Methods for extracting lithium carbonate from brine, lithium carbonate products, cathode materials, and lithium-ion batteries.

Abstract

This invention relates to the field of lithium carbonate preparation, and discloses a method for extracting lithium carbonate from brine, a lithium carbonate product, a cathode sheet, and a lithium-ion battery. The method includes: S1, mixing the brine and a first flocculant and performing a first centrifugal precipitation to obtain a first liquid phase product; mixing the first liquid phase product, a water-soluble polymer, and a second flocculant and performing a second centrifugal precipitation to obtain a second liquid phase product; S2, removing the residual first flocculant, water-soluble polymer, and second flocculant from the second liquid phase product to obtain a third liquid phase product; S3, removing calcium, magnesium, boron, and chlorine from the third liquid phase product to obtain a fourth liquid phase product; concentrating, precipitating lithium, separating, washing with water, and drying the fourth liquid phase product to obtain the lithium carbonate product. This method reduces the amount of alkali used and eliminates the need for energy-intensive and polluting calcination processes. The process can be continuous and has a short processing time.

Description

Technical Field

[0001] This invention relates to the field of lithium carbonate preparation, specifically to a method for extracting lithium carbonate from brine, lithium carbonate products, positive electrode sheets, and lithium-ion batteries. Background Technology

[0002] In existing technologies for lithium extraction from salt lakes, brine extraction refers to extracting lithium from lithium-containing brine and producing lithium carbonate products. Brine extraction typically involves stages such as solar evaporation in salt fields, obtaining different salts in stages, and purifying the salt solution. Finally, the lithium salt is separated and extracted from the solution to obtain the desired lithium salt product.

[0003] Lithium extraction from salt lake brines is a simple and low-cost process that has gradually replaced lithium ore production. Statistics show that salt lake brines account for approximately 70%-80% of total lithium resources, making lithium carbonate production from salt lake brines a key focus of lithium salt production. Domestic methods for extracting lithium from salt lake brines to produce lithium carbonate mainly include precipitation, extraction, ion exchange adsorption, carbonation, calcination leaching, and electrodialysis. Among these, precipitation, extraction, ion exchange adsorption, and carbonation are the most extensively studied and are the primary methods for extracting lithium carbonate from salt lake brines. Industrially, the extraction of lithium from salt lake brines to produce lithium carbonate generally employs the evaporation-crystallization-precipitation method.

[0004] The precipitation method is an industrially implemented process for producing lithium carbonate from brine in salt lakes by adding precipitants such as sodium carbonate. The basic principle involves evaporating and concentrating the lithium-containing brine in an evaporation tank, then acidifying it to remove boron, separating the remaining boron, calcium, and magnesium ions, and then adding sodium carbonate to precipitate the lithium as lithium carbonate. Finally, the product is dried to obtain the lithium carbonate product. Precipitation methods mainly include carbonate precipitation and aluminate precipitation.

[0005] The carbonate precipitation method is the earliest researched and industrially applied method for lithium extraction from salt lake brine. This method involves adding industrial soda ash to concentrated salt lake brine, causing lithium to precipitate as lithium carbonate. This method is suitable for lithium extraction from salt lake brines with low magnesium-to-lithium ratios. The specific production process is as follows: Figure 2 .

[0006] Aluminate precipitation methods include sodium aluminate precipitation and calcium aluminate precipitation. The basic principle of this method is that amorphous aluminates have a highly efficient selective precipitation effect on lithium in brine, forming a LiCl·2Al(OH)3·nH2O complex, thereby achieving the separation and recovery of lithium. The resulting lithium-containing precipitate is calcined and leached to obtain lithium chloride solution and alumina. Impurities such as magnesium and calcium in the lithium chloride solution are removed using lime milk and soda ash. After evaporation and concentration, sodium carbonate solution is added to obtain lithium carbonate. The specific production process for extracting lithium carbonate from the boron removal mother liquor of saturated magnesium chloride brine in salt lakes using the sodium aluminate precipitation method is described in [link to relevant documentation]. Figure 3 .

[0007] However, the processes of extracting lithium carbonate by carbonate precipitation and aluminate precipitation are time-consuming, require large amounts of acid and alkali, have high roasting energy consumption, cause significant environmental pollution, and produce lithium carbonate with many impurities, making it difficult to obtain high-purity lithium carbonate and hindering continuous production.

[0008] Therefore, there is an urgent need for a process to extract lithium carbonate from brine that does not require a high-energy-consuming and highly polluting calcination step, uses less alkali, and does not require investment in large nanofiltration membrane segments and expensive adsorbents to adsorb lithium, and that yields lithium carbonate with high purity. Summary of the Invention

[0009] The purpose of this invention is to overcome the problems of existing technologies that require energy-intensive and polluting calcination steps and large amounts of alkali when extracting lithium carbonate from brine using precipitation methods, or require large investments in nanofiltration membranes and expensive adsorbents for lithium adsorption in nanofiltration methods. This invention provides a method for extracting lithium carbonate from brine, as well as lithium carbonate products, positive electrode sheets, and lithium-ion batteries. This extraction method allows for continuous production, has a short process time, and offers significant advantages in production capacity compared to calcination and natural evaporation processes.

[0010] To achieve the above objectives, a first aspect of the present invention provides a method for extracting lithium carbonate from brine, wherein the method comprises:

[0011] S1. The brine and the first flocculant are mixed for the first time and centrifuged and precipitated once to obtain a first liquid phase product; the first liquid phase product, the water-soluble polymer, and the second flocculant are mixed for the second time and centrifuged and precipitated a second time to obtain a second liquid phase product.

[0012] S2. Remove the residual first flocculant, water-soluble polymer and second flocculant from the second liquid phase product to obtain the third liquid phase product;

[0013] S3. The third liquid phase product is subjected to calcium, magnesium, boron and chlorine removal to obtain a fourth liquid phase product; the fourth liquid phase product is concentrated, lithium is precipitated, separated, washed with water and dried to obtain the lithium carbonate product.

[0014] A second aspect of the present invention provides a lithium carbonate product obtained by the method provided by the present invention.

[0015] A third aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising the lithium carbonate product provided by the present invention.

