Method for preparing battery-grade lithium carbonate from low-grade crude lithium carbonate based on causticization method

Abstract

The application provides a method for preparing battery-grade lithium carbonate from low-grade crude lithium carbonate based on causticization, comprising the following steps: mixing and heating pre-processed crude lithium carbonate and calcium hydroxide to generate a causticizing solution; removing metal from the causticizing solution; heating and evaporating the causticizing solution to obtain a lithium hydroxide solid-liquid mixture; cooling and crystallizing the lithium hydroxide solid-liquid mixture according to a set grading cooling program to obtain lithium hydroxide crystals and lithium hydroxide mother liquor; performing particle grading through hydraulic diversion; dehydrating large-particle lithium hydroxide and adding a cleaning solution in a set proportion to perform agitation washing to obtain lithium hydroxide wet material; performing centrifugation and leaching synchronous treatment on the wet material to obtain lithium hydroxide solid; dissolving the lithium hydroxide solid in water and reacting with carbon dioxide to obtain battery-grade lithium carbonate. The application provides a high-value utilization method for low-grade crude lithium carbonate, and uses low-grade crude lithium carbonate and calcium hydroxide as raw materials to prepare battery-grade lithium carbonate which is stable in quality, high in grade, high in economic value and meets corresponding standard requirements.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium carbonate preparation, and particularly relates to a method for preparing battery-grade lithium carbonate from low-grade crude lithium carbonate based on a causticization method. BACKGROUND

[0002] Lithium primary resources related enterprises are limited by technical barriers of the backend purification step and production line construction problems, and most of them produce industrial-grade lithium carbonate as the external sales product. Industrial-grade lithium carbonate needs to be further processed into battery-grade lithium carbonate and battery-grade lithium hydroxide monohydrate to supply positive material and electrolyte manufacturers.

[0003] The existing causticization method for producing battery-grade lithium carbonate has high requirements for the quality of raw materials, otherwise there will be problems such as low yield, and it is difficult to industrialize batch production. Impurity elements such as fluorine and boron have different contents according to the type of lithium raw material, among which the fluorine content of lithium mica material is high, the boron, chloride ion and sulfate ion of salt lake material are high, and the recovered lithium raw material is related to the recovery process. Silicon and aluminum impurities are mostly derived from calcium hydroxide, and pure calcium hydroxide on the market reaches more than 3000 yuan / ton, which greatly increases the production cost; in addition, the conventional causticization method for purifying lithium carbonate is difficult to obtain pure battery-grade lithium carbonate that meets the relevant industry standards. SUMMARY

[0004] In view of this, the present application aims to provide a method for preparing battery-grade lithium carbonate from low-grade crude lithium carbonate based on a causticization method, which aims to solve at least one technical problem in the background art.

[0005] The present application is implemented as follows:

[0006] The method for preparing battery-grade lithium carbonate from low-grade crude lithium carbonate based on a causticization method comprises the following steps:

[0007] The pretreated low-grade crude lithium carbonate and calcium hydroxide are mixed and heated for causticization reaction to generate causticization liquid and calcium carbonate residue, and the main reaction equation is Li2CO3+Ca(OH)2=2LiOH+CaCO3↓; then the causticization liquid is subjected to demetallization treatment;

[0008] The demetallized causticization liquid is heated and concentrated to obtain condensed water and lithium hydroxide solid-liquid mixture, so that the lithium content of the lithium hydroxide solid-liquid mixture reaches the set concentration target;

[0009] The lithium hydroxide solid-liquid mixture is cooled and crystallized according to the set staged cooling program to obtain lithium hydroxide crystals and lithium hydroxide mother liquor;

[0010] The lithium hydroxide crystals and lithium hydroxide mother liquor are subjected to particle classification by hydraulic diversion to separate small-particle lithium hydroxide with high impurity content from large-particle lithium hydroxide with low impurity content.

[0011] The low-impurity-content large-particle lithium hydroxide is subjected to dehydration treatment, and then a cleaning solution is added in a set proportion for stirring and washing, and after solid-liquid separation, a stirred and washed solution and lithium hydroxide wet material are obtained; the lithium hydroxide wet material is subjected to centrifugal and leaching synchronous treatment, and a washing solution and lithium hydroxide solid are obtained;

[0012] The lithium hydroxide solid is dissolved in water and subjected to carbonation reaction with carbon dioxide, and the main reaction equation is: 2LiOH+2H2O+CO2=Li2CO3↓+3H2O, and after the carbonation is completed, centrifugal treatment is performed to obtain battery-grade lithium carbonate wet product and carbonation mother liquor;

[0013] The battery-grade lithium carbonate wet product is subjected to drying and crushing to obtain battery-grade lithium carbonate product.

[0014] Further, the target temperature during the cooling crystallization is set to 35-40 DEG C, and the node temperature is 65 DEG C-70 DEG C; the staged temperature reduction program is that during the reduction from the initial temperature to the node temperature, the temperature is reduced by 1 DEG C every 5.5-6.5 min; and during the reduction from the node temperature to the target temperature, the temperature is reduced by 1 DEG C every 3.5-4.5 min. The initial temperature refers to the initial temperature when the lithium hydroxide solid-liquid mixture after evaporation and concentration is transported to the crystallization equipment, which is equal to or slightly less than the temperature set during the evaporation and concentration, and the temperature during the evaporation and concentration is adjusted according to actual needs (generally, it can be set to 90-100 DEG C), and thus is not specifically limited herein.

