Recovery Method for Residual Lithium Elements in Lithium Precipitation Filtrate in the Process of Precipitating Lithium Carbonate from Lithium Sulfate

Abstract

The present application discloses a method for recovering residual lithium elements in the lithium precipitation filtrate in the process of precipitating lithium carbonate from lithium sulfate, including: S100, adding an acid to the lithium precipitation filtrate to adjust the pH to 8-10, and then adding an adsorbent to adsorb and extract lithium to obtain a sodium sulfate solution and a lithium-containing adsorbent; S200, pickling and de-lithifying the lithium-containing adsorbent to obtain a crude lithium chloride solution; S300, subjecting the crude lithium chloride solution to alkalization for impurity removal and filtering; S400, evaporating and crystallizing the filtrate to obtain a crude lithium chloride crystal, which is dissolved in an organic solvent and then filtered to obtain a recovery solution; S500, evaporating and crystallizing the recovery solution to obtain high-purity lithium chloride. By first adding an acid for pH regulation treatment before precipitating sodium sulfate in the traditional process, then adsorbing the lithium elements in the filtrate with an adsorbent, and then de-lithifying and removing impurities from the lithium-containing adsorbent, the present application realizes the efficient recovery of residual lithium elements in the lithium precipitation filtrate, with a recovery rate of over 90%, and the purity of sodium sulfate being over 99.9%.

Description

Technical Field

[0001] The present application relates to the technical field of lithium element recovery, and particularly to a method for recovering residual lithium elements in the lithium precipitation filtrate in the process of precipitating lithium carbonate from lithium sulfate. Background Art

[0002] With the rapid development of the global electric vehicle industry, the demand for lithium carbonate, a key raw material for preparing power batteries for electric vehicles, has increased sharply. As the demand for lithium carbonate rises, lithium carbonate and its preparation industry have received extensive attention in the industry.

[0003] Currently, the main source of lithium carbonate is to prepare lithium sulfate from lithium in lithium ore, salt lakes, and waste batteries through hydrometallurgical processes, and then transform lithium sulfate into lithium carbonate. The traditional process flow for converting lithium sulfate into lithium carbonate is as Figure 1 shown. Lithium carbonate is precipitated by reacting a lithium sulfate solution with excessive sodium carbonate, and the crude lithium carbonate is obtained through filtration. The filtrate is subjected to freeze crystallization and filtration to obtain solid sodium sulfate. Since lithium carbonate has a solubility of 13.3 g / L in aqueous solution and sodium carbonate and lithium sulfate cannot react completely, lithium ions remain in the filtrate after filtering the lithium carbonate solid. The residual lithium ions in the filtrate (sodium sulfate solution) will partially precipitate with sodium sulfate during the cooling crystallization of sodium sulfate, reducing the purity of the by-product sodium sulfate and also reducing the lithium recovery rate. In addition, sodium ions and lithium ions will also remain in the mother liquor after freeze crystallization of sodium sulfate, which will also reduce the lithium recovery rate.

[0004] The literature of the prior art mentions that by concentrating the filtrate after cooling crystallization and precipitation of sodium sulfate again to make the lithium ion content reach about 1%, secondary lithium precipitation is carried out to recover the residual lithium in the filtrate. However, this method still cannot fully recover the residual lithium elements in the filtrate. Summary of the Invention

[0005] In view of this, the present application provides a method for recovering residual lithium elements in the lithium precipitation filtrate in the process of precipitating lithium carbonate from lithium sulfate. Before precipitating sodium sulfate in the traditional process, sulfuric acid is first added to adjust the pH, and then the lithium elements in the filtrate are adsorbed and removed by an adsorbent, thus reducing the lithium content in the filtrate. Then, sulfuric acid is added to purify the sodium sulfate solution to obtain high-purity by-product sodium sulfate. At the same time, the adsorbent after adsorbing lithium elements (i.e., lithium-containing adsorbent) is de-lithiated and de-impurified to obtain high-purity lithium chloride, realizing the recovery of residual lithium elements in the lithium precipitation filtrate in the process of precipitating lithium carbonate from lithium sulfate, with a recovery rate of over 90%. That is, this process method takes into account the efficient recovery of lithium, the high purity of the by-product sodium sulfate, and the low total consumption of sulfuric acid.

