WO2025051228A1 - Method for extracting lithium carbonate from lithium-containing solution - Google Patents

Abstract

The disclosure relates to the field of lithium recovery. A method for extracting lithium carbonate from a lithium-containing solution is disclosed. The method comprises the following steps: S1, carrying out primary concentration and reduced-temperature potassium precipitation on a lithium-containing solution; S2, increasing the temperature of the potassium-precipitated solution obtained in S1, carrying out primary lithium precipitation, and carrying out solid-liquid separation to obtain a lithium carbonate product 1 and a lithium-precipitated mother solution 1; S3, carrying out secondary concentration on the lithium-precipitated mother solution 1; S4, freezing the concentrated solution obtained in S3; S5, carrying out impurity removal on the frozen solution obtained in step S4; and S6, carrying out secondary lithium precipitation on the purified solution obtained in step S5, and carrying out solid-liquid separation to obtain a lithium carbonate product 2 and a lithium-precipitated mother solution 2; wherein the lithium-precipitated mother solution 2 is then returned to S1.

Description

Method for extracting lithium carbonate from lithium-containing solution

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims the priority benefit of Chinese patent application No. 202311150665.6 filed on September 6, 2023, and incorporates the entirety of the patent application into this document.

Technical Field

The present invention relates to the field of lithium recovery, and in particular to a method for extracting lithium carbonate from a lithium-containing solution.

Background Art

Lithium is an important energy metal, known as "white oil", with a wide range of uses, and is becoming a new driving force for the development of world energy. At present, China has basically established a modern basic lithium industry based on lithium extraction from ores and brine, covering a series of products such as lithium carbonate, lithium chloride, lithium hydroxide, and lithium metal. At present, the raw materials used in the industry to extract lithium from ores are generally spodumene (Li ₂ O>5.0%), petalite (Li ₂ O>5.0%), lepidolite (Li ₂ O>2.5%), lithium aluminum phosphate (Li ₂ O>5.5%), etc., which have a high Li ₂ O content and less impurity ions in the solution. At present, there are relatively mature recovery processes in the industry. However, since the end of 2019, the price of lithium salts has continued to rise. In the context of high-quality lithium ore resources being monopolized by only a few high-quality lithium mining companies at home and abroad, research on lithium extraction technology from low-grade lithium mica (Li ₂ O <1.5%) and low-grade lithium-containing waste slag has attracted more and more attention. Low-grade lithium resources usually contain a large amount of impurity elements such as Na, K, Rb, Cs, Al, Si, and Ca. Taking low-grade lithium mica (Li ₂ O <1.5%) as the raw material as an example, lithium mica generally contains 6-10% potassium, the single Li content in the lithium extraction solution is usually between 2g/L-5g/L, the K content is usually between 25g/L-50g/L, and the Na content is usually between 20g/L-50g/L. The potassium and sodium content of the solution is nearly ten times higher than the lithium content.

Therefore, it is particularly important to develop a technically feasible and industrially feasible method for extracting lithium from a low-lithium, high-potassium, and high-sodium solution.

Summary of the invention

The purpose of the present invention is to overcome the problems of the prior art in that the process of extracting lithium from a low-lithium-containing solution is complicated, the direct yield is low, and the economic benefits are poor, and to provide a method for extracting lithium carbonate from a lithium-containing solution, which can efficiently separate the lithium-containing solution and obtain a high-quality lithium carbonate product.

In order to achieve the above object, the present disclosure provides a method for extracting lithium carbonate from a lithium-containing solution, wherein the method comprises the following steps:

S1, concentrating and cooling the lithium-containing solution to precipitate potassium, and performing solid-liquid separation to obtain a potassium precipitation solution and a mixed salt 1;

S2, heating the potassium precipitation solution and precipitating lithium once, and obtaining lithium carbonate product 1 and lithium precipitation mother by secondary solid-liquid separation. Liquid 1;

S3, the lithium precipitation mother liquor 1 is concentrated twice, and a concentrated solution and a mixed salt 2 are obtained by three solid-liquid separations;

S4, freezing the concentrated solution, and obtaining potassium sodium mirabilite and a frozen solution through four solid-liquid separations;

S5, removing impurities from the frozen liquid to obtain a purified liquid;

S6, subjecting the purified liquid to secondary lithium precipitation, and obtaining a lithium carbonate product 2 and a lithium precipitation mother liquor 2 after five solid-liquid separations; wherein the lithium precipitation mother liquor 2 is returned to S1.

Through the above technical solution, the beneficial effects of the present disclosure are:

The method for extracting lithium carbonate from a lithium-containing solution provided by the present invention comprises the steps of primary concentration and reverse heating, primary lithium precipitation, secondary concentration, freezing and separating sodium sulfate, purification and impurity removal, secondary lithium precipitation, etc., thereby realizing efficient separation of a low-lithium, high-potassium, and high-sodium solution.

