A method for preparing battery-grade lithium dihydrogen phosphate from low-lithium high-impurity mother liquor for extracting lithium from spodumene
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 四川天华时代锂能有限公司
- Filing Date
- 2026-05-28
- Publication Date
- 2026-08-07
AI Technical Summary
[0004]常规的沉淀法、萃取法或蒸发结晶法，难以在保证锂离子高回收率的同时，将钠、钾等与锂性质相近的杂质去除至电池级标准（通常要求Na、K<20 ppm）
1、本发明通过选择性吸附富集—纳滤除杂—沉淀磷酸锂除杂—结晶的组合除杂处理工艺，实现了对低锂高杂母液中高浓度钠离子、钾离子、硫酸根等杂质离子的深度去除，同时保证了锂离子的高效转化。最终产品中钠钾含量可稳定控制在20 ppm以下，硫酸根含量低于50 ppm，满足甚至优于电池级标准。
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor derived from spodumene. Background Technology
[0002] In the lithium extraction process using the spodumene sulfuric acid method, after the leachate undergoes reversion, calcium removal, and causticization freeze crystallization to separate sodium sulfate (Na₂SO₄·10H₂O), a large amount of sodium sulfate mother liquor is produced. This mother liquor has a complex composition and is characterized by high impurities and low lithium content: the lithium concentration is usually only 1.5-3.5 g / L, while the sodium ion concentration is as high as 20-40 g / L, and the sulfate concentration can reach over 50 g / L.
[0003] Currently, the mainstream treatment method for this sodium sulfate mother liquor in the industry is to return it to the main process for recycling. However, this method easily leads to the continuous accumulation of impurities (mainly sodium and potassium ions and sulfate ions) in the system, increasing the load on subsequent processing and causing lithium entrainment losses. If the goal is to directly recover lithium from this mother liquor and prepare high-value-added products, such as battery-grade lithium dihydrogen phosphate, the core technical bottleneck lies in how to efficiently convert low-concentration lithium ions from a background of extremely high concentrations of impurities such as sodium, potassium, and sulfate ions, while economically and deeply removing high-concentration impurities.
[0004] Conventional precipitation, extraction, or evaporation crystallization methods struggle to remove impurities like sodium and potassium, which have similar properties to lithium, to battery-grade standards (typically requiring Na and K < 20 ppm) while ensuring high lithium-ion recovery rates. Existing technologies either focus on preparing industrial-grade lithium carbonate / lithium hydroxide or have lengthy processes, high energy consumption, and difficulty in consistently achieving the required product purity.
[0005] In view of this, developing a short-process, low-cost new process for the direct preparation of battery-grade lithium dihydrogen phosphate, which can achieve efficient and selective enrichment of lithium, deep removal of impurities, and direct preparation of battery-grade lithium dihydrogen phosphate, has significant industrial value. Summary of the Invention
[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing battery-grade lithium dihydrogen phosphate from a low-lithium, high-impurity mother liquor using spodumene. This method solves the problem of deep removal of high-concentration sodium, potassium, sulfate, and other impurity ions from the low-lithium, high-impurity mother liquor by using a combined impurity removal process of selective adsorption enrichment, nanofiltration, precipitation of lithium phosphate, and crystallization.
[0007] The present invention specifically adopts the following technical solution: A method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor from spodumene lithium extraction includes the following steps: S1. Take a low-lithium, high-impurity mother liquor and pass it through an adsorption column packed with ion sieve adsorbent. After adsorption and penetration, desorption is performed to collect the lithium-rich desorbed liquid. S2. Adjust the pH of the lithium-rich desorption solution to neutral by adding alkaline solution, then remove impurities by nanofiltration and collect the nanofiltration permeate. S3. The obtained nanofiltration permeate is slowly added dropwise to a phosphate solution to precipitate lithium, and then filtered and washed to obtain crude lithium phosphate. S4. Dissolve the crude lithium phosphate in phosphoric acid and filter to obtain a lithium dihydrogen phosphate solution. S5. Evaporate the obtained lithium dihydrogen phosphate solution to crystallize, then centrifuge, wash and dry to obtain battery-grade lithium dihydrogen phosphate.
[0008] Furthermore, the low-lithium, high-impurity mother liquor mentioned in S1 is a sodium sulfate mother liquor produced by the spodumene sulfuric acid process; its lithium ion content is 1.5-3.5 g / L, sodium ion content is 20-40 g / L, sulfate content is 50-100 g / L, potassium ion content is 1-3 g / L, and pH value is 9-11.