[0006] First aspect, the present application provides a method for recovering residual lithium elements in the lithium precipitation filtrate in the process of precipitating lithium carbonate from lithium sulfate. The process of precipitating lithium carbonate from lithium sulfate includes: subjecting a lithium sulfate solution to a lithium precipitation reaction with a sodium hydroxide solution and a sodium carbonate solution, and then filtering to obtain crude lithium carbonate and a lithium precipitation filtrate. The recovery method at least includes the following steps: S100, adding an acid to the lithium precipitation filtrate to adjust the pH to 8-10, and then adding an adsorbent to adsorb and extract lithium to obtain a sodium sulfate solution and a lithium-containing adsorbent; S200, acid-washing the lithium-containing adsorbent to elute lithium to obtain a crude lithium chloride solution; S300, subjecting the crude lithium chloride solution to alkalization for impurity removal and then filtering to obtain a filtrate, and the filtrate contains Li + , Cl - and impurity cations; S400, subjecting the filtrate to a first evaporation crystallization to obtain crude lithium chloride crystals, dissolving the crude lithium chloride crystals in an organic solvent and then filtering to obtain a recovery liquid containing Li + and Cl - ; S500, subjecting the recovery liquid to a second evaporation crystallization to obtain high-purity lithium chloride. Among them, in step S100, adding an acid to the sodium sulfate solution and subjecting it to evaporation crystallization to obtain high-purity anhydrous sodium sulfate. In the present application, the lithium precipitation filtrate obtained after the lithium precipitation filtration of the lithium sulfate solution with the sodium hydroxide solution and the sodium carbonate solution is first adjusted to a pH of 8-10 with an acid. On the one hand, in a slightly alkaline environment, the lithium extraction adsorbent has a better effect of adsorbing lithium ions. Since the lithium precipitation filtrate contains OH - , CO3 2- , its overall is alkaline, but when the alkalinity is too strong, it will also damage the adsorbent and affect the lithium extraction effect. Therefore, adjusting the pH of the lithium precipitation filtrate to be within the range of 8-10 can obtain a better lithium adsorption effect while reducing the impact on the adsorbent; on the other hand, after the adsorbent adsorbs Li + , it will displace H + , resulting in the pH of the system changing towards the acidic direction. However, due to the residual alkaline ions in the system, such as CO3 2- , it will react with H + , making the system always maintain a neutral or alkaline state, which is beneficial to the adsorbent maintaining a high-efficiency state throughout the lithium adsorption and extraction process; on the other hand, the adsorbent displaces H + , and in an environment with a pH of 8-10, it reacts with CO3 2- , which not only weakens the interaction between Li + and CO3 2- , making Li in an ionic state easier to be adsorbed, but also reduces the CO3 2- in the systemThe content played an impurity removal effect, enabling high-purity sodium sulfate to be obtained by adding a small amount of acid solution to the sodium sulfate solution after lithium extraction. The total acid consumption was less, that is, while ensuring high purity of sodium sulfate, the total acid consumption was reduced. Then, in this application, an adsorbent was added to the lithium precipitation filtrate after adjusting the pH for lithium extraction by adsorption. After the lithium extraction by adsorption ended, a sodium sulfate solution and a lithium-containing adsorbent were obtained. The sodium sulfate solution was neutralized and purified with acid and then subjected to evaporation crystallization to obtain the by-product high-purity anhydrous sodium sulfate. Finally, the lithium-containing adsorbent was delithiated to obtain high-purity lithium chloride, realizing the efficient recovery of the residual lithium element in the lithium precipitation filtrate in the process of precipitating lithium carbonate from lithium sulfate and obtaining high-purity anhydrous sodium sulfate at the same time.

[0007] In this process, CO3 in the lithium precipitation filtrate was utilized 2- to displace H from the adsorbent + , and they cooperated with each other, that is, CO3 2- consumed H + , keeping the pH of the system always within the range of alkaline to neutral, ensuring the adsorption efficiency of the adsorbent; conversely, H + would also react with CO3 2- to remove it, generating CO2, which played an impurity removal role. The following reactions mainly occurred during the adsorption process, where R represents a lithium ion adsorbent:

[0008] 2R-H + +Li2CO3=2R-Li + +CO2+H2O

[0009] In some embodiments, the concentration of lithium ions in the lithium precipitation filtrate is 1.8 g / L to 2.0 g / L. When the concentration of lithium ions in the lithium precipitation filtrate is within the above range, it is more conducive to the full recovery of lithium elements. In this process, preferably, the pH of the lithium precipitation filtrate is adjusted by adding acid. When adjusting by adding acid, not only can the pH be 8-10, but also the concentration of lithium ions can be controlled within the range of 1.8 g / L to 2.0 g / L, that is, when adding acid, the concentration of lithium ions will not change too much.

[0010] In some embodiments, in step S100, the acidification includes: the acid added to the lithium precipitation filtrate includes a sulfuric acid solution. Preferably, the mass concentration of the sulfuric acid solution is 1% to 10%.

[0011] In some embodiments, in step S100, the adsorbent is a lithium ion adsorbent, and after the lithium ion adsorbent Li + it will displace H +, which includes any one of manganese dioxide ion sieve, titanium oxide ion sieve, high-valent amorphous phosphate, hydrated SnO2, and amorphous Al(OH)3. Specifically, in some examples, the adsorbent is a manganese dioxide ion sieve, and the lithium precipitation filtrate after adjusting the pH flows through the manganese dioxide ion sieve at a flow rate of 3 BV / h to 4 BV / h for lithium adsorption and extraction to obtain a lithium-containing adsorbent. Among them, the manganese dioxide ion sieve is granular, and its bulk density is 70 g / cm 3 to 75 g / cm 3 . In this way, it is more conducive to lithium adsorption and extraction by the manganese dioxide ion sieve. In other examples, the adsorbent is a titanium oxide ion sieve, and the lithium precipitation filtrate after adjusting the pH flows through the titanium oxide ion sieve at a flow rate of 5 BV / h to 7 BV / h for lithium adsorption and extraction to obtain a lithium-containing adsorbent. Among them, the titanium oxide ion sieve is powdery, and 90% of its particle size is between 1 μm and 3 μm, and the average particle size is 1.6 to 1.8 μm. In this way, it is more conducive to lithium adsorption and extraction by the titanium oxide ion sieve.

[0012] In some embodiments, in step S200, acid pickling for lithium desorption includes: mixing the lithium-containing adsorbent and hydrochloric acid solution for lithium desorption reaction, and the concentration range of the hydrochloric acid solution is 0.01 mol / L to 1 mol / L. The adsorbent after lithium desorption returns to step S100 for continuous lithium adsorption and extraction. In this application, after the lithium-containing adsorbent is pickled and desorbed with hydrochloric acid of a suitable concentration, a crude lithium chloride solution is obtained. The crude lithium chloride solution includes lithium chloride (obtained by displacement of Li + in the lithium-containing adsorbent and H + in hydrochloric acid), manganese chloride (generated by dissolution loss of the adsorbent), etc. The concentration of the hydrochloric acid solution within the above range is to avoid an increase in the dissolution loss rate of the adsorbent. In this application, controlling the dissolution loss rate within a suitable range is beneficial for obtaining high-purity lithium chloride with a high yield on the one hand, and can also save process costs, improve the effect and service life of the adsorbent, and is more conducive to large-scale industrial production.