The present invention adopts a process including one concentration, reverse heating and one lithium precipitation. The reverse heating means cooling down first to precipitate potassium and then heating up the potassium precipitation solution. On the one hand, the concentration of lithium sulfate in the lithium-containing solution is increased; on the other hand, a portion of potassium sulfate salt with higher purity is precipitated; on the third hand, in the pre-liquid for the one lithium precipitation, the mixed salt 1 (potassium sulfate and sodium sulfate) is in an unsaturated state, avoiding the lithium carbonate peritectic phenomenon during the lithium precipitation process caused by the crystallization of potassium sulfate and sodium sulfate, thereby improving the quality of the lithium carbonate product. The lithium _carbonate product 1 obtained by the one lithium precipitation has a percentage of _Li2CO3 component greater than or equal to 99.5wt% after stirring and washing.

The present invention adopts freezing and precipitation of mirabilite, purification and impurity removal, and secondary lithium precipitation processes to achieve deep removal of potassium and sodium salts and impurity ions. The lithium carbonate product 2 obtained by secondary lithium precipitation directly reaches the battery-grade lithium carbonate level after stirring and washing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of a method for extracting lithium carbonate from a lithium-containing solution in a specific embodiment of the present disclosure.

DETAILED DESCRIPTION

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

The present disclosure provides a method for extracting lithium carbonate from a lithium-containing solution, wherein the method comprises the following steps:

S1, concentrating and cooling the lithium-containing solution to precipitate potassium, and performing solid-liquid separation to obtain a potassium precipitation solution and a mixed salt 1;

S2, heating the potassium precipitation solution and subjecting it to primary lithium precipitation, and obtaining a lithium carbonate product 1 and a lithium precipitation mother liquor 1 through secondary solid-liquid separation;

S3, the lithium precipitation mother liquor 1 is concentrated twice, and a concentrated solution and a mixed salt 2 are obtained by three solid-liquid separations;

S4, freezing the concentrated solution, and obtaining potassium sodium mirabilite and a frozen solution through four solid-liquid separations;

S5, removing impurities from the frozen liquid to obtain a purified liquid;

S6, subjecting the purified liquid to secondary lithium precipitation, and obtaining a lithium carbonate product 2 and a lithium precipitation mother liquor 2 after five solid-liquid separations; wherein the lithium precipitation mother liquor 2 is returned to S1.

The lithium-containing solution is concentrated and cooled for potassium precipitation, and then solid-liquid separation is performed to obtain a mixed salt 1 (potassium sulfate and sodium sulfate) and a potassium precipitation solution. The concentration of lithium sulfate in the lithium-containing solution is increased by the first concentration; a portion of potassium sulfate with higher purity can be precipitated by cooling and potassium precipitation, and a small amount of sodium sulfate can also be precipitated; the potassium precipitation solution is heated and then lithium precipitation is performed again, so that part of the potassium sulfate and sodium sulfate fine crystals precipitated by the potassium precipitation solution are redissolved, and the potassium sulfate and sodium sulfate in the potassium precipitation solution are in an unsaturated state, avoiding the lithium carbonate peritectic phenomenon caused by the crystallization of potassium sulfate and sodium sulfate during the first lithium precipitation process, thereby improving the quality of the lithium carbonate product 1 obtained by the first lithium precipitation. The second concentration of the lithium precipitation mother liquor 1 can further increase the concentration of lithium ions and precipitate sodium sulfate. After the lithium precipitation mother liquor 1 is concentrated for the second time, solid-liquid separation is performed to obtain a mixed salt 2 of potassium sulfate and sodium sulfate (since more potassium sulfate has been precipitated in the first concentration, the sodium sulfate salt accounts for a larger proportion of the mixed salt precipitated in the second concentration) and a concentrated solution. The concentrated solution is frozen and crystallized to precipitate sodium and potassium sulfate (K ₃ Na(SO ₄ ) ₂ ·10H ₂ O), and potassium and sodium sulfate and frozen solution are obtained by solid-liquid separation. The frozen solution is impurity-removed to remove impurities including fluorine, silicon, calcium, magnesium and aluminum to obtain a purified solution. Only a part of the lithium can be precipitated in the first lithium precipitation. This is because as the lithium precipitation proceeds, the lithium concentration in the potassium precipitation solution gradually decreases. At this time, no matter how much lithium precipitation agent is added to precipitate lithium, the lithium will not be converted. Therefore, a second lithium precipitation is performed after impurity removal.

According to the present disclosure, in S1, the process of one concentration includes: evaporating the lithium-containing solution at an evaporation ratio of (1-6): 1. In some embodiments of the present disclosure, the evaporation ratio is (2-5): 1. It refers to the flow ratio of the lithium-containing solution and the concentrated solution obtained by the one concentration during evaporation concentration. One concentration at this evaporation ratio can increase the lithium ion concentration of the lithium-containing solution and ensure the direct recovery rate of lithium carbonate in the one lithium precipitation process.