[0015] The present application utilizes the crystallization rule difference of lithium hydroxide, lithium carbonate and impurities, improves the crystallization process, and is beneficial to the effective separation of the product and impurities.

[0016] The higher the temperature is, the more conducive to the crystal growth of lithium carbonate (generally, the suitable temperature is 80 DEG C), and the reduction of the temperature reduces the purity and particle size of lithium carbonate, and with the reduction of the temperature, the average particle size of lithium carbonate crystals is below 40 mu m; the particles of many impurities such as silicon, boron, aluminum and fluorine are small and medium-sized crystals.

[0017] The present application controls the cooling temperature of the solution during the crystallization, so that most of the lithium hydroxide forms coarse particles, and the particle size of the coarse lithium hydroxide particles is usually above 350 mu m, the impurity content in the small particle crystals is high, and the impurity content in the large particle crystals is low, which is further beneficial to the subsequent impurity separation through particle classification.

[0018] Further, the pretreatment steps of the low-grade coarse lithium carbonate and calcium hydroxide include:

[0019] The low-grade coarse lithium carbonate and calcium hydroxide are respectively mixed with a solution for slurry, and the solution selects at least one of water, condensed water obtained by evaporation and concentration, and carbonation mother liquor;

[0020] The mixed slurry is finely ground by wet grinding method.

[0021] The raw material calcium hydroxide does not require high quality, and the main content is not less than 85%.

[0022] Further, the temperature of the causticization reaction is 60-80 DEG C, and the reaction is kept for 2-3 hours; the specific steps of the demetallization treatment are that the causticizing liquid is flowed into a resin system, and then at least metal cations including calcium and magnesium are removed to obtain the preliminarily purified causticizing liquid.

[0023] Further, the method further comprises that the small-particle lithium hydroxide mother liquor with high impurity content is mixed with the causticizing liquid to remove crystals, and then filtration is performed to remove impurities, so as to obtain a crystal removal liquid; the crystal removal liquid is recycled and utilized, and is mixed with the causticizing liquid to perform evaporation concentration, so as to reduce the impurity concentration in the causticizing liquid.

[0024] Further, the volume ratio of the small-particle lithium hydroxide mother liquor to the causticizing liquid is 1:0.9-1.1.

[0025] Further, when the after-stirring liquid and the washing liquid meet the impurity requirement, the small-particle lithium hydroxide mother liquor with high impurity content and the causticizing liquid are mixed to remove crystals; the cleaning liquid is at least one of water, the after-stirring liquid meeting the impurity requirement or the washing liquid; the impurity requirement is that silicon is less than or equal to 20 mg / L, boron is less than or equal to 30 mg / L, aluminum is less than or equal to 20 mg / L, and fluorine is less than or equal to 40 mg / L.

[0026] Further, the concentration target is that the lithium content reaches 70-75 g / L.

[0027] Further, during the stirring, the weight ratio of the cleaning liquid to the large-particle lithium hydroxide after dehydration is 1.5-2.5:1; during the leaching, the weight ratio of the cleaning liquid to the lithium hydroxide wet material is 1:8-12.

[0028] Further, the carbonization reaction between the lithium hydroxide solid after being dissolved in water and carbon dioxide is specifically as follows:

[0029] Water is added to the lithium hydroxide solid in a solid-liquid ratio of 1:4.5-4.7 to dissolve the lithium hydroxide solid and form a lithium hydroxide solution;

[0030] The lithium hydroxide solution is filtered by an ultrafiltration membrane;

[0031] Carbon dioxide is introduced into the membrane-filtered lithium hydroxide solution to perform a carbonization reaction, the end point of the carbonization reaction is set to pH reaching 10.5-11.5, and the carbonization reaction temperature is set to 80-85 DEG C.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] 1. This invention provides a high-value utilization method for low-grade crude lithium carbonate, which uses low-grade crude lithium carbonate and calcium hydroxide as raw materials to prepare battery-grade lithium carbonate with stable quality, high grade, high economic value, and meeting the corresponding standard requirements. This solves the problems of existing technologies that can only use specific processes to process specific types of lithium battery waste, have high requirements for raw materials, low lithium extraction efficiency, and low economic value.

[0034] 2. This invention has low requirements for raw material quality, low cost, and meets the needs of industrial production.

[0035] 3. This invention utilizes a specific process flow to address the difficulty in removing anionic impurities under alkaline conditions. By comparing and analyzing the differences in crystallization patterns of lithium hydroxide, lithium carbonate, and other impurities, the invention improves the crystallization and separation processes to achieve effective separation of the target product and impurities, thereby enabling the classification and treatment of different impurities.

[0036] 4. This invention adheres to the principle of not adding or introducing any materials, and aims to achieve the industrial-scale mass production of battery-grade lithium carbonate using low-grade crude lithium carbonate such as recycled materials, thereby maximizing the utilization of lithium resources and contributing to the green recycling of lithium resources in the battery industry.

[0037] 5. The process of this invention produces no "three wastes" (waste gas, wastewater, and solid waste), consumes little energy, and has low economic cost, which is suitable for industrialized mass production and meets market demands. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0040] Example 1

[0041] like Figure 1 As shown, the method for preparing battery-grade lithium carbonate from low-grade crude lithium carbonate based on causticization includes the following steps:

[0042] (1) Criticism transformation

[0043] Take 150 grams of lithium carbonate powder extracted from Zabuye stone with a lithium carbonate content of 88.35%, add 2L of water and mix evenly to form a slurry.

