Method for improving quality of lithium hydroxide monohydrate product

Abstract

The invention relates to the technical field of battery-grade lithium hydroxide monohydrate, and discloses a method for improving the quality of a lithium hydroxide monohydrate product. The method comprises the following steps: carrying out flash evaporation concentration on a lithium hydroxide alkali solution to obtain a concentrated solution with the solid content of 15-40%; the concentrated solution is centrifuged, water is added to a solid product for washing, the weight ratio of the solid product to the water is 1: (0.2-0.3), crude salt and mother liquor are obtained, the mother liquor is evaporated, concentrated and centrifuged, and the crude salt and the mother liquor with Na < + > larger than or equal to 50 g / L are obtained; adding water into the crude salt for dissolving, and carrying out flash evaporation concentration on the obtained heavy solution to obtain a concentrated solution with the solid content of 15-40%; the concentrated solution is centrifuged, water is added to a solid product obtained through centrifugation for washing, the weight ratio of the solid product to the water is 1: (0.2-0.3), crude salt and mother liquor are obtained, and then the crude salt is dried. According to the method, a plurality of parameters in the evaporation process are controlled, so that the yield is improved, and the product quality reaches the battery grade standard.

Description

Technical Field

[0001] The invention relates to the technical field of battery-grade lithium hydroxide monohydrate, and in particular to a method for improving the quality of lithium hydroxide monohydrate products. Background Art

[0002] With the popularity of new energy electric vehicles, the market demand for lithium batteries continues to grow, and the demand for lithium-ion battery materials is also increasing. The lithium carbonate and lithium hydroxide markets were once in short supply, and prices soared. The lithium carbonate and lithium hydroxide factories invested in development and construction are also of different sizes. Lithium hydroxide monohydrate is an excellent lithium-ion battery positive electrode material due to its good conductivity and stability. At present, the lithium hydroxide production process is mainly through lithium extraction from ore, and the process of directly preparing lithium hydroxide monohydrate through salt lake brine has not yet been implemented. The existing technology for producing lithium hydroxide monohydrate includes roasting, causticization, electrolysis, etc.; the application of roasting method is greatly limited due to low production capacity, large amount of slag, low lithium yield, etc.; the development of causticization method is limited due to incomplete reaction conversion process and high impurity content of the product; electrolysis method has basically faded out of sight due to environmental pollution and low production efficiency; therefore, a new process technology with high yield, excellent product quality, high production capacity and no pollution to the environment is urgently needed.

[0003] Directly producing battery-grade lithium hydroxide monohydrate products from lithium-rich brine in salt lakes not only meets market demand, but also effectively fills the technical gap in directly producing battery-grade lithium hydroxide monohydrate products from salt lake brine. At the same time, the product production capacity, quality, and yield are more advanced than the ore method. However, in the process of producing lithium hydroxide monohydrate products from salt lakes, the control of process parameters for the evaporation and crystallization process is particularly important. Salt lake brine has a high magnesium-to-lithium ratio and contains a variety of metal elements, so it needs to be purified and impurities removed. There is almost no experience to draw on for direct production of battery-grade lithium hydroxide monohydrate technology from salt lake brine, and the market has relatively high quality requirements for battery-grade lithium hydroxide monohydrate products. Therefore, it is very necessary to develop a method to improve the quality of lithium hydroxide monohydrate products by evaporation and crystallization. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of low lithium yield, high impurity content of the product, serious environmental pollution, etc. in the prior art of producing lithium hydroxide monohydrate by ore method, and provide a method for improving the quality of lithium hydroxide monohydrate products. The method controls the solid content of the concentrated solution during the flash concentration process, the concentration of the mother liquor discharged, and the post-centrifugal washing process, so as to improve the yield and make the product quality reach the battery grade standard.

[0005] In order to achieve the above object, the present invention provides a method for improving the quality of lithium hydroxide monohydrate products, the method comprising the following steps:

[0006] (1) performing a first flash concentration on the lithium hydroxide alkali solution produced by bipolar membrane electrodialysis to obtain a first concentrated solution having a solid content of 15-40%;

[0007] (2) centrifuging the first concentrated liquid, and then washing the first solid product obtained by centrifugation with water, wherein the weight ratio of the first solid product to water is 1:0.2-0.3, to obtain a first crude salt and a first mother liquor, and then sequentially evaporating and concentrating the first mother liquor and centrifuging to obtain a second crude salt and Na + ≥50g / L of the second mother liquor, the second mother liquor is discharged, and the volume ratio of the lithium hydroxide alkali solution to the second mother liquor discharged is ≥20:1;

[0008] (3) mixing the first crude salt and the second crude salt, adding water to dissolve the mixture, and then performing a second flash concentration to obtain a second concentrated solution having a solid content of 15-40%;

[0009] (4) centrifuging the second concentrated liquid, and then washing the second solid product obtained by centrifugation with water, wherein the weight ratio of the second solid product to water is 1:0.2-0.3, to obtain a third crude salt and a third mother liquor, and then drying the third crude salt, and returning the third mother liquor to step (1) for reuse;

[0010] In step (2) and step (4), the flushing time is less than 40 s.