[0009] Furthermore, the ion sieve adsorbent in S1 is at least one of titanium-based ion sieve lithium adsorbent and manganese-based ion sieve lithium adsorbent; the low-lithium, high-impurity mother liquor flows through the adsorption column at a flow rate of 1.5-4 BV / h and an adsorption temperature of 15-80℃.
[0010] Furthermore, in S1, desorption is performed using a combined acid solution of dilute sulfuric acid and dilute hydrochloric acid. The volume of the acid solution is 20%-40% of the low-lithium, high-impurity mother liquor, and the concentration is 0.2-0.4 mol / L. The flow rate of the acid solution is controlled at 1.0-2.0 BV / h.
[0011] Furthermore, the nanofiltration membrane used for impurity removal in S2 is either Dow NF270-4040 or TimeWalton DL; the nanofiltration conditions are: pH 5.5-6.5, temperature 30-45℃, pressure 1.8-3.0 MPa, and water recovery rate 75%.
[0012] Furthermore, the lithium ion concentration in the nanofiltration permeate obtained in S2 is 8.0-12.0 g / L.
[0013] Furthermore, the phosphate mentioned in S3 is diammonium hydrogen phosphate, and its solution concentration is 0.9-1.1 mol / L; the addition ratio of nanofiltration permeate to phosphate solution is based on the molar ratio of lithium in nanofiltration permeate to phosphate in phosphate solution of 3:(1-1.2).
[0014] Furthermore, the conditions for lithium precipitation in S3 are as follows: while adding nanofiltration permeate, ammonia is slowly added to control the pH at the reaction endpoint to be 10-11, the reaction temperature is 50-70℃, and after the reaction is completed, the mixture is aged at 50-60℃ for 20-40 min.
[0015] Furthermore, after the crude lithium phosphate is completely dissolved, the pH needs to be adjusted to 1.5-3.0.
[0016] Further, the specific operation in S5 is as follows: the lithium dihydrogen phosphate solution is heated to 120-140℃ to evaporate, heating is stopped and stirring is continued to cool and crystallize; when the system cools down to 50-80℃, the wet material and the crystallization mother liquor are separated by centrifugation, and the wet material is washed and dried to obtain battery-grade lithium dihydrogen phosphate.
[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes a combined impurity removal process—selective adsorption enrichment, nanofiltration, lithium phosphate precipitation, and crystallization—to achieve deep removal of high concentrations of sodium, potassium, and sulfate ions from low-lithium, high-impurity mother liquor, while ensuring efficient lithium ion conversion. The final product exhibits stable sodium and potassium content below 20 ppm and sulfate content below 50 ppm, meeting or even exceeding battery-grade standards.
[0018] 2. The process of this invention achieves a comprehensive lithium utilization rate of over 90%. In addition, the process has low energy consumption, high product purity, and good batch consistency, making it easy to industrialize. It can guarantee the preparation of high-purity (≥99.90%) battery-grade lithium dihydrogen phosphate products from various high-impurity and low-lithium mother liquors, and has good prospects for industrial application. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.
[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0021] The sodium sulfate mother liquor used in the experiment of this invention was derived from crude sodium sulfate obtained by removing calcium, causticizing, and three-stage freezing of the leachate obtained during the lithium extraction process of spodumene using sulfuric acid. The crude sodium sulfate mother liquor was then subjected to back dissolution filtration, evaporation and crystallization. The concentration of each component was detected by ICP and is shown in Table 1.
[0022] Table 1. Concentration of Mother Liquor Components
[0023] Example 1 A method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor from spodumene, comprising the following steps: 1. Take 10 L of sodium sulfate mother liquor and pass it through an adsorption column packed with 1.5 L of H2TiO3 adsorbent (0.5 mm particle size) at a flow rate of 2 BV / h at 60℃. After adsorption breakthrough, wash the adsorption column with 1.5 BV of deionized water at a flow rate of 1.5 BV / h, and then desorb using a composite acid solution (equal volume ratio of 0.25 mol / L H2SO4 solution and 0.25 mol / L HCl solution) at a flow rate of 1.5 BV / h. Collect 2.4 L of lithium-rich desorbate. The concentrations of each component in the obtained lithium-rich desorbate were measured as follows: Li + 9.3 g / L, Na + 9.6 g / L, K + 0.6 g / L, SO4 2- 15.6 g / L.
