A low-sodium pure-phase bayerite and a preparation method thereof

Abstract

The application discloses a preparation method of low-sodium pure-phase bayerite, which comprises the following steps: mixing bayerite seeds with a mass fraction of beta-Al(OH)3 greater than or equal to 98% and a sodium aluminate solution to obtain a first slurry; introducing a gas containing carbon dioxide or adding an aluminum salt solution into the first slurry to perform a reaction; performing solid-liquid separation on the slurry obtained in the reaction and washing to obtain a filter cake; performing pressure boiling treatment on the filter cake after slurry; performing solid-liquid separation on the slurry after the pressure boiling treatment and washing again; and drying the filter cake to obtain the low-sodium pure-phase bayerite. The preparation method of the low-sodium pure-phase bayerite can obtain bayerite with high beta-Al(OH)3 content and low sodium oxide content.

Description

Technical Field

[0001] This application relates to the field of fine alumina technology, and in particular to a low-sodium pure-phase Bayerite and its preparation method. Background Technology

[0002] Bayerite, industrially known as high-carbon aluminum colloid, is one of the three common crystal forms of aluminum hydroxide (Al(OH)3). Compared to the other two crystal forms, gibbsite and Nordstrandite, Bayerite has a denser, more ordered crystal structure and higher thermal stability, making it suitable as a carrier for highly active catalysts or a precursor for special ceramics. However, Bayerite is susceptible to damage from caustic alkaline environments, where sodium ions easily embed into the crystal lattice or adsorb onto the surface, resulting in high sodium content and impure crystal phases in Bayerite products. While breakthroughs have been made in addressing the high sodium content, the presence of impurities such as Nordstrandite, gibbsite, and pseudoboehmite (a type of AlOOH crystal form) in Bayerite results in a consistently low actual content of pure Bayerite phase (β-Al(OH)3) in the products, making it impossible to produce Bayerite products that are both low in sodium and pure in phase.

[0003] Therefore, achieving simultaneous control of low sodium and pure phase remains a cutting-edge research goal in the preparation of Bayerite products. Summary of the Invention

[0004] This application provides a low-sodium pure phase Bayerite and its preparation method, which solves the technical problems of high sodium oxide content and low β-Al(OH)3 content in traditional Bayerite products.

[0005] A first aspect of this application provides a method for preparing low-sodium pure-phase Bayerite, comprising the following steps: mixing Bayerite seed crystals and a sodium aluminate solution to obtain a first slurry; wherein the mass fraction of β-Al(OH)3 in the Bayerite seed crystals is greater than or equal to 98%; introducing a gas containing carbon dioxide into the first slurry to carry out a first reaction until the pH of the first reaction endpoint is 12-13.5, to obtain a second slurry; or adding an aluminum salt solution to the first slurry to carry out a second reaction until the pH of the second reaction endpoint is 12-13.5, to obtain a third slurry; performing solid-liquid separation and washing on the second or third slurry to obtain a first filter cake; slurrying the first filter cake to obtain a fourth slurry; placing the fourth slurry in a sealed container for pressure cooking to obtain a fifth slurry; performing solid-liquid separation and washing on the fifth slurry to obtain a second filter cake; and drying the second filter cake to obtain low-sodium pure-phase Bayerite.

[0006] Optionally, the mass ratio of the Bayerite seed crystal to the alumina in the sodium aluminate solution is 3:20; and / or, the concentration of alumina in the sodium aluminate solution is 40 g / L to 80 g / L, and the volume ratio of the Bayerite seed crystal to the sodium aluminate solution is (6 g to 12 g) / L.

[0007] Optionally, the pH of the fourth slurry is less than 8.5.

[0008] Optionally, the temperature of the pressure cooking treatment is 150℃~160℃, and the time of the pressure cooking treatment is 90min~120min.

[0009] Optionally, the grain size D50 of the Bayerite seed crystal is less than 5 μm.

[0010] Optionally, the gas containing carbon dioxide is introduced at a rate of 0.5 L / min to 1.5 L / min; and / or, the volume fraction of carbon dioxide in the gas containing carbon dioxide is 35% to 40%.

[0011] Optionally, the amount of aluminum salt solution added is 0.9 to 3.2 times the volume of the sodium aluminate solution. The Al2O3 concentration in the aluminum salt solution is 10 g / L to 40 g / L; and / or, the aluminum salt solution is one or more of aluminum sulfate solution, aluminum chloride solution, or aluminum nitrate solution.

