A method for directly preparing a lithium tetraborate and lithium metaborate mixed fluxing agent by a liquid phase method

Abstract

The application discloses a method for directly preparing lithium tetraborate and lithium metaborate mixed flux by a liquid phase method. The method uses 99.9% lithium carbonate and 99.9% boric acid which are easy to obtain and have moderate prices to react in a liquid phase. By controlling the concentration of lithium carbonate in the feeding, the supersaturation dissolution characteristics of lithium tetraborate solution are broken, and lithium tetraborate and lithium metaborate mixed flux are directly precipitated in an aqueous solution. By controlling the reaction temperature and cooperating with the introduction of a certain mass of carbon dioxide into the reaction system, the generation of by-products is inhibited, and various forms of borate in the solution tend to generate the required mixed flux. The mixed flux required by the method is generated in a liquid phase by a chemical method, and the method has the advantages of low energy consumption, low cost, simple process, easy operation and convenience for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of mixed flux technology, specifically a method for directly preparing a mixed flux of lithium tetraborate and lithium metaborate 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. In particular, borates, unlike other inorganic salts, have complex and variable structures and properties. Their water solubility is characterized by the coexistence of multiple particles and the interaction between boron and oxygen anions. This results in borates appearing in aqueous solutions in multiple forms, which may lead to the generation of various byproducts in the synthesis reaction. This makes it extremely difficult to generate specific mixed fluxes.

[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.

[0004] Existing methods for obtaining mixed fluxes of lithium tetraborate and lithium metaborate all involve physically mixing separately prepared lithium metaborate and lithium tetraborate in a specific ratio. However, this method is complex, requiring the separate preparation of lithium metaborate and lithium tetraborate. Furthermore, physical mixing can result in uneven mixing and dust generation, leading to material loss. In contrast, the chemical method requires only a single reaction in one batch to produce the desired mixed flux. The process is simple and easy to operate. Currently, there is no chemical method for directly obtaining a mixed flux in a specific ratio in the liquid phase. Summary of the Invention

[0005] The purpose of this invention is to provide a method for directly preparing a mixed flux of lithium tetraborate and lithium metaborate using a liquid phase method, so as to solve the technical problems of difficult preparation and high preparation cost of mixed flux of lithium tetraborate and lithium metaborate.

[0006] To achieve its purpose, the present invention adopts the following technical solution:

[0007] A method for directly preparing a mixed flux of lithium tetraborate and lithium metaborate using a liquid-phase method includes the following steps:

[0008] (1) Take lithium carbonate with a purity of 99.9%, add boric acid with a purity of 99.9%, mix evenly to obtain a mixed powder; wherein, the amount of lithium carbonate (g) = (73.88a / 169.12) + (73.88b / 99.5); the amount of boric acid (g) = (247.24a / 169.12) + (61.81b / 49.75), where a and b are the mass ratio of lithium tetraborate to lithium metaborate in the prepared mixed flux; 73.88 is the molar mass of lithium carbonate, 169.12 is the molar mass of lithium tetraborate, 61.81 is the molar mass of boric acid, 49.75 is the molar mass of lithium metaborate, 247.24 is 4 × 61.81 (molar mass of boric acid), and 99.5 is 2 × 49.75 (molar mass of lithium metaborate).

[0009] The preferred mass ratio of lithium tetraborate to lithium metaborate is 1:0.49-2.

[0010] (2) Add pure water to the reaction vessel, add the mixed powder from step (1), and react at 20-30°C 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.

[0011] (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;

[0012] (4) Put the purified liquid from step (3) into the reaction vessel, introduce carbon dioxide, then heat the purified liquid to 75-80℃ and react for 1-3 hours to obtain the reaction liquid;

[0013] (5) Heat the reaction solution in step (4) to 100-130℃ and react for 3-5 hours. Then cool it down to 80-90℃ and continue to react for 1-5 hours to obtain a milky white slurry. Separate the solid and liquid while hot to obtain a wet flux mixture of lithium tetraborate and lithium metaborate.