[0011] Preferably, in step (1), the lithium hydroxide alkali solution contains the following components: Li + ≥10g / L, Cl - ≤2.5g / L, Na + ≤3.5g / L, K + ≤1g / L, B 3+ ≤0.01g / L, OH - ≥30g / L.

[0012] Preferably, step (1) further comprises: the lithium hydroxide alkali solution is preheated to a temperature ≥ 75°C before the first flash concentration, and then heated to a temperature ≥ 85°C.

[0013] Preferably, in step (2), the first crude salt contains the following components: Li + ≥15 wt%, Na + ≤1.6 wt%, Cl - ≤1.6 wt%.

[0014] Preferably, in step (2), the first mother liquor contains the following components: Li + ≤40g / L, Na + ≤32g / L, Cl -≤20g / L, OH - ≤100g / L.

[0015] Preferably, in step (2), the second crude salt contains the following components: Li + ≥16 wt%, Na + ≤2 wt%, Cl - ≤2.1 wt%.

[0016] Preferably, in step (3), the heavy solution contains the following components: Li + ≥20 g / L, Na + ≤1.5g / L, Cl - ≤1.8g / L.

[0017] Preferably, step (3) further comprises: the heavy solution is preheated to a temperature ≥ 75°C before the second flash concentration, and then heated to a temperature ≥ 85°C.

[0018] Preferably, in step (4), the third crude salt contains the following components: Li + ≥15 wt%, Na + ≤0.1 wt%, Cl - ≤0.1 wt%.

[0019] Preferably, in step (4), the third mother liquor contains the following components: Li + ≤40g / L, Na + ≤5g / L, Cl - ≤10g / L, OH - ≤90g / L.

[0020] Compared with the prior art, the present invention has at least the following advantages:

[0021] (1) The method of the present invention controls the parameters of the evaporation process, specifically, by simultaneously controlling the solid content, the mother liquor discharge volume and concentration, and the post-centrifugal washing process during the evaporation crystallization process, so that the product quality reaches the battery grade and the lithium yield is improved;

[0022] (2) The method described in the present invention does not produce any by-products, and the possibility of impurities in the product is greatly reduced, thereby improving production efficiency and complying with a low-energy consumption, low-cost production method. DETAILED DESCRIPTION

[0023] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0024] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0025] The method for improving the quality of lithium hydroxide monohydrate products provided by the present invention comprises the following steps:

[0026] (1) performing a first flash concentration on the lithium hydroxide alkali solution produced by bipolar membrane electrodialysis to obtain a first concentrated solution having a solid content of 15-40%;

[0027] (2) centrifuging the first concentrated solution, and then washing the first solid product obtained by centrifugation with water, wherein the weight ratio of the first solid product to water is 1:0.2-0.3, and the washing time is less than 40s, to obtain a first crude salt and a first mother liquor, and then sequentially evaporating and concentrating the first mother liquor and centrifuging to obtain a second crude salt and Na + ≥50g / L of the second mother liquor, the second mother liquor is discharged, and the volume ratio of the lithium hydroxide alkali solution to the second mother liquor discharged is ≤40:1;

[0028] (3) mixing the first crude salt and the second crude salt, adding water to dissolve the mixture, and then performing a second flash concentration to obtain a second concentrated solution having a solid content of 15-40%;

[0029] (4) Centrifuging the second concentrated liquid, and then washing the second solid product obtained by centrifugation with water, wherein the weight ratio of the second solid product to water is 1:0.2-0.3, and the washing time is less than 40s, to obtain a third crude salt and a third mother liquor, and then drying the third crude salt, and returning the third mother liquor to step (1) for reuse.

