A method for preparing high-purity lithium tetraborate by controlling lithium content in a reaction solution in a liquid phase

Abstract

The application discloses a method for preparing high-purity lithium tetraborate by controlling lithium content in a reaction solution in a liquid phase, and the method breaks the problem of supersaturated solution of borate solution, which does not precipitate solute and forms water glass solution, by controlling the concentration of lithium carbonate at 60-75 g / L. Meanwhile, in order to solve the problem of coexistence of multiple particles in the borate solution, complex and variable structure, easy formation of multiple structures, and inability to prepare single lithium tetraborate, the application sets a high-temperature reaction stage, when the reaction is carried out for a period of time, white precipitate is precipitated, the solution starts to become milky white, then every 10-12 min, the solution is discharged to test the lithium content in the solution. When the lithium content in the solution reaches 2.6-2.8 g / L, the lithium content in the product lithium tetraborate is closest to the theoretical content 8.21%. Therefore, under the high-temperature condition set in the application, the generated product is only lithium tetraborate without other by-products. The method is simple in process, easy to operate, low in cost and convenient for industrialized production and application.

Description

Technical Field

[0001] This invention relates to the field of lithium tetraborate preparation technology, specifically a method for preparing high-purity lithium tetraborate in a liquid phase by controlling the lithium content in the reaction solution. Background Technology

[0002] Boron compounds are diverse and structurally complex due to the presence of two types of coordination bonds, especially borates. Unlike other inorganic salts, borates exhibit complex and variable structures and properties, and their water solubility is characterized by the coexistence of multiple particles and interactions between boron-oxygen anions, leading to their multiple forms in aqueous solutions. The preparation of lithium tetraborate using lithium salts and boron-containing compounds in the liquid phase can generate various byproducts. Furthermore, existing methods for preparing high-purity lithium tetraborate often use high-purity lithium hydroxide as the lithium salt raw material. However, the preparation process of high-purity lithium hydroxide is complex and expensive, significantly increasing the cost of preparing high-purity lithium tetraborate. Therefore, the complexity of the reaction products and the need to prepare high-purity lithium salts make the preparation of high-purity lithium tetraborate extremely difficult.

[0003] Furthermore, borates commonly exhibit supersaturated dissolution, meaning that borates do not precipitate as solute in solution but instead form a water glass solution. Even after evaporation and concentration, the solute does not precipitate, resulting in no wet borate powder. Current methods for precipitating borates from water glass solutions involve adding ethanol. However, this method has the following problems in practice: 1. Adding ethanol to the borate water glass solution causes borates to precipitate instantly, but these borates are gel-like and highly viscous, causing them to stick to the stirring device and leading to stirring failure. 2. The resulting gel-like borates require further addition of large amounts of ethanol under strong stirring to obtain borate powder, resulting in high solvent consumption. Therefore, existing methods for precipitating borates using ethanol have poor production continuity, require sophisticated equipment, and are costly. Summary of the Invention

[0004] Based on the above, the purpose of this invention is to provide a method for preparing high-purity lithium tetraborate in a liquid phase by controlling the lithium content in the reaction solution, so as to solve the technical problems of low product purity and high cost in existing lithium tetraborate preparation methods.

[0005] To achieve its purpose, the present invention adopts the following technical solution:

[0006] A method for preparing high-purity lithium tetraborate in a liquid phase by controlling the lithium content in the reaction solution includes the following steps:

[0007] (1) Take lithium carbonate with a purity of 99.9%, add boric acid dry powder with a purity of 99.9%, mix evenly to obtain mixed powder;

[0008] (2) Add pure water to the reaction vessel, turn on the stirrer, add the mixed powder from step (1) and react for 50-70 minutes to obtain a clear and transparent solution; the amount of pure water added is based on the concentration of lithium carbonate in the solution being 60-75 g / L.

[0009] The purpose of controlling the lithium carbonate concentration in this step is to break the supersaturated solubility characteristics of the borate solution, prevent the solute from precipitating, and form a water glass-like solution, which is convenient for purification in step (3).

[0010] (3) The clear and transparent solution in step (2) is first filtered through a 3-stage precision filter, then impurities are removed by cation exchange resin, and finally filtered through a 1-stage precision filter to obtain the purified solution;

[0011] (4) High temperature reaction stage: The purified liquid in step (3) is heated to 120-150℃ under the action of condensation and reflux. After a white precipitate is formed, a small amount of solution is taken every 10-12 minutes, cooled to room temperature and the lithium content is measured. When the lithium content is 2.6-2.8 g / L, solid-liquid separation is performed to obtain lithium tetraborate wet material and filtrate.