[0012] Optionally, the temperature of the first reaction is 20℃ to 60℃, and the reaction time is 60 min to 180 min; and / or, the temperature of the second reaction is 20℃ to 60℃, and the reaction time is 60 min to 180 min.

[0013] Optionally, the drying temperature is 100℃~150℃.

[0014] A second aspect of this application provides a low-sodium pure-phase Bayerite, prepared by the preparation method described in the first aspect of this application, satisfying at least one of the following characteristics: (1) The mass fraction of sodium oxide in the low-sodium pure phase Bayerite is less than 0.1%; (2) The mass fraction of β-Al(OH)3 in the low-sodium pure phase Bayerite is 98%–99.6%; (3) The specific surface area of ​​the low-sodium pure phase Bayerite is 418.3 m. 2 / g~457.4m 2 / g.

[0015] Compared with the prior art, the technical solution provided in this application has the following beneficial effects: The method for preparing low-sodium pure-phase Bayerite in this application involves reacting an aluminum salt solution or a gas containing carbon dioxide with a sodium aluminate solution, causing the sodium aluminate to decompose and generate aluminum hydroxide precipitate. By adding Bayerite seed crystals, the content of the Bayerite phase (β-Al(OH)3) in the aluminum hydroxide precipitate is increased. Further pressure cooking is then performed to deeply remove sodium and to further transform imperfectly crystalline components in the slurry (such as boehmite), further increasing the content of the Bayerite phase (β-Al(OH)3). The Bayerite seed crystals added in this preparation method induce the transformation of the aluminum hydroxide precipitate into the Bayerite phase. Specifically, the mass fraction of β-Al(OH)3 in the Bayerite seed crystal is greater than or equal to 98%, and the mass fraction of sodium oxide is less than or equal to 0.1%. If the mass fraction of β-Al(OH)3 in the Bayerite seed crystal is too low, the mass fraction of β-Al(OH)3 in the low-sodium pure-phase Bayerite will decrease significantly.

[0016] The low-sodium pure-phase Bayerite obtained by the preparation method of this application has a sodium oxide mass fraction of less than 0.1% and a β-Al(OH)3 mass fraction of 98%–99.6%, while exhibiting a significantly increased specific surface area, reaching 418.3 μm. 2 / g~457.4m 2 / g. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and disclosure, and together with the description serve to explain the principles of this application and disclosure.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a method for preparing low-sodium pure phase Bayerite according to some embodiments of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0022] In this application, except where expressly stated, any matters or issues not mentioned are directly applicable to those known in the art without any modification. Furthermore, any implementation described in this application can be freely combined with one or more other implementations described in this application, and the resulting technical solutions or concepts shall be considered part of the original disclosure or original record of this application, and should not be regarded as new content not disclosed or anticipated in this application, unless those skilled in the art consider the combination to be clearly unreasonable.

[0023] Any method steps, processes, and operations described in this application should not be construed as necessarily requiring them to be performed in a specific order as discussed or shown, unless explicitly specified. It should also be understood that additional or alternative steps may be used unless otherwise stated.

[0024] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0025] Any specific numerical values ​​disclosed herein (including the endpoints of numerical ranges) are not limited to their exact values, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within ±5% of the exact value. Furthermore, with respect to the disclosed numerical ranges, one or more new numerical ranges can be obtained by arbitrarily combining the endpoint values ​​of the range, the endpoint values ​​with specific point values ​​within the range, and the specific point values ​​themselves; these new numerical ranges should also be considered as specifically disclosed herein.

[0026] Unless otherwise stated, the terms used herein have the same meaning as commonly understood by those skilled in the art, and if a term is defined herein and its definition differs from the common understanding in the art, the definition herein shall prevail.

[0027] The term "β-Al(OH)3" refers to β-phase aluminum hydroxide, i.e., Bayerite. The term "α-Al(OH)3" refers to gibbsite.