[0014] Steps (4)-(5) ensure that carbon dioxide is released slowly and uniformly within the reaction time of (4)-(5) until the carbon dioxide is completely discharged;

[0015] (6) Dry the wet flux mixture from step (5) to obtain the finished product of the mixed flux of lithium tetraborate and lithium metaborate.

[0016] As a further preferred embodiment of the technical solution of the present invention, in step (2), the reaction time is 1-2 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); the heating rate is 0.5-1℃ / min.

[0019] Furthermore, in step (5), the heating rate is 0.8-1℃ / min.

[0020] Furthermore, CO2 discharge rate = CO2 added mass / total reaction time of step (4) - (5).

[0021] Furthermore, in step (6), the drying temperature is 400-450℃ and the drying time is 2-3h.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. This invention uses 99.9% lithium carbonate and 99.9% boric acid, which are reasonably priced and readily available, 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 a mixed flux of lithium tetraborate and lithium metaborate is directly precipitated in the aqueous solution.

[0024] 2. This invention, by controlling the reaction temperature and introducing a certain mass of carbon dioxide into the reaction system, suppresses the generation of by-products, causing various forms of borates in the solution to tend to form the desired mixed flux. The mixed flux required by this method is generated entirely in the liquid phase, resulting in low energy consumption, low cost, simple process, ease of operation, and suitability for large-scale production.

[0025] 3. The chemical reaction equation for the preparation of a mixed flux from lithium carbonate and boric acid is as follows:

[0026] Li2CO3+4H3BO3=Li2B4O7+CO2+6H2O

[0027] LiC₂O₃ + 2H₃BO₃ = 2LiBO₂ + CO₂ + 3H₂O

[0028] As can be seen from the two chemical reaction equations, when a mixed solution of lithium carbonate and boric acid is added to the reaction vessel, lithium metaborate and lithium tetraborate will be produced in the forward direction of the reaction, along with other forms of borate byproducts, and a large amount of carbon dioxide will be generated.

[0029] (1) The purpose of controlling the temperature is that lithium metaborate and lithium tetraborate have different formation trends at different temperatures. A specific high temperature is conducive to the formation of lithium tetraborate, while a specific low temperature is conducive to the formation of lithium metaborate.

[0030] (2) The purpose of introducing a certain mass of carbon dioxide into the reactor is to suppress the generation of other by-products, thereby obtaining a high-purity lithium tetraborate and lithium metaborate mixed flux.

[0031] Therefore, the present invention introduces a certain mass of carbon dioxide into the reactor and controls the temperature difference reaction, so that the entire reaction tends to generate a high-purity mixed flux of lithium tetraborate and lithium metaborate.

[0032] 4. In this invention, the purified liquid is first reacted at a low temperature of 70-85℃ to prevent the temperature from rising too quickly and generating borate byproducts that cannot be converted into lithium tetraborate and lithium metaborate. Then, the reaction is carried out at a high temperature of 100-130℃. The reaction products tend to form lithium tetraborate. As lithium tetraborate is formed, the formation of lithium tetraborate powder will reduce the boric acid concentration in the reaction system, making it more likely to form lithium metaborate. Finally, taking advantage of the characteristic that low temperature is conducive to the formation of lithium metaborate, lithium metaborate is generated by cooling (cooling to 80-90℃), and a mixed flux of lithium tetraborate and lithium metaborate in a specific ratio is finally obtained. Attached Figure Description

[0033] Figure 1 The XRD pattern of the lithium tetraborate: lithium metaborate 67:33 mixed flux of the present invention is shown below.

[0034] Figure 2 The XRD pattern is shown for the 1:1 mixed flux of lithium tetraborate and lithium metaborate of this invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the embodiments.

[0036] In the following embodiments of the present invention, the purity of lithium carbonate is 99.9%, and the purity of boric acid is 99.9%. Precision filtration refers to filtration using a filter membrane with a pore size of 0.02 μm. The cation exchange resin is 001×7, and the purity of the mixed flux is calculated as (1 - the total amount of measured impurity metal ions) × 100%.