[0012] (5) Dry the wet lithium tetraborate material in step (4) to obtain lithium tetraborate powder.

[0013] As a further preferred embodiment of the technical solution of the present invention, in step (1), the amount of boric acid used is 1.02-1.05 times the theoretical amount of the reaction.

[0014] Furthermore, in step (2), the reaction temperature is 25-28℃.

[0015] Furthermore, in step (3), the precision filtration refers to filtration using a filter membrane with a pore size of 0.02 μm.

[0016] Furthermore, in step (4), the heating rate is 0.5-2℃ / min.

[0017] Furthermore, in step (4), the solution is rapidly cooled to 25-27°C using an ice-water bath method before the lithium content is tested.

[0018] Furthermore, in step (4), the filtrate is recycled as mother liquor. The lithium and boron content in the mother liquor is detected. In accordance with the requirements of step (1), lithium carbonate and boric acid are added to continue generating high-purity lithium tetraborate, which can further reduce the preparation cost of high-purity lithium tetraborate.

[0019] Furthermore, in step (5), the drying temperature is 400-450℃ and the drying time is 2-3h.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This invention controls the concentration of added lithium carbonate at 60-75 g / L, overcoming the problem of supersaturated borate solutions failing to precipitate solutes and forming water glass solutions. Specifically, when the concentration of lithium carbonate is below 60 g / L, regardless of changes to other reaction conditions, the supersaturated dissolution characteristic of borate solutions cannot be overcome; only water glass solutions are formed after the reaction, and lithium tetraborate does not precipitate. When the concentration of lithium carbonate is above 75 g / L, a clear and transparent intermediate solution cannot be formed, thus preventing the purification of the reaction solution and failing to obtain high-purity lithium tetraborate with a purity of 99.99%.

[0022] 2. To address the problem of multiple particles coexisting in borate solutions, resulting in complex and variable structures that easily form various structures and prevent the production of single-component lithium tetraborate, this invention incorporates a high-temperature reaction stage, causing complex borates to tend towards the formation of single-component lithium tetraborate. After the reaction has proceeded for a period, precipitate forms, and the solution begins to turn milky white. Every 10-12 minutes, the solution is drained to test the lithium content. There are three key points to achieving the high-temperature reaction: First, the reaction temperature must be between 100-150℃; second, boric acid must be in excess. If only the theoretical amounts of lithium carbonate and boric acid are added, the precipitation of lithium tetraborate later reduces the lithium and boron content in the solution, making the later product more likely to form lithium metaborate; third, after the precipitate appears and the solution turns milky white, the lithium content in the solution is continuously monitored. When the lithium content in the solution reaches between 2.6-2.8 g / L, the lithium content in the product lithium tetraborate is closest to the theoretical content of 8.21%. In summary, under the high-temperature conditions set by this invention, combined with monitoring of the liquid lithium content after the reaction, the generated product consists only of lithium tetraborate and contains no other byproducts.

[0023] 3. The method of the present invention is simple, easy to operate, low in cost, and convenient for industrial production application. Detailed Implementation

[0024] The present invention will now be described in detail with reference to specific embodiments.

[0025] In the following embodiments of the present invention, the lithium carbonate is high-purity lithium carbonate with a purity of 99.9%, and the boric acid is boric acid with a purity of 99.9%. The precision filtration refers to filtration using a filter membrane with a pore size of 0.02 μm. The cation exchange resin is D401 cation exchange resin.

[0026] Example 1

[0027] (1) Take 100g of lithium carbonate with a purity of 99.9%, add 350.7g of boric acid (1.05 times the theoretical amount of reaction) dry powder, mix evenly to obtain mixed powder;

[0028] (2) Add 1.43L of pure water to the reactor equipped with a reflux condenser, turn on the stirring, add the mixed powder from step (1), and react at 26°C for 50 minutes. The solution changes from a slurry to a clear and transparent solution. The amount of pure water added is based on the concentration of lithium carbonate in the solution being 70g / L.

[0029] (3) The clear and transparent solution in step (2) is first filtered through a 3-stage precision filter, then impurities are removed by a 3-stage cation exchange resin, and finally filtered through a 1-stage precision filter to obtain the purified solution;

[0030] (4) High temperature reaction stage: The purified liquid in step (3) is heated to 120°C under the action of reflux and white precipitate is formed. A small amount of solution is taken every 10 minutes and the temperature is quickly lowered to 26°C to determine the lithium content. When the lithium content is 2.7 g / L, solid-liquid separation is performed to obtain lithium tetraborate wet material and filtrate. The filtrate is used as mother liquor for recycling. The lithium and boron content in the mother liquor is detected. According to the requirements in step (1), lithium carbonate and boric acid are added to continue to generate high-purity lithium tetraborate.