[0044] Take 170 grams of calcium hydroxide powder with a purity of 85%, add 2L of water and mix evenly to form a slurry;

[0045] After the two slurries are thoroughly mixed, they are ground into a fine mixed slurry using a wet refining machine.

[0046] The mixed fine slurry is poured into a reaction kettle, heated to 60℃, and kept for 3 hours to obtain a causticizing liquid and calcium carbonate residue;

[0047] The causticizing liquid after solid-liquid separation is fed into a resin system by a delivery pump, and the metal cation impurities such as calcium and magnesium are removed by ion exchange to achieve preliminary purification of the causticizing liquid.

[0048] (2) Evaporation concentration and cooling crystallization

[0049] The causticizing liquid after demetallization is heated to 90℃, and evaporated and concentrated to obtain condensed water and a lithium hydroxide solid-liquid mixture, and the lithium content in the lithium hydroxide solid-liquid mixture reaches 70g / L;

[0050] The lithium hydroxide solid-liquid mixture is fed into a crystallization kettle for cooling crystallization, and the cooling crystallization speed is controlled to allow lithium hydroxide particles to grow, and the cooling speed is required to be 1℃ per 6min when the temperature is 90℃-65℃, and 1℃ per 4min when the temperature is 64℃-40℃, and after the cooling crystallization is completed, lithium hydroxide crystals and lithium hydroxide mother liquor are obtained.

[0051] (3) Particle classification

[0052] The lithium hydroxide crystals and lithium hydroxide mother liquor are classified by a hydrocyclone device to separate small lithium hydroxide particles with high impurity content from large lithium hydroxide particles with low impurity content. Hydrocyclone is a particle classification method that utilizes the different motion trajectories of lithium hydroxide particles of different sizes in a composite force field. The commonly used composite forces include gravity, centrifugal force, and fluid resistance, and the size of these forces is related to the particle size. The result of the action of these forces on the particles is that lithium hydroxide particles of different sizes produce different motion trajectories and are then collected separately. Different devices are formed according to different composite force fields, such as cross-flow classification equipment, centrifugal hydrocyclone equipment, and upflow hydrocyclone equipment, which can all achieve particle classification. Any of the above hydrocyclone devices can be used to classify lithium hydroxide particles in the present application.

[0053] In this embodiment, a hydrocyclone device (which belongs to a centrifugal hydrocyclone device) is used to classify lithium hydroxide particles. Specifically, the flow of the mixture of lithium hydroxide crystals and lithium hydroxide mother liquor is fed into the hydrocyclone from the tangent direction to produce outer and inner cyclones. Under the combined action of centrifugal force, fluid resistance, gravity, and buoyancy, large lithium hydroxide particles move towards the edge wall and are discharged from the underflow port, and small lithium hydroxide particles move towards the center and are discharged from the overflow port, thereby separating small lithium hydroxide particles with high impurity content from large lithium hydroxide particles with low impurity content.

[0054] (4) Stirring and washing to remove impurities and centrifugal leaching

[0055] The obtained large-particle lithium hydroxide is continuously conveyed to a scraper centrifuge for dewatering, and water is added to the large-particle lithium hydroxide at a liquid-solid ratio of 2:1 for stirring washing, so as to wash out a plurality of impurities such as silicon, boron, aluminum and fluorine, and obtain a stirring-washed liquid and lithium hydroxide wet material;

[0056] The lithium hydroxide wet material is conveyed to a centrifuge for centrifugation, and water is used for leaching at the same time, and the liquid-solid ratio is set to 1:10 during leaching, so as to obtain a washing liquid and lithium hydroxide solid.

[0057] (5) Preparation of battery-grade lithium carbonate wet product by dissolution and carbonation

[0058] The lithium hydroxide solid is conveyed into a reaction container and dissolved by adding deionized water, and the solid-liquid ratio is 1:4.5, forming a lithium hydroxide solution;

[0059] The lithium hydroxide solution is filtered by an ultrafiltration membrane;

[0060] Carbon dioxide is introduced into the membrane-filtered lithium hydroxide solution, and the temperature is raised to 80°C to cause carbonation reaction, and the reaction is terminated when the pH of the reaction liquid reaches 10.5;

[0061] After the carbonation is completed, the centrifuge is centrifuged to obtain a battery-grade lithium carbonate wet product and a carbonation mother liquor.

[0062] (6) Preparation of battery-grade lithium carbonate product

[0063] After the lithium carbonate wet product is dried, it is sent into an air flow crushing system through a pneumatic conveying system, crushed to a certain particle size, and packaged to obtain a battery-grade lithium carbonate product.

[0064] The battery-grade lithium carbonate product prepared in Example 1 is detected by inductively coupled plasma emission spectrometer (ICP-OES) and atomic absorption spectrophotometer, and the detection results are shown in Table 1.

[0065] Table 1 Composition of battery-grade lithium carbonate prepared in Example 1

[0066]

[0067] The battery-grade lithium carbonate line in Table 1 refers to YS / T 582-2013 Battery-Grade Lithium Carbonate. As can be seen from Table 1, the purity of the lithium carbonate prepared in this example is not less than 99.993%, and the impurity content is much lower than the composition requirement of the industry standard for battery-grade lithium carbonate.