[0037] Example 1: Preparation of a mixed flux of lithium tetraborate and lithium metaborate (12:22, 1:1.83)

[0038] (1) Take 108g of lithium carbonate, add 224g of boric acid, mix evenly to obtain a mixed powder (the molar ratio of boric acid to lithium carbonate is 2.5:1).

[0039] (2) Add 1.66L of pure water to a 3L reactor, add the mixed powder from step (1), and react at 26℃ for 60min to obtain a clear and transparent solution with a lithium carbonate concentration of 65g / L.

[0040] (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;

[0041] (4) Put the purified liquid from step (3) into the reaction vessel, introduce 0.09 kg of carbon dioxide, and then heat the purified liquid to 80°C at a heating rate of 1°C / min. React for 2 hours to obtain the reaction liquid; the mass of carbon dioxide added (kg) = 3L × 0.03 = 0.09 kg;

[0042] (5) The reaction solution in step (4) is heated to 120°C at a heating rate of 1°C / min and reacted for 5 hours. Then the temperature is lowered to 85°C and the reaction continues for 5 hours. In steps (4)-(5), carbon dioxide is continuously released slowly and uniformly within the reaction time of (4)-(5) until the carbon dioxide is exhausted. The carbon dioxide discharge rate is 0.09 kg / 12 h throughout the process. A milky white slurry is obtained. Solid-liquid separation is carried out while hot to obtain a mixed flux wet material of lithium tetraborate and lithium metaborate in a ratio of 12:22.

[0043] Calculation of carbon dioxide emission rate: Mass of carbon dioxide added / (4) - (5) Total reaction time = 0.09 kg / (2h + 5h + 5h) = 0.09 kg / 12h;

[0044] (6) The wet flux mixture from step (5) is dried at 400°C for 2 hours to obtain a 12:22 mixed flux powder of lithium tetraborate and lithium metaborate.

[0045] The mass ratio of lithium tetraborate to lithium metaborate in the obtained mixed flux was 12:22, and the purity was 99.99%. The results of the elemental analysis are shown in Table 1.

[0046] Table 1. Elemental analysis results (ppm) of the 12:22 mixed flux powder of lithium tetraborate and lithium metaborate.

[0047]

[0048] Example 2: Preparation of a mixed flux of lithium tetraborate and lithium metaborate 67:33 (1:0.49)

[0049] (1) Take 53.78g of lithium carbonate, add 139.02g of boric acid, mix evenly to obtain a mixed powder (the molar ratio of boric acid to lithium carbonate is 3.12:1).

[0050] (2) Add 1.66L of pure water to a 3L reactor, add the mixed powder from step (1), and react at 26℃ for 60min to obtain a clear and transparent solution with a lithium carbonate concentration of 70g / L.

[0051] (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;

[0052] (4) Put the purified liquid from step (3) into the reactor, introduce 0.09 kg of carbon dioxide, and then heat the purified liquid to 80°C at a heating rate of 1°C / min. React for 3 hours to obtain the reaction liquid; the mass of carbon dioxide added (kg) = 3L × 0.03 = 0.09 kg;

[0053] (5) The reaction solution in step (4) is heated to 120°C at a heating rate of 1°C / min and reacted for 4 hours. Then the temperature is lowered to 85°C and the reaction continues for 4 hours. In steps (4)-(5), carbon dioxide is continuously released slowly and uniformly within the reaction time of (4)-(5) until the carbon dioxide is exhausted. The carbon dioxide discharge rate is 0.09 kg / 12 h throughout the process. A milky white slurry is obtained. Solid-liquid separation is carried out while hot to obtain a mixed flux wet material of lithium tetraborate and lithium metaborate 67:33.

[0054] Calculation of carbon dioxide emission rate: Mass of carbon dioxide added / (4) - (5) Total reaction time = 0.09 kg / (2h + 5h + 5h) = 0.09 kg / 12h;

[0055] (6) The wet flux mixture from step (5) is dried at 400°C for 2 hours to obtain a 67:33 mixed flux powder of lithium tetraborate and lithium metaborate.

[0056] The XRD pattern of the resulting mixed flux is as follows: Figure 1 As shown, the mass ratio of lithium tetraborate to lithium metaborate is 67:33, and the purity is 99.99%. The results of the elemental analysis are shown in Table 2.

