Method for preparing aluminum oxide by recycling boric acid-containing solution

Abstract

The invention relates to a method for preparing aluminum oxide by recycling a boric acid-containing solution, which comprises the following steps: S1, adding a boric acid-containing aluminum oxide raw material and a liquid medium into a ball mill for wet ball milling treatment to prepare aluminum oxide slurry; s2, standing and precipitating the aluminum oxide slurry, and separating an upper clear liquid containing boric acid from a bottom aluminum oxide precipitate; and S3, mixing the boric acid-containing clear liquid with newly added pure water in proportion, and recycling the mixture as a liquid medium for next round of ball milling. Aluminum oxide powder which is pre-added with boric acid and is fired is purchased as a raw material, the boric acid-containing clear liquid is efficiently recycled after wet ball milling, and the boric acid-containing clear liquid and the pure water are mixed and recycled in proportion for next round of material preparation.

Description

Technical Field

[0001] The present invention relates to the field of aluminum oxide preparation, and in particular to a method for preparing aluminum oxide by cyclically utilizing a boric acid-containing solution. Background Art

[0002] In the traditional preparation process of alumina ceramic substrates, boric acid is used as an additive to improve the performance of alumina. Specifically, boric acid is mainly used as a mineralizer or structure regulator in the preparation of alumina. Its functions include promoting crystal transformation, reducing impurity content (such as Na2O), improving corrosion resistance, and adjusting pH value. After adding boric acid, alumina is more likely to form a stable α crystal form during high-temperature sintering, and the grain size increases, and the purity is improved. In addition, boric acid can also react with Na2O in alumina to form volatile compounds, thereby effectively reducing the sodium oxide content and reducing the impact of impurities on the molding and quality of ceramic products.

[0003] However, despite the important role of boric acid in alumina production, its recovery and recycling are not common in traditional processes. No effective boric acid recovery methods have been established in the prior art, and boric acid is often treated as waste liquid after use, resulting in resource waste and environmental pollution risks. Furthermore, the failure to recover boric acid can easily lead to increased production costs, as new boric acid needs to be continuously added to maintain the process effect, as follows:

[0004] (1) After boric acid is used as a disposable additive, its active ingredients are discharged with the waste liquid, resulting in resource waste and increased costs;

[0005] (2) If the boric acid remaining in the waste liquid is discharged directly without being recovered, it may cause potential pollution to the environment;

[0006] (3) The repeated addition of new boric acid during the preparation process can easily introduce impurity fluctuations and affect product consistency and stability;

[0007] (4) The utilization rate of boric acid in traditional processes is low, and its role in promoting crystal transformation and surface modification is not fully utilized.

[0008] Therefore, we proposed a method for preparing alumina by recycling boric acid solution. By purchasing alumina powder that has been pre-added with boric acid and fired as raw material, the boric acid-containing clear liquid is efficiently recovered after wet ball milling, and mixed with pure water in proportion and recycled for the next round of ingredients. Summary of the Invention

[0009] The purpose of the present invention is to overcome the shortcomings of the existing technology and meet actual needs. A method for preparing aluminum oxide by recycling a boric acid solution is provided to solve the technical problems that after the current boric acid is used as a one-time additive, its active ingredients are discharged with the waste liquid, resulting in resource waste and increased costs; if the boric acid remaining in the waste liquid is directly discharged without being recovered, it may cause potential pollution to the environment; new boric acid needs to be repeatedly added during multiple preparation processes, which easily introduces impurity fluctuations and affects the consistency and stability of the product; and the utilization rate of boric acid in the traditional process is low, and its role in promoting crystal transformation and surface modification cannot be fully utilized.

[0010] In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is to design a method for preparing aluminum oxide by recycling a boric acid solution, comprising the following steps:

[0011] S1. Adding a boric acid-containing alumina raw material and a liquid medium into a ball mill for wet ball milling to prepare an alumina slurry;

[0012] S2, allowing the alumina slurry to settle, and separating the upper boric acid-containing clear liquid and the bottom alumina precipitate;

[0013] S3. The boric acid-containing clear liquid is mixed with newly added pure water in proportion and recycled as the liquid medium for the next round of ball milling.

[0014] Preferably, the mass proportion of boric acid in the boric acid-containing alumina raw material in step S1 is 0.5%-3%, and the boric acid exists in the raw material in the form of boron oxide after calcination.

[0015] Preferably, in step S1, the rotation speed of the wet ball milling is 200-500 rpm, the ball milling time is 6-24 h, and the solid content of the alumina slurry is controlled at 30%-50%.