[0028] First aspect Please see Figure 1This application provides a method for preparing low-sodium pure-phase Bayerite, comprising the following steps: S1, Bayerite seed crystals and sodium aluminate solution are mixed to obtain the first slurry; wherein the mass fraction of β-Al(OH)3 in the Bayerite seed crystals is greater than or equal to 98%; S2, a gas containing carbon dioxide is introduced into the first slurry to carry out the first reaction until the pH of the first reaction endpoint is 12-13.5, to obtain the second slurry; or an aluminum salt solution is added to the first slurry to carry out the second reaction until the pH of the second reaction endpoint is 12-13.5, to obtain the third slurry; S3, the second or third slurry is subjected to solid-liquid separation and washing to obtain the first filter cake; S4, the first filter cake is pulped to obtain the fourth pulp; S5, the fourth pulp is placed in a sealed container for pressure cooking to obtain the fifth pulp; S6, the fifth slurry is subjected to solid-liquid separation and washing to obtain the second filter cake; and, S7. The second filter cake is dried to obtain low-sodium pure phase Bayerite.

[0029] The method for preparing low-sodium pure-phase Bayerite in this application involves reacting an aluminum salt solution or a gas containing carbon dioxide with a sodium aluminate solution, causing the sodium aluminate to decompose and generate aluminum hydroxide precipitate. By adding Bayerite seed crystals, the content of the Bayerite phase (β-Al(OH)3) in the aluminum hydroxide precipitate is increased. Further pressure cooking is then performed to deeply remove sodium and to further transform imperfectly crystalline components in the slurry (such as boehmite), further increasing the content of the Bayerite phase (β-Al(OH)3). The Bayerite seed crystals added in this preparation method induce the transformation of the aluminum hydroxide precipitate into the Bayerite phase. Specifically, the mass fraction of β-Al(OH)3 in the Bayerite seed crystal is greater than or equal to 98%, and the mass fraction of sodium oxide is less than or equal to 0.1%. If the mass fraction of β-Al(OH)3 in the Bayerite seed crystal is too low, the mass fraction of β-Al(OH)3 in the low-sodium pure-phase Bayerite will decrease significantly. The seed crystal size D50 of Bayerite is less than or equal to 5 μm, which is beneficial to increase the contact surface of reactants in the reaction, accelerate the formation of β-Al(OH)3 in low-sodium pure phase Bayerite, avoid the formation of other impurity phases, and thus further increase the mass fraction of β-Al(OH)3 in low-sodium pure phase Bayerite.

[0030] In some embodiments, the mass fraction of sodium oxide in the Bayerite seed crystal is less than or equal to 0.1%, which can further reduce the mass fraction of sodium oxide in the low-sodium pure phase Bayerite.

[0031] In some embodiments, the Bayerite seed crystals have a particle size D50 of less than 5 μm. A Bayerite seed crystal particle size D50 of less than 5 μm is beneficial for increasing the contact surface of reactants in the reaction, accelerating the formation of β-Al(OH)3 in low-sodium pure-phase Bayerite, avoiding the formation of other impurity phases, and thus further increasing the mass fraction of β-Al(OH)3 in low-sodium pure-phase Bayerite.

[0032] In some embodiments, the mass ratio of the Bayerite seed crystal to the volume ratio of the sodium aluminate solution is (6 g to 12 g) / L. Understandably, the mass ratio of the Bayerite seed crystal to the volume ratio of the sodium aluminate solution can be 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, or any value between them, or a range between any two values.

[0033] In some embodiments, the concentration of alumina in the sodium aluminate solution is 40 g / L to 80 g / L. Understandably, the concentration of alumina in the sodium aluminate solution can be 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, or any value between them, or a range between any two values. Within this range, the concentration of alumina in the sodium aluminate solution can control the supersaturation of the reaction system, suppress the formation of impurity crystals, and further increase the mass fraction of β-Al(OH)3 in low-sodium pure-phase Bayerite. The concentration of alumina in the sodium aluminate solution has a meaning known in the art, referring to the alumina concentration calculated from the total aluminum element in the sodium aluminate solution.

[0034] In some embodiments, the mass ratio of the Bayerite seed crystal to the alumina in the sodium aluminate solution is 3:20. Understandably, the mass ratio of the Bayerite seed crystal to the alumina in the sodium aluminate solution is 3:20, the concentration of alumina in the sodium aluminate solution is 40 g / L to 80 g / L, and the mass of the Bayerite seed crystal per 1 L of sodium aluminate solution can be 6 g / L to 12 g / L, or any value between these values ​​or any two of these values. Within this range, more β-Al(OH)3 products can be grown on the surface of the Bayerite seed crystal, avoiding the precipitation of aluminum hydroxide of other crystal forms, and further increasing the mass fraction of β-Al(OH)3 in the low-sodium pure-phase Bayerite.