[0057] Table 2. Elemental analysis results (ppm) of the 67:33 mixed flux powder of lithium tetraborate and lithium metaborate.

[0058]

[0059] Example 3: Preparation of a 1:2 mixed flux of lithium tetraborate and lithium metaborate

[0060] (1) Take 54g of lithium carbonate, add 139g of boric acid, mix evenly to obtain a mixed powder (the molar ratio of boric acid to lithium carbonate is 3.08:1).

[0061] (2) Add 1.66L of pure water to a 3L reactor, add the mixed powder from step (1), and react at 26℃ for 60min to obtain a clear and transparent solution with a lithium carbonate concentration of 65 / L.

[0062] (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;

[0063] (4) Put the purified liquid from step (3) into the reaction vessel, introduce 0.09 kg of carbon dioxide, and then heat the purified liquid to 80°C at a heating rate of 1°C / min. React for 2 hours to obtain the reaction liquid; the mass of carbon dioxide added (kg) = 3L × 0.03 = 0.09 kg;

[0064] (5) The reaction solution in step (4) is heated to 120°C at a heating rate of 1°C / min and reacted for 5 hours. Then the temperature is lowered to 85°C and the reaction continues for 4 hours. In steps (4)-(5), carbon dioxide is continuously released slowly and uniformly within the reaction time of (4)-(5) until the carbon dioxide is exhausted. The carbon dioxide discharge rate is 0.09 kg / 12 h throughout the process. A milky white slurry is obtained. Solid-liquid separation is carried out while hot to obtain a mixed flux wet material of lithium tetraborate and lithium metaborate in a ratio of 2:1.

[0065] Calculation of carbon dioxide emission rate: Mass of carbon dioxide added / (4) - (5) Total reaction time = 0.09 kg / (2h + 5h + 4h) = 0.09 kg / 11h;

[0066] (6) The wet flux mixture from step (5) is dried at 400°C for 2 hours to obtain a 2:1 mixed flux powder of lithium tetraborate and lithium metaborate.

[0067] The mass ratio of lithium tetraborate to lithium metaborate in the obtained mixed flux was 2:1, and the purity was 99.99%. The results of the elemental analysis are shown in Table 3.

[0068] Table 3. Elemental analysis results (ppm) of the 1:2 mixture of lithium tetraborate and lithium metaborate flux powder.

[0069]

[0070] Example 4: Preparation of a flux with a lithium tetraborate:lithium metaborate ratio of 1:1

[0071] (1) Take 70.79g of lithium carbonate, add 162g of boric acid, mix evenly to obtain a mixed powder (the molar ratio of boric acid to lithium carbonate is 2.74:1).

[0072] (2) Add 1.66L of pure water to a 3L reactor, add the mixed powder from step (1), and react at 26℃ for 60min to obtain a clear and transparent solution with a lithium carbonate concentration of 65g / L.

[0073] (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;

[0074] (4) Put the purified liquid from step (3) into the reactor, introduce 0.09 kg of carbon dioxide, and then heat the purified liquid to 80°C at a heating rate of 1°C / min. React for 3 hours to obtain the reaction liquid; the mass of carbon dioxide added (kg) = 3L × 0.03 = 0.09 kg;

[0075] (5) The reaction solution in step (4) is heated to 120°C at a heating rate of 1°C / min and reacted for 4 hours. Then the temperature is lowered to 85°C and the reaction continues for 5 hours. In steps (4)-(5), carbon dioxide is continuously released slowly and uniformly within the reaction time of (4)-(5) until the carbon dioxide is exhausted. The carbon dioxide discharge rate is 0.09 kg / 12 h throughout the process. A milky white slurry is obtained. Solid-liquid separation is carried out while hot to obtain a 1:1 mixed flux wet material of lithium tetraborate and lithium metaborate.

[0076] Calculation of carbon dioxide emission rate: Mass of carbon dioxide added / (4) - (5) Total reaction time = 0.09 kg / (3h + 4h + 5h) = 0.09 kg / 12h;

[0077] (6) The wet flux mixture from step (5) is dried at 400°C for 2 hours to obtain a 1:1 mixed flux powder of lithium tetraborate and lithium metaborate.

