Method for preparing alumina grinding beads by using mother liquor of Bayer process seed precipitation

Abstract

The present invention belongs to the technical field of the preparation of alumina grinding beads, and specifically relates to a method for preparing alumina grinding beads by using the mother liquor of Bayer process seed precipitation. The method for preparing alumina grinding beads by using the mother liquor of Bayer process seed precipitation according to the present invention includes process steps such as recrystallization, washing, hydrothermal synthesis, phase transformation, forming and sintering. Through the crystallization and multi-stage carbonation processes, the decomposition rate is controlled to reach 96-98%, generating high-purity aluminum hydroxide powder, which is then washed with pure water to remove water-soluble impurities, hydrothermally synthesized into boehmite, phase-transformed into α-alumina powder in a kiln, granulated into alumina beads and sintered to prepare high-purity alumina grinding beads. The alumina grinding beads prepared by using the method of the present invention have uniform and controllable particles, and have high purity, high wear resistance, high hardness and high impact toughness, meeting the requirements of grinding media for most alumina industries in the market.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of alumina grinding beads, and specifically relates to a method for preparing alumina grinding beads by using the mother liquor of the Bayer process seed precipitation. Background Art

[0002] The most common use of alumina is as a grinding material because of its excellent hardness, wear resistance and chemical stability. The main application fields of alumina grinding materials include industries such as metals, ceramics, plastics, electronics and petroleum. In the field of metal manufacturing, alumina grinding materials are used for polishing and rough grinding of metal materials such as steel, copper, aluminum and zinc. In the field of ceramic manufacturing, alumina grinding materials are commonly used for grinding and polishing products such as ceramics and tiles. In the field of plastic manufacturing, alumina grinding materials are commonly used for grinding and polishing polymer materials and other plastic products. And high-purity alumina grinding materials, due to their high hardness and chemical stability, are mainly applied in the field of precision ceramics, suitable for high-precision processing requirements.

[0003] During the seed precipitation decomposition process of the modified Bayer process, one of the high-purity alumina production processes, due to process limitations, generally the seed precipitation is decomposed to 35-55%, and the remaining mother liquor is recycled in production. The main component of the mother liquor is a high-purity sodium aluminate solution, but silicon, iron, calcium, magnesium, gallium and water-soluble sodium aluminate in it are all impurities harmful to high-purity alumina. During the continuous recycling process, the above-mentioned impurities will continuously accumulate. In order to ensure the purity of the high-purity alumina end product, only this part of the mother liquor can be discarded periodically, or processed into low-value alumina products, resulting in waste of resources.

[0004] Therefore, exploring a method for producing high-purity alumina grinding beads by using the residual mother liquor of the Bayer process seed precipitation process has become an urgent technical problem to be solved. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing alumina grinding beads by using the mother liquor of the Bayer process. The alumina grinding beads prepared by using this method have high purity and high wear resistance.

[0006] The method for preparing alumina grinding beads by using the mother liquor of the Bayer process according to the present invention comprises the following steps:

[0007] (1) Adding a dispersant to the mother liquor of the Bayer process seed precipitation to prepare a modified mother liquor of the Bayer process seed precipitation;

[0008] (2) First, introducing carbon dioxide with a flow rate of 300-600 Nm 3 / h into the modified mother liquor of the Bayer process seed precipitation prepared in step (1). After the initial appearance of aluminum hydroxide crystals, the carbon dioxide flow rate is reduced to 150-300 Nm 3 / h. When the decomposition rate reaches 62 - 68.5%, the carbon dioxide flow rate is further reduced to 20 - 50 Nm 3 / h until the decomposition rate reaches 96 - 98% to obtain a mixed slurry;

[0009] (3)Solid-liquid separation of the mixed slurry obtained in step (2) is carried out by a plate and frame filter press, and then high-purity water is used to wash the aluminum hydroxide powder in the filter press until the pH of the washing water is 8 - 9;

[0010] (4)The solid powder prepared in step (3) is mixed with water for hydrothermal synthesis reaction. After the reaction, solid-liquid separation is carried out to prepare boehmite;

[0011] (5)The boehmite solid powder prepared in step (4) is placed in a corundum crucible and calcined and phase-transformed in a bell jar kiln to obtain phase-transformed alumina powder;

[0012] (6)The phase-transformed alumina powder obtained in step (5) is granulated and formed by a coating machine, pre-sintered in a bell jar kiln, cooled to room temperature, and then secondarily sintered in a hydrogen protection furnace to obtain high-purity alumina grinding beads.

