阅读说明：本技术 锂盐的回收方法 (Method for recovering lithium salt ) 是由 徐杰锋 赵国军 陈义祥 唐勇 徐勇智 于 2020-11-19 设计创作，主要内容包括：本发明涉及锂盐的回收方法,具体涉及一种7-去氢胆固醇副产回收锂盐的方法。本发明提供的方法,将3-乙酰胆固醇-7-对甲苯磺酰腙的脱腙液经冷却过滤后、加水溶解,并将得到的含锂溶液与萃取剂进行萃取,避免了脱腙液直接加水卒灭后,物料由于乳化现象严重,无法通过分层操作回收锂盐；同时,该方法摒弃了传统工艺中磷酸的使用,避免了磷酸盐废水的产生,直接得到高含量的碳酸锂产品,提高了锂盐的回收率。(The invention relates to a method for recovering lithium salt, in particular to a method for recovering lithium salt from 7-dehydrocholesterol byproduct. According to the method provided by the invention, the dehydrohydrazone liquid of the 3-acetylcholesterol-7-p-toluenesulfonylhydrazone is cooled and filtered, then is dissolved by adding water, and the obtained lithium-containing solution is extracted with an extractant, so that the problem that the materials cannot be subjected to layered operation to recover lithium salt due to serious emulsification after the dehydrohydrazone liquid is directly quenched by adding water is avoided; meanwhile, the method abandons the use of phosphoric acid in the traditional process, avoids the generation of phosphate wastewater, directly obtains a high-content lithium carbonate product, and improves the recovery rate of lithium salt.)

1. A method for recovering a lithium salt, comprising the steps of:

(1) carrying out a dehydrozonation reaction on 3-acetylcholesterol-7-p-toluenesulfonylhydrazone, and carrying out first cooling and first solid-liquid separation on the obtained dehydrozonation liquid to obtain a mixed lithium salt containing lithium amide and lithium p-toluenesulfinate;

(2) dissolving the mixed lithium salt in water to obtain a lithium-containing solution;

(3) extracting the lithium-containing solution with an extracting agent, and introducing CO into the obtained raffinate₂Adjusting the pH to 9-10, mixing with a soluble carbonate, and subjecting the resulting mixture to a second stepFirstly, heat filtering to obtain a crude lithium carbonate product;

(4) dissolving the crude lithium carbonate in water, carrying out secondary cooling, and introducing CO₂And (4) clarifying, and sequentially carrying out decoloring, thermal decomposition and second thermal filtration on the obtained lithium bicarbonate solution to obtain a lithium carbonate product.

2. The method of claim 1, wherein the molar ratio of the mixed lithium salt to charged lithium amide is from 0.97 to 0.99: 1;

preferably, the molar ratio of the lithium amide to the lithium p-toluenesulfonate in the mixed lithium salt is 0.5 to 5: 1, preferably 2 to 3: 1;

preferably, in step (1), the temperature of the first cooling is 10 to 50 ℃, preferably 20 to 40 ℃.

3. The method of claim 1 or 2, wherein in step (2), the weight ratio of the mixed lithium salt to water is 1: 5-20, preferably 1: 10-15.

4. A process according to any one of claims 1 to 3, wherein the extractant is an organic solvent, preferably at least one selected from toluene, ethylbenzene, ortho-xylene, meta-xylene, para-xylene, chlorobenzene and dichloromethane;

preferably, the weight ratio of the extractant to the mixed lithium salt is 1-10: 1, preferably 2 to 5: 1.

5. the process of any of claims 1-4, wherein the molar ratio of the soluble carbonate salt to the mixed lithium salt is from 0.1 to 0.5: 1, wherein the moles of the soluble carbonate are calculated by the moles of the carbonate, and the moles of the mixed lithium salt are the sum of the moles of the lithium amide and the moles of the lithium p-toluenesulfonate;

preferably, the soluble carbonate is selected from at least one of sodium carbonate, potassium carbonate and ammonium carbonate.

