A process for directly producing battery-grade lithium carbonate from lithium iron phosphate powder

Abstract

The present application relates to a kind of lithium phosphate iron powder direct production battery-grade lithium carbonate production process, the process includes the following steps: pure water is added to the slurry of lithium phosphate iron powder, after slurry is completed, sulfuric acid, hydrogen peroxide, and leaching reaction is carried out;Leaching process produces leaching liquor, and sodium hydroxide solution is added to adjust pH and iron sulfate to remove phosphorus;After phosphorus removal, liquid is added under acidic conditions Barium sulfide, effectively remove metal ion impurities, after reaction is completed, liquid alkali is added to adjust pH, then it is filtered by filter press, after pressure filtration, resin is removed to remove calcium, magnesium impurities, then it is removed by pipeline magnetism device, finally it is transferred into first lithium precipitation reaction tank;Add purified saturated sodium carbonate solution after calcium and magnesium removal, insoluble matter removal, magnetic removal to lithium carbonate, lithium carbonate is filtered into filter press and is washed with water machine filter cake, after washing, filter cake is discharged to slurry tank and is slurried with pure water, then it is centrifuged by centrifuge, and battery-grade lithium carbonate is obtained.The present application reduces the process input of carbonization tower and carbon dioxide gas added in secondary purification process, not only reduces large amount of equipment capital investment, but also simplifies process flow, improves recovery efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium carbonate batteries, and particularly relates to a production process for directly producing battery-grade lithium carbonate from lithium iron phosphate powder. BACKGROUND

[0002] With the promotion and popularization of electric vehicles in China, the demand for power battery manufacturing materials cannot meet the supply, leading to a rapid increase in the price of battery materials. The service life of power batteries is 5-10 years, and many power batteries face the problem of retirement. Power batteries have great recycling value, and therefore battery material recycling enterprises are growing rapidly. However, the recycling enterprises have the problems of low recovery rate of valuable metals, serious environmental pollution, and high environmental treatment cost, and therefore it is a common problem for the enterprises to improve the recovery rate of valuable metals of battery materials and reduce the production cost.

[0003] The lithium carbonate recovered by the prior art once-lithium precipitation is industrial-grade lithium carbonate, and the qualified battery-grade lithium carbonate can be prepared only after a carbonization purification process. However, the sodium ions, sulfate ions and insoluble substances are over standard in the once-lithium precipitation process, and therefore the battery-grade lithium carbonate can be obtained by removing these impurities before lithium precipitation. SUMMARY

[0004] In view of the problems in the prior art, in order to solve the above defects of the prior art, the application provides a production process for directly producing battery-grade lithium carbonate from lithium iron phosphate powder.

[0005] The technical scheme of the application is as follows:

[0006] The production process for directly producing battery-grade lithium carbonate from lithium iron phosphate powder comprises the following steps:

[0007] (1) Leaching: pure water is added to slurry the lithium iron phosphate powder, and sulfuric acid and hydrogen peroxide are added after the slurry is completed to perform a leaching reaction;

[0008] (2) Phosphorus removal: sodium hydroxide solution is added to the leaching solution produced in the leaching process to adjust the pH and perform phosphorus removal with iron sulfate;

[0009] (3) Impurity removal: barium sulfide is added to the solution after phosphorus removal under acidic conditions to effectively remove metal ion impurities, liquid alkali is added to adjust the pH after the reaction is completed, then the solution is filtered by a filter press, the filtered solution is subjected to resin treatment to remove calcium and magnesium impurities, then the solution is subjected to pipeline magnetic removal, and finally the solution is transferred into a once-lithium precipitation tank;

[0010] (4) Once-lithium precipitation: the purified saturated sodium carbonate solution after calcium and magnesium removal, insoluble substance removal and magnetic removal is added to the solution after impurity removal to produce lithium carbonate, the lithium carbonate is filtered by a filter press and washed with a pure water machine, the washed filter cake is discharged to a slurry tank to be slurry with pure water, then the slurry is centrifuged by a centrifuge to obtain battery-grade lithium carbonate;

[0011] (5) Sodium sulfate production: the once lithium mother liquor, machine washing lithium water, centrifugal washing lithium water into the sodium sulfate production process, and the crystallization mother liquor returns to the impurity removal process.