[0013] Among them:

[0014] In the sodium aluminate solution of the Bayer process seed mother liquor in step (1), the concentration of sodium aluminate is 50 - 120 g / L, and the temperature of the Bayer process seed mother liquor is controlled at 40 - 60 °C.

[0015] In step (1), the dispersant is several of citric acid monohydrate, malic acid, salicylic acid or sodium dodecylbenzenesulfonate, and the mass of the dispersant accounts for 1.5 - 3% of the mass of the Bayer process seed mother liquor.

[0016] In step (3), the temperature of the high-purity water for washing is 75 - 85 °C.

[0017] In step (4), the mass ratio of the solid powder to water is 1:5 - 1:6, the hydrothermal synthesis temperature is 195 - 210 °C, the hydrothermal synthesis pressure is 1.45 MPa - 1.9 MPa, and the hydrothermal synthesis time is 1.5 - 2 h.

[0018] In step (5), the calcination and phase transformation temperature is 1020 - 1050 °C, and the calcination and phase transformation time is 2 - 3 h.

[0019] In step (6), the pre-sintering process is as follows: continuously heating from room temperature to 535 °C - 580 °C in 150 min - 200 min, then continuously heating to 920 °C - 975 °C in 220 min - 235 min, and then continuously heating to 1205 °C - 1235 °C in 120 min - 145 min, and holding at 1205 °C - 1235 °C for 100 min - 160 min.

[0020] The secondary sintering process of the hydrogen protection furnace described in step (6) is as follows: continuously heat from room temperature to 1380°C - 1440°C in 120 min - 140 min, then continuously heat to 1750°C - 1775°C in 65 min - 72 min, and keep the temperature at 1750°C - 1775°C for 100 min - 150 min.

[0021] The average diameter of the alumina grinding beads prepared in step (6) is 0.5 - 1.0 mm, the original crystal grain size D50 is 0.5 - 2.8 μm, the alumina purity is 99.999% - 99.9993%, the Mohs hardness is 9.0 - 9.5, and the wear is 0.05 - 0.1%.

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

[0023] (1) The method for preparing alumina grinding beads using the mother liquor of the Bayer process seed described in the present invention includes process steps such as recrystallization, washing, hydrothermal synthesis, phase transformation, forming and sintering. Through the crystallization and multi-stage carbonation processes, the decomposition rate is controlled to reach 96 - 98% to generate high-purity aluminum hydroxide powder, which is then washed with pure water to remove water-soluble impurities, hydrothermally synthesized into boehmite, phase-transformed into α-aluminum oxide powder in a kiln, granulated into alumina beads and sintered to prepare high-purity alumina grinding beads.

[0024] (2) The method for preparing alumina grinding beads using the mother liquor of the Bayer process seed described in the present invention adds a specific dispersant and adopts a multi-carbonation method. Since the carbonation process gives the alumina primary crystal gas pressure and stirring intensity, not only are the primary crystal particles fine enough in particle size, but also the internal structure undergoes local deformation to become a porous active state (which can be seen from the electron microscope photos), reducing the sanding, ball milling or jet milling crushing processes, reducing pollution and lowering costs. The average diameter of the powder primary crystals can be controlled to 0.1 - 0.3 μm, and the particle size can be controlled within 0.5 - 3.0 μm, which is very beneficial for granulating high-density alumina beads in subsequent steps and is also conducive to sintering and forming, improving the density and wear resistance of the grinding balls.

[0025] (3) The method for preparing alumina grinding beads using the mother liquor of the Bayer process seed described in the present invention, while preparing high-purity alumina grinding beads, makes full use of the residual value of the mother liquor of the seed. The mother liquor that could originally only be processed into ordinary aluminum hydroxide or alumina is processed into high-end alumina grinding beads. And the main component of the waste liquid generated during the preparation process of the present invention is sodium carbonate, which can be directly extracted to obtain high-purity sodium carbonate for other fields, combining energy conservation and environmental protection, and also reducing production costs.

