Method for preparing aluminum oxide grinding beads by using Bayer process seed precipitation mother liquor

Abstract

The invention belongs to the technical field of preparation of aluminum oxide grinding beads, and particularly relates to a method for preparing aluminum oxide grinding beads by using Bayer process seed precipitation mother liquor. The method for preparing the aluminum oxide grinding beads by using the Bayer process seed precipitation mother liquor comprises the process steps of recrystallization, washing, hydrothermal synthesis, phase change, molding sintering and the like, the decomposition rate is controlled to be 96-98% through crystallization and multi-stage carbon separation processes, high-purity aluminum hydroxide powder is generated, and the aluminum oxide grinding beads are prepared. And washing with pure water to remove water-soluble impurities, carrying out hydrothermal synthesis to obtain boehmite, carrying out kiln phase inversion to obtain alpha-alumina powder, granulating to obtain alumina beads, and sintering to prepare the high-purity alumina grinding beads. The aluminum oxide grinding bead prepared by the method is uniform and controllable in particle, has high purity, high abrasion resistance, high hardness and high impact toughness, and meets the requirements of most aluminum oxide industries on the market for grinding media.

Description

Technical Field

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

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

[0003] In the process of seed decomposition of the improved Bayer process, one of the high-purity alumina production processes, due to process limitations, the seed is generally decomposed to 35-55%, and the remaining mother liquor is recycled in production. The main component of the mother liquor is high-purity sodium aluminate solution, but the silicon, iron, calcium, magnesium, gallium and water-soluble sodium aluminate therein are all impurities that are harmful to high-purity alumina. In the continuous circulation process, the above impurities will continue to be enriched. In order to ensure the purity of the high-purity alumina terminal product, this part of the mother liquor can only be discarded in stages, or treated as a low-value alumina product, resulting in a waste of resources.

[0004] Therefore, exploring a method for producing high-purity alumina grinding beads using the residual mother liquor from the Bayer process seed separation process has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing alumina grinding beads using Bayer process seed and denominator solution. The alumina grinding beads prepared by the method have high purity and high wear resistance.

[0006] The method for preparing alumina grinding beads using Bayer process seed denominator liquid of the present invention comprises the following steps: (1) adding a dispersant to the Bayer process seed liquor to prepare a modified Bayer process seed liquor; (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 to obtain a phase-inverted 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.

[0007] in: 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.

[0008] The dispersant in step (1) is selected from the group consisting of citric acid monohydrate, malic acid, salicylic acid or sodium dodecylbenzene cyclopentane. The mass of the dispersant accounts for 1.5-3% of the mass of the Bayer process seed liquor.

[0009] The temperature of the high-purity water used for washing in step (3) is 75-85°C.

[0010] 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.

[0011] In step (5), the calcination phase transition temperature is 1020-1050°C, and the calcination phase transition time is 2-3h.

[0012] 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.

[0013] The secondary sintering process in the hydrogen protection furnace in step (6) is: continuously heating from room temperature to 1380°C-1440°C over 120min-140min, then continuously heating to 1750°C-1775°C over 65min-72min, and keeping at 1750°C-1775°C for 100min-150min.

[0014] The average diameter of the alumina grinding beads prepared in step (6) is 0.5-1.0 mm, the original 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 abrasion is 0.05-0.1%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The method for preparing alumina grinding beads using Bayer process seed liquor of the present invention comprises the steps of recrystallization, washing, hydrothermal synthesis, phase change, forming and sintering. Through crystallization and multi-stage carbon separation process, the decomposition rate is controlled to reach 96-98%, and high-purity aluminum hydroxide powder is generated. The powder is then washed with pure water to remove water-soluble impurities, hydrothermally synthesized into boehmite, and then phase-transformed into α-alumina powder in a kiln. The powder is granulated into alumina beads and sintered to prepare high-purity alumina grinding beads.

[0016] (2) The method of preparing alumina grinding beads using Bayer process seed liquor described in the present invention adds a specific dispersant and adopts a multiple carbonization method. Since the carbonization process provides air pressure and stirring force to the alumina raw crystals, not only the particle size of the raw crystals is fine enough, but also the internal structure is partially deformed, becoming a porous active state (as can be seen from electron microscope photos), reducing the sand milling, ball milling or air flow milling steps, reducing pollution and reducing costs. The average diameter of the powder raw crystals can be controlled to 0.1-0.3μm, and the particle size can be controlled to 0.5-3.0μm, which is very beneficial for the subsequent step of granulating high-density alumina beads, and is also beneficial for sintering and molding, thereby improving the density and wear resistance of the grinding balls.