[0024] 2. Adjust the pH of the above lithium-rich desorption solution to approximately 6.0 with 2 mol / L NaOH solution and preheat to 35°C. Filter using a Dow NF270-4040 nanofiltration membrane at an operating pressure of 2.5 MPa, with a water recovery rate controlled at 75%. Collect 1.95 L of nanofiltration permeate, and measure the concentrations of each component in the obtained permeate: Li + 10.2 g / L, Na + 2.8 g / L, K + 0.19 g / L, SO4 2- 0.21 g / L.
[0025] 3. Under continuous stirring, the above nanofiltration permeate was slowly added dropwise to a 1.0 mol / L (NH₄)₂HPO₄ solution (the volume ratio of the two added was 3:1.08 molar ratio of lithium to diammonium hydrogen phosphate), while ammonia was added dropwise to control the final pH of the reaction at 10.5. The reaction was carried out at a constant temperature of 60℃. After the reaction was completed, the mixture was aged at 55℃ for 0.5 h. After filtration, the filter cake was thoroughly washed with hot water at 70℃ to obtain crude lithium phosphate.
[0026] 4. Slurry the above crude lithium phosphate with an equal mass of deionized water, then slowly add 85% phosphoric acid to dissolve it, adjusting the pH to approximately 2.0. Filter to remove insoluble impurities, yielding a lithium dihydrogen phosphate solution.
[0027] 5. Heat the lithium dihydrogen phosphate solution to 132℃ to evaporate and concentrate it. Stop heating and continue stirring to cool and crystallize. When the system cools down to 65℃, centrifuge to separate the wet lithium dihydrogen phosphate and the crystallization mother liquor. Wash the wet material and vacuum dry it to obtain a white crystalline product, which is battery-grade lithium dihydrogen phosphate.
[0028] Example 2 A method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor from spodumene, comprising the following steps: 1. Take 10 L of sodium sulfate mother liquor and pass it through an adsorption column packed with 1.5 L of H2TiO3 adsorbent (0.5 mm particle size) at a flow rate of 1.5 BV / h at 50℃. After adsorption breakthrough, wash the adsorption column with 1.5 BV of deionized water at a flow rate of 1.5 BV / h, and then desorb using a composite acid solution (equal volume ratio of 0.25 mol / L H2SO4 solution and 0.25 mol / L HCl solution) at a flow rate of 1.5 BV / h. Collect 2.4 L of lithium-rich desorbate. The concentrations of each component in the obtained lithium-rich desorbate were measured as follows: Li + 9.2 g / L, Na + 9.8 g / L, K + 0.6 g / L, SO4 2- 16.1 g / L.
[0029] 2. Adjust the pH of the above lithium-rich desorption solution to approximately 5.5 with 2 mol / L NaOH solution and preheat to 35°C. Filter using a Dow NF270-4040 nanofiltration membrane at an operating pressure of 1.8 MPa, with a water recovery rate controlled at 75%. Collect 1.91 L of nanofiltration permeate. The concentrations of each component in the obtained permeate were measured as follows: Li + 9.9 g / L, Na + 3.2 g / L, K + 0.18 g / L, SO4 2- 0.26 g / L.
[0030] 3. Under continuous stirring, the above nanofiltration permeate was slowly added dropwise to a 1.0 mol / L (NH₄)₂HPO₄ solution (the volume ratio of the two added was 3:1 based on the molar ratio of lithium to diammonium hydrogen phosphate). Ammonia was added dropwise simultaneously to control the final pH at 10.5, and the reaction was carried out at a constant temperature of 60℃. After the reaction was complete, the mixture was aged at 55℃ for 0.5 h. The mixture was then filtered, and the filter cake was thoroughly washed with hot water at 70℃ to obtain crude lithium phosphate.
[0031] 4. Slurry the above crude lithium phosphate with an equal mass of deionized water, then slowly add 85% phosphoric acid to dissolve it, adjusting the pH to approximately 2.0. Filter to remove insoluble impurities, yielding a lithium dihydrogen phosphate solution.
[0032] 5. Heat the lithium dihydrogen phosphate solution to 120°C to evaporate and concentrate it. Stop heating and continue stirring to cool and crystallize. When the system cools down to 65°C, centrifuge to separate the wet lithium dihydrogen phosphate and the crystallization mother liquor. Wash the wet material and vacuum dry it to obtain a white crystalline product, which is battery-grade lithium dihydrogen phosphate.