According to an embodiment of the present disclosure, both the primary concentration and the secondary concentration are evaporated using a mechanical vapor recompression evaporation system (MVR system); the evaporation ratio is the ratio of the inlet flow rate to the outlet flow rate of the MVR system.

According to an embodiment of the present disclosure, the process of cooling potassium precipitation includes: cooling the liquid product obtained by evaporation to 0-60° C. In some embodiments of the present disclosure, the liquid product obtained by evaporation is cooled to 30-60° C. Cooling to this temperature can ensure that most of the potassium salt is precipitated while the subsequent comprehensive energy consumption of heating is low.

According to one embodiment of the present disclosure, in the lithium-containing solution, the content of lithium ions is less than or equal to 5 g/L, the content of potassium ions is greater than or equal to 25 g/L, and the content of sodium ions is greater than or equal to 25 g/L. For the lithium-containing solution whose contents of lithium ions, potassium ions and sodium ions meet the above conditions, the method for extracting lithium carbonate provided by the present disclosure can obtain a lithium carbonate product of high quality.

According to one embodiment of the present disclosure, the heating process includes: heating the potassium precipitation solution to 65-95° C. In one embodiment of the present disclosure, the potassium precipitation solution is heated to 75-95° C. Heating the potassium precipitation solution to this temperature can redissolve the precipitated fine-crystalline potassium sulfate salt and sodium sulfate salt.

According to the present disclosure, preferably, in S2, the process of primary lithium precipitation includes: mixing the potassium precipitation solution and the sodium carbonate aqueous solution 1 for reaction.

According to one embodiment of the present disclosure, the content of sodium carbonate in the sodium carbonate aqueous solution 1 is 15-32wt%, and the temperature of the sodium carbonate aqueous solution 1 is 80-90° C. When the content of sodium carbonate in the sodium carbonate aqueous solution 1 meets this range, the direct recovery rate of lithium can be improved, and the content of impurities wrapped by lithium carbonate is less; when the temperature of the sodium carbonate aqueous solution 1 meets this range, the lithium precipitation reaction can be promoted.

According to one embodiment of the present disclosure, based on the weight of the potassium precipitation liquid being 100 g, the amount of the sodium carbonate aqueous solution 1 is 30-50 g.

According to one embodiment of the present disclosure, in S3, the secondary concentration process includes: evaporating the lithium precipitation mother liquor 1 at an evaporation ratio of (1-6): 1. In one embodiment of the present disclosure, the lithium precipitation mother liquor 1 is evaporated at an evaporation ratio of (2-5): 1. The primary concentration at this evaporation ratio can increase the concentration of lithium, so that the secondary lithium precipitation can precipitate a high-quality lithium carbonate product, and at the same time, sodium sulfate can be precipitated.

According to one embodiment of the present disclosure, in S4, the freezing temperature is -5°C to 15°C. In one embodiment of the present disclosure, the freezing temperature is -5°C to 10°C. Within the above freezing temperature range, a higher potassium sodium and sodium salt precipitation efficiency can be ensured, and mother liquor freezing can be avoided, so that the secondary lithium precipitation can obtain higher quality lithium carbonate.

According to an embodiment of the present disclosure, in S5, the impurity removal process includes:

The refrigerant is mixed with an alkaline oxide for primary purification;

The liquid product obtained from the primary purification and the mixed alkali solution are subjected to secondary purification;

The liquid phase product obtained by the secondary purification is contacted with an ion exchange resin for tertiary purification to obtain a purified liquid.

The refrigerant is subjected to primary purification using alkaline oxides to remove fluorine and silicon from the refrigerant; the liquid product obtained by the primary purification is subjected to secondary purification by adjusting the pH with alkaline solution to remove impurities such as calcium, magnesium and aluminum from the refrigerant; the liquid product obtained by the secondary purification is contacted with ion exchange resins for tertiary purification to further remove impurities such as calcium and magnesium from the refrigerant.

According to one embodiment of the present disclosure, the conditions for primary purification include: pH value of 7-14, time of 0.5-3h, temperature of 25-95°C, wherein the pH value is the pH value of a mixed system of a freezing liquid and an alkaline oxide.

According to one embodiment of the present disclosure, the conditions for primary purification include: pH value of 9-12; time of 0.5-1.5h; temperature of 55-85°C; wherein the pH value is the pH value of a mixed system of a freezing liquid and an alkaline oxide.

According to one embodiment of the present disclosure, the conditions for secondary purification include: pH value of 7-14, time of 0.5-3h, temperature of 25-95°C, wherein the pH value is the pH value of the mixed system of the liquid product obtained by primary purification and the alkali solution.

According to an embodiment of the present disclosure, the conditions for secondary purification include: pH value of 9-12, time of 0.5-2h, temperature of 55-85° C. The pH value is the pH value of the mixed system of the liquid product obtained by primary purification and the alkali solution.