[0030] In the present invention, the lithium hydroxide alkali solution is obtained by bipolar membrane electrodialysis after membrane treatment and resin treatment of salt lake brine. Among them, the membrane treatment process specifically includes the removal of calcium and magnesium from the lithium-rich brine after electrodialysis concentration through primary nanofiltration, secondary nanofiltration, tertiary nanofiltration and second-stage nanofiltration to obtain three-stage nanofiltration water production, wherein the primary nanofiltration concentrated water is dialyzed to the second-stage nanofiltration, the concentrated liquid is discharged, the produced water is returned to the first-stage nanofiltration feed tank, the secondary nanofiltration concentrated water is returned to the first-stage nanofiltration feed, and the tertiary nanofiltration concentrated water is returned to the second-stage nanofiltration feed. The resin deep removal of calcium, magnesium and boron includes that the third-stage nanofiltration produced water first enters the chelated calcium and magnesium removal resin for ion exchange to remove calcium and magnesium, and then the qualified liquid enters the chelated boron removal resin for ion exchange to remove boron. The resin after calcium, magnesium and boron removal must be acid regenerated and alkali transformed for standby use. The pH of the resin stage calcium, magnesium and boron removal is>9.

[0031] In the present invention, step (1) also includes: heating the lithium hydroxide alkali solution before the first flash concentration to save steam during flash concentration. In one embodiment, the lithium hydroxide alkali solution is preheated to a temperature ≥75°C before the first flash concentration, and then heated to a temperature ≥85°C. In a more preferred embodiment, the heating process includes: injecting the lithium hydroxide alkali solution into a condensed water fresh steam plate preheater, exchanging heat with distilled water and fresh steam respectively, and after the alkali solution is preheated to a temperature ≥75°C, it is transported to a steam forced circulation heat exchanger through a forced circulation pump and heated to a temperature ≥85°C.

[0032] In the method described in the present invention, the lithium hydroxide alkali solution produced by bipolar membrane electrodialysis contains impurity elements such as chlorine, sodium, and potassium that are difficult to remove. In some embodiments, the lithium hydroxide alkali solution in step (1) contains the following components: Li + ≥10g / L, Cl - ≤2.5g / L, Na + ≤3.5g / L, K + ≤1g / L, B 3+ ≤0.01g / L, OH - ≥30g / L. In a more preferred embodiment, the lithium hydroxide alkali solution in step (1) contains the following components: Li + The content is 11-13g / L, Cl - The content is 2-2.5g / L, Na + The content is 1-3g / L, K + The content is 0.1-0.6g / L, B 3+ The content is ≤0.01g / L, OH - The content is ≥30g / L.

[0033] In the present invention, the inventors found that in the first flash concentration process, in order to improve the removal rate of impurities in the lithium hydroxide alkali solution and reduce lithium loss, thereby ensuring that lithium has a high yield and the lithium hydroxide product has a high quality, it is necessary to control the solid content of the obtained first concentrated solution within an appropriate range. In some embodiments, the solid content of the first concentrated solution can be 15%, 20%, 25%, 30%, 35% or 40%.

[0034] In some embodiments, the conditions of the first flash concentration include: liquid phase temperature ≥ 85°C, pressure 650-750 mbar. In the present invention, the first flash concentration is performed in a crystallization separator commonly used in the art.

[0035] In the method of the present invention, the first concentrated solution is centrifuged, and the specific operation of washing the first solid product obtained by centrifugation with water includes: conveying the first concentrated solution to a centrifuge for centrifugation to obtain a first solid product and a first centrifugal solution, and then washing the first solid product with water in the centrifuge to obtain a first crude salt and a first washing solution, and the first centrifugal solution and the first washing solution are combined into a first mother liquor. In the present invention, in order to wash away the impurities on the first solid product and prevent the loss of lithium from being dissolved in the washing solution due to long-term washing of the first solid product with water, it is necessary to reasonably control the amount of water and the washing time of water. In some embodiments, the weight ratio of the first solid product to water can be 1:0.2, 1:0.25 or 1:0.3. In other embodiments, the washing time of washing the first solid product obtained by centrifugation with water can be 10s, 15s, 20s, 25s, 30s or 35s.

[0036] In the present invention, the content of sodium and chlorine in the first crude salt in step (2) is relatively low. In some embodiments, the first crude salt in step (2) contains the following components: Li + ≥15 wt%, Na + ≤1.6 wt%, Cl - ≤1.6 wt%.

[0037] In the present invention, the first mother liquor in step (2) contains more sodium and chlorine, and the content of lithium ions is relatively high. In other embodiments, the first mother liquor in step (2) contains the following components: Li + ≤40g / L, Na + ≤32g / L, Cl - ≤20g / L, OH - ≤100g / L.