[0033] Example 3 A method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor from spodumene, comprising the following steps: 1. Take 10 L of sodium sulfate mother liquor and pass it through an adsorption column packed with 1.5 L of H2TiO3 adsorbent (0.5 mm particle size) at a flow rate of 4 BV / h at 70℃. After adsorption breakthrough, wash the adsorption column with 1.5 BV of deionized water at a flow rate of 1.5 BV / h, and then desorb using a composite acid solution (equal volume ratio of 0.25 mol / L H2SO4 solution and 0.25 mol / L HCl solution) at a flow rate of 1.5 BV / h. Collect 2.4 L of lithium-rich desorbate. The concentrations of each component in the obtained lithium-rich desorbate were measured as follows: Li + 8.9 g / L, Na + 10.2 g / L, K + 0.7 g / L, SO4 2- 16.5 g / L.
[0034] 2. Adjust the pH of the above lithium-rich desorption solution to approximately 6.5 with 2 mol / L NaOH solution and preheat to 35°C. Filter using a Dow NF270-4040 nanofiltration membrane at an operating pressure of 3.0 MPa, with a water recovery rate controlled at 75%. Collect 2.02 L of nanofiltration permeate. The concentrations of each component in the obtained permeate were measured as follows: Li + 9.8 g / L, Na + 2.9 g / L, K + 0.21 g / L, SO4 2- 0.23 g / L.
[0035] 3. Under continuous stirring, the above nanofiltration permeate was slowly added dropwise to a 1.0 mol / L (NH4)2HPO4 solution (the volume ratio of the two added was 3:1.2 based on the molar ratio of lithium to diammonium hydrogen phosphate). Ammonia was added dropwise simultaneously to control the final pH at 10.5, and the reaction was carried out at a constant temperature of 60℃. After the reaction was complete, the mixture was aged at 55℃ for 0.5 h. The mixture was then filtered, and the filter cake was thoroughly washed with hot water at 70℃ to obtain crude lithium phosphate.
[0036] 4. Slurry the above crude lithium phosphate with an equal mass of deionized water, then slowly add 85% phosphoric acid to dissolve it, adjusting the pH to approximately 2.0. Filter to remove insoluble impurities, yielding a lithium dihydrogen phosphate solution.
[0037] 5. Heat the lithium dihydrogen phosphate solution to 140℃ to evaporate and concentrate it. Stop heating and continue stirring to cool and crystallize. When the system cools down to 65℃, centrifuge to separate the wet lithium dihydrogen phosphate and the crystallization mother liquor. Wash the wet material and vacuum dry it to obtain a white crystalline product, which is battery-grade lithium dihydrogen phosphate.
[0038] Example 4 A method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor from spodumene, comprising the following steps: 1. Take 10 L of sodium sulfate mother liquor and pass it through an adsorption column packed with 1.5 L of H2TiO3 adsorbent (0.5 mm particle size) at a flow rate of 1.5 BV / h at 40℃. After adsorption breakthrough, wash the adsorption column with 1.5 BV of deionized water at a flow rate of 1.5 BV / h, and then desorb using a composite acid solution (equal volume ratio of 0.3 mol / L H2SO4 solution and 0.3 mol / L HCl solution) at a flow rate of 1.5 BV / h. Collect 2.4 L of lithium-rich eluent. The concentrations of each component in the obtained lithium-rich eluent were measured as follows: Li + 8.5 g / L, Na + 9.7 g / L, K + 0.5 g / L, SO4 2- 15.9 g / L.
[0039] 2. Adjust the pH of the above lithium-rich desorption solution to approximately 6.0 with 2 mol / L NaOH solution and preheat to 45°C. Filter using a TimeWharton DL nanofiltration membrane at an operating pressure of 2.5 MPa, with a water recovery rate controlled at 75%. Collect 1.97 L of nanofiltration permeate. The concentrations of each component in the obtained permeate were measured as follows: Li + 9.9 g / L, Na + 2.7 g / L, K + 0.22 g / L, SO4 2- 0.28 g / L.
[0040] 3. Under continuous stirring, the above nanofiltration permeate was slowly added dropwise to a 1.0 mol / L (NH₄)₂HPO₄ solution (the volume ratio of the two added was 3:1.08 molar ratio of lithium to diammonium hydrogen phosphate), while ammonia was added dropwise to control the final pH of the reaction at 10.5. The reaction was carried out at a constant temperature of 60℃. After the reaction was completed, the mixture was aged at 55℃ for 0.5 h. After filtration, the filter cake was thoroughly washed with hot water at 70℃ to obtain crude lithium phosphate.