[0012] In the step (1), the lithium iron phosphate powder comprises the following components in terms of mass fraction: Li 4.59%, Fe 35.54%, P 18.68%, Al 0.35%, Ni 0.32%, Co 0.09%, and Mn 0.08%.

[0013] Preferably, in the step (1), the lithium iron phosphate powder and pure water are slurried at a solid-liquid ratio of 1: (1-2) to the lithium iron phosphate powder, the mass ratio of the lithium iron phosphate powder to 98% sulfuric acid is (3.5-4.5):1, and the mass ratio of the lithium iron phosphate powder to hydrogen peroxide is (7-9):1, and the terminal pH of the leaching reaction is 1.5-2.5.

[0014] Preferably, the step (2) is specifically operated as follows: the leaching filtrate obtained by leaching pressure filtration flows into a phosphorus removal reaction tank, stirring is started, sodium hydroxide solution is added to adjust pH=3.5-4, steam is started to heat, the temperature is kept at 80-85℃, pressure filtration is performed after reaction, the phosphorus-removed liquid obtained by pressure filtration flows into a impurity removal reaction tank, and the filter residue is discharged and stored after the residue is discharged. The terminal pH, P≤0.001g / L, and Fe≤0.001g / L are controlled. Too high temperature causes energy waste, and too low temperature affects the phosphorus removal effect. Too much addition of solid ferric sulfate causes waste of auxiliary materials and too much residue, and too little addition affects the phosphorus removal effect and product quality. Too high or too low terminal pH can cause poor phosphorus removal effect.

[0015] Preferably, in the step (2), the solid ferric sulfate is added to the tank at 1.1-1.4 times the theoretical consumption amount according to the phosphorus content in the solution.

[0016] Preferably, in the step (2), the sodium hydroxide solution is added to adjust pH=3.8, and the terminal pH, P≤0.001g / L, and Fe≤0.001g / L are controlled.

[0017] The addition amount of ferric sulfate is calculated according to the content of hydrogen phosphate:

[0018] ,

[0019] ,

[0020] Preferably, in the step (3), 1-1.3 times the theoretical consumption of barium sulfide is added to the tank, barium sulfide is added to the phosphorus-removed liquid at pH=3-4 to effectively remove metal ion impurities, liquid alkali is added to adjust pH=11-12 after the reaction is completed, and the pH is stabilized for 25-35 min.

[0021] Preferably, in the step (3), the added amount of the theoretically consumed barium sulfide is determined according to the concentrations of Ni, Co, Mn, Cu, Ca, Mg, SO4 2- in the solution.

[0022] Preferably, in the step (3), the concentrations of Ni, Co, Mn, Cu, Ca, Mg, SO4 2- ≤0.001 g / L, Li + ≥20 g / L in the solution after the impurity removal are controlled.

[0023] Preferably, the step (4) specifically comprises the following: a sodium carbonate solution purification: the sodium carbonate solution is subjected to a resin column, a precision filter and a pipeline magnetic eliminator to obtain a sodium carbonate solution with Ca and Mg ≤0.001 g / L; b a lithium precipitation reaction: the solution after the impurity removal is stirred, the solution is heated, and the sodium carbonate solution is added to obtain lithium carbonate; c the lithium carbonate is fed into a pressure filter and washed with a pure water machine, the washed filter cake is discharged to a slurry tank, and pure water is added for slurry, then the slurry is centrifuged by a centrifuge, and after the centrifugation, the battery-grade lithium carbonate is obtained by washing with pure water, and the lithium concentration in the mother liquor after the first lithium precipitation is ≤2.0 g / L. +