[0038] In the present invention, in order to reduce the loss of lithium, the first mother liquor can be evaporated and concentrated and centrifuged to recover the lithium in the mother liquor. In order to increase the yield of lithium, it is necessary to increase the concentration of sodium ions in the second mother liquor, that is, the Na + ≥50g / L; while reducing the discharge volume of the second mother liquor, that is, the volume ratio of the lithium hydroxide alkali solution to the second mother liquor is ≥20:1, preferably 20-40:1. In the present invention, the evaporation concentration of the first mother liquor can be carried out in a common evaporator in the art, such as a single-effect evaporator or a multi-effect evaporator.

[0039] In some embodiments, the second crude salt in step (2) contains the following components: Li + ≥16 wt%, Na + ≤2 wt%, Cl -≤2.1 wt %. In order to reduce the loss of lithium, the second crude salt is mixed with the first crude salt and then the subsequent operation is performed.

[0040] In the present invention, in order to ensure the quality of the prepared product and improve the lithium yield, the lithium content in the heavy solution obtained after the first crude salt and the second crude salt are redissolved cannot be too low. In some embodiments, in step (3), the heavy solution contains the following components: Li + ≥20 g / L, Na + ≤1.5g / L, Cl - ≤1.8g / L, OH - ≤50g / L.

[0041] In the present invention, step (3) also includes: heating the heavy solution before the second flash concentration, saving steam during the second flash concentration. In one embodiment, step (3) also includes: preheating the heavy solution to a temperature ≥75°C before the second flash concentration, and then heating it to a temperature ≥85°C. In a more preferred embodiment, the heating process includes: pumping the heavy solution into a condensate fresh steam plate preheater, exchanging heat with distilled water and fresh steam respectively, and after the heavy solution is preheated to a temperature ≥75°C, it is transported to the second steam forced circulation heat exchanger through a second steam forced circulation pump and heated to a temperature ≥85°C.

[0042] In one embodiment, the conditions of the second flash concentration in step (3) include: a liquid phase temperature of ≥85°C and a pressure of 350-550 mbar. In the present invention, the second flash concentration is carried out in a crystallization separator commonly used in the art. Herein, the pressures of the first flash concentration and the second flash concentration refer to relative pressures.

[0043] In the present invention, the inventors found that in the second flash concentration process, in order to improve the removal rate of impurities in the heavy solution and reduce lithium loss, thereby ensuring that lithium has a higher yield and the lithium hydroxide product has a higher quality, it is necessary to control the solid content of the obtained second concentrated solution within an appropriate range. In some embodiments, the solid content of the second concentrated solution can be 15%, 20%, 25%, 30%, 35% or 40%.

[0044] In the method of the present invention, the specific operation of centrifuging the second concentrated solution and washing the second solid product obtained by centrifugation with water includes: conveying the second concentrated solution to a centrifuge for centrifugation to obtain a second solid product and a second centrifugal solution, and then washing the second solid product with water in the centrifuge to obtain a third crude salt and a second washing solution, and the second centrifugal solution and the second washing solution are combined into a third mother liquor. In the present invention, in order to wash away the impurities on the second solid product and prevent the loss of lithium from being dissolved in the washing solution due to long-term washing of the second solid product with water, it is necessary to reasonably control the amount of water and the washing time of water. In some embodiments, the weight ratio of the second solid product to water can be 1:0.2, 1:0.25 or 1:0.3. In other embodiments, the washing time of washing the second solid product obtained by centrifugation with water can be 10s, 15s, 20s, 25s, 30s, 35s or 40s.

[0045] In the present invention, the content of sodium and chlorine in the third crude salt is greatly reduced. In some embodiments, in step (4), the third crude salt contains the following components: Li + ≥15 wt%, Na + ≤0.1wt%,Cl - ≤0.1 wt %. The composition and content of the third crude salt are similar to those of the final lithium hydroxide monohydrate product.

[0046] In some embodiments, the third mother liquor in step (4) contains the following components: Li + ≤40g / L, Na + ≤5g / L, Cl - ≤10g / L, OH - ≤90g / L. The third mother liquor contains a certain amount of lithium, and the third mother liquor can be returned to step (1) for bipolar membrane electrodialysis or first flash concentration according to actual conditions.

[0047] In the present invention, the third crude salt can be dried in a manner well known in the art. In one embodiment, the third crude salt is dried in a rotary kiln drying system. In a more specific embodiment, the method further comprises: drying the third crude salt, separating it through a vibrating screen, and the screened material is the final product.

