Method for preparing battery-grade lithium dihydrogen phosphate by using lithium precipitation mother liquor

Abstract

The invention relates to the technical field of lithium dihydrogen phosphate, and discloses a method for preparing battery-grade lithium dihydrogen phosphate by using lithium precipitation mother liquor. The method comprises the following steps: (1) mixing a hydrochloric acid solution with a lithium precipitation mother solution until the pH value of the obtained reaction solution is 4-5; (2) heating the reaction solution, adding the sodium phosphate solution into the reaction solution to adjust the pH value to 9-10, and reacting to obtain crude lithium phosphate; (3) adding a phosphoric acid solution into the crude lithium phosphate until the pH value of the obtained mixed solution is 3-5.5; (4) carrying out first reduced pressure evaporation on the crude lithium dihydrogen phosphate solution, and carrying out solid-liquid separation on a first concentrate to obtain a first solid phase and a first mother solution; (5) dissolving the first solid phase in hot water, carrying out second reduced pressure evaporation, and carrying out solid-liquid separation on a second concentrate to obtain a second solid phase and a second mother solution; the solid content of the second concentrate is higher than that of the first concentrate. The lithium dihydrogen acid prepared by the method is high in purity, and the comprehensive yield of lithium is high.

Description

Technical Field

[0001] The invention relates to the technical field of lithium dihydrogen phosphate, and in particular to a method for preparing battery-grade lithium dihydrogen phosphate by utilizing lithium precipitation mother liquor. Background Art

[0002] Lithium dihydrogen phosphate (chemical formula LiH2PO4) is a white crystalline powder that is easily soluble in water and weakly acidic in water. As an important chemical raw material, lithium dihydrogen phosphate is widely used in lithium-ion batteries, glass and ceramic industries, chemical synthesis, and biomedicine. In the field of lithium-ion batteries, the ferrous oxalate plus lithium dihydrogen phosphate process route requires fewer types of materials to be mixed, is easy to mix evenly, and produces products with better performance and significantly reduced energy consumption compared to other process routes.

[0003] The traditional production process of lithium dihydrogen phosphate is mainly to react lithium hydroxide monohydrate (partially replaced by lithium carbonate to reduce costs) with phosphoric acid. The disadvantage is that the production cost is high, making the cost of lithium dihydrogen phosphate of equivalent lithium higher than that of lithium carbonate. In the patent "Method for preparing battery-grade lithium dihydrogen phosphate using high-purity lithium carbonate mother liquor" (CN102351160B), Ganfeng Lithium Industry adds phosphoric acid and sodium phosphate to the mother liquor (mainly lithium bicarbonate) for preparing high-purity lithium carbonate to obtain a mixture of lithium phosphate and dilithium hydrogen phosphate, and then adds phosphoric acid to generate lithium dihydrogen phosphate, which is evaporated and cooled to obtain lithium dihydrogen phosphate. In the process of removing carbonate in the early stage, a large amount of phosphoric acid is added, and then trisodium phosphate is added to adjust the pH, resulting in the introduction of excessive phosphate ions into the mother liquor, which seriously affects the environment. In addition, during the evaporation of lithium dihydrogen phosphate, the method adopts cooling crystallization, which takes a long time to cool down and has poor continuity. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of high cost, short process and serious environmental impact of the production process of lithium dihydrogen phosphate, and provide a method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor. The method introduces less phosphate radicals, has low cost, short process flow, small environmental pollution, and the prepared lithium dihydrogen phosphate has high purity and high comprehensive lithium yield.

[0005] In order to achieve the above object, the present invention provides a method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor, the method comprising the following steps:

[0006] (1) mixing a hydrochloric acid solution with a lithium precipitation mother liquor to react until the pH value of the resulting reaction solution reaches 4-5;

[0007] (2) heating the reaction solution, then adding a sodium phosphate solution to the heated reaction solution, adjusting the pH value of the reaction solution to 9-10, and then reacting, solid-liquid separation and washing to obtain crude lithium phosphate;

[0008] (3) adding a phosphoric acid solution to the crude lithium phosphate until the pH value of the resulting mixed solution is 3-5.5, thereby obtaining a crude lithium dihydrogen phosphate solution;

[0009] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation, and subjecting the obtained first concentrate to solid-liquid separation and washing to obtain a first solid phase and a first mother liquor, respectively;

[0010] (5) dissolving the first solid phase in hot water, and then performing a second reduced-pressure evaporation, performing solid-liquid separation on the obtained second concentrate to obtain a second solid phase and a second mother liquor, respectively, and drying the second solid phase;

[0011] The second concentrate has a higher solid content than the first concentrate.

[0012] Preferably, the lithium precipitation mother solution contains the following components: Li + 1.2-1.8g / L, CO3 2- 15-25g / L, Na + It is 18-26g / L, and Cl- is 100-140g / L.

[0013] Preferably, in step (1), the concentration of the hydrochloric acid solution is 25-35% by weight.

[0014] Preferably, in step (2), the reaction solution is heated to 80-95°C.

[0015] Preferably, in step (2), the sodium phosphate salt in the sodium phosphate salt solution is selected from at least one of trisodium phosphate, sodium monohydrogen phosphate and sodium dihydrogen phosphate.

[0016] Preferably, the concentration of phosphate in the sodium phosphate salt solution is 180-250 g / L.

[0017] Preferably, in step (2), the reaction is continued for 25-40 minutes.

[0018] Preferably, the purity of the crude lithium phosphate is 94-97 wt %.

[0019] Preferably, in step (3), the concentration of the phosphoric acid solution is 45-90% by weight.

[0020] Preferably, in step (3), the concentration of lithium dihydrogen phosphate in the crude lithium dihydrogen phosphate solution is 1200-2490 g / L.

[0021] Preferably, in step (4) and step (5), the conditions of the first reduced-pressure evaporation and the second reduced-pressure evaporation include: a temperature of 80-90° C. and a pressure of 380-450 bar.

