Method for extracting lithium carbonate from lithium-containing solution

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

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] 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 herein. Technical Field

[0003] The present disclosure relates to the field of lithium recovery, and in particular to a method for extracting lithium carbonate from a lithium-containing solution. Background Art

[0004] Lithium, a vital energy metal known as "white oil," has a wide range of uses and is becoming a new driver of global energy development. my country has established a modern, basic lithium industry based on ore and brine extraction, encompassing a range of products including lithium carbonate, lithium chloride, lithium hydroxide, and lithium metal. Currently, raw materials used in industrial lithium extraction are typically spodumene (Li2O > 5.0%), petalite (Li2O > 5.0%), lepidolite (Li2O > 2.5%), and lepidolite (Li2O > 5.5%). These materials have high Li2O contents and low levels of impurity ions in solution, leading to mature recovery processes within the industry. However, since the end of 2019, lithium salt prices have continued to rise. Against the background that high-quality lithium mineral resources are only monopolized by a few high-quality lithium mining companies at home and abroad, research on lithium extraction technology from low-grade lepidolite (Li2O<1.5%) and low-grade lithium-containing waste slag has attracted more and more attention. Low-grade lithium resources usually also contain large amounts of impurity elements such as Na, K, Rb, Cs, Al, Si, and Ca. Taking low-grade lepidolite (Li2O<1.5%) as the raw material as an example, lepidolite generally contains potassium between 6-10%. 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.

[0005] Therefore, it is particularly important to develop a technically feasible and industrially scalable method for extracting lithium from a low-lithium, high-potassium, and high-sodium solution.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to overcome the problems of the prior art in extracting lithium from low-lithium-containing solutions, such as complicated procedures, low direct yields, and poor economic benefits, and to provide a method for extracting lithium carbonate from lithium-containing solutions. The method can efficiently separate the lithium-containing solution and obtain a high-quality lithium carbonate product.

[0008] 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:

[0009] S1, concentrating the lithium-containing solution and cooling it to precipitate potassium, and performing a solid-liquid separation to obtain a potassium precipitation solution and a mixed salt 1;

[0010] 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;

[0011] 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;

[0012] S4, freezing the concentrated solution, and performing four solid-liquid separations to obtain potassium sodium thenardite and a frozen solution;

[0013] S5, removing impurities from the frozen liquid to obtain a purified liquid;

[0014] S6. The purified liquid is subjected to secondary lithium precipitation, and five solid-liquid separations are performed to obtain a lithium carbonate product 2 and a lithium precipitation mother liquor 2; wherein the lithium precipitation mother liquor 2 is returned to S1.

[0015] Through the above technical solution, the beneficial effects of the present disclosure are:

[0016] The method provided by the present disclosure for extracting lithium carbonate from a lithium-containing solution comprises the following steps: primary concentration and reverse heating, primary lithium precipitation, secondary concentration, freezing and separating sodium sulfate, purification and impurity removal, and secondary lithium precipitation, thereby achieving efficient separation of a low-lithium, high-potassium, and high-sodium solution.

[0017] The present disclosure adopts a process including one-time concentration, reverse heating and one-time lithium precipitation. The reverse heating is to first cool the solution to precipitate potassium and then heat the solution to precipitate potassium. 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 solution before the one-time lithium precipitation, the mixed salt 1 (potassium sulfate and sodium sulfate) is in an unsaturated state, thereby avoiding the lithium carbonate peritectic phenomenon during the lithium precipitation process caused by 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-time lithium precipitation has a percentage of Li2CO3 component greater than or equal to 99.5wt% after stirring and washing.