[0048] The method described in the present invention controls multiple parameters of the evaporation process so that the product quality reaches the battery grade and complies with the GB / T 26008-2020 standard. At the same time, the lithium yield is improved, and the yield is greater than 90%, achieving a balance between the quality of the lithium hydroxide monohydrate product and the lithium recovery rate. In addition, the method described in the present invention does not produce any by-products, and the possibility of the product being accompanied by impurities is greatly reduced, thereby improving production efficiency and complying with a low-energy consumption, low-cost production method.

[0049] The following examples further illustrate the method for improving the quality of lithium hydroxide monohydrate products of the present invention. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0050] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0051] In the present invention, the calculation method of lithium yield is: lithium amount in lithium hydroxide monohydrate product / lithium hydroxide alkali solution.

[0052] In this embodiment, the quality of the battery-grade lithium hydroxide monohydrate product must meet the composition and content requirements shown in Table 1. Among them, the main content (LiOH) and carbonate are determined by titration, chloride ions are determined by spectrophotometry, acid insolubles are determined by constant weight method, and the remaining elements are determined by standard working curves on an inductively coupled plasma atomic emission spectrometer.

[0053] Table 1

[0054]

[0055] Example 1

[0056] (1) 30m 3 The lithium hydroxide alkali solution produced by bipolar membrane electrodialysis was tested and analyzed, and the result was Li + :12.38g / L,Cl - :2.47g / L,Na + :1.37g / L,K + :0.20g / L,B 3+ :0.005g / L,OH -: 33.09g / L; the lithium hydroxide alkali solution is pumped into the condensate fresh steam plate preheater, and heat exchange is performed with distilled water and fresh steam respectively. After the lithium hydroxide alkali solution is preheated to 80°C, it is transported to a steam forced circulation heat exchanger through a forced circulation pump and heated to 85°C. After that, the first flash concentration is performed in a crystallization separator. The liquid phase temperature of the first flash concentration is 85°C and the pressure is 685mbar. When the solid content of the first concentrated liquid reaches 25%, it is pumped out by a discharge pump;

[0057] (2) The discharge pump transports the first concentrated liquid to a centrifuge for centrifugation to obtain a first solid product and a first centrifuge liquid, and then washes the first solid product with water in the centrifuge to obtain a first crude salt and a first washing liquid. The first centrifuge liquid and the first washing liquid are combined into a first mother liquor, wherein the weight ratio of the first solid product to water during washing is 1:0.3, the washing time is 40 seconds, and the Li in the first crude salt is 0.1%. + :15.60%,Na + :1.34%,Cl - : 1.20%, Li in the first mother liquor + :38.51g / L,Na + :28.94g / L,Cl - :16.33g / L,OH - : 95.82g / L; then the first mother liquor enters the single-effect mother liquor tank, and is sent to the single-effect evaporator through a high-concentration mother liquor pump for evaporation and concentration, and then centrifuged by a centrifuge to obtain the second crude salt and the second mother liquor. Li + : 16.28%, Na + :1.65%,Cl - : 1.82%, Li in the second mother liquor + :38.97g / L,Na + :55.64g / L,Cl - : 92.43%, the second mother liquor is discharged, and the discharge volume of the second mother liquor is 0.8m 3 ;

[0058] (3) The first crude salt and the second crude salt are mixed and then added to distilled water to dissolve the salt to obtain a heavy solution. + :24.06g / L,Na + :1.18g / L,Cl -: 1.34g / L; then the heavy solution is pumped into the condensate fresh steam plate preheater, and heat exchange is performed with distilled water and fresh steam respectively to preheat the heavy solution. After the heavy solution is preheated to 80°C, it is transported to the second steam forced circulation heat exchanger through the second steam forced circulation pump and heated to 85°C. After that, the second flash concentration is performed in the crystallization separator to a solid content of 30% to obtain a second concentrated solution. The liquid phase temperature of the second flash concentration is 85°C and the pressure is 425mbar;

[0059] (4) The second concentrated liquid is transported to a centrifuge for centrifugation to obtain a second solid product and a second centrifugal liquid, and then the second solid product is washed with water in the centrifuge to obtain a third crude salt and a second washing liquid. The second centrifugal liquid and the second washing liquid are combined into a third mother liquor, wherein the weight ratio of the second solid product to water during washing is 1:0.3, the washing time is 40 seconds, and the Li in the third mother liquor is + :38.61g / L,Na + :4.25g / L,Cl - :8.41g / L,OH - : 86.53g / L; then the third mother liquor is returned to step (1) for the first flash concentration and reuse, and the third crude salt is sent to the rotary kiln drying system. The dried salt is separated by a vibrating screen, and the screened material is a lithium hydroxide monohydrate product, and 2150kg of lithium hydroxide monohydrate product is obtained.