[0013] In some embodiments, in step S300, alkalization for impurity removal includes: adding alkali to the crude lithium chloride solution to adjust the pH to 7 - 8. Preferably, the alkali used in alkalization for impurity removal includes at least one of sodium hydroxide solution, lithium hydroxide solution, and sodium carbonate solution. More preferably, the alkali used in alkalization for impurity removal includes a sodium hydroxide solution with a mass percentage of 20 wt% - 25 wt%. In this application, the pH of the crude lithium chloride solution is adjusted to 7 - 8 by adding alkali. After the reaction, insoluble impurities such as manganese hydroxide (manganese chloride generated by dissolution loss of the adsorbent is converted to manganese hydroxide under alkaline conditions) are removed by filtration to obtain a filtrate, and the filtrate contains Li + , Cl - and impurity cations. In this way, it provides the possibility for subsequent purification treatment to obtain high-purity lithium chloride. Impurity cations include cations in the alkali solution, such as Na + etc.

[0014] In some embodiments, in step S400, the organic solvent is selected from anhydrous ethanol and / or anhydrous acetone. In the present application, the crude lithium chloride containing chloride salts is added with a suitable organic solvent for dissolution, which is more conducive to obtaining high-purity lithium chloride and improving its yield. After the dissolution is completed, the chloride salts are removed by filtration to obtain a recovery solution containing only Li + and Cl - .

[0015] In some embodiments, in step S500, the organic solvent obtained by subjecting the recovery solution to secondary evaporation crystallization and cooling is returned to step S400 to dissolve the crude lithium chloride, wherein the temperature range of the secondary evaporation crystallization is 100°C to 280°C. By regulating the temperature of the secondary evaporation crystallization within the above range in the present application, on the one hand, it is conducive to obtaining high-purity lithium chloride, and on the other hand, it is more conducive to the recycling of the organic solvent, further reducing the process cost.

[0016] In some embodiments, in the process of precipitating lithium carbonate from lithium sulfate, the concentration of the lithium sulfate solution is 200 g / L to 260 g / L, the concentration of the sodium carbonate solution is 150 g / L to 300 g / L, and the molar ratio of sodium carbonate in the sodium carbonate solution to lithium sulfate in the lithium sulfate solution is 1.0 to 1.2.

[0017] In some embodiments, the conditions for the lithium precipitation reaction include: lithium precipitation temperature: 15°C to 98°C, reaction time: 0.2 h to 3 h. In this way, it is more conducive to obtaining a lithium precipitation filtrate with a suitable lithium ion concentration, and further more conducive to the recovery of lithium elements. Preferably, the lithium precipitation temperature: 80°C to 90°C, reaction time: 0.2 h to 0.5 h.

[0018] In the present application, the pH of the lithium precipitation filtrate after filtering out the crude lithium carbonate is adjusted to 8 to 10 with acid, and then the lithium ions in the lithium precipitation filtrate are adsorbed by an adsorbent. After testing, the concentration of lithium ions in the lithium precipitation filtrate can be reduced by about 600 times or more after being adsorbed by the adsorbent. The lithium-containing adsorbent is eluted with hydrochloric acid to obtain a lithium-containing washing solution (i.e., a crude lithium chloride solution). The lithium-containing washing solution is added with alkali to remove impurities (such as manganese ions) generated by the dissolution loss of the adsorbent, filtered, and the filtrate is then subjected to evaporation crystallization to obtain a crude lithium chloride crystal (containing sodium chloride or potassium chloride). The crude lithium chloride crystal is dissolved in an organic solvent and filtered to separate out insoluble chloride salts (such as sodium chloride), and the organic solvent filtrate is then subjected to evaporation crystallization to obtain high-purity lithium chloride, thereby realizing the full recovery of residual lithium elements in the filtrate.

[0019] In the present application, by utilizing the interaction between CO3 2- in the lithium precipitation filtrate and H + in the adsorbent, not only the adsorption and recovery of Li + is realized, but more importantly, the adsorption process can be kept in a neutral or slightly alkaline environment all the time, maintaining the high adsorption capacity of the adsorbent, and the impurity CO32- Removing is beneficial to obtaining a high-purity sodium sulfate by-product. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following-described drawings are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0021] Figure 1 It is a schematic diagram of the traditional process flow for converting lithium sulfate to lithium carbonate;

[0022] Figure 2 It is a schematic diagram of the process flow for the recovery method of residual lithium elements in the lithium precipitation filtrate in the lithium carbonate precipitation process of lithium sulfate in the present application. Detailed Embodiments

[0023] In order to make the purpose, technical solutions and advantages of the present application clearer, the following further details the present application in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0024] Recovery method for residual lithium elements in lithium precipitation filtrate in the process of precipitating lithium carbonate with lithium sulfate

[0025] The lithium precipitation filtrate is obtained by the following process: reacting a lithium sulfate solution with a sodium hydroxide solution and a sodium carbonate solution for lithium precipitation reaction, and filtering to obtain crude lithium carbonate and a lithium precipitation filtrate. Specifically, the operation can refer to the conventional steps of the prior art or be obtained by the method disclosed in the present application.

[0026] See Figure 2 , the recovery method mainly includes the following steps:

[0027] S100. Add an acid to the lithium precipitation filtrate to adjust the pH to 8-10, then add an adsorbent to adsorb and extract lithium to obtain a sodium sulfate solution and a lithium-containing adsorbent. The sodium sulfate solution is neutralized and purified with an acid and then evaporated and crystallized to obtain high-purity anhydrous sodium sulfate;

[0028] S200. Acid-wash and de-lithiate the lithium-containing adsorbent to obtain a crude lithium chloride solution;

[0029] S300. Alkalize and remove impurities from the crude lithium chloride solution, and filter to obtain a filtrate containing Li + , Cl - and impurity cations;

[0030] S400. The filtrate is subjected to first evaporation crystallization to obtain crude lithium chloride crystals. After the crude lithium chloride crystals are dissolved in an organic solvent and filtered, a recovery solution containing Li + and Cl - is obtained;

[0031] S500. The recovery solution is subjected to second evaporation crystallization to obtain high-purity lithium chloride.

[0032] The conditions of the first evaporation crystallization and the second evaporation crystallization can be the same or different, preferably the same.