[0018] The present invention adopts the freezing and precipitation of mirabilite, purification and impurity removal, and secondary lithium precipitation process to achieve deep removal of potassium and sodium salts and impurity ions. The lithium carbonate product 2 obtained by the secondary lithium precipitation directly reaches the battery-grade lithium carbonate level after stirring and washing. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] 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

[0020] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0021] The present disclosure provides a method for extracting lithium carbonate from a lithium-containing solution, wherein the method comprises the following steps:

[0022] S1, concentrating the lithium-containing solution and cooling it to precipitate potassium, and performing a solid-liquid separation to obtain a potassium precipitation solution and a mixed salt 1;

[0023] 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;

[0024] 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;

[0025] S4, freezing the concentrated solution, and performing four solid-liquid separations to obtain potassium sodium thenardite and a frozen solution;

[0026] S5, removing impurities from the frozen liquid to obtain a purified liquid;

[0027] S6. The purified liquid is subjected to secondary lithium precipitation, and five solid-liquid separations are performed to obtain a lithium carbonate product 2 and a lithium precipitation mother liquor 2; wherein the lithium precipitation mother liquor 2 is returned to S1.

[0028] The lithium-containing solution is concentrated and cooled to precipitate potassium, and then separated into a solid-liquid phase to obtain a mixed salt 1 (potassium sulfate and sodium sulfate) and a potassium precipitation solution. The primary concentration increases the concentration of lithium sulfate in the lithium-containing solution; the cooling and potassium precipitation can precipitate a portion of potassium sulfate with higher purity, and a small amount of sodium sulfate will also precipitate; after the potassium precipitation solution is heated, a lithium precipitation is performed again to redissolve some of the potassium sulfate and sodium sulfate fine crystals precipitated from the potassium precipitation solution, leaving the potassium sulfate and sodium sulfate in the potassium precipitation solution in an unsaturated state. This avoids the peritectic phenomenon of lithium carbonate during the primary lithium precipitation process caused by the crystallization of potassium sulfate and sodium sulfate, thereby improving the quality of the lithium carbonate product 1 obtained by the primary lithium precipitation. The secondary concentration of the lithium precipitation mother liquor 1 can further increase the concentration of lithium ions and precipitate sodium sulfate. After the secondary concentration of the lithium precipitation mother liquor 1, solid-liquid separation is performed to obtain a mixed salt 2 of potassium sulfate and sodium sulfate (since a large amount of potassium sulfate has been precipitated in the primary concentration, the sodium sulfate salt accounts for a larger proportion in the mixed salt precipitated in the secondary concentration) and a concentrated solution. The concentrated solution is frozen and crystallized to precipitate sodium and potassium sulfate (K3Na(SO4)2·10H2O). Solid-liquid separation is then performed to obtain sodium and potassium sulfate and a frozen solution. The frozen solution is then cleaned of impurities including fluorine, silicon, calcium, magnesium, and aluminum to produce a purified solution. Only a portion of the lithium is precipitated during the first lithium precipitation. This is because the lithium concentration in the potassium precipitation solution gradually decreases as the precipitation proceeds. At this point, no matter how much lithium precipitation agent is added, the lithium will not be converted. Therefore, a second lithium precipitation is performed after the impurity removal.

[0029] According to the present disclosure, in S1, the primary concentration process 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. The ratio refers to the flow rate ratio of the lithium-containing solution to the concentrated solution obtained by the primary concentration during the evaporation concentration. Performing a primary concentration at this evaporation ratio can increase the lithium ion concentration of the lithium-containing solution and ensure the direct yield of lithium carbonate in the primary lithium precipitation process.

[0030] According to one 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.

[0031] According to one 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 potassium salts are precipitated while reducing the overall energy consumption of subsequent heating.

[0032] According to one embodiment of the present disclosure, the lithium-containing solution has a lithium ion content of less than or equal to 5 g / L, a potassium ion content of greater than or equal to 25 g / L, and a sodium ion content of greater than or equal to 25 g / L. For lithium-containing solutions whose lithium ion, potassium ion, and sodium ion contents meet these conditions, the method for extracting lithium carbonate provided by the present disclosure can produce a high-quality lithium carbonate product.

[0033] 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 and sodium sulfate.

[0034] 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 to react.

[0035] According to one embodiment of the present disclosure, the sodium carbonate content in the sodium carbonate aqueous solution 1 is 15-32 wt %, and the temperature of the sodium carbonate aqueous solution 1 is 80-90° C. When the sodium carbonate content in the sodium carbonate aqueous solution 1 is within this range, the direct recovery rate of lithium can be increased, and the content of impurities encapsulated by lithium carbonate is reduced; when the temperature of the sodium carbonate aqueous solution 1 is within this range, the lithium precipitation reaction can be promoted.