According to one embodiment of the present disclosure, the concentrations of Ca ²⁺ and Mg ²⁺ in the purified solution are independently less than or equal to 1mg/L.

According to one embodiment of the present disclosure, the basic oxide includes magnesium oxide and/or calcium oxide.

According to one embodiment of the present disclosure, the alkali solution includes sodium hydroxide and/or sodium carbonate.

According to one embodiment of the present disclosure, the ion exchange resin is selected from chelating ion exchange resins having an average pore size of 0.3-0.8 mm.

According to an embodiment of the present disclosure, in S6, the process of secondary lithium precipitation includes: mixing the purified liquid and the sodium carbonate aqueous solution 2 to react.

According to one embodiment of the present disclosure, based on the weight of the purified liquid being 100 g, the amount of the sodium carbonate aqueous solution 2 used is 60-80 g.

According to one embodiment of the present disclosure, the content of sodium carbonate in the sodium carbonate aqueous solution 2 is 15-32 wt %, and the temperature of the sodium carbonate aqueous solution 2 is 80-90° C.

According to one embodiment of the present disclosure, the method further comprises: washing the lithium carbonate product 1 with water at least once, preferably twice or more, and more preferably twice.

According to one embodiment of the present disclosure, the weight ratio of the lithium carbonate product 1 to water is 1:(2-10), preferably 1:(4-8).

According to one embodiment of the present disclosure, the method further includes: washing the lithium carbonate product 2 with water at least once. In some embodiments of the present disclosure, the lithium carbonate product 2 is washed with water more than twice. In some embodiments of the present disclosure, the lithium carbonate product 2 is washed with water twice.

According to one embodiment of the present disclosure, the weight ratio of the lithium carbonate product 2 to water is 1:(2-10). In some embodiments of the present disclosure, the weight ratio of the lithium carbonate product 2 to water is 1:(4-8).

According to one embodiment of the present disclosure, the content of lithium carbonate in the lithium carbonate product 1 is greater than or equal to 99.5 wt %.

According to one embodiment of the present disclosure, the lithium carbonate product 2 is battery-grade lithium carbonate.

In the present disclosure, the first solid-liquid separation, the second solid-liquid separation, the third solid-liquid separation, the fourth solid-liquid separation and the fifth solid-liquid separation can be performed by conventional methods in the art, for example, by filtering.

According to a specific embodiment of the present disclosure, as shown in FIG1 , a method for extracting lithium carbonate from a lithium-containing solution comprises the following steps:

S1, pumping the lithium-containing solution into the MVR system for evaporation (primary concentration), controlling the evaporation ratio (inlet flow rate/outlet flow rate) to (1-6): 1; cooling the concentrated liquid product to 0-60°C, cooling and precipitating potassium salt, and filtering to obtain potassium precipitation liquid;

S2, pumping the potassium precipitation solution into a heating tank and heating it to 65-95°C; adding the heated potassium precipitation solution to a sodium carbonate aqueous solution 1 with a concentration of 15-32wt% and a temperature of 80-90°C to precipitate lithium once (based on the weight of the potassium precipitation solution being 100g, the amount of the sodium carbonate aqueous solution 1 is 30-50g), and filtering to obtain a solid product and a lithium precipitation mother liquor 1; adding a liquid-to-solid ratio of (2-10): 1 The solid product was counter-currently washed twice with water to obtain a lithium carbonate product 1;

S3, pumping the lithium precipitation mother liquor 1 into the MVR system for evaporation and salt precipitation (secondary concentration), controlling the evaporation ratio (inlet flow/outlet flow) to (1-6): 1, and obtaining a concentrated solution by filtration;

S4, pumping the concentrated liquid into a freezing crystallization system, controlling the freezing temperature at -5°C to 15°C, and filtering to obtain potassium sodium mirabilite and frozen liquid;

S5, the frozen liquid is mixed with alkaline oxides for primary purification to remove fluorine and silicon, the pH value of the mixed system is controlled to be 7-14, the purification time is 0.5-3h, the purification temperature is 25-95°C, and purified liquid 1 and purified residue 1 are obtained by filtration; the purified liquid 1 is adjusted to pH with alkali solution for secondary purification to remove impurities such as calcium, magnesium and aluminum, the pH value of the system is controlled to be 7-14, the purification time is 0.5-3h, the purification temperature is 25-95°C, and purified liquid 2 and purified residue 2 are obtained by filtration; the purified liquid 2 is contacted with a chelating ion exchange resin with an average pore size of 0.3-0.8mm for tertiary purification to deeply remove impurities such as calcium and magnesium to obtain purified liquid 3; the concentrations of Ca2 ⁺ and Mg2 ⁺ in the purified liquid 3 are both less than or equal to 1mg/L;

S6, pump the purified liquid 3 into a heating tank, and then add it to a sodium carbonate aqueous solution 2 with a concentration of 15-32wt% and a temperature of 80-90°C for secondary lithium precipitation (based on the weight of the purified liquid 3 being 100g, the amount of the sodium carbonate aqueous solution 2 is 60-80g), and obtain a lithium carbonate product 2 and a lithium precipitation mother liquor 2 after filtration; add water with a liquid-to-solid ratio of (2-10):1 to countercurrent wash the lithium carbonate product 2 twice; the lithium precipitation mother liquor 2 is returned to S1.