[0033] In this application, the lithium precipitation filtrate after filtering the lithium precipitation of the lithium sulfate solution with the sodium hydroxide solution and the sodium carbonate solution is first subjected to pH regulation treatment by adding acid. The lithium precipitation filtrate after pH regulation is then subjected to lithium extraction by a lithium adsorbent. In this way, the lithium ion concentration in the sodium sulfate solution is reduced by about 600 times or more compared with the lithium ion concentration in the lithium precipitation filtrate, thereby improving the purity of the by-product sodium sulfate. At the same time, in this application, the lithium-containing washing solution (crude lithium chloride solution) after acid-washing and lithium elution of the lithium-containing adsorbent is further subjected to alkalization and impurity removal to obtain crude lithium chloride crystals, and then the crude lithium chloride crystals are dissolved and purified by an organic solvent, and finally high-purity lithium chloride is obtained by secondary evaporation crystallization, realizing the full recovery of the residual lithium element in the lithium precipitation filtrate, and the recovery rate of the lithium element is as high as more than 90%.

[0034] In some embodiments, the lithium ion concentration in the lithium precipitation filtrate is 1.8 g / L to 2.0 g / L. Adjusting the lithium ion concentration in the lithium precipitation filtrate appropriately is more conducive to realizing the recovery of the residual lithium element in the lithium carbonate precipitation filtrate. Exemplarily, the lithium ion concentration in the lithium precipitation filtrate is 1.8 g / L, 1.83 g / L, 1.85 g / L, 1.87 g / L, 1.89 g / L, 1.9 g / L, 1.91 g / L, 1.95 g / L, 1.98 g / L, 2.0 g / L or values within the range composed of any two of these values.

[0035] In some embodiments, in step S100, adjusting the pH to 8-10 by adding acid includes: adding sulfuric acid solution to the lithium precipitation filtrate to adjust the pH value to 8-10. Adjusting the pH by adding acid within the above range is beneficial to improving the lithium absorption effect of the adsorbent on the one hand, and can further improve the purity of sodium sulfate and maintain the high performance of the adsorbent on the other hand. Exemplarily, adding sulfuric acid solution to the lithium precipitation filtrate to adjust the pH value to 8, 8.5, 9, 9.5, 10 or values within the range composed of any two of these values.

[0036] In some embodiments, the mass concentration of the sulfuric acid solution is 1 wt% to 10 wt%. Thus, it is beneficial to convert the residual lithium carbonate in the lithium precipitation filtrate into lithium sulfate with high solubility, further improving the recovery rate of lithium elements. Exemplarily, the mass concentration of the sulfuric acid solution is 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 8 wt%, 10 wt% or a value within the range composed of any two of these values.

[0037] In some embodiments, in step S100, the adsorbent is a lithium ion adsorbent, which includes any one of manganese dioxide ion sieve, titanium oxide ion sieve, high-valent amorphous phosphate, hydrated SnO2, and amorphous Al(OH)3. Among them, the manganese dioxide ion sieve is preferably used as the lithium adsorbent because of its low price, good cycling performance, and large lithium adsorption capacity.

[0038] Exemplarily, the adsorbent is a manganese dioxide ion sieve, and the acidified lithium precipitation filtrate flows through the manganese dioxide ion sieve at a flow rate of 3 BV / h to 4 BV / h for lithium adsorption and extraction. The manganese dioxide ion sieve is granular, and its bulk density is 70 g / cm 3 to 75 g / cm 3 . Exemplarily, the flow rate of the acidified lithium precipitation filtrate flowing through the manganese dioxide ion sieve is 3 BV / h, 3.2 BV / h, 3.3 BV / h, 3.5 BV / h, 3.6 BV / h, 3.8 BV / h, 4 BV / h or a value within the range composed of any two of these values. Exemplarily, the bulk density of the manganese dioxide ion sieve is 70 g / cm 3 , 71 g / cm 3 , 72 g / cm 3 , 73 g / cm 3 , 74 g / cm 3 , 75 g / cm 3 or a value within the range composed of any two of these values.

[0039] Exemplarily, the adsorbent is a titanium oxide ion sieve. The acidified lithium precipitation filtrate flows through the titanium oxide ion sieve at a flow rate of 5 BV / h to 7 BV / h for lithium adsorption and extraction. The titanium oxide ion sieve is in powder form, with 90% of its particle size ranging from 1 μm to 3 μm and an average particle size of 1.6 μm to 1.8 μm. Exemplarily, the flow rate of the acidified lithium precipitation filtrate flowing through the titanium oxide ion sieve is 5 BV / h, 5.3 BV / h, 5.5 BV / h, 5.8 BV / h, 6 BV / h, 6.5 BV / h, 6.8 BV / h, 7 BV / h, or a value within the range formed by any two of these values. Exemplarily, 90% of the particle size of the titanium oxide ion sieve is 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, or a value within the range formed by any two of these values. Exemplarily, the average particle size of the titanium oxide ion sieve is 1.6 μm, 1.65 μm, 1.68 μm, 1.7 μm, 1.75 μm, 1.8 μm, or a value within the range formed by any two of these values.

[0040] In some embodiments, in step S200, acid washing for lithium desorption includes: mixing the lithium-containing adsorbent and hydrochloric acid solution for lithium desorption reaction. The concentration range of the hydrochloric acid solution is 0.01 mol / L to 1 mol / L, and the lithium-desorbed adsorbent is returned to step S100 for continuous lithium adsorption and extraction. In this application, a hydrochloric acid solution with a certain concentration is used for acid washing and lithium desorption of the lithium-containing adsorbent, with good lithium desorption effect, and the obtained crude lithium chloride solution is more conducive to recovering lithium elements. Exemplarily, the concentration of the hydrochloric acid solution is 0.01 mol / L, 0.03 mol / L, 0.05 mol / L, 0.07 mol / L, 0.09 mol / L, 1 mol / L, or a value within the range formed by any two of these values.