[0036] 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.

[0037] 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. Performing a primary concentration at this evaporation ratio can increase the lithium concentration, so that the secondary lithium precipitation can precipitate a high-quality lithium carbonate product and simultaneously precipitate sodium sulfate.

[0038] 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 high potassium and sodium salt precipitation efficiency can be ensured, and freezing of the mother liquor can be avoided, thereby enabling the secondary lithium precipitation to obtain higher quality lithium carbonate.

[0039] According to one embodiment of the present disclosure, in S5, the impurity removal process includes:

[0040] The refrigerated liquid is mixed with alkaline oxide for primary purification;

[0041] The liquid product obtained from the primary purification is mixed with the alkali solution and subjected to secondary purification;

[0042] The liquid phase product obtained by the secondary purification is contacted with an ion exchange resin for tertiary purification to obtain a purified liquid.

[0043] The refrigerant is subjected to primary purification using alkaline oxides to remove fluorine and silicon from the refrigerant; the liquid product obtained after 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 after the secondary purification is contacted with ion exchange resin for tertiary purification to further remove impurities such as calcium and magnesium from the refrigerant.

[0044] According to one embodiment of the present disclosure, the conditions for primary purification include: pH value of 7-14, time of 0.5-3h, and temperature of 25-95°C, wherein the pH value is the pH value of the mixed system of the freezing liquid and the alkaline oxide.

[0045] 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 the mixed system of the freezing liquid and the alkaline oxide.

[0046] According to one embodiment of the present disclosure, the conditions for secondary purification include: pH value 7-14, time 0.5-3h, temperature 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.

[0047] According to one embodiment of the present disclosure, the conditions for secondary purification include: pH 9-12, time 0.5-2 hours, and temperature 55-85° C. The pH value is the pH value of the mixed system of the liquid product obtained from the primary purification and the alkali solution.

[0048] According to one embodiment of the present disclosure, the Ca in the purified liquid 2+ and Mg 2+ The concentration of each is independently less than or equal to 1 mg / L.

[0049] According to one embodiment of the present disclosure, the basic oxide includes magnesium oxide and / or calcium oxide.

[0050] According to one embodiment of the present disclosure, the alkali solution includes sodium hydroxide and / or sodium carbonate.

[0051] 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.

[0052] According to one embodiment of the present disclosure, in S6, the secondary lithium precipitation process includes: mixing the purified liquid and the sodium carbonate aqueous solution 2 to react.

[0053] 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.

[0054] 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.

[0055] According to one embodiment of the present disclosure, the method further comprises: washing the lithium carbonate product 1 with water at least once, preferably more than twice, and more preferably twice.

[0056] 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).

[0057] 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.

[0058] 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).

[0059] 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 %.

[0060] According to one embodiment of the present disclosure, the lithium carbonate product 2 is battery-grade lithium carbonate.

[0061] 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 filtration.

[0062] According to a specific embodiment of the present disclosure, as shown in FIG1 , a method for extracting lithium carbonate from a lithium-containing solution includes the following steps:

[0063] S1. Pumping the lithium-containing solution into the MVR system for evaporation (primary concentration), controlling the evaporation ratio (inlet flow / outlet flow) to (1-6):1; cooling the concentrated liquid product to 0-60°C, cooling and precipitating potassium salt, and filtering to obtain a potassium precipitation liquid;

[0064] 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 having a concentration of 15-32wt% and a temperature of 80-90° C. to perform a lithium precipitation (based on the weight of the potassium precipitation solution as 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 water with a liquid-to-solid ratio of (2-10): 1 to countercurrent wash the solid product twice to obtain a lithium carbonate product 1;

[0065] 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;

[0066] 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 thenardite and frozen liquid;

[0067] 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 the purified liquid 1 and purified residue 1 are obtained by filtration; the purified liquid 1 is adjusted to pH by 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 the 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; Ca in the purified liquid 3 is reduced to 0.5-1.5; and the purified liquid 3 is further purified. 2+ and Mg 2+ The concentrations were all less than or equal to 1 mg / L;

[0068] S6, the purified liquid 3 is pumped into a heating tank, and then added 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 a lithium carbonate product 2 and a lithium precipitation mother liquor 2 are obtained by filtration; water with a liquid-to-solid ratio of (2-10): 1 is added to the lithium carbonate product 2 for two countercurrent washings; the lithium precipitation mother liquor 2 is returned to S1.