[0035] In some embodiments, the rate at which the carbon dioxide-containing gas is introduced is from 0.5 L / min to 1.5 L / min.

[0036] In some embodiments, the volume fraction of carbon dioxide in the carbon dioxide-containing gas is 35% to 40%. Understandably, the volume fraction of carbon dioxide in the carbon dioxide-containing gas can be 35%, 36%, 37%, 38%, 39%, 40%, or any value or range between any two of these values. A volume fraction of carbon dioxide in the carbon dioxide-containing gas within this range is more advantageous for controlling the reaction rate of the carbonation decomposition reaction between sodium aluminate solution and carbon dioxide, avoiding excessively vigorous reactions that could cause local supersaturation, and resulting in lower-sodium pure-phase Bayerite with better crystallization and more uniform particle size.

[0037] It should be noted that the gas containing carbon dioxide contains other gases besides carbon dioxide. In some embodiments, the other gases are nitrogen. The gas containing carbon dioxide includes carbon dioxide with a volume fraction of 35% to 40% and nitrogen with a volume fraction of 60% to 65%.

[0038] In some embodiments, the amount of aluminum salt solution added is 0.9 to 3.2 times the volume of the sodium aluminate solution.

[0039] In some embodiments, the concentration of Al2O3 in the aluminum salt solution is 10 g / L to 40 g / L. Understandably, the concentration of Al2O3 in the aluminum salt solution can be 10 g / L, 20 g / L, 30 g / L, 40 g / L, or any value between them, or a range between any two values. A concentration of Al2O3 within this range is more conducive to controlling the reaction rate of the neutralization and precipitation reaction between the sodium aluminate solution and the aluminum salt, avoiding excessively vigorous reactions that could cause local supersaturation, and resulting in lower-sodium pure-phase Bayerite with better crystallization and more uniform particle size.

[0040] It should be noted that the concentration of Al2O3 in aluminum salt solutions has a well-known meaning in the art; it is a standardized equivalent indicator representing the total amount of aluminum. Specifically, it refers to the mass concentration of Al2O3 converted from all aluminum elements in the aluminum salt solution.

[0041] In some embodiments, the aluminum salt solution is one or more of aluminum sulfate solution, aluminum chloride solution, or aluminum nitrate solution.

[0042] In some embodiments, to further avoid an overly vigorous reaction, the aluminum salt solution can be added dropwise to the sodium aluminate solution.

[0043] In some embodiments, the temperature of the first reaction is 20°C to 60°C, and the reaction time is 60 min to 180 min. Understandably, the temperature of the first reaction can be independently selected from 20°C, 30°C, 40°C, 50°C, 60°C, and any value or range between these values. Temperatures within this range are more favorable for the formation of β-Al(OH)3. Understandably, the reaction time can be independently selected from 60 min, 70 min, 80 min, 100 min, 120 min, 140 min, 160 min, or 180 min, and any value or range between these values. A reaction time within this range can further increase the mass fraction of β-Al(OH)3.

[0044] In some embodiments, the temperature of the second reaction is 20°C to 60°C, and the reaction time is 60 min to 180 min. Understandably, the temperature of the second reaction can be independently selected from 20°C, 30°C, 40°C, 50°C, 60°C, and any value or range between them. Temperatures within this range are more favorable for the formation of β-Al(OH)3. Understandably, the reaction time can be independently selected from 60 min, 70 min, 80 min, 100 min, 120 min, 140 min, 160 min, or 180 min, and any value or range between them. A reaction time within this range can further increase the mass fraction of β-Al(OH)3.

[0045] It should be noted that the first reaction is a carbonation decomposition reaction of sodium aluminate solution under the influence of carbon dioxide gas, causing sodium aluminate to decompose and form aluminum hydroxide precipitate. The second reaction is a neutralization precipitation reaction between sodium aluminate solution and aluminum salt solution, which can also cause sodium aluminate to decompose and form aluminum hydroxide precipitate. The endpoint pH of both the first and second reactions is 12–13.5. Within this pH range, the β-Al(OH)3 product can preferentially grow on the surface of Bayerite seed crystals, avoiding spontaneous nucleation of aluminum hydroxide to form other crystal forms.

[0046] In some embodiments, the pH value of the fourth slurry is less than 8.5. If the pH value of the fourth slurry is too high, α-Al(OH)3 impurities are likely to appear during the pressure cooking process, leading to a decrease in the mass fraction of β-Al(OH)3 in the final low-sodium pure phase Bayerite.