[0060] In this embodiment, the yield of lithium is 96%. The components and contents of the lithium hydroxide monohydrate product are shown in Table 2.

[0061] Table 2

[0062]

[0063] Example 2

[0064] (1) 25m 3 The lithium hydroxide alkali solution produced by bipolar membrane electrodialysis was tested and analyzed, and the result was Li + :11.38g / L,Cl - :2.03g / L,Na + :1.58g / L,K + :0.18g / L,B 3+ :0.008g / L,OH -: 32.16g / L; the lithium hydroxide alkali solution is pumped into the condensate fresh steam plate preheater, and heat exchange is performed with distilled water and fresh steam respectively. After the lithium hydroxide alkali solution is preheated to 80°C, it is transported to a steam forced circulation heat exchanger through a forced circulation pump and heated to 85°C. After that, the first flash concentration is performed in a crystallization separator. The liquid phase temperature of the first flash concentration is 85°C and the pressure is 703mbar. When the solid content of the first concentrated liquid reaches 35%, it is pumped out by a discharge pump;

[0065] (2) The discharge pump transports the first concentrated liquid to a centrifuge for centrifugation to obtain a first solid product and a first centrifuge liquid, and then washes the first solid product with water in the centrifuge to obtain a first crude salt and a first washing liquid. The first centrifuge liquid and the first washing liquid are combined into a first mother liquor, wherein the weight ratio of the first solid product to water during washing is 1:0.25, the washing time is 20 seconds, and the Li in the first crude salt is 1:0.25. + : 16.02%, Na + :1.54%,Cl - : 1.58%, Li in the first mother liquor + :36.79g / L,Na + :30.81g / L,Cl - :18.65g / L,OH - : 98.70g / L; then the first mother liquor enters the single-effect mother liquor tank, and is sent to the single-effect evaporator through a high-concentration mother liquor pump for evaporation and concentration, and then centrifuged by a centrifuge to obtain the second crude salt and the second mother liquor. Li + :16.58%,Na + :1.73%,Cl - : 2.08%, Li in the second mother liquor + :40g / L,Na + :70.22g / L,Cl - : 95.56 g / L, the second mother liquor is discharged, and the discharge volume of the second mother liquor is 1.3 m 3 ;

[0066] (3) The first crude salt and the second crude salt were mixed and added with distilled water to dissolve the salt to obtain a heavy solution. The heavy solution contained 25.47 g / L Li+ and 25.47 g / L Na + :1.20g / L,Cl -: 1.60g / L; then the heavy solution is pumped into the condensate fresh steam plate preheater, and heat exchange is performed with distilled water and fresh steam respectively to preheat the heavy solution. After the heavy solution is preheated to 80°C, it is transported to the second steam forced circulation heat exchanger through the second steam forced circulation pump and heated to 85°C. After that, the second flash evaporation is performed in the crystallization separator to concentrate the solid content to 40%, thereby obtaining a second concentrated solution. The liquid phase temperature of the second flash evaporation concentration is 85°C and the pressure is 505mbar;

[0067] (4) The second concentrated liquid is transported to a centrifuge for centrifugation to obtain a second solid product and a second centrifugal liquid, and then the second solid product is washed with water in the centrifuge to obtain a third crude salt and a second washing liquid. The second centrifugal liquid and the second washing liquid are combined into a third mother liquor, wherein the weight ratio of the second solid product to water during washing is 1:0.2, the washing time is 10s, and the Li in the third mother liquor is + :40g / L,Na + :3.85g / L,Cl - :7.51g / L,OH - : 80.29g / L; then the third mother liquor is returned to step (1) for the first flash concentration and reuse, the third crude salt is sent to the rotary kiln drying system, the dried salt is separated by a vibrating screen, the screened material is a lithium hydroxide monohydrate product, and 1680 kg of lithium hydroxide monohydrate product is obtained.

[0068] In this embodiment, the yield of lithium is 99%, and the components and contents of the lithium hydroxide monohydrate product are shown in Table 3.