[0068] Example 2

[0069] On the basis of Example 1, a desolvation filtration step is added, and the small-particle lithium hydroxide with high impurity content obtained after particle classification in step (3) is desolvated, specifically as follows:

[0070] The small particle lithium hydroxide mother liquor is mixed with the causticizing liquid obtained in step (1) to remove crystals, and the volume ratio of the mixture is 1:1. After the mixed removal of crystals, the mixture is filtered to obtain a crystal removal liquid, and the solid impurities containing silicon, boron, aluminum, fluorine, etc. are filtered out;

[0071] The crystal removal liquid is returned to step (2), and the crystal removal liquid is mixed with the causticizing liquid to evaporate and concentrate. This step reduces the impurity concentration in the evaporation liquid of step (2).

[0072] The battery-grade lithium carbonate product prepared in Example 2 is detected by inductively coupled plasma emission spectrometer (ICP-OES) and atomic absorption spectrophotometer, and the detection results are shown in Table 2.

[0073] Table 2 Composition of battery-grade lithium carbonate prepared in Example 2

[0074]

[0075] As can be seen from Table 2, the purity of lithium carbonate prepared in this example is not less than 99.995%, and the impurity content is much lower than the composition requirement of the industry standard for battery-grade lithium carbonate.

[0076] Example 3

[0077] As Figure 1 shown, the method for preparing battery-grade lithium carbonate from low-grade crude lithium carbonate based on causticization method includes the following steps:

[0078] (1) Causticization transformation

[0079] Take 150 grams of low-grade lithium carbonate powder recovered from waste batteries (lithium carbonate content is 87%), add 2L water and mix uniformly into a slurry;

[0080] Take 170 grams of calcium hydroxide powder with a purity of 92%, add 2L water and mix uniformly into a slurry;

[0081] After the two slurries are thoroughly mixed, a wet grinding machine is used to grind them into a fine mixture;

[0082] Pour the fine mixture into a reaction kettle, heat to 70°C, and keep the temperature for 2.5 hours to obtain a causticizing liquid and calcium carbonate residue;

[0083] The causticizing liquid after solid-liquid separation is fed into the resin system by a delivery pump, and the calcium, magnesium and other metal cation impurities are removed by ion exchange to achieve the preliminary purification of the causticizing liquid.

[0084] (2) Evaporation concentration and cooling crystallization

[0085] The caustic liquor after demetallization treatment and the lithium hydroxide solution obtained in step (3) are mixed, heated and warmed to 95℃, and concentrated by evaporation to obtain condensed water and a lithium hydroxide solid-liquid mixture, the lithium content of the lithium hydroxide solid-liquid mixture reaching 75 g / L, and the condensed water is recycled and used as the dissolving water of the slurry in step (1);

[0086] The lithium hydroxide solid-liquid mixture is transported to a crystallization kettle for cooling crystallization, the cooling crystallization speed is controlled to allow the lithium hydroxide particles to grow, the cooling speed is required to be 1℃ per 6.5 min when the temperature is reduced from 95℃ to 70℃, and 1℃ per 4.5 min when the temperature is reduced from 69℃ to 35℃, and the lithium hydroxide crystals and lithium hydroxide mother liquor are obtained after the cooling crystallization is completed.

[0087] (3) Particle classification and deliquoring filtration

[0088] The lithium hydroxide crystals and lithium hydroxide mother liquor are classified by a hydrocyclone, and the small-particle lithium hydroxide mother liquor with high impurity content is separated from the large-particle lithium hydroxide with low impurity content.

[0089] The small-particle lithium hydroxide mother liquor with high impurity content is mixed with the caustic liquor obtained in step (1) for deliquoring, the mixing volume ratio is 1:1.1, and the mixture is filtered after deliquoring to remove solid impurities such as silicon, boron, aluminum and fluorine; the deliquored liquor is returned to step (2), and the deliquored liquor is mixed with the caustic liquor for evaporation and concentration, and this step is to reduce the impurity concentration in the evaporation liquid in step (2).

[0090] (4) Stirring washing, centrifugal washing

[0091] The large-particle lithium hydroxide with low impurity content is subjected to dewatering treatment, and water is added to the large-particle lithium hydroxide at a liquid-solid ratio of 2:1 for stirring washing to wash out numerous impurities such as silicon, boron, aluminum and fluorine to obtain a stirring-washed liquor and lithium hydroxide wet material;

[0092] The lithium hydroxide wet material is transported to a centrifuge for centrifugation, and washed with water at the same time, the liquid-solid ratio is set to 1:10 to obtain a washing liquor and lithium hydroxide solid.

[0093] After detection, the impurity contents of the stirring-washed liquor and the washing liquor are silicon 18.2 mg / L, boron 24.6 mg / L, aluminum 15.9 mg / L and fluorine 33.3 mg / L, which can be returned to step (2) and mixed with the deliquored liquor and the caustic liquor for evaporation and concentration; or mixed with water as the cleaning liquid for stirring and washing in this step.

[0094] (5) Preparation of battery-grade lithium carbonate wet product by dissolution and carbonization

[0095] The lithium hydroxide solid is transported into a reaction container, deionized water is added for dissolution, the solid-liquid ratio is 1:4.7, and a lithium hydroxide solution is formed;

[0096] The lithium hydroxide solution was filtered through an ultrafiltration membrane.