[0047] In some embodiments, step S3 includes: filtering the second slurry or the third slurry and washing it with water at 60°C to 100°C until the pH value of the filtrate at the washing endpoint is less than or equal to 8.5, to obtain a first filter cake. This step ensures that the pH value of the fourth slurry obtained after the first filter cake is slurried is less than 8.5.

[0048] In some embodiments, step S4, the pulping step, includes mixing the first filter cake and solvent at a mass ratio of 1:10 to 1:3. Exemplarily, the solvent is deionized water.

[0049] In some embodiments, the temperature of the pressure cooking treatment is 150°C to 160°C, and the time of the pressure cooking treatment is 90 min to 120 min.

[0050] Understandably, the temperature of the pressure cooking process can be independently selected from 150°C, 152°C, 154°C, 156°C, 158°C, or 160°C, or any value or range between these values. Within this range, the pressure cooking temperature can further increase the mass fraction of β-Al(OH)3 in low-sodium pure-phase Bayerite. Too low a temperature will result in a decrease in desodiumification. Too high a temperature will result in the appearance of boehmite impurities.

[0051] Understandably, the pressure of the pressure cooking process originates from the autogenous pressure generated by the solvent in the fourth slurry at the temperature of the pressure cooking process.

[0052] Understandably, the pressure cooking time can be independently selected from 90 min, 100 min, 110 min, or 120 min, or any value between them, or any range between two values. Within this range, the pressure cooking time can further reduce the mass fraction of sodium oxide in low-sodium pure-phase Bayerite. Too short a pressure cooking time will result in a decreased desodiuming effect and an increased mass fraction of sodium oxide in low-sodium pure-phase Bayerite. Too long a pressure cooking time will not result in a significant decrease in desodiuming effect, leading to wasted energy.

[0053] In some embodiments, step S6, which involves solid-liquid separation of the fifth slurry to obtain a second filter cake, includes: filtering the fifth slurry and washing it with water at 60°C to 100°C until the pH of the filtrate at the washing endpoint is less than or equal to 7, thereby obtaining a second filter cake. This step can further remove impurities, improve the purity of low-sodium pure-phase Bayerite, and wash away sodium oxide to reduce the mass fraction of sodium oxide in the low-sodium pure-phase Bayerite.

[0054] In some embodiments, the drying temperature is 100°C to 150°C. A drying temperature within this range can further maintain the stability of β-Al(OH)3 in the low-sodium pure phase Bayerite, preventing phase transformation.

[0055] Second aspect A second aspect of this application provides a low-sodium pure-phase Bayerite, prepared by the preparation method described in the first aspect of this application.

[0056] The low-sodium pure phase Bayerite is achieved based on the above preparation method. The specific characteristics of the above preparation method can be referred to the above embodiments. Since the low-sodium pure phase Bayerite adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0057] In some embodiments, the mass fraction of sodium oxide in the low-sodium pure phase Bayerite is less than 0.1%.

[0058] In some embodiments, the mass fraction of β-Al(OH)3 in the low-sodium pure phase Bayerite is 98% to 99.6%, for example, it can also be 98.2%, 98.5%, 99.0%, 99.2% or 99.5%.

[0059] In some embodiments, the specific surface area of ​​the low-sodium pure-phase Bayerite is 418.3 μm. 2 / g~457.4m 2 / g, for example, it can also be 419m 2 / g、420m 2 / g、430m 2 / g、440m 2 / g or 450m 2 / g.

[0060] Example To better understand this application, the following description, in conjunction with embodiments, further illustrates this application. However, the scope of protection claimed in this application is not limited to the scope of the embodiments.

[0061] In the following examples, unless otherwise specified, all experimental instruments, raw materials, and quantities involved are commercially available products or can be prepared by known methods. Experimental methods not specifying particular conditions in the examples were performed under conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0062] Unless otherwise specified, the specific parameters used in each step of the material preparation process in each embodiment and comparative example are the same.

[0063] Example 1 S1. Take a 5L reaction vessel, add 1L of sodium aluminate with an alumina concentration of 40g / L, add 6g of Bayerite seed crystals with a particle size D50 of less than 5μm, and stir evenly to obtain the first slurry. The Bayerite seed crystals contain β-Al(OH)3 with a mass fraction greater than or equal to 98% and sodium oxide with a mass fraction less than or equal to 0.1%.