[0026] (4) In the method for preparing alumina grinding beads using the mother liquor of the Bayer process seed precipitation described in the present invention, since the solid obtained from the final reaction in step (2) is aluminum hydroxide, and hydrothermal reaction is carried out after washing, the sodium ion impurities encapsulated in the agglomerates can diffuse out and be removed by washing. Additionally, the sodium aluminate solution is purified by using a dispersant and the multiple carbonation method, and most of the residual impurities such as silicon, iron, and gallium are removed under the action of the dispersant. In the secondary sintering process of step (6), since the sintering temperature reaches above 1700 °C, most of the residual impurities such as calcium, magnesium, and sodium can be removed under the action of high-temperature volatilization. Finally, the alumina grinding beads prepared by this solution have extremely low impurity content, and the alumina purity can reach over 99.999%.

[0027] (5) In the method for preparing alumina grinding beads using the mother liquor of the Bayer process seed precipitation described in the present invention, in step (6), the grain growth in the later stage of alumina sintering plays an important role in sintering densification. In the present invention, these two stages are calcined in two steps. The purpose of pre-calcination is to carry out the first stage of sintering, remove pores and moisture, and is beneficial to grain growth in the later stage of sintering. The sintering curve of the secondary sintering is divided into two heating segments with two heating rates and one holding segment. In the first heating segment, the pre-calcined alumina balls go through the process of removing pores again, the pore removal is more thorough, the density further increases, and at the same time, the temperature growth rate is controlled to reduce the breakage of the alumina balls. The second heating segment adjusts a specific heating rate to adjust the alumina grain growth rate, and further controls the density, hardness, and volume of the alumina balls through this grain growth rate, so that the obtained alumina grinding beads meet the grinding requirements.

[0028] (6) The alumina grinding beads prepared by using the method described in the present invention have uniform and controllable particles, and have high purity, high wear resistance, high hardness, and high impact toughness, meeting the grinding medium requirements of most alumina industries in the market. Description of the Drawings

[0029] Figure 1 SEM image of the original crystal powder of the alumina grinding beads prepared in Example 1;

[0030] Figure 2 Photo of the alumina grinding beads prepared in Example 1;

[0031] Figure 3 SEM image of the original crystal powder of the alumina grinding beads prepared in Comparative Example 1;

[0032] Figure 4 SEM image of the original crystal powder of the alumina grinding beads prepared in Comparative Example 2. Detailed Description of the Invention

[0033] The present invention will be further described below in conjunction with examples.

[0034] Example 1

[0035] The method for preparing alumina grinding beads using the mother liquor of Bayer process seed precipitation in this Example 1 consists of the following steps:

[0036] (1) After starting stirring, add a dispersant (0.5% each of citric acid monohydrate, malic acid, and salicylic acid) with a mass ratio of 1.5% to the mother liquor of Bayer process seed precipitation, control the temperature of the mother liquor of Bayer process seed precipitation at 40°C, stir evenly for 15 min, and prepare a modified mother liquor of Bayer process seed precipitation. Among them, the alumina concentration in the mother liquor of Bayer process seed precipitation is 50 g / L.

[0037] (2) Keep stirring and start to introduce 300 Nm 3 / h of food-grade CO 2 , until white aluminum hydroxide appears in the clarified solution, then reduce the CO 2 flow rate to 150 Nm 3 / h. During this period, regularly detect the decomposition rate. When the decomposition reaches 65.6%, reduce the CO 2 flow rate to 20 Nm 3 / h. Finally, when the decomposition rate detection reaches 96.8%, end the decomposition to obtain a mixed slurry.

[0038] (3) Perform solid-liquid separation through a plate and frame filter press. The liquid is discharged into a sodium carbonate storage tank, and the solid powder is repeatedly washed with hot pure water at 85°C until the pH value of the discharged washing water is detected to be 8 with litmus paper.

[0039] (4) Put the washed solid powder and high-purity water into a magnetically driven high-pressure reactor at a mass ratio of 1:5, heat up to 195°C, and maintain for 2 h. Control the pressure at 1.9 MPa to carry out a hydrothermal synthesis reaction, then cool down and reduce the pressure, and perform solid-liquid separation using a plate and frame filter press to prepare boehmite.