[0022] Preferably, in step (4), the washing process comprises: first eluting the solid phase obtained by solid-liquid separation with the second mother liquor, and then washing the solid phase with water.

[0023] Preferably, the solid content of the second concentrate is 2-10% higher than the solid content of the first concentrate.

[0024] Preferably, the solid content of the first concentrate is 15-20%.

[0025] Preferably, the solid content of the second concentrate is 20-30%.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] (1) The present invention uses hydrochloric acid solution to adjust the pH of the lithium precipitation mother liquor to a specific range to remove carbonate ions in the lithium precipitation mother liquor, which not only reduces the amount of phosphate introduced and reduces environmental pollution, but also can fully remove carbonate ions to avoid affecting subsequent operations, which is beneficial to improving the purity of the product.

[0028] (2) After removing carbonate ions from the lithium precipitation mother liquor, the present invention can fully generate insoluble lithium phosphate from the lithium ions in the solution by adding sodium phosphate and allowing the reaction solution to react at a specific pH value, which can not only improve the lithium yield but also effectively remove impurities.

[0029] (3) The method of the present invention can remove the remaining impurities through two reduced pressure evaporation concentrations, thereby improving the purity of the lithium dihydrogen phosphate product to meet battery grade standards.

[0030] (4) In a more preferred embodiment, the second mother liquor containing a small amount of phosphate obtained by the second reduced-pressure evaporation is used to wash the first solid phase obtained by the first reduced-pressure evaporation, which can reduce the solubility of lithium dihydrogen phosphate and improve the yield. DETAILED DESCRIPTION

[0031] 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.

[0032] 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.

[0033] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor provided by the present invention comprises the following steps:

[0034] (1) mixing a hydrochloric acid solution with a lithium precipitation mother liquor to react until the pH value of the resulting reaction solution reaches 4-5;

[0035] (2) heating the reaction solution, then adding a sodium phosphate solution to the heated reaction solution, adjusting the pH value of the reaction solution to 9-10, and then reacting, solid-liquid separation and washing to obtain crude lithium phosphate;

[0036] (3) adding a phosphoric acid solution to the crude lithium phosphate until the pH value of the resulting mixed solution is 3-5.5, thereby obtaining a crude lithium dihydrogen phosphate solution;

[0037] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation, and subjecting the obtained first concentrate to solid-liquid separation and washing to obtain a first solid phase and a first mother liquor, respectively;

[0038] (5) dissolving the first solid phase in hot water, and then performing a second reduced-pressure evaporation, performing solid-liquid separation on the obtained second concentrate to obtain a second solid phase and a second mother liquor, respectively, and drying the second solid phase;

[0039] The second concentrate has a higher solid content than the first concentrate.

[0040] In the present invention, the lithium precipitation mother solution used to prepare lithium dihydrogen phosphate is a low-lithium, high-sodium solution, which also contains some other common components. In some embodiments, the lithium precipitation mother solution contains the following components: Li + 1.2-1.8g / L, CO3 2- 15-25g / L, Na + It is 18-26g / L, and Cl- is 100-140g / L.

[0041] The purpose of step (1) of the present invention is to react with carbonate ions in lithium sinking mother liquor by hydrochloric acid to remove carbonate ions. The process of step (1) includes: slowly adding hydrochloric acid solution to lithium sinking mother liquor, hydrochloric acid continues to react with carbonate ions in lithium sinking mother liquor, when the pH value of the obtained reaction solution is 4-5, it indicates that carbonate ions in lithium sinking mother liquor are completely removed, and the addition of hydrochloric acid solution is stopped. Step (1) adjusts the pH of lithium sinking mother liquor to a specific range by adding hydrochloric acid solution to achieve the purpose of removing carbonate ions in lithium sinking mother liquor, not only reduces the amount of phosphate introduced, reduces environmental pollution, and can fully remove carbonate ions, which is beneficial to improve the purity of the product. In some embodiments, the concentration of the hydrochloric acid solution described in step (1) can be 25-35% by weight, such as 25% by weight, 28% by weight, 30% by weight, 31% by weight, 33% by weight or 35% by weight.

[0042] In step (2) of the present invention, phosphate ions are provided by adding a sodium phosphate salt solution to allow the reaction solution to react at a specific pH value, so that lithium is fully converted into lithium phosphate that is not easily soluble, and impurities can be effectively removed while increasing the yield of lithium. In the method described in the present invention, the sodium phosphate salt solution can be quickly added to the heated reaction solution, and then the reaction is continued to generate lithium phosphate as much as possible from the lithium in the reaction solution. In some preferred embodiments, in step (2), the reaction can be continued for 25-40 minutes.

[0043] In order to further increase the amount of lithium phosphate produced and improve the yield, in a more preferred embodiment, before adding the sodium phosphate solution to the reaction solution, the reaction solution in step (2) can be heated to 80-95°C, specifically, for example, 80°C, 85°C, 90°C or 95°C, which is the optimal reaction temperature of lithium phosphate.

[0044] In the present invention, the sodium phosphate salt in the sodium phosphate salt solution can be a conventional choice in the art, as long as it can provide phosphate radicals and does not introduce other impurities. In some embodiments, the sodium phosphate salt in the sodium phosphate salt solution in step (2) can be selected from at least one of trisodium phosphate, sodium monohydrogen phosphate and sodium dihydrogen phosphate. In a more preferred embodiment, in order to further increase the amount of lithium phosphate generated, the concentration of phosphate radicals in the sodium phosphate salt solution can be 180-250 g / L.

[0045] In the method of the present invention, the solid-liquid separation described in step (2) can be various operations well known in the art, preferably filtration. In the present invention, the washing operation described in step (2) includes: first slurry-washing the solid phase product obtained by solid-liquid separation in water, and then adding water to a centrifuge for elution to remove impurities on the surface of the lithium phosphate. In the present invention, the crude lithium phosphate obtained after washing has a high purity. In some embodiments, the purity of the crude lithium phosphate is 94-97% by weight.