[0097] Carbon dioxide was introduced into the lithium hydroxide solution after membrane filtration and the temperature was raised to 85°C to initiate a carbonization reaction. The carbonization was terminated when the pH of the reaction solution reached 11.5.

[0098] After carbonization, the product is centrifuged to obtain battery-grade lithium carbonate wet product and carbonization mother liquor. The carbonization mother liquor is returned to step (1) to be used for slurry preparation (as a solution for making slurry).

[0099] (6) Preparation of battery-grade lithium carbonate products

[0100] After being dried, wet lithium carbonate is fed into an air jet milling system via a pneumatic conveying system. After being pulverized to a certain particle size, it is packaged to obtain battery-grade lithium carbonate products.

[0101] The battery-grade lithium carbonate product prepared in Example 3 was tested using an inductively coupled plasma optical emission spectrometer (ICP-OES) and an atomic absorption spectrophotometer. The test results are shown in Table 3.

[0102] Table 3. Composition of battery-grade lithium carbonate obtained in Example 3

[0103]

[0104] As shown in Table 3, the lithium carbonate obtained in this embodiment has a purity of not less than 99.995%, and the content of various impurities is far lower than the industry standard requirements for the composition of battery-grade lithium carbonate.

[0105] Example 4

[0106] like Figure 1 As shown, the method for preparing battery-grade lithium carbonate from low-grade crude lithium carbonate based on causticization includes the following steps:

[0107] (1) Criticism transformation

[0108] Take 150 grams of low-grade lithium carbonate powder (lithium carbonate content is 94%) extracted from salt lake lithium carbonate powder, add 2L of water and mix evenly to form a slurry.

[0109] Take 170 grams of calcium hydroxide powder with a purity of 86%, add 2L of water and mix evenly to form a slurry;

[0110] After the two slurries are thoroughly mixed, they are ground into a fine mixed slurry using a wet refining machine.

[0111] The mixed slurry was poured into a reaction vessel, heated to 80°C, and kept at that temperature for 2 hours to obtain causticizing liquid and calcium carbonate slag.

[0112] The caustic liquor after solid-liquid separation is fed into the resin system by a delivery pump to remove metal cation impurities such as calcium and magnesium by ion exchange, thereby achieving preliminary purification of the caustic liquor.

[0113] (2) Evaporation concentration and cooling crystallization

[0114] The caustic liquor after demetallization treatment and the lithium hydroxide solution obtained in step (3) are mixed, heated and warmed to 90°C, and evaporated and concentrated to obtain condensed water and a lithium hydroxide solid-liquid mixture, the lithium content of the lithium hydroxide solid-liquid mixture reaching 72 g / L, and the condensed water is recycled and used as the dissolving water for the slurry in step (1).

[0115] The lithium hydroxide solid-liquid mixture is fed into a crystallization kettle for cooling crystallization, the cooling crystallization speed is controlled to allow lithium hydroxide particles to grow, the cooling speed is required to be 1°C per 5.5 min when the temperature is lowered from 90°C to 66°C, and 1°C per 3.5 min when the temperature is lowered from 65°C to 35°C, and after the cooling crystallization is completed, lithium hydroxide crystals and lithium hydroxide mother liquor are obtained.

[0116] (3) Particle classification and decrystallization filtration

[0117] The lithium hydroxide crystals and lithium hydroxide mother liquor are subjected to particle classification by a cross-flow classifier to obtain small-particle lithium hydroxide mother liquor with high impurity content and large-particle lithium hydroxide with low impurity content.

[0118] The small-particle lithium hydroxide mother liquor with high impurity content is mixed with the caustic liquor obtained in step (1) for decrystallization, the mixing volume ratio is 1:0.9, after mixing decrystallization, filtration is performed to obtain a decrystallization solution, and solid impurities such as silicon, boron, aluminum and fluorine are filtered out; the decrystallization solution is returned to step (2), and the decrystallization solution is mixed with the caustic liquor for evaporation concentration, and the purpose of this step is to reduce the impurity concentration in the evaporation liquid in step (2).

[0119] (4) Stirring washing, centrifugal rinsing

[0120] The large-particle lithium hydroxide with low impurity content is subjected to dehydration treatment, water is added at a liquid-solid ratio of 2.5:1 to stir and wash the large-particle lithium hydroxide, and numerous impurities such as silicon, boron, aluminum and fluorine are washed out to obtain a stirred and washed solution and lithium hydroxide wet material;

[0121] The lithium hydroxide wet material is fed into a centrifuge for centrifugation, and rinsing is performed at the same time, the liquid-solid ratio is set to 1:8, and a washing solution and lithium hydroxide solid are obtained.

[0122] After detection, the impurity contents of the stirred and washed solution and the washing solution are silicon 18.6 mg / L, boron 24.0 mg / L, aluminum 15.7 mg / L and fluorine 32.3 mg / L, which can be returned to step (2) and mixed with the decrystallization solution and the caustic liquor for evaporation concentration; or mixed with water as the cleaning liquid for stirring and rinsing in this step.