[0078] The XRD pattern of the resulting mixed flux is as follows: Figure 2 As shown, the mass ratio of lithium tetraborate to lithium metaborate was 1:1, and the purity was 99.99%. The results of the elemental analysis are shown in Table 1.

[0079] Table 4. Elemental analysis results (ppm) of the 1:1 mixture of lithium tetraborate and lithium metaborate flux powder.

[0080]

[0081] Examples 5-12

[0082] Examples 5-12 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 5.

[0083] Table 5 shows the effect of lithium carbonate concentration on whether lithium carbonate powder precipitates during the high-temperature reaction and whether a clear and transparent intermediate solution is formed during the low-temperature reaction stage.

[0084]

[0085] As shown in Table 5, 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 a high-purity mixed flux with a purity greater than 99.99%. Therefore, a lithium carbonate concentration of 60-75 g / L is optimally chosen.

[0086] Examples 13-20

[0087] Examples 13-20 are identical to Example 1 in all other steps, except for the heating rate in step (4). The effect of reaction time on the purity of the mixed flux is shown in Table 6.

[0088] Table 6. Effect of heating rate on the purity of the mixed flux.

[0089]

[0090] As can be seen from the experimental data in Table 6, when the heating rate is 0.5-1℃ / min, the purity of the mixed flux is ≥99.99%, and the preferred heating rate is 1℃ / min.

[0091] Examples 21-26

[0092] Examples 21-26 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 the mixed flux is shown in Table 7.

[0093] Table 7. Effect of reaction temperature on the purity of the mixed flux.

[0094]

[0095] As shown in Table 7, the purity of the mixed flux obtained at a reaction temperature of 75-80℃ is ≥99.99%. Therefore, a reaction temperature of 75-80℃ is preferred.

[0096] Examples 27-32

[0097] Examples 27-32 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 the mixed flux is shown in Table 8.

[0098] Table 8. Effect of carbon dioxide mass on the purity of mixed fluxes

[0099]

[0100] As shown in Table 8, when the amount of carbon dioxide added is (0.03V-0.05V) kg, the purity of the mixed flux is ≥99.99%. Therefore, the preferred amount of carbon dioxide added is (0.03V-0.04V) kg; where V represents the volume of the reactor.

[0101] Examples 33-38

[0102] Examples 33-38 are identical to Example 1 in all other steps, except for the reaction time in step (4). The effect of reaction time on the purity of the resulting mixed flux is shown in Table 9.

[0103] Table 9. Effect of reaction time on the purity of the obtained mixed flux.

[0104]

[0105] As can be seen from the experimental data in Table 9, when the reaction time of step (4) is 1-3h, the purity of the mixed flux is ≥99.99%, and the preferred reaction time is 3h.

[0106] Examples 39-46

[0107] Examples 39-46 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 the mixed flux is shown in Table 10.

[0108] Table 10 Effect of heating rate on the purity of mixed flux

[0109]

[0110] As can be seen from the experimental data in Table 10, when the heating rate is 0.8-1℃ / min, the purity of the mixed flux is ≥99.99%, and the heating rate of 1℃ / min is preferred.

[0111] Examples 47-56

[0112] Examples 47-56 are identical to Example 1 in all other steps, except for the change in the heating reaction time in step (5). Table 11 shows the effect of reaction time on the purity of the resulting mixed flux.

[0113] Table 11 Effect of reaction time on the purity of the obtained mixed flux

[0114]

[0115] The experimental data from the above embodiments show that when the reaction time is 3-5 hours, the ratio of lithium tetraborate to lithium metaborate in the prepared mixed flux is 12:22, which is consistent with the target ratio, and its purity is ≥99.99%.

[0116] Examples 57-68

[0117] Examples 57-68 are the same as Example 1 in other steps, except that the cooling reaction temperature in step (5) is changed. The effect on the purity of the resulting mixed flux is shown in Table 12.