[0016] A fourth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising the positive electrode sheet provided by the present invention.

[0017] The beneficial effects of the present invention through the above technical solution are as follows:

[0018] This invention involves adding a first flocculant to form a complex precipitate of divalent hydroxide ions and some chloride salts. After filtration, the salt content in the brine is significantly reduced. Then, a second solid-liquid separation is achieved by adding a water-soluble polymer and a second flocculant to induce aggregation and sedimentation. This removes most of the divalent metal ions from the brine. Finally, the remaining first flocculant, water-soluble polymer, and second flocculant are removed. The filtered water-soluble polymer and second flocculant are reusable and do not discharge, thus reducing operating costs. This invention features a simple process with low equipment investment. It does not require a large number of nanofiltration membranes or expensive adsorbents to adsorb lithium, nor does it require a high-energy-consuming and polluting calcination process. This process allows for continuous production, has a short process time, and offers significant advantages in production capacity compared to calcination and natural evaporation processes.

[0019] In a preferred embodiment of the present invention, compared to the conventional precipitation method which requires a higher pH value of around 12, a pH value below 10 is sufficient, significantly reducing the amount of alkali used. Furthermore, by further selecting appropriate pH values ​​for the brine before mixing with magnesium iron silicate, the weight-average molecular weights of magnesium iron silicate and polyethylene glycol, the centrifugation rates for the first and second centrifugation sedimentation, the types of water-soluble polymers, the first flocculant, and the second flocculant, the concentration and evaporation temperature, and the amounts of magnesium iron silicate, the water-soluble polymer, and the second flocculant, not only can the quality of the lithium carbonate product be further improved, but the continuous and stable operation of the equipment can also be ensured. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for extracting lithium carbonate from brine in a specific embodiment of the present invention.

[0021] Figure 2 This is a process flow diagram of lithium extraction from salt lake brine using the carbonate precipitation method in existing technologies;

[0022] Figure 3 This is a process flow diagram of the sodium aluminate precipitation method for extracting lithium carbonate from the boron removal mother liquor of saturated magnesium chloride brine in salt lakes. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] This invention provides a method for extracting lithium carbonate from brine, wherein the method includes:

[0025] S1. The brine and the first flocculant are mixed for the first time and centrifuged and precipitated once to obtain a first liquid phase product; the first liquid phase product, the water-soluble polymer, and the second flocculant are mixed for the second time and centrifuged and precipitated a second time to obtain a second liquid phase product.

[0026] S2. Remove the residual first flocculant, water-soluble polymer and second flocculant from the second liquid phase product to obtain the third liquid phase product;

[0027] S3. The third liquid phase product is subjected to calcium, magnesium, boron and chlorine removal to obtain a fourth liquid phase product; the fourth liquid phase product is concentrated, lithium is precipitated, separated, washed with water and dried to obtain the lithium carbonate product.

[0028] This invention, by adding a first flocculant, causes most of the divalent ions in the brine to form hydroxide colloids. Under the catalysis of the first flocculant, the ionic repulsion between the colloids is reduced, leading to aggregation and precipitation, forming complex divalent ion hydroxides and precipitates containing some chloride salts. After one centrifugation and solid-liquid separation, the salt content in the brine is reduced by a large portion, but some divalent ions remain. Since the concentration of divalent ions is very low, they are not easily precipitated. Therefore, a water-soluble polymer is added to reduce the solubility of most salts in water. Aggregation and sedimentation occur in the presence of a second flocculant, followed by a second centrifugation and solid-liquid separation. After this, most of the divalent metal ions in the brine are basically removed. Then, the residual first flocculant (most of which was removed after the first and second centrifugation, with a small amount remaining), water-soluble polymer, and second flocculant are removed. The filtered water-soluble polymer and second flocculant can be reused without being discharged, thus reducing operating costs.

[0029] After undergoing one and two centrifugal sedimentation processes to remove residual first flocculant, water-soluble polymer, and second flocculant, the impurity ions in the brine are already low. Further refining is then carried out to remove small amounts of residual calcium, magnesium, and boron ions, as well as some residual chloride ions, reducing the corrosion of the concentration equipment by chloride ions. Industrial-grade or battery-grade lithium carbonate is obtained through concentration, lithium precipitation, water washing, and drying.

[0030] According to the present invention, preferably, the first flocculant is selected from polyferric magnesium silicate and / or polyaluminum chloride, and more preferably polyferric magnesium silicate.

[0031] To further improve the flocculation effect of the first flocculant, preferably, the weight-average molecular weight of the polyferric magnesium silicate is 300,000-7,000,000 g / mol, more preferably 400,000-6,000,000 g / mol.

[0032] Preferably, the polyaluminum chloride has a weight-average molecular weight of 300,000 to 8,000,000 g / mol.

[0033] According to the present invention, preferably, in S1, the pH value of the brine is first adjusted to 8-10, and then the first mixture is carried out with the first flocculant.

[0034] According to the present invention, preferably, in S1, the pH value of the second mixed liquid is adjusted to 8-10, and then the second centrifugation sedimentation is performed.

[0035] According to the present invention, preferably, the conditions for the first centrifugal sedimentation include: a centrifugation rate of 8000-30000 r / min and a time of 3-5 min. By adding a first flocculant to the brine, under high-speed rotation at a centrifugation rate of 8000-30000 r / min, before the first mixing with the first flocculant, the pH value of the brine only needs to be adjusted to below 10 to remove most of the salt in the brine. Compared with the ordinary sedimentation method, which requires a higher pH value (around 12), this greatly reduces the amount of alkali used.

[0036] According to the present invention, preferably, the amount of the first flocculant is 1-3 wt% based on the weight of the brine. Too high a concentration not only increases costs but also makes it more difficult to dissolve.

[0037] According to the present invention, preferably, after the first centrifugation precipitation, the obtained solid-liquid mixture is filtered through a filter bag with an average pore size of 4-6 micrometers to obtain the first liquid phase product.

[0038] According to the present invention, preferably, the conditions for the secondary centrifugal sedimentation include: a centrifugation rate of 12,000-30,000 r / min and a time of 3-5 min. By adding a first flocculant to the brine and performing a first centrifugal sedimentation, followed by adding a water-soluble polymer and a second flocculant and performing a second centrifugal sedimentation, at a high-speed rotation speed of 12,000-30,000 r / min, the pH value only needs to be below 10 to further remove salt from the brine.