[0040] (5) Put the prepared boehmite solid powder into a corundum crucible, enter a bell jar furnace for phase transformation roasting, the phase transformation temperature is 1020°C, keep for 2 hours and then discharge to obtain phase-transformed alumina powder.

[0041] (6) After the phase-transformed alumina powder is granulated by a coating machine to form round particles, put it into a corundum crucible and enter a bell jar furnace for pre-sintering. The pre-sintering process is as follows: continuously heat up from room temperature to 535°C in 158 min, then continuously heat up to 920°C in 230 min, and then continuously heat up to 1205°C in 130 min, and keep warm at 1205°C for 100 min. Cool down to room temperature, then put the alumina beads into a molybdenum crucible and enter a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: heat up from room temperature to 1380°C in 130 min, then continuously heat up to 1750°C in 65 min, and keep warm at 1750°C for 100 min; prepare high-purity alumina grinding beads.

[0042] In step (6), the average diameter of the prepared alumina grinding beads is 0.6 mm, the original crystal grain size D50 is 0.9 μm. The purity of the sintered high-purity alumina beads is detected by a glow discharge mass spectrometer. The alumina purity is 99.9993%, the Mohs hardness is 9.2, and the abrasion is 0.08%.

[0043] The SEM image of the original crystal powder of the alumina grinding beads prepared in Example 1 is shown in the appendix Figure 1 , and the photo of the prepared alumina grinding beads is shown in the appendix Figure 2 , through the appendix Figure 1 It can be seen that the crystal form and morphology of the alumina powder prepared by this method are very uniform, the particles reach the nanometer level, and the coral-like particles show a porous active state. Through processing, the powder particles will adsorb and combine more tightly with each other, which is beneficial to the subsequent processing of grinding beads. Through the appendix Figure 2 It can be seen that the finished grinding beads have good sphericity and thorough porcelainization, comparable to the commonly used zirconia grinding beads on the market.

[0044] Example 2

[0045] The method for preparing alumina grinding beads using the mother liquor of the Bayer process seed in this Example 2 consists of the following steps:

[0046] (1) After starting stirring, add a dispersant (1.1% each of malic acid and sodium dodecylbenzenesulfonate) with a mass ratio of 2.2% to the mother liquor of the Bayer process seed, control the temperature of the mother liquor of the Bayer process seed at 55 °C, and stir evenly for 15 min to prepare a modified mother liquor of the Bayer process seed. Among them, the alumina concentration in the mother liquor of the Bayer process seed is 65 g / L.

[0047] (2) Keep stirring and start to introduce 490 Nm 3 / h of food-grade CO 2 , until white aluminum hydroxide appears in the clarified solution, reduce the CO 2 flow rate to 230 Nm 3 / h. During this period, regularly detect the decomposition rate. When the decomposition reaches 68.5%, reduce the CO 2 flow rate to 45 Nm 3 / h, and finally when the decomposition rate detection is 97.5%, end the decomposition.

[0048] (3) Perform solid-liquid separation through a plate and frame filter press. The liquid is discharged into the sodium carbonate storage tank, and the solid powder is repeatedly washed with 75 °C hot pure water until the pH value of the discharged washing water is detected to be 8.5 with a test paper.

[0049] (4) The washed solid powder and high-purity water are put into a magnetically driven high-pressure reactor at a mass ratio of 1:5.5, heated to 205 °C, and maintained for 1.5 hours. The pressure is controlled at 1.8 MPa for hydrothermal synthesis reaction, and then the temperature and pressure are reduced. Solid-liquid separation is carried out using a plate-and-frame filter press to obtain boehmite monohydrate.

[0050] (5) The synthesized solid powder is loaded into a corundum crucible and subjected to phase transformation roasting in a bell jar furnace. The phase transformation temperature is 1040 °C, and after maintaining for 2.5 hours, the material is discharged to obtain phase-transformed alumina powder.