6. The process according to any one of claims 1 to 5, wherein in step (3) the temperature of the first hot filtration is 60 to 100 ℃, preferably 80 to 90 ℃.

7. The method according to any one of claims 1 to 6, wherein in step (4), the weight ratio of crude lithium carbonate to water is 1: 5-30, preferably 1: 10-15 parts of;

preferably, the temperature of the second cooling is 0-25 ℃, preferably 0-10 ℃.

8. The method according to any one of claims 1 to 7, wherein in step (4), the decolorizing comprises: contacting the lithium bicarbonate solution with a decolorizing agent to obtain a decolorized product;

preferably, the decolorizing agent is selected from at least one of activated carbon, clay and adsorbent resin, preferably activated carbon.

9. The method of claim 8, wherein the weight ratio of the lithium bicarbonate solution to the decolorizing agent is 1: 0.001-0.02, preferably 1: 0.003-0.01;

preferably, the decolorized product is subjected to a second solid-liquid separation prior to the thermal decomposition.

10. The method of any one of claims 1-9, wherein the conditions of the thermal decomposition comprise: the temperature is 60-100 ℃, preferably 80-90 ℃; the time is 1 to 10 hours, preferably 2 to 8 hours;

preferably, the temperature of the second hot filtration is 60 to 100 ℃, preferably 80 to 90 ℃.

Technical Field

The invention relates to a method for recovering lithium salt, in particular to a method for recovering lithium salt from 7-dehydrocholesterol byproduct.

Background

Vitamin D₃The cholecalciferol is also called as cholecalciferol and is widely used in a plurality of fields of pharmacy, food and beverage additives, feed additives, cosmetics and the like. Industrially, vitamin D₃Is usually prepared by taking cholesterol as a starting material and carrying out a plurality of steps of chemical reactions. In the above preparation process, 7-dehydrocholesterol (7-D)HC) is a key intermediate for synthesizing vitamin D3, and the synthesis of the vitamin D3 is carried out by taking 3-acetylcholinesterase-7-p-toluenesulfonylhydrazone as a raw material and carrying out dehydrozone and saponification, and the synthesis method is as follows:

in the traditional process, after the dehydrohydrazone reaction is finished and water is added for quenching, lithium salt is dissolved in water, although the system simultaneously comprises an oil phase and a water phase, the phenomenon of material emulsification is serious, and the lithium salt cannot be removed through layering operation. After neutralization by addition of phosphoric acid, the lithium salt precipitates as insoluble lithium phosphate, which can be separated by filtration. The method is also a common practice in the industry at present, but the process generates a large amount of phosphate wastewater, and the obtained by-product lithium phosphate has many impurities, is difficult to purify and narrow in application range, and is not beneficial to industrial recycling. If phosphoric acid is replaced with another acid, the yield of 7-dehydrocholesterol is affected, resulting in an increase in production cost.

CN106745099A, CN108862335A and CN109264748A disclose methods for preparing lithium carbonate from lithium phosphate, which convert lithium phosphate into lithium carbonate through steps of acidification, filtration, precipitation, etc., but the operation is complicated, and phosphate wastewater is inevitably generated, so that the industrial application is limited.

Disclosure of Invention

The invention aims to overcome the technical problems and provide a method for recovering lithium salt, in particular to a method for recovering lithium salt from 7-dehydrocholesterol byproduct. The method provided by the invention abandons the use of phosphoric acid in the traditional process, avoids the generation of phosphate wastewater, directly obtains a high-content lithium carbonate product, and simultaneously has simple process and is convenient for industrial production.