[0039] Furthermore, the centrifugation rate of the secondary centrifugation sedimentation is 15000-27000 r / min.

[0040] According to the present invention, preferably, based on the weight of the brine, the amount of the water-soluble polymer is 5-10 wt%, and the amount of the second flocculant is 3-5 wt%. The role of the water-soluble polymer is to reduce the solubility of most salts in the brine, which then aggregates and settles in the presence of the second flocculant. When the amounts of the water-soluble polymer and the second flocculant are within this range, divalent metal ions in the brine can be removed more effectively. The amounts of the water-soluble polymer and the second flocculant should not be excessive. If the amounts are too high, some of the polymer and the second flocculant will not dissolve in the brine, resulting in waste and increasing the risk of membrane clogging.

[0041] According to the present invention, preferably, the weight-average molecular weight of the water-soluble polymer is 600-25000 g / mol. When the weight-average molecular weight of the water-soluble polymer meets this range, it is easily soluble in water and can be completely filtered out by the polyceramic membrane during subsequent removal of the water-soluble polymer. Water-soluble polymers with too low a molecular weight are not easily filtered out by the polyceramic membrane, while those with too high a molecular weight are not easily soluble in water.

[0042] According to the present invention, preferably, the water-soluble polymer is selected from at least one of polyethylene glycol, starch, and hydroxymethyl cellulose, and more preferably polyethylene glycol. Polyethylene glycol dissolves rapidly in water, is low in toxicity, and is inexpensive. For example, commercially available polyethylene glycol 600 can be used as the water-soluble polymer.

[0043] According to the present invention, preferably, the second flocculant is selected from at least one of polyacrylamide, polyaluminum chloride, and polyferric chloride, and more preferably polyacrylamide (PAM). PAM is inexpensive, has excellent flocculation performance, and has a sedimentation effect on both organic and inorganic substances.

[0044] According to the present invention, preferably, the weight-average molecular weight of the second flocculant is 5 million to 20 million g / mol. When the weight-average molecular weight of the second flocculant meets this range, it can achieve good flocculation effect while being easily soluble in water.

[0045] According to the present invention, preferably, after the secondary centrifugation and precipitation, the resulting solid-liquid mixture is filtered through a filter bag with an average pore size of 4-6 micrometers to obtain the second liquid phase product.

[0046] According to the present invention, preferably, in S2, the removal method includes: passing the second liquid phase product through an oleophobic polyceramic membrane. Filtration with the oleophobic polyceramic membrane can effectively remove residual water-soluble polymers and the second flocculant from the second liquid phase product. The present invention does not particularly limit the type of oleophobic polyceramic membrane, as long as it can remove the first flocculant, the water-soluble polymer, and the second flocculant. For example, an oleophobic polyceramic membrane purchased from Shanghai Polyceramic Technology Co., Ltd. can be used, which can intercept and filter organic matter with a weight-average molecular weight greater than 500 g / mol. The water-soluble polymers and the second flocculant filtered out by the oleophobic polyceramic membrane can be reused.

[0047] According to the present invention, preferably, the method for removing calcium and magnesium includes contacting the third liquid phase product with a calcium and magnesium removal resin. The present invention does not particularly limit the type of calcium and magnesium removal resin, as long as it can achieve a calcium and magnesium removal rate of 99% or higher. For example, the calcium and magnesium removal resin can be a cation exchange calcium and magnesium removal resin or a chelate ion exchange calcium and magnesium removal resin, etc., preferably a commercially available cation exchange calcium and magnesium removal resin used for water purification and softening, such as the cation exchange calcium and magnesium removal resin with brand name D402 purchased from Jiangsu Suqing Water Treatment Engineering Group Co., Ltd.

[0048] According to the present invention, preferably, the boron removal method includes contacting the calcium and magnesium removed solution with a boron removal resin. The present invention does not particularly limit the type of boron removal resin, as long as it can achieve a boron removal rate of 90% or higher. For example, the boron removal resin can be an ion exchange boron removal resin or a chelating boron removal resin, preferably a chelating boron removal resin, such as the chelating boron removal resin with brand name D403 purchased from Jiangsu Suqing Water Treatment Engineering Group Co., Ltd.

[0049] This invention does not impose special requirements on the dosage of the calcium-magnesium removal resin and the boron removal resin. The dosage of these resins is determined by the production capacity; the more resin used, the more third-phase product is processed per unit time. Both the calcium-magnesium removal resin and the boron removal resin can be reused repeatedly and can be restored by regeneration after adsorption saturation. The brine (third-phase product) obtained after two centrifugal sedimentation separations and removal of residual water-soluble polymers and the second flocculant is passed sequentially through a resin column packed with calcium-magnesium removal resin and a resin column packed with boron removal resin at a certain flow rate of 2-6 BV / h (i.e., the volume of solution passing through per hour is 2-6 times the volume of the resin bed). This achieves a good removal effect of calcium, magnesium, and boron.

[0050] This invention does not impose any particular limitation on the method of dechlorination; conventional methods in the art can be used. For example, reverse osmosis, electrolysis, or the use of dechlorination resins can be employed. Reverse osmosis is a more cost-effective method for dechlorination and offers a larger operating capacity.

[0051] According to one specific embodiment of the present invention, a dechlorination resin is used for dechlorination. The dechlorination method includes contacting the boron-removed liquid with the dechlorination resin to perform the dechlorination. The present invention does not particularly limit the type of dechlorination resin, as long as it can achieve a chlorine removal rate of 80% or higher. For example, the dechlorination resin can be an anionic dechlorination resin, preferably an anionic dechlorination resin that removes no less than 40 kg of chlorine per ton of resin, such as anionic dechlorination resin purchased from Shanghai Kaiping Resin Co., Ltd., with the brand name KP302.

[0052] When using dechlorination resin for dechlorination, the feed solution that has passed through calcium and magnesium removal resin and boron removal resin is passed through a resin column filled with dechlorination resin at a flow rate of 2-6 BV / h to achieve a good dechlorination effect.