[0123] (5) Preparation of battery-grade lithium carbonate wet product by dissolving carbonization

[0124] The lithium hydroxide solid is transported into a reaction container, and is dissolved by adding deionized water, with a solid-liquid ratio of 1:4.7, to form a lithium hydroxide solution;

[0125] The lithium hydroxide solution is filtered by an ultrafiltration membrane;

[0126] Carbon dioxide is introduced into the membrane-filtered lithium hydroxide solution, and the temperature is raised to 83°C to cause a carbonization reaction, and the reaction is terminated when the pH of the reaction solution reaches 11.2;

[0127] After the carbonization is completed, centrifugation is performed by a centrifuge to obtain a battery-grade lithium carbonate wet product and a carbonization mother liquor, and the carbonization mother liquor is returned to step (1) for pulping (as a solution for making slurry).

[0128] (6) Preparation of battery-grade lithium carbonate product

[0129] After the lithium carbonate wet product is dried, it is sent into an air flow crushing system by a pneumatic conveying system, is crushed to a certain particle size, and is packaged to obtain a battery-grade lithium carbonate product.

[0130] The battery-grade lithium carbonate product prepared in Example 4 is detected by an inductively coupled plasma optical emission spectrometer (ICP-OES) and an atomic absorption spectrophotometer, and the detection results are shown in Table 4.

[0131] Table 4 Composition of battery-grade lithium carbonate prepared in Example 4

[0132]

[0133] As can be seen from Table 4, the purity of the lithium carbonate prepared in this example is not less than 99.995%, and the content of each impurity is far lower than the composition requirement of the industry standard for battery-grade lithium carbonate.

[0134] Example 5

[0135] As shown in the following, Figure 1 a method for preparing battery-grade lithium carbonate from low-grade coarse lithium carbonate based on causticization, includes the following steps:

[0136] (1) Causticization transformation

[0137] Take 150 grams of lithium mica containing 96% lithium carbonate powder, add 2L water to mix uniformly into a slurry;

[0138] Take 170 grams of calcium hydroxide powder with a purity of 90%, add 2L water to mix uniformly into a slurry;

[0139] After the two slurries are thoroughly mixed, a wet grinding machine is used to grind them into a fine mixed slurry;

[0140] The mixed fine slurry is poured into a reaction kettle, heated to 65℃, and kept for 3 hours to obtain causticizing liquid and calcium carbonate residue;

[0141] The causticizing liquid after solid-liquid separation is fed into the resin system by a delivery pump, and the metal cation impurities such as calcium and magnesium are removed by ion exchange to achieve the preliminary purification of the causticizing liquid.

[0142] (2) Evaporation concentration and cooling crystallization

[0143] The causticizing liquid after demetallization treatment and the lithium hydroxide solution obtained in step (3) are mixed, heated and warmed to 90℃, and evaporated and concentrated to obtain condensed water and lithium hydroxide solid-liquid mixture, and the lithium content in the lithium hydroxide solid-liquid mixture reaches 72g / L, and the condensed water is recycled and used as the dissolving water for the slurry in step (1).

[0144] The lithium hydroxide solid-liquid mixture is fed into a crystallization kettle for cooling crystallization, and the cooling crystallization speed is controlled to allow the lithium hydroxide particles to grow, and the cooling speed is required to be 1℃ per 5.5min when the temperature is reduced from 90℃ to 66℃, and 1℃ per 3.5min when the temperature is reduced from 65℃ to 35℃, and after the cooling crystallization is completed, lithium hydroxide crystals and lithium hydroxide mother liquor are obtained.

[0145] (3) Particle classification and decrystallization filtration

[0146] The lithium hydroxide crystals and lithium hydroxide mother liquor are classified by the upflow hydrocyclone to obtain small particle lithium hydroxide mother liquor with high impurity content and large particle lithium hydroxide with low impurity content.

[0147] The small particle lithium hydroxide mother liquor with high impurity content is mixed with the causticizing liquid obtained in step (1) for decrystallization, and the volume ratio of the mixture is 1:0.9, and after the mixed decrystallization, filtration is performed to obtain a decrystallization liquid, and solid impurities such as silicon, boron, aluminum and fluorine are filtered out; the decrystallization liquid is returned to step (2), and the decrystallization liquid is mixed with the causticizing liquid for evaporation concentration, and the purpose of this step is to reduce the impurity concentration in the evaporation liquid in step (2).

[0148] (4) Stirring washing and centrifugal washing

[0149] The large particle lithium hydroxide with low impurity content is subjected to dehydration treatment, and water is added to the large particle lithium hydroxide at a liquid-solid ratio of 2.5:1 for stirring washing, and a large number of impurities such as silicon, boron, aluminum and fluorine are washed out to obtain a stirring washing liquid and lithium hydroxide wet material;

[0150] The lithium hydroxide wet material is fed into a centrifuge for centrifugation, and at the same time, it is washed with water, and the liquid-solid ratio is set to 1:12 to obtain a washing liquid and lithium hydroxide solid.

[0151] The impurity content of the stirred washing liquid and the washing liquid is 18.6 mg / L of silicon, 24.0 mg / L of boron, 15.7 mg / L of aluminum, and 32.3 mg / L of fluorine, which can be returned to step (2) and mixed with the desalting liquid and the causticizing liquid for evaporation and concentration; or mixed with water as the cleaning liquid for stirring washing and leaching in this step.

