A method for preparing high-purity lithium tetraborate powder by liquid phase method

Abstract

This invention discloses a liquid-phase method for preparing high-purity lithium tetraborate powder. It utilizes readily available and inexpensive 99.999% lithium carbonate and 99.9% boric acid in a liquid phase. By controlling the concentration of lithium carbonate in the feed, the supersaturated solubility characteristic of lithium tetraborate solution is overcome, allowing 99.99% pure lithium tetraborate powder to precipitate directly from the aqueous solution. This method eliminates the need for ethanol and utilizes the insolubility of lithium tetraborate in ethanol to precipitate it from the water glass solution. It also eliminates the need for other reagents, solving the problem of highly viscous lithium tetraborate obtained after adding ethanol, which sticks to the stirring device and hinders production. By controlling the reaction temperature and introducing a certain mass of carbon dioxide into the reaction system, the generation of by-products is suppressed, causing various forms of borate in the solution to tend towards the formation of a single lithium tetraborate. This method generates lithium tetraborate entirely in the liquid phase, resulting in low energy consumption, low cost, simple process, ease of operation, and suitability for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of lithium tetraborate preparation technology, specifically a method for preparing high-purity lithium tetraborate powder using a liquid-phase method. 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 and the coexistence of multiple particles allow them to appear in various forms in aqueous solutions. When preparing lithium tetraborate using lithium salts and boron-containing compounds in the liquid phase, various byproducts may be generated. Furthermore, existing methods for preparing high-purity lithium tetraborate often use high-purity lithium hydroxide as the lithium salt raw material. However, the strong alkalinity of lithium hydroxide solutions makes the preparation process of high-purity lithium hydroxide complex and difficult, and the high price of high-purity lithium hydroxide significantly increases the production cost of high-purity lithium tetraborate. Therefore, the complexity of the reaction products and the preparation of high-purity lithium salts make the preparation of high-purity lithium tetraborate extremely difficult.

[0003] Furthermore, due to the complex polymerization and association between borate ions and the interaction between the ions and the solvent water, its supersaturated solution exhibits considerable stability, making crystallization difficult. Its highly supersaturated aqueous solution readily forms a gel-like substance similar to water glass, without any precipitation. This significantly increases the difficulty of preparing high-purity lithium tetraborate in the liquid phase. Chinese invention patent CN115304074A aims to overcome the supersaturation of lithium tetraborate solution by adding alcohol to precipitate lithium tetraborate. However, this method has the following problems in practical operation: 1. Lithium tetraborate precipitates instantly after adding alcohol, but this lithium tetraborate is gel-like and highly viscous, which can stick to the stirring device, causing stirring failure. 2. The obtained gel-like lithium tetraborate requires the subsequent addition of a large amount of ethanol under strong stirring to obtain lithium tetraborate powder, resulting in high solvent consumption. Therefore, the existing method of using ethanol to precipitate borate has poor production continuity, high equipment requirements, and high costs. To address this issue, Chinese invention patent CN 115304074 A proposed adding lithium chloride to the solution to solve the problem of excessively sticky precipitated lithium tetraborate. However, this method still relies on ethanol to precipitate lithium tetraborate, and then uses lithium chloride to solve the problem of excessive stickiness. This method consumes a large amount of reagent and does not fundamentally solve the problem of supersaturated dissolution of lithium tetraborate solution, meaning that lithium tetraborate powder is not actually precipitated in the solution. Furthermore, the use of lithium chloride introduces chloride ions, leading to severe corrosion of the reaction vessel, high equipment requirements, and increased costs. 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 powder by liquid phase method, so as to solve the technical problems of difficulty in preparing high-purity lithium tetraborate by liquid phase method, large reagent consumption and high preparation cost.

