Method for recovering lithium from waste

Abstract

A method for recovering lithium from waste according to the present invention comprises the steps of: preparing lithium carbonate; converting the lithium carbonate into slurry containing lithium hydroxide and calcium carbonate by using calcium hydroxide; performing solid-liquid separation of the slurry; first purifying the solid-liquid separated lithium hydroxide aqueous solution to obtain solid waste and a purified lithium hydroxide aqueous solution; second purifying the purified lithium hydroxide aqueous solution through an ion exchange resin; crystallizing the lithium hydroxide aqueous solution subjected to the second purification to obtain lithium hydroxide, wherein the second purification step utilizes an acid regeneration method to regenerate the ion exchange resin, thereby generating acid-regeneration wastewater and a lithium hydroxide purge solution is generated in the step of crystallizing the lithium hydroxide aqueous solution; carbonating the lithium hydroxide purge solution to obtain lithium carbonate and lithium carbonate purge wastewater; preparing a wastewater mixture by mixing the acid-regeneration wastewater, the lithium carbonate purge wastewater, and the solid waste; neutralizing the wastewater mixture; introducing a lithium adsorbent into the neutralized wastewater mixture to selectively adsorb lithium; desorbing the adsorbed lithium to obtain a desorption solution; carbonating the desorption solution to obtain lithium carbonate and a carbonated filtrate; and recycling the carbonated filtrate to the step of neutralizing the wastewater mixture.

Description

Method to recover lithium from waste

[0001] This application claims priority to Korean Patent Application No. 10-2024-0191965, and the contents of the said priority application specification are incorporated into this specification.

[0002] The present invention relates to a method for recovering lithium from waste, specifically a method for recovering lithium from waste generated during a lithium compound manufacturing process.

[0003] Lithium waste is generated during processes such as lithium mining, the production of lithium compounds, and the manufacturing of lithium-ion batteries. Effective methods for treating and utilizing this waste are crucial for environmental protection and resource recycling.

[0004] Known methods for treating lithium waste include methods that separate and recover only lithium ions from the waste using ion exchange, precipitation, or membrane separation technologies, and methods that recover lithium by separating it into precipitates in the form of lithium carbonate or lithium hydroxide through chemical precipitation reactions by adding carbonates or hydroxides.

[0005] To remove ecotoxic lithium from waste, environmentally friendly treatment methods can be employed, such as neutralizing and stabilizing acidic or basic wastewater, removing organic matter from wastewater through the decomposition of organic pollutants using microorganisms, or converting wastewater by adsorbing pollutants using adsorbents like activated carbon or zeolite.

[0006] After undergoing this treatment process, if the lithium concentration is at an appropriate level, it can be used for agricultural purposes, and small-scale lithium-containing wastewater can be used in specific engineering projects, but this must meet regulatory and safety standards.

[0007] Currently, the use of lithium as a raw material for batteries in electric vehicles and various electric products is increasing. However, as usage grows, the amount of waste generated also increases; therefore, measures to reduce waste generation itself must be sought through process improvements or technological innovation.

[0008] The present invention aims to provide a method for recovering lithium from waste, which can increase the lithium recovery rate and facilitate wastewater treatment by reintroducing waste generated during the high-purity lithium hydroxide manufacturing process back into the process.

[0009] The present invention comprises the steps of: preparing lithium carbonate; converting the lithium carbonate into a slurry containing lithium hydroxide and calcium carbonate using calcium hydroxide; separating the solid and liquid phases of the slurry; first purifying the solid-liquid separated lithium hydroxide aqueous solution to obtain solid waste and a purified lithium hydroxide aqueous solution; second purifying the purified lithium hydroxide aqueous solution through an ion exchange resin; and crystallizing the lithium hydroxide aqueous solution obtained from the second purification step to obtain lithium hydroxide; wherein, in the second purification step, an acid regeneration method is used to regenerate the ion exchange resin, thereby generating acid regeneration wastewater; wherein, in the step of crystallizing the lithium hydroxide aqueous solution, a lithium hydroxide purge solution is generated, and the lithium hydroxide purge solution is carbonated to obtain lithium carbonate and lithium carbonate purge wastewater; and, wherein, the acid regeneration wastewater, the lithium carbonate purge wastewater, and the solid waste are mixed to prepare a wastewater mixture; and, wherein, the wastewater mixture is neutralized. A method for recovering lithium from waste is provided, further comprising: a step of introducing a lithium adsorbent into the neutralized wastewater mixture to selectively adsorb lithium; a step of desorbing the adsorbed lithium to obtain a desorbed solution; a step of carbonating the desorbed solution to obtain lithium carbonate and a carbonation filtrate; and a step of recycling the carbonation filtrate to the step of neutralizing the wastewater mixture.

[0010] The method for recovering lithium from waste according to the present invention has the advantage of increasing the lithium recovery rate and making wastewater treatment easier by utilizing waste generated during the lithium manufacturing process by introducing it into the process.