[0118] Table 12 Effect of cooling temperature on the purity of the obtained mixed flux

[0119]

[0120] The experimental data from the above embodiments show that when the cooling temperature is 80-90℃, the ratio of lithium tetraborate to lithium metaborate in the mixed flux is 12:22, which is consistent with the target ratio, and its purity is ≥99.99%.

[0121] Examples 66-71

[0122] 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 the mixed flux is shown in Table 13.

[0123] Table 13 Effect of drying temperature on the purity of mixed cosolvents

[0124]

[0125] As can be seen from the experimental data in Table 13, when the drying temperature is 400-450℃, the purity of the flux is ≥99.99%, and the optimal drying temperature is 400℃.

Claims

1. A method for directly preparing a mixed flux of lithium tetra borate and lithium metaborate by a liquid phase method, characterized in that, It comprises the following steps: (1) Take lithium carbonate with a purity of 99.9%, add boric acid with a purity of 99.9%, and mix them evenly to obtain a mixed powder; wherein the amount of lithium carbonate = (73.88a / 169.12) + (73.88b / 99.5); the amount of boric acid = (247.24a / 169.12) + (61.81b / 49.75), wherein a is the mass of lithium tetraborate in the prepared mixed flux, and b is the mass of lithium metaborate in the prepared mixed flux; the amount of lithium carbonate, the amount of boric acid, and a and b are all in grams; (2) Add pure water to the reaction container, add the mixed powder in step (1), and react at 20-30°C to obtain a clear transparent solution; the amount of pure water added is based on the concentration of lithium carbonate in the solution being 60-75 g / L; (3) The clear transparent solution in step (2) is first subjected to 3-stage precision filtration, then impurity removal by cation exchange resin, and finally 1-stage precision filtration to obtain a purified liquid; (4) Put the purified liquid in step (3) into a reaction kettle, introduce carbon dioxide, then warm the purified liquid to 75-80°C, and react for 1-3 h to obtain a reaction liquid; (5) Warm the reaction liquid in step (4) to 100-130°C, react for 3-5 h, then cool to 80-90°C, continue to react for 1-5 h to obtain a milky white slurry, and perform solid-liquid separation while hot to obtain a lithium tetraborate and lithium metaborate mixed flux wet material; Steps (4)-(5) continuously ensure that the carbon dioxide is slowly and uniformly released until the carbon dioxide is exhausted during the reaction time of (4)-(5); (6) Dry the mixed flux wet material in step (5) to obtain a lithium tetraborate and lithium metaborate mixed flux finished product.

2. The method of claim 1, wherein the lithium tetra borate and lithium metaborate mixed flux is directly prepared by the liquid phase method, characterized in that, In step (2), the reaction time is 1-2 h.

3. The method of claim 1, wherein the lithium tetra borate and lithium metaborate mixed flux is directly prepared by the liquid phase method, characterized in that, In step (3), the precision filtration refers to filtration using a filter membrane with a pore size of 0.02 μm.

4. The method of claim 1, wherein the lithium tetra borate and lithium metaborate mixed flux is directly prepared by the liquid phase method, characterized in that, In step (4), the amount of carbon dioxide added = the number of reaction kettles × the amount of carbon dioxide added per liter of reaction kettle, and the amount of carbon dioxide added per liter of reaction kettle is 0.03-0.05 kg; the unit of the amount of carbon dioxide added is kg.

5. The method of claim 1, wherein the lithium tetra borate and lithium metaborate mixed flux is directly prepared by the liquid phase method, characterized in that, In step (4), the warming rate is 0.5-1°C / min.

6. The method of claim 1, wherein the lithium tetra borate and lithium metaborate mixed flux is directly prepared by the liquid phase method, characterized in that, In step (5), the warming rate is 0.8-1°C / min.

7. The method of claim 1, wherein the lithium tetra borate and lithium metaborate mixed flux is directly prepared by the liquid phase method, characterized in that, The CO2 discharge rate = CO2 addition mass / total reaction time of steps (4)-(5).

8. The method of claim 1, wherein the lithium tetra borate and lithium metaborate mixed flux is directly prepared by the liquid phase method, characterized in that, In step (6), the drying temperature is 400-450°C, and the drying time is 2-3 h.

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