[0041] In some embodiments, in step S300, alkalization for impurity removal includes: adding alkali to the crude lithium chloride solution to adjust the pH to 7 - 8. The purpose of adding alkali to adjust the pH to 7 - 8 is to neutralize the excessive acid in acid washing for lithium desorption and impurities (such as manganese chloride) generated by the loss of the lithium-containing adsorbent in an acidic environment. In some examples, the alkali used in alkalization for impurity removal includes at least one of sodium hydroxide solution, lithium hydroxide solution, and sodium carbonate solution. In other examples, the alkali used in alkalization for impurity removal includes a 20 wt% - 25 wt% sodium hydroxide solution. When the type of alkali and the pH value of the solution are appropriate, it is more conducive to obtaining high-yield high-purity lithium chloride.

[0042] In some embodiments, in step S400, the organic solvent is selected from anhydrous ethanol and / or anhydrous acetone. Anhydrous ethanol and / or anhydrous acetone are more conducive to dissolving the chloride salts in the crude lithium chloride to obtain a recovery liquid containing only Li + and Cl - .

[0043] In some embodiments, in step S500, the organic solvent obtained by subjecting the recycled liquid to secondary evaporation crystallization is returned to step S400 to dissolve the crude lithium chloride crystals, and the temperature range of the secondary evaporation crystallization is 100°C to 280°C. Exemplarily, the temperature range of the secondary evaporation crystallization is 100°C, 130°C, 150°C, 180°C, 200°C, 220°C, 250°C, 260°C, 280°C, or values within the range formed by any two of these values.

[0044] In some embodiments, in the process of precipitating lithium carbonate from lithium sulfate, the concentration of the lithium sulfate solution is 200 g / L to 260 g / L, the concentration of the sodium hydroxide solution is 40 g / L to 80 g / L (about 4 wt% to 8 wt%), the concentration of the sodium carbonate solution is 150 g / L to 300 g / L, and the molar ratio of sodium carbonate in the sodium carbonate solution to lithium sulfate in the lithium sulfate solution is 1.0 to 1.2; and / or, the conditions for the lithium precipitation reaction include: lithium precipitation temperature: 15°C to 98°C, reaction time: 0.2 h to 3 h. Exemplarily, the concentration of the lithium sulfate solution is 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L, 245 g / L, 250 g / L, 260 g / L, or values within the range formed by any two of these values. Exemplarily, the concentration of the sodium hydroxide solution is 40 g / L, 45 g / L, 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, or values within the range formed by any two of these values. Exemplarily, the concentration of the sodium carbonate solution is 150 g / L, 160 g / L, 180 g / L, 200 g / L, 230 g / L, 260 g / L, 270 g / L, 280 g / L, 300 g / L, or values within the range formed by any two of these values. Exemplarily, the molar ratio of sodium carbonate in the sodium carbonate solution to lithium sulfate in the lithium sulfate solution is 1.0, 1.05, 1.1, 1.13, 1.15, 1.18, 1.2, or values within the range formed by any two of these values.

[0045] The following describes possible implementation manners

[0046] The main object of the present invention is to provide a method for recovering residual lithium elements in the lithium precipitation mother liquor in the process of precipitating lithium carbonate from lithium sulfate, aiming to solve the problems that the residual lithium elements in the lithium precipitation filtrate cannot be fully recovered in the existing technical solutions.

[0047] To achieve the above object, the present invention provides a method for recovering residual lithium elements in the lithium precipitation mother liquor in the process of precipitating lithium carbonate from lithium sulfate, which includes the following steps:

[0048] S1. Mix the lithium sulfate solution with the sodium hydroxide solution and the sodium carbonate solution in sequence for the lithium precipitation reaction. After the lithium precipitation reaction is completed, filter to obtain crude lithium carbonate and filtrate. The crude lithium carbonate is washed to obtain the product high-purity lithium carbonate. Further, first mix the lithium sulfate solution and the sodium hydroxide solution. The pH of the mixed solution is in an alkaline environment, and then add the sodium carbonate solution for the lithium precipitation reaction.

[0049] S2. Add sulfuric acid to the filtrate obtained in S1 to adjust the pH. The pH range of the adjusted solution is 8 - 10. The purpose of pH adjustment is to provide a good molecular sieve adsorption environment while protecting the molecular sieve from deterioration. In addition, the consumption of acid can be reduced by reacting the hydrogen ions displaced by adsorption with the carbonate ions in the solution.

[0050] S3. Adsorb and extract lithium from the filtrate with the pH adjusted in S2 using a lithium adsorbent. After the lithium adsorption and extraction is completed, obtain a sodium sulfate solution and a lithium-containing adsorbent. Neutralize, purify, evaporate, and crystallize the sodium sulfate solution to obtain the by-product high-purity anhydrous sodium sulfate.

[0051] S4. Add hydrochloric acid solution to the lithium-containing adsorbent obtained in S3 for acid washing to remove lithium. After the acid washing is completed, obtain a lithium adsorbent and a crude lithium chloride solution. The lithium adsorbent is returned to the S3 process for reuse.

[0052] S5. Add a strong base to the crude lithium chloride solution obtained in S4 to adjust the pH range to 7 - 8. After the reaction is completed, filter to remove insoluble impurities such as manganese hydroxide to obtain a filtrate, and then perform the first evaporation and crystallization to obtain a crude lithium chloride crystal containing chloride salts.

[0053] S6. Add an organic solvent to dissolve the crude lithium chloride crystal obtained in S5 (LiCl is easily soluble in, for example, ethanol). After the dissolution is completed, filter to remove the impurity chloride salts to obtain a filtrate.

[0054] S7. Perform the second evaporation and crystallization on the filtrate obtained in S6 to obtain an organic solvent and the by-product high-purity lithium chloride. The organic solvent is returned to S6 for recycling.

[0055] Further, in the above S1 step, the lithium sulfate can be obtained from lithium ore, salt lake, and through smelting of waste batteries, or it can be commercially available. Its concentration range is 165 - 240 g / L. The pH range of the solution after adding the sodium hydroxide solution is 11 - 12. The concentration range of the sodium carbonate solution is 150 - 300 g / L, and the addition amount of sodium carbonate is 1.0 - 1.2 times the molar amount of lithium sulfate, preferably 1.02 - 1.07 times.