[0152] (5) Preparation of battery-grade lithium carbonate wet product by dissolution and carbonization

[0153] The lithium hydroxide solid is delivered into a reaction container and dissolved in deionized water, with a solid-liquid ratio of 1:4.7, to form a lithium hydroxide solution;

[0154] The lithium hydroxide solution is filtered by an ultrafiltration membrane;

[0155] Carbon dioxide is introduced into the membrane-filtered lithium hydroxide solution, and the temperature is raised to 83°C to cause a carbonization reaction, which is terminated when the pH of the reaction liquid reaches 11.2;

[0156] After the carbonization is completed, the centrifuge is used to obtain a battery-grade lithium carbonate wet product and a carbonization mother liquor, and the carbonization mother liquor is returned to step (1) for pulping (as a solution for making slurry).

[0157] (6) Preparation of battery-grade lithium carbonate product

[0158] After the lithium carbonate wet product is dried, it is sent to an air flow crushing system by a pneumatic conveying system, crushed to a certain particle size, and packaged to obtain a battery-grade lithium carbonate product.

[0159] The battery-grade lithium carbonate product prepared in Example 5 is detected by inductively coupled plasma emission spectrometer (ICP-OES) and atomic absorption spectrophotometer, and the detection results are shown in Table 5.

[0160] Table 5 Composition of battery-grade lithium carbonate prepared in Example 5

[0161]

[0162] As shown in Table 5, the purity of the lithium carbonate prepared in this example is not less than 99.996%, and the impurity content is much lower than the composition requirement of the industry standard for battery-grade lithium carbonate.

[0163] Comparative Example 1

[0164] The cooling and temperature reduction program in Example 1 is set to a temperature drop of 1°C every 4 min from 90°C to 40°C, and the rest is the same as Example 1.

[0165] Comparative Example 2

[0166] The cooling and temperature reduction program in Example 1 is set to a temperature drop of 1°C every 6 min from 90°C to 40°C, and the rest is the same as Example 1.

[0167] Comparative Example 3

[0168] The cooling temperature reduction procedure in Example 1 was set to decrease the temperature by 1℃ every 8min from 90℃ to 65℃ and decrease the temperature by 1℃ every 4min from 64℃ to 40℃, and the rest was the same as Example 1.

[0169] Comparative Example 4

[0170] The cooling temperature reduction procedure in Example 1 was set to decrease the temperature by 1℃ every 6min from 90℃ to 65℃ and decrease the temperature by 1℃ every 3min from 64℃ to 40℃, and the rest was the same as Example 1.

[0171] Comparative Example 5

[0172] The particle classification procedure in step (3) was deleted, and the lithium hydroxide crystals were directly dehydrated, stirred, centrifuged and rinsed, and the rest was the same as Example 1.

[0173] The lithium carbonate products prepared in Comparative Examples 1 to 5 were detected by inductively coupled plasma optical emission spectrometer (ICP-OES) and atomic absorption spectrophotometer, and the detection results are shown in Table 6.

[0174] Table 6 Comparison of battery-grade lithium carbonate prepared in Comparative Examples 1 to 5 and Example 1

[0175]

[0176] Comparative Examples 1 and 2 did not use a staged temperature reduction procedure, but were directly cooled from the initial temperature to the target crystallization temperature at the same cooling rate. According to the lithium carbonate composition data recorded in Table 6, the impurity content of the lithium carbonate prepared in Comparative Examples 1 and 2 both met the industry standard, but the content of each impurity component was higher than that of Example 1, especially Na, Ca, Mg, Si, Al, SO4 2- and the like. According to the comparison of Example 1 with Comparative Examples 1 and 2, the impurity removal effect of the staged temperature reduction procedure during cooling crystallization was better than that of the non-staged temperature reduction procedure.

[0177] Comparative Examples 3 and 4 both used a staged temperature reduction procedure, but the cooling rate in the first stage of Comparative Example 3 was much lower than that of Example 1, and the cooling rate in the second stage of Comparative Example 4 was higher than that of Example 1. According to the lithium carbonate composition data recorded in Table 6, the impurity content of the lithium carbonate prepared in Comparative Examples 3 and 4 both met the industry standard, but the content of each impurity component was higher than that of Example 1 and slightly lower than that of Comparative Examples 1 and 2, especially Na, Ca, Mg, Si, Al, SO4 2-etc. By comparing example 1 with comparative examples 3 and 4, it can be seen that the impurity removal effect of example 1 is better than that of comparative examples 3 and 4. In addition, by comparing comparative examples 3 and 4 with comparative examples 1 and 2, it is further verified that the impurity removal effect of using the staged cooling procedure in the cooling crystallization is better than that of not using the staged cooling procedure.

[0178] Comparative example 5 does not use the staged procedure compared with example 1, and the impurity removal effect is greatly reduced. In combination with the lithium carbonate component data recorded in table 6, it can be seen that the content of most impurities of the lithium carbonate prepared in comparative example 5 meets the industry standard, but the content of some impurities such as Si, Al, Mn and Mg exceeds the standard requirement, and the content of the impurities is higher than that of example 1.

[0179] Example 1 of the present application sets a specific staged cooling procedure for cooling crystallization combined with a particle grading process, and high-purity battery-grade lithium carbonate is prepared, which is much better than comparative examples 1 to 5.

