Method for preparing lithium hexafluorophosphate

Abstract

The invention discloses a method for preparing lithium hexafluorophosphate, which takes spodumene concentrate, fluorite concentrate and apatite concentrate as raw materials. The spodumene concentrate is acidized with sulfuric acid, leached to remove impurities, concentrated and subjected to lithium precipitation with sodium fluoride, and then lithium fluoride is prepared. The fluorite concentrate and the apatite concentrate are mixed and then react with sulfuric acid, and generated gas is washed with sulfuric acid to prepare phosphorus pentafluoride. And dissolving the obtained lithium fluoride in anhydrous hydrogen fluoride, introducing phosphorus pentafluoride for reaction, cooling and crystallizing the obtained lithium hexafluorophosphate solution, filtering, and drying to obtain the finished product lithium hexafluorophosphate.

Description

Technical Field

[0001] The present invention relates to a method for preparing lithium hexafluorophosphate, belonging to the field of lithium-ion batteries. Background Art

[0002] With the development of the new energy industry in recent years, the demand for lithium hexafluorophosphate as an electrolyte for lithium-ion batteries has been increasing continuously. At present, since lithium carbonate is used as a raw material for preparing lithium hexafluorophosphate, the cost is subject to the price of lithium carbonate, resulting in high costs. Summary of the Invention

[0003] The object of the present invention is to provide a method for preparing lithium hexafluorophosphate, which can effectively improve production efficiency and reduce production costs.

[0004] To achieve the above object, the technical solution of the present invention adopts a method for preparing lithium hexafluorophosphate by using low-grade ore resources, including the following steps.

[0005] I. Preparation of Lithium Fluoride (1) High-temperature roasting: The spodumene concentrate with 5%-6% lithium oxide content and -200 mesh particle size is roasted at a high temperature. During the roasting process, the temperature reaches 1050-1100 °C, and the roasting time is 40-50 min. The lithium oxide in the lithium concentrate undergoes crystal form transformation from α-type to β-type. After cooling, a roasted material with a transformation rate of more than 96% is obtained.

[0006] (2) Acidified roasting: The roasted material obtained in the previous step is added with sulfuric acid for acidified roasting. The ratio of material to acid is 3.7-4.2, and the acidification reaction temperature is controlled at 230-260 °C, and the reaction time is 30-40 minutes. The lithium oxide in the lithium concentrate reacts with sulfuric acid to form lithium sulfate, and other basic oxides react to form sulfates. An acidified clinker is prepared, and the main components are sulfates, silicon dioxide and sulfuric acid.

[0007] (3) Leaching and impurity removal: The cooled acidified clinker is leached to obtain a leaching solution, the main components of which are lithium sulfate, iron sulfate, ferrous sulfate, magnesium sulfate, aluminum sulfate and a small amount of calcium sulfate. The leaching solution is heated to 70-80 °C and then sodium hydroxide is added, and the reaction is carried out for 15-20 min to make the pH value stable at 11-12. According to the concentration of Ca 2+ in the leaching solution, the metered Na2CO3 is added according to the reaction formula Ca 2+ +CO3 2- àCaCO3, and the reaction continues for 30-40 min. The iron ions, ferrous ions, magnesium ions, aluminum ions and calcium ions in the leaching solution form hydroxide precipitates and insoluble carbonates. After solid-liquid separation, a purified solution of lithium sulfate (Li2O: 20-25 g / L) is prepared, and the main component is lithium sulfate.

[0008] (4)Concentration: Concentrate the purified liquid into a finished liquid containing 55 ± 5 g / L of Li2O.

[0009] (5)Preparation of sodium fluoride solution: Use ultrapure water to prepare a sodium fluoride solution at a temperature of 60 - 80°C. The concentration is 4%.