[0031] (5) Dry the wet lithium tetraborate material in (4) at 400℃ for 2 hours to obtain lithium tetraborate powder.

[0032] The main content and elemental analysis results of the prepared lithium tetraborate are shown in Table 1.

[0033] Table 1. Main content and elemental analysis results of lithium tetraborate in Example 1

[0034]

[0035] Currently, the industry standard for high-purity lithium tetraborate requires a B2O3:Li2O ratio between 0.2125 and 0.2145. As can be seen from the results in Table 1, the lithium tetraborate mass ratio in Example 1 of this invention meets the industry standard for the B2O3:Li2O mass ratio in high-purity lithium tetraborate.

[0036] Examples 2-7

[0037] Examples 2-7 are the same as Example 1 in other steps, except that the amount of boric acid in step (1) is changed. The effect of the amount of boric acid on the purity of lithium tetraborate is shown in Table 2.

[0038] Table 2 Effect of boric acid dosage on the purity of lithium tetraborate

[0039]

[0040] The data from the above embodiments show that when the theoretical amount of boric acid is 1.02-1.05 times, the purity of the prepared lithium tetraborate is ≥99.99%. Therefore, the amount of boric acid is selected to be 1.02-1.05 times the theoretical amount.

[0041] Examples 8-13

[0042] Examples 8-13 are the same as Example 1 in other steps, except that the reaction time in step (2) is changed. The effect of reaction time on whether a transparent solution is formed is shown in Table 3.

[0043] Table 3. Effect of reaction time on whether a transparent solution is formed.

[0044]

[0045] The data from the above embodiments show that a transparent solution can be obtained when the reaction time of step (2) is greater than 50 min. The preferred reaction time for step (2) is 50-60 min.

[0046] Examples 14-28

[0047] Examples 14-28 are the same as Example 1 in other steps, except that the lithium carbonate concentration in step (2) is changed. The effect of lithium carbonate concentration on whether a transparent solution is formed and whether lithium tetraborate will precipitate in the liquid phase during the high-temperature reaction stage is shown in Table 4.

[0048] Table 4 shows the effect of lithium carbonate concentration on the formation of a transparent solution and the high-temperature reaction stage, as well as the precipitation of lithium tetraborate.

[0049]

[0050] The experimental data from the above embodiments show that when the concentration of lithium carbonate is 60-75 g / L, the supersaturation property of lithium tetraborate, which prevents solute precipitation, can be broken, and purification can also be achieved. Therefore, a lithium carbonate concentration of 60-75 g / L is preferred.

[0051] Examples 29-32

[0052] Examples 29-32 are the same as Example 1 in other steps, except that the heating rate in step (4) is changed. The effect of the heating rate on the purity of the generated lithium tetraborate is shown in Table 5.

[0053] Table 5 Effect of heating rate on the purity of the generated lithium tetraborate

[0054]

[0055] The experimental data from the above embodiments show that a heating rate of 0.5-2℃ / min has no effect on the purity of lithium tetraborate. Therefore, a heating rate of 0.5-2℃ / min is acceptable.

[0056] Examples 33-43

[0057] Examples 33-43 are the same as Example 1 in other steps, except that the heating temperature in step (4) is changed. The heating temperature affects the purity of the generated lithium tetraborate.

[0058] Table 6. Effect of heating temperature on the purity of the generated lithium tetraborate.

[0059]

[0060] The experimental data from the above embodiments show that when the reaction temperature after heating is between 120℃ and 150℃, the purity of the obtained lithium tetraborate is ≥99.99%. Considering energy consumption, a reaction temperature of 120-130℃ is preferred.

[0061] Examples 44-54

[0062] Examples 44-54 are identical to Example 1 in all other steps, except for the sampling interval in step (4), to investigate the effect of the sampling interval on the purity of the generated lithium tetraborate. The effect of the sampling interval on the purity of the generated lithium tetraborate is shown in Table 7.

[0063] Table 7. Effect of sampling interval on the purity of the generated lithium tetraborate.

[0064]

[0065] The experimental data from the above embodiments show that when the sampling interval is 10-12 min, the purity of the obtained lithium tetraborate is ≥99.99%. Therefore, a sampling interval of 10-12 min is preferred.

[0066] Examples 55-65

[0067] Examples 55-65 are the same as Example 1 in other steps, except that the lithium content in the post-reaction solution in step (4) is changed. The effect of the lithium content in the post-reaction solution on the purity of the generated lithium tetraborate is shown in Table 8.

