Battery-grade lithium carbonate and a method for preparing the same

Abstract

The application provides a battery-grade lithium carbonate and a preparation method thereof, wherein the preparation method comprises the following steps: lithium carbonate slurry preparation, lithium carbonate causticization, high-temperature calcination of causticization residues to generate calcium carbonate, calcium removal from the causticization liquid, fluorine removal, carbonization and crude lithium carbonate refining, and finally, the crude lithium carbonate is washed, dried, crushed, iron-removed, packaged and battery-grade lithium carbonate is obtained. The preparation method uses calcium oxide or calcium hydroxide to remove sulfate, avoids the formation of barium sulfate precipitate by using barium salt, and avoids the filtration problem; the generated causticization residues are calcined again, the generated calcium oxide can be recycled, and the generated carbon dioxide gas can be used for synthesizing lithium carbonate, thereby reducing the amount of raw materials and realizing the rational utilization of resources; no mother liquor treatment is needed, after lithium carbonate synthesis, solid-liquid separation is performed, the mother liquor is a sodium carbonate solution, can be used for the previous process of industrial lithium carbonate preparation, and is used for adjusting pH, thereby realizing the maximum utilization of resources.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery-grade lithium carbonate, and particularly to a battery-grade lithium carbonate and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have become the first choice of power supply for digital, communication, aviation, portable electronic products and the like due to high specific energy, long service life, high rated voltage, high power bearing capacity, low self-discharge rate, light weight, strong adaptability to high and low temperature and the like. With the popularization and application of lithium ion batteries in power automobiles and high-power energy storage facilities, the demand for lithium ion batteries is increasing.

[0003] Among them, lithium carbonate as the core of the positive material, the demand is also growing, and the demand is also increasing, and the industrial-grade lithium carbonate has been unable to meet the demand of power batteries. Further purification of crude lithium carbonate to battery-grade lithium carbonate is a problem to be solved at present. However, the raw material lithium carbonate contains impurities, including sulfate, calcium ions, and magnesium, sodium and hydrochloric acid insoluble substances. Since it is a sulfuric acid system, it is easy to cause the sulfate to be wrapped during the synthesis of lithium carbonate, resulting in incomplete washing of the sulfate. At the same time, the calcium ions in the impurities will form calcium carbonate precipitate with excess carbonate in the synthesis of lithium carbonate, so the synthesized lithium carbonate will be mixed with calcium carbonate precipitate. Based on this problem, the present application provides a new battery-grade lithium carbonate and a preparation method thereof. SUMMARY

[0004] Based on the above description, the present application provides a battery-grade lithium carbonate and a preparation method thereof to solve the technical problem that the performance of lithium carbonate is affected by the excessive impurities such as calcium, magnesium, sodium, sulfate and hydrochloric acid insoluble substances in the raw material lithium carbonate in the prior art.

[0005] The technical solution of the present application to solve the above technical problem is as follows:

[0006] In a first aspect, the present application provides a preparation method of battery-grade lithium carbonate, comprising the following steps:

[0007] Step (1): Lithium carbonate slurry preparation; lithium carbonate and pure water are mixed in a certain proportion to obtain a slurry, which is stirred for use;

[0008] Step (2): Lithium carbonate causticization; calcium oxide or calcium hydroxide powder is added to the slurry obtained in step (1) for causticization reaction, and after solid-liquid separation, causticization liquid and causticization residue are obtained;

[0009] Step (3): High-temperature calcination of calcium carbonate in causticization residue; the causticization residue obtained in step (2) is dried and high-temperature calcined to obtain calcium oxide and carbon dioxide gas. The calcium oxide is reused in step (2) for causticization reaction, and the purified carbon dioxide gas is reserved;

[0010] Step (4): calcium removal from caustic liquor; a calcium removal agent is added to the caustic liquor obtained in step (2) to control the reaction temperature at 50-70 DEG C, and the reaction time is 1-2 h, and solid-liquid separation is performed to obtain calcium-removed liquor;

[0011] Step (5): fluorine removal; a fluorine removal agent is added to the calcium-removed liquor obtained in step (4) to perform reaction, and solid-liquid separation is performed after the reaction to obtain fluorine-removed liquor;

[0012] Step (6): carbonization; the fluorine-removed liquor obtained in step (5) is pumped into a carbonization kettle, and carbon dioxide gas is introduced to perform carbonization reaction, wherein the carbon dioxide is the purified carbon dioxide gas in step (3);

[0013] Step (7): purification of crude lithium carbonate; the slurry obtained after the carbonization reaction is filtered to obtain crude lithium carbonate and mother liquor, the mother liquor is sodium carbonate solution, and the crude lithium carbonate is washed, dried, crushed, iron-removed and packaged to obtain battery-grade lithium carbonate.