[0017] (3) The method of preparing alumina grinding beads using Bayer process seed liquor described in the present invention makes full use of the surplus value of the seed liquor while preparing high-purity alumina grinding beads, and processes the mother liquor that can only be processed into ordinary aluminum hydroxide or aluminum oxide into high-end alumina grinding beads. In addition, the main component of the waste liquid generated in the preparation process of the present invention is sodium carbonate, and high-purity sodium carbonate can be directly extracted for use in other fields, which achieves both energy saving and environmental protection and reduces production costs.

[0018] (4) In the method for preparing alumina grinding beads using Bayer process seed liquor described in the present invention, the solid obtained in the final reaction of step (2) is aluminum hydroxide, and a hydrothermal reaction is performed after washing, so that the sodium ion impurities encapsulated in the agglomerates can diffuse out and be removed by washing. In addition, the sodium aluminate solution is purified by a dispersant and a multiple carbon fractionation method, and most of the residual impurities such as silicon, iron, and gallium therein are removed by 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 by high-temperature volatilization. Finally, the alumina grinding beads prepared by this scheme have an extremely low impurity content, and the purity of alumina can reach above 99.999%.

[0019] (5) In the method for preparing alumina grinding beads using Bayer process denominator solution described in the present invention, in step (6), the grain growth of alumina in the later stage of sintering plays an important role in sintering densification. The present invention divides these two stages into two steps of calcination. The purpose of pre-sintering is to carry out the first stage of sintering, eliminate pores and moisture, which is conducive to the growth of grains in the later stage of sintering. The sintering curve of the secondary sintering is divided into two heating sections with two heating rates and one insulation section. In the first heating section, the pre-sintered alumina balls undergo the process of eliminating pores again. The pores are eliminated more thoroughly, and the density is further increased. At the same time, the temperature growth rate is controlled to reduce the breakage of the alumina balls. The second heating section adjusts a specific heating rate to adjust the alumina grain growth rate, and the density, hardness and volume of the alumina balls are further controlled by the grain growth rate, so that the obtained alumina grinding beads meet the grinding requirements.

[0020] (6) The alumina grinding beads prepared by the method described in the present invention have uniform and controllable particles, high purity, high wear resistance, high hardness and high impact toughness, and meet the grinding medium requirements of most alumina industries on the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the SEM image of the original crystal powder of alumina grinding beads prepared in Example 1; Figure 2 This is a photo of the alumina grinding beads prepared in Example 1; Figure 3 This is the SEM image of the original crystal powder of alumina grinding beads prepared in Comparative Example 1; Figure 4 This is the SEM image of the original crystal powder of alumina grinding beads prepared in Comparative Example 2. DETAILED DESCRIPTION

[0022] The present invention is further described below with reference to the embodiments.

[0023] Example 1 The method for preparing alumina grinding beads using Bayer process seed liquor described in Example 1 comprises the following steps: (1) After starting stirring, add 1.5% by mass of dispersant (0.5% each of citric acid monohydrate, malic acid and salicylic acid) to the Bayer process seed liquor, control the temperature of the Bayer process seed liquor to 40°C, stir evenly for 15 minutes, and prepare a modified Bayer process seed liquor, wherein the concentration of alumina in the Bayer process seed liquor is 50 g / L.

[0024] (2) Continue stirring and start to introduce 300Nm 3 / h of food grade CO2 until white aluminum hydroxide appears in the clear solution, then reduce the CO2 flow rate to 150Nm 3 / h, and regularly check the decomposition rate. When the decomposition rate reaches 65.6%, reduce the CO2 flow rate to 20Nm 3 / h, and finally the decomposition rate was detected to be 96.8%, then the decomposition was completed and a mixed slurry was obtained.

[0025] (3) Use a plate and frame filter press to separate the solid and liquid. The liquid is discharged into a sodium carbonate storage tank. The solid powder is repeatedly washed with 85°C hot pure water. The pH value of the discharged washing water is detected by a test paper until it reaches 8.

[0026] (4) The washed solid powder and high-purity water were placed in a magnetically driven high-pressure reactor at a mass ratio of 1:5, the temperature was raised to 195°C, and maintained for 2 hours. The pressure was controlled at 1.9 MPa to carry out a hydrothermal synthesis reaction. The temperature and pressure were then reduced, and a plate and frame filter press was used for solid-liquid separation to prepare boehmite.

