Method for removing impurities from lithium-containing materials

Abstract

The present application discloses a method for removing impurities from a lithium-containing material, wherein the lithium-containing material contains a lithium compound and impurities, wherein the lithium compound includes at least one of LiCl and LiOH, and the impurities include at least one of NaCl and KCl, and optionally at least one of NaOH and KOH. The method comprises: S1, obtaining a lithium-containing material, adding anhydrous ethanol to dissolve and filter the lithium-containing material to obtain a crude lithium-containing filtrate, S2, adding water to the crude lithium-containing filtrate to obtain a blended solution, and then distilling the blended solution to obtain a solid-liquid mixture containing a solid and a mother liquor, and S3, filtering the solid-liquid mixture, then washing and drying the solid to obtain a high-purity lithium compound, wherein the mother liquor includes unremoved impurities and a composite solvent, wherein the composite solvent includes water and ethanol, and the mass percentage of ethanol is 50wt% to 70wt% based on the mass of the composite solvent. The method of the present application can precipitate a high-purity lithium salt product with low lithium salt loss and high yield.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and in particular to a method for removing impurities from lithium-containing materials. Background Art

[0002] With the vigorous development of new energy vehicles, the market for lithium battery positive electrode materials has gradually shifted from lithium iron phosphate to ternary composite materials. In particular, the development of high-nickel ternary materials has prompted the demand for lithium salts to gradually shift from lithium carbonate to lithium hydroxide / lithium chloride. Therefore, the research and preparation of high-quality lithium hydroxide / lithium chloride products is of great significance. From the perspective of lithium extraction technology, whether it is lithium extraction from ore or brine, the current main technology is the wet process, that is, lithium enters the solution together with other elements, and lithium is subsequently extracted from the solution. Among them, since potassium, sodium and other ions are monovalent and belong to the same group of elements as lithium ions, with similar properties, it is more difficult to remove potassium and sodium ions.

[0003] The traditional methods for removing potassium and sodium from monovalent lithium compounds are as follows: ① Lithium sulfate freezing method: The lithium concentrate is roasted, acidified, pulped, and leached to obtain a preliminary concentrated lithium sulfate solution, sodium hydroxide is added, and the temperature is cooled and frozen to 5°C to 10°C. After sodium sulfate is precipitated, lithium hydroxide monohydrate is obtained. However, Na is not completely removed, and a large amount of Na2SO4 will remain in the solution, reducing the purity of lithium hydroxide. ② Electrolysis method: Using brine or lithium sulfate, lithium carbonate as raw materials, lithium hydroxide is obtained by ion migration under the action of an electric field. A method for removing sodium and potassium from a lithium sodium potassium solution in the prior art comprises the following steps: subjecting the lithium sodium potassium solution to electrodialysis, wherein the sodium and potassium ions migrate under the action of an electric field, thereby removing sodium and potassium, and obtaining a lithium-containing solution. After other treatments, lithium hydroxide is obtained. The cost of the permeable membrane of this method is high, and the instability leads to the need for frequent replacement, which increases costs. ③ Adding a sodium removal refiner to the lithium product: In the prior art, according to Na in the solution of crude lithium hydroxide, + A special refining agent is added to a concentration of 5wt% to obtain a refined liquid. However, this method depends on the refining agent, which increases the cost of the refining agent and the complexity of the refining process. ④ Multiple recrystallization method: The existing technology evaporates and concentrates the lithium hydroxide aqueous solution to a slurry solid content of 5wt% to 10wt%, then cools it to 30℃ to 40℃ to precipitate lithium hydroxide monohydrate crystals, separates the slurry into solid and liquid, and washes the crystals to obtain lithium hydroxide monohydrate wet crystals. The obtained lithium hydroxide monohydrate product is not pure enough, and the recrystallization production process is repeated until lithium hydroxide monohydrate crystals with qualified product quality are obtained. Although this method is simple, it has the problems of unstable product quality, repeated production operations, and low production efficiency. Therefore, there is a need for a new simple method for removing sodium and potassium ions from a solid or solution (lithium-containing material) containing lithium ions, sodium ions and potassium ions. Summary of the Invention

[0004] In view of this, the present application provides a method for removing impurities from lithium-containing materials. First, the lithium-containing material is dissolved in anhydrous ethanol, and insoluble impurities are removed by filtration. Then, an appropriate amount of water is added to the ethanol solution of high-concentration lithium salt to form a blended solution. The blended solution is distilled and crystallized, and the ethanol concentration in the mother liquor at the end point of the distillation is coordinated and controlled to precipitate a high-purity lithium salt product, and the lithium salt loss is small, the yield is high, and the distillation loss is low.

[0005] In a first aspect, the present application provides a method for removing impurities from a lithium-containing material, wherein the lithium-containing material contains a lithium compound and impurities, wherein the lithium compound includes at least one of LiCl and LiOH, and the impurities include at least one of NaCl and KCl, and optionally at least one of NaOH and KOH.

[0006] The method comprises at least the following steps:

[0007] S1. Obtain a lithium-containing material, dissolve the lithium-containing material in anhydrous ethanol, and filter to obtain a crude lithium-containing filtrate and a filter residue, wherein the filter residue contains at least one of the impurities. S2. Add water to the crude lithium-containing filtrate to obtain a blended solution, and then distill the blended solution to obtain a solid-liquid mixture containing a solid and a mother liquor. S3. Filter the solid-liquid mixture, and then wash and dry the solid to obtain a high-purity lithiate. The mother liquor comprises unremoved impurities and a composite solvent, the unremoved impurities are dissolved in the composite solvent, and the composite solvent comprises water and ethanol, wherein the mass percentage of the ethanol is n wt%, based on the mass of the composite solvent, and the value of n is in the range of 50≤n≤70.