In order to achieve the above object, the present invention provides a method for recovering a lithium salt, the method comprising the steps of:

(1) carrying out a dehydrozonation reaction on 3-acetylcholesterol-7-p-toluenesulfonylhydrazone, and carrying out first cooling and first solid-liquid separation on the obtained dehydrozonation liquid to obtain a mixed lithium salt containing lithium amide and lithium p-toluenesulfinate;

(2) dissolving the mixed lithium salt in water to obtain a lithium-containing solution;

(3) extracting the lithium-containing solution with an extracting agent, and introducing CO into the obtained raffinate₂Adjusting the pH value to 9-10, mixing with soluble carbonate, and carrying out first heat filtration on the obtained mixture to obtain a crude lithium carbonate product;

(4) dissolving the crude lithium carbonate in water, carrying out secondary cooling, and introducing CO₂And (4) clarifying, and sequentially carrying out decoloring, thermal decomposition and second thermal filtration on the obtained lithium bicarbonate solution to obtain a lithium carbonate product.

Compared with the prior art, the invention has the following advantages:

(1) the method provided by the invention directly converts the 7-dehydrocholesterol byproduct lithium salt into lithium carbonate, eliminates the use of phosphoric acid in the traditional process, avoids the generation of phosphate wastewater, directly obtains a high-content lithium carbonate product, and improves the recovery rate of the lithium salt;

(2) according to the method provided by the invention, the 3-acetylcholesterol-7-p-toluenesulfonylhydrazone removing liquid is cooled, filtered, dissolved in water, and extracted with the obtained lithium-containing solution and the extracting agent, so that the separation process of lithium salt in the removing liquid is simplified;

(3) the method provided by the invention simplifies the process flow, is simple to operate and is convenient for industrial production.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The present invention provides a method for recovering lithium salt, comprising the steps of:

(1) carrying out a dehydrozonation reaction on 3-acetylcholesterol-7-p-toluenesulfonylhydrazone, and carrying out first cooling and first solid-liquid separation on the obtained dehydrozonation liquid to obtain a mixed lithium salt containing lithium amide and lithium p-toluenesulfinate;

(2) dissolving the mixed lithium salt in water to obtain a lithium-containing solution;

(3) extracting the lithium-containing solution with an extracting agent, and introducing CO into the obtained raffinate₂Adjusting the pH value to 9-10, mixing with soluble carbonate, and carrying out first heat filtration on the obtained mixture to obtain a crude lithium carbonate product;

(4) dissolving the crude lithium carbonate in water, carrying out secondary cooling, and introducing CO₂And (4) clarifying, and sequentially carrying out decoloring, thermal decomposition and second thermal filtration on the obtained lithium bicarbonate solution to obtain a lithium carbonate product.

In the present invention, the first and second are only the same process operation for distinguishing different stages without a special case of explanation, for example, the first cooling and the second cooling only indicate cooling of different stages; the first thermal filtration and the second thermal filtration are the same.

The inventor of the invention finds in research that: in the dehydrohydrazone liquid of 3-acetylcholesterol-7-p-toluenesulfonylhydrazone, excessive lithium amide and lithium p-toluenesulfinate exist in a system in a solid form, the lithium amide and the lithium p-toluenesulfinate (mixed lithium salt) are separated from the dehydrohydrazone liquid by filtration, the obtained mixed lithium salt is dissolved in water, and a hydrophobic solvent is used for extraction to remove a small amount of residual organic matters. The raffinate is passed over CO₂And adjusting the pH value to 9-10 to convert lithium hydroxide in the mixed lithium salt into lithium carbonate, adding soluble carbonate to convert the p-toluene sulfinic acid lithium in the mixed lithium salt into lithium carbonate, and filtering to obtain a crude lithium carbonate product.

Simultaneously, in order to remove soluble salt and trace colored impurities in the crude lithium carbonate product, CO is introduced₂And converting the crude lithium carbonate aqueous solution into a soluble lithium bicarbonate solution, and finishing decoloring and thermal decomposition in the lithium bicarbonate solution to finally obtain a high-content lithium carbonate product.