[0056] Further, in the above S1 step, the lithium precipitation temperature is 15 - 98 °C, preferably 80 - 95 °C. The decrease in the solubility of lithium carbonate at high temperature helps to improve the lithium carbonate yield. The reaction time can be 0.2 - 3 h, preferably 0.4 - 0.6 h.

[0057] Further, in the above step S3, the lithium adsorption can be selected from manganese dioxide ion sieve, titanium oxide ion sieve, high-valent amorphous phosphates such as titanium phosphate, tin phosphate and zirconium phosphate, hydrated SnO2, amorphous Al(OH)3, etc. Among them, the manganese dioxide ion sieve is preferably used as the lithium adsorbent because of its low price, good cycle performance and high lithium adsorption capacity.

[0058] Further, the distillation and crystallization temperature range of the sodium sulfate solution in the above step S3 can be 150 - 300 °C.

[0059] Further, the concentration range of hydrochloric acid used for eluting lithium in the above step S4 is 0.01 - 1 mol / L, and the preferred concentration range is 0.3 - 0.6 mol / L.

[0060] Further, the purpose of adding an alkali (such as Na2CO3) to adjust the pH to 7 - 8 in the above step S5 is to neutralize the excessive acid in the acid elution and precipitate the impurities generated by the loss of the lithium adsorbent.

[0061] Further, the organic solvent used in the above step S6 is an alcohol organic solvent, which can be one or more mixed solvents such as methanol and ethanol.

[0062] Further, the second evaporation and crystallization temperature range of lithium chloride in the above step S7 can be 100 - 280 °C, and the preferred range is 170 - 260 °C.

[0063] Hereinafter, examples and comparative examples are given to illustrate the embodiments of the present application more specifically. Unless otherwise stated, the parts, percentages and ratios listed are based on mass.

[0064] The manganese dioxide ion sieve used in the examples is an existing substance, and its preparation method is briefly introduced below:

[0065] Mix Li 1.6 Mn 1.6 O4, PVC powder and KCl fine powder evenly, add N-N-dimethylformamide solvent, stir until it forms a gel, dry at 80 °C, crush the sample and soak it in water to dissolve all the KCl in it. After drying the sample, a granular adsorbent precursor is obtained. Then, through acid leaching for lithium removal, water washing and drying, a granular ion sieve adsorbent can be obtained.

[0066] Example 1

[0067] Add 1.22 g of 5% sodium hydroxide solution to 1 L of lithium sulfate solution with a concentration of 220 g / L to adjust the pH of the solution to 11.2. Then add 0.86 L of sodium carbonate solution with a concentration of 260 g / L and react at 85 °C for 0.5 h. After the reaction, filter to obtain crude lithium carbonate and the filtrate obtained from the reaction (lithium precipitation filtrate). Wash the crude lithium carbonate three times with deionized water to obtain 129.58 g of lithium carbonate with a purity of 99.57%.

[0068] Add 2.7 g of 5% sulfuric acid to the filtrate obtained from the reaction to adjust the pH, and adjust the pH value of the solution to 10. At this time, the measured lithium ion concentration is 1.910 g / L. Flow the filtrate obtained after adjusting the pH through 580 g of manganese dioxide ion sieve for lithium adsorption at a flow rate of 3.5 BV / h. The manganese dioxide ion sieve is granular and is prepared from Li 1.6 Mn 1.6 O4 and PVC organic resin binder and pore-forming agent N-N-dimethylformamide. The mass ratio of Li 1.6 Mn 1.6 O4 and organic resin PVC is about 7:2, and the bulk density is about 72 g / cm 3 . Test the sodium sulfate solution obtained by lithium adsorption, and its lithium content drops to 2 mg / L, which is about 950 times lower than the lithium ion content (1.91 g / L) before adsorption. Add 32.98 g of 30% sulfuric acid to the sodium sulfate solution after adsorption, and then evaporate and crystallize to obtain 298.81 g of high-purity sodium sulfate with a purity of 99.93%. The results are shown in Table 1.

[0069] Perform a delithiation reaction on the lithium adsorbent with 1.78 L of 0.5 mol / L hydrochloric acid. Add 64 g of 25% sodium hydroxide solution to the delithiated solution (i.e., crude lithium chloride solution) and then filter to remove impurities. Evaporate and crystallize the filtrate after impurity removal to obtain crude lithium chloride. Add the crude lithium chloride to 30 g of ethanol solution for dissolution, and after the dissolution is completed, filter, evaporate and crystallize to obtain 20.7 g of lithium chloride with a purity of 99.97%.

[0070] In this experiment, 220 g of lithium sulfate was put in, and the equivalent lithium was 27.79 g. 129.58 g of lithium carbonate with a purity of 99.57% was obtained, and the equivalent lithium was 24.24 g. That is, the remaining equivalent lithium in the lithium carbonate filtrate (i.e., the lithium precipitation filtrate) was 3.55 g. After subsequent recovery, 20.7 g of lithium chloride with a purity of 99.97% was produced, and the equivalent lithium was 3.39 g. The residual lithium recovery rate in the solution was Q1 = 3.39 / 3.55 * 100 = 95.5%.

[0071] Example 2

[0072] Add 7.96 g of a 5% sodium hydroxide solution to 1 L of a lithium sulfate solution with a concentration of 245 g / L to adjust the pH of the solution to 12. Then add 0.9 L of a sodium carbonate solution with a concentration of 270 g / L and react at 85 °C for 0.5 h. After the reaction, filter to obtain crude lithium carbonate and the filtrate obtained from the reaction (lithium precipitation filtrate). Wash the crude lithium carbonate three times with deionized water to obtain 145.33 g of lithium carbonate with a purity of 99.62%.