[0046] In step (3) of the present invention, phosphoric acid is added to dissolve lithium phosphate and react to obtain lithium dihydrogen phosphate. The process of step (3) includes: slowly adding phosphoric acid solution to crude lithium phosphate, phosphoric acid dissolving lithium phosphate to generate lithium dihydrogen phosphate, until the pH value of the obtained mixed solution is 3-5.5, indicating that the lithium phosphate is completely dissolved and lithium dihydrogen phosphate is generated, at which time the addition of phosphoric acid solution is stopped.

[0047] In some embodiments, the concentration of the phosphoric acid solution in step (3) can be 45-90 weight%, for example, 45 weight%, 50 weight%, 55 weight%, 60 weight%, 65 weight%, 70 weight%, 75 weight%, 80 weight%, 85 weight% or 90 weight%.

[0048] In some embodiments, the concentration of lithium dihydrogen phosphate in the crude lithium dihydrogen phosphate solution in step (3) can be 1200-2490 g / L. In addition to lithium dihydrogen phosphate, the crude lithium dihydrogen phosphate solution also contains impurities such as sodium, potassium, chlorine, calcium, and magnesium, with the content of sodium being 3-7 g / L, and the content of potassium, chlorine, calcium, and magnesium being 0.5-1 g / L.

[0049] In the present invention, the crude lithium dihydrogen phosphate solution can be purified into battery-grade lithium dihydrogen phosphate by two reduced-pressure evaporations.

[0050] In some embodiments, the conditions of the first reduced pressure evaporation in step (4) include: the temperature can be 80-90° C., such as 80° C., 83° C., 85° C., 88° C. or 90° C.; the pressure can be 380-450 bar, such as 380 bar, 390 bar, 400 bar, 410 bar, 420 bar, 430 bar, 440 bar or 450 bar. The pressure is a relative pressure.

[0051] In order to further improve the removal rate of impurities in the first reduced pressure evaporation process and ensure a higher yield, in a preferred embodiment, the first reduced pressure evaporation is performed until the solid content of the first concentrate is 15-20%. In the present invention, the percentage of the solid content is a mass percentage.

[0052] In the present invention, the solid-liquid separation in step (4) is carried out by centrifugation to obtain a solid phase and a liquid phase, respectively. In a preferred embodiment, the washing process in step (4) includes: first eluting the solid phase with the second mother liquor, and then washing the solid phase with water; wherein the second mother liquor contains phosphate ions, and the second mother liquor on the surface of the lithium dihydrogen phosphate can be used to wash the solid phase to improve the yield, and then the second mother liquor on the surface of the lithium dihydrogen phosphate is washed with water to improve the purity of the lithium dihydrogen phosphate product. In a preferred embodiment, the solid-liquid separation and washing of the obtained first concentrate to obtain the first solid phase and the first mother liquor respectively include: centrifuging the first concentrate to obtain a solid phase and a liquid phase, respectively; then eluting the solid phase with the second mother liquor for 40-60s, and then washing the solid phase with water for 10-30s to obtain a first solid phase, collecting the washing liquid obtained by eluting and washing with water, and combining the liquid phase and the washing liquid to obtain a first mother liquor. In order to recover a small amount of lithium in the first mother liquor, the first mother liquor can be returned to the lithium precipitation mother liquor of step (1) for reuse, or returned to step (4) for first reduced pressure evaporation. Before obtaining the second mother liquor, the first solid phase is directly washed with water, that is, the obtained first concentrate is subjected to solid-liquid separation and washing, and the process of obtaining the first solid phase and the first mother liquor respectively comprises: centrifuging the first concentrate to obtain a solid phase part and a liquid phase part respectively; then washing the solid phase part with water for 10-30s to obtain the first solid phase, collecting the washing liquid obtained by washing with water, and combining the liquid phase part and the washing liquid to obtain the first mother liquor.

[0053] In one embodiment, the first solid phase is dissolved using hot water at 80-90° C. before the second reduced-pressure evaporation.

[0054] In other embodiments, the conditions of the second reduced pressure evaporation in step (5) include: the temperature can be 80-90°C, such as 80°C, 83°C, 85°C, 88°C or 90°C; the pressure can be 380-450 bar, such as 380 bar, 390 bar, 400 bar, 410 bar, 420 bar, 430 bar, 440 bar or 450 bar. Wherein, the pressure is a relative pressure.

[0055] In the present invention, in order to further improve the removal rate of impurities in the lithium dihydrogen phosphate product and ensure a higher yield, the solid content of the second concentrate is higher than that of the first concentrate. In some preferred embodiments, the solid content of the second concentrate may be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% higher than that of the first concentrate. In order to further improve the removal rate of impurities in the second reduced pressure evaporation process and ensure a higher yield, in a preferred embodiment, the second reduced pressure evaporation is performed until the solid content of the second concentrate is 20-30%.

[0056] In the method described in the present invention, the solid-liquid separation method in step (5) can be centrifugation; centrifugation is used to obtain a solid phase part and a liquid phase part respectively, wherein the second solid phase is washed with water for 10-30s and then dried to obtain battery-grade lithium dihydrogen phosphate; the washing liquid obtained by water washing is combined with the liquid phase part to obtain the second mother liquor, and the second mother liquor is returned to the solid phase part obtained by washing the solid-liquid separation in step (4).

[0057] The invention can prepare battery-grade lithium dihydrogen phosphate from lithium precipitation mother liquor with low lithium content and high sodium content, with low one-time investment, short process flow, no need for other impurity removal processes, easy industrial production, less three wastes and in line with the national energy conservation and emission reduction policy; the lithium in the lithium precipitation mother liquor is converted into lithium phosphate for recycling, with high comprehensive yield; the prepared product has low impurities and high purity, which is of great help in improving the circulation performance of lithium iron phosphate products; magnetic foreign matter is removed by magnets, so that the lithium iron phosphate used in the production of the product has excellent safety performance; the raw and auxiliary materials used are all common industrial products, with low prices and easy purchase.

