Method for impurity removal of a lithium-containing solution, use and system thereof

Abstract

The application discloses a method for removing impurities from a lithium-containing solution, application and system thereof, and belongs to the technical field of lithium ion battery materials. The method provided by the application comprises the following steps: reacting the lithium-containing solution with a calcium compound, and then performing solid-liquid separation; the calcium compound comprises at least one of calcium oxide and calcium hydroxide; the lithium-containing solution further contains magnesium ions and sulfate ions; and the mass ratio of the one with a larger amount in the magnesium ions and the sulfate ions to the calcium compound is 1:1.05-1.3. The method provided by the application can remove most of calcium, magnesium and sodium impurities in the lithium-containing solution through one-step method, and the impurity removal step is simple and low in cost. The application also provides application of the method and a system for implementing the method.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and in particular to a method for removing impurities from lithium-containing solutions, its application, and a system thereof. Background Technology

[0002] Lithium is a crucial element driving modernization and the development of science and technology industries. In recent years, lithium and its compounds have been widely used in battery energy, glass ceramics, aerospace, and other fields. Especially driven by the new energy vehicle industry, lithium products have significant growth potential in the future.

[0003] Currently, lithium salts or metallic lithium are mainly extracted from lithium ores (such as spodumene, petalite, lepidolite, ferrophosphorus, and lithium aluminum phosphate) and lithium-containing seawater. These raw materials typically contain calcium, magnesium, and sulfate impurities. Furthermore, current lithium extraction methods often involve sulfuric acid leaching, resulting in a particularly high sulfate impurity content in the products. Both these metal ion impurities and sulfate impurities significantly affect the performance of lithium salts or metallic lithium.

[0004] To address these issues, relevant technologies often use strong alkalis such as NaOH to adjust the pH of the leachate to remove metallic impurities, and membrane osmosis methods such as electrodialysis to remove anionic impurities. However, these impurity removal steps are complex and costly. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for removing impurities from lithium-containing solutions, which can remove most of the calcium, magnesium, sulfate, and sodium impurities from lithium-containing solutions in a one-step process. The impurity removal steps are simple and low in cost.

[0006] The present invention also provides a lithium purification solution obtained by the above method.

[0007] The present invention also provides a system for implementing the above-described method.

[0008] According to an embodiment of a first aspect of the present invention, a method for removing impurities from a lithium-containing solution is provided, the method comprising reacting the lithium-containing solution with a calcium compound followed by solid-liquid separation;

[0009] The calcium compound includes at least one of calcium oxide and calcium hydroxide;

[0010] The lithium-containing solution also contains impurities such as magnesium ions and sulfate ions;

[0011] The molar ratio of the magnesium ion and sulfate ion with the larger amount to the calcium compound is 1:1.05 to 1.3.

[0012] The method according to embodiments of the present invention has at least the following beneficial effects:

[0013] (1) In this invention, the compound is used for magnesium removal, and the following reaction occurs during the process:

[0014] CaO + H2O == Ca(OH)2 (1);

[0015] Ca(OH)2 + MgSO4 == Mg(OH)2 ↓ + CaSO4↓ (2);

[0016] Therefore, it can be seen that magnesium removal can also be achieved using calcium compounds. The price of industrial-grade CaO (quicklime) is about 500 yuan / ton, the price of calcium hydroxide is comparable to that of calcium oxide, and the price of sodium hydroxide (caustic soda flakes) is about 3,500 yuan / ton. In terms of unit price, the price of CaO (quicklime) or calcium hydroxide is only 1 / 7 of that of sodium hydroxide. Therefore, the method of this invention can greatly save the cost of alkali.

[0017] Furthermore, the solubility of calcium hydroxide in water is only 0.165 g / 100 g H₂O (0.89 g / L calcium ions in a saturated solution at 20°C), while the solubility of the generated calcium sulfate in water is 0.2036 g / 100 g H₂O (0.474 g / L calcium ions in a saturated solution at 20°C). This solubility is significantly lower than that of sodium hydroxide, or sodium sulfate generated when sodium hydroxide is used. Furthermore, in the same aqueous system, the solubility of calcium hydroxide and calcium sulfate competes with each other, further reducing their solubility, thereby further removing calcium and sulfate ions from the water. Therefore, compared with the method of removing magnesium using sodium hydroxide, the method provided by this invention introduces a very low content of new impurities (calcium ions) while removing magnesium, resulting in a low impurity content in the obtained lithium purification solution. Moreover, even if the compound is added in excess during the implementation of the method, it will not significantly affect the purity of the obtained lithium purification solution.