The present disclosure will be described in detail below through examples and comparative examples. In the following examples, unless otherwise specified, all methods are conventional methods; and the reagents and materials used, unless otherwise specified, can be obtained from commercial sources.

The purity of Li ₂ CO ₃ , the mass percentage of Na, K and SO ₄ ^2- are determined in accordance with GB/T 11064-2013 "Chemical analysis method for lithium carbonate, lithium hydroxide monohydrate and lithium chloride".

The chemical compositions of the lithium-containing solutions of the embodiments and comparative examples are shown in Table 1.

Table 1

The following examples are used to illustrate the method for extracting lithium carbonate from a lithium-containing solution.

Example 1

S1. Pump the lithium-containing solution into the MVR system for evaporation (one-time concentration), and control the evaporation ratio (flow rate of the lithium-containing solution/flow rate of the concentrated solution obtained by the one-time concentration) to be 3:1; cool the concentrated liquid product to 60°C, cool it down to precipitate potassium salt, and obtain potassium precipitation liquid by filtration;

S2, pumping the potassium precipitation solution into a heating tank and heating it to 90°C; adding the heated potassium precipitation solution to a sodium carbonate aqueous solution 1 with a concentration of 20wt% and a temperature of 90°C to precipitate lithium once (based on the weight of the potassium precipitation solution being 100g, the amount of the sodium carbonate aqueous solution 1 is 50g), and filtering to obtain a solid product and a lithium precipitation mother liquor 1; adding water with a liquid-to-solid ratio of 5:1 to precipitate lithium on the solid product; Perform two countercurrent washings to obtain lithium carbonate product 1;

S3, pumping lithium precipitation mother liquor 1 into the MVR system for evaporation and salt precipitation (secondary concentration), controlling the evaporation ratio (inlet flow/outlet flow) to 3.5:1, and obtaining a concentrated solution by filtration;

S4, pumping the concentrated liquid into a freezing crystallization system, controlling the freezing temperature at 10°C, and filtering to obtain potassium sodium mirabilite and freezing liquid;

S5, the frozen liquid is mixed with calcium oxide for primary purification to remove fluorine and silicon, the pH value of the mixed system is controlled to be 10, the purification time is 1h, the purification temperature is 85°C, and purified liquid 1 and purified slag 1 are obtained by filtration; the purified liquid 1 is adjusted to pH by a mixed solution of sodium hydroxide and sodium carbonate (the content of sodium hydroxide in the mixed solution is 20wt%, and the content of sodium carbonate is 32wt%) for secondary purification to remove impurities such as calcium, magnesium and aluminum, the pH value of the system is controlled to be 12, the purification time is 1h, the purification temperature is 85°C, and purified liquid 2 and purified slag 2 are obtained by filtration; the purified liquid 2 is contacted with a chelating ion exchange resin with an average pore size of 0.3mm for tertiary purification to deeply remove impurities such as calcium and magnesium to obtain purified liquid 3; the concentrations of Ca2 ⁺ and Mg2 ⁺ in the purified liquid 3 are 0.5mg/L and 0.2mg/L, respectively;

S6, pump the purified liquid 3 into a heating tank, control the temperature of the purified liquid 3 at 90°C, and then add it to a sodium carbonate aqueous solution 2 with a concentration of 32wt% and a temperature of 90°C for secondary lithium precipitation (based on the weight of the purified liquid 3 being 100g, the amount of the sodium carbonate aqueous solution 2 is 70g), and obtain a lithium carbonate product 2 and a lithium precipitation mother liquor 2 after filtration; add water with a liquid-to-solid ratio of 5:1 to countercurrent wash the lithium carbonate product 2 twice; the lithium precipitation mother liquor 2 is returned to S1.

Example 2

S1. Pump the lithium-containing solution into the MVR system for evaporation (one-time concentration), and control the evaporation ratio (flow rate of the lithium-containing solution/flow rate of the concentrated solution obtained by the one-time concentration) to be 4:1; cool the concentrated liquid product to 35°C, cool it down to precipitate potassium salt, and obtain potassium precipitation liquid by filtration;

S2-S6 are the same as in Example 1; wherein the concentrations of Ca ²⁺ and Mg ²⁺ in the purified solution 3 obtained in S5 are 0.5 mg/L and 0.2 mg/L, respectively.