[0027] (5) The prepared boehmite solid powder is loaded into a corundum crucible and placed in a bell kiln for phase inversion calcination at a phase inversion temperature of 1020° C. The phase inversion temperature is maintained for 2 hours and then the material is discharged to obtain a phase inversion alumina powder.

[0028] (6) The alumina powder after phase inversion is processed into round particles by a coating machine granulation process, then loaded into a corundum crucible and placed in a bell kiln for pre-sintering. The pre-sintering process is as follows: continuously heating from room temperature to 535°C for 158 minutes, then continuously heating to 920°C for 230 minutes, then continuously heating to 1205°C for 130 minutes, and keeping at 1205°C for 100 minutes. After cooling to room temperature, the alumina beads are then loaded into a molybdenum crucible and placed in a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: continuously heating from room temperature to 1380°C for 130 minutes, then continuously heating to 1750°C for 65 minutes, and keeping at 1750°C for 100 minutes. High-purity alumina grinding beads are prepared.

[0029] The average diameter of the alumina grinding beads prepared in step (6) is 0.6 mm, and the original grain size D50 is 0.9 μm. The purity of the sintered high-purity alumina beads is detected by glow discharge mass spectrometry. The purity of the alumina is 99.9993%, the Mohs hardness is 9.2, and the abrasion is 0.08%.

[0030] The SEM image of the original crystal powder of alumina grinding beads prepared in Example 1 is attached. Figure 1 The photo of the prepared alumina grinding beads is attached. Figure 2 , by attaching Figure 1 It can be seen that the alumina powder prepared by this method has a very uniform crystal form and morphology, the particles reach the nanometer level, and the coral-like particles are porous and active. Through processing, the powder particles are adsorbed and combined more closely, which is conducive to the subsequent processing of grinding beads. Figure 2 It can be seen that the finished grinding beads have good sphericity and are thoroughly vitrified, comparable to the commonly used zirconia grinding beads on the market.

[0031] Example 2 The method for preparing alumina grinding beads using Bayer process seed liquor described in Example 2 comprises the following steps: (1) After starting stirring, add 2.2% by mass of a dispersant (1.1% each of malic acid and sodium dodecylbenzene cyclopentane) to the Bayer process seed liquor, control the temperature of the Bayer process seed liquor to 55°C, stir evenly for 15 minutes, and prepare a modified Bayer process seed liquor, wherein the concentration of alumina in the Bayer process seed liquor is 65 g / L.

[0032] (2) Continue stirring and start to introduce 490Nm 3 / h of food grade CO2 until white aluminum hydroxide appears in the clear solution, and then reduce the CO2 flow rate to 230Nm 3 / h, and regularly check the decomposition rate. When the decomposition rate reaches 68.5%, reduce the CO2 flow rate to 45Nm 3 / h, and finally the decomposition rate reaches 97.5%, then the decomposition is finished.

[0033] (3) Use a plate and frame filter press to separate the solid and liquid. The liquid is discharged into a sodium carbonate storage tank. The solid powder is repeatedly washed with 75°C hot pure water. The pH value of the discharged washing water is detected by a test paper until it reaches 8.5.

[0034] (4) The washed solid powder and high-purity water were placed in a magnetically driven high-pressure reactor at a mass ratio of 1:5.5, the temperature was raised to 205°C, and maintained for 1.5 hours, the pressure was controlled to be 1.8 MPa, a hydrothermal synthesis reaction was carried out, and then the temperature and pressure were reduced, and a plate and frame filter press was used for solid-liquid separation to prepare boehmite.

[0035] (5) The synthesized solid powder is loaded into a corundum crucible and placed in a bell kiln for phase inversion calcination at a phase inversion temperature of 1040°C. The material is kept for 2.5 hours and then discharged to obtain phase inversion alumina powder.

[0036] (6) The alumina powder after phase inversion is processed into round particles by a coating machine granulation process, then loaded into a corundum crucible and placed in a bell kiln for pre-sintering. The pre-sintering process is as follows: continuously heating from room temperature to 560°C for 180 minutes, then continuously heating to 950°C for 220 minutes, then continuously heating to 1225°C for 120 minutes, and keeping at 1225°C for 130 minutes. After cooling to room temperature, the alumina beads are then loaded into a molybdenum crucible and placed in a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: continuously heating from room temperature to 1390°C for 120 minutes, then continuously heating to 1755°C for 68 minutes, and keeping at 1755°C for 130 minutes; thus, high-purity alumina grinding beads are prepared.