[0018] (2) Based on the above analysis, it can be seen that the present invention uses calcium compounds for impurity removal, which can also remove some sulfate impurities in lithium-containing solutions, and the following reactions occur simultaneously:

[0019] Ca(OH)2 + Na2SO4 == NaOH + CaSO4↓ (causticization reaction) (3);

[0020] The sodium hydroxide generated in formula (3) can also be used in the magnesium impurity removal reaction, thereby further reducing the content of impurity magnesium in the obtained lithium purification solution.

[0021] Furthermore, considering the amount of calcium compound used as specified in this invention, the calcium compound is almost completely converted into calcium sulfate. Given the solubility of calcium sulfate, almost no calcium ions are introduced during the magnesium removal process.

[0022] (3) Since no calcium ions are introduced during the magnesium removal process, and the content of impurity calcium is reduced due to the competitive reaction, the amount of sodium carbonate used for deep magnesium removal and deep calcium removal can be reduced. Therefore, compared with the traditional impurity removal method, the sodium content in the lithium purification solution is reduced, and sodium entrainment during the lithium precipitation process is avoided.

[0023] In other words, this invention, through a single purification process, reduces the content of impurities such as calcium and magnesium, as well as sulfate and sodium ions, in the resulting purified lithium solution to within controllable ranges, except for lithium hydroxide. The operation method is simple and inexpensive.

[0024] According to some embodiments of the present invention, the lithium-containing solution includes at least one of lithium ore leaching solution, lithium-ion battery leaching solution, and salt lake brine.

[0025] According to some embodiments of the present invention, when the lithium-containing solution includes the lithium ore leaching solution, the method for obtaining the lithium-containing solution includes salt-doped roasting of the lithium ore and acid leaching of the roasting product.

[0026] According to some embodiments of the present invention, the lithium ore includes at least one of spodumene, petalite, lepidolite, lepidolite, and phosphogypsum.

[0027] According to some embodiments of the present invention, before the lithium ore is subjected to salt-blended roasting, the salt and lithium ore are further mixed and ground.

[0028] According to some embodiments of the present invention, after mixing and grinding, the mixture can pass through a 150-mesh sieve. This results in more uniform mixing and reduces the difficulty of the reaction during calcination (increasing the probability of reactant contact). Furthermore, mixing and grinding also has the effect of activating the surface, thereby further improving the thoroughness of the reaction during calcination.

[0029] According to some embodiments of the present invention, in the salt-blended roasting, the salt used includes at least one of sulfate and hydrochloride. When the sulfate is used, the lithium in the lithium ore can be converted from a poorly soluble state to a readily soluble lithium sulfate. When the hydrochloride is used, the poorly soluble metal ions are converted into the corresponding chlorides, thereby improving the efficiency of subsequent acid leaching.

[0030] According to some embodiments of the present invention, the sulfate includes at least one of potassium sulfate, sodium sulfate, and calcium sulfate.

[0031] According to some embodiments of the present invention, the hydrochloride salt includes at least one of sodium chloride, potassium chloride, and calcium chloride.

[0032] According to some embodiments of the present invention, the mass ratio of the salt to the lithium ore is 1:2 to 10.

[0033] According to some embodiments of the present invention, the mass ratio of the salt to the lithium ore is 1:4 to 6. For example, it can be approximately 1:5.

[0034] According to some embodiments of the present invention, the salt-added roasting temperature is 800–1100°C.

[0035] According to some embodiments of the present invention, the salt-added roasting temperature is 900–1050°C. For example, it can be approximately 1000°C.

[0036] According to some embodiments of the present invention, the salt-added roasting time is 1 to 3 hours.

[0037] According to some embodiments of the present invention, the salt-added roasting time is 2 to 2.5 hours.

[0038] According to some embodiments of the present invention, the heating rate of the salt-doped roasting is 1 to 10 °C / min.

[0039] According to some embodiments of the present invention, the acid used in the acid leaching is at least one of sulfuric acid and hydrochloric acid.

[0040] According to some embodiments of the present invention, in the acid leaching, the amount of acid used is 1.05 to 1.5 times the amount of acid required for the complete reaction of the lithium ore.