In the present invention, the dehydrohydrazone reaction refers to a reaction between a p-toluenesulfonylhydrazone group in 3-acetylcholesterol-7-p-toluenesulfonylhydrazone and an amino group in a charged lithium amide to obtain 7-dehydroacetylcholesterol, unless otherwise specified.

In the present invention, the conditions for the dehydrohydrazone reaction have a wide range of options as long as acetylcholinesterase-7-p-toluenesulfonylhydrazone is completely converted into 7-dehydroacetylcholine. Preferably, the conditions of the dehydrazone reaction include: the temperature is 90-130 ℃, preferably 100-120 ℃; the time is 0.5-3h, preferably 1-2 h.

In the present invention, since the filtration of the dehydrazone liquid causes a certain loss of the mixed lithium salt, it is preferable that the molar ratio of the mixed lithium salt to the charged lithium amide is 0.97-0.99: 1, for example, 0.97:1, 0.98:1, 0.99:1, wherein the number of moles of the mixed lithium salt is the sum of the number of moles of lithium amide and lithium p-toluenesulfonate.

According to the present invention, preferably, the molar ratio of lithium amide to lithium p-toluenesulfonate in the mixed lithium salt is 0.5 to 5: 1, preferably 2 to 3: 1.

in the present invention, the first cooling is intended to improve the separation effect of the mixed lithium salt (i.e., lithium amide and lithium p-toluenesulfonate) in the hydrazone removal liquid. Preferably, in step (1), the temperature of the first cooling is 10 to 50 ℃, preferably 20 to 40 ℃.

In the present invention, the first cooling temperature is a temperature after the first cooling of the hydrazone removing liquid, unless otherwise specified.

In the present invention, the first solid-liquid separation method may be selected from a wide range, and the first cooled dehydrohydrazone liquid may be separated into a solid and a liquid.

According to a preferred embodiment of the invention, 3-acetylcholinesterase-7-p-toluenesulfonyl is subjected to a hydrazone removal reaction, the obtained reaction liquid is cooled to 20-40 ℃, and then the reaction liquid is filtered to obtain a mixed lithium salt containing lithium amide and lithium p-toluenesulfonate.

According to the present invention, preferably, in the step (2), the weight ratio of the mixed lithium salt to water is 1: 5-20, preferably 1: 10-15. The preferable conditions are adopted, which is more favorable for decomposing the excessive lithium amide in the mixed lithium salt,and dissolving the p-toluenesulfinic acid lithium in the mixed lithium salt to improve Li in the lithium-containing solution⁺And the content of the lithium carbonate in the crude lithium carbonate product is further increased.

In the present invention, the extractant has a wide range of choice, as long as the aqueous phase and the oil phase in the lithium-containing solution are separated. Preferably, the extractant is an organic solvent, preferably at least one selected from the group consisting of toluene, ethylbenzene, ortho-xylene, meta-xylene, para-xylene, chlorobenzene and dichloromethane.

In order to improve the extraction separation effect of the lithium-containing solution, preferably, in the step (3), the weight ratio of the extracting agent to the mixed lithium salt is 1-10: 1, preferably 2 to 5: 1.

according to a preferred embodiment of the present invention, the raffinate is a solution containing lithium hydroxide and lithium p-toluenesulfonate; to increase the recovery of lithium salts, CO is introduced into the raffinate₂And adjusting the pH to 9-10 to convert the lithium hydroxide into lithium carbonate.

In the present invention, the soluble carbonate is intended to convert all of the lithium p-toluenesulfonate in the raffinate to lithium carbonate. Preferably, the molar ratio of the soluble carbonate to the mixed lithium salt is 0.1-0.5: 1, wherein the moles of the soluble carbonate are calculated by the moles of the carbonate, and the moles of the mixed lithium salt are the sum of the moles of the lithium amide and the moles of the lithium p-toluenesulfonate. The preferable conditions are adopted, so that the lithium salt as the 7-dehydrocholesterol byproduct is completely converted into lithium carbonate.