[0016] Preferably, the precipitation time in step S2 is 12-48 hours, and the boric acid concentration in the separated supernatant is 0.1-0.8 mol / L.

[0017] Preferably, the mixing ratio of the recovered boric acid-containing clear liquid and pure water in step S3 is 1.3:50, and the number of cycles is not less than 5 times.

[0018] Preferably, the liquid medium in step S1 is deionized water or a boric acid-containing clear solution recovered from a previous cycle, and its pH value is adjusted to 4.5-6.5.

[0019] Preferably, the total mass ratio of the boric acid-containing clear liquid recycled in step S3 to the boron oxide in the new raw material is 1:8-1:15.

[0020] Preferably, the slurry obtained after wet ball milling is dried and calcined at a temperature of 1200-1600° C. for 2-6 hours.

[0021] Preferably, the ball milling medium in step S1 is zirconia ceramic balls, the ball-to-material ratio is 2:1-5:1, and the particle size distribution includes three levels: 3 mm, 5 mm, and 8 mm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The boric acid pre-bound in the raw materials of the present invention can still be dissolved and recovered after ball milling, thereby reducing boric acid consumption and raw material costs.

[0024] 2. The present invention recycles the boric acid-containing clear liquid, reduces waste liquid discharge, and has both environmental and economic benefits.

[0025] 3. The present invention maintains process stability and boric acid concentration by precisely controlling the mixing ratio of the recovered liquid to pure water (e.g., 1.3:50), avoids impurity accumulation, and ensures product performance consistency.

[0026] 4. The repeated use of boric acid in the circulation process of the present invention can further promote the transformation of alumina crystals, reduce the Na2O content to below 0.05wt%, and at the same time strengthen the formation of the surface boron oxide film, thereby improving the corrosion resistance and durability of the material.

[0027] In summary, the present invention purchases alumina powder pre-added with boric acid and fired as a raw material, efficiently recovers the boric acid-containing clear liquid after wet ball milling, and mixes it with pure water in proportion and recycles it for the next round of ingredients. This solves the technical problems that after the current boric acid is used as a one-time additive, its effective ingredients are discharged with the waste liquid, resulting in waste of resources and increased costs; if the boric acid remaining in the waste liquid is directly discharged without being recovered, it may cause potential pollution to the environment; new boric acid needs to be repeatedly added during multiple preparation processes, which is easy to introduce impurity fluctuations and affect product consistency and stability; the utilization rate of boric acid in traditional processes is low, and its role in promoting crystal transformation and surface modification cannot be fully exerted. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0030] A method for preparing aluminum oxide by recycling a boric acid solution, see Figure 1 , including the following steps:

[0031] S1. Adding a boric acid-containing alumina raw material and a liquid medium into a ball mill for wet ball milling to prepare an alumina slurry;

[0032] S2, allowing the alumina slurry to settle, and separating the upper boric acid-containing clear liquid and the bottom alumina precipitate;

[0033] S3. Mix the boric acid-containing clear liquid with newly added pure water in proportion and recycle it as the liquid medium for the next round of ball milling.

[0034] Specifically, in step S1, the mass proportion of boric acid in the boric acid-containing alumina raw material is 0.5%-3%, and the boric acid exists in the raw material in the form of boron oxide after calcination.

[0035] More specifically, in step S1, the rotation speed of the wet ball milling is 200-500 rpm, the ball milling time is 6-24 hours, and the solid content of the alumina slurry is controlled at 30%-50%.

[0036] Furthermore, the precipitation time in step S2 is 12-48 hours, and the boric acid concentration in the separated supernatant is 0.1-0.8 mol / L.

[0037] Furthermore, in step S3, the mixing ratio of the recovered boric acid-containing clear liquid and pure water is 1.3:50, and the number of cycles is not less than 5 times.

[0038] It is worth noting that the liquid medium in step S1 is deionized water or the boric acid-containing clear solution recovered from the previous cycle, and its pH value is adjusted to 4.5-6.5.

[0039] It is noteworthy that the total mass ratio of the boric acid-containing clear solution recycled in step S3 to the boron oxide in the new raw material is 1:8-1:15.

[0040] It is worth mentioning that the slurry obtained after wet ball milling is dried and calcined at a temperature of 1200-1600° C. for 2-6 hours.

[0041] It is worth noting that the ball milling medium in step S1 is zirconia ceramic balls, the ball-to-material ratio is 2:1-5:1, and the particle size distribution includes three levels: 3 mm, 5 mm, and 8 mm.