[0041] According to some embodiments of the present invention, the specific operation of acid leaching includes adding water to make a pulp, and then mixing the resulting pulp with acid.

[0042] The solid-liquid ratio for the water-based pulping process is 1:3 to 4.

[0043] The acid used in the mixture is undiluted, for example, sulfuric acid with a concentration ≥96% or hydrochloric acid with a concentration ≥30%.

[0044] Therefore, adding water first to prepare the pulp can prevent air bubbles generated during the pulping process from affecting the heat and improving the uniformity of subsequent mixing of acid and pulp. If acid is added directly, it can cause localized and violent reactions, which not only affects the uniformity of acid leaching but also prolongs the reaction time and poses safety hazards.

[0045] According to some embodiments of the present invention, the acid leaching time is 1 to 12 hours. This time is the time after the addition of acid.

[0046] According to some embodiments of the present invention, the reaction time of the lithium-containing solution and the calcium compound is 5 to 15 hours.

[0047] According to some embodiments of the present invention, the reaction between the lithium-containing solution and the calcium compound includes sequential mixing, a first aging stage, and a second aging stage.

[0048] The mixing must be carried out under sealed conditions to avoid boiling caused by the heat released when calcium oxide or calcium hydroxide dissolves in water, thereby preventing safety accidents. The mixing time is 1–3 hours. Because the reaction is very vigorous during this stage, no operations that could improve mass transfer are performed.

[0049] The first stage of aging is carried out under closed conditions to prevent carbon dioxide in the air from affecting the conversion of calcium hydroxide to calcium sulfate; the duration of the first stage of aging is 3.5–10 hours. Although the solubility of calcium hydroxide is less than that of calcium sulfate, theoretically calcium hydroxide can be converted into calcium sulfate, in reality, the solubility of calcium hydroxide in water is very small, and the conversion process is slow, thus taking a long time.

[0050] The second aging process is carried out under open conditions, which promotes the reaction between the slurry from the first aging process and carbon dioxide in the air, thereby consuming excess calcium compounds. The duration of the second aging process is 0.5–2 hours.

[0051] According to some embodiments of the present invention, the first and second stages of aging are carried out under stirring conditions. The stirring speed is 50–300 rpm. This can improve the mass transfer rate.

[0052] According to some embodiments of the present invention, the solid-liquid separation method includes at least one of pressure filtration, vacuum filtration, centrifugation, and free sedimentation.

[0053] According to some embodiments of the present invention, the method further includes removing calcium from the liquid phase obtained by the solid-liquid separation.

[0054] According to some embodiments of the present invention, the calcium removal includes mixing the liquid phase and the carbonate to obtain a clear solution. The reaction that occurs in this step is as follows (taking sodium carbonate as an example):

[0055] CaSO4 + Na2CO3 == Na2SO4 + CaCO3↓ (4).

[0056] After adding this calcium removal step, the calcium concentration in the resulting lithium purified solution is ≤10ppm.

[0057] According to some embodiments of the present invention, the carbonate includes at least one of sodium carbonate and potassium carbonate.

[0058] According to some embodiments of the present invention, the molar ratio of carbonate ions in the carbonate to calcium ions in the liquid phase is 1.01 to 1.05:1.

[0059] To avoid introducing impurity metal ions, calcium removal can also be carried out by introducing carbon dioxide into the liquid phase. Since the solubility of calcium carbonate is significantly lower than that of lithium carbonate, the introduced carbon dioxide will preferentially combine with calcium ions to form a precipitate.

[0060] The amount of carbon dioxide introduced should be 1.05 to 1.2 times the amount of calcium ions in the liquid phase. Therefore, a slight excess of carbon dioxide will reduce the concentration of calcium ions in the resulting lithium purification solution. Furthermore, considering the solubility of carbon dioxide in the solution and the solubility of lithium carbonate, the aforementioned amount of carbon dioxide will not cause lithium carbonate precipitation, i.e., it will not affect the lithium yield.

[0061] According to some embodiments of the present invention, the method further includes purification after calcium removal. The further purification method includes resin adsorption. As a result, the concentrations of calcium and magnesium in the purified lithium solution can be reduced to <1 mg / L, meeting the quality standards of lithium-containing solutions before battery-grade lithium carbonate precipitation.