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

[0006] A method for preparing high-purity lithium tetraborate powder by liquid phase method includes the following steps:

[0007] (1) Take lithium carbonate with a purity of 99.999%, add boric acid with a purity of 99.9%, mix evenly to obtain a mixed powder;

[0008] (2) Add pure water to the reaction vessel, add the mixed powder from step (1), and react at room temperature 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] If too much pure water is added, causing the concentration of lithium carbonate to be lower than the required range, the supersaturation characteristic of the lithium tetraborate solution cannot be broken. After the reaction, only a water glass-like supersaturated lithium tetraborate solution can be obtained, and lithium tetraborate cannot be precipitated. To precipitate lithium tetraborate, ethanol must be added. If the concentration of lithium carbonate is higher than this range, a transparent solution cannot be obtained in the room temperature stage of step (2), and only a slurry can be obtained, which makes the reaction solution unable to be purified. The purity of the prepared lithium tetraborate does not reach the standard of 99.99%.

[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) Put the purified liquid from step (3) into the reaction vessel, introduce carbon dioxide, and then heat the purified liquid to 70-85℃ and react for 1-3 hours to obtain the reaction liquid;

[0012] (5) Heat the reaction solution in step (4) to 120-130℃ to react and obtain a milky white slurry. Separate the solid and liquid while hot to obtain wet lithium tetraborate.

[0013] During the reaction time of steps (4)-(5), ensure that carbon dioxide is released slowly and at a constant rate until all carbon dioxide is exhausted.

[0014] (6) Dry the wet lithium tetraborate material in step (5) to obtain high-purity lithium tetraborate powder.

[0015] As a further preferred embodiment of the technical solution of the present invention, in step (1), the molar ratio of lithium carbonate to boric acid is 1:4.02-4.1.

[0016] Furthermore, in step (2), the reaction time is 1-3 hours.

[0017] Furthermore, in step (3), the precision filtration refers to filtration using a filter membrane with a pore size of 0.02 μm.

[0018] Further, in step (4), the mass of carbon dioxide added (kg) = the volume of the reactor (L) × (0.01-0.05kg).

[0019] Furthermore, the heating rate is 0.5-1℃ / min.

[0020] Furthermore, in step (5), the heating rate is 0.5-1℃ / min.

[0021] Furthermore, CO2 discharge rate = CO2 added mass / total reaction time of step (4) - (5).

[0022] Furthermore, in step (5), the reaction time is 8-9 hours.

[0023] Furthermore, in step (6), the drying temperature is 400-450℃ and the drying time is 2-3h.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention uses readily available and reasonably priced 99.9% lithium carbonate and 99.9% boric acid to react in the liquid phase. By controlling the concentration of lithium carbonate in the feed, the supersaturated solubility characteristic of lithium tetraborate solution is broken, and lithium tetraborate powder with a purity of 99.99% is directly precipitated in aqueous solution. There is no need to add ethanol, and the insolubility of lithium tetraborate in ethanol is used to precipitate lithium tetraborate in water glass solution. No other reagents are needed, which solves the problem that the lithium tetraborate obtained after adding ethanol is very viscous and sticks to the stirring device, causing production obstruction.

[0026] 2. This invention, by controlling the reaction temperature and introducing a certain mass of carbon dioxide into the reaction system, suppresses the formation of byproducts, causing various forms of borate in the solution to tend to form a single lithium tetraborate. This method generates lithium tetraborate entirely in the liquid phase, resulting in low energy consumption, low cost, simple procedures, ease of operation, and suitability for large-scale production. Detailed Implementation

[0027] The present invention will now be described in detail with reference to specific embodiments.

[0028] In the following embodiments of the present invention, the lithium carbonate has a purity of 99.999%, and the boric acid has 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 001×7.

[0029] Example 1

[0030] (1) Take 100g of lithium carbonate, add 334.8g of boric acid (molar ratio 1:4.02), mix evenly to obtain a mixed powder;

[0031] (2) Add 1.54L of pure water to the high-pressure stainless steel reactor, add the mixed powder from step (1), and react at room temperature to obtain a clear and transparent solution with a lithium carbonate concentration of 65g / L.