[0011] FIG. 1 is a diagram showing the process of generating acid-recycled wastewater, lithium carbonate purge wastewater, and solid waste in a method for recovering lithium from waste according to some embodiments of the present invention.

[0012] FIG. 2 is a diagram showing the process of recovering lithium using a wastewater mixture in a method for recovering lithium from waste according to some embodiments of the present invention.

[0013] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0014] In the present invention, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0015]

[0016] One aspect of the present invention comprises the steps of: preparing lithium carbonate; converting the lithium carbonate into a slurry containing lithium hydroxide and calcium carbonate using calcium hydroxide; separating the slurry from the solid and liquid phases; first purifying the solid-liquid separated aqueous lithium hydroxide solution to obtain solid waste and purified aqueous lithium hydroxide solution; second purifying the purified aqueous lithium hydroxide solution through an ion exchange resin; and crystallizing the aqueous lithium hydroxide solution obtained from the second purification step to obtain lithium hydroxide; wherein, in the second purification step, an acid regeneration method is used to regenerate the ion exchange resin, thereby generating acid regeneration wastewater; wherein, in the step of crystallizing the aqueous lithium hydroxide solution, a lithium hydroxide purge solution is generated, and the lithium hydroxide purge solution is carbonated to obtain lithium carbonate and lithium carbonate purge wastewater; and, wherein, the acid regeneration wastewater, the lithium carbonate purge wastewater, and the solid waste are mixed to prepare a wastewater mixture; and, wherein, the wastewater mixture is neutralized. The present invention relates to a method for recovering lithium from waste, comprising the steps of: introducing a lithium adsorbent into the neutralized wastewater mixture to selectively adsorb lithium; desorbing the adsorbed lithium to obtain a desorbed solution; carbonating the desorbed solution to obtain lithium carbonate and a carbonation filtrate; and recycling the carbonation filtrate in the step of neutralizing the wastewater mixture.

[0017] Specifically, the method for recovering lithium from waste according to the present invention recovers lithium from a wastewater mixture containing three types of waste generated during the high-purity lithium hydroxide manufacturing process using Direct Lithium Extraction (DLE) technology utilizing an adsorbent. In addition, the desorbed solution, from which most impurities have been removed through an adsorption-desorption process using a lithium adsorbent, separates the precipitated impurities and the remaining lithium-containing solution into solid and liquid phases. The solid phase is then heat-treated and hydrated to be recycled into calcium hydroxide, while the liquid phase is carbonated to produce lithium carbonate for recycling.

[0018] Figure 1 illustrates the process of generating acid-recycled wastewater, lithium carbonate purge wastewater, and solid waste in a method for recovering lithium from waste according to the present invention.

[0019] FIG. 2 illustrates a method for recovering lithium from waste according to the present invention, wherein lithium is recovered from Type 3 waste through a DLE process using a lithium adsorbent.

[0020]

[0021] Steps to prepare lithium carbonate

[0022] A method for recovering lithium from wastewater according to the present invention includes the step of preparing lithium carbonate.

[0023] The above lithium carbonate may be low-grade lithium carbonate. In short, the method for recovering lithium from wastewater according to the present invention has the excellent advantage of being able to produce high-grade lithium hydroxide using low-grade lithium carbonate.

[0024]

[0025] In the present invention, “low-grade lithium carbonate” may refer to lithium carbonate with a purity of 90% or less, specifically at a level of 80 to 90%.

[0026] The above lithium carbonate may be extracted from a lithium-containing solution.

[0027] The above lithium-containing solution may refer to all solutions containing lithium.

[0028] Specifically, the lithium-containing solution may be one or more selected from the group consisting of a solution of lithium extracted from dissolved in the ocean, a solution generated in a process of recycling spent lithium batteries, a solution of lithium ore leached out, brine, salt lake, lithium-containing hot spring water, lithium-containing groundwater, and lithium-containing brine.

[0029] Specifically, the lithium-containing solution may be a brine or a salt lake.

[0030] The method of extracting the lithium carbonate from the above lithium-containing solution is not limited in the present invention.

[0031] For example, the lithium carbonate can be extracted by concentrating the lithium-containing solution and then evaporating it, but is not limited thereto. Specifically, it can be extracted by concentrating the lithium-containing solution, removing magnesium, and then evaporating it.

[0032] Alternatively, it can be extracted by adding sodium carbonate to the lithium-containing solution to precipitate lithium carbonate, but is not limited thereto.

[0033]

[0034] Step of converting into slurry

[0035] The method for recovering lithium from waste according to the present invention includes the step of converting the aforementioned lithium carbonate into a slurry comprising lithium hydroxide and calcium carbonate using calcium hydroxide.

[0036] For example, lithium carbonate and / or calcium hydroxide or calcium oxide can be added to a solvent to prepare an aqueous solution and then mixed to react, or lithium carbonate and calcium hydroxide or calcium oxide can be reacted in a solvent to convert it into a slurry containing lithium hydroxide and calcium carbonate.

[0037] The calcium hydroxide above may be recycled calcium hydroxide obtained from the step of converting calcium carbonate obtained in the step of separating solids and liquids from a slurry to be described later into calcium hydroxide, and the calcium hydroxide may be provided in the form of an aqueous solution.