[0062] According to some embodiments of the invention, the resin used for resin adsorption includes PLS850. This enables deep removal of calcium and magnesium.

[0063] According to some embodiments of the present invention, the method includes the following steps:

[0064] S1. Mix and grind lithium ore and salt;

[0065] S2. The mixture obtained in step S1 is subjected to salt-added roasting;

[0066] S3. The roasted product obtained from acid leaching step S2 yields a lithium-containing solution;

[0067] S4. After reacting the lithium-containing solution with the calcium compound, solid-liquid separation is performed to obtain the liquid phase;

[0068] S5. Remove impurities from the liquid phase to obtain a lithium purification solution.

[0069] According to some embodiments of the present invention, step S3 further includes solid-liquid separation after the acid leaching.

[0070] According to some embodiments of the present invention, step S5 further includes solid-liquid separation of the purified reaction mixture.

[0071] Unless otherwise specified, the solid-liquid separation method in this invention includes at least one of vacuum filtration, pressure filtration, ordinary filtration, centrifugation, and natural sedimentation. Any method that achieves the standard of solid-liquid separation is acceptable and is not strictly limited.

[0072] According to an embodiment of the second aspect of the present invention, a lithium purification solution obtained by the method is provided.

[0073] Since the lithium purification solution adopts all the technical solutions of the methods in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0074] According to some embodiments of the present invention, the sulfate content in the lithium purification solution is ≤15.5mmol / L.

[0075] According to some embodiments of the present invention, the sulfate content in the lithium purification solution is ≤10 mmol / L.

[0076] According to some embodiments of the present invention, the concentration of magnesium ions in the lithium purification solution is ≤10ppm.

[0077] According to some embodiments of the present invention, the concentration of magnesium ions in the lithium purification solution is ≤1 ppm.

[0078] According to some embodiments of the present invention, the concentration of calcium ions in the lithium purification solution is ≤10ppm.

[0079] According to some embodiments of the present invention, the concentration of calcium ions in the lithium purification solution is ≤1 ppm.

[0080] According to an embodiment of a third aspect of the present invention, a system for carrying out the method is provided, the system comprising a stirred tank and a solid-liquid separation device connected in sequence via pipes.

[0081] Since the system employs all the technical solutions of the methods described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Furthermore, the system provided by this invention is simple, easy to operate, and facilitates the implementation of the method.

[0082] According to some embodiments of the present invention, the stirred tank has a sealing lid.

[0083] According to some embodiments of the present invention, the sealing cover is pneumatically controlled. This allows for remote control of whether it is opened.

[0084] According to some embodiments of the present invention, a thermometer is provided inside the stirred tank. This allows monitoring to determine whether the mixing phase of the reaction between the lithium-containing solution and the calcium compound has ended. Specifically, the reaction ends when the temperature begins to decrease.

[0085] According to some embodiments of the present invention, the stirred tank is provided with a stirred tank exhaust valve, thereby preventing overpressure of the stirred tank and improving safety.

[0086] According to some embodiments of the present invention, a filter element is provided at the exhaust valve port of the stirred tank, thereby preventing material from spraying out of the stirred tank.

[0087] According to some embodiments of the present invention, the system further includes an exhaust gas absorption tank. The exhaust gas absorption tank is connected to the exhaust valve to prevent the gas discharged from the exhaust valve from polluting the environment.

[0088] The emitted gases include alkaline water vapor, so water absorption is sufficient.

[0089] According to some embodiments of the present invention, the system further includes a calcium-magnesium slag temporary storage tank, which is connected to the solid-liquid separation device.

[0090] According to some embodiments of the present invention, the system further includes a grinding unit, a roasting unit, and an acid leaching unit connected in sequence via pipes; the acid leaching unit is connected to the stirring tank via pipes.

[0091] According to some embodiments of the present invention, the calcination unit is provided with a calcination exhaust valve. The calcination exhaust valve is connected to the tail gas absorption tank, thereby avoiding environmental pollution. Similar to the exhaust valve of the stirred tank, a filter element is provided at the port of the calcination exhaust valve.

[0092] According to some embodiments of the present invention, the acid leaching unit includes an acid leaching reactor and an acid leaching solid-liquid separation device connected in communication, wherein the acid leaching solid-liquid separation device is connected to the stirring tank.