[0069] The present disclosure will be described in detail below through examples and comparative examples. In the following examples, unless otherwise specified, conventional methods are used; and the reagents and materials used, unless otherwise specified, can be obtained from commercial sources.

[0070] Li2CO3 purity, Na, K and SO4 2- The mass percentage content is determined in accordance with GB / T 11064-2013 "Chemical analysis method of lithium carbonate, lithium hydroxide monohydrate and lithium chloride".

[0071] The chemical compositions of the lithium-containing solutions of the Examples and Comparative Examples are shown in Table 1.

[0072] Table 1

[0073] The following examples are used to illustrate the method for extracting lithium carbonate from a lithium-containing solution.

[0074] Example 1

[0075] S1. Pump the lithium-containing solution into the MVR system for evaporation (primary concentration), and control the evaporation ratio (flow rate of the lithium-containing solution / flow rate of the concentrated liquid obtained by the primary concentration) to 3:1; cool the concentrated liquid product to 60° C., cool it down to precipitate potassium salt, and filter it to obtain a potassium precipitation liquid;

[0076] S2, pumping the potassium precipitation liquid into a heating tank and heating it to 90° C.; adding the heated potassium precipitation liquid to a sodium carbonate aqueous solution 1 having a concentration of 20wt% and a temperature of 90° C. to perform lithium precipitation once (based on the weight of the potassium precipitation liquid 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 countercurrent wash the solid product twice to obtain a lithium carbonate product 1;

[0077] S3. Pump the lithium precipitation mother liquor 1 into the MVR system for evaporation and salt precipitation (secondary concentration), control the evaporation ratio (inlet flow / outlet flow) to 3.5:1, and obtain the concentrated solution through filtration;

[0078] S4, pumping the concentrated liquid into a freezing crystallization system, controlling the freezing temperature at 10°C, and filtering to obtain potassium sodium thenardite and frozen liquid;

[0079] 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 residue 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%) to perform 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, and the purification temperature is 85°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 0.3mm for tertiary purification to deeply remove impurities such as calcium and magnesium to obtain purified liquid 3; Ca in purified liquid 3 2+ and Mg 2+ The concentrations were 0.5 mg / L and 0.2 mg / L respectively;

[0080] 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 perform two countercurrent washings on the lithium carbonate product 2; and return the lithium precipitation mother liquor 2 to S1.

[0081] Example 2

[0082] S1. Pump the lithium-containing solution into the MVR system for evaporation (primary concentration), and control the evaporation ratio (flow rate of the lithium-containing solution / flow rate of the concentrated liquid obtained by primary concentration) to 4:1; cool the concentrated liquid product to 35° C., cool it down to precipitate potassium salt, and filter it to obtain a potassium precipitation liquid;

[0083] S2-S6 are the same as in Example 1; wherein, the Ca in the purified solution 3 obtained in S5 is 2+ and Mg 2+ The concentrations were 0.5 mg / L and 0.2 mg / L respectively.

[0084] Obtain lithium carbonate product 1 and lithium carbonate product 2.

[0085] Example 3

[0086] S1. Pump the lithium-containing solution into the MVR system for evaporation (primary concentration), and control the evaporation ratio (flow rate of the lithium-containing solution / flow rate of the concentrated liquid obtained by primary concentration) to 3.5:1; cool the concentrated liquid product to 40°C, cool it down to precipitate potassium salt, and filter it to obtain a potassium precipitation liquid;

[0087] S2 is the same as in Example 1; lithium carbonate product 1 is obtained;

[0088] S3. Pump the lithium precipitation mother liquor 1 into the MVR system for evaporation and salt precipitation (secondary concentration), control the evaporation ratio (inlet flow / outlet flow) to 4:1, and obtain the concentrated solution through filtration;

[0089] S4, pumping the concentrated liquid into a freezing crystallization system, controlling the freezing temperature at 0°C, and filtering to obtain potassium sodium thenardite and frozen liquid;

[0090] S5 is the same as in Example 1, and the Ca content in the purified solution 3 is obtained. 2+ and Mg 2+ The concentrations were 0.5 mg / L and 0.2 mg / L respectively;

[0091] S6 is the same as in Example 1; lithium carbonate product 2 is obtained.