Obtain lithium carbonate product 1 and lithium carbonate product 2.

Example 3

S1. Pump the lithium-containing solution into the MVR system for evaporation (one-time concentration), and control the evaporation ratio (flow rate of the lithium-containing solution/flow rate of the concentrated solution obtained by the one-time concentration) to be 3.5:1; cool the concentrated liquid product to 40°C, cool it down to precipitate potassium salt, and obtain potassium precipitation liquid by filtration;

S2 is the same as in Example 1; obtaining lithium carbonate product 1;

S3, pumping lithium precipitation mother liquor 1 into the MVR system for evaporation and salt precipitation (secondary concentration), controlling the evaporation ratio (inlet flow/outlet flow) to 4:1, and obtaining a concentrated solution by filtration;

S4, pumping the concentrated liquid into a freezing crystallization system, controlling the freezing temperature at 0°C, and filtering to obtain potassium sodium mirabilite and frozen liquid;

S5 is the same as in Example 1, and the concentrations of Ca ²⁺ and Mg ²⁺ in the purified solution 3 obtained are 0.5 mg/L and 0.2 mg/L respectively;

S6 is the same as in Example 1; lithium carbonate product 2 is obtained.

Example 4

Lithium carbonate is extracted from the lithium-containing solution according to the method of Example 1, except that the evaporation ratio of the primary concentration is different. Specifically, in S1, the evaporation ratio (flow rate of the lithium-containing solution/flow rate of the concentrated solution obtained by the primary concentration) is controlled to be 6:1. The concentrations of Ca ²⁺ and Mg ²⁺ in the obtained purified solution 3 are 0.5 mg/L and 0.2 mg/L, respectively; lithium carbonate product 1 is obtained, and then lithium carbonate product 2 is obtained.

Example 5

Lithium carbonate is extracted from a lithium-containing solution according to the method of Example 1, except that the temperature for cooling and precipitating potassium salt is different. Specifically, in S1, the concentrated liquid product is cooled to 65°C and cooled to precipitate potassium salt. The concentrations of Ca ²⁺ and Mg ²⁺ in the obtained purified solution 3 are 0.5 mg/L and 0.3 mg/L, respectively; lithium carbonate product 1 is obtained, and then lithium carbonate product 2 is obtained.

Example 6

Lithium carbonate was extracted from the lithium-containing solution according to the method of Example 1, except that in S2, the potassium precipitation solution was pumped into the heating tank and heated to 70° C. The concentrations of Ca ²⁺ and Mg ²⁺ in the obtained purified solution 3 were 0.5 mg/L and 0.2 mg/L, respectively; lithium carbonate product 1 was obtained, and then lithium carbonate product 2 was obtained.

Example 7

Lithium carbonate was extracted from the lithium-containing solution according to the method of Example 1, except that the evaporation ratio of the secondary concentration was different. Specifically, in S3, the evaporation ratio (inlet flow rate/outlet flow rate) was controlled to be 6:1. The concentrations of Ca ²⁺ and Mg ²⁺ in the obtained purified solution 3 were 0.5 mg/L and 0.1 mg/L, respectively; lithium carbonate product 1 was obtained, and then lithium carbonate product 2 was obtained.

Example 8

Lithium carbonate was extracted from the lithium-containing solution according to the method of Example 1, except that in S4, the temperature of the freezing crystallization was controlled at 15° C. The concentrations of Ca ²⁺ and Mg ²⁺ in the obtained purified solution 3 were 0.5 mg/L and 0.2 mg/L, respectively; lithium carbonate product 1 was obtained, and then lithium carbonate product 2 was obtained.

Embodiment 9

Lithium carbonate is extracted from the lithium-containing solution according to the method of Example 1, except that the conditions of the primary purification are different. In S5, the frozen liquid is mixed with alkaline oxides for primary purification to remove fluorine and silicon, the pH value of the mixed system is controlled to be 8, the purification temperature is 85°C, and purified liquid 1 and purified slag 1 are obtained by filtration. The concentrations of Ca ²⁺ and Mg ²⁺ in the obtained purified liquid 3 are 0.5 mg/L and 0.2 mg/L respectively; lithium carbonate product 1 is obtained, and then lithium carbonate product 2 is obtained.

Example 10

Lithium carbonate is extracted from a lithium-containing solution according to the method of Example 1, except that the conditions for secondary purification are different. Specifically, in S5, the purified liquid 1 is subjected to secondary purification by adjusting the pH with an alkaline solution to remove impurities such as calcium, magnesium and aluminum, the pH value of the system is controlled to be 7, the purification temperature is 80°C, and purified liquid 2 and purified slag 2 are obtained by filtration. The concentrations of Ca ²⁺ and Mg ²⁺ in the obtained purified liquid 3 are 0.5 mg/L and 0.2 mg/L, respectively; lithium carbonate product 1 is obtained, and then lithium carbonate product 2 is obtained.