[0053] According to the present invention, preferably, in S3, the concentration method includes: evaporating the fourth liquid phase product; wherein the evaporation conditions include: the pH value of the fourth liquid phase product is 5-8, the temperature is 80-120℃, and the time is 1-3h. When the pH value of the fourth liquid phase product meets this range, it can prevent corrosion of the evaporation equipment; otherwise, it may easily lead to corrosion of the evaporation equipment pipes or cavities. After the product from which the first flocculant, water-soluble polymer, and second flocculant have been removed, and calcium, magnesium, boron, and chlorine have been removed, if the pH value exceeds the range of 5-8, a pH adjuster needs to be used to adjust the pH value of the fourth liquid phase product to 5-8. For example, hydrochloric acid or sodium hydroxide can be used as a pH adjuster. Meeting this evaporation condition ensures that the lithium content in the concentrated liquid after evaporation is 15-25 g / L. A lithium content within this range is beneficial for improving the efficiency of subsequent lithium precipitation.

[0054] According to one specific embodiment of the present invention, the evaporation is performed using a mechanical vapor recompression evaporator (MVR).

[0055] According to the present invention, preferably, step S3 further includes: cooling the concentrated solution obtained by concentration to 20-40°C, then filtering the cooled concentrated solution through a precision filter with an average pore size of 1-5 micrometers, and then performing the lithium precipitation. The purpose of the filtration is to remove precipitates or flocculants contained in the concentrated solution, thereby obtaining a lithium carbonate product with higher purity.

[0056] According to the present invention, preferably, in step S3, the method for lithium precipitation includes: reacting the concentrated solution obtained from the concentration with carbonate. The product obtained from the reaction is subjected to solid-liquid separation to obtain a lithium carbonate precipitate.

[0057] According to the present invention, preferably, the reaction time is 20-40 min.

[0058] In this invention, the carbonate can be sodium carbonate and / or potassium carbonate. Sodium carbonate is less expensive, and it is preferred to use sodium carbonate for lithium precipitation in this invention.

[0059] According to a preferred embodiment of the present invention, in the concentrated solution obtained by concentration, the amount of sodium carbonate used is 8-11g based on 1g of lithium element, that is, the amount of sodium carbonate used is 8-11 times the weight of lithium element content in the concentrated solution after evaporation and concentration.

[0060] According to the present invention, preferably, in step S3, the lithium carbonate is washed with water more than twice. Increasing the number of water washes can further improve the purity of the lithium carbonate product, thereby obtaining an industrial-grade or battery-grade lithium carbonate product.

[0061] According to one specific embodiment of the present invention, a disc dryer is used for the drying process. According to the present invention, preferably, the drying temperature is 80-110°C.

[0062] According to the present invention, preferably, the method further includes: crushing and demagnetizing the dried product to obtain the lithium carbonate product.

[0063] According to a specific embodiment of the present invention, such as Figure 1 As shown, the method for extracting lithium carbonate from brine includes the following steps:

[0064] S1. Pour the brine into a high-speed rotating tank and add a pH adjuster to adjust the pH value of the brine to 8-10. Based on the weight of the brine, add 1-3 wt% of polyferric magnesium silicate to the tank. Turn on the high-speed rotation button of the tank to make the brine rotate at a high speed of 8000-30000 r / min for centrifugal sedimentation. After 3-5 minutes, stop the centrifugal rotation and then discharge the solid-liquid mixture from the bottom of the tank and filter it into a filter bag with an average pore size of 4-6 micrometers to obtain the first liquid phase product. The first liquid product is then introduced into another high-speed rotating tank. Based on the weight of the brine, 5-10 wt% of polyethylene glycol 600 and 3-5 wt% of PAM flocculant are added. The pH is adjusted to 8-10 with a pH adjuster, and centrifugation is performed again at a speed of 12,000-30,000 rpm for 3-5 minutes. The solid-liquid mixture is then discharged from the bottom of the tank and filtered through a filter bag with an average pore size of 4-6 micrometers. The resulting second liquid product is then stored in a post-processing buffer tank for later use.

[0065] S2. The second liquid phase product in the post-treatment buffer tank is passed into an oleophobic polyceramic membrane system for filtration to remove residual magnesium iron silicate, polyethylene glycol 600, and PAM flocculant. The filtered third liquid phase product is then allowed to settle in the buffer tank. The filtered-out polyethylene glycol 600 and PAM flocculant can be returned to S1 for reuse.

[0066] S3. The third liquid phase product obtained in S2 is further purified by sequentially passing it through calcium and magnesium removal resin, boron removal resin, and chlorine removal resin. Then, the pH value of the resulting fourth liquid phase product is confirmed to be within the range of 5-8 (during resin treatment, the pH may not be within the appropriate range; if it does, a pH adjuster is used to bring the brine pH back to the above range). Then, MVR (Medium-Vapor Reduction) is performed for further concentration and evaporation at a temperature of 80-120℃ for 1-3 hours. The concentrated purified brine (concentrate) is then cooled and allowed to stand for 1 hour in a buffer tank. After cooling to 20-40℃, it is filtered through a precision filter with an average pore size of 1-5 micrometers. It then enters a lithium precipitation reactor to react with sodium carbonate. The amount of sodium carbonate (by weight) is 8-11 times the weight of the lithium element in the purified brine. After reacting for 20-40 minutes, lithium carbonate precipitates out and is discharged from the bottom. It is then filtered, washed with water, filtered again, washed with water, and washed at least twice. Finally, the material is discharged into a disc dryer and dried at 80-110℃. After drying in a disc dryer, the material enters the subsequent processing steps, including crushing and demagnetization, and is then fed to obtain industrial-grade or battery-grade lithium carbonate.

[0067] A second aspect of the present invention provides a lithium carbonate product obtained by the method provided by the present invention.

[0068] A third aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising the lithium carbonate product provided by the present invention.

[0069] A fourth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising the positive electrode sheet provided by the present invention.