[0032] (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;

[0033] (4) Put the purified liquid from step (3) into the reaction vessel, introduce 0.12 kg (3 × 0.04 kg) of carbon dioxide, and then heat the purified liquid to 80 °C at a heating rate of 1 °C / min. React for 2 h to obtain the reaction liquid.

[0034] (5) The reaction solution in step (4) is heated to 120°C at a heating rate of 1°C / min and reacted for 7 hours to obtain a milky white slurry. Solid-liquid separation is performed while hot to obtain lithium tetraborate wet material. In steps (4)-(5), carbon dioxide is continuously released slowly and uniformly within the reaction time of (4)-(5) until the carbon dioxide is completely discharged. The CO2 discharge rate of the whole process is 0.12kg / 9h (the gas discharge rate is the mass of carbon dioxide added / the total reaction time of (4)-(5) = 0.12kg / (2h+7h) = 0.12kg / 9h).

[0035] (6) Place the wet lithium tetraborate material from step (5) into an oven and dry it at 400°C for 2 hours to obtain high-purity lithium tetraborate powder.

[0036] The detection data of lithium tetraborate prepared in Example 1 are shown in Table 1.

[0037] Table 1. Detection data of lithium tetraborate in Example 1

[0038]

[0039] Examples 2-12

[0040] Examples 2-12 are identical to Example 1 in all other steps, except for the change in the molar ratio of lithium carbonate to boric acid in step (1). The effect of the molar ratio of lithium carbonate to boric acid on the purity of lithium tetraborate is shown in Table 2.

[0041] Table 2. Effect of the molar ratio of lithium tetraborate to boric acid on the purity of lithium tetraborate.

[0042]

[0043] As shown in Table 2, when the molar ratio of lithium carbonate to boric acid is 1:4.02-4.1, the purity of the prepared lithium tetraborate is ≥99.99%. Furthermore, the mass ratio of B₂O₃:Li₂O in the tested product is between 0.2125 and 0.2145, which meets the requirements. Therefore, a molar ratio of lithium carbonate to boric acid of 1:4.02-4.1 is optimally selected.

[0044] Examples 13-20

[0045] Examples 13-20 are identical to Example 1 in all other steps, except for the concentration of lithium carbonate in step (2). The effect of the concentration of lithium carbonate on whether lithium carbonate powder is precipitated at high temperature and whether a clear and transparent intermediate solution is formed in the low temperature reaction stage is shown in Table 3.

[0046] Table 3 shows the effect of lithium carbonate concentration on whether lithium carbonate powder precipitates at high temperatures and whether a clear, transparent intermediate solution forms during the low-temperature reaction stage.

[0047]

[0048] As shown in Table 3, when the lithium carbonate concentration is greater than 60 g / L, lithium tetraborate powder precipitates during the high-temperature reaction stage, breaking the supersaturation of the lithium tetraborate solution and preventing precipitation to form a glassy aqueous solution. When the lithium carbonate concentration is less than 75 g / L, a clear and transparent solution forms during the low-temperature reaction stage, facilitating purification through ion exchange resin and ensuring the subsequent precipitation of high-purity lithium tetraborate with a purity of 99.99%. Therefore, a lithium carbonate concentration of 60-75 g / L is optimally chosen.

[0049] Examples 20-25

[0050] Examples 20-25 are identical to Example 1 in all other steps, except for the removal of step (3) purification process from Example 1. The purity of the resulting lithium tetraborate without the purification process is shown in Table 4.

[0051] Table 4. Effect of no purification process on the purity of the prepared lithium tetraborate.

[0052]

[0053] As can be seen from the five repeated examples of Examples 20-24, when the purification step (3) is not performed, the purity of the obtained lithium tetraborate is only about 98%, which is far from the target product of high-purity lithium tetraborate with a purity of 99.99%.