[0042] Example 1

[0043] step:

[0044] S1. Select alumina powder containing 1.2% boric acid by mass (boric acid exists in the form of boron oxide after firing);

[0045] S2. The raw materials were mixed with deionized water (liquid medium) at a solid content of 40%, and zirconia ceramic balls (ball-to-material ratio 3:1, particle sizes of 3 mm, 5 mm, and 8 mm) were added. The mixture was ball-milled at 350 rpm for 12 hours to prepare an alumina slurry.

[0046] S3. The slurry was allowed to settle for 24 hours, and the upper layer of boric acid-containing clear liquid (boric acid concentration 0.5 mol / L) was separated from the alumina precipitate at the bottom;

[0047] S4, the recovered boric acid-containing clear liquid was mixed with pure water in a ratio of 1.3:50 and used as the liquid medium for the next round of ball milling, and recycled for 6 times;

[0048] S5. After the alumina precipitate is dried, it is calcined at 1400° C. for 4 hours to obtain an alumina ceramic substrate.

[0049] result:

[0050] The boric acid utilization rate reached 88% and the Na2O content was reduced to 0.04wt%.

[0051] The product has a crystal conversion rate of 97%, and a uniform boron oxide film is formed on the surface, which significantly improves corrosion resistance.

[0052] Example 2

[0053] step:

[0054] S1, alumina powder containing 2.5% by mass of boric acid;

[0055] S2, the liquid medium is the previously recovered boric acid-containing clear solution (pH = 5.5), solid content 45%, ball milling speed 450 rpm, time 18 hours;

[0056] S3, precipitation for 36 hours, the boric acid concentration of the supernatant is 0.7 mol / L;

[0057] S4, mixing ratio 1.3:50, recycled 8 times;

[0058] S5. Calcination at 1500°C for 5 hours.

[0059] result:

[0060] The utilization rate of boric acid is 91%, and the content of Na2O is 0.03wt%.

[0061] The product crystal conversion rate is 98% and the compressive strength is increased by 15%.

[0062] Example 3

[0063] step:

[0064] S1, alumina powder containing 0.8% by mass of boric acid;

[0065] S2, ball-to-material ratio 4:1, rotation speed 250 rpm, time 8 hours, solid content 35%;

[0066] S3, precipitation for 18 hours, the boric acid concentration of the clear solution is 0.3 mol / L;

[0067] S4, mixing ratio 1.3:50, recycled 5 times;

[0068] S5. Calcination at 1300°C for 3 hours.

[0069] result:

[0070] The utilization rate of boric acid is 85%, and the content of Na2O is 0.05wt%.

[0071] The product has no cracks on the surface and excellent thermal stability.

[0072] Example 4

[0073] step:

[0074] S1, alumina powder containing 3% by mass of boric acid;

[0075] S2, the liquid medium is a mixture of recycled liquid and pure water (pH = 6.0), the ball milling speed is 500 rpm, and the time is 24 hours;

[0076] S3, precipitation for 48 hours, the boric acid concentration of the clear solution is 0.8 mol / L;

[0077] S4, mixing ratio 1.3:50, recycled 10 times;

[0078] S5. Calcination at 1600°C for 6 hours.

[0079] result:

[0080] The utilization rate of boric acid is 92%, and the content of Na2O is 0.02wt%.

[0081] The product density reaches 3.95g / cm 3 , insulation performance is improved by 20%.

[0082] Comparative Example 1

[0083] step:

[0084] S1, alumina raw powder without pre-addition of boric acid, fresh boric acid (1.2% by mass) was directly added during ball milling;

[0085] S2, deionized water as the medium, ball milling conditions are the same as in Example 1;

[0086] S3. After sedimentation, the supernatant is directly discharged without recycling;

[0087] S4. Same as Example 1.

[0088] result:

[0089] Boric acid is consumed once and its utilization rate is only 35%.

[0090] The residual amount of Na2O is 0.15wt%, the product crystal conversion rate is 82%, and the surface is easily corroded.

[0091] Comparative Example 2

[0092] step:

[0093] S1, alumina powder containing 4% by mass of boric acid;

[0094] S2, speed 600 rpm, time 30 hours;

[0095] S3, mixing ratio 1:20, recycled 3 times.

[0096] result:

[0097] The slurry viscosity is too high, the precipitation is incomplete, and the clear liquid is turbid.