[0014] On the basis of the above technical solution, the application can also be improved as follows.

[0015] Further, in step (1), the slurry preparation conditions of lithium carbonate are as follows: the solid-liquid mass ratio of lithium carbonate and pure water is controlled to be 1:(5-10), and after mixing, the stirring is performed at 300-350 rpm for 5-10 min.

[0016] Further, in step (2), the causticization reaction conditions are as follows: the reaction temperature is controlled to be 80-90 DEG C, the stirring intensity is 400-600 rpm, and the reaction time is 90-180 min.

[0017] Further, the caustic liquor includes LiOH, NaOH, Ca(OH)2 and CaSO4.

[0018] The caustic residue includes CaCO3, CaSO4, unreacted Mg(OH)2, hydrochloric acid insoluble substance and the mixed LiOH.

[0019] Further, in step (3), the calcination temperature of high-temperature calcination is 1000-1200 DEG C.

[0020] Further, in step (4), the addition amount of the calcium removal agent is 2.05-2.1 times of the amount of substance of calcium ions in the solution.

[0021] The calcium removal agent is one of NaF, KF, NH4F and LiF.

[0022] Further, in step (5), the fluorine removal agent is a strong alkaline anion exchange resin fluorine removal agent, and the amount of the fluorine removal agent is 0.2-0.5% of the mass of the solution.

[0023] The reaction conditions of the defluorination reaction are: a reaction temperature of 50 DEG C, and a reaction time of 45-90 min.

[0024] Further, in step (6), the reaction conditions of the carbonization reaction are: a reaction pressure of 1.5-2.5 MPa, a reaction temperature of 80-95 DEG C, a CO2 feeding speed of 50-100 L / h, and a stirring speed of 300-400 rpm.

[0025] In a second aspect, the present application also provides battery-grade lithium carbonate prepared by the preparation method of battery-grade lithium carbonate according to the first aspect.

[0026] Compared with the prior art, the technical scheme of the present application has the following beneficial technical effects:

[0027] Compared with the prior art, the preparation method of battery-grade lithium carbonate provided by the present application has the following advantages:

[0028] 1. The preparation method uses calcium oxide or calcium hydroxide to remove sulfate, avoiding the formation of barium sulfate precipitate by using barium salt, since the barium sulfate precipitate particles are very small, filtration is very difficult, and the use of calcium oxide or calcium hydroxide for impurity removal can avoid the filtration problem.

[0029] 2. The preparation method does not use carbonic acid hydrogenation and pyrolysis process, since the solubility of lithium bicarbonate is not large, a large amount of mother liquor will be formed during pyrolysis, the amount of mother liquor to be treated is extremely large, and the efficiency is low, the carbonization effect of the method is better, and the efficiency is higher.

[0030] 3. The preparation method recalcines the generated causticizing residue, the generated calcium oxide can be recycled, and the generated carbon dioxide gas can be used for synthesizing lithium carbonate, reducing the amount of raw materials, and realizing rational utilization of resources.

[0031] 4. The preparation method does not have mother liquor treatment, after lithium carbonate is synthesized, solid-liquid separation is performed, the mother liquor is a sodium carbonate solution, can be used for the previous process of industrial lithium carbonate preparation, and is used for adjusting pH, thereby realizing maximum utilization of resources.

[0032] 5. The preparation method converts lithium carbonate into lithium hydroxide during causticization, and easily realizes magnesium-lithium separation. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 A flowchart of the preparation method of battery-grade lithium carbonate provided by the embodiment of the present application is shown in the figure.