[0008] Both monovalent lithium compounds and sodium / potassium impurity salts have high solubility in water. The existing technology uses pure water to remove sodium / potassium impurity salts from lithium-containing materials, which will result in a large loss of lithium, reduce the yield of lithium salts, and require multiple recrystallizations, which increases the experimental process and increases costs. In view of the miscibility of water and some organic solvents, this application first uses an ethanol solution to remove most of the impurities in the lithium-containing material, and then adds water for distillation and crystallization. The solubility difference of lithium compounds and sodium / potassium impurity salts in organic solvent-water blended solutions at different ratios is utilized to dissolve the lithium compounds as little as possible in the mixed solvent, while the sodium / potassium impurity salts are guaranteed to dissolve as much as possible, thereby achieving efficient removal of sodium / potassium impurity salts from the lithium-containing material.

[0009] The present application first dissolves the lithium-containing material (solid) in anhydrous ethanol, removes insoluble impurities by filtration to obtain an ethanol solution of high-concentration lithium salt (crude lithium-containing filtrate), and then adds a certain proportion of water to the ethanol solution of high-concentration lithium salt to form a mixed solution, and then precipitates the lithium salt product by distillation, crystallization, and regulation of the distillation end point. In this way, on the one hand, by regulating the composite solvent in the mother liquor at the distillation end point so that the ethanol content is within the range of 50≤n≤70, the present application can ensure that the impurities are completely dissolved in the solvent at the distillation end point, the loss of lithium salt is minimized, and the direct yield is improved. On the other hand, the solvent is evaporated and collected in the form of an azeotrope (ethanol-water), which can lower the boiling point of the solution, reduce distillation losses, and improve efficiency.

[0010] In some embodiments, in step S1, the amount of anhydrous ethanol added is m 醇 The method for determining the lithium-containing material comprises: S1-a, obtaining the mass of the lithium compound in the lithium-containing material, recorded as m 锂 , S1-b, according to the mass m of the lithiation 锂 And the solubility S of the lithium compound in anhydrous ethanol 锂 , determine the amount of anhydrous ethanol added m 醇 , unit: g. The solubility of the lithium compound LiCl in anhydrous ethanol ranges from 115 g / L to 125 g / L. The solubility of the lithium compound LiOH in anhydrous ethanol ranges from 1.3 g / 100 g to 1.4 g / 100 g.

[0011] In some embodiments, step S1-b includes: step S1-b1, according to the mass m of the lithiation 锂 And the solubility S of the lithium compound in anhydrous ethanol 锂 , determine the theoretical addition amount m of the anhydrous ethanol 理 Step S1-b2: According to the theoretical amount of anhydrous ethanol added m 理 , through formula Ⅰ, the amount of anhydrous ethanol added m can be obtained 醇 ;

[0012] m 理 ≤m 醇 ≤m 理 ╳k1 Formula Ⅰ

[0013] Among them, the value range of k1 is 1.0≤k1≤1.5.

[0014] In this application, the solubility range of LiCl in anhydrous ethanol is selected as 115g / L~125g / L, and the solubility range of LiOH in anhydrous ethanol is selected as 1.3g / 100g~1.4g / 100g. According to the type and mass of the lithium compound and the corresponding solubility in anhydrous ethanol, the theoretical amount of anhydrous ethanol added can be determined, and then the actual amount of anhydrous ethanol added in this application (m 醇 ), so that most of the impurities can be removed after dissolving and filtering the lithium-containing material, and the obtained crude lithium-containing filtrate is an ethanol solution of high-concentration lithium salt, and the loss of lithium salt in the lithium-containing material is small, which is beneficial to improving the yield of the lithium salt product.

[0015] In the present application, the solubility of the lithium compound in ethanol fluctuates slightly due to the influence of the actual physical and chemical environment. Therefore, the solubility of the lithium compound in ethanol can take any value within the above range.

[0016] Illustratively, the dissolution conditions include: dissolution temperature: 55°C to 65°C, and dissolution time: 1h to 2h.

[0017] In some embodiments, in step S2, the amount of water added is m 水 Methods for determining , including:

[0018] S2-a, pre-obtaining the mass m of the composite solvent used to dissolve the impurities not removed 复 ;

[0019] The impurities not removed refer to the other substances except the lithiate in the crude lithium-containing filtrate after the lithium-containing material is dissolved and filtered with anhydrous ethanol in step S1, and the lithiate and the other substances are dissolved in the crude lithium-containing filtrate;

[0020] S2-b, according to the mass m of the composite solvent 复 The content of ethanol in the composite solvent is n'wt%, and the mass of ethanol in the composite solvent is m 醇1 ;

[0021] Wherein, n' is selected from any value in the value range of n;

[0022] S2-c, according to the mass m of ethanol in the composite solvent 醇1 And the amount of anhydrous ethanol added in step S1 m 醇 , through formula II, we can get the mass m of ethanol distilled during the distillation process 醇2 ;

[0023] m 醇2 =m 醇 -m 醇1 Formula II

[0024] S2-d, according to the mass m of distilled ethanol 醇2 , through formula III, we can get the mass m of water distilled during the distillation process 水2 ;

[0025]

[0026] Wherein, in formula III, the range of k2 is 0.95≤k2≤1.05;

[0027] S2-e, according to the mass m of the distilled water 水2 And the mass m of water in the composite solvent 水1 , through formula Ⅳ, the water addition amount m can be obtained 水 ;

[0028] m 水 =m 水2 +m 水1 Formula IV.