[0093] According to some embodiments of the present invention, the acid leaching unit includes an acid leaching exhaust valve, which is connected to the tail gas absorption tank. Thus, the acidic gas generated in the acid leaching reactor can neutralize the alkaline gas generated in the stirred tank, avoiding pH adjustment during the wastewater harmless treatment process.

[0094] Similar to the exhaust valves of other units, the acid immersion exhaust valve port is equipped with a filter element.

[0095] According to some embodiments of the present invention, the acid leaching unit further includes an acid leaching residue storage tank, which is connected to the acid leaching solid-liquid separation device for collecting and temporarily storing the acid leaching residue solid residue.

[0096] According to some embodiments of the present invention, the system further includes a calcium removal unit connected in communication with the solid-liquid separation device.

[0097] According to some embodiments of the present invention, the calcium removal unit includes a calcium removal vessel and a calcium removal solid-liquid separation device connected in sequence with the solid-liquid separation device.

[0098] According to some embodiments of the present invention, the calcium removal unit further includes a calcium carbonate temporary storage tank, and the calcium carbonate temporary storage tank is connected to the calcium removal solid-liquid separation device.

[0099] According to some embodiments of the present invention, the system further includes a deep impurity removal unit connected to the calcium removal unit.

[0100] According to some embodiments of the present invention, the deep impurity removal unit includes a resin adsorption unit connected to the calcium removal solid-liquid separation device.

[0101] According to an embodiment of the fourth aspect of the present invention, an application of the method is provided in the recycling of lithium-ion batteries.

[0102] Since the lithium-ion battery recycling method adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0103] At this point, the lithium-containing solution is a lithium-ion battery leaching solution.

[0104] According to an embodiment of the fifth aspect of the present invention, the application of the lithium purification solution is provided in the preparation of lithium carbonate for lithium-ion batteries.

[0105] Because the lithium purification solution has high purity, it can produce high-purity lithium carbonate suitable for use in lithium-ion batteries.

[0106] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0107] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0108] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0109] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0110] Figure 1 This is a flowchart of Embodiment 1 of the present invention.

[0111] Figure 2 This is a schematic diagram of the system used in Embodiment 1 of the present invention.

[0112] Figure label:

[0113] Grinding unit 100;

[0114] Calcination unit 200, calcination exhaust valve 211;

[0115] Acid leaching unit 300, acid leaching reactor 310, acid leaching exhaust valve 311, acid leaching solid-liquid separation device 320, acid leaching residue temporary storage tank 330;

[0116] Stirring vessel 410, stirring vessel exhaust valve 411, thermometer 412; solid-liquid separation device 420; calcium-magnesium slag temporary storage tank 430;

[0117] Calcium removal unit 500, calcium removal kettle 510, calcium removal solid-liquid separation device 520, calcium carbonate temporary storage tank 530;

[0118] Exhaust gas absorption tank 600;

[0119] Filter element 700;

[0120] Pipeline 800. Detailed Implementation

[0121] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0122] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0123] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0124] Unless otherwise specified, in the specific implementation method, the concentration of sulfate ions is determined by barium sulfate titration, and the concentration of metal ions is obtained by ICP-OES.

[0125] Example 1

[0126] refer to Figure 2 This embodiment provides a system for implementing a method for removing impurities from lithium-containing wastewater. The system specifically includes:

[0127] The system comprises, via pipeline 800, a grinding unit 100, a roasting unit 200, an acid leaching unit 300, a stirring tank 410, a solid-liquid separation device 420, and a calcium removal unit 500, all connected in sequence; a tail gas absorption tank 600 for absorbing tail gas; and a calcium-magnesium slag temporary storage tank 430 for storing the solid slag produced by the solid-liquid separation device 420.

[0128] The roasting unit 200 is equipped with a roasting exhaust valve 211, and the end of the roasting exhaust valve 211 is equipped with a filter element 700. The roasting exhaust valve 211 is connected to the exhaust gas absorption tank 600 via a pipe 800.

[0129] The acid leaching unit 300 includes an acid leaching reactor 310, an acid leaching solid-liquid separation device 320, and an acid leaching residue storage tank 330, which are connected in sequence via a pipeline 800. The acid leaching reactor 310 is connected to the roasting unit 200 and is used to acid leach the roasting product of the roasting unit 200. It is equipped with an acid leaching exhaust valve 311 for introducing the gas generated by acid leaching into the tail gas absorption tank 600. The end of the acid leaching exhaust valve 311 is equipped with a filter element 700. The liquid phase generated by the acid leaching solid-liquid separation device 320 flows into the stirring tank 410, and the solid phase is transferred to the acid leaching residue storage tank 330.