[0073] Add 22.91 g of 10 wt% sulfuric acid to the filtrate obtained from the reaction to adjust the pH to 8. At this time, the measured lithium ion concentration is 1.902 g / L. Flow the filtrate obtained after adjusting the pH through 115 g of H2TiO3 ion sieve at a flow rate of 6 BV / h for lithium adsorption. The ion sieve used is in powder form, and 90% of the particle size is between 1 - 3 μm, with an average particle size of about 1.8 microns. Test the sodium sulfate solution obtained after lithium adsorption, and its lithium content drops to 3 mg / L, which is about 634 times lower than the lithium ion content before adsorption (1.902 g / L). Add 21.85 g of 30% sulfuric acid to the adsorbed sodium sulfate solution, and then evaporate and crystallize to obtain 326.87 g of high-purity sodium sulfate with a purity of 99.91%. The results are shown in Table 1.

[0074] Perform a delithiation reaction on the lithium adsorbent with 1.25 L of 0.5 mol / L hydrochloric acid. Add 61.27 g of 25% sodium hydroxide solution to the delithiated solution (crude lithium chloride solution) and then filter to remove impurities. After impurity removal, evaporate and crystallize the filtrate to obtain crude lithium chloride. Add the crude lithium chloride to 40 g of ethanol solution for dissolution. After dissolution, filter and evaporate and crystallize to obtain 21.2 g of lithium chloride with a purity of 99.94%.

[0075] In this experiment, 245 g of lithium sulfate was input, and the equivalent lithium was 30.95 g. 145.33 g of lithium carbonate with a purity of 99.62% was obtained, and the equivalent lithium was 27.20 g. That is, the remaining equivalent lithium in the lithium carbonate filtrate (i.e., the lithium precipitation filtrate) was 3.75 g. After subsequent recovery, 21.2 g of lithium chloride with a purity of 99.94% was produced, and the equivalent lithium was 3.47 g. The recovery rate of residual lithium in the solution was Q1 = 3.47 / 3.75 * 100 = 92.5%.

[0076] Comparative Example 1 (without acid addition to adjust the pH treatment, and directly using the adsorbent to extract lithium from the lithium precipitation filtrate)

[0077] Add 1.22 g of a 5% sodium hydroxide solution to 1 L of a lithium sulfate solution with a concentration of 220 g / L to adjust the pH of the solution to 11.2. Then add 0.86 L of a sodium carbonate solution with a concentration of 260 g / L and react at 85 °C for 0.5 h. After the reaction, perform a filtration operation to obtain lithium carbonate and filtrate. Wash the lithium carbonate three times with deionized water to obtain 130.46 g of lithium carbonate with a purity of 99.28%. Test the lithium ion concentration in the filtrate after lithium precipitation, which is 1.913 g / L and the pH is 11.2. Without adjusting the pH of the filtrate, directly flow it through 580 g of the same ion sieve as in Example 1 at a flow rate of 3.5 BV / h. Test the sodium sulfate solution obtained by adsorption and lithium extraction, and its lithium content is 58 mg / L, which is only reduced by 32.98 times compared to the lithium ion content before adsorption. Add 33.38 g of 30% sulfuric acid to the adsorbed sodium sulfate solution, and then evaporate and crystallize to obtain 303.75 g of sodium sulfate with a purity of 98.28%.

[0078] In Example 1, the filtrate after lithium precipitation was adjusted in pH and then the lithium was adsorbed and extracted using an ion sieve. After adsorption, the lithium ion content was significantly reduced by 950 times. In addition, the purity of sodium sulfate obtained using sulfuric acid reached 99.93%. In Comparative Example 1, the filtrate after lithium precipitation was directly adsorbed and extracted using an ion sieve without pH adjustment, and its lithium ion content was only reduced by 32.98 times, and the purity of the obtained sodium sulfate was only 98.28%. This shows that adjusting the pH of the filtrate after lithium precipitation and then performing molecular sieve adsorption and lithium extraction can significantly improve the lithium ion adsorption efficiency. This may be because directly performing adsorbent lithium extraction on the filtrate results in a relatively high pH and a strong alkaline environment, which can damage the adsorbent, leading to a decrease in adsorption performance and thus a decrease in the adsorption capacity. In the experiment, it was also observed that there was a phenomenon of dissolution and loss of the adsorbent. Moreover, the purity of sodium sulfate in Example 1 was higher, indicating that using H in the adsorbent + can achieve a good impurity removal effect and Li + is effectively adsorbed.

[0079] Comparative Example 2 (adjust the pH to 7 with acid)

[0080] Add 1.22 g of a 5% sodium hydroxide solution to 1 L of a lithium sulfate solution with a concentration of 220 g / L to adjust the pH of the solution to 11.2. Then add 0.86 L of a sodium carbonate solution with a concentration of 260 g / L and react at 85 °C for 0.5 h. After the reaction, perform a filtration operation to obtain lithium carbonate and filtrate. Wash the lithium carbonate three times with deionized water to obtain 130.91 g of lithium carbonate with a purity of 99.31%. Add 350.31 g of 10 wt% sulfuric acid to the filtrate obtained from the reaction to adjust the pH to 7. Measure the lithium ion concentration in the filtrate, which is 1.904 g / L. Flow the filtrate obtained by adjusting the pH through a manganese dioxide ion sieve for adsorption and lithium extraction in the same way as in Example 1. Test the sodium sulfate solution obtained by adsorption and lithium extraction, and its lithium content is reduced to 635 mg / L, and its lithium ion content is only reduced by 3 times.

[0081] After evaporating, crystallizing, washing, and drying the adsorbed sodium sulfate solution, 311.69 g of sodium sulfate with a purity of 95.78% was obtained. Compared with Example 1, the total sulfuric acid consumption in Comparative Example 2 was 0.357 mol, and the total sulfuric acid consumption in Example 1 was 0.102 mol. The sulfuric acid consumption in Comparative Example 2 increased significantly by 250%. The lithium ions in the solution after molecular sieve adsorption still maintained a relatively high content, indicating a poor lithium adsorption effect. This may be mainly because the initial pH was neutral, and as the H + was displaced, the whole system changed towards acidity, reducing the adsorption capacity of the adsorbent; moreover, the purity of sodium sulfate was low, and the impurity removal effect was also poor. The main reason for the low purity of the obtained sodium sulfate was that the unadsorbed residual lithium ions in the solution entered the sodium sulfate.