[0029] In some embodiments, step S2-a includes:

[0030] S2-a1, obtaining the mass m of the unremoved impurities in the crude lithium-containing filtrate by detection 杂 ;

[0031] Wherein, the mass of the impurities not removed m 杂 Calculated by the mass of the target impurity, the target impurity is the chloride salt with the largest mass among NaCl and KCl;

[0032] S2-a2, obtaining the solubility S of the target impurity in the composite solvent 杂 , unit: g / 100g;

[0033] Wherein, the ethanol content in the composite solvent is n'wt%;

[0034] S2-a3, according to the mass m 杂 and solubility S 杂 , the mass m of the composite solvent used to dissolve the impurities not removed can be obtained in advance 复 .

[0035] In some embodiments, step S2-a3 includes:

[0036] When the mass of the impurities not removed m 杂 When the mass m of the composite solvent used to dissolve the impurities not removed is obtained in advance according to formula V-1: 复 ;

[0037]

[0038] Among them, the value range of k3 is 1.0≤k3≤1.5.

[0039] When the mass of impurities not removed is large (m 杂 >0.5g), the mass of the composite solvent in the mother liquor needs to be controlled within the above range, so as to better dissolve the impurities that have not been removed and precipitate the lithium salt product, and the lithium salt product has high purity and good yield.

[0040] When the mass of the impurities not removed m 杂 When ≤0.5g, according to formula V-2, the mass m of the composite solvent used to dissolve the impurities not removed is obtained in advance 复 ;

[0041]

[0042] Among them, the value range of p1 is 2≤p1≤10, and the value range of p2 is 12≤p2≤18.

[0043] When the mass of impurities not removed is less (m 杂 ≤0.5g), the mass of the composite solvent in the mother liquor needs to be appropriately increased and within the above range. Otherwise, if the amount of the composite solvent is too small, the solid-liquid mixture will be relatively viscous, resulting in the inability to subsequently filter and obtain the lithium salt product.

[0044] The present application obtains a blended solution by adding an appropriate amount of water in step S2. During the negative pressure distillation process, the blended solution can regulate the ethanol concentration of the composite solvent in the mother liquor to precipitate as much solid phase of the lithium compound as possible, while dissolving as much sodium and potassium impurities as possible in the mother liquor, so that the crude lithium-containing filtrate after dissolution and filtration with anhydrous ethanol can further remove sodium and potassium impurities, thereby achieving high purity and high yield of the lithium compound. Excessive water content in the blended solution will result in excessive loss of lithium salts, which is not conducive to taking into account the high yield of the lithium compound. Excessive water content in the blended solution is not conducive to removing sodium and potassium impurities from the crude lithium-containing filtrate, which is not conducive to taking into account the high purity of the lithium compound. It can be seen that the blended solution prepared by the amount of water added calculated above and the ethanol concentration n of the composite solvent in the mother liquor after negative pressure distillation are also suitable, which can take into account the high purity and high yield of the lithium compound.

[0045] Illustratively, the conditions for negative pressure distillation include: vacuum degree: -0.06 MPa to -0.04 MPa, and distillation temperature: 85°C to 90°C.

[0046] Specifically, in the present application, ethanol + water are distilled and separated in a mass ratio of approximately 95.6:4.4, so that the lithium compound dissolved in the distillate is precipitated. The amount of water added is adjusted to keep the ethanol content in the remaining mother liquor within 50wt% to 70wt%, so that as much sodium and potassium impurities as possible are dissolved in the mother liquor, and the sodium and potassium impurities not removed in the first step are separated from the lithium compound. In a composite solvent with an ethanol content of 50wt% to 70wt%, the solubility of the lithium compound and the sodium and potassium impurities differ significantly. The sodium and potassium impurities have a higher solubility in the composite solvent, while the lithium compound (LiCl, LiOH) has a lower solubility in the composite solvent. This solubility difference is utilized to minimize the precipitation of the sodium and potassium impurities, thereby improving the purity of the lithium compound and allowing the lithium compound to precipitate in large quantities, thereby ensuring the yield of the lithium compound.

[0047] In some embodiments, the lithium-containing material is a solid lithium-containing material, or the lithium-containing material is a solid lithium-containing material obtained by negative pressure evaporation of a liquid lithium-containing material. Based on the mass of the lithium-containing material, the mass percentage of the lithium compound is W1 wt%, W1 ≥ 30, and the mass percentage of the impurities is W2 wt%, 10 ≤ W2 ≤ 70. Preferably, at least one of the following conditions is met: (1) 60 ≤ n ≤ 65; (2) 55 ≤ W1 ≤ 75; (3) 30 ≤ W2 ≤ 45. The present application further regulates the state, parameters and distillation endpoint conditions of the lithium-containing material within the above range, which is more conducive to the removal of impurities from the lithium-containing material, especially the removal of potassium, sodium and other ions that are monovalent and in the same group as lithium ions, while also taking into account the improvement of the yield of the lithium salt product.

[0048] In some embodiments, in step S3, the filtered mother liquor is returned to the lithium-containing material in step S1 after negative pressure operation. + This is because LiCl and LiOH also have a certain solubility in the composite solvent of ethanol and water. The mother liquor is converted into a solid lithium-containing material through negative pressure operation and then circulated, which further improves the yield of the lithium salt product.