[0038] The above solvent may be water.

[0039] The concentration of lithium in the total solvent may be 5 to 15 g / L, preferably 8 to 15 g / L, and more preferably 8 to 10 g / L.

[0040] If the concentration of lithium in the solvent satisfies the above range, it is desirable as there is an advantage of improved process efficiency.

[0041]

[0042] The concentration of calcium hydroxide in the total solvent may be 20 to 80 g / L, preferably 40 to 60 g / L. The concentration of calcium hydroxide may be appropriately added within the above range depending on the concentration of lithium carbonate. Specifically, the amount of calcium hydroxide added to react with the lithium carbonate can be controlled according to the amount of lithium carbonate.

[0043] The above calcium hydroxide may have a purity of 90% or higher. If the purity of the above calcium hydroxide is 90% or higher, it is desirable to increase the yield of the product obtained and minimize the number of acid washes of the ion exchange resin described later.

[0044]

[0045] The step of converting to the above slurry can be performed at 60 to 80°C for 1 to 5 hours, preferably 2 to 3 hours.

[0046] If the step of converting to the above slurry is performed within the above temperature and time range, it is desirable that the conversion to a slurry containing lithium hydroxide and calcium carbonate is sufficiently achieved while minimizing the process time.

[0047] Specifically, the calcium oxide is introduced in the form of a slurry of about 10 to 15% in an amount of 1 to 2 equivalents, preferably 1 to 1.3 equivalents, relative to the equivalent amount of lithium, and reacted to obtain a slurry in which liquid lithium hydroxide and solid calcium carbonate are mixed.

[0048]

[0049] The step of converting the aforementioned lithium carbonate according to the present invention into a slurry comprising lithium hydroxide and calcium carbonate using calcium hydroxide can be carried out through the following reaction scheme 1.

[0050] [Reaction Equation 1]

[0051] Li2CO3+ Ca(OH)2→ LiOH(l) + CaCO3(s)

[0052] In this case, when calcium oxide is used, the calcium oxide reacts with water to be converted into Ca(OH)2, and the above reaction equation 1 can proceed.

[0053]

[0054] Step of separating solids and liquids from the slurry;

[0055] The method for recovering lithium from waste according to the present invention includes the step of separating the solid and liquid of the aforementioned slurry.

[0056] That is, a slurry containing lithium hydroxide and calcium carbonate can be separated into solid and liquid phases to obtain a calcium carbonate cake and an aqueous lithium hydroxide solution.

[0057] The above-mentioned high-liquid separation can be performed using methods commonly used in the industry.

[0058] For example, it may be performed using solid-liquid separation equipment such as the above-mentioned filter press, decanter, clarifier, or thickener, but is not limited thereto.

[0059] At this stage, the purity of the calcium carbonate may be 90% or higher. Since the purity of the calcium carbonate satisfies the above range, there is an advantage in that the purity of the recycled calcium oxide or the calcium hydroxide produced through the hydration reaction is increased.

[0060]

[0061] In one embodiment of the present invention, the step of converting calcium carbonate obtained in the step of separating the solid and liquid of the slurry into calcium hydroxide may be further included.

[0062] In another embodiment of the present invention, the step of converting the calcium carbonate into calcium hydroxide may include: a step of obtaining calcium oxide by heat-treating the calcium carbonate separated by solid-liquid separation; and a step of converting the calcium oxide into calcium hydroxide using a hydration reaction.

[0063] The step of obtaining calcium oxide by heat-treating the calcium carbonate above can be performed at 1,000 to 1,100°C for at least 1 hour, preferably 1 to 5 hours, more preferably 1 to 3 hours.

[0064] When the step of obtaining calcium oxide by heat-treating the calcium carbonate is performed within the temperature and time ranges, calcium oxide with a purity of 95% or more, specifically 97% or more, and more specifically 98% or more can be obtained, and high-purity calcium hydroxide can be obtained by hydrating the calcium oxide obtained in this way with water.

[0065] Specifically, calcium oxide can be obtained by thermally decomposing the calcium carbonate, and more specifically, the reaction can proceed according to the following reaction scheme 2.

[0066] [Reaction Equation 2]

[0067] CaCO3→ CaO + CO2(g)

[0068]

[0069] Subsequently, the above calcium oxide can be converted into calcium hydroxide using a hydration reaction.

[0070] Specifically, water can be added to the calcium oxide above to convert it into calcium hydroxide using a hydration reaction, and the reaction can proceed according to the following reaction equation 3.

[0071] [Reaction Equation 3]

[0072] CaO + H2O → Ca(OH)2

[0073]

[0074] Specifically, the water may be reverse osmosis water at room temperature, and the CaO may be added to the reverse osmosis water at room temperature and hydrated for 40 to 60 minutes to form 10 to 15% of Ca(OH)2 and reacted.

[0075]

[0076] The calcium hydroxide obtained at this stage can be recycled in the step of converting the lithium carbonate into a slurry containing lithium hydroxide and calcium carbonate using the calcium hydroxide.