[0024] Further preferably, in the step b, the lithium precipitation reaction: the solution after the impurity removal is stirred, the solution is heated to control the temperature of the solution at 90-95℃, then the sodium carbonate solution is added at a flow rate of 1.0-1.2 m 3 / h to obtain 270-290 g / L of lithium carbonate; the lithium carbonate is fed into a pressure filter and washed with a pure water machine, the amount of washing water is added according to the solid-liquid ratio of 1: (15-25), the washed filter cake is discharged to a slurry tank, and pure water is added for slurry according to the solid-liquid ratio of 1: (4-6), then the slurry is centrifuged by a centrifuge, and after the centrifugation, the battery-grade lithium carbonate is obtained by washing with pure water according to the solid-liquid ratio of 1: (15-25), and the lithium concentration in the mother liquor after the first lithium precipitation is ≤2.0 g / L. + The concentration of the sodium carbonate solution is controlled in the range of 270-290 g / L, so as to ensure that the carbonate radical in the solution reaches the lithium precipitation concentration, and too much addition will increase the consumption of sulfuric acid and the operation cost of MVR in the process of removing carbon and phosphorus from the solution after the second lithium precipitation.

[0025] The present application has the following beneficial effects:

[0026] 1. The process reduces the process investment of the carbonation tower and carbon dioxide gas added in the second purification process, thereby reducing the large equipment investment and simplifying the process flow and improving the recovery benefit.

[0027] ​In the impurity removal process of the leaching solution, barium sulfide is added to effectively remove heavy metal ions and part of sulfate ions in the leaching solution, effectively reducing SO4 2- and heavy metals Cu, Mn, Cr, Ni, etc. in the lithium precipitation process.

[0028] 2. After the impurity removal and filtration, the solution is treated by a precision filter, a resin calcium removal system, and a pipeline magnetic remover, so that the calcium and magnesium meet the requirements of the pre-lithium precipitation solution, and the ion impurities such as Ca and Mg are effectively removed.

[0029] 3. The purified sodium carbonate solution is obtained after the sodium carbonate solution sequentially passes through the resin calcium removal system, the pipeline magnetic remover, and the precision filter, and the proportion of the sodium carbonate solution is strictly controlled according to the lithium content in the solution, and the battery-grade lithium carbonate is precipitated, and the ion impurities such as Ca and Mg are effectively removed. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The application relates to a production process for directly producing battery-grade lithium carbonate from lithium iron phosphate powder. DETAILED DESCRIPTION

[0031] The application will be further described below in combination with examples and drawings.

[0032] In the waste lithium iron phosphate powder, the lithium iron phosphate powder comprises the following components in terms of mass fraction: Li 4.59%, Fe 35.54%, P 18.68%, Al 0.35%, Ni 0.32%, Co 0.09%, Mn 0.08%, and the balance is graphite.

[0033] Example 1

[0034] (1) Leaching: pure water, waste lithium iron phosphate powder are sequentially added to the leaching reaction tank according to the solid-liquid ratio of 1:1.5, the solution is uniformly stirred, 98% concentrated sulfuric acid is added to the solution according to the raw material ratio of 98% sulfuric acid: 4:1, and hydrogen peroxide is added to the solution according to the raw material ratio of hydrogen peroxide: 8:1, leaching reaction is carried out, the reaction endpoint PH=2, and after complete leaching, the solution is punched into a filter press for pressure filtration;

[0035] (2) Phosphorus removal: the leaching solution obtained by pressure filtration is flowed to a phosphorus removal reaction tank, the solution volume of each tank is 25 m 3 , stirring is started, 20% sodium hydroxide solution is added, pH=3.8 is adjusted, steam heating is started, the temperature is kept at 80 DEG C, according to the phosphorus content in the solution, 1.2 times of the theoretical consumption of iron sulfate solid is added to the tank, pressure filtration is carried out after 1 h of reaction, the phosphorus-removed solution obtained by pressure filtration is flowed into an impurity removal reaction tank, and the filter residue is discharged and stored, the endpoint control pH=3.8, P≤0.001 g / L, Fe≤0.001 g / L. The chemical reactions involved in the process are as follows.