[0064] S2, a 35% CO2 gas was introduced into the first slurry at a rate of 0.5 L / min to carry out the first reaction. The first reaction temperature was 20℃, the first reaction time was 90 min, and the first reaction endpoint pH was 12.5, thus obtaining the second slurry.

[0065] S3. Filter the second slurry and wash it with 100°C water until the pH value of the filtrate is less than 8.5 at the end of the washing process to obtain the first filter cake.

[0066] S4. The first filter cake and deionized water are mixed at a mass ratio of 1:10 to form a pulp, resulting in the fourth pulp. The pH value of the fourth pulp is less than 8.5.

[0067] S5. Place the fourth pulp in a sealed pressure cooker and cook it at 160°C for 120 minutes to obtain the fifth pulp.

[0068] S6. Filter the fifth slurry and wash it with 100°C water until the pH of the filtrate is less than 7 at the end of the washing process to obtain the second filter cake.

[0069] S7. The second filter cake is dried at 120°C to obtain low-sodium pure phase Bayerite.

[0070] Example 2 S1. Take a 5L reaction vessel, add 1L of sodium aluminate with an alumina concentration of 60g / L, add 9g of Bayerite seed crystals with a particle size D50 of less than 5μm, and stir evenly to obtain the first slurry. The Bayerite seed crystals contain β-Al(OH)3 with a mass fraction greater than or equal to 98% and sodium oxide with a mass fraction less than or equal to 0.1%.

[0071] S2, 1.2 L of aluminum sulfate solution with an Al2O3 concentration of 20 g / L was added dropwise to the first slurry to initiate the second reaction, with a dropping rate of 8.57 mL / min. The second reaction temperature was 30 °C, the second reaction time was 140 min, and the endpoint pH of the second reaction was 13, yielding the third slurry.

[0072] S3. Filter the third slurry and wash it with 100°C water until the pH value of the filtrate is less than 8.5 at the end of the washing process to obtain the first filter cake.

[0073] S4, the first filter cake and deionized water are mixed at a mass ratio of 1:8 to form a pulp, resulting in the fourth pulp. The pH of the fourth pulp is less than 8.5.

[0074] S5. Place the fourth pulp in a sealed pressure cooker and cook at 150°C for 120 minutes to obtain the fifth pulp.

[0075] S6. Filter the fifth slurry and wash it with 100°C water until the pH of the filtrate is less than 7 at the end of the washing process to obtain the second filter cake.

[0076] S7. The second filter cake is dried at 120°C to obtain low-sodium pure phase Bayerite.

[0077] Example 3 S1. Take a 5L reaction vessel, add 1L of sodium aluminate with an alumina concentration of 80g / L, add 12g of Bayerite seed crystals with a particle size D50 of less than 5μm, stir evenly to obtain the first slurry. The Bayerite seed crystals contain β-Al(OH)3 with a mass fraction greater than or equal to 98%, and sodium oxide with a mass fraction less than or equal to 0.1%.

[0078] S2, 3.2 L of aluminum sulfate solution with an Al2O3 concentration of 10 g / L was added dropwise to the first slurry to initiate the second reaction, with a dropping rate of 17.8 mL / min. The second reaction temperature was 60℃, the second reaction time was 180 min, and the pH of the second reaction endpoint was 13.5, yielding the third slurry.

[0079] S3. Filter the third slurry and wash it with 100°C water until the pH value of the filtrate is less than 8.5 at the end of the washing process to obtain the first filter cake.

[0080] S4, the first filter cake and deionized water are mixed at a mass ratio of 1:6 to form a pulp, resulting in the fourth pulp. The pH of the fourth pulp is less than 8.5.

[0081] S5. Place the fourth pulp in a sealed pressure cooker and cook it at 160°C for 120 minutes to obtain the fifth pulp.

[0082] S6. Filter the fifth slurry and wash it with 100°C water until the pH of the filtrate is less than 7 at the end of the washing process to obtain the second filter cake.

[0083] S7. The second filter cake is dried at 120°C to obtain low-sodium pure phase Bayerite.

[0084] Example 4 S1. Take a 5L reaction vessel, add 1L of sodium aluminate with an alumina concentration of 50g / L, add 7.5g of Bayerite seed crystals with a particle size D50 of less than 5μm, stir evenly to obtain the first slurry. The Bayerite seed crystals contain β-Al(OH)3 with a mass fraction greater than or equal to 98%, and sodium oxide with a mass fraction less than or equal to 0.1%.