[0077] At this stage, the calcium hydroxide may have a purity of 90% or more.

[0078]

[0079] The lithium hydroxide aqueous solution at this stage may have a lithium concentration of 8 to 10 g / L, which may be the maximum value excluding losses due to the process.

[0080]

[0081] In another embodiment of the present invention, the calcium hydroxide may be introduced into the step of converting into the slurry.

[0082] In summary, the method for recovering lithium from waste according to the present invention can convert calcium carbonate obtained in the step of separating solids and liquids of a slurry containing lithium hydroxide and calcium carbonate into calcium hydroxide and recycle it as a raw material to react with lithium carbonate.

[0083] First purification step

[0084] A method for recovering lithium from waste according to the present invention comprises the step of first purifying the above-described solid-liquid separated aqueous lithium hydroxide solution to obtain solid waste and purified aqueous lithium hydroxide solution.

[0085] The above-mentioned first purification step, that is, the step of first purifying the aforementioned solid-liquid separated aqueous lithium hydroxide solution to obtain solid waste and purified aqueous lithium hydroxide solution, can be performed using a filtering device.

[0086] It is desirable to perform the first purification step using the filtering device above, as this can reduce process costs.

[0087] Specifically, the first purification step described above may be performed using a candle filter, but is not limited thereto.

[0088] The pore size of the candle filter may be 5 to 15 μm, preferably 8 to 12 μm, but is not limited thereto.

[0089]

[0090] The above solid waste exhibits a relatively strong base, has a high Ca content, and may have a relatively low Li content.

[0091] The above solid waste may have a Ca content of 50% by weight or more with respect to the total weight, specifically 55 to 70% by weight, and more specifically 60 to 67% by weight.

[0092] The above solid waste may have a Li content of 5% by weight or less with respect to the total weight, specifically 0.5 to 5% by weight, and more specifically 0.7 to 3% by weight.

[0093] The above-mentioned solid waste may be disposed of or recovered and recycled, but is not limited thereto.

[0094]

[0095] Second purification step

[0096] A method for recovering lithium from waste according to the present invention comprises a step of secondarily purifying the purified aqueous lithium hydroxide solution through an ion exchange resin, wherein, in the second purification step, an acid regeneration method is used to regenerate the ion exchange resin, thereby generating acid regeneration wastewater.

[0097] Specifically, the second purification step may be to remove ionic impurities including at least one of Ca ions, Mg ions, B ions, heavy metals such as Al, Fe and Mn, Sr and Si, and the content of ionic impurities may be controlled to 3 ppm or less through the second purification step.

[0098] At this time, Ca as needed 2+ Mg 2+ To remove divalent impurities, the pH of the purified aqueous lithium hydroxide solution may be adjusted to 3 or higher, but is not limited thereto.

[0099] For example, it can be performed by adding lithium hydroxide to adjust the pH to 10 or higher, but is not limited thereto.

[0100]

[0101] When undergoing the second purification step described above, the ion exchange resin may be in a state where impurities such as calcium are adsorbed. Therefore, the ion exchange resin is regenerated using acid, and acid-regenerated wastewater is generated from this process.

[0102] The above acid may be, for example, HCl, H2SO4, etc., but is not limited thereto and may use any acid commonly used in the industry.

[0103]

[0104] For example, 3 to 5 BV can be flowed through the ion exchange resin using hydrochloric acid at a concentration of 3 to 5% to regenerate it until the pH of the initial hydrochloric acid is reached, and after regeneration, the hydrochloric acid on the surface of the ion exchange resin can be removed using distilled water, etc.

[0105] The acid regeneration wastewater generated by regenerating the above-mentioned ion exchange resin may be a strong acid.

[0106] In the present invention, “acid regeneration wastewater” may refer to wastewater containing all of the acid-containing solution, washing solution, etc., used to regenerate the ion exchange resin.

[0107]

[0108] In another embodiment of the present invention, the acid-recycled wastewater may have a pH of 1 or less.

[0109]

[0110] Step of obtaining lithium hydroxide

[0111] A method for recovering lithium from waste according to the present invention comprises the step of obtaining lithium hydroxide by crystallizing an aqueous lithium hydroxide solution that has undergone the aforementioned second purification step.

[0112] Specifically, lithium hydroxide can be obtained by concentrating and crystallizing the aqueous lithium hydroxide solution that has undergone the second purification step described above.

[0113] The step of obtaining the above lithium hydroxide may be performed using an electrodialysis device, specifically a bipolar electrodialysis device, or by using evaporative concentration, but is not limited thereto.

[0114] Specifically, the step of obtaining lithium hydroxide after the second purification step described above may utilize evaporative concentration.

[0115] The above lithium hydroxide may have a purity of 99% or more, specifically 99 to 99.5%.

[0116]

[0117] In the step of crystallizing the aqueous lithium hydroxide solution that has undergone the second purification step above, a lithium hydroxide purge solution is generated.