[0049] In some embodiments, in step S3, during the solid washing process, the detergent contains ethanol and water, the mass content of the ethanol in the detergent is nwt%, and the washing times are 2 to 3 times. Preferably, the detergent after washing (containing Li + ), after negative pressure operation, returns to the lithium-containing material in step S1. The detergent after washing contains Li + , which is converted into a solid lithium-containing material through negative pressure operation and circulated, which is beneficial to improving the yield of lithium salt products.

[0050] In some embodiments, the vacuum drying conditions include: vacuum temperature: 145° C. to 155° C., vacuum time: 1 h to 3 h.

[0051] The present application first dissolves a lithium-containing material in anhydrous ethanol to remove most impurities, and then adds an appropriate amount of water to the obtained ethanol solution of a high-concentration lithium salt to form a blended solution. During the negative pressure distillation process, the blended solution can regulate the ethanol concentration of the composite solvent in the mother liquor to enable the solid phase precipitation of the lithium compound with a high yield, and the unremoved impurities are largely dissolved in the mother liquor. In particular, at the end point of the distillation, the impurities are almost completely dissolved in the mother liquor, resulting in a small loss of the lithium salt product and a high purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0053] Figure 1 Schematic diagram of the process flow of the method for removing impurities from lithium-containing materials in this application. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0055] The inventive concept of this process is to remove sodium and potassium impurities in the lithium compound in two steps. In the first step, anhydrous ethanol is used to remove most of the impurities with low solubility in anhydrous ethanol (precipitated in the form of precipitation) to obtain a high-concentration lithium salt ethanol solution. Then, in the second step, water is added to the obtained high-concentration lithium salt ethanol solution. By vacuum distillation and regulating the concentration of ethanol in the mother liquor, the lithium compound is precipitated in the solid phase, while the sodium and potassium impurities are dissolved in the mother liquor as much as possible, thereby further removing the sodium and potassium impurities. This process takes into account both the purity and yield of the lithium compound.

[0056] Method for removing impurities from lithium-containing materials

[0057] The lithium-containing material contains lithium compounds and impurities, wherein the lithium compounds include at least one of LiCl and LiOH, and the impurities include at least one of NaCl and KCl, and optionally at least one of NaOH and KOH.

[0058] See also Figure 1 , including the following steps:

[0059] S1. Obtain a lithium-containing material, add anhydrous ethanol to dissolve the lithium-containing material, and filter to obtain a crude lithium-containing filtrate and a filter residue, wherein the filter residue contains at least one impurity;

[0060] S2, adding water to the crude lithium-containing filtrate to obtain a blended solution, and then distilling the blended solution to obtain a solid-liquid mixture containing solid and mother liquor;

[0061] S3. Filter the solid-liquid mixture, then wash and dry the solid (high-purity lithium-containing solid) (vacuum drying) to obtain a high-purity lithiate (lithium salt product);

[0062] The mother liquor includes unremoved impurities and a composite solvent, the unremoved impurities are dissolved in the composite solvent, the composite solvent includes water and ethanol, and based on the mass of the composite solvent, the mass percentage of ethanol is nwt%, and the value range of n is 50≤n≤70.

[0063] The method of the present application mainly includes two steps. The first step is to dissolve the solid lithium-containing material in anhydrous ethanol, remove insoluble impurities by dissolving and filtering, and obtain an ethanol solution of high concentration lithium salt (crude lithium-containing filtrate). The first step can remove most of the insoluble impurities in the lithium-containing material, including NaCl, KCl, NaOH, KOH or other impurities. The second step is to add an appropriate amount of water to the ethanol solution of high concentration lithium salt to form a blended solution. The amount of water added in the second step is very critical. The amount of water added is too little, resulting in the inability of lithium compound to be efficiently precipitated, and the mother liquor is too viscous, and the subsequent lithium compound product cannot be obtained at a high rate. The amount of water added is too much, and the lithium salt loss is large (also unable to be efficiently precipitated), and the yield is low. At the same time, the blended solution needs to coordinate the ethanol concentration of the composite solvent in the mother liquor to regulate the lithium compound as much as possible during the distillation and crystallization process so that the impurities are dissolved as much as possible while the lithium compound is precipitated, which is beneficial to improving the direct yield and purity. The solvent is evaporated and collected in the form of an azeotrope (ethanol-water), which can reduce the boiling point of the solution, reduce distillation losses, and improve efficiency.

[0064] In the present application, the mass content of ethanol in the composite solvent is 50wt% to 70wt%. At this time, the solubility of the lithium compound and the solubility of the impurities are greatly different, about 1:4. Therefore, the lithium compound can be effectively precipitated into the solid phase and the impurities can be dissolved in the liquid phase as much as possible.

[0065] In this process, the mass content of ethanol in the composite solvent is 50 wt% to 70 wt%. Those skilled in the art can determine it by any suitable method based on the teachings of this application. A possible method is described below:

[0066] Step S100: Using the mass ratio of the organic solvent in the mixed solvent as the horizontal coordinate and the solubility of the target impurity as the vertical coordinate, a curve y1=f is fitted to determine the corresponding relationship between the solubility of the target impurity and the mass ratio of the organic solvent in the mixed solvent. 1 (n) , f 1 (n) is a quadratic function of n;

[0067] Step S200: Using the mass ratio of the organic solvent in the mixed solvent as the horizontal axis and the solubility of lithium hydroxide and / or lithium chloride as the vertical axis, a curve y2=f is fitted to determine the corresponding relationship between the solubility of the lithium compound and the mass ratio of the organic solvent in the mixed solvent. 2 (n) , f 2 (n) is a quadratic function of n;

[0068] Step S300, according to y1=f 1 (n) and y2 = f 2 (n) , determine the range of n values, including:

[0069] Determine two real roots n1 and n2 according to formula I, and n1<n2;

[0070] f 1 (n) / f 2 (n) ≥Q Formula I

[0071] Among them, the value range of Q is 3≤Q≤4.5;

[0072] The value range of n is n1≤n≤n2.