[0070] The present invention will be described in detail below through examples and comparative examples. Unless otherwise specified, all methods used in the following examples are conventional; the reagents and materials used are commercially available unless otherwise specified. The brine composition in each example and comparative example, by mass percentage, is as follows:

[0071] <![CDATA[H3BO3]]> B Ca Li Mg K Na <![CDATA[SO4]]> Cl <![CDATA[H2O]]> 0.31 0.05 0.02 0.11 0.82 1.49 8.1 2.19 15.22 71.69

[0072] The purity of lithium carbonate products was tested according to the YS / T582-2013 standard, where all content refers to mass percentage. Specifically,

[0073] The content of Li2CO3 was determined by acid-base titration.

[0074] The Na and K contents were determined using the AAS method;

[0075] ICP-OES was used to determine Mg, Ca, Fe, Zn, Cu, Pb, Si, Al, Mn, Ni, and SO4. 2- and the content of magnetic materials;

[0076] Determination of Cl by spectrophotometry - content;

[0077] The moisture and hydrochloric acid insoluble content were determined by gravimetric method.

[0078] Particle size distribution was determined using laser particle size distribution method.

[0079] Example 1

[0080] Extract lithium carbonate from brine using the following steps:

[0081] S1. Pour the brine into a high-speed rotating tank and add a pH adjuster to adjust the pH of the brine to 9. Based on the weight of the brine, add 2 wt% of polyferric magnesium silicate (weight average molecular weight of 1 million g / mol) to the tank. Turn on the high-speed rotation button of the tank, so that the brine rotates at a high speed of 12,000 r / min for centrifugal sedimentation. After 4 minutes, stop the centrifugation and then discharge the solid-liquid mixture from the bottom of the tank and filter it into a filter bag with an average pore size of 5 micrometers to obtain the first liquid phase product (represented by Na in the brine). + Content and Mg 2+ Based on the content, the Na content of the first liquid phase product + The removal rate was 74.92%, Mg 2+ The removal rate was 72.69%. The first liquid product was then transferred to another high-speed rotating tank. Based on the weight of the brine, 7 wt% polyethylene glycol 600 and 3 wt% PAM flocculant (weight average molecular weight of 10 million g / mol) were added. The pH was adjusted to 10 with a pH adjuster, and the mixture was centrifuged again at 20,000 r / min for 4 min. The solid-liquid mixture was then discharged from the bottom of the tank and filtered through a filter bag with an average pore size of 5 micrometers. The resulting second liquid product was stored in a post-processing buffer tank for later use.

[0082] S2. The second liquid phase product in the post-treatment buffer tank is passed into an oleophobic polyceramic membrane (purchased from Shanghai Polyceramic Technology Co., Ltd.) system for filtration. The content of polyethylene glycol 600 in the obtained product is 0.27 g / L. After filtration, it is placed in a buffer tank for settling.

[0083] S3. The third liquid phase product obtained in S2 is passed sequentially at a flow rate of 4 BV / h through a resin column packed with calcium and magnesium removal resin (cation exchange calcium and magnesium removal resin purchased from Jiangsu Suqing Water Treatment Engineering Group Co., Ltd., brand name D402), a resin column packed with boron removal resin (chelating boron removal resin purchased from Jiangsu Suqing Water Treatment Engineering Group Co., Ltd., brand name D403), and a resin column packed with chlorine removal resin (anion chlorine removal resin purchased from Shanghai Kaiping Resin Co., Ltd., brand name KP302). The resulting fourth liquid phase product has a pH value of 7. Then, it is further concentrated and evaporated by MVR at a temperature of 90℃ (vacuum distillation) for 2 hours. The concentrated refined brine (concentrate) is cooled and allowed to stand for 1 hour in a buffer tank. After cooling to 40°C, it is filtered through a precision filter with an average pore size of 2 micrometers. Then, it enters a lithium precipitation reactor to react with sodium carbonate. The amount of sodium carbonate used (by weight) is 9 times the weight of the lithium element in the concentrate. After reacting for 30 minutes, lithium carbonate precipitates out and is discharged from the bottom. After filtration, washing with water, secondary filtration, and washing with water, the material is then discharged into a disc dryer at 90°C for drying. After drying in the disc dryer, it enters the next stage of processing, undergoing crushing and demagnetization, and is then discharged to obtain lithium carbonate product P1.

[0084] Example 2

[0085] Extract lithium carbonate from brine using the following steps:

[0086] S1. Pour the brine into a high-speed rotating tank and add a pH adjuster to adjust the pH of the brine to 8. Based on the weight of the brine, add 1 wt% of polyferric magnesium silicate (weight average molecular weight of 1 million g / mol) to the tank. Turn on the high-speed rotation button of the tank, so that the brine rotates at a high speed of 8000 r / min for centrifugal sedimentation. After 4 minutes, stop the centrifugation and then discharge the solid-liquid mixture from the bottom of the tank and filter it into a filter bag with an average pore size of 5 micrometers to obtain the first liquid phase product (represented by Na in the brine). + Content and Mg 2+ Based on the content, the Na content of the first liquid phase product + The removal rate was 72.82%, Mg 2+ The removal rate was 70.11%. The first liquid product was then transferred to another high-speed rotating tank. Based on the weight of the brine, 5 wt% polyethylene glycol 600 and 4 wt% PAM flocculant (weight average molecular weight of 10 million g / mol) were added. The pH was adjusted to 8 with a pH adjuster, and the mixture was centrifuged again at 15,000 r / min for 4 min. The solid-liquid mixture was then discharged from the bottom of the tank and filtered through a filter bag with an average pore size of 5 micrometers. The resulting second liquid product was stored in a post-processing buffer tank for later use.

[0087] S2. The second liquid phase product in the post-treatment buffer tank is passed into an oleophobic polyceramic membrane (purchased from Shanghai Polyceramic Technology Co., Ltd.) system for filtration. The content of polyethylene glycol 600 in the obtained product is 0.21 g / L. After filtration, it is placed in a buffer tank for settling.