[0010] (6)Lithium precipitation: Add the sodium fluoride solution to the lithium precipitation kettle, and then add the finished liquid (lithium sulfate solution) evenly at a rate that takes 100 minutes to add completely. After adding the finished liquid, raise the temperature to ≥95°C and carry out the lithium precipitation reaction for 30 - 40 minutes. Since the reverse addition method has advantages such as less peritectic phenomenon, high lithium precipitation rate, and large crystal particles, the reverse addition method is adopted. The added sodium fluoride solution and the purified liquid react in the lithium precipitation kettle as follows: 2NaF + Li2SO4 === Na2SO4 + 2LiF↓. After lithium precipitation is completed, a lithium fluoride slurry is obtained, washed, and after centrifugal separation, lithium fluoride finished product is obtained and used in step three (synthesis of lithium hexafluorophosphate). II. Preparation of phosphorus pentafluoride (1)Roasting: Mix the fluorite concentrate (90% CaF2) and apatite concentrate (30% P2O5) evenly and add them to the reaction kettle. Gradually add concentrated sulfuric acid (H2SO4) and heat the reaction kettle to about 240 - 250°C for 30 minutes. The main reaction in the reaction kettle is CaF2 + P2O5 + H2SO4 ---> PF5 + CaSO4 + H2O. The waste residue generated by the reaction is treated and discharged, and the mixed gas of phosphorus pentafluoride and water generated is introduced into the next step.

[0011] (2)Washing: Wash the mixed gas of phosphorus pentafluoride and water with concentrated sulfuric acid. The sulfuric acid containing water after washing can be used as the feed (concentrated sulfuric acid) for step (1) of roasting after adding SO3 to neutralize the water. The anhydrous gas after washing is phosphorus pentafluoride and is used in step three (synthesis of lithium hexafluorophosphate).

[0012] III. Synthesis of lithium hexafluorophosphate (1)Preparation of lithium fluoride solution: Dissolve the lithium fluoride obtained in step one in anhydrous hydrogen fluoride to obtain an anhydrous hydrogen fluoride solution of lithium fluoride with a concentration of 18 - 20%.

[0013] (2)Synthesis: Pass the phosphorus pentafluoride gas into the lithium fluoride solution, control the reaction temperature at -10 - 0°C, and keep a slight negative pressure in the kettle. React phosphorus pentafluoride with lithium fluoride to obtain a hydrogen fluoride solution of lithium hexafluorophosphate.

[0014] (3)Crystallization: Cool and crystallize the lithium hexafluorophosphate solution obtained in the previous step at a crystallization temperature of -40 - 45°C. Filter the obtained crystallization liquid to obtain crude lithium hexafluorophosphate, which contains residual hydrogen fluoride.

[0015] (4) Drying: The crude lithium hexafluorophosphate is pulverized and then dried at a temperature of 55 - 60°C. The residual hydrogen fluoride volatilizes, and the finished product of lithium hexafluorophosphate is obtained. Embodiment Example

[0016] Preparation of lithium fluoride: Take 197.4 g of spodumene concentrate with 5% lithium oxide content and calcine it at 1100°C for 40 min. Add sulfuric acid to the obtained calcined material and continue to calcine at 260°C for 40 minutes to obtain 189 g of acidified clinker. Leach the obtained acidified clinker to obtain 2000 g of leaching solution. Heat the leaching solution to 70 - 80°C and then add sodium hydroxide to keep the pH value stable at 11 - 12 for 20 min during the reaction process. According to the measured concentration of Ca 2+ in the leaching solution, add Na2CO3 and continue to react for 40 min. After solid-liquid separation, 1896 g of purified lithium sulfate solution with a lithium sulfate content of 36.19 g is obtained. Concentrate the purified lithium sulfate solution to 756 g. Prepare 691 g of sodium fluoride solution with 27.64 g of sodium fluoride content in a container, and then add the lithium sulfate solution at a rate of adding it up in 100 minutes. After that, heat the material to 95°C and react for 30 min to obtain a lithium fluoride slurry. After solid-liquid separation, washing and drying, 17.11 g of finished lithium fluoride product is obtained.

[0017] Preparation of phosphorus pentafluoride: Mix 142.6 g of fluorite concentrate (90% CaF2) and 155.7 g of apatite concentrate (30% P2O5) evenly, gradually add 164.5 g of concentrated sulfuric acid (98% H2SO4), and heat to 250°C. React for 30 min, and wash the generated gas with concentrated sulfuric acid to obtain 82.91 g of phosphorus pentafluoride gas.