[0073] <Method for determining the amount of anhydrous ethanol added>

[0074] S1-a, obtain the mass of lithium compound in the lithium-containing material, denoted as m 锂 ;

[0075] S1-b, according to the mass m of the lithiation 锂 And the solubility of lithium compounds in anhydrous ethanol S 锂 , determine the amount of anhydrous ethanol added m 醇 , unit g.

[0076] Wherein, step S1-b includes: step S1-b1, according to the mass m of the lithiation 锂 And the solubility S of the lithium compound in anhydrous ethanol 锂 , determine the theoretical addition amount m of the anhydrous ethanol 理 Step S1-b2, according to the theoretical amount of anhydrous ethanol added m 理 , through formula Ⅰ, the amount of anhydrous ethanol added m can be obtained 醇 ;

[0077] m 理 ≤m 醇 ≤m 理 ╳k1 Formula Ⅰ

[0078] Among them, the value range of k1 is 1.0≤k1≤1.5.

[0079] In the present application, the solubility of LiCl in anhydrous ethanol ranges from 115 g / L to 125 g / L, and the solubility of LiOH in anhydrous ethanol ranges from 1.3 g / 100 g to 1.4 g / 100 g.

[0080] <Method for determining the amount of water added>

[0081] S2-a, pre-obtaining the mass m of the composite solvent used to dissolve the impurities not removed 复 .

[0082] Step S2-a includes:

[0083] S2-a1, obtaining the mass m of the unremoved impurities in the crude lithium-containing filtrate by detection 杂 ;

[0084] Wherein, the mass of the impurities not removed m 杂 Calculated by the mass of the target impurity, the target impurity is the chloride salt with the largest mass among NaCl and KCl;

[0085] S2-a2, obtaining the solubility S of the target impurity in the composite solvent 杂 , unit g / 100g; wherein the ethanol content in the composite solvent is n'wt%;

[0086] In this process, the solubility of the target impurity in the composite solvent is S 杂 The method for obtaining the solubility of the impurity can be obtained by those skilled in the art according to actual needs, for example, directly preparing a composite solvent with an ethanol ratio of n'wt%, slowly adding the target impurity, and obtaining its solubility S 杂 Of course, you can also configure composite solvents with different ethanol proportions of n'wt%, obtain the solubility of the corresponding target impurities therein, and then draw a corresponding relationship curve. According to the corresponding relationship curve, calculate the solubility of the target impurity when the ethanol content is n'wt%.

[0087] S2-a3, according to the mass m 杂 and solubility S 杂 , the mass m of the composite solvent used to dissolve the impurities not removed can be obtained in advance 复 .

[0088] Wherein, when the mass of the impurities not removed m 杂 When the mass m of the composite solvent used to dissolve the impurities not removed is obtained in advance according to formula V-1: 复 ;

[0089]

[0090] The value range of k3 is 1.0≤k3≤1.5; or,

[0091] When the mass of the impurities not removed m 杂 When ≤0.5g, according to formula V-2, the mass m of the composite solvent used to dissolve the impurities not removed is obtained in advance 复 ;

[0092]

[0093] Among them, the value range of p1 is 2≤p1≤10, and the value range of p2 is 12≤p2≤18.

[0094] S2-b, according to the mass m of the composite solvent 复 The content of ethanol in the composite solvent is n'wt%, and the mass of ethanol in the composite solvent is m 醇1 ;

[0095] Wherein, n' is selected from any value in the value range of n.

[0096] S2-c, according to the mass m of ethanol in the composite solvent 醇1 And the amount of anhydrous ethanol added in step S1 m 醇 , through formula II, we can get the mass m of ethanol distilled during the distillation process 醇2 ;

[0097] m 醇2 =m 醇 -m 醇1 Formula II.

[0098] S2-d, according to the mass m of distilled ethanol 醇2 , through formula III, we can get the mass m of water distilled during the distillation process 水2 ;

[0099]

[0100] Wherein, in formula III, the range of k2 is 0.95≤k2≤1.05.

[0101] S2-e, according to the mass m of the distilled water 水2 And the mass m of water in the composite solvent 水1 , through formula Ⅳ, the water addition amount m can be obtained 水 ;

[0102] m 水 =m 水2 +m 水1 Formula IV.

[0103] The following are possible implementations

[0104] The technical solution proposed in this application includes the following five main steps: 1. obtaining a solid lithium salt material (lithium-containing material); 2. dissolving and filtering the solid lithium salt in an ethanol solution (anhydrous ethanol); 3. adding water to prepare a mixed lithium salt solution (blended solution) in a certain proportion, and crystallizing the lithium salt by negative pressure distillation; 4. filtering and washing the solid lithium salt; and 5. vacuum drying the solid lithium salt to obtain a high-purity lithium salt. The product of this process is a high-purity lithium salt product.

[0105] The raw material to be purified (solid or solution with OH - 、Cl - 、SO4 2- as anion) through a series of operations such as negative pressure distillation to obtain high-purity lithium salt solid.