[0092] Example 4

[0093] Lithium carbonate was extracted from the lithium-containing solution according to the method of Example 1, except that the evaporation ratio of the primary concentration was 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) was controlled to be 6:1. The Ca in the purified solution 3 obtained was 2+ and Mg 2+ The concentrations 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.

[0094] Example 5

[0095] Lithium carbonate was extracted from the lithium-containing solution according to the method of Example 1, except that the temperature for cooling and precipitating potassium salt was different. Specifically, in S1, the concentrated liquid product was cooled to 65°C and cooled to precipitate potassium salt. The Ca in the purified solution 3 was 2+ and Mg 2+ The concentrations 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.

[0096] Example 6

[0097] 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 Ca content in the purified solution 3 was 2+ and Mg 2+ The concentrations 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.

[0098] Example 7

[0099] 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 Ca content in the purified solution 3 was 2+ and Mg 2+ The concentrations are 0.5 mg / L and 0.1 mg / L respectively; lithium carbonate product 1 is obtained, and then lithium carbonate product 2 is obtained.

[0100] Example 8

[0101] Lithium carbonate was extracted from the lithium-containing solution according to the method of Example 1, except that the temperature of the freeze crystallization in S4 was controlled at 15°C. 2+ and Mg 2+ The concentrations 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.

[0102] Example 9

[0103] Lithium carbonate was extracted from the lithium-containing solution according to the method of Example 1, except that the conditions of the primary purification were different. Specifically, in S5, the frozen liquid was mixed with alkaline oxides for primary purification to remove fluorine and silicon. The pH value of the mixed system was controlled to be 8, the purification temperature was 85°C, and purified liquid 1 and purified slag 1 were obtained by filtration. The Ca content in the obtained purified liquid 3 was 0.0447 W / v. 2+ and Mg 2+ The concentrations 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.

[0104] Example 10

[0105] Lithium carbonate was extracted from the lithium-containing solution according to the method of Example 1, except that the conditions for secondary purification were different. Specifically, in S5, the purified liquid 1 was subjected to secondary purification by adjusting the pH with alkaline solution to remove impurities such as calcium, magnesium and aluminum. The pH value of the system was controlled to be 7, and the purification temperature was 80°C. Purified liquid 2 and purified residue 2 were obtained by filtration. The Ca in the obtained purified liquid 3 was 0.0447 W / m. 2+ and Mg 2+ The concentrations 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.

[0106] Comparative Example 1

[0107] Lithium carbonate is extracted from a lithium-containing solution according to the method of Example 1, except that S1 does not cool down to precipitate potassium salts, and S2 does not heat up. Specifically, in S1, the lithium-containing solution is pumped into an MVR system for evaporation, with the evaporation ratio controlled at 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 to precipitate lithium once (based on the weight of the filtrate being 100g, the amount of sodium carbonate aqueous solution 1 is 50g). After filtration, a solid product and lithium precipitation mother liquor 1 are obtained; 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. Lithium carbonate product 2 is then obtained.

[0108] Comparative Example 2

[0109] Lithium carbonate was 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 were not performed. In S6, the concentrated solution obtained in S3 was directly added to the sodium carbonate aqueous solution 2 for secondary lithium precipitation. Lithium carbonate product 1 was obtained, and then lithium carbonate product 2 was obtained.

[0110] Determine the purity of Li2CO3 in lithium carbonate product 1 and lithium carbonate product 2 obtained in each embodiment and comparative example, as well as the Na ion, K ion and SO4 2- The results are shown in Table 2.