Comparative Example 1

Lithium carbonate is extracted from the lithium-containing solution according to the method of Example 1, except that S1 does not cool down to precipitate potassium salt, and S2 does not heat up. Specifically, in S1, the lithium-containing solution is pumped into the MVR system for evaporation, the evaporation ratio is controlled to be 3:1, and the evaporated slurry is filtered; in S2, the filtrate obtained in S1 is added to a sodium carbonate aqueous solution 1 with a concentration of 20wt% and a temperature of 90°C for lithium precipitation (based on the weight of the filtrate being 100g, the amount of sodium carbonate aqueous solution 1 is 50g), and a solid product and lithium precipitation mother liquor 1 are obtained after filtration; water with a liquid-to-solid ratio of 5:1 is added to the solid product for two countercurrent washings to obtain lithium carbonate product 1. Then lithium carbonate product 2 is obtained.

Comparative Example 2

Lithium carbonate is extracted from the lithium-containing solution according to the method of Example 1, except that the freezing crystallization step in S4 and the impurity removal step in S5 are not performed, and in S6, the concentrated solution obtained in S3 is directly added to the sodium carbonate aqueous solution 2 for secondary lithium precipitation. Lithium carbonate product 1 is obtained, and then lithium carbonate product 2 is obtained.

The purity of Li ₂ CO ₃ and the mass percentage of Na ions, K ions and SO ₄ ^2- in the lithium carbonate products 1 and 2 obtained in the examples and comparative examples were measured. The results are shown in Table 2.

Table 2

It can be seen from the results of Table 2 that the method for extracting lithium carbonate from a lithium-containing solution provided by the present disclosure is adopted. The purity of the lithium carbonate product 1 obtained by the first lithium precipitation of Examples 1-10 is above 98.5wt%, and reaches the industrial grade standard; the purity of the lithium carbonate product 2 obtained by the second lithium precipitation is above 99.5wt%, and reaches the battery grade standard. Comparative Example 1 does not perform cooling and potassium salt precipitation and heating, and directly performs a first lithium precipitation after evaporation. Due to the serious peritectic of potassium sulfate and sodium sulfate, the purity of the lithium carbonate product 1 obtained by the first lithium precipitation is lower than 98.5wt%, and even cannot reach the standard of industrial grade lithium carbonate; however, Comparative Example 1 undergoes frozen salt precipitation and three-stage purification process, which greatly removes impurities such as potassium and sodium, and the secondary lithium carbonate can reach the battery grade standard. Comparative Example 2 does not perform frozen crystallization and purification and impurity removal, and directly performs a second lithium precipitation. Although the purity of the obtained lithium carbonate product 2 is greater than 99.5wt%, it can only reach the industrial grade standard.

In addition, Example 4 increases the evaporation ratio of the primary concentration, Example 5 increases the temperature of cooling potassium salt, and Example 6 reduces the temperature of heating the potassium solution to redissolve potassium sulfate and sodium sulfate fine crystal salt. Although the lithium carbonate product 1 obtained by the primary lithium precipitation also meets the industrial grade standard, compared with Example 1, the content of Na, K and SO ₄ ^2- in the lithium carbonate product 1 is increased or the purity of Li ₂ CO ₃ is reduced. Example 7 increases the evaporation ratio of the secondary concentration, Example 8 increases the temperature of freezing crystallization, and Examples 9 and 10 respectively change the conditions of the primary purification and the secondary purification. Compared with Example 1, the lithium carbonate product 2 obtained by the secondary lithium precipitation also meets the battery grade standard, but compared with Example 1, the content of Na, K and SO ₄ ^2- in the lithium carbonate product 2 is increased or the purity of Li ₂ CO ₃ is reduced. It shows that the evaporation ratio of the first concentration, the temperature for cooling the potassium salt, and the temperature for heating the potassium precipitation solution to redissolve potassium sulfate and sodium sulfate fine crystals have a certain influence on the quality of the lithium carbonate product 1 obtained by the first lithium precipitation, but have little effect on the quality of the lithium carbonate product 2 obtained by the second lithium precipitation; while the evaporation ratio of the second concentration, the temperature of the freezing crystallization, and the purification conditions will affect the quality of the lithium carbonate product 2 obtained by the second lithium precipitation.