[0106] In this process, the purity of lithium salt in the lithium-containing material is greater than or equal to 30wt%, and the main impurities are NaCl, KCl, NaOH, KOH, etc. (content 10-70wt%, and a small amount of other impurities content 0-2wt%).

[0107] First, the solid material enters the ethanol dissolution, filtration, and impurity removal stage. The required amount of ethanol is calculated based on the solubility of the lithium salt in the material in ethanol, and the amount used is 1-1.5 times the theoretical amount corresponding to the saturated solubility of the lithium salt. After dissolution, the solid impurities insoluble in ethanol are filtered to remove, initially obtaining a high-concentration lithium salt ethanol solution.

[0108] A certain proportion of water is added to the ethanol solution of the lithium salt, the water content being such that, during the distillation operation, the ethanol:water ratio is 95.6:4.4 by weight, and the ethanol content in the remaining mother liquor is within a range of 50 wt% to 70 wt% (e.g., 64.16 wt%) of the composite solvent, ensuring that impurities are completely dissolved in the solution and that the lithium salt dissolves as little as possible. The mixed solution is then concentrated by negative pressure distillation to obtain a solid-liquid mixture, which is then filtered and washed to obtain a lithium salt solid.

[0109] The filtrate containing sodium and potassium impurity ions and lithium salt solids are removed by filtering and washing, and the filter membrane is a 0.22 μm organic filter membrane. The filtrate (mainly containing Na+, Li+, K cations, Cl-, OH-, SO4 2- The lithium salt is then extracted from the first process (one of which is the main anion) and the fraction is processed and reused. The vacuum degree is -0.06MPa to -0.04MPa.

[0110] The washing liquid is selected to be a solution with the same mass ratio of ethanol to water as that in the mother liquor, and the washing is performed three times. The washing liquid is recovered and returned to the first process together with the filtrate to circulate and extract the lithium salt.

[0111] Finally, the filtered solid is vacuum dried to obtain a high-purity lithium salt product. The vacuum drying temperature is controlled at 100℃-190℃ and the drying time is 1-4h. The evaporation and drying process is conducive to controlling CO3 2- , reducing the Li element to exist in the form of Li2CO3.

[0112] The following examples and comparative examples are given to illustrate the embodiments of the present application in more detail. Unless otherwise stated, the parts, percentages and ratios listed are all based on mass.

[0113] Example 1

[0114] Step S1: Take 20 g of lithium salt solid (mainly composed of LiCl, NaCl and KCl, of which LiCl accounts for 56%, KCl accounts for 19%, and NaCl accounts for 25%) as the initial raw material (lithium-containing material), add 100 mL (about 79 g) of anhydrous ethanol according to the solubility of LiCl of 120 g / L (test data, NaCl in the solution is about 1.1 g, KCl is about 0.2 g), stir at 60 ° C for 1 hour, and then perform solid-liquid separation operation to remove most of the insoluble impurities NaCl (about 3.9 g) and KCl (about 3.6 g);

[0115] Step S2: 13.55 g (including 10.8 g of water in the mother liquor and 2.75 g of distilled water) of water was added to the ethanol solution of LiCl (crude lithium-containing filtrate) and the mixture was stirred for 0.5 h. The mixed solution was distilled under negative pressure at 85° C. (vacuum degree was -0.06 MPa to -0.04 MPa). The distillation was stopped when the fraction mass was 62.55 g (59.8 g of ethanol + 2.75 water). 30 g of a composite solvent containing 64 wt% ethanol and water was obtained (theoretically soluble NaCl was 1.2 g and KCl was 0.37 g). When the mixture was naturally cooled to room temperature, a solid-liquid separation operation was performed, and the solid was washed with 5 mL×3 of a detergent containing 64 wt% ethanol and water;

[0116] Step S3: The collected solid was dried in a vacuum drying oven at 150° C. for 2 h to obtain 10.23 g of high-purity LiCl product with a purity of 99.1% and a yield of 91.3%.

[0117] Specifically:

[0118] 1. The calculation process of the amount of anhydrous ethanol added is as follows:

[0119] Step S1-a: The mass of LiCl is 11.2 g, i.e., m 锂 11.2g;

[0120] Step S1-b: Theoretical addition amount of anhydrous ethanol m 理 for:

[0121] Step S1-b1, 11.2 g / m 理 =12g / (0.789g / mlⅹ100ml), m 理 =73.64g;

[0122] The amount of anhydrous ethanol added m 醇 for:

[0123] Steps S1-b2, m 理 ≤m 醇 ≤m 理 ⅹk1, when k1=1.1, 73.64≤m 醇 ≤81g, take m 醇 =79g.

[0124] 2. The amount of water added m 水 The calculation of is as follows:

[0125] Step S2-a: Pre-obtaining the mass m of the composite solvent used to dissolve the impurities not removed 复 ;

[0126] Step S2-a1: Detect and obtain the mass m of the target impurity NaCl 杂 =1.1g;

[0127] Step S2-a2: Take the ethanol content n'wt%=64wt% in the composite solvent used to dissolve the impurities not removed; obtain the solubility S of NaCl in the composite solvent with 64wt% ethanol. 杂 =4g / 100g;

[0128] Step S2-a3: According to the mass m of the target impurity NaCl 杂 =1.1g (>0.5g), the mass m of the composite solvent is obtained 复 for:

[0129] 1.1gⅹ100g / 4g≤m 复 ≤k3ⅹ1.1gⅹ100g / 4g

[0130] When k3=1.1, 27.5g≤m 复 ≤30.25g, take m 复 =30g.