[0088] S3. The third liquid phase product obtained in S2 is passed sequentially at a flow rate of 2 BV / h through a resin column packed with calcium and magnesium removal resin (cation exchange calcium and magnesium removal resin purchased from Jiangsu Suqing Water Treatment Engineering Group Co., Ltd., brand name D402), a resin column packed with boron removal resin (chelating boron removal resin purchased from Jiangsu Suqing Water Treatment Engineering Group Co., Ltd., brand name D403), and a resin column packed with chlorine removal resin (anion chlorine removal resin purchased from Shanghai Kaiping Resin Co., Ltd., brand name KP302). The resulting fourth liquid phase product has a pH value of 6. Then, it is further concentrated and evaporated by MVR at a temperature of 80℃ (vacuum distillation) for 1 hour. The concentrated refined brine (concentrate) is cooled and allowed to stand for 1 hour in a buffer tank. After cooling to 20°C, it is filtered through a precision filter with an average pore size of 2 micrometers. Then, it enters a lithium precipitation reactor to react with sodium carbonate. The amount of sodium carbonate used (by weight) is 8 times the weight of the lithium element in the concentrate. After reacting for 20 minutes, lithium carbonate precipitates out and is discharged from the bottom. It is then filtered, washed with water, filtered a second time, and washed with water again. The discharged material is then dried in a disc dryer at 90°C. After drying in the disc dryer, it enters the next stage of processing, where it undergoes crushing and demagnetization. Finally, it is discharged to obtain lithium carbonate product P2.

[0089] Example 3

[0090] Extract lithium carbonate from brine using the following steps:

[0091] S1. Pour the brine into a high-speed rotating tank and add a pH adjuster to adjust the pH value of the brine to 10. Based on the weight of the brine, add 3 wt% of polyferric magnesium silicate (weight average molecular weight of 1 million g / mol) to the tank. Turn on the high-speed rotation button of the tank, so that the brine rotates at a high speed of 30,000 r / min for centrifugal sedimentation. After 4 minutes, stop the centrifugation and then discharge the solid-liquid mixture from the bottom of the tank and filter it into a filter bag with an average pore size of 5 micrometers to obtain the first liquid phase product (represented by Na in the brine). + Content and Mg 2+ Based on the content, the Na content of the first liquid phase product + The removal rate was 77.6%, Mg 2+The removal rate was 74.2%. The first liquid product was then transferred to another high-speed rotating tank. Based on the weight of the brine, 10 wt% polyethylene glycol 600 and 5 wt% PAM flocculant (weight average molecular weight of 10 million g / mol) were added. The pH was adjusted to 10 with a pH adjuster, and the mixture was centrifuged again at 27,000 r / min for 4 min. The solid-liquid mixture was then discharged from the bottom of the tank and filtered through a filter bag with an average pore size of 5 micrometers. The resulting second liquid product was stored in a post-processing buffer tank for later use.

[0092] S2. The second liquid phase product in the post-treatment buffer tank is passed into an oleophobic polyceramic membrane (purchased from Shanghai Polyceramic Technology Co., Ltd.) system for filtration. The content of polyethylene glycol 600 in the obtained product is 0.32 g / L. After filtration, it enters the buffer tank for settling.

[0093] S3. The third liquid phase product obtained in S2 is passed sequentially at a flow rate of 2 BV / h through a resin column packed with calcium and magnesium removal resin (cation exchange calcium and magnesium removal resin purchased from Jiangsu Suqing Water Treatment Engineering Group Co., Ltd., brand name D402), a resin column packed with boron removal resin (chelating boron removal resin purchased from Jiangsu Suqing Water Treatment Engineering Group Co., Ltd., brand name D403), and a resin column packed with chlorine removal resin (anion chlorine removal resin purchased from Shanghai Kaiping Resin Co., Ltd., brand name KP302). The resulting fourth liquid phase product has a pH value of 8. Then, it is further concentrated and evaporated by MVR at a temperature of 120℃ for 3 hours. The concentrated refined brine (concentrate) is cooled and allowed to stand for 1 hour in a buffer tank. After cooling to 30°C, it is filtered through a precision filter with an average pore size of 2 micrometers. Then, it enters a lithium precipitation reactor to react with sodium carbonate. The amount of sodium carbonate used (by weight) is 11 times the weight of the lithium element in the concentrate. After reacting for 20 minutes, lithium carbonate precipitates out and is discharged from the bottom. It is then filtered, washed with water, filtered a second time, and washed with water again. The discharged material is then dried in a disc dryer at 90°C. After drying in the disc dryer, it enters the next stage of processing, where it undergoes crushing and demagnetization. Finally, it is discharged to obtain lithium carbonate product P3.

[0094] Example 4

[0095] Lithium carbonate was extracted from brine according to the method in Example 1, except that in S1, the brine was placed in a high-speed rotating tank, and a pH adjuster was added to adjust the pH of the brine to 7.5. The Na+ content in the brine was then used to extract lithium carbonate. + Content and Mg 2+ Based on the content, the Na content of the first liquid phase product was determined. + The removal rate was 41.1%, Mg 2+ The removal rate was 47.2%. Lithium carbonate product P4 was obtained.

[0096] Example 5

[0097] Lithium carbonate was extracted from brine according to the method in Example 1, except that "polyferric magnesium silicate with a weight average molecular weight of 1,000,000 g / mol" was used instead of "polyferric magnesium silicate with a weight average molecular weight of 300,000 g / mol". The Na in the brine was used as the basis for the extraction. + Content and Mg 2 + Based on the content, the Na content of the first liquid phase product was determined. + The removal rate was 61.7%, Mg 2+ The removal rate was 66.3%. Lithium carbonate product P5 was obtained.

[0098] Example 6

[0099] Lithium carbonate was extracted from brine according to the method in Example 1, except that the centrifugation rate for the first centrifugation sedimentation was different. Specifically, after adding magnesium iron silicate to the tank, the high-speed rotation button of the tank was turned on, causing the brine to rotate at a high speed of 7000 r / min for centrifugal sedimentation. The Na in the brine was then used as the basis for the extraction. + Content and Mg 2+ Based on the content, the Na content of the first liquid phase product was determined. + The removal rate was 43.3%, Mg 2+ The removal rate was 62.5%. Lithium carbonate product P6 was obtained.

[0100] Example 7

[0101] Lithium carbonate was extracted from brine according to the method of Example 1, except that the weight-average molecular weight of the polyethylene glycol was different. Specifically, in S1, "polyethylene glycol 600" was replaced with "polyethylene glycol with a weight-average molecular weight of 500 g / mol". The lithium carbonate product P7 was obtained.