[0051] (6) After the phase-transformed alumina powder is granulated by a coating machine to form round particles, it is loaded into a corundum crucible and subjected to pre-sintering in a bell jar furnace. The pre-sintering process is as follows: continuously heated from room temperature to 560 °C in 180 min, then continuously heated to 950 °C in 220 min, and then continuously heated to 1225 °C in 120 min, and held at 1225 °C for 130 min. Cool to room temperature, and then load the alumina beads into a molybdenum crucible and enter a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: heated from room temperature to 1390 °C in 120 min, and then continuously heated to 1755 °C in 68 min, and held at 1755 °C for 130 min; high-purity alumina grinding beads are prepared.

[0052] The average diameter of the alumina grinding beads prepared in step (6) is 0.5 mm, the original crystal grain size D50 is 1.2 μm, and the purity of the sintered high-purity alumina beads is detected by a glow discharge mass spectrometer. The alumina purity is 99.9991%, the Mohs hardness is 9.0, and the abrasion is 0.09%.

[0053] Example 3

[0054] The method for preparing alumina grinding beads using the mother liquor of Bayer process seed precipitation in this Example 3 consists of the following steps:

[0055] (1) After starting stirring, a dispersant (0.6% each of malic acid, salicylic acid, and sodium dodecylbenzenesulfonate) with a mass ratio of 1.8% is added to the mother liquor of Bayer process seed precipitation, and the temperature of the mother liquor of Bayer process seed precipitation is controlled at 58 °C and stirred evenly for 15 min to obtain a modified mother liquor of Bayer process seed precipitation, wherein the alumina concentration in the mother liquor of Bayer process seed precipitation is 85 g / L.

[0056] (2) Keep stirring and start to introduce 520 Nm 3 / h of food-grade CO 2 , until white aluminum hydroxide appears in the clarified solution, then reduce the CO 2 flow rate to 190 Nm 3 / h. During this period, regularly detect the decomposition rate. When the decomposition reaches 62%, reduce the CO 2 flow rate to 35 Nm 3 / h, and finally the decomposition rate is detected to be 97.3%, and the decomposition ends.

[0057] (3) Solid-liquid separation is carried out through a plate-and-frame filter press. The liquid is discharged into a sodium carbonate storage tank, and the solid powder is repeatedly washed with hot pure water at 80 °C until the pH value of the discharged washing water is detected by a test paper to be 8.3.

[0058] (4) The washed solid powder and high-purity water are put into a magnetically driven high-pressure reactor at a mass ratio of 1:6, heated to 200 °C, and maintained for 1.8 hours. The pressure is controlled at 1.75 MPa for hydrothermal synthesis reaction, and then the temperature and pressure are reduced. Solid-liquid separation is carried out by using a plate-and-frame filter press to prepare boehmite.

[0059] (5) The synthesized solid powder is loaded into a corundum crucible and enters a bell jar furnace for phase conversion roasting. The phase conversion temperature is 1035 °C. After maintaining for 2.3 hours, the material is discharged to obtain phase-converted alumina powder.

[0060] (6) After phase conversion, the alumina powder is processed into round particles by using a coating machine granulation process, loaded into a corundum crucible, and enters a bell jar furnace for pre-sintering. The pre-sintering process is as follows: continuously heated from room temperature to 580 °C in 195 min, then continuously heated to 975 °C in 235 min, and then continuously heated to 1215 °C in 145 min, and kept at 1215 °C for 140 min. Cool to room temperature, and then load the alumina beads into a molybdenum crucible and enter a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: heated from room temperature to 1440 °C in 140 min, and then continuously heated to 1765 °C in 72 min, and kept at 1765 °C for 135 min; high-purity alumina grinding beads are prepared.

[0061] The average diameter of the alumina grinding beads prepared in step (6) is 0.8 mm, the original crystal grain size D50 is 0.5 μm. The purity of the sintered high-purity alumina beads is detected by a glow discharge mass spectrometer. The alumina purity is 99.9992%, the Mohs hardness is 9.4, and the abrasion is 0.05%.

[0062] Example 4

[0063] The method for preparing alumina grinding beads by using the mother liquor of Bayer process seed precipitation in this Example 4 consists of the following steps:

[0064] (1) After starting stirring, a dispersant (1.5% each of citric acid monohydrate and sodium dodecylbenzenesulfonate) with a mass ratio of 3.0% is added to the mother liquor of Bayer process seed precipitation, and the temperature of the mother liquor of Bayer process seed precipitation is controlled at 60 °C and stirred evenly for 15 min to prepare a modified mother liquor of Bayer process seed precipitation, wherein the alumina concentration in the mother liquor of Bayer process seed precipitation is 120 g / L.