[0085] S2, 2L of aluminum chloride solution with an Al2O3 concentration of 10g / L was added dropwise to the first slurry to carry out the second reaction, with a dropping rate of 17.4mL / min. The second reaction temperature was 40℃, the second reaction time was 115min, and the pH of the second reaction endpoint was 13, yielding the third slurry.

[0086] S3. Filter the third slurry and wash it with 100°C water until the pH value of the filtrate is less than 8.5 at the end of the washing process to obtain the first filter cake.

[0087] S4, the first filter cake and deionized water are mixed at a mass ratio of 1:4 to obtain the fourth slurry. The pH of the fourth slurry is less than 8.5.

[0088] S5. Place the fourth pulp in a sealed pressure cooker and cook it at 155°C for 120 minutes to obtain the fifth pulp.

[0089] S6. Filter the fifth slurry and wash it with 100°C water until the pH of the filtrate is less than 7 at the end of the washing process to obtain the second filter cake.

[0090] S7. The second filter cake is dried at 120°C to obtain low-sodium pure phase Bayerite.

[0091] Example 5 S1. Take a 5L reaction vessel, add 1L of sodium aluminate with an alumina concentration of 70g / L, add 10.5g of Bayerite seed crystals with a particle size D50 of less than 5μm, stir evenly to obtain the first slurry. The Bayerite seed crystals contain β-Al(OH)3 with a mass fraction greater than or equal to 98%, and sodium oxide with a mass fraction less than or equal to 0.1%.

[0092] S2, 0.93 L of aluminum chloride solution with an Al2O3 concentration of 30 g / L was added dropwise to the first slurry to initiate the second reaction, with a dropping rate of 8.48 mL / min. The second reaction temperature was 60 °C, the second reaction time was 110 min, and the pH of the second reaction endpoint was 13.5, yielding the third slurry.

[0093] S3. Filter the third slurry and wash it with 100°C water until the pH value of the filtrate is less than 8.5 at the end of the washing process to obtain the first filter cake.

[0094] S4, the first filter cake and deionized water are mixed at a mass ratio of 1:3 to form a fourth slurry. The pH of the fourth slurry is less than 8.5.

[0095] S5. Place the fourth pulp in a sealed pressure cooker and cook it at 155°C for 120 minutes to obtain the fifth pulp.

[0096] S6. Filter the fifth slurry and wash it with 100°C water until the pH of the filtrate is less than 7 at the end of the washing process to obtain the second filter cake.

[0097] S7. The second filter cake is dried at 120°C to obtain low-sodium pure phase Bayerite.

[0098] Comparative Example 1 The preparation method is the same as in Example 1, except that the mass fraction of β-Al(OH)3 in the Bayerite seed crystal is 81.2%.

[0099] Comparative Example 2 The preparation method is the same as in Example 2, except that the pH value of the washing endpoint filtrate in step S3 is 9, which is the pH value of the fourth slurry in step S4 is 9.

[0100] Comparative Example 3 The preparation method is the same as in Example 3, except that in step S5, the fourth slurry is pressure cooked at 140°C for 120 minutes.

[0101] Comparative Example 4 The preparation method is the same as in Example 4, except that in step S5, the fourth slurry is pressure cooked at 165°C for 120 minutes.

[0102] Comparative Example 5 The preparation method is the same as in Example 5, except that in step S5, the fourth slurry is pressure cooked at 155°C for 60 minutes.

[0103] Comparative Example 6 The preparation method is the same as in Example 1, except that the particle size D50 of the Bayerite seed crystals is greater than 5 μm.

[0104] The low-sodium pure-phase Bayerite obtained in each embodiment and comparative example was subjected to performance tests, and the results are listed in Table 1, as shown below: Table 1

[0105] A comparison of Example 1 and Comparative Example 1 shows that a low mass fraction of β-Al(OH)3 in the Bayerite seed crystals will result in a low mass fraction of β-Al(OH)3 in the final product, low-sodium pure phase Bayerite.

[0106] By comparing Example 2 and Comparative Example 2, it can be seen that if the pH value of the washing solution at the end of step S2 is too high, α-Al(OH)3 impurity phase is likely to appear during the pressure cooking process, resulting in a decrease in the mass fraction of β-Al(OH)3 in the final low-sodium pure phase Bayerite.

