to-liquid ratio (g/L) of 1000, followed by heat treatment at 700 C. for 4 hours to suppress the incorporation of aluminum sulfate. The conversion product was then water leached under a solid-to-liquid (conversion product/water) ratio of 100 (g/L), resulting in a lithium solution with a lithium ion concentration of approximately 3159 ppm.
[0234] Afterwards, to produce a higher-concentration lithium solution, the lithium in the recovered solution was converted into lithium phosphate (Li.sub.3PO.sub.4, 17.9%), an intermediate with a lithium content (17.9%) higher than that of LiAl LDH (3.2%).
[0235] For the conversion to lithium phosphate, NaOH and H.sub.3PO.sub.4 were added to the solution to adjust the Li/PO.sub.4 and Na/PO.sub.4 molar ratios to 3. A precipitation reaction was carried out at a stirring speed of 300 RPM for 24 hours.
[0236] The resulting precipitate was then separated, filtered, washed, and dried to recover lithium phosphate, as shown in
Exemplary Embodiment 12: Preparation of Lithium Sulfate
[0237] The preparation of lithium carbonate typically involves precipitating it as a poorly soluble compound by reacting a high-concentration lithium solution (>1%) with a carbonate. To enhance the efficiency of lithium carbonate production, a high-concentration lithium solution is required. In the present disclosure, a wet substitution reaction using sulfate-based compounds (Me-SO.sub.4) was applied to produce a high-concentration lithium sulfate solution.
[0238] Sulfate-based compounds such as MgSO.sub.4, (NH.sub.4).sub.2SO.sub.4, and Al.sub.2(SO.sub.4).sub.3 were used, and the conversion reaction was conducted at 80 C. under a Li/SO.sub.4 molar ratio of 2.
[0239] Each sulfate compound was dissolved in distilled water, and lithium phosphate was added under a solid-to-liquid ratio of 100 (g/L). To prevent the evaporation of the aqueous solution during the reaction, a reflux apparatus was employed to proceed the conversion reactions.
[0240] As shown in Table 19 and
[0241] Furthermore, when Al.sub.2(SO.sub.4).sub.3 was used, the solid-to-liquid ratio of the lithium phosphate to the sulfate solution was varied from 100 to 300, and the wet substitution reaction was conducted at 80 C. The results showed that lithium ion concentrations increased under Al/Li molar ratios ranging from 0.317 to 0.367, depending on the solid-to-liquid ratio. Specifically, at solid-to-liquid ratios of 100 and 200, the lithium ion concentration peaked at the stoichiometric Al/Li molar ratio of 0.333, while at a solid-to-liquid ratio of 300, the highest peak lithium ion concentration was observed at an Al/Li molar ratio of 0.367.
TABLE-US-00019 TABLE 19 Conversion of Li.sub.3PO.sub.4 to Li.sub.2SO.sub.4 Solution Experimental Conditions Solid-to- Molar Liquid Stirring Reaction Concentra- Sulfate ratio Ratio Speed Temperature/ Sample tion (ppm) source (Li/Metal) (g/L) (r.p.m.) Time Name Li MgSO.sub.4 2/1 100/1 300 80 C., 8 hr Initial Final 7993.99 (NH.sub.4).sub.2SO.sub.4 1/1 100/1 300 80 C., 8 hr Initial Final 2796.43 Al.sub.2(SO.sub.4).sub.3 3/1 100/1 300 80 C., 8 hr Initial Final 13224.2
Exemplary Embodiment 13: Preparation of Lithium Carbonate
[0242] A lithium-containing leachate (Li: 13,664 ppm, Al: 158 ppm) was prepared by conducting five cycles of water leaching (solid-to-liquid ratio: 100) using the conversion product obtained from sulfuric acid roasting of LiAl LDH (3M H.sub.2SO.sub.4, 300 C. for 1 hour, 50 g/50 mL) followed by heat treatment at 700 C. for 4 hours. The results are shown in Table 20 below.
[0243] Subsequently, 200 mL of the lithium-containing leachate (Li: 13,664 ppm, Al: 158 ppm) was treated by adding Ca(OH).sub.2 to achieve a Ca/Al molar ratio of 1, followed by stirring for 12 hours to separate aluminum ions. The composition of the reaction filtrate is shown in Table 21.
[0244] After filtration and separation of the resulting precipitate, NaOH solution was added to the remaining solution to adjust the pH to 11 in order to remove residual Ca ions, and the mixture was stirred for an additional 12 hours. The composition of the resulting filtrate is provided in Table 22. The efficiency of Ca ion removal at different pH values is illustrated in
[0245] The lithium-containing leachate, after removal of Al and Ca ions, was reacted with Na.sub.2CO.sub.3 at a Li/CO.sub.3 molar ratio of 2 to synthesize lithium carbonate. The composition of the obtained lithium carbonate is listed in Table 23.
[0246] The resulting lithium carbonate (Li.sub.2CO.sub.3) was further subjected to hot water washing using 2 L of water at 80 C. to remove residual Na ions from the surface. The XRD pattern of the produced lithium carbonate is shown in
TABLE-US-00020 TABLE 20 Water Leaching Results after 3M Sulfuric Acid Roasting and Secondary Heat Treatment (5 times) Water Leaching Solid-to- Stirring Li Al Condition Liquid Ratio Speed conc. conc. ( C.-h) (g/L) (RPM) (ppm) (ppm) pH Room Tem- 100 300 13664.22 158.53 2.39 perature-24
TABLE-US-00021 TABLE 21 Primary Purification of Leachate after 3M Sulfuric Acid Roasting/Secondary Heat Treatment/Water Leaching (using Ca(OH).sub.2) Leachate Leaching Stirring Li Al Ca Volume Purification Condition Speed Reaction conc. conc. conc. (mL) Condition ( C.-h) (RPM) Time (ppm) (ppm) (ppm) pH 200 Ca/Al molar Room 300 Initial 13664.22 158.53 2.39 ratio:1 Temper- Final 13347.68 201.48 4.21 ature-24
TABLE-US-00022 TABLE 22 Secondary Purification of Leachate after 3M Sulfuric Acid Roasting/Secondary Heat Treatment/Water Leaching (using NaOH) Leachate Leaching Stirring Li Al Ca Na Volume Purification Condition Speed Reaction conc. conc. conc. conc. (mL) Condition ( C.-h) (RPM) Time (ppm) (ppm) (ppm) (ppm) pH 180 pH 11> Room 300 Initial 13347.68 201.48 321.12 4.21 Temper- Final 13087.15 31269.75 11.08 ature-24
TABLE-US-00023 TABLE 23 Lithium Carbonate Preparation Leachate Production Stirring Li Al Ca Na Volume Production Condition Speed Reaction conc. conc. conc. conc. (mL) Condition ( C.-h) (RPM) Time (ppm) (ppm) (ppm) (ppm) pH 150 Li/CO.sub.3 molar 80-24 300 Initial 13087.15 31269.75 11.08 ratio:2 Final 1896.12 57541.66 11.59
INDUSTRIAL APPLICABILITY
[0247] The method for recovering high-efficiency lithium from a low-concentration lithium waste liquid according to the present disclosure enables the recovery of valuable lithium ions from low-concentration lithium waste liquids that have conventionally been treated as wastewater, and provides an environmentally friendly and highly efficient lithium recovery technology by reducing the use of precipitants and alkaline agents.