[0069] Table 3

[0070]

[0071]

[0072] Example 3

[0073] (1) 20m 3 The lithium hydroxide alkali solution produced by bipolar membrane electrodialysis was tested and analyzed, and the result was Li + :11.29g / L,Cl - :2.18g / L,Na + :2.36g / L,K + :0.51g / L,B 3+ :0.006g / L,OH -: 37.15g / L; the lithium hydroxide alkali solution is pumped into the condensate fresh steam plate preheater, and heat exchange is performed with distilled water and fresh steam respectively. After the lithium hydroxide alkali solution is preheated to 80°C, it is transported to a steam forced circulation heat exchanger through a forced circulation pump and heated to 85°C. After that, the first flash concentration is performed in a crystallization separator. The liquid phase temperature of the first flash concentration is 85°C and the pressure is 670mbar. When the solid content of the first concentrated liquid reaches 30%, it is pumped out by a discharge pump;

[0074] (2) The discharge pump transports the first concentrated liquid to a centrifuge for centrifugation to obtain a first solid product and a first centrifuge liquid, and then washes the first solid product with water in the centrifuge to obtain a first crude salt and a first washing liquid. The first centrifuge liquid and the first washing liquid are combined into a first mother liquor, wherein the weight ratio of the first solid product to water during washing is 1:0.3, the washing time is 30 seconds, and the Li in the first crude salt is 0.1%. + :15.38%,Na + :1.30%,Cl- - : 1.24%, Li in the first mother liquor + :38.82g / L,Na + :28.91g / L,Cl - :16.28g / L,OH - : 96.77g / L; then the first mother liquor enters the single-effect mother liquor tank, and is sent to the single-effect evaporator through a high-concentration mother liquor pump for evaporation and concentration, and then centrifuged by a centrifuge to obtain the second crude salt and the second mother liquor. Li in the second crude salt + : 16.28%, Na + :1.47%,Cl - : 1.69%, Li in the second mother liquor + :34.81g / L,Na + :60.18g / L,Cl - : 80.53 g / L, the second mother liquor is discharged, and the discharge volume of the second mother liquor is 1.5 m 3 ;

[0075] (3) The first crude salt and the second crude salt are mixed and then added to distilled water to dissolve the salt to obtain a heavy solution. + :25.44g / L,Na + :1.36g / L,Cl -: 1.50g / L; then the heavy solution is pumped into the condensate fresh steam plate preheater, and heat exchange is performed with distilled water and fresh steam respectively to preheat the heavy solution. After the heavy solution is preheated to 80°C, it is transported to the second steam forced circulation heat exchanger through the second steam forced circulation pump and heated to 85°C. After that, the second flash concentration is performed in the crystallization separator to a solid content of 25% to obtain a second concentrated solution. The liquid phase temperature of the second flash concentration is 85°C and the pressure is 393mbar;

[0076] (4) The second concentrated liquid is transported to a centrifuge for centrifugation to obtain a second solid product and a second centrifugal liquid, and then the second solid product is washed with water in the centrifuge to obtain a third crude salt and a second washing liquid. The second centrifugal liquid and the second washing liquid are combined into a third mother liquor, wherein the weight ratio of the second solid product to water during washing is 1:0.3, the washing time is 20 seconds, and the Li in the third mother liquor is + :36.67g / L,Na + :3.88g / L,Cl - :7.14g / L,OH - : 85.73g / L; then the third mother liquor is returned to step (1) for the first flash concentration and reuse, the third crude salt is sent to the rotary kiln drying system, the dried salt is separated by a vibrating screen, the screened material is a lithium hydroxide monohydrate product, and 1240 kg of lithium hydroxide monohydrate product is obtained.

[0077] In this embodiment, the yield of lithium is 91%, and the components and contents of the lithium hydroxide monohydrate product are shown in Table 4.

[0078] Table 4

[0079]

[0080] Comparative Example 1

[0081] The method of Example 2 is followed, except that in step (1), the first concentrated liquid is pumped out when the solid content reaches 45%.

[0082] In this comparative example, since the solid is easy to crystallize when the solid content is greater than 40%, the pipeline plugging material crystallization cannot be produced normally.

[0083] Comparative Example 2

[0084] The method of Example 2 is followed, except that in step (2), the flushing time is 60 seconds.

[0085] In this comparative example, the yield of lithium is 85%, and the composition and content of the lithium hydroxide monohydrate product are shown in Table 5.

[0086] Table 5

[0087]

[0088] Comparative Example 3

[0089] The method of Example 2 is followed, except that in step (2), the weight ratio of the first solid product to water during flushing is 1:1.

[0090] In this comparative example, the yield of lithium is 70%, and the composition and content of the lithium hydroxide monohydrate product are shown in Table 6.