[0034] Figure 2 A process flowchart of the preparation method of battery-grade lithium carbonate provided by the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0035] For the purpose of promoting the understanding of the present application, the present application will be more fully described by reference to the following drawings. The following drawings are presented to illustrate embodiments of the present application. The present application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. In the drawings, the same reference numbers indicate similar or corresponding features.

[0036] The present application will be further described in detail with reference to the following Figure 1 , accompanying drawings and examples, which are presented for the purpose of Figure 2 illustrating the present application and are not intended to limit the present application in any way.

[0037] The present application provides a preparation method of battery-grade lithium carbonate, which specifically comprises the following steps:

[0038] Step S1, slurry preparation of lithium carbonate

[0039] The lithium carbonate and pure water are mixed, and the solid-liquid mass ratio of the lithium carbonate and the water is controlled to be 1:(5-10). The stirring is performed at 300-350 rpm for 5-10 min. The specific values can be set according to actual needs, and the slurry preparation of lithium carbonate can be realized under the conditions in this range.

[0040] The raw material lithium carbonate includes industrial-grade lithium carbonate and crude lithium carbonate.

[0041] The raw material lithium carbonate includes lithium carbonate with a main content of 80-99.2%, sulfate with a content of not more than 3%, sodium ions with a content of not more than 2%, calcium ions with a content of not more than 1%, magnesium ions with a content of not more than 2%, and hydrochloric acid insolubles with a content of not more than 0.5%.

[0042] Table 1 Chemical composition of raw material lithium carbonate product

[0043]

[0044]

[0045] Step S2, causticization of lithium carbonate

[0046] Calcium oxide or calcium hydroxide powder is added to the slurry obtained in step S1 to perform a causticization reaction. In a specific example, calcium oxide is preferred here, wherein the amount of calcium oxide powder added is 1.05-1.2 times the sum of the amounts of CO3 2- and SO4 2- in the slurry. The reaction temperature is controlled to be 80-90℃, the stirring intensity is controlled to be 400-600 rpm, and the reaction time is controlled to be 90-180 min. Solid-liquid separation is performed to obtain a causticization liquid and a causticization residue.

[0047] The caustic liquor comprises LiOH, NaOH, a small amount of Ca(OH)2 and a small amount of CaSO4; the caustic residue comprises CaCO3, CaSO4, unreacted Mg(OH)2, hydrochloric acid insoluble matter and impurities of LiOH.

[0048] The caustic residue is directly calcined at high temperature without washing, and the lithium therein is not lost because the calcined residue is reused. The reaction occurring in step S2 is:

[0049] CaO + H2O = Ca(OH)2

[0050] Li2CO3 + Ca(OH)2 = CaCO3↓ + 2LiOH

[0051] Na2SO4 + Ca(OH)2 = CaSO4↓ + 2NaOH

[0052] Step S3, high-temperature calcination of the caustic residue to obtain calcium carbonate

[0053] The caustic residue is dried and then put into a furnace for high-temperature calcination, with the calcination temperature being controlled at 1000-1200℃, to obtain calcium oxide and carbon dioxide gas. At this time, the carbon dioxide gas contains a small amount of sulfur dioxide gas.

[0054] The obtained solid calcium oxide can be reused in step S2 for caustic reaction; the carbon dioxide gas is passed through a saturated sodium bicarbonate solution to absorb the sulfur dioxide gas, and then the purified carbon dioxide gas is introduced into a CO2 high-pressure storage tank for standby use. The reaction occurring in step S3 is:

[0055]

[0056]

[0057]

[0058]

[0059] 2N a HCO3 + SO2 = Na2SO3 + H2O + 2CO2 (CO2 purification)

[0060] Step S4, calcium removal from the caustic liquor

[0061] A calcium removal agent is added to the caustic liquor, wherein the calcium removal agent is one of NaF, KF, NH4F and LiF, and LiF is preferred (because LiF has low solubility, it can not only remove calcium but also reduce the introduction of F ions). The amount of the calcium removal agent added is 2.05-2.1 times the amount of substance of calcium ions in the solution, the reaction temperature is controlled at 50-70℃, the reaction time is 1-2h, and solid-liquid separation is performed to obtain a calcium-removed liquor.