[0058] The following examples further illustrate the method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor 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.

[0059] 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.

[0060] Example 1

[0061] In this embodiment, the lithium precipitation mother solution contains the following components: Li + 1.28g / L, CO3 2- 19.6 g / L, Na + It is 20.7g / L and Cl- is 116.1g / L.

[0062] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor comprises the following steps:

[0063] (1) taking 1000 L of lithium precipitation mother liquor into a reaction tank, slowly adding a 31 wt % hydrochloric acid solution, allowing the lithium precipitation mother liquor and the hydrochloric acid solution to react to remove carbonate in the lithium precipitation mother liquor, until the pH value of the resulting reaction solution reaches 5, and then stopping adding the hydrochloric acid solution;

[0064] (2) heating the reaction solution obtained in step (1) to 85° C., then quickly adding a mixed solution of trisodium phosphate and sodium dihydrogen phosphate with a phosphate ion concentration of 200 g / L (the molar ratio of trisodium phosphate to sodium dihydrogen phosphate is 5:1) and stirring, adjusting the pH value of the reaction solution to 9, then continuing the reaction for 35 minutes and filtering, then adding water to the solid phase obtained by filtration for slurry washing, and then adding water to the centrifuge for elution to obtain crude lithium phosphate with a purity of 95.8% by weight;

[0065] (3) slowly adding a 50 wt % phosphoric acid solution into the crude lithium phosphate and stirring until the pH value of the resulting mixed solution reaches 4, thereby obtaining a crude lithium dihydrogen phosphate solution with a concentration of 1240 g / L;

[0066] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation at 85° C. and 420 bar until the solid content of the first concentrate is 20%, and then dehydrating the product by centrifuge to obtain a solid phase and a liquid phase, respectively; then, the solid phase is rinsed with water for 20 seconds to obtain a first solid phase, and the washing liquid obtained by the water rinsing is collected, and the liquid phase and the washing liquid are combined to obtain a first mother liquor, and the first mother liquor is returned to the lithium precipitation mother liquor in step (1) for reuse;

[0067] (5) After the first solid phase is dissolved in hot water at 80° C., a second reduced-pressure evaporation is performed at 85° C. and 420 bar until the solid content of the second concentrate is 25%, and then the concentrate is discharged and dehydrated by a centrifuge to obtain a solid phase and a liquid phase, respectively. The second solid phase is rinsed with water for 20 seconds and then dried at 100° C. for 2 hours to obtain lithium dihydrogen phosphate. The washing liquid obtained by rinsing with water is combined with the liquid phase to obtain a second mother liquor. The second mother liquor is returned to the solid phase obtained by rinsing the solid-liquid separation in step (4). The second mother liquor contains phosphate and impurities such as sodium, potassium, chlorine, calcium, and magnesium.

[0068] Example 2

[0069] In this embodiment, the lithium precipitation mother solution contains the following components: Li + 1.33 g / L, CO3 2- 23.1 g / L, Na + It is 22.5g / L and Cl- is 118.4g / L.

[0070] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor comprises the following steps:

[0071] (1) taking 1000 L of lithium precipitation mother liquor into a reaction tank, slowly adding a 31 wt % hydrochloric acid solution, allowing the lithium precipitation mother liquor and the hydrochloric acid solution to react to remove carbonate in the lithium precipitation mother liquor, until the pH value of the obtained reaction solution is 4.4, and then stopping adding the hydrochloric acid solution;

[0072] (2) heating the reaction solution obtained in step (1) to 89° C., then quickly adding a mixed solution of trisodium phosphate and sodium dihydrogen phosphate with a phosphate ion concentration of 220 g / L (the molar ratio of trisodium phosphate to sodium dihydrogen phosphate is 6:1) and stirring, adjusting the pH value of the reaction solution to 10, then continuing the reaction for 30 minutes and filtering, then adding water to the solid phase obtained by filtration for slurry washing, and then adding water to the centrifuge for elution to obtain crude lithium phosphate with a purity of 95.3% by weight;

[0073] (3) slowly adding a phosphoric acid solution having a concentration of 80 wt % into the crude lithium phosphate and stirring until the pH value of the resulting mixed solution reaches 3, thereby obtaining a crude lithium dihydrogen phosphate solution having a concentration of 2388 g / L;

[0074] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation at 90° C. and 450 bar until the solid content of the first concentrate is 18%, and then dehydrating the product by centrifuge to obtain a solid phase and a liquid phase, respectively; then, the solid phase is firstly eluted with the second mother liquor obtained in Example 1 for 50 seconds, and then rinsed with water for 20 seconds to obtain a first solid phase, and the washing liquid obtained by the water washing is collected, and the liquid phase and the washing liquid are combined to obtain a first mother liquor, and the first mother liquor is returned to step (4) for a first reduced-pressure evaporation;

[0075] (5) After the first solid phase is dissolved in hot water at 85° C., a second reduced-pressure evaporation is performed at 90° C. and 450 bar until the solid content of the second concentrate is 20%, and then the concentrate is discharged and dehydrated by a centrifuge to obtain a solid phase and a liquid phase, respectively. The second solid phase is rinsed with water for 20 seconds and then dried at 100° C. for 2 hours to obtain lithium dihydrogen phosphate. The washing liquid obtained by rinsing with water is combined with the liquid phase to obtain a second mother liquor. The second mother liquor is returned to the solid phase obtained by rinsing the solid-liquid separation in step (4). The second mother liquor contains phosphate and impurities such as sodium, potassium, chlorine, calcium, and magnesium.

[0076] Example 3

[0077] In this embodiment, the lithium precipitation mother solution contains the following components: Li + 1.38g / L, CO3 2- 22.4 g / L, Na + It is 21.8g / L and Cl- is 115.2g / L.