[0091] Table 6

[0092]

[0093]

[0094] Comparative Example 4

[0095] The method of Example 2 is followed, except that in step (3), a second flash evaporation concentration is performed to a solid content of 10%.

[0096] In this comparative example, the yield of lithium is 65%, and the composition and content of the lithium hydroxide monohydrate product are shown in Table 7.

[0097] Table 7

[0098]

[0099] Comparative Example 5

[0100] The method of Example 2 is followed, except that in step (4), the flushing time is 60 seconds.

[0101] In this comparative example, the yield of lithium is 80%, and the composition and content of the lithium hydroxide monohydrate product are shown in Table 8.

[0102] Table 8

[0103]

[0104] Comparative Example 6

[0105] The method of Example 2 is followed, except that in step (4), the weight ratio of the second solid product to water during flushing is 1:1.

[0106] In this comparative example, the yield of lithium is 50%, and the composition and content of the lithium hydroxide monohydrate product are shown in Table 9.

[0107] Table 9

[0108]

[0109] It can be seen from the above embodiments and comparative examples that the method described in the present invention controls the parameters of the evaporation process to make the product quality reach battery grade, while improving the lithium yield without any by-products; while according to the method in the comparative example, not only can the battery-grade lithium hydroxide monohydrate product not be prepared, but also the lithium yield is low.

[0110] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for improving the quality of lithium hydroxide monohydrate products, characterized in that: The method comprises the following steps: (1) performing a first flash concentration on the lithium hydroxide alkali solution produced by bipolar membrane electrodialysis to obtain a first concentrated solution having a solid content of 15-40%; (2) centrifuging the first concentrated liquid, and then washing the first solid product obtained by centrifugation with water, wherein the weight ratio of the first solid product to water is 1:0.2-0.3, to obtain a first crude salt and a first mother liquor, and then sequentially evaporating and concentrating the first mother liquor and centrifuging to obtain a second crude salt and Na + ≥50g / L of the second mother liquor, the second mother liquor is discharged, and the volume ratio of the lithium hydroxide alkali solution to the second mother liquor discharged is ≥20:1; (3) mixing the first crude salt and the second crude salt, adding water to dissolve the mixture, and then performing a second flash concentration to obtain a second concentrated solution having a solid content of 15-40%; (4) centrifuging the second concentrated liquid, and then washing the second solid product obtained by centrifugation with water, wherein the weight ratio of the second solid product to water is 1:0.2-0.3, to obtain a third crude salt and a third mother liquor, and then drying the third crude salt, and returning the third mother liquor to step (1) for reuse; In step (2) and step (4), the flushing time is less than 40 s.

2. The method according to claim 1, characterized in that: In step (1), the lithium hydroxide alkali solution contains the following components: Li + ≥10g / L, Cl - ≤2.5g / L, Na + ≤3.5g / L, K + ≤1g / L, B 3+ ≤0.01g / L, OH - ≥30g / L.

3. The method according to claim 1 or 2, characterized in that: Step (1) also includes: the lithium hydroxide alkali solution is preheated to a temperature ≥ 75°C before the first flash concentration, and then heated to a temperature ≥ 85°C.

4. The method according to any one of claims 1 to 3, characterized in that: In step (2), the first crude salt contains the following components: Li + ≥15 wt%, Na + ≤1.6 wt%, Cl - ≤1.6 wt%.

5. The method according to any one of claims 1 to 4, characterized in that: In step (2), the first mother liquor contains the following components: Li + ≤40g / L, Na + ≤32g / L, Cl - ≤20g / L, OH - ≤100g / L.

6. The method according to any one of claims 1 to 5, characterized in that: In step (2), the second crude salt contains the following components: Li + ≥16 wt%, Na + ≤2 wt%, Cl - ≤2.1 wt%.

7. The method according to any one of claims 1 to 6, characterized in that: In step (3), the heavy solution contains the following components: Li + ≥20 g / L, Na + ≤1.5g / L, Cl - ≤1.8g / L.

8. The method according to any one of claims 1 to 7, characterized in that: Step (3) also includes: the heavy solution is preheated to a temperature ≥ 75°C before the second flash concentration, and then heated to a temperature ≥ 85°C.

9. The method according to any one of claims 1 to 8, characterized in that: In step (4), the third crude salt contains the following components: Li + ≥15 wt%, Na + ≤0.1wt%,Cl - ≤0.1 wt%.

10. The method according to any one of claims 1 to 9, characterized in that: In step (4), the third mother liquor contains the following components: Li + ≤40g / L, Na + ≤5g / L, Cl - ≤10g / L, OH - ≤90g / L.

Images