[0107] A comparison between Example 3 and Comparative Example 3 shows that if the pressure cooking temperature is too low, the sodium removal effect will decrease.

[0108] A comparison between Example 4 and Comparative Example 4 shows that if the pressure cooking temperature is too high, α-AlOOH diaspore impurity phase will appear.

[0109] A comparison between Example 5 and Comparative Example 5 shows that a shorter cooking time leads to a decrease in sodium removal efficiency and an increase in the mass fraction of sodium oxide in low-sodium pure phase Bayerite.

[0110] A comparison between Example 1 and Comparative Example 6 shows that a grain size D50 greater than 5 μm in Bayerite seed crystals leads to a decrease in the mass fraction of β-Al(OH)3 in the final low-sodium pure phase Bayerite.

[0111] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

[0112] Although preferred embodiments have been described in this specification, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this specification.

[0113] Obviously, those skilled in the art can make various modifications and variations to this specification without departing from its spirit and scope. Therefore, if such modifications and variations fall within the scope of the claims and their equivalents, this specification is also intended to include such modifications and variations.

Claims

1. A method for preparing low-sodium pure-phase Bayerite, characterized in that, Includes the following steps: Bayerite seed crystals and sodium aluminate solution are mixed to obtain a first slurry; wherein the mass fraction of β-Al(OH)3 in the Bayerite seed crystals is greater than or equal to 98%; A gas containing carbon dioxide is introduced into the first slurry to carry out a first reaction until the pH of the first reaction endpoint is 12-13.5, to obtain a second slurry; or an aluminum salt solution is added to the first slurry to carry out a second reaction until the pH of the second reaction endpoint is 12-13.5, to obtain a third slurry; The second slurry or the third slurry is subjected to solid-liquid separation and washing to obtain a first filter cake; The first filter cake is slurried to obtain a fourth slurry; The fourth slurry was placed in a sealed container and pressure cooked to obtain the fifth slurry. The fifth slurry is subjected to solid-liquid separation and washing to obtain a second filter cake; and, The second filter cake was dried to obtain low-sodium pure phase Bayerite.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the Bayerite seed crystal to the alumina in the sodium aluminate solution is 3:20; and / or, the concentration of alumina in the sodium aluminate solution is 40 g / L to 80 g / L, and the volume ratio of the Bayerite seed crystal to the sodium aluminate solution is (6 g to 12 g) / L.

3. The preparation method according to claim 1, characterized in that, The pH value of the fourth slurry is less than 8.

5.

4. The preparation method according to claim 1, characterized in that, The pressure cooking temperature is 150℃~160℃, and the pressure cooking time is 90min~120min.

5. The preparation method according to claim 1, characterized in that, The grain size D50 of the Bayerite seed crystals is less than 5 μm.

6. The preparation method according to claim 1, characterized in that, The gas containing carbon dioxide is introduced at a rate of 0.5 L / min to 1.5 L / min; and / or, The volume fraction of carbon dioxide in the gas containing carbon dioxide is 35% to 40%.

7. The preparation method according to claim 1, characterized in that, The amount of aluminum salt solution added is 0.9 to 3.2 times the volume of the sodium aluminate solution, and the concentration of Al₂O₃ in the aluminum salt solution is 10 g / L to 40 g / L; and / or, The aluminum salt solution is one or more of aluminum sulfate solution, aluminum chloride solution, or aluminum nitrate solution.

8. The preparation method according to any one of claims 1 to 7, characterized in that, The temperature of the first reaction is 20℃~60℃, and the reaction time is 60min~180min; and / or, The temperature of the second reaction is 20℃~60℃, and the reaction time is 60min~180min.

9. The preparation method according to any one of claims 1 to 7, characterized in that, The drying temperature is 100℃~150℃.

10. A low-sodium pure-phase Bayerite, prepared by the preparation method according to any one of claims 1 to 9, characterized in that, It meets at least one of the following characteristics: (1) The mass fraction of sodium oxide in the low-sodium pure phase Bayerite is less than 0.1%; (2) The mass fraction of β-Al(OH)3 in the low-sodium pure phase Bayerite is 98%–99.6%; (3) The specific surface area of ​​the low-sodium pure phase Bayerite is 418.3 m. 2 / g~457.4m 2 / g.

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