[0068] Table 8. Effect of lithium content in the solution after reaction on the purity of the generated lithium tetraborate.

[0069]

[0070] The experimental data from the above embodiments show that when the lithium content in the solution after the reaction is controlled at 2.6-2.8 g / L, the purity of the obtained lithium tetraborate is ≥99.99%. Therefore, it is preferable to control the lithium content in the solution after the reaction at 2.6-2.8 g / L.

[0071] Examples 66-71

[0072] Examples 66-71 were performed in the same manner as Example 1, except that the drying temperature in step (5) was changed to investigate the effect of drying temperature on the purity of the generated lithium tetraborate. The effect of drying temperature on the purity of the generated lithium tetraborate is shown in Table 9.

[0073] Table 9. Effect of drying temperature on the purity of the generated lithium tetraborate.

[0074]

[0075] The experimental data from the above embodiments show that when the drying temperature is 400-450℃, the purity of the obtained lithium tetraborate is greater than 99.99%. Considering energy consumption, the drying temperature of 400-420℃ is preferred.

[0076] Comparative Examples 1-5

[0077] Comparative Example 1 - The comparative example is identical to Example 1 in all other steps except for the removal step (3), to investigate the effect of the removal step on the purity of the generated lithium tetraborate. The effect of the removal step on the purity of the generated lithium tetraborate is shown in Table 10.

[0078] Table 10. Effect of the impurity removal process on the purity of the generated lithium tetraborate.

[0079]

[0080] As can be seen from the repeated comparative examples 1-5 above, when the impurity removal process (3) in Example 1 is removed, the purity of the obtained lithium tetraborate is only about 99.5%, which is low and does not meet the requirement of 99.99% high purity lithium tetraborate.

Claims

1. A method for producing high-purity lithium tetraborate by controlling the lithium content in a reaction solution in a liquid phase, characterized by, The method comprises the following steps: (1) Take lithium carbonate with a purity of 99.9%, and add dry boric acid powder with a purity of 99.9% to mix uniformly to obtain mixed powder; (2) Add pure water to a reaction container, start stirring, and add the mixed powder in step (1) to react for 50-70 min to obtain a clear and transparent solution; the amount of pure water is added according to the concentration of lithium carbonate in the solution being 60-75 g / L; (3) The clear and transparent solution in step (2) is first subjected to 3-stage precision filtration, then impurities are removed through cation exchange resin, and finally 1-stage precision filtration is performed to obtain a purified solution; (4) High-temperature reaction stage: the purified solution in step (3) is heated to 120-150°C under the action of condensation reflux, white precipitate is precipitated, a small amount of solution is taken every 10-12 min, the lithium content in the solution is determined after cooling to room temperature, when the lithium content is 2.6-2.8 g / L, solid-liquid separation is performed to obtain lithium tetraborate wet material and filtrate; (5) Dry the lithium tetraborate wet material in step (4) to obtain lithium tetraborate powder.

2. The method for preparing high purity lithium tetraborate by controlling the lithium content in the reaction solution in a liquid phase according to claim 1, characterized in that, In step (1), the amount of boric acid is 1.02-1.05 times the theoretical amount of reaction.

3. The method for preparing high purity lithium tetraborate by controlling the lithium content in the reaction solution in a liquid phase according to claim 1, characterized in that, In step (2), the reaction temperature is 25-28°C.

4. The method for preparing high purity lithium tetraborate by controlling the lithium content in the reaction solution in a liquid phase according to claim 1, characterized in that, In step (3), the precision filtration refers to filtering with a filter membrane with a pore size of 0.02 μm.

5. The method for preparing high purity lithium tetraborate by controlling the lithium content in the reaction solution in a liquid phase according to claim 1, characterized in that, In step (4), the heating rate is 0.5-2°C / min.

6. The method for preparing high purity lithium tetraborate by controlling the lithium content in the reaction solution in a liquid phase according to claim 5, characterized in that, In step (4), the solution is rapidly cooled to 25-27°C using an ice water bath method, and then the lithium content is tested.

7. The method for preparing high purity lithium tetraborate by controlling the lithium content in the reaction solution in a liquid phase according to claim 6, characterized in that, In step (4), the filtrate is used as a mother liquor for recycling, the contents of lithium and boron in the mother liquor are detected, lithium carbonate and boric acid are added according to the requirements in step (1) to continue generating high-purity lithium tetraborate.

8. The method for preparing high purity lithium tetraborate in liquid phase by controlling lithium content in reaction solution according to any one of claims 1-7, characterized in that, In step (5), the drying temperature is 400-450°C, and the drying time is 2-3 h.

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