[0041] 4. Slurry the above crude lithium phosphate with an equal mass of deionized water, then slowly add 85% phosphoric acid to dissolve it, adjusting the pH to approximately 2.0. Filter to remove insoluble impurities, yielding a lithium dihydrogen phosphate solution.
[0042] 5. Heat the lithium dihydrogen phosphate solution to 132℃ to evaporate and concentrate it. Stop heating and continue stirring to cool and crystallize. When the system cools down to 65℃, centrifuge to separate the wet lithium dihydrogen phosphate and the crystallization mother liquor. Wash the wet material and vacuum dry it to obtain a white crystalline product, which is battery-grade lithium dihydrogen phosphate.
[0043] Comparative Example 1 Referring to the steps and parameters of the embodiments of the present invention, the only difference is that in step 1, only 0.25 mol / L H2SO4 solution is used to desorb the adsorption column after adsorption penetration.
[0044] Comparative Example 2 Referring to the steps and parameters of the embodiments of the present invention, the only difference is that titanium ion sieve adsorption is not used, and the sodium sulfate mother liquor is directly subjected to nanofiltration treatment in step 2.
[0045] Comparative Example 3 Referring to the steps and parameters of this embodiment, the only difference is that the nanofiltration conditions in step 2 are adjusted as follows: the pH is adjusted to approximately 7.0 with 2 mol / L NaOH solution, and the solution is preheated to 35°C. A Dow NF270-4040 nanofiltration membrane is used, and filtration is performed at an operating pressure of 1.0 MPa, with a water recovery rate controlled at 75%.
[0046] Comparative Example 4 Referring to the steps and parameters of the embodiments of the present invention, the only difference is that nanofiltration is not used, and the lithium-rich desorption solution from step 1 is directly subjected to lithium phosphate precipitation for impurity removal in step 3.
[0047] Comparative Example 5 Referring to the steps and parameters of this embodiment, the only difference is that step 3, the lithium phosphate precipitation process for impurity removal, is omitted, and phosphoric acid is directly added to the nanofiltration permeate obtained in step 2 to adjust the pH to 2.0.
[0048] Test case The lithium dihydrogen phosphate samples obtained in the above examples and comparative examples were subjected to quantitative analysis of impurity elements using ICP-OES. The results are shown in the table below. It should be noted that, considering the high solubility of lithium dihydrogen phosphate (20℃, 126 g / 100mL water), the crystallization mother liquor obtained in the evaporation and concentration stages of the above examples and comparative examples underwent multiple batches of cyclic experiments using the same process to eliminate the problem of low Li direct recovery rate in a single batch due to the presence of a large amount of lithium dihydrogen phosphate in the crystallization mother liquor. The yield in Table 2 refers to the comprehensive yield from low-lithium, high-impurity mother liquor (sodium sulfate mother liquor) to finished lithium dihydrogen phosphate product.
[0049] Table 2 Yield and Product Quality Results
[0050] Combining the yield and product quality results in Table 2, it can be seen that the process of this invention has a good treatment effect on this type of low-lithium, high-impurity mother liquor, ensuring a lithium yield of nearly 90% or more, while the product purity reaches over 99.90%, and the content of impurities such as sodium, potassium, and sulfate meets battery-grade standards. As shown in Comparative Example 1, compared to elution and desorption using a composite acid solution, the desorption rate using sulfuric acid of the same concentration is lower. While appropriately increasing the concentration can improve the desorption rate, it easily leads to a deterioration in the adsorbent's cycle performance, severely affecting its service life. As shown in Comparative Example 2, directly performing nanofiltration on the mother liquor to be treated results in a significantly reduced lithium retention rate in the nanofiltration permeate. This may be because the sulfate concentration is relatively high, leading to a significant increase in the lithium ion rejection rate during the nanofiltration process. As shown in Comparative Example 3, suitable weak acidity and high pressure can better ensure the sulfate removal rate and reduce the lithium rejection rate. This may be because it weakens the electrostatic repulsion of sulfate by the nanofiltration membrane, but the overall rejection rate can be supplemented by the physical pore size barrier effect, while allowing lithium ions to pass through more freely, thereby effectively reducing losses. Comparative Example 4 shows that the lack of nanofiltration treatment leads to a sharp increase in sodium, potassium, and sulfate content. Comparative Example 5 shows that omitting the lithium phosphate precipitation impurity removal process results in product quality far below battery-grade standards.