[0078] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor comprises the following steps:

[0079] (1) taking 1000 L of lithium precipitation mother liquor into a reaction tank, slowly adding a 31 wt % hydrochloric acid solution, allowing the lithium precipitation mother liquor and the hydrochloric acid solution to react to remove carbonate in the lithium precipitation mother liquor, until the pH value of the obtained reaction solution reaches 4, and then stopping adding the hydrochloric acid solution;

[0080] (2) heating the reaction solution obtained in step (1) to 89° C., then quickly adding a mixed solution of trisodium phosphate and sodium dihydrogen phosphate with a phosphate ion concentration of 220 g / L (the molar ratio of trisodium phosphate to sodium dihydrogen phosphate is 5.5:1) and stirring, adjusting the pH value of the reaction solution to 9.5, then continuing the reaction for 30 minutes and filtering, then adding water to the solid phase obtained by filtration for slurry washing, and then adding water to the centrifuge for elution to obtain crude lithium phosphate with a purity of 95.5% by weight;

[0081] (3) slowly adding a phosphoric acid solution having a concentration of 85 wt % into the crude lithium phosphate and stirring until the pH value of the resulting mixed solution reaches 3, thereby obtaining a crude lithium dihydrogen phosphate solution having a concentration of 2455 g / L;

[0082] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation at 90° C. and 450 bar until the solid content of the first concentrate is 18%, and then dehydrating the product by centrifuge to obtain a solid phase and a liquid phase, respectively; then, the solid phase is firstly eluted with the second mother liquor obtained in Example 1 for 50 seconds, and then rinsed with water for 20 seconds to obtain a first solid phase, and the washing liquid obtained by the water washing is collected, and the liquid phase and the washing liquid are combined to obtain a first mother liquor, and the first mother liquor is returned to step (4) for a first reduced-pressure evaporation;

[0083] (5) After the first solid phase is dissolved in hot water at 85° C., a second reduced-pressure evaporation is performed at 90° C. and 450 bar until the solid content of the second concentrate is 20%, and then the concentrate is discharged and dehydrated by a centrifuge to obtain a solid phase and a liquid phase, respectively. The second solid phase is rinsed with water for 20 seconds and then dried at 100° C. for 2 hours to obtain lithium dihydrogen phosphate. The washing liquid obtained by rinsing with water is combined with the liquid phase to obtain a second mother liquor. The second mother liquor is returned to the solid phase obtained by rinsing the solid-liquid separation in step (4). The second mother liquor contains phosphate and impurities such as sodium, potassium, chlorine, calcium, and magnesium.

[0084] Comparative Example 1

[0085] The method of Example 1 is followed, except that in step (1), the pH value of the reaction solution is reduced to 6 instead of 5.

[0086] In this comparative example, the lithium precipitation mother solution contains the following components: Li+ 1.28g / L, CO3 2- 19.6 g / L, Na + It is 20.7g / L and Cl- is 116.1g / L.

[0087] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor comprises the following steps:

[0088] (1) taking 1000 L of lithium precipitation mother liquor into a reaction tank, slowly adding a 31 wt % hydrochloric acid solution, allowing the lithium precipitation mother liquor and the hydrochloric acid solution to react to remove carbonate in the lithium precipitation mother liquor, until the pH value of the obtained reaction solution reaches 6, and then stopping adding the hydrochloric acid solution;

[0089] (2) heating the reaction solution obtained in step (1) to 85° C., then quickly adding a mixed solution of trisodium phosphate and sodium dihydrogen phosphate with a phosphate ion concentration of 200 g / L (the molar ratio of trisodium phosphate to sodium dihydrogen phosphate is 5:1) and stirring, adjusting the pH value of the reaction solution to 9, then continuing the reaction for 35 minutes and filtering, then adding water to the solid phase obtained by filtration for slurry washing, and then adding water to the centrifuge for elution, to obtain crude lithium phosphate with a purity of 94.5% by weight;

[0090] (3) slowly adding a 50 wt % phosphoric acid solution into the crude lithium phosphate and stirring until the pH value of the resulting mixed solution reaches 4, thereby obtaining a crude lithium dihydrogen phosphate solution with a concentration of 1252 g / L;

[0091] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation at 85° C. and 420 bar until the solid content of the first concentrate is 20%, and then dehydrating the product by centrifuge to obtain a solid phase and a liquid phase, respectively; then, the solid phase is rinsed with water for 20 seconds to obtain a first solid phase, and the washing liquid obtained by the water rinsing is collected, and the liquid phase and the washing liquid are combined to obtain a first mother liquor, and the first mother liquor is returned to the lithium precipitation mother liquor in step (1) for reuse;

[0092] (5) After the first solid phase is dissolved in hot water at 80° C., a second reduced-pressure evaporation is performed at 85° C. and 420 bar until the solid content of the second concentrate is 25%, and then the concentrate is discharged and dehydrated by a centrifuge to obtain a solid phase and a liquid phase, respectively. The second solid phase is rinsed with water for 20 seconds and then dried at 100° C. for 2 hours to obtain lithium dihydrogen phosphate. The washing liquid obtained by rinsing with water is combined with the liquid phase to obtain a second mother liquor. The second mother liquor is returned to the solid phase obtained by rinsing the solid-liquid separation in step (4). The second mother liquor contains phosphate and impurities such as sodium, potassium, chlorine, calcium, and magnesium.

[0093] Comparative Example 2

[0094] The method of Example 1 is followed, except that in step (2), the pH value of the reaction solution is adjusted to 11 instead of 9.

[0095] In this comparative example, the lithium precipitation mother solution contains the following components: Li + 1.28g / L, CO3 2- 19.6 g / L, Na + It is 20.7g / L and Cl- is 116.1g / L.