[0111] Table 2

[0112] As can be seen from the results of Table 2, the method for extracting lithium carbonate from a lithium-containing solution provided by the present disclosure is used. The purity of the lithium carbonate product 1 obtained by the first precipitation of lithium in Example 1-10 is above 98.5wt%, and reaches the industrial grade standard; the purity of the lithium carbonate product 2 obtained by the second precipitation of lithium is above 99.5wt%, and reaches the battery grade standard. Comparative Example 1 does not undergo cooling and potassium salt precipitation and heating, and directly undergoes a first precipitation of lithium after evaporation. Due to the serious peritectic formation of potassium sulfate and sodium sulfate, the purity of the lithium carbonate product 1 obtained by the first precipitation of lithium is lower than 98.5wt%, and even cannot reach the standard of industrial grade lithium carbonate; However, Comparative Example 1 undergoes frozen precipitation of mirabilite 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 undergo frozen crystallization and purification and impurity removal, and directly undergoes a second precipitation of lithium. Although the purity of the obtained lithium carbonate product 2 is greater than 99.5wt%, it can only reach the industrial grade standard.

[0113] In addition, Example 4 increases the evaporation ratio of the first concentration, Example 5 increases the temperature for cooling the potassium salt, and Example 6 reduces the temperature for heating the potassium solution to redissolve potassium sulfate and sodium sulfate fine crystals. Although the lithium carbonate product 1 obtained by the first precipitation of lithium also meets the industrial grade standard, compared with Example 1, the Na, K and SO4 in the lithium carbonate product 1 are lower. 2- The content of Li2CO3 increases or the purity of Li2CO3 decreases. Example 7 increases the evaporation ratio of the secondary concentration, Example 8 increases the temperature of the freezing crystallization, and Examples 9 and 10 change the conditions of the primary purification and secondary purification respectively. Compared with Example 1, the lithium carbonate product 2 obtained by the secondary precipitation also meets the battery grade standard, but compared with Example 1, the Na, K and SO4 in the lithium carbonate product 2 are lower than those in Example 1. 2- The content of Li2CO3 increases or the purity of Li2CO3 decreases. This indicates 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 impact on the quality of the lithium carbonate product 1 obtained by the first lithium precipitation, but have little impact on the quality of the lithium carbonate product 2 obtained by the second lithium precipitation; the evaporation ratio of the second concentration, the temperature of the freeze crystallization, and the purification conditions will all affect the quality of the lithium carbonate product 2 obtained by the second lithium precipitation.

[0114] 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, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. 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 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.

2. The method according to claim 1, wherein: In S1, the primary concentration process includes: evaporating the lithium-containing solution at an evaporation ratio of (1-6):

1.

3. 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.

4. The method according to any one of claims 1 to 3, wherein: In S2, the heating process includes: 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.

5. The method according to claim 4, wherein: In S2, the heating process includes: 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.

6. The method according to any one of claims 1 to 5, wherein: In S3, the secondary concentration process includes: evaporating the lithium precipitation mother solution 1 at an evaporation ratio of (1-6):

1.

7. The method according to any one of claims 1 to 5, wherein: In S3, the secondary concentration process includes: 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.

8. The method according to claim 7, wherein: In S4, the freezing temperature is -5°C to 10°C.

9. The method according to any one of claims 1 to 8, wherein: In S5, the impurity removal process includes: 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.

10. The method according to claim 9, wherein: The conditions for the primary purification include: pH value of 7-14, time of 0.5-3h, and temperature of 25-95°C.

11. 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, Ca in the purified liquid 2+ and Mg 2+ The concentrations are each independently less than or equal to 1 mg / L.

12. The method according to claim 11, wherein: The conditions of the secondary purification include: pH value of 9-12, time of 0.5-2h, and temperature of 55-85°C.

13. The method according to any one of claims 9 to 12, wherein: The basic oxide includes 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.

14. The method according to any one of claims 1 to 13, wherein: In S6, the secondary lithium precipitation process includes: mixing the purified liquid and the sodium carbonate aqueous solution 2 to react.

15. The method according to claim 14, wherein: 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.

16. 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.

17. 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).

18. 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).

19. 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%.

20. The method according to any one of claims 1 to 19, wherein: The lithium carbonate product 2 is battery-grade lithium carbonate.

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