In the present invention, the soluble carbonate refers to a carbonate which is easily soluble in water or soluble in water by the aid of an auxiliary agent, unless otherwise specified.

Preferably, the soluble carbonate is selected from at least one of sodium carbonate, potassium carbonate and ammonium carbonate. In the present invention, the concentration of the soluble carbonate is not particularly limited as long as the soluble carbonate converts all of the lithium p-toluenesulfonate into lithium carbonate.

According to the present invention, preferably, in step (3), the temperature of the first hot filtration is 60 to 100 ℃, preferably 80 to 90 ℃. Because the solubility of the lithium carbonate in hot water is less than that in cold water, the optimal conditions are adopted, and the recovery rate of the crude lithium carbonate product is further improved.

In some embodiments of the present invention, preferably, the lithium carbonate content in the crude lithium carbonate product is 70 to 90%, preferably 75 to 85%; further preferably, the recovery rate of lithium salt in the crude lithium carbonate product is 85-98%, preferably 90-95%.

In the invention, in order to further reduce impurities in the crude lithium carbonate product, the crude lithium carbonate product is firstly mixed with water to obtain a turbid lithium carbonate solution, and then CO is introduced₂The lithium carbonate is converted to lithium bicarbonate, thereby increasing its solubility in water.

According to the present invention, preferably, in the step (4), the weight ratio of the crude lithium carbonate to the water is 1: 5-30, preferably 1: 10-15.

Preferably, the temperature of the second cooling is 0-25 ℃, preferably 0-10 ℃. The purpose of this is that since lithium bicarbonate is not thermally stable, a lower temperature is beneficial to keep the lithium bicarbonate stable, preventing it from decomposing back into lithium carbonate.

In some embodiments of the invention, the CO in step (4)₂The amount depends on the content of lithium carbonate in the crude lithium carbonate, and the introduction of the lithium carbonate solution is stopped when the solution is turbid to clear.

Preferably, in step (4), the decoloring comprises: and contacting the lithium hydrocarbon solution with a decoloring agent to obtain a decolored product.

In some embodiments of the present invention, preferably, the weight ratio of the lithium carbonate solution to the decoloring agent is 1: 0.001-0.02, preferably 1: 0.003-0.01. The adoption of the optimized conditions is more beneficial to removing colored impurities in the crude lithium carbonate product and improving the content of lithium carbonate in the lithium carbonate product.

In the present invention, there is a wide range of selection of the kind of the decoloring agent as long as the decoloring agent has an adsorption effect. Preferably, the decolorizing agent is selected from at least one of activated carbon, clay and adsorbent resin, preferably activated carbon.

In the present invention, there is a wide range of choices for the source of the decolorizer, which can be obtained by self-production or by commercial production, but the present invention is not limited thereto.

According to the present invention, preferably, the decolorized product is subjected to a second solid-liquid separation before the thermal decomposition; and the second solid-liquid separation aims at removing a decolorizing agent in a decolorized product to obtain a filtrate containing lithium bicarbonate.

In the present invention, the conditions for the thermal decomposition may be selected from a wide range, and the lithium carbonate may be obtained by decomposing the filtrate containing lithium hydrogencarbonate. Preferably, the conditions of thermal decomposition include: the temperature is 60-100 ℃, preferably 80-90 ℃; the time is 1-10h, preferably 2-8 h.

According to the present invention, preferably, in step (4), the temperature of the second hot filtration is 60 to 100 ℃, preferably 80 to 90 ℃.

According to the present invention, preferably, the method further comprises: drying the second hot filtered product; the drying method and conditions may be selected from a wide range, and the moisture remaining on the surface of the lithium carbonate may be removed.

According to the invention, preferably, the lithium carbonate content in the lithium carbonate product is greater than or equal to 99 wt%, preferably 99.1-99.8 wt%; further preferably, the lithium recovery rate in the lithium carbonate product is more than or equal to 82%, and preferably 85-95%.