[0130] The stirred tank 410 is equipped with a stirred tank exhaust valve 411 and a thermometer 412. The stirred tank exhaust valve 411 is connected to the tail gas absorption tank 600, and a filter element 700 is provided at the end of the stirred tank exhaust valve 411. The stirred tank 410 is equipped with a pneumatically controlled sealing cover to facilitate its opening and closing.

[0131] The liquid phase generated by the solid-liquid separation device 420 is transferred to the calcium removal unit 500, and the solid phase generated is transferred to the calcium-magnesium slag temporary storage tank 430.

[0132] The calcium removal unit 500 includes a calcium removal vessel 510, a calcium removal solid-liquid separation device 520, and a calcium carbonate temporary storage tank 530 connected in sequence. The liquid generated by the calcium removal solid-liquid separation device 520 flows directly out of the system to produce lithium salt as a lithium purification solution, or is further purified by resin. The solid phase generated by the calcium removal solid-liquid separation device 520 is transferred to the calcium carbonate temporary storage tank 530.

[0133] Example 2

[0134] refer to Figure 2 The flowchart shown illustrates a method for removing impurities from lithium-containing solutions. This embodiment uses the system shown in Example 1 to provide a method for removing impurities from lithium-containing solutions. The method is as follows:

[0135] S1. Mix and grind lepidolite and sodium sulfate at a mass ratio of 5:1 until they can pass through a 100-mesh sieve;

[0136] S2. The mixture obtained in step S1 is subjected to salt-added roasting; the specific constant temperature is 980℃, the constant temperature time is 2h, the heating rate is 3℃ / min, the atmosphere is dry air, and after naturally cooling to room temperature, proceed to the next step.

[0137] S3. The roasted product obtained in step S2 and water are mixed into a slurry at a solid-liquid ratio of 1:4. Then, 98% sulfuric acid is added for acid leaching, wherein the amount of sulfuric acid added is 1.1 times the theoretical amount, and the acid leaching time is 5 hours.

[0138] The mixture after acid leaching is subjected to solid-liquid separation (pressure filtration), and the resulting liquid phase (lithium-containing solution) proceeds to the next step.

[0139] S4. The concentrations of magnesium ions and sulfate ions in the lithium-containing solution obtained in step S3 were tested, showing a high concentration of sulfate ions. Calcium oxide was prepared at 1.1 times the molar amount of sulfate ions.

[0140] The calcium oxide and lithium-containing solution were sealed and mixed until the overall temperature began to drop, which took about 1.5 hours (mixing stage). The mixture was then stirred at 150 rpm and aged in a sealed environment for 8 hours (first stage aging). Finally, the mixture was aged in an open environment for 1 hour while maintaining the stirring speed (second stage aging).

[0141] The mixture was separated into solid and liquid phases by pressure filtration to obtain the liquid phase.

[0142] S5. Remove impurities from the liquid phase to obtain a purified lithium solution. Specifically, analyze the concentration of calcium ions in the obtained liquid phase, add 1.02 molar amounts of sodium carbonate, and then perform solid-liquid separation to obtain a purified lithium solution.

[0143] Example 3

[0144] This embodiment provides a method for removing impurities from a lithium-containing solution, which differs from Embodiment 2 in that:

[0145] In step S4, the calcium compound used is calcium hydroxide.

[0146] Example 4

[0147] This embodiment provides a method for removing impurities from a lithium-containing solution, which differs from Embodiment 2 in that:

[0148] In step S4, calcium oxide is prepared according to 1.25 molar amounts of sulfate.

[0149] Example 5

[0150] This embodiment provides a method for removing impurities from a lithium-containing solution, which differs from Embodiment 2 in that:

[0151] In step S5, sodium carbonate is replaced with an equal amount of carbon dioxide.