[0065] (2) Keep stirring and start to introduce 600 Nm 3Food-grade CO per hour 2 , until white aluminum hydroxide appears in the clarified solution, and reduce the CO 2 flow rate to 300 Nm 3 / h. During this period, regularly detect the decomposition rate. When the decomposition reaches 68.5%, reduce the CO 2 flow rate to 50 Nm 3 / h. Finally, when the decomposition rate detection reaches 97.6%, end the decomposition.

[0066] (3) Carry out solid-liquid separation through a plate-and-frame filter press. Drain the liquid into a sodium carbonate storage tank. Wash the solid powder repeatedly with 83°C hot pure water until the pH value of the discharged washing water is 9 as detected by litmus paper.

[0067] (4) Put the washed solid powder and high-purity water into a magnetically driven high-pressure reactor at a mass ratio of 1:6. Heat up to 210°C and maintain for 1.6 hours. Control the pressure at 1.45 MPa to carry out a hydrothermal synthesis reaction. Then cool down and reduce the pressure, and use a plate-and-frame filter press for solid-liquid separation to prepare boehmite.

[0068] (5) Load the synthesized solid powder into a corundum crucible and enter a bell jar furnace for phase transformation roasting. The phase transformation temperature is 1050°C. After maintaining for 3 hours, discharge the material to obtain phase transformation alumina powder.

[0069] (6) Use the granulation process of a coating machine for the phase-transformed alumina powder. After processing it into round particles, load it into a corundum crucible and enter a bell jar furnace for pre-sintering. The pre-sintering process is as follows: Continuously heat up from room temperature to 540°C in 165 min, then continuously heat up to 955°C in 230 min, and then continuously heat up to 1235°C in 145 min. Keep it at 1235°C for 160 min. Cool down to room temperature. Then load the alumina beads into a molybdenum crucible and enter a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: Heat up from room temperature to 1390°C in 125 min, then continuously heat up to 1775°C in 68 min, and keep it at 1775°C for 150 min; Prepare high-purity alumina grinding beads.

[0070] The average diameter of the alumina grinding beads prepared in step (6) is 1.0 mm, the original crystal grain size D50 is 2.8 μm. Detect the purity of the sintered high-purity alumina beads by a glow discharge mass spectrometer. The alumina purity is 99.999%, the Mohs hardness is 9.5, and the abrasion is 0.1%.

[0071] Comparative Example 1

[0072] The method for preparing alumina grinding beads using the mother liquor of the Bayer process seed described in this Comparative Example 1 consists of the following steps:

[0073] (1) Control the temperature of the Bayer process seed mother liquor at 40 °C and stir evenly for 15 min to prepare the Bayer process seed mother liquor without adding a dispersant. Among them, the alumina concentration in the Bayer process seed mother liquor is 50 g / L.

[0074] (2) Keep stirring and start to introduce 300 Nm 3 / h of food-grade CO 2 , until white aluminum hydroxide appears in the clarified solution, then reduce the CO 2 flow rate to 150 Nm 3 / h. During this period, regularly detect the decomposition rate. When the decomposition reaches 65.6%, reduce the CO 2 flow rate to 20 Nm 3 / h. Finally, when the decomposition rate is detected to be 96.8%, end the decomposition to obtain a mixed slurry.

[0075] (3) Perform solid-liquid separation through a plate-and-frame filter press. The liquid is discharged into a sodium carbonate storage tank, and the solid powder is repeatedly washed with 85 °C hot pure water until the pH value of the discharged washing water is detected to be 8 with litmus paper.

[0076] (4) Put the washed solid powder and high-purity water into a magnetically driven high-pressure reactor at a mass ratio of 1:5, heat up to 195 °C and maintain for 2 h, control the pressure at 1.9 MPa, carry out a hydrothermal synthesis reaction, then cool down and reduce the pressure, and use a plate-and-frame filter press for solid-liquid separation to prepare boehmite.