[0131] Step S2-b: obtaining the masses of ethanol and water in the composite solvent;

[0132] The mass of ethanol in the composite solvent m 醇1 =30×64wt%=19.2g,

[0133] The mass of water in the composite solvent is m 水1 =30 x 36 wt% = 10.8 g;

[0134] Step S2-c: Obtain the mass m of ethanol distilled during the distillation process 醇2 ;

[0135] The mass of distilled ethanol m 醇2 =79g-19.2g=59.8g;

[0136] Step S2-d: Obtain the mass m of water distilled during the distillation process 水2 ;

[0137] The mass of distilled water m 水2 for:

[0138] 59.8 / m 水2 =95.6 / 4.4ⅹk2, when k2=1, m 水2 =2.75g;

[0139] Step S2-e: Obtaining the amount of water added m 水

[0140] Water addition amount m 水 =10.8+2.75=13.55g.

[0141] Example 2

[0142] Step S1: Take 10 g of lithium salt solid (mainly composed of LiOH, NaCl and NaOH, of which LiOH accounts for 70%, NaCl accounts for 23%, and NaOH accounts for 7%) as the initial raw material (lithium-containing material), add 600 g of anhydrous ethanol according to the solubility of LiOH of 1.33 g / 100 g (test data, the solution contains about 0.2 g of NaCl and about 0.5 g of NaOH), stir at 60 ° C for 2 h, and then perform solid-liquid separation operation to remove most of the insoluble impurities NaCl (about 2.1 g) and a small amount of NaOH (about 0.2 g);

[0143] Step S2: add 50g (wherein, 24g water in the mother liquor + 26g distilled water) of water to the ethanol solution of LiOH (crude lithium-containing filtrate) and mix and stir for 0.5h, distill the blended solution under negative pressure at 90°C (vacuum degree is -0.06MPa to -0.04MPa), and stop distillation when the fraction mass is 590g (564g ethanol + 26g water). The mother liquor is 60g of a mixed solution of 60wt% ethanol and water (if the liquid phase in the mother liquor is too little, it is relatively viscous, affecting the subsequent filtration effect), the theoretically soluble NaCl is 0.2x15g, and the dissolved NaOH is greater than 0.5g. When it is naturally cooled to room temperature, a solid-liquid separation operation is performed, and the solid is washed with a detergent of 60wt% ethanol and water for 10mLx3;

[0144] Step S3: The collected solid was dried in a vacuum drying oven at 150° C. for 2 h to obtain 6.09 g of high-purity LiOH product with a purity of 99.8% and a yield of 87%.

[0145] Specifically:

[0146] 1. The calculation process of the amount of anhydrous ethanol added is as follows:

[0147] Step S1-a: The mass of LiOH is 7 g, i.e., m 锂 7g;

[0148] Step S1-b1, theoretical addition amount of anhydrous ethanol m 理 :7g / m 理 =1.33g / 100g, m 理 =526g;

[0149] Step S1-b2, the amount of anhydrous ethanol added m 醇 is: m 理 ≤m 醇 ≤m 理 ⅹk1,

[0150] When k1=1.2, 526≤m 醇 ≤631g, take m 醇 =600g.

[0151] 2. The amount of water added m 水 The calculation of is as follows:

[0152] Step S2-a: Pre-obtaining the mass m of the composite solvent used to dissolve the impurities not removed 复 ;

[0153] Step S2-a1: Detect and obtain the mass m of the target impurity NaCl 杂 =0.2g;

[0154] Step S2-a2: taking the ethanol content in the composite solvent used to dissolve the impurities not removed to n'wt%=60wt%;

[0155] Obtain the solubility S of NaCl in the composite solvent containing 60 wt% ethanol. 杂 =5g / 100g;

[0156] Step S2-a3: According to the mass m of the target impurity NaCl 杂 =0.2g (≤0.5g), the mass m of the composite solvent is obtained 复 for:

[0157] p1×100×0.2 / 5≤m 母≤p2×100×0.2 / 5, take p1=10, p2=15, then 40g≤m 复 ≤60g,

[0158] Select m 复 = 60g of composite solvent to dissolve the impurities that have not been removed;

[0159] Step S2-b: obtaining the masses of ethanol and water in the composite solvent;

[0160] The mass of ethanol in the composite solvent m 醇1 =60×60 wt%=36 g;

[0161] The mass of water in the composite solvent is m 水1 =60 x 40 wt% = 24 g;

[0162] Step S2-c: Obtain the mass m of ethanol distilled during the distillation process 醇2 ;

[0163] The mass of distilled ethanol m 醇2 =600g-36g=564g;

[0164] Step S2-d: Obtain the mass m of water distilled during the distillation process 水2 ;

[0165] The mass of distilled water m 水2 for:

[0166] 564 / m 水2 =95.6 / 4.4ⅹk2, when k2=1, m 水2 =26g;

[0167] Step S2-e: Obtaining the amount of water added m 水

[0168] Water addition amount m 水 =24+26=50g.