[0037] The average diameter of the alumina grinding beads prepared in step (6) is 0.5 mm, and the original grain size D50 is 1.2 μm. The purity of the sintered high-purity alumina beads is detected by glow discharge mass spectrometry. The purity of the alumina is 99.9991%, the Mohs hardness is 9.0, and the abrasion is 0.09%.

[0038] Example 3 The method for preparing alumina grinding beads using Bayer process seed liquor described in Example 3 comprises the following steps: (1) After starting stirring, add 1.8% by mass of dispersant (0.6% each of malic acid, salicylic acid and sodium dodecylbenzene cyclopentane) to the Bayer process seed liquor, control the temperature of the Bayer process seed liquor to 58°C, stir evenly for 15 minutes, and prepare a modified Bayer process seed liquor, wherein the concentration of alumina in the Bayer process seed liquor is 85 g / L.

[0039] (2) Continue stirring and start to introduce 520Nm 3 / h of food grade CO2 until white aluminum hydroxide appears in the clear solution, and then reduce the CO2 flow rate to 190Nm 3 / h, and regularly check the decomposition rate. When the decomposition rate reaches 62%, reduce the CO2 flow rate to 35Nm 3 / h, and finally the decomposition rate was detected to be 97.3%, and the decomposition was ended.

[0040] (3) Use a plate and frame filter press to separate the solid and liquid. The liquid is discharged into a sodium carbonate storage tank. The solid powder is repeatedly washed with 80°C hot pure water. The pH value of the discharged washing water is detected by a test paper until it reaches 8.3.

[0041] (4) The washed solid powder and high-purity water were placed in a magnetically driven high-pressure reactor at a mass ratio of 1:6, and the temperature was raised to 200°C and maintained for 1.8 hours. The pressure was controlled to be 1.75 MPa to carry out a hydrothermal synthesis reaction. The temperature and pressure were then lowered, and a plate and frame filter press was used for solid-liquid separation to prepare boehmite.

[0042] (5) The synthesized solid powder was loaded into a corundum crucible and placed in a bell kiln for phase inversion calcination at a phase inversion temperature of 1035°C. The material was kept at this temperature for 2.3 hours and then discharged to obtain phase inversion alumina powder.

[0043] (6) The alumina powder after phase inversion is processed into round particles by a coating machine granulation process, then loaded into a corundum crucible and placed in a bell kiln for pre-sintering. The pre-sintering process is as follows: continuously heating from room temperature to 580°C for 195 minutes, then continuously heating to 975°C for 235 minutes, then continuously heating to 1215°C for 145 minutes, and keeping at 1215°C for 140 minutes. After cooling to room temperature, the alumina beads are then loaded into a molybdenum crucible and placed in a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: continuously heating from room temperature to 1440°C for 140 minutes, then continuously heating to 1765°C for 72 minutes, and keeping at 1765°C for 135 minutes. High-purity alumina grinding beads are prepared.

[0044] The average diameter of the alumina grinding beads prepared in step (6) is 0.8 mm, and the original grain size D50 is 0.5 μm. The purity of the sintered high-purity alumina beads is tested by glow discharge mass spectrometry, and the purity of the alumina is 99.9992%, the Mohs hardness is 9.4, and the abrasion is 0.05%.

[0045] Example 4 The method for preparing alumina grinding beads using Bayer process seed liquor described in Example 4 comprises the following steps: (1) After starting stirring, add 3.0% by weight of a dispersant (1.5% each of citric acid monohydrate and sodium dodecylbenzene cyclopentane) to the Bayer process seed liquor, control the temperature of the Bayer process seed liquor to 60°C, stir evenly for 15 minutes, and prepare a modified Bayer process seed liquor, wherein the concentration of alumina in the Bayer process seed liquor is 120 g / L.

[0046] (2) Continue stirring and start to introduce 600Nm 3 / h of food grade CO2 until white aluminum hydroxide appears in the clear solution, and then reduce the CO2 flow rate to 300Nm 3 / h, and regularly check the decomposition rate. When the decomposition rate reaches 68.5%, reduce the CO2 flow rate to 50Nm 3 / h, and finally the decomposition rate was detected to be 97.6%, and the decomposition was ended.