The present invention will be described in detail below by way of examples.

Example 1

(1) Adding 70g of 3-acetylcholesterol-7-p-toluenesulfonylhydrazone into 430g of lithium amino chlorobenzene suspension (lithium amino charge 9g) for dehydrozone reaction at 100 ℃ for 1.5h, cooling 500g of the obtained dehydrozone liquid to 40 ℃, and filtering to obtain 27.20g of mixed lithium salt, wherein the mixed lithium salt is lithium amino and lithium p-toluenesulfinate, the folding weight is 24.45g, and the molar ratio of the lithium amino to the lithium p-toluenesulfinate is 2.4: 1;

(2) dissolving the mixed lithium salt in 300g of water, and stirring at room temperature to obtain a lithium-containing solution;

(3) mixing lithium-containing solution with 50g of toluene, stirring and extracting for 0.5h, standing to separate a toluene layer, introducing CO into a water layer₂Adjusting the pH value to 9, adding 6.5g of sodium carbonate, stirring for 1h, heating to 80 ℃, and carrying out hot filtration to obtain 16.70g of crude lithium carbonate P1;

(4) dissolving crude lithium carbonate P1 in 300g of water, cooling to 10 ℃, and introducing CO₂Adding 1g of activated carbon into the obtained lithium bicarbonate solution until the solution is clear, stirring and decoloring for 0.5h, filtering to remove the activated carbon, heating the filtrate to 85 +/-2 ℃ for thermal decomposition for 6h, and performing thermal filtration and drying at 85 ℃ to obtain 12.67g of a lithium carbonate product S1;

the content of lithium carbonate in crude lithium carbonate P1 and lithium carbonate product S1 and the recovery rate of lithium salt are shown in Table 1.

Example 2

(1) Adding 70g of 3-acetylcholesterol-7-p-toluenesulfonylhydrazone into 430g of lithium amino chlorobenzene suspension (lithium amino charge 9g) for dehydrozone reaction at 100 ℃ for 1.5h, cooling 500g of the obtained dehydrozone liquid to 30 ℃, and filtering to obtain 27.3g of mixed lithium salt, wherein the mixed lithium salt is lithium amino and lithium p-toluenesulfinate, the folding weight is 24.52g, and the molar ratio of the lithium amino to the lithium p-toluenesulfinate is 2.4: 1;

(2) dissolving the mixed lithium salt in 300g of water, and stirring at room temperature to obtain a lithium-containing solution;

(3) extracting lithium-containing solution with 50g toluene, stirring and extracting for 0.5h, standing to separate a toluene layer, introducing CO into the water layer₂Adjusting the pH value to 9.5, adding 8.5g of potassium carbonate, stirring for 1h, heating to 80 ℃, and carrying out hot filtration to obtain 15.8g of crude lithium carbonate P2;

(4) dissolving crude lithium carbonate P2 in 330g of water, cooling to 10 ℃, and introducing CO₂Adding 1g of activated carbon into the obtained lithium bicarbonate solution until the solution is clear, stirring and decoloring for 0.5h, filtering to remove the activated carbon, heating the filtrate to 90 +/-2 ℃ for thermal decomposition for 4h, and performing thermal filtration and drying at 90 ℃ to obtain 12.81g of a lithium carbonate product S2;

the content of lithium carbonate in crude lithium carbonate P2 and lithium carbonate product S2 and the recovery rate of lithium salt are shown in Table 1.