[0152] Comparative Example 1

[0153] This comparative example provides a method for removing impurities from a lithium-containing solution, which differs from Example 2 in that:

[0154] In step S4, calcium oxide is prepared at 1.1 times the molar amount of magnesium ions;

[0155] A sulfate removal step is added between step S4 and step S5. Specifically, the amount of sulfate in the liquid phase obtained in step S4 is tested, and calcium chloride with 1.1 molar amount of sulfate is added. After the reaction is complete, solid-liquid separation is performed, and the resulting liquid phase enters step S5.

[0156] Comparative Example 2

[0157] This comparative example provides a method for removing impurities from a lithium-containing solution, which differs from Comparative Example 1 in that:

[0158] In step S4, calcium oxide is replaced with an equal amount of calcium hydroxide.

[0159] Comparative Example 3

[0160] This comparative example provides a method for removing impurities from a lithium-containing solution, which differs from Example 2 in that:

[0161] In step S4, calcium oxide is prepared according to 1.35 times the molar amount of sulfate.

[0162] Comparative Example 4

[0163] This comparative example provides a method for removing impurities from a lithium-containing solution, which differs from Example 2 in that:

[0164] In step S4, calcium oxide is prepared according to a 1 molar amount of sulfate.

[0165] Test case

[0166] This example tested the components of the lithium-containing solution entering step S4, the liquid phase entering step S5, and the lithium purification solution obtained in step S5 in Examples 2-5 and Comparative Examples 1-4. The test results are shown in Table 1.

[0167] Table 1 shows the processes and final results obtained in Examples 2-5 and Comparative Examples 1-4.

[0168]

[0169] The results in Table 1 show that the method provided by the present invention hardly loses the concentration of lithium ions during the process and can significantly reduce impurities such as calcium, magnesium, sulfate, and sodium ions in the lithium purification solution.

[0170] A comparison of Examples 2 and 3 shows that changing the type of calcium compound has little impact on the results. However, when calcium oxide is used, the reaction generates a large amount of heat, which affects the solubility of each component, resulting in a slight difference in the composition of the solution entering step S5.

[0171] A comparison of Examples 2 and 4 shows that, within the scope provided by the present invention, increasing the amount of calcium compound can reduce the concentration of magnesium and sulfate, but will slightly increase the calcium content.

[0172] A comparison of Example 2 and Comparative Example 1 shows that the two-step method for removing magnesium and sulfate has a similar removal effect to that of this application. However, it increases the number of steps and costs, and the concentration of calcium ions in the liquid phase entering step S5 is significantly increased, which puts a burden on subsequent deep impurity removal.

[0173] Comparing Examples 1 and 2, it can be seen that sodium hydroxide and calcium hydroxide have similar magnesium removal effects, but this will further increase the sodium ion impurity content in the liquid phase entering step S5.

[0174] As can be seen from the comparison between Example 2 and Comparative Examples 3-4, if the amount of calcium compound used is not within the range required by the present invention, the impurity content in the lithium purification solution will be significantly increased.

[0175] In summary, the method provided by this invention, through the control of parameters and conditions, can achieve deep purification of lithium-containing solutions in a simple process. The resulting purified lithium solution also meets the requirements for the preparation of battery-grade lithium salts, possessing high economic value. Furthermore, due to the similarity of the process, the method provided by this invention is also expected to find wide application in lithium-ion battery recycling.

[0176] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for removing impurities from a lithium-containing solution, characterized in that, The method includes reacting the lithium-containing solution with a calcium compound followed by solid-liquid separation. The method for obtaining the lithium-containing solution includes roasting lithium ore with added salt and leaching the roasted product with acid; the salt used is sodium sulfate, and the mass ratio of the salt used to the lithium ore is 1:2~10; the lithium ore includes at least one of spodumene, petalite, lepidolite, ferromagnetic mica, and phosphogypsum. The calcium compound includes at least one of calcium oxide and calcium hydroxide; The lithium-containing solution also contains impurities such as magnesium ions and sulfate ions; The molar ratio of the magnesium ion and sulfate ion with the larger amount to the calcium compound is 1:1.05~1.3; The reaction between the lithium-containing solution and the calcium compound includes sequential mixing, a first stage of aging, and a second stage of aging.

2. The method according to claim 1, characterized in that, The method further includes removing calcium from the liquid phase obtained from the solid-liquid separation.

3. The method according to claim 1, characterized in that, The reaction time between the lithium-containing solution and the calcium compound is 5-15 hours.

4. The application of the method as described in any one of claims 1 to 3 in the recycling of lithium-ion batteries.

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