[0047] (3) Use a plate and frame filter press to separate the solid and liquid. The liquid is discharged into a sodium carbonate storage tank. The solid powder is repeatedly washed with 83°C hot pure water. The pH value of the discharged washing water is detected by a test paper until it reaches 9.

[0048] (4) The washed solid powder and high-purity water were placed in a magnetically driven high-pressure reactor at a mass ratio of 1:6, the temperature was raised to 210°C, and maintained for 1.6 hours with the pressure controlled at 1.45 MPa to carry out a hydrothermal synthesis reaction, and then the temperature and pressure were lowered, and a plate and frame filter press was used for solid-liquid separation to prepare boehmite.

[0049] (5) The synthesized solid powder is loaded into a corundum crucible and placed in a bell kiln for phase inversion calcination at a phase inversion temperature of 1050°C. The phase inversion temperature is maintained for 3 hours and then the material is discharged to obtain a phase inversion alumina powder.

[0050] (6) The alumina powder after phase inversion is processed into round particles by a coating machine granulation process, then loaded into a corundum crucible and placed in a bell kiln for pre-sintering. The pre-sintering process is as follows: continuously heating from room temperature to 540°C for 165 minutes, then continuously heating to 955°C for 230 minutes, then continuously heating to 1235°C for 145 minutes, and keeping at 1235°C for 160 minutes. After cooling to room temperature, the alumina beads are then loaded into a molybdenum crucible and placed in a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: continuously heating from room temperature to 1390°C for 125 minutes, then continuously heating to 1775°C for 68 minutes, and keeping at 1775°C for 150 minutes. High-purity alumina grinding beads are prepared.

[0051] The average diameter of the alumina grinding beads prepared in step (6) is 1.0 mm, and the original grain size D50 is 2.8 μm. The purity of the sintered high-purity alumina beads is tested by glow discharge mass spectrometry, and the purity of the alumina is 99.999%, the Mohs hardness is 9.5, and the abrasion is 0.1%.

[0052] Comparative Example 1 The method for preparing alumina grinding beads using Bayer process seed liquor described in Comparative Example 1 is composed of the following steps: (1) The temperature of the Bayer process seed liquor was controlled at 40°C and stirred evenly for 15 minutes to prepare a Bayer process seed liquor without adding a dispersant, wherein the concentration of alumina in the Bayer process seed liquor was 50 g / L.

[0053] (2) Continue stirring and start to introduce 300Nm 3 / h of food grade CO2 until white aluminum hydroxide appears in the clear solution, then reduce the CO2 flow rate to 150Nm 3 / h, and regularly check the decomposition rate. When the decomposition rate reaches 65.6%, reduce the CO2 flow rate to 20Nm 3 / h, and finally the decomposition rate was detected to be 96.8%, then the decomposition was completed and a mixed slurry was obtained.

[0054] (3) Use a plate and frame filter press to separate the solid and liquid. The liquid is discharged into a sodium carbonate storage tank. The solid powder is repeatedly washed with 85°C hot pure water. The pH value of the discharged washing water is detected by a test paper until it reaches 8.

[0055] (4) The washed solid powder and high-purity water were placed in a magnetically driven high-pressure reactor at a mass ratio of 1:5, the temperature was raised to 195°C, and maintained for 2 hours. The pressure was controlled at 1.9 MPa to carry out a hydrothermal synthesis reaction. The temperature and pressure were then reduced, and a plate and frame filter press was used for solid-liquid separation to prepare boehmite.

[0056] (5) The prepared boehmite solid powder is loaded into a corundum crucible and placed in a bell kiln for phase inversion calcination at a phase inversion temperature of 1020° C. The phase inversion temperature is maintained for 2 hours and then the material is discharged to obtain a phase inversion alumina powder.

[0057] (6) The alumina powder after phase inversion is processed into round particles by a coating machine granulation process, then loaded into a corundum crucible and placed in a bell kiln for pre-sintering. The pre-sintering process is as follows: continuously heating from room temperature to 535°C for 158 minutes, then continuously heating to 920°C for 230 minutes, then continuously heating to 1205°C for 130 minutes, and keeping at 1205°C for 100 minutes. After cooling to room temperature, the alumina beads are then loaded into a molybdenum crucible and placed in a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: continuously heating from room temperature to 1380°C for 130 minutes, then continuously heating to 1750°C for 65 minutes, and keeping at 1750°C for 100 minutes; thus, high-purity alumina grinding beads are prepared.