[0118]

[0119] In the present invention, the term “lithium hydroxide purge solution” may refer to a solution generated in the step of obtaining lithium hydroxide by crystallizing the lithium hydroxide aqueous solution that has undergone the second purification step from the lithium hydroxide aqueous solution that has undergone the second purification step.

[0120] Specifically, referring to Fig. 1, through evaporation, the aqueous lithium hydroxide solution is crystallized into solid lithium hydroxide, which can then be converted into solid BG (Battery Grade) LHM (Lithium Hydroxide Monohydrate). The remaining solution becomes a solution containing impurities other than lithium hydroxide, and this step is performed to obtain high-purity solid lithium hydroxide.

[0121] The lithium hydroxide purge solution exists as a mixture of low-purity lithium hydroxide and crystallization filtrate, which is subsequently separated into a liquid phase, the lithium hydroxide crystallization filtrate, through solid-liquid separation. Since the lithium hydroxide crystallization filtrate contains impurities along with uncrystallized lithium, it can be re-introduced into low-grade lithium carbonate through carbonation; however, the separation of the solid lithium carbonate from this process generates lithium carbonate purge wastewater.

[0122] Specifically, the step of obtaining the lithium hydroxide may include: a step of evaporating and concentrating the aqueous lithium hydroxide solution that has undergone the second purification step; and a step of separating the solid and liquid of the evaporated and concentrated aqueous lithium hydroxide solution.

[0123] In short, in the present invention, the “lithium hydroxide purge solution” may refer to all of the purge solution, crystallization filtrate, etc. generated from the evaporation concentration step; and / or the solid-liquid separation step.

[0124]

[0125] The above lithium hydroxide purge solution may have a lithium concentration of 5 g / L or less, preferably 3 g / L or less, and more preferably 1 to 3 g / L.

[0126] The above lithium hydroxide purge solution may have a calcium concentration of 3 ppm or less.

[0127] The above lithium hydroxide purge solution may be a strong base.

[0128] In another embodiment of the present invention, the lithium hydroxide purge solution may have a pH of 12 or higher, specifically 13 or higher.

[0129] Since the above lithium hydroxide purge solution is strongly basic, it is mixed with the above acid-recycled wastewater to neutralize the above acid-recycled wastewater, and by extracting lithium again from this mixed solution, it has the excellent advantage of increasing the overall lithium recovery rate, improving the productivity of high-purity lithium hydroxide, and making waste disposal easier.

[0130]

[0131] In addition, lithium carbonate and lithium carbonate purge wastewater are obtained by carbonating the above lithium hydroxide purge solution.

[0132] The above carbonation may involve reacting with carbonated gas or a carbonated substance.

[0133] For example, the above carbonation can be carried out by sodium carbonate, potassium carbonate, ammonium carbonate, CO2 gas, etc.

[0134] Specifically, the lithium hydroxide purge solution can be recycled by being introduced into the carbonation step; in this case, there is an excellent advantage of being able to suppress lithium loss in the entire process.

[0135]

[0136] In another embodiment of the present invention, the lithium hydroxide purge solution introduced into the carbonation step may have a pH of 9 or higher, preferably 10 or higher. The lithium hydroxide purge solution introduced into the carbonation step is mixed with a portion of the acid regeneration wastewater and a portion of the lithium carbonate purge wastewater, and the mixed solution may have a pH of 6 to 8. In this case, there is an advantage that it can be easily recycled into a process for recovering lithium without the need for separate neutralization treatment.

[0137]

[0138] Step of preparing wastewater mixture

[0139] The method for recovering lithium from waste according to the present invention includes the step of preparing a wastewater mixture by mixing the aforementioned acid-recycled wastewater, lithium carbonate purge wastewater, and solid waste.

[0140] The wastewater mixture obtained by mixing the above-mentioned acid-recycled wastewater, the above-mentioned lithium carbonate purge wastewater, and the above-mentioned solid waste is strongly acidic. Specifically, since the pH of the above-mentioned wastewater mixture is very low at 1 or less, the above-mentioned solid waste can also be obtained in a state where it is completely dissolved.

[0141] The above wastewater mixture may have a lithium concentration of 2 to 5 g / L, specifically 2 to 4 g / L.

[0142] The above wastewater mixture may have a calcium concentration of 2 to 5 g / L, specifically 3 to 5 g / L.

[0143] The above wastewater mixture may have a chlorine concentration of 30 to 40 g / L, specifically 30 to 35 g / L.

[0144]

[0145] Step of neutralizing the wastewater mixture

[0146] The method for recovering lithium from waste according to the present invention includes the step of neutralizing the wastewater mixture.

[0147] Since the above wastewater mixture is strongly acidic, a step of neutralizing the above wastewater mixture is performed.

[0148] Neutralization of the above wastewater mixture can be performed by adding an alkaline agent.

[0149] The above alkali agent may be used, for example, NaOH, KOH, etc., but is not limited thereto.

[0150] Preferably, the alkali agent may be NaOH. It is preferable that the alkali agent be NaOH, as this offers the advantages of a faster reaction rate and the generation of fewer residual byproducts.