[0096] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor comprises the following steps:

[0097] (1) taking 1000 L of lithium precipitation mother liquor into a reaction tank, slowly adding a 31 wt % hydrochloric acid solution, allowing the lithium precipitation mother liquor and the hydrochloric acid solution to react to remove carbonate in the lithium precipitation mother liquor, until the pH value of the resulting reaction solution reaches 5, and then stopping adding the hydrochloric acid solution;

[0098] (2) heating the reaction solution obtained in step (1) to 85° C., then quickly adding a mixed solution of trisodium phosphate and sodium dihydrogen phosphate with a phosphate ion concentration of 200 g / L (the molar ratio of trisodium phosphate to sodium dihydrogen phosphate is 5:1) and stirring, adjusting the pH value of the reaction solution to 11, and then continuing the reaction for 35 minutes and filtering, then adding water to the solid phase obtained by filtration for slurry washing, and then adding water to the centrifuge for elution, to obtain crude lithium phosphate with a purity of 93.6% by weight;

[0099] (3) slowly adding a 50 wt % phosphoric acid solution into the crude lithium phosphate and stirring until the pH value of the resulting mixed solution reaches 4, thereby obtaining a crude lithium dihydrogen phosphate solution with a concentration of 1240 g / L;

[0100] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation at 85° C. and 420 bar until the solid content of the first concentrate is 20%, and then dehydrating the product by centrifuge to obtain a solid phase and a liquid phase, respectively; then, the solid phase is rinsed with water for 20 seconds to obtain a first solid phase, and the washing liquid obtained by the water rinsing is collected, and the liquid phase and the washing liquid are combined to obtain a first mother liquor, and the first mother liquor is returned to the lithium precipitation mother liquor in step (1) for reuse;

[0101] (5) After the first solid phase is dissolved in hot water at 80° C., a second reduced-pressure evaporation is performed at 85° C. and 420 bar until the solid content of the second concentrate is 25%, and then the concentrate is discharged and dehydrated by a centrifuge to obtain a solid phase and a liquid phase, respectively. The second solid phase is rinsed with water for 20 seconds and then dried at 100° C. for 2 hours to obtain lithium dihydrogen phosphate. The washing liquid obtained by rinsing with water is combined with the liquid phase to obtain a second mother liquor. The second mother liquor is returned to the solid phase obtained by rinsing the solid-liquid separation in step (4). The second mother liquor contains phosphate and impurities such as sodium, potassium, chlorine, calcium, and magnesium.

[0102] Comparative Example 3

[0103] The method of Example 1 is followed, except that in step (2), the pH value of the reaction solution is adjusted to 8 instead of 9.

[0104] In this comparative example, the lithium precipitation mother solution contains the following components: Li + 1.28g / L, CO3 2- 19.6 g / L, Na + It is 20.7g / L and Cl- is 116.1g / L.

[0105] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor comprises the following steps:

[0106] (1) taking 1000 L of lithium precipitation mother liquor into a reaction tank, slowly adding a 31 wt % hydrochloric acid solution, allowing the lithium precipitation mother liquor and the hydrochloric acid solution to react to remove carbonate in the lithium precipitation mother liquor, until the pH value of the resulting reaction solution reaches 5, and then stopping adding the hydrochloric acid solution;

[0107] (2) heating the reaction solution obtained in step (1) to 85° C., then quickly adding a mixed solution of trisodium phosphate and sodium dihydrogen phosphate with a phosphate ion concentration of 200 g / L (the molar ratio of trisodium phosphate to sodium dihydrogen phosphate is 5:1) and stirring, adjusting the pH value of the reaction solution to 8, then continuing the reaction for 35 minutes and filtering, then adding water to the solid phase obtained by filtration for slurry washing, and then adding water to the centrifuge for elution to obtain crude lithium phosphate with a purity of 96.7% by weight;

[0108] (3) slowly adding a 50 wt % phosphoric acid solution into the crude lithium phosphate and stirring until the pH value of the resulting mixed solution reaches 4, thereby obtaining a crude lithium dihydrogen phosphate solution with a concentration of 1266 g / L;

[0109] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation at 85° C. and 420 bar until the solid content of the first concentrate is 20%, and then dehydrating the product by centrifuge to obtain a solid phase and a liquid phase, respectively; then, the solid phase is rinsed with water for 20 seconds to obtain a first solid phase, and the washing liquid obtained by the water rinsing is collected, and the liquid phase and the washing liquid are combined to obtain a first mother liquor, and the first mother liquor is returned to the lithium precipitation mother liquor in step (1) for reuse;

[0110] (5) After the first solid phase is dissolved in hot water at 80° C., a second reduced-pressure evaporation is performed at 85° C. and 420 bar until the solid content of the second concentrate is 25%, and then the concentrate is discharged and dehydrated by a centrifuge to obtain a solid phase and a liquid phase, respectively. The second solid phase is rinsed with water for 20 seconds and then dried at 100° C. for 2 hours to obtain lithium dihydrogen phosphate. The washing liquid obtained by rinsing with water is combined with the liquid phase to obtain a second mother liquor. The second mother liquor is returned to the solid phase obtained by rinsing the solid-liquid separation in step (4). The second mother liquor contains phosphate and impurities such as sodium, potassium, chlorine, calcium, and magnesium.

[0111] Comparative Example 4

[0112] The method of Example 1 is followed, except that in step (3), the pH value of the mixed solution is changed from 4 to 6.

[0113] In this comparative example, the lithium precipitation mother solution contains the following components: Li + 1.28g / L, CO3 2- 19.6 g / L, Na + It is 20.7g / L and Cl- is 116.1g / L.