[0082] Table 1

[0083]

[0084] Combined with Table 1, by comparing Example 1, 2 with Comparative Example 1, it can be seen that in Comparative Example 1, the lithium precipitation filtrate was directly subjected to lithium ion adsorption by the lithium ion adsorbent without adjusting the pH. The alkalinity was too strong, and the lithium extraction effect was poor. This may be because the alkalinity was too strong, resulting in damage to the adsorbent; moreover, the purity of sodium sulfate in Comparative Example 1 was also relatively low, indicating that the use of H in the adsorbent + had a good impurity removal effect on CO3 2- .

[0085] By comparing Example 1, 2 with Comparative Example 2, it can be seen that when the pH was controlled in the range of 8 - 10, the lithium extraction effect was significantly improved. This may be because after the adsorbent removed H + , it combined with CO3 2- , making the whole adsorption Li + process, the adsorbent was in a suitable alkaline condition, so it had good adsorption performance; moreover, the purity of sodium sulfate was also better. This was because not only Li + was effectively adsorbed, but also CO3 2- could react with the H + removed by the adsorbent, having an impurity removal effect; and the amount of acid added to the lithium precipitation filtrate in the examples was also very small. For example, adding acid to adjust the pH to 7 - 8 in the comparative examples would consume a large amount of sulfuric acid.

[0086] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for recovering residual lithium elements in the lithium precipitation filtrate of the lithium carbonate precipitation process from lithium sulfate, characterized in that, The lithium sulfate precipitation lithium carbonate process comprises: subjecting lithium sulfate solution to lithium precipitation reaction with sodium hydroxide solution and sodium carbonate solution, filtering to obtain crude lithium carbonate and lithium precipitation filtrate; The recovery method comprises at least the following steps: S100. Add an acid to the lithium precipitation filtrate to adjust the pH to 8 - 10, then add an adsorbent to adsorb and extract lithium to obtain a sodium sulfate solution and a lithium-containing adsorbent; the adsorbent is a lithium ion adsorbent, and when the lithium ion adsorbent adsorbs Li + it will displace H + ; the concentration of lithium ions in the lithium precipitation filtrate is 1.8 g / L to 2.0 g / L; Adding acid to the sodium sulfate solution, and evaporating and crystallizing to obtain high-purity anhydrous sodium sulfate; S200, removing lithium from the lithium-containing adsorbent with acid to obtain a crude lithium chloride solution; S300, alkalizing and removing impurities from the crude lithium chloride solution, filtering, and obtaining a filtrate; The filtrate contains Li + , Cl - and impurity cations; S400. Perform first evaporation crystallization on the filtrate to obtain crude lithium chloride crystals. After dissolving the crude lithium chloride crystals in an organic solvent, filter to obtain a recovery liquid containing Li + and Cl - . The organic solvent is selected from absolute ethanol and / or absolute acetone; S500, subjecting the recovered liquid to a second evaporation crystallization to obtain high-purity lithium chloride.

2. The recycling method according to claim 1, wherein In step S100, the acid added to the lithium precipitation filtrate includes a sulfuric acid solution, and the mass concentration of the sulfuric acid solution is 1wt%~10wt%.

3. The recovery method according to claim 1, wherein In step S100, the adsorbent includes any one of manganese dioxide ion sieve, titanium oxide ion sieve, high-valent amorphous phosphate, hydrated SnO2, and amorphous Al(OH)3.

4. The recycling method according to claim 1, characterized in that The adsorbent is manganese dioxide ion sieve. The lithium precipitation filtrate after pH adjustment flows through the manganese dioxide ion sieve at a flow rate of 3 BV / h to 4 BV / h for lithium adsorption. The manganese dioxide ion sieve is granular, and its bulk density is 70 g / cm 3 to 75 g / cm 3 .

5. The recovery method according to claim 1, characterized in that, The adsorbent is titanium oxide ion sieve. The lithium precipitation filtrate after pH adjustment flows through the titanium oxide ion sieve at a flow rate of 5BV / h to 7BV / h for adsorption and lithium extraction. The titanium oxide ion sieve is in powder form, 90% of which has a particle size between 1μm and 3μm, and an average particle size of 1.6μm to 1.8μm.

6. The recovery method according to claim 1, wherein In step S200, the acid-eluting lithium removal includes: mixing the lithium-containing adsorbent and a hydrochloric acid solution to perform a lithium removal reaction, wherein the concentration range of the hydrochloric acid solution is 0.01 mol / L to 1 mol / L, and the adsorbent after lithium removal is returned to step S100 to continue to adsorb and extract lithium.

7. The recovery method according to claim 1, wherein In step S300, the alkalization and impurity removal includes: adding alkali to the crude lithium chloride solution to adjust the pH to 7-8.

8. The recycling method according to claim 1, characterized in that In step S300, the alkali used in the alkalization and impurity removal includes at least one of a sodium hydroxide solution, a lithium hydroxide solution, and a sodium carbonate solution.

9. The recovery method according to claim 1, characterized in that The alkali used in the alkalization and impurity removal includes a sodium hydroxide solution with a mass content of 20wt% to 25wt%.

10. The recycling method according to claim 1, wherein In step S500, the organic solvent obtained by the second evaporation and crystallization of the recovered liquid is returned to step S400 to dissolve the crude lithium chloride crystals; Wherein, the temperature range of the second evaporation crystallization is 100°C~280°C.

11. The recycling method according to claim 1, characterized in that, In the lithium sulfate precipitation lithium carbonate process, the concentration of the lithium sulfate solution is 200g / L~260g / L, and the concentration of the sodium carbonate solution is 150g / L~300g / L.

12. The recovery method according to claim 1, wherein The molar ratio of sodium carbonate in the sodium carbonate solution to lithium sulfate in the lithium sulfate solution is 1.0-1.

2.

13. The recovery method according to claim 1, characterized in that, The conditions of the lithium precipitation reaction include: Lithium deposition temperature: 15℃~98℃; Reaction time: 0.2h~3h.

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