[0102] Example 8

[0103] Lithium carbonate was extracted from brine according to the method of Example 1, except that the types of water-soluble polymers and flocculants were different. Specifically, in S1, "hydroxymethyl cellulose with a weight average molecular weight of 5000 g / mol and polyferric chloride flocculant with a weight average molecular weight of 20 million g / mol" replaced "polyethylene glycol 600 and PAM flocculant with a weight average molecular weight of 10 million g / mol". The resulting lithium carbonate product P8 was obtained.

[0104] Example 9

[0105] Lithium carbonate was extracted from brine according to the method of Example 1, except that the amounts of polyethylene glycol 600 and PAM flocculant were different. Specifically, in S1, 15 wt% of polyethylene glycol 600 and 7 wt% of PAM flocculant were added based on the weight of the brine. Lithium carbonate product P9 was obtained. Some PAM and polyethylene glycol remained undissolved in the brine.

[0106] Example 10

[0107] Lithium carbonate was extracted from brine according to the method in Example 1, except that the evaporation temperature and time were different. Specifically, in S3, "evaporation temperature of 90°C (vacuum distillation) and time of 2 hours" were replaced with "evaporation temperature of 75°C (vacuum distillation) and time of 3 hours". The resulting lithium carbonate product P10 was obtained.

[0108] Example 11

[0109] Lithium carbonate was extracted from brine according to the method in Example 1, except that in S3, after lithium precipitation, the sample was filtered, stirred, and washed four times with water. The resulting lithium carbonate product was P11.

[0110] Example 12

[0111] Lithium carbonate was extracted from brine according to the method in Example 1, except that in S1, "adjusting the pH to 9 with a pH adjuster, then centrifuging again at 10000 r / min for 4 min" was replaced with "adjusting the pH to 10 with a pH adjuster, then centrifuging again at 20000 r / min for 4 min". The resulting lithium carbonate product P12 was obtained.

[0112] Example 13

[0113] Lithium carbonate was extracted from brine according to the method of Example 1, except that in S1, polyaluminum chloride (PAC) with a weight-average molecular weight of 2 million g / mol was used instead of an equal weight of magnesium iron silicate. The Na in the brine was used to extract lithium carbonate. + Content and Mg 2+ Based on the content, the Na content of the first liquid phase product was determined. + The removal rate was 51.29%, Mg 2+ The removal rate was 57.84%. Lithium carbonate product P13 was obtained.

[0114] It can be seen that replacing an equal weight of polyferric magnesium silicate with PAC reduces the aggregation and deposition effect.

[0115] Comparative Example 1

[0116] Lithium carbonate was extracted from brine according to the method in Example 1, except that after adding magnesium iron silicate to the tank, centrifugation was not used to accelerate sedimentation; instead, natural sedimentation was allowed for 3 hours. The Na+ content in the brine was then used as the basis for the extraction.+ Content and Mg 2+ Based on the content, the Na content of the first liquid phase product was determined. + The removal rate was 23.09%, Mg 2+ The removal rate was 27.71%. Lithium carbonate product D1 was obtained.

[0117] It can be seen that after adding magnesium iron silicate to the tank, without centrifugation to accelerate sedimentation, a large amount of sodium and magnesium ions in the brine did not precipitate out, causing the calcium and magnesium removal resin, boron removal resin and chlorine removal resin to become clogged. The resins became ineffective after supersaturation, and the MVR equipment suffered from severe scaling, which could easily cause equipment damage.

[0118] Comparative Example 2

[0119] Lithium carbonate was extracted from brine according to the method in Example 1, except that S2 was not performed; that is, the second liquid phase product obtained in S1 was not filtered through the oleophobic polyceramic membrane system, but was directly subjected to S3. The content of polyethylene glycol 600 in the second liquid phase product was 84.31 g / L.

[0120] Without S2, the residual organic matter after the brine is centrifuged twice cannot be recovered, and the residual polyethylene glycol 600 and a small amount of flocculant will cause pollution and dissolution of the subsequent calcium and magnesium removal resin, leading to the failure of the later process.

[0121] Comparative Example 3

[0122] Lithium carbonate was extracted from brine according to the method in Example 1, except that in S3, the third liquid phase product obtained in S2 was not passed through the calcium and magnesium removal resin, boron removal resin, and anion dechlorination resin. Lithium carbonate product D3 was obtained.

[0123] Comparative Example 4

[0124] Lithium carbonate was extracted from brine according to the method in Example 1, except that polyethylene glycol 600 and PAM flocculant were not added to the first liquid phase product and no secondary centrifugation was performed. Lithium carbonate product D4 was obtained.

[0125] Comparative Example 5

[0126] Lithium carbonate was extracted from brine according to the method of Example 1, except that after adding polyethylene glycol 600 and PAM flocculant to the first liquid phase product, it was not subjected to secondary centrifugation and sedimentation, but was allowed to settle naturally to obtain lithium carbonate product D5.

[0127] The purity of the lithium carbonate products obtained in each example and comparative example was tested, and the results are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] Table 1 (continued 1)

[0132]

[0133]

[0134] Table 1 (continued 2)

[0135]

[0136]

[0137] Table 1 (continued 3)

[0138]

[0139]

[0140] As shown in Table 1, the lithium carbonate extracted from brine using the method of this invention in Examples 1-13 yielded lithium carbonate products with a purity of over 97%. Among them, lithium carbonate product P1, except for slightly lower lithium carbonate content and slightly excessive magnesium and chloride ion content, met the battery-grade lithium carbonate standard and is considered a superior grade industrial product. Example 11 further enhanced the water washing effect after lithium precipitation, and the resulting lithium carbonate product P11 met the battery-grade lithium carbonate standard. In Comparative Example 1, after adding magnesium iron silicate, natural sedimentation was allowed instead of centrifugation to accelerate sedimentation, resulting in reduced sedimentation efficiency. The brine after secondary sedimentation and filtration still contained significant salt content, clogging the calcium-magnesium removal resin, boron removal resin, and chlorine removal resin. This led to severe scaling in the MVR equipment, and the purity of the resulting lithium carbonate product was significantly reduced, while the impurity content increased significantly. In Comparative Example 2, S2 was omitted, and the second liquid phase product obtained from S1 was directly subjected to S3. The residual organic matter after the secondary centrifugation of the brine could not be recovered, and the residual polyethylene glycol 600 and a small amount of flocculant caused contamination and dissolution of the subsequent calcium-magnesium removal resin, leading to failure of later processes. In Comparative Example 3, calcium-magnesium, boron, and chlorine removal were omitted. In Comparative Example 4, polyethylene glycol 600 and PAM flocculant were not added, and secondary centrifugation was not performed. In Comparative Example 5, polyethylene glycol 600 and PAM flocculant were added, but secondary centrifugation was not performed; natural sedimentation was used instead. The purity of the resulting lithium carbonate product was significantly reduced, and the impurity content increased significantly.