[0036] ,

[0037] ,

[0038] (3) Impurity removal: the solution in the impurity removal reaction tank is controlled at 25 m 3 , the stirring is started, 1.1 times of the theoretical consumption of barium sulfide is added into the tank, the barium sulfide is mainly added according to the amount of sulfate ions, the barium sulfide is added under acidic conditions with pH = 3.8, the stirring is reacted for 1 h, the metal ion impurities are effectively removed, after the reaction is completed, the liquid alkali is added to adjust the pH = 11~12, the pH is stable for 30 min, then the discharge pump is used to hit the impurity removal filter press, the impurity removal residue is stored, the filtered solution tank after the impurity removal is collected to enter the resin calcium removal system to remove calcium and magnesium, then the pipeline magnetic device is used to remove the magnetism, finally, it is transferred into the primary lithium precipitation reaction tank, the Ni, Co, Mn, Cu, Ca, Mg, 0.001 g / L, SO4 2- ≤0.05 g / L, Li + ≥20 g / L; the impurity removal process involves the following chemical reactions:

[0039] ,

[0040] ,

[0041] ,

[0042] (4) Primary lithium precipitation: a sodium carbonate solution purification: the sodium carbonate solution passes through the resin column, the precision filter, and the pipeline magnetic device to obtain the purified sodium carbonate solution (260 g / L) with calcium and magnesium ≤0.001 g / L; b lithium precipitation reaction: about 25 m 3 of the solution after the impurity removal is started to stir, the steam valve is opened to heat the solution, the temperature of the solution is controlled at 90~95℃, the sodium carbonate solution is added, and the sodium carbonate content in the solution is more than 180 g / L, c the lithium carbonate is put into the filter press and washed with the pure water machine, the washing water is added according to the solid-liquid ratio of 1:20, the filter cake is discharged to the slurry tank after washing, the pure water is added according to the solid-liquid ratio of 1:6 for slurry, then the centrifuge is used for centrifugation, after the centrifugation is completed, the pure water is added for washing according to the solid-liquid ratio of 1:20 to obtain the battery-grade lithium carbonate, the lithium precipitation mother liquor Li + ≤2.0 g / L;

[0043] (5) Sodium sulfate production: the primary lithium precipitation mother liquor, the machine-washed lithium water, and the centrifugal-washed lithium water are transferred into the sodium sulfate production process, and the crystallization mother liquor is returned to the impurity removal process.

[0044] Comparative Example 1

[0045] Based on Example 1, other conditions are unchanged, and the change is the operation in step (1): 98% sulfuric acid >4:1 sulfuric acid is added into the leaching tank; result: the reaction endpoint pH >2, which leads to incomplete leaching of the raw materials, and the leaching solution has a low content.

[0046] Table 1 contents of the solution in the process of Example 1

[0047] .

[0048] Table 2 data of the battery-grade lithium carbonate prepared in Example 1

[0049] .

[0050] Table 3 contents of the solution in the process of Comparative Example 1

[0051] .

[0052] Based on Example 1, other things being the same, the change is (1) operation: add raw materials to the leaching tank: 98% sulfuric acid < 4: 1 sulfuric acid;

[0053] Result: the reaction endpoint pH is less than 2, resulting in too high acidity of the solution, and more liquid alkali is consumed in step (2), causing waste of auxiliary materials.

[0054] Comparative Example 2

[0055] Based on Example 1, other things being the same, the change is step (1) operation: add raw materials to the leaching tank: hydrogen peroxide > 8: 1; result: incomplete leaching of raw materials, low content of leaching solution;

[0056] Table 4 contents of the solution in the process of Comparative Example 2

[0057] .

[0058] (2) operation: add raw materials to the leaching tank: hydrogen peroxide < 8: 1;

[0059] Result: the same effect, but causing waste of auxiliary materials, leading to cost increase;

[0060] Comparative Example 3

[0061] Based on Example 1, other things being the same, the change is step (2): add theoretical amount < 1.2 times of iron sulfate; result: incomplete phosphorus removal.

[0062] Table 5 contents of the solution in the process of Comparative Example 3 .

[0063] Based on Example 1, other things being the same, the change is step (2): add theoretical amount > 1.2 times of iron sulfate; result: the same effect, but causing waste of auxiliary materials, leading to cost increase.