[0054] Examples 25-30

[0055] Examples 25-30 are identical to Example 1 in all other steps, except for the reaction temperature in step (4). The effect of reaction temperature on the purity of lithium tetraborate is shown in Table 5.

[0056] Table 5. Effect of reaction temperature on the purity of lithium tetraborate

[0057]

[0058] As shown in Table 5, the purity of lithium tetraborate obtained at a reaction temperature of 75-80℃ is ≥99.99%. Furthermore, the mass ratio of B2O3:Li2O in the tested product is between 0.2125 and 0.2145, which meets the requirements. Therefore, a reaction temperature of 75-80℃ is optimally chosen.

[0059] Examples 31-37

[0060] Examples 31-37 are identical to Example 1 in all other steps, except for the reaction temperature in step (5). The effect of reaction temperature on the purity of lithium tetraborate is shown in Table 6.

[0061] Table 6. Effect of reaction temperature on the purity of lithium tetraborate

[0062]

[0063] As shown in Table 6, the purity of lithium tetraborate obtained at a reaction temperature of 120-130℃ is ≥99.99%. Furthermore, the mass ratio of B2O3:Li2O in the tested product is between 0.2125 and 0.2145, which meets the requirements. Therefore, a reaction temperature of 120-130℃ is optimally chosen.

[0064] Examples 38-42

[0065] Examples 38-42 are identical to Example 1 in all other steps, except that the heating step (4) in Example 1 is removed. The effect of omitting the heating step (4) on the purity of the obtained lithium tetraborate is shown in Table 7.

[0066] Table 7 shows the effect of step (4) heating process on the purity of the obtained lithium tetraborate.

[0067]

[0068] As can be seen from the five repeated examples of Examples 38-42, when the heating step (4) is omitted, the purity of the obtained lithium tetraborate is only about 99.9%, which is different from the target purity of 99.99%. The reason is that suddenly raising the reaction temperature to the high temperature in step (5) will produce a small amount of other borates, which cannot be converted into lithium tetraborate during the high-temperature reaction stage. A lower reaction temperature range is needed to buffer the reaction and avoid the formation of borates that cannot be converted into lithium tetraborate during the high-temperature stage, thus affecting the purity of the obtained lithium tetraborate.

[0069] Examples 43-48

[0070] Examples 43-48 are identical to Example 1 in all other steps, except for the mass of carbon dioxide added in step (4). The effect of the mass of carbon dioxide on the purity of lithium tetraborate is shown in Table 8.

[0071] Table 8. Effect of carbon dioxide mass on the purity of lithium tetraborate

[0072]

[0073] As shown in Table 8, when the amount of carbon dioxide added is (0.04V-0.05V) kg, the purity of the prepared lithium tetraborate is greater than 99.99%. Furthermore, the mass ratio of B2O3:Li2O in the tested product is between 0.2125 and 0.2145, which meets the requirements. Therefore, the optimal amount of carbon dioxide added is (0.04V-0.05V) kg; where V represents the volume of the reactor.

[0074] Examples 49-56

[0075] Examples 49-56 are identical to Example 1 in all other steps, except for the heating rate in step (5). The effect of reaction time on the purity of lithium tetraborate is shown in Table 9.

[0076] Table 9 Effect of heating rate on the purity of lithium tetraborate

[0077]

[0078] As shown in Table 9, the purity of the prepared lithium tetraborate is ≥99.99% when the heating rate is 0.5-1℃ / min. Furthermore, the mass ratio of B2O3:Li2O in the tested product is between 0.2125 and 0.2145, which meets the requirements. Therefore, a heating rate of 1℃ / min is optimally selected.

[0079] Examples 57-65

[0080] Examples 57-65 are identical to Example 1 in all other steps, except for the reaction time in step (5). The effect of reaction time on the purity of lithium tetraborate is shown in Table 10.