[0062] Step S5, fluoride removal

[0063] A fluoride removal agent is added to the above calcium removal solution for reaction. The fluoride removal agent is a strong alkaline anion exchange resin fluoride removal agent, which can effectively remove fluoride from the solution in an alkaline environment. The amount of fluoride removal agent is 0.2-0.5% of the mass of the solution, the reaction temperature is 50°C, the reaction time is controlled to be 45-90 min, and solid-liquid separation is performed to obtain a fluoride removal solution.

[0064] Step S6, carbonization

[0065] The above fluoride removal solution is fed into a carbonization kettle for carbonization reaction. The carbonization kettle is provided with a stirring mechanism having two layers of paddles, a turbine type blade at the lower part and a propeller type blade at the upper part. The bottom part is provided with a discharge port and six CO2 gas inlets, and the top part is provided with a feeding port, an observation port, a pressure relief port and a CO2 gas outlet. The reaction kettle is a closed pressure reaction kettle. During operation, CO2 gas is introduced from the gas inlet pipe, and the CO2 gas rises in the kettle body and is fully refined into bubbles under the action of the paddles at each layer, thereby increasing the contact area between the CO2 gas and the liquid and improving the gas-liquid contact, so as to accelerate the carbonization reaction process. The unreacted CO2 gas is discharged from the CO2 gas outlet to a CO2 gas pressure storage tank for recycling.

[0066] According to the process safety and the variation curve of the solubility of CO2 in water with pressure and temperature, the reaction conditions of this process are as follows: the carbonization reaction pressure is controlled to be 1.5-2.5 MPa, and the reaction temperature is controlled to be 80-95°C. The purpose of controlling the high temperature reaction is to reduce the solubility of Li2CO3 and improve the yield, and to prevent the generated Li2CO3 and CO2 from further undergoing a bicarbonate reaction to generate lithium bicarbonate. The introduction speed of CO2 is controlled to be 50-100 L / h, the stirring speed is 300-400 rpm, and after 1.0 h of reaction, the lithium content in the solution is detected by sampling. When the lithium content is less than 3 g / L, the carbonization reaction is stopped, or the reaction can also be terminated according to the pH of the solution. The chemical reactions are as follows:

[0067] 2LiOH + CO2 = Li2CO3 + H2O

[0068] Li2CO3 + CO2 + H2O = 2LiHCO3

[0069]

[0070] 2NaOH + CO2 = Na2CO3 + H2O

[0071] Na2CO3 + CO2 + H2O = 2NaHCO3

[0072]

[0073] Step S7, purification of crude lithium carbonate

[0074] The slurry is filtered to obtain crude lithium carbonate and a mother liquor, which is a Na2CO3 solution and can be used in the previous process of industrial lithium carbonate preparation for adjusting pH, and the crude lithium carbonate is washed, dried, crushed, de-ironed and packaged to obtain battery-grade lithium carbonate.

[0075] The following provides comparative data of Examples 1 to 3 to further support the technical effects of the present application. The specific example data is shown in Tables 2 and 3:

[0076] Table 2: Specific example data

[0077]

[0078]

[0079] Table 3: Chemical composition of battery-grade lithium carbonate

[0080]

[0081] In summary, it can be seen from the above tables that the Li2CO3 content of the battery-grade lithium carbonate prepared by the embodiments of the present application is higher than the standard YS / T 582-201, and can reach more than 99.7%, and the impurity content is much lower than the standard. Therefore, the battery-grade lithium carbonate prepared by the preparation method of the present application meets the national standard requirements of battery-grade lithium carbonate, and has the following advantages compared with the prior art:

[0082] 1. The preparation method uses calcium oxide or calcium hydroxide to remove sulfate, avoiding the use of barium salt to form barium sulfate precipitate. Since the barium sulfate precipitate particles are very small, it is very difficult to filter. Using calcium oxide or calcium hydroxide to remove impurities can avoid the difficulty of filtration.

[0083] 2. The preparation method does not use carbonation and pyrolysis processes. Since the solubility of lithium bicarbonate is not large, a large amount of mother liquor will be formed during pyrolysis, which requires a large amount of treatment and has low efficiency. The carbonation effect of this method is better and more efficient.