[0151] The above alkali agent may be added until the pH of the wastewater mixture becomes neutral, specifically 6 to 8.

[0152]

[0153] Step of adsorbing lithium

[0154] A method for recovering lithium from waste according to the present invention comprises the step of introducing a lithium adsorbent into the neutralized wastewater mixture to selectively adsorb lithium.

[0155] The adsorption capacity of the above lithium adsorbent may be 3 to 15 mg / g, and may be appropriately added depending on the concentration of the lithium solution in the wastewater mixture.

[0156]

[0157] The above lithium adsorbent may be an aluminum-based adsorbent.

[0158] Specifically, the lithium adsorbent may include aluminum hydroxide.

[0159] When using the aluminum-based adsorbent containing the above aluminum hydroxide, it is desirable because the adsorption amount of lithium dissolved in the wastewater mixture is high, and there is almost no loss of aluminum in the subsequent deposition step, which extends the lifespan of the lithium adsorbent, thus offering the advantage of excellent economic efficiency.

[0160] The above aluminum-based adsorbent may be a molded body comprising adsorbent powder and a binder.

[0161] The above-mentioned adsorbent powder may be, for example, an adsorbent powder containing aluminum hydroxide. The advantages of using an adsorbent powder containing aluminum hydroxide are the same as those described above.

[0162] The above binder is intended to manufacture the adsorbent powder into a molded body of a suitable shape and serves to bind the adsorbent powders together.

[0163] The binder may include, for example, at least one of polyvinyl chloride (PVC), polysulfone, and polyaniline. Specifically, it is preferable that the binder include polyvinyl chloride (PVC), which can provide excellent bonding strength between adsorbent powders.

[0164]

[0165] Meanwhile, the step of passing the wastewater mixture through an aluminum-based adsorbent to adsorb lithium onto the aluminum-based adsorbent may include, for example, the reaction of the following reaction formula 4.

[0166] [Reaction Equation 4]

[0167] LiCl (1-x) .Al(OH)3.nH2O + xLiCl → LiCl.Al(OH)3.nH2O + (1-x) LiCl

[0168]

[0169] The solution generated from the above step of adsorbing lithium can be treated as wastewater. Specifically, the adsorbed liquid generated from this step is easy to treat as wastewater because lithium has been removed.

[0170]

[0171] Step of obtaining the desorbent

[0172] A method for recovering lithium from waste according to the present invention comprises the step of desorbing the aforementioned adsorbed lithium to obtain a desorbed solution.

[0173] Specifically, a desorbent is obtained by performing a desorption process on the above-mentioned lithium-adsorbed adsorbent using a dilute sodium chloride solution, a lithium chloride solution, or pure water.

[0174] More specifically, the above desorption process can be performed using the condensate generated during the reverse osmosis concentration process described later. It is desirable for the above desorption process to be performed using the condensate generated during the reverse osmosis concentration process described later, as this can increase process efficiency and economic feasibility.

[0175] The above detachment process can be performed in three stages.

[0176] More specifically, referring to FIG. 2, the primary desorption liquid initially discharged may contain impurities adhering to the surface of the adsorbent, so it can be treated as wastewater like the adsorption filtrate generated during the step of adsorbing lithium. Subsequently, the secondary desorption liquid discharged has a high lithium concentration and a low impurity concentration, so it can be recycled into lithium carbonate through the concentration and extraction processes described later.

[0177] The tertiary desorption solution discharged thereafter has a very low concentration of lithium or impurities, so it can be reintroduced into the desorption process.

[0178] In short, the desorbed solution in the step of obtaining the desorbed solution by desorbing the adsorbed lithium above refers to the secondary desorbed solution.

[0179] The above-mentioned desorption solution may have a lithium concentration of 0.8 to 1.3 g / L, specifically 0.8 to 1.0 g / L.

[0180] Through the above adsorption and desorption process, about 95 to 98% of impurities can be removed.

[0181]

[0182] Step of obtaining lithium carbonate and carbonation filtrate

[0183] A method for recovering lithium from waste according to the present invention comprises the step of carbonating the aforementioned desorption solution to obtain lithium carbonate and a carbonation filtrate.

[0184] In another embodiment of the present invention, the method may further include the step of carbonating the desorbent to obtain lithium carbonate and a carbonation filtrate; and the step of concentrating the desorbent prior to carbonation.

[0185] The concentration of the above desorbent may be performed using a reverse osmosis (R / O; Reverse Osmosis Water) method, but is not limited thereto.

[0186] The above reverse osmosis method has the advantage of allowing the condensate, which is almost free of impurities, to be recycled and used as a desorbent along with the concentration. The concentration can be up to 10 to 20 times depending on the composition of the desorbent, and for example, if the lithium concentration of the desorbent is 0.3 to 1 g / L, it can be concentrated to 3 g / L to 20 g / L.

[0187] In short, the above-mentioned concentrated desorbent can be carbonated to obtain lithium carbonate and carbonation filtrate.

[0188] The above carbonation may involve reacting with carbonated gas or a carbonated substance.