[0169] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for removing impurities from a lithium-containing material, characterized in that: The lithium-containing material contains lithium compounds and impurities; The lithium compound includes at least one of LiCl and LiOH; The impurities include at least one of NaCl and KCl; Using two steps to remove sodium and potassium impurities from the lithiate; The method comprises at least the following steps: S1. Obtain a lithium-containing material, add anhydrous ethanol to dissolve the lithium-containing material, and filter to obtain a crude lithium-containing filtrate and a filter residue, wherein the filter residue contains at least one of the impurities; S2, adding water to the crude lithium-containing filtrate to obtain a blended solution, and then distilling the blended solution to obtain a solid-liquid mixture containing solid and mother liquor; S3, filtering the solid-liquid mixture, and then washing and drying the solid to obtain a high-purity lithiate; wherein the mother liquor comprises unremoved impurities and a composite solvent, and the unremoved impurities are dissolved in the composite solvent; The composite solvent includes water and ethanol. Based on the mass of the composite solvent, the mass percentage of the ethanol is n wt%, and the value range of n is 50≤n≤70; Based on the mass of the lithium-containing material, the mass percentage of the lithium compound is W1wt%, W1≥30, and the mass percentage of the impurities is W2wt%, 10≤W2≤70.

2. The method according to claim 1, characterized in that The impurities further include at least one of NaOH and KOH.

3. The method according to claim 1, characterized in that In step S1, the amount of anhydrous ethanol added is m 醇 Methods for determining , including: S1-a, obtaining the mass of the lithiation in the lithium-containing material, recorded as m 锂 ; S1-b, according to the mass m of the lithiation 锂 And the solubility S of the lithium compound in anhydrous ethanol 锂 , determine the amount of anhydrous ethanol added m 醇 , unit g; The lithium compound is LiCl, and the solubility of LiCl in anhydrous ethanol ranges from 115 g / L to 125 g / L. The lithium compound is LiOH, and the solubility of LiOH in anhydrous ethanol ranges from 1.3 g / 100 g to 1.4 g / 100 g.

4. The method according to claim 3, characterized in that Step S1-b includes: Step S1-b1, according to the mass m of the lithiation 锂 And the solubility S of the lithium compound in anhydrous ethanol 锂 , determine the theoretical addition amount m of the anhydrous ethanol 理 ; Step S1-b2, according to the theoretical amount of anhydrous ethanol added m 理 , through formula Ⅰ, the amount of anhydrous ethanol added m can be obtained 醇 ; m 理 ≤m 醇 ≤m 理╳ k1 formula Ⅰ Among them, the value range of k1 is 1.0≤k1≤1.

5.

5. The method according to claim 1, wherein In step S2, the amount of water added is m 水 Methods for determining , including: S2-a, pre-obtaining the mass m of the composite solvent used to dissolve the impurities not removed 复 ; S2-b, according to the mass m of the composite solvent 复 And the content of ethanol in the composite solvent n'wt% to obtain the mass m of ethanol in the composite solvent 醇1 ; Wherein, n' is selected from any value in the value range of n; S2-c, according to the mass m of ethanol in the composite solvent 醇1 And the amount of anhydrous ethanol added in step S1 m 醇 , through formula II, we can get the mass m of ethanol distilled during the distillation process 醇2 ; m 醇2 =m 醇 -m 醇1 Formula II S2-d, according to the mass m of distilled ethanol 醇2 , through formula III, we can get the mass m of water distilled during the distillation process 水2 ; Formula III Wherein, in formula III, the range of k2 is 0.95≤k2≤1.05; S2-e, according to the mass m of the distilled water 水2 And the mass m of water in the composite solvent 水1 , through formula Ⅳ, the water addition amount m can be obtained 水 ; m 水 = m 水2 + m 水1 Formula IV.

6. The method according to claim 5, characterized in that Step S2-a includes: S2-a1, obtaining the mass m of the unremoved impurities in the crude lithium-containing filtrate by detection 杂 ; Wherein, the mass of the impurities not removed m 杂 Calculated by the mass of the target impurity, the target impurity is the chloride salt with the largest mass among NaCl and KCl; S2-a2, obtaining the solubility S of the target impurity in the composite solvent 杂 , unit: g / 100g; Wherein, the ethanol content in the composite solvent is n'wt%; S2-a3, according to the mass m 杂 and solubility S 杂 , the mass m of the composite solvent used to dissolve the impurities not removed can be obtained in advance 复 .

7. The method according to claim 6, characterized in that Step S2-a3 includes: When the mass of the impurities not removed m 杂 When the mass m of the composite solvent used to dissolve the impurities not removed is obtained in advance according to formula V-1: 复 ; Formula V-1 The value range of k3 is 1.0≤k3≤1.5; or, When the mass of the impurities not removed m 杂 When ≤0.5g, according to formula V-2, the mass m of the composite solvent used to dissolve the impurities not removed is obtained in advance 复 ; Formula V-2 Among them, the value range of p1 is 2≤p1≤10, and the value range of p2 is 12≤p2≤18.

8. The method according to claim 1, characterized in that The lithium-containing material is a solid lithium-containing material, or the lithium-containing material is a solid lithium-containing material obtained by evaporating a liquid lithium-containing material under negative pressure.

9. The method according to claim 8, characterized in that At least one of the following conditions is met: (1) 60≤n≤65； (2) 55≤W1≤75； (3)30≤W2≤45。 10. The method according to claim 1, characterized in that In step S3, the filtered mother liquor is returned to the lithium-containing material in step S1 after negative pressure operation.

11. The method according to claim 1, characterized in that In step S3, during the solid washing process, the detergent contains ethanol and water, the mass content of the ethanol in the detergent is nwt%, and the number of washing times is 2 to 3 times.

12. The method according to claim 11, characterized in that In step S3, the detergent after washing is returned to the lithium-containing material in step S1 after negative pressure operation.

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