[0180] The above-described examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A process for the production of battery grade lithium carbonate from low grade crude lithium carbonate based on the causticization method, characterized in that, The method comprises the following steps: The pretreated low-grade crude lithium carbonate and calcium hydroxide are mixed and heated for causticization reaction to generate caustic liquor and calcium carbonate residue, and the caustic liquor is subjected to demetallization treatment to remove metal impurities; the demetallization treatment step is: the caustic liquor flows into a resin system to remove metal cations including at least calcium and magnesium; The demetallized caustic liquor is heated to evaporate and concentrate to obtain condensed water and lithium hydroxide solid-liquid mixture, so that the lithium content in the lithium hydroxide solid-liquid mixture reaches the concentration target of 70-75 g / L; The lithium hydroxide solid-liquid mixture is cooled and crystallized according to a set staged cooling program to obtain lithium hydroxide crystals and lithium hydroxide mother liquor; the target temperature is set to 35-40℃ and the node temperature is set to 65-70℃ during the cooling and crystallization; the staged cooling program is: during the period from the initial temperature to the node temperature, the temperature is set to decrease by 1℃ for 5.5-6.5 min; during the period from the node temperature to the target temperature, the temperature is set to decrease by 1℃ for 3.5-4.5 min; The lithium hydroxide crystals and the lithium hydroxide mother liquor are subjected to particle classification by hydraulic diversion to separate small-particle lithium hydroxide with high impurity content from large-particle lithium hydroxide with low impurity content; The large-particle lithium hydroxide with low impurity content is subjected to dehydration treatment, then a cleaning liquid with a set proportion is added for stirring and washing, and then solid-liquid separation is performed to obtain a post-stirring and washing liquid and lithium hydroxide wet material; the lithium hydroxide wet material is subjected to synchronous centrifugation and leaching treatment to obtain a washing liquid and lithium hydroxide solid; The lithium hydroxide solid is dissolved in water and subjected to carbonation reaction with carbon dioxide, and then centrifugation treatment is performed to obtain battery-grade lithium carbonate wet product and carbonation mother liquor; The battery-grade lithium carbonate wet product is dried and crushed to obtain battery-grade lithium carbonate product.

2. The process for the preparation of battery grade lithium carbonate from low grade crude lithium carbonate based on causticization process as claimed in claim 1 wherein, The pretreatment step of the low-grade crude lithium carbonate and calcium hydroxide comprises: The low-grade crude lithium carbonate and calcium hydroxide are respectively mixed with a solution to be slurried, and the solution is selected from at least one of water and carbonation mother liquor; The slurried crude lithium carbonate and calcium hydroxide are fully mixed, and the mixed slurry is finely ground by wet grinding.

3. The process for the preparation of battery grade lithium carbonate from low grade crude lithium carbonate based on causticization process as claimed in claim 2 wherein, The solution is selected from condensed water obtained by evaporation and concentration.

4. The process for the production of battery grade lithium carbonate from low grade crude lithium carbonate based on causticization process as claimed in claim 1 or 2 wherein, The temperature of the causticization reaction is 60-80℃, and the reaction is kept for 2-3 h.

5. The process for the preparation of battery grade lithium carbonate from low grade crude lithium carbonate based on causticization process as claimed in claim 1 wherein, The method further comprises: mixing the small-particle lithium hydroxide mother liquor with high impurity content with the caustic liquor to eliminate crystals, and then performing filtration to remove impurities to obtain an elimination liquid; the elimination liquid is recycled and used, and is mixed with the caustic liquor for evaporation and concentration to further reduce the impurity concentration in the caustic liquor.

6. The process for the preparation of battery grade lithium carbonate from low grade crude lithium carbonate based on causticization process as claimed in claim 5 wherein, The volume ratio of the small-particle lithium hydroxide mother liquor to the caustic liquor is 1:0.9-1.

1.

7. The process for the preparation of battery grade lithium carbonate from low grade crude lithium carbonate based on causticization process as claimed in claim 5 wherein, When the post-stirring and washing liquid and the washing liquid meet the impurity requirements, they are mixed with the small-particle lithium hydroxide mother liquor with high impurity content and the caustic liquor to eliminate crystals; the cleaning liquid is selected from at least one of water, the post-stirring and washing liquid or the washing liquid that meet the impurity requirements; the impurity requirements are: silicon ≤20 mg / L, boron ≤30 mg / L, aluminum ≤20 mg / L, and fluorine ≤40 mg / L.

8. The process for the preparation of battery grade lithium carbonate from low grade crude lithium carbonate based on causticization process as claimed in claim 1 wherein, During the stirring and washing, the weight ratio of the cleaning liquid to the large-particle lithium hydroxide after dehydration is 1.5-2.5:1; during the leaching, the weight ratio of the cleaning liquid to the lithium hydroxide wet material is 1:8-12.

9. The process for the preparation of battery grade lithium carbonate from low grade crude lithium carbonate based on causticization process as claimed in claim 1 wherein, The lithium hydroxide solid is dissolved in water and reacts with carbon dioxide, specifically including: According to the solid-liquid ratio of 1:4.5~4.7, water is added to the lithium hydroxide solid to dissolve and form a lithium hydroxide solution; The lithium hydroxide solution is filtered by an ultrafiltration membrane; Carbon dioxide is introduced into the membrane-filtered lithium hydroxide solution to undergo carbonation reaction, and the end point of the carbonation reaction is set to pH 10.5-11.5, and the carbonation reaction temperature is set to 80℃~85℃.

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