[0189] For example, the above carbonation can be carried out by sodium carbonate, potassium carbonate, ammonium carbonate, CO2 gas, etc.

[0190] At this time, the carbonated gas or carbonate-containing material may be introduced in a range of 1.0 to 1.5 equivalents, specifically 1.0 to 1.2 equivalents, based on the lithium equivalent of the desorbent, specifically the concentrated desorbent.

[0191] When the above carbonated gas or carbonate-containing material is introduced within the above range, it is desirable as it offers the advantage of a higher yield of lithium carbonate and also the advantage of increased economic efficiency.

[0192] For example, when carbonation is performed using sodium carbonate, the reaction of the following reaction scheme 5 may be included.

[0193] [Reaction Equation 5]

[0194] 2Li + + Na2CO 3 → Li2CO3 + 2Na +

[0195]

[0196] The carbonation step described above can be performed at a temperature of 20 to 100°C, specifically 50 to 90°C.

[0197] It is desirable that the above carbonation step be performed within the above temperature range, as this can further improve the lithium recovery rate. Specifically, as the temperature increases, the solubility of lithium carbonate decreases, which has the effect of improving the lithium recovery rate.

[0198] The lithium carbonate obtained at this stage can have a purity of 80 to 90 percent.

[0199]

[0200] Since the lithium carbonate obtained at this stage may be of low quality, it can be reintroduced into the step of preparing the lithium carbonate described above to obtain high-purity lithium hydroxide.

[0201]

[0202] Specifically, the above-mentioned desorbent can be carbonated, and the lithium carbonate and carbonation filtrate can be obtained through solid-liquid separation.

[0203] The above carbonation filtrate may have a lithium concentration of 0.5 to 3 gL, specifically 0.5 to 2.5 g / L, and more specifically 1.5 to 2.5 g / L.

[0204]

[0205] Step of recycling carbonation liquid

[0206] A method for recovering lithium from waste according to the present invention includes the step of recycling the aforementioned carbonation filtrate in the step of neutralizing the aforementioned wastewater mixture.

[0207] In another embodiment of the present invention, the carbonation filtrate may have a pH of 10 or higher.

[0208] Since the above carbonation filtrate is strongly alkaline, it can be usefully utilized when introduced into the step of neutralizing the above wastewater mixture.

[0209]

[0210] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0211]

[0212] Examples

[0213] To produce high-purity battery-grade lithium hydroxide using low-grade lithium carbonate, the following steps were performed (see Fig. 1). Lithium carbonate with a purity of 80% was used as the low-grade lithium carbonate. Subsequently, calcium hydroxide with a purity of 99% was used to convert the mixture into a slurry containing liquid lithium hydroxide and solid calcium carbonate.

[0214] After the lithium hydroxide conversion reaction, the aqueous lithium hydroxide solution obtained through solid-liquid separation was first purified using a candle filter to remove impurities, and then an ion exchange resin was used to secondarily purify the purified aqueous lithium hydroxide solution. The ion exchange resin was treated with hydrochloric acid for regeneration after use for a certain period. Specifically, 4% hydrochloric acid (4 BV) was flowed through the ion exchange resin to regenerate it until the pH returned to that of the initial hydrochloric acid, and then washed with distilled water. This resulted in the generation of strongly acidic regenerated wastewater containing a certain concentration of lithium. The composition of the regenerated wastewater is shown in Table 1 below.

[0215] In addition, the composition of the solid waste obtained during the first purification process is shown in Table 2 below. Specifically, the solid material is filtered through a candle filter after the solid material is settled in a clarifier following the lithium hydroxide conversion reaction and the solid fine powder that did not settle in the upper liquid phase is in the form of a Ca compound excluding the lithium hydroxide present in the liquid phase.

[0216]

[0217] Subsequently, a crystallization step was performed to produce high-purity lithium hydroxide, through which a lithium hydroxide purge solution was generated. After solid-liquid separation, the lithium hydroxide purge solution underwent a carbonation process to obtain solid lithium carbonate and lithium carbonate purge wastewater (LC purge wastewater). The composition of the lithium carbonate purge wastewater is shown in Table 1 below. The obtained lithium carbonate was reused in the lithium hydroxide conversion reaction.

[0218]

[0219] Wastewater (g / L)LiNaKCaBClCO3SO4SiO2pH Acid Regeneration Wastewater 2.2 0.0 10.0 1.5 0.0 6 0.0 0.0 10 -0.1 LC Purge Wastewater 3.6 2.8 1.4 -0.3 1.5 15.4 2.1 0.3 10.8 6

[0220] ComponentLi2CO3Ca(OH)2CaCO3CaSO4Mg(OH)2SiO2 Generation (kg / h)0.515.9212.480.110.070.06

[0221] The product obtained from the lithium hydroxide conversion reaction is in the form of a slurry mixed with an aqueous lithium hydroxide solution and calcium carbonate precipitated during the reaction, which is then separated into solid and liquid phases through a precipitation tank. The solid calcium carbonate is recycled into calcium hydroxide through a hydration reaction after heat treatment at 1,000°C for 1 hour, and the liquid lithium hydroxide solution is filtered to separate the solid material before being fed into the next process. At this stage, the filtered solid material is treated as waste.