[0051] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they are not intended to limit the present invention. It should be noted that various changes and modifications can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the concept and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor from spodumene lithium extraction, characterized in that, Includes the following steps: S1. Take a low-lithium, high-impurity mother liquor and pass it through an adsorption column packed with ion sieve adsorbent. After adsorption and penetration, desorption is performed to collect the lithium-rich desorbed liquid. S2. Adjust the pH of the lithium-rich desorption solution to neutral by adding alkaline solution, then remove impurities by nanofiltration and collect the nanofiltration permeate. S3. The obtained nanofiltration permeate is slowly added dropwise to a phosphate solution to precipitate lithium, and then filtered and washed to obtain crude lithium phosphate. S4. Dissolve the crude lithium phosphate in phosphoric acid and filter to obtain a lithium dihydrogen phosphate solution. S5. Evaporate the obtained lithium dihydrogen phosphate solution to crystallize, then centrifuge, wash and dry to obtain battery-grade lithium dihydrogen phosphate.
2. The method for preparing battery-grade lithium dihydrogen phosphate using low-lithium, high-impurity mother liquor from spodumene according to claim 1, characterized in that, The low-lithium, high-impurity mother liquor mentioned in S1 is sodium sulfate mother liquor produced by the spodumene sulfuric acid process; its lithium ion content is 1.5-3.5 g / L, sodium ion content is 20-40 g / L, sulfate content is 50-100 g / L, potassium ion content is 1-3 g / L, and pH value is 9-11.
3. The method for preparing battery-grade lithium dihydrogen phosphate using low-lithium, high-impurity mother liquor from spodumene according to claim 1, characterized in that, The ion sieve adsorbent described in S1 is at least one of titanium-based ion sieve lithium adsorbent and manganese-based ion sieve lithium adsorbent; the low-lithium, high-impurity mother liquor flows through the adsorption column at a flow rate of 1.5-4 BV / h and an adsorption temperature of 15-80℃.
4. The method for preparing battery-grade lithium dihydrogen phosphate using low-lithium, high-impurity mother liquor from spodumene according to claim 1, characterized in that, In S1, desorption is performed using a combined acid solution of dilute sulfuric acid and dilute hydrochloric acid. The volume of the acid solution is 20%-40% of the low-lithium, high-impurity mother liquor, and the concentration is 0.2-0.4 mol / L. The flow rate of the acid solution is controlled at 1.0-2.0 BV / h.
5. The method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor from spodumene according to claim 1, characterized in that, The nanofiltration membrane used for impurity removal in S2 is either Dow NF270-4040 or TimeWalton DL; the nanofiltration conditions are: pH 5.5-6.5, temperature 30-45℃, pressure 1.8-3.0 MPa, and water recovery rate 75%.
6. The method for preparing battery-grade lithium dihydrogen phosphate using low-lithium, high-impurity mother liquor from spodumene according to claim 1, characterized in that, The lithium ion concentration in the nanofiltration permeate obtained from S2 is 8.0-12.0 g / L.
7. The method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor from spodumene according to claim 1, characterized in that, The phosphate mentioned in S3 is diammonium hydrogen phosphate, and its solution concentration is 0.9-1.1 mol / L; the addition ratio of nanofiltration permeate to phosphate solution is based on the molar ratio of lithium in nanofiltration permeate to phosphate in phosphate solution of 3:(1-1.2).
8. The method for preparing battery-grade lithium dihydrogen phosphate using low-lithium, high-impurity mother liquor from spodumene according to claim 1, characterized in that, The conditions for lithium precipitation in S3 are as follows: while adding nanofiltration permeate, ammonia is slowly added dropwise to control the pH at the reaction endpoint to 10-11, the reaction temperature is 50-70℃, and after the reaction is completed, the mixture is aged at 50-60℃ for 20-40 min.
9. The method for preparing battery-grade lithium dihydrogen phosphate using low-lithium, high-impurity mother liquor from spodumene according to claim 1, characterized in that, After the crude lithium phosphate is completely dissolved, the pH needs to be adjusted to 1.5-3.
0.
10. The method for preparing battery-grade lithium dihydrogen phosphate using a low-lithium, high-impurity mother liquor from spodumene according to claim 1, characterized in that, The specific operation in S5 is as follows: the lithium dihydrogen phosphate solution is heated to 120-140℃ to evaporate, heating is stopped and stirring is continued to cool and crystallize; when the system cools down to 50-80℃, the wet material and the crystallization mother liquor are separated by centrifugation, and the wet material is washed and dried to obtain battery-grade lithium dihydrogen phosphate.