[0098] After calcination, the product showed local uneven sintering and the crystal conversion rate was only 75%.

[0099] The specific comparison data is as follows:

[0100]

[0101]

[0102] Comparative Example 1 adopts the traditional method, directly adding new boric acid without recovering the clear liquid.

[0103] The parameters of Comparative Example 2 exceeded the recommended ranges of the present invention (boric acid content, ball milling speed, time and mixing ratio), resulting in process failure.

[0104] The newly added 1.2% means that in Comparative Example 1, no raw material pre-added with boric acid was used, but new boric acid was directly added during ball milling.

[0105] Comparison points:

[0106] Boric acid utilization rate: in the examples, the utilization rate reaches 85%-92% through recycling, while in the comparative example 1, the utilization rate is only 35%.

[0107] Impurity control: The Na2O content in the embodiment is reduced to 0.02-0.05wt%, while the residual content in the comparative example 1 is as high as 0.15wt%.

[0108] Process stability: The embodiment ensures consistency through parameter optimization (such as mixing ratio 1.3:50), while the comparative example 2 causes precipitation and sintering problems due to parameter out-of-range.

[0109] in conclusion

[0110] Examples 1 to 4 significantly improve the boric acid utilization rate (85%-92%) by recycling the boric acid-containing clear solution, reduce the Na2O content to 0.02wt%-0.05wt%, and stably improve product performance. Comparative Example 1 (traditional method) does not recover boric acid, resulting in resource waste and impurity residues; Comparative Example 2 (parameters out of range) causes process instability and reduced product quality due to operating conditions deviating from the patent scope. The method of the present invention is superior to the existing technology in terms of environmental protection, cost control, and product performance.

[0111] In addition, the components designed in the present invention are all universal standard parts or components known to those skilled in the art. Their structures and principles can be known to those skilled in the art through technical manuals or conventional experimental methods. They can be fully implemented by those skilled in the art. Needless to say, the content protected by the present invention does not involve improvements to internal structures and methods.

Claims

1. A method for preparing aluminum oxide by circulating a boric acid solution, characterized in that: The following steps are involved: S1. Adding a boric acid-containing alumina raw material and a liquid medium into a ball mill for wet ball milling to prepare an alumina slurry; S2, allowing the alumina slurry to settle, and separating the upper boric acid-containing clear liquid and the bottom alumina precipitate; S3. The boric acid-containing clear liquid is mixed with newly added pure water in proportion and recycled as the liquid medium for the next round of ball milling.

2. The method for preparing aluminum oxide by recycling a boric acid solution according to claim 1, wherein: In the step S1, the mass proportion of boric acid in the boric acid-containing aluminum oxide raw material is 0.5%-3%, and the boric acid exists in the raw material in the form of boron oxide after being fired.

3. The method for preparing aluminum oxide by recycling a boric acid solution according to claim 1, wherein: In step S1, the rotation speed of the wet ball milling is 200-500 rpm, the ball milling time is 6-24 hours, and the solid content of the alumina slurry is controlled at 30%-50%.

4. The method for preparing aluminum oxide by recycling a boric acid solution according to claim 1, wherein: The precipitation time in step S2 is 12-48 hours, and the boric acid concentration in the separated supernatant is 0.1-0.8 mol / L.

5. The method for preparing aluminum oxide by recycling a boric acid solution according to claim 1, wherein: The mixing ratio of the recovered boric acid-containing clear liquid and pure water in step S3 is 1.3:50, and the number of cycles is not less than 5 times.

6. The method for preparing aluminum oxide by recycling a boric acid solution according to claim 1, characterized in that: The liquid medium in step S1 is deionized water or the boric acid-containing clear solution recovered from the previous cycle, and its pH value is adjusted to 4.5-6.

5.

7. The method for preparing aluminum oxide by recycling a boric acid solution according to claim 1, characterized in that: The total mass ratio of the boric acid-containing clear liquid recycled in step S3 to the boron oxide in the new raw material is 1:8-1:

15.

8. The method for preparing aluminum oxide by recycling a boric acid solution according to claim 1, characterized in that: The slurry obtained after the wet ball milling is dried and calcined at a temperature of 1200-1600° C. for 2-6 hours.

9. The method for preparing aluminum oxide by recycling a boric acid solution according to claim 1, wherein: In step S1, the ball milling medium is zirconia ceramic balls, the ball-to-material ratio is 2:1-5:1, and the particle size distribution includes three levels: 3 mm, 5 mm, and 8 mm.

Images