[0141] Furthermore, Example 4 lowered the pH of the brine before mixing with magnesium iron silicate; Example 5 used magnesium iron silicate with a lower weight-average molecular weight; Example 6 used a lower centrifugation rate for the first centrifugation sedimentation; Example 7 used polyethylene glycol with a lower weight-average molecular weight; Example 8 changed the types of water-soluble polymers and flocculants; Example 10 lowered the concentration and evaporation temperature; Example 12 lowered the centrifugation rate for the second centrifugation sedimentation; and Example 13 changed the type of the first flocculant. Compared with Examples 4-8 and 10-13, Example 1 yielded a lithium carbonate product with higher purity and lower impurity content. Example 9 increased the amount of water-soluble polymers and flocculants. Compared with Example 9, Example 1 not only yielded a lithium carbonate product with higher purity but also eliminated the risk of membrane clogging by the ceramic membrane. This demonstrates that by further selecting appropriate pH values ​​of the brine before mixing with magnesium iron silicate, weight-average molecular weights of magnesium iron silicate and polyethylene glycol, centrifugation rates for primary and secondary centrifugation, types of water-soluble polymers, the first flocculant, and the second flocculant, concentration and evaporation temperatures, and dosages of water-soluble polymers and the second flocculant, not only can the quality of lithium carbonate products be further improved, but the continuous and stable operation of the equipment can also be ensured.

[0142] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for extracting lithium carbonate from brine, characterized in that, The method includes: S1. The brine and the first flocculant are first mixed and centrifuged once to obtain a first liquid phase product; the first liquid phase product, the water-soluble polymer, and the second flocculant are second mixed and centrifuged twice to obtain a second liquid phase product; wherein, the first flocculant is selected from magnesium iron silicate and / or polyaluminum chloride; the second flocculant is selected from at least one of polyacrylamide, polyaluminum chloride, and polyferric chloride. S2. Remove the residual first flocculant, water-soluble polymer and second flocculant from the second liquid phase product to obtain the third liquid phase product; S3. The third liquid phase product is subjected to calcium, magnesium, boron and chlorine removal to obtain a fourth liquid phase product; the fourth liquid phase product is concentrated, lithium is precipitated, separated, washed with water and dried to obtain the lithium carbonate product.

2. The method according to claim 1, characterized in that, The first flocculant is magnesium iron silicate.

3. The method according to claim 1, characterized in that, The weight-average molecular weight of the polyferric magnesium silicate is 300,000 to 7,000,000 g / mol.

4. The method according to claim 1, characterized in that, The weight-average molecular weight of the polyferric magnesium silicate is 400,000 to 6,000,000 g / mol.

5. The method according to any one of claims 1 to 4, characterized in that, In step S1, the pH value of the brine is first adjusted to 8-10, and then it is mixed with the first flocculant.

6. The method according to claim 1, characterized in that, In step S1, the pH value of the second mixed liquid is adjusted to 8-10, and then the second centrifugation sedimentation is performed.

7. The method according to claim 1, characterized in that, The conditions for the first centrifugal sedimentation include: a centrifugation rate of 8000-30000 r / min and a time of 3-5 min.

8. The method according to claim 1 or 2, characterized in that, Based on the weight of the brine, the amount of the first flocculant is 1-3 wt%.

9. The method according to claim 1 or 2, characterized in that, The conditions for the secondary centrifugation sedimentation include: a centrifugation rate of 12,000-30,000 r / min and a time of 3-5 min.

10. The method according to any one of claims 1 to 4, characterized in that, Based on the weight of the brine, the amount of the water-soluble polymer is 5-10 wt%, and the amount of the second flocculant is 3-5 wt%.

11. The method according to claim 1, characterized in that, The weight-average molecular weight of the water-soluble polymer is 600-25000 g / mol.

12. The method according to claim 1, characterized in that, The water-soluble polymer is selected from at least one of polyethylene glycol, starch, and hydroxymethyl cellulose.

13. The method according to claim 12, characterized in that, The water-soluble polymer is polyethylene glycol.

14. The method according to claim 1, characterized in that, The second flocculant is polyacrylamide.

15. The method according to claim 1 or 14, characterized in that, The weight-average molecular weight of the second flocculant is 5 million to 20 million g / mol.

16. The method according to claim 1, characterized in that, In S2, the removal method includes passing the second liquid phase product through an oleophobic polyceramic membrane.

17. The method according to claim 1, characterized in that, In S3, the concentration method includes: evaporating the fourth liquid phase product; wherein the evaporation conditions include: the pH value of the fourth liquid phase product is 5-8, the temperature is 80-120℃, and the time is 1-3h.

18. The method according to claim 1, characterized in that, In S3, the lithium precipitation method includes: reacting the concentrated solution obtained from the concentration with carbonate; The reaction time is 20-40 minutes.

19. The method according to claim 18, characterized in that, The carbonate is sodium carbonate and / or potassium carbonate.

20. The method according to claim 18, characterized in that, In the concentrated solution obtained by concentration, the amount of sodium carbonate used is 8-11g, with 1g of lithium element as the weight.

21. The method according to any one of claims 1 to 4, characterized in that, The method further includes: crushing and demagnetizing the dried product to obtain the lithium carbonate product.

22. A lithium carbonate product obtained by the method of any one of claims 1-21.

23. A positive electrode plate, characterized in that, The positive electrode includes the lithium carbonate product as described in claim 22.

24. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 23.

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