[0114] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor comprises the following steps:

[0115] (1) taking 1000 L of lithium precipitation mother liquor into a reaction tank, slowly adding a 31 wt % hydrochloric acid solution, allowing the lithium precipitation mother liquor and the hydrochloric acid solution to react to remove carbonate in the lithium precipitation mother liquor, until the pH value of the resulting reaction solution reaches 5, and then stopping adding the hydrochloric acid solution;

[0116] (2) heating the reaction solution obtained in step (1) to 85° C., then quickly adding a mixed solution of trisodium phosphate and sodium dihydrogen phosphate with a phosphate ion concentration of 200 g / L (the molar ratio of trisodium phosphate to sodium dihydrogen phosphate is 5:1) and stirring, adjusting the pH value of the reaction solution to 9, then continuing the reaction for 35 minutes and filtering, then adding water to the solid phase obtained by filtration for slurry washing, and then adding water to the centrifuge for elution to obtain crude lithium phosphate with a purity of 95.8% by weight;

[0117] (3) slowly adding a 50 wt % phosphoric acid solution into the crude lithium phosphate and stirring until the pH value of the resulting mixed solution reaches 6, thereby obtaining a crude lithium dihydrogen phosphate solution with a concentration of 1027 g / L;

[0118] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation at 85° C. and 420 bar until the solid content of the first concentrate is 20%, and then dehydrating the product by centrifuge to obtain a solid phase and a liquid phase, respectively; then, the solid phase is rinsed with water for 20 seconds to obtain a first solid phase, and the washing liquid obtained by the water rinsing is collected, and the liquid phase and the washing liquid are combined to obtain a first mother liquor, and the first mother liquor is returned to the lithium precipitation mother liquor in step (1) for reuse;

[0119] (5) After the first solid phase is dissolved in hot water at 80° C., a second reduced-pressure evaporation is performed at 85° C. and 420 bar until the solid content of the second concentrate is 25%, and then the concentrate is discharged and dehydrated by a centrifuge to obtain a solid phase and a liquid phase, respectively. The second solid phase is rinsed with water for 20 seconds and then dried at 100° C. for 2 hours to obtain lithium dihydrogen phosphate. The washing liquid obtained by rinsing with water is combined with the liquid phase to obtain a second mother liquor. The second mother liquor is returned to the solid phase obtained by rinsing the solid-liquid separation in step (4). The second mother liquor contains phosphate and impurities such as sodium, potassium, chlorine, calcium, and magnesium.

[0120] Comparative Example 5

[0121] The method of Example 1 is followed, except that in step (3), the pH value of the mixed solution is reduced to 2 instead of 4.

[0122] In this comparative example, the lithium precipitation mother solution contains the following components: Li + 1.28g / L, CO3 2- 19.6 g / L, Na + It is 20.7g / L and Cl- is 116.1g / L.

[0123] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor comprises the following steps:

[0124] (1) taking 1000 L of lithium precipitation mother liquor into a reaction tank, slowly adding a 31 wt % hydrochloric acid solution, allowing the lithium precipitation mother liquor and the hydrochloric acid solution to react to remove carbonate in the lithium precipitation mother liquor, until the pH value of the resulting reaction solution reaches 5, and then stopping adding the hydrochloric acid solution;

[0125] (2) heating the reaction solution obtained in step (1) to 85° C., then quickly adding a mixed solution of trisodium phosphate and sodium dihydrogen phosphate with a phosphate ion concentration of 200 g / L (the molar ratio of trisodium phosphate to sodium dihydrogen phosphate is 5:1) and stirring, adjusting the pH value of the reaction solution to 9, then continuing the reaction for 35 minutes and filtering, then adding water to the solid phase obtained by filtration for slurry washing, and then adding water to the centrifuge for elution to obtain crude lithium phosphate with a purity of 95.8% by weight;

[0126] (3) slowly adding a 50 wt % phosphoric acid solution into the crude lithium phosphate and stirring until the pH value of the resulting mixed solution reaches 2, thereby obtaining a crude lithium dihydrogen phosphate solution with a concentration of 1169 g / L;

[0127] (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation at 85° C. and 420 bar until the solid content of the first concentrate is 20%, and then dehydrating the product by centrifuge to obtain a solid phase and a liquid phase, respectively; then, the solid phase is rinsed with water for 20 seconds to obtain a first solid phase, and the washing liquid obtained by the water rinsing is collected, and the liquid phase and the washing liquid are combined to obtain a first mother liquor, and the first mother liquor is returned to the lithium precipitation mother liquor in step (1) for reuse;

[0128] (5) After the first solid phase is dissolved in hot water at 80° C., a second reduced-pressure evaporation is performed at 85° C. and 420 bar until the solid content of the second concentrate is 25%, and then the concentrate is discharged and dehydrated by a centrifuge to obtain a solid phase and a liquid phase, respectively. The second solid phase is rinsed with water for 20 seconds and then dried at 100° C. for 2 hours to obtain lithium dihydrogen phosphate. The washing liquid obtained by rinsing with water is combined with the liquid phase to obtain a second mother liquor. The second mother liquor is returned to the solid phase obtained by rinsing the solid-liquid separation in step (4). The second mother liquor contains phosphate and impurities such as sodium, potassium, chlorine, calcium, and magnesium.

[0129] Comparative Example 6

[0130] The method of Example 1 is followed, except that only the second reduced pressure evaporation is performed, i.e., the first reduced pressure evaporation of step (4) is not performed.

[0131] In this comparative example, the lithium precipitation mother solution contains the following components: Li + 1.28g / L, CO3 2- 19.6 g / L, Na + It is 20.7g / L and Cl- is 116.1g / L.