[0064] Comparative Example 4

[0065] Based on example 1, other things remain unchanged, the change is in step (3): add the theoretical amount <1.1 times barium sulfide, the result: sulfate removal is not complete, resulting in unqualified products.

[0066] Table 6 content of solution in the process of comparative example 4

[0067] .

[0068] Table 7 battery grade lithium carbonate data of comparative example 4

[0069] .

[0070] Based on example 1, other things remain unchanged, the change is in (2) operation: add the theoretical amount >1.1 times barium sulfide, the result: the same effect, but causing the waste of auxiliary materials, resulting in cost increase.

[0071] Example 2

[0072] Based on example 1, in step (3), in the process of adding barium sulfide, also add 1.2 ‰ of dextran and chitosan mixture with mass ratio of 1:1.5 by liquid volume percentage, H2S is passed, 40℃ reaction 0.5 h, effectively remove metal ion impurities, after the reaction is completed, add liquid alkali to adjust pH=11~12, pH stable for 30 min, then use the discharge pump to hit the impurity removal filter press, the impurity removal residue is stored, after impurity removal, the liquid filter tank is collected and then enters the resin calcium removal system to remove calcium and magnesium, then through the pipeline magnetic device to remove the magnetism, finally into the first lithium precipitation tank, control Ni, Co, Mn, Cu, Ca, Mg, 0.001g / L, SO4 2- ≤0.05g / L, Li + ≥20g / L; the results of this example are shown in tables 8-9. The inventors accidentally invented, the reaction time of this example adding barium sulfide is shortened by half, and the effect of impurity removal is good.

[0073] Table 8 content of solution in the process of example 2

[0074] .

[0075] Table 9 battery grade lithium carbonate data corresponding to example 2 .

[0076] The above embodiments are merely preferred technical solutions of the present application, and should not be regarded as a limitation on the present application. The embodiments in the present application and the features in the embodiments can be combined with each other in any manner without conflict. The protection scope of the present application should be subject to the technical solutions recited in the claims, and include equivalent replacement solutions of the technical features recited in the claims. That is, equivalent replacement improvements within this range are also within the protection scope of the present application.

Claims

1. A process for the direct production of battery grade lithium carbonate from lithium iron phosphate powder, characterized in that, The process comprises the following steps: (1) leaching: adding pure water to slurry the lithium iron phosphate powder, adding sulfuric acid and hydrogen peroxide after slurry is completed, and performing leaching reaction; (2) phosphorus removal: adding sodium hydroxide solution to adjust pH and adding iron sulfate to remove phosphorus in the leaching solution produced in the leaching process; (3) impurity removal: after the phosphorus removal, barium sulfide is added under acidic conditions to effectively remove metal ion impurities, after the reaction is completed, liquid alkali is added to adjust the pH, then the pressure filter is pressed, the pressure filtered liquid is removed from the resin to remove calcium and magnesium impurities, then the pipeline magnetic device is used to remove the magnetism, and finally it is transferred into the first lithium precipitation reaction tank; in step (3), 1-1.3 times of the theoretical consumption of barium sulfide is added to the tank, the phosphorus removal liquid is added with barium sulfide at pH=3-4, the metal ion impurities are effectively removed, after the reaction is completed, liquid alkali is added to adjust the pH to 11-12, and the pH is stable for 25-35 min; the addition amount of the theoretically consumed barium sulfide is determined according to the concentrations of Ni, Co, Mn, Cu, Ca, Mg, SO4 2- in the solution; (4) One-time lithium precipitation: during the lithium precipitation process, add the purified saturated sodium carbonate solution after removing calcium and magnesium, insoluble substances and impurities to the lithium carbonate solution, and then put the lithium carbonate into a filter press and wash the filter cake with a pure water machine. After washing, the filter cake is discharged to a slurry tank and added with pure water for slurry, and then centrifuged by a centrifuge to obtain battery-grade lithium carbonate; step (4) specifically includes the following: a. Purification of sodium carbonate solution: the sodium carbonate solution is passed through a resin column, a precision filter and a pipeline magnetic eliminator to obtain a sodium carbonate solution with calcium or magnesium ≤0.001 g / L; b. Lithium precipitation reaction: the impurity-removed solution is stirred, the solution is heated, and sodium carbonate solution is added to obtain lithium carbonate; c. Lithium carbonate is put into a filter press and the filter cake is washed with a pure water machine. After washing, the filter cake is discharged to a slurry tank and added with pure water for slurry, and then centrifuged by a centrifuge. After centrifugation, pure water is added for washing to obtain battery-grade lithium carbonate, and the mother liquor Li + ≤2.0 g / L; (5) production of anhydrous sodium sulfate: the once lithium precipitation mother liquor, machine washing lithium water and centrifugal washing lithium water are transferred into the anhydrous sodium sulfate production process, and the crystallization mother liquor is returned to the impurity removal process.