[0077] (5) Put the prepared boehmite solid powder into a corundum crucible and enter a bell jar furnace for phase transformation roasting. The phase transformation temperature is 1020 °C. After maintaining for 2 hours, discharge the material to obtain phase transformation alumina powder.

[0078] (6) After the phase transformation, the alumina powder is processed into round particles by a coating machine granulation process, then put into a corundum crucible and enter a bell jar furnace for pre-sintering. The pre-sintering process is as follows: continuously heat up from room temperature to 535 °C in 158 min, then continuously heat up to 920 °C in 230 min, and then continuously heat up to 1205 °C in 130 min, and keep the temperature at 1205 °C for 100 min. Cool down to room temperature, then put the alumina beads into a molybdenum crucible and enter a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: heat up from room temperature to 1380 °C in 130 min, then continuously heat up to 1750 °C in 65 min, and keep the temperature at 1750 °C for 100 min; prepare high-purity alumina grinding beads.

[0079] The average diameter of the alumina grinding beads prepared in step (6) is 1.5 mm, the original crystal grain size D50 is 2.3 μm. The purity of the sintered high-purity alumina beads is detected by a glow discharge mass spectrometer. The alumina purity is 99.9958%, the Mohs hardness is 7.5, and the abrasion is 2.6%. From the appendix Figure 3As can be seen from the SEM, the powder particles prepared without adding a dispersant in step (1) have uneven sizes, and the crystal form and morphology are not conducive to subsequent processing into abrasive beads. Moreover, the particles are relatively thick. Finally, the purity of the finished abrasive beads is far from meeting the standard, and the hardness and wear also belong to the level of low-end abrasive beads on the market.

[0080] Comparative Example 2

[0081] The method for preparing alumina abrasive beads using the mother liquor of the Bayer process seed described in this Comparative Example 2 consists of the following steps:

[0082] (1) After starting stirring, add a dispersant (0.5% each of citric acid monohydrate, malic acid, and salicylic acid) with a mass ratio of 1.5% to the mother liquor of the Bayer process seed, control the temperature of the mother liquor of the Bayer process seed at 40 °C, and stir evenly for 15 min to prepare a modified mother liquor of the Bayer process seed. Among them, the alumina concentration in the mother liquor of the Bayer process seed is 50 g / L.

[0083] (2) Keep stirring and introduce 150 Nm 3 / h of food-grade CO 2 , and continue to ventilate until the decomposition rate is detected to be 96.8%, then end the decomposition to obtain a mixed slurry.

[0084] (3) Perform solid-liquid separation through a plate and frame filter press. The liquid is discharged into a sodium carbonate storage tank, and the solid powder is repeatedly washed with hot pure water at 85 °C until the pH value of the discharged washing water is detected to be 8 with litmus paper.

[0085] (4) Put the washed solid powder and high-purity water into a magnetically driven high-pressure reactor at a mass ratio of 1:5, heat up to 195 °C, and maintain for 2 h, control the pressure at 1.9 MPa, carry out a hydrothermal synthesis reaction, then cool down and reduce the pressure, and use a plate and frame filter press for solid-liquid separation to prepare boehmite.

[0086] (5) Load the prepared boehmite solid powder into a corundum crucible, enter a bell jar furnace for phase transformation roasting, the phase transformation temperature is 1020 °C, keep it for 2 hours and then discharge to obtain phase transformation alumina powder.

[0087] (6) After the phase transformation, the alumina powder is processed into round particles by a coating machine granulation process, loaded into a corundum crucible, and enter a bell jar furnace for pre-sintering. The pre-sintering process is as follows: continuously heat up from room temperature to 535 °C in 158 min, then continuously heat up to 920 °C in 230 min, and then continuously heat up to 1205 °C in 130 min, and keep it at 1205 °C for 100 min. Cool down to room temperature, then load the alumina beads into a molybdenum crucible and enter a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: heat up from room temperature to 1380 °C in 130 min, then continuously heat up to 1750 °C in 65 min, and keep it at 1750 °C for 100 min; prepare high-purity alumina abrasive beads.