[0081] Table 10 Effect of reaction time on the purity of lithium tetraborate

[0082]

[0083] As shown in Table 10, when the reaction time is greater than 8 hours, the purity of the prepared lithium tetraborate is ≥99.99%. Furthermore, the mass ratio of B₂O₃:Li₂O in the tested product is between 0.2125 and 0.2145, which meets the requirements. Therefore, a reaction time of 8 hours is optimally chosen.

[0084] Examples 66-71

[0085] Examples 66-71 are identical to Example 1 in all other steps, except for the drying temperature in step (6). The effect of drying temperature on the purity of lithium tetraborate is shown in Table 11.

[0086] Table 11 Effect of drying temperature on the purity of lithium tetraborate

[0087]

[0088] As shown in Table 11, the purity of lithium tetraborate obtained at a drying temperature of 400-450℃ is ≥99.99%. Furthermore, the mass ratio of B2O3:Li2O in the tested product is between 0.2125 and 0.2145, which meets the requirements. Therefore, a drying temperature of 400℃ is optimally selected.

Claims

1. A method for preparing high-purity lithium tetraborate powder by a liquid phase method, characterized in that, The method comprises the following steps: (1) taking lithium carbonate with a purity of 99.999%, adding boric acid with a purity of 99.9%, and mixing uniformly to obtain mixed powder; (2) adding pure water to a reaction container, adding the mixed powder in step (1), and reacting at room temperature to obtain a clear and transparent solution; the amount of pure water added is determined according to the concentration of lithium carbonate in the solution being 60-75 g / L; (3) subjecting the clear and transparent solution in step (2) to 3-stage precision filtration, then removing impurities through cation exchange resin, and finally subjecting the solution to 1-stage precision filtration to obtain purified solution; (4) placing the purified solution in step (3) into a reaction kettle, introducing carbon dioxide, then heating the purified solution to 70-85 DEG C, and reacting for 1-3 h to obtain reaction solution; (5) heating the reaction solution in step (4) to 120-130 DEG C to react, obtaining milky white slurry, and separating the slurry while hot to obtain lithium tetraborate wet material; (6) drying the lithium tetraborate wet material in step (5) to obtain high-purity lithium tetraborate powder.

2. The method according to claim 1, wherein the method is characterized by, In step (1), the molar ratio of lithium carbonate to boric acid is 1:4.02-4.

1.

3. The method of claim 1, wherein the method is a liquid phase method for preparing high purity lithium tetraborate powder, characterized in that, In step (2), the reaction time is 1-3 h.

4. The method of claim 1, wherein the method is characterized by, In step (3), the precision filtration refers to using a filter membrane with a pore size of 0.02 μm for filtration.

5. The method of claim 1, wherein the method is a liquid phase method for preparing high purity lithium tetraborate powder, characterized in that, In step (4), the mass of carbon dioxide added = reaction kettle volume x (0.01-0.05), wherein the mass of carbon dioxide added is in kg, and the volume of the reaction kettle is in L.

6. The method of claim 5, wherein the lithium tetraborate powder has a purity of 99.99% or more. The heating rate is 0.5-1 DEG C / min.

7. The method of claim 1, wherein the method is a liquid phase method for preparing high purity lithium tetraborate powder, characterized in that, In step (5), the heating rate is 0.5-1 DEG C / min.

8. The method of claim 5, wherein the lithium tetraborate powder has a purity of 99.99% or more. The CO2 discharge rate = CO2 addition mass / total reaction time from step (4) to step (5).

9. The method for preparing high-purity lithium tetraborate powder by liquid phase method as described in claim 8, characterized in that, In step (5), the reaction time is 8-9 h.

10. The method for preparing high-purity lithium tetraborate powder by liquid phase method according to any one of claims 1-9, characterized in that, In step (6), the drying temperature is 400-450 DEG C, and the drying time is 2-3 h.

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