[0058] The average diameter of the alumina grinding beads prepared in step (6) is 1.5 mm, and the original grain size D50 is 2.3 μm. The purity of the sintered high-purity alumina beads is tested by glow discharge mass spectrometry. The purity of the alumina is 99.9958%, the Mohs hardness is 7.5, and the wear is 2.6%. Figure 3 It can be seen from the SEM that the powder produced in step (1) without adding a dispersant has uneven particle size and crystal morphology that is not conducive to subsequent processing into grinding beads. In addition, the particles are coarse. The purity of the final grinding beads is far from meeting the standard, and the hardness and abrasion are also at the level of low-end grinding beads on the market.

[0059] Comparative Example 2 The method for preparing alumina grinding beads using Bayer process seed liquor described in this comparative example 2 consists of the following steps: (1) After starting stirring, add 1.5% by mass of dispersant (0.5% each of citric acid monohydrate, malic acid and salicylic acid) to the Bayer process seed liquor, control the temperature of the Bayer process seed liquor to 40°C, stir evenly for 15 minutes, and prepare a modified Bayer process seed liquor, wherein the concentration of alumina in the Bayer process seed liquor is 50 g / L.

[0060] (2) Continue stirring and introduce 150Nm 3 / h of food-grade CO2, and continue to ventilate until the decomposition rate reaches 96.8%, then end the decomposition and obtain a mixed slurry.

[0061] (3) Use a plate and frame filter press to separate the solid and liquid. The liquid is discharged into a sodium carbonate storage tank. The solid powder is repeatedly washed with 85°C hot pure water. The pH value of the discharged washing water is detected by a test paper until it reaches 8.

[0062] (4) The washed solid powder and high-purity water were placed in a magnetically driven high-pressure reactor at a mass ratio of 1:5, the temperature was raised to 195°C, and maintained for 2 hours. The pressure was controlled at 1.9 MPa to carry out a hydrothermal synthesis reaction. The temperature and pressure were then reduced, and a plate and frame filter press was used for solid-liquid separation to prepare boehmite.

[0063] (5) The prepared boehmite solid powder is loaded into a corundum crucible and placed in a bell kiln for phase inversion calcination at a phase inversion temperature of 1020° C. The phase inversion temperature is maintained for 2 hours and then the material is discharged to obtain a phase inversion alumina powder.

[0064] (6) The alumina powder after phase inversion is processed into round particles by a coating machine granulation process, then loaded into a corundum crucible and placed in a bell kiln for pre-sintering. The pre-sintering process is as follows: continuously heating from room temperature to 535°C for 158 minutes, then continuously heating to 920°C for 230 minutes, then continuously heating to 1205°C for 130 minutes, and keeping at 1205°C for 100 minutes. After cooling to room temperature, the alumina beads are then loaded into a molybdenum crucible and placed in a hydrogen protection furnace for secondary sintering. The secondary sintering process is as follows: continuously heating from room temperature to 1380°C for 130 minutes, then continuously heating to 1750°C for 65 minutes, and keeping at 1750°C for 100 minutes. High-purity alumina grinding beads are prepared.

[0065] The average diameter of the alumina grinding beads prepared in step (6) is 8 mm, and the original grain size D50 is 22 μm. The purity of the sintered high-purity alumina beads is tested by glow discharge mass spectrometry. The purity of the alumina is 99.9972%, the Mohs hardness is 6.1, and the wear is 5.5%. Figure 4 It can be seen from the SEM that 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. The final grinding beads are not of high purity, and the hardness and abrasion are far lower than the finished product of 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; (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 to obtain a phase-inverted 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.

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 dispersant in step (1) is selected from the group consisting of citric acid monohydrate, malic acid, salicylic acid or sodium dodecylbenzene cyclopentane. The mass of the dispersant 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: In step (5), the calcination phase transition temperature is 1020-1050°C, and the calcination phase transition time is 2-3h.

7. 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.

8. The method for preparing alumina grinding beads using Bayer process seed liquor according to claim 1, characterized in that: The secondary sintering process in the hydrogen protection furnace in step (6) is: continuously heating from room temperature to 1380°C-1440°C over 120min-140min, then continuously heating to 1750°C-1775°C over 65min-72min, and keeping at 1750°C-1775°C for 100min-150min.

9. The method for preparing alumina grinding beads using Bayer process seed liquor according to claim 1, characterized in that: The average diameter of the alumina grinding beads prepared in step (6) is 0.5-1.0 mm, the original 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 abrasion is 0.05-0.1%.

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