[0222]

[0223] The composition of the wastewater mixture produced when three types of waste—namely, industrial wastewater, LC purge solution, and solid waste—were mixed is shown in Table 3 below. The pH was very low, at 1 or less, so all solid materials were dissolved and obtained in the form of a solution.

[0224]

[0225] Component LiNa KCaCl CO3SO4SiBM g pH Concentration (g / L) 3.1 38 1.3 9 10.6 6 9 4.3 7 2 30.8 4 30.1 33 0.3 5 50.0 7 50.1 7 80.0 1 30.95

[0226] Since the obtained Type 3 waste was highly acidic, NaOH was added to neutralize it until the pH reached 7, after which the DLE process was performed. The neutralized solution was subjected to an adsorption process using an aluminum-based adsorbent to adsorb lithium, and the resulting solution was treated as wastewater. At this stage, the wastewater is treated more easily as lithium has been removed. After the adsorption process was completed, a desorption process was performed using a dilute sodium chloride solution, a lithium chloride solution, or pure water. The primary desorption solution discharged initially contained some impurities on the surface of the adsorbent and was treated as wastewater along with the adsorption filtrate. The secondary desorption solution discharged thereafter had a high lithium concentration and a low impurity concentration, so it was fed into the next process to undergo concentration and extraction, thereby being recycled into lithium carbonate. The tertiary desorption solution discharged thereafter had very low concentrations of lithium and impurities and was re-feed into the desorption process.

[0227]

[0228] The utilization of lithium waste must comprehensively consider technical, economic, and environmental factors. The method for recovering lithium from waste according to the present invention enables the sustainable use of lithium resources and minimizes environmental pollution by efficiently performing waste treatment and resource recovery.

[0229] In addition, the method for recovering lithium from waste according to the present invention is expected to produce hundreds of tons of lithium carbonate or calcium hydroxide annually, and through this, the lithium recovery rate is expected to improve by more than 1%.

[0230]

[0231] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Step of preparing lithium carbonate; A step of converting the above lithium carbonate into a slurry containing lithium hydroxide and calcium carbonate using calcium hydroxide; A step of separating the solid and liquid of the above slurry; A step of first purifying the above solid-liquid separated aqueous lithium hydroxide solution to obtain solid waste and purified aqueous lithium hydroxide solution; A step of secondarily purifying the purified aqueous lithium hydroxide solution through an ion exchange resin; and A step of obtaining lithium hydroxide by crystallizing the aqueous lithium hydroxide solution that has undergone the second purification step above; Includes, In the second purification step above, an acid regeneration method is used to regenerate the ion exchange resin, and acid regeneration wastewater is generated therefrom, and In the step of crystallizing the above lithium hydroxide aqueous solution; a lithium hydroxide purge solution is generated, and Lithium carbonate and lithium carbonate purge wastewater are obtained through the step of carbonating the above lithium hydroxide purge solution; A step of preparing a wastewater mixture by mixing the above-mentioned industrial wastewater, the above-mentioned lithium carbonate purge wastewater, and the above-mentioned solid waste; A step of neutralizing the above wastewater mixture; A step of adding a lithium adsorbent to the neutralized wastewater mixture to selectively adsorb lithium; A step of obtaining a desorbed solution by desorbing the adsorbed lithium; A step of carbonating the above desorption solution to obtain lithium carbonate and carbonation filtrate; and A step of recycling the above carbonation filtrate to the step of neutralizing the above wastewater mixture; A method for recovering lithium from waste that further includes 2. In Paragraph 1, A method for recovering lithium from waste, wherein the step of obtaining the above-mentioned desorption solution is that the desorption solution is a secondary desorption solution.

3. In Paragraph 1, A method for recovering lithium from waste in which the above-mentioned industrial wastewater has a pH of 1 or less.

4. In Paragraph 1, A method for recovering lithium from waste, wherein the above carbonation filtrate has a pH of 10 or higher.

5. In Paragraph 1, A method for recovering lithium from waste, wherein the neutralized wastewater mixture has a pH of 6 to 8.

6. In Paragraph 1, A method for recovering lithium from waste, further comprising the step of converting calcium carbonate obtained in the step of separating solids and liquids from the above slurry into calcium hydroxide.

7. In Paragraph 6, A method for recovering lithium from waste, wherein the calcium hydroxide is introduced into the step of converting to the slurry.

8. In Paragraph 7, The step of converting the above calcium carbonate into calcium hydroxide; is, A step of obtaining calcium oxide by heat-treating the calcium carbonate separated from the solid and liquid; and A method for recovering lithium from waste, comprising the step of converting the calcium oxide into calcium hydroxide using a hydration reaction.

9. In Paragraph 1, A method for recovering lithium from waste, further comprising the step of carbonating the desorbent to obtain lithium carbonate and carbonation filtrate; and the step of concentrating the desorbent prior to.

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