[0018] Preparation of lithium hexafluorophosphate: Dissolve 17.11 g of lithium fluoride in 68.44 g of anhydrous hydrogen fluoride. Pass 82.91 g of phosphorus pentafluoride gas into the lithium fluoride-hydrogen fluoride solution, and the reaction temperature is -10°C to obtain a lithium hexafluorophosphate-hydrogen fluoride solution. Cool it for crystallization at a crystallization temperature of -40°C to obtain a crystallization solution. Filter it and dry it at a drying temperature of 60°C to obtain 100 g of finished lithium hexafluorophosphate.

Claims

1. A method for preparing lithium hexafluorophosphate, characterized in that, Including the following steps (1) Preparation process of lithium fluoride: The spodumene concentrate is acidified with sulfuric acid, leached to remove impurities and concentrated, and then lithium fluoride is obtained by precipitating lithium with sodium fluoride; (2) Preparation process of phosphorus pentafluoride: The fluorite concentrate and apatite concentrate are mixed and then reacted with sulfuric acid, and the generated gas is washed with sulfuric acid to obtain phosphorus pentafluoride; (3) Synthesis process of lithium hexafluorophosphate: The obtained lithium fluoride above is dissolved in anhydrous hydrogen fluoride, and phosphorus pentafluoride is introduced for reaction. The obtained lithium hexafluorophosphate solution is cooled, crystallized, filtered and dried to obtain the finished product of lithium hexafluorophosphate.

2. The method for preparing lithium hexafluorophosphate according to claim 1, wherein, In the process of preparing lithium fluoride in step (1), during the acidification of the lithium concentrate. The lithium concentrate is first roasted at a roasting temperature of 1050 - 1100 °C and a roasting time of 40 - 50 min. Then acidification is carried out with a material - acid ratio of 3.7 - 4.2, and the acidification reaction temperature is controlled at 230 - 260 °C and the reaction time is 30 - 40 minutes.

3. The method for preparing lithium hexafluorophosphate according to claim 1, wherein, In step (1) during the preparation of lithium fluoride, in the process of leaching and impurity removal of acidified clinker. In the process of impurity removal with sodium hydroxide, the temperature is 70 - 80 °C, the time is 15 - 20 min, and the final pH value is 11 - 12; in the process of impurity removal with sodium carbonate, according to the concentration of Ca 2+ in the leaching solution, metered Na2CO3 is added and the reaction lasts for 30 - 40 min.

4. The method for preparing lithium hexafluorophosphate according to claim 1, characterized in that, In the process of preparing lithium fluoride in step (1), during the concentration of the purified liquid. The final converted Li2O concentration is 55 ± 5 g / L.

5. The method for preparing lithium hexafluorophosphate according to claim 1, wherein In the process of preparing lithium fluoride in step (1), during the lithium precipitation process. The reverse addition method is adopted and added uniformly at a rate of adding up in 100 minutes, with a reaction temperature of 95 °C and a reaction time of 30 - 40 min.

6. The method for preparing lithium hexafluorophosphate according to claim 1, characterized in that, In the process of preparing phosphorus pentafluoride in step (2), during the roasting process. The roasting temperature is 240 - 250 °C and the reaction time is 30 min.

7. The method for preparing lithium hexafluorophosphate according to claim 1, characterized in that, In the process of preparing phosphorus pentafluoride in step (2), during the washing process of phosphorus pentafluoride gas. It is washed with sulfuric acid, and after adding SO3 to neutralize the moisture, it can be recycled.

8. The method for preparing lithium hexafluorophosphate according to claim 1, wherein In the process of synthesizing lithium hexafluorophosphate in step (3). The concentration of the anhydrous hydrogen fluoride solution of lithium fluoride is 18 - 20%. The reaction temperature is controlled at - 10 - 0 °C, and the inside of the kettle is slightly negative pressure.

9. The method for preparing lithium hexafluorophosphate according to claim 1, wherein In the process of crystallization and drying of the lithium hexafluorophosphate solution in step (3). The crystallization temperature is - 40 - 45 °C and the drying temperature is 55 - 60 °C.