Example 3

(1) Adding 70g of 3-acetylcholesterol-7-p-toluenesulfonylhydrazone into 430g of lithium amino chlorobenzene suspension (lithium amino charge 9g) for dehydrozone reaction at 100 ℃ for 1.5h, cooling 500g of the obtained dehydrozone liquid to 20 ℃ to obtain 28.1g of mixed lithium salt, wherein the mixed lithium salt is lithium amino and lithium p-toluenesulfinate, the folding weight is 24.65g, and the molar ratio of the lithium amino to the lithium p-toluenesulfinate is 2.4: 1;

(2) dissolving the mixed lithium salt in 300g of water, and stirring at room temperature to obtain a lithium-containing solution;

(3) extracting lithium-containing solution with 50g toluene, stirring and extracting for 0.5h, standing to separate a toluene layer, introducing CO into the water layer₂Adjusting the pH value to 10, adding 6.0g of ammonium carbonate, stirring for 1h, heating to 90 ℃, and carrying out hot filtration to obtain 16.0g of crude lithium carbonate P3;

(4) dissolving crude lithium carbonate P3 in 330g of water, cooling to 5 ℃, and introducing CO₂Adding 1g of activated carbon into the obtained lithium bicarbonate solution until the solution is clear, stirring and decoloring for 0.5h, filtering to remove the activated carbon, heating the filtrate to 85 +/-2 ℃ for thermal decomposition for 6h, and performing thermal filtration and drying at 85 ℃ to obtain 13.44g of a lithium carbonate product S3;

the content of lithium carbonate in crude lithium carbonate P3 and lithium carbonate product S3 and the recovery rate of lithium salt are shown in Table 1.

Example 4

The method of example 1 was followed except that, in step (1), the hydrazone had been removed by cooling to 30 ℃; in the step (2), 80g of toluene is replaced by 80g of toluene to obtain crude lithium carbonate P4, and the rest steps are the same to obtain a lithium carbonate product S4;

the content of lithium carbonate in crude lithium carbonate P4 and lithium carbonate product S4 and the recovery rate of lithium salt are shown in Table 1.

Example 5

The method of example 4 was followed, except that, in step (4), crude lithium carbonate P1 was dissolved in 340g of water, cooled to 0 ℃, and the same steps were followed to obtain lithium carbonate product S5;

the lithium carbonate product S5 contains lithium carbonate and has a lithium salt recovery rate shown in table 1.

Example 6

The procedure of example 1 was followed, except that, in step (3), crude lithium carbonate P1 was dissolved in 510g of water, and the remaining steps were the same, to give a lithium carbonate product S6;

the lithium carbonate product S6 contains lithium carbonate and has a lithium salt recovery rate shown in table 1.

Example 7

The procedure of example 1 was followed, except that in step (4), the amount of activated carbon was replaced with 3g, and the remaining steps were the same, to give a lithium carbonate product S7;

the lithium carbonate product S7 contains lithium carbonate and has a lithium salt recovery rate shown in table 1.

Comparative example 1

The method of example 1 is followed, except that in step (1), 500g of the dehydrazone was directly filtered, and the rest steps are the same, to obtain crude lithium carbonate DP1 and lithium carbonate DS 1;

the lithium carbonate content and lithium salt recovery rate of the crude lithium carbonate DP1 and the lithium carbonate product DS1 are shown in Table 1.

Comparative example 2

The procedure of example 1 was followed, except that, in the step (3), 50g of toluene was not added, that is, 6.5g of sodium carbonate was directly added to the lithium-containing solution to mix, and the remaining steps were the same, to obtain crude lithium carbonate DP2 and lithium carbonate product DS 2;

the lithium carbonate content and lithium salt recovery rate of the crude lithium carbonate DP2 and the lithium carbonate product DS2 are shown in Table 1.

TABLE 1

Note: 1-lithium carbonate content in the crude lithium carbonate product; 2-lithium salt recovery rate in the lithium carbonate crude product; 3-the content of lithium carbonate in the lithium carbonate product; 4-lithium salt recovery rate in lithium carbonate product.

The results in table 1 show that the method provided by the invention can effectively improve the content of lithium carbonate in the crude lithium carbonate product and the recovery rate of lithium salt, and particularly, the method directly converts the lithium salt as the 7-dehydrocholesterol byproduct into lithium carbonate without adding phosphate, thereby simplifying the process flow and avoiding the generation of phosphate wastewater.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.