[0088] The average diameter of the alumina grinding beads prepared in step (6) is 8 mm, the original crystal grain size D50 is 22 μm, the purity of the sintered high-purity alumina beads is detected by a glow discharge mass spectrometer, the alumina purity is 99.9972%, the Mohs hardness is 6.1, and the wear is 5.5%. As can be seen from the attached Figure 4 SEM, the powder particles prepared by the single-gas carbonization process in step (2) are severely agglomerated, and the crystal form and morphology are not conducive to the subsequent processing of grinding beads. Finally, the finished grinding beads have low purity, and the hardness and wear are much lower than those of the finished product in Example 1.

Claims

1. A method for preparing alumina grinding beads using Bayer process seed liquor, characterized in that: It consists of the following steps: (1) adding a dispersant to the Bayer process seed liquor to prepare a modified Bayer process seed liquor, wherein the dispersant is selected from the group consisting of citric acid monohydrate, malic acid, salicylic acid, and sodium dodecylbenzene sulfonate; (2) First, a flow rate of 300-600 Nm is introduced into the modified Bayer process seed liquor prepared in step (1). 3 / h of carbon dioxide, after the first occurrence of aluminum hydroxide crystallization, the carbon dioxide flow rate is reduced to 150-300Nm 3 / h, when the decomposition rate reaches 62-68.5%, the carbon dioxide flow rate is further reduced to 20-50Nm 3 / h, until the decomposition rate reaches 96-98%, and a mixed slurry is obtained; (3) The mixed slurry obtained in step (2) is separated into solid and liquid by a plate and frame filter press, and then the aluminum hydroxide powder in the filter press is washed with high-purity water until the pH of the washing water is 8-9; (4) mixing the solid powder prepared in step (3) with water to carry out a hydrothermal synthesis reaction, and after the reaction is completed, separating the solid and the liquid to prepare boehmite; (5) placing the boehmite solid powder prepared in step (4) in a corundum crucible and calcining it in a bell kiln for phase transition, the calcining phase transition temperature being 1020-1050° C. and the calcining phase transition time being 2-3 h to obtain a phase transition alumina powder; (6) The phase-inverted alumina powder obtained in step (5) is granulated and formed by a coating machine, pre-sintered in a bell kiln, cooled to room temperature, and then secondary sintered in a hydrogen protection furnace to obtain high-purity alumina grinding beads. The secondary sintering process in the hydrogen protection furnace is as follows: the temperature is continuously increased from room temperature to 1380°C-1440°C for 120min-140min, and then continuously increased to 1750°C-1775°C for 65min-72min, and kept at 1750°C-1775°C for 100min-150min; The average diameter of the prepared alumina grinding beads is 0.5-1.0 mm, the original grain size D50 is 0.5-2.8 μm, the purity of alumina is 99.999%-99.9993%, the Mohs hardness is 9.0-9.5, and the abrasion is 0.05-0.1%.

2. The method for preparing alumina grinding beads using Bayer process seed liquor according to claim 1, characterized in that: In step (1), the concentration of sodium aluminate in the Bayer process seed liquor is 50-120 g / L, and the temperature of the Bayer process seed liquor is controlled to be 40-60°C.

3. The method for preparing alumina grinding beads using Bayer process seed liquor according to claim 1, characterized in that: The mass of the dispersant in step (1) accounts for 1.5-3% of the mass of the Bayer process seed liquor.

4. The method for preparing alumina grinding beads using Bayer process seed liquor according to claim 1, characterized in that: The temperature of the high-purity water used for washing in step (3) is 75-85°C.

5. The method for preparing alumina grinding beads using Bayer process seed liquor according to claim 1, characterized in that: In step (4), the mass ratio of solid powder to water is 1:5-1:6, the hydrothermal synthesis temperature is 195-210° C., the hydrothermal synthesis pressure is 1.45 MPa-1.9 MPa, and the hydrothermal synthesis time is 1.5-2 h.

6. The method for preparing alumina grinding beads using Bayer process seed liquor according to claim 1, characterized in that: The pre-sintering process in step (6) is as follows: continuously heating from room temperature to 535°C-580°C over 150min-200min, continuously heating to 920°C-975°C over 220min-235min, continuously heating to 1205°C-1235°C over 120min-145min, and keeping at 1205°C-1235°C for 100min-160min.

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