2. The process as claimed in claim 1, wherein the process for direct production of battery grade lithium carbonate from lithium iron phosphate powder is characterized by: In the step (1), the lithium iron phosphate powder and the pure water are slurred according to a solid-liquid ratio of 1: (1-2), the mass ratio of the lithium iron phosphate powder to the 98% sulfuric acid is (3.5-4.5): 1, and the mass ratio of the lithium iron phosphate powder to the hydrogen peroxide is (7-9): 1; the end point pH of the leaching reaction is 1.5-2.

5.

3. The process as claimed in claim 1, wherein the process for direct production of battery grade lithium carbonate from lithium iron phosphate powder is characterized by: The step (2) is specifically operated as follows: the leaching solution obtained by pressure filtration is flowed to a phosphorus removal reaction tank, stirring is started, sodium hydroxide solution is added to adjust pH=3.5-4, steam is started to heat, the temperature is kept at 80-85℃, pressure filtration is performed after reaction, the phosphorus-removed solution obtained by pressure filtration is flowed into an impurity removal reaction tank, the filter residue is discharged and then stored, and the end point pH, P and Fe are controlled to be 3.5-4, ≤0.001 g / L and ≤0.001 g / L respectively.

4. The process as claimed in claim 3, wherein the process for direct production of battery grade lithium carbonate from lithium iron phosphate powder is characterized by: In the step (2), according to the phosphorus content in the solution, 1.1-1.4 times of the theoretical consumption of iron sulfate solid is added to the tank, and the theoretical consumption of iron sulfate is calculated according to the content of hydrogen phosphate.

5. The process as claimed in claim 3, wherein the process for direct production of battery grade lithium carbonate from lithium iron phosphate powder is characterized by: In the step (2), the sodium hydroxide solution is added to adjust pH=3.8, and the end point pH, P and Fe are controlled to be 3.8, ≤0.001 g / L and ≤0.001 g / L respectively.

6. The process for directly producing battery-grade lithium carbonate from lithium iron phosphate powder according to claim 1, characterized in that: The step (3), controlling Ni, Co, Mn, Cu, Ca, Mg or SO4 in the solution after impurity removal 2- ≤ 0.001 g / L, Li + ≥ 20 g / L.

7. The process for directly producing battery-grade lithium carbonate from lithium iron phosphate powder according to claim 1, characterized in that: The step b lithium precipitation reaction: after the impurity removal, the solution is stirred, the solution is heated, the temperature of the solution is controlled at 90-95℃, then 270-290 g / L sodium carbonate solution is added at a flow rate of 1.0-1.2 m 3 / h to obtain lithium carbonate; c the lithium carbonate is put into a filter press and washed with a water machine, the machine washing water is added according to a solid-liquid ratio of 1: (15-25), the filter cake is discharged to a slurry tank after washing, and pure water is added for slurry according to a solid-liquid ratio of 1: (4-6), then the slurry is centrifuged by a centrifugal machine, and the centrifugation is completed, then the filter cake is washed by adding pure water according to a solid-liquid ratio of 1: (15-25), and battery-grade lithium carbonate is obtained, and the Li+ content in the first lithium precipitation mother liquor is less than or equal to 2.0 g / L.

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