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

Claims (20)

A method for extracting lithium carbonate from a lithium-containing solution, wherein the method comprises the following steps: S1, concentrating and cooling the lithium-containing solution to precipitate potassium, and performing solid-liquid separation to obtain a potassium precipitation solution and a mixed salt 1; S2, heating the potassium precipitation solution and subjecting it to primary lithium precipitation, and obtaining a lithium carbonate product 1 and a lithium precipitation mother liquor 1 through secondary solid-liquid separation; S3, the lithium precipitation mother liquor 1 is concentrated twice, and a concentrated solution and a mixed salt 2 are obtained by three solid-liquid separations; S4, freezing the concentrated solution, and obtaining potassium sodium mirabilite and a frozen solution through four solid-liquid separations; S5, removing impurities from the frozen liquid to obtain a purified liquid; S6, subjecting the purified liquid to secondary lithium precipitation, and obtaining a lithium carbonate product 2 and a lithium precipitation mother liquor 2 after five solid-liquid separations; wherein the lithium precipitation mother liquor 2 is returned to S1. The method according to claim 1, wherein in S1, the primary concentration process comprises: evaporating the lithium-containing solution at an evaporation ratio of (1-6):1. The method according to claim 2, wherein in S1, the primary concentration process comprises: evaporating the lithium-containing solution at an evaporation ratio of (2-5):1; And/or, the cooling potassium precipitation process comprises: cooling the liquid product obtained by evaporation to 0-60° C.; And/or, in the lithium-containing solution, the content of lithium ions is less than or equal to 5 g/L, the content of potassium ions is greater than or equal to 25 g/L, and the content of sodium ions is greater than or equal to 25 g/L. The method according to any one of claims 1 to 3, wherein in S2, the heating process comprises: heating the potassium precipitation solution to 65-95° C.; The primary lithium precipitation process comprises: mixing the potassium precipitation solution and a sodium carbonate aqueous solution 1 to react. The method according to claim 4, wherein in S2, the heating process comprises: heating the potassium precipitation solution to 75-95° C.; And/or, the content of sodium carbonate in the sodium carbonate aqueous solution 1 is 15-32wt%, and the temperature of the sodium carbonate aqueous solution 1 is 80-90°C. The method according to any one of claims 1 to 5, wherein in S3, the secondary concentration process comprises: evaporating the lithium precipitation mother liquor 1 at an evaporation ratio of (1-6):1. The method according to any one of claims 1 to 5, wherein in S3, the secondary concentration process comprises: evaporating the lithium precipitation mother solution 1 at an evaporation ratio of (2-5):1; And/or, in S4, the freezing temperature is -5°C to 15°C. The method according to claim 7, wherein in S4, the freezing temperature is -5°C to 10°C. The method according to any one of claims 1 to 8, wherein in S5, the impurity removal process comprises: The refrigerated liquid is mixed with an alkaline oxide for primary purification; The liquid product obtained by the primary purification is mixed with alkali solution and subjected to secondary purification; The liquid phase product obtained by the secondary purification is contacted with an ion exchange resin for tertiary purification to obtain the purified liquid. The method according to claim 9, wherein the conditions for the primary purification include: a pH value of 7-14, a time of 0.5-3 hours, and a temperature of 25-95°C. The method according to claim 9, wherein the conditions of the primary purification include: pH value of 9-12, time of 0.5-1.5h, temperature of 55-85°C; And/or, the conditions of the secondary purification include: pH value of 7-14, time of 0.5-3h, temperature of 25-95°C; And/or, the concentrations of Ca ²⁺ and Mg ²⁺ in the purified liquid are each independently less than or equal to 1 mg/L. The method according to claim 11, wherein the conditions for the secondary purification include: pH value of 9-12, time of 0.5-2h, and temperature of 55-85°C. The method according to any one of claims 9 to 12, wherein the basic oxide comprises magnesium oxide and/or calcium oxide; and/or, the alkali solution comprises sodium hydroxide and/or sodium carbonate; And/or, the ion exchange resin is selected from chelating ion exchange resins with an average pore size of 0.3-0.8 mm. The method according to any one of claims 1 to 13, wherein in S6, the secondary lithium precipitation process comprises: mixing the purified liquid and the sodium carbonate aqueous solution 2 for reaction. The method according to claim 14, wherein the content of sodium carbonate in the sodium carbonate aqueous solution 2 is 15-32wt%, and the temperature of the sodium carbonate aqueous solution 2 is 80-90°C. The method according to any one of claims 1 to 15, wherein the method further comprises: washing the lithium carbonate product 1 with water at least once; And/or, the method further comprises: washing the lithium carbonate product 2 with water at least once. The method according to claim 16, wherein the method satisfies at least one of the following conditions: Washing the lithium carbonate product 1 with water for more than 2 times; The weight ratio of the lithium carbonate product 1 to water is 1:(2-10); Washing the lithium carbonate product 2 with water for more than 2 times; The weight ratio of the lithium carbonate product 2 to water is 1:(2-10). The method according to claim 17, wherein the weight ratio of the lithium carbonate product 1 to water is 1:(4-8); And/or, the weight ratio of the lithium carbonate product 2 to water is 1:(4-8). The method according to any one of claims 1 to 18, wherein the content of lithium carbonate in the lithium carbonate product 1 is greater than or equal to 99.5wt%. The method according to any one of claims 1 to 19, wherein the lithium carbonate product 2 is battery grade lithium carbonate. lithium.