[0132] The method for preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor comprises the following steps:

[0133] (1) taking 1000 L of lithium precipitation mother liquor into a reaction tank, slowly adding a 31 wt % hydrochloric acid solution, allowing the lithium precipitation mother liquor and the hydrochloric acid solution to react to remove carbonate in the lithium precipitation mother liquor, until the pH value of the resulting reaction solution reaches 5, and then stopping adding the hydrochloric acid solution;

[0134] (2) heating the reaction solution obtained in step (1) to 85° C., then quickly adding a mixed solution of trisodium phosphate and sodium dihydrogen phosphate with a phosphate ion concentration of 200 g / L (the molar ratio of trisodium phosphate to sodium dihydrogen phosphate is 5:1) and stirring, adjusting the pH value of the reaction solution to 9, then continuing the reaction for 35 minutes and filtering, then adding water to the solid phase obtained by filtration for slurry washing, and then adding water to the centrifuge for elution to obtain crude lithium phosphate with a purity of 95.8% by weight;

[0135] (3) slowly adding a 50 wt % phosphoric acid solution into the crude lithium phosphate and stirring until the pH value of the resulting mixed solution reaches 4, thereby obtaining a crude lithium dihydrogen phosphate solution with a concentration of 1240 g / L;

[0136] (4) The crude lithium dihydrogen phosphate solution is evaporated under reduced pressure at 85° C. and 420 bar until the solid content of the concentrate is 20%, and then the concentrate is discharged and dehydrated by a centrifuge to obtain a solid phase and a liquid phase, respectively; the solid phase is then rinsed with water for 20 seconds to obtain a solid phase, and the washing liquid obtained by the water rinsing is collected, and the liquid phase and the washing liquid are combined to obtain a first mother liquor, and the first mother liquor is returned to the lithium precipitation mother liquor in step (1) for reuse.

[0137] Test Example 1

[0138] The ingredients and contents of the products prepared in Example 1 and Comparative Example 1 were measured, and the results are shown in Table 1.

[0139] Among them, the main content (lithium dihydrogen phosphate content) is determined by weight method, Na, K, Ca, Fe, Pb, SO4 2- The content of is determined by ICP, the chlorine by spectrophotometry, and the water-insoluble matter by weight.

[0140] Table 1

[0141]

[0142]

[0143] It can be seen from the data in Table 1 that the content of lithium dihydrogen phosphate prepared by the method described in the present invention is ≥99.65%, which meets the battery grade standard.

[0144] Test Example 2

[0145] The yields of lithium in the examples and comparative examples were calculated, and the results are shown in Table 2.

[0146] The yield is calculated as follows: lithium amount in the lithium dihydrogen phosphate product / lithium amount in the lithium precipitation mother liquor*100%, and the lithium amount is determined by ICP.

[0147] Table 2

[0148] serial number Yield / % Example 1 96.3 Example 2 97.1 Example 3 96.5 Comparative Example 1 95.6 Comparative Example 2 97.5 Comparative Example 3 92.1 Comparative Example 4 95.8 Comparative Example 5 96.5 Comparative Example 6 96.8

[0149] It can be seen from Table 2 that the yield of lithium is greater than 96% using the method of the embodiment of the present invention.

[0150] It can be seen from the results in Table 1 and Table 2 that the method described in the present invention is used to prepare lithium dihydrogen phosphate, with a high yield, low impurity content and good product quality.

[0151] 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 preparing battery-grade lithium dihydrogen phosphate using lithium precipitation mother liquor, characterized in that: The method comprises the following steps: (1) mixing a hydrochloric acid solution with a lithium precipitation mother liquor to react until the pH value of the resulting reaction solution reaches 4-5; (2) heating the reaction solution, then adding a sodium phosphate solution to the heated reaction solution, adjusting the pH value of the reaction solution to 9-10, and then reacting, solid-liquid separation and washing to obtain crude lithium phosphate; (3) adding a phosphoric acid solution to the crude lithium phosphate until the pH value of the resulting mixed solution is 3-5.5, thereby obtaining a crude lithium dihydrogen phosphate solution; (4) subjecting the crude lithium dihydrogen phosphate solution to a first reduced-pressure evaporation, and subjecting the obtained first concentrate to solid-liquid separation and washing to obtain a first solid phase and a first mother liquor, respectively; (5) dissolving the first solid phase in hot water, and then performing a second reduced-pressure evaporation, performing solid-liquid separation on the obtained second concentrate to obtain a second solid phase and a second mother liquor, respectively, and drying the second solid phase; The second concentrate has a higher solid content than the first concentrate.

2. The method according to claim 1, characterized in that: The lithium precipitation mother solution contains the following components: Li + 1.2-1.8g / L, CO3 2- 15-25g / L, Na + It is 18-26g / L, and Cl- is 100-140g / L.

3. The method according to claim 1 or 2, characterized in that: In step (1), the concentration of the hydrochloric acid solution is 25-35% by weight.

4. The method according to any one of claims 1 to 3, characterized in that: In step (2), the reaction solution is heated to 80-95°C.

5. The method according to any one of claims 1 to 4, characterized in that: In step (2), the sodium phosphate salt in the sodium phosphate salt solution is selected from at least one of trisodium phosphate, sodium monohydrogen phosphate and sodium dihydrogen phosphate; Preferably, the concentration of phosphate in the sodium phosphate salt solution is 180-250 g / L.

6. The method according to any one of claims 1 to 5, characterized in that: In step (2), the reaction is continued for 25-40 minutes; Preferably, the purity of the crude lithium phosphate is 94-97 wt %.

7. The method according to any one of claims 1 to 6, characterized in that: In step (3), the concentration of the phosphoric acid solution is 45-85% by weight; Preferably, in step (3), the concentration of lithium dihydrogen phosphate in the crude lithium dihydrogen phosphate solution is 1200-2490 g / L.

8. The method according to any one of claims 1 to 7, characterized in that: In step (4) and step (5), the conditions of the first reduced-pressure evaporation and the second reduced-pressure evaporation include: a temperature of 80-90° C. and a pressure of 380-450 bar.

9. The method according to any one of claims 1 to 8, characterized in that: In step (4), the washing process includes: firstly eluting the solid phase obtained by solid-liquid separation with the second mother liquor, and then washing the solid phase with water.

10. The method according to any one of claims 1 to 9, characterized in that: The solid content of the second concentrate is 2-10% higher than the solid content of the first concentrate; Preferably, the solid content of the first concentrate is 15-20%; Preferably, the solid content of the second concentrate is 20-30%.

Images