[0084] 3. The preparation method recalcines the generated causticizing residue, the generated calcium oxide can be recycled, and the generated carbon dioxide gas can be used to synthesize lithium carbonate, reducing the amount of raw materials and realizing the rational utilization of resources.

[0085] 4. The preparation method does not have mother liquor treatment. After the synthesis of lithium carbonate, solid-liquid separation is performed, and the mother liquor is a sodium carbonate solution, which can be used in the previous process of industrial lithium carbonate preparation for adjusting pH, and realizes the maximum utilization of resources.

[0086] 5. The preparation method converts lithium carbonate into lithium hydroxide in the caustic process, easily realizing magnesium-lithium separation.

[0087] In the description of the present specification, the description referring to the terms "specific example" or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example.

[0088] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for producing battery-grade lithium carbonate, characterized by, The method comprises the following steps: Step (1): lithium carbonate slurry; mixing lithium carbonate and pure water in proportion to obtain a slurry, stirring for use; Step (2): lithium carbonate causticization; adding calcium oxide or calcium hydroxide powder to the slurry obtained in step (1) to perform causticization reaction, and after solid-liquid separation, a causticizing liquid and a causticizing residue are obtained; Step (3): high-temperature calcination of causticizing residue calcium carbonate; the causticizing residue obtained in step (2) is dried and high-temperature calcined, the calcination temperature is 1000-1200℃, calcium oxide and carbon dioxide gas are obtained, the calcium oxide is reused in step (2) to continue the causticization reaction, and the purified carbon dioxide gas is reserved; Step (4): calcium removal from causticizing liquid; adding a calcium removal agent to the causticizing liquid obtained in step (2) to control the reaction temperature to 50-70℃, the reaction time is 1-2h, and solid-liquid separation is performed to obtain a calcium removal liquid, wherein the calcium removal agent is one of NaF, KF, NH4F and LiF, and the addition amount of the calcium removal agent is 2.05-2.1 times the amount of substance of calcium ions in the solution; Step (5): fluorine removal; adding a fluorine removal agent to the calcium removal liquid obtained in step (4) to perform reaction, the fluorine removal agent is a strong alkaline anion exchange resin fluorine removal agent, the amount of the fluorine removal agent is 0.2-0.5% of the mass of the solution, the reaction conditions of the fluorine removal are: the reaction temperature is 50℃, the reaction time is controlled to 45-90min, and after the reaction, solid-liquid separation is performed to obtain a fluorine removal liquid; Step (6): carbonization; the fluorine removal liquid obtained in step (5) is pumped into a carbonization kettle, and carbon dioxide gas is introduced to perform carbonization reaction, wherein the carbon dioxide is the purified carbon dioxide gas in step (3); Step (7): crude lithium carbonate refining; filtering the slurry obtained after the carbonization reaction to obtain crude lithium carbonate and a mother liquor, the mother liquor is a sodium carbonate solution, and the crude lithium carbonate is washed, dried, crushed, iron removed and packaged to obtain battery-grade lithium carbonate.

2. The method of producing battery-grade lithium carbonate according to claim 1, characterized by, In step (1), the conditions for lithium carbonate slurry are: the solid-liquid mass ratio of lithium carbonate and pure water is controlled to be 1:(5-10), after mixing, stirring is performed at 300-350rpm for 5-10min.

3. The method of claim 1, wherein the battery-grade lithium carbonate is prepared by the steps of: In step (2), the conditions for causticization reaction are: the reaction temperature is controlled to be 80-90℃, the stirring intensity is 400-600rpm, and the reaction time is 90-180min. ​ 4. The method of producing battery-grade lithium carbonate according to claim 3, characterized by, The causticizing liquid comprises LiOH, NaOH, Ca(OH)2 and CaSO4; The causticizing residue comprises CaCO3, CaSO4, unreacted Mg(OH)2, hydrochloric acid insoluble substance and impurities LiOH.

5. The method of claim 1, wherein the battery-grade lithium carbonate is prepared by the steps of: In step (6), the reaction conditions for carbonization reaction are: the reaction pressure is controlled to be 1.5-2.5Mpa, the reaction temperature is 80-95℃, the introduction speed of CO2 is controlled to be 50-100L / h, and the stirring speed is 300-400rpm. ​

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